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Co-production of hydrogen and sulfuric acid by electrolysis
h [electronic resource] /
by Maheshkumar Chettiar.
[Tampa, Fla.] :
University of South Florida,
Thesis (M.S.E.E.)--University of South Florida, 2004.
Includes bibliographical references.
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ABSTRACT: Hydrogen gas is the cleanest fuel which produces only water as a combustion product with no greenhouse or toxic gases. The combustible hydrogen fuel is an energy carrier but not an energy source. As an element, hydrogen is widely available in nature as a component of water and of hydrocarbons. An energy source is needed to extract the element from these compounds and convert it to the combustible hydrogen gas. Today, the energy source for nearly all hydrogen production is fossil fuel, principally natural gas. The supply of natural gas is limited and its price is increasing. Greenhouse gas and air pollutants are emitted when natural gas is used. Electrolytic extraction of hydrogen from water can overcome these stated problems but is more expensive with the present price of natural gas. Manufacturing the hydrogen with a valuable co-product would address this cost disadvantage. Sulfuric acid is a valuable chemical that is produced in large quantities. This research project helps to develop a procedure for extracting hydrogen from water while producing sulfuric acid as a co-product. An electrochemical cell was designed and developed for the production of hydrogen which uses sulfuric acid as electrolyte. In this electrochemical cell with sulfuric acid as an electrolyte we produce hydrogen at the negative electrode while the positive electrode is bathed in sulfur dioxide which it oxidizes to sulfuric acid. The sulfuric acid is collected at the bottom of the cell as valuable co-product. The presence of SO2 to scavenge the anode substantially reduces the equilibrium voltage required for the direct dissociation of water into hydrogen and oxygen. Various design parameters and the fabrication of the reactor are discussed briefly in the thesis. Experimental results of hydrogen production and current voltage curves are discussed. Sulfuric acid corrosion of cell materials is also discussed.
Adviser: Elias K. Stefanakos.
Co-adviser: Burton Krakow.
x Electrical Engineering
t USF Electronic Theses and Dissertations.
Co-Production of Hydrogen and Sulfuric Acid by Electrolysis by Maheshkumar Chettiar A thesis submitted in partial fulfillment of the requirement for the degree of Master of Science in Electrical Engineering Department of Electrical Engineering College of Engineering University of South Florida Co-Major Professor: Elias K. Stefanakos, Ph.D. Co-Major Professor: Burton Krakow, Ph.D. Venkat Bhetanabotla, Ph.D. Date of Approval: June 14, 2004 Keywords: Scavenger, Conductivity, Polarization, Overvoltage Copyright 2004, Maheshkumar Chettiar
DEDICATION This work is dedicated to my family in India.
ACKNOWLEDGEMENTS I wish to express my sincere appreciation to my major professor Dr. Elias K. Stefanakos and Co-advisor Dr. Burt Krakow, for their valu able guidance and s upport for the thesis work. Thanks are due to Dr.Venkat Bethanabotla for serving as a member of my thesis committee. I would like to express my gratitude to my co lleague Mr. Eric Weaver for helping me at every step. His hard work and company helped me in getting this work done. Special thanks are also extended to Matt Sm ith and Kiran Gaikwad and other colleagues in the Clean Energy Research Center and my friends at the University of South Florida who never let me feel away from home. Th e financial support pr ovided by the NASA and the University of Central Fl orida is greatly appreciated.
i TABLE OF CONTENTS LIST OF TABLES iv LIST OF FIGURES v ABSTRACT vi CHAPTER 1 INTRODUCTION 1 1.1 Hydrogen Production Techniques 2 1.1.1 Natural Gas Steam Reforming 2 1.1.2 Coal Gasification 2 1.1.3 Electrolysis 3 1.1.4 Photoelectrolysis 4 1.1.5 Biomass Gasification and Pyrolysis 4 1.2 Motivation for Research 5 1.3 Theoretical Consideration 7 1.3.1 Electrochemical Hydrogen Production 7 1.3.2 Photoelectro chemical Hydrogen Production 8 1.4 Thesis Organization 9 CHAPTER 2 LITERATURE REVIEW AND BACKGROUND WORK 10 2.1 Introduction 10 2.2 Westinghouse Electric Corporation 10 2.3 General Atomic Company 12 2.4 Mark 13 Process 14 2.5 Photo Electrochemical Hydrogen Production at NREL 15 2.6 Research Strategy 16 CHAPTER 3 DESIGN AND DEVELOPM ENT OF THE ELECTROLYZER 17 3.1 Process Concept 17 3.2 Design Issues 18 3.2.1 Thermodynamic Considerations 18 126.96.36.199 Conductivity of Sulfuric Acid 19 188.8.131.52 Solubilty of Sulfur Dioxide 21 3.2.2 Kinetic Considerations 22 3.3 Selection of Electrode Materials 22 3.4 Fabrication of the Electrolyzer 23 3.4.1 Cell Body 27 3.4.2 Electrodes 28 3.4.3 Liquid and Gas Feedthroughs 29
ii 3.4.4 Electric Connections 29 3.5 Operation of the Electrolyzer 30 3.6 Measurement System 31 3.7 Flow Control System 33 3.7.1 Water Pressure Test Procedure 36 3.7.2 Loading the Cell with Sulfuric Acid for Electrolysis 39 3.7.3 Shutting Down the System 41 3.8 Hydrogen Gas Collection System 42 3.8.1 Gas Analysis through Water Displacement 42 3.8.2 Gas Analysis without Water Displacement 43 CHAPTER 4 EXPERIMENTS AND RESULTS 45 4.1 Electrolysis I 45 4.1.1 Electrode Materials 45 4.1.2 Preparation of Electrodes 45 4.1.3 Results and Discussion 48 4.1.4 Interpretation 50 4.2 Electrolysis II 51 4.2.1 Electrode Materials 51 4.2.2 Preparation of Electrodes 51 4.2.3 Results and Discussion 53 4.2.4 Interpretation 54 4.3 Electrolysis III 55 4.3.1 Electrode Materials 55 4.3.2 Preparation of Electrodes 55 4.3.3 Results and Discussion 56 4.3.4 Interpretation 58 4.4 Electrolysis IV 59 4.4.1 Electrode Materials 59 4.4.2 Preparation of Electrodes 60 4.4.3 Results and Discussion 60 4.4.4 Interpretation 62 4.5 Electrolysis V 64 4.5.1 Electrode Materials 64 4.5.2 Preparation of Electrodes 64 4.5.3 Results and Discussion 64 4.5.4 Interpretation 66 4.6 Electrolysis VI 67 4.6.1 Electrode Materials 67 4.6.2 Preparation of Electrodes 67 4.6.3 Results and Discussion 67 4.6.4 Interpretation 68 4.7 Electrolysis Summary 69 4.8 Catalyst Deposition 72 CHAPTER 5 SUMMARY AND CONCLUSIONS 73
iii CHAPTER 6 RECOMMENDATIONS FOR FUTURE WORK 75 REFERENCES 77 APPENDICES 79 Appendix A: Testing of Electrode Materials 80 Appendix B: Calculation of Flow Rates 81 Appendi x C: Electrolysis I 88 Appendix D: Electrolysis II 90 Appendix E: Electrolysis III 93 Appendix F: Electrolysis IV 99 Appendix G: Electrolysis V 105 Appendix H: Electrolysis VI 110
iv LIST OF TABLES Table 1.1 Sulfuric Acid Ranking in Top10 Chemicals 6 Table 3.1 Nomenclatures for Figure 3.5 35 Table 4.1 Electrolysis Summary 70 Table A.1 Test Results of Different Electrodes 80 Table B.1 Fraction of H 2 SO4 and H 2 O Flow 82 Table C.1 Current Voltage Data Electrolysis I 88 Table D.1 Current Voltage Data Electrolysis II 90 Table E.1 Current Voltage Data Electrolysis III 94 Table F.1 Current Voltage Da ta Electrolysis IV 100 Table F.2 Residual Voltage Meas urements (Electrolysis IV) 104 Table G.1 Current Voltage Data Electrolysis V 106 Table G.2 Residual Voltage Measurements (Electrolysis V) 109 Table H.1 Current Voltage Da ta Electrolysis VI 110
v LIST OF FIGURES Figure 2.1 Process Schematic of Westinghouse Sulfur Cycle 12 Figure 2.2 Schematic of the Monolithic PEC/PV Device at NREL 15 Figure 3.1 Conductivity vs Concentration 20 Figure 3.2 Cross Sectiona l View of the Electrolyzer 25 Figure 3.3 Tilted View of the Electrolyzer 26 Figure 3.4 Level Sensor Circuit 32 Figure 3.5 Flow Control System 34 Figure 3.6 Hydrogen Gas Collection System 42 Figure 4.1 Process Flow Diagram Electrolysis I 47 Figure 4.2 Current Voltage Curve Electrolysis I 49 Figure 4.3 Electrode View Electrolysis I 50 Figure 4.4 Current Voltage Curve Electrolysis II 53 Figure 4.5 Current Voltage Curve Electrolysis III 57 Figure 4.6 Current Voltage Curve Electrolysis IV 61 Figure 4.7 GC Analysis of the Gas Sample (Electrolysis IV) 62 Figure 4.8 Current Voltage Curve Electrolysis V 65 Figure 4.9 Current Voltage Curve Electrolysis VI 68
vi CO-PRODUCTION OF HYDROGE N AND SULFURIC ACID BY ELECTROLYSIS Maheshkumar Chettiar ABSTRACT Hydrogen gas is the cleanest fuel which produces only water as a combustion product with no greenhouse or toxic gases. Th e combustible hydrogen fu el is an energy carrier but not an energy source. As an elemen t, hydrogen is widely av ailable in nature as a component of water and of hydrocarbons. An energy source is need ed to extract the element from these compounds and convert it to the combustible hydrogen gas. Today, the energy source for nearly al l hydrogen production is fossil fuel, principally natural gas. The s upply of natural gas is limited and its price is increasing. Greenhouse gas and air pollutants are emitted when natural gas is used. Electrolytic extraction of hydrogen from water can overcome these stated problems but is more expensive with the present price of natural gas. Manuf acturing the hydrogen with a valuable co-product would address this cost disadvantage. Sulfuric acid is a valuable chemical that is produced in large quantities. This research project helps to de velop a procedure for extrac ting hydrogen from water while producing sulfuric acid as a co-product. An electrochemical cell was designed and developed for the production of hydrogen which us es sulfuric acid as electrolyte. In this electrochemical cell with sulf uric acid as an electrolyte we produce hydrogen at the
vii negative electrode while the positive electrod e is bathed in sulf ur dioxide which it oxidizes to sulfuric acid. The sulfuric acid is collected at the bottom of the cell as valuable co product. The presence of SO2 to scavenge the anode substantially reduces the equilibrium voltage required for the dir ect dissociation of water into hydrogen and oxygen. Various design parameters and the fabricati on of the reactor is discussed briefly in the thesis. Experimental results of hydroge n production and current voltage curves are discussed. Sulfuric acid corrosion of cell materials is also discussed.
CHAPTER 1 INTRODUCTION Fossil fuel resources are finite and provide around 70 % of todays energy demand. Only seven percent of todays energy comes from renewable energy sources . In 1870 Jules Verne mentioned in his story Th e Mysterious Island that when the fossil fuel age comes to an end ,water will be employed as a fuel that hydrogen and oxygen which constitute it and when used singly or together will furnish an inexhaustible source of heat and light of an intensity of which coal is not capable He said water would be the coal for the future. Hydrogen is one of the most abundant elements found in th e earths crust. Hydrogen as gas (H 2 ) doesnt exist natura lly but its found only in compound forms. Combined with oxygen, hydrogen becomes wa ter. Combined with carbon it forms organic compounds, such as methane (CH 4 ), coal and petroleum. In 1839, Sir William Grove was the first scientist to split wate r in order to produce hydrogen and oxygen. He also discovered the fuel cell in the same year John OM. Bockris first referred to the concept of Hydrogen Economy and depicted the use of hydrogen as a general purpose fuel .
1.1 Hydrogen Production Techniques Today, nearly all hydrogen production is based on fossil fuel raw materials. Worldwide 48% of hydrogen is produced from natural gas 30% from oil ( mostly consumed in refineries ) 18% from coal a nd the remaining ( 4% ) via electrolysis  The most well known techniques to produce hydrogen are described below. 1.1.1 Natural Gas Steam Reforming Methane (CH 4 ) from natural gas is the most common feedstock for hydrogen production. The process by whic h hydrogen is produced from natural gas is known as Natural Gas Steam Reforming. It is the most popular form of producing hydrogen. In this process hydrogen is separated from th e carbon atoms in the methane by subjecting the natural gas to high temperature steam. Carbon monoxide produced in the reaction is again combined with steam to produce more hydrogen and carbon dioxide. This process is found to be the most cost effective process of producing hydrogen today but it uses fossil fuel for the manufacturing process a nd also for the heat source. Today, most hydrogen in the United States, and about half of the world's hydrogen supply, is produced through the steam reforming of natural gas. 1.1.2 Coal Gasification Today, hydrogen is produced from coal by gasification and the subsequent processing of the resulting synthesis gas. This approach is currently used primarily to produce ammonia for fertilizers. In its simplest form, coal gasification works by first reacting coal with oxygen and steam under high pressures and temperatures to form a
synthesis gas consisting primarily of hydrogen gas, carbon monoxide, and carbon dioxide. This synthesis gas is cleaned of virtually all of its impurities and shifted to produce additional hydrogen. The clean gas is se nt to a separation system to recover hydrogen. It is almost twice as expensive to produce hydrogen from coal as from natural gas due to the ratio of hydrogen to carbon. This method of production becomes economically viable if CO 2 is sequestered and used to recover methane trapped in unminable coal beds. 1.1.3 Electrolysis Electrolysis is the simplest form of producing hydrogen. It is a process where water is split into its basic elements of hydrogen and oxygen by passing an electric current through it to separate the atoms. Hydrogen is produced at the negatively charged cathode and oxygen is produced at the positively charged anode. The equilibrium voltage reaction is 1.23 volts under standard conditions. Hydrogen produced by electrolysis is extremely pure, and electricity from renewable energy sources can be used, but it is very expe nsive at this time. Today, hydrogen from electrolysis is ten times as cos tly as from natural gas and three times as costly as gasoline per Btu. On the other ha nd water is abundant and renewable, and advances in technology in renewable electr ic power could make electrolysis a more attractive way of producing hydrogen in the future. The hydrogen fuel made from H 2 O available by electrolysis will not pollute the atmosphere.
1.1.4 Photoelectrolysis In photoelectrolysis water is split into its component s (hydrogen and oxygen) by the absorption of sunlight into a semiconduc tor, a device that produces the potential difference needed for electrolysis. When light is absorbed by a certain type of semiconductor the energy absorbed results in the form of positive and negative charge carriers in the solid. The negative charge is carried by the electrons which are freed from the individual atoms to travel free in the crystal lattice of the solid. The positive charge carriers are the holes which are left in the cr ystal lattice by removal of electrons. The holes and electrons in an ordinary semic onductor do not have sufficient energy to split water molecules, but they are enough to drive an electric current through a semiconductor. Multijunction cell technology developed by the photovo ltaic industry is capable of producing a high enough voltage fo r water splitting. This type of system results in a 10 to 20 % efficiency rate. 1.1.5 Biomass Gasification and Pyrolysis In biomass gasification, wood chips and agricultural wastes are super heated until they turn into hydrogen and other gases. Biom ass is a combustible solid and some of the concepts similar to coal are applicable. Biomass pyrolysis produces a liquid product (biooil) that like petroleum contains a wide sp ectrum of components that can be separated into valuable chemicals and fuels. Bio-oil contains a significant number of highly reactive oxygenated components derived ma inly from carbohydrates and lignin. These components can be transformed into products including hydrogen.
Scientists have also discovered that some algae and bacteria produce hydrogen under certain conditions, using sunlight as their energy source. Experiments are underway to find ways to induce these mi crobes to produce hydrogen efficiently. 1.2 Motivation for Research At present the majority of hydrogen is us ed as fuel in National Aeronautics and Space Administration (NASA) space program. Every shuttle launched at the Kennedy Space Center, Cape Canaveral, Florida de pends on cutting edge technology, and highly trained engineers and technicians. NAS As supply of hydrogen depends on hydrogen derived from natural gas in the mid west (New Orleans and Texas), with hydrogen transported hundreds of miles away from wh ere it is produced. Each time the shuttle roars in to the orbit, 300,000 pounds of hydrogen fuel is tran sported to the launch site . This massive transportation costs hundreds of thousand of dollars for a shuttle launch. If the hydrogen required for NASA is produced at Cape Canaveral or closer to the launch site then the cost would be cu t in half, since transportation is a huge part of the cost. On the other hand present existing industrial hydrogen production techniques release large amounts of carbon dioxide to the atmosphere which create a global problem so called green house effect. NASA would like to fi nd a cleaner alternativ e, producing hydrogen near the Kennedy Space Center, in an environm entally friendly manner and reduced cost. Sulfuric acid ranks as the worlds larges t volume chemical commodity in terms of quantity produced. Sulfuric acid has many dive rse applications in a chemical industry. Table 1.1 shows the ranki ng of sulfuric acid in top 10 chemicals . 75% of the U.S sulfuric acid production is produced and used in Florida. The only process in which
sulfuric acid is consumed in significant quantities is that of phosphate fertilizer manufacture which yields gyps um byproduct. The petrochemical industry uses sulfuric acid in alkylations and paraffin refining. The inorganic branch of the chemical industry uses sulfuric acid in the production of chromic and hydrof luoric acids, aluminum sulfate and sodium sulfate. The organic arm employ s sulfuric acid in the manufacture of explosives, soaps, detergents, dyes, isocya nates, plastics, pharmaceuticals, etc . Table 1.1 Sulfuric Acid Ranking in Top10 Chemicals 2000 RANK (by mass) CHEMICAL 2000 PRODUCTION (in 10 9 kg) 1 Sulfuric acid 39.62 2 Ethylene 25.15 3 Lime 20.12 4 Phosphoric acid 16.16 5 Ammonia 15.03 6 Propylene 14.45 7 Chlorine 12.01 8 Sodium Hydroxide 10.99 9 Sodium carbonate 10.21 10 Ethylene Chloride 9.92 Even though Florida is poor in other minerals particularly in natural gas, the state has rich deposits of the phosphate rock us ed in making phosphate fertilizer. Phosphate rock reacts with sulf uric acid to produce phosphoric acid and phosphoric acid reacts with ammonia to form Diammonium Phospha te (DAP) and Monoammonium Phosphate (MAP). Large quantities of sulfuric acid are ma nufactured in Florida by oxidizing sulfur and sulfur compounds with oxygen from air. This is done by fertilizer manufacturers who
need the sulfuric acid for their manufacturing process. It is also done for sulfur clean up in coal fired electric power production. If the oxygen required for this reaction is derived from water instead of air by an electrochemical or photo electrochemical approach, then hydrogen would be produced as a valuable byproduct with sulfuric acid. The hydrogen produced by this technique does not have to deal with carbon dioxide emissions, it would be environmentally benign and would provide the hydrogen needed by NASA. 1.3 Theoretical Consideration 1.3.1 Electrochemical Hydrogen Production In an electrochemical cell an equilibrium voltage of 1.23 volts is required to decompose water into hydrogen and oxygen in the ideal case. The presence of sulfur dioxide to scavenge the anode can reduce the equilibrium voltage from 1.23 volts to 0.17 volts. The equations shown below are reactions showing the energy requirements. 2H 2 O 2H 2 + O 2 4 Faradays @ 1.2V G o =113 kcal/mole (184.108.40.206) 2SO 2 + 4H 2 O 2H 2 SO 4 + 2H 2 4 Faradays @ 0.17V G o =15 kcal/mole (220.127.116.11) The thermo chemical free energy is reduced from 113kcal/mole to 15kcal/mole if sulfur dioxide is used as a scavenger. In an electrochemical cell with sulfuric acid as the electrolyte and sulfur dioxide as the scavenger hydrogen would be produced at the negative electrode, and at the positive electrode sulfur dioxide would be oxidized to produce sulfuric acid which would be withdrawn from the bottom of the cell for industrial uses.
1.3.2 Photoelectrochemical Hydrogen Production For a single band gap semiconductor ba sed direct conversion water splitting system, the thermodynamic potential, over voltage and semiconductor losses imply a minimum semiconductor band gap greater than 1.8 electron volts. Most well known semiconductors are unsuitable for electrolysis since they either have too large a band gap for efficient light absorption or too small a ba nd gap thus requiring an external bias. SO 2 used as a scavenger in our approach re duces the minimum required semiconductor band gap from 1.8 to less than 0.8 volts. Many well known less expensive single junction semiconductors have band gaps of this magnitude. Establishing the system for SO 2 scavenging would benefit future work on photoelectrochemical hydrogen production, where the electrodes would be replaced by a semiconductor. A considerable amount of technically successful research was done by Westinghouse and General Atomic between 1970 and 1990 on hydrogen production by splitting water. Their process involved interm ediate production of sulfuric acid. They were motivated by the hydrogen economy and it was then considered to be the most practical reaction for producing hydrogen without fossil fuel. Westinghouse used electrochemical hydrogen production and Gene ral Atomic used a thermo chemical process .Both of these techniques would be discussed in detail in Chapter 2. Our research would be focuses on adapting and advancing the Westinghouse approach since it can be modified for use with solar energy.
1.4 Thesis Organization This thesis is organized in five chapte rs. The second chapter gives a detailed description of literature review and background work .Chapter 3 deals more on the design and development of the electrolyzer .The design issues, design pr oblems, and design of the fluid flow system will be discussed in detail in this chapter. Chapter 4 discusses mainly the experiments and resu lts for different electrolyses done during the course of the research. Summary and conclusions of the th esis work are presented in Chapter 5 and finally directions for future research are provided in the sixth chapter.
CHAPTER 2 LITERATURE REVIEW AN D BACKGROUND WORK 2.1 Introduction Hydrogen is seen as a future energy carri er by virtue of the fact that it is renewable, does not evolve the "greenhouse gas" CO 2 in combustion, liberates large amounts of energy per unit weight in combusti on, and is easily converted to electricity by fuel cells A large amount of research and developm ent was done in the 1970 to 1990 period in the United States and Europe by va rious organizations to produce hydrogen by splitting water. Work was done on sulfuric ac id cycles by three major organizations 1) Westinghouse Electric Corporat ion 2) General Atomic Comp any and 3) The commission of European Communities Joint Research Ce nter (JRC), Ispra (Varese), known as the Mark 13 process .They were motivated by the idea of a hydrogen economy and it was considered to be most practical and ec onomical way of producing hydrogen without fossil fuels. 2.2 Westinghouse Electric Corporation Westinghouse developed a hybrid electroch emical / thermochemical process for hydrogen production. It was a two step process where the first step involved hydrogen production in an electrochemical cell where sulf ur dioxide is used to scavenge the anode.
The electrolyte used in the cell was sulfuric acid. The second step vaporized sulfuric acid and thermally decomposed it at high temperatures to sulfur trioxide, sulfur dioxide, water and oxygen. A catalyst was used to accelerate the rate of sulfur trioxide reduction to sulfur dioxide and oxygen. After separation, sulfur dioxide was recycled to the electrolyzer and oxygen was either used in some other process or vented. The overall process is schematically shown in Figure 2.1  and involves the following reactions: Step 1: SO 2 + 2H 2 O H 2 SO4 + H 2 (by electrolysis) (2.2.1) Step 2: H 2 SO 4 H 2 O + SO 3 H 2 O + SO 2 + O 2 (high temperature) (2.2.2) The theoretical equilibrium voltage required to decompose water under standard conditions is 1.23 volts, with many of the commercial electrolyzers requiring more than 2.0 volts to deal with system efficiency and overvoltage. The theoretical equilibrium voltage required for the reaction in step 1 (Eq. 2.2.1) is just 0.17 volts thereby reducing the theoretical power required per unit of hydrogen produced over that required in water electrolysis. The advantage of this step is partially offset by the need to add thermal energy for the process in the acid vaporizer and the sulfur trioxide reduction reactor in step 2 (Eq. 2.2.2). The performance analysis of the sulfur cycle plant showed that the overall efficiency of hydrogen production was 47 % when the electrolyzer cell is operating at 600mv . The energy source for the water decomposition system is a very high temperature nuclear reactor (VHTR) producing both electric power and high temperature helium stream for the process. The VHTR introduced the major cost to the whole process. Recycling the sulfur in this process was found to be very expensive and difficult from an economic point of view. It was found that the electrolysis capital cost is high but the
power requirement is low. The system also requires considerable amount of high quality process heat to decompose the sulfuric acid. ( D.C POWER H 2 THERMAL ENERGY O 2 H 2 O SO 2 H 2 O THERMAL ENERGY SO 2 H 2 O, O 2 H 2 SO4 H 2 SO4 OXYGEN GENERATION H 2 SO 4 H 2 O + SO 2 + O 2 OXYGEN RECOVERY SULFURIC ACID VAPORIZATION HYDROGEN GENERATION SO 2 + 2H 2 O H 2 SO4 + H 2 (ELECTROLYZER) Figure 2.1 Process Schematic of Westinghouse Sulfur Cycle 2.3 General Atomic Company Researchers at the General Atomic Company found that the Electrolysis cell used by Westinghouse Corporation did not scale up with the size of the hydrogen producing system after a very nominal size. The alternative for increasing the capacity of the plant
was unit repetition. It was found that a more complicated pure large size thermochemical cycle has the possibility of overcoming capital cost advantages of the simpler electrolytic process in the small systems . The General Atomic Process is well known as sulfur iodine cycle which is a fully thermochemical water splitting cycle. The process can be described by the following three chemical equations . Step 1: 2H 2 O + I 2 + SO 2 H 2 SO 4 (sol) + 2HI x (sol) (370K) (2.3.1) Step 2: H 2 SO 4 (sol) H 2 O + SO 2 + O 2 (up to 1150K) (2.3.2) Step 3: 2HIx (sol) H 2 + xI 2 (500 K) (2.3.3) Where the x in the reactions represents the average of several polyiodides (hydrated) formed in the initial solution reaction. The above three equations looks very simple but in reality the process is more complex than the three equations. In short these reactions can be explained as, Sulfur dioxide reacts with a concentrated solution of iodine to produce solutions of sulfuric acid and hydrogen polyiodide After separation of the solution, hydrogen polyiodide is decomposed thermochemically into hydrogen and finally iodine is recycled. One of the best parts of the Sulfur iodine cycle relates to the high temperature reactions for the cycles for the decomposition of H 2 SO 4 as compared to the Westinghouse. The H 2 SO 4 can accept heat at varying temperatures such as that available from the helium coolant of an HTGR. It will accept sufficient heat so that cycle closing reactions need not be particularly energetic .The most complicated and capital intensive part of the project is step 3. The separation of HI from water is more difficult since HI and water form azeotrope and thus they cannot be separated by distillation. Phosphoric
acid used for these separations and separation of phosphoric acid from water solutions is the most energy intensive part and it is accomplished by a method of multistage flash evaporation with vapor recompression . 2.4 Mark 13 Processes The Mark 13 process is well known as brominesulfur cycle process of the Commission of the European Communities JRC Ispra Establishments, Italy. It was invented by Schultz and Fielbelmann in 1974. Mark 13 process differs from the General Atomic process in using bromine in place of iodine and in achieving the decomposition of the hydrobromic acid by electrochemical means rather than by a pure thermochemical process. The process consists of the following three reactions . Step 1: 2H 2 O + Br 2 + SO 2 H 2 SO 4 + 2HBr (320370K) (2.4.1) Step 2: 2HBr (sol) H 2 + Br 2 (Electrochemical) (2.4.2) Step 3: H 2 SO 4 H 2 O + SO 2 + O 2 (10001100K) (2.4.3) In the Mark 13 process sulfur dioxide reacts spontaneously with bromine in water to produce gaseous HBr and sulfuric acid solution. The HBr is dissociated electrochemically and the bromine recycled. Development of the Mark 13 process cycle was found to be more advanced than the other two processes (Westinghouse and General Atomic) .It was found that electrode kinetics is generally better for the electrolysis of SO 2 by electrolyzing the product of the BrSO 2 -H 2 O reaction that is HBr. It was also found that theoretical potentials are somewhat higher . The reaction between Br 2 SO 2 and H 2 O can produce quite concentrated reactants, which means that less process heat is required to decompose the H 2 SO 4 among all the other three processes cited here
2.5 Photo Electrochemical Hydrogen Production at NREL The photo electrolysis of water using semiconductor electrodes has drawn a significant amount of attraction in recent years. In 1972 Fujishma and Honda described the photosensitized electrolysis of water on n-type TiO 2 single crystal electrodes and proposed this reaction to be used for solar energy conversion and storage in the form of hydrogen. Later on it was found that these oxide semiconductors have too larger band gaps for efficient light absorption or their semiconductor characteristics are poor. Kahaselev and Turner at the National Renewable Energy Laboratory (NREL) have demonstrated a monolithic multijunction photovoltaic direct photoelectrochemical splitting of water into hydrogen and oxygen using 3 M solution of Sulfuric acid as electrolyte . Their system used a PEC device that is voltage biased with an integrated PV device. They used a 2 band gap GaInP 2 device that was voltage biased with a GaAs Photo voltaic device. A schematic of their process is shown in Figure 2.2 below. Figure 2.2 Schematic of the Monolithic PEC/PV Device at NREL Even though their system was an efficient combination of semiconductors it requires two photons (one per junction) to produce one electron in the external circuit. There was
economic analysis done by another group at NREL, Mann, Dipietro, Iannucci and Eyer, and according to them it was found that the work done by Khaselev and Turner would be only economical with lower cost cells. 2.6 Research Strategy The processes described by Westinghouse, General Atomic and Mark 13 produce 40-80 % acid. In all three proces ses this must be raised to 95% before decomposing it to recycle the sulfur. thermally decomposing the sulfuric ac id and separating the sulfur dioxide and oxygen produced. Recycling the su lfur proved to be the most difficult, expensive and energy intensive part of the proce ss. One of the key goals in this project is to avoid implementing this hard part. The va lue of the sulfuric ac id co product is too great to be ignored since it has a gr eater market value than oxygen. A two compartment electrochemical cell us ing sulfuric acid as the electrolyte operating at 100 psig would be used for the production of hydrogen and sulfuric acid. The scavenging of the anode by a 2-phase mixture of liquid sulfur dioxide and water solution would result in a voltage way below the 1.23 V required to dissociate water under standard conditions. The hydrogen produced would be the only gas in the cell with the remaining materials inside the cell in the liq uid state. The use of sulfur dioxide also motivates the system for future work for phot oelectrochemical applic ations using single low band gap semiconductors that can produc e hydrogen without any need for external bias.
CHAPTER 3 DESIGN AND DEVELOPMENT OF THE ELECTROLYZER 3.1 Process Concept The equilibrium voltage required to dissociate water is 1.23V under standard conditions. In a sulfur dioxide electrolyzer where the positive electrode is exposed to sulfur dioxide, with sulfuric acid as an electrolyte, the equilibrium voltage is reduced from 1.23 to 0.17 volts. The overall reaction occurring electrochemically in the cell is shown below for the sulfur dioxide electrolysis. SO 2 + 2H 2 O H 2 SO 4 + H 2 (3.1.1) The above equation is comprised of two separate reactions as shown below. Positive Electrode: Oxidation of Sulfur Dioxide SO 2 + 2H 2 O H 2 SO 4 + 2H + + 2e (3.1.2) Negative Electrode: Production of Hydrogen 2H + + 2e H 2 (3.1.3) In the electrochemical sulfur dioxide electrolyzer ( Figure 3.2 ) water and sulfur dioxide are pumped through the bottom of the cell where sulfur dioxide is oxidized at the anode (positive electrode) converting it to sulfuric acid. The positive hydrogen ion migrates towards the negative electrode (cathode) where it combines with an electron to form a hydrogen molecule. The hydrogen molecules accumulate at the surface of the electrode where they form bubbles, break away and get lifted from the surface of the
electrode and discharged. The current is determined by the fact that two electrons are required to discharge one molecule of hydrogen. Designing and developing the electrolyzer was the most crucial part of the project. Various factors were taken into consideration while designing the electrolyzer, the cell design was changed few times in the course of the research .All the design issues considered while designing the cell would be discussed in detail in this chapter. 3.2 Design Issues 3.2.1 Thermodynamic Considerations As mentioned earlier the thermochemical free energy ( G) required for the reaction shown in equation 1 to proceed is 15kcal/mole and the required equilibrium voltage (E) is 0.17 volts under standard condi tions at 25degree Celsius .The equilibrium voltage E depends on the temperature, pressure , and concentration of the electrolyte. On the other hand the electric resistance of the electrodes is increased in the presence of gases on the surface of the electrodes. Sinc e the electrical conductivity of gas is practically zero, it is always important to ke ep the gas coverage of the electrodes as low as possible. The volumetric ratio of gas to li quid flow can also be decreased by increasing the velocity of forced convection of the circulated electrolyte . Sulfuric acid was used as the electrolyte in the system and liquid sulfur dioxide was the scavenger used for the anode compartm ent. Sulfur dioxide was used in the liquid state for simpler control of the migration of su lfur dioxide into the negative compartment. The pressure and temperature of the system were also considered in determining the
properties of sulfuric acid at different concentrations and the solubility of sulfur dioxide in the liquid state. 18.104.22.168 Conductivity of Sulfuric Acid Sulfuric acid (H 2 SO 4 ) is a very strong acid with a density of 1.84g/cc. It is highly corrosive and changes from a reducing agent in dilute solutions to an oxidizing agent in concentrated solutions . Sulfuric acid when mixed with water ionizes to form hydronium ions and hydrogen sulfate ions. In more diluted solutions the hydrogen sulfate ions are further dissociated forming more hydronium ions and sulfate ions. The dissociation of sulfuric acid in a solution with water is shown by the equations shown below. H 2 SO 4 H + + HSO 4 (Bi-sulfate) (22.214.171.124.1) HSO 4 H + + SO 4 2 (Sulfate) (126.96.36.199.2) Conductivity of a solution is defined as the ability of the solution to pass electric current. The ions formed in the solution are responsible for carrying current. Conductivity of a solution depends on a number of factors like concentration of ions, mobility of ions, valence of ions, temperature of the solution, etc. There is a peak conductivity vs concentration value for most of the solutions. Conductivity proceeds positively before the peak value is reached with respect to concentration and after the peak value it correlates negatively. Figure 3.1 shows the correlation of conductivity and concentration for sulfuric acid . From the figure it is seen that sulfuric acid has a maximum conductivity between 20 to 40 % (by weight). Beyond 40 % the conductivity of sulfuric acid decreases. This affect is due to the fact that hydrogen ion concentration in dilute
sulfuric acid increases with concentration but at higher concentrations it decreases again . Corrosiveness of sulfuric acid also depends upon the temperature and concentration. Increase in temperature generally gives a corresponding increase in corrosion rate, increasing the acid concentration can increase or decrease the corrosion rate depending upon the actual concentration. Figure 3.1 Conductivity vs Concentration In our system initial concentrations were low so as to leave room for sulfuric acid production as the electrolysis makes it more concentrated. However it cant be so low that the conductivity is inadequate for electrolysis to proceed. An initial concentration of 15 to 20% is considered suitable. The anticipated limit for the high concentrated electrolysis process is expected to be in the 60 to 80 % range. It was decided to operate the system at ambient temperature to make the system easy to work with.
188.8.131.52 Solubility of Sulfur Dioxide In aqueous sulfuric acid solutions, SO 2 exists in molecular and ionic forms. When SO 2 is dissolved in sulfuric acid, the dissociation of SO 2 in the solution is shown by the following reactions . SO 2 + H 2 O H 2 SO 3 (Sulfurous Acid) (184.108.40.206 .1) H 2 SO 3 HSO 3 (Bi-sulfite) + H + (220.127.116.11 .2) HSO 3 SO 3 2(Sulfite) + H + (18.104.22.168 .3) H 2 O H + + OH (22.214.171.124 .4) H 2 SO 4 H + + HSO 4 (Bi-sulfate) (126.96.36.199 .5) It was found that in high concentration of sulfuric acid solutions the SO 2 dissolved is mostly in its molecular form rather ionic form .Work done in France by A.J Appleby  in late 1976 has shown that solubility of sulfur dioxide in sulfuric acid solutions is relatively independent of acid concentration in the range of 50-80 wt % H 2 SO 4 but it falls tenfold in the temperature range 2090 0 C .Further research has showed that the ionization of SO 2 becomes negligible at sulfuric acid concentrations greater than 22 wt%. On the other hand at room temperature SO 2 evaporates at 40psig and becomes a liquid above 40psig. As the temperature increases the vapor pressure increases, therefore it was decided to operate the cell at a pressure of 100psig to keep sulfur dioxide in the liquid state taking into consideration there would be some amount of heat generated from the reaction.
3.2.2 Kinetic Considerations The actual cell voltage required for the cell reaction under practical conditions is always higher than the required equili brium voltage of 0.17V. There are always efficiency losses due to the resistance of the el ectrolyte, change in the electrode potentials due to concentration polarizati ons, such as hydrogen ion con centration, voltage gradient set up at the electrode electrolyte interface an d some small losses in the metals parts of the external circuit. The difference between the actual cell voltage and the equilibrium voltage is commonly known as overvoltage. In general, the actual cell voltage is composed of the equilibrium voltage, ohmic voltage drop (IR) and the anodi c and cathodic over potentials .The actual cell voltage can therefore be written as Actual cell voltage = (Equilibrium voltage) + (Voltage drop in cell) + (Overvoltage) 3.3 Selection of Electrode Materials Materials evaluation and selection of elec trode materials for the electrolyzer was the toughest and most time consuming part for the project, since these materials have to withstand the corrosive environment of sulfur ic acid. Sulfuric acid changes its behavior from an acid reducing to an oxidizing e nvironment depending upon the concentration and temperature. The selection of electrode materials for th e anode and th e cathode should meet the following requirements for effici ent operation of the system [12, 13]. Long term stability Good electrical conduction Good selectivity Large specific surface area
Minimized gas bubble problems Low cost and large availability Health safety Good mechanical properties Good catalytic properties Satisfying the above requirements and finding electrode materials for the sulfuric acid environment was very difficult. Various meta ls and alloys were tested for electrode materials but most of them corroded when used as the anode in sulfuric acid. Most of the metals tested had satisfactory results as the negative electrode. The various metals tested were Lead, Alloy C-276, Alloy C-2000, 316SS, Carbon, Gold, Zirconi um and Tungsten Carbide. The test results of these materials are presented in Appendix A. Electrolysis was carried out with lead, Alloy C-276, 316SS and Carbon. Test runs with lead and Alloy C276 electrodes were not satisfa ctory, later it was decided to use carbon as the anode and stainless steel coated with platinum as the cathode since platinum provides the purpose of catalyst for the hydrogen electrode. Gold and pl atinum were found to be appropriate for sulfuric acid but the cost of gold or plati num was not affordable for use as electrode material. All the experimental results of the el ectrolysis with different type of electrodes will be explained in detail in Chapter 4. More information is still needed in this area. 3.4 Fabrication of the Electrolyzer The key component for the resear ch was a versatile electrolyzer that can be used for both electrochemical and photoelectrochemi cal experiments. A sectional view of the electrolyzer is shown in Figure 3.2. The cell wa s operated at due sout h tilt of 28 degrees, the latitude in central Florida. The cell is mounted on a stand as shown in Figure 3.3. The
cell pressure was maintained at 100psig by a back pressure re gulator at the outlet and was operated at ambient temperature. A detailed description of individual components of the cell is contained in Section 3.4.1 to 3.4.4 below. Numbers us ed for labeling different co mponents in the figure would be used to explain the cell description.
Figure 3.2 Cross Sectional View of the Electrolyzer
Figure 3.3 Tilted View of the Electrolyzer
3.4.1 Cell Body The cell is circular in shape when seen from the top. The cell body was made of Teflon, since Teflon is non corrosive to sulfuric acid and easy to machine. It consists of two teflon sections (11 & 13) which are bolted together using stainl ess steel bolts (15). Steel plates (10 & 14) at the top and botto m surfaces to reinforce the Teflon and help withstand the pressure. A torque wrench (3 0 pounds max) was used for tightening the bolts. Viton O-rings (16) were used to seal the system. The top cover of the cell was made intially of glass and later on replaced by aluminum and teflon disc. The description of these is given below. A glass window of 1 1/4 thick was used to cover the cell. It serves as a view port from the top to have a clear view of the negative compartment. It also provides light access for the photoel ectrochemical experiments. A gas pocket was always maintained at the hydrogen outlet. The size of the pocket was monitored by looking through the glass window. An alumimum (3) and teflon (4) disc repl aced the glass since the glass cracked a couple of times while pressure testing the system. Since there was no view port to observe the gas pocket a level sensor was installed. The level sensor consists of three probes made of gold plated stainle ss steel bolts (5, 8, & 9). The edge of the pocket was always maintained between th e probes 8 & 9. The working principle of the level sensor is discussed in section 3.6.
3.4.2 Electrodes The cell incorporates three electrodes, the positive electrode (17), the negative electrode (6), and the sensor ring positive electrode (2 ). The positive and negative electrodes were 4 inch diameter electrodes se parated by a glass or Teflon (19) insulator. Experiments were performed using a variety of electrode materials. The experimental results are discussed in chapter 4. Negative Electrode: The negative electrode (6 ) was platinum coat ed stainless steel electrode. It was 4 inches in diameter a nd 1/16 thick. Platinum on the surface of the electrode served the purpose of the catalyst. Positive Electrode: The positive electrode (17) was made of carbon which was 4 inches in diameter and 3/32 thick. The positive electrode was screwed on the barrier (7) using 4-40 flat head machine sc rews. The barrier is made of carbon. It consists of a thick, 4 diameter disk with a thick, 1 diameter hub projecting from its upper surface. Four sma ll holes extend radially from the center to the edge of the hub di stributing sulfur dioxide in all directions below the surface of the positive electrode. The space between the positive electrode and the barrier is packed with gra phite yarn. The graphite yarn increases the surface area for the oxidation of sulfur dioxide. The ba rrier is used as a support for wrapping the graphite yarn and also as support for the electrodes. Sensor Ring Positive Electrode: The sensor ring (2) is made of carbon. It is placed near the periphery of the positive compar tment surrounding the positive barrier. It has a voltage bias that is slightly more positive relati ve to the positive electrode but its voltage is still too small for direct decomposition of water. The sensor ring
served three important purposes 1) Sens ing the sulfur dioxide. 2) Repulsion of hydrogen ions from the positive compartment to the negative compartment. 3) Oxidizing the sulfur dioxide. 3.4.3 Liquid and Gas Feedthroughs The cell contains th ree liquid feed throughs and one gas feedthrough two inlets and one outlet for liquid and one gas outle t for the hydrogen gas. The three liquid feedthroughs are 1) Sulfur dioxide and water in let at the bottom of the cell. 2) Sulfuric acid outlet at the bottom of the cell and 3) Water inlet at the top of th e cell. All the liquid feedthroughs for the cell were made of 1/16 316 SS tubi ng. Initially the tubing was inserted through straight holes in the tefl on walls and was sealed with Apeizon W wax. Later on to make the system mechanically st urdy it was decided to use 316 SS 1/8 NPT pipe fitting (1,21,12) that was threaded onto Teflon which helped in better sealing the system to prevent leakage All the external tubings used were made of Teflon 1/16.A detailed description and working of the flow control system will be discussed in section 3.7. 3.4.4 Electrical Connections The conductors carrying the elec trical current through th e walls of the cell are stainless steel bolts that fit snugly into hol es drilled through the cell walls. The inside ends of the holes are tapered and the outside ends are flat. The bolt is passed through the holes in the cell wall from the inside to the outside. An O-ring fits sn ugly around the inside end of the bolt and seats between the head of the bolt and the tapered inside edge
of the hole in the cell wall. A nut on the bolt outside the cell wall is tightened so as to squeeze the O-ring between the bolt head and the cell wall. In this way the O-ring provides the seal preventing a ny fluid from leaking out of the cell. When the cell is pressurized, the pressure provides additional force on the O-ring making the seal firmer. The bolts heads of the electric feedth roughs are connected to the cell electrodes by stainless steel wires. The one end of the st ainless steel wire is soldered to the bolt head. The other end is connected to a nu t and bolt combinati on. The bolt in this combination passes through a hole in the ca rbon electrode and holds the nut firmly against the carbon when the nut and the bolt combination is tightened. All the wires, solder joints, nuts and bolts is completely coated with teflon and wax to protect them from corrosion. 3.5 Operation of the Electrolyzer In either the electrochemical or photoe lectrochemical mode, sulfur dioxide and water are pumped in through a tube at the bottom of the cell as shown in the Figure 3.2 and distributed over the lower surface of th e positive electrode. The sulfuric acid produced flows through grooves near the periphery and in the base of the cell to an exit tube through which it is w ithdrawn and collected. The hydroge n ions are produced at the positive electrode flow to the negative (upper) compartment across the electrolyte bridge around the periphery of the electrodes. There, they are converted to hydrogen gas that rises to the top where it can be removed thr ough the withdrawn tube. The gas is collected through a water displacement process. The gas co llection system is explained in detail in section 3.8.
Initially flows are controlled using two metering pumps that insert the sulfur dioxide and water. The cell pressure is maintained at 100psig with a back pressure regulator at the sulfuric acid outlet. A sma ll insertion tube in the negative compartment allows addition of small quantities of water or sulfuric acid. Init ial experiments were performed using this setup but the results s howed the reduction of sulfur dioxide in the negative compartment in spite of the sensor ring used. Later on various studies were done to stop the problem of migration of sulfur dioxide to the negative compartment. It was decided to operate the system with a con tinuous flow from the negative compartment to the positive compartment, controlled by a metering pump. To implement this, a third metering pump was used to insert fluid contin uously through the insertion tube into the center of the negative compartment. The inse rted fluid flows from the negative to the positive compartment through the electrolyte bridge, sweeping any diffusing sulfur dioxide back into the positive compartment. Experiments were conducted using this setup and it was found to be working to prevent the reduction of sulfur dioxide as compared to previous runs with two pumps. Further resear ch has to be performed to make the system more efficient to avoid the sulfur dioxide reduction. A complete description of loading and unloading the system is described in sections 3.7. 3.6 Measurement System With the help from Kiran Gaikwad (one of our graduate students) and Matt Smith (CERC engineer ) a complete data acquisiti on system was designed for the electrolyzer to monitor pressure, control pumps and reco rd the current voltage behavior for the system.
Initially the cell was operated using a glass window which provided a view port for the negative compartment. A gas pocket was always maintained at the hydrogen outlet to prevent the sulfuric acid from entering the hydrogen line by looking through the glass window. When the glass window was replaced with an opaque cover, a sensor probe had to be installed for sensing the size of the pocket. The working principle of the level sensor is shown in the Figure 3.4. Figure 3.4 Level Sensor Circuit Consider two electrodes A & B made of the same material as the level sensor used in the cell immersed in sulfuric acid of the desired concentration. In other words consider the beaker to be the electrochemical cell with two level sensors at the top. A resistance R of known value is connected in series with one of the electrodes. A high frequency AC signal (V) is applied to the circuit as shown in the Figure 3.4. An AC signal is preferred instead of a DC signal to avoid polarization effects. When both the electrodes are covered
by the acid a sharp AC signal is seen on th e CRO. When the electrodes are uncovered there is no signal on the CRO. The electrodes us ed for the level sensor used in the cell were 316 SS gold plated machine screws. The sa me principle can be applied in carrying out conductivity measurements. The current calcul ation for the circuit is as shown below. V= V1 + V2 (188.8.131.52) I = V1/R (184.108.40.206) R is known and V1, obtained from the CRO output, can be used to calculate the current. Since the circuit is in series, current I would be the same for both electrodes. Voltage V2 can be calculated from the first equation. Selection of R 50.5 ohms, V = 1 volt peak to peak and frequency = 10 kHz, produced a sharp signal on the CRO. The electrical feedthroughs for the three probes consist of bolt seals with O-rings like those for the electrical feedthrough. 3.7 Flow Control System The complete process flow diagram is shown schematically in Figure 3.5. The system has three metering pumps. Two pu mps are used for pumping water and liquid sulfur dioxide respectively to the bottom of the cell, and the third pump is used for pumping water from the top of the cell. Each of the three pumps is connected to a 1000 psig back pressure regulator. The pressure insi de the cell is maintained at 100psig with a 100 psig BPR at the outlet line.
Figure 3.5 Flow Control System
As seen in the figure two back pressure re gulators are connected in parallel to avoid breakdown of the system during experiments. If one of them gets clogged, the operation of the system is shifted to the second one while the first one is cleaned. The pressure inside the cell was monitored using a pressu re sensor placed at the inlet line to the electrolyzer. The pressure se nsor was connected to the data acquisition system for monitoring pressure. The hydrogen gas was collected using a water displacement process. All the tubing used in the flow system was made of Teflon since it is non corrosive to sulfuric acid. Calculations of flow rates for the system are shown in Appendix B. Nomenclature for Figur e 3.5 is shown in Table 3.1 below. Table 3.1 Nomenclatures for Figure 3.5 A, B, C Pumps AV-1, BV-1, CV-1 Prime Valves AR 1000 BR 1000 CR 1000 1000psig Back Pressure Regulators SR 100 (1), SR 100 (2) 100 psig Back Pressure Regulators AV-2,NV-1,PV-1,PV-2,BV-2,BV-4,BV-5,SV-1,SV2,SV-3,CV-3,CV-4,CV-5,CV-6,HV-1,HV-5,HV4,HV-3,HV-6,HV-7 Shut Off Valves HV-2 Proportional Control Valve BV-3 Check Valve L A L B L C Level Sensors PH Hydrometer F Filter PS Pressure Sensor PG Pressure Gauge IR Pressure Gauge VP Vacuum Pump E-1, E-2, E-3, E-4 Glass Beakers
After the cell is assembled it is pressure tested with water to check for any leaks using the flow control system shown in the figure. Once the cell has passed the leak test it is ready for experiments with sulfuric acid. 3.7.1 Water Pressure Test Procedure All the three pumps are used for filling th e cell with DI water. All the three pumps are first checked individually for prime. The procedure of water pres sure testing is shown below 1. Check Pump A for prime. Valves Closed: all Open Valve PV-1. Turn ON Pump A. Connect a Leur Lock Syringe to the prime valve (AV-1). Run the pump at a flow rate of 3-5ml/min. Prime the pump by pulling mobile phase and any air bubbles through th e system and into the syringe ( a minimum of 20ml) Remove the syringe and keep the pump running for couple of minutes. Water pumped by the pump is collected in beaker E-3 Turn off pump A. Close valve PV-1. 2. Check Pump B for prime. Valves Closed: all Open Valves: BV-2, BV-4, and PV-2. Turn on Pump B.
Connect a Leur Lock Syringe to the prime valve (BV-1). Run the pump at a flow rate of 3-5ml/min. Prime the pump by pulling mobile phase and any air bubbles through th e system and into the syringe ( a minimum of 20ml) Remove the syringe and keep the pump running for couple of minutes. Water pumped by the pump is collected in beaker E-3. Turn off pump B. Close valves BV-2, BV-4 and PV-2 3. Check Pump C for prime. Pump C is used for pumping liquid Sulfur dioxide during the actual experiment. It is important to rem ove the air present in valve CV-5 by releasing some liquid sulfur dioxide through the line in beaker E-2 filled with water. To do that keep valve CV-6 closed and keep valve CV-4 and CV-3 open. Slowly open valve CV-5 connected to the Sulfur dioxide tank, bubble out some sulfur dioxide th rough water in beaker E-2 and then close valve CV-5.The flow through CV-3 in this step is opposite to the normal direction these valves. Valve CV-5 would remain close till we need to pass sulfur dioxide in the ce ll during experiments. Dispose of the water in beaker E-2 and fill it with fresh DI water for priming the pump C. After this is done follow the pr ocedure for priming the pump. Valves Closed: all except CV-3 and CV-4 Open Valve: CV-2 and PV-2. Turn on Pump C.
Connect a Leur Lock Syringe to the prime valve (CV-1). Run the pump at a flow rate of 3-5ml/min. Prime the pump by pulling mobile phase and any air bubbles through th e system and into the syringe ( a minimum of 20ml) Remove the syringe and keep the pump running for couple of minutes. Water pumped by the pump is collected in beaker E-3. Turn off pump C. Close all valves 4. Water Pressure Testing Turn on all the three pumps. Valves Closed : all Line between HV-1 and HV-2 is disconn ected during water pressure test. Open Valves : AV-2,SV-2,SV-1,BV-2,BV-4,BV-5,CV-2,CV-3,CV-4, HV-1. Run all the three pumps at the flow rate of 10ml/min since that is the max flow rate the pumps can go. Once the ce ll is filled with water and the valve HV-1 is filled. Close the valve HV-1 and monitor the pressure inside the cell on the computer. Once the pressu re reaches 90psig reduce the flow rates of all the three pumps such th at the combined flow rates of the pumps not exceed 1ml/min. This is done since the back pressure regulator SR100 at the outlet cannot withstand higher flow rates. Keep the system running for one hour and check for le aks. The water from the cell is withdrawn in beaker E-4. Turn off the pumps. Close all valves.
5. Draining the cell Once the cell has passed the le ak test the cell is drained. Valves Closed: all Open Valves: PV-2, PV-1, AV-2, SV-1 and BV-5. Disconnect line between SV-1 and F Introduce Nitrogen or compressed gas by opening valve NV-1. The gas helps in draining the cell fast. Once the cell is drained the cell is ready for electrolysis. Reconnect SV-1 and F and close all valves. 3.7.2 Loading the Cell with Sulfu ric Acid for Electrolysis For loading the system with sulfuric aci d only two pumps A and B are used. The third pump C is only turned on to allow flow of liquid sulfur dioxide. A gas pocket is always maintained between level sensors LB & LC. The procedure for priming the pump would still remain the same as explained in sec tion 3.7.1. The procedure for loading the system with sulfuric acid is explained below. 1. Fill the beaker E-1 with the desired concentration of sulfuric acid. 2. Check the prime of the pump as explained in section 3.7.1. 3. Valves Closed : all 4. Open Valves: AV-2, SV-2, BV-2, BV-4, BV-5, SV-1, and HV-1. 5. Run the pumps A & B at their maximum flow rates. Give a high frequency AC signal between the electrodes LA and the top inlet line (refer section 3.6) for
circuit connection. As soon as signal is seen between th e two electrodes turn off the pumps. 6. Open valve NV-1 and pass nitrogen inside the cell. This is used for purging the cell with nitrogen to flush out any traces of air inside the cell. Close valve HV-1 and then close NV-1. Give AC signal between probes LA and LB. Turn on the pumps and check the signal between the two electrodes. Once the electrodes are covered, monitor the pressure and turn off the pumps. If the pressure is less than 100psig keep the pumps running till th e pressure reaches 100psig. Once the pressures reach 100psig turn down the flow rates to the desired flow rates and check the pocket. If the pocket is between LB & LC then the system is ready for the electrolysis. If the pressure is more than 100psig turn of the pumps and release some pressure through valve HV-1 till it co mes back to 100psig. This is continued till we maintain a pocket between the level sensors LB & LC. Keep the pumps running for 1hour so that system has no traces of water and it is full of sulfuric acid inside the cell. 7. Connection between valves HV-1 and HV-2 was disconnected for water pressure test. Reconnect these lines During the electrolysis the hydrogen gas produced is collected through a water displacemen t process and analyzed using Gas Chromatography and Infrared Spectrosc opy. The hydrogen collection system is described in detail in Section 3.8. 8. During the electrolysis sulfur dioxide is introduced in the cel l when required. For introducing sulfur dioxide valves CV-2 and CV-5 are opened and pump C is switched on. Pressure inside the cell a nd pocket between the level sensors is
always monitored. Density of sulfuric acid collected in beaker E-4 is monitored with a hydrometer (PH). 9. Once sulfur dioxide is passed inside the cell, pressure is never released from the top. It is always released from the botto m of the cell to prev ent migration of the sulfur dioxide into the negative co mpartment and to form sulfur. 3.7.3 Shutting Down the System Shutting down and flushing the system is very carefully done once sulfur dioxide is inside the cell. After the experiment, poten tial is still given across the electrodes to oxidize the sulfur dioxide during flushing of the system. The shut down procedure is given below. 1. Close valves CV-5 2. Open Valves: CV-3, CV-4 and CV-6. 3. Turn OFF pumps A & B and replace dilute sulfuric acid in beakers E-1 & E-2 with DI water. Water is used instead of acid to flush the pumps and the lines. 4. Turn pumps A & B back ON. 5. Set the flow rate of pump C at ha lf the flow rate of Pump B. 6. Keeping the systems running for 2 hours, under this setup, helps the removal of any sulfur dioxide inside the cell and al so flushes the sulfur dioxide pump. 7. For draining the system follow step 5 in section 3.7.1.
3.8 Hydrogen Gas Collection System A detailed schematic of hydrogen gas collection system is shown in Figure 3.6. The gas was collected through a water displacement apparatus as shown in the figure. When the gas is released from the top, liquid is only pumped through the top of the cell and no liquid is pumped through the bottom of the cell .The hydrogen gas was analyzed using gas chromatography and infrared spectroscopy. The setup has a means of analyzing the gas collected through the water displacement process and also samples extracted directly from the cell outlet to find any traces of water soluble gases. Both the procedures for analyzing the samples are explained below. Figure 3.6 Hydrogen Gas Collection System 3.8.1 Hydrogen Gas Analysis through Water Displacement During the electrolysis, a gas pocket is always maintained between level sensors LB and LC. Once the gas pocket is maintained HV-1 is opened. Valve HV-2 is a proportional control valve. The proportional control valve is set to balance the rate of gas
release with the rate of hydrogen production. The setting is changed when level sensors LB and LC indicate that this balance is not maintained. The procedure for gas analysis is described below. 1. Remove the air in the lines using the vacuum pump. Valves closed HV-5, HV-3 and HV-2; Valves opened HV-6, HV-7, and HV-4. 2. Turn on the vacuum pump and keep it running for 10 minutes. Open valve HV-5 (stop cock valve) so that water in th e displacement tube rises up to the stopcock .Close valve HV-5 and keep the pump runni ng for 5 minutes so th at all the air in the line is removed. 3. Close valve HV-6 followed by HV-7 and turn off the pump. 4. Release the hydrogen gas by opening valv e HV-2 it is bubbled through water and collected in the flask. Close valve HV-2. Open valve HV-6 followed by HV-5 and pressure gauge reads atmospheric pressure. Place the syringe in the septum and take some gas out for analysis. Close valves HV-5 and HV-6 3.8.2 Hydrogen Gas Analysis without Water Displacement In this process the hydroge n gas is not passed through water. The procedure is described below. 1. Remove the air in lines using the v acuum pump. Valves closed HV-5, HV-6, HV4 and HV-2; Valves opened HV-3 and HV-7. 2. Turn on the vacuum pump and keep it running for 10 minutes and then close HV3 followed by HV-7.Turn off the pump.
3. Open valve HV-2. Place the syringe in th e septum and take some gas out for analysis. Once the gas is taken out in the syringe close valve HV-2. Collecting the gas in the infrared cell is si milar to the process explained in section 3.8.1 and 3.8.2.
CHAPTER 4 EXPERIMENTS AND RESULTS After the preparatory work of designing the cell and flow control system. The cell was ready for the experiments. The various electrolysis experiments conducted will be discussed in this chapter. For all the experi ments, measurements were started with a low voltage at which water could not be electrolyzed so ampera ge was negligible. Voltage was increased in steps until current was substantial. The voltage was then cut back to a level near the beginning of the current rise, the sensor ring vo ltage was kept fixed. At this voltage setting, SO 2 was introduced at a flow rate of 0.01ml/min. When the sensor ring showed an increase in current the SO 2 flow rate was cut back or SO 2 pump was turned off so that the sensor ring current comes down, the electrode voltage was also increased simultaneously so that the SO 2 is oxidized in the positive compartment. 4.1 Electrolysis I 4.1.1 Electrode Materials Positive Electrode: Gold Plated 316 Stainless Steel. Negative Electrode: Platinum Coated 316 Stainless Steel. Sensor Ring: Gold Plated C-276Alloy welding rod. 4.1.2 Preparation of Electrodes Positive Electrode: The 316 Stainless st eel electrodes are first cleaned with dish detergent and then rinsed with DI water. The electrodes are then soaked
in alkaline solution for 10 minu tes and again rinsed with DI water. Finally the electrodes are rinsed in 20% HCL acid solution and rinsed with DI water. After the electrodes were cleaned gold was deposited on the surface of the electrodes using an Electron Beam Evaporator. The gold deposited was 800 A 0 thick. Negative Electrode: Cleaning procedur e for the 316 SS is the same as described for the positive electrode. 800 A 0 thick platinum layers were deposited using an Electron Beam Evaporator. Platinum served the purpose of catalyst for the hydrogen electrode. Sensor Ring: The C-276 alloy weld ing rod used for the sensor ring underwent the same cleaning procedure and deposition used for stainless steel as the positive electrode. Carbon Barrier: The carbon usually contains an organic binder which is a non conductor. It is important to rem ove any excess binder on the surface, and depending on the binder, it may be bette r to use either an aliphatic or an aromatic solvent or carbon tetrachlo ride. Since the type of binder was unknown the carbon was cleaned with both types of solvents. After cleaning, the carbon is wipe d with a Kimwipe and rins ed with DI water. If water beads up on the surface of the elec trode, then the carbon is not clean enough. After cleaning an 800 A 0 thick layer of gold was deposited using evaporation.
The positive electrode was screwed down to the barrier using 4-40 machine screws. The space between the positive electrode and barrier was packed with graphite yarn. A glass insulator was used between the positive and the negative electrodes. A glass window was used at the top to give a clear view of the negative compartment. In this electrolysis set up only two pumps were used. The process flow diagram for Electrolysis I was different from that shown in chapter 3. The process flow block diagram for electrolysis I is shown in Figure 4.1. After the cell was assembled it was pressure tested with water to check leaks in the system. Once the cell passed the leak test it was ready for the electrolysis experiment. Figure 4.1 Process Flow Diagram Electrolysis I
Liquid sulfur dioxide and water were pumped at specifie d rates using two metering pumps. The flows are mixed and passed into the electrolysis cell where they react to produce hydrogen that is withdrawn at the t op of the cell and sulfuric acid that is withdrawn at the bottom of the cell. The cell pr essure is maintained at 100psig by a back pressure regulator in the sulfuric acid exit line. 4.1.3 Results and Discussions With SO 2 in the cell current rose and we could see increased bubbling of hydrogen from the negative electrode could be seen by looking through the window. The experimental results are shown in Appendix C .The current voltage curve is shown in Figure 4.2. Reduction of voltage reduced the amperage and hydrogen production but they continued to exist to voltages well below th e voltage required to electrolyze water. An analysis of the gas product wa s not possible at that time. During the electrolysis it wa s found that the acid change d color. The sensor ring made of alloy C-276 corroded under positive pot ential discharging a yellow stream from the surface. Gold deposited on the surface of the sensor ring peeled of during the electrolysis. Platinum coated on the negative el ectrode also flaked off. All this electrode deteriorations were observed through the glass window. The sensor ring was disconnected from the power s upply to stop its corrosion, this prevented us from sensing the sulfur dioxide migrating through the posit ive. At the end of the electrolysis the negative electrode was coated with a yellow color which was thought to be sulfur deposits. At the end of the experiment we were not able to flush the system because the fitting on the sulfur dioxide pumped cracked. The positive compartment of the cell was
examined after the cell was taken apart. It was found that gold deposited on the positive electrode also flaked off. Gold deposited on the carbon barrier was still adherant. Figure 4.3 shows the surface of the electrodes after electrolysis. 00.050.10.150.220.127.116.110.40.418.104.22.168.70.80.922.214.171.124.4Voltage (V)Current (amps)00.511.522.53H2 Production (ml/min) With SO2 Without SO2 Figure 4.2 Current Voltage Curve Electrolysis I
Negative Electrode coated with Sulfur Cell view from top Positive 316 SS Electrode Graphite yarn on Barrier Figure 4.3 Electrode View Electrolysis I 4.1.4 Interpretation On the basis of the experimental results and observations the following conclusions can be reached: Alloy C-276 used for the sensor ring was not considered suitable as a positive electrode material because of corrosion. It was decided to make the sensor ring out of carbon. Gold evaporated onto the positive stainless steel electrode peeled of during the electrolysis. Evaporation used for the deposition was not a good approach for gold
deposition. In later experiments it was d ecided to make the positive electrode out of carbon and deposit gold on its surface using electroplating. Platinum on the surface of the negative electrode peeled of during electrolysis. Later on it was found that platinum ha s bad adhesion on stainless steel if deposited directly on the el ectrode without a seed laye r. It was decided to use Acid Gold Strike as seed layer whic h would give a good adhesion to platinum. Gold Strike was selected since it was non co rrosive to acid. It is a ready to use solution manufactured by Technic Inc (Newyork). All of the above changes were made prior to the second electrolysis experiment (Electrolysis II). 4.2 Electrolysis II 4.2.1 Electrode Materials Positive Electrode: Gold Plated Carbon. Negative Electrode: Platinum Coated 316S tainlessSteel (Gold Strike as seed layer). Sensor Ring: Carbon. 4.2.2 Preparation of Electrodes Positive Electrode: Carbon underwent the same cleaning procedure explained in Electrolysis I. Gold was deposited on carbon using electroplating. Technic OROSTRIKE C an acid gold strike solution was used for electroplating. The electrop lating was performed using a 316SS
anode. The voltage used for the elec troplating was between 1.8 to 2.0 volts at 100 0 F for 30 minutes. Negative Electrode: 316SS underwen t the same cleaning procedure explained in Electrolysis I. Gold was depositing on 316SS using electroplating. Technic Acid Gold Stri ke an acid gold strike solution was used for electroplating. The solution provides excellent ad hesion directly on Stainless Steel. The electroplating wa s performed using a 316SS anode. The voltage used for the electroplating was 2.0 volts at room temperature for 30minutes. Platinum was evapor ated on the surface of gold. Sensor Ring: Carbon was cleaned using the same cleaning procedure described previously. Carbon Barrier: It was the same barrier used in Electrolysis I. It underwent the cleaning procedure used for cleaning carbon. The positive electrode was screwed down to th e barrier using 4-40 machine screws. The space between the positive electrode and barrie r was packed with graphite yarn. A glass insulator was used between the positive and the negative electrode. Glass window at the top was replaced by an aluminum and Teflon disc. Three level sensors were used to maintain the pocket in the negative compar tment (refer to sec tion 3.4.1). The process flow diagram for Electrolysis II is the same as for Electrolysis I. After the cell was assembled it was pressure tested with water to check leaks in the system. Once the cell passed the leak test it was ready for electrolysis.
4.2.3 Results and Discussions The sensor ring voltage was kept fixed at 1.8V (see appendix D). At this voltage setting, SO2 was introduced at a flow rate of 0.01ml/min. The current voltage curve is shown in Figure 4.4. 00.10.20.30.126.96.36.199.188.8.131.52184.108.40.206.51.6Volts (V)Current (amps)00.511.522.533.54H2 Production (ml/min) With SO2 Without SO2 Figure 4.4 Current Voltage Curve Electrolysis II A view of the negative compartment was not available since the top was covered. Liquid level was maintained between level sensors LB & LC (Refer chapter 3). When the sensors are uncovered hydrogen gas is released with the help of the proportional control valve and collected through the water displacement apparatus. The SO 2 pump is switched off and water or sulfuric acid flow is switched from bottom to the top. Pressure is
monitored very carefully while releasing th e gas. This is done till the pocket size is reduced and liquid level is maintained betw een level sensors LB & LC. Any change in the acid color was monitored through the outle t line. It was seen that the acid turned yellow in color. After the experiment the system was flushed with DI water. The cell was examined once it was taken apart. It was found th at in spite of the co ntrol of the sensor ring current, we had not stopped the diffusion of sulfur dioxide into the negative compartment The negative electrode had depos its of sulfur. The platinum on the surface of the electrode turned black, it was anticipated that it would be the formation of platinum hydride by the absorption of hydrogen and secondly it could also be platinum getting poisoned by the formation of sulfur. Some amo unt of platinum also peeled of from the surface of the electrode. The platinum had bette r ( but not perfect ) adhesion to stainless steel with the use of gold strike in this experiment as comp ared to the first experiment without the gold strike. The positive electrode was much more stable and the gold deposited was still adherant. 4.2.4 Interpretation On the basis of the experimental results and observation related to th e second electrolysis experiment, the following conclusions can be drawn: To stop the problem of migration of sulf ur dioxide to the negative compartment we must operate the system with a continuous flow from the negative compartment to the positive compartment, controlled by a metering pump. To implement this a third metering pump was used in later experiments.
It was speculated that the reduced current may be because of ionic buildup in the cell compartments. It was decided to tr y a porous negative electrode (stainless steel gauze) with a porous glass diaphrag m for the next experiment (electrolysis III). 4.3 Electrolysis III 4.3.1 Electrode Materials Positive Electrode: Gold Plated Carbon Barrier. Negative Electrode: Platinum Coated 316 Stainless Steel wire gauze (Gold Strike as seed layer). Sensor Ring: Carbon. 4.3.2 Preparation of Electrodes Positive Electrode: The Carbon electrode was removed for this experiment since there was no space for the 8mm th ick glass diaphragm inside the cell. Electric connection was made to the car bon barrier. The carbon barrier used in this experiment was the same as th at used in the previous experiments. Negative Electrode: 316SS wire gauze underwent the same cleaning procedure used for cleaning stainless steel. Four layer wire gauze of 5inch diameter consisting of 2 layers of wire diameter 0.0055 with an opening of 0.178 mm and two with a wire diamet er 0.0045 with an opening of 0.140 mm were used. All four wire gauze la yers were connected to each other using 4-40 machine screws. Platinum wa s evaporated on both sides of each layer.
Sensor Ring: The carbon was cleaned using the same cleaning procedure described previously. The glass diaphragm of 5 inch diameter of pore size 1015 micr ons was placed on the top of the barrier. The space between the glas s and the barrier was packed with graphite yarn. The fluid feedthrough from the top of cell was made of 316 SS capillary tubing was used as a means of connecting to the negative electrode .The electr olysis was done using three metering pumps. The process flow diag ram for Electrolysis III was different from the previous two electrolyses (refer to Figure 3.5). After the cell was assembled it was pressure tested with water to check leaks in the system. Once the cell passed the leak test it was ready for electrolysis. The operating procedure for the cell with three pumps is discussed in chapter 3 (section 3.7.1 to 3.7.3). 4.3.3 Results and Discussions The sensor ring voltage was kept fixed at 1.8V. At this voltage setting, SO2 was introduced at a flow rate of 0.01ml/min (see appendix E). When th e sensor ring showed an increase in current the SO2 flow rate wa s cut back or SO2 pump was turned off. Keeping in mind the max flow ra te of the back pressure regu lator fluid flow from the top was increased so that it sweeps away the sulf ur dioxide from the negative to the positive compartment. The current voltage curve is shown in Figure 4.5.
00.050.10.150.220.127.116.110.40.418.104.22.168.922.214.171.124.41.51.6Volts (V)Current (amps)00.511.522.53H2 Production (ml/min) With SO2 Without SO2 Figure 4.5 Current Voltage Curve Electrolysis III A view of the negative compartment was not available since the top was covered. The liquid level was maintained between the level sensors LB & LC. When the sensors are uncovered hydrogen gas is released with the help of the proportional control valve and collected through a water displacement apparatus. While releasing the gas liquid flow from bottom of the cell is turned off and liquid flow into the top compartment is increased to 1ml/min (i.e. max limit of 100 psig back pressure regulator).The Pressure is monitored very carefully while releasing the gas. This is done untill the pocket size is reduced and liquid level is maintained between level sensor LB & LC The GC analysis of the hydrogen gas showed that it was 30% hydrogen. At this point we were not able to analyze remaining percentage of gas. Any change in the acid color was monitored through the outlet line. It was seen that the acid turned yellow in color. After the
experiment the system was flushed with DI water. The cell was examined once it was taken apart. It was found that in spite of th e control of the sensor ring current and flow from the top, we were not able to stop the transport of sulfur dioxide to the negative compartment. The negative electrode had depos its of sulfur. The gl ass separator had lot of yellow deposits on the surface. The platin um on the surface of the electrode turned black, it was speculated that it was the forma tion of platinum hydride by the absorption of hydrogen and or platinum getting poisoned by the formation of sulfur. The positive electrode was stable and the de posited gold was still adherent. 4.3.4 Interpretation On the basis of the experimental results and observation related to the third electrolysis experiment, the following conclusions can be drawn: Deposits of sulfur on the negative electrode and the glass separator showed that the use of porous negative electrode and use of glass separator was not satisfactory It was decided to perform an additional experiment without porous electrode and with a good control of the fluid from th e top. In this way we could have a better comparison of the experime nts with and without porous electrodes. The hydrogen gas analyzed showed that it was 30 % hydrogen. Since the analysis of the gas was done couple of days after th e experiment it was anticipated that the gas must have been contaminated. The UV analysis done for the sulfuric acid sample show ed strong peaks of sulfur dioxide. This showed that the sulfur dioxi de was not completely oxidized in the positive compartment and the unreacted sulfur dioxide was withdrawn from the
bottom of the cell along with the sulfuric acid. It was deci ded to fill the gap between the outside diameter of the barrier and the inside diameter of the sensor ring with Teflon so that sulfur dioxide has a longer path in contact with the surface of the sensor ring which would help in oxidizing the sulfur dioxide before coming out from the bottom of the cell It was decided to make these changes in later experiments. 4.4 Electrolysis IV 4.4.1 Electrode Materials Positive Electrode: Gold Plated Carbon. Negative Electrode: Platinum Coated 316 Stainless Steel (Gold Strike as seed layer). Sensor Ring: Carbon. 4.4.2 Preparation of Electrodes All the electrodes were prepared the same way as for Electrolysis II (section 4.2.2) The positive electrode was screwed down to the barrier using 4-40 machine screws. The space between the positive electrode and barrier was packed with graphite yarn. A glass insulator was used between the positive and the negative electrode. The fluid feedthrough from the top of cell made of 316 SS capillary tubing was used as a means of connection for the negative electr ode .The electrolysis was done using three metering pumps. The operating procedure of the cell is same as done in Electrolysis III.
After the cell was assembled it was pressure tested with water to check leaks in the system. Once the cell passed the leak test it was ready for electrolysis. 4.4.3 Results and Discussions The sensor ring voltage was kept fixed at 1.6Volts (see appendix F) .At this voltage setting, SO2 was introduced at a flow rate of 0.01ml/min. The electrode voltage was adjusted to a minimum value to see substantia l amount of current with sulfur dioxide in the positive compartment. It was found that 0.9 volts was th e minimum voltage required to see substantial amount of current. The curr ent voltage curve is shown in Figure 4.6. When the sensor ring showed an increase in current the SO2 flow rate was cut back or SO2 pump was turned off. Keeping in mind the max flow rate of the back pressure regulator, fluid flow from the top was increase d so that it sweeps away the sulfur dioxide from the negative to the positive compartment. A view of the negative compartment was not available since the top was covered. Liquid level was maintained between level sensor LB & LC. When the sensors are uncove red hydrogen gas is released with the help of the proportional control valve and collected through water displacement apparatus. While the gas is released flow from bottom of the cell is turned off and fluid flow from the top compartment is increased to 1ml/mi n (i.e. max limit of 100 psig back pressure regulator) .Pressure is monitored very carefully while releasing the ga s. This is done till the pocket size is reduced and liquid level is maintained between level sensor LB & LC. The GC analysis of the hydrogen gas showed that it was 75% hydrogen.
00.050.10.150.126.96.36.1990.40.70.80.9188.8.131.52.184.108.40.206.9Volts (V)Current (amps)00.511.522.5H2 Production ( ml/min ) With SO2 Without SO2 Figure 4.6 Current Voltage Curve Electrolysis IV The GC analysis of the gas sample is shown in Figure 4.7 below. Two columns were used two analyze the sample. One column was used to detect hydrogen and the other one was used to separate sulfur compounds from air. There was no sulfur compounds detected in the analysis. The Infrared analysis showed that there were no sulfur compounds in the collected gas. Any change in the acid color was monitored through the outlet line. It was seen that there was no change in acid color. An UV analysis was done on the sample sulfuric acid collected.
HP-Plot Molesieve Column 5.0 6.0 7.0 8.0 9.0 10.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 ~75% Hydrogen 10 20 30 40 50 60 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 ~5% water ~20% air GS-GasPro Column Figure 4.7 GC Analysis of the Gas Sample (Electrolysis IV) After the experiment the system was flushed with DI water. The cell was examined once it was taken apart. It was found that the negative electrode was stable and there were hardly any signs of sulfur .The little sulfur found was observed near the bottom portion of the negative electrode and the inlet tube. This showed that the fluid flow from the top compartment helped in preventing the migration of sulfur dioxide to the negative compartment up to great extent as compared to all the previous experiments. 4.4.4 Interpretation On the basis of the experimental results and observation related to the fourth electrolysis experiment, the following conclusions can be drawn:
No change in sulfuric acid color was a good sign, which showed that there was no corrosion of metals inside the cell. This improvement may have been the result of improved technique for sealing the electrode leads. During the experiment it was observed th at the pressure inside the cell was increasing. This may be a result of clogg ing of the graphite yarn or the 100psig back pressure regulator. The same back pressure regulator was used for the last three experiments. It was decided to perf orm later experiments with out graphite yarn. The back pressure regulator was cleaned. The negative electrode showed that there were hardly any deposits of sulfur. It was seen that the flow from the negative compartment to the positive compartment helped the prevention of sulfur dioxide to the negative compartment. The Infrared analysis also showed that the produced gas didnt have any sulfur compounds. The GC analysis detected 75% hydrogen, 20% air, and 5% wate r. Later on it was found that air infiltration resulted from a stopcock leak in the gas collection apparatus. Electrolysis IV was one of the successful experiments in terms of stopping the electrode corrosion and also preventing the formation of sulfur in the negative compartment as compared to all the pr evious experiments. Since all the electrodes are stable inside the cell it wa s decided to operate the same cell for the next experiment (Electrolysis V) with a new negative electrode and no graphite yarn
4.5 Electrolysis V 4.5.1 Selection of Electrode Materials Positive Electrode: Gold Plated Carbon. Negative Electrode: Platinum Coated 316 Stainless Steel (Gold Strike as seed layer). Sensor Ring: Carbon. 4.5.2 Preparation of Electrodes The cell used for Electrolysis V was the same cell used for Electrolysis IV. The cell used in the last experiment was rinsed thoroughly with DI water. Graphite yarn was removed from the barrier and the cell was reassembled with new negative electrode. 4.5.3 Results and Discussions The sensor ring voltage was kept fixed at 1.6Volts (see appendix G). .At this voltage setting; SO2 was introduced at a flow rate of 0.01ml/min. The electrode voltage was adjusted to a minimum value to see substantia l amount of current with sulfur dioxide in the positive compartment. It was found that 1.0 volts was th e minimum voltage required to see substantial amount of current. The curre nt voltage curve is shown in Figure 4.8. It was observed that the current seen across the electrode was less as compared to electrolysis IV. This was anticipated due to the fact there was no graphite yarn in the positive compartment. The pressure inside the cell was stable and not rising as seen in previous experiment. This showed that graphi te yarn was building up the pressure in the previous experiment as anticipated. When the sensor ring showed an increase in current
the SO2 flow rate was cut back or SO2 pump was turned off. Keeping in mind the max flow rate of the back pressure regulator, fluid flow from the top was 00.020.040.060.080.10.120.140.220.127.116.1118.104.22.168.22.214.171.124.81.922.1VoltsCurrent00.20.40.60.811.2H2 Production ( ml/min ) With SO2 Without SO2 Figure 4.8 Current Voltage Curve Electrolysis V increased so that it sweeps away the sulfur dioxide from the negative to the positive compartment. A view of the negative compartment was not available since the top was covered. Liquid level was maintained between level sensor LB & LC. When the sensors are uncovered hydrogen gas is released with the help of the proportional control valve and collected through water displacement apparatus. Flow from bottom of the cell is turned off and fluid flow from the top compartment is increased to 1ml/min (i.e. max limit of 100 psig back pressure regulator) .Pressure is monitored very carefully while releasing the gas. This is done till the pocket size is reduced and liquid level is
maintained between level sensor LB & LC. An y change in the acid color was monitored through the outlet line. It was seen that there was no change in acid color. An UV analysis was done on the sample sulfuric acid collected After the experiment the system was flushed with DI water. The cell was examined once it was taken apart. It was f ound that the negative electrode was stable and there was hardly any signs of sulfur .This showed that the fluid flow from the top compartment helped in preventing the migr ation of sulfur dioxi de to the negative compartment up to great extent as compared to all the previous experiments. 4.5.4 Interpretation On the basis of the experimental results and observation related to the fifth electrolysis experiment, the following conclusions can be drawn: No change in sulfuric acid color was a good sign, which showed that there was no corrosion of metals inside the cell. Pressure inside the cell was stable a nd not increasing. This showed that the graphite yarn was building up the pr essure in the last experiment. The negative electrode showed that there were hardly any deposits of sulfur. It was seen that the flow from the negative compartment to the positive compartment helped the prevention of sulfur dioxide to the negative compartment. It was found that Electrolysis V and IV were 2 of the successful experiments in terms of stopping the corrosion and also prev enting the formation of sulfur in the negative compartment as compared to all the previous experiments.
4.6 Electrolysis VI 4.6.1 Selection of Electrode Materials Positive Electrode: Tungsten Carbide coated Carbon. Negative Electrode: Platinum Coated 316 Stainless Steel (Gold Strike as seed layer). Sensor Ring: Tungsten carbide coated Carbon. 4.6.2 Preparation of Electrodes Positive Electrode: Carbon was cleaned using the cleaning procedure used in previous experiments. Tungsten Ca rbide was then evaporated on Carbon. Tungsten carbide is used as a catalyst for oxidizing sulfur dioxide. Negative Electrode: The electrode was prepared the same way as done in Electrolysis II. Sensor Ring: Tungsten carbide was evaporated on the carbon ring. Again graphite yarn was not used in this expe riment. The cell was assembled the same way as done all the other expe riments described before. 4.6.3 Results and Discussions Measurements were started w ith a low voltage (1volt) at which water could not be electrolyzed so amperage was negligible (see appendix H). Voltage was increased in steps until current was substantial. It was s een that the over voltage was reduced by 0.3 volts as compared to previous experiments. The current voltage curve is shown in Figure 4.9. The system started behavi ng very weirdly after 1.8volts. Due to this unusual behavior sulfur dioxide was not introduced into the cell. The cell was examined once it
00.020.040.060.080.10.120.91.126.96.36.199.92.12.3Voltage (V)Current (amps)00.10.20.30.188.8.131.52.8H2 Production (ml/min) with WC Without WC Figure 4.9 Current Voltage Curve Electrolysis VI was taken apart. It was found that tungsten carbide flaked off from the positive electrode and the sensor ring. That probably explains the unusual behavior of the cell 4.6.4 Interpretation On the basis of the experimental results and observation related to the sixth electrolysis experiment, the following conclusions can be drawn: Electron beam evaporation of tungsten carbide is not a good approach for depositing tungsten carbide. Various literature studies were done on tungsten carbide deposition. It was found that reactive sputtering may be a better approach for deposition. Tungsten carbide electrodes can also be used as an electrode
material. Various electrode materials and catalyst materials needs to be tried for future experiments. 4.7 Electrolysis Summary The summary of all the six electrol ysis is tabulated in Table 4.1.
Table 4.1 Electrolysis Summary Electrodes Electrode Analysis after experiment Experiments Cathode Anode Sensor Ring Cathode Anode Sensor Ring Over -voltage reduction @ 0.1 amps Sulfuric Acid Insertion Comments Electrolysis I Platinum coated 316SS Gold Plated 316 SS, Carbon yarn, Gold coated carbon barrier Gold Plated C-276 Alloy Platinum peeled off Gold peeled off Gold peeled off 0.5V Single insertion point : positive compartment Sulfuric Acid changed colored (Yellow), Sulfur deposited on the negative electrode Electrolysis II Platinum coated 316 SS ( Acid Gold Strike as seed layer) Gold coated carbon, Carbon yarn, Gold coated carbon barrier Carbon Turned black and some amount of platinum peeled off. Stable Stable 0.5V Single insertion point :positive compartment Sulfuric acid changed color (yellow), Sulfur deposited on the negative electrode Electrolysis III Platinum coated 316 SS wire gauze (Acid Gold Strike as seed layer ) Carbon yarn, Gold coated carbon barrier Carbon Turned black and electrode fell apart Stable Stable 0.6V Double insertion point: positive and negative compartment Porous glass separator turned yellow in color, Sulfuric acid changed color (yellow), Sulfur deposited on the negative electrode
Table 4.1 (Continued) Electrolysis IV Platinum coated 316 SS (Acid Gold Strike as seed layer ) Gold coated carbon, Carbon barrier, Carbon yarn Carbon Stable Stable Stable 0.45V Double insertion point :positive and negative compartment No change in Sulfuric acid color Hardly any signs of sulfur on the negative electrode, Gas Analysis showed 75% Hydrogen and 25% air, Infrared analysis showed no signs of sulfur Electrolysis V Platinum coated 316 SS (Acid Gold Strike as seed layer ) Gold coated carbon and carbon barrier Carbon Stable Stable Stable 0.75V Double insertion point : positive and negative compartment No change in Sulfuric acid color Hardly any signs of sulfur on the negative electrode, Electrolysis VI Platinum coated 316 SS (Acid Gold Strike as seed layer ) Tungsten Carbide coated carbon and carbon barrier Tungsten carbide carbon Stable Tungsten carbide peeled off Tungsten carbide peeled off 0.3V Double insertion point: positive and negative compartment No change in Sulfuric acid color SO2 was not introduced in the cell due to unusual behavior of the cell
4.8 Catalyst Deposition Literature studies have shown that Carbon, Platinum, Tungsten Carbide and Ruthenium dioxide are potential catalysts for hydrogen production. Platinum is a well known catalyst for the negative electrode. Platinum was deposited on the negative electrode in all the experiment s using evaporation. Literature studies have shown that Pt cathodes employed in acidic media have proved to be sulfur sensitive and poisoned . Carbides of tungsten are also known as cata lysts for the anodic oxidation of hydrogen as well as the cathodic reduction of hydrogen i ons. Tungsten carbide was used as the catalyst in Electrolysis VI. Tungsten carb ide was evaporated on all the positive electrodes. Analysis of the el ectrodes after the experiment showed that tungsten carbide peeled off from the surface of the electrodes. Later studies indicated that evaporation is not a good approach for tungsten carbide deposition. Tungsten carbide is insensitive to sulfur. Oxides of platinum metal like ruth enium dioxide can also be used instead of platinum in acidic media. RuO 2 was prepared as described in reference . Rutenium dioxide catalyst was prepared by evaporating solvent from 0.1M RuCl 3 in 20% aqueous HCl and redissolved in a minm um volume of 2-proponal. A sa mple electrode of carbon was coated with RuCl 3 2-proponal by brush and annealed for 15minutes at 350 0 C. This coating was repeated depending on how thicker and uniform co ating is required and then 1hour annealed at 350 0 C. The sample electrode was then te sted in 20% wt of sulfuric acid and it was found that the coating peeled of fr om the surface. Because of time constraint the preparation of RuO 2 was not tried again in the research work for electrolysis experiments.
CHAPTER 5 SUMMARY AND CONCLUSIONS An electrolysis cell was developed for producti on of hydrogen and sulfuric acid. The cell was operated at room temperature and at 100p sig pressure. As the research progressed various changes were made in the cell desi gn and flow control system as knowledge was gained. Six electrolysis experime nts were carried out in this research. At the end of each experiment a better understanding of the process was gained. From the experimental results of the electrolyses following thi ngs can be concluded for the research. 1. Presence of sulfur dioxide in the cell showed an increased current/voltage ratio as compared to the ratio with out sulfur dioxide. Curr ent was observed at a voltage well below the voltage needed to electrolyze water indicating that sulfur dioxide was being oxidized. 2. Testing of different electrode material s showed that gold and carbon can serve as positive electrodes. All metals tested were stable as negative electrodes. Further study of electrodes is needed. 3. Electrolyses I & II were performe d using two pumps for pumping fluid from the bottom of the cell. Some sulfur dioxide migrated into the negative compartment during these experiments. The negative electrode examined showed the formation of sulfur. In s ubsequent electrolyses a third pump was added to the system to insert liquid into th e top of the negative compartment
to sweep away the sulfur dioxide migrating to the negative compartment from the positive compartment. Experiments done with this setup showed that the formation of sulfur in the negative elec trode was reduced to a great extent. 4. The use of tungsten carbide in Electro lysis VI showed that the over voltage was reduced by 0.3 volts as co mpared to previous experiments 5. The GC analysis of the gas showed that the detected gas produced was hydrogen and there were no signs of any sulfur compounds in the gas collected. In this research, we have gained some kno wledge on the oxidation of sulfur dioxide in sulfuric acid as an electrol yte. The results are encouragi ng and more knowle dge is needed before we can benefit from this project.
CHAPTER 6 RECOMMENDATIONS FOR FUTURE WORK At the end of this thesis project, many possi bilities for improvements had developed that could be pursued further by future work. B ecause of the time constraint, these items could not be included in this work. Followi ng things could be recommended for future work. 1. Initially the cell was operated using a gla ss window which provided a view port for the negative compartment. The glass window cracked during two experiments and then the glass was replaced with an opaque lid. The glass could have cracked due to the reasons listed below. Mounting of the cell uses the two bolts that is used to tighten the glass this could have caused stress in the glass. Initially the cell was accidentally opera ted at high pressure when the back pressure was operated beyond its reco mmended maximum flow the maximum flow rate. A torque wrench was not used for tighten ing the first glass window to the cell. This could have contributed to the pr oblem by causing an uneven stress in the glass. However, the second window that broke was never tightened with out a torque wrench.
The cell mount might need redesign to addr ess the first of the three reasons given above. 2. Literature studies have shown that tungsten carbide and ruthenium dioxide are the potential candidates as catalyst materials. Tungsten carbide was deposited on carbon electrodes using electron beam evaporation. The tungsten carbide peeled off in all the cases. Various literature studies were done on tungsten carbide deposition. It was found that tungsten carbide films have been deposited successfully by reactive sputtering. Tungsten carbide el ectrodes with out binders can be used as electrode materials. Ruthenium dioxide was depos ited chemically on sample pieces of electrode and it was found that it had bad adhesion on the surface. Reactive sputtering could be a good approach.
REFERENCES  Why Hydrogen, National Hydrogen Association. www.hydrogenus.com  Lawerence O Williams. (1980). Hydroge n Power: An Introduction to Hydrogen Energy and its Applications. Pergamon Press.  Hydrogen Production. Department of Energy. www.eren.doe.gov/hydrogen  NASAs Hydrogen Research at Florida Universities. http://www.fsec.ucf.edu/hydrogen/nasa.htm  Top 20 Chemicals. http://scifun.chem.wise.edu/chemweek  C.M.Evans (Kvaerner Chemetics). Practical Considerations in the Concentration and Recovery of Nitartion Spent Acids. Presen ted at ACS Nitration Symposium Anaheim, April, 1995.  G.H. Parker and P.W.T.Lu. Laboratory Model and Electrolyzer Development for the Sulfur Cycle Hydrogen Production Process. Westinghouse Electric Corporation, 1979.  Economic Comparison of H ydrogen Production Using Sulfuric Acid Electrolysis and Sulfur Cycle Water Decomposition. EM789, Research Project 1086-2, Westinghouse Electric Corporation, Final Report, June 1978.  Thermochemical Water Splitting Cycle, Bench Scale Investigation, and Process Engineering. DE-86001139, General Atomic T echnologies, Inc, Final Report, May 1982.  D.Van Velzen et al. Development, Design and Operation of a Continuous Laboratory Scale Plant for Hydrogen Production by the Ma rk-13Cycle. Commission of the European Communities, JRCIspra Establishment, Italy.  Oscar Khaselev and John A Turner. A Monolithic PhotovoltaicPhotoelectrochemical Device for Hydr ogen Production via Water Splitting. www.sciencemag.org.SCIENCE.VOL.28 17 April 1998.  Hartmut Wendt. Electrochemical Hydrogen Technologies: Electrochemical Production and Combustion of Hydroge. Elesevier, 1990.
 M.S,Casper. Hydrogen Manufacture by Electrolysis, Thermal Decomposition and Unusual Techniques. Noyes Data Corporation, New Jersey, 1978.  R.T Webster and T.L. Yau. Zirconium in Sulfuric Acid Applications. National Association of Corrosion E ngineers, February 1998.  PercentageConcentration. Yokogawa Corporation of North America http://www.us.yokogawa.com/downl oads/applicationnotes.htm  Lisa Connock. Mitigating Corrosion in Sulfuric Acid Production. Sulphur, Nov-Dec 2001, P39.  Qinglin Zhang et.al. So lubility of Sulfur Dioxide in Sulfuric Acid of High Concentration. Ind. Eng. Chem. Res.1998,37,1167-1172.  A.J. Appleby and B.Pinchon. Electr ochemical Aspects of the H2SO4-SO2 Thermochemical Cycle for Hydrogen Productio n. Internal Journal of Hydrogen Energy. Vol.5, pp 253-267.  B.D.Struck et.al. A Three Compartmen t Electrolytic Cell fo r Anodic Oxidation of Sulfur Dioxide and Cathodic Production of H ydrogen International Journal of Hydrogen Energy, Vol 7, No.1, pp 43-49, 1982.  S.Licht et.al. Solar Water Splitting Exemplified by RuO2Catalyzed AlGaAs/Si Photoelectrolysis. Journal of Phys ical Chemistry B2000, Volume 104, No.38, 2000.
Appendix A: Testing of Electrode Materials Samples of different metals were tested in 20wt % of sulfuric acid without sulfur dioxide in the solution at room temperature and atmos pheric pressure. The te st results are shown in Table A.1 below. Table A.1 Test Results of Different Electrodes Metals Positive Electrode Negative Electrode Comments Lead Electrodes started turning reddish brown in color at 2.2volts No change electrode color No change in acid color Alloy C-276 Electrode started turning slight yellow in color at 1.5V. A visible stream of reddish brown color was seen dripping from the electrode No change in electrode color Acid turned yellow in color Alloy C-2000 A visible stream of reddish brown color was seen dripping from the electrode at 1.8V. A very slight change in electrode color was seen No change in electrode color Acid turned yellow in color Alloy 20 The results were similar to Alloy C-2000 No change in color Acid turned yellow in color 316 SS Change in color at 1.7V. The results were similar to C-276, C2000, and Alloy -20 Turns black Acid color was yellow. Carbon Stable Stable No change in acid color Gold coated carbon Electrodes were stable Electrodes were stable No change in acid color Various metals and alloys tested as electr ode materials showed that most of them corroded when used as anode in sulfuric acid. Most of the metals tested have satisfactory results as a negative electrode Only gold and carbon was found to be stable as positive electrode.
Appendix B: Calculation of Flow Rates Solar Insolation: 1000 W/m 2 Consider efficiency of the cell: 10% Consider cell voltage: 0.5 V. A 4 inch diameter silicon solar cell produces 1.5 Amperes under standard insolation. Consider the reaction shown below. SO 2 + nH 2 O H 2 SO 4 + (n-2) H 2 O + 2H + + 2e (B.1) Molecular weight of SO2: 64 Molecular Weight of H2O: 18 Molecular Weight of H2SO4: 98 SO2 density: 1.43 gm/cc Molar volume of ideal hydrogen gas: 22.4 lit/mole. Faradays Constant: 96500 coulombs/equivalent Let current I = 1.5 Amperes = 1.5 c/sec = 0.0000155 equivalents/sec 90c/min = 0.0009326 equivalents /min 5400 c/hr = 0.0559585 equivalents/hr SO 2 flow rate: From equation B.1 it is seen that to oxidize one molecule of SO 2 we need 2C. SO 2 flow = 0.0559585 equivalents/hr / 2 = 0.0279793 moles/hr
Appendix B: (Continued) 0.0279793 moles/hr MW of SO2 = 0.0279793 moles/hr 64 = 1.790675 gm/hr 1.790675 gm/hr / density of SO2 = 1.24872634 ml/hr SO 2 flow rate = 1.24872634 ml/hr. H 2 Flow: 0.0559585 equivalents/hr / 2 = 0.0279793 moles/hr 0.0279793 moles/hr molar volume of ideal hydrogen gas 0.0279793 moles/hr 22.4 = 0.626736 l/hr = 10.4455959 ml/min Table B.1 Fraction of H 2 SO 4 and H 2 O Flow n n-2 Fraction of H2SO4 H2O Flow(moles/hr) H2O flow (gm/hr) H2O flow ( cc/hr) 2 0 1.0000 0.0560 1.0073 1.0073 2.10888 0.10888 0.9804 0.0590 1.0621 1.0621 2.27222 0.27222 0.9524 0.0636 1.1444 1.1444 2.38111 0.38111 0.9346 0.0666 1.1992 1.1992 2.54444 0.54444 0.9091 0.0712 1.2814 1.2814 3 1 0.8448 0.0839 1.5109 1.5109 4 2 0.7313 0.1119 2.0145 2.0145 5 3 0.6447 0.1399 2.5181 2.5181 6 4 0.5765 0.1679 3.0218 3.0218 7 5 0.5213 0.1959 3.5254 3.5254 8 6 0.4757 0.2238 4.0290 4.0290 9 7 0.4375 0.2518 4.5326 4.5326 10 8 0.4050 0.2798 5.0363 5.0363 11 9 0.3769 0.3078 5.5399 5.5399 12 10 0.3525 0.3358 6.0435 6.0435 13 11 0.3311 0.3637 6.5472 6.5472 14 12 0.3121 0.3917 7.0508 7.0508 15 13 0.2952 0.4197 7.5544 7.5544 16 14 0.2800 0.4477 8.0580 8.0580 17 15 0.2663 0.4756 8.5617 8.5617 18 16 0.2539 0.5036 9.0653 9.0653 19 17 0.2426 0.5316 9.5689 9.5689 20 18 0.2322 0.5596 10.0725 10.0725
Appendix B: (Continued) Table B.1 (Continued) 21 19 0.2227 0.5876 10.5762 10.5762 22 20 0.2140 0.6155 11.0798 11.0798 23 21 0.2059 0.6435 11.5834 11.5834 24 22 0.1984 0.6715 12.0871 12.0871 25 23 0.1914 0.6995 12.5907 12.5907 26 24 0.1849 0.7275 13.0943 13.0943 27 25 0.1788 0.7554 13.5979 13.5979 28 26 0.1731 0.7834 14.1016 14.1016 29 27 0.1678 0.8114 14.6052 14.6052 30 28 0.1628 0.8394 15.1088 15.1088 31 29 0.1581 0.8674 15.6124 15.6124 32 30 0.1536 0.8953 16.1161 16.1161 33 31 0.1494 0.9233 16.6197 16.6197 34 32 0.1454 0.9513 17.1233 17.1233 35 33 0.1416 0.9793 17.6270 17.6270 36 34 0.1380 1.0073 18.1306 18.1306 37 35 0.1346 1.0352 18.6342 18.6342 38 36 0.1314 1.0632 19.1378 19.1378 39 37 0.1283 1.0912 19.6415 19.6415 40 38 0.1253 1.1192 20.1451 20.1451 41 39 0.1225 1.1472 20.6487 20.6487 42 40 0.1198 1.1751 21.1524 21.1524 43 41 0.1172 1.2031 21.6560 21.6560 44 42 0.1148 1.2311 22.1596 22.1596 45 43 0.1124 1.2591 22.6632 22.6632 46 44 0.1101 1.2870 23.1669 23.1669 47 45 0.1079 1.3150 23.6705 23.6705 48 46 0.1058 1.3430 24.1741 24.1741 49 47 0.1038 1.3710 24.6777 24.6777 50 48 0.1019 1.3990 25.1814 25.1814 51 49 0.1000 1.4269 25.6850 25.6850 52 50 0.0982 1.4549 26.1886 26.1886 53 51 0.0965 1.4829 26.6923 26.6923 54 52 0.0948 1.5109 27.1959 27.1959 55 53 0.0932 1.5389 27.6995 27.6995 56 54 0.0916 1.5668 28.2031 28.2031 57 55 0.0901 1.5948 28.7068 28.7068 58 56 0.0886 1.6228 29.2104 29.2104 59 57 0.0872 1.6508 29.7140 29.7140 60 58 0.0858 1.6788 30.2176 30.2176 61 59 0.0845 1.7067 30.7213 30.7213 62 60 0.0832 1.7347 31.2249 31.2249 63 61 0.0819 1.7627 31.7285 31.7285
Appendix B: (Continued) Table B.1 (Continued) 64 62 0.0807 1.7907 32.2322 32.2322 65 63 0.0795 1.8187 32.7358 32.7358 66 64 0.0784 1.8466 33.2394 33.2394 67 65 0.0773 1.8746 33.7430 33.7430 68 66 0.0762 1.9026 34.2467 34.2467 69 67 0.0752 1.9306 34.7503 34.7503 70 68 0.0741 1.9586 35.2539 35.2539 71 69 0.0731 1.9865 35.7575 35.7575 72 70 0.0722 2.0145 36.2612 36.2612 73 71 0.0712 2.0425 36.7648 36.7648 74 72 0.0703 2.0705 37.2684 37.2684 75 73 0.0694 2.0984 37.7721 37.7721 76 74 0.0685 2.1264 38.2757 38.2757 77 75 0.0677 2.1544 38.7793 38.7793 78 76 0.0668 2.1824 39.2829 39.2829 79 77 0.0660 2.2104 39.7866 39.7866 80 78 0.0652 2.2383 40.2902 40.2902 81 79 0.0645 2.2663 40.7938 40.7938 82 80 0.0637 2.2943 41.2974 41.2974 83 81 0.0630 2.3223 41.8011 41.8011 84 82 0.0623 2.3503 42.3047 42.3047 85 83 0.0616 2.3782 42.8083 42.8083 86 84 0.0609 2.4062 43.3120 43.3120 87 85 0.0602 2.4342 43.8156 43.8156 88 86 0.0595 2.4622 44.3192 44.3192 89 87 0.0589 2.4902 44.8228 44.8228 90 88 0.0583 2.5181 45.3265 45.3265 91 89 0.0576 2.5461 45.8301 45.8301 92 90 0.0570 2.5741 46.3337 46.3337 93 91 0.0565 2.6021 46.8373 46.8373 94 92 0.0559 2.6301 47.3410 47.3410 95 93 0.0553 2.6580 47.8446 47.8446 96 94 0.0547 2.6860 48.3482 48.3482 97 95 0.0542 2.7140 48.8519 48.8519 98 96 0.0537 2.7420 49.3555 49.3555 99 97 0.0531 2.7700 49.8591 49.8591 100 98 0.0526 2.7979 50.3627 50.3627 101 99 0.0521 2.8259 50.8664 50.8664 102 100 0.0516 2.8539 51.3700 51.3700 103 101 0.0511 2.8819 51.8736 51.8736 104 102 0.0507 2.9098 52.3772 52.3772 105 103 0.0502 2.9378 52.8809 52.8809
Appendix B: (Continued) Table B.1 (Continued) 106 104 0.0497 2.9658 53.3845 53.3845 107 105 0.0493 2.9938 53.8881 53.8881 108 106 0.0489 3.0218 54.3918 54.3918 109 107 0.0484 3.0497 54.8954 54.8954 110 108 0.0480 3.0777 55.3990 55.3990 111 109 0.0476 3.1057 55.9026 55.9026 112 110 0.0472 3.1337 56.4063 56.4063 113 111 0.0468 3.1617 56.9099 56.9099 114 112 0.0464 3.1896 57.4135 57.4135 115 113 0.0460 3.2176 57.9172 57.9172 116 114 0.0456 3.2456 58.4208 58.4208 117 115 0.0452 3.2736 58.9244 58.9244 118 116 0.0448 3.3016 59.4280 59.4280 119 117 0.0445 3.3295 59.9317 59.9317 120 118 0.0441 3.3575 60.4353 60.4353 121 119 0.0438 3.3855 60.9389 60.9389 122 120 0.0434 3.4135 61.4425 61.4425 123 121 0.0431 3.4415 61.9462 61.9462 124 122 0.0427 3.4694 62.4498 62.4498 125 123 0.0424 3.4974 62.9534 62.9534 126 124 0.0421 3.5254 63.4571 63.4571 127 125 0.0417 3.5534 63.9607 63.9607 128 126 0.0414 3.5814 64.4643 64.4643 129 127 0.0411 3.6093 64.9679 64.9679 130 128 0.0408 3.6373 65.4716 65.4716 131 129 0.0405 3.6653 65.9752 65.9752 132 130 0.0402 3.6933 66.4788 66.4788 133 131 0.0399 3.7212 66.9824 66.9824 134 132 0.0396 3.7492 67.4861 67.4861 135 133 0.0393 3.7772 67.9897 67.9897 136 134 0.0390 3.8052 68.4933 68.4933 137 135 0.0388 3.8332 68.9970 68.9970 138 136 0.0385 3.8611 69.5006 69.5006 139 137 0.0382 3.8891 70.0042 70.0042 140 138 0.0380 3.9171 70.5078 70.5078 141 139 0.0377 3.9451 71.0115 71.0115 142 140 0.0374 3.9731 71.5151 71.5151 143 141 0.0372 4.0010 72.0187 72.0187 144 142 0.0369 4.0290 72.5223 72.5223 145 143 0.0367 4.0570 73.0260 73.0260 146 144 0.0364 4.0850 73.5296 73.5296 147 145 0.0362 4.1130 74.0332 74.0332
Appendix B: (Continued) Table B.1 (Continued) 148 146 0.0360 4.1409 74.5369 74.5369 149 147 0.0357 4.1689 75.0405 75.0405 150 148 0.0355 4.1969 75.5441 75.5441 151 149 0.0353 4.2249 76.0477 76.0477 152 150 0.0350 4.2529 76.5514 76.5514 153 151 0.0348 4.2808 77.0550 77.0550 154 152 0.0346 4.3088 77.5586 77.5586 155 153 0.0344 4.3368 78.0622 78.0622 156 154 0.0341 4.3648 78.5659 78.5659 157 155 0.0339 4.3928 79.0695 79.0695 158 156 0.0337 4.4207 79.5731 79.5731 159 157 0.0335 4.4487 80.0768 80.0768 160 158 0.0333 4.4767 80.5804 80.5804 161 159 0.0331 4.5047 81.0840 81.0840 162 160 0.0329 4.5326 81.5876 81.5876 163 161 0.0327 4.5606 82.0913 82.0913 164 162 0.0325 4.5886 82.5949 82.5949 165 163 0.0323 4.6166 83.0985 83.0985 166 164 0.0321 4.6446 83.6021 83.6021 167 165 0.0319 4.6725 84.1058 84.1058 168 166 0.0318 4.7005 84.6094 84.6094 169 167 0.0316 4.7285 85.1130 85.1130 170 168 0.0314 4.7565 85.6167 85.6167 171 169 0.0312 4.7845 86.1203 86.1203 172 170 0.0310 4.8124 86.6239 86.6239 173 171 0.0309 4.8404 87.1275 87.1275 174 172 0.0307 4.8684 87.6312 87.6312 175 173 0.0305 4.8964 88.1348 88.1348 176 174 0.0303 4.9244 88.6384 88.6384 177 175 0.0302 4.9523 89.1420 89.1420 178 176 0.0300 4.9803 89.6457 89.6457 179 177 0.0298 5.0083 90.1493 90.1493 180 178 0.0297 5.0363 90.6529 90.6529 181 179 0.0295 5.0643 91.1566 91.1566 182 180 0.0294 5.0922 91.6602 91.6602 183 181 0.0292 5.1202 92.1638 92.1638 184 182 0.0290 5.1482 92.6674 92.6674 185 183 0.0289 5.1762 93.1711 93.1711 186 184 0.0287 5.2041 93.6747 93.6747 187 185 0.0286 5.2321 94.1783 94.1783 188 186 0.0284 5.2601 94.6820 94.6820 189 187 0.0283 5.2881 95.1856 95.1856 190 188 0.0281 5.3161 95.6892 95.6892
Appendix B: (Continued) Table B.1 (Continued) 191 189 0.0280 5.3440 96.1928 96.1928 192 190 0.0279 5.3720 96.6965 96.6965 193 191 0.0277 5.4000 97.2001 97.2001 194 192 0.0276 5.4280 97.7037 97.7037 195 193 0.0274 5.4560 98.2073 98.2073 196 194 0.0273 5.4839 98.7110 98.7110 197 195 0.0272 5.5119 99.2146 99.2146 198 196 0.0270 5.5399 99.7182 99.7182 199 197 0.0269 5.5679 100.2219 100.2219 200 198 0.0268 5.5959 100.7255 100.7255 Sample calculation for Table B.1: Fraction of H2SO4: 98/ ((n-2) *18 + 98) H 2 0 Flow in moles/hr= n* 0.02799793 moles/hr = 0.0560 moles/hr H 2 O Flow in gms/hr: 0.0560* Molecular Weight of H2O = 0.0560*18 = 1.008 gms/hr H 2 O Flow in ml/hr: 1.008 gms/hr / density = 1.008 ml/hr.
Appendix C: Electrolysis I Electrodes: 1) Positi ve electrode: Gold plat ed 316 stainless steel. 2) Negativ e electrode: Platinum coated 316 stainless steel. 3) Sensor ring: Gold plated alloy C-276 Acid Concentration: 20 wt % Table C.1 Current Voltage Data Electrolysis I Electrodes Sensor Ring Flow Rates Voltage (V) Current (mA) Voltage (V) Current (mA) H2SO4 Pump (ml/min) SO2 Pump (ml/min) Comments 1 0.01 0.9 0.005 0.36 0.0 1.1 0.02 1 0.004 0.36 0.0 Platinum flaking off 1.2 0.02 1.1 0.004 0.36 0.0 1.3 0.05 1.25 0.005 0.36 0.0 1.4 0.11 1.3 0.009 0.36 0.0 1.5 0.21 1.4 0.015 0.36 0.0 Change in acid color (Yellow ) Gold flaking off from sensor ring 1.6 0.3 1.5 0.021 0.36 0.0 Bubbles (negative electrode) 1.4 0.14 1.3 0.008 0.36 0.01 Turn on SO2 pump 1.4 0.80 1.3 0.013 0.36 0.2 Increase the flow rate of SO2 to 0.2 for one hour 1.4 0.3 0.0 0.0 0.36 0.2 Turn off sensor ring due increased corrosion in Alloy C-276 1.4 0.47 0.0 0.0 0.36 0.02 Cutback the flow rate of SO2 due to increase in electrode current 1.4 0.40 0.0 0.0 0.36 0.02
Appendix C: (Continued) Table C.1 (Continued) 1.4 0.45 0.0 0.0 0.72 0.04 Keep the flow rates constant for both the pumps and decrease the voltage and monitor current. 1.3 0.39 0.0 0.0 0.72 0.04 1.2 0.34 0.0 0.0 0.72 0.04 1.1 0.28 0.0 0.0 0.72 0.04 1.0 0.19 0.0 0.0 0.72 0.04 0.9 0.11 0.0 0.0 0.72 0.04 0.8 0.70 0.0 0.0 0.72 0.04 0.7 0.30 0.0 0.0 0.72 0.04 0.6 0.0 0.0 0.0 0.72 0.04
Appendix D: Electrolysis II Electrodes: 1) Positive electrode: Gold plated carbon. 2) Negativ e electrode: Platinum coated 316 stainless steel. 3) Sensor ring: Carbon Acid Concentration: 20 wt % Level Sensor: 1) Series resistance R S : 50.5 ohms 2) Frequency: 10 kHz 3) AC signal: 1volts (0 to peak) Table D.1 Current Voltage Data Electrolysis II Electrodes Sensor Ring Flow Rates Voltage (V) Current (A) Voltage (V) Current (A) H2SO4 Pump (ml/min) SO2 Pump (ml/min) Comments 1 0.01 1 0.008 0.43 0.00 1.2 0.03 1.2 0.01 0.43 0.00 1.3 0.05 1.3 0.01 0.43 0.00 1.4 0.08 1.4 0.01 0.43 0.00 1.5 0.18 1.5 0.01 0.43 0.00 1.6 0.21 1.6 0.02 0.43 0.00 1.7 0.31 1.7 0.03 0.43 0.00 1.8 0.36 1.8 0.05 0.43 0.00 1.9 0.43 1.9 0.07 0.43 0.00 2.0 0.47 2 0.08 0.43 0.00 1.6 0.12 1.9 0.06 0.43 0.01 Start SO2 flow no change in current increase the flow rate to 0.2 for 10minutes
Appendix D: (Continued) Table D.1 (Continued) 1.6 0.18 1.9 0.04 0.43 0.2 Increase the flow rate from 0.2 to 0.3 for 15minutes 1.6 0.25 1.9 0.02 0.43 0.3 Change in acid color at outlet to yellow 1.6 0.18 1.9 0.03 0.43 0.04 SO2 flow cut back since increase in sensor ring current 1.6 0.24 1.9 0.02 0.43 0.2 1.6 0.4 1.9 0.02 0.43 0.2 1.6 0.6 1.9 0.003 0.43 0.2 Lost the pocket shutoff H2SO4 pump and SO2 pump release hydrogen 1.6 0.54 1.9 0.006 0.00 0.00 Release hydrogen 1.6 0.45 1.9 0.007 0.00 0.00 Release hydrogen 1.6 0.38 1.9 0.007 0.00 0.00 Release hydrogen 1.6 0.35 1.9 0.007 0.00 0.00 Not able to get the pocket back decrease the electrode voltage to reduce the production of hydrogen 1.2 0.15 1.8 0.024 0.00 0.00 Increase the voltage of electrode till the sensor ring current is zero 1.6 0.41 1.9 0.004 0.00 0.00 Saw the pocket 1.6 0.47 1.9 0.004 0.43 0.20 Check the minimum voltage to see current 0.9 0.11 1.9 0.02 0.43 0.20 0.9 0.1 1.9 0.06 0.43 0.20 Increase in sensor ring current TURN OFF SO2 0.9 0.11 1.9 0.03 0.43 0.00 1.1 0.2 1.9 0.05 0.43 0.00 1.2 0.26 1.9 0.05 0.43 0.00 1.3 0.35 1.9 0.05 0.43 0.00 1.4 0.42 1.9 0.05 0.43 0.00 1.5 0.52 1.9 0.04 0.43 0.00 1.6 0.65 1.9 0.02 0.43 0.00
Appendix D: (Continued) Table D.1 (Continued) 1.7 0.71 1.9 0.02 0.43 0.00 TURN ON the SO2 flow to 0.2 and check the minimum electrode voltage to see some current ( neglect the sensor ring ) 0.7 0.02 0.43 0.2 0.8 0.03 0.43 0.2 0.9 0.08 0.43 0.2 1 0.14 0.43 0.2 1.1 0.2 0.43 0.2 1.2 0.23 0.43 0.2 1.3 0.33 0.43 0.2 1.4 0.45 0.43 0.2 1.5 0.51 0.43 0.2 1.6 0.58 1.6 0.07 0.43 0.2 Turn on the sensor ring 1.5 0.34 1.9 0.23 0.43 0.2 1.4 0.27 1.9 0.25 0.43 0.2 1.3 0.2 1.9 0.27 0.43 0.2 1.2 0.1 1.9 0.27 0.43 0.2
Appendix E: Electrolysis III Electrodes: 1) Posi tive electrode: Gold plated carbon barrier. 2) Negative electrode: Platinum coated 316 stainless steel gauze. 3) Sensor ring: Carbon Acid Concentration: 20 wt % Level Sensor: 1) Series resistance R S : 50.5 ohms 2) Frequency: 10 kHz 3) AC signal: 1volts (0 to peak) The current voltage data for Electro lysis III is given in Table E.1.
Table E.1 Current Voltage Data Electrolysis III Voltage (V) Electrodes Sensor Ring Interval Time (P.M) Current electrodes ( A) Current Sensor Ring ( A) SO2 Flow (ml/min ) H20 Bottom (ml/min) H20 Top (ml/min) Pressure (psig) Initial 2:31:08 0.545 0.295 0 0.02 0.42 108.844 1 1 Final 2:46:08 0.008 0.012 0 0.02 0.42 95.53 Initial 2:46:17 0.164 0.052 0 0.02 0.42 95.823 1.2 1.2 Final 3:04:38 0.006 0.005 0 0.02 0.42 109.528 Initial 3:04:47 0.036 0.041 0 0.02 0.42 109.763 1.3 1.3 Final 3:15:08 0.009 0.005 0 0.02 0.42 93.902 Initial 3:15:17 0.057 0.047 0 0.02 0.42 93.721 1.4 113.317 1.4 Final 3:27:28 0.018 0.005 0 0.02 0.42 Initial 3:27:37 0.102 0.04 0 0.02 0.42 113.497 1.5 1.5 Final 3:44:38 0.042 0.003 0 0.02 0.42 103.255
Table E.1 (Continued) Initial 3:44:47 0.155 0.048 0 0.02 0.42 103.53 1.6 1.6 Final 3:55:48 0.119 0.016 0 0.02 0.42 101.446 Initial 3:55:57 0.24 0.054 0 0.02 0.42 101.717 1.7 1.7 Final 4:07:38 0.213 0.002 0 0.02 0.42 115.264 Initial 4:07:47 0.364 0.103 0 0.02 0.42 115.602 1.8 1.8 Final 4:18:08 0.275 0.1 0 0.02 0.42 119.291 Initial 4:18:28 0.099 0.1 0 0.02 0.42 119.688 1.2 1.8 Final 4:56:57 0.004 0.059 0 0.02 0.42 103.515 Initial 4:57:08 0.004 0.059 0.01 0.02 0.42 103.713 1.2 1.8 Final 5:00:48 0.004 0.048 0.01 0.02 0.42 108.227 Initial 5:00:58 0.147 0.052 0.3 0.6 0.42 108.442 1.4 1.8 Final 5:08:17 0.051 0.002 0.3 0.6 0.42 101.712 Initial 5:08:28 0.062 0.002 0.01 0.02 0.42 101.895 1.4 1.8 Final 5:35:07 0.194 0.002 0.01 0.02 0.42 106.032
Table E.1 (Continued) Initial 5:35:17 0.193 0.002 0.02 0.04 0.84 106.5 1.4 1.8 Final 6:38:08 0.323 0.002 0.02 0.04 0.84 97.796 Initial 6:38:18 0.322 0.002 0.01 0.02 0.42 98.433 1.4 1.8 Final 6:43:57 0.328 0.002 0.01 0.02 0.42 111.916 Initial 6:44:07 0.193 0.002 0.01 0.02 0.42 112.262 1.2 1.8 Final 7:06:38 0.18 0.002 0.01 0.02 0.42 132.008 Initial 7:06:57 0 0.002 0.01 0.02 0.42 131.83 1.1 1.8 Final 7:14:08 0.117 0.002 0.01 0.02 0.42 117.775 Initial 7:14:18 0.176 0.002 0.01 0.02 0.42 118.182 1.2 1.8 Final 7:15:58 0.164 0.002 0.01 0.02 0.42 120.228 Initial 7:40:18 0.164 0.001 0.01 0.02 0.42 101.645 0.8 1.8 Final 7:46:18 0.034 0.002 0.01 0.02 0.42 111.299 Initial 7:51:37 0.695 0.002 0.01 0.02 0.42 118..206 0.9 1.8 Final 8:02:27 0.056 0.002 0.01 0.02 0.42 103.843
Table E.1 (Continued) Initial 8:02:37 0.16 0.002 0.01 0.02 0.42 104.057 1 1.8 Final 8:14:37 0.086 0.002 0.01 0.02 0.42 117.652 Initial 8:16:11 0.486 0.002 0.01 0.02 0.42 121.061 1.1 1.8 Final 8:24:11 0.125 0.002 0.01 0.02 0.42 125.458 Initial 8:24:21 0.207 0.002 0.01 0.02 0.42 125.553 1.2 1.8 Final 8:30:51 0.184 0.002 0.01 0.02 0.42 110.788 Initial 8:31:01 0.185 0.002 0.01 0.12 0.32 111.218 1.2 1.8 Final 8:40:51 0.211 0.002 0.01 0.12 0.32 121.227 Initial 8:41:01 0.212 0.002 0.02 0.24 0.32 121.859 1.2 1.8 Final 9:25:41 0.302 0.002 0.02 0.24 0.32 123.918 Initial 9:26:11 0.434 0.002 0.02 0.24 0.32 124.451 1.3 1.8 Final 9:36:51 0.403 0.002 0.02 0.24 0.32 130.68 Initial 9:37:01 0.293 0.002 0.02 0.24 0.32 130.731 1.2 1.8 Final 9:52:01 0.313 0.002 0.02 0.24 0.32 107.544
Table E.1 (Continued) Initial 9:52:11 0.184 0.002 0.02 0.24 0.32 107.842 1.1 1.8 Final 10:03:51 0.232 0.002 0.02 0.24 0.32 126.274 Initial 10:04:01 0.233 0.002 0.02 0.24 0.68 106.739 1.1 1.8 Final 10:09:51 0.232 0.002 0.02 0.24 0.68 103.022 Initial 10:10:01 0.232 0.002 0.02 0.48 0.44 103.377 1.1 1.8 Final 10:29:51 0.25 0.002 0.02 0.48 0.44 102.675 Initial 10:30:01 0.25 0.002 0.02 0.54 0.44 104.242 1.1 1.8 Final 11:10:01 0.289 0.002 0.02 0.54 0.44 116.655
Appendix F: Electrolysis IV Electrodes: 1) Positive electrode: Gold plated carbon. 2) Negativ e electrode: Platinum coated 316 stainless steel. 3) Sensor ring: Carbon Acid Concentration: 20 wt % Level Sensor: 1) Series resistance R S : 50.5 ohms 2) Frequency: 10 kHz 3) AC signal: 1volts (0 to peak) The current voltage data for Electro lysis IV is given in Table F.1.
Table F.1 Current Voltage Data Electrolysis IV Voltage (V) Electrodes Sensor Ring Interval Time Current electrodes ( A) Current Sensor Ring ( A) SO2 Flow (ml/min ) H20 Bottom (ml/min) H20 Top (ml/min) Pressure (psig) Initial 10:56:57 A.M 0.421 0.175 0 0.2 0.3 110.128 1 1 Final 11:14:30 A.M 0.007 0.007 0 0.2 0.3 112.569 Initial 11:14:40 A.M 0.053 0.048 0 0.2 0.3 113.568 1.2 1.2 Final 11:26:00 A.M 0.007 0.008 0 0.2 0.3 116.786 Initial 11:26:10 A.M 0.03 0.027 0 0.2 0.3 117.865 1.3 1.3 Final 11:37:10 A.M 0.007 0.007 0 0.2 0.3 120.564
Table F.1 (Continued) 11:37:30 AM to 11:58:20 AM power supplies disconnected to check the capacitances. Refer Table F.2 Initial 11:58:40 A.M 0.134 0.124 0 0.2 0.3 122.023 1.3 1.3 Final 12:10:30 P.M 0.008 0.006 0 0.2 0.3 125.236 Initial 12:10:40 P.M 0.031 0.094 0 0.2 0.3 125.896 1.4 1.4 Final 12:25:50 P.M 0.01 0.009 0 0.2 0.3 127.023 Initial 12:26:00 P.M 0.045 0.04 0 0.2 0.3 128.235 1.5 1.5 Final 12:36:40 P.M 0.023 0.013 0 0.2 0.3 130.256 Initial 12:36:50 P.M 0.07 0.049 0 0.2 0.3 132.568 1.6 1.6 Final 12:46:30 P.M 0.044 0.021 0 0.2 0.3 135.523 Initial 12:46:40 P.M 0.142 0.069 0 0.2 0.3 110.235 1.7 1.7 Final 1:03:21 P.M 0.071 0.027 0 0.2 0.3 112.265
Table F.1 (Continued) Initial 1:03:32 P.M 0.098 0.079 0 0.2 0.3 112.985 1.8 1.8 Final 1:14:00 P.M 0.108 0.013 0 0.2 0.3 114.563 Initial 1:14:10 P.M 0.18 0.076 0 0.2 0.3 114.998 1.9 1.9 Final 1:37:20 P.M 0.136 0.104 0 0.2 0.3 116.523 Initial 1:41:02 P.M 0.027 0.015 0.01 0.2 0.3 118.562 0.9 1.6 Final 2:17:20 P.M 0.003 0.012 0.01 0.2 0.3 120.563 Initial 2:17:30 P.M 0.003 0.012 0.03 0.6 0.3 120.986 0.9 1.6 Final 2:55:40 P.M 0.011 0.009 0.03 0.6 0.3 122.562 Initial 2:55:50 P.M 0.011 0.009 0.01 0.2 0.3 122.966 0.9 1.6 Final 3:22:40 P.M 0.014 0.01 0.01 0.2 0.3 124.565 Initial 3:22:50 P.M 0.064 0.002 0.01 0.2 0.3 125.554 1 1.6 Final 3:28:10 P.M 0.034 0.007 0.01 0.2 0.3 127.563
Table F.1 (Continued) Initial 3:28:20 P.M 0.094 0.001 0.01 0.2 0.3 128.056 1.2 1.6 Final 4:03:10 P.M 0.048 0.006 0.01 0.2 0.3 129.856 Initial 4:03:20 P.M 0.074 0.004 0.01 0.2 0.3 130.046 1.3 1.6 Final 4:12:40 P.M 0.072 0.005 0.01 0.2 0.3 132.569 Initial 4:12:50 P.M 0.1 0.003 0.01 0.2 0.3 132.9 1.4 1.6 Final 4:38:30 P.M 0.114 0.004 0.01 0.2 0.3 133.965 Initial 4:38:40 P.M 0.137 0.001 0.01 0.2 0.3 134.023 1.5 1.6 Final 5:03:20 P.M 0.191 0.002 0.01 0.2 0.3 135.965 Initial 5:03:30 P.M 0.192 0.054 0.02 0.4 0.3 136.235 1.5 1.7 Final 6:56:20 P.M 0.412 0.028 0.02 0.4 0.3 138.563 Initial 6:56:30 P.M 0.411 0.029 0.01 0.2 0.3 138.625 1.5 1.7 Final 7:47:30 P.M 0.366 0.03 0.01 0.2 0.3 140.563
Appendix F : (Continued) Table F.2 Residual Voltage Measurements (Electrolysis IV) Residual Voltages Electrodes Before Discharge Discharge for 1 minute Discharge for another minute Positive & Negative 1.2V 0.5V 380mV Sensor Ring & Positive 8.0mV 85mV 50mV Sensor Ring & Negative 1.15mV 0.6V 0.5V
Appendix G: Electrolysis V Electrodes: 1) Po sitive electrode: Gold plated carbon 2) Negativ e electrode: Platinum coated 316 stainless steel. 3) Sensor ring: Carbon Acid Concentration: 20 wt % Specific Gravity: 1.13 (20% Acid) Level Sensor: 1) Series resistance R S : 50.5 ohms 2) Frequency: 10 kHz 3) AC signal: 1volts (0 to peak) The current voltage data for Electro lysis V is given in Table G.1.
Table G.1 Current Voltage Data Electrolysis V Voltage (V) Electrodes Sensor Ring Interval Time Current electrodes ( A) Current Sensor Ring ( A) SO2 Flow (ml/min ) H20 Bottom (ml/min) H20 Top (ml/min) Pressure (psig) Initial 10:26:07 A.M 0.073 0.523 0 0.2 0.3 100.523 1 1 Final 10:50:52 A.M 0.003 0.004 0 0.2 0.3 101.562 Initial 10:51:01 A.M 0.042 0.057 0 0.2 0.3 101.652 1.2 1.2 Final 11:10:11 A.M 0.003 0.004 0 0.2 0.3 101.986 Initial 11:10:21 A.M 0.026 0.067 0 0.2 0.3 102.01 1.3 1.3 Final 11:30:52 A.M 0.004 0.004 0 0.2 0.3 102.123 Initial 11:31:01 A.M 0.024 0.042 0 0.2 0.3 102.201 1.4 1.4 Final 11:49:13 A.M 0.007 0.006 0 0.2 0.3 102.215 Initial 11:49:21 A.M 0.034 0.041 0 0.2 0.3 102.325 1.5 1.5 Final 12:11:21 P.M 0.014 0.01 0 0.2 0.3 102.401
Table G.1 (Continued) 12:11:31 PM to 12:37:52 PM Residual Voltage measurements. Power supplies disconnected. Refer Table G.2 Initial 12:38:01 P.M 0.583 0.174 0 0.2 0.3 102.421 1.6 1.6 Final 1:07:21 P.M 0.02 0.017 0 0.2 0.3 104.514 Initial 1:07:31 P.M 0.064 0.052 0 0.2 0.3 104.865 1.7 1.7 Final 1:28:12 P.M 0.033 0.03 0 0.2 0.3 105.213 Initial 1:28:32 P.M 0.085 0.076 0 0.2 0.3 105.561 1.8 1.8 Final 1:52:12 P.M 0.049 0.046 0 0.2 0.3 105.62 Initial 1:52:21 P.M 0.104 0.099 0 0.2 0.3 105.715 1.9 1.9 Final 1:58:11 P.M 0.079 0.074 0 0.2 0.3 105.81 1:58:22 PM to 2:13:52 PM Residual Voltage measurement before turning on the SO2.
Table G.1 (Continued) Initial 2:14:02 P.M 0.035 0.134 0.03 0.6 0.3 105.989 1 1.6 Final 3:19:01 P.M 0.013 0.015 0.03 0.6 0.3 106.01 Initial 3:19:11 P.M 0.013 0.015 0.01 0.2 0.3 106.194 1 1.6 Final 4:27:41 P.M 0.046 0.023 0.01 0.2 0.3 107.562 Initial 4:27:51 P.M 0.105 0.021 0.01 0.2 0.3 108.211 1.1 1.6 Final 6:24:52 P.M 0.077 0.093 0.01 0.2 0.3 109.213 Initial 6:25:02 P.M 0.147 0.07 0.01 0.2 0.3 110.103 1.2 1.6 Final 7:16:12 P.M 0.088 0.097 0.01 0.2 0.3 110.521 Initial 7:16:22 P.M 0.129 0.076 0.01 0.2 0.3 111.101 1.3 1.6 Final 7:56:42 P.M 0.109 0.109 0.01 0.2 0.3 111.564 Initial 7:56:51 P.M 0.151 0.085 0.01 0.2 0.3 114.67 1.4 1.6 Final 8:44:12 P.M 0.128 0.099 0.01 0.2 0.3 115.56
Appendix G: (Continued) Specific Gravity of sulfuric acid meas ured at the end of the experiment. Specific Gravity: 1.140 (8.15 P.M) Specific Gravity: 1.142 (8.45 P.M) Table G.2 Residual Voltage Meas urements (Electrolysis V) Residual Voltages Electrodes Before Discharge Discharge for 1 minute Discharge for another minute Positive & Negative 0.9V 0.7V 0.6V Sensor Ring & Positive 7.5mV 4.8mV 17mV Sensor Ring & Negative 0.9V 0.7V 0.6V
Appendix H: Electrolysis VI Electrolysis VI Electrodes: 1) Posi tive electrode: Tungste n Carbide coated carbon 2) Negativ e electrode: Platinum coated 316 stainless steel. 3) Sensor ring: Tungsten carbide Carbon Acid Concentration: 20 wt % Level Sensor: 1) Series resistance R S : 50.5 ohms 2) Frequency: 10 kHz 3) AC signal: 1volts (0 to peak) Table H.1 Current Voltage Data Electrolysis VI Electrodes Sensor Ring Flow Rates Voltage (V) Current (A) Voltage (V) Current (A) H2O Bottom (ml/min) H2O Top (ml/min) SO2 Pump (ml/min) 1 0.008 1 0.007 0.02 0.42 0.00 1.1 0.011 1.1 0.008 0.02 0.42 0.00 1.2 0.017 1.2 0.009 0.02 0.42 0.00 1.3 0.020 1.3 0.009 0.02 0.42 0.00 1.4 0.030 1.4 0.014 0.02 0.42 0.00 1.5 0.047 1.5 0.026 0.02 0.42 0.00 1.6 0.061 1.6 0.042 0.02 0.42 0.00 1.7 0.074 1.7 0.06 0.02 0.42 0.00 1.8 0.101 1.8 0.093 0.02 0.42 0.00