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Development of a Method to Determine Vapor Pressure Data of Low Volatile Chemicals from a Knudsen Effusion Technique by Andrew R. Harshman A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering Department of Chemical Engineering College of Engineering University of South Florida Major Professor: Venka t Bhethanabotla, Ph.D. John Wolan, Ph.D. Scott Campbell, Ph.D. Date of Approval: March 29, 2007 Keywords: pesticide, thermodynamic data catechol, naphthalene, vacuum Copyright 2007, Andrew R. Harshman
Dedication I dedicate this thesis to my wife, Kri ssy, my life, my love, and my inspiration. You have given me the courage to do what I want to do and to be more than I thought I could. Thank you for helping me to realize my potential and for giving me the strength to pursue happiness. I also dedicate this work to my pare nts, Jim and Judy. The support, education, and encouragement you have provided have fo rmed who I am and have given me the strength to accomplish my goals. Thank you for being a guiding light, showing me the way to live a happy and successful life.
Acknowledgments I would like to thank my major profe ssor, Dr. Venkat Bhethanabotla, for his continuing mentorship and undeniable faith in my success. I would also like to thank my committee members Dr. John Wolan and Dr. Scott Campbell for the advice and time spent helping my complete this thesis. An infinite amount of gratitude is also reserved for Mr. Stefan Cular, whose ideas and skills were of the utmost importance to the success of this work. I would also like to mention: The USF Department of Chemical Engineering faculty and staff for their constant support of my education. The members of the Sensors Research Laboratory and Dr. Wolans research group at USF for their continued help and guidan ce toward the completion of this thesis. Daniel Magro and the rest of the sta ff of Envisors, LLC for their support and encouragement toward the achievement of my educational goals.
i Table of Contents List of Figures ii Abstract iv Chapter 1 Introduction 1 1.1 Pesticides 1 1.2 Knudsen Effusion Method 2 Chapter 2 Apparatus and Experimental Design 3 2.1 Components 3 2.2 Experimental Procedure 6 Chapter 3 Theory and Calculations 8 3.1 General Equation Derivations 8 3.2 Corrections 9 Chapter 4 Results and Discussion 11 4.1 Naphthalene 11 4.2 Catechol 12 Chapter 5 Conclusions 16 References 18 Appendices 20 Appendix A: Laser Drilled Holes in Orifice Plates 21 Appendix B: Direct Coating Procedure 26
ii List of Figures Figure 1. Knudsen Effusion Cell and Temperature Control Feedthrough 5 Figure 2. Overall Knudsen Effusion Apparatus 6 Figure 3. Naphthalene Vapor Pressure Data 12 Figure 4. Catechol Frequency Shifts at Various Temperatures 14 Figure 5. Catechol Vapor Pressure Data 15 Figure 6. Catechol Vapor Pressure Data 15 Figure 7. Orifice A.1 21 Figure 8. Orifice A.2 21 Figure 9. Orifice A.3 21 Figure 10. Orifice A.4 21 Figure 11. Orifice A.5 22 Figure 12. Orifice A.6 22 Figure 13. Orifice A.7 22 Figure 14. Orifice A.8 22 Figure 15. Orifice A.9 22 Figure 16. Orifice A.10 22 Figure 17. Orifice B.1 23 Figure 18. Orifice B.2 23 Figure 19. Orifice B.3 23 Figure 20. Orifice B.4 23
iii Figure 21. Orifice B.5 24 Figure 22. Orifice B.6 24 Figure 23. Orifice B.7 24 Figure 24. Orifice B.8 24 Figure 25. Orifice B.9 25 Figure 26. Orifice B.10 25
iv Development of a Method to Determine Vapor Pressure Data of Low Volatile Chemicals from a Knudsen Effusion Technique Andrew R. Harshman ABSTRACT Vapor pressure data are vital to understanding impacts that substances, specifically pesticides, may exert on the environment. Th ey enter into atmospheric deposition models for such chemicals which determine the fate and transport of these species in the environment. At normal application temper atures (i.e. room temperature) the vapor pressures of many of these chemicals are too lo w to be determined by conventional means. An isothermal Knudsen effusion technique was designed and developed in our laboratory for such measurements. The effusion mass as a f unction of time is measured in our technique using a thickness shear mode (TSM) acoustic wa ve sensor, which allo ws for extremely high (few nanograms) sensitivity. This sensitivity a llows for much more rapid determination of low vapor pressures (10 -1 to 10 -5 Pa) than is possible by other Knudsen effusion techniques. Basing the effusion mass measurement on the TSM se nsor as in our apparatus eliminates the typically seen dependence on vibration in conventional microbalance-based effusion techniques. Full design details of our appara tus and specifically the Knudsen cell, based on original equations derived by Knudsen, and many corrections that have been noted in the literature for cell and effusion-hole dimensions, are presented. The accu racy of our method
v was tested by a comparison of published vapor pre ssure data to vapor pressure data acquired in our laboratory with measurements on naphthalene and catechol.
1 Chapter 1 Introduction 1.1 Pesticides Pesticides are very useful in the protecti on of foods that are threatened by insects during growth. Pesticide sales in the United States is a multi-billion dollar business, and companies work to develop new pesticides each year that are made to fit the needs of their consumers. The Environmental Prot ection Agency (EPA) reported in 2001 that $11.1 billion was spent on pesticides in the United States alone, accounting for 35% of the World market . The majority of the money is spent for agricultural purposes. While the pesticide business is vast, the potential dangers that they pose to humans and other living things are substantial and must not be overlooked. Certain properties of every pesticide must be known and submitted to the EPA before it can be used legally in the United States due to th e potential threats they pose to humans and the environment in general . One of the pr operties of each pesticide that must be submitted in order to pass EPA certification is vapor pressure, the pressure (at a certain temperatures) at which the pesticide changes pha se from a solid or liquid to a vapor. This property is vital to understan ding the potential harmful imp acts pesticides pose to the environment. It has been estimated that of the pesticide applied, only 0.1% impacts the insects, leaving 99.9% lost to the environment . This research focuses on low-vapor pressure pesticides. With a lower vapor pressure a nd subsequent relative vo latility, the chemical
2 will tend not to vaporize and in turn will disp lay properties of higher solubility in water and higher absorptivity ont o the land. This creates a haza rd for the environment and can negatively influence water and crops. By knowing the vapor pressure data, the EPA can regulate the amount of pollution created by c ontrolling the use of these contaminants. 1.2 Knudsen Effusion Method Vapor pressure determination may be accomplished by a variety of methods. The method chosen for this research was the Knudsen Effusion method  because of temperature control and time constraint a dvantages over other methods. The Knudsen Effusion method utilizes an isothermal cell (K-Cell) with a very small orifice (0.11.0mm.) out of which a chemical effuses (f lows under pressure). The measured mass loss over time is proportional to the vapor pressure. The mass effusion rate is measured using a quartz crystal microbalance (QCM). A QCM is an extremely sensitive mass senor able to sense mass changes in the nanogram (10 -9 g.) level. This makes it extremely attractive for use in a small application like this. The QCM consists of a piezoelectric device on a thin qua rtz plate with two electrodes attached to the plate. Vibrations from mass collection change th e frequency of the QCM. The frequency change is directly proportional to the mass accumulation rate. The sensitivity and subsequent accuracy of the QCM make it a very attractive option for the mass change measurement.
3 Chapter 2 Apparatus and Experimental Design 2.1 Components The apparatus was constructed with the QCM and K-Cell serving as the basis of design. Goodman  construc ted an apparatus utilizing both a Knudsen Effusion method and a QCM. As with Goodmans design, Conflat components comprise the base structure for the apparatus. The Conflat components are comprised of a stainless steel frame with flanges designed for a tight seal for all connections using copper or viton rubber gaskets and bolts and nuts for tensi on. The structure and s eals are designed to withstand the low vacuum associated with the objectives of this research. The apparatus includes a vacuum to re duce pressure, a QCM with temperature control, a K-Cell with temperature control, a pressure gauge to for chamber pressure estimation, and a thermocouple to determine an accurate temperature of the cell enclosed in a 5-way cross. The K-Cell requires temperature control because of the strict isothermal conditions required for vapor pr essure data collection and calculations. Temperature control is obtained using a water chamber fed through and welded to the bottom of a blind flange. Two stainless steel tubes ar e fed into the chambe r and connected to a temperature controlled water bath. The base of the K-cell is machined directly on top of the chamber to provide good heat transfer. A notch is formed around the top of the base so an o-ring may be placed to provide a seal between the base and a lid. Another notch is
formed around the circumference of the base below the top to ensure compression between the other o-ring and the lid. Th in (0.0254 mm. or 0.1016 mm. thick) stainless steel plates were constructe d to fit on top of the o-ring. Small (0.1 1.0 mm. diameter) orifices were laser drilled in the center of each plate. Pictures of these holes and their respective areas may be found in Appendix A. A stainless steel lid fits directly over the orifice plate and along the side of the base. A graphical representation of the K-Cell is shown in Figure 1. The QCM holder is fed into the side of th e 5-way cross so that it is parallel to the K-Cell, with the sensor directly above the orifice. The QCM is housed in a chamber through which refrigerated liquid passes, keepin g the QCM at its desired temperature. It must be at a temperature significantly below wh at the K-Cell temperature is so that the molecules recrystalize after effusion. The QCM holder was purchased from and fabricated by Maxtek, Inc. The QCM electrode itself is connected to an oscillator, which transmits the frequency of the sensor at any given time to a counter, from which data is transmitted to a computer. The computer is equipped with a LabView program which is designed to display and store the freque ncy change of the crystal over time. The experimental vapor pressures that ar e deemed accessible to this apparatus are in the range of 10 -5 -10 -1 Pa. Pressures that are at leas t two orders of magnitude lower should be maintained outside th e Knudsen cell. To achieve this a turbomolecular vacuum pump from Leybold (model BMH-70, which in cludes the roughing pump) is utilized. A flexible hose connects the vacuum to the side of the 5-way cross. A pressure gauge (Leybold model ITR 90) is utilized to monitor the chamber pressure. 4
A thermocouple is fed through the top of the apparatus. Conn ected to this are wires that transmit a temperature reading to a LED readout so that the temperature of the Knudsen cell may be read during runs. Th e thermocouple wires are attached via an adhesive to the side of the K-Cell. The thermoc ouple was calibrated using a NIST traceable mercury-in-glass thermometer. Two Thermo (NESLAB RTE 17 AND 740) te mperature contolled water baths are connected by Tygon rubber hose to the K-Ce ll water bath and the crystal holder, respectively. A mixture of commercial antif reeze and deionized water is used as the control liquid in each bath. A graphical representation of the entire apparatus configurat ion is shown in Figure 2. F B A C D E G Figure 1. Knudsen Effusion Cell and Liquid Temp erature Control Feedthroug h. A. Cell lid; B. Orifice plate; C. Sealing O-rings; D. Cell cham ber; E. Liquid temperatu re control chamber; F. Liquid feedthrough tubes; G. Conflat flange 5
A B C D E F G H H I Figure 2. Overall Knudsen Effusion Apparatus. A. Turbomolecular vacuum pump; B. Pressure gauge; C. Thermocouple feedthroug h and temperature readout; D. QCM in holder; E. Oscillator; F. Frequency counter; G. Computer; H. Liquid recircu lating baths; I. K-cell/ liquid feedthrough 2.2 Experimental Procedure A small amount of the chemical of which va por pressure data is desired is placed in the base of the K-Cell. Th e o-rings, orifice plate, and lid are then placed on the base. The K-Cell/temperature control feedthrough is fed into the bottom of the apparatus and sealed. The thermocouple readout, oscillator, counter, and computer are all turned on. Assuming all connections are s ealed properly and a properly f unctioning crystal is placed in the holder, the vacuum pump is initiated. The water bath contro lling the temperature of the K-Cell is then initiated, followed by the water bath controlling the temperature of the crystal. Once the thermocouple readout and frequency shift ar e stable, the initial frequency is recorded and the LabView program is initiated and run for approximately 10 minutes. The temperature of the water bath controlling the K-Cell temperature is then 6
7 changed, and all subsequent proc edure steps are repeated. This process is repeated for each desired temperature.
Chapter 3 Theory and Calculations 3.1 General Equation Derivations The vapor pressure at each temperature was calculated from the measured frequency shift data by applying several corre ctions to the equation given below, which applies to substances under Knusden Effusion conditions : 2 121 W e oM RT dt dM A p (1.1) Where p is the pressure (Pa), A o is the cross-sectional area of the orifice (m 2 ), dt dMe is the mass effusion rate (kg/s), R is the unive rsal gas constant (J/(mol*K)), T is the temperature of the K-Cell (K), and M W is molecular weight (kg/mol). The mass effusion rate is obtained us ing the measured frequency shift dt fd (Hz/s) with the following equation, which additionally corrects for the distance between the orifice hole and the QCM : dt fd C r dt dMf q e 1 coscos2 (2.1) 8
Where r q is the radius of the active area of the QCM sensor (m), and are angles between the QCM and the orifice hole as shown in Fig. 3, and C f is a conversion factor found using the following equation: qq q ff C22 (2.2) Where is the frequency of the crystal wi thout any deposited material (Hz), qf q is the density of the quartz (kg/m 3 ), and q is the shear wave velocity of the crystal (m/s). 3.2 Corrections To correct for the length of the orifice and the effect of the orifice on the equilibrium pressure of the K-Cell, th e following equation is derived : pspo1KClausingAoAs 1 1 W 2 (3.1) Where p s is the equilibrium vapor pressure in K-Cell (Pa), p o is the pressure near the orifice (Pa), A s is the cross sectional area of K-Cell (m 2 ), a is the vaporization coefficient ( 1 for loosely-packed solids), and the constants K Clausing and W are found using the following equations: K Clausing 1 1 3L 8 ro (3.2) and 9
c ch r W (3.3) Where L is the length of the orifice (m), r o is the radius of the orifice (m), r c is the radius of inside of the K-Cell (m), and h c is the height of K-Cell (m). When all of the equations and correction factors are combined, the following equation results and is used in the determination of vapor pressures for various temperatures. ps 1 KClausing 1 Ao rq 2coscos 1 Cf d fdt 2RT MW 1 2 1 KClausingAoAs 1 1 W 2 (4.0) 10
11 Chapter 4 Results and Discussion 4.1 Naphthalene Naphthalene was tested due to its known volatility and use in a similar Knudsen Effusion apparatus by Torres  to determine its enthalpy of sublimation at various temperatures. The experimental vapor pressure data evidenced by Fi gure 3 is erratic and does not reproduce accepted published results by Ambrose, et. al. . Although the results by Torres  were reported as accura te in terms of enthalpy change, a simple calculation using the enthalpy of sublimation reported proved to be quite puzzling. Using the equations provided in the text of Torres , it was found that the effusion rate naphthalene at a temperature of 298 K was 8.96 x 10 -24 kg/s resulting in a vapor pressure of 1.77 x 10 -13 Pa. The vapor pressure reported by Ambrose, et. al.  at 298 K is around 11 Pa. This major discrepancy between the data retrieved through the Knudsen method (This work and Torres ) and the accepted data (Ambrose, et. al. ) suggests that the Knudsen method should not be used with chemicals as volatile as naphthalene.
0 5 10 15 20 25 30 35 290 295 300 305 310Temp (K) This Work Ambrose, et. al Figure 3. Naphthalen e Vapor Pressure Data 4.2 Catechol Following the testing and subsequent resu lts of naphthalene, it was determined that chemicals with lower volatility at applic ation temperatures (i.e. room temperature) should be tested. Vapor pressure data for ch emicals commonly used in pesticides were collected by Chen  utilizing a Knudsen Effusion method and th ese chemicals were selected to be tested using the apparatus to validate the accuracy of the apparatus in collecting vapor pressure data. These chem icals and respective temperature ranges for vapor pressure measurement are anthra cene (320-360 K), catechol (290-310 K), hydroquinone (320-340 K), caffeic acid (410-430 K), ferulic acid (360-390 K), gentisic acid (360-380 K), and myoinositol (440-460 K). Catechol was sele cted to be tested first 12
based on the temperature range being close to room temperat ure (25 C) for ease of testing. Individual frequency shift data fo r catechol (301-310 K) may be found in Figure 4. These data were compiled utilizing an orifice plate 0.0254 mm. thick and with a hole diameter of 0.275 mm. Figure 5 shows the calculated vapor pressure data as compared to Chen . These experimental data, while resembling the trend of the published data, are not within acceptable agreement with it. One of the major c ontributors to this error may have been the sizeable distance between the orifice and the sensor (1.905 cm.). This distance was lessened to 1.003 cm. with the addition of Teflon washers between the orifice plate and the o-ring seal normally below th e plate. The results of this test may be found in Figure 6. While this test slightly decreases the difference between published and experimental data, it does not change it enough to make the data acceptable. The results of these two tests seemingly dictate that the apparatus does not produce accurate results. Reasons for this error may include the distance between the orifice and the sensor, possible leaks in the K-Cell, and vacuum chamber contamination. The distance between the orifice and the sensor is a factor in that all the mass that effused out of the cell did not collect on the sensor. This was evident by the observation of mass on the QCM holder following tests. The ma ss observed on the QCM holder also suggests possible K-Cell leaking. If the seal between the lid and the orifice plate was not sufficient, the mass may have escaped out in th at gap. The result of all of the mass not collecting on the sensor shows that the vacuum chamber was contaminated for future runs. Therefore, when the apparatus is r unning, vapor already in the chamber collected on the sensor impeding the results. 13
Steps were taken to minimize the error, including the afor ementioned distance reduction between the orifice and the sensor, us ing Kapton tape to seal the orifice plate directly to the K-Cell, and baking the chamber overnight to try and remove containments. Other tests followed, including ch anging the orifice size and di rect coating of the QCM to measure mass loss. The procedure for direct coating of the QCM may be found in Appendix B. No alternatives provided accu rate results for catechol. Other chemicals were not tested due to time constraints and the fact that they were less volatile than catechol and would have theoretically effused at even slower rates. The error is not thought to be attributed to the chemical that was tested, rather someth ing internal with the apparatus or process. -60 -50 -40 -30 -20 -10 0 0 50 100 150 200 250 Time (s) 37oC 34oC 31oC 28oC Figure 4. Catechol Frequency Shifts at Various Temperatures. 1.905 cm. distance from orifice to sensor; 0.275 mm. diameter orif ice; 0.0254 mm. plate thickness 14
0.0001 0.001 0.01 0.1 1 20 22 24 26 28 30 32 34 36 Temp (C) This Work Chen, et.al. Figure 5. Catechol Vapor Pressure Data. 1.905 cm. distance from orifice to sensor; 0.275 mm. diameter orifice; 0.0254 mm. plate thickness 0.001 0.01 0.1 1 20222426283032343638 Temp (C) Chen, et.al. This Work Figure 6. Catechol Vapor Pressure Data. 1.003 cm. distance from orifice to sensor; 0.275 mm. diameter orifice; 0.0254 mm. plate thickness 15
Chapter 5 Conclusions It is concluded that the apparatus does not accurately measure vapor pressure data of low-volatile chemicals as it is currently configured. While the basis of the apparatus design stemmed from earlier research, accura te comparability with the vapor pressure data obtained from that research did not result for the chemicals naphthalene and catechol. Naphthalene is too volatile at possible operati ng temperatures to obtain accurate vapor pressure data. Distance be tween orifice and sensor, cell leaks, and vacuum chamber contamination may all have b een factors in the error associated with obtaining accurate data for catechol. While th ere is a correction for the distance between the sensor and orifice included, it is only valid as a slight correcti on to reasonable data. With the degree of variance observed, this co rrection does not adjust the data within accurate limits. The respectably sizable distance was put in place to assure uniform coating of the sensor, but actually hindered the process. It was evident that most of the mass did not collect on the crystal by observa tions of solid mass on the perimeter of the crystal holder itse lf following operation. To eliminate po ssible error, direct coating of the sensor with the construction of a Knudsen Ce ll around it should be explored. This will ensure that all of the mass e ffusing out of the K-Cell is accounted for by the measurement of the mass loss of the crystal instead of mass gain. This option was briefly explored in this work by taping an orifice plate to th e crystal holder after co ating the sensor, but results are not included due to observati on of the crystal holde r following operation 16
finding that the tape did not remain sealed an d thus resulted in not all of the chemical effusing through the orifice. A device needs to be designed and built to seal the new KCell mechanically. The Knudsen Effusion Method has been utilized for almost a century, providing accurate vapor pressure and enth alpy data for low-volatile ch emicals. While the Quartz Crystal Microbalance has many advantages, its use in conjunction with the Knudsen Effusion Method as shown in this research may need to be modified. In this apparatus, only a fraction of the effused mass was collect ed, and a mathematical correlation between that and the total mass could not be obtained. It is the finding of the work that to obtain truly accurate data, the tota l amount of mass escaping the Knudsen Cell must be accounted for. 17
References 1. Kiely, T., D. Donaldson, and A. Grube, Pesticide Industry Sales and Usage, 2000 and 2001 Market Estimates, U.S.E.P. Agency, Washington, D.C., 2004. p. 4-7. 2. Code of Federal Regulations, Title 40--Protection of Environment, U.S. Government Printing Office via GPO Access., Washington, D.C., 2005 p. 77-129. 3. Rose, J., ed. Environmental Toxicolo gy: Current Developments. Vol. 7. 1998, Gordon and Breach Science Publishers: Amsterdam. 4. Goodman, M.A., Vapor Pressure of Agrochemic als by the Knudsen Effusion Method Using a Quartz Crystal Microbalance. J. Chem. Eng. Data, 1997. 42(6): p. 1227-1231. 5. Lu, C. and A.W. Czanderna, eds. Applications of Pizoelectric Quartz Crystal Microbalances. Methods and Phenomena, ed. S. P.W.a.A.W. Czanderna. Vol. 7. 1984, Elsevier Science Publishers B.V.: Amsterdam. 393. 6. Chen, X., et al., Vapor Pressure Characterization of Several Phenolics and Polyhydric Compounds by Knudsen Effusion Method. J. Chem. Eng. Data, 2006. 51(2): p. 386-391. 7. Torres, L.A., et al., The Problem of Counting the Number of Molecules and Calculating Thermodynamic Properties. J. Chem. Education, 1995. 72(1): p. 6770. 8. Ambrose, D., et al., The Vapor Pressure of Naphthalene. J. Chem. Thermodynamics, 1975. 7: p. 1173-1176. 9. Whitman, C.I., On the Measurement of Vapor Pressures by Effusion. J. Chem. Physics, 1952. 20(1): p. 161-164. 10. Paulechka, Y.U., Zaitsau, DZ.H., Kabo, G.J., & Strechan, A.A. Vapor Pressure and Thermal Stability of Ionic Li quid 1-butyl-3-metnylimidazolium Bis(trifluoromethylsulfonyl)amide. Thermochimica Act, 2005. 439: p. 158-160. 11. Rebelo, L.P.N., Lopez, J.N.C., Esperanca, J.M.S.S., & Filipe, E. On the Critical Temperature, Normal Boiling Point, and Vapor Pressure of Ionic Liquids. Journal of Physical Chemistry Letters, 2005. 109: p. 6040-6043. 18
12. Zaitsau, DZ.H., Vervkin, S.P., Paulechka, Y.U., Kabo, G.J., & Sevruk, V.M. Comprehensive Study of Vapor Pressure s and Enthalpies of Vaporization of Cyclohexyl Esters. J. Chem. Eng. Data, 2003. 48: p. 1393-1400. 13. Torres, L.A., Campos, E., Enriquez, E., & Patino, R. The Enthalpy of Sublimation of 5,10,15,20-tetraphenylporphine and 5,10,15,20-tetrakis(4methoxyphenyl)porphine. J. Chem. Thermodynamics, 2002. 34: p. 293-302. 14. Patina, R., Campos, M., & Torres, L.A. A Thermochemical Study of 5,10,15,20tetraphenylporphine Zinc(II) by Rotati ng Bomb Combustion Calorimetry and by Knudsen Effusion Experiments. J. Chem Thermodynamics, 2002. 34: p. 193-204. 15. Torres, L.A., Gudino, R., Sabbah, R., & Guardado, J.A. Standard Reference Material Proposed for Enthalpy -of-Sublimation Measurement. A Comparative Study of the Standard Molar Ent halpy of Sublimation of Fe(c-C 5 H 5 ) 2 (ferrocene) by Calorimetry and Knudsen-effusion Techniques. J. Chem. Thermodynamics, 1995. 27: p. 1261-1266. 16. Torres-Gomez, L.A., Barreiro-Rodriguez, G., & Galarza-Mondragon, A. A New Method for the Measurement of Enthalpi es of Sublimation Using Differential Scanning Calorimetry. Thermochimica Acta, 1998. 124: p. 229-233. 17. Monte, M.J.S., Santos, L.M.N.B.F., Fulem, M., Fonseca, J.M.S., & Sousa, C.A.D. New Static Apparatus and Vapor Pressure of Reference Materials: Napthalene, Benzoic Acid, Benzophenone, and Ferrocene. J. Chem. Eng. Data, 2006. 51: p. 757-766. 18. Oja, V. & Suuberg, E.M. Vapor Pressures and Enthalpi es of Sublimation of DGlucose, D-Xylose, Cell obiose, and Levoglucosan. J. Chem. Eng. Data, 1999. 44: p. 26-29. 19. Oja, V. & Suuberg, E.M. Development of a Nonisothermal Knudsen Effusion Method and Application to PAH and Cellulo se Tar Vapor Pressure Measurement. Anal, Chem., 1997. 66: p. 4619-4626. 20. Oja, V. & Suuberg, E.M. Vapor Pressures and Enthal pies of Sublimation of Polycyclic Aromatic Hydrocarbons and Their Derivatives. J Chem. Eng. Data, 1998. 43: p. 486-492. 19
Appendix A: Laser Drilled Holes in Orifice Plates Pictures and measurements acquired using a Le ica DMI 4000B Inverted Fluorescent Microscope with a Leica 340FX Cooled CCD Camera utilizing Media Cybernetix Image-Pro Plus Softaware. PGX = Measured Area of Orifice Thickness A = 0.1016 mm. Figure 7. Orifice A.1 Figure 8. Orifice A.2 Figure 9. Orifice A.3 Figure 10. Orifice A.4 21
Appendix A: (Continued) Figure 11. Orifice A.5 Figure 12. Orifice A.6 Figure 13. Orifice A.7 Figure 14. Orifice A.8 Figure 15. Orifice A.9 Figure 16. Orifice A.10 22
Appendix A: (Continued) Thickness B = 0.0254 mm. Figure 17. Orifice B.1 Figure 18. Orifice B.2 Figure 19. Orifice B.3 Figure 20. Orifice B.4 23
Appendix A: (Continued) Figure 21. Orifice B.5 Figure 22. Orifice B.6 Figure 23. Orifice B.7 Figure 24. Orifice B.8 24
Appendix A: (Continued) Figure 25. Orifice B.9 Figure 26. Orifice B.10 25
Appendix B: Direct Coating Procedure 1. Record initial frequency of crystal by pl acing it in the hold er and connecting to frequency counter. 2. Dissolve chemical to be tested in appr opriate solvent (Make sure to record concentration on vial). 3. Place a drop of the solution on a clea n crystal and let stand for 30 min. 4. Place an orifice plate over the crystal holder and seal every possible outlet (Record size of hole). 5. Place the crystal in the holder and seal every possible outlet. 6. Record frequency of crystal and use this to calculate the approximate mass of chemical on crystal. If frequency is not stable, clean the crystal and lower the concentration of the tested chemical. Repeat from step 3. 7. Place crystal holder into apparatus an d seal all arms of the chamber. 8. Turn on water bath to cont rol temperature of QCM. 9. Start Labview program and set to 5 sec./read. Run under name Pumpdown and save in folder of name Chemical_Date (i.e. Catechol_02092007). 10. Turn on forepump and then turbopump. 11. Watch frequency change on the monitor. When frequency shift stabilizes at a steady increase and the pressu re reading stabalizes, begi n recording data and save in the same folder as Chemical_Tempe rature (i.e. Catec hol_22oC). Record for 5-10 min. and then stop recording. 12. Change the temperature of the water bath to the next desired setting. Record data as Chemical_Temperature1-Temperat ure2 (i.e Catechol_22oC-25oC). 13. Repeat step 12. Allow for at least 5 min. after water bath temperature has stabilized for QCM to reach that temperature. 14. Repeat steps 13 and 14 for all s ubsequent desired temperatures. 15. Once tests are completed, turn off water bath, then turbopump, then forepump. 16. Once the vacuum has shut down, open valv e to release pressure, remove crystal holder, and clean crystal. 26
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Harshman, Andrew R.
Development of a method to determine vapor pressure data of low volatile chemicals from a Knudsen effusion technique
h [electronic resource] /
by Andrew R. Harshman.
[Tampa, Fla.] :
b University of South Florida,
ABSTRACT: Vapor pressure data are vital to understanding impacts that substances, specifically pesticides, may exert on the environment. They enter into atmospheric deposition models for such chemicals which determine the fate and transport of these species in the environment. At normal application temperatures (i.e. room temperature) the vapor pressures of many of these chemicals are too low to be determined by conventional means. An isothermal Knudsen effusion technique was designed and developed in our laboratory for such measurements. The effusion mass as a function of time is measured in our technique using a thickness shear mode (TSM) acoustic wave sensor, which allows for extremely high (few nanograms) sensitivity. This sensitivity allows for much more rapid determination of low vapor pressures (10-1 to 10-5 Pa) than is possible by other Knudsen effusion techniques. Basing the effusion mass measurement on the TSM sensor as in our apparatus eliminates the typically seen dependence on vibration in conventional microbalance-based effusion techniques. Full design details of our apparatus and specifically the Knudsen cell, based on original equations derived by Knudsen, and many corrections that have been noted in the literature for cell and effusion-hole dimensions, are presented. The accuracy of our methodwas tested by a comparison of published vapor pressure data to vapor pressure data acquired in our laboratory with measurements on naphthalene and catechol.
Thesis (M.S.)--University of South Florida, 2007.
Includes bibliographical references.
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Advisor: Venkat Bhethanabotla, Ph.D.
x Chemical Engineering
t USF Electronic Theses and Dissertations.