DETERMINATION OF SATURATION VAPOR PRESSURE OF LOW VOLATILE SUBSTANCES THROUGH THE STUDY OF EVAPORATION RATE BY THERMOGRAVIMETRIC ANALYSIS

Subject of Study.Research of vapor pressure of low volatile substances is a complicated problem due to both direct experimental implementation complexity and, most significantly, the issues faced correctness of the analysis and processing of experimental data. That is why it is usually required engaging the reference substances (with vapor pressures well studied). The latter drastically reduces the effectiveness of the experimental methods used and narrows their applicability. The paper deals with an approach to the evaporation process description (sublimation) of low volatile substances based on molecular kinetic description in view of diffusive and convection processes. The proposed approach relies on experimental thermogravimetricfindingsina wide range of temperatures, flow rates ofthe purge gas and time. Method. A new approach is based on the calculation of the vapor pressure and uses the data about the speed of evaporation by thermogravimetric analysis depending on the temperature, the flow rate of the purge gas, and the evaporation time. The basis for calculation is the diffusion-kinetic description of the process of evaporation (mass loss) of the substance from the exposed surface. The method is applicable to determine the thermodynamic characteristics for both the evaporation (the equilibrium liquid - vapor) and sublimation (the equilibrium solid - vapor). We proposed the appropriate method of the experiment and analysis of its data in order to find the saturated vapor pressure of individual substances of low volatility. Main Results. The method has been tested on substances with insufficiently reliable and complete study of the thermodynamic characteristics but, despite this, are often used (because of the other data limitations) as reference ones. The vaporization process (liquid-vapor) has been studied for di-n-butyl phthalate C16H22O4 at 323,15–443,15 К, and sublimation for benzoic acid C7H6O2at 303,15–183,15 К. Both processes have been carried in a stream of nitrogen N₂ (20-250 ml·min^-1); the duration of evaporation-sublimation (each TGA experiment) is 10 hours. As a result, the vapor pressure of these substances has been determined in a wide temperature range; analysis of the dependence for the evaporation coefficients on TGA experiment conditions has been carried out; recommendations on their choice for determination of the enthalpy of vaporization and sublimation of the evaporation rate have been given. Practical Relevance. The presented theoretical and experimental apparatus allows determining the vapor pressure by TGA method for wide classes of compounds with varying volatility (including low volatility). The proposed method requires only necessary data on isothermal evaporation (sublimation) and no standards. It is advisable to use this approach for the study of a wide range of high boiling compounds, such as pharmacologically active substances, oils, "green solvents", including ionic liquids, and others.

1. Suvorov A.V. Termodinamicheskaya Khimiya Paroobraznogo Sostoyaniya. Tenzimetricheskie Issledovaniya Geterogennykh Ravnovesii [Thermodynamic Chemistry of the Vapor State. Strain Gage Study of Heterogeneous Equilibriums]. Leningrad, Khimiya Publ., 1970, 208 p.
2. de Nevers N. Physical and Chemical Equilibrium for Chemical Engineers. 2nd ed. Wiley, 2012, 384 p.
3. Yaws C.L. Thermophysical Properties of Chemicals and Hydrocarbons. 2nd ed. Elsevier, 2014, doi: 10.1016/B978-0-323-28659-6.00025-2
4. Brooks B.W., Huggett D.B. Human Pharmaceuticals in the Environment: Current and Future Perspectives. Springer, 2012, 302 p.
5. Järvik O., Rannaveski R., Roo E., Oja V. Evaluation of vapor pressures of 5-methylresorcinol derivatives by thermogravimetric analysis. Thermochimica Acta, 2014, vol. 590, pp. 198–205. doi: 10.1016/j.tca.2014.07.001
6. Verevkin S.P., Ralys R. V., Zaitsau D. H., Emel'yanenko V.N., Schick C. Express thermo-gravimetric method for the vaporization enthalpies appraisal for very low volatile molecular and ionic compounds. Thermochimica Acta, 2012, vol. 538, pp. 55–62. doi: 10.1016/j.tca.2012.03.018
7. Maton C., De Vos N., Stevens C.V. Ionic liquid thermal stabilities: decomposition mechanisms and analysis tools. Chemical Society Reviews, 2013, vol. 42, no. 13, pp. 5963–5977. doi: 10.1039/c3cs60071h
8. Verevkin S.P. 2 Phase changes in purecomponent systems: liquids and gases. Experimental Thermodynamics, 2005, vol. 7, pp. 5–30. doi: 10.1016/S1874-5644(05)80004-9
9. Varushchenko R.M., Druzhinina A.I. Determination of saturated vapor pressure of organic substances from the triple to critical point. High Temperature, 2010, vol. 48, no. 3, pp. 328–335. doi: 10.1134/S0018151X10030041
10. Lundblad R.L. Approaches to the Conformational Analysis of Biopharmaceuticals. CRC Press, 2009, 366 p.
11. Paulechka Y.U., Zaitsau Dz.H., Kabo G.J., Strechan A.A. Vapor pressure and thermal stability of ionic liquid 1-butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide. Thermochimica Acta, 2005, vol. 439, no. 1–2, pp. 158–160. doi: 10.1016/j.tca.2005.08.035
12. Wunderlich B. Thermal Analysis of Polymeric Materials. Berlin, Springer, 2005, 907 p. doi: 10.1007/b137476
13. Goodrum J.W., Geller D.P. Rapid thermogravimetric measurements of boiling points and vapor pressure of saturated medium- and long-chain triglycerides. Bioresource Technology, 2002, vol. 84, no. 1, pp. 75–80. doi: 10.1016/S0960-8524(02)00006-8
14. Price D.M., Hawkins M. Vapour pressures of hydroxybenzophenone UV absorbers. Thermochimica Acta, 1999, vol. 329, no. 1, pp. 73–76.
15. Langmuir I. The Vapor pressure of metallic tungsten. Physical Review, 1913, vol. 2, no. 5, pp. 329–342. doi: 10.1103/PhysRev.2.329
16. Gückel W., Synnatschke G., Rittig R. A method for determining the volatility of active ingredients used in plant protection. Pesticide Science, 1973, vol. 4, no. 1, pp. 137–147. doi: 10.1002/ps.2780040119
17. Elder J.P. Sublimation measurements of pharmaceutical compounds by isothermal thermogravivletry. Journal of Thermal Analysis and Calorimetry, 1997, vol. 49, no. 2, pp. 897–905. doi: 10.1007/BF01996775
18. Price D.M. Volatilisation, evaporation and vapour pressure studies using a thermobalance. Journal of Thermal Analysis and Calorimetry, 2001, vol. 64, no. 1, pp. 315–322. doi: 10.1023/A:1011522020908
19. Burnham L., Dollimore D., Alexander K. Calculation of the vapor pressure-temperature relationship using thermogravimetry for the drug allopurinol. Thermochimica Acta, 2001, vol. 367–368, pp. 15–22. doi: 10.1016/S0040-6031(00)00652-3
20. Pieterse N., Focke W.W. Diffusion-controlled evaporation through a stagnant gas: estimating low vapour pressures from thermogravimetric data. Thermochimica Acta, 2003, vol. 406, no. 1–2, pp. 191–198. doi: 10.1016/S0040-6031(03)00256-9
21. Ralys R., Uspenskiy Al., Slobodov A. Evaporation rate converted into saturated vapor pressure from TGA data. Proc. 13th Joint European Thermodynamic Conference, JETC-2015. Nancy, France, 2015, pp. 90–91.
22. Slobodov A., Uspenskiy An., Ralys R., Kremnev D. Thermodynamic modelling of phase-chemical transformations as the method for study of rheological properties of substances. Építőanyag – Journal of Silicate Based and Composite Materials, 2015, vol. 67, no. 4, pp. 163–167.
doi: 10.14382/epitoanyag-jsbcm.2015.27
23. Slobodov A.A., Ralis R.V., Uspenskii A.B., Sochagin A.A., Gavrilov A.V. Razrabotka kriteriev kachestva sistem i baz termodinamicheskikh dannykh dlya issledovaniya mnogokomponentnykh fiziko-khimicheskikh prirodnykh i tekhnologicheskikh system [Quality criteria development for systems and databases of thermodynamic data for the study of physical and chemical multicomponent of natural and technological systems]. Bulletin of SPbSIT(TU), 2015, no. 31(57), pp. 8–12.
24. Heym F., Etzold B.J.M., Kern C., Jess A. Analysis of evaporation and thermal decomposition of ionic liquids by thermogravimetrical analysis at ambient pressure and high vacuum. Green Chemistry, 2011, vol. 13, no. 6, pp. 1453–1466. doi: 10.1039/c0gc00876a
25. Chatterjee K., Dollimore D., Alexander K. A new application for the Antoine equation in formulation development. International Journal of Pharmaceutics, 2001, vol. 213, no. 1–2, pp. 31–44. doi: 10.1016/S0378-5173(00)00644-X
 

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License