Estimation of Vapor Pressures

The Pitzer three-parameter corresponding states expression  

Vapor pressure data tend to be, in general, accurate at pressures above 0.1 atm. At lower pressures the uncertainty increases. Thus at 1 mm Hg and below, errors of 10% and higher are typical. For a method of screening a large number of vapor pressure data and correlating them with see Wilsak and Thodos (1984) and for the latter only, Reid et al. 

Equation 8.13.4 is applicable, in principle, to nonpolar compounds and gives very good results as demonstrated in Table 8.7 for n-butane. Notice that good results are obtained down to very low pressures. 

But even for polar compounds reasonable estimates are obtained, however, as demonstrated with acetone ( = 2.8 Debye), also included in Table 8.7, Notice that the accuracy improves drastically at higher temperatures where the impact of dipole-dipole interactions diminishes, as we have seen in Chapter 7. 

1n obtaining the results of Table 8.7 the y values of Appendix C were used. Reid et al suggest that o should be calculated from an empirical correlation. 

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Bidleman, T. F. (1984) Estimation of vapor pressures for nonpolar organic compounds by capillary gas chromatography. Anal. Chem. 56, 2490-2496. 

Burkhard, L. P, Andren, A. W., Armstrong, D. E. (1985a) Estimation of vapor pressures for polychlorinated biphenyls A comparison... 

Dobbs, A. J., Cull, M. R. (1982) Volatilization of chemical relative loss rates and the estimation of vapor pressures. Environ. Pollut. Ser.B., 3, 289-298. 

Passivirta, J., Sinkkonen, S., Mikkelson, P., Rantio, T., Wania, F. (1999) Estimation of vapor pressures, solubilities and Henry s law constants of selected persistent organic pollutants as functions of temperature. Chemosphere 39, 811-832. 

Basak, S. C. and Mills, D. Quantitative structure-property relationships (QSPRs) for the estimation of vapor pressure A hierarchical approach using mathematical structural descriptors. J. Chem. Inf. Comput. Sci. 2001, 41, 692-701. 

On examination of Equations 14 and 16, it is clear that estimates of vapor pressure lowering and ks are all that are required to determine the influence of a given salt on the vapor-liquid equilibrium behavior of a binary solvent mixture. 

Method of Macknick and Prausnitz The method of Macknick and Prausnitz [11] allows estimation of vapor pressures for liquid hydrocarbons in the range 10 to 1500 mmHg. The method is based on the following equation proposed by Miller [12] ... 

Burkhard, L. P., A. W. Andren, and D. E. Armstrong, Estimation of Vapor Pressures for Polychlorinated Biphenyls A Comparison of Eleven Predictive Methods. Chemosphere, 1985 19, 500-507. 

Edwards, D. R., and J. M. Prausnitz. Estimation of Vapor Pressures of Heavy Liquid Hydrocarbons Containing Nitrogen or Sulfur by a Group-Contribution Method. Ind. Eng. Chem. Res., 1981 20, 280-283. 

Ambrose, D., The Correlation and estimation of vapor pressures I. A. comparison of the three vapor-pressure equations. J. Chem. Thermodynamics, 1978 10, 765-769. 

The objective of this section is to provide clear descriptions of the alternative methods for the determination of gravimetric water content (Chapter Al) and of the range of methods available for the estimation of vapor pressure or its related parameters (Chapter A2). 

He found that C frequently is close to 1.75, and it is the practice of some workers to use this value for all substances and vary only A, B and D. While Eqs. (6) and (7) give a better fit to the vapor pressures of some compounds than the Antoine equation, the accuracy is more often not quite as good. Also, the estimation of vapor pressures by the extrapolation of Eqs. (6) and (7) beyond the highest pressure of the original data appears to lead to more error than one would obtain upon extrapolation of the Antoine equation. Finally, Eqs. (6) and (7) are much more difficult to use when one wishes to find the temperature corresponding to a given pressure. 

A better estimate of vapor pressures for a variety of organic compounds can be made by means of the correlations of Hass and Newton. This procedure is easiest to use if the normal boiling point is known, but it may be used in an iterative fashion if the vapor pressure is known at an arbitrary temperature. The description is available in the Handbook of Chemistry and Physics, so it will not be repeated here.8... 

While very approximate, this relationship is useful for order-of-magnitude estimation of vapor pressures, which is often adequate in establishing trial conditions for trap-to-trap fractionation. For this purpose, a family of curves based on Eq. (13) is presented in Fig. V.l. 

All the estimations of vapor pressure of liquids discussed above depend on the accuracy of the enthalpy of vaporization. Use of the Fishtine expression gives results that are not expected to be more accurate that 3% for AH ,. That implies that, even if the equation used to describe the temperature dependence of vapor pressure were exact, we still would expect no better than 3% accuracy in the estimated value of log (P /Pfc) the lower the vapor pressure the greater the expected error. For a vapor pressure of 10 kPa, the expected error is 7% for 100 Pa, 23% for 1 Pa, 41% and for 10 mPa, 62%. 

Mishra, D.S., Yalkowsky, S.H. (1991) Estimation of vapor pressure of some organic compounds. Ind. Eng. Chem. Res. 30,1609-1612. Miyake, K., Tereda, H. (1982) Determination of partition coefficients of very hydrophobic compounds by high-performance liquid chromatography on glyceryl-coated controlled-pore glass. J. Chromatogr. 240, 9-20. 

Tsuzuki, M., (2000) Thermodynamic estimation of vapor pressure fo organophosphorus pesticides. Environ. Toxiccol. Chem. 19, 1717-2000. 

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