The estimation of the vapor pressure for pure substances

Abstract

Vapor pressure and normal boiling point are importance properties to design unit equipment. Normally, these properties are taken from an experimental data but experimental measurements are often expensive and some substances are a health hazardous substance. Group contribution method and COSMO-SAC model are alternative methods to determine the normal boiling point temperature and the vapor pressure. The group contribution method uses only knowledge of molecule structure to determine vapor pressure. Similarly, COSMO-SAC model using two parameters for input in model which are sigma profile and molar volume of each substance. Therefore, the purpose of this research was to investigate an accuracy and to determine the optimal estimation method for n-alkanes , 1-alkenes , alkyne , alcohol , aldehyde and ketone. This research compared the estimated values (the normal boiling point , Tb and the vapor pressure at 298.15 Kelvin, P@298.15K) with the experimental data by calculating coefficience of determination (R2) and average absolute deviation relation (ADDR). The result showed that the group contribution method was accurate to estimate Tb (R2= 0.9949, AADR= 0.0152) and P@298.15K (R2= 0.9890, AADR= 0.3770) for six groups. The COSMO-SAC model is accurate to estimate Tb (0.9887, AADR = 0.0249) and P@298.15K (R2= 0.9906, AADR= 0.5493) for six groups. Due to the accuracy of estimation, the group contribution and the COSMO-SAC model in which using the different estimated techniques could calculate the vapor pressure to ensure the estimated vapor pressure without doing the experiment. To accurately estimate these properties in other groups, the parameter of COSMO-SAC model should be modified.