A prediction method of vapor pressures by using boiling point data

Abstract

A new method to predict vapor pressure is proposed by directly determining the constants of the vapor pressure equation from the boiling point data from the viewpoint of engineering. A series of observed vapor pressure data of a substance shows linear relation between logarithm of measured vapor pressure and reciprocal value of its absolute temperature. In addition, the slope of the linear relation is almost same for homologous series. By using this slope of homologous substance, for the homologous substance of which vapor pressure is not observed, the intercept of the vapor pressure equation can be determined from one point of vapor pressure data, that is, boiling point data. As the vapor pressure equation, the Clapeyron and the Antoine equation are chosen. This method was applied for the following homologous substances: alcohols, acids, esters, ketones, organophosphors, pinenes, and silanes. The average absolute deviations (AAD) of these homologous substances were 0.615 and 0.709 kPa for the Antoine and the Clapeyron equations, respectively. Then, the accuracy of the method is satisfactory from the point of engineering use. However, it depends on the selection of reference substance and temperature range to be used for prediction. Since this method is based on thermodynamically derived Clausius-Clapeyron relation, it is a widely and generally applicable method and there is no limitation by substance, temperature and pressure.