Vapor Pressures of Alkyl Aromatic Hydrocarbons.

Abstract

VAPOR PRESSURE data for the aromatic hydrocarbons in the high pressure region are limited. Consequently, it becomes necessary to extrapolate the low pressure data to obtain information near the critical point. The usual straight-line extrapolation expressing the logarithmic vapor pressure-reciprocal absolute temperature relationship is inadequate for properly defining the vapor pressure of liquids over the entire range included between the triple point and the critical point. For normal paraffins, a nonlinear vapor pressure relationship exists which exhibits a reversal in curvature in the high pressure region (14). This vapor pressure function resembles an elongated S-shaped curve between the triple point and the critical point. Numerous equations have been employed to define the vapor pressure function accurately over limited ranges. For example, the Antoine equation (2) gives reliable results in the low pressure region, but fails in the critical region. Gamson and Watson (6) propose the following empirical reduced state vapor pressure equation: Equation 2 becomes linear in the high pressure region where the exponential term becomes insignificant. Waring (15) reviews several vapor pressure equations and proposes a method for testing the consistency of experimental data over the entire range. Barrow (3) uses the heat capacities of the liquid and vapor in equilibrium to define the vapor pressure function as E C