Critical Properties and Vapor Pressure Equation for Alkanes CnH2n+2: Normal Alkanes With n⩽36 and Isomers for n=4 Through n=9

Abstract

A correlation for estimating the vapor pressure of normal alkanes from methane through n-hexatriacontane and isomers of butane to nonane is reported. This work extends the correlation for normal alkanes (CnH2n+2), with n⩽20, reported by Ambrose, to both normal alkanes with n⩽36 and their isomers with n⩽9. This vapor pressure equation was based on the Wagner equation and is similar to that used by Ambrose. Literature vapor pressure measurements have been reviewed. Tables are given that list the type of apparatus, measurement range and precision, and chemical purity. These criteria were initially used to select measurements for inclusion in the regression analyses to determine the coefficients of the correlation. Vapor pressures estimated from the correlation were compared with all vapor pressure (p1+g) measurements reviewed in this work. At pressures greater than 1 kPa, the vapor pressure equation presented here has the following accuracies: 0.0001⋅p1+g for methane, 0.001⋅p1+g for ethane, propane, and n-butane, 0.002⋅p1+g for n-pentane through n-octane, 2-methylpropane, and 2-methylbutane, 0.005⋅p1+g for 2,2-dimethylpropane, n-nonane, n-decane, and the isomers of hexane through nonane, 0.01⋅p1+g for n-undecane to n-hexadecane, 0.02⋅p1+g for n-heptadecane to n-eicosane, 0.05⋅p1+g for n-heneicosane to n-octacosane, and 0.10⋅p1+g for n-nonacosane to n-hexatriacontane. Equations for the critical temperatures and pressures of the normal alkanes as functions of the carbon number are also reported.