Group contribution method for estimating the critical pressures of C₁C₂₀ n-alkanes

Abstract

To develop a new and useful method for evaluating and predicting the critical pressures ( P_c )
of n-fatty acids and esters, logarithmic equations were developed that correlate, with good
agreement, the n-fatty acid and ester critical pressures with the corresponding n-alkane
critical pressure. The test with n-alkanes showed that even without the compressibility factor
( ΔZ_b ), the error in estimated P_c was never more than about 20%. However, when ΔZ_b is
estimated from an equation of state, the error is never more than 10%; indeed the majority of the values lie around 5%.

Key Words: critical pressures, n-alkanes, enthalpies of vapourisation, Trouton’s rule,
Clausius-Clapeyron equation.