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 ( Pc )of n-fatty acids and esters, logarithmic equations were developed that correlate, with goodagreement, the n-fatty acid and ester critical pressures with the corresponding n-alkanecritical pressure. The test with n-alkanes showed that even without the compressibility factor( ΔZb ), the error in estimated Pc was never more than about 20%. However, when ΔZb isestimated 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