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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 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
( ΔZb ), the error in estimated Pc was never more than about 20%. However, when ΔZb 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,