Predictive correlations for liquid heat capacity – including the critical region

Abstract

A predictive correlation relating isobaric liquid specific heat capacity to absolute temperature and elemental composition was recently reported. The Dadgostar–Shaw correlation, valid where CV≫T(∂V/∂T)P(∂P/∂T)V, is modified in the present work to accommodate the critical region and the consequent variation of liquid phase isobaric heat capacity among isomers at the same absolute temperature. The results obtained for a training data set and a test data set are presented and compared with results obtained with the Dadgostar–Shaw correlation, and two variants of the Rowlinson–Bondi correlation. The CP° contribution is calculated using either compound specific correlations or the predictive universal Laštovka–Shaw equation for ideal gases. For pure hydrocarbon liquids where compound specific CP° correlations, Tc and ω are available, the Rowlinson–Bondi based approach should be used to compute saturated liquid heat capacities. If only Tc and ω are available, the Rowlinson–Bondi based approach+the predictive Laštovka–Shaw equation for CP° values is preferred. If the liquid is a multicomponent or ill-defined hydrocarbon liquid, the modified Dadgostar–Shaw correlation is preferred over the Dadgostar correlation as long as Tc is available or can be estimated. The accuracy penalty for use of the modified Dadgostar–Shaw correlation appears small relative to either Rowlinson–Bondi based calculation approaches.