Sobaric Heat Capacity Calculation of Light Hydrocarbons by Means of Equations of State

Abstract

Four equations of state, Peng-Robinson, Simonet-Behar-Rauzy-Jullian, Chain-of-Rotators and Lee-Kesler, very different in their structure, have been tested for their ability to calculate the residual isobaric heat capacity of light hydrocarbons, methane, ethane, propane, isobutane and normal butane. The calculations have been compared with quasi-experimental data from the specific equations of state proposed by Younglove and Ely. In order to examine the regions where these equations of state predict very well or very badly the residual isobaric heat capacity, error maps have been drawn in a large range of temperature and pressure. We have also tested the ability of these equations of state to calculate the residual isobaric heat capacity on the saturation curve. Error graphs have been drawn for each equation and for each compound. So, we have been able to give a general evaluation of these four equations of state in the different regions of a PT diagram : in the liquid, vapour and supercritical phases, on the saturation line, and close to the critical point. Finally, with the purpose of finding some analysis of the error stucture, error maps have been drawn for the three terms included in the residual isobaric heat capacity calculation.