ISOBARIC HEAT-CAPACITY CALCULATION OF LIGHT-HYDROCARBONS BY MEANS OF EQUATIONS OF STATE

Four equations of state, Peng-Robinson, Simonet-Behar-Rauzy-Jullian, C hain-of-Rotators and Lee-Kesler, very different in their structure, ha ve been tested for their ability to calculate the residual isobaric he at capacity of light hydrocarbons, methane, ethane, propane, isobutane and normal butane. The calculations have been compared with quasi-exp erimental data from the specific equations of state proposed by Youngl ove and Ely. In order to examine the regions where these equations of state predict very well or very badly the residual isobaric heat capac ity, error maps have been drawn in a large range of temperature and pr essure. 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 equ ations of state in the different regions of a PT diagram: in the liqui d, vapouur and supercritical phases, on the saturation line, and close to the critical point. Finally, with the purpose of finding some anal ysis of the error stucture, error maps have been drawn for the three t erms included in the residual isobaric heat capacity calculation: resi dual isochoric heat capacity, (partial derivative P/partial derivative V)T, (partial derivative P/partial derivative T)(2)v. Thus, we have s hown the influence of each of these three terms on the residual isobar ic heat capacity calculation.