Addition of the sulfhydryl group (SH) to the PPR78 model: Estimation of missing group-interaction parameters for systems containing mercaptans and carbon dioxide or nitrogen or methane, from newly published data

In 2008, the PPR78 model (Predictive Peng–Robinson 1978) was extended to mercaptan-containing systems by adding the sulfhydryl group (SH), that is, by determining the values of the group-interaction parameters between the group SH and the fourteen other groups already present in the PPR78 model. Unfortunately, due to a lack of experimental data reported in the open literature, it was not possible to characterize interactions between the group SH and the three groups: ethane, CO2 and N2. Very recently, vapor–liquid equilibrium data for three binary systems containing methanethiol and respectively methane, nitrogen and carbon dioxide were however measured. It was thus decided to use these data to estimate two of the missing group-interaction parameters (SH/CO2 and SH/N2). For such systems, deviations observed with the PPR78 model are compared to those obtained with the CPA equation of state.