How To Represent Hydrogen Sulfide within the CPA Equation of State

The objective of this work is to evaluate whether hydrogen sulfide can be considered an associating compound in the cubic-plusassociation (CPA) equation of state (EOS). This EOS is applied in order to calculate its pure substance properties (vapor pressure and saturated liquid volume) and fluid phase equilibrium with hydrocarbons. The investigation was undertaken considering two kinds of association schemes (3B and 4C). The comparison of the CPA results with data taken from the literature gives a good agreement in almost every case. It was observed that the CPA EOS gives reasonable estimates of the vapor-liquid equilibria of hydrocarbon-H2S mixtures (i.e., without binary interaction parameter), while the Soave-Redlich-Kwong EOS needs a binary interaction parameter. Different combining rules for the association energy and association volume parameters have been tested to predict mixtures containing two associating compounds such as H2S-methanol and H2S-water. The 3B association scheme with the "CR-4" mixing rules is finally selected.