Force field comparison and thermodynamic property calculations for the phase behavior of H2S+CO2 using Monte Carlo simulations

Abstract

A considerable amount of oil and gas reservoirs has carbon dioxide and hydrogen sulfide as contaminants. These substances increase the corrosion rates of pipes and equipment and need to be within the specification limit for commercialization, thus requiring the design of CO2 and H2S removal units to allow for gas transport and sales. Most of the removal units work based on phase equilibrium behavior. In this work, phase diagrams for the mixture H2S+CO2 were obtained by molecular simulation using the Monte Carlo method. Five different combinations of models and force fields available but not extensively tested in literature were evaluated. Also, a single site SAFT-γ Mie force field using the same parameters previously adjusted by Perez et al. [1] using the SAFT VR Mie equation of state is proposed to model pure H2S. Among all combinations tested, the CO2 united model with force field parameters proposed by Iwai et al. [2] combined with the H2S three site model with force field parameters proposed by Kamath et al. [3] presented better results than the combinations previously reported in literature. Also, a reasonable agreement with experiments was achieved when using the low computationally demanding united atom models with SAFT-γ Mie force field.