Application of Gibbs Ensemble and NPT Monte Carlo Simulation to the Development of Improved Processes for H₂S-rich Gases

Abstract

The design of improved processes for producing hydrogen sulphide (H₂S)-rich natural gases faces a general scarcity of experimental data, because of the high toxicity and corrosive character of H₂S. We present here a prospective application of Monte Carlo simulation to predict desired fluid properties.

A first step was the selection of intermolecular potentials for water, H₂S, carbon dioxide (CO₂) and methane on the basis of pure component properties (vapour pressures, vapourisation enthalpies, liquid densities, supercritical densities at high pressure). A second step involved the prediction of phase diagrams of binary and ternary mixtures of the methane–H₂S–water system, using two-phase and three-phase Gibbs ensemble simulations. In a third step the density and excess enthalpy of the CO₂–H₂S system were computed for a large range of pressure, temperature and compositions.

Comparison with available experimental data showed that all investigated properties could be consistently predicted without needing parameter calibration on binary data. The results also provided a qualitative understanding of water solubility in H₂S-rich fluids based on molecular self-association.

Keywords:

• Hydrogen sulphide
• Water
• Methane
• Carbon dioxide
• Computer simulation (MC and MD)
• Phase equilibrium

Acknowledgements

This work has been made in cooperation with the Compu Total, whose contribution is gratefully acknowledged. Special thanks are due to Anne Boutin and to the many researchers of the Laboratory of Chemical Physics and IFP who contributed to algorithm implementation and code development. We thank the referees whose suggestions contributed to improve the quality of this article.