Experimental High-Pressure Hydrogen Sulfide Partial Oxidation and Equilibrium Calculation by Gibbs Energy Minimization

Abstract

Both H2S and CO2 are removed from raw natural gas sources for product quality and safety reasons. If a cryogenic method is used for separation, the acid gas components (H2S + CO2) may be recovered as a high-pressure liquid. It is suggested herein that the removal of H2S from dense phase CO2 could occur by oxidation of H2S to elemental sulfur. This processing route would give producers the benefit of marketable sulfur recovery in addition to a purified high-pressure CO2 stream. This work describes the exploration of high-pressure H2S oxidation equilibria in CO2 rich fluids, with a focus on sulfur recovery from low-quality high-pressure acid gas (∼1% H2S in CO2). A model was developed to calculate the equilibria involving H2S oxidation under high-pressure CO2, where fugacity coefficients were calculated from previous studies with chemical species H2S, O2, SO2, COS, CS2, H2O, and S n within CO2. The fugacity coefficients of each species within CO2 were applied in a Gibbs energy minimization (GEM) routine to explore the equilibria of the chemical species at high pressures. These calculations were supported by experimental data of H2S oxidation to elemental sulfur over Al2O3, TiO2, and TiO2-doped Al2O3 catalysts. The experimental data for oxidation of 0.5 to 1.7% H2S in 10 and 20 MPa of CO2 were in agreement with the corresponding GEM calculations. Calculated and experimental results showed an increased reaction of H2S + O2 at lower temperatures and high pressures.