Natural Gas Desulfurization by Adsorption: Feasibility and Multiplicity of Cyclic Steady States

The feasibility of simultaneous removal and concentration of H₂S from natural gas by pressure swing adsorption (PSA) is established. The predried feed contains 1000 ppm H₂S and 5% CO₂. The purified adsorption product contains below 1 ppm H₂S at methane product recoveries above 95%. At the same time a desorption product with 2% H₂S is obtained which can be readily converted into sulfur by known processes. In the PSA system, there is a region of feed velocities where two stable cyclic steady states and an unstable steady state exist. Under the same PSA conditions considered, the product impurities in the two stable steady states are approximately 100 and 1 ppm H₂S, depending on the initial bed conditions. Upon examining the differences between the H₂S concentration profiles in the bed at the two steady states, the lower steady state is described by a single wave kept short from breaking through the bed, while the upper steady state is described by a combined wave with transfer zones at each end of the bed, connected by a “middle” constant zone.