Acid Gas: Effect on Membrane Properties

Acidic gas removal is the largest application of gas separation membranes and a vital process in the natural gas processing industry. Membranes used in this process are designed to separate H₂S and CO₂, and this process is known as natural gas sweetening. This is readily required for low-quality natural gas reserves, which need to be processed to achieve pipeline specifications of CO₂ <2 mol% and H₂S <4 ppm (Baker 2001). The removal of acidic gases is also required for biogas and gasification, where H₂S and CO₂ are separated from CH₄, CO, and H₂. For natural gas sweetening, the membrane must exhibit high permeability for H₂S and CO₂, with a large selectivity relative to methane.

In general, nonporous polymeric membranes are applied in acidic gas removal, taking advantage of the solution-diffusion mechanism and the high solubility of H₂S and CO₂, compared to CH₄. Also polymeric membranes almost always demonstrate selectivity for H₂S over CO₂, again because of the higher condensability...