H2S stability and separation performance of cobalt oxide silica membranes

This work investigates the effect of hydrogen sulfide (H2S) exposure on cobalt oxide silica (CoOxSi) xerogels and membranes to determine their robustness under sour gas conditions. Fourier transform infra-red spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed no detectable traces of sulfur or any sulfur compounds in CoOxSi xerogels exposed to 50 ppm H2S in helium (He) at 200 and 500 °C. Similarly N2 adsorption showed no significant change of average pore size or pore volume of the xerogel samples after 48 h of H2S exposure. Gravimetric analysis of the xerogels showed that the H2S adsorbs on the CoOxSi surface, possibly by physisorption as no H2S sorption was observed during post-testing analysis with XPS. A CoOxSi membrane was exposed to varied dosings of H2S in He over a period of 160 h at 200 °C, including an additional testing with 3.2 vol% H2O vapour. It was observed that exposure to H2S resulted in a temporary reduction in single gas permeation with the largest effect occurring with the highest concentration of H2S. These results are attributed to physisorbed H2S on the CoOxSi surface, thus slightly impeding the diffusion of He. H2O exposure and H2S + H2O exposure showed similar reversible effects to that of H2S individually, leading to the conclusion that there was no significant interaction between H2S, H2O and the CoOxSi surface. Although H2S permeation was initially measured through the membrane, this quickly became undetectable for the remainder of the experiment. As a result, the CoOxSi membrane concentrated H2S to 70 ppm in the retentate stream from a maximum feed H2S 50 ppm concentration.

• The structure of cobalt oxide silica (CoOxSi) showed no major changes when exposed to 50 ppm H2S at 200 and 500 °C.
• H2S adsorbed on the CoOxSi surface, resulting in low coverage possibly by physisorption.
• Helium permeation was temporary reduced when the CoOxSi membrane was exposed to H2S at varied dosing up to 50 ppm.
• Physisorbed H2S on the CoOxSi surface may have slightly impeded the diffusion of helium.
• The CoOxSi membrane concentrated H2S to 70 ppm in the retentate stream from a maximum feed H2S 50 ppm concentration.