Multilayer thin-film composite membranes for helium enrichment

This paper describes a novel approach to fabricate a multilayer composite membrane for recovering and enriching helium from natural gas processing using commercially available thin-film composite polyamide reverse osmosis (RO) membranes. The RO membranes, which are defective in a dry state, were caulked with different polymeric materials to seal the defects; then, the permeation and separation properties were characterized using pure and mixed gases. A benchmark (Nafion (R) - 117) membrane was selected for its superior selectivity towards helium over carbon dioxide, and the performances of the caulked RO membranes were compared. The experimental results show that the ideal selectivity of He/CO2 in the pure gas tests is in the range 20-55, while the permeance of helium is in the range 8-40 GPU depending on the caulking material. A quaternary mixture of CH4, N-2, CO2, and He was used to evaluate the separation performance of the novel membrane, which was compared with that of the benchmark membrane. This study confirms that the proposed novel approach for membrane fabrication is technically practical to recover and enrich helium from CO2-containing natural gas streams.