Gamma-alumina supported carbon molecular sieve membrane for propylene/propane separation

Carbon molecular sieve (CMS) membranes are able to efficiently separate gases that have a small difference in molecular sizes. To withstand the large transmembrane pressures required to attain high gas flux, it is preferred to prepare CMS membranes as composite configurations using inorganic supports. This paper reports on the synthesis and properties of novel CMS membranes on mesoporous γ-alumina supports. Such supports allow coating of thin, high-quality polymer films and subsequent CMS membranes. Thin CMS membranes were obtained by pyrolysis of defect-free polymer/ceramic composite membranes in an oxygen-free inert gas environment. Compared to macroporous α-alumina supported membranes, both polymer and CMS membranes prepared on γ-alumina show better gas permeation and separation characteristics. A 1.6 μm thick CMS membrane on γ-alumina support offers a pure-gas ideal separation factor of 45 for He/N₂ and 5.1 for O₂/N₂. When tested with a 50/50 C₃H₆/C₃H₈ mixture, the CMS membrane shows a mixed-gas C₃H₆/C₃H ₈ selectivity up to 36 with a C₃H₆ permeance of around 3 × 10^-9 mol/Pa·s·m² (9 gpu).