Effect of Condensable Impurities in CO2/CH4 Gas Feeds on Carbon Molecular Sieve Hollow-Fiber Membranes

The presence of vapor impurities in gas streams presents problems for both polymeric and carbon materials. For natural gas processing applications, it is suspected that condensable hydrocarbons can cause significant performance declines for polymer membranes. This paper investigates the effect of these condensable vapor impurities on the performance of carbon molecular sieve (CMS) hollow-fiber membranes. Toluene and n -heptane were separately used as representative aromatic and paraffinic impurities, respectively, in 10% CO 2 /90% CH 4 gas feed streams. Shell-side feed pressures of up to 900 psia and temperatures of 35 and 50 °C were used. Experimental results reveal that the CMS membranes maintained CO 2 /CH 4 selectivity with a maximum of 20% reduction in CO 2 permeance during exposure to gas feeds containing these impurities, in comparison to “clean” gas feeds without these impurities. Furthermore, a simple in situ regeneration procedure of moderate heating (70−90 °C) with dry N 2 purge gas resulted in almost complete recovery of CO 2 permeance without loss of CO 2 /CH 4 selectivity. Comparisons with polyimide membrane performance in similar adverse environments are also presented. The robustness and regeneration capabilities of the CMS fibers offer noteworthy advantages over polyimide fibers, which can display significant losses in membrane performance under similar conditions.