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

Abstract

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.

Current Status and Future Prospect of Polymer‐Layered Silicate Mixed‐Matrix Membranes for CO2/CH4 Separation

“…Zeolite is one of the most widely used porous inorganic fillers incorporated in MMMs for CO 2 /CH 4 separation. PSf/Matrimid® hollow‐fiber membranes exhibited a 50 % increase in selectivity by adding zeolite to its selective skin layers 17, 32. In comparison to neat polymers, addition of CMS to Matrimid® and Ultem® improved the membrane selectivity by 45 % and 40 %, respectively, for CO 2 /CH 4 systems 25.…”

Gas Separations using Ceramic Membranes

“…This is within the target cost range defined by the commercial benchmark (cellulose acetate) of $415 per m 3 /hr/bar. Based upon our economic model developed from several literature studies [1,26], in a hypothetical NG upgrading system treating 35 MMSCFD at 25% CO 2 , the cellulose acetate membrane cost represents about 30 to 40% of the total capital investment. Using the higher permeance CMS/C membrane data, the TCI could be reduced by about 12%.…”

The effect of ethane on the performance of commercial polyphenylene oxide and Cardo-type polyimide hollow fiber membranes in CO2/CH4 separation applications

“…The decrease in performance is very crucial in industrial applications and real gas mixture separation. Vu et al [2] have investigated the effect of condensable impurities on the performance of carbon molecular sieve hollow-fiber membranes in CO 2 /CH 4 separation applications. In this context, the experimental studies by Koros et al [3] suggested that competition of permeating components for Langmuir adsorption locations (or free volumes) in glassy membranes will mainly end up in a decrease in their permeability, selectivity and increased cost of operation.…”

“…Vu et al [10][11][12] have also investigated the effects of condensable impurities on the performance of CO 2 /CH 4 separation of hollow fiber molecular sieve membranes. Their results were compared with the results obtained from polyimide polymeric membranes.…”