Carbon molecular sieve membranes: a promising alternative for selected industrial applications

Carbon molecular sieve (CMS) membranes (hollow fibers) have been studied for application as possible separation units for selected industrial gas streams. Gas streams at petrochemical plants (polypropene and polyethene) and upgrading of biogas to fuel specifications have been in focus. Gases present in biogas (N(2), CO(2), H(2)O(vap), and CH(4)) and gas streams at polyolefin plants (C(2)H(4), C(3)H(6), and C(3)H(8)) have been measured; both as pure gases and in mixtures. Aging of the CMS-membranes as a function of humidity and pore blocking is discussed; likewise, possible regeneration methods when flux decrease is experienced. Transport mechanisms depending on pore size and molecular properties are also discussed. Excellent separation properties were documented for these applications, but also the need for frequent regeneration of the membrane in order to maintain permeability flux. The mixed gas experiments documented clearly the need for careful pore tailoring in order to optimize selectivity when the membranes were used for alkane-alkene separation.