New carbon molecular sieves for propylene/propane separation with high working capacity and separation factor

The effects of the precursor composition and pyrolysis conditions on the properties of the polyvinylidene chloride copolymer (PVDC) derived carbon materials were systematically investigated. A set of eighteen carbon molecular sieve (CMS) adsorbents, chosen using design of experiment (DOE) methodology, was synthesized by direct pyrolysis of PVDC copolymer beads. High throughput transient adsorption measurements were conducted on the eighteen CMS adsorbents using ten probe gas molecules with kinetic diameters ranging from 3.3 to 6.2 Å. Results revealed that the effective micropore size of the resultant CMS adsorbents was controlled by two factors; pyrolysis temperature and precursor crystallinity, which was in turn controlled by comonomer type and content. The effective micropore sizes of these CMS adsorbents were in the range of 4.0-6.2 Å. For propylene/propane separations, one material from this study (CMS-18) gave a substantial improvement in performance over two commercial materials (MSC-4K and zeolite 4A), as determined by separation factor, propylene capacity, and working capacity. Relative to MSC-4K, the new CMS-18 material has 8.5 times higher C3H6/C3H8 separation factor, 1.5 times propylene capacity, and 2.3 times working capacity. Relative to zeolite 4A, the new CMS-18 material gave 1.5 times propylene capacity, and 16.7 times working capacity.

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