Composite membranes of cellulose acetate dense films on fine paper supports for gas separation application

Abstract

Composite membranes of cellulose acetate (CA) dense skins on fine paper supports were prepared by spin-coating from cyclohexanone and DMF solution. The morphology of membrane surfaces and cross-sections was examined by scanning electron microscopy, and the thickness of polymer skin layers was observed from several hundred nanometers to several micrometers depending on spin-coating condition. Gas separation performances of the membranes were evaluated from permeation measurements on each pure gas of hydrogen, carbon dioxide, methane, nitrogen and the binary 50:50 mixtures of H2/CH4, CO2/CH4, CO2/N2 under 4 atm, 35 ℃. Permeabilities in CA films of several-micrometer thickness were measured as 11, 7, 0.35, and 0.2 barrer for hydrogen, carbon dioxide, methane, and nitrogen, respectively. For the separation of CO2/CH4 mixture, the selectivity increased from 1.9 to 20 as the CA skin thickness increased from 0.52 to 3.7 micrometer. For H2/CH4 mixture, the ideal perm-selectivity exceeded experimental selectivity determined from permeation experiments of the 50:50 mixture. The experimental selectivity increased from 2.8 to 32 as the skin thickness increased from 0.65 to 3.7 micrometer.