Gas permeation properties of cellulose acetate films on fine paper support

Abstract

Composite membranes with cellulose acetate (CA) dense skins on fine paper support were prepared by spin-coating from cyclohexanone solution. The spin speed ranged from 800 to 2400 rpm, and the concentration from 1 to 4 wt%. Prepared membranes were dried at 75 ℃ in a vacuum oven for 1 hr. The morphology of membranes was studied by SEM, and the thickness of polymer skin layers observed from a few hundred nanometers to a micrometer depending on polymer concentration and spin speed. The gas separation performance of membranes was evaluated by permeation measurements on pure gases of methane, hydrogen, and carbon dioxide and their 50:50 mixtures under 35 ℃. The permeance of the pure gases were 330 GPU for CO2, 550 for CH4 and 1460 for H2 with 230 nm skin layers of CA. The ideal selectivity was 2.69 for the mixture of H2/CH4 and 1.61 for that of CH4/CO2 while the real selectivity decreased to 1.05 for H2/CH4 and to 1.19 for CH4/CO2, respectively. However, The real selectivity increased to 1.67 for H2/CH4 as the CA thickness increased to 930 nm, while the ideal selectivity decreased to 2.52 and the permeance of pure gases decreased to 40.8 for H2 and 16.2 for CH4.