Preparation of polyethyleneglycol (PEG) and cellulose acetate (CA) blend membranes and their gas permeabilities

Abstract Miscible blend membranes containing 10 wt % PEG of low molecular weight 200, 600, 2000, and 6000, and 10 wt %, 20 wt %, 30 wt %, 40 wt %, 50 wt %, and 60 wt % of molecular weight 20,000 were prepared to investigate the effect of PEG on gas permeabilities and selectivities for CO 2 over N 2 and CH 4 . The permeabilities of CO 2 , H 2 , O 2 , CH 4 , and N 2 were measured at temperatures from 30 to 80°C and pressures from 20 cmHg to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane, which contained 10% PEG 20,000, exhibited higher permeability for CO 2 and higher permselectivity for CO 2 over N 2 and CH 4 than those of the membranes that contained 10% PEG of the molecular weight ranging from 200 to 6000. The high PEG 20,000 content blend membranes showed remarkable permeation properties such that the permeability coefficients of CO 2 and the ideal separation factors for CO 2 over N 2 reached above 200 barrer and 22, respectively, at 70°C and 20 cmHg. Based on the data of gas permeability coefficients, time lags, and characterization of the membranes, it is proposed that the apparent solubility coefficients of all CA and PEG blend membranes for CO 2 were lower than those of the CA membrane. However, almost all of the blend membranes containing PEG 20,000 showed higher apparent diffusivity coefficients for CO 2 , resulting in higher permeability coefficients of CO 2 than those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG 20,000 blend membranes that their ideal separation factors for CO 2 over N 2 were higher than those of the CA membrane in the temperature range from 50 to 80°C, even though the ideal separation factors of all CA and PEG blend membranes for CO 2 over CH 4 became lower than those of the CA membrane over nearly the full temperature range from 30 to 80°C. © 1995 John Wiley & Sons, Inc.