Effect of polyethyleneglycol (PEG) on gas permeabilities and permselectivities in its cellulose acetate (CA) blend membranes

Abstract

The effect of polyethyleneglycol (PEG) on gas permeabilities and selectivities was investigated in a series of miscible cellulose acetate (CA) blend membranes. The permeabilities of CO 2, H 2, O 2, CH 4, N 2 were measured at temperatures from 30 to 80°C and pressures from 20 to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane having 10 wt% PEG20000 exhibited higher permeability for CO 2 and higher permselectivity for CO 2 over N 2 and CH 4 than those of the membranes which contained 10% PEG of the molecular weight in the range 200–6000. The CA blend containing 60 wt% PEG20000 showed that its permeability coefficients of CO 2 and ideal separation factors for CO 2 over N 2 reached above 2 × 10 −8 [cm 3 (STP) cm/cm 2 s cmHg] 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 the blend membranes containing PEG20000 showed higher apparent diffusivity coefficients for CO 2, resulting in higher permeability coefficients of CO 2 with relation to those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG20000 blend membranes that their ideal separation factors for CO 2 over N 2 were higher than those of the CA membrane in the range 50–80°C, even though the ideal separation factors of almost all PEG blend membranes for CO 2 over CH 4 became lower than those of the CA membrane over nearly the full range from 30° to 80°C.