The pervaporation properties of sulfonyl-containing polyimide membranes to aromatic/aliphatic hydrocarbon mixtures

Membranes of polyimide from 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA) and dimethyl-3,7-diaminobenzothiophene-5,5'-dioxide (DBT), in which each monomer has a sulfonyl group, were investigated for pervaporation (PV) separation of aromatic/aliphatic binary and multi-component systems. The sorption amounts of benzene (Bz) and toluene (Tol) in the membrane were 11 and 15 g/100 g dry polymer, and those of aliphatics were much lower. The diffusion coefficient of the pure liquid was in the order of n-hexane (n-Hx)>n-octane (n-Ot)>Bz>Tol>>cyclohexane (CHx)>iso-octane (i-Ot). The membranes were preferentially permeable to aromatics over aliphatics. The dependence of separation factor alpha and total specific permeation flux Ql on the feed composition was more significant for the Bz/CHx and Tol/i-Ot systems than for the Bz/n-Hx and Tol/n-Ot systems. The dependence of alpha and Ql on temperature was investigated. The membrane displayed good durability and higher PV performance as compared with other common polyimides, for example, alpha = 32, Ql = 0.93 kg mu m/m(2) h for Bz/CHx and alpha = 113 and Ql = 2.8 kg mu m/m(2) h for Tol/i-Ot at x(Bz) or x(Tol) of 60 wt% and 351 K.