In this work, four kinds of cellulose aliphatate esters, cellulose acetate(CA), cellulose propionate(CP), cellulose butyrate(CB) and cellulose acetate butyrate(CAB) are synthesized by the homogeneous acylation reactions in cellulose/AmimCl solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution(DS) and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases(O2, N2, CH4, CO and CO2) increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA(distribution order of acetate substituent: C6 > C3 > C2) is superior to the heterogeneously synthesized CA(distribution order of acetate substituent: C3 > C2 > C6) in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.
