Modified polyacrylonitrile (PAN) membranes were prepared by emulsion or emulsifier-free emulsion polymerization technique. Separation capacity was determined at several operating temperatures (25, 40, 55 and 70 degrees C) to dehydrate 56wt% pyridine aqueous solution through modified PAN membranes having different functional groups. All these PAN-based membranes were selective toward water to different degrees depending on the nature of functional groups present in the membranes. Pervaporation characteristics of PAN-based membranes are so different and classified into three categories depending on the type of the functional groups in PAN copolymers. Among PAN-based membranes, the in situ complex membranes show the best separation capacity over the operating temperatures.