Permselective membrane of polyacrylonitrile copolymer and process for producing the same

A permselective membrane of a polyacrylonitrile copolymer for separation of an organic substance from a mixture with water or another organic substance, comprising:

• at least one polyacrylonitrile copolymer having about 90 to 97 mol % of acrylonitrile monomer units;
• and at least one comonomer unit selected from the group consisting of comonomers represented by the general formula:
• R.sup.1 (R.sup.2)C.dbd.C(R.sup.3)R.sup.4
• wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent a substituent selected from the group consisting of a hydrogen atom, alkyl, hydroxyl, carboxyl, acid anhydride, amide, imide, sulfonic, phosphoric, amino, pyridyl, and glycidyl groups, and derivatives thereof, except wherein:
• all substituents are hydrogen atoms, or
• one substituent is a methyl group and three substituents are hydrogen atoms, wherein the membrane is characterized by having:
• a rate, Q (kg/m.sup.2 hr) of selective permeation of water times the membrane thickness, L (.mu.m), of at least 0.5 kg.multidot..mu.m/m.sup.2 .multidot.hr,
• a separation factor of .alpha..gtoreq.10, and log.alpha..gtoreq.-1.77.times.log(QL)+2.77, when the pervaporation performance of a 5-30 .mu.m-thick membrane is evaluated using, as a liquid feed, an 80 wt. % aqueous solution of acetic acid at a temperature of 70.degree. C.