Abstract: A separatory membrane is provided which has a sufficient durability and shows a high rate of permeation therethrough and a high separation factor to a variety of organic substances and a wide range of concentration thereof in mutual separation of organic substances and separation of a water/organic substance mixture by pervaporation, vapor permeation or perstraction. The separatory membrane shows the performance that water permeates selectively through the membrane while satisfying such conditions that the product (QL) of the rate Q (kg/m.sup.2 .multidot.hr) of permeation and the thickness L (.mu.m) of the membrane is at least 0.5 kg.multidot..mu.m/m.sup.2 .multidot.hr and that the separation factor .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 dense uniform membrane is evaluated using as a liquid feed, an 80 wt. % aqueous solution of acetic acid at a temperature of 70.degree. C.

Abstract: A separatory membrane is provided which has sufficient durability and shows a high rate of permeation therethrough, a high separation factor to a variety of organic substances having a wide range of concentration thereof in mutual separation of organic substances and separation of a water/organic substance mixture by pervaporation, vapor permeation or perstraction. The separatory membrane shows that water permeates selectively through the membrane while satisfying such conditions that the product (QL) of the rate Q (kg/m.sup.2.hr) of permeation and the thickness L (.mu.m) of the membrane is at least 0.5 kg..mu.m/m.sup.2.hr, and that the separation factor .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 dense uniform membrane is evaluated using, as a liquid feed, an 80 wt. % aqueous solution of acetic acid at a temperature of 70.degree. C.