Cellulose ester blend membranes, process for making same and their use

A method for removing C.sub.1 -C.sub.3 alkanols from their mixtures with hydrocarbons or heteroatom-containing hydrocarbons, said method comprising

• (a) contacting a feed mixture comprising at least one C.sub.1 -C.sub.3 -alkanol and at least one hydrocarbon or heteroatom-containing hydrocarbon in liquid phase or after evaporation with a first side (feed side) of a non-porous layer of a membrane,
• (b) maintaining a gradient of a partial vapor pressure of the C.sub.1 -C.sub.3 -alkanol across said non-porous separating layer of said membrane,
• (c) recovering from a second side (permeate side) of said membrane as a permeate a mixture richer in said C.sub.1 -C.sub.3 -alkanol and leaner in said hydrocarbon or heteroatom-containing hydrocarbon than the feed mixture, said permeate being recovered as a vapor at a pressure below the partial vapor pressure of said lower alcohol at the feed side, and
• (d) recovering from the feed side of said membrane a product which is leaner in said C.sub.1 -C.sub.3 -alkanol and richer in said hydrocarbon or heteroatom-containing hydrocarbon,
• wherein the improvement comprises utilizing a membrane comprising a non-porous separation layer of a cellulose ester-containing polymeric material, characterized in that said polymeric material is a polymer blend of a first polymer selected from cellulose esters and at least one second polymer selected from polyvinylpyrrolidone (PVP), copolymers of vinylpyrrolidone and vinylacetate (VP-co-VA), polyethylene glycol (PEG), N,N-dialkylated polyacrylic amides (DPAA) and cellulose esters other than said first polymer.