module and a permeate vapor each having a different composition from the feed solution representative examples include a a feed solution comprising about 10 ethanol in water separated into a permeate vapor containing 40 ethanol and a residue solution containing 2 or 3 ethanol using silicone rubber membranes in the modules b a feed solution of raw gasoline in a refinery comprising a total of 30 toluene benzene and other aromatics separated into a residue gasoline stream containing below 25 total aromatics and a permeate vapor containing 70 aromatics using a fluorinated dioxole membrane c a feed solution of 5 water in acetic acid dehydrated to a 0 5 water residue solution and a permeate vapor containing 60 water vapor using a polyvinyl alcohol pva membrane as the separation occurs the latent heat required to evaporate the permeating components is supplied from the feed liquid so the residue solution leaving the module is significantly cooler such as 5 u00b0 c 10 u00b0 c or more cooler depending on how much permeate vapor is produced the residue solution exits the module through aperture 212 and flows into and across the reheating space as indicated generally by dashed arrow 220 to become the feed solution for the next module a heating fluid is passed through the outer casing as indicated by dashed arrows 228 and 229 and flows in contact with the outside surface of the tube the residue of the feed solution that is flowing in the reheating space is reheated by heat exchange with the heating.