Patent ID: 8293112

Claim:
A method of removing water from a feed composition consisting essentially of 3-15 wt % water and a complementary amount of ethanol, the method comprising the steps of (i) providing a membrane separation system comprising at least one membrane and having a plurality of membrane separators in a serial flow arrangement such that a product retentate stream or a byproduct permeate stream of a preceding membrane separator is a feed stream to a subsequent membrane separator, charging a feed stream comprising the feed composition into a membrane separator of the arrangement, permeating ethanol and water through a membrane of each membrane separator, and withdrawing a product retentate stream of dehydrated ethanol from a membrane separator of the arrangement, the at least one membrane comprising a selectively permeable layer comprising a perfluoropolymer, (ii) introducing the feed composition into the membrane separation system and contacting the feed composition with said membrane, (iii) applying a driving force across said membrane effective to cause vapor permeation, pervaporation or a combination thereof of the feed composition through said membrane in which the water transfers through said membrane preferentially relative to ethanol, thereby selectively removing water from the feed composition, and (iv) recovering from said membrane separation system a product composition comprising the water at a concentration less than about 0.5 wt % in which the perfluoropolymer is a polymer or copolymer of perfluoro-2,2-dimethyl-1,3-dioxole, and in which the method comprises (A) charging the feed composition into a first membrane separator, (B) permeating ethanol and water through the first membrane separator, thereby forming an intermediate retentate stream enriched in ethanol relative to the feed composition, (C) permeating said intermediate retentate stream through a second membrane separator, (D) recycling into the feed composition for the first membrane separator an intermediate permeate stream from the second membrane separator, and (E) withdrawing the product retentate stream of the product composition from the second membrane separator, in which the streams in contact with the membranes are all in the vapor state.