Patent ID: 8152999

Claim:
A multistage cascade separation system using at each stage a membrane-containing separation step that preferentially rejects at least a first species relative to at least a second species while substantially permeating at least a third species which acts as a solvent, the system comprising at least three stages, wherein each stage comprises a housing defining a chamber, a selectively permeable membrane forming at least part of a barrier dividing the chamber into a first and a second compartment, the selectively permeable membrane capable of preferentially rejecting at least the first species relative to the second species while substantially permeating solvent such that the first compartment contains the retentate of the selectively permeable membrane and the second compartment contains the permeate of the selectively permeable membrane, and a feed for accepting a flow stream comprising the first, second and third species in communication with the first compartment, wherein: (a) the first stage feed is capable of accepting a flow stream at least partially from a source outside of the system, and the first stage further comprises two conduits, the first conduit capable of carrying the retentate from the first compartment to the feed of the second stage, and the second conduit capable of carrying the permeate from the second compartment of the first stage to the feed of the third stage; (b) the second stage further comprises a recirculation conduit capable of carrying the permeate from the second compartment of the second stage to the feed of the first stage, and a product conduit capable of removing retentate from the first compartment from the system; and (c) the third stage further comprises a recirculation conduit capable of carrying the retentate from the first compartment to the feed of the first stage, and a product conduit capable of removing permeate from the second compartment from the system.