Patent ID: 7141171

Claim:
A counter flow cascade separation system for separating a solute/solute pair in a solvent, comprising a series of interconnected stages in which each stage comprises: a feed for accepting a flow stream containing a solute/solute pair in a solvent; a diafilter in communication with the feed wherein said diafilter has a diafilter membrane preferentially permeable for a first solute of the solute/solute pair in the solvent and less permeable to the second solute wherein said first solute is preferentially conveyed to a diafilter permeate flow and the remaining second solute is preferentially retained in a diafilter retentate flow; and an ultrafilter positioned to accept said diafilter permeate flow wherein said ultrafilter has an ultrafilter membrane exclusively permeable to the solvent contained in the diafilter permeate flow wherein solvent in the diafilter permeate flow passes through said ultrafilter membrane to a solvent flow; wherein said series of interconnected stages includes a first feed stage receiving said flow stream from a source outside the system, the stream retained by the diafilter of the feed stage is directed to a second stage and the stream retained by the ultrafiltration membrane in the feed stage is directed to a third stage, wherein the stages are interconnected so that each stage beyond a first stage accepts an intermixed flow stream formed by combining retentate flow and permeate flow from different subsequent stages, wherein the intermixed retentate and permeate flow each has the solute/solute pair present in substantially the same molar ratio; the first solute and second solute exiting said system at different terminal stages.