Patent ID: 7854846

Claim:
A method of separating a feedstock into permeate and retentate with a membrane device that receives feedstock at a feed end face, comprising: a) providing a crossflow membrane element that receives the feedstock at a feed end face, and separates the feedstock into permeate and retentate, the membrane element comprising: i) a membrane support containing at least one monolith of porous material defining a plurality of passageways with passageway wall surfaces, the passageways extending longitudinally from the feed end face of the monolith to a retentate end face of the monolith; ii) a microfiltration or ultrafiltration membrane with a mean pore size in the range of 10 nanometers to 1 micron applied to the passageway wall surfaces of at least the channels through which the feedstock flows; and iii) at least one permeate conduit formed within the monolith, the conduit containing a plurality of longitudinal permeate chambers extending substantially the entire length of the monolith, transected proximate the feed end face by at least one permeate channel and proximate the retentate end face by at least one other permeate channel; b) providing a housing assembly that contains the membrane element, the assembly comprising: i) a housing that contains the element; ii) a feedstock inlet port in communication with the feed end face of the monolith, and a retentate outlet port in communication with the retentate end face of the monolith; iii) a permeate circulation inlet port in fluid communication with the permeate channel or channels proximate the feed end face, to allow for the introduction of circulated permeate into the permeate chambers and flow of at least some of the circulated permeate along the length of the permeate chambers; iv) a permeate outlet port in fluid communication with the permeate channel or channels proximate the retentate end face, to allow for the withdrawal of the permeate from the permeate chambers, v) one or more seals for separating the permeate flows from the feed and retentate flows; c) introducing a feedstock and withdrawing retentate; and d) circulating a portion of the permeate through the permeate conduit co-currently with the feedstock flow under independent permeate circulation flow control such that the permeate back pressure along the length of the permeate chambers decreases in a manner that substantially parallels the feedstock pressure drop within the feedstock flow channels, thereby generating a substantially uniform transmembrane pressure along the length of the membrane element.