Cross-flow filtration unit

Abstract

An improved cross-flow filtration unit utilizing at least one two-ply membrane is disclosed that has a particular pore size relationship in the two membrane layers.

1 . A cross-flow filtration device comprising a feed inlet and feed flow channel; a permeate flow channel and a permeate outlet; a retentate outlet; and at least one two-ply microporous separation membrane having a front side ply facing said feed channel and a back side ply facing said permeate channel wherein the flow of liquid feed through said separation membrane is from the front side ply to the back side ply, and wherein the pores of said separation membrane are sized such that the average pore size of said front side ply is 1.3 to 5 times the average pore size of said back side ply.  
   
   
       2 . The filtration device of  claim 1  containing a plurality of said separation membranes.  
   
   
       3 . The filtration device of  claim 1  with a single two-ply separation membrane.  
   
   
       4 . The filtration device of any of claims  1 - 3  wherein the average pore size of said back side ply is such as to impart to said back side ply a molecular weight cutoff of at least 1000 Daltons.  
   
   
       5 . The filtration device of  claim 4  wherein the maximum average pore size of said back side ply is 1.2 microns.  
   
   
       6 . The filtration device of any of claims  1 - 3  wherein the average pore size of said back side ply is from 0.2 to 1.2 microns.  
   
   
       7 . The filtration device of  claim 6  in the form of a cassette.