Reduced Lateral Leakage in Reverse Osmosis Devices

Abstract

Spiral wound reverse osmosis devices with reduced lateral leakage and thereby increased salt rejection are made by compacting a microporous layer within a composite reverse osmosis membrane longitudinally along its lengthwise periphery. Means and method for causing longitudinal indentations in composite membranes during manufacturing operations are disclosed and described.

1 . A spirally wound membrane device capable of producing potable water from seawater by reverse osmosis, comprising sequential layers of feed water channel spacer, reverse osmosis membrane, permeate water channel spacer, and reverse osmosis membrane, wherein the reverse osmosis membrane comprises a nonwoven web support, a microporous plastic layer disposed thereon, and a semipermeable salt rejecting polymer layer disposed on a topmost surface of the microporous plastic layer, the device being further characterized by having at least one longitudinally indented surface strip along a portion of each lengthwise edge of the membrane, the indented surface being in contact with an underlying compacted strip of the microporous plastic coating. 
     
     
         2 . The spirally wound membrane device of  claim 1  having a plurality therein of membrane leaves bonded together by means of cured glue, the combination of glue and the indented strips along each lengthwise edge of the membrane leaves restricting lateral microleakage of seawater through the microporous plastic layer. 
     
     
         3 . A method of making a reverse osmosis membrane with reduced lateral leakage comprising embossing a sheet of the membrane along its length to generate a longitudinally indented surface adjacent to a side edge along the length of the membrane. 
     
     
         4 . The method of  claim 3  wherein the surface is indented by contact of a sheet of the membrane with a device comprising a cylindrical disk having a raised ridge positioned on the circumference thereof. 
     
     
         5 . The method of  claim 4  wherein the sheet is part of a continuous web comprising a nonwoven web coated with a microporous plastic layer upon which an ultrathin salt-rejecting layer is deposited. 
     
     
         6 . The method of  claim 3  wherein the embossing is performed by contact of a sheet comprising a layer of a microporous plastic on a nonwoven web with an embossing disk, the nonwoven web being supported by an idler roller, a drive roller, or a stationary shoe at the point of contact. 
     
     
         7 . The method of  claim 5  wherein at least two longitudinally indented surfaces are generated, at least one each of which is adjacent each edge of the web. 
     
     
         8 . The method of  claim 7  wherein embossing is done by means of a cylindrical roller having at least two raised ridges, at least one being adjacent a first edge of the web and at least one being adjacent a second edge of the web. 
     
     
         9 . The method of  claim 7  wherein more than one longitudinally indented surface is generated adjacent each edge of the web