Forward osmosis membranes

Abstract

Forward osmosis membranes include an active layer and a thin support layer. A bilayer substrate including a removable backing layer may allow forward osmosis membranes with reduced supporting layer thickness to be processed on existing manufacturing lines.

What is claimed is: 
     
         1 . A method of making a forward osmosis membrane, comprising:
 providing a support structure including at least a first layer and a second layer;   applying a material to a first layer of the support structure to form a membrane support layer;   applying a barrier material to the membrane support layer to form the forward osmosis membrane; and   releasing the forward osmosis membrane by separating the first layer of the support structure from the second layer of the support structure.   
     
     
         2 . The method of  claim 1 , wherein the support structure comprises a bilayer structure. 
     
     
         3 . The method of  claim 1 , wherein the first layer of the support structure has a Frazier air permeability of greater than about 50 cfm/ft 2 min. 
     
     
         4 . The method of  claim 1 , wherein the material applied to the first layer of the support structure is applied in a coating of between about 5 and 20 g/m 2 . 
     
     
         5 . The method of  claim 1 , wherein the forward osmosis membrane has an overall thickness of less than about 125 microns. 
     
     
         6 . The method of  claim 1 , wherein the barrier material comprises a semipermeable material. 
     
     
         7 . The method of  claim 6 , wherein the barrier material comprises a polymer. 
     
     
         8 . The method of  claim 7 , wherein the barrier material comprises a polyamide urea, polypiperazine, or a block co-polymer. 
     
     
         9 . The method of  claim 1 , wherein the support structure comprises a polymeric paper. 
     
     
         10 . The method of  claim 9 , wherein the support structure comprises PET or polypropylene. 
     
     
         11 . The method of  claim 1 , further comprising rewetting the forward osmosis membrane. 
     
     
         12 . The method of  claim 1 , further comprising adding an additive to one or more layers of the membrane. 
     
     
         13 . The method of  claim 1 , wherein the step of releasing the forward osmosis membrane by separating the first and second layers of the support structure comprises modifying a pore structure in at least a section of the forward osmosis membrane. 
     
     
         14 . The method of  claim 1 , further comprising reusing the second layer of the support structure. 
     
     
         15 . A method of making a forward osmosis membrane, comprising:
 casting a paperless support structure on a fabrication belt or drum;   depositing a barrier material on the paperless support structure; and   delaminating the paperless support structure from the fabrication belt to form the forward osmosis membrane.   
     
     
         16 . The method of  claim 15 , wherein the belt or drum is constructed and arranged to provide a surface which retains a portion of the support structure. 
     
     
         17 . The method of  claim 15 , wherein retained support structure is removed prior to full rotation of the belt or drum. 
     
     
         18 . A method of facilitating a forward osmosis separation operation, comprising:
 providing a support structure;   applying a material to the support structure to form a membrane support layer;   applying a barrier layer to the membrane support layer to form a forward osmosis membrane; and   configuring the forward osmosis membrane in a forward osmosis membrane module such that the support structure may provide a spacer or a flow channel for a draw solution or a feed solution supplied to the module during the forward osmosis separation operation.   
     
     
         19 . The method of  claim 18 , wherein providing the support structure comprises providing a bilayer structure. 
     
     
         20 . The method of  claim 18 , further comprising providing a source of the draw solution. 
     
     
         21 . A forward osmosis membrane, comprising:
 a fabric layer of less than about 75 microns;   a support layer of less than about 50 microns applied on the fabric layer; and   a barrier layer applied on the support layer,   wherein the forward osmosis membrane has an overall thickness of less than about 125 microns.   
     
     
         22 . The membrane of  claim 21 , wherein the barrier layer comprises polyamide. 
     
     
         23 . The membrane of  claim 21 , wherein the support layer comprises PET.