Asymmetric forward osmosis membranes

• US 20060226067A1
• Filed: 04/07/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: Hydration Systems LLC
• Original Assignee: Hydration Technologies, Inc.
• Inventors: Herron, Jack
• Granted Patent: US 7,445,712 B2
• Time in Patent Office: Days
• US Class Current: 210/490
• CPC Class Codes: B01D 2325/022 Asymmetric membranes
• CPC Class Codes: B01D 2325/0231 Dense layers being placed on the outer side of the cross-section
• CPC Class Codes: B01D 2325/026 Sponge structure
• CPC Class Codes: B01D 2325/04 Characteristic thickness
• CPC Class Codes: B01D 2325/24 Mechanical properties, e.g. strength
• CPC Class Codes: B01D 67/0009 by phase separation, sol-gel transition, evaporation or solvent quenching
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/10 Supported membranes; Membrane supports
• CPC Class Codes: B01D 69/1071 Woven, non-woven or net mesh
• CPC Class Codes: B01D 71/16 Cellulose acetate
• CPC Class Codes: B01D 71/18 Mixed esters, e.g. cellulose acetate-butyrate

Abstract

There is disclosed a membrane formulation having high flux for forward osmosis applications. There is disclosed a forward osmosis filtration membrane having a salt rejection 99+% or greater, and comprising an asymmetric hydrophobic porous backing and cellulosic fibers. The membranes of the present invention find use in a variety of applications including osmotic-driven water purification and filtration, desalination of sea water, purification of contaminated aqueous waste streams, and the like. Specifically, there is disclosed a forward osmosis filtration membrane having a skin layer for salt rejection and a porous scaffold layer having a woven or non-woven mesh embedded within it.

Claims

1. An asymmetric forward osmosis membrane having three layers comprising:

(a) a skin layer made from polymeric material having a top surface as a rejection surface of the asymmetric forward osmosis membrane, and a bottom surface, wherein the density of the skin layer is greater than 50% polymer (by volume);

(b) a porous scaffold layer bonded to the bottom surface of the skin layer, wherein the scaffold layer is made from the same polymeric material as the skin layer and wherein the density of the scaffold layer is from about 15% to about 30% (by volume); and

(c) a hydrophilic woven or nonwoven porous fabric bonded to the second surface of the scaffold layer.

2. The asymmetric forward osmosis membrane having three layers of claim 1 wherein the skin layer has an average thickness of from about 8 to about 18 microns.

3. The asymmetric forward osmosis membrane having three layers of claim 1 wherein the scaffold layer has an average thickness of from about 25 to about 75 microns.

4. The asymmetric forward osmosis membrane having three layers of claim 1 wherein the polymeric skin layer and porous scaffold layer material is selected from the group consisting of cellulose acetate, cellulose triacetate, cellulose proprianate, cellulose butyrate, cellulose acetate propionate, cellulose diacetate, cellulose dibutyrate, cellulose tributyrate, and combinations thereof.

5. The asymmetric forward osmosis membrane having three layers of claim 1 wherein the hydrophilic porous fabric is selected from the group consisting of cotton, non-woven cellulose polyolefin blends, EVA (ethylene vinyl acetate) nonwoven cloths and screens, nonwoven polyester-polyolefin composites, nonwoven acrylic composites, and extruded hydrophilic microporous membrane sheets having average pores greater than 0.1 microns.

6. An asymmetric forward osmosis membrane having two layers comprising:

(a) a skin layer made from polymeric material having a top surface as a rejection surface of the asymmetric forward osmosis membrane, and a bottom surface, wherein the density of the skin layer is greater than 50% polymer (by volume);

(b) a porous scaffold layer bonded to the bottom surface of the skin layer, wherein the scaffold layer is made from the same polymeric material as the skin layer and wherein the density of the scaffold layer is from about 15% to about 30% (by volume); and

(c) a mesh or nonwoven fabric having greater than 50% open area embedded within the porous scaffold layer.

7. The asymmetric forward osmosis membrane having two layers of claim 6 wherein the skin layer has an average thickness of from about 8 to about 18 microns.

8. The asymmetric forward osmosis membrane having two layers of claim 6 wherein the scaffold has an average thickness of from about 75 to about 150 microns.

9. The asymmetric forward osmosis membrane having two layers of claim 6 wherein the mesh is a woven monofilament mesh.

10. The asymmetric forward osmosis membrane having two layers of claim 9 wherein the mesh or nonwoven fabric is selected from the group consisting of polyester woven screens, polypropylene woven screens, woven acrylics woven nylon screens, and combinations thereof.

11. The asymmetric forward osmosis membrane having two layers of claim 6 wherein the polymeric membrane material is selected from the group consisting of cellulose acetate, cellulose triacetate, cellulose acetate proprianate, cellulose butyrate, cellulose acetate propionate, cellulose diacetate, cellulose dibutyrate, cellulose tributyrate, and combinations thereof.

12. An immersion/precipitation process for making a supported forward osmosis membrane comprising:

(a) applying a casting solution slurry of polymeric material in a solvent onto a surface of a rotating drum to form a casting solution layer, wherein the casting solution comprises from about 70% to about 90% (by volume) of a solvent formulation and from about 10% to about 30% (by volume) of a polymeric solid material;

(b) pulling a non-woven fabric or woven mesh support material having at least about 50% open area into the casting solution slurry on the surface of the rotating drum so that the support material is fully embedded within the casting solution slurry; and

(c) immersing the casting solution-imbedded support material into a water bath, whereby the casting solution-imbedded support material coagulates the polymeric material into a supported forward osmosis membrane.

13. The immersion/precipitation process for making a supported forward osmosis membrane of claim 12 wherein the non-woven fabric is selected from the group consisting of polyester, polypropylene, polyolefin blends polyester-polyolefin composites, and nylon.

14. The immersion/precipitation process for making a supported forward osmosis membrane of claim 12 wherein the woven mesh is selected from the group consisting of polyester woven screens, polypropylene woven screens, woven acrylics, woven nylon screens, and combinations thereof.

15. The immersion/precipitation process for making a supported forward osmosis membrane of claim 12 wherein the solvent formulation comprises ketones, organic acids and a short chain alcohol.

16. The immersion/precipitation process for making a supported forward osmosis membrane of claim 12 wherein the polymeric membrane material is selected from the group consisting of cellulose acetate, cellulose triacetate, cellulose proprianate, cellulose butyrate, cellulose acetyl propionate, cellulose diacetate, cellulose dibutyrate, cellulose tributyrate, and combinations thereof.