Vacuum enhanced direct contact membrane distillation

• US 20060144788A1
• Filed: 12/02/2005
• Published: 07/06/2006
• Est. Priority Date: 12/03/2004
• Status: Active Grant

• Current Assignee: Board of Regents Nevada System of Higher Education (State of Nevada)
• Original Assignee: Board of Regents Nevada System of Higher Education (State of Nevada)
• Inventors: Childress, Amy E., Cath, Tzahi Y., Adams, V. Dean
• Granted Patent: US 7,608,188 B2
• Time in Patent Office: Days
• US Class Current: 210/640
• CPC Class Codes: B01D 61/364 Membrane distillation
• CPC Class Codes: C02F 1/447 by membrane distillation distillation and evaporation without the use of membranes C02F1/04

Abstract

The present disclosure provides methods and systems for purifying an impaired liquid. In a particular example, the disclosure provides methods and systems for purifying water containing a solute. A feed stream of solute containing water is introduced in a flow chamber. A permeate stream of water at least substantially free of the solute is placed in the flow chamber. A hydrophobic membrane is placed between the feed stream and the permeate stream. A vacuum is applied to the permeate stream. A vapor pressure differential causes water to vaporize from the feed stream, pass through the hydrophobic membrane, and condense in the permeate stream.

Claims

1. A fresh water extraction system comprising:

a feed stream comprising impaired water;

a permeate stream running adjacent to the feed stream;

a membrane positioned intermediate the feed stream and the permeate stream;

a first pump in communication with the feed stream, whereby the first pump causes the feed stream to flow on the membrane;

a second pump in communication with the permeate stream, whereby the second pump causes the pressure in the permeate stream to be lower than the pressure of the feed stream;

whereby a partial vapor pressure differential across the membrane causes solvent to evaporate from the feed stream, pass through the membrane, and condense in the permeate stream.

2. The system of claim 1, wherein the temperature of the feed stream is higher than the temperature of the permeate stream.

3. The system of claim 1, wherein a solute is dissolved in the feed stream.

4. The system of claim 3, wherein the solute comprises sodium chloride.

5. The system of claim 3, wherein the solute comprises sea salt.

6. The system of claim 1, wherein the feed stream is selected from the group consisting of treated wastewater, liquid foods, biological substances, runoff water, and seawater.

7. The system of claim 1, wherein the permeate stream is selected from the group consisting of distilled deionized water, potable water, and water having relatively low total dissolved solids.

8. The system of claim 1, wherein the permeate stream and the feed stream each have a flow velocity and the flow velocity of the permeate stream is at least approximately equal to the flow velocity of the feed stream.

9. The system of claim 1, wherein the feed stream runs countercurrent to the permeate stream.

10. The system of claim 1, wherein the membrane is microporous.

11. The system of claim 1, wherein the membrane is hydrophobic.

12. The system of claim 11, wherein the hydrophobic membrane is a composite membrane comprising a polytetrafluoroethylene active layer and a polypropylene support sublayer.

13. The system of claim 11, wherein the hydrophobic membrane is a symmetric, isotropic membrane made from pure polypropylene.

14. The system of claim 1, wherein the first pump causes the pressure in the feed stream to be lower than atmospheric pressure.

15. A method for extracting fresh water from an impaired water source, the method comprising:

supplying impaired water in a feed stream;

supplying a permeate stream adjacent to the feed stream;

positioning a membrane between the feed stream and the permeate stream; and

applying a vacuum to the permeate stream;

whereby a vapor pressure differential across the membrane causes water to evaporate from the solution in the feed stream, pass through the membrane, and condense in the permeate stream.

16. The method of claim 15, wherein the temperature of the feed stream is higher than the temperature of the permeate stream.

17. The method of claim 15, wherein the impaired water comprises sodium chloride.

18. The method of claim 15, wherein the impaired water comprises sea salt.

19. The method of claim 15, wherein the permeate stream is distilled deionized water.

20. The method of claim 15, wherein the permeate stream and feed stream each have a flow velocity and the flow velocity of the permeate stream is at least approximately equal to the flow velocity of the feed stream.

21. The method of claim 15, wherein the feed stream is supplied in a direction countercurrent to the permeate stream.

22. The method of claim 15, wherein the membrane is hydrophobic.

23. The method of claim 22, wherein the hydrophobic membrane is microporous.

24. The method of claim 22, wherein the hydrophobic membrane is a composite membrane comprising a polytetrafluoroethylene active layer and a polypropylene support sublayer.

25. The method of claim 22, wherein the hydrophobic membrane is a symmetric, isotropic, polypropylene membrane.

26. The method of claim 15, further comprising applying a vacuum to the feed stream.

27. A water extraction system comprising:

(A) a feed cycle, the feed cycle comprising

(i) a feed stream of impaired water;

(ii) a feed cycle pump in communication with the feed stream;

(iii) a feed stream temperature gauge in communication with the feed stream;

(iv) a feed stream flow meter in communication with the feed stream;

(B) a permeate cycle, the permeate cycle comprising;

(i) a permeate stream;

(ii) a permeate cycle pump in communication with the permeate stream;

whereby the pump is configured to place the permeate stream under vacuum;

(iii) a permeate stream temperature gauge in communication with the permeate stream;

(iv) a permeate stream flow meter in communication with the permeate stream;

(v) a permeate stream pressure gauge; and

(C) a flow cell, the flow cell comprising;

(i) a permeate side comprising a permeate inlet in fluid communication with the permeate stream;

(ii) a feed side comprising a feed inlet in fluid communication with the feed stream;

(iii) a membrane interposed between the permeate side and the feed side;

whereby a partial pressure differential across the membrane causes solvent to evaporate from the feed stream, pass through the membrane, and condense in the permeate stream.

28. The water extraction system of claim 27, wherein the feed cycle pump is configured to place the feed stream under vacuum.

29. The water extraction system of claim 27, the flow cell further comprising a gasket, the gasket abutting the membrane.

30. The water extraction system of claim 27, wherein the membrane is one of a plurality of membranes, further comprising a plurality of gaskets, each of the plurality of gaskets abutting a membrane and forming a stack having a plurality of alternating layers of membranes and gaskets.

31. The water extraction system of claim 30, wherein a first portion of the plurality of gaskets are in communication with the feed stream and a second portion of the plurality of gaskets are in communication with the permeate stream, each of the plurality of membranes abutted by a gasket in communication with the permeate stream and a gasket in communication with the feed stream.

32. The water extraction system of claim 27, wherein the flow cell comprises a pressure vessel and the membrane is rolled inside the pressure vessel, forming a plurality of membrane layers, each layer being abutted on a first side by the feed stream and being abutted on a second side by the permeate stream.