Osmotic desalination process

Patent metadata

Field	Value
Publication number	US-9433901-B2
Application number	US-201414268518-A
Country	US
Kind code	B2
Filing date	May 2, 2014
Priority date	Feb 1, 2001
Publication date	Sep 6, 2016
Grant date	Sep 6, 2016

Abstract

An energy efficient desalination process that does not produce waste products involves the extraction of water from a first solution, such as seawater, by using a second concentrated solution to draw the water from the first solution across a semi-permeable membrane. By manipulating the equilibrium of the soluble and insoluble species of solute within the second solution in favor of the soluble species of the solute, a saturated second solution can be used to generate osmotic pressure on the first solution. Also, by adjusting the equilibrium in favor of the less soluble species after the water has been drawn from the first solution, a portion of the solute can easily be precipitated out. Heating the second solution decomposes the solute into its constituent gases. The constituent gases and precipitated solute may be recycled through the process to affect the changes in equilibrium and eliminate waste products. Additionally, by using the waste steam from industrial sources and a heat pump to effectively distribute heat through the present method, the present method exhibits greater energy efficiency than prior art methods.

First claim

What is claimed is:

1. A method for extracting a solvent from a solution using forward osmosis, the method comprising the steps of:
providing a semi-permeable membrane;
introducing a first solution to a first surface of the semi-permeable membrane;
introducing a second solution to a second surface of the semi-permeable membrane, wherein the second solution comprises at least two species of a solute, a soluble species of the solute and a less soluble species of the solute, where the ratio of the soluble species of the solute to the less soluble species of the solute is greater than 1:1 at equilibrium so as to generate an increased osmotic pressure on the first solution;
drawing a solvent from the first solution through the semi-permeable membrane and into the second solution, thereby creating a solvent-enriched second solution; and
removing at least one of the at least two species of the solute from the solvent-enriched second solution, wherein the step of removing at least one of the at least two species of the solute comprises:
exposing the solvent enriched second solution to a heat source;
decomposing at least one of the at least two species of the solute into constituent gases;
vaporizing the constituent gas out of the solvent-enriched second solution, wherein the heat source is derived from at least one of solar, wind, or geothermal energy, and
recovering at least a portion of the solvent from the solvent-enriched second solution.

2. The method of claim 1 , wherein the second solution comprises a concentrated solution of ammonia and carbon dioxide, ammonium carbonate, ammonium bicarbonate, and ammonium carbamate.

3. The method of claim 1 , wherein the first solution comprises at least one of seawater, brackish water, wastewater, contaminated water, or other aqueous solution.

4. The method of claim 1 , further comprising the step of recycling the constituent gases back into the second solution to maintain a desired concentration of the second solution.

5. The method of claim 1 , wherein the step of removing at least one of the at least two species of the solute further comprises adjusting an equilibrium of the solvent-enriched second solution to increase an amount of the less-soluble species of the solute.

6. The method of claim 5 , wherein the step of adjusting the equilibrium comprises adding a reagent to the solvent-enriched second solution to cause a portion of the less soluble species of the solute to precipitate out of the solvent-enriched second solution.

7. The method of claim 1 , wherein the step of removing at least one of the at least two species of the solute further comprises filtering the solvent-enriched second solution previous to exposing to the heat source.

8. The method of claim 1 , further comprising the step of recycling the at least one species of the solute removed from the solvent-enriched second solution back into the second solution to maintain a desired concentration of the second solution.

9. The method of claim 1 , further comprising the step of applying an external pressure to the first solution to increase solvent flux through the semi-permeable membrane.

10. The method of claim 1 further comprising the step of manipulating the ratio of the soluble species of the solute to the less-soluble species of solute to increase the solute concentration in the second solution to about 6 molal.

11. The method of claim 1 further comprising the step of manipulating the ratio of the soluble species of the solute to the less-soluble species of solute to increase the solute concentration in the second solution to between 6 molal and 12 molal.

12. An apparatus for the extraction of a solvent from a first solution using forward osmosis comprising:
a first chamber for receiving a first solution;
a second chamber containing a second solution, wherein the second solution comprises ammonia and carbon dioxide in a molar ratio of greater than 1:1 at equilibrium so as to generate an increased osmotic pressure on the first solution;
a semi-permeable membrane coupling the first chamber and the second chamber, wherein the semi-permeable membrane allows a solvent from the first chamber to pass through to the second chamber, thereby producing a solvent-enriched second solution in the second chamber; and
a heating chamber coupled to the second chamber for removing at least one of the ammonia and carbon dioxide from the solvent-enriched second solution, wherein the heating chamber comprises a heat exchanger in communication with a heat source to decompose at least one of the ammonia and carbon dioxide into constituent gases and vaporize the constituent gases out of the solvent-enriched second solution in the heating chamber, wherein the heat source is derived from at least one of solar energy, wind energy, or geothermal energy.

13. The apparatus of claim 12 , wherein the apparatus further comprise a filtration module.

14. The apparatus of claim 12 further comprising recycling means for recycling the constituent gases of at least one of the ammonia and carbon dioxide from the heating chamber to the second chamber, whereby a desired concentration of the second solution is maintained in the second chamber.

15. The apparatus of claim 12 further comprising means for applying an external pressure coupled to the first chamber for increasing solvent flux through the semi-permeable membrane.

Assignees

• Univ Yale

Inventors

• Mcginnis Robert L

Classifications

• B01D61/002 Primary

  Forward osmosis or direct osmosis · CPC title

• C02F1/02

  by heating (methods of steam generation F22B; preheating boiler feed-water or accumulating preheated boiler feed-water F22D) · CPC title

• C02F1/445

  by forward osmosis · CPC title

• C02F2103/08

  Seawater, e.g. for desalination · CPC title

• B01D61/005

  Osmotic agents; Draw solutions · CPC title