Ion sequestration for scale prevention in high-recovery desalination systems

Patent metadata

Field	Value
Publication number	US-9617179-B2
Application number	US-201313958968-A
Country	US
Kind code	B2
Filing date	Aug 5, 2013
Priority date	Mar 14, 2013
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

Cations that can precipitate from an aqueous composition to produce scaling are sequestered by adding a multi-dentate ligand to the aqueous composition. The multi-dentate ligand bonds with the cation to form a non-scaling ionic complex; and the aqueous solution with the ionic complex is used in a process that produces substantially pure water from the aqueous composition, where the cation, absent formation of the ionic complex, is subject to scaling. The pH of the aqueous composition (or a brine including components of the aqueous composition) is then reduced to release the cation from the multi-dentate ligand; and the multi-dentate ligand, after the cation is released, is then reused in a predominantly closed loop.

First claim

What is claimed is:

1. A method for sequestering cations that can precipitate from an aqueous composition, the method comprising:
adding a multi-dentate ligand to an aqueous composition that includes monovalent ions and at least one type of dissolved divalent cation that can precipitate from the aqueous composition to produce scaling;
then enabling the multi-dentate ligand to bond with the dissolved divalent cation to form an aqueous non-scaling ionic complex;
then filtering the aqueous non-scaling ionic complex from the aqueous composition with a membrane that retains the aqueous non-scaling ionic complex in a retentate stream and that passes a filtrate stream comprising water and monovalent ions;
reducing the pH of the retentate stream to release the dissolved divalent cation from the multi-dentate ligand;
after the non-scaling ionic complex is filtered from the aqueous composition, separating purified water from at least a portion of the filtrate of the aqueous composition and leaving a concentrated remainder of the filtrate of the aqueous composition in a high-recovery desalination system where the divalent cation, absent formation and removal of the ionic complex, would be subject to scaling; and
after the dissolved divalent cation is released from the multi-dentate ligand, reintroducing the multi-dentate ligand into additional aqueous composition to form additional non-scaling ionic complex in a predominantly closed loop.

2. The method of claim 1 , wherein the dissolved divalent cation includes at least one of the following: calcium, barium, strontium and magnesium.

3. The method of claim 1 , wherein the aqueous composition includes flowback water or produced water from oil or gas extraction.

4. The method of claim 1 , wherein the aqueous composition includes at least one of sea water and brackish water.

5. The method of claim 1 , wherein the aqueous composition includes waste water.

6. The method of claim 1 , wherein the pH of the retentate is reduced via addition of an acid to release the scaling component from the multi-dentate ligand.

7. The method of claim 1 , wherein the separation of the purified water from the monovalent ions of the filtrate of the aqueous composition in the high-recovery desalination system is performed via a desalination process selected from at least one of the following: reverse osmosis, multi-stage flash distillation, multiple-effect distillation, mechanical vapor recompression, electrodialysis, membrane distillation, directional solvent extraction and humidification-dehumidification.

8. The method of claim 1 , further comprising heating the filtrate of the aqueous composition up to a temperature at which the cation would precipitate from the aqueous composition absent bonding of the scaling component in the non-scaling ionic complex.

9. The method of claim 8 , wherein the filtrate of the aqueous composition is heated up to a temperature of at least 50° C.

10. The method of claim 1 , wherein the monovalent ions include at least one dissolved component selected from NaCl, KCl, Na 2 SO 4 , and Na 2 CO 3 .

11. The method of claim 1 , wherein the pH of the retentate including the ionic complex is reduced by adding an acid to the retentate, the method further comprising adding a base to the retentate after the multi-dentate ligand is released and removed, wherein the base neutralizes the acid.

12. The method of claim 1 , wherein the retentate including the ionic complex is cooled to less than 20° C. after the pH is reduced to increase the amount of multi-dentate ligand released from the cation.

13. The method of claim 1 , wherein the multi-dentate ligand comprises an ethylenediamine tetra-acetate ion.

14. The method of claim 7 , wherein the desalination process is a humidification-dehumidification process.

Assignees

• Massachusetts Inst Technology

Inventors

• Govindan Prakash Narayan
• Sung Windsor
• Lam Steven
• St John Maximus G
• Lienhard V John H
• Mirhi Mohammed
• Bajpayee Anurag

Classifications

• C02F1/04

  by distillation or evaporation · CPC title

• C02F2103/08

  Seawater, e.g. for desalination · CPC title

• B01D61/58

  Multistep processes · CPC title

• C02F2101/10

  Inorganic compounds · CPC title

• B01D2311/08

  Specific process operations in the concentrate stream · CPC title