METHOD AND APPARATUS FOR DESALINATION AND PURIFICATION

• US 20110308953A1
• Filed: 06/21/2011
• Published: 12/22/2011
• Est. Priority Date: 06/21/2010
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Bazant, Martin Z., Deng, Daosheng, Dydek, EthelMae Victoria, Mani, Ali
• Granted Patent: US 8,801,910 B2
• Time in Patent Office: Days
• US Class Current: 204/520
• CPC Class Codes: B01D 2313/345 Electrodes
• CPC Class Codes: B01D 61/425 Electro-ultrafiltration
• CPC Class Codes: B01D 61/427 Electro-osmosis
• CPC Class Codes: B01D 61/4271 comprising multiple electro-osmosis steps
• CPC Class Codes: B01D 61/44 Ion-selective electrodialysis
• CPC Class Codes: B01D 61/445 with bipolar membranes; Water splitting
• CPC Class Codes: B01D 61/46 Apparatus therefor
• CPC Class Codes: B01D 61/48 having one or more compartments filled with ion-exchange material , e.g. electrodeionisation
• CPC Class Codes: B01D 61/485 Specific features relating to the ion-exchange material
• CPC Class Codes: B01D 61/50 Stacks of the plate-and-frame type
• CPC Class Codes: B01D 63/06 Tubular membrane modules
• CPC Class Codes: C02F 1/46109 Electrodes
• CPC Class Codes: C02F 1/46114 Electrodes in particulate form or with conductive and/or non conductive particles between them
• CPC Class Codes: C02F 1/469 by electrochemical separation, e.g. by electro-osmosis, electrodialysis, electrophoresis
• CPC Class Codes: C02F 1/4691 Capacitive deionisation
• CPC Class Codes: C02F 1/4693 electrodialysis
• CPC Class Codes: C02F 1/4695 electrodeionisation
• CPC Class Codes: C02F 1/4698 electro-osmosis
• CPC Class Codes: C02F 2001/46161 Porous electrodes
• CPC Class Codes: C02F 2201/4611 Fluid flow
• CPC Class Codes: C02F 2201/46115 : Electrolytic cell with membranes or diaphragms
• CPC Class Codes: C02F 2201/4613 : Inversing polarity
• CPC Class Codes: C02F 2201/46165 : Special power supply, e.g. solar energy or batteries
• CPC Class Codes: C02F 2305/08 : Nanoparticles or nanotubes
• CPC Class Codes: Y02A 20/124 : Water desalination
• CPC Class Codes: Y02A 20/131 : Reverse-osmosis
• CPC Class Codes: Y02W 10/37 : using solar energy

Abstract

A liquid electrolyte can be desalinated and purified using a system that includes a first electrode and a configuration selected from (a) a second electrode and at least one distinct ion-selective boundary and (b) a second electrode that also serves as the ion-selective boundary. The ion-selective boundary is contained in the liquid conduit adjacent to a porous medium that defines pore channels filled with the liquid and that have a surface charge, and the charge of the ion-selective boundary and the surface charge of the pore channels share the same sign. A liquid including at least one charged species flows through the pore channels, forming a thin diffuse electrochemical double layer at an interface of the liquid and the charged surface of the pore channels. A voltage differential is applied between the electrodes across the porous medium to draw ions in the liquid to the electrodes to produce brine at the electrodes and to create a shock in the dissolved-ion concentration in the bulk volume of the liquid within the pore channels, wherein a depleted zone with a substantially reduced concentration of dissolved ions forms in the liquid bulk volume between the shock and the ion-selective boundary.

Claims

1. A desalination and purification system for a source liquid containing co-ions and counter-ions selected from dissolved ions, charged impurities, charged droplets and combinations thereof, wherein the co-ions and counter-ions have charges of opposite signs, the system comprising:

a conduit for liquid flow including a liquid inlet port, a desalinated/purified liquid outlet port, and a waste liquid outlet port;

a first electrode;

a second electrode and ion-selective boundary configuration selected from;

a) a second electrode and at least one distinct ion-selective boundary, and

b) a second electrode that also serves as the ion-selective boundary, wherein the electrodes are configured to drive ionic current in the source liquid when the source liquid fills the conduit and to produce brine/waste liquid from the source liquid, and wherein the ion-selective boundary is configured to conduct the ionic current and selectively transmit or remove the counter-ions and block the co-ions from the source liquid; and

at least one porous medium, adjacent to the ion-selective boundary in the conduit and on an opposite side of the ion-selective boundary from the second electrode, wherein the porous medium has a surface charge with a sign that is the same as the sign of the co-ions to enable conduction of an additional ionic current via the counter-ions and consequent production of a region of desalinated/purified liquid, wherein the desalinated/purified liquid outlet port is positioned to extract the desalinated/purified liquid from the porous medium.

2. The desalination and purification system of claim 1, wherein the source liquid comprises water that contains dissolved salts and suspended particles or droplets.

3. The desalination and purification system of claim 1, wherein only one ion-selective boundary is included in the system, and wherein the ion-selective boundary separates only one electrode from the liquid inlet port.

4. The desalination and purification system of claim 1, wherein channels defined by the porous medium have a mean diameter of at least about 10 nm.

5. The desalination and purification system of claim 1, wherein the porous medium is selected from porous glass, porous ceramic, porous metal oxide, porous polymer, porous functionalized polymer, porous cross-linked polymer, and porous zeolite materials.

6. The desalination and purification system of claim 1, where the porous medium is an array of channels fabricated in silica glass, silicon, or a polymeric material.

7. The desalination and purification system of claim 1, wherein the porous medium is a packed bed of particles having diameters of about 100 microns or less.

8. The desalination and purification system of claim 1, wherein the porous medium has at least one of

(a) non-uniform porosity,

(b) non-uniform surface charge, and

(c) non-uniform microstructure

on a scale at least an order of magnitude greater than average pore size to generate non-uniform liquid flow or control of the salt concentration profile across different regions of the system.

9. The desalination and purification system of claim 1, where one or both electrodes are also porous.

10. The desalination and purification system of claim 1, wherein the ion-selective boundary and porous medium are selected from at least one of the following:

(a) a cation exchange membrane positioned between the second electrode and the porous medium, wherein the second electrode is a cathode, and wherein the porous medium has a negative surface charge and (b) an anion exchange membrane positioned between the second electrode and the porous medium, wherein the second electrode is an anode, and wherein the porous medium has a positive surface charge.

11. The desalination and purification system of claim 10, wherein the membrane and the porous medium comprise a first layer in an alternating sequence of at least two membranes and porous media with internal charge of the same sign, terminating with another ion-selective boundary of the same internal charge sign, placed in between the two electrodes.

12. The desalination and purification system of claim 10, further comprising an additional porous medium and membrane, both with an opposite charge to the porous medium and membrane of claim 10, wherein the oppositely charged porous media are adjacent to each other and sandwiched between the membranes.

13. The desalination and purification system of claim 12, wherein a plurality of layers of the oppositely charged porous media sandwiched between membranes are sequentially aligned between the two electrodes.

14. The desalination and purification system of claim 10, wherein the second electrode is porous and the ion-exchange membrane is connected to the second electrode in a membrane-electrode assembly.

15. The desalination and purification system of claim 1, wherein the ion-selective surface is also the second electrode and selectively removes counter-ions either by capacitive charging of the double layers or by electrochemical reactions.

16. The desalination and purification system of claim 1, wherein the porous medium has non-uniform pores, including at least one of the following:

graded pore structure, discontinuous changes in pore structure, or pores ranging in size by a factor of at least five.

17. The desalination and purification system of claim 1, wherein the porous medium is an agglomerate of different porous materials.

18. A method for desalination and purification of a liquid electrolyte utilizing a system that includes a liquid conduit that has an inlet port and at least two outlet ports for desalinated/purified liquid and for waste liquid and that includes a first electrode and a second-electrode-and-ion-selective-boundary configuration selected from (a) a second electrode and at least one distinct ion-selective boundary and (b) a second electrode that also serves as the ion-selective boundary, wherein the ion-selective boundary has a charge and is contained in the liquid conduit adjacent to a porous medium that defines pore channels that are filled with the liquid and that have a surface charge, wherein the charge of the ion-selective boundary and surface charge of the pore channels share a sign, the method comprising:

flowing a liquid including at least one charged species selected from dissolved ions, charged particles, and charged droplets into the inlet port and through the pore channels, forming a thin diffuse electrochemical double layer at an interface of the liquid and the charged surface of the pore channels in the porous medium;

applying a voltage differential between the electrodes across the porous medium to draw ions in the liquid to the electrodes, wherein at least some of the ions with a charge opposite to that of the first electrode flow to the first electrode and at least some of the ions with a charge opposite to that of the second electrode flow to the second electrode;

via the application of the voltage differential, producing brine at the electrodes by either Faradaic reactions or by capacitive charging and discharging and creating a shock in the dissolved-ion concentration in the bulk volume of the liquid within the pore channels, wherein the concentration of the charged species in a depleted zone of the liquid bulk volume between the shock and the ion-selective boundary is substantially lower than the concentration of dissolved ions in the liquid bulk volume between the shock and the first electrode, and wherein electric current flows primarily through the double layers or micropores in the region between the shock and the ion-selective boundary, while electric current flows primarily through the liquid bulk volume in the region between the shock and the first electrode; and

extracting desalinated and purified liquid from the depleted zone of the bulk volume in the porous medium by flow to an outlet port.

19. The method of claim 18, further comprising extracting liquid higher in dissolved salts and impurities than the desalinated and purified liquid from an enriched zone of the bulk volume in the porous medium by flow to an outlet port.

20. The method of claim 19, wherein the liquid higher in dissolved salts and impurities extracted from the porous medium is a product stream in continuous chemical processing.

21. The method of claim 20, wherein the extracted liquid with higher dissolved salts and impurities contains increased concentrations of at least one of the following:

acids, nanoparticles, colloids, minerals, organic molecules, biological molecules, viruses, cells and micro-organisms.

22. The method of claim 18, wherein the desalinated and purified liquid is extracted by pressure-driven flow parallel to the interface of the porous medium and the ion-selective boundary to one or more outlet ports.

23. The method of claim 18, wherein the desalinated and purified liquid removed by electro-osmotic flow in the porous medium, leading to or amplifying a pressure-driven flow parallel to the interface of the porous medium and the ion-selective membrane to one or more outlet port.

24. The method of claim 18, wherein the liquid is selected from seawater, brackish water, sewage, contaminated drinking water, radioactive waste, industrial wastewater, oil-well wastewater and agricultural wastewater.

25. The method of claim 18, wherein the desalination and purification is carried out multiple times and the system is transported by a person, vehicle, or ship between uses.

26. The method of claim 18, wherein the desalination and purification is carried out in a portable device powered by a battery, solar cell, or fuel cell.

27. The method of claim 18, wherein the ion-selective boundary is a surface of an electrode undergoing an electro-deposition or electro-dissolution reaction, or capacitive charging of its double layers.

28. The method of claim 18, wherein the pore channels filter at least one of charged particles and droplets from the liquid.

29. The method of claim 18, wherein the charged species includes surfactant-stabilized colloids or inverse micelles, and wherein the liquid is a non-aqueous solvent.