Ion-selective separation by shock electrodialysis

Patent metadata

Field	Value
Publication number	US-12383866-B2
Application number	US-202017414215-A
Country	US
Kind code	B2
Filing date	Jan 3, 2020
Priority date	Jan 3, 2019
Publication date	Aug 12, 2025
Grant date	Aug 12, 2025

Abstract

Ion-selective separation by shock electrodialysis is performed by applying a voltage differential between electrodes across a porous medium to selectively draw a first species in a liquid toward at least one of the electrodes to a greater degree than a degree to which a second species in the liquid is drawn toward the same electrode. The voltage differential creates a shock in the charged-species concentration in the bulk volume of the liquid within pore channels of the porous medium, wherein the concentration of the first 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 the second species in the liquid bulk volume between the shock and the first electrode. A dilute stream including the second species is extracted from the depleted zone separate from a concentrated stream including the first species.

First claim

What is claimed is:

1. A method for ion-selective separation by shock electrodialysis utilizing a system that includes at least one liquid conduit with at least one inlet port, at least one outlet port for a dilute stream, and at least one outlet port for a concentrated stream, wherein the system also 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 an ion-selective boundary, wherein the at least one distinct ion-selective boundary or the second electrode has a charge and is contained in the at least one liquid conduit adjacent to a porous medium or that functions as the porous medium, wherein the porous medium defines pore channels that are filled with a liquid including a plurality of species having a charge of the same sign, wherein the pore channels have a surface charge, and wherein the charge of the ion-selective boundary and surface charge of the pore channels share a sign, the method comprising:
flowing the liquid 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 with a liquid bulk volume beyond the double layer in the pore channels;
applying a voltage differential between the electrodes across the porous medium, wherein the voltage differential has a magnitude set to selectively draw a first of the species in the liquid toward at least one of the electrodes to a greater extent than an extent to which a second of the species is drawn toward the same electrode, wherein the species are dissolved ion species, and wherein the first species has a higher valence than the second species;
via the application of the voltage differential, producing current at the electrodes by either Faradaic reactions or by capacitive charging and discharging and creating a shock in the charged-species concentration in the bulk volume of the liquid within the pore channels, wherein the concentration of the first 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 the second species 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;
extracting the dilute stream from the depleted zone of the bulk volume in the porous medium by flow to the at least one outlet port for the dilute stream between the shock and the ion-selective boundary; and
flowing the first species in the concentrated stream on an opposite side of the shock from the depleted zone, wherein the at least one outlet port for the concentrated stream is separated across the porous medium from the at least one outlet port for the dilute stream by the shock and not by a membrane.

2. The method of claim 1 , wherein the electrodes comprise a cathode and an anode.

3. The method of claim 2 , wherein the first and second species are both cations, wherein the system includes a pair of cation exchange membranes, wherein a first of the cation exchange membranes is between the anode and the porous medium, and wherein a second of the cation exchange membranes is between the cathode and the porous medium.

4. The method of claim 3 , wherein three inlet streams are fed into the system, including a first and a second electrode flush stream and a feed stream, wherein the first and second electrode flush streams respectively flow through (a) a first flush channel between the first cation exchange membrane and the anode and (b) a second flush channel between the second cation exchange membrane and the cathode, and wherein the feed stream flows between the cation exchange membranes.

5. The method of claim 4 , further comprising adding acid to the second flush channel.

6. The method of claim 4 , further comprising adding a buffer to at least one of the electrode flush streams.

7. The method of claim 6 , wherein the buffer is sodium citrate.

8. The method of claim 1 , wherein the charged species of the higher valence is magnesium, and wherein the charged species of the lower valence is sodium.

9. The method of claim 1 , wherein a plurality of inlet streams is fed into the system, the method further comprising determining and establishing a flow rate of at least one of the streams that increases the selectivity with which the first species is drawn to the electrode.

10. The method of claim 1 , further comprising determining and utilizing a pore size for the porous medium that increases the selectivity with which the first species is drawn to the electrode.

11. The method of claim 1 , further comprising determining and utilizing a surface charge for the porous medium that increases the selectivity with which the first species is drawn to the electrode.

12. The method of claim 1 , further comprising positioning a splitter to establish a boundary separating the outlet for the dilute stream and the outlet for the concentrated stream such that the first species is selectively drawn into the dilute stream.

13. The method of claim 1 , further comprising determining and establishing the magnitude of the voltage differential as a function of the dissolved ion content in the liquid.

14. The method of claim 1 , wherein the liquid fed to the system is selected from flowback water from hydraulic fracturing, radioactively contaminated waste from nuclear energy production, feed for tap water, and liquid recovered from a lithium battery.

15. The method of claim 1 , wherein the species are selected from ion species, proteins, other molecules, liquids, particles, and microbes.

16. The method of claim 1 , wherein the second species, which is less drawn toward the same of the at least one of the electrodes as the first species, is removed in the dilute stream as a target species substantially isolated from other species, which are selectively drawn to the concentrated stream.

17. The method of claim 1 , wherein the pore channels have a width in a range from 100 nm to 10 μm.

Assignees

• Massachusetts Inst Technology

Inventors

• Bazant Martin Z
• Conforti Kameron

Classifications

• C25B1/14

  Alkali metal compounds · CPC title

• C02F2201/4618

  Supplying or removing reactants or electrolyte · CPC title

• C02F2201/46145

  Fluid flow · CPC title

• C02F2201/46135

  Voltage · CPC title

• C02F2103/10

  from quarries or from mining activities · CPC title