Control of ph kinetics in an electrolytic cell having an acid-intolerant alkali-conductive membrane

Abstract

Systems and methods for recovering chlorine gas or an alkali metal from an electrolytic cell having an acid-intolerant, alkali-ion-selective membrane are disclosed. In some cases, the cell has an anolyte compartment and a catholyte compartment with an acid-intolerant, alkali-ion selective membrane separating the two. While a cathode is disposed within a catholyte solution in the catholyte compartment, a chlorine-gas-evolving anode is typically disposed within an aqueous alkali-chloride solution in the anolyte compartment. As current passes between the anode and cathode, chlorine ions in the anolyte solution can be oxidized to form chlorine gas. In some cases, the cell is configured so the chlorine gas is rapidly removed from the cell to inhibit a chemical reaction between the chlorine gas and the anolyte solution. In some cases, a vacuum or a heating system is used to increase the rate at which chlorine gas exits the cell. Other implementations are also described.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to, and the benefit of, U.S. Provisional Application No. 61 / 431,356, filed Jan. 10, 2011, entitled “Recovery of Useful Chemicals from Alkyl Sulfonate Stream,” the entire disclosure of which is hereby incorporated by reference.FIELD OF THE INVENTION[0002]The present invention relates in general to electrochemical cells. More particularly, the present invention relates to systems and methods for operating an electrochemical cell comprising an acid-intolerant, alkali-ion-selective membrane (such as a NaSICON-type or a LiSICON-type membrane).BACKGROUND OF THE INVENTION[0003]Electrolytic cells comprising ceramic membranes that selectively transport ions are used in a variety of processes. By having an ion-selective membrane in an electrolytic cell, certain ions are allowed to pass between the cell's anolyte compartment and catholyte compartment while other chemicals are maintained in their original compartments....

AI Technical Summary

Benefits of technology

[0010]In another non-limiting example, the anode is permeable to chlorine gas so as to prevent the anode from blocking the chlorine gas' egress from the anolyte compartment. In another non-limiting example, a vacuum system is used to lower pressure in the anolyte compartment and, thereby, increase the rate at which chlorine gas exits the anolyte solution. Lowering the pressure also decreases the solubility of chlorine gas in the anolyte solution. In still another non-limiting example, a heating system is used to heat the anolyte solution to reduce the solubility of chlorine gas in the anolyte solution and, thereby, increase the rate at which the gas exits the anolyte compartment. In still another non-limiting example, the concentration of the alkali-chloride (such as NaCl or LiCl) in the anolyte solution is relatively high (e.g., between about 10 and about 40% by weight for NaCl or between about 10 and about 80% by weight for LiCl) to reduce the solubility of chlorine gas in the solution. In yet another non-limiting example, a hydrophobic membrane that is permeable to chlorine gas is placed over the anolyte compartment to allow the chlorine gas to escape from the compartment while preventing the anolyte solution from evaporating out of the anolyte compartment.

Problems solved by technology

Additionally, as some electrolytic reactions occur in the anolyte compartment, such reactions can result in proton and acid formation and, thereby, result in the corresponding lowering of pH within that compartment.

Low pH anolyte solutions in electrolytic cells having an alkali-conducting ceramic membrane may cause some challenges for cell operation—especially where the cell membrane is intolerant to such low pH conditions.

Accordingly, as the electrolytic cell operates and acid is produced in the anolyte compartment, the cell becomes less efficient or even inoperable.

In another example, acid produced in the anolyte compartment can actually damage the NaSICON-type or LiSICON-type membrane and thereby shorten the membrane's useful lifespan.

Thus, while electrolytic cells comprising a catholyte compartment and an anolyte compartment that are separated by a cation-conductive membrane are known, challenges still exist.

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