METHODS FOR ELECTROCHEMICAL DECHLORINATION OF ANOLYTE BRINE FROM NaCl ELECTROLYSIS

Abstract

Methods for the reductive post-treatment of NaCl-containing solutions, wherein such methods comprise: providing a NaCl-containing solution obtained from an anode side of an NaCl electrolysis cell, the solution comprising reducible components; and subjecting the solution to cathodic electrochemical reduction.

Description

BACKGROUND OF THE INVENTION[0001]Conventionally, membrane electrolysis methods are used, for example, for electrolyzing sodium chloride-containing solutions (see, e.g., Peter Schmittinger, CHLORINE, Wiley-VCH Verlag, 2000). A divided electrolysis cell can be used in this case, which divided cell consists of an anode compartment with an anode and a cathode compartment with a cathode. The anode and cathode compartments can be separated by an ion-exchange membrane. A sodium chloride-containing solution, also referred to hereinafter as brine, having a sodium chloride concentration of conventionally approx. 300 g / l, is introduced into the anode compartment of such a cell. The chloride ion in the brine is oxidized to yield chlorine on the anode, and the chlorine can then be conveyed out of the cell with the depleted sodium chloride-containing solution, also referred to herein as the anolyte brine, which can have a remaining sodiumchloride concentration of approx. 200 g / l.[0002]So that the...

AI Technical Summary

Benefits of technology

[0011]The methods according to the invention may be used to remove dissolved chlorine, hypochlorite which is still present, chlorate and other reducible compounds such as for example nitrogen trichloride, without reaction products passing into the NaCl-containing solutions, whereby markedly smaller quantities of the NaCl-containing solution have to be worked-up, or removed and discarded. The economic viability and environmental compatibility of NaCl electrolysis performed using the methods according to the various embodiments of the invention are markedly improved.

Problems solved by technology

One disadvantage of using sodium bisulfite and similar sulfur-containing compounds for chemical dechlorination is that sulfate arises in the NaCl solution as a reaction product of the chemical reduction with bisulfite or sulfur-containing compounds.

However, the sulfate cannot be electrochemically degraded, such that it gradually accumulates in the NaCl-containing solution.

Modern high performance ion exchange membranes are damaged by relatively high concentrations of sulfates, however.

An excessively high concentration of sulfate in the brine brings about the formation of oxygen on the anode and reduces current efficiency, so impairing the economic viability of the electrolysis method.

Damage to the coating of the anode is likewise possible.

In this way, large amounts of sodium chloride are lost, which has a negative effect on the economic viability and environmental compatibility of the electrolysis method.

One disadvantage of such methods is that sulfate formation is not prevented, but rather an additional method step is necessary in order to remove sulfate from the brine.