Method for recovering performance of electrolyzer for use in production of polysulfide and method for stopping holding electrolyzer

Abstract

In an electrolyzer comprising an anode compartment provided with porous anodes, a cathode compartment, and a membrane providing a partition between the anode compartment and the cathode compartment, wherein a solution containing sulfide ions is introduced into the anode compartment, and an aqueous solution containing caustic soda is introduced into the cathode compartment, thereby producing a polysulfide containing polysulfide sulfur through electrolytic oxidation, wherein the anode compartment of the electrolyzer is cleaned with the use, of an aqueous solution containing at least either one of an inorganic acid, a chelating agent, and a scale-cleaning agent, thereby recovering performance of the electrolyzer. Further, when the contents of the anode compartment are replaced with an alkaline aqueous solution containing not more than 0.1 mass % of sulfide ions and not more than 0.1 mass % of carbonate ions upon stopping the electrolytic oxidation, thereby maintaining the performance of the electrolyzer.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a method for recovering performance of an electrolyzer for use in production of polysulfide by electrolytic oxidation of a white liquor or a green liquor, a method for stopping-holding an electrolyzer and a method for efficiently producing polysulfide by making use of the method for recovering the performance of the electrolyzer and the method for stopping-holding the electrolyzer.BACKGROUND OF THE INVENTION[0002]To attain a higher production yield at the time of production of chemical pulp is an important issue for effective utilization of wood resources. There is available a polysulfide cooking process as one of high yield technologies for production of kraft pulp currently in the mainstream of the chemical pulp. As disclosed in, for example, JP 61-259754 A, and JP 53-92981 A, a digesting liquor in the polysulfide cooking process is produced by oxidizing an alkaline aqueous solution containing sodium sulfide, the so-call...

AI Technical Summary

Benefits of technology

[0010]More specifically, it is an object of the invention to provide a method for recovering performance of an electrolyzer, important to maintain the performance of the electrolyzer over the long term, and a method for producing polysulfide by making use of, or taking advantage of the method for recovering the performance of the electrolyzer, with the use of an electrolyzer comprising an anode compartment provided with porous anodes, a cathode compartment, and a membrane providing a partition between the anode compartment and the cathode compartment, capable of obtaining polysulfide sulfur in high concentration from an aqueous solution containing sulfide ions by an electrolytic process, particularly capable of producing a digesting liquor containing polysulfide sulfur in high concentration from a white liquor, or a green liquor, in a pulp production process, at a high selectivity, and at high current efficiency, with very low generation of thiosulfate ions as a by-product.

[0013]More specifically, it is another object of the invention to provide a method for stopping-holding electrolytic oxidation, important to maintain the performance of an electrolyzer for use in production of polysulfide, and a method for producing polysulfide by making use of, or taking advantage of the method for stopping-holding electrolytic oxidation with the use of an electrolyzer comprising an anode compartment provided with porous anodes, a cathode compartment, and a membrane providing a partition between the anode compartment and the cathode compartment, capable of obtaining polysulfide sulfur in high concentration from an aqueous solution containing sulfide ions in an aqueous solution containing sulfide ions by an electrolytic process, particularly capable of producing a digesting liquor containing polysulfide sulfur in high concentration from a white liquor, or a green liquor, in a pulp production process, at a high selectivity, and at high current efficiency, with very low generation of thiosulfate ions as a by-product.

[0023]By virtue of the aspects (1), (2) of the invention, it becomes sufficiently possible to remove scales that are formed due to calcium and other trace constituents being precipitated on the membrane, so that the anode does not undergo dissolution. Accordingly, a voltage required for electrolytic oxidation can be effectively restored (lowered) even if a rise in the voltage occurs over time.

[0024]By virtue of the aspects (3), (4) of the invention, it is possible to prevent a voltage required for electrolytic oxidation from rising above that before stopping-holding of electrolytic oxidation when electrolytic oxidation is resumed after stopping-holding of electrolytic oxidation in the electrolyzer.

Problems solved by technology

The electrolyzer described as above had a problem in that calcium and other trace constituents, contained in the solution introduced into the anode compartment, were precipitated on the membrane to be turned into scales, to thereby induce an increase in the membrane resistance, causing a rise in voltage.

This problem is economically undesirable because it will bring about an increase in electricity required for production of polysulfide.

Further, it is not easy to remove impurities, such as calcium and so forth, deposited on the membrane, and if an attempt is made to clean impurities with a strong acid, this will raise a possibility that an anode corrosion problem occurs.

Those problems are taken as a first issue.

With the method for producing polysulfide with the use of the electrolyzer described as above, a problem has been encountered in that when electrolytic oxidation is started again after stopping-holding of the electrolytic oxidation, a voltage required for electrolytic oxidation becomes higher than before stopping of the electrolytic oxidation.

This problem is undesirable because it will bring about an increase in electricity required for production of polysulfide as is the case with the first issue.

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