Method of purification of a redox mediator before electrolytic regeneration thereof

Abstract

A method for purifying a Redox mediator used in a chemical process of oxidation of organic compounds. The desired purification is obtained by recovering the mediator in the form of a solution and heating this solution to evaporate the volatile impurities contained in it and to oxidize the non volatile impurities into compounds which precipitate and are extracted by filtration. The purification takes place before the mediator is regenerated in the electrolysis cell. This prevents the impurities contained in the mediator solution to negatively affect the operation of this cell.

Description

[0001] The invention relates to a method for purifying a Redox mediator before electrolytic regeneration thereof during a chemical oxidation process of organic compounds.DESCRIPTION OF PRIOR ART[0002] It is well known that oxidation of unsaturated long chain fatty acids such as oleic acid, yields short chain fatty diacids, such as azelaic acid or pelargonic acid. Usually, such an oxidation is carried out with a solution of chromic (Cr VI) acid and sulfuric acid produced by electrolysis of an aqueous solution of chromium (Cr III) sulphate and sulfuric acid. During the electrolysis, hydrogen is released at the cathode and the chromium sulfate is converted into chromic acid and sulfuric acid at the anode (see U.S. Pat. No. 2,450,858 granted in 1948).[0003] When this type of oxidation (also called indirect electrosynthesis) is used, it is customary to recover the solution of chromium sulfate and sulfuric acid obtained after the oxidation reaction. The so-recovered solution is then recyc...

AI Technical Summary

Benefits of technology

[0014] More precisely, the object of the present invention is to provide a method that is both simple and efficient to solve the problem that was previously mentioned. This method essentially consists of purifying the solution containing the Redox mediator that is recovered from the oxidation reactor before introducing it into the electrolysis cell where the regeneration takes place. This purifying step is of a great importance since it allows removal of organic impurities that tend to deposit on the electrodes or consume regenerated mediator if they are not extracted from the electrolytic solution and which can therefore affect the operation of the electrolysis cell and the efficiency of the regeneration.

[0019] This series of steps constitutes the heart of the invention since it considerably increases the technical and economical feasability of the whole chemical process.

[0020] In this connection, it is worth mentioning that this method for purifying an electrolyte, is generic, economical and compatible with all the processes used for the treatment of an electrolyte in view of efficiently recycling it.

Problems solved by technology

A major difficulty of this process of recovering and regeneration of the electrolyte lies in the presence of organic impurities in the electrolytic solution.

This results in a reduction of the electrolysis current efficiency.

However, even in these cases, the presence of soluble organic compounds in the mediator solution recovered at the end of the reaction considerably affects the regeneration efficiency of the catalyst in an electrolytic cell.

More precisely, these compounds affect the current efficiency and the lifetime of the electrodes and they generate drawbacks of operation in continuous mode.

It turns out that the presence of organic compounds can block the surfaces of the electrodes and therefore reduce the production rate of the Redox mediator.

First of all, it is costly because the consumption of activated charcoal expressed in kg per kg of obtained product is high (this is a direct consequence of the low electrolyte concentration and therefore of the high V.sub.electrolyte / kg.sub.product ratio).

Secondly, after use, the activated charcoal must either be discarded or regenerated, but before doing so, the redox mediator must be recovered for economic and environmental reasons. Such can be done by washing the activated charcoal with water. However, concentrating the recovered redox reagent by evaporation is energy intensive. Handling of wet activated charcoal is also a labour intensive activity (this is a time consuming operation that results in higher labor costs and production costs).

Thirdly, this method cannot be used on non organic molecules and non-aromatic products having a low affinity for activated charcoal.

Secondly, oxidation of most of the organic molecules results in the formation of organic acids.

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