DE19603181A1 - Complete separation of anolyte and catholyte in electrochemical processes - Google Patents

Abstract

Complete separation of the anolyte and catholyte in the electrochemical production of bulk or fine chemicals is achieved using an ionic-conductive solid permeable membrane based on beta-alumina or another cation-conductive ceramic.

Description

It is known to make alcoholates by reacting alkali metal amalgam from chlorine-alkali electrolysis with an alcohol on an electrocatalytically active contact (see Ullmann's Encyclopedia of Technical Chemistry, Weinheim 1974, page 221 or Kirk-Otmer, Encyclopedia of Chemical Technology, Vol. 2, 3rd edition, Wiley, New York 1978).

An industrially widely practiced process for making simple Alcoholates is linked to chlor-alkali electrolysis using the amalgam process.

With this procedure it cannot be excluded that mercury in small amounts can get into the environment through exhaust air and waste water.

Traces of mercury can also remain in the alkali alcoholate formed.

The production of alcoholates is straight from the metal or through transesterification comparatively expensive compared to the amalgam process.

Another possibility is that in a process of the beginning given type in an electrolytic cell through the anode compartment and the cathode compartment a cation exchange membrane are separated and in the cathode compartment under water Substance development from alcohol alcoholate anions and in the anode compartment from the Alkali metal compound Alkali metal ions released and the latter through the cation exchange membrane be transported into the cathode compartment (EP-A 0 146 771).

A disadvantage of this method is the fact that the membrane and anode Can never completely separate the cathode compartment. This reduces the yield and the Purity of the products.  

The invention has for its object to avoid these disadvantages and thus bypassing the amalgam process, the production of basic and fine chemicals lien, especially the production of alcoholates from the alcohol in question and one To enable alkali metal compound.

Surprisingly, this object was achieved by a method according to the patent claims solved.

The invention relates to the use of an ion-conducting solid body bran as a separating element, which only the cations, but not the anions and the Allows solvent. The ion-conducting ceramic is used as the ion-conducting ceramic So-called β-alumina (doped aluminum oxide, approximate composition: Na₂O 11 Al₂O₃) used.

This is a mixture of stoichiometrically not precisely defined Sodium oxide and aluminum oxide. There are other compositions of these or other compounds possible, which provide a sodium ion-conducting ceramic, whereby the mobile sodium ions are exchanged for other cations can.

On both sides of the membrane there must be an anhydrous, opposite the Aluminum membrane not used (as acid) reactive solvent or no substance that meets this criterion may arise in the course of electrosynthesis not fulfilled. This is the most important requirement for using beta alumina as membrane material.

The working temperature should be chosen as high as possible. This favors the Conductivity of the membrane and the electrolyte as well as the dissolving power of the solvent used on the anode side for the cation-releasing Anode reagent.

The upper temperature limit represents the boiling point of the used Solvent. Beta Alumina is still effective even above 300 ° C. At Use of methanolic solutions (boiling point 67 ° C) was at 50 ° C worked to be able to do without a reflux condenser.  

example 1

An electrolysis of 0.15 m NaCl in MeOH as anolyte and 1 m MeOHa in MeOH performed.

Pt networks were used as electrodes as anodes and cathodes. 15 stitches / cm², 0.075 mm wire diameter.

So-called "doped β-Al₂O₃" was used as the ion-conducting ceramic.

With this arrangement, an electrolysis current of 50 m / cm² at 5 V cell voltage reached. 50 ° C was specified as the working temperature.

The current yield in relation to the amount of base formed was 100% quantitatively.

Contained traces of water react to alkali hydroxide and were therefore in the Determination of yield also recorded. Halide ions could not in the catholyte be detected.

The use of the solid membrane still offers the advantage of freedom in the choice of non-aqueous media on the anode and cathode side. In this manner can be many electro-organic processes with improved yield and Establish product purity.

Further processes can also run according to the method according to the invention:

• - Alkaline alcoholates of electrochemically reductively convertible alcohols and polyols
• - Generally all metal ion compounds Me⁺R⁻ with organic anion R⁻ and monovalent metal cation Me⁺, formally according to the following reaction equation be formed by electroreduction: R-X + e⁻ → R + X with R-X as any organic molecule and X as a leaving group

The counter ion required for the reaction (alkaline application) becomes from the anode reaction released and selectively transported from the ceramic membrane into the catholyte to deliver the reaction product Me⁺R⁻ there.

Claims (3)

1. Electrochemical process for the production of organic basic and fine chemicals, characterized in that an ion-conducting solid membrane based on β-alumina or other cation-conducting ceramics is used for the complete separation of the anolytes and catholytes. 2. The method according to claim 1, characterized, an anhydrous solvent on both sides of the solid membrane is used. 3. The method according to any one of the preceding claims, characterized, that by using the solid membrane alkali alcoholates from the alcohol and an alkali metal compound.