Process for improving the purity of quaternary ammonium hydroxides by electrolysis in a two-compartment cell
View Patent ↗The present invention relates to a process for purifying a recycle base solution waste stream of a composition comprising a quaternary ammonium hydroxide comprising the steps of (a) providing an electrolysis cell which comprises an anolyte compartment containing an anode, a catholyte compartment containing a cathode, and a cation-selective membrane separating the anolyte and catholyte compartments, (b) charging the recycle base solution waste stream comprising the quaternary ammonium hydroxide to be purified to the anolyte compartment and charging water, optionally containing a quaternary ammonium hydroxide, to the catholyte compartment, (c) passing a current through the electrolysis cell to produce a purified aqueous quaternary ammonium hydroxide solution in the catholyte compartment, (d) recovering the purified aqueous quaternary ammonium hydroxide solution from the catholyte compartment, (e) washing the anolyte compartment with a suitable solvent, and (f) repeating steps (b)-(e). The process is particularly suitable for improving the purity of an aqueous solution comprising tetramethyl ammonium hydroxide, which was used in the production of 4-aminodiphenylamine for a number of reaction cycles.
1. A process for purifying a recycle base solution waste stream of a composition comprising a quaternary ammonium hydroxide comprising the steps of
(a) providing an electrolysis cell which consisting of an anolyte compartment containing an anode, a catholyte compartment containing a cathode, and a cation-selective membrane separating the anolyte and catholyte compartments,
(b) charging the recycle base solution waste stream comprising an aqueous solution of the quaternary ammonium hydroxide that was used in the production of 4-aminodiphenylamine, to be purified to the anolyte compartment and charging water, optionally containing a quaternary ammonium hydroxide, to the catholyte compartment,
(c) passing a current through the electrolysis cell to produce a purified aqueous quaternary ammonium hydroxide solution in the catholyte compartment,
(d) recovering the purified aqueous quaternary ammonium hydroxide solution from the catholyte compartment,
(e) washing the anolyte compartment with a suitable solvent to dissolve solid materials fouling the anode and the anolyte compartment, the suitable solvent being one selected from the group of aniline, N,N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide, and
(f) repeating steps (b)-(e).
2. The process according to claim 1 wherein the anolyte compartment is charged with an aqueous solution comprising tetramethyl ammonium hydroxide (TMAH).
3. The process according to claim 1 wherein the anolyte compartment is charged with an aqueous solution containing 5 to 40 wt. % of TMAH.
4. The process according to claim 1 wherein the recycle base solution waste stream further comprises aniline.
5. The process according to claim 1 wherein the catholyte compartment is charged with an aqueous solution of a quaternary ammonium hydroxide, which is the same as the quaternary ammonium hydroxide present in the composition to be purified.
6. The process according to claim 5 wherein the catholyte compartment is charged with an aqueous 5 to 25 wt. % TMAH solution.
7. The process according to claim 1 wherein the electrolysis is stopped once a ph of 1 to 7, preferably 4 to 7, is reached in the anolyte compartment.
8. The process according to claim 1 wherein the cation-selective membrane is a perfluorinated membrane.
9. The process according to claim 1 wherein between steps e) and f) the process further comprises the step of washing the anolyte compartment with water.
10. The process according to claim 1 wherein the recycle base solution waste stream comprises a quaternary ammonium hydroxide and a quantity of a quaternary ammonium salt or a mixture of quaternary ammonium salts that can be converted to the quaternary ammonium hydroxide by electrolysis.
11. The process according to claim 10 wherein the recycle base solution waste stream comprises TMAH and at least one of tetramethyl ammonium carbonate and tetramethyl ammonium hydrogen carbonate.