Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Patent
1997-07-17
1999-11-30
Phasge, Arun S.
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
204537, 204539, 204631, B01D 6144
Patent
active
059936290
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the field of electrodialysis and the subject of the invention is more particularly the regeneration of strong organic acids by electrodialysis using bipolar membranes.
BACKGROUND OF THE INVENTION
Acids and bases are important intermediates in the manufacture of a large number of chemicals. After they have been used, these acids and these bases generally are in the form of saline aqueous solutions from which it is necessary to strip them. For environmental and economic reasons, it is desirable to regenerate the initial acids and bases directly from the salts contained in these industrial effluents.
Electrodialysis using bipolar membranes enables such regeneration to be carried out. This known method uses electrical energy to dissociate the water of the saline solution and to recover the acid and the base separately according to the reaction: ##STR1##
In order to carry out this reaction and to keep the species separate, ion-exchange membranes and, more particularly bipolar membranes consisting of two faces, respectively selective to the anions and to the cations, are used. Under the influence of an electric field, these membranes allow the following reaction:
The H.sup.+ +OH.sup.- ions are then recombined respectively with the anions X.sup.- and cations M.sup.+ coming from the salt, and the species obtained are kept separate by conventional (monopolar) ion-exchange membranes in a three-compartment cell.
This method of regeneration from salts into acids and into bases has already been applied to many cases, for example: and the article by S. SRIDHAR "Elektrodialyse mit bipolaren Membranen [Electrodialysis using bipolar membranhes]" in Chem. Ing. Tech. 61 (1989) No. 5, pp. 428-429); 109(2): 11524u, 92(6): 43961f and 92(4): 25083s]; SRIDHAR); 30673m]; 5,221,443].
The bipolar membranes currently available on the market exhibit performance characteristics which vary depending on the technology used to manufacture them and depending on the supplier. Owing to their nature, bipolar membranes are in principle nonpermeable to cations and to anions which are respectively stopped by the anionic and cationic layers of the bipolar membrane.
DESCRIPTION OF THE INVENTION
The inventors have observed that, during the regeneration of strong organic acids from their salts, by electrodialysis using bipolar membranes, there was contamination of the acid obtained from the cation of the salt, in particular from sodium. This contamination, which varies depending on the level of concentration of the base chosen for working with, is highly problematic when it is desired to obtain an acid of high purity. Thus, in order to regenerate methanesulfonic acid (MSA) from aqueous solutions of mesylates, this contamination constitutes a very considerable obstacle when MSA has subsequently to be concentrated to a high level; the salt present in the acid also concentrates and, for a certain value of concentration, an MSA/salt of MSA/water ternary mixture precipitates and sets solid.
The inventors have determined that the contamination of the acid with alkaline cation comes from the base compartment, which is separated from the acid compartment by the bipolar membrane, and not from the salt compartment, which is separated from the acid compartment by a monopolar anionic membrane.
The inventors have thus found that in fact the bipolar membranes used hitherto exhibit cation leakage, in particular sodium leakage, causing contamination of the acid during the regeneration operation.
The inventors have then found that the permeability of the bipolar membranes to cations, in particular sodium, may be considerably reduced, without a substantial contrary effect on the electrodialysis process, by adding an anionic membrane on the anionic face of the bipolar membranes. The anion-exchange membranes have a very low transport number for cations and consequently constitute very effective barriers for limiting their diffusion. Joining together an anionic membrane A,10 and a bipolar membrane BP, as sho
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patent: 5288378 (1994-02-01), Chlanda
Chemical Abstracts 117:153850m "Use of bipolar membranes for ion exchange resin regenerant production", H. R. Bolton, J. Chem. Technol. Biotechnol. 1992, 54(4), 341-7.
Chemical Abstracts, vol. 109, p. 320, 115424u "On-site generation of acid and base with bipolar membranes: a new alternative to purchasing and storing regenerants", Davis, et al, Proc. --Int. Water Conf. Eng. Soc. West. Pa. 1987 48th 316-23.
Chemical Abstracts, vol. 92, 1980 p. 116, 43961f "Production of caustic soda amd hydrochloric acid from sea water by electrodialysis with bipolar membranes, Part 1. Current efficiency of acid and alkali." V. Greben, et al.
Chemical Abstracts, vol. 92, p. 168, 25083s Production of caustic soda and hydrochloric acid from sea water by electro dialysis with bipolar membranes, Part 2. Voltage drop across the membranes. V. Greben 1980.
Chemical Abstracts, vol. 116, p. 529, 182124n "Conversion of sodium butyrate in electrodialysis with bipolar membranes", Krasova, et al. 1991.
Chemical Abstracts, vol. 107 p. 419, 29755p Electrodialysis method with bipolar membranes for the regeneration of boric acid from a spent coolant, Dudnik, et al. 1985.
Chemical Abstracts, vol. 114, p. 431, 30673m "Electrodialysis of boron-containing solutions with the use of a bipolar membrane MB-2" Pilipenko, et al. 1990.
Organic Analytical Chemistry, vol. 71, p. 533, 5644f "Thin-layer chromatography for identification of isomeric ketones", Zalesskaya, et al. 1968.
Gancet Christian
Gavach Claude
Mirassou Alfred
Perie Frederic
Elf Atochem S.A.
Phasge Arun S,.
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