Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-02-08
2001-04-10
Phasge, Arun S. (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S530000, C204S531000, C204S541000
Reexamination Certificate
active
06214190
ABSTRACT:
The present invention relates to a process for isolating, by membrane electrodialysis, a catalyst from a solution containing it.
More precisely, it relates to the isolation of a catalyst used in an oxidation reaction by means of molecular oxygen in homogeneous phase.
Oxidation processes using homogeneous catalysis are relatively numerous. Thus, the oxidation of cycloalkanes to corresponding diacids can be carried out by employing a soluble salt of heavy metals like cobalt or manganese.
U.S. Pat. No. 2,223,493, published in December 1940, describes the oxidation of cyclic hydrocarbons to corresponding diacids, in liquid phase generally containing acetic acid, at a temperature of at least 60° C., with the aid of a gas containing oxygen and in the presence of an oxidation catalyst such as a cobalt compound. This patent envisages an isolation of the adipic acid formed by crystallization, but does not teach anything about the manner of recycling the catalyst into a new oxidation operation, nor, with still greater reason, about the activity which a catalyst recycled one or more times would possess.
Patent FR-A-2 722 783 describes a process for isolating and recycling a cobalt catalyst which has been used for the oxidation of cyclohexane to adipic acid, after separation of the main reaction products and of at least a proportion of the acetic acid solvent from the reaction mixture. This process consists essentially in extracting most of the catalyst with the aid of cyclohexane or of a mixture of cyclohexane and acetic acid. This process is efficient and the recycled catalyst has not lost its activity. However, it involves large quantities of solvent and requires several successive operations.
It therefore appears desirable to have available a process for isolating a homogeneous catalyst dissolved in a reaction mixture, which is equally efficient while being simpler to implement.
Patent FR-A-1 591 176 describes a process for recovering metal catalysts and nitric acid which are present in the mother liquors resulting from the separation of the reaction mass obtained during the nitric oxidation of cyclohexanol and/or of cyclohexanone, consisting in passing a proportion of the mother liquors containing the metal salts, the nitric acid and the organic acids into an electrodialysis cell. The metal catalysts employed are copper salts or vanadium salts.
Patent FR-A-2 026 288 describes a process for recovering a large proportion of nitric acid and of metal ions from an acidic residual liquid produced during the manufacture of adipic acid by liquid phase oxidation of cyclohexanone or cyclohexanol, including the introduction of this liquid into an electrodialysis device consisting of one or more electrodialysers, to recover the nitric acid and the metal ions in a recovery liquid which may be water or a dilute solution of nitric acid. The metal catalysts employed are copper salts or vanadium salts.
These two processes are very similar, or even identical, and use solutions containing high concentrations of nitric acid. This particular feature considerably promotes the separation of the metal salts, in the form of nitrates, of the undissociated carboxylic acids.
The present invention relates to the isolation of a homogeneous catalyst used in the oxidation of cyclohexane with oxygen and therefore not comprising nitric acid.
It relates more precisely to a process for isolating a homogeneous catalyst dissolved in a mixture also containing at least one aliphatic diacid, characterized in that the catalyst contains cobalt and the isolation is performed by membrane electrodialysis.
The homogeneous catalysts are metal compounds usually employed for the oxidation of cycloalkanes to aliphatic diacids. They are more particularly catalysts containing cobalt, alone or with other metals such as manganese, copper, iron, vanadium or cerium or mixtures of these metals. These metals are in the form of compounds which are soluble in the reaction mixture for cycloalkane oxidation. Such compounds are hydroxides, oxides and organic or inorganic salts. The preferred compounds are cobalt salts, alone or in combination with other compounds based on metals such as manganese and/or copper and/or iron and/or cerium and/or vanadium.
Examples of these cobalt salts which may be mentioned are cobalt chloride, cobalt bromide, cobalt nitrate and cobalt carboxylates such as cobalt acetate, cobalt propionate, cobalt adipate, cobalt glutarate or cobalt succinate. Since one of the solvents most frequently employed for the oxidation of cycloalkanes is acetic acid, cobalt acetate tetrahydrate is particularly preferred.
The mixture subjected to the membrane electrodialysis contains at least one diacid formed during the oxidation of the cycloalkane and often one or more other diacids also formed as by-products. It may also contain all the by-products of the reaction. When the catalyst is employed for the oxidation of cyclohexane, adipic acid is obtained predominantly, but so are glutaric acid and succinic acid, as well as more or less considerable quantities of cyclohexanol, cyclohexanone, cyclohexyl esters, lactones and hydroxycarboxylic acids.
Although the oxidation reaction is generally carried out in an organic solvent, preferably acetic acid in the case of cyclohexane oxidation, or, where appropriate, without solvent, the mixture to be electrodialysed preferably contains water.
The mixture in which the homogeneous catalyst is to be found therefore preferably includes water, it being possible for the solvent which may have been used in the process which has produced the solution to be treated to be entirely or partially replaced with water before the electrodialysis. The water generally represents from 10% to 100% of the solvent mixture of the solution subjected to the electrodialysis and preferably from 50% to 100% of this solvent mixture.
In its outline, electrodialysis is a process which, under the effect of a direct electrical field, enables the ionized species present in the solution to be treated to be extracted by migration through ion exchange membranes.
The electrodialysis apparatus used consists of various compartments bounded alternately by cationic membranes and anionic membranes. These compartments are divided into dilution compartments (D) which become depleted in compound to be isolated, that is to say in catalyst in the process of the invention, and concentration compartments (C) which, in contrast, become enriched in compound to be isolated.
In fact, under the action of the electrical field the cations in the solution to be treated migrate towards the cathode, leaving the compartment (D) where they are to be found, through a cation exchange membrane (cationic membrane). When they have moved into the next compartment (C), they cannot leave it because of the presence of the next anion exchange membrane (anionic membrane). Simultaneously, the anions migrate towards the anode, passing through an anionic membrane and enter an adjacent compartment (C), which they cannot subsequently leave because of the presence of the next cationic membrane.
Two adjacent compartments (C) and (D) form an electrodialysis cell. An electrodialyser comprises a stack of a number of cells. This number of cells per electrodialyser is generally as high as possible. For example, this number can advantageously vary between 10 and 500 cells.
In practice the anionic and cationic membranes are placed alternately in a system of filter-press type.
The homopolar membranes employed in the process of the invention are divided up into two large classes, according to their method of manufacture.
They are, first of all, heterogeneous membranes, prepared from ion exchange resins mixed with a binder such as polyvinyl chloride, polyethylene or the like. The combination thus formed can coat a screen like, for example, a polyester or polyacrylonitrile fabric.
They are also homogeneous membranes, obtained by introducing a functional group onto an inert support by chemical or radiochemical grafting. The chemical method, more widely employed, generally consists in func
Fache Eric
Horbez Dominique
Leconte Philippe
Burns Doane Swecker & Mathis L.L.P.
Phasge Arun S,.
Rhodia Fiber and Resin Intermediates
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