Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2001-05-31
2003-05-06
Raymond, Richard L. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06559339
ABSTRACT:
This application is a national stage application, filed under 35 U.S.C. 371, of PCT/FR99/0281, filed Sep. 14, 1999.
The present invention relates to a process for the crystallization of carboxylic acid, more particularly adipic acid, and a process for manufacturing crystalline carboxylic acid, more specifically a process for treating the reaction medium from the direct oxidation of a hydrocarbon into carboxylic acid such as adipic acid, for example.
Adipic acid is one of the two starting materials in the preparation of polyamides, such as polyamide 6-6, and of various other polymers. The applications of polyamide 6-6 require highly controlled properties in terms of both chemical and physicochemical composition. In order to obtain such a polymer, it is necessary to have very high purity at the stage of the monomers, such as adipic acid or dicarboxylic acids.
Adipic acid is also one of the important starting materials in the manufacture of polyurethanes.
Depending on the process for the synthesis of adipic acid, the impurities it contains are obviously different. However, it is always necessary to involve a step of purification of the adipic acid produced.
The purification processes generally used are crystallization processes using water as solvent. Such a process is described, for example, in French patent application No. 2,749,299.
However, depending on the synthetic process used and the nature of the product to be purified, the known crystallization solvent, namely water, does not allow certain impurities to be removed, such as organic impurities, for example.
One of the aims of the present invention is to provide a process for the crystallization of carboxylic acid, and more particularly of adipic acid, in solvents capable of removing the said organic impurities.
To this end, the invention provides a process for the crystallization of carboxylic acid, characterized in that the said crystallization or recrystallization is carried out from an organic solvent or a mixture of solvents, at least one of which is an organic solvent, in which the carboxylic acid has a solubility of less than or equal to 15% by weight at a temperature of 20° C., and in that the said solvent is chosen from the families of organic compounds comprising ether, alcohol, ketone, ester, nitrile, amide, sulphoxide or carbonate functions and halogen-containing, nitro or phosphorus-containing organic solvents.
According to a preferred characteristic of the invention, the organic solvent is chosen if the solubility of the carboxylic acid in the said solvent at a temperature of 100° C., or at its boiling point if this is lower than 100° C., is at least 5% higher than that at 20° C. in the same solvent, preferably 10% higher. Furthermore, the solubility at 100° C. should advantageously be at least 15% by weight.
The term “higher solubility” should be understood as meaning a difference in solubility as an absolute value.
The carboxylic acids which can advantageously be crystallized by the process of the invention are preferably dicarboxylic acids such as adipic acid, succinic acid, glutaric acid, terephthalic acid and isophthalic acid. The preferred carboxylic acid of the invention is adipic acid.
As solvents which are suitable for the process of the invention, mention may be made, for example, of 1,4-dioxane; diglyme (diethylene glycol dimethyl ether); aliphatic, cycloaliphatic, aromatic or arylaliphatic ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl phenyl ketone, cyclohexanone, tetrahydrofuran; n-butanol; isopropanol; 3-methoxyethanol; acetonitrile; dimethylformamide; acetamide; dichloromethane; ethyl acetate; 1,2-dichloroethane; dimethyl sulphoxide; nitromethane; N-methylpyrrolidone. This list is not exhaustive, the use of other organic solvents which satisfy the general criteria of solubility of the acids being included in the context of the present invention.
The organic solvents can be used alone or as mixtures with another solvent in accordance with the invention or otherwise. Thus, these organic solvents can be used with water.
Advantageously, the organic solvent of the invention has a boiling point which is compatible for carrying out the crystallization under industrially exploitable operating conditions. Thus, suitable solvents advantageously have a boiling point of between 40° C. and 250° C., preferably between 80° C. and 120° C. The crystallization can be performed at atmospheric pressure or under pressure.
The solvents which are suitable for the invention also advantageously have a certain affinity for water, allowing washing of the crystalline adipic acid with water to remove the traces of organic crystallization solvent.
The process of the invention is carried out according to the known techniques of crystallization processes. Briefly, this process comprises a step of dissolution under hot conditions of the carboxylic acid to be crystallized, followed by a step of cooling after optionally filtering the hot acid solution. It is also possible to concentrate the hot acid solution before it is cooled. This crystallization can be improved by any known means and in particular by the use of microwaves.
Needless to say, the crystallization process can be repeated. Similarly, the solution recovered after a crystallization can be concentrated while hot and then cooled in order to recover a further crop of acid.
The present process can be applied to carboxylic acids and more particularly to an adipic acid from various synthetic processes, such as, for example, the adipic acid from the nitric oxidation of cyclohexanol and/or cyclohexanone, from the double hydroxycarbonylation of butadiene or alternatively from the direct oxidation of cyclohexane in air.
The process of the invention applies particularly to the process for the hydroxycarbonylation of butadiene, which consists of a first hydroxycarbonylation of butadiene leading to a mixture of pentenoic acids, mainly 3-pentenoic acid, and a second hydroxycarbonylation performed on the pentenoic acids obtained in the first reaction and leading to adipic acid also containing a certain amount of 2-methylglutaric acid and 2-ethylsuccinic acid, as well as other compounds already originating from the first hydroxycarbonylation reaction, such as &ggr;-valerolactone, unconverted pentenoic acids and methylbutenoic acid. These organic impurities are advantageously removed by a crystallization process in accordance with the invention.
The process of the invention also applies more particularly to the treatment and recovery of carboxylic acid such as adipic acid synthesized by direct oxidation of a hydrocarbon such as cyclohexane with air. This process is described in particular in patent application WO-A-94/07834.
This document describes the oxidation of cyclic hydrocarbons into the corresponding diacids, in a liquid phase comprising a solvent, using a gas containing oxygen and in the presence of an oxidation catalyst such as a cobalt compound, the said solvent comprising an organic acid containing only primary or secondary hydrogen atoms. That patent more particularly develops the phases for treating the final reaction mixture. This treatment consists in separating the diacid formed, by cooling the mixture in order to bring about precipitation of the said diacid, in separating, by filtration, the diacid from two liquid phases, a nonpolar phase which is recycled, and a polar phase which is also at least partially recycled after an optional hydrolysis and a separation of an additional amount of diacid.
That patent more particularly provides a solution for the one-step oxidation of cyclohexane into adipic acid with industrially acceptable selectivity, but it does not provide an industrially applicable solution to the treatment of the reaction mixture obtained from the oxidation, taking into account the separation of the various products and by-products of the reaction, the unconverted materials and in particular the recycling of the catalyst.
Patent EP-A-0,772,581 describes a more complete process for treating the rea
Costantini Michel
Fache Eric
Burns Doane Swecker & Mathis L.L.P.
Raymond Richard L.
Rhodia Fiber & Resin Intermediates
Tucker Zachary C.
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