Method of recycling a catalyst in a reaction involving the direc

Details Method of recycling a catalyst in a reaction involving the direc Method of recycling a catalyst in a reaction involving the direc

1997-02-26

1998-05-26

Geist, Gary

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

562590, 562593, C07C 5131, C07C 5100, C07C 5142

Patent

active

057568375

DESCRIPTION:

BRIEF SUMMARY
This application was filed as a 35 U.S.C. .sctn.371 of PCT/FR95/00944, which designated the United States.
The present invention relates to the field of the one-step oxidation of cyclohexane to adipic acid, using a gas containing oxygen, in liquid phase and in he presence of a catalyst containing cobalt.
The direct oxidation of cyclohexane to adipic acid is a process which has been worked at for a long time, in particular on account of the obvious advantages there would be in converting cyclohexane into adipic acid, in a single step and without using an oxidant such as nitric acid, this compound generating nitrogen oxides which must then be treated in order to avoid any contamination.
Thus, American patent U.S. Pat. No. 2,223,493, published in December 1940, describes the oxidation of cyclic hydrocarbons to corresponding diacids, in a liquid phase generally containing acetic acid, at a temperature of at least 60.degree. C., using a gas containing oxygen and in the presence of an oxidation catalyst such as a cobalt compound. This patent makes provision for a separation of the adipic acid formed by crystallization, but teaches nothing about the manner of recycling the catalyst, in a new oxidation operation, and less still about the activity which a catalyst that has been recycled one or more times would have.
Patent Application WO-A-94/07833 describes a similar process, specifying that the solvent represents less than 1.5 mol per mole of cyclic hydrocarbon, that the said solvent comprises an organic acid having only primary or secondary hydrogen atoms and that the reaction is carried out in the presence of at least 0.002 mol of cobalt-based catalyst per 1000 g of reaction mixture. At the end of the reaction, the diacid formed in isolated.
Patent Application WO-A-94/07834, filed on the same day as the above patent application, also describes the same process, but develops the phases for the treatment of 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, and in separating by filtration the diacid from two liquid phases, a non-polar one which is recycled, and a polar one which is also recycled after an optional hydrolysis and a separation of an additional mount of diacid.
These various patents present solutions which allow the one-step oxidation of cyclohexane to adipic acid with an industrially acceptable selectivity, but they do not address the specific problem of the progressive and relatively rapid deactivation of the catalyst during its recycling.
Indeed, when the reaction mixture obtained from the cyclohexane oxidation reaction is cooled in order to crystallize some of the adipic acid, and then filtered in order to separate out this precipitated adipic acid, the filtrate thus obtained contains the catalyst, residual adipic acid, the reaction by-products (especially glutaric acid, succinic acid, cyclohexanol, cyclobextaone, hydroxycaproic acid and cyclohexyl esters), the arencted cyclohexane, the acetic acid solvent and the water formed.
Some of these various compounds definitely influence the deactivation of the catalyst. In the process described in Patent Application WO-A-94/07834, the larger part of these various compounds is recycled to the oxidation, optionally after addition of further amounts of cyclohexane and optionally after separation of an additional amount of adipic acid remaining in the mixture. It turns out that when the catalyst and the various by-products are recycled in a new oxidation reaction, relatively rapid deactivation of the catalyst is observed. Thus, it is indicated in the various examples of WO-A-94/07834 that the rate of formation of the adipic acid decreases by 26% to 43% after four cycles of the catalyst.
One of the subjects of the present invention is thus to allow the recycling of the cobalt catalyst with little or no deactivation.
In order to achieve this aim, the process of the invention includes a step for the treatment of the reaction mixture obtained durin

REFERENCES:
patent: 2223493 (1940-12-01), Loder
patent: 4202797 (1980-05-01), Jones

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