Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Patent
1997-06-03
1998-06-23
Geist, Gary
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C07C 5112
Patent
active
057707685
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The object of the present invention is a method for preparing carboxylic acids by carbonylation of a reagent, notably selected from the alcohols, in the presence of an iridium-based catalyst.
The carbonylation methods which use soluble iridium-based catalysts for the preparation of carboxylic acids are known methods. Generally, they are carried out in installations which essentially comprise three zones. The first corresponds to the actual reaction zone which comprises a reactor under pressure in which the carbonylation is effected. The second is constituted of a zone for separating the acid formed. This operation is carried out by partial vaporisation of the reaction mixture in an apparatus (called <<flash>>) wherein the pressure is maintained below that in the reactor. The vaporised part is then sent into a third zone wherein the carboxylic acid produced is purified. This zone comprises various distillation columns in which the carboxylic acid produced is separated from water, reagents, and by-products. The part of the mixture which has remained in liquid form upon leaving the vaporisation zone, and which notably comprises the catalyst, is recycled to the reactor. This is classically carried out by means of a pump.
During the implementation of these methods, a decrease in the activity of the catalyst was noticed after passing the unvaporised fraction comprising the catalyst several times in the recycling loop of the flash to the reactor.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is a method for preparing carboxylic acids by carbonylation in the presence of an iridium-based catalyst, in which method the catalyst is reactivated in a simple and efficient way.
Thus, the method for preparing carboxylic acids according to the invention consists in carrying out the reaction, in the presence of an iridium-based catalyst, in liquid phase in a first zone, then in partially vaporising the reaction mixture obtained in a second zone; the vaporised fraction, which contains the carboxylic acid produced, is subsequently purified and the unvaporised liquid fraction which contains the catalyst is recycled to the first zone. The characteristic of the method is that the unvaporised liquid fraction resulting from the second zone is placed in contact with carbon monoxide in such a way that said compound does not return to the second zone.
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and characteristics shall appear more clearly upon reading the following description and drawings, for which:
FIG. 1 represents a first embodiment in which the unvaporised fraction is placed in contact with gaseous carbon monoxide.
FIG. 2 represents a second embodiment in which carbon monoxide is dissolved in a part of the unvaporised liquid fraction resulting from the flash.
FIG. 3 represents a variant of the preceding embodiment in which carbon monoxide is dissolved in a part of the unvaporised liquid fraction resulting from the flash, which has been treated beforehand on an ion exchange resin.
DETAILED DESCRIPTION OF THE INVENTION
The method according to the invention enables preventing any loss of carbon monoxide, which is one of the reagents of the carbonylation. In fact, if this gas had been introduced for example into the actual flash zone, there would have been an inevitable loss of said compound. First of all, in order to obtain an effective amount of carbon monoxide so as to reactivate the catalyst, it is necessary to carry out industrially very significant outputs of said gas, even though the partial carbon monoxide pressure maintained is relatively low. Now, the implementation of significant outputs may have consequences on the installation itself, e. g. concerning the size of the fittings. Moreover, the dissolution of carbon monoxide can only be done correctly in the presence of strong stirring. Now a flash does not comprise such means. Thus, the major part of the flow of carbon monoxide under these conditions cannot be conserved in the flash, or a r
REFERENCES:
patent: 3772380 (1973-11-01), Paulik et al.
patent: 4381221 (1983-04-01), Isshiki et al.
patent: 5237097 (1993-08-01), Smith et al.
Denis Philippe
Perron Robert
Schwartz Joel
Acetex Chimie
Geist Gary
Keys Rosalynd
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