Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1998-09-23
2002-05-28
Geist, Gary (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S518000, C562S519000, C562S607000, C560S232000
Reexamination Certificate
active
06395927
ABSTRACT:
BACKGROUND OF THE INVENTION
The object of the present invention is the preparation of acetic acid and/or methyl acetate, by using an isomerisation reaction and a carbonylation reaction.
Various means of access to acetic acid are known and used industrially. Amongst these is the carbonylation reaction of methanol. This carbonylation reaction may notably be carried out in the liquid phase, under the pressure of carbon monoxide, which is one of the reagents, in the presence of a homogeneous catalytic system comprising a compound based on rhodium and/or iridium and an iodinated promoter.
Another means of access is constituted by the isomerisation reaction of methyl formate in the presence of a catalyst based on rhodium or iridium.
The known iridium-catalysed isomerisation methods are carried out under a nitrogen atmosphere. It has in fact been noted that the carbon monoxide did not bring about any particular advantage during the reaction and could even be the cause of a certain inhibition of the isomerisation reaction, it favouring side reactions. It is to be noted that such a behaviour is entirely different from that which is observed when the catalytic system is rhodium-based, in which case the presence of carbon monoxide is essential for keeping the metal in the homogeneous phase. This iridium-catalysed type of method, whose interest is not questioned here, does not have any real interest industrially since the reaction which is described therein is not sufficiently efficient. In fact, the reaction rates are only in the order of 2 mol/h/l of acid and/or ester produced.
It has been proposed, in order to improve the results of the above-mentioned method, to use the isomerisation reaction in the presence of a strong acid of the sulphonic acid type, such as paratoluenesulphonic acid for example. Under the conditions of this method, the reaction is carried out using significant amounts of methyl formate to be isomerised, which is consequently also used as solvent for the reaction. If this improvement contributes to the improvement of the activity of the reaction, it does nevertheless have the disadvantage of necessitating the use of a further compound, which does not simplify the method.
Further, it is possible that this acid degrades under the conditions of the composition of the reaction medium and its use.
SUMMARY OF THE INVENTION
An aim of the present invention is to propose a method of preparation of acetic acid and/or methyl acetate in carrying out simultaneously an isomerisation reaction of methyl formate and a carbonylation reaction of a reagent which provides a methyl radical, such as methanol for example.
Such a method has the advantage of softening the functioning conditions of the isomerisation method or even of that of carbonylation.
In fact, it is possible to use commercial methyl formate, i. e. that contains up to a few percent of methanol, and it is noted that the presence of this alcohol brings about its contribution to the production of acetic acid and/or the corresponding ester. Furthermore, the possibility of carrying out the isomerisation of methyl formate may enable increasing the capacity of production of an installation of methanol carbonylation, without taking on the high investments necessary for increasing the production of carbon monoxide which is one of the reagents employed for this reaction.
Furthermore, and whether it be in one or the other above cases, to bring about a diversification of the reagents is an advantage which is well understandable.
It is entirely remarkable that, despite implementation conditions which are not a priori favourable to it, the carbonylation reaction takes place with a good productivity.
These and other goals are met by the present invention which has therefore for object the preparation of acetic acid and/or methyl acetate, by reaction of reagents which provide formyl radicals and reagents which provide methyl radicals, in the presence of carbon monoxide, water, a solvent and a catalytic system comprising at least one halogenated promoter and at least one iridium-based compound. According to this method, a partial carbon monoxide pressure is kept between 0.1·10
5
Pa and 25·10
5
Pa, and an amount of reagents which provide the formyl radicals of below or equal to 20% by weight of the reaction mixture, and the reagents which provide the methyl and formyl radicals are fed in in a molar ratio of methyl radicals to the formyl radicals of greater than 1.
The above conditions enable simultaneously carrying out the isomerisation of the ester coming from the formyl radicals and the carbonylation of the methyl radicals fed in.
It has in fact been noted, on the contrary to what was asserted in the prior art, that the presence of carbon monoxide was essential for the isomerisation reaction of the ester in the presence of iridium.
Furthermore, the carbon monoxide is consumed and intervenes as reagent in the carbonylation reactor.
According to the second characteristic above, the content of reagent providing the formyl radicals is kept at lower than 20% by weight of the reaction mixture.
Furthermore, the ratio of the methyl radicals to the formyl radicals enables determining the nature of the reaction(s) which are carried out during the method. In fact, when this ratio is equal to 1, only the isomerisation reaction is carried out and this leaves the context of the present invention, whereas if this ratio is greater than 1, both the isomerisation and carbonylation reactions take place.
DETAILED DESCRIPTION OF THE INVENTION
The method of the invention is carried out in the presence of a catalytic system which comprises at least one halogenated promoter and at least one iridium-based compound.
The halogenated promoter, which represents one of the constituents of the catalytic system, is selected preferably from iodinated compounds.
The halogenated promoter may be in the form of iodine, alone or in combination with other elements such as for example hydrogen, a C
1
-C
10
alkyl radical, a C
1
-C
10
acyl radical, or even alkali metal iodides or metal iodides, such as transition metal iodides, or iodides of metals of column IIA of the periodic classification of the elements.
It is to be noted that the halogenated promoter may be constituted of a mixture of several of the above-mentioned promoters.
The context of the present invention shall not be left in preparing said alogenated promoters in situ with the aid of appropriate precursors.
According to a particularly advantageous embodiment of the invention, the halogenated promoter is selected from iodine, hydroiodic acid, methyl iodide, aluminium iodide, chromium iodide, lithium iodide, potassium iodide; these compounds being used alone or as mixtures. Preferably, the halogenated promoter comprises iodine and a methyl-type radical.
Furthermore, the amount of halogenated promoter kept during the reaction is more particularly between 0.1 and 20% by weight of the reaction mixture. Preferably, the halogenated promoter content is between 1 and 15% by weight of the reaction mixture.
It is to be noted that the amounts of promoter indicated above are given as an indication. In fact, the person skilled in the art has even to find the optimal compromise between, on the one hand, a maximal efficiency of this compound, which has a beneficial effect on the activity and the stability of the catalyst, and on the other hand, economical considerations linked to the cost engaged in the recycling of this compound in the method.
The second element of the catalytic system used in the method according to the invention is constituted by at least one iridium-based compound.
First of all, the reaction according to the invention is more particularly carried out in the presence of a homogeneous catalyst. In other words, this signifies that the iridium-based compound is notably in a form which is soluble in the reaction mixture. It is to be noted that the presence of a part of said iridiumbased compound in a non-dissolved form does not present any major difficulty for the implementation of the reaction.
All the iridiu
Patois Carl
Perron Robert
Thiebaut Daniel
Acetex Chimie
Deemie Robert W.
Dennison, Scheiner & Schultz
Geist Gary
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