Catalyst – solid sorbent – or support therefor: product or process – Stabilized
Reexamination Certificate
2003-05-01
2004-08-10
Wilson, James O. (Department: 1624)
Catalyst, solid sorbent, or support therefor: product or process
Stabilized
C560S232000, C562S607000
Reexamination Certificate
active
06774083
ABSTRACT:
The aim of the present invention is a process for improving the stability and/or preventing the deactivation of the catalyst in processes of manufacture of acetic acid and/or of methyl acetate, as well as a complete process of manufacture of acetic acid and/or of methyl acetate comprising this process.
More specifically, the aim of the present invention is an improved process which enables improving the stability and/or preventing the deactivation of the catalyst in the cases of the processes of manufacture of acetic acid and/or of methyl acetate by isomerisation of methyl formate and optionally by carbonylation of methanol, in the presence of a catalytic system comprising at least one halogenated promoter and at least one iridium-based compound.
The invention also relates to the particular conditions under which this stabilisation process is applied in a particularly advantageous manner.
Various means of access to acetic acid and/or to methyl acetate are known and made use of industrially. Amongst these figures the reaction of carbonylation of methanol which is carried out in liquid phase, under pressure of carbon monoxide which is one of the reagents, in the presence of a homogenous catalytic system. Another means of access to acetic acid consists in carrying out the isomerisation of methyl formate. This reaction is, itself, generally carried out in the presence of a catalytic system in a homogenous phase. Finally, according to another process, the carbonylation of methanol and the isomerisation of methyl formate are carried out simultaneously.
The process of carbonylation with rhodium is a known process, which is made use of industrially, and which has been the subject of numerous articles and patents, such as, for example, American patents U.S. Pat. Nos. 3,769,329 and 3,813,428.
European patents EP 618 183 and EP 618 184, as well as European patents EP 785 919 and EP 759 022, describe a process of carbonylation in the presence of a catalytic system which is based on iridium and which, if need be, further contains rhodium.
A process of carbonylation with iridium and ruthenium, which is currently made use of industrially, is described in European patent EP 643 034.
More recently, a new means of access constituted by a methyl formate isomerisation reaction in the presence of iridium has been proposed in French patent FR 2,746,794 and International application WO 97/35829.
In parallel, a process of preparation of acetic acid and/or of methyl acetate is proposed in the patent FR 2,746,795 and the International application WO 97/35828, said process simultaneously makes use of a methyl formate isomerisation reaction and a methanol carbonylation reaction.
These various processes of production of acetic acid are generally carried out continuously in installations which essentially comprise three zones. The first corresponds to the reaction zone per se, which comprises a reactor under pressure in which the carbonylation and/or the isomerisation are carried out in liquid phase. The second is constituted by a zone for separating the acid formed. This operation is carried out by partial vaporisation of the reaction mixture in an apparatus called a flash apparatus wherein the pressure is maintained lower than in the reactor. The vaporised part is then sent into a third zone wherein the acetic acid is purified. This zone comprises, for example, various distillation columns in which the acetic acid produced is separated from the water, the reagents and the by-products. The part of the mixture which remains in the form of liquid leaving the vaporisation zone, and which notably comprises the catalyst, is recycled to the reactor.
It is known to the person skilled in the art that the second zone of the installations of production of acetic acid and/or of methyl acetate is generally the site of a deactivation and/or of a precipitation of the catalyst, and this whatever the process employed, amongst the processes described supra, be.
These phenomena are generally caused by the low carbon monoxide pressure which prevails in this zone, and these phenomena are accentuated by low water contents. In U.S. Pat. No. 5,237,097, a proposed solution consists in introducing carbon monoxide into the liquid supply to the flash, in order to maintain a sufficient partial pressure of said component in the flash.
French patent FR 2,726,556 and International application WO 96/14286 describe a process of injection of carbon monoxide into the liquid fraction originating from the flash, in order to reactivate the catalyst recycled to the reactor.
European patent EP 0 616 997 and the corresponding European Divisional Application EP 0 786 447 propose an improvement of the process of manufacture of acetic acid by carbonylation catalysed with iridium, this improvement consisting in maintaining the water content at higher than 0.5% by weight in the liquid fraction originating from the flash, in order to stabilise the catalyst present in this fraction.
The prior art does not propose any improvement in relation to the stabilisation of the catalyst in processes of manufacture of acetic acid and/or of methyl acetate by isomerisation of methyl formate and optionally processes of carbonylation of methanol catalysed with iridium.
The inventors of the present invention have now discovered in an entirely surprising way that the problem of the deactivation and of the destabilisation of the catalyst could be solved by the upkeep of a sufficient overall content of formic acid and of methyl formate in the liquid fraction originating from the flash and, this, even in the presence of a particularly low water content in this part of the installation, and even for water contents of less than 0.5% by weight with respect to the non-vaporised liquid fraction, and even in the almost absence of carbon monoxide in the medium although, up to present, the person skilled in the art considered that a relatively high water content, and in any case greater than 0.5%, was necessary in order to ensure the stability of the catalyst, and that a minimal carbon monoxide content enabled the catalyst to be stabilised.
Hence, the invention relates, according to a first object, to an improvement which can be applied to the processes of manufacture of acetic acid and/or of methyl acetate which make use of an iridium-based catalytic system, this improvement being intended for improving the stability and/or preventing the deactivation of the catalyst.
This stabilisation process enables lowering the water content considerably, both in the reaction medium and in the flash zone, and this constitutes a non-negligible advantage from an economical point of view, since it enables limiting costs in the additional step of recovery of the product formed. This stabilisation of the catalyst has thus enabled defining the conditions of an improved process of preparation of acetic acid and/or of methyl acetate which includes the improvement intended to stabilise the catalyst and according to which, furthermore, a particularly reduced water content is used.
Hence, according to a second aspect, the invention relates to a complete process of manufacture of acetic acid and/or of methyl acetate, under satisfactory conditions, both as regards the stabilisation of the catalyst, and the water concentration, and this constitutes a double advantage from an economical point of view with respect to the processes which exist at present.
More specifically, according to the first aspect supra, the invention relates to a process for improving the stability and/or preventing the deactivation of the catalyst in processes of manufacture of acetic acid and/or of methyl acetate according to which processes, in a first step, referred to as the reaction step, at least one methyl formate isomerisation reaction is carried out in liquid phase, in the presence of carbon monoxide and of a catalytic system comprising at least one halogenated promoter and at least one iridium-based catalytic compound, and, in a second step, referred to as the flash step, the partial vaporisation of the reaction medium ori
Layeillon Lise
Marchand Daniel
Patois Carl
Thiebaut Daniel
Acetex Chimie
Dennison Schultz Dougherty & MacDonald
Tucker Zachary C.
Wilson James O.
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