Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1998-10-23
2001-04-03
Wilson, James O. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C560S232000, C562S890000
Reexamination Certificate
active
06211405
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to homogeneous carbonylation catalyst systems, and more particularly to multimetal homogeneous carbonylation catalyst system stabilized and co-promoted with a soluble inorganic iodide salt, in particular, an alkali metal or alkaline earth metal salt or quaternary iodide salt of nitrogen or phosphorus.
DESCRIPTION OF RELATED ART
Producing acetic acid by means of methanol carbonylation with a rhodium salt catalyst is a well-known commercial process as disclosed in U.S. Pat. No. 3,769,329 issued by Paulik et al. and described by Eby and Singleton (
Appl. Ind. Catal.
1,275, (1983). U.S. '329 discloses the use of organic halides such as methyl iodide to promote the reaction. It is stated in U.S. '329 that a substantial quantity of water, typically about 14-15 wt % is necessary to attain a high reaction rate. Hjortjaer and Jensen (
Ind. Eng. Chem; Proc. Res. Dev.
16, 281-285 (1977)) have shown that increasing the reaction water from about a finite amount to about 14 wt % increases the reaction rate of methanol carbonylation. However having a large amount of water present in the process incurs an expensive operating cost to separate water from the acetic acid product desired.
It has been found that under the Paulik et al. conditions at lower than 14-15 wt % water content in a carbonylation reaction system, the carbonylation rate decreases significantly and the rhodium catalyst tends to destabilize and thus precipitate out of the reaction system.
U.S. Pat. Nos. 5,001,259; 5,026,908; and 5,144,068, Smith et al., disclose a method to solve the difficulties of high reaction water and catalyst destabilization described above. These patents disclose the use of a rhodium salt catalyst in a low water carbonylation system, i.e., water concentration from at least a finite amount to less than 14 wt %, preferably less than 7 wt %. The carbonylation reaction is further promoted and the catalyst is stabilized to prevent precipitation by using a soluble alkali or alkaline earth metal iodide salt, i.e, such as lithium iodide, or by using a soluble quaternary ammonium or phosphonium iodide salt.
A disadvantage of the process described in U.S. '259 et al. is described in U.S. Pat. No. 5,155,265; U.S. Pat. No. 5,155,266; U.S. Pat. No. 5,202,481; U.S. Pat. No. 5,206,434; U.S. Pat. Nos. 5,371,286, and 5,783,731. The process increases the concentration of iodide, unsaturates, and carbonyl impurities. These patents stress the necessity to remove these impurities from the process.
Another disadvantage of the process of U.S. '259 et al. is that as the water content is decreased, so is the rate of reaction. Therefore efforts have been directed at maintaining and increasing the rate of reaction under water conditions of less than 14-15 wt %. A method of increasing the rate of reaction, as shown in the U.S. '608, is to increase the hydrogen partial pressure in the reaction system. Increasing hydrogen partial pressure can be accomplished by having hydrogen in the carbon monoxide feedstock fed to the carbonylation reaction. Commercial carbon monoxide feedstocks frequently contain hydrogen as an impurity, and under normal circumstances, there is no need to remove these impurities.
U.S. Pat. No. 4,994,608 stresses the necessity to control the hydrogen in the carbon monoxide feed to reduce the formation of carbon dioxide. In addition to having hydrogen present in the carbon monoxide feed, hydrogen can be generated in-situ by the competing water-gas shift reaction that occurs during the reaction. Thus, because of the formation of this in-situ hydrogen, the amount of hydrogen in the carbon monoxide feed is suggested in U.S. '608 to be from about 0.3 to about 10 mol %.
The iridium-catalyzed methanol carbonylation process as described in EP 752,406 stresses the necessity to maintain a low hydrogen concentration in the carbon monoxide feed to the reactor to avoid the formation of hydrogenated by-products. Iridium is a strong hydrogenation catalyst under the conditions of the iridium-catalyzed process. Therefore, the amount of hydrogen in the carbon monoxide feed is suggested in EP '406 to be less than 0.3 mol % and the partial pressure of hydrogen in the carbonylation reactor to be less than 0.3 bar.
Methods disclosed in the art to enhance the rate of carbonylation with catalysts containing rhodium include the use of promoters. EP 643,034 describes the use of ruthenium or osmium as co-promoters. EP 618,813 broadly describes the use of rhodium as a promoter to enhance the rate of iridium catalyzed carbonylation reactions. Similarly, GB 2,298,200 broadly describes the use of ruthenium, osmium, or rhenium with rhodium also as a co-promoter to enhance the iridium-catalyzed carbonylation reaction.
However, it is not clear from these references whether iridium could be added to a rhodium-catalyzed system when inorganic iodide salts are present. Ionic iodides, such as the alkali or alkaline earth metal iodides, had been previously thought to inhibit and consequently deactivate the iridium catalyst. Dekleva and Forster in
Adv. Catalysis,
34, 81 (1986) and references cited therein, particularly Forster,
J. Chem. Soc., Dalton Trans.,
1979, p. 1639, have indicated that ionic iodides decrease the rate of methanol carbonylation when an iridium catalyst is employed.
The use of rhodium salt and iridium salt catalysts for methanol carbonylation is disclosed in Canadian 2,120,407 and GB 2,298,200. Can '407 and GB '200 also teach that ionic iodides poison the iridium catalyst. It is suggested therein to limit the amount of ionic iodides from 0 to about 2 wt %. Sources of ionic iodides include: 1) from alkali or alkaline earth metals as a promoter; 2) from corrosion metals common in the reaction system; and 3) from phosphonium or ternary ammonium ions as promoters.
More recent patent publications also teach that the use of alkali metal iodides and alkaline earth iodides are to be avoided in the iridium-catalyzed carbonylation. These references include WO 98/22420, EP 846 674 A1, EP 849 248 A1, EP 849 251 A1. Although, EP 849 248 A1 indicates that under certain conditions wherein the water concentration in the reactor is at or below that at which the maximum in the graph of carbonylation rate versus water concentration occurs, iodides of alkali metals and alkaline earth metals may be added. It is taught that under these conditions the presence of iodide ion in high concentration may be detrimental, when the carbonylation catalyst is solely iridium. No mention therein is made of the use of alkali metal or alkaline earth metal iodides in a mixed rhodium-iridium catalyzed carbonylation reaction by generating iodide ions in the liquid reactor composition.
EP 752,406 cautions to minimize the ionic contaminants derived from corrosion metals, particularly, nickel, iron and chromium, or phosphines and nitrogen containing compounds, or ligands which may quaternize in situ due to the belief that these ions also poison the iridium salt catalyst system. The poisoning occurs by generating iodide ion in the liquid reaction composition which has an adverse effect on the reaction rate.
The present invention addresses the technical difficulties described above. Disclosed is a method to improve the rate of carbonylation while maintaining the stability of the rhodium catalyst and limiting the formation of impurities.
SUMMARY OF THE INVENTION
The present invention relates to a process for producing a carboxylic acid by carbonylation of an alkyl alcohol and/or a reactive derivative thereof, i.e. an alkyl ester or ether, in the presence of a homogeneous catalyst of rhodium salt, an ionic iodide catalyst stabilizer/co-promoter, iridium salt, and an alkyl iodide promoter. The ionic iodide stabilizer/co-promoter may be in the form of a soluble salt of an alkali metal or alkaline earth metal salt or a quaternary ammonium or phosphonium salt that will generate an effective amount of iodide ion in the reaction solution. The stabilizer/co-promoter is preferably a so
Cheung Hung-Cheun
Sibrel Elaine C.
Tanke Robin S.
Torrence G. Paull
Celanese International Corporation
Deemie Robert W.
Spiering M. Susan
Wilson James O.
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