Process for producing carboxylic acid anhydrides

Abstract

The present invention relates to a process for producing carboxylic acid anhydrides, in which a carboxylic acid ester, derived from an alcohol and a carboxylic acid, and carbon monoxide containing a small amount of hydrogen are used as raw materials and subjected to a carbonylation reaction in a liquid reaction medium in the presence of a Group VIII B catalyst to produce a carboxylic acid anhydride. The reaction medium comprises the Group VIII B catalyst, an organic halide, the carboxylic acid ester, an alkali metal salt, at least one organic promoter, the carboxylic acid anhydride and the carboxylic acid, wherein the organic promoter is selected from at least one of the following structural forms (I), (II) and (III). According to the process of the present invention, the reaction rate of the carbonylation reaction is increased by the use of the specified organic promoters.

Description

FIELD OF THE INVENTION [0001]The present invention relates to a process for producing carboxylic acid anhydrides by way of the carbonylation reaction of a derivative from an alcohol and a carboxylic acid with carbon monoxide, and in particular, a process for producing acetic anhydride by way of the carbonylation reaction of methyl acetate with carbon monoxide, which is characterized in that in a catalytic system containing a Group VIII B catalyst, one or more organic compounds are added as the promoter to increase the reaction rate, so that the operational range for the reaction can be extended, enabling the reaction to be carried out under milder conditions.BACKGROUND TO THE INVENTION[0002]Acetic anhydride is a well-known raw material widely used in the chemical industry, which is mainly used for producing chemicals such as cellulose acetate and is an important raw material for synthesizing medicines, flavors, dyes, etc. There are currently three industrial processes for producing ...

AI Technical Summary

Benefits of technology

[0024]The main object of the present invention is to produce carboxylic acid anhydrides under anhydrous conditions, which can also increase the reaction rate.

[0028]Compared with the aforementioned prior art, the process of the present invention is using different organic promoters, which can form a stable complex compound with the Rh catalyst and has the effect of increasing the carbonylation reaction rate. The addition of alkali metal iodine salts in the conventional anhydrous carbonylation process has the effect of stabilizing rhodium; however, the sequent purification, separation and deiodination processes for the product have resulted in much trouble. The addition of organic promoters can increase the carbonylation reaction rate and reduce the sequent operation of the equipment for the deiodination process, which has the advantage of reducing the cost of purifying the acetic anhydride product.

Problems solved by technology

Among these processes, the ketene process, which belongs to an old-fashioned process and is small in scale, is adopted by many manufacturers and is thus predominant; however, the largest-scale single process for commercially producing acetic anhydride at present is the methyl acetate carbonylation process due to the high energy consuming and other drawbacks of the ketene process.

The reaction temperature of this process is up to 750° C.; therefore, this process will gradually go out of use in the future for its high energy-consuming demand.

However, according to the disclosure of this patent, the reaction requires a time of several hours to several tens hours, depending on the conditions, and the conversion rate is substantially low.

However, this patent describes neither what structures of heterocyclic aromatic compounds are effective and how much performance they improve, nor the influence of addition of metal iodide salts.

However, this patent does not disclose the difference in performance between the organic promoters and the aromatic organic additives.

Although the organic compounds as mentioned in the above patent all need to be used with a metal co-catalyst such as an iodide containing lithium, Tin, aluminum, etc., yet there is no disclosure of the improved performance of the reaction after the addition of organic promoters to the metal iodides that have been contained in the original reaction composition.

However, this patent does not disclose the influence of the catalyst stabilizer on the reaction rate under low water content conditions or even anhydrous conditions, and the examples of applying the catalyst stabilizer in an acetic anhydrides process.

Also, the catalyst stabilizer is liable to, with rhodium, form a hardly soluble complex, which will be precipitated from the solution.

However, although this patent discloses the stabilizing effect of the iodide stabilizer but does not investigate the influence of the acetic anhydride process under anhydrous conditions on the reaction rate.

However, these patents do not investigate the performance of addition of organic additives.

However, this patent does not investigate the influence of addition of organic promoters on the space-time yield of acetic anhydrides.

Images