Process for producing acetic acid

Details Process for producing acetic acid Process for producing acetic acid

1996-12-13

1998-03-03

Geist, Gary

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

562517, C07C 5112, C07C 5110

Patent

active

057236607

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/JA96/01087, filed Apr. 22, 1996.


BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a novel process for producing acetic acid formed by carbonylating at least one selected from methanol, methyl acetate, and dimethyl ether in the presence of an eighth group metal-containing catalyst. More specifically, the present invention relates to a novel process for producing high purity acetic acid, wherein organic iodine compounds and carbonyl compounds which are impurities contained in the product are reduced in producing acetic acid formed by rhodium-catalyzed carbonylation while notably reducing energy necessary for purifying it.
2. Description of the Related Art
Acetic acid is used in large quantities as a raw material for acetic esters, acetic anhydride, vinyl acetate, and terephthalic acid and is an essential compound necessary for many industries including the polymer industry and the chemical industry.
Various processes are known as an industrial process for producing acetic acid. At present, a process in which methanol is continuously reacted with carbon monoxide in the presence of water using a rhodium catalyst and methyl iodide is widely employed as the industrial process for producing acetic acid (JP-B-47-3334).
According to a process for producing acetic acid by carbonylation of methanol, which is described in Applied Industrial Catalysis written by R. T. Eby and T. C. Singleton, vol. 1. pp. 275 to 296, 1983, crude acetic acid is purified by the continuous three distillation steps shown below. That is, (1) a low boiling components-separating column for separating low boiling components in the top part and high boiling components in the bottom part from side stream crude acetic acid in order to circulate them into a carbonylation reactor; (2) a dehydrating column for separating water from the side stream crude acetic acid wirthdrawn from the above column and circulating the separated water into the carbonylating reactor; and (3) a high boiling components-removing column for separating by-produced propionic acid from dried acetic acid. Since in this kind of process, a water content in a carbonylation reactor is as relatively high as 14 to 15 wt %, and a lot of propionic acid is by-produced, an enormous amount of purifying energy is necessary for obtaining product acetic acid.
In this process for producing acetic acid by carbonylation of methanol, the reaction conditions and a process for improving catalysts have recently been investigated, and for example, a process in which a catalyst stabilizer such as iodide salts is added is disclosed (JP-A-60-54334 and JP-A-60-239434). It is disclosed therein that the amounts of by-products such as carbon dioxide and propionic acid can be decreased by reducing a water content in a carbonylation reactor. Further, it is proposed that a purifying process for obtaining product acetic acid can be simplified by reducing a water content in a reactor (JP-A-6-040999). However, when the water content in the carbonylation reactor is decreased, the components which increase in amounts as the productivity of acetic acid grows and deteriorate the quality of product acetic acid are included in by-produced trace impurities. Components which particularly exert influences to some kind of applications are included as well in these trace impurities. For example, catalysts used for producing vinyl acetate from ethylene and acetic acid are very sensitive to these impurities (JP-A-4-282339). It is also known that impurities contained in acetic acid thus obtained are, to be concrete, carbonyl compounds such as acetaldehyde, crotonaldehyde and 2-ethylcrotonaldehyde, and organic iodine compounds such as hexyl iodide (JP-A-1-211548 and JP-B-5-21031). It is known as well that among the products shown above, the carbonyl compounds such as acetaldehyde, crotonaldehyde and 2-ethylcrotonaldehyde deteriorate assay values in a quality test by which the amounts of trace reductive impurities present in acetic acid are determined, wh

REFERENCES:
patent: 5371286 (1994-12-01), Blay et al.
patent: 5599976 (1997-02-01), Scates et al.
patent: 5663430 (1997-09-01), Morris et al.

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