Method for preparation of acetic anhydride and acetic acid by means of carbonyl synthesis of methyl acetate and methanol azeotrope and method for separation

Abstract

The invention discloses a method for preparation of acetic anhydride and acetic acid by means of carbonyl synthesis of methyl acetate and methanol azeotrope. The synthesis reaction is operated in a carbonyl synthesizing kettle (1) which is provided with a mixer, a bypass circulation device controlled by a high-pressure pump and a gas distributor (8) at the bottom. The method includes steps of adding azeotrope and catalyst from the upper portion of the kettle, and gaseous carbon monoxide is fed into the kettle from the bottom of the kettle through the gas distributor (8). The internal pressureof the kettle is 3.0-4.5MPa, and the reaction temperature is 140-220 GEG C. The catalyst includes rhodium catalyst, catalysis-supporting methyl iodide and lithium acetate, the rhodium catalyst with the concentration ranging from 200ppm to 800ppm is selected from rhodium triiodide or rhodium chloride, adding quantity of the methyl iodide is 10-30% of that of the azeotrope, and the concentration ofthe lithium acetate is two to three times of that of the rhodium catalyst. Reaction liquid sequentially passes through a flash evaporation kettle (2), a light component removing tower (3), an acetic acid tower (4) and an acetic anhydride tower (5) to obtain acetic anhydride with purity higher than 97% and acetic acid with purity higher than 99%. The method effectively resolves the problem of comprehensive utilization of methyl acetate and methanol azeotrope.

Description

1. Technical field [0001] The invention relates to a method for preparing basic organic chemical raw materials acetic anhydride and acetic acid. To be precise, the by-product methyl acetate and methanol azeotrope in the production of polyvinyl alcohol are used as raw materials, and the carbonylation synchronously generates acetic anhydride and acetic acid and separates them. method. 2. Background technology [0002] The traditional preparation methods of acetic anhydride include the ketene method using acetic acid as raw material, the oxidation method using acetaldehyde as raw material, etc. In recent years, there has been a direct carbonylation method of methyl acetate and CO under the action of a rhodium catalyst. The traditional preparation methods of acetic acid include acetaldehyde oxidation, butane liquid-phase oxidation, methanol high-pressure carbonylation and methanol low-pressure carbonylation, etc. [0003] Polyvinyl alcohol is prepared by reacting polyvinyl acet...

AI Technical Summary

Problems solved by technology

The production of one ton of polyvinyl alcohol requires 1.5 tons of methyl acetate and methanol azeotrope as a by-product. The methyl acetate and methanol azeotrope cannot be used in the production of polyvinyl alcohol, and the separation is difficult. It needs to be hydrolyzed into acetic acid and methanol. It can be used in production after separation and purification, which consumes a lot of steam and discharges a lot of waste water

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