Process for the production of acetic acid

Abstract

A process for the reduction and / or removal of permanganate reducing compounds formed by the carbonylation of methanol in the presence of a Group VIII metal carbonylation catalyst to produce acetic acid is disclosed. More specifically, a process for reducing and / or removing permanganate reducing compounds or their precursors from intermediate streams during the formation of acetic acid by said carbonylation processes is disclosed. In particular, a process in which a low boiling overhead vapor stream from a light ends column is subjected to a single distillation to obtain an overhead that is subjected to an extraction to selectively remove and / or reduce PRC's from the process is disclosed.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to a process for the production of acetic acid and, in particular, to an improved process for the reduction and / or removal of permanganate reducing compounds formed by the carbonylation of methanol in the presence of a Group VIII metal carbonylation catalyst to produce acetic acid. More specifically, this invention relates to an improved process for reducing and / or removing permanganate reducing compounds or their precursors from intermediate streams during the formation of acetic acid by said carbonylation processes. [0003] 2. Technical Background [0004] Among currently employed processes for synthesizing acetic acid, one of the most useful commercially is the catalyzed carbonylation of methanol with carbon monoxide as taught in U.S. Pat. No. 3,769,329, issued to Paulik et al. on Oct. 30, 1973. The carbonylation catalyst contains rhodium, either dissolved or otherwise dispersed in a liquid re...

AI Technical Summary

Benefits of technology

[0017] This invention relates to a process for the production of acetic acid and, in particular, an improved process for the reduction and/or removal of permanganate reducing compounds and alkyl iodides formed by the carbonylation of methanol in the presence of a Group VIII metal carbonylation catalyst to produce acetic acid. More specifically, this invention relates to an improved process for reducing and/or removing permanganate reducing compounds or their precursors from intermediate streams during the formation of acetic acid by said carbonylation processes.

[0018] In one aspect, the present invention provides a process for the reduction and/or removal of permanganate reducing compounds (PRC's) formed in the carbonylation of a carbonylatable reactant to produce a carbonylation product comprising acetic acid. The process comprises the steps of: (a) separating the carbonylation product to provide a vapor overhead stream comprising acetic acid and a less volatile catalyst phase; (b) distilling the vapor overhead stream to yield a purified acetic acid product and a low boiling overhead vapor stream comprising methyl iodide, water, acetic acid, methyl acetate, and at least one PRC; (c) condensing the low boiling overhead vapor stream and biphasically separating it to form a condensed heavy liquid phase and a condensed light liquid phase; (d) distilling the condensed light liquid phase in a single distillation column to form a second vapor phase stream overhead and a higher boiling liquid phase residuum, wherein the second vapor phase stream is enriched with PRC's with respect to the condensed light liquid phase; and (e) condensing the second vapor phase stream and extracting the condensed stream with water to obtain an aqueous acetaldehyde stream comprising PRC and a raffinate comprising methyl iodide. In certain variations, the process can be operated with or without a sidestream comprising methyl acetate being taken from the distillation column of step (d).

[0019] In another aspect, the present invention provides a process for the reduction and/or removal of permanganate reducing compounds (PRC's) formed in the carbonylation of a carbonylatable reactant to produce a carbonylation product comprising acetic acid, comprising the steps of: (a) separating the carbonylation product to provide a vapor overhead stream comprising acetic acid and a less volatile catalyst phase; (b) distilling the vapor overhead stream to yield a purified acetic acid product and a low boiling overhead vapor strea

Problems solved by technology

These trace impurities affect quality of acetic acid, especially when they are recirculated through the reaction process, which, among other things, can result in the build up over time of these impurities.

However, the additional treatment of the final product adds cost to the process, and distillation of the treated acetic acid product can result in additional impurities being formed.

While it is possible to obtain acetic acid of relatively high purity, the acetic acid product formed by the low-water carbonylation process and purification treatment described above frequently remains somewhat deficient with respect to the permanganate time due to the presence of small proportions of residual impurities.

Because a sufficient permanganate time is an important commercial test, which the acid product may be required to meet to be suitable for many uses, the presence of impurities that decrease permanganate time is objectionable.

Moreover, it has not been economically or commercially feasible to remove minute quantities of these impurities from the acetic acid by distillation because some of the impurities have boiling points close to that of the acetic acid product or halogen-containing catalyst promoters, such as methyl iodide.

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