Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-05-03
2002-01-15
Keys, Rosalynd (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S607000, C562S608000
Reexamination Certificate
active
06339171
ABSTRACT:
FIELD OF INVENTION
This invention relates to a novel process for the removal of permanganate reducing compounds and alkyl iodides formed by the carbonylation of methanol in the presence of a Group VIII metal carbonylation catalyst. More specifically, this invention relates to a novel process for reducing and/or removing precursors of permanganate reducing compounds and alkyl iodides from intermediate streams during the formation of acetic acid by said carbonylation processes.
BACKGROUND OF THE INVENTION
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 comprises rhodium, either dissolved or otherwise dispersed in a liquid reaction medium or else supported on an inert solid, along with a halogen containing catalyst promoter as exemplified by methyl iodide. The rhodium can be introduced into the reaction system in any of many forms, and it is not relevant, if indeed it is possible, to identify the exact nature of the rhodium moiety within the active catalyst complex. Likewise, the nature of the halide promoter is not critical. The patentees disclose a very large number of suitable promoters, most of which are organic iodides. Most typically and usefully, the reaction is conducted with the catalyst being dissolved in a liquid reaction medium through which carbon monoxide gas is continuously bubbled.
An improvement in the prior art process for the carbonylation of an alcohol to produce the carboxylic acid having one carbon atom more than the alcohol in the presence of a rhodium catalyst is disclosed in commonly assigned U.S. Pat. Nos. 5,001,259, issued Mar. 19, 1991; 5,026,908, issued Jun. 25, 1991 and 5,144,068, issued Sep. 1, 1992 and European patent 161,874 B2, published Jul. 1, 1992. As disclosed therein acetic acid is produced from methanol in a reaction medium comprising methyl acetate, methyl halide, especially methyl iodide, and rhodium present in a catalytically effective concentration. The invention therein resides primarily in the discovery that catalyst stability and the productivity of the carbonylation reactor can be maintained at surprisingly high levels, even at very low water concentrations, i.e. 4 weight (wt) % or less, in the reaction medium (despite the general industrial practice of maintaining approximately 14 wt % or 15 wt % water) by maintaining in the reaction medium, along with a catalytically effective amount of rhodium, at least a finite concentration of water, methyl acetate and methyl iodide, a specified concentration of iodide ions over and above the iodide content which is present as methyl iodide or other organic iodide. The iodide ion is present as a simple salt, with lithium iodide being preferred. The patents teach that the concentration of methyl acetate and iodide salts are significant parameters in affecting the rate of carbonylation of methanol to produce acetic acid especially at low reactor water concentrations. By using relatively high concentrations of the methyl acetate and iodide salt, one obtains a surprising degree of catalyst stability and reactor productivity even when the liquid reaction medium contains water in concentrations as low as about 0.1 wt %, so low that it can broadly be defined simply as “a finite concentration” of water. Furthermore, the reaction medium employed improves the stability of the rhodium catalyst, i.e. resistance to catalyst precipitation, especially during the product recovery steps of the process wherein distillation for the purpose of recovering the acetic acid product tends to remove from the catalyst the carbon monoxide which in the environment maintained in the reaction vessel, is a ligand with stabilizing effect on the rhodium. U.S. Pat. Nos. 5,001,259, 5,026,908 and 5,144,068 are herein incorporated by reference.
It has been found that a low water carbonylation process for the production of acetic acid reduces such by-products as carbon dioxide, hydrogen, and propionic acid. However, the amount of other impurities, present generally in trace amounts, is also increased, and the quality of acetic acid sometimes suffers when attempts are made to increase the production rate by improving catalysts, or modifying reaction conditions.
These trace impurities affect quality of acetic acid, especially when they are recirculated through the reaction process. Among the impurities, which decrease the permanganate time of the acetic acid, are carbonyl compounds, and unsaturated carbonyl compounds. As used herein, the phrase “carbonyl” is intended to mean compounds which contain aldehyde or ketone functional groups which compounds may or may not possess unsaturation. See
Catalysis of Organic Reaction
, 75, 369-380 (1998), for further discussion on impurities in a carbonylation reaction system.
The present invention is directed to reduction and/or removal of permanganate reducing compounds (PRC's) such as acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, and 2-ethyl butyraldehyde and the like, and the aldol condensation products thereof. It also leads to reduction of propionic acid. Reduction of other impurities include alkyl iodides such as ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide, and the like.
It is desirable to remove alkyl iodides from the reaction product since traces of these impurities (in the acetic acid product) tend to poison the catalyst used in the production of vinyl acetate, the product most commonly produced from acetic acid. The present invention is thus also directed to removal of alkyl iodides, in particular C
2-12
alkyl iodide compounds. The carbonyl impurities may further react with iodide catalyst promoters to form multi-carbon alkyl iodides, e.g., ethyl iodide, butyl iodide, hexyl iodide and the like. Since many impurities originate with acetaldehyde, it is therefore a primary objective to remove or reduce the acetaldehyde and alkyl iodide content in the reaction system.
Conventional techniques to remove impurities include treatment of acetic acid with oxidizers, ozone, water, methanol, activated-carbon, amines, and the like, which treatment may or may not be combined with distillation of the acetic acid. The most typical purification treatment involves a series of distillations of the final product. It is known to remove carbonyl impurities from organic streams by treating the organic streams with an amine compound such as hydroxylamine which reacts with the carbonyl compounds to form oximes followed by distillation to separate the purified organic product from the oxime reaction products. However, the additional treatment of the final product adds cost to the process and it has been found that 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 above described low water carbonylation process and purification treatment, frequently remains deficient with respect to the permanganate time. This is due to the presence therein of small proportions of residual impurities. Since a sufficient permanganate time is an important commercial test, which the acid product must meet for many uses, the presence therein of such impurities that decrease permanganate time is objectionable. The removal of minute quantities of these impurities from the acetic acid by conventional treatment and distillation techniques is not economically or commercially feasible by distillation since the impurities have boiling points close to that of the acetic acid product.
It is important to determine where in the carbonylation process impurities can be removed. It is also important to determine by what economically viable process impurities can be removed without risk of further contamination to the final product or unnecessary added costs. JP patent application 5-169205 dis
Blay George A.
Karnilaw Michael L.
Meilchen Melchior A.
Singh Madan
Tanke Robin Suzanne
Celanese International Corporation
Keys Rosalynd
Mullen James J.
Spiering M. Susan
LandOfFree
Removal or reduction of permanganate reducing compounds and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Removal or reduction of permanganate reducing compounds and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Removal or reduction of permanganate reducing compounds and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2835181