United States Patent
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`Singh et al.
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`[19]
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`[11] Patent Number:
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`[45] Date of Patent:
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`6,143,930
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`Nov. 7, 2000
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`US006143930A
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`4—338357
`5—140024
`5—169204
`9-40590
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`11/1992
`Japan .
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`6/1993
`Japan .
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`7/1993
`Japan .
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`2/1997
`Japan .
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`OTHER PUBLICATIONS
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`CRC Press, 56th ED., Periodic Table, 1975-1976.
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`Watson, Derrick J ., “The Cativa Process for the Production
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`of Acetic Acid”, Catalysis of Organic Reactions, 75, pp.
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`369-380 (1998).
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`Primary Examiner—Samuel Barts
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`Assistant Examiner—Rosalynd Keys
`Attorney, Agent, or Firm—Susan Spiering
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`[57]
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`ABSTRACT
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`Disclosed is a method to manufacture high purity acetic
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`acid. Although described in relation to that produced by a
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`low water carbonylation process the present invention is
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`applicable to other mechanisms for production of acetic acid
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`which results in formation of permanganate reducing com-
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`pounds such as acetaldehyde, propionic acid, and alkyl
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`iodide impurities in intermediate process streams. It has
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`been found that permanganate reducing compounds and
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`alkyl iodides may be conveniently removed from a light
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`phase of an intermediate stream in the reaction process by
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`employing a multiple distillation process coupled with an
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`optional extraction of acetaldehyde. The distillation process
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`involves first distilling a light phase to concentrate the
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`permanganate reducing compounds, and in particular the
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`acetaldehyde, and then separating the permanganate reduc-
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`ing compounds and alkyl iodides in a second distillation
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`tower. The second distillation serves to remove the perman-
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`ganate reducing compounds and alkyl iodides from methyl
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`iodide, methyl acetate, and methanol mixture. As an optional
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`third step, the twice distilled stream may be directed to an
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`extractor to remove any remaining quantities of methyl
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`iodide from the aqueous acetaldehyde stream to obtain
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`acetic acid as a final product in greater than 99% purity.
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`It has been found that this process removes at least 50% of
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`the permanganate reducing compounds and alkyl iodides
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`and at least 20% of the propionic acid impurity from the
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`intermediate light phase stream, and results in lower alkyl
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`iodide concentration in the carbonylation reaction process,
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`and in particular in the carbonylation reactor.
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`It has also been found that during shut down of the inventive
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`process, polymers of acetaldehyde tend to form in the base
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`of the second distillation tower. To avoid or minimize the
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`formation of these polymers, a constant flow of solvent is
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`passed through the base of the column.
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`18 Claims, 1 Drawing Sheet
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`CE Ex. 2006
`Daicel v. Celanese
`|PR2014—00173
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`[54] REMOVAL OF PERMANGANATE
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`REDUCING COMPOUNDS AND ALKYL
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`IODIDES FROM A CARBONYLATION
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`PROCESS STREAM
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`[75]
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`Inventors: Madan Singh; George A. Blay, both of
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`Corpus Christi; Michael L. Karnilaw,
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`Houston, all of Tex.; Melchior A.
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`Meilchen, Koenigstein, Germany;
`Wayne David Picard; Valerie
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`Santillan, both of Houston, Tex.; Mark
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`O. Scates, Friendswood, Tex.; Robin
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`Suzanne Tanke; G. Paull Torrence,
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`both of Corpus Christi, Tex.; Richard
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`F. Vogel, Jr., League City, Tex.; R. Jay
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`Warner, Corpus Christi, Tex.
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`[73] Assignee: Celanese International Corp, Dallas,
`Tex.
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`[21] Appl. No.: 08/951,952
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`Filed:
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`Oct. 17, 1997
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`[22]
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`Related U.S. Application Data
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`[51]
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`[63] Continuation-in-part of application No. 08/735,361, Oct. 18,
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`1996, abandoned.
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`Int. Cl.7 ......................... .. C07C 51/42; C07C 51/12;
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`C07C 67/36
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`......................... .. 562/608; 562/519; 560/232
`[52] U.S. Cl.
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`[58] Field of Search ................................... .. 562/519, 608;
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`560/232
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`[56]
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`References Cited
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`U.S. PATENT DOCUMENTS
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`3,769,329
`10/1973 Paulik et al.
`.......................... .. 260/488
`
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`3/1991 Smith etal.
`.......................... .. 562/519
`5,001,259
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`6/1991 Smith et al.
`.... ..
`.. 562/519
`5,026,908
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`5,057,192 10/1991 Zoeller et al.
`203/46
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`5,144,068
`9/1992 Smith etal.
`.... ..
`.. 562/519
`
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`5,262,014
`11/1993 Cooper et al.
`203/53
`
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`3/1996 Fillers et al.
`.... ..
`562/608
`5,502,249
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`4/1997 Miura et al.
`.......................... .. 562/519
`5,625,095
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`.
`2/1997 Yoshiaki et al.
`9,040,590
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`FOREIGN PATENT DOCUMENTS
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`079461
`3/1992 China .
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`11/1985 European Pat. Off.
`161874 B2
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`5/1992 European Pat. Off.
`487284 B1
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`0 687 662 12/1995
`European Pat. Off.
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`687662 A2 12/1995
`European Pat. Off.
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`61-2052
`1/1986
`Japan .
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`Japan .
`61-56151
`3/1986
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`4—201464
`7/1992
`Japan .
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`.
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`1
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`

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`U.S. Patent
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`Nov. 7, 2000
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`6,143,930
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`8
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`_..O_n_
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`2
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`

`
`6,143,930
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`
`
`1
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`REMOVAL OF PERMANGANATE
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`REDUCING COMPOUNDS AND ALKYL
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`IODIDES FROM A CARBONYLATION
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`PROCESS STREAM
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`This application is a CIP of 08/735,361 filed Oct. 18,
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`1996, which is now abandoned.
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`FIELD OF INVENTION
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`This invention relates to a novel process for the removal
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`iodides
`of permanganate reducing compounds and alkyl
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`formed by the carbonylation of methanol in the presence of
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`a Group VIII metal carbonylation catalyst. More
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`specifically, this invention relates to a novel process for
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`reducing and/or removing permanganate reducing com-
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`pounds and alkyl iodides from intermediate streams during
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`the formation of acetic acid by said carbonylation processes.
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`BACKGROUND OF THE INVENTION
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`Among currently employed processes for synthesizing
`acetic acid one of the most useful commercially is the
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`catalyzed carbonylation of methanol with carbon monoxide
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`as taught in U.S. Pat. No. 3,769,329 issued to Paulik et al on
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`Oct. 30, 1973. The carbonylation catalyst comprises
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`rhodium, either dissolved or otherwise dispersed in a liquid
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`reaction medium or else supported on an inert solid, along
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`with a halogen containing catalyst promoter as exemplified
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`by methyl iodide. The rhodium can be introduced into the
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`reaction system in any of many forms, and it is not relevant,
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`if indeed it is possible, to identify the exact nature of the
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`rhodium moiety within the active catalyst complex.
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`Likewise, the nature of the halide promoter is not critical.
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`The patentees disclose a very large number of suitable
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`promoters, most of which are organic iodides. Most typi-
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`cally and usefully, the reaction is conducted with the catalyst
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`being dissolved in a liquid reaction medium through which
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`carbon monoxide gas is continuously bubbled.
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`An improvement in the prior art process for the carbony-
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`lation of an alcohol to produce the carboxylic acid having
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`one carbon atom more than the alcohol in the presence of a
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`rhodium catalyst is disclosed in commonly assigned U.S.
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`Pat. Nos. 5,001,259, issued Mar. 19, 1991; 5,026,908, issued
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`Jun. 25, 1991 and 5,144,068,
`issued Sept. 1, 1992 and
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`European patent 161,874 B2, published Jul. 1, 1992. As
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`disclosed therein acetic acid is produced from methanol in a
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`reaction medium comprising methyl acetate, methyl halide,
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`especially methyl iodide, and rhodium present in a catalyti-
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`cally effective concentration. The invention therein resides
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`primarily in the discovery that catalyst stability and the
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`productivity of the carbonylation reactor can be maintained
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`at surprisingly high levels, even at very low water
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`concentrations, i.e. 4 weight (wt) % or less, in the reaction
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`medium (despite the general industrial practice of maintain-
`ing approximately 14 wt % or 15 wt % water) by maintain-
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`ing in the reaction medium, along with a catalytically
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`effective amount of rhodium, at least a finite concentration
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`of water, methyl acetate and methyl
`iodide, a specified
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`concentration of iodide ions over and above the iodide
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`content which is present as methyl iodide or other organic
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`iodide. The iodide ion is present as a simple salt, with
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`lithium iodide being preferred. The patents teach that the
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`concentration of methyl acetate and iodide salts are signifi-
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`cant parameters in affecting the rate of carbonylation of
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`methanol to produce acetic acid especially at low reactor
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`water concentrations. By using relatively high concentra-
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`tions of the methyl acetate and iodide salt, one obtains a
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`10
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`45
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`65
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`2
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`surprising degree of catalyst stability and reactor productiv-
`ity even when the liquid reaction medium 0 contains water
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`in concentrations as low as about 0.1 wt %, so low that it can
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`broadly be defined simply as “a finite concentration” of
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`water. Furthermore,
`the reaction medium employed
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`improves the stability of the rhodium catalyst, i.e. resistance
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`to catalyst precipitation, especially during the product recov-
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`ery steps of the process wherein distillation for the purpose
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`of recovering the acetic acid product tends to remove from
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`the catalyst the carbon monoxide which in the environment
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`maintained in the reaction vessel, is a ligand with stabilizing
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`effect on the rhodium. U.S. Pat. Nos. 5,001,259; 5,026,908
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`and 5,144,068 are herein incorporated by reference.
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`It has been found that a low water carbonylation process
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`for the production of acetic acid reduces such by-products as
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`carbon dioxide and propionic acid. However, the amount of
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`other impurities, present generally in trace amounts, is also
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`increased, and the quality of acetic acid sometimes suffers
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`when attempts are made to increase the production rate by
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`improving catalysts, or modifying reaction conditions.
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`These trace impurities affect quality of acetic acid, espe-
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`cially when they are recirculated through the reaction pro-
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`cess. Among the impurities which decrease the permanga-
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`nate time of the acetic acid are carbonyl compounds,
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`unsaturated carbonyl compounds, and organic iodides. As
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`used herein,
`the phrase “carbonyl” is intended to mean
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`compounds which contain aldehyde or ketone functional
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`groups which compounds may or may not possess unsat-
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`uration.
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`The present invention is directed to removal of perman-
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`ganate reducing compounds (PRC’s) such as acetaldehyde
`which leads to formation of unsaturated aldehydes and other
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`carbonyl impurities such as acetone, methyl ethyl ketone,
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`butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, and
`2-ethyl butyraldehyde and the like, and the aldol condensa-
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`tion products thereof. Other PRC’s include alkyl iodides
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`such as ethyl iodide, propyl iodide, butyl iodide, pentyl
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`iodide, hexyl iodide, and the like. Still other PRC’s include
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`propionic acid, a by-product of the acetic acid process.
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`PRC’s typically have boiling points very close to those of
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`iodide catalyst promoters (e.g., Mel) and it is difficult to
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`sufficiently remove alkyl iodides. It is desirable to remove
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`alkyl iodides from the reaction product since traces of these
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`impurities (in the acetic acid product) tend to poison the
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`catalyst used in the production of vinyl acetate, the product
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`most commonly produced from acetic acid. The present
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`invention is thus also directed to removal of alkyl iodides, in
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`particular C242 alkyl
`iodides compounds. The carbonyl
`impurities may further react with iodide catalyst promoters
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`to form multi-carbon alkyl iodides, e.g., ethyl iodide, butyl
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`lo iodide, hexyl iodide and the like. Since many impurities
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`originate with acetaldehyde, it is therefore a primary objec-
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`tive to remove or reduce the acetaldehyde and alkyl iodide
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`content in the reaction system.
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`Conventional techniques to remove impurities include
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`treatment of acetic acid with oxidizers, ozone, water,
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`methanol, activated-carbon, amines, and the like, which
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`treatment may or may not be combined with distillation of
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`the acetic acid. The most
`typical purification treatment
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`involves a series of distillations of the final product. It is
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`known to remove carbonyl impurities from organic streams
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`by treating the organic streams with an amine compound
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`such as hydroxylamine which reacts with the carbonyl
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`compounds to form oximes followed by distillation to
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`separate the purified organic product from the oxime reac-
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`tion products. However, the additional treatment of the final
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`product adds cost to the process and it has been found that
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`3
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`6,143,930
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`3
`distillation of the treated acetic acid product can result in
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`additional impurities being formed.
`While it is possible to obtain acetic acid of relatively high
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`purity, the acetic acid product formed by the above described
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`low water carbonylation process and purification treatment,
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`frequently remains deficient with respect to the permanga-
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`nate time. This is due to the presence therein of small
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`proportions of residual impurities. Since a sufficient per-
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`manganate time is an important commercial test which the
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`acid product must meet for many uses, the presence therein
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`of such impurities that decrease permanganate time is obj ec-
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`tionable. The removal of minute quantities of these impu-
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`rities from the acetic acid by conventional treatment and
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`distillation techniques is not economically or commercially
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`feasible by distillation since the impurities have boiling
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`points close to that of the acetic acid product.
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`It is important to determine where in the carbonylation
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`process impurities can be removed. It is also important to
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`determine by what economically viable process impurities
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`can be removed without risk of further contamination to the
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`final product or unnecessary added costs.
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`JP patent application 5-169205 discloses a method for
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`manufacture of high purity acetic acid by adjusting the
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`acetaldehyde concentration of the reaction solution below
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`1500 ppm. By maintaining the acetaldehyde concentration
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`in the reaction solution below 1500 ppm, it is stated that it
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`is possible to suppress the formation of impurities and
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`manufacture high purity acetic acid by performing only
`basic distillation operations during purification of the crude
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`acetic acid formed.
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`EP 487,284, B1, published Apr. 12, 1995, states that
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`carbonyl impurities present in the acetic acid product gen-
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`erally concentrate in the overhead from the light ends
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`column. Accordingly,
`the light ends column overhead is
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`treated with an amine compound i.e., hydroxylamine which
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`reacts with the carbonyl compounds to allow such carbonyls
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`to be separated from the remaining overhead by distillation,
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`resulting in an acetic acid product which has improved
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`permanganate time.
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`EP 0 687 662 A2 describes a process for producing high
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`purity acetic acid whereby an acetaldehyde concentration of
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`400 ppm or less is maintained in the reactor by removal
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`thereof using a single or multi-stage distillation process.
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`Streams suggested for processing to remove acetaldehyde
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`include a light phase comprising primarily water, acetic acid
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`and methyl acetate; a heavy phase comprising primarily
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`methyl iodide, methyl acetate and acetic acid; an overhead
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`stream comprising primarily methyl
`iodide and methyl
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`acetate; or a recirculating stream comprising the light and
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`heavy phase combined. Although four streams are suggested
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`for processing, the reference teaches and exemplifies use of
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`the heavy phase. No teaching or suggestion is given regard-
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`ing which stream(s) possesses the greatest concentration of
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`acetaldehyde.
`Also disclosed in EP’662 is management of reaction
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`conditions to control the formation of acetaldehyde in the
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`reactor. By controlling the formation of acetaldehyde, it is
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`stated that reduction of by-products such as crotonaldehyde,
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`2-ethylerotonaldehyde, and alkyl
`iodides are reduced.
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`is pointed out that management of reaction
`However,
`it
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`conditions “have a defect to increase a by-production speed
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`of propionic acid.” indicating that propionic acid is a prob-
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`lem with the disclosed process of ’662.
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`Hence, EP’662 describes optimization of reaction condi-
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`tions to avoid formation of acetaldehyde as well as removal
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`of any acetaldehyde beyond a level of 400 ppm formed in
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`the reactor.
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`4
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`While the above-described processes have been success-
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`ful in removing carbonyl impurities from the carbonylation
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`system and for the most part controlling acetaldehyde levels
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`and permanganate time problems in the final acetic acid
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`product, further improvements can still be made. There
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`remains a need to determine where in the carbonylation
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`process the permanganate reducing compounds, and in
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`particular, acetaldehyde and alkyl iodides are most concen-
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`trated and therefore can be removed so as to insure consis-
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`tent purity of product. At the same time, there remains a need
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`to provide a process for removal of such carbonyl materials
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`and iodide compounds without sacrificing the productivity
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`of the carbonylation process or without incurring substantial
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`additional operating costs.
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`SUMMARY OF THE INVENTION
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`It has now been discovered that a light ends phase from
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`the light ends distillation column contains carbonyl contain-
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`ing permanganate reducing compounds, and in particular
`acetaldehyde which may be further concentrated and
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`removed from the process. In one aspect of this invention,
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`the light ends phase is distilled twice, once through a distiller
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`column which serves to separate the acetaldehyde, methyl
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`iodide, and methyl acetate from acetic acid and water. The
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`second distillation column serves to separate acetaldehyde
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`from methyl iodide and methyl acetate and essentially serves
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`to concentrate and purge the acetaldehyde from the process.
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`Optionally, in another aspect of the invention, the resulting
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`distillate from the second distillation is directed to an
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`extractor to separate out concentrated acetaldehyde and
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`return a residual saturated organic iodide solution to the
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`carbonylation reactor.
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`iodide
`In another aspect of the invention, alkyl
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`compounds, in particular C242, may be removed or signifi-
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`cantly reduced employing the described dual distillation
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`process.
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`It has been found that when shutting down the carbony-
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`lation system,
`in particular the distillation columns
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`employed in the present process, polymers of acetaldehyde
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`tend to form and build up in the base of the second column.
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`Another aspect of the present invention describes a method
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`to deal with this problem. It has been found that a constant
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`flow of solvent
`to maintain contact between the stream
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`within the second distillation column and a solvent from an
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`internal stream (such as one that contains a large percentage
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`of acetic acid or methyl acetate) results in a polymer-free
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`column base upon shut down of the unit. By having the base
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`devoid of polymer build up, one may shut down and
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`subsequently start up the column in a relatively trouble free,
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`efficient, and cost effective manner.
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`The present invention utilizes a light phase which is an
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`internal, intermediate stream in the process, instead of a
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`heavy phase (as suggested in EP’662), for removal of PRC’s
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`and alkyl iodide compounds. The art traditionally employs a
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`heavy phase for treatment or removal of carbonyl impurities
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`and in particular, removal of acetaldehyde. To date, the art
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`was not aware that light phase was the better option com-
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`pared to the heavy phase to concentrate and remove acetal-
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`dehyde therefrom. It was found that structured packing
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`resulted in greater separation of carbonyl impurities than
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`trays in the second distillation column. Generally, the art
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`employs an extractor before the second distillation; it has
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`been found that the use of an extractor after the second
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`distillation results in greater removal of acetaldehyde. It has
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`also been found that due to the dual distillation process
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`coupled with the extractor essentially no methyl iodide is
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`4
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`6,143,930
`
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`6
`about 50%, most often greater than 60%. The permanganate
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`time has been observed to increase by a factor of about 8 or
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`a percentage of about 50%, usually greater than 70% with
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`the inventive process.
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`Once the inventive process was operational and shut
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`down of the system was on-going, it was discovered that
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`polymers of acetaldehyde tended to build up in the second
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`column and plug the column. It was found that this problem
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`could be avoided by contacting the stream flowing through
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`the second distillation column with about 1 gpm solvent
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`stream flow in an amount sufficient and at a flow rate
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`sufficient to avoid aldol condensation polymer formation or
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`to avoid formation of polymers of acetaldehyde. The solvent
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`may be selected from acetic acid, methyl acetate, methanol,
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`water, methyl iodide, acetaldehyde and the like or combi-
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`nations thereof with acetic acid being preferred in view of
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`the abundance of an internal stream to utilize. Generally,
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`amounts sufficient
`to avoid aldol condensation reactions
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`from occurring are rates of about 0.25—5 gallon per minute
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`(gpm), preferably about 0.5-2 gpm with most preferable rate
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`being about 1 gpm. It is undesirable to use an excess of
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`solvent since this places a greater load on the system to
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`reprocess the excess solvent. Although various positions of
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`ingress of the solvent are acceptable, it is preferred that the
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`solvent be contacted with the stream in the second distilla-
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`tion column at the base of the column.
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`DRAWINGS
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`FIG. 1 illustrates a preferred embodiment for the removal
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`of carbonyl impurities from an intermediate stream of the
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`carbonylation process for the production of acetic acid by a
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`carbonylation reaction.
`DETAILED DESCRIPTION OF THE
`
`INVENTION
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`The purification process of the present invention is useful
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`in any process used to carbonylate methanol to acetic acid in
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`the presence of a Group VIII metal catalyst such as rhodium
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`and an iodide promoter. A particularly useful process is the
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`low water rhodium catalyzed carbonylation of methanol to
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`acetic acid as exemplified in aforementioned U.S. Pat. No.
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`5,001,259. Generally, the rhodium component of the catalyst
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`system is believed to be present in the form of a coordination
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`compound of rhodium with a halogen component providing
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`at least one of the ligands of such coordination compound.
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`In addition to the coordination of rhodium and halogen, it is
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`also believed that carbon monoxide coordinates with
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`rhodium. The rhodium component of the catalyst system
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`may be provided by introducing into the reaction zone
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`rhodium in the form of rhodium metal, rhodium salts such
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`as the oxides, acetates, iodides, etc., or other coordination
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`compounds of rhodium, and the like.
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`The halogen promoting component of the catalyst system
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`consists of a halogen compound comprising an organic
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`halide. Thus, alkyl, aryl, and substituted alkyl or aryl halides
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`can be used. Preferably, the halide promoter is present in the
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`form of an alkyl halide in which the alkyl radical corre-
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`sponds to the alkyl radical of the feed alcohol which is
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`carbonylated. Thus,
`in the carbonylation of methanol to
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`acetic acid, the halide promoter will comprise methyl halide,
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`and more preferably methyl iodide.
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`The liquid reaction medium employed may include any
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`solvent compatible with the catalyst system and may include
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`pure alcohols, or mixtures of the alcohol feedstock and/or
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`the desired carboxylic acid and/or esters of these two
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`compounds. The preferred solvent and liquid reaction
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`5
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`purged from the process and a very small amount (0.42 gpm
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`for a 335 gpm methanol unit) of aqueous waste stream
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`results (2 wt % Mel, 25 wt % water, 73 wt % acetaldehyde)
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`for processing/disposing. It has been found that the forma-
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`tion of meta- and paraldehyde in the second column can be
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`inhibited or suppressed by the use of an internal stream
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`comprising approximately 70 wt % water and 30 wt % acetic
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`acid. Because the stream is internal, it does not place an
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`added water load to the process. It has further been found
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`that the recycle of the first column’s residue to the light ends
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`column decanter can be used to extract more acetaldehyde
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`from the heavy phase into the light phase and thus improve
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`acetaldehyde and alkyl iodide removal overall from the
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`process.
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`invention is
`A preferred embodiment of the present
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`directed towards a process for reduction and/or removal of
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`permanganate reducing compounds and C2_12 alkyl iodide
`compounds formed in the carbonylation of methanol to a
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`product of acetic acid, wherein said methanol is carbony-
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`lated in a suitable liquid phase reaction medium comprising
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`a Group VIII metal catalyst, an organic iodide and iodide salt
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`catalyst promoter; the products of said carbonylation are
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`separated into a volatile phase comprising product, and a
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`less volatile phase comprising Group VIII metal catalyst,
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`acetic acid, and iodide catalyst promoter; said product phase
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`distilled in a distillation tower to yield a purified product and
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`an overhead comprising organic iodide, methyl acetate,
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`water, acetic acid, and unreacted methanol, directing at least
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`a portion of the overhead to an overhead receiver decanter
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`which separates the overhead into a light phase, comprising
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`acetic acid and water, and a heavy phase comprising methyl
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`acetate and organic iodide; and recycling the heavy phase to
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`the carbonylation reactor, the improvement which comprises
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`(a) directing the light phase comprising acetic acid and water
`to a distiller which separates the mixture into two streams:
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`residue stream (1) comprising water and acetic acid, and
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`overhead stream 2) comprising methyl
`iodide, methyl
`acetate, methanol, C2_12 alkyl iodides, and permanganate
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`reducing compounds(PRC’s);
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`(b) cooling stream (1) of step (a) and ultimately recycling
`stream 1 to the reactor, and directing stream (2) of step (a)
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`to a second distiller which serves to strip the PRC’s and
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`alkyl iodides from the mixture forming a PRC enriched
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`overhead stream and a residue stream comprising methyl
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`iodide, methyl acetate, methanol, and water;
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`(c) optionally, forwarding the overhead stream step (b) to an
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`extractor to remove any remaining small amounts of
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`organic iodide compounds therefrom; and,
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`(d) separating out concentrated PRC’s and alkyl iodides for
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`disposal and returning the organic iodide phase of (b) or
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`(c) as a stream containing a lower percentage of PRC’s
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`and C2_12 alkyl iodides to the carbonylation reactor.
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`The