MXPA06010006A - Removal of permanganate reducing compounds from methanol carbonylation process stream - Google Patents

Abstract

An improvement of the methanol carbonylation process for manufacturing acetic acid is disclosed. Specifically disclosed is a method for removing permanganate reducing compounds ("PRC's") from the condensed light ends overhead stream, including (a) distilling at least a portion of the condensed light ends overhead to yield a PRC enriched second overhead stream;(b) extracting the second overhead stream with water and separating therefrom an aqueous stream containing PRC's;and (c) returning at least a portion of the extracted second overhead to the second distiller.

Description

REMOVAL OF PERMANGANATE REDUCING COMPOUNDS FROM METHANOL CARBONYLATE FLOW PROCEDURE FIELD OF THE INVENTION The present invention relates to an improved process for the removal of permanganate reducing compounds and alkyl iodides formed by the carbonylation of methanol in the presence of a group VIII metallation catalyst. More specifically, the present invention relates to an improved process for reducing and / or removing the precursors of permanganate reducing compounds and alkyl iodides from intermediate flows during the formation of acetic acid by said carbonylation processes.

BACKGROUND OF THE INVENTION Among the methods currently employed for the synthesis of acetic acid, one of the most commercially used is the catalyzed carbonylation of methanol with carbon monoxide as taught in the U.S. Patent. No. 3,769,329 issued to Paulik et al, on October 30, 1973. The carbonylation catalyst comprises rhodium, either dissolved or otherwise dispersed in a liquid reaction medium or supported in an inert solid, together with a catalyst promoter. which contains halogen as exemplified by methyl iodide. Rhodium can be introduced into the reaction system in any of several ways, and the exact nature of the rhodium portion within the active catalyst complex is uncertain. Similarly, the nature of the halide promoter is not critical. The owners of the patent describe a very large number of suitable promoters, most of which are organic iodides. More typically and with greater utility, the reaction is carried out by the continuous bubbling of carbon monoxide gas through a liquid reaction medium in which the catalyst is dissolved. An improvement in the prior art processes for the carbonylation of an alcohol to produce the carboxylic acid having a carbon atom more than the alcohol in the presence of a rhodium catalyst is described in U.S. Patents. Commonly assigned Nos. 5,001, 259 issued on March 19, 1991; 5,026,908 issued June 25, 1991; and 5,144,068 issued September 1, 1992; and European Patent No. EP 0 161 874 B2, published July 1, 1992. As described in the present description, acetic acid is produced from methanol in the reaction medium containing methyl acetate, halide methyl, especially methyl and rhodium iodide present in a catalytically effective concentration. These patents disclose that the stability of the catalyst and the productivity of the carbonylation reactor can be maintained at surprisingly high levels, even at very low water concentrations, ie, 4 weight percent or less, in the reaction medium (independently of general industrial practice to maintain approximately from 14 to 15 weight percent of water) by keeping in the reaction medium, together with the catalytically effective amount of rhodium and at least a finite concentration of water, a specific amount of ions of iodide above and below the iodide content that is present as a methyl iodide or other organic iodide. The iodide ion is present as a simple salt, being preferred of lithium iodide. The patents teach that the concentration of methyl acetate and iodide salts are significant parameters for affecting the carbonylation rate of methanol to produce acetic acid, especially at low water concentrations in the reactor. By using relatively high concentrations of methyl acetate and iodide salt, a surprising degree of catalyst stability and reactor productivity is obtained even when the liquid reaction medium contains water at concentrations as low as approximately 0.1% by weight, so low that they can be broadly defined as simply "a finite concentration" of water. Additionally, the reaction medium employed improves the stability of the rhodium catalyst, that is, the strength for catalyst precipitation, especially during the process product recovery steps. In these steps, distillation for the purpose of recovery of acetic acid product tends to remove carbon monoxide from the catalyst, which in the environment maintained in the reaction vessel, is a ligand with rhodium stabilizing effect. The Patents of E.U.A. Nos. 5,001, 259; 5,026,908 and 5,144,068 are incorporated herein by reference. It has been found that although a low carbonylation process for the production of acetic acid reduces such by-products as carbon dioxide, hydrogen and propionic acid, the amount of other impurities, generally present in trace amounts, also increases and the The quality of acetic acid sometimes suffer when attempts are made to increase the rate of production by improving the catalysts or modifying the reaction conditions. These trace impurities affect the quality of the acetic acid, especially when these are circulated again through the reaction process. Impurities that decrease the time of the permanganate of acetic acid include carbonyl compounds and unsaturated carbonyl compounds. As used in the present description, the phrase "carbonyl" means those compounds that contain aldehyde or ketone functional groups, which compounds may or may not possess unsaturation. See Catalysis of organic reaction, 75, pages 369 to 380 (1998), for a further discussion on impurities in carbonylation processes. The present invention is directed to reducing and / or removing the permanganate reducing compounds (PRCs) such as acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde, crotonaldehyde, 2-ethyl crotonaldehyde, and 2-ethyl butyraldehyde and the like, and the products of aldol condensation thereof. The present invention is also directed to the reduction of propionic acid. The carbonyl impurities described above, such as acetaldehyde can be reacted with iodide catalyst promoters to form alkyl carbodium iodides, for example, ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl iodide and the similar ones. It is desirable to remove the alkyl iodides from the reaction product because even small amounts of these impurities in the acetic acid product tend to poison the catalyst used in the production of vinyl acetate, the product that is most commonly produced from of acetic acid. The present invention is therefore directed to the removal of alkyl iodides, in particular, C 2 -? 2 alkyl iodide compounds. Therefore, because many impurities are originated with acetaldehyde, it is a primary objective to remove or reduce the content of acetaldehyde and alkyl iodide in the process. Conventional techniques for removing impurities include the treatment of the acetic acid product with oxidants, ozone, water, methanol, activated by carbon, amines and the like, which treatment may or may not be combined with the distillation of acetic acid. The most typical purification treatment involves a series of distillations of the final product. It is known that, for example, from the Patent of E.U.A. Do not. ,783,731 to remove the carbonyl impurities from organic flows by treating the organic flows 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, additional treatment of the final product adds cost to the processes and the distillation of the treated acetic acid product can result in the formation of additional impurities. Although it is possible to obtain acetic acid of relatively high purity, the acetic acid product formed by the low carbonylation process in water and the purification treatment described above often remains somewhat deficient with respect to the permanganate time due to the presence of small portions of residual impurities. Because a sufficient permanganate time is an important commercial test, whose acid product must be achieved to be suitable for many uses, the presence of impurities that decrease the permanganate time can be objected. In addition, it is not economically or commercially feasible to remove minute amounts of these acetic acid impurities by distillation because some of the impurities have boiling points close to those of the acetic acid product. Accordingly, it has become important to identify economically viable methods for removing impurities elsewhere that occur in the carbonylation process without contaminating the final product or adding unnecessary costs. The Patent of E.U.A. No. 5,756,836, incorporated by reference in the present description, discloses a method for manufacturing a high purity acetic acid by adjusting the aldehyde concentration of the reaction solution below 1500 ppm. It is established that by maintaining the concentration of acetaldehyde below this threshold, it is possible to suppress the formation of impurities, so that only the distillation of the crude acetic acid product is necessary to obtain high purity acetic acid. European Patent No. 0 487 284 B1, published on April 12, 1995, discloses that the carbonyl impurities present in the acetic acid product are generally concentrated in the distillation column form from the low density ends of the column. Accordingly, the ends of the low density column of the distillation column are treated with an amine compound (such as hydroxylamine), which reacts with the carbonyl compounds to form oxime derivatives that can be separated from the remainder of the column. distillation by distillation, resulting in an acetic acid product with improved permanganate time. European Patent Application No. EP 0 687 662 A2 and the Patent of E.U.A. No. 5,625,095, incorporated herein by reference, describe a process for producing high purity acetic acid in which, an acetaldehyde concentration of 400 ppm or less is maintained in a reactor using a single or multi-stage distillation process for Remove the acetaldehyde. The flows suggested for processing to remove acetaldehyde include a low density phase that mainly contains water, acetic acid and methyl acetate; a high density phase containing mainly methyl iodide, methyl acetate and acetic acid; a distillation column flow containing mainly methyl iodide and methyl acetate; or a newly circulating flow formed by the combination of the low density phase and the high density phase. These references do not identify which of these flows has the highest concentration of acetaldehyde. Patent EP 0 687 662 A2 and the Patent of E.U.A. No. 5,625,095 also describe the handling of the reaction conditions to control the formation of acetaldehyde in the reactor. Although it is established that the formation of derivative products such as crotonaldehyde, 2-ethylcrotonaldehyde and alkyl iodides is reduced by controlling the formation of acetaldehyde, it is also noted that the handling of the reaction conditions as proposed increases the formation of propionic acid, an undesirable by-product. More recently, it has been described in the Patents of E.U.A. Commonly assigned Nos. 6,143,930 and 6,339,171, it is possible to significantly reduce the undesirable impurities in the acetic acid product by performing a multi-step purification on the distillation column low density column ex. These patents describe a purification process in which the low density ends of the distillation column are distilled twice, in each case taking the distillation column of acetaldehyde and returning a residue rich in methyl iodide to the reactor. The distillate rich in acetaldehyde is extracted with water to remove most of the acetaldehyde for disposal, leaving a significantly lower concentration of acetaldehyde in the refining solvent that is recycled to the reactor. The Patents of E.U.A. Nos. 6,143,930 and 6,339,171 are incorporated by reference in the present description. Although the processes described above have been successful in the removal of carbonyl impurities from the carbonylation system and for most of the problems of acetaldehyde control levels and permanganate time in the final acetic acid product, further improvements can be made. Accordingly, the need remains for alternative procedures to improve the efficiency of acetaldehyde removal. The present invention provides said alternative solution.

BRIEF DESCRIPTION OF THE INVENTION In one aspect, the present invention provides a process for producing acetic acid that includes the following steps: (a) reacting methane! and carbon dioxide in a suitable reaction medium including a catalyst and an organic iodide; (b) separating the products of the reaction in a volatile product phase containing acetic acid, organic iodide and at least one permanganate reducing compound (PCR) and a less volatile phase containing the catalyst and acetic acid; (c) distilling the volatile product phase to produce a purified product and a first distillation column containing organic iodide, water, acetic acid and methanol without being reacted; (d) distilling at least a portion of the first distillation column to produce a second distillation column enriched for PRC; (e) extracting the second distillation column with water and separating it from an aqueous extract containing concentrated PRC to be discarded; and (f) distilling at least a portion of the second distillation column extracted together with the first portion of the distillation column. Preferably, another portion of the extracted second distillation column is recirculated to the reactor.

In another aspect, the present invention provides an improved method for separating a mixture containing water, acetic acid, methyl iodide, methyl acetate, methanol or at least C2-? 2 alkyl iodide and at least one reducing compound of permanganate (PCR). The improved method includes the following steps: (a) distilling the mixture to form a distillation column stream enriched with PRC; (b) extracting the flow from the PRC enriched distillation column with water and separating therefrom an aqueous stream containing at least one PRC; and (c) distilling at least a portion of the distillation column enriched with PRC extracted together with the mixture. In yet another aspect, the present invention provides an improved method for the reduction and / or removal of permanganate-reducing compounds (PRCs) and C-γ-2-alkyl iodide compounds formed in the methanol carbonylation of a product. of acetic acid. In the improved method, the methanol is carbonylated in a reaction medium containing a catalyst, and an organic iodide; the products of the carbonylation reaction are separated into (1) a volatile phase containing a product of acetic acid, organic iodide, water and at least one PRC, and (2) a less volatile phase containing the catalyst; the volatile phase is distilled to produce a purified product and a first distillation column containing organic iodide, water, acetic acid and PRC. The improvement includes the steps of (a) distilling the first distillation column to form a second PRC enriched distillation column flow; (b) extracting the second distillation column stream with water and separating them from an aqueous stream containing PRCs; and (c) distilling at least a portion of the second distillation column extracted together with the first distillation column. In the particularly preferred embodiments of the present invention, the second distillation column or enriched distillation column of PRC contains dimethyl ether in an amount effective to reduce the solubility of methyl iodide in an amount effective to reduce the solubility of methyl iodide in the flow of aqueous extract.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the prior art process as described in the U.S. Patent. No. 6,339,171, for the removal of carbonyl impurities from an intermediate flow of the carbonylation process for the production of acetic acid by a carbonylation reaction. Figure 2 illustrates a preferred embodiment of the present invention. Although the present invention is susceptible to various modifications and alternative forms, the specified embodiments have been shown by way of example in the drawings and will be described in detail in the present description. It should be understood, however, that the invention is not intended to be limited to the particular forms described. Instead, the present invention is intended to encompass all modifications, equivalents and alternatives that are within the scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE MODALITIES The illustrative embodiments of the present invention are described below. With the interest of achieving clarity, all the characteristics of a current implementation will not be described in this specification. Of course it will be appreciated that in the development of any of these current modalities, several implementation specific decisions must be made to achieve the specific goals of those who develop them, such as compliance with the limitations related to the system and related to the business, which will vary from one implementation to another. Additionally, it will be appreciated that said development effort must be complex and slow, although it could nevertheless be a routine approached by those experts in the field who have the benefit of this description. The purification process of the present invention is useful in any process used for carbonylated methanol (or other carbonizable reagent such as methyl acetate, formate or dimethyl ether) in acetic acid in the presence of a group VIII metal catalyst. , such as rhodium and an iodide promoter. A particularly useful method is the low rhodium-catalyzed carbonylation of methanol to acetic acid as exemplified in the U.S. Patent. No. 5,001, 259. Generally, the rhodium component of the catalyst system is considered to be present in the form of a coordination compound of rhodium with a halogen component that provides at least one of the ligands of said coordination compound. In addition to the coordination of rhodium and halogen, carbon monoxide is also considered to coordinate with rhodium. The rhodium component of the catalyst system can be provided by the introduction into the reaction zone of rhodium in the form of a rhodium metal, rhodium salts such as oxides, acetates, iodides, etc., or other rhodium coordination compounds. and the similar ones. The halogen promoter component of the catalyst system consists of a halogen compound comprising an organic halide. Therefore, alkyl, aryl and substituted alkyl or aryl halides can be used. Preferably, the halide promoter is present in the form of an alkyl halide, in which the alkyl radical corresponds to the alkyl radical of the fed alcohol, which is carbonylated. Therefore, in the carbonylation of methanol to acetic acid, the halide promoter will contain methyl halide, and more preferably methyl iodide. The liquid reaction medium employed can include any solvent compatible with the catalyst system and can include pure alcohols, or mixtures of the desired alcohol and / or carboxylic acid feed supply and / or esters of these two compounds. The preferred solvent and the liquid reaction medium for the low carbonylation process in water is the carboxylic acid product. Therefore, in the carbonylation of methanol to acetic acid, the preferred solvent is acetic acid. The water is contained in the reaction medium although at concentrations well below those, which to date have been considered practical to achieve sufficient reaction rates. It has been previously considered that in the rhodium catalyzed carbonylation reactions of the type established in this invention, the addition of water exerts a beneficial effect from the reaction index (Patent of US Pat. No. 3,769,329). Therefore, most commercial operations run at water concentrations of at least about 14 percent by weight. Accordingly, it is not expected that the reaction rates are substantially the same as and below the reaction rates obtained with said high levels of water concentration which can be obtained with water concentrations below 14% by weight and so low as approximately 0.1% by weight. According to the carbonylation process most used in the manufacture of acetic acid according to the present invention, the desired reaction rates are obtained even at low concentrations of water, including the reaction medium of ethyl acetate and an additional iodide ion, which is above and below the iodide which is present as a catalyst promoter. such as methyl iodide or organic iodide. The additional iodide promoter is a iodide salt, with a lithium iodide being preferred. It has been found that under low water concentrations, the acetylation of meityl and the halide iodide act as index-only promoters when relatively high concentrations of each of these components are present and that promotion is further when both components are present in Simular form (United States Pamphlet No. 5,001, 259). The concentration of lithium iodide used in the reaction medium of the preferred carbonylation reaction system is considered very much in comparison to a little of what the prior art is handling with the use of halide salts in the reaction systems of this kind. The absolute concentration of the iodide ion content is not a limitation on the utility of the present invention. The carbonylation reaction of meianol to aceric acid product can be carried out by bringing into contact the feed of methanol, which is in the liquid phase, with bubbling carbon monoxide gas through a liquid acetic acid solvent reaction medium. it contains the rhodium catalyst, methyl iodide promoter, methyl acetate and additional soluble iodide salt, at suitable temperature and pressure concentrations to form the carbonylation product. It will also be generally recognized that this is the concentration of the iodide ion in the catalyst system that is important and not the cation associated with the iodide and that at a given molar concentration of iodide, the color of the cation is not significant as The effect of iodide concentration.

Any metal iodide salt or any iodide salt of any organic cation or quaternary cation, such as an amine or quaternary phosphine or inorganic cation, can be used as long as the salt is sufficiently soluble in the reaction medium to provide the desired level of I last. When iodide is added as a honeydew, it is preferably an iodide salt of an element of the group consisting of metals of group IA and the HA group of the periodic table as set forth in "Handbook of Chemistry and Physics" published by CRC Press, Cleveland, Ohio, 1975-76 (56th Edition). In particular, alkali metal iodides are useful, with lithium iodide being preferred. In the most useful low water carbonylation process of the present invention, the additional iodide above and below the organic iodide promoter is present in the cationizer solution in amounts from about 2 years to about 20% by weight, Methyl acetyl is present in amounts from about 0.5 to about 30% by weight and the lithium iodide is present in amounts from about 5 to about 20% by weight. The rhodium catalyst is present in amounts from about 200 to about 2000 parts per million (ppm). The typical reaction conditions for the carbonylation will be from about 150 to about 250 ° C, with the lemperairy inlet being preferred from about 180 to about 220 ° C. The partial pressure of the carbon monoxide in the reactor can vary widely although it is usually from about 2 to about 30 atmospheres, and preferably, from about 3 to about 10 atmospheres. Because the partial pressure of the byproducts and the vapor pressure of the contained liquids, the ional reactor pressure will vary within a range from approximately 15 to approximately 40 atmospheres. A typical reaction and the acidic recovery system used for the catholylated carbonylation of rhodium promoted by meium-iodide to acetic acid is shown in Figure 1, and includes a liquid phase carbonylation reactor, a flasher and a column. of low density acidic acid density of methylated iodide 14, which has a lateral flow of acetic acid 17, which proceeds to further purification. The reactor and the flasher are not shown in Figure 1. These are considered standard equipment well known in the majority of the carbonylation processes. The carbonylation reactor is usually either an agitated container or a bubble column reactor, within which the reaction liquid or paste contents are kept in an auimomatic form at a consis- tent level. In this reactor, there is freshly produced fresh monomer in continuous form, carbon monoxide, sufficient water as necessary to maintain at least a finite concentration of water in the reaction medium, recycled catalyst solution from the base of the flasher, an iodide of recycled methylate and a methylated acetyl phase and a recycled aqueous acetic acid phase from a receiver decanizer of the distillation column of the low density end of acetic acid of meifyl iodide or separating column 14. The desilylation systems are employed by They provide a means for the recovery of crude acetic acid and the recycling of the cayalizing solution, mephyl iodide, and meityl acetyl to the reactant. In a preferred process, the carbon monoxide is ineliminated in a sinuous form of the carbonylation reactant just below the water carrier, which is used to agitate the content. The gaseous feed is completely dispersed through the reaction liquid by means of the agiiating medium. A gas purge flow is discharged from the reactor to prevent the accumulation of gaseous by-products and to maintain a partial pressure group of carbon monoxide at a given reactor pressure. The reactor lemperairy is controlled and the carbon monoxide feed is produced at a rate sufficient to maintain the desired total reactor pressure. The liquid product is extracted from the carbonylation reactor at an index sufficient to maintain a constant level therein and is introduced to the flasher. In the flasher, the catalyst solution is extracted as a base flux (predominantly acetic acid containing rhodium and iodide salt together with minor amounts of mephyl acetylation, mephyl iodide and water), although the column current of The vapor discharge of the flasher contains to a large extent the product of acetic acid June with methyl iodide, methyl acetate and water. The dissolved gases leave the reactor and re-enter the desiller consisting of a portion of the carbon monoxide together with the gaseous portion by products such as methane, hydrogen and carbon dioxide and leave the deseller as part of the distillation column flow. The distiller column stream is directed to the low density ends or separator column 14 as the flow 26. In U.S. Pat. Nos. 6,143,930 and 6,339,171 it has been described that there is a greater concentration, approximately 3 times, of the PRC and in particular of acelaldehyde content in the low density phase than in the alpha density phase flow leaving the 14 column. Accordingly, according to the present invention, the flow conforming PRC 28 is directed to a decanter column receiving decanter 16 wherein the phase of the low density ejectors, the flow 30, is directed to the distillation column 18. The present invention can be broadly considered as an improved process for the desilylation of PRCs, mainly of aldehydes and alkyl iodides, from a flow of acetic acid of vapor phase. The vapor phase flow is distilled and extracted to remove PRC. An especially preferred method for removing alkyl aldehydes and iodides from a first vapor phase acetic acid flow and reducing levels of propionic acid in the acidic acid product includes the following steps: a) condensing the first flow of acetic acid of vapor phase in a first condenser and separating it in biphasic form to form a first production of liquid phase of alpha density and a first production of liquid phase of low density, wherein said first liquid phase of alia density coniiene higher proportion of catalytic components that said first low-density liquid phase production; b) defile the low-density liquid phase product in a first defilization column to form a second vapor phase acetic acid product, which is enriched with alkyl aldehydes and iodides with respect to said first flow of acetic acid of vapor phase; c) condensing the second vapor phase flux in a second condenser to form a second liquid phase product; d) distilling the second liquid phase production in a second deflation column to form a third vapor phase flow; e) condensing the third vapor phase flow and expelling the condensed flow with water to remove residual acetaldehyde; and f) recycling at least a portion of the expelled vapor phase flow to the second deflation column. A modality of the prior art as described in the Patent of E.U.A. No. 6,339,171 is shown in FIG. 1. Referring to FIG. 1, the first steam phase acetic acid flow (28) contains methyl iodide, meityl acetyl, acelaldehyde, and other carbonyl compounds. This flow is then condensed and separated (in vessel 16) to separate the high density phase production which contains the largest proportion of catalytic components - which are circulated back into the reactor (not shown in Figure 1) - and a low density phase (30) which contains acetaldehyde, water and acetic acid. Any phase of the low density deflection column ends can be subsequently desylated to remove the PRC and mainly the acetaldehyde component of the flow, although it is preferred to remove the PRC from the low density phase, (30) because it has been discovered that the concentration of acelaldehyde is somewhat higher in that phase. In the modality represented and described in the present description, the desylation is carried out in two stages; although it will be appreciated that the slip can also be performed in a single column. The low density phase (30) is directed to the column 18, which serves to form a second vapor phase (36) enriched in alkyl aldehydes and iodides with respect to the flow 28. The flow 36 is condensed (vessel 20) and separated in biphasic form to form a second high density liquid phase product and a second low density liquid phase product. This second high-density liquid phase contains a higher portion of catalytic components than the second low-density liquid phase and is subsequently circulated back to the reactor. The second low density liquid phase (40) containing acetaldehyde, methyl iodide, methanol, and meityl acetamide is directed to a second desylation column (22), where the acealdehyde is separated from the other components. This inventive process has been found to reduce and / or remove at least 50% of the discovered alkyl iodide impurities in a flow of acidic acid. It has also been shown that acealdehyde and its derivatives are reduced and / or removed by at least 50%, more frequently by more than 60%. As a resulfonate, it is possible to maintain the concentration of propionic acid in the acetic acid product below about 400 parts per million by weight, and preferably below 250 parts per million. From the top of the low density ejectors or the separating column 14, the vapors are removed by means of the flow 28, condensed and directed to the vessel 16. The vapors are cooled to a temperature sufficient to condense and separate the methyl iodide that It can be condensed, melta acetal, acetaldehyde and other carbonyl components and water in two phases. A portion of the stream 28 contains gases that can not be condensed, such as carbon dioxide, hydrogen and the like, and can be discharged as shown in the stream 29 of Figure 1. Also leaving the receiver decanter from the distillation column., although not illustrated in Figure 1, is the high density phase of the flow 28. Ordinarily, this high density phase is circulated back to the reactant, although a separation flow, generally a small amount, for example, a volume of 25%, preferably less than about a volume of 20% of the ally density phase, can also be directed to a process for carbonyl ester extraction and the remainder is recycled to the reactor or reaction system. This separation flow of the high density phase can be brought individually or combined with the low density phase (flow 30) for further desylation and removal of the carbonyl impurities. The low density phase (flow 30) is directed to the deflection column 18. A portion of the flow 30 is directed back to the low density column ends 14 as a reflux flow 34. The remainder of the flow 30 enters the column 18 as flow 32 in approximately half of the column. Column 18 serves to concentrate the aldehyde components of flow 32 in the distillation column flow 36 by separating water and acetic acid from the lower density components. The flow 32 is distilled in the first distillation column 18, which preferably contains about 40 trays, and the intervals of time in it from about 283 ° F (139.4 ° F) in the bottom to about 191 ° F (88.3 °). C) at the top of the column. When leaving the bottom of point 18 is the flow 38 which contains approximately 70% water and 30% acidic acid. The flow 38 is processed, generally cooled using a heat exchanger, is recycled to the distillation column decanter from the low density column ends 16 via flow 46, 48 and ultimately to the reactor or reaction system. It has been found that recycling a portion of the flow 38 is identified as the flow 46 back through the decanter 16 which increases the efficiency of the inventive process and allows more aldehyde to be present in the low density phase, the flow 32. Flow 36 has been found to have approximately seven times more aldehyde content when flow 38 is recycled through decanter 16 in this form. Leaving the top of column 18 is the flow 36 containing the PRC and in particular the acealdehyde, melon iodide, methyl acetate, and methanol and alkyl iodides. The flow 36 is then directed to a distillation column receiver 20 after it has been cooled to condense any condensable gases present. On exiting the scroll column receiver 20 is the stream 40 containing acetaldehyde, methyl iodide, methyl acetate and methanol. A portion of the flow 40 is returned to the column 18 as a reflux flow 42. The remainder of the flow 40 enters the second distillation column 22 that closes the bottom of the column. Column 22 serves to remove most acetaldehyde from methyl iodide, mephyl acetate, and methanol in stream 40. In one embodiment, column 22 contains approximately 100 trays and is operated at a temperature ranging from about 224 ° C (106.6 ° C) at the bottom to approximately 175 ° F (79.4 ° C) at the top. In an alternate, the preferred embodiment, column 22 contains a sealed package instead of the trays. Preferred packages are a structured packing with an interfacial area of approximately 65 ft2 / ft3, preferably made from a metal alloy similar to 2205 or other similar packaging material, as long as it is compatible with the compositions to be purified in the column. During the experimentation it was observed that the uniform column load, which is required for good separation, was better with the structured packaging than with the trays. In an aligning way, the ceramic packing can be used. The residue from column 22, flow 44, exits at the bottom of the column and is recycled to the carbonylation process. As described in the United States Pa.ent. No. 6,339,171, it has been found that during heating of column 22, high molecular weight polymers form acetaldehyde. These polymers of higher molecular weight (molecular weight greater than about 1000) are considered to be formed during the processing of the low density phase and are viscous and thixoropropic. As heat is applied to the system, they tend to harden and adhere to the walls of the tower, where their removal is annoying. Once polymerized, they are only slightly soluble in organic or aqueous solvents and can be removed from the system only by mechanical means. Therefore, an inhibitor is needed, preferably in column 22 to reduce the formation of these impurities, ie, metaldehyde and paraldehyde higher molecular weight polymers of acelaldehyde (AcH). The inhibitors generally consist of CMO alkanols, preferably methanol; Water; acidic acid and the like used individually or in combination with each other or with one or more different inhibitors. The stream 46, which is a portion of the coindumn residue 18 and a flow separation stream 38, contains water and acetic acid and can therefore serve as an inhibitor. As shown in Figure 1, flow 46 is separated to form flows 48 and 50. Flow 50 is added to column 22 to inhibit the formation of metaldehyde and paraldehyde impurities and higher molecular weight polymers. Because the residue in the second column 22 is recycled to the reactor, any aggregate inhibitors must be compatible with the reaction chemistry. It has been found that small amounts of water, methanol, acetic acid, or a combination thereof, do not interfere with the reaction chemistry and virtually eliminate the formation of acetaldehyde polymers. The flow 50 is also preferably used as an inhibitor because it does not change the water balance of the reactor. Although water is not particularly preferred as an inhibitor, other important advantages are obtained by adding water to the column 22 as will be explained below. Exiting the top of column 22 is flow 52 containing the PRC. The flow 52 is directed to the condenser and then the distillation column receiver 24. After condensation, any materials that can not be condensed are discharged from the receiver 24; the condensed materials leave the receiver 24 as the flow 54. The flow 56, a flow of separation of the flow 54 is used as reflux for the column 22. When leaving the bottom of the column 22 is the flow 44 which confers methyl iodide, methanol, methyl acetate, methanol and water. That flow is combined with the flow 66, which will be described later and is directed to the reactor. It is important for the extraction mechanism that the distillation column flow in column 22 remain cool, generally at a lemperairy of approximately 13 ° C. This flow can be obtained or maintained at about a temperature of 13 ° C by conventional techniques known to those skilled in the art or any mechanism generally accepted by the industry. Upon exiting the receiver 24, the flow 58 is preferably sent through a condenser / cooler (now the flow 62) and then to an extractor 27 to remove and recycle small amounts of methyl iodide from an aqueous PRC flow. In the extractor 27, the PRC and the alkyl iodides are extracted with water, preferably water from the internal flow in such a way that the water balance is maintained within the reaction system. As a result of this extraction, the methyl iodide is separated from the aqueous PRC and the alkyl iodide phase. In a preferred embodiment, a mixer-colonizer with a feed to water ratio of about 2 is employed. The flow of aqueous extract 64 leaves the extractor from the top thereof. This rich PRC, and in particular, aqueous phase rich in acetaldehyde is directed to the treatment of waste. Also upon exiting the extractor is the flow of refining solvent 66 which confers methyl iodide, which is normally recycled to the reaction system and ultimately to the reactor. The present applicants have now discovered that the return of at least a portion of the stream of refining solvent 66 to the stripping column 22, improves the removal efficiency of aldehyde from the system in its tofality. This can be achieved by returning at least a portion of the flow 66 to any point between the flow 32 (the supply to the column 18) and the extractor 27. In the embodiment shown in Figure 2, a portion of the flow 66 is separated into the flow shape 68 and feeds the column 22, either by mixing it with the feed flow column 40 or mediating the feed flow 68 directly to the column at another point. In an embodiment of the present invention, flow 66 can be returned to column 22. However, it has been found that it is preferable to return at least a portion of flow 66 to the reaction system instead of returning the full flow to column 22. When applicants they began to make tests of the present invention, it was observed that the pressure in column 22 rose significantly with the time, indicating the accumulation of a volatile component in the system that is not being removed in the extrusion. The applicants discovered that there are a number of chemical reactions occurring in the column 22, including the hydrolysis of methyl acetyl and methyl iodide to methanol and the subsequent formation of dimethyl ether (DME). The DME was idenified as the volatile component that was causing the increase in column pressure when all the refining solvent flow 66 of the extractor 27 is recycled to the column 22, the DME formed in the column is not removed from the system. However, it follows that the problem can be solved by recycling a portion of the flow 66 directly or indirectly to the reactor system. For example, the flow 66 can be recycled to the container 16, where it is combined with the high density phase returning to the reactor as described above. Because the DME can be carbonylated in the reactor to produce acetic acid, recycling a portion of the flow containing DME 66 directly or indirectly to the reactor effectively prevents the DME from accumulating in the acetaldehyde removal system. However, at the same time, the present applicants also discovered an unexpected advantage of the presence of small amounts of DME in the acealdehyde removal system. Specifically, it follows that the DME reduces the solubility of meityl iodide in water. Therefore, the presence of DME in the feed to exluoror 27 reduces the amount of extruded mephyl iodide in stream 64 and is lost in the trailing water stream. By way of example, the applicants observed that the concentration of methyl iodide in stream 64 fell from approximately 1.8% when the DME was not present to approximately 0.5% when the DME is present. As explained herein, because methyl iodide is a particularly expensive component of the reaction system, it is highly desirable to reduce to a minimum the amount of methyl iodide that is removed from the process as waste in a manner that reduces the amount of fresh methyl iodide that must be fed to the reactant. Accordingly, a further aspect of the present invention includes the step of injecting additional DME in upstream stream of exorcium 27, for example, in stream 62, to reduce the loss of melon iodide in the aqueous exlude 64 stream. altemative, it is possible to generate additional DME within the process by mediating the additional supply of water to column 22 in any feed flow 40 or reflux flow 65. Although the present invention has been described with reference to preferred embodiments, modifications and alterations obvious are possible by those experts in the related field. In particular, although the present invention has been described generally above using the low density column phase ends 14, any flux in the carbonylation process having high concentration of the PRC and the alkyl iodides can be treated in accordance with the present invention. Accordingly, it is in the interest that the present invention includes all modifications and alterations in their entirety that will be found within the scope of the following claims or equivalents thereof.

Claims (36)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for the reduction and / or removal of permanganate reducing compounds (PRCs) and C2-? 2 alkyl iodide compounds formed in the carbonylation of a carbonizable reagent selected from the group consisting of methanol, acetylate mephyl, mephyl formate and dimethyl ether and mixtures thereof to produce a product comprising acetic acid, the process comprises the steps of: separating said carbonylation product to provide a volatile phase comprising acetic acid, and a less volatile phase; distilling said volatile phase to produce a purified acetic acid product and a first desilylation column comprising organic iodide, water, acetic acid and at least one PRC; parading at least a portion of the first desylation column in a slip apparatus to form an enriched PRC of second distillation column; extracting the second distillation column with water and separating therefrom an aqueous stream comprising said at least one PRC; and recycling at least a first portion of the second deflection column extracted to said distillation apparatus.

2. The process according to claim 1, further characterized in that the improvement further comprises introducing at least a second portion of the second distillation column extracted directly or indirectly in the reaction medium.

3. The process according to claim 2, further characterized in that said second distillation column comprises dimethyl ether in an effective amount to reduce the solubility of methyl iodide in said aqueous flow.

4. The process according to claim 2, further characterized in that it additionally comprises the step of adding dimethyl ether to the second distillation column.

5. The process according to claim 2, further characterized in that it additionally comprises forming dimethyl ether in said desylation apparatus.

6. The method according to claim 5, further characterized in that it additionally comprises the step of adding water to a flow associated with said distillation apparatus, whereby the dimethyl ether is formed in the deflection apparatus.

7. The process according to claim 1, further characterized in that the first recycled portion of the second distillation distillation column is fed to the distillation apparatus together with the first portion of the distillation column.

8. The process according to claim 1, further characterized in that the first recycled portion of the second exillated desilylation column is fed to the desylation apparatus separately from the first desilylation column portion.

9. The process according to claim 1, further characterized in that it further comprises the step of adding dimethylether in at least one flow selected from the group consisting of said volatile phase, said first desylation column, said second desylation column. , a reflux flow associated with the desylation of said volatile phase and a reflux flow of said deflation apparatus.

10. The process according to claim 1, further characterized in that said at least one PRC comprises acealdehyde.

11. The process according to claim 10, further characterized in that a sufficient amount of said acetaldehyde is removed from said volatile phase to maintain a concentration of less than about 400 parts per million by weight of propionic acid in said acetic acid product. purified.

12. The process according to claim 10, further characterized in that a sufficient amount of said acetaldehyde is removed from said volatile phase to maintain a concentration of less than about 250 parts per million by weight of propionic acid in said acrylic acid production. purified.

13. The method according to claim 1, further characterized in that the step of parading said first desylation column comprises a plurality of consecutive deflection steps, and wherein the first portion of said second desiraion column exhaled is recycled to a flow associated with the second or last step of said steps of distillation.

14. A process for producing acetic acid, comprising the steps of: (a) carbonylating at least one reagent selected from the group consisting of meianol, meityl acetylate, melyyl formate and dimethyl ether in a reactor that contains a medium of adequate reaction; (b) separating the products of said carbonylation in a volatile production phase comprising acetic acid and at least one permanganane reductive compound (PRC), and a less volatile phase; (c) distilling said volatile product phase to produce a purified acetic acid product and a first distillation column comprising organic iodide, water, acetic acid and said at least one PRC; (d) distilling at least a portion of the first distillation column to produce a second defrosting column enriched with PRC; and (e) Extruding the second distillation column with water and separating therefrom an aqueous extract containing concentrated PRC for disposal, wherein at least a first portion of the second exhalation desiraion column is recycled and desylated in step (d) with the first desylation column.

15. The process according to claim 14, further characterized in that said second distillation column comprises dimethyl ether in an amount effective to reduce the solubility of the mephyl iodide in said aqueous flow.

16. The process according to claim 14, further characterized in that it further comprises the step of adding dimethyl ether to at least one stream selected from the group consisting of said volatile phase, said first distillation column, said second distillation column , a reflux flow associated with the distillation of the volatile phase, and a flow associated with the distillation of the first deflation column portion.

17. The process according to claim 14, further characterized in that it further comprises recycling at least a second portion of the second desiraion column exhausted directly or indirectly to the reactor.

18. The process according to claim 17, further characterized in that it additionally comprises forming dimethyl ether during the distillation of the first portion of the distillation column and reacting at least a portion of the dimethyl ether with carbon monoxide in the reactor.

19. The process according to claim 18, further characterized in that it additionally comprises the step of injecting water into the first desilylation column or into the first portion of the second desirated exillation column to promote the formation of dimethylether during desilylation. of the first column portion of desylation.

20. The process according to claim 14, further characterized in that the distillation step of at least a portion of the first distillation column comprises a plurality of consecutive stripping steps, and wherein the first portion of said second column The extracted distillation is recycled to a flow associated with the second or last step of said distillation steps.

21. The process according to claim 14, further characterized in that said at least one PRC comprises acetaldehyde.

22. The process according to claim 21, further characterized in that a sufficient amount of said acetaldehyde is removed from said volatile phase to maintain a concentration of less than about 400 parts per million by weight of propionic acid in said acetic acid product. purified.

23. The process according to claim 21, further characterized in that a sufficient amount of said acetaldehyde is removed from said volatile phase to maintain a concentration of less than about 250 parts per million by weight of propionic acid in said acetic acid product. purified.

24. A process for separating a mixture containing water, acetic acid, methyl iodide, meilyyl acetate, meianol, at least one C2-? 2 alkyl iodide and at least one permanganate-reducing compound (PRC) , which comprises: (a) distilling the mixture to provide a distillation column flow enriched by PRC comprising methyl iodide, water and said at least one PRC; (b) Extracting the flow of distillation column enriched with PRC with water and separating therefrom an aqueous flow conferring said at least one PRC; and (c) parading at least a first portion of the scroll column enriched with PRC excreted with the mixture.

25. The process according to claim 24, further characterized in that the step of parading the mixture comprises a plurality of consecutive desylation steps, and wherein the first portion of said de-ionization column enriched with exfoliated PRC is recycled to a flow associated with the second or last step of said distillation steps.

26. The method according to claim 24, further characterized in that it further comprises the step of adding dimethyl ether to at least one stream selected from the group consisting of said mixture, said distillation column enriched with PRC and the flows associated with said distillation.

27. The process according to claim 24, further characterized in that said second distillation column comprises dimethyl ether in an effective amount to reduce the solubility of the meityl iodide in said aqueous flow.

28. - The method according to claim 24, further characterized in that it additionally comprises the step of providing said mixture by means of the separation of a liquid composition in a low density phase and a high density phase, wherein said liquid composition comprises water, acid acetic acid, methyl iodide, methyl aceiate, meianol, at least one C2-12 alkyl iodide and said at least one PRC, wherein the low density phase comprises said mixture and the high density phase comprises iodide of mefilo.

29. The process according to claim 28, further characterized in that it further comprises the steps of: performing a vapor-liquid phase separation of the effluent from a methanol carbonylation reactor to form a vapor phase and a liquid phase; parading the vapor phase to form a first distillation column and a liquid product; and condensing at least one portion of the first deflection column to provide said liquid composition.

30. The method according to claim 29, further characterized in that said at least one PRC comprises acetaldehyde.

31. The process according to claim 30, further characterized in that a sufficient amount of said acetaldehyde is removed from said volatile phase to maintain a concentration of less than about 400 parts per million by weight of propionic acid in said acetic acid product. purified.

32. The process according to claim 30, further characterized in that a sufficient amount of said acealdehyde is removed from said volatile phase to maintain a concentration of less than about 250 parts per million by weight of propionic acid in said purified acetic acid prodrug.

33. The process according to claim 29, further characterized in that it further comprises recycling at least a portion of the distillation column enriched by PRC exirated directly or indirectly to the carbonylation reagent. 34.- The method according to claim 33, further characterized in that it additionally comprises the step of adding dimefil ether to the drainage column enriched with PRC. The process according to claim 33, further characterized in that it additionally comprises forming dimethyl ether during the desilylation of said mixture and reacting at least a portion of the dimethyl ether with carbon monoxide in the reactor. 36.- The method according to claim 35, further characterized in that it additionally comprises the step of adding water to the mixture, to a flow associated with the distillation of the mixture or in the first portion of the distillation column enriched with extracted PRC to promote the formation of dimethyl ether during distillation.