MXPA98003321A - Procedure to improve the productivity of a catalyzing solution of carbonilation by removing corrosive metals - Google Patents

Abstract

A process for treating low water carbonylation catalyst solutions containing a rhodium component and an alkali metal component for removing metal corrosion products is described, the method comprising contacting the catalyst solution with an ion exchange resin. , preferably in the form of lithium and a sufficient amount of water to reduce the concentration of alkali metal ions to optimize the removal of corrosion products.

Description

PROCEDURE TO IMPROVE THE PRODUCTIVITY OF A CATALYZING SOLUTION OF CARBONILATION BY REMOVING METALS FROM CORROSION FIELD OF THE INVENTION This invention generally relates to an improvement in the process for carbonylating methanol to acetic acid in the presence of a rhodium-containing catalyst. Very particularly, the invention relates to an improved process for regenerating a catalyst solution employed in a carbonylation reaction process with a low water content.

BACKGROUND OF THE INVENTION Among the methods currently employed to synthesize acetic acid, one of the most commercially useful is the catalyzed carbonylation of methanol with carbon monoxide as taught in E.U.A. 3,769,329 issued to Pauli et al. On October 30, 1973. The carbonylation catalyst comprises rhodium, either dissolved or otherwise dispersed in a liquid reaction medium or supported on an inert solid, together with a halogen-containing catalyst promoter. as illustrated with methyl iodide. Rhodium can be introduced into the vat reaction system in many ways, and it is not relevant, if in fact it is possible to identify the exact nature of the rhodium portion within the active catalyst complex. Also, the nature of the halide promoter is not critical. E.U.A. 329 describes a number of suitable promoters, most of which are organic iodides, very typically and usefully, the reaction is conducted with the catalyst being dissolved in a liquid reaction medium through which carbon monoxide is continuously bubbled. gaseous. An improvement in the prior art process for the carbonylation of an alcohol to produce the carboxylic acid having a carbon atom more than the alcohol in the presence of the nodium catalyst is described in E.U.A. 5,001,259 and European Patent 161,874 B2. As described therein, acetic acid (HAc) is produced from methane (MeOH) in a reaction medium comprising methyl acetate (MeOAc), methyl halide, methyl iodide (Mel) and rhodium present in a Catalystically effective concentration. The invention therein lies in the discovery that catalyst stability and carbonylation reactor productivity can be maintained at surprisingly high levels, even at very low water concentrations, i.e. 4% by weight or less, in the reaction medium (despite the general industrial practice of maintaining approximately 14% by weight or 15% by weight of water). As described in E.U.A. 259, the carbonylation reaction proceeds by maintaining in the reaction medium a catalytically effective amount of rhodium, at least a finite concentration of water, methyl acetate and methyl iodide and a specific concentration of iodide ions in and above the iodide content that is present as methyl iodide or other organic iodide. The iodide ion is present as a salt, with lithium iodide being preferred. E.U.A. '259 and EP' 874 teach that the concentration of methyl acetate and iodide salts are significant parameters that affect the rate of methanol carbonylation to produce acetic acid especially at low reactor water concentrations. 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 about 1% by weight; so low that they can be broadly defined simply as a "finite concentration" of water. In addition, the reaction medium used improves the stability of the rhodium catalyst. This stability of the catalyst is improved by having a resistance to precipitation of the catalyst, especially during the recovery steps of the process product where the distillation for the purpose of recovery of acetic acid product tends to remove, of the catalyst, the carbon monoxide that in the environment maintained in the reaction vessel is a ligand with stabilized effect on the rhodium. E .U .A. 5,001, 259 is hereby incorporated by reference. During the operation of the process for the carbonylation of methanol to acetic acid on a continuous basis, a solution containing the soluble catalyst complex is separated from the reactor effluent and recycled to the reactor. However, with an operation for prolonged periods, the corrosion products dissolve from the vessels of the metallurgical stream v. g r. , iron, nickel, molybdenum, chromium and the like and accumulate in the recirculation stream of the catalyst. Such foreign metals, if present in sufficient quantity, are known to interfere with the carbonylation reaction or accelerate competition reactions such as the water-gas exchange reaction (formation of carbon dioxide and hydrogen) and methane formation. In this way, the presence of these metallic corrosion contaminants has an adverse effect on the process, in particular, a consequent loss in performance based on carbon monoxide. In addition, foreign metals can react with ionic iodine thus making this catalyst system component not available for reaction with rodi and producing instability in the catalysed system r. In view of the high cost of the rhodium-containing catalyst, the replacement of spent catalyst can be effected only at a prohibitive cost. As a consequence, a method for regenerating the catalyst is not only desirable but necessary. In accordance with E.U.A. No. 4,007,130, a carbonylation catalyst solution comprising the reaction product of a rhodium component complex or an iridium component, a halogen and carbon monoxide component containing metal corrosion products is in close contact with an ion exchange resin. ions in their hydrogen form and the recovered catalyst solution free of metal corrosion products. As described in E.U.A. 130, the contact is made by passing the catalyst solution containing the undesirable corrosive metal contaminants through a bed of the ion exchange resin and recovering as the bed effluent, the catalyst solution containing the rhodium component complex. and iridium but substantially free of corrosion products that are absorbed onto and removed by the fact of resin. When exhausted, as indicated by the breakdown of metallic products of corrosion in the effluent, the fact of resin is regenerated by treatment with a mineral acid such as hydrochloric, sulfuric, phosphoric, hydroiodic acid and reused. However, E.U.A. '130 does not contemplate the use of catalyst solutions such as are disclosed in the aforementioned E.U.A. 5,001,259. Thus, in the improved catalyst solutions as described above, a specific concentration of iodide ions is present above and above the content of iodide which is present as methyl iodide or other organic iodide. This additional iodide ion is present as a salt, and most preferably as lithium iodide. What has been discovered is that by regenerating the catalyst solution to remove the metal contaminants by passing the catalyst solution through a bed of a cation exchange resin in the hydrogen form as described in US-4,007,130, the ion Alkali metal in the catalyst solution is preferably removed. The removal of the alkali metal ion from the catalyst solution greatly reduces the reactivity and stability of the reaction medium. Therefore, it is necessary to avoid an improved procedure to regenerate carbonylation catalyst solutions containing alkali metal ions., in particular lithium, to allow the removal of metallic corrosion contaminants from the catalyst solutions and to prevent the removal of the desirable components from said solutions. Therefore, an object of the present invention is to provide a process for treating carbonylation catalyst solutions containing lithium to remove the metallic corrosion products thereof and to recover the catalyst solution in a suitable form to return to the process as a active catalyst without the need for excessive replacement of the components in it. E.U.A. 4,894,477 incorporated herein by reference, teaches the use of a strongly acidic ion exchange resin in the lithium form to remove corrosion metals (e.g., iron, nickel, molybdenum, chromium and the like) from the carbonylation reaction system . The procedure described in E.U.A. 477 is particularly applicable to those processes which are useful for the carbonylation of methanol to acetic acid under conditions of low water content, as set forth in E.U.A. 5,001,259. The conditions of low water content improve the process of purification / production of acetic acid. However, since the lithium concentrations in the carbonylation reactor under low water conditions are increased to increase the stability of the rhodium and since the water levels in the reaction system are reduced, the capacity of the removal process of corrosion metals by ion exchange per cycle is reduced. Stated alternatively, there is a greater tendency for corrosion metals to accumulate in the carbonylation catalyst solution in a low water content process. The conditions of low water content make it difficult to remove corrosion metals from the carbonylation reaction. This problem was not recognized at the time of presenting the U.S. Patent. 477 Accordingly, it is desirable to provide a process for treating carbonylation catalyst solutions for removing metal corrosion products from a carbonylation process under conditions of low water content.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a process for regenerating or improving the productivity of a carbonylation catalyst solution under conditions of low water content. The catalyst solution contains soluble rhodium complexes and metal corrosion contaminants. The improved process comprises bringing the catalyst solution in close contact with an ion exchange resin (RII) in the form of an alkali metal, preferably in the form of lithium, and a sufficient amount of water to optimize the removal of corrosion metals from the catalyst solution and recover a catalyst solution of reduced metal contaminant content. Corrosion metal contaminants include iron, nickel, chromium, molybdenum and the like. Generally, the catalyst solution has a water concentration of from about 5 to 50% by weight, preferably from about 5 to about 30% by weight and most preferably from about 5 to about 15% by weight to improve metal removal from corrosion. According to the present invention, a catalyst solution comprising rhodium and at least a finite concentration of alkali metal ions, preferably lithium ions, which is contaminated with corrosion metals and has a certain concentration of water is brought into close contact with an ion exchange resin wherein an additional amount of water is added to the resin in an amount sufficient to increase the concentration of water (or reduce the concentration of the alkali metal ions) in the catalyst solution and a catalyst solution is recovered free or substantially reduced metal contaminants. In general, the contact is carried out by passing the catalyst solution containing the undesirable metal contaminants through an ion exchange resin bed in the form of an alkali metal, preferably Li-form, and recovering the solution as the bed effluent. catalyst that contains the rhodium component and the lithium component, but substantially free of the corrosion products that are removed by the resin bed. Upon depletion of the ion exchange resin, the resin bed can be regenerated by treatment with a lithium salt such as lithium acetate and can be reused. Water sources for the resin bed for ion exchange include but are not limited to fresh water added to the resin bed, or water from processing streams throughout the reaction system where water may be the only component or main component of the carbonylation reaction system.

The process of the invention solves a problem associated with low water content carbonylation reaction systems. It is described herein with reference to a carbonylation process employing an ion exchange resin in the form of lithium. However, the ion associated with the resin can be any known alkali metal cation, for example, lithium, sodium, potassium, and the like, provided that the corresponding ion is used as the iodide promoter in the reaction system.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram illustrating the process current flow used in the catalytic carbonylation of methanol to acetic acid and the removal of metal corrosion products from the process streams.

DETAILED DESCRIPTION OF THE INVENTION One embodiment of the present invention relates to an improvement in the process for the carbonylation of methanol to acetic acid in a carbonylation reactor by passing carbon monoxide and methanol to the reaction medium contained in a reactor and comprising a solution of acetic acid of low water content containing rhodium, a promoter of methyl iodide, methyl acetate and lithium iodide. The product, acetic acid, is recovered from the effluent of the reactor by reducing the pressure of the solution to separate as a vapor the product of the catalyst solution, said catalyst solution being then recirculated to the reactor. During the reaction and during the various process steps, the corrosion metals dissolve from the vessels and towers and will appear in the processing streams. In this way, these currents can contain the corrosion metal contaminants and are the currents that must be brought into contact with an ion exchange resin to remove metal contaminants from corrosion. The improvement of this invention comprises increasing the water content, preferably from the processing streams, by passing through the ion exchange resin in an amount sufficient to optimize the removal of corrosion metal contaminants and recovering a process stream of substantially reduced metal contaminant content. Another embodiment of the present invention relates to a method for improving the productivity of a catalyst solution comprising a determined concentration of water, a determined concentration of alkali metal ions and corrosion metal contaminants selected from the group consisting of iron, nickel, chromium, molybdenum and mixtures thereof, said process comprising contacting the catalyst solution closely with an ion exchange resin in the form of an alkali metal, preferably the lithium form, and an aqueous medium preferably water, in an amount sufficient to reduce the concentration of metal ions in the catalyst solution and recover a catalyst solution of reduced corrosion metal contaminant contents. The process of the present invention is applicable to the regeneration or improvement of the productivity of low water content catalyst solutions containing metal salts, soluble rhodium complexes and metal contaminants. The catalyst solutions to which the regeneration technique of the invention is particularly applicable are those which are useful for the carbonylation of methanol to acetic acid under conditions of low water content as set forth in US Pat. No. 5,001,259. Therefore, the catalyst solutions which are to be improved in accordance with the process of the present invention will preferably contain the rhodium catalyst and the lithium ion which are present as a lithium iodide salt. Although the present invention is directed and illustrated with respect to the production of acetic acid, the invention is equally applicable to processes for the production of other carbonylation products. For example, the present inventive technology can be applied to the production of acetic anhydride or the co-production of acetic acid and acetic anhydride. Generally, anhydrous conditions are used for the carbonylation process for the production of acetic anhydride or the coproduction of acetic anhydride and acetic acid. In accordance with the present invention, for the production of acetic anhydride or the coproduction of acetic anhydride and acetic acid, the aqueous medium, preferably water can be added to the bed of ion exchange resin to improve the process of removal of corrosion metals. and thus improve the productivity of the catalyst solution. Other processes in which the present invention may be employed include the carbonylation of alcohols, esters or ethers or their corresponding acids or anhydrides or mixtures thereof. In general, these alcohols, esters or ethers contain from 1 to approximately 20 carbon atoms. In the carbonylation of low water content of methanol to acetic acid, as illustrated in E.U.A. 5,001,259, the catalyst used includes a rhodium component and a halogen promoter in which the halogen is either bromine or iodine, or bromine or iodine compounds. In general, the rhodium component of the catalyst system is believed to be present in the form of a coordination compound of rhodium with a halogen component providing at least one of the ligands of said coordination compound. In addition to the coordination of rhodium and halogen, it is also believed that carbon monoxide ligands form coordination compounds or complexes with rhodium. The rhodium component of the catalyst system can be provided by introducing rhodium metal in the rhodium reaction zone, rhodium salts and rhodium oxides, organo rhodium compounds, rhodium coordination compounds and the like. The halogen promoter component of the catalyst system consists of a halogen compound comprising an organic halide. Therefore, substituted alkyl, aryl and 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. For example, in the carbonylation of methanol to acetic acid, the halide promoter will comprise methyl halide and most 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 supply material and / or esters of these two compounds. The preferred solvent and the liquid reaction medium for the low water carbonylation process comprises the carboxylic acid product. Thus, in the carbonylation of methanol to acetic acid, the preferred solvent is acetic acid. Water is also added to the reaction medium, but at conrations well below what has hitherto been considered practical to achieve sufficient reaction rates. It is known that in the rhodium-catalyzed carbonylation reactions, the addition of water exerts a beneficial effect under the reaction rate (E.U.A. 3,769,329). In this way, commercial operations are carried out at water conrations of at least 14% by weight. In accordance with E.U.A. 259, it is highly expected that reaction rates substantially equal to and above the region velocities obtained with said high levels of water conration can be achieved with water conrations below 14% by weight and as low as 0.1%. in weigh. In accordance with the carbonylation process described in E.U.A. 477, the desired reaction rates are obtained even at low water conrations by including in the reaction medium an ester corresponding to the alcohol which is being carbonylated and the acid product of the carbopylation reaction and an additional iodide ion which is in and above the iodide which is present as a catalyst promoter such as methyl iodide or other organic iodide. Thus, in the carbonylation of methanol to acetic acid, the ester is methyl acetate and the additional iodide promoter is an iodide salt, e.g., lithium iodide. It has been found that under low water content conrations, methyl acetate and lithium iodide act as speed promoters only when relatively high conrations of each of these components are present and that promotion is greater when these two components are present. present simultaneously. This has not been recognized previously. It is believed that the conration of lithium iodide used in the reaction medium described in E.U-. '477 is high compared to how little the prior art is dealing with the use of halide salts in reaction systems of this type. As mentioned above, carbonylation catalyst solutions are useful in carbonylation alcohols. Useful supplies that can be carbonylated include alkanols having 1 to 20 carbon atoms. Preferred supply materials are alkanols containing 1-10 carbon atoms, and most preferred are alkanols of 1-6 carbon atoms. Methanol is the particularly preferred feed and is converted to acetic acid. The carbonylation reaction can be carried out by closely contacting the defined feed alcohol, which is in the liquid phase, with gaseous carbon monoxide bubbled through a liquid reaction medium containing the rhodium catalyst, promoter component containing halogen, alkyl ester and additional soluble iodide salt promoter, under conditions of temperature and pressure suitable to form the carbonylation product. Thus, if the feed is methanol, the halogen-containing promoter component will comprise methyl iodide and the alkyl ester comprising methyl acetate. It will generally be recognized that it is the concentration of 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 nature of the cation is not as significant as the effect of iodide concentration. Any metal iodide salt, or any iodide salt of any organic cation can be used as long as the salt is sufficiently soluble in the reaction medium to provide the desired level of iodide. The iodide salt may be a quaternary salt of an organic cation or the iodide salt of an inorganic cation, preferably it is an iodide salt of a member of the group consisting of the metals of group 1 and 2 of the periodic table (as is disclosed in "Handbook of Chemistry and Physics," published by CRC Press, Cleveland, Ohio, 1995-96 (7th edition).) In particular, alkali metal iodides are useful, with lithium iodide being preferred. the use of lithium iodide and the inadvertent loss thereof during the removal of metal contaminants from catalyst solutions by ion exchange is the problem directly solved by the catalyst regeneration process of this invention. typical for carbonylation will be approximately 150-250 ° C, with the temperature scale of approximately 180-220 ° C being the preferred scale.The partial pressure of carbon monoxide in the The reactor can vary widely but is typically from about 2 to 30 atmospheres and preferably from 4 to 15 atmospheres. Due to the partial pressure of by-products and the vapor pressure of the contained liquids, the total pressure of the reactor will vary from approximately 15 to 40 atmospheres. Figure 1 illustrates a reaction system that can be employed in the catalyst regeneration process of the present invention. The reaction system comprises a liquid phase carbonylation reactor, a vaporizer, a separation column of methyl iodide-acetic acid (hereinafter separating column), a decanter, a drying column and an ion exchange resin. . For purposes of illustration, an RII is shown in Figure 1. It is understood that the carbonylation process may have more than one RII bed available for use. The carbonylation reactor is typically a stirred autoclave within which the content of reaction liquid is automatically maintained at a constant level. Carbon monoxide, fresh methanol, water sufficient to maintain at least a finite concentration of water in the reaction medium, recirculated catalyst solution from the base of the vaporizer, and methyl iodide and recirculated methyl acetate from the reactor are continuously introduced into this reactor. of the head of the separation column. Alternate distillation systems can be employed while providing means for recovering the crude acetic acid and for recirculating to the reaction catalyst solution, methyl iodide and methyl acetate. In the preferred procedure, the carbon monoxide feed is continuously introduced to the carbonylation reactor just below the agitator. The gaseous feed is dispersed uniformly through the reaction liquid by mixing. A gas purge stream is vented from the reactor to prevent the accumulation of gaseous by-products and to maintain the partial pressure of carbon monoxide at a given total reactor pressure. The temperature of the reactor is controlled automatically and the carbon monoxide feed is introduced at a sufficient rate to maintain the desired total reactor pressure. The liquid product is expelled from the carbonylation reactor at a sufficient rate to maintain a constant level therein and is introduced into the vaporizer at an intermediate point between the upper part and the lower part thereof. In the vaporizer, the catalyst solution is carried as a base current (predominantly acetic acid containing rhodium and iodide salt together with minor amounts of methyl acetate, methyl iodide and water), while the head of the vaporizer comprises for the most part the product acetic acid together with methyl iodide, methyl acetate and water. A portion of the carbon monoxide together with gaseous byproducts such as methane, hydrogen and carbon dioxide leave the top of the vaporizer. The acetic acid product from the base of the separation column (can also be carried as a side stream) is then expelled for final purification as desired by methods that are obvious to those skilled in the art and are beyond the scope of the present invention. The use of a dry column is a means of purification of acetic acid product. The head of the separation column, which comprises mainly methyl iodide and methyl acetate, is recirculated to the carbonylation reactor together with fresh methyl iodide; the fresh methyl iodide is introduced at a sufficient rate to maintain the desired concentration of methyl iodide in the liquid reaction medium in the cbolylation reactor. Fresh methyl iodide is necessary to compensate for small losses of methyl iodide in the vaporizer and carbonation reactor vent streams. A portion of the head of the separation column is introduced into a decanter which divides the stream of methyl iodide and methyl acetate to a heavy phase of aqueous methyl iodide and methyl acetate and a light phase comprising aqueous acetic acid. Any water from the purification step that will contain small amounts of acetic acid can be combined with the light aqueous acetic acid phase of the decanter to return to the reactor. It has been found that metal contaminants, in particular iron, nickel, chromium and molybdenum, can be present in any of the process streams as described above. The accumulation of these metal contaminants has an adverse effect on the rate at which acetic acid is produced and the stability of the process in general. Accordingly, an ion exchange resin is put into the processing scheme to remove these metal contaminants from the processing streams. In Figure 1, an ion exchange resin is used to remove corrosive metal contaminants from the recirculated catalyst solution from the base of the vaporizer to the reactor. It should be understood that any of the processing streams can be treated with the ion exchange resin to remove metal contaminants therefrom. The only necessary criterion is that the processing current can be at a temperature that does not deactivate the resin. In general, the processing streams that are treated will have a finite concentration of the rhodium catalyst and / or lithium cation of the additional lithium iodide salt that is added as a catalyst promoter. In Figure 1, the stream from the base of the separation column is treated to remove metals from corrosion, and water is directed from the stream of diluted acetic acid to the ion exchange resin. Sources for adding water to the resin include fresh water from the outside of the reaction system or water from the interior of the reaction system that is finally returned to the reactor. It is preferred that the water inside the reaction system be directed to the resin for use in the improved corrosion metal removal process. A water balance then remains within the carbonylation reaction system. Examples of water sources include (but are not limited to) water contained in recirculated dilute acetic acid streams, water from the light phase or water from the combined streams (eg, combined heavy and light phase streams, or the combined light phase and dilute acetic acid streams) which together may have a high concentration of water present. The water can be cooled from any point within the reaction system. The addition of water to the ion exchange resin can be varied to optimize the removal of corrosion metal. Under carbonylation reactor conditions employing 14% by weight or 15% by weight of water, only small improvements in the amount of corrosion metal removal per ion exchange resin depletion cycle would be expected. However, under conditions of low water content carbonylation, the need for an appropriate concentration of water in the RII corrosion removal process is significant. Generally, the water content in the catalyst solution is from about 5 to about 50% by weight. However, a preferred scale is from about 5 to about 30% by weight and a scale of about 5 about 15% by weight is very preferred. The resins useful for regenerating the catalyst solutions according to the present invention are cation exchange resins of either the strong acid or the weak acid type. As mentioned earlier, any cation is acceptable provided that the corresponding cation is used in the iodide promoter. For purposes of illustrating the present invention, a cation exchange resin in its lithium form is employed. The strong acid and weak acid type resins are readily available as commercial products. The weak acid cation exchange resins are mostly copolymers of acrylic or methacrylic acid or esters of the corresponding nitriles, but a few of these resins sold are phenolic resins. The strong acid cation exchange resins, which are the preferred resins for use in the present invention, consist predominantly of sulfonated styrene-divinylbenzene copolymers, although some of the available resins of this type are phenol-foraldehyde condensation polymers. . Either the gel-type resin or the macroreticular type resin is suitable, but the latter is preferred since the organic components are present in the catalyst solutions that are being treated.

Acrylic-resin resins are commonly used in the catalytic art. They require a minimum of water to maintain swelling properties. The present invention is particularly surprising since those skilled in the art believe that with the use of macroreticular type resin very little water is needed for its use. As such, the problems are not anticipated with the resin when the carbonylation process is changed from a high water content process to a low water content process. However, it was found here that, as the concentration of water in the reaction process was decreased, the ability to remove metals from corrosion in the presence of a high lithium ion concentration using a macroreticular retina also decreased. The contact of the catalyst solutions contaminated with metal and the resin can be carried out in a stirred vessel where the resin is suspended with the catalyst solution with good agitation and the catalyst solution is then recovered by decanting, filtration, centrifugation, etc. . However, the treatment of the catalyst solutions is generally effected by passing the metal contaminated solution through a fixed bed column of the resin. The regeneration of catalyst can be carried out as an intermittent, semi-continuous or continuous operation with either manual or automatic control using methods and techniques well known in the ion exchange art. The ion exchange treatment can be carried out at temperatures on the scale from about OßC to about 120 * C, although lower or higher temperatures are limited only by the stability of the resin to be used. Preferred temperatures are those that are on the scale of about 20 * C to about 90 ° C; Chromium removal is more efficient at higher temperatures. At higher temperatures, a purge with nitrogen or CO is desirable. If temperatures above the boiling point of the catalyst solutions are used, then operation under pressure will be required to maintain the solution in the liquid phase. However, pressure is not a critical variable. In general, an atmospheric pressure or pressure slightly above atmospheric is used, but if desired, superatpheric or sub-atmospheric pressures can be used. The flow rate of the catalyst solution through the resin during the metal removal process in general will be recommended by the resin manufacturer and will usually be around 1 to about 20 bed volumes per hour. Preferably, the flow rates will be from about 1 to about 12 bed volumes per hour. After contacting the bed with rhodium-containing processing streams, washing or rinsing the resin bed with water or the carbonylation product proceeds from the process from which the catalyst being treated, such as acid, is depleted. acetic, it is essential to remove all the rhodium from the resin bed. The rinsing or washing is carried out at flow rates similar to those of the removal step. After the resin has been exhausted, it is to say, when the metal contaminants are passing to the effluent, the resin can be regenerated by passing through it a solution of organic salts, for illustrative purposes, preferably salts. of lithium. Generally, the lithium salt used in the regeneration cycle has a concentration on the scale of about 1% by weight to about 20% by weight. The quantities and procedures used are those well established in the art and recommended by resin manufacturers. Aqueous lithium acetate is preferred as a regenerating agent since the acetate anion is employed in the reaction system and is readily available for its use. A further advantage is that their use eliminates the rinsing step normally required after the regeneration process when other regeneration compounds are employed. To maximize the corrosion metal regeneration capacity and to maximize the performance of resin bed column at relatively high concentrations of lithium acetate, the lithium acetate regeneration solution must contain some acetic acid or product that is being produced, to avoid the formation of any insoluble corrosion metal compounds during the regeneration cycle. The precipitation of these compounds during the regeneration cycle could reduce the regeneration performance of the column and could also clog the resin bed. Typically, acetic acid concentrations of about 0.1 to about 95% by weight can be used, with acetic acid concentrations of about 0.1 to about 20% by weight being preferred. The treatment of the catalyst solution can be operated as an intermittent operation or a continuous operation. The preferred type of operation is continuous. In a continuous process, a slip current from a catalyst solution that is being recirculated to the reactor to produce the acids, is collected, passed through the ion exchange resin bed, together with an aqueous recirculation stream to provide sufficient water concentration to increase the amount of corrosion products being absorbed thereon, and the effluent, free of corrosion products, together with the combined aqueous recirculation material is returned to the catalyst recirculation stream and therefore to the reactor. The ion exchange operation can be cyclical (where more than one resin is available for use). As the resin is exhausted in a bed of resin, the slipstream of the catalyst solution can be diverted to a cold bed while the spent bed is subjected to regeneration. The invention is further illustrated by the following non-limiting examples.

EXAMPLES TABLE 1 Comparison of removal of corrosion metal from catalyst solution * at various concentrations of water (Li / Fe molar ratio in catalyst solution, approximately 86 +/- 5: 1).

Example Water,% by weight Removal of Fe. G / L RGI 1 1.23 0.09 2 6.4 0.36 3 10.96 0.93 4 15.1 1.85 5 46.0 6.9 * The catalyst solution was obtained from the vaporizer residue. The exhaust cycle was carried out at a feed rate (typically at a bed volume of 1-2 per hour) through 100 ml of strong macroreticular ion exchange resin from Rohm & Hass, Amberlyst-15 (A-15) in the form of Li followed by a step of rinsing and regenerating the RII bed using 10% by weight of an aqueous solution of LiAc typically containing about 10% by weight of acetic acid.

TABLE 2 Comparison of removal of corrosion metal from a synthetic catalyst solution ** at various concentrations of water (Li / Fe molar ratio in a catalyst solution of approximately 54: 1).

Water Example % by weight Removal of Fe. q / L RII 6 0.27 0.456- 7 1.70 0.471 8 5.34 1.325 9 10.62 2.760 10 14.81 3.137 11 19.02 3.341 12 34.45 3.673 13 47.36 3.940 ** A series of intermittent experiments were conducted each with approximately 13.3 rolls of A-15 RII, 80 g of an acetic acid solution containing approximately 973 ppm of Fe and approximately 6.502 ppm of Li with various additions of water. Samples were analyzed after 13 and 29.5 hours to establish a balance. The results of Examples 6-13 show a trend similar to that illustrated by catalyst operations of Examples 1-5.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for improving the productivity of a carbonylation catalyst solution used in conditions of low water content, said carbonylation catalyst solution containing rhodium, alkali metal and also containing corrosion metal contaminants, said method comprising contacting the catalyst solution of carbonylation with an ion exchange resin and water in an amount sufficient to bring the concentration of water of the catalyst solution as it proceeds through the contact cycle within a range of about 0.25% by weight to about 50% by weight. weight and recover a catalyst solution of the reduced corrosion metal contaminant content.

2. The process according to claim 1, further characterized in that the resin is a strong acid cation exchange resin.

3. The process according to claim 1, further characterized in that said contact is made by passing the catalyst solution through a fixed bed column of said resin.

4. The process according to claim 1, further characterized in that said resin is regenerated after exhaustion by washing with an alkali metal salt.

5. The process according to claim 4, further characterized in that said alkali metal salt is lithium acetate.

6. The process according to claim 4, further characterized in that the alkali metal is potassium.

7. The process according to claim 4, further characterized in that the alkali metal is sodium.

8. In a process for the carbonylation of methanol to acetic acid in a carbonylation reactor by passing carbon monoxide through a reaction medium contained in said reactor and comprising methanol and a catalyst solution of the low water content comprising rhodium, a promoter of methyl iodide, methyl acetate and lithium iodide to produce acetic acid and said acetic acid is recovered from the reactor effluent by concentrating the effluent into a variety of processing streams comprising one or more of the components of said Catalyst solution and acetic acid product where said streams contain lithium and metallic corrosion contaminants, and said currents are put in contact with a cation exchange resin to remove metallic contaminants from corrosion, the improvement includes: increasing the water content that passes through the cation exchange resin to carry the co Water concentration of the catalyst solution as it proceeds through the contact cycle within a range of about 0.25 wt% to about 50 wt% to optimize the removal of corrosive metal contaminants and recover a stream of water substantially reduced metal contaminant content.

9. The process according to claim 8, further characterized in that the resin is a strong acid cation exchange resin.

10. The method according to claim 8, further characterized in that said contacting is carried out by passing the catalyst solution through a fixed bed column of said resin.

11. The process according to claim 8, further characterized in that said resin is regenerated after exhaustion by washing with a lithium salt.

12. The process according to claim 11, further characterized in that said lithium salt is lithium acetate.

13. A process for improving the productivity of a carbonylation catalyst solution under conditions of low water content, said solution comprising a concentration of alkali metal and fixed water and metal corrosion contaminants selected from the group consisting of iron, nickel, chromium, molybdenum and mixtures thereof, said process comprising contacting the catalyst solution in a contact cycle with a cation exchange resin and water in an amount sufficient to bring the concentration of water of the catalyst solution to As it proceeds through the contact cycle within the range of about 0.25% to about 50% by weight.

14. A process for improving the productivity of a carbonylation catalyst solution used in conditions of low water content, said solution containing rhodium and alkali metal and also containing metallic corrosion contaminants, said method comprising contacting the catalyst solution with a ion exchange resin and water in an amount sufficient to bring the concentration of water of the catalyst solution as it proceeds through the contact cycle on a scale of about 0.25% by weight to about 50% by weight and recover a catalyst solution of reduced corrosion metal contaminant content.

15. The process according to claim 1, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 30% by weight. weight.

16. The process according to claim 15, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 15% by weight. weight.

17. The process according to claim 13, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 30% by weight. weight.

18. The process according to claim 17, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 15% by weight. weight.

19. The process according to claim 14, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 30%. in weigh.

20. The process according to claim 19, further characterized in that the concentration of water of the catalyst solution as it proceeds through the contact cycle is within the range of about 5% by weight to about 15% by weight. weight.