NL8204901A - PURIFICATION OF CARBONYLATION PRODUCTS. - Google Patents

Description

Purification of carbonylation products.

The invention relates to the purification of carbonylation products, in particular the purification of carboxylic acids, especially acetic acid.

Processes have been developed to prepare carboxylic acids, carboxylic anhydrides and carboxylic acid esters by reacting olefins, alcohols, esters, ethers or halide derivatives thereof with carbon monoxide in the presence of a catalyst system consisting of a metal catalyst component and an iodide component, generally hydrogen iodine or an alkyl iodide, in particular hydrogen iodine or methyl iodide. Methods of this nature involving a Group VIII noble metal catalyst, such as rhodium, palladium, iridium and the like, are disclosed, for example, in U.S. Patents 3,579 * 551, 3 * 579 * 552, 3 * 769 * 329, 3,772,380 and 4,115ΛΜ and in British patents 1Λ68.9 ^ 0 and 1,538,782. Catalyst systems of the nature indicated, where the metal component is composed of nickel or nickel compounds, are described, for example, in U.S. Pat. Nos. 2,729,651, 4,133 * 963 and 1 + .218.3 ^ 0. The effluents from these processes are treated, usually by distillation, to separate the relatively non-volatile metal-containing catalyst component, and the liquid effluent effluent portion is then separated, such as by fractional distillation, into the various components, including the product. of the reaction, whether it be an acid, an anhydride or an ester. Even with relatively efficient distillation, the products inevitably contain a small amount of iodine or an iodine compound, such as hydrogen iodide or methyl iodide, while most of the iodine core can be separated in the effluent by such distillation and recycled to the carbonylation zone to providing the iodine core required in the production of further amounts of 8204901 2 * carbonylation products of the type indicated above.

Although the amount of the iodine core remaining in the products is generally very small, the products are still contaminated to an extent which is undesirable in many cases and often interferes with their utilization. Attempts to eliminate or reduce the amount of iodine contamination to acceptable levels by fractional distillation have presented problems. One of the problems encountered is due to the fact that carbonylation products contain iodine impurities, which are very resistant to distillation separation. U.S. Pat. No. 2, 6,195 provides a process for removing iodine nuclei, especially organic iodine compounds, from carbonylation products by treating the iodine-contaminated products with cesium acetate, potassium acetate or sodium acetate. U.S. Pat. No. 3,772,156 purifies acetic acid by removing iodine by multiple distillation combined with chemical treatment. While these processes are effective, it is desirable to provide a less complicated treatment method, which will reduce the iodine content to low levels.

It is therefore an object of the invention to provide an improved method of removing iodine impurities from carbonation products which effectively reduces such impurities to low levels.

According to the invention, it has now surprisingly been found that when the carbonylation product to be purified is treated with an anion exchange resin under moderate temperature conditions and for a relatively short duration, the iodine cores present as impurities in the carbonylation product are usually resistant to separation by distillation. can be removed almost completely leaving a effluent, which can then be distilled to form a purified product substantially free of the iodine nuclei, ie they are left behind 8204901 ----- 3 0- * in concentrations as low as a few parts per million and in an entirely acceptable form for technical use.

According to the process of the invention, a liquid stream containing the carbonylation product to be purified and iodine-core impurities is brought into thorough contact with an anion exchange resin, and the stream is then distilled by conventional fractional distillation to provide a product substantially free of the iodine impurities. Contacting is usually accomplished by passing the stream containing the undesired iodine impurities through a bed of the anion exchange resin and recovering from the bed as the effluent the carbonylation product stream containing the carbonylation product but substantially free of the iodine nuclei. resistant to distillation removal adsorbed on the resin bed.

The carbonylation product feed according to the process according to the invention is one consisting essentially of a carboxylic acid, for example acetic acid and / or a carboxylic anhydride, for example acetic anhydride and / or an alkanol, for example acetaldehyde and / or an alkylidene diester, for example ethylidene diacetate and / or a vinyl ester, for example vinyl acetate and / or an alkanoic acid ester, for example methyl acetate, and which contains iodine impurities corresponding to or derived from the iodine cores, which are present in the carbonylation zone, in which the carbonylation feed is produced by the carbonylation of alcohols, olefins, esters or ethers in the presence of a Group VIII metal-containing catalyst and an iodine core, as described in U.S. Pat. Nos. 2,729 * 651, 3,579 * 551, 3 * 579 * 552, 3 * 769 * 329, 3 * 772,380, U.115.UUU , k. 133,963 and 1,218,3 ^ 0 and British Pat. Nos. 1U68.9UO and 1,538,782. What is disclosed in said U.S. and British patents is to be considered incorporated herein. The method according to the invention can be carried out in a relatively anhydrous system or in an aqueous system. Usually contaminated 8204901 u carboxylic acid streams contain water and can be treated before or after removal of the water. In U.S. Pat. No. 238,291 and British Pat. No. 899,288, ion exchange resins are used to treat effluents from the catalytic oxidation of substituted aromatics in the presence of catalyst systems containing bromine or chlorine nuclei, but such oxidation reactions differ from carbonylation reactions carried out in the absence of oxygen, and the halogen compounds contained in these oxidation effluents are different from those pertaining to the present process.

The iodine impurity content of the carbonylation product feed according to the process of the invention may vary, the limiting factor for the impurity level in the feed being substantially an economic factor. Complete removal of impurities from the feed by distillation for use in the process of the invention is generally not economical and, in practical terms, has not been found practicable. The greater the content of iodine contamination in the feed to the process of the invention, the greater the required resin bed depth or the more often the need for regeneration of the anion exchange resin. In any case, the impurity level in the feed therefore represents an economic balance between costs of pre-distillation and use of the treatment resin. Such considerations normally dictate foods containing less than 1000 parts per million iodine contaminants in the diet, generally less than 500 parts per million and usually at most 300 parts per million, with all amounts referring to the iodine contained therein. basis of the total diet.

The anion exchange resins useful according to the invention are either of the strongly basic or weakly basic type. Both types are readily available as commercial products. Strongly basic resins generally contain 35 quaternary ammonium groups attached to a poly (styrene-8204901 divinylbenzene) soil mass. They can be produced by chloromethylation of the copolymer bead using chloromethyl ether and a Friedel-Crafts condensation catalyst, such as AlCl 2 SnCl 2, FeCl 2 or ZnCl 2. Typical products are those derived from trimethylamine, sold under brands such as Amberlite IRA-HOO, Amberlite IRA-1 + 01, Amberlite IRA-U02, Amberlite IRA-900, Duolite A-101-D, Duolite ES-111, Dowex 1, Dowex 11, Dowex 21K, and Ionac A-5 ^ 0 and some are derived from dimethylethanolamine, for example, Amberlite IRA-U10, 10 Amberlite IRA-911, Dowex 2, Duolite A-102-D, Ionac A-5 ^ 2 and

Ionac A-5 ^ 2 and Ionac A-550. Several resins of mixed basicity, some of them weak and some of them strong, are likely prepared by the alkylation of a weakly basic resin with an alkyl halide or sulfate. Examples of this type of resin are Duolite A-30 and Ionac A-300.

Weakly basic anion exchange resins contain primary, secondary and / or tertiary amine groups, generally a mixture. A wide variety of products are available, generally condensation products of aliphatic polyamines with formaldehyde or with alkyl dihalides such as ethylene dichloride, or with epichlorohydrin. Examples of these products are Dowex kk, Duolite A-7Ionac A-2o0 and Amberlite IRA-68. Another group of weakly basic anion exchange resins is that prepared by reacting an amine or polyamine with the chloromethylated styrene divinyl benzene copolymer bead. tAmberlite IR-U5, Amberlite IRA-93> Dowex 3, Dowex MWA-1 and Duolite A-14). Both the gel type resin and the macroreticular type resin are suitable, but the latter is preferred, since organic components are present in the streams being treated.

Contacting the carbonylation product stream with the resin can be accomplished in a stirred vessel in which the resin is slurried with the liquid stream with good stirring and the liquid stream is then recovered by decantation, filtration, centrifugation and of such.

8204901 6

Treatment of the stream, however, is generally accomplished by passing it through a fixed bed column of the resin. The treatment can be carried out as a discontinuous, semi-continuous or continuous operation, either by 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 in the range of 10-80 ° C, although lower or higher temperatures can be used, which are only limited by the stability of the resin. Preferred temperatures are those in the range of 20-60 ° C. When temperatures above the boiling point of the liquid stream are used, pressurization will be required to keep the solution in the liquid phase. However, the pressure is not a critical variable. In general, atmospheric pressure or a pressure slightly above atmospheric is used, but if desired, superatmospheric or subatmospheric pressures can be used.

The flow rate of the carbonylation liquid through the resin will generally be that recommended by the resin manufacturer and will usually be 2-12 gallons per minute per square foot cross-sectional area.

After it is exhausted, that is, when significant amounts of iodine nuclei break through into the effluent, the resin can be regenerated by passing a solution of sodium hydroxide through it. Generally, the regenerant has a concentration in the range of 2-U%. The amounts and procedures used are those established in the art and recommended by the resin manufacturers.

The treatment of the carbonylation product stream can, as mentioned, be a discontinuous or continuous operation. The preferred type of operation is a continuous one, in which the current is passed through the anion exchange resin, the iodine nuclei are adsorbed thereon, and the effluent, which is substantially free of these impurities, is recovered 8204901 τ. The anion exchange treatment can be cyclic.

If the resin becomes exhausted in a bed, the flow of carbonylation product can be diverted to a fresh bed, while the exhausted bed is subjected to regeneration. The greater the depth of the resin bed, the less often there will be a need for regeneration, as will be apparent to those skilled in the art. Usually the minimum bed depth should be about 3 feet.

When the treatment with the anion exchange resin 10 has been carried out by contact in a stirred vessel containing the resin as slurry in the carbonylation stream, it will of course be necessary to filter the treated stream to remove the resin for reuse. When the carbonylation product stream is passed through a bed of the resin, such filtration is not necessary, but in both cases the treated product is subjected to final distillation to recover the desired product in the purest possible form. When the carbonylation stream contains water, which is generally the case with a carboxylic acid containing carbonylation product stream, the treated product is subjected to dehydration distillation to remove most, if not all, of water. No subsequent distillation may be required, although final distillation may be used if desired. Such distillations are of course known to those skilled in the art and are not features of the present invention. Generally, a minimum of 20 theoretical plates are required at the distillation stage.

The following examples of specific application will serve to provide a more complete understanding of the invention, but it will be understood that these examples are given for illustrative purposes only, and should not be construed as limiting the invention.

Example I

In this example, 150 ml of a weakly 35 basic resin are marketed under the trade name Dowex MWA-1 in an 8204901 8 3A inch diameter glass tube to form a bed 21 inches high and pass through this bed at a flow rate of 100 ml / hour, a stream consisting of approximately 86 parts per acetic acid and 1 part per cent water and with an iodine content of 220 parts per million. The stream was obtained from the reaction product of the carbonylation of methanol in the presence of a Group VIII metal catalyst and methyl iodide. The reaction product was distilled off from the catalyst and then subjected to distillation to separate by-product methyl 10-acetate, unreacted methanol and as much methyl iodide as possible. The stream was passed continuously through the bed for 10 hours. The total iodine analysis of the resin bed effluent was 27 parts per million.

The effluent is then subjected to distillation in a 2 inch Oldershaw column with 70 trays in a 2: 1 return ratio to separate the water from the acetic acid.

The column bottom product, consisting of substantially pure acetic acid, contained 1-3 parts per million of total iodine.

Example II

Example I is repeated, but now the treated stream is distilled as described without first passing it through the resin bed. The acetic acid bottoms of the column contained 100 parts per million of total iodine.

Example III

The procedure of Example 1 is repeated, but now the feed is distilled first to remove water before it is passed through the catalyst bed and the catalyst effluent is distilled as described in Example 1 to obtain a product equivalent to that described in Example I.

Example IV

In two tests, Example I is repeated, but now the treated streams are composed of acetic anhydride, one obtained by the carbonylation of methyl acetate and the other by the carbonylation of dimethyl ether. The feed streams 8204901 * 9 are virtually vessel free and contain iodine in an amount of about 225 parts per million. After passing through the resin bed and distillation as described in Example I, the iodine content of the product effluent streams corresponds to that of the product stream obtained in Example I.

Example V

Example IV is repeated, but now the acetic anhydride is accompanied by about 25% of an ester, in this case methyl acetate. The iodine removal results obtained are similar to those obtained in Example IV.

8204901

Claims (3)

Process for purifying carbonylation products to remove iodine impurities, characterized in that said products are treated with an anion exchange resin. 2. Process according to claim 1, characterized in that said carbonylation products contain less than 1000 parts per million of said iodine impurities. 3 * Method according to claim 1, characterized in that the amount of iodine contamination is reduced to at most about 3 parts per million. H. Any of the methods or products or devices, or any combination thereof, substantially as described herein. 15 820 4 9 0 1