MXPA99004556A - Method for the production of (meth)acrylic acid esters - Google Patents

Abstract

The invention relates to a method for producing (meth)acrylic acid esters by reacting (meth)acrylic acid with C 4-C 12-alkanols in the presence of sulfuric acid or of a sulfuric acid mono-C 4-C 12-alkyl ester as a catalyst, wherein the catalyst is regenerated by extraction with water from the reaction mixture and the aqueous catalyst solution is reintroduced into the esterification. The concentration of non-reacted alkanol in the reaction mixture that is to be extracted amounts to a maximum of 5 wt.%in relation to said reaction mixture.

Description

PREPARATION OF ACRYLIC STEREOS (MET) The invention relates to a process for preparing esters of acrylic acid or methacrylic acid [(meth) acrylic acid]. (Meth) acrylic esters are usually prepared industrially by esterification of (meth) acrylic acid with alkanols in the presence of strong acids as esterification catalysts (for example a mineral acid, such as sulfuric acid or phosphoric acid, alkanesulfonic acids or arylsulfonic acids) ) • Processes of this type are described in, for example Kir Othmer, Encyclopedia of Chemical Technology, vol.1, pp. 347-348.The content of catalysts in the esterification mixture can vary by an order of magnitude of a tenth of a hundred to several hundred.When using polybasic mineral acids as catalysts, the mineral acid is rapidly esterified by the alkanol present, forming the monoester, which is the actual esterification catalyst.The reaction mixture contains a relatively large amount of This monoester when the esterification is complete Acids used as catalysts and their esters They can form must be removed from the reaction mixture before further processing. Generally, this is carried out by extraction and neutralization of the reaction mixture with hydroxide solution or solutions of alkali metal carbonate and alkaline earth metal. This operation produces wastewater whose disposal is complex and pollutes the environment. If sulfuric acid is used as a catalyst, as mentioned, the monoester of sulfuric acid is mainly formed with the alkanol in question. The salts of the sulfuric monoesters, in particular of the esters with higher alkanols, are surface active and their elimination could considerably deteriorate the quality of the waste water of the process and could cause a not insignificant loss of the valuable product. For economic and ecological reasons, the recovery and recycling of the catalyst, in this way, is desirable. The prior art includes a plurality of processes, however, all essentially present considerable disadvantages. EP-A-0 609 127 describes a process for the preparation of (meth) acrylic esters in which the alcohol component is recovered by acid hydrolysis of the corresponding sulfuric monoester which is formed of sulfuric acid and the alcohol during the esterification. This process is complex, contaminating the environment and not economic. CZ-B-179 808 describes a process for recovering mineral acids from esterification mixtures by extraction of the esterification mixture with water, concentrating the aqueous phase by distillation and recycling the aqueous catalyst solution, concentrated, thus obtained, to the esterification reaction. This process consumes energy. EP-A-0 618 187 (US-A-5, 386, 052) describes a process for preparing (meth) acrylic esters, in which the catalyst is extracted with water and the extract, with or without concentration by distillation, is recycle to the esterification reaction. However, here it is particularly emphasized that sulfuric acid, due to the poor extractability of monoalkyl sulfate, is unsuitable as a catalyst, because the large amount of water that may be necessary for an adequate extraction of monoalkyl sulfate could adversely affect the esterification reaction. Therefore, as a catalyst, use is made of alkylsulfonic or arylsulfonic acids (column 2, lines 55ff), which are, however, considerably more expensive than sulfuric acid. It is an object of the present invention to develop an economically and technically simple process for preparing (meth) acrylic esters which successfully use sulfuric acid as an esterification catalyst and which allow the separation of the esterification catalyst (sulfuric acid or monoalkyl sulfate) from a very simple and substantially complete mode of the resulting reaction mixture. further, the catalyst must be recyclable directly to the esterification, that is, without additional concentration by distillation, without affecting the esterification. It has been found, surprisingly, that the catalyst can be extracted from the reaction mixture (esterification mixture) if the content of alkanol in the mixture is no greater than 5% by weight. We have found that this objective is carried out by a process for the preparation of (meth) acrylic esters by reaction of (meth) acrylic acid with C4-C12 alkanols, preferably C4-C10 alkanols, particularly preferable C4-C8 alkanols , in the presence of sulfuric acid or a C4-C12 monoalkyl sulfate as a catalyst, comprising the regeneration of the catalyst by extraction with water of the reaction mixture and the recycling of the aqueous catalyst solution back to the esterification, the concentration of alkanol which did not react in the reaction mixture to be extracted being no more than 5% by weight, based on the reaction mixture that is to be extracted. It has been found, surprisingly, that the alkanol content has a great influence on the extraction capacity of monoalkyl sulfate, which is formed of sulfuric acid and alkanol and which acts as the actual esterification catalyst.; surprisingly, the catalyst can be extracted from the reaction mixture (esterification mixture) if the content of alkanol in the mixture is not more than 5% by weight (see Table 1). As a result, the catalyst can be extracted with small amounts of water, so that the extract can be directly recycled to the esterification. Preferably, a reaction mixture whose alkanol content is < 3% by weight, and in particular < 1% by weight To achieve an alkanol content of not more than 5% by weight, a high degree of esterification is preferably carried out, for example, by distillation of the water of reaction; and / or an appropriate ratio of the starting materials is selected. If the residual alkanol content is then still more than 5% by weight, the alkanol is distilled in a conventional distillation apparatus (for example a column equipped with perforated plates, Raschig rings, ordered packing etc.). Surprisingly, in spite of the presence of the strongly acidic esterification catalyst, side reactions not catalyzed by acid, such as the formation of ether or olefins or addition of the alkanol in the double bond of the (meth) acrylate (Michael addition), can be observed in any significant degree. The distillation is carried out in a customary manner; the distillation conditions depend on the type of alkanol used. The alkanol is preferably distilled to a residual alkanol content in the reaction mixture that allows the catalyst (sulfuric acid) to be extracted with water without problems. In particular, the residual alkanol content is = 5% by weight, preferably < 3% by weight, particularly preferably = 15 by weight, based on the reaction mixture. Preferably, the conditions for the extraction of the catalyst from the esterification mixture are selected in such a way that the concentration of catalyst (sulfuric acid and monoalkyl sulfate) in the aqueous phase is at least 20%, in particular at least 25% by weight, based on the aqueous extract, and the degree of extraction is at least 70% by weight, in particular at least 80% by weight, based on the amount of catalyst in the reaction mixture. To achieve this, from about 5 to 20% by weight of water, in particular from about 8 to 15% by weight of water, based on the total weight of the esterification mixture, is used for extraction. The resulting extract can be recycled, without concentrating it, back to the esterification. The extraction can be carried out in a manner known per se. Preferably, the extraction is carried out countercurrently, for example, in columns that do not have energy consumption, pulsed columns, columns equipped with internal elements, mixer-settler devices 0 static mixers. The extraction can be carried out at room temperature or approximately, but conveniently, in the range from about 15 to 40 ° C. The esterification is carried out essentially in a conventional manner, i.e. by acid reaction (met) acrylic with C 4 -C 12 alkanol in the presence of a catalyst and at elevated temperature. The molar ratio of alkanol: acrylic acid or methacrylic acid is generally 1: 0.8-1.2. The C 4 -C 2 alkanols are, for example, pentanol, hexanol, heptanol, octanol, 2-ethylhexanol, nonanol, 2-propylheptanol, decanol, undecanol, dodecanol and, preferably, butanols, in particular n-butanol. The concentration of sulfuric acid in the reaction mixture is generally from 0.5 to 10% by weight, preferably from 1 to 5% by weight, based on the total lot. As polymerization inhibitors, use is made, for example, of phenothiazine, hydroquinone, hydroquinone monomethyl ether, or mixtures thereof with or without air (from 0.1 to 10 1 / hx 1) in an amount from 100 to 5000 ppm, with base in the reaction mixture. As the entrainer to remove water from the reaction mixture, use may be made in the process according to the invention of saturated (for example cyclohexane) or aromatic hydrocarbons (for example, toluene); however, preferably, the reaction is carried out without additional entrainer. The reaction is generally carried out at from about 70 to 160 ° C, preferably from 90 to 130 ° C. The reaction time is generally from about 1 to 10, preferably from 1 to 6 hours. The reaction can be carried out under atmospheric pressure, reduced pressure or superatmospheric pressure. Preferably, the pressure is adjusted so that the water formed during the esterification is distilled, for example, in the form of a mixture of water, C4-C12 alkanol and ester (the organic components are fed back to the esterification in this case). The esterification can be carried out continuously or in batches, the continuous process is preferred. The esterification is carried out in conventional apparatuses, for example in a unit of one or more reactors with agitation, heatable (cascade), which can be equipped with columns, condensers and phase separation vessels. The contents of the reactor are mixed by agitation or other suitable and customary measures.

If, after extraction of the catalyst, another extraction / neutralization of the residual acids (catalyst and (meth) acrylic acid) is necessary using an aqueous base, this can be done in a conventional extraction apparatus (see above), being smaller the requirement of the base due to the high degree of extraction of the catalyst and the extraction, surprisingly, being carried out without the phase separation problems described in EP-A-0 566 074. The ester is separated in a conventional manner, in particular by distillation , for example by distillation in a column of perforated plates, of the reaction mixture that has been liberated from the catalyst and, if appropriate, from the residual carboxylic acids and low-boiling substances. The following examples illustrate the invention, without restricting it, the percentages are by weight. A cascade of tanks with agitation consisting of 3 reactors with agitator, each of 1 1 of reaction volume, which are equipped with column, condenser and phase separation vessel, was loaded with 558 g of acrylic acid, 648 g of n-butanol, 16 g of sulfuric acid and 1 g of phenothiazine per hour. The reaction temperature in the reactors was 106 ° C, 118 ° C, and 123 ° C, respectively and the pressure was 700 mbar. At the top of the column, a mixture of water, n-butanol and n-butyl acrylate was produced, which was separated into an aqueous and an organic phase, the aqueous phase being fed as reflux to the column. The reaction effluent (1070 g / h) contained, according to the analysis: 90.2% n-butyl acrylate 2.7% n-butanol 0.5% acrylic acid 2.2% monobutyl sulfate The rest: by-products, polymers, oligomers, phenothiazine rate of rotation of acrylic acid: 99% , 98% conversion The reaction effluent cooled to 25 ° C was extracted in a mixer-settler apparatus at approximately 25 ° C with 90 g / h of water. The aqueous phase (97 g / h) that contained 20.5% of mono-n-butyl sulfate (recovery 85%) and 0.5% of sulfuric acid. This aqueous phase was recycled to the bottom of the distillation column of the first reactor, with the addition of fresh sulfuric acid had a decrease up to 1.3 g / h.

The rotation rate of acrylic acid was again 99%, the conversion 98%. The ratio between the degree of extraction of the catalyst and the n-butanol content of the reaction mixture fed to the extraction was determined by extraction of esterification mixtures, which had been prepared by esterifying acrylic acid with n-butanol in the presence of sulfuric acid , and that had different contents of n-butanol, once in a separatory funnel with 10% by weight of water at 25 ° C. The results of these experiments are shown in Table 1 and verify the importance of a reaction procedure that preserves the unreacted alkanol content of less than 5%, preferably from

Claims (1)

1. CLAIMS A process for the preparation of (meth) acrylic esters by reaction of (meth) acrylic acid with a C4-C12 alkanol in the presence of sulfuric acid or a C4-C12 monoalkyl sulfate as a catalyst, comprising the regeneration of the catalyst by extraction with water, from the reaction mixture, the concentration of unreacted alkanol in the reaction mixture, to be extracted, being no more than 5% by weight, based on the reaction mixture to be extracted. The process, as mentioned in claim 1, wherein the concentration of alkanol is from 0.1 to 3% by weight. The process, as mentioned in claim 1 or 2, wherein the aqueous solution of the catalyst regenerated by extraction with water of the reaction mixture is recycled back to the esterification. The process, as mentioned in one of claims 1 to 3, wherein the catalyst is extracted in such a way that the degree of extraction is at least 70% by weight, in particular at least 80% by weight, based on the amount of catalyst in the reaction mixture. The process, as mentioned in one of claims 1 to 4, wherein the catalyst is extracted in such a way that the concentration of catalyst in the aqueous phase is at least 20% by weight, in particular at least 25% by weight, based on the aqueous extract. The process, as mentioned in one of claims 1 to 5, wherein the extraction is carried out from 15 to 40 ° C. The process, as mentioned in claims 1 to 6, wherein the extraction is carried out countercurrently in a static mixer The process, as mentioned in one of claims 1 to 7, wherein the alkanol used is n-butanol or isobutanol The process, as mentioned in one of claims 1 to 8, wherein the reaction is carried out from 70 to 160 ° C, in particular from 90 to 130 ° C. mentioned in one of claims 1 to 9, wherein the reaction time is from 1 to 10, in particular from 1 to 6 hours.