MXPA99006488A - Process for the esterification of (meth)acrylic acid with an alkanol - Google Patents

Abstract

The invention concerns a process for the esterification of (meth)acrylic acid with an alkanol, oxyesters formed as a by-product of esterification being cleaved in turn in an acid-catalysed manner by the addition of monomeric and/or oligomeric (meth)acrylic acid and water.

Description

ESTERIFICATION OF CRYLIC ACID (MET) WITH A ALCANOL The present invention relates to a process for esterifying (meth) acrylic acid with an alkanol in the presence of a catalyst for esterification, in which the initial compounds that do not react and the methacrylic ester formed are separated from the reaction mixture. by distillation with a lower product containing remaining oxy-ester, and: a) the monomeric and / or oligomeric (meth) acrylic acid is directly added to the residual product and then the oxy esters present in the waste product are dissociated by the action of elevated temperature in the presence of acid catalysts other than monomeric (meth) acrylic acid and oligomeric, or b) the oxy-esters are first separated from the residual product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then the oxy esters present therein are dissociated by the action of elevated temperature in presence of acidic catalysts other than monomeric and oligomeric (meth) acrylic acid.

The term (meth) acrylic acid, as is customary, defines in the present acid acrylic or methacrylic acid. The definition of oligomeric (meth) acrylic acid means the products of Michael addition of (meth) acrylic acid with itself and with the resulting side products. The Michael addition products of this type can be characterized by the formula (III).

R 'R' CH2 = C C02 (CH2 CH-C02) -H (III) where Z = an integer from 1 to 5, and R = H or CH3, and must be differentiated in the present from (meth) acrylic acid (monomeric) - and from the polymers of (meth) acrylic acid (which are obtained by free radical polymerization of (meth) acrylic acid). It is important that the product of Michael addition of (meth) acrylic acid with itself and with the resulting by-products be reversible. Oligomeric (meth) acrylic acid is produced, for example in the distillation of (for example crude) acid (meth) acrylic (the term "crude" indicates a small amount of aldehyde impurities, in particular, still present) in the lower phase (see DE-A 22 35 326, for example) .The alkyl esters of (meth) acrylic acid , because of their activated C = C ethylenically unsaturated double bonds, are important starting compounds for preparing polymers generated by free radical polymerization, which are used as gums, for example, the alkyl (meth) acrylates are usually they prepare by esterifying the (meth) acrylic acid with alkanols at elevated temperature in the liquid phase with or without solvent and in the presence of acid catalysts other than (meth) acrylic acid (see DE-A 23 39 519, for example). this method of preparation is that, under the aforementioned esterification conditions, the initial alcohol which does not react forms a compound of the formula I as seen below and the (meth) acrylic acid which does not react. ona forms a compound of formula II, by addition to the ethylenically unsaturated double bond (Michael addition) of the already formed alkyl (meth) acrylate, as side reactions. Multiple successive addition is also possible. In addition, mixed types can occur. These addition products (alkoxy esters and acyloxy esters) are called oxy esters: R ' RC (CH2 CH-C02) x-R (I) R 'R' CH2 = C C02 (CH2 CH C02) and -R (II), where X, Y = an integer from 1 to 5, R = alkyl, and R '= H or CH3. In the preparation of the acrylic esters, the formation of the oxy ester is particularly problematic, being the oxy esters mainly formed alkoxy propionic ester and acyloxy propionic ester where X, Y, = 1. In preparation of the methacrylic esters, the formation of the oxy ester proceeds to a lesser extent, the formation of the oxy esters is described, inter alia, in DE-A 23 39 529. The above-mentioned open request to the public confirms that the formation of the oxy esters is essentially independent of the specific conditions of the esterification. The formation of the oxy ester is of particular importance in the preparation of acrylic esters of the Ci-Cβ alkanols, in particular the C-C8 alkanols, very particularly in the preparation of n-butyl acrylate and 2-ethylhexyl acrylate.

It is characteristic of oxy-esters that their boiling point is above the boiling points of the initial acid, the initial alcohol, the ester formed and any org solvent used in the assembly. Any particular esterification reaction mixture is usually worked in such a way that the unreacted starting compounds and the objective ester are separated from the reaction mixture by distillation, in which case the catalyst used for the esterification can be separated. in advance by extracting with water and / or aqueous solution of alkali metal hydroxide (see, for example, Ullmann's Encyclopedia of Industrial Chemistry, vol. Al, 5th ed., VCH, pp. 167 ff.). The residual product remaining after such distillation treatment contains the oxy esters, which results in a considerable loss in yield. The use of very varied procedures, therefore, has been tried to diminish the problems resulting from the presence of oxy esters. Thus, JP-A 82/6229 describes the alkaline saponification of the high-boiling esterification residue. Although some of the alcohol and acrylic acid used and ß-hydroxypropionic acid are recovered in this way, it is not possible to recycle them easily and economically to the esterification reaction, due to their salt content by the alkaline saponification conditions, which is a disadvantage. JP-B-72/15936 refers to the reaction of ß-alkoxypropionic esters with acrylic acid in the presence of strong acids with the production of acrylic esters (transesterficación). However, as a byproduct, an equimolar amount of ß-alkoxypropionic acid is produced, which could not be recycled to the esterification of the acid (met) acrylic. JP-A-93/25086 relates to the dissociation of the addition product of Michael β-butylated butoxypropionate (see formula I, X = 1, R = butyl) at elevated temperature and in the presence of sulfuric acid and an excess of Water. A disadvantage of this procedure is the conversion rate that is only 30%. JP-A-94/65149 describes the dissociation of the addition products of Michael I and II in the presence of titm alkoxides. A disadvantage in this case is the conversion rate in the same comparatively low way (< 60%) and the requirements for titanates. GB-B 923 595 describes the treatment of the residue of the esterification of acrylic acid with alkanols in the absence of molecular oxygen. It is recommended that, among others, all volatile monomers be removed before dissociation, the dissociation is carried out in the presence of sulfuric acid and that the dissociation products are removed using a stream of inert gas. According to the illustrative examples, the dissociation is carried out at least at 300 ° C. The residue formed is carbon, which must be mechally separated from the reactor. Therefore, this procedure is neither economical nor can it be carried out on an industrial scale. CN-A 1,063,678 describes the dissociation of the alkoxy propionic ester present in the esterification residue in the presence of sulfuric acid in a cascade, the temperature and the concentration of the catalyst in each reactor being different. A distillation to separate alkanol and acrylate is coupled to the dissociation. The procedure is highly laborious and does not obtain high conversion rates. CN-A 1,058,390 refers to the dissociation of the alkoxy propionic esters in the presence of sulfuric acid, et cetera, in alkanols and acrylic esters. This procedure is performed in separate steps. First, the dissociation is carried out at reflux, and then the products of the reaction are distilled. The ester residues containing acrylic acid from the preparation of ethyl acryl / methyl acrylate [sic] (ethyl ethoxypropionate, methyl ethoxypropionate) are dissociated in the presence of ethanol or methanol, respectively. This procedure is also complicated and high yields are not obtained.

DE-A 19547459 and DE-A 19547485 relates to the dissociation of the oxy esters in the presence of monomeric or oligomeric (meth) acrylic acid and in the presence of acids other than the aforementioned acids. The formation of unwanted dissociation by-products can be markedly diminished by this means, but the reaction rate is not satisfactory. US-A 3 227 746 proposes to dissociate alkyl alkoxypropionates in the presence of dehydration catalyst and water. The presence of monomeric or oligomeric (meth) acrylic acid [sic] is not incorporated. According to Example 6, butyl butoxy propionate is dissociated in the presence of 100% by weight (based on the oxy ester) of phosphoric acid at 85% concentration by weight and 10% by weight (based on the oxy ester) of water. The presence of water, according to US Pat. No. 3,227,746, makes the presence of superfluous alkanol possible and prevents the unreacted alkyl alkoxypropionate from passing to the distillate. A disadvantage of this method is the high amount of catalyst used. In addition, the reaction rate is not satisfactory, as is the formation of the dissociation byproducts. An object of the present invention is, therefore, to carry out the dissociation of the oxy esters formed during the esterification of (meth) acrylic acid with an alkanol in a more advantageous manner than in the prior art and to integrate it into the esterification process. We have found that this objective is obtained, therefore, by a process for esterifying (meth) acrylic acid with an alkanol in the presence of an esterification catalyst, in which the initial compounds that do not react and the (meth) acrylic ester which is are separated from the reaction mixture by distillation, with a residual product containing remaining oxy-ester, and a) the monomeric and / or oligomeric (meth) acrylic acid is directly added to the residual product and then the oxy esters present in the waste product are dissociated by the action of elevated temperature in the presence of acid catalysts other than monomeric (meth) acrylic acid and oligomeric, or b) the oxy esters are first separated from the residual product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then the oxy esters present are dissociated by the action of elevated temperature in the presence of catalysts. acids other than monomeric and oligomeric (meth) acrylic acid, which includes adding more water to dissociate the separated oxy-esters by distillation of the residual product, or adding more water to dissociate the residual product. In general, from 5 to 50% by weight, preferably from 10 to 40% by weight of the monomeric (meth) acrylic acid and / or oligomeric acid is added, based on the oxy esters to be dissociated. Commonly, monomeric and / or oligomeric (meth) acrylic acid is added in a manner that is known per se and which is stabilized by polymerization inhibitors. In a convenient way, the acid (met) acrylic used for the novel process is • the residual phase produced in the purification of crude (meth) acrylic acid by distillation, whose residual phase mainly contains compounds of the formula III. The monomeric (meth) acrylic acid and / or (meth) acrylic oligomers can be added to the mixture to be dissociated before dissociation. However, these can also be fed separately to the dissociation reactor. Under the conditions of redissociation, the oligomeric (meth) acrylic acids are redissolved, as a result of which free (meth) acrylic acid is continuously produced in the nascent state. Compared to the addition of (meth) acrylic acid in advance, this has the advantage that the added (meth) acrylic acid is not distilled immediately together with the cleavage products, but that the dissociation continues in the presence of acid (met). ) acrylic, which gives rise to a particularly low formation of their product (dialkyl ethers, olefins). The amount of water added according to the invention for dissociation, based on the oxy esters to be dissociated, is generally from 0.1 to 20% by weight, preferably from 1 to 10% by weight. According to an advantageous development of the invention, the process is carried out in the presence of molecular oxygen. According to another advantageous development of the invention, in addition to the catalyst for acid esterification which can still be present and is different from the monomeric and oligomeric (meth) acrylic acid, other acids can be added to the product to be dissociated, selected from the group consisting of mineral acids, such as sulfuric acid or phosphoric acid, and organic acids that are different from monomeric and oligomeric (meth) acrylic acid, such as alkyl sulphonic or aryl sulphonic acids, for example methanesulfonic or p-toluene sulphonic acids . In this development, the total amount of acid which is different from the monomeric and oligomeric (meth) acrylic acid which is then present may be from 1 to 20% by weight, preferably from 5 to 15% by weight, based on the amount of the product that is going to be dissociated.

It has been found to be convenient if a separation current passes, as a separator for the products of the dissociation, through the product to be dissociated during the process according to the invention, whose separation gas preferably contains molecular oxygen. For convenience, the separation gas used is air or air mixture with inert gas (for example nitrogen). The advantages of the process according to the invention are, mainly, that in this process the dissociation first proceeds at an increased speed and, secondly, at the same time few by-products are formed as ethers or olefins. In this way, among others, the reduced losses of the initial materials, especially alcohols, occurs, unlike the known processes. In addition, high dissociation rates can be obtained and the direct recycling of the products of the dissociation to the esterification does not give rise to any adverse effect on the (meth) acrylic ester unit. In the separation of the oxy esters from the residual product by distillation, the distillation conditions depend on the type of the alcohol component used in the esterification. In general, 100 to 300 ° C and a pressure of 1 to 50 mbar are considered. Any conventional distillation apparatus is suitable for the distillation process. Since only a simple separation activity is carried out, a simple splash protection is generally sufficient, that is, a column is usually not necessary. For the treatment according to the invention of the oxy esters produced in the residual product during the esterification, or of the distillate of the oxy ester separated from the residual product of the esterification, it is possible to use a simple reactor with stirring, which can be heated, having chamfered heating or a heating coil, or a forced circulation evaporator, for example a falling film evaporator or flat evaporator, coupled to a holding container can be used. For a better separation of the dissociation products from the residual product or the distillate of the oxy ester, a grinding apparatus mounted on the dissociation apparatus may be convenient, for example a column containing random or arranged packing or trays. This rectification apparatus generally operates stabilized with polymerization inhibitors (for example phenothiazine, hydroquinone monomethyl ether, etc.). The common conditions for carrying out the process according to the invention of the dissociation of the oxy esters produced in the waste product during esterification or separated from the waste product are as follows: catalyst: at least one acid selected from the group consisting of mineral acids as sulfuric acid and phosphoric acid, and organic acids other than (meth) acrylic acid such as alkyl sulphonic or aryl sulphonic acids, for example methanesulfonic acid or p-toluenesulfonic acid.

Catalyst amount: 1-20% by weight, preferably 5-15% by weight, based on the amount of the residual product or the amount of the oxy-ester distillate separated from the residual product.

Amount of monomeric and / or oligomeric (meth) acrylic acid: 5-50% by weight, preferably 10-40% by weight, based on the amount of the residual product, or on the amount of the distillate oxy ester separated from the residual product .

Amount of water: 0.1-20% by weight, preferably 1-10% by weight, based on the amount of the residual product, or on the amount of the oxy ester distillate separated from the residual product.

Temperature: 150-250 ° C, preferably 180-230 ° C.

Pressure: preferably atmospheric or reduced pressure (so that the products of the dissociation evaporate immediately) Separation gas, when used: speed: 1-100 / h x 1 reaction time: 1-10 hours conversion rate: > 90% The reaction is carried out, for example, in such a way that the residual product to be dissociated is continuously expelled from the treatment by distillation of the esterification mixture and fed to the dissociation reactor together with the catalyst for dissociation, water and acid ( met) monomeric and / or oligomeric acrylic. However, the reaction can also be carried out batchwise, that is, in batches. It is also possible to carry out the reaction in a semi-continuous manner, in which the product to be dissociated, the water and the monomeric and / or oligomeric (meth) acrylic acid are continuously fed to the dissociation reactor which contains the catalyst of dissociation and the residual product is not batch removed from the dissociation reactor until the dissociation is complete. The dissociation products are continuously removed by distillation and conveniently recycled to the esterification. If the esterification is carried out in such a way that the water formed during the esterification is continuously separated by a rectification column mounted on the esterification reactor, the dissociation products are preferably recycled to the esterification by means of this rectification column (Conveniently, the recycled material passes to the lower half of the rectification column). The monomeric and / or oligomeric (meth) acrylic acid and water can be fed to the dissociation reactor separately or together, or even in a mixture with the product to be dissociated. The applicability of the dissociation process described is not limited to a special nature of the esterification process, according to the by-products from which the oxy-esters originate, i.e., addition compounds I and II. In general, esters are prepared by the usual processes (see Ullmann's Encyclopedia of Industrial Chemistry, vol.Al, 5th ed., VCH, pp. 167 ff). A common example of the conditions under which the esterification preceding the dissociation of the oxy esters can be carried out is described shortly as follows: Alcohol: (meth) acrylic acid 1: 0.7-11.2 (molar) catalyst: sulfuric acid or sulfonic acids (for example p-toluene sulphonic acid) catalyst: 0.1-10% by weight (preferably 0.5-5% by weight) based on the initial material.

Stabilization: 200-2000 ppm of phenothiazine (based on the weight of the initial materials).

Reaction temperature: 80-160 ° C, preferably 90-130 ° C Reaction time: 1-10 hours, preferably 1-6 hours.

A separating agent (for example cyclohexane or toluene) can be used to remove water from the esterification. The esterification can be carried out at atmospheric pressure, under reduced pressure or under superatmospheric pressure, continuously or in batches.

In the acid-catalyzed esterification of acrylic acid with alkanols, the resulting residual product after separating the catalyst from the acid esterification, the initial materials which do not react and the acrylic ester generally have the following composition: 1-20% by weight of acrylic ester. 50-80% by weight of alkoxy propionate (see formula I) 5-30% by weight of acyloxypropionate (see formula II) the remainder: mainly stabilizers (phenothiazine) and polymers.

Other details and advantages of the process according to the invention can be taken from the illustrative example described below. First, a result obtained with a process not according to the invention is described with reference to the comparative example.

Comparative example 1 A glass circulation reactor (volume: 11) heated by a heating tube was charged with 50 g of an oxy ester distillate, produced from the residue of the esterification in the preparation of n-butyl acrylate released from the catalyst of acid esterification, and 40 g of p-toluene sulphonic acid. The distillate oxy ester contains: 11. 0% by weight of butyl acrylate 64.8% by weight of butoxy ester I (R = C4H9) 20.5% by weight of acyloxy ester II (R = C4H9). 10 1 of air were introduced into the mixture per hour.

The temperature of the dissociation was 195 ° C and the operating pressure was one atmosphere. The residue of the esterification to be dissociated was fed continuously during the dissociation to the dissociation reactor under level control. The dissociation products were removed in the vapor state and condensed in the upper part of the column (50 cm * 2.8 cm, empty) mounted on the dissociation reactor. Over the course of 119.5 hours, 7401 g of mixture (62 g / h) were fed for dissociation and 7080 g of the dissociation products were condensed. According to the analysis by gas chromatography, the condensate content: 72. 0% by weight of butyl acrylate 13.9% by weight of butanol 4.8% by weight of acrylic acid 1.4% by weight of dibutyl ether 6.6% by weight of butenes 0.2% by weight butyl butoxypropionate conversion rate: 96% by weight, based on the oxy ester.

Example Example of the method according to the invention A glass circulation reactor (volume 1 1) heated with a heating tube was charged with 500 g of the oxy ester distillate from Comparative Example 1, 40 g of p-toluene sulfonic acid, 100 g of acrylic acid (stabilized with 300 ppm of phenothiazine) and 20 g of water. 10 liters of air were introduced per hour into the mixture. The dissociation temperature was 195 ° C, the operating pressure was one atmosphere. Under level control, the oxy-ester distilled to be dissociated, 20% by weight of acrylic acid and water (4% by weight, based on the distilled oxy ester) were continuously fed to the dissociation reactor. The dissociation products were condensed "at the top of the column (50 cm x 2.8 cm, empty) mounted in the reactor.

Over the course of 100 hours, 15,250 g of distilled oxy ester (153 g / h), 3050 g of stabilized acrylic acid and 600 g of water were fed for dissociation and 18,350 g of the product mixture were condensed. According to the gas chromatographic analysis, the condensate contained, without the water: 73. 8% by weight of butyl acrylate 6.5% by weight of butanol 12.9% by weight of acrylic acid 0.7% by weight of dibutyl ether 2.8% by weight of butenes < 1% by weight butyl butoxypropionate conversion rate: 97% by weight, based on the oxy ester.

Comparative example 2: The procedure of the example was followed, but without the addition of water. Yield: 108 g / h at a conversion rate of 96% by weight (based on the oxy ester). Byproducts (total olefin and dibutyl ether): 4.0% by weight, based on condensate.

Claims (15)

1. CLAIMS A process for esterifying (meth) acrylic acid with an alkanol in the presence of an esterification catalyst, in which the initial compounds which do not react and the (meth) acrylic ester to be formed are separated from the reaction mixture by distillation , with a residual product containing remaining oxy-ester, and a) monomeric and / or oligomeric (meth) acrylic acid is directly added to the residual product and then the oxy esters present in the waste product are dissociated by the action of elevated temperature in the presence of acid catalysts other than monomeric (meth) acrylic acid and oligomeric, or b) the oxy esters are first separated from the residual product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then the oxy esters present are dissociated by the action of elevated temperature in the presence of catalysts. acids other than monomeric and oligomeric (meth) acrylic acid. which consists of adding more water for the dissociation to the oxy esters separated by distillation of the residual product, or adding more water to dissociate the residual product.
2. 2. The process, as mentioned in claim 1, wherein the amount of monomeric (meth) acrylic and / or oligomeric acid added to the product to be dissociated is from 5 to 50% by weight, based on the product that is going to dissociate.
3. 3. The process, as mentioned in claim 1, wherein the amount of monomeric (meth) acrylic and / or oligomeric acid added to the product to be dissociated is from 10 to 40% by weight, based on the product that is going to dissociate.
4. 4. The process, as mentioned in one of claims 1 to 3, wherein the amount of water added to the product to be dissociated is from 0.1 to 20% by weight, based on the product to be dissociated .
5. The process, as mentioned in one of claims 1 to 3, wherein the amount of water added to the product to be dissociated is from 1 to 10% by weight, based on the product to be dissociated .
6. The process, as mentioned in one of claims 1 to 5, wherein the process is carried out in the presence of molecular oxygen.
7. The process, as mentioned in one of claims 1 to 6, wherein the product to be dissociated is dissociated from 150 ° C to 250 ° C.
8. The process, as mentioned in one of claims 1 to 7, wherein the acid added to the product to be dissociated is a mineral acid and / or an organic acid other than monomeric and oligomeric (meth) acrylic acid.
9. The process, as mentioned in claim 8, wherein the amount of added acid different from the monomeric and oligomeric (meth) acrylic acid is from 1 to 20% by weight, based on the product to be dissociated.
10. The process, as mentioned in claim 8, wherein the amount of added acid different from the monomeric and oligomeric (meth) acrylic acid is from 5 to 15% by weight, based on the product to be dissociated.
11. The process, as mentioned in one of claims 1 to 10, wherein the dissociation is carried out at reduced pressure (< 1 atmosphere).
12. 12. The process, as mentioned in one of claims 1 to 11, wherein a separating gas is conducted through the product to be dissociated to remove the products of the dissociation.
13. The process, as mentioned in claim 12, wherein the spacer gas used is a gas containing oxygen.
14. The process as mentioned in one of claims 1 to 13, wherein the resulting dissociation products are recycled directly to the esterification.
15. 15. The process, as mentioned in one of claims 1 to 14, wherein the alkanol is an alkanol of Ci-Cs-16. The process, as mentioned in claim 15, wherein the alkanol is n-butanol or 2-ethylhexanol.