EP0956279A1

EP0956279A1 - Process for the esterification of (meth)acrylic acid with an alkanol

Info

Publication number: EP0956279A1
Application number: EP98904042A
Authority: EP
Inventors: Heinrich Aichinger; Michael Fried; Gerhard Nestler; Holger Herbst
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1997-01-20
Filing date: 1998-01-08
Publication date: 1999-11-17
Anticipated expiration: 2018-01-08
Also published as: DE19701737A1; WO1998031656A1; EP0956279B1; JP2001508076A; KR20000070185A; DE59805307D1; CN1244189A; BR9806781A; US20010047106A1; AU6207798A

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

Process for the esterification of (meth) acrylic acid with an alkanol

description

The present invention relates to a process for the esterification of (meth) acrylic acid with an alkanol in the presence of an esterification catalyst, in which unreacted starting compounds and the (meth) acrylic acid ester to be formed are separated off from the reaction mixture, leaving a bottom product containing oxyester, and either

a) monomers and / or oligomeric (meth) acrylic acid are added directly to the bottom product and then the oxyesters contained in the bottom product are cleaved in the presence of acid catalysts other than monomeric and oligomeric (meth) acrylic acid by the action of elevated temperature,

or

b) the oxyesters are first separated from the bottom product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then, in the presence of acid catalysts different from monomeric and oligomeric (meth) acrylic acid, the oxyesters contained therein are cleaved by the action of elevated temperature .

The term (meth) acrylic acid denotes in a known manner acrylic or methacrylic acid. The term oligomeric (meth) acrylic acid means the Michael adducts of (meth) acrylic acid with itself and the resulting products. Such Michael adducts can be represented by the general formula (III)

R ¹ R '

CH = C C0 ₂ (CH ₂ CH C0 ₂ ) _z H (III),

with Z = an integer from 1 to 5, and R '= H or CH ₃ ,

characterize and differentiate here from (monomeric) (meth) acrylic acid and from (meth) acrylic acid polymers (which can be obtained by radical polymerization of (meth) acrylic acid). It is important that the Michael addition of (meth) acrylic acid with itself and the resulting products is reversible. Oligomeric (meth) acrylic acid is obtained, for example, in the distillation of (for example, crude) (meth) acrylic acid (the term "crude" indicates a small amount of, in particular, aldehydic impurities still present) in the sump (see, for example, DE-A-22 35 326).

Because of their activated ethylenically unsaturated C = C double bond, alkyl esters of (meth) acrylic acid are important starting compounds for the preparation of polymers produced by free-radical polymerization, which e.g. find use as adhesives.

Alkyl esters of (meth) acrylic acid are usually prepared by esterification of (meth) acrylic acid with alkanols at elevated temperature in the liquid phase with or without solvent and in the presence of acids other than (meth) acrylic acid as a catalyst (cf., for example, DE-A 23 39 519). The disadvantage of this method of preparation is that under the aforementioned esterification conditions, unreacted starting alcohol forms as side reactions to form a compound of the general formula I listed below and unreacted (meth) acrylic acid to form a compound of the general formula II on the ethylenically unsaturated double bond of already formed (meth) acrylic acid - alkyl ester added (Michael addition).

A successive multiple addition is also possible. Mixed types can also occur. These adducts (alkoxy esters and acyl oxyesters) are called oxyesters for short:

R ¹

RO (CH ₂ CH C0 ₂ ) _x R (I),

R ' _R '

I I

CH ₂ = C C0 ₂ (CH ₂ CH C0 ₂ ) _y R (II), with X, Y = an integer from 1 to 5, R = alkyl and R ¹ = H or CH ₃ .

The problem of oxyester formation is particularly pronounced in the preparation of esters of acrylic acid, the main oxyesters formed being the alkoxypropionic acid esters and the acyloxypropionic acid esters with X, Y = 1. In the production of esters of methacrylic acid, the oxyester formation takes place in low to a lesser extent. The formation of oxyesters is described in DE-A 23 39 529, among others. The above publication confirms that the formation of oxyesters takes place essentially independently of the special esterification conditions. Of particular importance is the formation of oxyesters in the production of acrylic acid esters of the Ci to Cg alkanols, especially the C - to Cs alkanols, very particularly in the production of n-butyl acrylate and 2-ethylhexyl acrylate.

It is characteristic of the oxyesters that their boiling point lies above the boiling points of the starting acid, starting alcohol, target ester formed and any organic solvent used.

Any esterification reaction mixture is usually worked up in such a way that unreacted starting compounds and the target ester are separated from the reaction mixture by distillation, the acid catalyst used for the esterification possibly being separated beforehand by extraction with water and / or aqueous alkali (cf., for example, Ullmann's Encyclopedia of Industrial Chemistry, Vol.AI, 5th Ed., VCH p. 167ff). The bottom product remaining in the course of such a work-up by distillation contains the oxyesters, which cause a considerable loss in yield.

The attempt was therefore made to use a wide variety of methods in order to reduce the problems arising from the occurrence of the oxyesters.

JP-A-82/62229 describes the alkaline saponification of the high-boiling esterification residue. Although part of the alcohol and acrylic acid and β-hydroxypropionic acid used are obtained in this way, their simple and economical recycling into the esterification reaction is not possible owing to their salt content which can be attributed to the alkaline saponification conditions, which is a disadvantage.

JP-AS-72/15936 relates to the reaction of β-alkoxypropionic acid esters with acrylic acid in the presence of strong acids to obtain acrylic acid esters (transesterification). As a by-product, however, β-alkoxypropionic acid is obtained in an equimolar amount, which could not be returned to the (meth) acrylic acid esterification.

JP-A-93/25086 relates to the cleavage of the Michael addition product β-butoxypropionic acid butyl ester (see formula I, X = 1, R = butyl) at elevated temperature and in the presence of sulfur acid and an excess of water. A disadvantage of this procedure is that the conversion is only about 30%.

JP-A-94/65149 describes the cleavage of Michael addition products I and II in the presence of titanium alcoholates. The comparatively low (<60%) turnover and the need for titanates are disadvantageous here.

GB-PS 923 595 discloses working up the residue of the esterification of acrylic acid with alkanols in the absence of molecular oxygen. We recommend the removal of all escaping monomers before the cleavage, the cleavage in the presence of sulfuric acid and the removal of the cleavage products with the aid of an inert gas stream. According to the exemplary embodiments, the cleavage is carried out at at least 300 ° C. Carbon is formed as a residue, which must be removed mechanically from the reactor. Therefore, this procedure can not be carried out economically or on an industrial scale.

CN-A 1,063,678 describes the cleavage of the alkoxypropionic acid ester contained in the esterification residue in the presence of sulfuric acid in a cascade, the temperature and catalyst concentration being different in each reactor. Coupled with the cleavage is a distillation to separate alkanol and acrylate. The process is very cumbersome and does not achieve high sales.

CN-A 1,058,390 relates to the splitting of alkoxypropionic acid esters in the presence of sulfuric acid etc. into alkanols and acrylic acid esters. This is done step by step. The cleavage is first carried out under reflux and then the reaction products are distilled off. The splitting of the acrylic acid-containing ester residues from ethyl / methyl acryl production (ethyl ethoxypropionate, methyl methoxypropionate) is carried out in the presence of ethanol or methanol. This too

The procedure is complicated and does not achieve high sales.

DE-A 19547459 and DE-A 19547485 relate to the cleavage of the oxyesters in the presence of monomeric or oligomeric (meth) acrylic acid and in the presence of acids other than the aforementioned acids. The formation of the undesired cleavage by-products can be reduced significantly as a result, but the reaction rate is unsatisfactory.

US Pat. No. 3,227,746 proposes the cleavage of alkoxypropionic acid alkyl esters in the presence of dehydration catalysts and water. A presence of monomeric or oligomeric (Meth) acrylic acid is not included. According to Ex. 6, butoxypropionic acid butyl ester is 85% in the presence of 100% by weight (with respect to oxyester). - Split phosphoric acid and 10 wt .-% (with respect to oxyester) water. According to the teaching of US Pat. No. 3,227,746, the presence of the water renders the presence of alkanol superfluous and prevents unreacted alkyl alkoxypropionate from being converted into the distillate. The disadvantage of this procedure is the high amount of catalyst used. Furthermore, the reaction rate is just as unsatisfactory as the formation of cleavage by-products.

The invention was therefore based on the object of performing the cleavage of the oxyesters formed in the esterification of (meth) acrylic acid with an alkanol in a more advantageous manner than in the prior art and integrating them into the esterification process.

Accordingly, a process for the esterification of (meth) acrylic acid with an alkanol in the presence of an esterification catalyst, in which unreacted starting compounds and the (meth) acrylic acid ester to be formed are separated from the reaction mixture to leave an oxyester-containing bottom product, and either

a) monomers and / or oligomeric (meth) acrylic acid are added directly to the bottom product and then the oxyesters contained in the bottom product are cleaved by the action of elevated temperature in the presence of acid catalysts other than monomeric and oligomeric (meth) acrylic acid

or

b) the oxyesters are first separated from the bottom product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then, in the presence of acid catalysts different from monomeric and oligomeric (meth) acrylic acid, the oxyesters contained therein are cleaved by the action of elevated temperature ,

which is characterized in that water is additionally added to the bottom product or the oxyesters separated by distillation from the bottom product for the cleavage.

As a rule, based on the oxyesters to be cleaved, 5 to 50% by weight, preferably 10 to 40% by weight, of monomeric and / or oligomeric (meth) acrylic acid are added. The monomeric and / or oligomeric (meth) acrylic acid is normally added in form known per se, stabilized by means of polymerization inhibitors. The oligomeric (meth) acrylic acid used advantageously is the sump obtained in the purification of crude (meth) acrylic acid by distillation, which mainly contains compounds of the general formula III.

The monomeric (meth) acrylic acid and / or the (meth) acrylic acid oligomers can be added to the mixture to be cleaved before the cleavage. However, they can also be fed separately to the cleavage reactor.

Under the cleavage conditions, the oligomeric (meth) acrylic acids are cleaved back, as a result of which free (meth) acrylic acid is continuously produced in statu nascendi. Compared to the addition of (meth) acrylic acid in advance, this has the advantage that the (meth) acrylic acid added does not immediately distill off together with the cleavage products, but that the cleavage takes place continuously in the presence of (meth) acrylic acid, which results in particularly low by-product formation ( Dialkyl ether, olefins) due.

The amount of water to be added for the cleavage, based on the oxyesters to be cleaved, is generally 0.1 to 20% by weight, preferably 1 to 10% by weight.

According to an advantageous embodiment of the invention, the method is carried out in the presence of molecular oxygen.

According to a further advantageous embodiment of the invention, in addition to the acidic esterification catalyst which may also be present and which is different from monomeric and oligomeric (meth) acrylic acid, further acids from the group comprising mineral acids, such as sulfuric acid or phosphoric acid, and monomeric and oligomeric (meth) acrylic acid various organic acids such as alkyl or arylsulfonic acids, for example methanesulfonic acid or p-toluenesulfonic acid added.

The total amount of acid then contained, different from monomeric and oligomeric (meth) acrylic acid, can be 1 to

20% by weight, preferably 5 to 15% by weight, based on the amount of the product to be cleaved.

It has proven to be advantageous if a stripping gas which preferably contains molecular oxygen is passed through the product to be cleaved as an entrainer for the cleavage products in the process according to the invention. Expediently as Stripping gas air or mixtures of air with inert gas (eg nitrogen) are used.

The advantages of the process according to the invention can be seen above all in the fact that, on the one hand, the cleavage proceeds at an increased rate and, on the other hand, few by-products such as ethers or olefins are formed. Thus, among other things lower losses of feedstocks, especially alcohols, than with known processes. In addition, high cleavage conversions can be achieved and the direct recycling of the cleavage products into the esterification does not cause the (meth) acrylic ester unit to deteriorate.

When the oxyesters are separated off from the bottom product by distillation, the distillation conditions depend on the type of alcohol component used in the esterification. As a rule, a temperature of 100 to 300 ° C and a pressure of 1 to 50 mbar are provided. Any conventional distillation apparatus is suitable for the distillation process. Since only a simple separation task has to be solved, a simple splash guard is usually sufficient, i.e. a column is normally not required.

A simple heatable stirred reactor with double-wall heating or heating coil or else a forced-circulation evaporator, for example a falling-film evaporator or flat evaporator, coupled with a residence time container, can be used for the inventive workup of the oxyesters obtained in the bottom product during the esterification in the bottom product or of the oxyester distillate separated from the esterification bottom. For better separation of the cleavage products from the bottom product or oxyester distillate, a rectification device placed on the cleavage apparatus, e.g. a packed column, packed column or tray column is appropriate. This rectification device is usually operated stabilized with polymerization inhibitors (e.g. phenothiazine, hydroquinone monomethyl ether, etc.).

Typical conditions for carrying out the process according to the invention of cleaving the oxyesters obtained in the esterification in the bottom product or separated off from the bottom product are as follows:

Catalyst: at least one acid from the group comprising mineral acids, such as sulfuric acid and phosphoric acid, and organic acids other than (meth) acrylic acid, such as alkyl or Arylsulfonic acids, for example methanesulfonic acid or p-toluenesulfonic acid

Amount of catalyst: 1 - 20% by weight, preferably 5 -

15% by weight, based on the amount of the bottom product or on the amount of the oxyester distillate separated from the bottom product, monomeric and / or oligomeric

Amount of (meth) acrylic acid: 5-50% by weight, preferably 10-40

% By weight, based on the amount of the bottom product or on the amount of the oxyester distillate separated from the bottom product

Amount of water: 0.1-20% by weight, preferably 1-10% by weight, based on the amount of the bottom product or on the amount of the oxyester-distillate separated from the bottom product

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

Pressure: preferably unpressurized or reduced pressure (so that the fission products evaporate immediately)

if necessary stripping gas quantity: 1 - 100 1 / h x 1

Response time: 10 hours

Sales> 90%

The reaction is carried out, for example, in such a way that the bottom product to be cleaved is continuously discharged from the work-up of the esterification mixture by distillation and fed to the cleavage reactor with the cleavage catalyst, the water and the monomeric and / or oligomeric (meth) acrylic acid. However, the reaction can also be carried out batchwise. Also, a semi-continuous reac ^¬ tion guidance is possible, in which the product to be cleaved, of water and the monomeric and / or oligomeric (meth) acrylic acid continuously to the cleavage reactor which contains the cleavage catalyst, is fed to the bottom roduct only after the cleavage from the Cleavage reactor is removed batchwise. The Fission products are continuously separated off by distillation and expediently returned to the esterification.

If the esterification is carried out in such a way that the water formed during the esterification is continuously separated off via a rectification column attached to the esterification reactor, the cleavage products are preferably returned to the esterification via this rectification column (it is expedient to recycle into the lower half of the rectification column).

The monomeric and / or oligomeric (meth) acrylic acid and the water can be fed to the cleavage reactor separately or together or else as a mixture with the product to be cleaved.

The applicability of the cleavage process described is not restricted to a special nature of the esterification process, as the by-products of which the oxyesters, ie the addition compounds I and II, are obtained. As a rule, the esters are prepared by the customary processes (see Ullmann's Encyclopedia of Industrial Chemistry, Vol. AI, 5th Ed., VCH, p. 167ff).

A typical example of the conditions under which the esterification preceding the cleavage of the oxyesters can take place can be briefly illustrated as follows:

Alcohol: (meth) acrylic acid 1: 0.7 - 1.2 (molar)

Catalyst: sulfuric acid or sulfonic acids (e.g. p-toluenesulfonic acid)

Amount of catalyst: 0.1-10% by weight (preferably 0.5-5% by weight) with regard to starting materials

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

Reaction temperature: 80 160 ° C, preferably 90 - 130 ° C

Response time: 10 hours, preferably 1-6 hours.

If necessary, an entrainer (eg cyclohexane or toluene) is used to remove the water of esterification. The esterification can be carried out either continuously or batchwise without pressure, with positive or negative pressure. In the acid-catalyzed esterification of acrylic acid with alkanols, the bottom product resulting from the removal of the acidic esterification catalyst, the unreacted starting materials and the acrylic ester generally has the following composition:

1 - 20% by weight acrylic ester

50 - 80% by weight alkoxypropionates (see formula I) 5 - 30% by weight acyloxypropionates (see formula II) balance: mainly stabilizers (phenothiazine) and polymers.

Further details and advantages of the method according to the invention can be found in the exemplary embodiment described below.

First, a result obtained with a method not according to the invention will be described with the aid of a comparative example.

Comparative Example 1

A circulation reactor made of glass (volume: 1 1), heated with a heating plug, was filled with 500 g of an oxyester distillate, obtained from the esterification residue freed from the acidic esterification catalyst, and 40 g of p-toluenesulfonic acid. The oxyester distillate contained

11.0% by weight of butyl acrylate, 64.8% by weight of butoxyester I (R = CH ₉ ) 20.5% by weight of acyloxyester II (R = C ₄ H ₉ ).

10 l of air were introduced into the mixture every hour.

The gap temperature was 195 ° C and the working pressure was

1 atm.

The esterification residue to be cleaved was fed continuously to the cleavage reactor during level cleavage.

The cleavage products were removed in vapor form and condensed at the top of the column (50 cm × 2.8 cm, empty) placed on the cleavage reactor. Within 119.5 hours, 7401 g of mixture (62 g / h) were fed to the cleavage and 7080 g of cleavage products were condensed. According to the gas chromatographic analysis, the condensate contained:

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 wt. -% butenes

0.2% by weight of butyl propionic acid butyl ester

Turnover: 96% by weight based on oxyester

example

Example of the procedure according to the invention

A circulation reactor made of glass (volume 11), heated with a heating plug, was filled with 500 g of the oxyester distillate from comparative example 1, 40 g of p-toluenesulfonic acid, 100 g of acrylic acid (stabilized with 300 ppm of phenothiazine) and 20 g of water. 10 l of air were introduced into the mixture every hour.

The gap temperature was 195 ° C, the working pressure 1 atm.

The oxyester distillate to be cleaved, 20% by weight of acrylic acid and water (4% by weight, based on oxyester distillate) were fed continuously to the cleavage reactor. The cleavage products were condensed at the top of the column placed on the reactor (50 cm × 2.8 cm, empty).

Within 100 hours, 15250 g of oxyester distillate (153 g / h), 3050 g of stabilized acrylic acid and 600 g of water were fed to the cleavage and 18350 g of product mixture were condensed. According to the gas chromatographic analysis, the condensate after the water was removed:

73.8% by weight of butyl acrylate 6.5% by weight of butanol

12.9% by weight acrylic acid 0.7% by weight dibutyl ether

2.8% by weight of butenes

<1% by weight of butyl propionate

Turnover: 97% by weight, based on oxyester. Comparative Example 2:

The procedure is as in the example, but without the addition of water. Throughput: 108 g / h at 96% by weight conversion (based on oxyester). By-products (sum of olefin and dibutyl ether): 4.0% by weight, based on condensate.

Claims

claims

1. A process for the esterification of (meth) acrylic acid with an alkanol in the presence of an esterification catalyst, in which unreacted starting compounds and the (meth) acrylic acid ester to be formed are separated from the reaction mixture to leave a bottom product containing oxyester, and either

or

b) the oxyesters are first separated from the bottom product by distillation, the distillate is mixed with monomeric and / or oligomeric (meth) acrylic acid and then in the presence of acid catalysts different from monomeric and oligomeric (meth) acrylic acid the oxyesters contained are cleaved by the action of elevated temperature,

characterized in that water is additionally added to the bottom product or the oxyesters separated from the bottom product by distillation for the cleavage.

2. The method according to claim 1, characterized in that the amount of monomeric and / or oligomeric (meth) acrylic acid added to the product to be cleaved is 5 to 50% by weight, based on the product to be cleaved.

3. The method according to claim 1, characterized in that the amount of monomeric and / or oligomeric (meth) acrylic acid added to the product to be cleaved is 10 to 40% by weight, based on the product to be cleaved.

4. The method according to any one of claims 1 to 3, characterized in that the amount of water added to the product to be split is 0.1 to 20% by weight, based on the product to be split.

5. The method according to any one of claims 1 to 3, characterized in that the amount of water added to the product to be split is 1 to 10% by weight, based on the product to be split.

5

6. The method according to any one of claims 1 to 5, characterized in that the method is carried out in the presence of molecular oxygen.

10 7. The method according to any one of claims 1 to 6, characterized in that the product to be split is split at temperatures of 150 ° C to 250 ° C.

8. The method according to any one of claims 1 to 7, characterized in that the product to be cleaved is added a mineral acid and / or an organic acid other than monomeric and oligomeric (meth) acrylic acid as acid.

20 9. The method according to claim 8, characterized in that the amount of acid added, different from monomeric and oligomeric (meth) acrylic acid, is 1 to 20% by weight, based on the product to be cleaved.

25 10. The method according to claim 8, characterized in that the amount of acid added which is different from monomeric and oligomeric (meth) acrylic acid is 5 to 15% by weight, based on the product to be cleaved.

30 11. The method according to any one of claims 1 to 10, characterized in that the cleavage is carried out at reduced pressure (<1 atm).

12. The method according to any one of claims 1 to 11, characterized in that a stripping gas is passed through the product to be cleaved to remove the cleavage products.

13. The method according to claim 12, characterized in that an oxygen-containing gas is used as stripping gas.

40

14. The method according to any one of claims 1 to 13, characterized in that the resulting cleavage products are returned directly to the esterification.

45 15. The method according to any one of claims 1 to 14, characterized in that the alkanol is a Ci to C ₈ alkanol.

16. The method according to claim 15, characterized in that the alkanol is n-butanol or 2-ethylhexanol.