DD152540A1 - PROCESS FOR THE PREPARATION OF 2-HYDROXYALKYL ACRYLATES - Google Patents

Abstract

The invention relates to a process for the preparation of 2-hydroxyalkyl acrylates from unsaturated carboxylic acids and alkylene oxides, preferably from acrylic acid or methacrylic acid and ethylene oxide or propylene oxide, in the presence of the customary catalysts and polymerization inhibitors. Characteristics of the process are the use of a reactor with external cooling circuit, via which the bulk of the heat of reaction is removed, as well as the careful workup of the reaction mixture by a Duennschichtdestillation. This method makes it possible to produce the target products with a high space-time yield.

Description

Process for the preparation of 2-hydroxyalkyl acrylates

The invention relates to a process for preparing 2-hydroxyalkyl acrylates from unsaturated carboxylic acids, preferably acrylic acid and methacrylic acid, and alkylene oxides, preferably ethylene oxide and propylene oxide.

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Characteristic of the "known teohnisohen solu tions

Discloses the preparation of 2-hydroxyalkyl Alleylenoxiden from, for example, ethylene oxide or propylene oxide, - and unsaturated Garbonsäuren _s such as acrylic acid or methacrylic acid * in -Gegenwart a catalyst (DE-AS 1 14426). It is also known that usually the reaction is carried out in a stirred autoclave. The unsaturated carboxylic acid with the catalyst, for example iron (III) chloride, and a polymerization inhibitor, for example , hydroquinone, are initially charged in the reactor _. heated to a certain temperature and then mixed with the alkylene oxide. Because of the strong exothermic nature of the reaction, the alkylene oxide is added over a certain period of time in liquid or gaseous form and metered in with constant heat removal. To obtain a high conversion of the acid component, an excess of alkylene oxide is used, which can be recovered at the end of the reaction by evaporation from the reaction mixture.

However, this procedure has some disadvantages. Thus, the reaction mixture tends greatly to the formation of oligomers or «polymers.

As a result of the formation of alkylene diacrylates occurring in a polar reaction, very reactive and interfering by-products are obtained. These diesters are very susceptible to polymerization and, in addition to the losses in yield, bring about considerable problems in the workup and further processing of the 2-hydroxyalkyl acrylates with

Both the formation of these diacrylates as the oligomers and polymers during the 2-Hydroxyalkylacrylather position by longer residence times and higher

"Favored. .To avoid"! Pemperaturen or reduction of unwanted by-products that occur despite the addition of polymerization inhibitors' Reaktipnstemperaturen at the usual residence must be of several hours lower than 90 ⁰ G. The Haum time yields of 2-hydroxyalkyl acrylates achieved are not very large.

The distillative workup must be as gentle as possible? so that no additional secondary products are formed in this phase. The boiling temperatures of the reaction products, z _e B _{4 of} the 2-hydroxyethyl acrylate and the Bthylenglykoldiacrylats ₅ have only minor differences to the rope, so that the separation is complicated and can be expected with secondary products in the final product, which limit its linsetzbarkeit. To improve the Ea um-time - Yielding en with simultaneous reduction of the production of secondary products by reducing the residence time is known, the reaction between the unsaturated carboxylic acid and the Alley lenoxid under pressure .durchführen «In DE-AS

1 568 537 the IDinsatz a pressure operated flow tube is described as a reactor, however, requires a much higher technical effort.

It is also known ,, that by the addition of certain compounds, for _e * B-tin (II) chloride or "bromide, at the end of the reaction, the catalyst system (iron (III) salts) is inactivated and the formation of secondary products characterized can be reduced (DE-AS.

2 027 44-4).

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The highly exothermic reaction between the alkylene oxide and the unsaturated carboxylic acid sets the reactor size and the throughput limits, so that must be expected on an industrial scale with temperature peaks in which the formation of secondary products occurs increasingly. · ·

Object of the invention

The object of the invention is to improve the process for the preparation of '2-hydroxyalkyl acrylates so that by a suitable process control the! Or by-product formation is reduced during the entire process and high space-time yields are achieved.

Principle of the invention _n

- Problem of the invention

The object of the invention is to develop a process for preparing 2-hydroxyalkyl acrylates by reacting unsaturated carboxylic acids, preferably acrylic acid or methacrylic acid, with alkylene oxides, preferably ethylene oxide or propylene oxide, in the presence of customary catalysts and polymerization inhibitors in a stirred reactor. that the reaction is carried out at medium temperatures and short residence times by a suitable heat dissipation and the subsequent work-up is done as gently as possible, so that the above-mentioned objectives can be achieved.

Features of the invention

The object is achieved in that the reaction is carried out in the stirred reactor with an external cooling circuit and the alkylene oxide liquid

is metered into the cooling circuit in front of the radiator, the majority of the heat of reaction is discharged through the cooling circuit and the resulting 2-Eydroxyalkylacrylate by a thin film evaporation at a temperature of 60 to 150 ⁰ G and a pressure of 1 to 50 u orr are continuously separated, wherein the Dünnschichtverdampfunun is carried out so-that the vapor space is stabilized by injecting a polymerization inhibitor. -

The inventive preparation of the 2-Eydroxyalky acrylates! Occurs that the unsaturated carboxylic acid, catalyst and polymerization reactor initially charged in the stirring, and heated to a temperature of 70 to 110 ⁰ C 'The stirred reactor has a cooling circuit with a pump and a so _s or more heat exchangers. The metering of the alkylene oxide takes place at one or more points directly in front of the heat exchanger in the circulation or in..die liquid phase of Rührreaktorsc The reactor operates without pressure or at low pressure and has a suitable reflux condenser for condensing evaporating alkylene oxides. The metering rate of the alkylene oxides is determined by the heat removal and is so large that a reaction time of the order of one hour can be achieved.

The proposed solution thus enables a high space-time yield. Due to the short residence time and the possibility of exact compliance with the particular reaction temperature, the formation of 3? oil and by-products reduced «

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To obtain the pure 2-hydroxyalkyl acrylates, the crude product is subjected immediately after completion of the reaction and the evaporation of the excess alkylene oxide continuously a thin film distillation, preferably in a rotary thin-film evaporator. The separation is carried out as gently as possible at an absolute pressure of 1 to 50 Torr and temperatures of 60 to 150 ⁰ G, preferably 75 to 100 ⁰ G ₉

In order to avoid undesirable phenomena of vaporization in the vapor phase, a polymerization inhibitor is suitably sprayed into the vapor space.

It has been shown that by this reaction and the simple thin-film evaporation, a yield of 2-hydroxyalkyl acrylates - based on. the unsaturated acid - reached by more than 95 % - will. The Bndprodukte obtained by this procedure can be used directly as monomers in polymerization processes without further purification.

Comparative example

3 A 2 m stirred reactor is charged with 685 kg of acrylic acid containing 0.97 kg of iron (III) chloride and 0.194 kg of copper powder and 0.176 kg of hydroquinone. 2u this mixture are added 460 kg of ethylene oxide at a reaction temperature of 90 ⁰ G (± 1.5 degrees) in 3 h. · A conversion of acrylic acid is achieved of 99%.

The heat of reaction is dissipated only via the cooling jacket of the reactor and thus essentially determines the residence time of the Bthylenoxids and thus the reaction time. The Ethylenoxidübei shot is at the end

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the reaction by .Degassing of Bohgem.isoh.es zurückgewönneηο.

The crude product is then subjected to a simple bubble distillation, at one pressure. of 15 Torr and a Semper at-ur of 100 ⁰ G, the 2-Hydroxyethylacrylat.abdestilliert. It is, 817 j 4 kg head product won * This corresponds to a yield of 85 %% based on the acrylic acid used. The space-time yield is 136.2 kg / m h. The purity of the top product was 96.5 %.

In a 2 m -Rührreaktor be 685 kg Acrylic acid 0.97 kg of iron (III) chloride, 0.194 kg of copper powder and 0.176 kg hydroquinone vorgelegt..Each the heating will be at a reaction temperature of 90 ⁰ O (i 1.5 degrees) 460 kg of ethylene oxide are added in 60 minutes »The heat of reaction is removed via a circuit with a shell-and-tube heat exchanger at a circulation rate of 50 Bi / h. During this time, the acrylic acid is converted to 99 _S 5 % . The excess of ethylene oxide is recovered by the degassing at the end of the reaction. Immediately thereafter, the crude mixture becomes a rotary thinner. fed and subjected to distillative separation at 75 ⁰ G and a pressure of 2 Sorr. The vapor phase is stabilized by spraying an amount of O ₅ 05 kg of hydroquinone dissolved in 2-hydroxy and hyaluronic acid.

There were recovered 961.7 kg of 2-hydroxyethyl acrylate. This corresponds to a yield of -97 »5 % based on the acrylic acid at a purity of 9B%» The space-time yield is 480.9 kg / m. H.

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Example 2 '·

In a 2 m · - stirred reactor 700 kg of methacrylic acid with Oj98 kg of iron (III) chloride 'and 0.2 kg of copper powder and 0.18 kg of hydroquinone are presented. For this purpose, 393 kg of ethylene oxide are metered at a reaction temperature of 90 ⁰ C in 60 minutes. The reaction and recovery of the 2-hydroxyethyl methacrylate are carried out as in Example 1.

In this case, 1036.6 kg of 2-Bydroxyethylmethacrylat were recovered. This corresponds to a yield of 98 % based on methacrylic acid or a space-time JUisbeute of 518.3 kg / nr. The purity was 98.3%.

Claims (1)

Process for the preparation of 2-hydroxyalkyl acrylates by reacting unsaturated carboxylic acids, preferably acrylic acid or methacrylic acid _s ' with alkylene oxides; preferably [ethylene oxide or propylene oxide, under conventional reaction conditions in a Rührreak'tor and subsequent workup, characterized; that the reaction is carried out in a stirred reactor with external cooling circuit, the main amount of heat removal takes place via the cooling circuit and the resulting 2 ~ hydroxyalkyl acrylates through a Dünnschichtverdampfuxtg at a 'temperature of 60 to 150 ⁰ O and a Bruck of' 1 to 50 pounds of orr are separated continuously, the thin-film evaporation being carried out so as to stabilize the vapor space by blowing a polymerization inhibitor,