WO2023169863A1

WO2023169863A1 - Process for preparing high purity (meth)acrylates

Info

Publication number: WO2023169863A1
Application number: PCT/EP2023/054908
Authority: WO
Inventors: Yongqiang Zhu; Yongyan Lu; Minju SONG; Luyan DONG; Shiliang Huang; Steffen Krill; Florian Klasovsky
Original assignee: Röhm Gmbh; Roehm Chemical (Shanghai) Co., Ltd.
Priority date: 2022-03-08
Filing date: 2023-02-28
Publication date: 2023-09-14

Abstract

The present invention relates to a process for preparing high purity (meth)acrylates, in particular hydroxyl-functional (meth)acrylates having high purity. The process employs at least one suitable reactor, an intermediate vessel, in which the crude solution formed in the reactor is intermediately stored before being fed to a suitable distillative purification set-up comprising at least two purification cycles.

Description

Process for preparing high purity (meth)acrylates

Technical Field

The present invention relates to a process for preparing (meth)acrylates of high purity, using at least one suitable reactor, an intermediate vessel, in which the crude solution formed in the reactor is intermediately stored before being fed to a suitable distillative purification set-up comprising at least two purification cycles from which in turn the polymerization-prone (meth) acrylate compounds are obtained in a form meeting specifications.

Background Art

Monomers, such as styrene or (meth)acrylates, have a tendency toward undesired side reactions during preparation and storage, extending as far as the development of discoloration and premature polymerization. To prevent this, during the preparation and the subsequent storage and/or further processing, polymerization inhibitors are used for stabilization and in particular short residence times are implemented during the preparation process. The preparation process generally consists here of a reaction process and a purification process.

JP 2008-143814 describes a reaction process for obtaining polymerization-prone hydroxyalkyl methacrylates. The purification process is not explained further in this document.

JP 2008-127302 describes a process for obtaining polymerization-prone alkylene oxide derivatives. In this case, a batch reactor is used, and the crude solution obtained after the reaction is transferred into a separate distillation apparatus and distilled therein batchwise.

EP 1 125 919 describes a stabilized hydroxyalkyl (meth)acrylate containing a hydroxyalkyl ester of a saturated carboxylic acid in a concentration of 0.0001 % to 2% by weight and a phenol compound in a concentration of from 0.001% to 0.5% by weight, based in each case on the hydroxyalkyl (meth)acrylate, wherein the mixing ratio of the hydroxyalkyl ester of a saturated carboxylic acid to the phenol compound is in the range from 0.1 to 100, based on the weight, and wherein the hydroxyalkyl ester of a saturated carboxylic acid is at least one component selected from the group made up of hydroxyethyl acetate, hydroxyethyl propionate, hydroxyethyl isobutyrate, hydroxypropyl acetate, hydroxypropyl propionate and hydroxypropyl isobutyrate. This makes it possible to prevent or delay undesired polymerization, for example during storage.

EP 1 090 904 discloses a purification process, wherein a reaction mixture comprising hydroxyalkyl (meth)acrylates can be purified particularly efficiently by a distillation combined with a thin-film evaporator.

EP 0 999 200 describes a process for preparing a monomer selected from methacrylic acid and methyl methacrylate, including: (A) hydrolyzing acetone cyanohydrin to produce a hydrolysis mixture including a- hydroxyisobutyramide, a-sulfato isobutyramide, methacrylamide, and methacrylic acid; (B) thermally converting the hydrolysis mixture in a cracker reactor including a plug flow thermal conversion apparatus with the necessary retention time to produce a cracker reactor mixture including 2-methacrylamide and methacrylic acid; (C) reacting the cracker reactor mixture and a material selected from methanol and water in at least one reactor to produce a monomer selected from methacrylic acid and methyl methacrylate.

WO 2010/127909 describes a method for purifying monomers, wherein at least part of the monomers is contained in a starting composition. At least part of the starting composition is evaporated in a short-path evaporator, wherein the mass flow density of the vapours fulfil a certain relation. In a first step low-boiling impurities are separated from the reaction mixture, followed by a second step in which the product monomers are separated and high-boiling impurities remain as residue. Examples for the purification of 2- hydroxyethyl methacrylate with a purity of up to 99.5 wt.-% are reported.

DE 10 2007 056 926 discloses a method for the purification of unsaturated compounds which is carried out in a system comprising at least two evaporators. The evaporators are connected in such a way that part of the unsaturated compound is circulated, the vapours condensed in the first evaporator are isolated and the vapours condensed in the second evaporator are introduced into the first evaporator. The mass flow with which the condensed vapours are isolated from the mixture to be purified in the first evaporator is smaller than the mass flow, with which the condensed vapours from the second evaporator are introduced into the first evaporator. Examples for the purification of 2-hydrxoyethyl methacrylate with a purity of up to 99.1 wt.-% are reported.

The known processes and plants for preparing polymerization-prone (meth)acrylate compounds lead to acceptable yields and qualities of the desired products. However, there remains a constant need to processes providing products with exceptional high purities of > 99.5 % by weight, e.g. for sensitive applications such as applications in contact to human bodies or food. At the same time, the processes should be realizable with conventional apparatuses set-ups.

Disclosure of the Invention

Object of Invention

In consideration of the prior art, a problem addressed by the present invention was providing a process for preparing a high-purity polymerization-prone (meth)acrylate compounds in which the plants of the reaction and purification process are used in a highly efficient manner.

In particular, a problem addressed by the present invention in general was that of providing a process for preparing and isolating polymerization-prone (meth)acrylate compounds, especially particularly polymerization-prone hydroxyl-functional (meth)acrylates, where the reaction part is carried out in a batchwise or semi-batchwise mode and the purification in contrast can be performed continuously or semi-continuously. From this arose the further problem of providing the isolated polymerization-prone (meth)acrylate compound in a consistently high monomer quality and of preventing fluctuations which generally result from a batchwise or semi-batchwise mode.

Further problems which are not stated explicitly may become apparent from the following description of the invention, the claims, the examples or the overall context of the present invention.

Detailed Description of Invention

These problems were solved by the provision of a novel process for preparing polymerization-prone (meth)acrylate compounds, in particular (meth)acrylates.

According to the invention, the novel process for the preparation of high-purity (meth) acrylates starts from (meth)acrylic acid and an epoxy-functional compound, wherein the process comprises at least the following process steps: a) reaction of (meth)acrylic acid with at least one epoxy-functional compound in the presence of a catalyst in a reactor, b) transfer of the (meth)acrylate-containing reaction mixture present as liquid phase in the reactor after the reaction is completed to a first intermediate vessel V1 , c) purification of the target high-purity (meth)acrylates in a purification process comprising at least a first purification cycle P1 and a second purification cycle P2, wherein each purification cycle is carried out at least once and wherein the first purification cycle P1 is carried out prior to the second purification cycle P2, wherein in the first purification cycle P1 high-boiling constituents are separated off from the (meth)acrylate-containing reaction mixture, and wherein in the in the second purification cycle P2 low-boiling constituents and high-boiling constituents are separated off from the remainder obtained from the first purification cycle P1 , wherein the remainder obtained from the second purification cycle P2 consists of > 99.5 wt.-% of the target (meth)acrylate, and further comprises

1 to 1500 ppm, preferably 1 to 1000 ppm, more preferable 1 to 800 ppm, of ethylene glycol dimethacrylate (EGDMA),

1 to 1500 ppm, preferably 1 to 500 ppm, more preferably 1 to 50 ppm, of diethylene glycol methacrylate (DEGMA), and 1 to 1000 ppm, preferably 1 to 500 ppm, more preferably 1 to 300 ppm, of glycerol monomethacrylate (GMMA), wherein the remainder obtained from the second purification cycle P2 has a color number in the range from 1 to 10, preferably from 1 to 8, wherein low-boiling constituents are chemical compounds comprised in the reaction mixture having a boiling temperature below the boiling temperature of the target (meth)acrylate at a given pressure, and wherein high-boiling constituents are chemical compounds comprised in the reaction mixture having a boiling temperature above the boiling temperature of the target (meth) acrylate at a given pressure.

A polymerization-prone (meth)acrylate compounds can be simply and efficiently obtained in high purity by this novel process in a manner that could not be foreseen.

In terms of the present invention, ppm (parts per million) means weight-based ppm, e.g. mg/kg.

The process according to the invention is particularly suitable for the preparation of hydroxyalkyl (meth)acrylates. The expression "hydroxyalkyl (meth)acrylates" in this case encompasses hydroxyalkyl methacrylates, hydroxyalkyl acrylates, and mixtures thereof. The same applies, mutatis mutandis, to the wording "(meth)acrylic acid", which encompasses both methacrylic acid and acrylic acid or mixtures thereof.

In the technical field, hydroxyalkyl (meth)acrylates are well known esters of (meth)acrylic acid, the alcohol radical of which has at least one hydroxyl group. For example, preferred hydroxyalkyl (meth)acrylates include 2- hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl methacrylates, especially 2- hydroxypropyl methacrylate and 3-hydroxypropyl methacrylate, and/or hydroxypropyl acrylates, especially 2-hydroxypropyl acrylate and 3-hydroxypropyl acrylate.

The epoxy-functional compound is preferably an oxirane, particularly preferably ethylene oxide or propylene oxide. Correspondingly, the (meth) acrylate is preferably a hydroxyalkyl-substituted (meth)acrylate, particularly preferably 2-hydroxyethyl methacrylate or hydroxypropyl methacrylate. Hydroxypropyl methacrylate can in turn be 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate or an isomeric mixture thereof.

The molar ratio of the overall (meth)acrylic acid used to the overall epoxy-functional compound used can favorably be in the range from 2:1 to 1 :2, particularly preferably in the range from 1.1 :1 to 0.9:1 .

Interfering by-products include for example diethylene glycol (meth) acrylate (DEGMA), glycerol monomethacrylate (GMMA) or - as a particularly critical by-product - ethylene glycol di(meth)acrylate (EGDMA). Ethylene glycol di(meth)acrylate is particularly critical here since it functions as a crosslinker which can severely disrupt the end product properties, especially in desired polymerization processes, as a result of crosslinking. For example, in applications of hydroxyalkyl (meth)acrylates for the preparation of sensitive products such as contact lenses, the presence of EGDMA may result in distortions of the geometry of the contact lenses due to crosslinking. Also, the presence of low-boiling by-products and starting materials such as (meth)acrylic acid and hydroxyethyl acetate in the product is undesired since these materials are prone to migrate from the polymerized (meth)acrylates during the intended application. This is often not acceptable, for example in sensitive applications contact to human bodies or food, e.g. in contact lenses.

In process step a), preferably first the methacrylic acid is provided together with the catalyst and optional auxiliaries such as stabilizers. After reaching a reaction start temperature, which lies in the region of the reaction temperature T1 , the addition of the epoxy-functional compound is begun, for example by means of uniform metering. The reaction time t1 according to the invention starts from the beginning of the addition. The addition can in theory be effected until the end of t1 as uniform metering or as addition of individual batches. However, the addition is generally ended long before t1 has elapsed. Alternatively, however, other methods are also conceivable, in which the methacrylic acid and/or the catalyst are added subsequently. A variant would also be possible in which all raw materials are initially charged, and the reaction is started by increasing the temperature. In this latter case, t1 starts at the moment at which exothermicity can first be recorded.

The catalyst used is preferably a metal-containing compound. Alternatively, two or more metal-containing compounds may for example also be used. Preferred catalysts are disclosed inter alia in EP 12 312 04.

The catalyst can be used in solid form or as catalyst composition, such as solution or dispersion. Preferably, the catalyst is used in an amount in the range of 0.01 to 1 wt.-%, preferably 0.1 to 0.5 wt.-%, based on the (meth)acrylic acid. The amount given above is based on the amount of active catalyst, e.g. if used in form of solution or dispersion.

Further preferably, the reaction in process step a) is effected at a temperature T1 of between 40 and 120°C, preferably between 50 and 100°C, and particularly preferably between 60 and 80°C. The temperature T1 is in this case not a constant temperature, but rather a temperature window within which the reaction is effected during t1 . The temperature T1 can by all means vary within this scope especially as a result of the metered addition, the exothermicity of the reaction, and evaporation processes within the reactor. It is also not excluded that the temperature rises a little above 100°C for a very short time, i.e. of less than 5 min. However, preference is given to a reaction regime in which this is avoided.

(Meth)acrylic acid can be reacted with epoxide either continuously or batchwise or semi-batchwise. The batchwise or semi-batchwise mode of operation has become commercially established since it is simple to carry out in terms of apparatus and the reaction can be conducted to the desired end point. The process for preparing hydroxyalkyl (meth)acrylates can be performed in bulk, that is to say without the use of a further solvent. If desired, an inert solvent can also be used. The degree of conversion, based on (meth)acrylic acid, is preferably at least 99 mol%, particularly preferably at least 99.5 mol%. The degree of conversion can in particular be adjusted via the reaction duration and the reaction temperature.

The reaction time ti in the batchwise or semi-batchwise mode according to the invention is typically between 2 and 10 hours, preferably 4 to 8 hours. The pressure used for the preparation of the hydroxyalkyl (meth)acrylate is preferably in a range from 0.5 to 25 bar, particularly preferably in the range from 1 to 3 bar, these figures respectively being the absolute pressure.

The reaction of the present process can be performed in one or else in a plurality of reactors and the reactors are all connected to the first intermediate vessel via V1 one or more pipelines and the respective liquid phases are emptied into said intermediate vessel V1 .

(Meth)acrylic acid can be reacted with epoxide in the presence of polymerization inhibitors, these possibly already being used in the reactor in many cases. The polymerization inhibitors to be used with preference include in particular phenol compounds, such as for example hydroquinones, hydroquinone ethers, such as hydroquinone monomethyl ether, tert-butylhydroquinone, 2,6-di-tert-butylhydroquinone, 2,5-di-tert- butylhydroquinone, 2,4-dimethyl-6-tert-butylphenol or di-tert-butylcatechol; p-phenylenediamines, such as for example N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N , N'-d i-p-tolyl-p- phenylenediamine, N-1 ,3-dimethylbutyl-N'-phenyl-p-phenylenediamine and N-1 ,4-dimethylpentyl-N'- phenyl-p-phenylenediamine; amines, such as for example thiodiphenylamine and phenothiazine; copper dialkyldithiocarbamates, such as for example copper dimethyldithiocarbamates, copper diethyldithiocarbamates and copper dibutyldithiocarbamates; nitroso compounds, for example nitrosodiphenylamine, isoamyl nitrite, N-nitrosocyclohexylhydroxylamine, N-nitroso-N-phenyl-N- hydroxylamine and salts thereof; and N-oxyl compounds, for example 2,2,4, 4-tetramethylazetidine 1-oxyl, 2,2-dimethyl-4,4-dipropylazetidine 1-oxyl, 2,2,5,5-tetramethylpyrrolidine 1-oxyl, 2,2,5,5-tetramethyl-3- oxopyrrolidine 1-oxyl, 2,2,6,6-tetramethylpiperidine 1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl, 6-aza-7,7-dimethylspiro[4.5]decane 6-oxyl, 2,2,6,6-tetramethyl-4-acetoxypiperidine 1-oxyl and 2, 2,6,6- tetramethyl-4-benzoyloxypiperidine 1-oxyl; methylene blue, nigrosin base BA, 1 ,4-benzoquinone, sterically hindered phenols, for example 2,4-dimethyl-6-tert-butylphenol and/or tocopherol compounds, preferably a-tocopherol.

The polymerization inhibitors can be used individually or in the form of mixtures and are generally commercially available. Further details may be found in the relevant specialist literature, in particular Rompp-Lexikon Chemie; editors: J. Falbe, M. Regitz; Stuttgart, New York; 10th edition (1996); keyword “Antioxidantien” and the literature references cited there.

Surprising advantages can be achieved in particular by reaction mixtures which preferably contain 1 to 5000 ppm, particularly preferably 5 to 1000 ppm, and very particularly preferably 10 to 200 ppm of polymerization inhibitor, based on the (meth)acrylic acid. The (meth)acrylic acid is reacted with the epoxy-functional compound in the presence of a catalyst in a reactor, the gas phase and the liquid phase in the reactor being mixed with one another.

After the reaction time t1 , the content of epoxy-functional compound in the gas phase and the liquid phase is reduced by removing gas phase from the reactor. Preferably, the reaction time t1 ends when the (meth)acrylic acid concentration in the liquid phase is less than 1 .0% by weight, preferably less than 0.5% by weight, particularly preferably less than 0.1 % by weight. The time at which the (meth)acrylic acid concentration in the liquid phase is less than 1 .0% by weight can initially be determined for example by sampling, pH measurements or measurements of the refractive index, or other optical methods. With more experience of the reaction regime, the time can be determined during the reaction from outside by those skilled in the art, ideally without sampling, simply on the basis of the temperature profile and/or other easy-to-measure process parameters. Removing of the gas is preferably effected at a temperature T2 of between 60 and 100°C, that is to say at a temperature which is similar to the actual reaction temperature and may absolutely even be higher than the reactor internal temperature during the start of the reaction on account of the exothermic nature of the reaction.

Moreover, it has proved to be favorable if the reduction in the content of epoxy-functional compounds is effected in combination with a pressure reduction. Epoxy-functional compound dissolved in the liquid phase is additionally removed with the gas phase from the reactor.

After the reaction time t1 , a (meth)acrylate-containing mixture, which is present as liquid phase in the reactor, is subsequently removed and this liquid phase is transferred into a first intermediate vessel V1 (process step b)). The (meth)acrylate-containing mixture is also called reaction mixture or crude reaction mixture within the present description.

The first intermediate vessel V1 is connected with the reactor(s) via at least one line and can also optionally be equipped with cooling and/or heating elements, which are fitted internally or externally, preferably externally.

According to one particular configuration, after the reaction process in the reaction apparatus or the vessel for intermediate storage and before the purification process, the liquid phase respectively present can be treated with gas. To this end, in particular, air or nitrogen can be passed through the liquid phase. This configuration makes it possible to remove gaseous or highly volatile constituents from the liquid phase present here before it is subject to further purification. This treatment is preferably achieved using a stripping column. Suitable apparatuses are known in the art.

It is preferable for the residence time t2 in the intermediate vessel V1 to be shorter than 200 h, particularly preferably shorter than 100 h and especially preferably shorter than 50 h. In particular, it is preferable for the ratio of the residence time t2 to the reaction time t1 to be less than 25, preferably less than 12 and particularly preferably less than 6. It is conceivable, although not necessary according to the invention and therefore less preferable, to use more than one intermediate vessel, likewise set up parallel to each other. Independently thereof, it is also possible to use a plurality (more than one) of distillation set-ups parallel to each other.

After an average residence time t2 of the mixture in the first intermediate vessel V1 , the mixture is transferred from the intermediate vessel V1 into a distillation set-up described in the following.

In process step c), the reaction mixture comprising the target (meth)acrylate is transferred to a purification set-up comprising at least a first purification cycle P1 and a second purification cycle P2. The process carried out in purification cycle P1 is also abbreviated as process step c-P1) herein, whereas process carried out in purification cycle P2 is also abbreviated as process step c-P2). Each of purification cycle P1 (i.e. process step c-P1) and purification cycle P2 (i.e. process step c-P2)) is carried out at least once. The first purification cycle P1 is carried out prior to the second purification cycle P2.

For process step c), the reaction mixture may be used as obtained from the reactor, i.e. in form a crude reaction mixture. However, it is often advantageous to perform a purification step in advance to purification cycle P1 . This purification step may include the removal of gaseous constituents from the crude reaction mixture (e.g. by using stripping columns) and/or conventional distillative purification processes in order to obtain a pre-purified reaction mixture having a content of the target (meth)acrylate (in particular 2-hydroxyethyl methacrylate (HEMA)) of at least 97 wt.-%, more preferably at least 98 wt.-%, based on the total weight of the thus obtained pre-purified reaction mixture. Suitable purification processes are known and described in the art, for example in DE 10 2007 056 926.

In the first purification cycle P1 (i.e. in process step c-P1), high-boiling constituents are separated off from the (meth)acrylate-containing reaction mixture. Separation is for example achieved by distillation methods. The remainder obtained from the first purification cycle P1 (i.e. fractions comprising low-boiling constituents as well as the target (meth)acrylate) is subsequently transferred to the second purification cycle P2 (i.e. in process step c-P1) in order to separated off low-boiling constituents and remaining high- boiling constituents. The remainder of purification cycle P2 is thus constituted by the middle fraction of the second purification cycle P2 and comprises the target (meth)acrylates in high purity.

The term “low-boiling constituents” as used herein refers to chemical compounds comprised in the reaction mixture having a boiling temperature below the boiling temperature of the target (meth) acrylate at a given pressure.

The term “high-boiling constituents” as used herein refers to chemical compounds comprised in the reaction mixture having a boiling temperature above the boiling temperature of the target (meth) acrylate at a given pressure.

The remainder obtained from the second purification cycle P2 consists of > 99.5 wt.-%, preferably 5= 99.6 wt.-%, of the target (meth)acrylate, and further comprises: 1 to 1500 ppm, preferably 1 to 1000 ppm, more preferable 1 to 800 ppm, of ethylene glycol dimethacrylate (EGDMA),

1 to 1500 ppm, preferably 1 to 500 ppm, more preferably 1 to 50 ppm, of diethylene glycol methacrylate (DEGMA), and

1 to 1000 ppm, preferably 1 to 500 ppm, more preferably 1 to 300 ppm, of glycerol monomethacrylate (GMMA).

More preferably, remainder obtained from the second purification cycle P2 comprises (or consists of): 5= 99.6 wt.-%, of the product 2-hydroxyethyl methacrylate (HEMA),

1 to 1000 ppm, preferable 1 to 800 ppm, of ethylene glycol dimethacrylate (EGDMA).

1 to 500 ppm, preferable 1 to 50 ppm, of diethylene glycol methacrylate (DEGMA), and

1 to 500 ppm, preferable 1 to 300 ppm, of glycerol monomethacrylate (GMMA).

Moreover, the remainder obtained from the second purification cycle P2 has a color number in the range from 1 to 10, preferably from 1 to 8.

It has been found by the present inventors that the process of the present invention allows for the preparation of (meth)acrylates with exceptional high purity by using conventional purification apparatuses, in particular conventional distillation columns or combinations of conventional distillation columns and further separation devices such as thin-film evaporators and/or short-path evaporators. The obtained high purity (meth)acrylates can be used in numerous chemical reactions which require reduced amounts of critical impurities typically present in (meth)acrylates prepared by conventional processes, in particular EGDMA (ethylene glycol dimethacrylate), DEGMA (diethylene glycol methacrylate) and GMMA (glycerol monomethacrylate). Moreover, further impurities are also significantly reduced by the present process, such as hydroxyethyl acetate (HEAc), typically added polymerization inhibitors such as hydroquinone monomethyl ether (HMQE); starting materials, in particular methacrylic acid. Finally, if the apparatus used in the present invention is used for the production of different (meth)acrylates, e.g. for the preparation of hydroxyethyl methacrylate (HEMA) and hydroxypropyl methacrylate (HPMA) it is possible to remove residual amounts of the undesired compound which may be present in the reaction apparatus from previous productions.

Process step c-P1) (i.e. the first purification cycle) can typically be subdivided in several subsequent process steps, for example 1 to 5, 1 to 4 or 1 to 3 process steps wherein in each process step a fractionation process is carried out with at least a partial fraction obtained from the reaction mixture.

In one embodiment, process step c-P1) comprises at least a first sub-step c-P1 .1 wherein the process step c-P1 .1) comprises: c-P1 .1) transfer of the (meth)acrylate-containing reaction mixture from the first intermediate vessel V1 to a first separation set-up, comprising at least a first distillation column (distillation column D1 .1), wherein in the first purification cycle P1 the (meth)acrylate-containing reaction mixture is separated into at least the following two fractions:

(I) at least one overhead fraction containing the target (meth)acrylate and further containing low-boiling constituents (fraction F1 .1 .1), the obtained fraction representing the remainder obtained from the first purification cycle P1 , and

(ii) at least one bottom fraction containing high-boiling constituents (fraction F1 .1 .2).

In a further embodiment, the process step c-P1) comprises at least a first sub-step c-P1 .1 and at least a second sub-step c-P1 .2, wherein the process step c-P1 .1) is defined as above and the second sub-step c-P.1 .2) comprises: c-P1 .2) transfer of the at least one bottom fraction containing high-boiling constituents obtained in step c-P1 .1) (fraction F1 .1 .2) to at least one further distillation column (distillation column D1 .2), wherein in the further distillation column (distillation column D1 .2) the bottom fraction containing high-boiling constituents obtained in step C-P1.1) (fraction F1.1.2) is separated into at least the following two fractions:

(I) at least one overhead fraction containing low-boiling constituents and residual (meth)acrylate (fraction F1 .2.1), the obtained fraction being at least partially recycled continuously or discontinuously to the first distillation column used in process step c- P1 .1) (distillation column D1.1), and

(ii) at least one bottom fraction containing high-boiling constituents (fraction F1 .2.2).

In a further embodiment, the process step c-P1) comprises at least a first sub-step c-P1 .1 , a second substep c-P1 .2 and a third sub-step c-P.1 .3), wherein the process steps c-P1 .1) and c-P.1 .2) are defined as above and the third sub-step c-P.1 .3) comprises: c-P1 .3): transfer of the at least one bottom fraction containing high-boiling constituents obtained in step c-P1 .2) (fraction F1 .2.2) to at least one further separation device (separation device S1), wherein in the further separation device (separation device S1) the bottom fraction containing high-boiling constituents obtained in step C-P1.2) (fraction F1.2.2) is separated into at least the following two fractions:

(I) at least one fraction containing low-boiling constituents (fraction F1 .3.1), the obtained fraction being at least partially recycled continuously or discontinuously to the first distillation column used in process step c-P1 .2) (distillation column D1 .2), and

(ii) at least one fraction containing high-boiling constituents (fraction F1 .3.2).

Each of the sub-steps c-P1 .1 , c-P1 .2 and c-P.1 .3 may be carried out independently with the provision that the sub-step C-P1.1 is carried out prior to C-P1.2 and c-P.1.3 and sub-steps C-P1.2 and c-P.1.3 are carried out with fractions obtained from sub-step c-P1 .1 . Moreover, sub-steps c-P1 .3 is carried out with fractions from c-P.1 .2.

Preferably, the sub-steps c-P1 .1 , c-P1 .2 and c-P.1 .3) are carried out continuously and in parallel.

According to the present invention, the first purification cycle P1 , in particular process steps c-P1 .1 and c- P1 .2, is carried out at least once. However, it has been found advantageous to carry out the first purification cycle P1 repeatedly, e.g. preferably 2 to 5 times, more preferably 2 to 4 times, and often 3 times, wherein the repetition of the purification cycle P1 is achieved by recycling the remainder obtained from the first purification cycle P1 as starting material for the next repetition (recycling of fraction F1.1.1 to the distillation column D1 .1). It was found that the repetition of the first purification cycle P1 , in particular process steps c-P1 .1 and c-P1 .2, allows to increase the overall product yield and to decrease to amount of high-boiling impurities.

The first purification cycle P1 is preferably carried out under a pressure of from 0.1 to 20 mbar absolute, particularly preferably in the range from 0.5 to 10 mbar and very particularly preferably 1 to 7 mbar absolute. Pressure is controlled by means of pressure control which is preferably connected to the first distillation column D1 .1 .

The first purification cycle P1 is preferably carried out at a temperature between from 40 to 130°C, particularly preferably in the range from 60 to 110°C, and very particularly preferably 70 to 90°C. Temperature controlled individually by means of temperature control which is preferably connected to distillation column D1 .1 and optionally to distillation column D1 .2 and/or separating device S1 . Thus, distillation column D1 .1 and optionally distillation column D1 .2 and/or separating device S1 are preferably equipped with cooling and/or heating elements, which are fitted internally or externally, preferably externally.

The overhead fraction containing the target (meth)acrylate and further containing low-boiling constituents (fraction F1 .1 .1), the obtained fraction representing the remainder obtained from the first purification cycle P1 , is subsequently transferred to the second purification cycle P2. However, it may be desirable to collect fraction F1.1.1 prior to the realization of the second purification cycle P2. Thus, in one embodiment of the invention, fraction F1.1.1 is collected in a second intermediate vessel V2 and subsequently transferred continuously or discontinuously to the second purification cycle. The residence time in the second intermediate vessel V2 is preferably from 1 min to 1000 h, more preferably from 1 h to 800 h. The temperature of fraction F1 .1 .1 during the residence in the intermediate vessel V2 is preferably kept below 100°C. For this purpose, the intermediate vessel V2 is optionally equipped with cooling and/or heating elements, which are fitted internally or externally, preferably externally.

In one embodiment of the invention, the purification step c) comprises a process step C-P2.1), wherein process step C-P2.1) represents a process step of the second purification cycle P2, wherein the process step C-P2.1) comprises: C-P2.1) transfer of the remainder obtained from the first purification cycle P1 (fraction F1 .1 .1) to a second separation set-up, comprising at least a first distillation column (distillation column D2.1) and optionally at least a second distillation column (distillation column D2.2), wherein in the second purification cycle P2 the remainder obtained from the first purification cycle P1 (overhead fraction F1 .1 .1) is separated into at least the following three fractions:

(I) at least one overhead fraction containing low-boiling constituents (fraction F2.1 .1),

(II) at least one bottom fraction containing high-boiling constituents (fraction F2.2.2), and

(ill) a product fraction containing the target (meth)acrylate having a purity of > 99.5 wt.-%, representing the remainder obtained from the second purification cycle P2 (fraction F2.2.1).

In a further embodiment, the process step c-P2) comprises at least a first sub-step C-P2.1 and at least a second sub-step C-P2.2, wherein the process step C-P2.1) is defined as above and the second sub-step c-P.2.2) comprises:

C-P2.2) transfer of the at least one bottom fraction containing high-boiling constituents obtained in step C-P2.1) (fraction F2.1 .2) to at least one further distillation column (distillation column D2.2), wherein in the further distillation column (distillation column D2.2) the bottom fraction containing high-boiling constituents obtained in step C-P2.1) (fraction F2.1.2) is separated into at least the following two fractions:

(I) at least one overhead fraction containing low-boiling constituents (fraction F2.2.1), and (ii) at least one bottom fraction containing high-boiling constituents (fraction F2.2.2).

In a further embodiment, the process step c-P2) comprises at least a first sub-step C-P2.1 , a second substep C-P2.2 and a third sub-step c-P.2.3), wherein the process steps C-P2.1) and C-P2.2) are defined as above and the third sub-step C-P2.3) comprises: c-P2.3): transfer of the at least one bottom fraction containing high-boiling constituents obtained in step C-P2.2) (fraction F2.2.2) to at least one further separation device (separation device S2), wherein in the further separation device (separation device S1) the bottom fraction containing high-boiling constituents obtained in step C-P2.2) (fraction F2.2.2) is separated into at least the following two fractions:

(I) at least one fraction containing low-boiling constituents (fraction F2.3.1), the obtained fraction being at least partially recycled continuously or discontinuously to the first distillation column used in process step C-P2.2) (distillation column D2.2), and

(ii) at least one fraction containing high-boiling constituents (fraction F2.3.2).

According to the invention, the second purification cycle P2 is carried out at least once. However, it has been found advantageous to carry out the second purification cycle P2, in particular process step C-P2.1 and process step C-P2.2, repeatedly, preferably 2 to 3 times, and often 2 times, wherein the repetition of the purification cycle P2 is achieved by recycling the remainder obtained from the second purification cycle P2 as starting material forthe next repetition (recycling of product fraction F2.2.1 to the distillation column D2.1). It was found that the repetition of the second purification cycle P2, in particular process step C-P2.1 and process step C-P2.2, allows to increase the overall product yield and at the same time to increase the purity of the target (meth)acrylate.

The second purification cycle P2 is preferably carried out under a pressure of from 0.1 to 20 mbar absolute, particularly preferably in the range from 0.5 to 10 mbar and very particularly preferably 1 to 7 mbar absolute. Pressure is controlled by means of pressure control which is preferably connected to the first distillation column D2.1 .

The second purification cycle P2 is preferably carried out at a temperature between from 40 to 130°C, particularly preferably in the range from 60 to 110°C, and very particularly preferably 70 to 90°C. Temperature is controlled individually by means of temperature control which is preferably connected to distillation column D2.1 and optionally to distillation column D2.2 and/or separating device S2. Thus, distillation column D2.1 and optionally distillation column D2.2 and/or separating device S2 are preferably equipped with cooling and/or heating elements, which are fitted internally or externally, preferably externally.

Each of the sub-steps C-P2.1 , C-P2.2 and c-P.2.3 may be carried out independently with the provision that the sub-step C-P2.1 is carried out prior to C-P2.2 and c-P.2.3 and sub-steps C-P2.2 and c-P.2.3 are carried out with fractions obtained from sub-step C-P2.1 . Moreover, sub-steps C-P2.3 is carried out with fractions from c-P.2.2.

Preferably, the sub-steps C-P2.1 , C-P2.2 and C-P2.3 are carried out continuously and in parallel. Process steps c-P1 and c-P2 may be carried out continuously or discontinuously. Process steps c-P1 and c-P2 may be carried out subsequently or in parallel. In one embodiment, process steps c-P1 and c-P2 are carried out subsequently.

In one embodiment, process steps c-P1 and c-P2 are carried out subsequently in the same separation set-up, wherein distillation column D1.1 and distillation column D2.1 are identical. In one embodiment, if present, distillation column D1 .2 and distillation column D2.2 are identical. In one embodiment, if present, separation device S1 and separation device S2 are identical.

The remainder obtained from the second purification cycle P2 (product fraction F2.2.1) is transferred to a product vessel V3 and represents the product fraction having the specifications as defined herein.

In one embodiment of the invention, fraction F2.3.1 comprising low-boiling constituents obtained from separation device S2 is at least partially recycled continuously or discontinuously to the distillation column D2.2. In one embodiment of the invention, fraction F1.3.1 comprising low-boiling constituents obtained from separating device S1 is recycled to the first intermediate vessel V1 and/or to the first distillation column D1.1.

In one embodiment of the invention, fraction F1.1.2 comprising high-boiling constituents obtained from distillation column D1 .1 in step c-P1 contains catalysts and catalyst derivatives from the reaction mixture. Preferably, said fraction F1 .1 .2 is at least partially recycled continuously or discontinuously to the reactor.

In one embodiment, fraction F2.3.2 comprising high-boiling constituents obtained from process step c- P2.3 is discarded.

The invention also relates to a device for carrying out the process for the preparation of high-purity (meth)acrylates described herein, comprising at least one reactor, at least one intermediate vessel V1 , and at least two separation set-ups, wherein the first separation set-up is designed to carry out the first purification cycle P1 and the second separation set-up is designed to carry out the second purification cycle P2, and wherein the first separation set-up and the second separation set-up may be the same or different from each other.

According to the invention, the first separation set-up comprises at least a first distillation column (distillation column D1.1). In a preferred embodiment, the first separation set-up further comprises at least one additionally separating device, in particular a second distillation column (distillation column D1.2). In an alternative embodiment, the first separation set-up further comprises at least two additionally separating device, in particular a second distillation column (distillation column D1 .2) and a further separating device S1 , preferably selected from a distillation column, a thin-film evaporator and a shortpath evaporator.

Also according to the invention, the second separation set-up comprises a first distillation column (distillation column D2.1). In a preferred embodiment, the second separation set-up further comprises at least one additionally separating device, in particular a second distillation column (distillation column D2.2). In an alternative embodiment, the second separation set-up further comprises at least two additionally separating device, in particular a second distillation column (distillation column D2.2) and a further separating device S2, preferably selected from a distillation column, a thin-film evaporator and a short-path evaporator.

The distillation columns used in the purification set-ups can be selected from any distillation column known in the art. However, it was surprisingly found to be advantageous if the first distillation columns of each purification set-up, i.e. distillation column D1.1 and distillation column D2.1 , exhibit a low separating performance. As a result of this configuration, the yield and the energy efficiency of the plant can be improved in particular. Accordingly, the distillation column I used has no more than 4, particularly preferably no more than 3, separating stages. In the present invention, the number of separating stages is to be understood as meaning the number of trays in a tray column or the number of theoretical separating stages in the case of a column comprising structured packings or a column comprising random packings.

In this respect, the first distillation columns of each purification set-up may comprise internals or may comprise no internals with separating action.

In a preferred embodiment of the invention, first distillation columns of each purification set-up, i.e. distillation column D1 .1 and distillation column D2.1 , are selected from flash columns with or without internals, and are more preferably represented by flash columns without internals. This allows to reduce the pressure loss within the first and second separation set-up to achieve the desired low pressure.

The second distillation columns of each purification set-up, i.e. distillation column D1 .2 and distillation column D2.2, preferably also exhibit a low separating performance. As a result of this configuration, the yield and the energy efficiency of the plant can be improved in particular. Accordingly, the distillation column I used has no more than 4, particularly preferably no more than 3, separating stages. In this respect, the second distillation columns of each purification set-up may comprise internals or may comprise no internals with separating action. Preference is given to configurations of the present invention involving the use of distillation columns D1 .2 and/or D2.2 which have no internals with separating action. In a preferred embodiment, distillation columns D1 .2 and/or D2.2 are selected from flash columns with or without internals and are more preferably represented by flash columns without internals. This allows to reduce the pressure loss within the first and second separation set-up to achieve the desired low pressure.

If internals are present within the distillation columns, the crude solution can be fed into the distillation column above or below the above-stated internals and it is also possible, depending on the nature of these internals, to introduce the crude solution within the region of the internals. Particular advantages can be achieved inter alia when the crude solution is fed into the distillation column above the internals. The term "above the internals" means that the high-boiling constituents of the introduced composition are conducted through the internals before they are withdrawn from the distillation column. This can achieve in particular advantages with respect to the yields and the purity. The process can in addition be performed particularly efficiently.

The distillation columns of the present invention can be operated with or without column reflux, wherein a particularly high purity can surprisingly be achieved by an embodiment without column reflux. These advantages can preferably be achieved by feeding the composition of the present invention into the distillation column above any internals that may be present. In a preferred embodiment of the invention, distillation column D1 .2 and/or distillation column D2.2 are operated without column reflux.

Preferably, the distillation in each of distillation columns D1.1 , D1.2, D2.1 and D2.2 is independently performed at a temperature in the range from 40 to 130°C, particularly preferably in the range from 60 to 110°C, and very particularly preferably 70 to 90°C, these figures being based on the bottom temperature and possibly differing depending on the end product produced. The pressure at which the distillation in each of distillation columns D1 .1 , D1 .2, D2.1 and D2.2 is independently effected can preferably be in the range from 0.1 to 20 mbar absolute, particularly preferably in the range from 0.5 to 10 mbar and very particularly preferably 1 to 7 mbar absolute, these figures being based on the column top pressure.

In one embodiment, the separating device S1 and/or the separation device S2 are selected from a distillation column, a thin-film evaporator and a short-path evaporator. In one embodiment, the separating device S1 and the separating device S2 are identical, provided that both the separating device S1 and the separating device S2 are present in the separating set-up.

The device for carrying for carrying out the process for the preparation of high-purity (meth)acrylates described herein preferably comprises at least one reactor, at least one product vessel V3 and at least two distillation columns D1 .1 and D2.1 . Preferably, the device further comprises at least one stripping column. In one embodiment, the device may comprise at least one first intermediate vessel V1 , at least one second intermediate vessel V2, further distillation columns D1.2 and D2.2, and/or further separating devices S1 , S2.

Preferably, the device for carrying out the process for the preparation of high-purity (meth)acrylates described herein comprises at least one means for pressure control, such as a steam-jet vacuum ejector. The means for pressure control is preferably designed to keep the pressure within the purification cycle P1 and the purification cycle P2 during the purification process within a range of from 0.1 to 20 mbar absolute, particularly preferably in the range from 0.5 to 10 mbar and very particularly preferably 1 to 7 mbar absolute, these figures being based on the column top pressure of distillation columns D1.1 and D2.1. The means of pressure control is at least connected to the column top of distillation column D1.1.

In one embodiment of the invention, at least one means for pressure control, such as a steam-jet vacuum ejector, is connected with the at least one stripping column. The means for pressure control is preferably designed to keep the pressure within the at least one stripping column during the purification process within a range of from 0.1 to 100 mbar, more preferably 0.5 to 50 mbar, in particular 5 to 40 mbar absolute, these figures being based on the column top pressure of stripping column. The temperature within the stripping column is preferably regulated by means for temperature control, i.e. a heating device and/or a cooling device, to a temperature within the range of from 30 to 100°C, preferably 40 to 85°C and more preferably from 50 to 70°C.

The reactor is connected with at least one pipeline designed to supply the reactor with the starting materials for the reaction. The reactor further typically comprises at least one means for temperature control and at least one means for agitating the reaction mixture.

In one embodiment, the reactor and the first intermediate vessel V1 are connected to another by means of a pipeline. In an alternative embodiment, the reactor and the stripping column are connected to another by means of a pipeline. In one embodiment, the first intermediate vessel V1 and the stripping column are connected to another by means of a pipeline.

In an alternative embodiment, the first intermediate vessel V1 and the first distillation column D1 .1 are connected to another by means of a pipeline.

In an alternative embodiment, the stripping column and the first distillation column D1 .1 are connected to another by means of a pipeline.

In a preferred embodiment, the reactor and the first intermediate vessel V1 are connected to another by means of a pipeline, the first intermediate vessel V1 and the stripping column are connected to another by means of a pipeline, and the stripping column and the first distillation column D1 .1 are connected to another by means of a pipeline.

Distillation column D1 .1 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, distillation column D1 .1 and intermediate vessel V2 are connected to another by means of a pipeline. In an alternative embodiment, distillation column D1.1 and distillation column D2.1 are connected to another by means of a pipeline. In one embodiment, distillation column D1 .1 and distillation column D1 .2 are connected to another by means of a pipeline.

Distillation column D1 .2 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, distillation column D1 .2 and distillation column D1 .1 are connected to another by means of a pipeline. In one embodiment, distillation column D1 .2 and distillation reactor are connected to another by means of a pipeline. In an alternative embodiment, distillation column D1 .2 and separating device S1 are connected to another by means of a pipeline.

Separating device S1 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, separating device S1 and distillation column D1.2 are connected to another by means of a pipeline. In one embodiment, separating device S1 and a disposal system are connected to another by means of a pipeline.

In one embodiment, intermediate vessel V2 is equipped with at least one means of temperature control. In one embodiment, intermediate vessel V2 and distillation column D1 .1 are connected to another by means of a pipeline.

In one embodiment, intermediate vessel V2 and distillation column D2.1 are connected to another by means of a pipeline.

Distillation column D2.1 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, distillation column D2.1 and intermediate vessel V2 are connected to another by means of a pipeline. In an alternative embodiment, distillation column D2.1 and distillation column D1.1 are connected to another by means of a pipeline. In one embodiment, distillation column D2.1 and distillation column D2.2 are connected to another by means of a pipeline. In an alternative embodiment, distillation column D2.1 and product vessel V3 are connected to another by means of a pipeline.

Distillation column D2.2 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, distillation column D2.2 and 1 and product vessel V3 are connected to another by means of a pipeline. In one embodiment, distillation column D2.2 and separating device S2 are connected to another by means of a pipeline.

Separating device S2 is preferably equipped with at least one means of temperature control and at least one means for pressure control. In one embodiment, separating device S2 and distillation column D2.2 are connected to another by means of a pipeline. In one embodiment, separating device S2 and a disposal system are connected to another by means of a pipeline.

The stripping column, the first separating set-up and/or the second separating set-up is equipped with at least one means for pressure control. The means for pressure control is configured to provide the required preferred pressure ranges as disclosed herein above. The means for pressure control may be connected to the stripping column, distillation column D1.1 , distillation column D1.2, separating device S1 , distillation column D2.1 , distillation column D2.2 and/or separating device S2. In a preferred embodiment, the means for pressure control is connected to the stripping column, distillation column D1 .1 , and distillation column D2.1 .

When performing the process according to the invention in accordance with this description, even without the preferred embodiments, it can often be observed that the catalyst freshly used in the reactor at least to some extent includes a different anion from the catalyst present in the bottoms fraction of the distillation column D1 .1 and/or distillation column D1 .2. In particular, the catalyst present in the bottoms fraction of the distillation column D1 .1 and/or distillation column D1 .2. is present in whole or in part as metal (meth)acrylate.

A particularly preferred configuration of the process according to the invention is characterized in that process steps a) and b) are performed semi-continuously in such a manner that, after emptying the reactor in process step b), the reactor can be directly filled again within a time t3 in order to directly perform process step a) anew. In this case, t3 should preferably be shorter than t1. In this particularly preferred case, process step c) can then be performed continuously, semi-continuously or batch-wise.

Such a process can then take a form such that the liquid phase after the reaction has ended is conveyed out of the reactor into the intermediate vessel and then a new batch or semi-batch can be carried out in the reactor after only a short time without downtime. At the same time, the intermediate vessel V1 supplies crude solution to the purification process, consisting of at least two purification cycles P1 and P2. Ideally, the workup of the products in process step c), is performed batch-wise. The present invention is intended to be described below using examples, without this being intended to constitute a limitation.

Examples

Preparation of (meth)acrylate-containinq reaction mixture

Example 1 Methacrylic acid was reacted with ethylene oxide in a plant. Typically, 5300 kg (61 .6 kmol) of methacrylic acid were added to the reactor - having a working volume of 8 m³ - and to this were added 12 kg (52.4 mol) of chromium acetate as catalyst and 2.5 kg (20.1 mol) of hydroquinone monomethyl ether (HQME) as stabilizer, and the mixture was heated to a temperature of 70°C. Pumped circulation of the mixture through an external circuit was then commenced, a circulating volume flow rate of approx. 70 m³/h being set and the mixture being metered back into the reactor at the top via an injector-mixer nozzle. Then, 2720 kg (61 .7 kmol) of ethylene oxide were added. The amount metered in was selected so that a reaction temperature of 70°C was not exceeded. The metered amount was set to approx. 900 kg/h (20.4 kmol/h). The time from filling of the methacrylic acid to the end of the ethylene oxide metering was 3 hours.

After addition of the prescribed amount, the reaction mixture was held at a temperature of 70°C through the external circuit as described above. After a further 3 hours, a sample was taken from the reactor contents every hour and analyzed for residual methacrylic acid content by means of acid-base titration. The first sample had a residual methacrylic acid content of 0.63% by weight, the second sample after 7 hours 0.18% by weight, and the third sample after 8 hours 0.05% by weight. This process step was therefore ended after 5 hours. The ethylene oxide flow rate was reduced to a third during the last two hours.

Thereafter, the reaction mixture was cooled down to 60°C. The pressure was then released slowly over a number of minutes via a needle valve fitted to the lid of the reaction apparatus. The off-gas here is sent to a gas scrubbing plant via pipelines.

The 8 tons of crude solution obtained were then released into an intermediate vessel V1 . This process took 15 minutes. Thereafter, a new reaction of methacrylic acid with ethylene oxide was directly effected as described above in the reactor.

The crude solution (reaction mixture) obtained was analysed, with the proportion of 2-hydroxyethyl methacrylate being approx. 99.1 % by weight. This was determined by means of GC-FID (gas chromatography combined with a flame ionization detector). Diethylene glycol methacrylate formed the largest proportion of byproduct, with a proportion of approx. 3.60% by weight. A particularly critical byproduct was ethylene glycol dimethacrylate, with a proportion of approx. 0.14% by weight. Further byproducts are listed in Table 1.

From the first intermediate vessel V1 , the crude solution was then fed to a continuously operated distillative purification apparatus. The distillative purification apparatus consisted of a stripping column, a first distillation column D1 .1 , a second distillation column D1 .2, packing column combined with a wiped film evaporate S1 , and a second intermediate vessel V2. Each distillation column is equipped with a top cooler.

The crude reaction mixture is sent from the intermediate vessel V1 to the stripping column to remove residue ethylene oxide. The inlet flow rate is 1000 kg/h, inlet temperature is 65°C, pressure on the outlet of the stripping column is controlled to 30 mbar.

First purification cycle

After leaving the stripping column, the obtained material was transferred to the first distillation column D1 .1 with nearly the same flowrate of 1000 kg/h. The material was fed into the distillation column D1 .1 . This distillation column D1 .1 was a flash vapor column with no packing inside and no reflux from top cooler. The low-boiling fraction F1 .1 .1 including the product were transferred to the second intermediate vessel V2 and which will use as the raw material for further distillation. The bottom fraction F1 .1 .2 primarily contained high-boiling secondary components and also the catalyst, which to a very substantial extent was present as chromium methacrylate.

High-boiling constituents accumulated in the bottom fraction F1 .1 .2 of the first distillation column D1 .1 and were then transferred to the second distillation column D1 .2 This distillation column D1 .2 was a flash vapor column with no packing inside and no reflux from top cooler. The flow rate was controlled from 1050 kg/h to 1950kg/h. The low-boiling fraction F1 .2.1 obtained in the second distillation column D1 .2 was transferred back to the bottom section of the first distillation column D1 .1 .

High-boiling fraction F1 .2.2 of the second distillation column D1 .2 was transferred to a further distillation system which was formed by a packing column combined with a wiped film evaporator S1 . The inlet flow rate of this distillation was 350 kg/h to 400 kg/h. The low-boiling fraction F1 .3.1 obtained from the wiped film evaporator S1 was transferred to the second distillation column D1 .2 and high-boiling fraction F1 .3.2 was discharged. The discharge flow rate was around 80 kg/h.

From the first distillation column D1 .1 . to the wiped film evaporator S1 , the vacuum was controlled using a steam ejector. The vacuum was controlled at the top cooler of the first distillation column D1 .1 . The set point was 5 mbar. At the same time, the temperature in the entire first purification cycle P1 was kept at 80°C. The fraction F1 .1 .1 was collected in the intermediate vessel V2 and had a yield of around 92%. The first purification cycle was repeated two more times. For each repetition, the fraction F1 .1 .1 was transferred from the intermediate vessel V2 to the first distillation column D1 .1 .

Second purification cycle

After passing the first purification cycle three times, the amount of HEMA in fraction F1 .1 .1 increased to > 99.4 wt.-%. However, also low-boiling constituent accumulated in fraction F1 .1 .1 , which were separated off in the second purification cycle. The second purification cycle used essentially the identical set-up, i.e. comprising a first distillation column D2.1 (previously used as distillation column D1 .1), a second distillation column D2.2 (previously used as distillation column D1 .2), a packing column combined with a wiped film evaporate S2 (previously used as packing column combined with a wiped film evaporate S1), and a product vessel V3. Temperature in the entire second purification cycle P2 was kept at 80°C and the pressure was maintained at 5 mbar.

For the second purification cycle, the fraction F1 .1 .1 was transferred from the intermediate vessel V2 to the first distillation column D2.1 at 1000 kg/h. 300 kg/h to 350 kg/h of the low-boiling fraction F2.1 .1 accumulated in a day tank. This fraction was HEMA having a purity of < 99 wt.-%.

650 kg/h to 700 kg/h of the bottom fraction F2.1 .2 obtained in distillation column D2.1 were transferred to the second distillation column D2.2. During the second purification cycle, the distillation process in column D2.2 was changed compared to the first purification cycle. The top outlet of distillation column D2.2 was directly connected to the product vessel V3. Around 570 kg/h to 620 kg/h of low-boiling fraction F2.2.1 were transferred as product fraction F2.2.1 to the product vessel V3. 350 kg/h to 400 kg/h of high-boiling fraction F2.2.2 were transferred from the bottom section of distillation column D2.2 to the packing column combined with a wiped film evaporate S2. Around 80 kg/h bottom fraction F2.3.2 were discharged from the bottom section of the WFE S2 and 270 kg/h to 330 kg/h of low-boiling fraction F2.3.1 were transferred from the WFE S2 to the second distillation column D2.2.

The second purification cycle was repeated twice. For repetition, the fraction F2.2.1 was transferred from the product vessel V3 to the first distillation column D2.1 . The final product was collected as product fraction F2.2.1 in product vessel V3.

After the purification of the crude solution of the first batch has ended, the distillative purification of the second batch, which has already been pumped into the first intermediate vessel V1 , was immediately effected without interruption. This procedure was continued until all batches have been prepared and purified.

After purification, 2-hydroxyethyl methacrylate was obtained with a purity of 99.62% by weight, which contained approx. 5 ppm hydroquinone monomethyl ether. Further byproducts are listed in Table 1. The color number of the 2-hydroxyethyl methacrylate obtained was measured by the method presented in DE 10 131 479. The color number was

6. Table 1 - part

Table 1 - part

P1 purification cycle 1

P2 purification cycle 2

R1 repetition 1

R2 repetition 2

R3 repetition 3 R4 repetition 4

HEMA 2- hydroxyethyl methacrylate

EGDMA ethylene glycol dimethacrylate

DEGMA diethylene glycol methacrylate

GMMA glycerol monomethacrylate HEAc Hydroxyethyl acetate

HOME hydroquinone monomethyl ether

MAA methacrylic acid Example 2

Example 2 was carried out essentially identical to example 1 .

The purity of the obtained product is shown in table 2. The abbreviations used in table 2 are identical to those used in table 1 .

Table 2 - part

Table 2 - part

Comparative Example 3

Methacrylic acid was reacted with ethylene oxide in a plant. Typically, 5300 kg (61 .6 kmol) of methacrylic acid were added to the reactor - having a working volume of 8 m³ - and to this were added 12 kg (52.4 mol) of chromium acetate as catalyst and 2.5 kg (20.1 mol) of hydroquinone monomethyl ether (HQME) as stabilizer, and the mixture was heated to a temperature of 70°C. Pumped circulation of the mixture through an external circuit was then commenced, a circulating volume flow rate of approx. 70 m3/h being set and the mixture being metered back into the reactor at the top via an injector-mixer nozzle. Then, 2720 kg (61 .7 kmol) of ethylene oxide were added. The amount metered in was selected so that a reaction temperature of 70°C was not exceeded. The metered amount was set to approx. 900 kg/h (20.4 kmol/h). The time from filling of the methacrylic acid to the end of the ethylene oxide metering was 3 hours.

After addition of the prescribed amount, the reaction mixture was held at a temperature of 70°C through the external circuit as described above. After a further 3 hours, a sample was taken from the reactor contents every hour and analyzed for residual methacrylic acid content by means of acid-base titration. The first sample had a residual methacrylic acid content of 0.63% by weight, the second sample after 7 hours 0.18% by weight, and the third sample after 8 hours 0.05% by weight. This process step was therefore ended after 5 hours. The ethylene oxide flow rate was not reduced during the process. The purification steps were carried out as described in example 1. The purity of the obtained product is shown in table 3. The abbreviations used in table 3 are identical to those used in table 1 .

Table 3 - part

Table 3 - part

From comparative example 3 it can be seen that if the ethylene oxide flow rate is not reduced, the obtained starting material has a significantly lower purity. Therefore, also the obtained product has significantly lower purity.

Description of Figures

Figure 1 is a schematic illustration of a plant which is suitable for the preparation of a polymerization- prone (meth)acrylate compounds according to the present invention.

Figure 2 is a schematic illustration of a plant according to Figure 1 which is further detailed in some respect.

Figure 3 is a schematic illustration of an alternative embodiment of the plant according to Figure 1 and 2 which is further detailed in some respect.

Figure 4 is a schematic illustration of a plant which is suitable for the preparation of a polymerization- prone (meth)acrylate compounds and has an additional intermediate vessel V2 compared to the plants depicted in Figures 2 and 3. Figure 1 is a schematic illustration of a plant which is suitable for the preparation of a polymerization- prone (meth)acrylate compounds according to the present invention, without this being intended to constitute a limitation.

(Meth)acrylic acid and the epoxy-functional compound each pass via feed lines 10 and 20 into reactor, in which the reaction process is performed in the batchwise or semi-batchwise mode. Auxiliaries such as catalysts and/or stabilizers can be fed to the reaction apparatus e.g. via further feed line 30. After the reaction process has ended, the crude reaction mixture obtained is transferred into an intermediate vessel V1 via line 40. From this intermediate vessel V1 , the crude reaction mixture is transferred into a purification set-up comprising at least a first purification cycle P1 and a second purification cycle P2. The crude reaction mixture is transferred to the first purification cycle P1 via line 50. The first purification cycle P1 is designed to separate the crude reaction mixture into a fraction of high-boiling constituents (fraction F1 .1 .2) and a remainder fraction comprising low-boiling constituents and the target product (meth)acrylate (fraction F1 .1 .1). Typically, high-boiling constituents are separated by means of destillative separation, wherein the remainder fraction (fraction F1.1.1) comprising low-boiling constituents and the target product (meth)acrylate are evaporated and condensed and the high-boiling constituents remain as bottom fraction (fraction F1 .1 .2). High-boiling constituents are removed from the first purification cycle P1 via line 80. Optionally, the high-boiling constituents of fraction F1.1.2 may be recycled in whole or in part into the reactor via line 81 .

The remainder fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth)acrylate is transferred to the second purification cycle P2 via line 60. Alternatively, the remainder fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth)acrylate may be recycled in whole or in part into the first purification cycle P1 via line 61 at least once before it is transferred to the second purification cycle P2.

In the second purification cycle P2, the remainder fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth) acrylate obtained from the first purification cycle P1 is separated into at least three fractions: a fraction comprising low-boiling constituents (fraction F2.1.1), a fraction comprising high- boiling constituents (fraction F2.2.2) and a remainder (middle) fraction comprising the target product (meth)acrylate (fraction F2.2.1). Typically, separation is achieved by means of distillative separation. Low- boiling constituents (fraction F2.1 .1) are removed from the second purification cycle P2 via line 90. High- boiling constituents (fraction F2.2.2) are removed from the second purification cycle P2 via line 100.

The target product (meth)acrylate fraction F 2.2.1 is removed from the second purification cycle P2 vial line 70 and may be transferred to the product vessel V3. Alternatively, the target product (meth)acrylate fraction F2.2.1 may be recycled in whole or in part into the second purification cycle P2 via line 71 at least once before it is transferred to the product vessel V3.

Figure 2 is a schematic illustration of a plant according to Figure 1 which is further detailed in some respect. In addition to the features of the plant depicted in Figure 1 , the plant illustrated in Figure 2 comprises additionally a stripping column which is located between the first intermediate vessel V1 and the first purification cycle P1 . The first intermediate vessel V1 is connected with the inlet of the stripping column via line 51 , and the outlet of the stripping column is connected with the first purification cycle P1 via line 52. In the stripping column gaseous constituents are removed from the reaction mixture bevor it is transferred to the first purification cycle P1 .

The plant illustrated in Figure 2 is, compared to Figure 1 , further detailed with respect to the implementation of the purification cycles P1 and P2. Purification cycle P1 comprises a first distillation column D1 .1 and a second distillation column D1 .2. The first distillation column D1 .1 is connected with the stripping column via line 52. The reaction mixture is transferred to the first distillation column D1 .1 via line 52. In the first distillation column D1 .1 , the reaction mixture is separated into a fraction of high-boiling constituents (fraction F1 .1 .2) and a remainder fraction comprising low-boiling constituents and the target product (meth)acrylate (fraction F1 .1 .1). The remainder fraction F1 .1.1 comprising low-boiling constituents and the target product (meth)acrylate is removed from the first purification cycle P1 via line 60 and/or line 61 , as described for the plant depicted in Figure 1 . The fraction of high-boiling F1 .1 .2 constituents remains as bottom fraction in the first distillation column D1 .1 and is transferred to the second distillation column D1 .2 via line 62. In distillation column D1 .2, fraction F1 .1 .2 comprising high- boiling constituents is separated into a fraction of high-boiling constituents (fraction F1 .2.2) and a fraction comprising low-boiling constituents and the target product (meth)acrylate (F1 .2.1). The latter fraction F1 .2.1 is recycled in whole or in part into the first distillation column D1 .1 The fraction F1 .2.2 comprising high-boiling constituents is removed from the first purification cycle P1 via line 80. Optionally, the fraction F1 .2.2 may be recycled in whole or in part into the reactor via line 81 .

Purification cycle P2 of the pant illustrated in Figure 2 comprises a first distillation column D2.1 . The distillation column D2.1 is connected with the distillation column D1 .1 via line 60 and retrieves the fraction comprising low-boiling constituents and the target product (meth)acrylate (fraction F1 .1 .1) via said line 60. In the distillation column D2.1 , the fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth)acrylate is separated into at least three fractions: a fraction comprising low-boiling constituents (fraction F2.1.1), a fraction comprising high-boiling constituents (fraction F2.2.2) and a remainder (middle) fraction comprising the target product (meth)acrylate (fraction F2.2.1). In the embodiment illustrated in Fig. 2 this is achieved by a distillation column with vaporous sidestream removal.

Figure 3 is a schematic illustration of an alternative embodiment of the plant according to Figure 1 and 2 which is further detailed in some respect. In addition to the features of the plant depicted in Figure 2, the plant illustrated in Figure 3 comprises an additional second distillation column D2.2 in the second purification cycle P2. Thus, the purification cycle P2 of the pant illustrated in Figure 3 comprises a first distillation column D2.1 and a second distillation column D2.2. The distillation column D2.1 is connected with the distillation column D1.1 via line 60 and retrieves the fraction comprising low-boiling constituents and the target product (meth)acrylate (fraction F1 .1 .1) via said line 60. In the distillation column D2.1 , the fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth)acrylate is separated into two fractions: a fraction comprising low-boiling constituents (fraction F2.1 .1) and a fraction comprising high-boiling constituents and the target product (meth) acrylate (fraction F2.1 .2). Low-boiling constituents (Fraction F2.1 .1) are removed from the second purification cycle P2 via line 90. Fraction F2.1 .2 comprising high-boiling constituents and the target product (meth)acrylate is transferred to the second distillation column D2.2 via line 72. In the distillation column D2.2, fraction F2.1.2 comprising high-boiling constituents and the target product (meth)acrylate is separated into further two fractions: a fraction comprising high-boiling constituents (fraction F2.2.2) and a fraction comprising the target product (meth)acrylate (F2.2.1). High-boiling constituents (F2.2.2) are removed from the second distillation column via line 100. The target product (meth)acrylate fraction F2.2.1 is removed from the second purification cycle P2 via line 70 which is connected to the product vessel V3. The target product (meth)acrylate fraction F2.2.1 may be transferred to the product vessel V3. Alternatively, the target product (meth)acrylate fraction F2.2.1 may be recycled in whole or in part into the second purification cycle P2 via line 71 at least once before it is transferred to the product vessel V3.

A particularly preferred plant for preparing a polymerization-prone (meth)acrylate compounds is additionally shown by way of example in Figure 4: Figure 4 is a schematic illustration of a plant which is suitable for the preparation of a polymerization-prone (meth)acrylate compounds and has an additional intermediate vessel V2 compared to the plants depicted in Figures 2 and 3. Moreover, compared to the plant depicted in Figure 3, the plant illustrated in Figure 4 comprises a further separation device S1 within the first purification cycle P1 and a further separation device S2 within the second purification cycle P2. Without this being intended to constitute a limitation, the additional features of the plant illustrated in Figure 4 are discussed in further detail herein below.

In addition to the features of the plant depicted in Figure 3, the plant illustrated in Figure 4 additionally comprises a second intermediate vessel V2 which is located between the first purification cycle P1 and the second purification cycle P2. The outlet of the distillation column D1.1 from which low-boiling constituents and the target (meth)acrylate (fraction F1.1.1) is removed is connected with the inlet of the intermediate vessel V2 via line 60. The outlet of the intermediate vessel V2 is connected is connected with the inlet of distillation column D2.1 via line 66.

The separation device S1 is part of the first purification cycle P1 and is connected to the distillation column D1 .2 via lines 64 and 65. The high-boiling constituents obtained in distillation column D1 .2 (fraction F1 .2.2) are removed therefrom via line 64 and are transferred to the further separation device S1 . Optionally, the high-boiling constituents fraction F1 .2.2 may be recycled in whole or in part into the reactor via line 81 . Separation device S1 is a means of refractional separation and for example represents a thin film evaporator. The fraction comprising high-boiling constituents is further separated in a fraction comprising low boiling constituents and the target (meth)acrylate (fraction F1 .3.1) and a fraction comprising high-boiling constituents (fraction F1.3.2). The fraction F1.3.1 comprising low boiling constituents and the target (meth)acrylate is removed from separation device S1 and transferred to the inlet of distillation column D1 .2 via line 65. High-boiling constituents fraction F1 .3.2 is removed from the separation device S1 via line 80. Fraction F1 .1.1 comprising low-boiling constituents and the target product (meth)acrylate obtained from distillation column D1 .1 is transferred to intermediate vessel V2 via line 60. Alternatively, fraction F1 .1 .1 comprising low-boiling constituents and the target product (meth)acrylate obtained from distillation column D1 .1 may be recycled in whole or in part into the first purification cycle P1 via line 61 at least once before it is transferred to the second intermediate vessel V2. In a further alternative embodiment, fraction comprising F1 .1.1 low-boiling constituents and the target product (meth)acrylate obtained from distillation column D1 .1 may be recycled in whole or in part into the first purification cycle P1 via line 67 at least once after it is transferred to the second intermediate vessel V2.

The contents of intermediate vessel V2 (combined fractions F1 .1 .1) are continuously or discontinuously transferred to distillation column D2.1 via line 66. In the distillation column D2.1 , the fraction comprising low-boiling constituents and the target product (meth)acrylate is separated into two fractions: a fraction comprising low-boiling constituents (fraction F2.1.1) and a fraction comprising high-boiling constituents and the target product (meth)acrylate (fraction F2.1 .2). Low-boiling constituents fraction F2.1 .1 is removed from the second purification cycle P2 via line 90. Fraction F2.1 .2 comprising high-boiling constituents and the target product (meth)acrylate is transferred to the second distillation column D2.2 via line 72. In the distillation column D2.2, fraction F2.1.2 comprising high-boiling constituents and the target product (meth)acrylate is separated into further two fractions: a fraction comprising high-boiling constituents (fraction F2.2.2) and a fraction the target product (meth)acrylate (fraction F2.2.1). The target product (meth)acrylate fraction F2.2.1 is removed from the second purification cycle P2 vial line 70 which is connected to the product vessel V3. The target product (meth) acrylate fraction F2.2.1 may be transferred to the product vessel V3. Alternatively, the target product (meth)acrylate fraction F2.2.1 may be recycled in whole or in part into the second purification cycle P2 via line 71 at least once before it is transferred to the product vessel V3. In a further alternative embodiment illustrated in Figure 4, the target product (meth)acrylate fraction F2.2.1 may be transferred to the intermediate vessel V2 via line 77. From intermediate vessel V2, the target product (meth)acrylate fraction F2.2.1 may recycled in whole or in part into the second purification cycle P2 at least once before it is transferred to the product vessel V3.

The high-boiling constituents fraction F2.2.2 is removed from the second distillation column D2.2 via line 74 and transferred to a further separation device S2. Separation device S2 is a means of refractional separation and for example represents a thin film evaporator. Fraction F2.2.2 comprising high-boiling constituents is further separated into a fraction comprising low boiling constituents and the minor amounts of target (meth)acrylate (fraction F2.3.1) and a fraction comprising high-boiling constituents (fraction F2.3.2). Fraction F2.3.1 comprising low boiling constituents and the target (meth)acrylate) is removed from separation device S2 and transferred to the inlet of distillation column D2.2 via line 75. High-boiling constituents fraction F2.3.2 is removed from the separation device S2 via line 100.

List of Reference Signs

Items concerning Figure 1 10 feed line for starting material, e.g. (meth)acrylic acid

20 feed line for starting material, e.g. epoxy-functional compound

30 feed line(s) for auxiliaries (e.g. stabilizer(s), catalyst(s))

R reactor

40 line for crude reaction mixture from reactor R into intermediate vessel V1

V1 intermediate vessel V1

50 line for crude solution from intermediate vessel V1 into purification cycle P1

P1 purification cycle P1

60 line for the transfer of fraction F1.1.1 from purification cycle P1 to purification cycle P2

61 line for recycling of fraction F1.1.1 to the purification cycle P1

P2 purification cycle P2

70 line for transfer of (meth)acrylate fraction F2.2.1 to the product vessel V3 in a form meeting specifications = target product

71 line for recycling of fraction F2.2.1 to the purification cycle P1

V3 product vessel V3

80 removal line for high-boiling constituents fraction F1 .2.2

81 optional: line for recycled high-boiling stream (F1 .2.2)

90 removal line for low-boiling constituents fraction F2.1 .1

100 removal line for high-boiling constituents fraction F2.2.2 Additional Items concerning Figure 2

51 line for transfer of the crude reaction mixture from the intermediate vessel V1 into the stripping column

SC stripping column

52 line for transfer of the reaction mixture from the stripping column to the distillation column D1 .1

D1 .1 distillation column D1 .1

62 line for transfer of the high-boiling constituents (fraction F1.1.2) from distillation column D1 .1 to distillation column D1 .2

D1 .2 distillation column D1 .2

63 line for transfer of low-boiling constituents (fraction F1.2.1) from distillation column D1 .2 to distillation column D1 .1

D2.1 distillation column D2.1

Additional Items concerning Figure 3

72 line for transfer of the high-boiling constituents and target (meth)acrylate (fraction

F2.1 .2) from distillation column D2.1 to distillation column D2.2

D2.2 distillation column D2.2 Additional Items concerning Figure 4

64 line for transfer of the high-boiling constituents (fraction F1 .2.2) from distillation column D1 .2 to separation device S1

65 line for transfer of low-boiling constituents (fraction F1 .3.1) from separation device S1 to distillation column D1 .2

51 separation device S1 , e.g. thin film evaporator

V2 intermediate vessel V2

66 line for transfer of the contents of intermediate vessel V2 into distillation column D2.1

67 line for recycling of the contents of intermediate vessel V2 into distillation column D1 .1

74 line for transfer of the high-boiling constituents (fraction F2.2.2) from distillation column D2.2 to separation device S2

75 line for transfer of low-boiling constituents (fraction F2.3.1) from separation device S2 to distillation column D2.2

52 separation device S2, e.g. thin film evaporator

77 line for recycling of the (meth)acrylate fraction F2.1 .1 obtained from the second purification cycle P2 (in particular from distillation column D2.2) into intermediate vessel V2

Claims

Claims Process for the preparation of high-purity (meth)acrylates starting from (meth)acrylic acid and an epoxy-functional compound, comprising at least the following process steps: a) reaction of (meth)acrylic acid with at least one epoxy-functional compound in the presence of a catalyst in a reactor R, wherein after a reaction time t1 the content of epoxy-functional compound in the gas phase and the liquid phase is reduced by removing gas phase from the reactor, wherein the reaction time t1 ends when the (meth)acrylic acid concentration in the liquid phase is less than 1 .0 % by weight, b) transfer of the (meth)acrylate-containing reaction mixture present as liquid phase in the reactor R after the reaction is completed to a first intermediate vessel V1 , c) purification of the target high-purity (meth)acrylates in a purification process comprising at least a first purification cycle P1 and a second purification cycle P2, wherein each purification cycle is carried out at least once and wherein the first purification cycle P1 is carried out prior to the second purification cycle P2, wherein in the first purification cycle P1 high-boiling constituents are separated off from the (meth)acrylate-containing reaction mixture, and wherein in the in the second purification cycle P2 low-boiling constituents and high-boiling constituents are separated off from the remainder obtained from the first purification cycle P1 , wherein the remainder obtained from the second purification cycle P2 consists of > 99.5 wt.-% of the target (meth)acrylate, and further comprises

1 to 1000 ppm, preferably 1 to 500 ppm, more preferably 1 to 300 ppm, of glycerol monomethacrylate (GMMA), wherein the remainder obtained from the second purification cycle P2 has a color number in the range from 1 to 10, preferably from 1 to 8, wherein low-boiling constituents are chemical compounds comprised in the reaction mixture having a boiling temperature below the boiling temperature of the target (meth)acrylate at a given pressure, and wherein high-boiling constituents are chemical compounds comprised in the reaction mixture having a boiling temperature above the boiling temperature of the target (meth)acrylate at a given pressure wherein the purification step c) comprises a process step c-P1 .1), wherein process step c-P1 .1) represents a process step of the first purification cycle P1 , wherein the process step c-P1 .1) comprises: c-P1 .1) transfer of the (meth)acrylate-containing reaction mixture from the first intermediate vessel V1 to a first separation set-up, comprising at least a first distillation column (distillation column D1.1), wherein in the first purification cycle P1 the (meth)acrylate-containing reaction mixture is separated into at least the following two fractions:

(I) at least one overhead fraction containing the target (meth)acrylate and further containing low-boiling constituents (fraction F1.1.1), the obtained fraction representing the remainder obtained from the first purification cycle P1 , and

(ii) at least one bottom fraction containing high-boiling constituents (fraction F1 .1 .2), wherein the purification step c) comprises a process step C-P2.1), wherein process step C-P2.1) represents a process step of the second purification cycle P2, wherein the process step C-P2.1) comprises:

C-P2.1) transfer of the remainder obtained from the first purification cycle P1 (fraction F1 .1 .1) to a second separation set-up, comprising at least a first distillation column (distillation column D2.1) and optionally at least a second distillation column (distillation column D2.2), wherein in the second purification cycle P2 the remainder obtained from the first purification cycle P1 (overhead fraction F1.1.1) is separated into at least the following three fractions:

(I) at least one overhead fraction containing low-boiling constituents (fraction F2.1.1),

(ill) a product fraction containing the target (meth)acrylate having a purity of > 99.5 wt.-%, representing the remainder obtained from the second purification cycle P2 (fraction F2.2.1). The process according to claim 1 , wherein the first purification cycle P1 is carried out at least once, preferably 2 to 5 times, wherein the repetition of the purification cycle P1 is achieved by recycling the remainder obtained from the first purification cycle P1 as starting material for the next repetition (recycling of fraction F1.1.1 to the distillation column D1.1). The process according to any of claims 1 or 2, wherein the second purification cycle P2 carried out at least once, preferably 2 to 3 times, wherein the repetition of the purification cycle P2 is achieved by recycling the remainder obtained from the second purification cycle P2 as starting material for the next repetition (recycling of product fraction F2.2.1 to the distillation column D2.1). Process according to any of claims 1 to 3, wherein the first purification cycle P1 and the second purification cycle P2 are carried out in the same separation set-up. Process according to claim 1 to 4, wherein the purification step c) comprises the process step c-

P1 .1) and at least one further process step c-P1 .2), wherein process step c-P1 .1) and process step c-P1 .2) represent process steps of the first purification cycle P1 , and wherein process step c-P.1 .2) comprises: c-P1 .2) transfer of the at least one bottom fraction containing high-boiling constituents obtained in step C-P1.1) (fraction F1.1.2) to at least one further distillation column (distillation column D1.2), wherein in the further distillation column (distillation column D1.2) the bottom fraction containing high-boiling constituents obtained in step C-P1.1) (fraction F1.1.2) is separated into at least the following two fractions:

(I) at least one overhead fraction containing low-boiling constituents and residual (meth)acrylate (fraction F1 .2.1), the obtained fraction being at least partially recycled continuously or discontinuously to the first distillation column used in process step c- P1.1) (distillation column D1.1), and

(ii) at least one bottom fraction containing high-boiling constituents (fraction F1 .2.2). Process according to claim 5, wherein the purification step c) comprises the process step c-P1 .1), the process step c-P1 .2) and at least one further process step c-P1 .3), wherein process steps c- P1 .1), c-P1 .2) and c-P1 .3) represent process steps of the first purification cycle P1 , and wherein process step c-P.1.3) comprises: c-P1 .3): transfer of the at least one bottom fraction containing high-boiling constituents obtained in step c-P1 .2) (fraction F1 .2.2) to at least one further separation device (separation device S1), wherein in the further separation device (separation device S1) the bottom fraction containing high-boiling constituents obtained in step C-P1.2) (fraction F1.1.2) is separated into at least the following two fractions: (i) at least one fraction containing low-boiling constituents (fraction F1 .3.1), the obtained fraction being at least partially recycled continuously or discontinuously to the first distillation column used in process step c-P1 .2) (distillation column D1 .2), and

(II) at least one fraction containing high-boiling constituents (fraction F1 .3.2). Process according to claim 6, wherein the separating device S1 is selected from a distillation column, a thin-film evaporator and a short-path evaporator. Process according to any of claims 1 to 7, wherein the epoxy-functional compound is an oxirane, preferably ethylene oxide or propylene oxide, and the (meth)acrylate is a hydroxyalkyl-substituted (meth)acrylate, preferably 2-hydroxyethyl methacrylate or hydroxypropyl methacrylate. Process according to any of claims 1 to 8, wherein the remainder obtained from the second purification cycle P2 (product fraction F2.2.1) comprises:

> 99.6 wt.-%, of the product 2-hydroxyethyl methacrylate (HEMA),

1 to 500 ppm, preferable 1 to 300 ppm, of glycerol monomethacrylate (GMMA). Process according to any of claims 1 to 9, wherein the remainder obtained from the first purification cycle P1 (fraction F1 .1 .1) is transferred to a second intermediate vessel V2 before it is transferred to the second purification cycle P2. Process according to any of claims 1 to 10, wherein the remainder obtained from the first purification cycle P2 (product fraction F2.2.1) is transferred to a product vessel V3. Process according to any of claims 1 to 11 , wherein the residence time of the (meth)acrylate- containing reaction mixture in the first intermediate vessel V1 in process step b) is shorter than 200 h, preferably shorter than 100 h and more preferably shorter than 50 h. Device for carrying out a process according to any of claims 1 to 12, comprising at least one reactor R, at least one intermediate vessel V1 , and at least two separation set-ups, wherein the first separation device is designed to carry out the first purification cycle P1 and the second separation device is designed to carry out the second purification cycle P2, and wherein the first separation set-up and the second separation set-up may be the same or different from each other.