Continuous production method of heavy alkyl acrylates

Abstract

The present invention relates to a continuous synthesis process of heavy alkyl acrylates by an ester exchange reaction using a hydrogensite as a heterogeneous catalyst.

Description

Technology Field

[0001] The present invention relates to a continuous synthesis process of heavy alkyl acrylates by an ester exchange reaction using a heterogeneous catalyst. Background Technology

[0002] Transesterification is a commonly used process for producing (meth)acrylic acid esters. It is known to produce (meth)acrylic acid esters of formula (I) below through a transesterification reaction involving the reaction of an alkyl (meth)acrylate of formula (II) below and an alcohol of formula (III) below:

[0003] [Chemical Formula I]

[0004]

[0005] [In the above formula, R is a hydrogen atom or a methyl group, and R1 may be a linear or branched alkyl radical, or a cycloaliphatic, aryl, alkylaryl, or arylalkyl radical containing a heteroatom]

[0006] [Chemical Formula II]

[0007]

[0008] [In the above formula, R has the meaning mentioned above, and R2 may be a linear or branched alkyl group containing 1 to 4 carbon atoms]

[0009] [Chemical Formula III]

[0010]

[0011] [In the above formula, R1 has the meaning mentioned above].

[0012] During the synthesis process, light alcohol R2-OH is produced and removed in the form of an azeotropic mixture with light alkyl (meth)acrylate (II).

[0013] The synthesis of (meth)acrylic acid esters by transesterification generally takes place in the presence of a catalyst, which may be homogeneous or heterogeneous. The selection of the catalyst depends on various criteria, particularly the characteristics of the alkyl (meth)acrylate (II) or alcohol (III) used, as well as the characteristics of the process, such as whether it is a batch process or a continuous process.

[0014] For example, alkoxy titanates described in FR 2777561 and FR 2876375 or tin oxide derivatives described in JP 2001172234 and JP 2001187763 enable highly selective catalysis of the formation of acrylic acid esters by transesterification. In all cases, since the catalyst is a poison to the purification of heavy alkyl acrylates by distillation, a preliminary purification step is required to remove the catalyst by tailing.

[0015] To reduce catalyst usage costs and facilitate their recycling into the reaction, supported heterogeneous catalysts have been developed for the synthesis of heavy alkyl acrylates by transesterification reactions. Catalysts on metallic polymer supports of titanium (FR 2913612) or zirconium (EP 0557131) are used in one or more transesterification reactors in series. However, these catalysts have a relatively short service life due to the high temperatures associated with transesterification reactions.

[0016] The use of inorganic salts insoluble in the reaction medium as transesterification catalysts for the production of aminoalkyl (meth)acrylates is described in US 2013 / 178 592. The addition of water (300 to 3000 ppm) to the reaction makes it possible to significantly improve the selectivity of such heterogeneous catalysts. However, K3PO4, the preferred catalyst, has very low selectivity (< 25%) in the synthesis of acrylic acid esters.

[0017] FR 2175104 describes a process for the synthesis of aminoalkyl acrylates in the presence of zinc compounds, the molar content of which is 0.01% to 30% relative to alkylamino alcohols. Among the numerous catalysts composed of zinc compounds listed in the aforementioned literature is the basic zinc carbonate described in Example 28. More specifically, the above example describes the synthesis of dimethylaminoethyl acrylate by a batch-based transesterification process starting with ethyl acrylate and dimethylaminoethanol in the presence of phenothiazine and basic zinc carbonate, the content of said carbonate being 1.045 mol% relative to dimethylaminoethanol. A yield of 84.5% of dimethylaminoethyl acrylate is reported therein. However, the corresponding catalytic activity determined for the TOF (Turning Frequency of Flow) value, calculated according to the formula shown below, is very low (only 9.5 h -1 ).

[0018] Consequently, there is currently a demand for an ester exchange process suitable for the continuous production of heavy alkyl acrylates that overcomes the disadvantages listed above.

[0019] To this end, the present invention relates to a heterogeneous catalyst, wherein the hydrazine (chemical formula Zn5(CO3)2(OH)6 or [ZnCO3]2·[Zn(OH)2]3 or C2H 12 O 12 A continuous synthesis process for heavy alkyl acrylates by an ester exchange reaction using the chemical formula of Zn5 is provided. This catalyst maintains high catalytic activity and enables very high production yields when used at very low concentrations (less than 1% molar content relative to heavy alcohols).

[0020] In addition, since the catalyst is separated from the reaction mixture by filtration, the purification of the desired alkyl acrylate occurs in only two steps (topping and subsequent tailing) by two distillation columns, instead of three steps as reported in the prior art.

[0021] The present invention relates to a process for continuously synthesizing a (meth)acrylic acid ester of the following formula (I) by reacting an alkyl (meth)acrylate of the following formula (II) with an alcohol of the following formula (III) in the presence of a hydroxyl site as a heterogeneous catalyst:

[0022] [Chemical Formula I]

[0023]

[0024] [In the above formula, R is a hydrogen atom or a methyl group, and R1 is a linear or branched alkyl radical, or a cycloaliphatic, aryl, alkylaryl, or arylalkyl radical comprising 4 to 40 carbon atoms, or a linear or branched alkyl radical comprising at least one heteroatom and 3 to 40 carbon atoms]

[0025] [Chemical Formula II]

[0026]

[0027] [In the above formula, R has the meaning mentioned above, and R2 is a linear or branched alkyl group containing 1 to 3 carbon atoms]

[0028] [Chemical Formula III]

[0029]

[0030] [In the above formula, R1 has the meaning mentioned above].

[0031] Characteristically, the process uses a catalyst content in the range of 0.01 mol% to 0.5 mol% with respect to alcohol.

[0032] Advantageously, the purification of alkyl acrylates occurs in two stages of topping and subsequent tailing by two distillation columns.

[0033] The present invention makes it possible to overcome the disadvantages of the prior art. More particularly, the present invention provides a simplified, economical, and efficient synthesis method for the continuous production of heavy alkyl acrylates. The present invention, in particular, makes it possible to significantly reduce the cost of using catalysts, improve production yield, and avoid the treatment of metal residues at the plant outlet.

[0034] Furthermore, this method requires a very low content of catalyst, which yields a high final product. Catalytic efficiency quantified by TOF is significantly improved, up to 50 h -1 It is an excess value. Specific details for implementing the invention

[0035] The present invention is now described in more detail and in a non-limiting manner in the following description.

[0036] The synthesis of heavy alkyl acrylates by homogeneous catalytic transesterification involves a preliminary step of removing the catalyst by distillation (tailing). A portion of the tail from this distillation, which contains metal residues, is sent for destruction (external recycling), significantly increasing the cost of catalyst use and associated ecological impacts.

[0037] Additionally, the head from this distillation contains the desired heavy alkyl acrylate, as well as light alkyl acrylate and unreacted heavy alcohol. Further distillation (heading) is required to separate the heavy alkyl acrylate from the lighter starting material. The tail from this second distillation subsequently contains the desired heavy alkyl acrylate and an excess of polymerization inhibitor(s). Subsequently, a final distillation step (purification) is required to obtain the desired heavy alkyl acrylate of the desired specifications.

[0038] Therefore, the direct removal of the catalyst from the reaction allows this purification process to be carried out in only two steps (heading and subsequent tailing) instead of three, thereby lowering the construction costs of the production plant and also the costs associated with the energy required for production.

[0039] The present invention relates to a process for the continuous synthesis of heavy alkyl acrylates by an ester exchange reaction using a hydrogensite as a heterogeneous catalyst, wherein the purification of the final product is performed in two steps.

[0040] The present invention relates to a process for continuously synthesizing a (meth)acrylic acid ester of the following formula (I) by reacting an alkyl (meth)acrylate of the following formula (II) with an alcohol of the following formula (III) in the presence of a hydrogensite as a heterogeneous catalyst and at least one polymerization inhibitor, wherein the catalyst content is 0.01 mol% to 0.5 mol% relative to the alcohol:

[0041] [Chemical Formula I]

[0042]

[0043] [In the above formula, R is a hydrogen atom or a methyl group, and R1 is a linear or branched alkyl radical, or a cycloaliphatic, aryl, alkylaryl, or arylalkyl radical comprising 4 to 40 carbon atoms, or a linear or branched alkyl radical comprising at least one heteroatom and 3 to 40 carbon atoms]

[0044] [Chemical Formula II]

[0045]

[0046] [In the above formula, R has the meaning mentioned above, and R2 is a linear or branched alkyl group containing 1 to 3 carbon atoms]

[0047] [Chemical Formula III]

[0048]

[0049] According to various embodiments, the process comprises the following combined features where appropriate.

[0050] According to one embodiment, the transesterification reaction takes place in a stirred reactor at a temperature of 80 to 150°C, preferably 90 to 130°C, and the reaction mixture discharged from the reactor comprises a heavy alcohol, a light alcohol and unreacted light acrylate as a light product, and a polymerization inhibitor(s) and a heavy alkyl acrylate together with the heavy reaction product as a heavy product. The light acrylate / light alcohol azeotropic mixture is removed by a distillation column (azeotropic column) mounted in the reactor. The reaction mixture is processed in a liquid / solid separation step to separate the catalyst.

[0051] The catalyst may be introduced into the reaction as a suspension in the reaction mixture, or otherwise placed in a fixed bed of the transesterification reactor(s). General liquid / solid separation techniques (filtration, electrofiltration, absorption, centrifugation, or decantation) enable the extraction of the unrefined product from the reactor outlet that is catalyst-free or substantially free (catalyst content of less than 500 ppm).

[0052] According to one embodiment, the polymerization inhibitor comprises at least one N-oxyl compound and at least one polymerization inhibitor other than the N-oxyl compound.

[0053] The N-oxyl compound is selected from 2,2,6,6-tetramethylpiperidine 1-oxyl (called TEMPO) and derivatives thereof, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-OH-TEMPO or 4-HT) or 4-oxo-2,2,6,6-tetramethylpiperidine 1-oxyl (4-oxo-TEMPO) and mixtures of these compounds.

[0054] According to one embodiment, the polymerization inhibitor is selected from phenol compounds and phenothiazine compounds.

[0055] The term "phenol compound" means a compound derived from phenol, naphthol, and quinone. As phenol compounds, the following compounds may be mentioned, but are not limited to this list: p-aminophenol, p-nitrosophenol, 2-tertiary-butylphenol, quaternary-butylphenol, 2,4-di-tertiary-butylphenol, 2-methyl-quaternary-butylphenol, 4-methyl-2,6-tertiary-butylphenol (or 2,6-tertiary-butyl-p-cresol) or quaternary-butyl-2,6-dimethylphenol, hydroquinone (HQ), hydroquinone methyl ether (HQME).

[0056] The term "phenothiazine compound" means phenothiazine and derivatives thereof, preferably phenothiazine (PTZ). Preferably, the stabilizing composition comprises at least one polymerization inhibitor selected from phenothiazine, 4-methyl-2,6-tertiary-butylphenol, hydroquinone, and hydroquinone methyl ether.

[0057] According to one embodiment, the N-oxyl compound is in excess in the stabilization composition.

[0058] According to one embodiment, the mass ratio of the N-oxyl compound to the polymerization inhibitor(s) is 1 to 10, preferably 2 to 10, more preferentially 4 to 10, particularly 5 to 10, and the mass ratio is expressed as including a limit value.

[0059] Advantageously, the total mass content of the polymerization inhibitor is 0.001% to 0.5% in the reaction mixture.

[0060] Advantageously, the (meth)acrylic acid ester of formula (I) is purified according to the following steps:

[0061] a. The above reaction mixture is sent to a first distillation column (C1) under reduced pressure (1,000 to 20,000 Pa), where distillation is performed,

[0062] o At the top, a stream containing unreacted starting material and a small amount of heavy product (Michael adduct), and

[0063] o In the tail, a step of generating a stream essentially comprising a heavy alkyl acrylate;

[0064] b. The tail stream from the first distillation column (C1) is sent to the second distillation column (C2) under reduced pressure (1,000 to 20,000 Pa), where distillation is performed,

[0065] o At the top, the desired heavy alkyl acrylate,

[0066] o In the tail, a step of generating a polymerization inhibitor, and also a heavy reaction product.

[0067] According to one embodiment, the process according to the present invention includes an additional step of sending a head stream from a first distillation column (C1) to an ester exchange reactor to recirculate the starting material.

[0068] According to one embodiment, in the reactor, the molar ratio between the alkyl (meth)acrylate of formula (II) (known as "heavy alkyl acrylate") and the alcohol of formula (III) (known as "heavy alcohol") is 1.1 to 3, preferably 1.7 to 2.2.

[0069] According to one embodiment, the (meth)acrylic acid ester of formula (I) is dimethylaminoethyl acrylate.

[0070] According to one embodiment, the alcohol is dimethylaminoethanol.

[0071] Surprisingly, it has been found that the process according to the present invention can significantly reduce the formation of Michael adducts, which are formed from the Michael addition reaction of alcohol molecules (containing unstable hydrogen atoms) on the double bonds of (meth)acrylic acid esters during the transesterification reaction of (meth)acrylic derivatives. This is observed particularly in relation to the formation of Michael adducts in the presence of a high concentration of basic zinc carbonate catalyst.

[0072] For example, in the case of the production of DMAEA by ester exchange between a light acrylate, such as methyl acrylate (MA) or ethyl acrylate (EA), and N,N-dimethylaminoethanol (DMAE), the unreacted alcohol or the light alcohol (methanol or ethanol) produced during the reaction is added to the double bond of the already formed DMAEA or unreacted light acrylate (MA or EA) to form a heavy Michael addition byproduct [DMAE + DMAEA].

[0073] These heavy by-products are typically concentrated into a "heavy fraction" that is separated during the process for purifying raw DMAEA. The removal of this heavy fraction is problematic because it must generally be incinerated, resulting in a significant loss of the starting material (particularly DMAE) and the final product (DMAEA) that exist in this fraction in free form or as Michael adducts.

[0074] Now, measurements of the concentration of this type of adduct in the tail stream from the first distillation column (C1) of the process according to the present invention indicate that its mass content does not exceed 5%, and this value is significantly lower than that measured in the heavy fraction obtained through the process described in FR 2175104, and when the catalyst content is greater than 0.5 mol% with respect to alcohol.

[0075] The content of Michael adducts is measured by gas chromatography. Furthermore, it has been found that the process according to the present invention, using hydrogensite as a heterogeneous catalyst at a very low content (molar content in the range of 0.01% to 0.5% relative to heavy alcohol, including limit values), enables very high production yields, which are accompanied by high catalytic activity. More precisely, catalytic activity is determined by the TOF (Turning Frequency of Flow) value calculated according to the following mathematical formula. The residence time is determined as a function of the extraction flow rate at the bottom of the transesterification reactor.

[0076] [Mathematical Formula]

[0077]

[0078] The process according to the present invention is 50 h -1 It is characterized by an excess TOF value.

[0079] Examples

[0080] The following examples illustrate the invention, but are not limited thereto.

[0081] General protocol for Examples 1 to 3

[0082] In the following examples, the following abbreviations were used:

[0083] EA: Ethyl Acrylate

[0084] DMAE: Dimethylaminoethanol

[0085] DMAEA: Dimethylaminoethyl acrylate

[0086] PTZ: Phenothiazine

[0087] 4-HT: 4-OH-TEMPO

[0088] Zn5(CO3)2(OH)6: Hydrogensite

[0089] Ti(OEt)4: tetraethyl titanate

[0090] TOF: Conversion frequency (catalytic efficiency or activity)

[0091] EA, heavy alcohol (DMAE), and an ester exchange catalyst (Ti(OEt)4) or Zn5(CO3)2(OH)6) are continuously introduced into a stirred 0.5 L reactor heated by the circulation of oil maintained at 135°C in a self-temperature controlled manner in a jacket, and a distillation column with Multiknit packing is mounted on the reactor, and a condenser containing a water-glycol mixture, a reflux head, a vacuum separator, a receiver, and a trap are provided in the column head. A polymerization inhibitor (PTZ, 4-HT, HQME, or a mixture of these compounds) is continuously injected into the top as a mixture with EA.

[0092] Throughout the synthesis, air was sprayed onto the reaction mixture. The reaction was carried out at a temperature of 119 to 121°C under a vacuum of 86 to 87 kPa (860 to 870 mbar). The ethanol formed during the reaction was gradually removed as it formed as an EA / ethanol azeotropic mixture. The degree of conversion was monitored by refractive index analysis of the azeotropic mixture. The ethanol content was 58% to 62%. The unpurified reaction mixture was extracted by overspill and recovered from a receiver.

[0093] The content of heavy alcohol, heavy (meth)acrylate (DMAEA), and ethanol in the distillate and tail stream was analyzed by gas chromatography after 120 hours of operation to determine the yield of the desired ester, the conversion rate of the heavy alcohol, and selectivity. Inhibitors were analyzed and quantified by HPLC methods. Heavy impurities (catalyst + polymer) were quantified using a thermal balance. Unless otherwise noted, all concentrations are provided as mass percentage and mass ppm.

[0094] Based on this analysis, the catalytic activity after 120h was also determined by the TOF value calculated by the mathematical formula shown above.

[0095] Example 1 - Continuous synthesis of DMAEA using 0.2 mol% hydrogensite (According to the present invention)

[0096] The catalyst was introduced into the supply tank and mechanically stirred. A reaction mixture containing EA (61.7 g / h), DMAE (34.2 g / h), and catalyst (0.4 g / h) was subsequently introduced into the reactor.

[0097] The reactor temperature was maintained at 120°C for 120 hours, and the reaction mixture was recovered into a storage tank by overfill (78.4 g / h). At the end of the 120 hours, the reaction mixture and the azeotropic mixture were analyzed, and the following results were provided:

[0098] ● DMAEA Yield = 82.0%

[0099] ● DMAE Conversion Rate = 80.8%

[0100] ● Sum of adjuncts = 4.5%

[0101] ● TOF = 71.6 h -1 .

[0102] Example 2 - Continuous synthesis of DMAEA using 0.8 mol% hydrogensite (comparison)

[0103] The catalyst was introduced into the supply tank as a suspension and mechanically stirred. A reaction mixture containing EA (64.3 g / h), DMAE (35.7 g / h), and catalyst (1.7 g / h) was subsequently introduced into the reactor.

[0104] The reactor temperature was maintained at 120°C for 120 hours, and the reaction mixture was recovered into a storage tank by overfill (78.5 g / h). At the end of the 120 hours, the reaction mixture and the azeotropic mixture were analyzed, and the following results were provided:

[0105] ● DMAEA yield = 83.4%

[0106] ● DMAE Conversion Rate = 83.7%

[0107] ● Sum of adjuncts = 7.7%

[0108] ● TOF = 18.3 h -1 .

[0109] Example 3 - 0.2 mol% Ti(OEt) 4 Sequential synthesis of DMAEA using (comparison)

[0110] The catalyst Ti(OEt)4 was uniformly introduced into the supply tank. A reaction mixture containing EA (64.2 g / h), DMAE (35.6 g / h), and catalyst (0.2 g / h) was then continuously introduced into the reactor.

[0111] The reactor temperature was maintained at 120°C for 120 hours, and the reaction mixture was recovered into a storage tank by overfill (82.5 g / h). At the end of the 120 hours, the reaction mixture and the azeotropic mixture were analyzed, and the following results were provided:

[0112] ● DMAEA yield = 53.6%

[0113] ● DMAE Conversion Rate = 55.5%

[0114] ● Sum of adjuncts = 0.7%

[0115] ● TOF = 45.5 h -1 .

[0116] Catalytic activity is higher (higher TOF value) when the hydrogensite concentration is lowered to 0.2 mol% for DMAE (Example 1), rather than in the case of ethyl titanate (Example 3) due to loss of yield.

[0117] In addition, the formation of Michael adducts is lower when the hydrogensite concentration for DMAE is lowered to 0.2 mol% (Example 1) compared to a higher concentration (Comparative Example 2). This agreement between catalyst concentration and the formation of Michael adducts is not observed in ethyl titanate (Comparative Example 3).

[0118] Examples 4 and 5

[0119] Example 4 - Unpurified reaction Zn after filtration 5 (CO 3 ) 2 (OH) 6 purification of (According to the present invention)

[0120] A sample (0.5 L) of the unrefined reaction mixture obtained after 120 hours in Example 2 was filtered to remove the catalyst from the suspension. Subsequently, the filtrate was placed in a stirred 0.5 L reactor and heated by the circulation of oil maintained at 100°C in a jacketed, self-temperature controlled manner. A distillation column with Multiknit packing was mounted on the reactor, and the column head was equipped with a condenser containing a water-glycol mixture, a reflux head, a vacuum separator, a receiver, and a trap.

[0121] Subsequently, the reaction mixture was distilled under strict vacuum (32 to 15 kPa) to extract a first column head fraction containing mainly EA. The same process was performed under stricter vacuum (15 to 4 kPa) to extract a second column head fraction containing mainly DMAE.

[0122] Finally, DMAEA was purified by distillation while raising the oil temperature to 140°C and applying a vacuum of 12 kPa. The purified acrylate was collected in a column head receiver. GC analysis provides the following composition:

[0123] ● DMAEA Purity = 99.9%

[0124] ● Residual EA = 243 ppm

[0125] ● Residual DMAE = 557 ppm.

[0126] The purity of DMAEA is acceptable (> 99.8%), and the content of the light product EA / DMAE derived from the decomposition of DMAEA by the action of a catalyst is less than the desired specifications for these products (300 ppm for EA and 1000 ppm for DMAE).

[0127] Example 5 - Unpurified reaction Ti(OEt) 4 purification of (Counterexample)

[0128] A sample (0.5 L) of the unrefined reaction mixture obtained after 120 hours in Example 3 is placed in a stirred 0.5 L reactor and heated by the circulation of oil maintained at 100°C in a jacketed, self-temperature controlled manner. A distillation column with Multiknit packing is mounted on the reactor, and a condenser containing a water-glycol mixture, a reflux head, a vacuum separator, a receiver, and a trap are provided in the column head.

[0129] Since the Ti(OEt)4 catalyst is soluble without heating, the filtration step was not performed.

[0130] DMAEA GC analysis provides the following composition:

[0131] ● DMAEA Purity = 99.7%

[0132] ● Residual EA = 1602 ppm

[0133] ● Residual DMAE = 1016 ppm

[0134] The purity of DMAEA is unacceptable (< 99.8%), and the content of the light product EA / DMAE derived from the decomposition of DMAEA by the action of a catalyst exceeds the desired specifications for these products (300 ppm for EA and 1000 ppm for DMAE).

Claims

Claim 1 A method for continuously synthesizing a (meth)acrylic acid ester of the following formula (I) by reacting an alkyl (meth)acrylate of the following formula (II) with an alcohol of the following formula (III) in the presence of a hydrozincite as a heterogeneous catalyst and at least one polymerization inhibitor, wherein the catalyst content is 0.01 mol% to 0.5 mol% with respect to the alcohol, and the TOF (transition frequency) value is 50 h -1 Method characterized by excess: [Chemical Formula I] [In the above formula, R is a hydrogen atom or a methyl group, and R1 is a linear or branched alkyl radical, or a cycloaliphatic, aryl, alkylaryl, or arylalkyl radical containing 4 to 40 carbon atoms, or a linear or branched alkyl radical containing at least one heteroatom and 3 to 40 carbon atoms][Chemical Formula II] [In the above formula, R has the meaning mentioned above, and R2 is a linear or branched alkyl group containing 1 to 3 carbon atoms][Chemical Formula III] Claim 2 A method according to claim 1, wherein the transesterification reaction takes place in a stirred reactor at a temperature of 80°C to 150°C, and the reaction mixture discharged from the reactor comprises, as a light product, a heavy alcohol and a light alcohol and an unreacted light acrylate, and as a heavy product, a polymerization inhibitor(s) and, together with the heavy reaction product, a heavy alkyl acrylate, and the reaction mixture is processed in a liquid / solid separation step to separate the catalyst. Claim 3 A method according to claim 2, wherein the (meth)acrylic acid ester of formula (I) is purified according to the steps of: a. sending the reaction mixture to a first distillation column (C1) under a pressure of 1,000 to 20,000 Pa and performing distillation therein to produce a stream containing, at the top, unreacted starting material and a small amount of heavy product (Michael adduct), and at the tail, a stream essentially containing heavy alkyl acrylate; b. sending the tail stream from the first distillation column (C1) to a second distillation column (C2) under a pressure of 1,000 to 20,000 Pa and performing distillation therein to produce, at the top, a desired heavy alkyl acrylate, at the tail, a polymerization inhibitor, and also a heavy reaction product. Claim 4 A method according to paragraph 3, comprising an additional step of sending a head stream from a first distillation column (C1) to an ester exchange reactor to recirculate the starting material. Claim 5 A method according to paragraph 2, wherein the liquid / solid separation step comprises a technique selected from filtration, electrofiltration, absorption, centrifugation, and decantation, and the catalyst content of the unrefined product processed thereby is less than 500 ppm. Claim 6 A method according to paragraph 2 in which the catalyst is introduced as a suspension in the reaction mixture within the reaction, or the catalyst is placed in a fixed bed of an ester exchange reactor. Claim 7 A method according to claim 1, wherein the polymerization inhibitor used comprises at least one N-oxyl compound, and the mass ratio of the N-oxyl compound to the polymerization inhibitor is 1 to 10 (including a limit value). Claim 8 In claim 7, the N-oxyl compound is selected from 2,2,6,6-tetramethylpiperidine 1-oxyl (called TEMPO), derivatives thereof, and mixtures of these compounds. Claim 9 A method according to claim 1, wherein the polymerization inhibitor used is selected from phenol compounds and phenothiazine compounds. Claim 10 The method of claim 1, wherein the polymerization inhibitor is selected from phenothiazine, 4-methyl-2,6-tertiary-butylphenol, hydroquinone, hydroquinone methyl ether, p-aminophenol, p-nitrosophenol, 2-tertiary-butylphenol, 4-tertiary-butylphenol, 2,4-di-tertiary-butylphenol, 2-methyl-4-tertiary-butylphenol, 4-methyl-2,6-tertiary-butylphenol (or 2,6-tertiary-butyl-p-cresol), or 4-tertiary-butyl-2,6-dimethylphenol, hydroquinone (HQ), and hydroquinone methyl ether (HQME). Claim 11 A method according to claim 1, wherein the mass content of the polymerization inhibitor in the reaction mixture is 0.001% to 0.5%. Claim 12 A method according to claim 1, wherein the mass content of Michael adduct in the tail stream from the first distillation column (C1) is 5% or less. Claim 13 A method according to any one of claims 1 to 12, wherein the (meth)acrylic acid ester of formula (I) is dimethylaminoethyl acrylate.

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