Method for purifying light alkyl acrylates

Abstract

The present invention relates to the production of light (meth)acrylic esters such as methyl or ethyl (meth)acrylate, by direct esterification of (meth)acrylic acid with the corresponding light alcohol. In particular, the invention relates to a method for recovering / purifying C1-C2 alkyl acrylate, comprising a hydrolysis step that makes it possible to transform Michael adducts into acid products of which the boiling point is very different from that of acrylic acid, thereby simplifying the purification sequence.

Description

[0001] PROCESS FOR THE PURIFICATION OF LIGHT ALKYL ACRYLATES

[0002] TECHNICAL FIELD

[0003] The present invention relates to the production of light (meth)acrylic esters such as methyl or ethyl (meth)acrylate, by direct esterification of (meth)acrylic acid with the corresponding light alcohol.

[0004] The invention more particularly relates to a process for the recovery / purification of C1-C2 alkyl acrylate comprising an acidolysis step making it possible to transform Michael adducts into acid products, the boiling point of which is much higher than that of acrylic acid, which simplifies the purification process.

[0005] PRIOR ART AND TECHNICAL PROBLEM

[0006] It is known to produce (meth)acrylic esters by implementing an esterification reaction between an alcohol and a (meth)acrylic acid. This reaction is a balanced catalyzed reaction with generation of water. It is also accompanied by side reactions producing impurities.

[0007] It is necessary to remove the produced water to shift the equilibrium, remove impurities, as well as recycle unreacted reagents.

[0008] To this end, a series of distillations and / or extractions and decantations are generally carried out, which is both relatively complex to implement, particularly due to the presence of azeotropic mixtures, and costly in terms of energy.

[0009] The problems that arise in the manufacture of light (meth)acrylic esters, in particular C1-C2 alkyl acrylic esters, will now be explained, for convenience, on the basis of the example of methyl acrylate obtained by esterification of acrylic acid with methanol. However, the problems and the solution proposed by the invention can be applied to the use of ethanol in the esterification reaction.

[0010] As side reactions during the manufacture of methyl acrylate, unreacted acrylic acid can form oligomers, such as 3-acryloxypropionic acid (n=2) or 3-acryloxy 3-propioxy propionic acid, (n=3), which are heavy by-products with a higher boiling point than acrylic acid. As another side reaction, Michael addition can produce Michael adducts; in particular, Michael addition between already formed methyl acrylate and methanol leads to the formation of methyl methoxy propionate.

[0011] Methyl methoxy propionate (MPM) is a so-called heavy by-product because its boiling point (142°C at atmospheric pressure) is significantly higher than that of the methyl acrylate produced (80°C at atmospheric pressure), and it is formed in significant quantities in the process as the esterification reaction progresses along with the acrylic acid oligomers.

[0012] Methyl methoxy propionate is problematic because it has a vapor pressure close to that of acrylic acid. Its boiling point is close to that of acrylic acid (144°C at atmospheric pressure), and it can form an azeotrope with water. It will be concentrated mainly in the recycling loop of unreacted acrylic acid. It is then necessary to purge this recycling loop, which can lead to a significant loss of acrylic acid. Furthermore, MPM is the lightest of the heavy by-products compared to acrylic acid oligomers; it can interfere with the final purification of methyl acrylate and alter the quality of the finished product.

[0013] In order to limit the formation of methyl methoxy propionate, it was proposed in document US 6,025,520 to carry out the esterification reaction under reduced pressure with an excess of acid. These conditions make it possible to improve the yield and selectivity of the esterification reaction and to significantly reduce the formation of heavy by-products generated by the addition of methanol such as methyl methoxy propionate, which is problematic for the purification train of the desired ester.

[0014] The process described in WO 2015 / 063388 proposes to significantly reduce the formation of alkyl alkoxy propionate during the synthesis of methyl or ethyl (meth)acrylate in conventional fixed bed reactor technology by carrying out the esterification reaction under atmospheric pressure, under conditions where the acid is in excess of the alcohol and where the hourly volumetric velocities are high.

[0015] The process described in document US 2001 / 0047106 proposes to transform the oxy esters formed during esterification by high-temperature catalytic cracking (150 to 250°C) with the addition of acrylic acid and water. The product formed is then mainly an ester and the addition of water makes it possible to limit the formation of olefins and ether at high temperature. However, this type of reaction requires a lot of energy to reach this temperature level.

[0016] In its patent FR3083233, the applicant company has shown that it is possible to partially remove methyl methoxy propionate by side withdrawal during the azeotropic distillation of the reaction mixture carried out in a single distillation column equipped with a side withdrawal. This invention makes it possible to remove the MPM / water azeotrope, but has no effect on the MPM present at the bottom of this azeotropic column in a stream mainly composed of acrylic acid.

[0017] However, there is still a need to eliminate methyl methoxy propionate formed during the synthesis of methyl acrylate, which is detrimental to the material balance of the process (loss of raw materials during purges) and to the purification train (complexity in achieving high purity).

[0018] Surprisingly, the inventors discovered that it is possible to remove methyl methoxy propionate (or ethyl methoxy propionate) and obtain high-purity methyl acrylate (or ethyl acrylate) by efficiently removing the Michael adducts formed during this process, by acidolysis, which transforms the Michael adduct into a high-boiling acid, which can then be removed at the bottom of the cracker. This purifies the alkyl ester stream, which can be recycled to the reaction.

[0019] One of the objectives of the present invention is therefore to provide a process for the recovery / purification of methyl acrylate, and more generally of methyl or ethyl acrylate, allowing efficient removal of methyl methoxy propionate, in the presence of acrylic acid, by continuously implementing an acidolysis reaction to form 3-methoxypropionic acid and methyl acrylate.

[0020] SUMMARY OF THE INVENTION

[0021] The subject of the present invention is a process for the recovery / purification of C1-C2 alkyl acrylate from a reaction mixture resulting from the esterification of acrylic acid with an alcohol chosen from methanol and ethanol, characterized in that it comprises an acidolysis treatment making it possible to continuously transform the alkoxy esters of methyl acrylate or ethyl acrylate into alkoxy propionic acid.

[0022] According to one embodiment, the acidolysis reaction takes place at temperatures close to those of the esterification reaction. According to one embodiment, the alcohol is methanol, the alkyl acrylate is methyl acrylate: the alkyl alkoxy propionate is methyl methoxy propionate (MPM), and the alkoxy propionic acid is methoxypropionic acid (AMP).

[0023] According to one embodiment, the alcohol is ethanol, the alkyl acrylate is ethyl acrylate: the alkyl alkoxy propionate is ethyl ethoxy propionate (EPE), and the alkoxy propionic acid is ethoxy propionic acid (EPA).

[0024] According to one embodiment, the reaction mixture is obtained from the esterification of acrylic acid with a stoichiometric excess of alcohol.

[0025] According to one embodiment, the reaction mixture is obtained from the esterification of acrylic acid with an alcohol under conditions of stoichiometric excess of acid.

[0026] Acidolysis treatment involves the following reactions: In the presence of water and acrylic acid (AA), MPM hydrolyzes to form methoxypropionic acid and methanol (MeOH). MPM reacts with acrylic acid to form methyl acrylate and methoxypropionic acid.

[0027] MPM hydrolysis reaction:

[0028] MPM + H2O --> AMP (methoxypropionic acid) + MeOH MPM cidolysis:

[0029] One or both of these reactions take place depending on the reactants present.

[0030] These reactions take place in temperature ranges close to that of the esterification reaction (75°C-85°C); they are catalyzed by strong acids, for example a strong cationic resin.

[0031] The reactions will transform methyl methoxypropionate into methoxypropionic acid (boiling temperature: 206°C at atmospheric pressure). Since the vapor pressure of the latter is very different from that of acrylic acid, it can be easily separated from the latter.

[0032] The products from the reactor are sent to an azeotropic column. Azeotropic distillation means the separation of an azeotrope (or azeotropic mixture) consisting of a ternary mixture of alkyl acrylate / alcohol / water. This azeotropic column separating the reaction mixture can be equipped with a side draw-off to remove the MPM / water azeotrope, as described in document FR3083233. The bottom flow of the azeotropic column feeds all or part of the heavy products treatment column. This separates at the top a flow comprising unreacted (meth)acrylic acid and traces of alcohol and light products, and at the bottom a flow of heavy by-products.

[0033] These heavy by-products rich in alkoxyester adducts and oligomers can be subjected to thermal treatment in a cracking reactor releasing a stream of valuable products which returns to the reaction and generates a residue.

[0034] The overhead stream from the azeotropic column feeds the liquid / liquid extraction purification train and one or two distillation columns to recover the purified ester.

[0035] The acidolysis reactor treats all heavy streams rich in MPM and allows the recovery of valuable raw materials and the transformation of methyl methoxypropionate into methoxypropionic acid.

[0036] According to one embodiment, the method according to the invention is implemented in an installation comprising: an esterification reactor, an azeotropic distillation column, an acidolysis reactor, a second distillation column and / or a film evaporator, a cracking reactor, a liquid / liquid extraction column, a purification system optionally comprising a partition column

[0037] According to one embodiment, the acidolysis reactor is placed at the feed of the heavy treatment column at the bottom of the azeotropic column.

[0038] According to one embodiment, the acidolysis reaction placed at the feed of the heavy treatment column treats this bottom flow of the azeotropic column, possibly the flow from the side draw-off, possibly that of the purge from the bottom of the purification column.

[0039] According to one embodiment, the process according to the invention comprises the following steps: a) Azeotropic distillation of the reaction mixture using a first distillation column making it possible to separate at the top an azeotropic mixture comprising alkyl acrylate, unreacted alcohol and water, and at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, a fraction rich in alkyl alkoxy propionate by-product being removed by side draw-off;b) An acidolysis step which makes it possible to transform the alkyl alkoxypropionate into alkoxy propionic acid, which creates a stream free of alkyl alkoxypropionate which feeds the heavy separation column. c) The separation in a column of the bottom stream of the azeotropic column into a stream essentially comprising the unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream essentially comprising heavy by-products which is subjected to thermal cracking releasing a stream of recoverable products which can be recycled; d) A cracking step which makes it possible to recover the raw materials contained in the by-products and to purge the residue;e) The liquid / liquid extraction of the overhead stream of the first distillation column by an aqueous stream making it possible to separate an organic phase essentially comprising the alkyl acrylate, and an aqueous phase, the aqueous phase being distilled to recover on the one hand an alcohol-rich fraction which can be recycled to the reactor, and on the other hand a water-rich fraction which can be used as an aqueous stream in the liquid / liquid extraction step; f) The purification of said organic phase making it possible to recover the purified alkyl acrylate. g) The possible recycling of the purge from the purification train, rich in alkoxyester, after an acidolysis step.;

[0040] The present invention overcomes the disadvantages of the prior art related to the formation of alkyl alkoxy propionate by-product in a process for the synthesis of methyl acrylate or ethyl acrylate by direct esterification of acrylic acid with the corresponding alcohol.

[0041] The process according to the invention makes it possible to effectively eliminate alkyl alkoxy propionate, and to reduce the losses of recoverable products caused by the purges imposed by the accumulation of alkyl alkoxy propionate in the purification train.

[0042] Thus the invention provides a simplified process for producing high purity methyl or ethyl acrylate, and optimizes the material balance of the process. BRIEF DESCRIPTION OF THE FIGURES

[0043] Figure 1 schematically represents an installation for producing methyl acrylate including the acidolysis step according to the invention.

[0044] DETAILED DESCRIPTION OF THE INVENTION

[0045] The invention is now described in more detail and in a non-limiting manner in the following description, in comparison with a method of the prior art.

[0046] For simplification, the description is based on the example of methyl acrylate obtained by esterification of acrylic acid with methanol. The solution proposed by the invention applies in the same way to the use of ethanol in the esterification reaction, as well as to other configurations of the purification train (process with azeotropic distillation without a side draw-off, tailing column and rectification column or partition column for the final purification).

[0047] A prior art methyl acrylate production facility is shown in Figure 1.

[0048] The reaction section comprises an esterification reactor RI. The reactor RI is fed by an acrylic acid supply line 1, a methanol supply line 2. The reactor preferably contains a heterogeneous catalyst of the cation exchange acid resin type. In the case of homogeneous catalysis, the reactor is further fed by a catalyst supply line (not shown). The esterification reaction can be carried out in excess methanol or in excess acrylic acid.

[0049] The esterification reaction can be carried out in excess alcohol, in which case the acid / alcohol molar ratio is between 0.6 and 1, or in excess acrylic acid, in which case the acid / alcohol molar ratio is between 1.05 and 3, it being understood that the acid / alcohol molar ratio refers to the acid and alcohol contents of all the streams feeding the esterification reactor (pure product streams and recycled streams).

[0050] The esterification reaction can be carried out under pressure ranging from atmospheric pressure (100,000 Pa) to 3 times this value (300,000 Pa), or under reduced pressure.

[0051] The esterification reaction is carried out in the presence of an acid catalyst, for example a cation exchange acid resin in the case of heterogeneous catalysis; or as catalyst in the case of homogeneous catalysis, it is possible to use, for example, sulfuric acid, or an organic sulfonic acid, such as methane sulfonic acid, para-toluene sulfonic acid, benzene sulfonic acid, dodecyl sulfonic acid, or mixtures thereof. Preferably, the esterification reaction is carried out under heterogeneous catalysis, under atmospheric pressure.

[0052] The reaction is generally carried out in the presence of one or more polymerization inhibitors which are introduced into the reactor, at a rate of 500 to 5000 ppm relative to the crude reaction mixture.

[0053] At the outlet of the reactor RI, the reaction mixture 3 is sent to an azeotropic distillation unit C8. The configuration of the distillation column C8 makes it possible to separate, at the top, a stream 11 consisting of an azeotropic mixture comprising the methyl acrylate formed, unreacted methanol and the water generated by the reaction, as well as light impurities and heavy impurities, at the bottom, a stream 6 essentially comprising the unreacted acrylic acid, traces of light products and heavy products, and a stream 19 withdrawn laterally.

[0054] Stream 19 includes a significant fraction of the MPM formed as a by-product during esterification. Stream 19 is an MPM-rich stream, but may contain methyl acrylate, methanol, acrylic acid, and water.

[0055] Stream 19 can advantageously be sent to the acidolysis reactor R2 which will transform the MPM into AMP and then feed the column C2 for treating heavy by-products.

[0056] Alternatively, stream 19 may be subjected to purification (not shown) in order to recover the purified methyl methoxy propionate on the one hand, and the recoverable compounds such as methyl acrylate, methanol and acrylic acid on the other hand.

[0057] The distillation column C8 separates, at the bottom, a stream 6 comprising essentially unreacted acrylic acid, traces of light products (boiling temperature lower than that of acrylic acid), and heavy products having a boiling temperature higher than acrylic acid (oligomers of acrylic acid and Michael adducts).

[0058] Stream 6 is sent in whole or in part to the acidolysis reactor R2 then to a distillation column and / or a film evaporator C2 which separates a stream 7 comprising the residual acrylic acid and the lighter products, and a stream 8 consisting essentially of the heavy products. Stream 7 is advantageously recycled into the reactor RI.

[0059] Stream 8 may be subjected to thermal cracking to recycle the noble products (starting compounds or finished product) potentially recoverable from the heavy product fraction. Thermal cracking is generally carried out at a temperature ranging, for example, from 120°C to 220°C, possibly in the presence of an acid catalyst such as sulfuric acid or a sulfonic acid. The final residue from this cracker is sent for incineration while the recovered products are recycled via stream 23 to the reaction.

[0060] The azeotropic distillation unit separates at the top a stream 11 consisting of an azeotropic mixture comprising the methyl acrylate formed, unreacted methanol and the water generated by the reaction, as well as light impurities and heavy impurities.

[0061] The head stream 11 from the azeotropic distillation unit is sent to a decantation section (decanter or contactor) which generates, on the one hand, an aqueous phase 17A containing essentially methanol and on the other hand, an organic phase 12.

[0062] The liquid / liquid extraction section generally consists of a stirred or packed liquid / liquid extraction column, a mixer-decanter battery, and one or more decanters in series. It generates an organic phase 14 depleted in alcohol and an aqueous phase 17B.

[0063] In the installation described in Figure 1, the aqueous phase 17 is subjected to distillation on a distillation column C5 to separate the methanol which is recycled into the reactor (stream 5) after possibly a dehydration step, the aqueous stream 18 depleted in methanol being able to be recycled for the liquid / liquid extraction phase.

[0064] Organic phase 14 is subjected to a purification train in order to recover the methyl acrylate with the purity necessary for its subsequent use. Generally, a purity greater than 99.5%, or even greater than 99.8%, is sought.

[0065] To do this, the organic phase 14 can be subjected to one or more additional serial distillation steps.

[0066] According to one embodiment of the invention, the purification of the organic phase 14 is carried out using a purification system comprising at least one partition column equipped with an internal partial partition creating separation zones in the column and a decanter. In Figure 1 this purification system is represented by C9 which separates, at the top a flow 13 comprising most of the light compounds, at the bottom a flow 16 comprising most of the heavy compounds, and a flow 15 of purified methyl acrylate withdrawn laterally.

[0067] Stream 13 is composed of the condensed light streams in the form of an aqueous phase and an organic phase. The organic phase is partially used as reflux from the partition column and purged; the aqueous phase is treated to a biological station.

[0068] Stream 16 is purged but can also be recycled to acidolysis reactor R2. Acidolysis reactor R2 therefore receives a combination of MPM-rich streams: stream 19, stream 16 and stream 6; the feed contains at least 50% acrylic acid. To promote the reaction, an aqueous stream can also be added (stream 18), not shown.

[0069] The effectiveness of the inhibitors is also linked to the injection of air or depleted air into the different columns used.

[0070] Examples of polymerization inhibitors that may be used include phenothiazine (PTZ), hydroquinone (HQ), hydroquinone monomethyl ether (EMHQ), di-tert-butyl para-cresol (B HT), paraphenylenediamine, TEMPO (2, 2,6,6-tetramethyl-l-piperidinyloxy), di-tert-butylcatechol, or TEMPO derivatives, such as OH-TEMPO, alone or mixtures thereof in all proportions, at contents in the reaction medium that may be between 50 ppm and 5000 ppm, optionally in the presence of depleted air, but generally at contents between 150 ppm and 1000 ppm.

[0071] The addition of polymerization inhibitors can be done at different points, with the introduction of the reactants or at the top of the distillation column.

[0072] The invention makes it possible to limit the losses of recoverable materials such as acrylic acid, alcohol or alkyl acrylate in a process for producing light alkyl acrylate by direct esterification.

[0073] The acidolysis reactor, fed by several streams, contains a high content of MPM and acrylic acid; depending on the streams added, it contains variable contents of light esters, water and oligomers.

[0074] The acidolysis catalyst is an acid catalyst selected from the list: sulfuric acid, methylsulfonic acid, paratoluenesulfonic acid, and strong acid cationic resin.

[0075] According to one embodiment, the catalyst is a homogeneous catalyst. Acids such as sulfuric acid, methylsulfonic acid, or paratoluenesulfonic acid may be used as homogeneous catalysts.

[0076] According to one embodiment, the catalyst is a heterogeneous catalyst. In heterogeneous catalysis, the catalyst is a strong acid, gel or macroporous cationic resin, such as Amberlyst 131 or Amberlyst 15, used in the form of a fixed bed reactor or a stirred (slurry) reactor.

[0077] The residence time in the acidolysis reactor may vary between 0.2 and 6 h, preferably between 0.5 and 5 h. The temperature in the acidolysis reactor is a temperature close to that of the esterification reaction, between 50 and 100°C, preferably between 70 and 90°C, while maintaining the reactants in their liquid form. According to one embodiment, the molar ratio between AA and MPM is between 1 and 11, preferably from 4 to 9. An aqueous stream may be added to the mixture to promote the hydrolysis reaction.

[0078] The following examples illustrate the present invention and are not intended to limit the scope of the invention as defined by the appended claims.

[0079] EXPERIMENTAL PART

[0080] In the examples, percentages are given by weight unless otherwise stated, and the following abbreviations have been used:

[0081] AA: acrylic acid

[0082] AM: Methyl acrylate

[0083] MPM: methyl methoxy propionate

[0084] MeOH: methanol

[0085] Example 1. Acidolysis reaction of MPM with or without water: case AA + MPM with excess AA (with and without water)

[0086] The acidolysis reaction of MPM without or in the presence of water is carried out in batch. In a flask, AAt (technical grade acrylic acid with a purity > 99%) and MPM are introduced in excess of AA (AAt / MPM molar ratio = 5) and 20% by mass of dry resin is added. The mixture is placed for 5 hours at 80°C and total reflux. Table 1 summarizes the reaction conditions.

[0087] Transformation rate = (Final mole number - initial mole number) / initial MeOH mole number.

[0088] Table 1

[0089] Under these conditions, MPM is easily transformed into methoxypropionic acid by acidolysis without water; a significant amount of AM is also formed (conversion rate 69 to 85%). The presence of water promotes the disappearance of MPM, probably by a hydrolysis reaction.

Claims

CLAIMS 1. Process for the purification of C1-C2 alkyl acrylate from a reaction mixture resulting from the esterification of acrylic acid with an alcohol chosen from methanol and ethanol, characterized in that said reaction mixture being rich in acrylic acid resulting from the esterification, the process comprises an acidolysis treatment making it possible to continuously transform the alkoxy esters of methyl acrylate or ethyl acrylate into alkoxy propionic acid in the presence of a homogeneous or heterogeneous catalyst and at a temperature between 50 and 100°C, preferably between 70 and 90°C.

2. Method according to claim 1, implemented in an installation comprising: an esterification reactor, an azeotropic distillation column, an acidolysis reactor, a second distillation column and / or a film evaporator, a cracking reactor, a liquid / liquid extraction column, a purification system optionally comprising a partition column.

3. A method according to claim 1 or 2, wherein the alcohol is methanol, and the alkyl acrylate is methyl acrylate, the alkyl alkoxy propionate is methyl methoxy propionate, and the alkoxy propionic acid is methoxypropionic acid.

4. The method of claim 1 or 2, wherein the alcohol is ethanol, and the alkyl acrylate is ethyl acrylate, the alkyl alkoxy propionate is ethyl ethoxy propionate, and the alkoxy propionic acid is ethoxy propionic acid.

5. A method according to any one of the preceding claims, wherein the acidolysis catalyst is an acid catalyst selected from the list: sulfuric acid, methylsulfonic acid, paratoluenesulfonic acid, and strong acid cationic resin.

6. Process according to any one of the preceding claims, wherein the temperature in the acidolysis reactor is between 50 and 100°C, preferably between 70 and 90°C.

7. Method according to any one of the preceding claims, in which the pressure in the acidolysis reactor is between 100,000 Pa and 300,000 Pa.

8. Method according to any one of the preceding claims, in which the residence time in the acidolysis reactor is between 0.2 and 6 h.

9. Process according to any one of the preceding claims, in which the molar ratio between acrylic acid (AA) and methyl methoxy propionate (MPM) at the inlet of the acidolysis reactor is between 1 and 11, preferably from 4 to 9.

10. Process according to any one of the preceding claims, in which the reaction mixture is obtained from the esterification of acrylic acid with a stoichiometric excess of alcohol, the acid / alcohol molar ratio being between 0.6 and 1.

11. Process according to any one of claims 1 to 4, in which the reaction mixture is obtained from the esterification of acrylic acid with an alcohol under conditions of stoichiometric excess of acid, the acid / alcohol molar ratio being between 1.05 and 3.

12. The method of claim 5, wherein when the catalyst is a strong acid cationic resin, the catalytic esterification reactor is a fixed bed reactor or a stirred reactor.

13. Process according to any one of the preceding claims, in which polymerization inhibitors are introduced into the esterification reactor, at a rate of 500 to 5000 ppm relative to the crude reaction mixture.

14. A process according to any preceding claim, wherein the azeotropic column may be provided with a side draw.

15. A process according to any preceding claim, wherein the cracking is thermal cracking without catalyst.

16. Process according to claim 2, said process comprising the following steps: a) Azeotropic distillation of the reaction mixture using a first distillation column making it possible to separate at the top an azeotropic mixture comprising alkyl acrylate, unreacted alcohol and water, and at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, a fraction rich in alkyl alkoxy propionate by-product being removed by side draw-off; b) An acidolysis step which makes it possible to transform the alkyl alkoxypropionate into alkoxy propionic acid which creates a stream free of alkyl alkoxypropionate which feeds the heavy separation column. c) The separation in a column of the bottom stream of the azeotropic column into a stream comprising essentially unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream comprising essentially heavy by-products which is subjected to thermal cracking releasing a stream of recoverable products which can be recycled; d) A cracking step which makes it possible to recover the raw materials contained in the by-products and to purge the residue;e) The liquid / liquid extraction of the overhead stream of the first distillation column by an aqueous stream making it possible to separate an organic phase essentially comprising alkyl acrylate, and an aqueous phase, the aqueous phase being distilled to recover on the one hand an alcohol-rich fraction which can be recycled to the reactor, and on the other hand a water-rich fraction which can be used as an aqueous stream in the liquid / liquid extraction step; f) The purification of said organic phase making it possible to recover the purified alkyl acrylate. g) The possible recycling of the purge from the purification train, rich in alkoxyester, after an acidolysis step.;

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