Method for purifying light acrylic acid esters

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 a corresponding light alcohol. More specifically, the present invention relates to a method for recovering / purifying C1-C2 alkyl acrylic acid, comprising the steps of thermally decomposing the ester adduct alone or in combination with heavy products of an acrylic acid production facility, and hydrothermally gasifying the bottom product of this cracker and the wastewater from this method.

Description

Technical Field

[0001] The present invention relates to the production of light (meth)acrylic esters such as methyl (meth)acrylate or ethyl (meth)acrylate by direct esterification of (meth)acrylic acid with the corresponding light alcohol.

[0002] More specifically, the present invention relates to a method for the recovery / purification of C1-C2 alkyl acrylates, comprising the step of thermally decomposing an ester adduct alone or in combination with heavy substances from an acrylic acid production facility, and the step of hydrothermally gasifying the bottom product from this cracker and the wastewater from this method.

Background Art

[0003] It is known to produce (meth)acrylic esters, especially methyl acrylate or methyl methacrylate, and ethyl acrylate or ethyl methacrylate, by carrying out an esterification reaction between an alcohol and (meth)acrylic acid. This reaction is a catalytic reaction balanced with the generation of water. It is further accompanied by side reactions that produce impurities, especially heavy compounds, i.e., compounds having a high boiling point exceeding the boiling point of the desired ester.

[0004] In such a process, for environmental and economic reasons, it is essential to recycle unreacted reactants to the reaction, but also to upgrade the heavy products generated in the process while seeking a high-purity final product.

[0005] For this purpose, a set of separations by distillation and / or extraction, sedimentation is generally carried out, but these are relatively complex to implement, especially as a result of the presence of azeotropic mixtures, and are costly from an energy perspective, showing the disadvantage of generating a final residue that cannot be upgraded and presenting losses of starting materials.

[0006] The problems that arise during the production of light (meth)acrylic esters, particularly C1-C2 alkyl acrylates, can be explained here, for convenience, based on the example of methyl acrylate obtained by esterification of acrylic acid with methanol. However, the problems and solutions proposed by the present invention can be applied to the use of methacrylic acid on the one hand and ethanol on the other hand in the esterification reaction.

[0007] The temperature and pressure operating conditions for the distillation line, particularly for the azeotropic distillation column, are not critical in this process and can be determined according to known distillation methods using state-of-the-art technology. However, preferably, the azeotropic distillation column is operated at a pressure below atmospheric pressure, thereby minimizing the formation of heavy by-products and preventing polymerization of existing unsaturated products. These compounds are heavy products that reduce the recovery yield due to the consumption of acrylic acid monomers.

[0008] It is essentially the following problem: - Another acrylic acid molecule: 3-acryloyloxypropionic acid, also called "acrylic acid dimer" or "AA dimer," is an addition derivative of acrylic acid to a double bond. - "AA trimers" formed by the sequential addition of acrylic acid to the double bond of the aforementioned AA oligomer, and other oligomers, which are derivatives of AA dimer molecules formed by the addition of acrylic acid to the double bond, - Addition derivatives of carboxylic acids formed as by-products of acrylic acid or water to the double bond of AA or the above-mentioned oligomer.

[0009] As another side reaction, Michael addition may produce Michael adducts, particularly methyl methoxypropionate, which is formed between methyl acrylate and methanol.

[0010] Methyl methoxypropionate (MMP) exhibits a vapor pressure similar to that of acrylic acid. Its boiling point is also close to that of acrylic acid (144°C, atmospheric pressure). Consequently, it concentrates in the recycling loop of unreacted acrylic acid, like other heavy by-products. Furthermore, it interferes during the final purification of methyl acrylate and, being the lightest of the by-products, can negatively impact the quality of the final product.

[0011] Similar to radical polymerization, this covalent reaction that forms Michael derivatives is strongly accelerated by temperature. Consequently, column equipment with numerous rectification plates to meet the required quality of the final ester is disadvantageous in terms of product loss, which can only be compensated for by additional high-temperature cracking treatment of the Michael derivative to regenerate the monomer, or by the specific bleed-off of methyl methoxypropionate, which cracks with great difficulty under standard conditions of cracker use.

[0012] To limit the formation of methyl methoxypropionate, reference US6025520 proposed carrying out the esterification reaction under reduced pressure with an excess of acid. These conditions allow for improved yield and selectivity of the esterification reaction and significantly reduce the formation of heavy by-products such as methyl methoxypropionate, which are problematic in the line for purifying the desired ester. Treatment of the acrylic acid recirculation loop is briefly described.

[0013] The method described in reference WO2015 / 063388 allows for a significant reduction in the formation of alkyl alkoxypropionates during the synthesis of ethyl (meth)acrylate by carrying out the esterification reaction in a conventional fixed-bed reactor under conditions of atmospheric pressure, an excess of acid relative to the alcohol, and a high space rate per unit time. To improve the quality of the adduct, a partial treatment of the recirculation loop is performed by utilizing a distillation column or evaporator, which allows for the first reconcentration of the heavy by-products at the bottom of the latter, and then sending them to a thermal cracker or contact cracker to release essentially acrylic acid and poorly converted ethyl ethoxypropionate into the reactor and heavy residue intended for incineration. The fate of the material bled off from the column of the separation line is not explained.

[0014] In patent FR3083233, the applicant company demonstrated that it is possible to partially remove methyl methoxypropionate by sidestream extraction during azeotropic distillation of a reaction mixture performed in a single distillation column where sidestream extraction is provided. The present invention makes it possible to remove the MMP / water azeotropic mixture, but without affecting the MMP present at the bottom of this azeotropic column in a flow predominantly composed of acrylic acid. Heavy by-products in the recirculation loop are treated by thermal decomposition, or thermal decomposition and catalytic decomposition. The fate of the material bled off from the column in the separation line, and also the residue from the cracker, is not described.

[0015] Reference EP2334633 also explains that heavy by-product streams originating from acrylic acid plants can be recycled into ester plants such as butyl acrylate plants (especially if the latter is equipped with crackers that allow for the regeneration of acrylic acid from the dimer of this acid).

[0016] In cases where light ester (methyl acrylate (MA) or ethyl acrylate (EA)) production occurs near an acrylic acid (AA) production unit, co-cracking of each heavy substance improves the performance and quality of monomer recovery.

[0017] Therefore, as shown in reference EP717031, when cracking is performed starting from a mixture of heavy materials originating from AA production units and acrylic acid ester (AE) production units, it is possible to improve the efficiency of recovering these valuable, high-grade products compared to individual cracking of heavy material flows from these units. The effect of adding heavy materials originating from ester units (AEHS) to heavy materials originating from AA units (AAHS) is to reduce the viscosity of the final residue. The cracking reaction is performed starting from a mixture having an AA heavy material / ester heavy material ratio of 9 / 1 to 1 / 9, at a temperature of 180°C to 220°C, under atmospheric pressure, and with a residence time of 0.5 to 3 hours. Therefore, the plant for performing the process must be equipped with a reactor and top condenser operating at the same pressure, a distillation column operating under reduced pressure and supplied with condensed products, a boiler at the bottom, a condenser at the top, reflux equipment, and the supply of inhibitors. This arrangement is complex and costly.

[0018] Reference FR3110571 suggests that combining partial condensation with a cracking reactor can increase the cracking yield without significant effects on the viscosity of the residue.

[0019] Application FR2206330, applied alone to heavy acrylic acid substances, enables improvement of regeneration yield in a continuous process without a significant increase in dynamic viscosity close to 1 Pa.s by performing hydrolysis of heavy by-products with water:heavy acrylic acid substance in a mass ratio of 0.1 to 1.3 before performing thermal decomposition at a pressure higher than atmospheric pressure to maintain the mixture in liquid state. However, this improvement is not described for mixtures of heavy ester substances and heavy acrylic acid substances.

[0020] More generally, the evaporation of light compounds during cracking leads to the concentration of heavy products in the residue flow and an increase in the viscosity of this flow. The residue must retain sufficient fluidity to be transported after cooling and then processed with its decomposition in mind, while allowing for the maximum recovery of valuable products.

[0021] In the case of treating heavy acrylic acid (AAHS) alone, it was also intended that a solvent be added to the residue.

[0022] However, these solutions present several drawbacks, such as the generation of waste to be incinerated, the need for additional equipment to carry out the mixing, or energy consumption, assuming that water is chosen as the solvent and must be evaporated. Moreover, most of these solvents generate nitrogen-containing or sulfur-containing derivatives during incineration.

[0023] None of these solutions improve the quality of wastewater from processes intended for biological plants. Furthermore, instead of converting it to CO2 by combustion, it would be desirable to be able to improve the final residue resulting from (meth)acrylic acid production into exportable methane gas.

[0024] The oxidation (incineration) of organic matter with carbon dioxide and water is often used to process organic residues and generate heated steam. In conventional processes, the rapid oxidation of organic fuel is used to generate heat, which is then transferred to a fluid such as water in a heat exchanger. A heat loss of 10-15% is expected as a result of losses that inevitably occur in the exhaust column of conventional boilers. In addition to potential blockages by solids supplied to the boiler, the accumulation of salt in boiler tubes, or the accumulation of ash on the surface of tubes exposed to flames or hot gases, reduces good heat conduction and consequently heat transfer efficiency, and can even lead to very costly losses as a result of tube wall rupture.

[0025] As a result, there is a need to eliminate heavy by-products and upgrade the final residue obtained from the production of light (C1-C2) acrylic acid alkyl esters.

Prior Art Documents

Patent Documents

[0026]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0027] Therefore, one of the objectives of the present invention is to provide an improved process for the recovery / purification of C1-C2 alkyl acrylates and to enable the optimization of the upgrading of various residues obtained therefrom.

Means for Solving the Problems

[0028] The subject of the present invention is a method for recovering / purifying C1-C2 alkyl acrylates from a reaction mixture obtained from the esterification of acrylic acid with an alcohol selected from methanol and ethanol, carried out in the presence of a polymerization inhibitor, comprising at least the following steps: - Using a first distillation column to azeotropically distill the reaction mixture to obtain - At the top, a stream containing alkyl acrylate, unreacted alcohol and water, - At the bottom, a fraction containing unreacted acrylic acid and heavy products, - By-stream extraction yields aqueous fraction rich in alkyl alkoxypropionate by-products. The process that brings about the separation, - A step of treating the top flow from the first distillation column by liquid / liquid extraction to generate an aqueous phase essentially containing alcohol and an organic phase rich in alkyl acrylate, - In the second distillation column, the alkyl acrylate-rich organic phase is treated, - At the top, purified alkyl acrylate, - At the bottom, heavy products and polymerization inhibitors The process of separating and - In the third distillation column, the aqueous phase is treated by distillation. - At the top, the alcohol is recycled for the esterification reaction, and - At the bottom, a watery flow with reduced alcohol content. The process of separating and - A fourth distillation column and / or film evaporator is used to process the bottom flow from the first distillation column. - At the top, a flow containing residual acrylic acid and lighter products, and - At the bottom, a flow consisting of heavy products. The process of separating and - A process that allows for the thermal decomposition of the bottom flow from the fourth distillation column to obtain valuable products such as alkyl acrylate and the final residue. Includes, The method is characterized by including a hydrothermal gasification step, which enhances the quality of the aqueous effluent containing methane and hydrogen, the final residue from cracking, and also the by-flow extraction fraction from the first distillation column, the bottom flow from the third distillation column, and partly the bottom flow from the second column. It is a method.

[0029] According to one embodiment, the alcohol is methanol, the alkyl acrylate is methyl acrylate, and the alkyl alkoxypropionate is methyl methoxypropionate (MMP).

[0030] According to one embodiment, the alcohol is ethanol, the alkyl acrylate is ethyl acrylate, and the alkyl alkoxypropionate is ethyl ethoxypropionate (EEP).

[0031] According to one embodiment, the acid is methacrylic acid.

[0032] According to one embodiment, the AA heavy substance produced in units of acrylic acid is essentially, - Addition derivatives of acrylic acid to the double bond of another acrylic acid molecule: 3-acryloyloxypropionic acid (also called "acrylic acid dimer" or "AA dimer") - Derivatives formed by the addition of acrylic acid to the double bond of an AA dimer molecule to form an "AA trimer," and other oligomers formed by the sequential addition of acrylic acid to the double bond of the aforementioned AA oligomer. - Addition derivatives of carboxylic acids formed as byproducts of acrylic acid, or addition derivatives of water to the double bond of AA or the above-mentioned oligomers. That is the case.

[0033] Unless otherwise specified, the stated content is expressed in terms of mass. The boundary is the range of values ​​indicated.

[0034] According to one embodiment, the final purification to obtain commercial-grade methyl acrylate can be performed by using not only two columns but also a split-wall column DWC.

[0035] According to one embodiment, only the heavy substance of methyl acrylate is supplied to the cracker.

[0036] According to one embodiment, only the heavy substance of ethyl acrylate is supplied to the cracker.

[0037] According to one embodiment, the heavy acrylic acid substance is mixed directly with the heavy ester substance.

[0038] According to one embodiment, the heavy acrylic acid substance is hydrolyzed in advance in a hydrolysis reactor (hydrolysis apparatus) before being mixed with the heavy ester substance.

[0039] According to one embodiment, the ester heavy substance and the acrylic acid heavy substance are hydrolyzed in advance in a hydrolysis reactor (hydrolysis apparatus) before entering the cracker.

[0040] According to one embodiment, the pressure in the hydrolysis apparatus fluctuates between 0.1 and 2 MPa, preferably between 0.5 and 1.5 MPa.

[0041] According to one embodiment, the water / addition substance ratio in the hydrolysis apparatus varies from 0.1 to 1.3 (including the boundary).

[0042] According to one embodiment, the temperature in the hydrolysis apparatus fluctuates between 80°C and 200°C, preferably between 150°C and 200°C.

[0043] According to one embodiment, the method of the present invention is a method for producing industrial (meth)acrylic esters of high purity, that is, having a purity exceeding 99.5% by mass, and in fact exceeding 99.8% by mass.

[0044] According to one embodiment, the reaction mixture is produced by the esterification of acrylic acid with a stoichiometrically excess alcohol.

[0045] According to one embodiment, the reaction mixture is produced by the esterification of acrylic acid with an alcohol under conditions of a stoichiometric excess of the acid.

[0046] According to one embodiment, the thermal decomposition reaction occurs in the absence of a catalyst.

[0047] According to one embodiment, the cracking temperature is between 140°C and 260°C, preferably between 160°C and 210°C.

[0048] According to one embodiment, thermal decomposition is performed on an ester (heavy) adduct.

[0049] According to one embodiment, thermal decomposition is performed on a mixture of acrylic acid (heavy) adducts and ester (heavy) adducts.

[0050] According to one embodiment, the residence time of the reaction mixture in the cracking reactor is between 0.5 hours and 10 hours, preferably between 4 hours and 10 hours.

[0051] According to one embodiment, the thermal decomposition reaction occurs at atmospheric pressure or under a small pressure (maximum 0.2 MPa).

[0052] According to one embodiment, the top product from the cracker is recycled for an esterification reaction.

[0053] According to one embodiment, the top product from the cracker is mixed with a portion of the flow from the bottom of the azeotropic column.

[0054] According to one embodiment, the bottom flow from the reactor (residue) obtained upon completion of the pyrolysis operation exhibits a dynamic viscosity of less than 1 Pa.s, preferably less than 10 Pa.s, when measured at a temperature of 100°C using, for example, a cone-plate type Brookfield "CAP 1000+" viscometer.

[0055] According to one embodiment, the hydrothermal gasification equipment includes a first reactor, a second reactor, and a gas-liquid separator.

[0056] According to one embodiment, the residue is directly injected into the gasification process, and water necessary for hydrothermal treatment is further injected.

[0057] According to one embodiment, the residue is mixed with water necessary for hydrothermal treatment before being introduced into gasification.

[0058] According to the embodiment, hydrothermal gasification is carried out at a temperature of 350-450°C and a pressure of 25 MPa.

[0059] According to the embodiment, hydrothermal gasification includes a gasification apparatus that allows for the separation of salt at the bottom and a mixture of gas and liquid at the top.

[0060] According to one embodiment, hydrothermal gasification includes a separator, a gasifier, and a gas-liquid separator that enable the separation of salts under critical conditions.

[0061] According to one embodiment, hydrothermal gasification includes a salt separator, a gasification apparatus including a catalyst, and a gas-liquid separator.

[0062] According to one embodiment, the concentration of residue / water + residue during hydrothermal gasification is between 10 g / l and 400 g / l.

[0063] According to one embodiment, the water used to carry out hydrothermal gasification may be desalinated water, water obtained by drilling, or weakly mineralized water.

[0064] According to one embodiment, some of the water used to carry out hydrothermal gasification is withdrawn at the bottom of the alcohol recovery column (third distillation column).

[0065] According to one embodiment, the product obtained by sidestream extraction from an azeotropic column is mixed with heavy acrylic acid material before hydrolysis.

[0066] According to one embodiment, the product obtained by sidestream extraction from the azeotropic column is sent directly to hydrothermal gasification.

[0067] According to one embodiment, a portion of the material bled off from the bottom of the methyl acrylate purification column (second distillation column) is sent directly to hydrothermal gasification.

[0068] According to one embodiment, the water at the outlet of the gasification plant is free of organic compounds and can be advantageously recycled to feed a separator, to feed a hydrolysis plant, or to a liquid / liquid extraction column.

[0069] According to one embodiment, the obtained and separated salt can be processed to a high grade for use as fertilizer.

[0070] According to one embodiment, 94% to 99% of the carbon introduced into the gasification process is converted to a high-quality gaseous form.

[0071] According to one embodiment, the gas obtained from gasification consists of 40-70% methane, 5-20% hydrogen, and 20-40% carbon dioxide.

[0072] According to one embodiment, the gas can be further fractionated to isolate methane from other compounds.

[0073] According to one embodiment, the method of the present invention involves the following steps: a) A step of carrying out the reaction using a fixed-bed esterification reactor containing an ion exchange resin, in which alcohol and acrylic acid are supplied via a loop that recirculates the unreacted alcohol and acrylic acid, b) A step that allows the reaction mixture to be azeotropically distilled using a first distillation column, separating the azeotropic mixture containing alkyl acrylate, unreacted alcohol and water at the top, the fraction containing unreacted acrylic acid and heavy by-products at the bottom, and the fraction rich in alkyl alkoxypropionate by-products, which is sent to a purification line or otherwise to a hydrolysis apparatus as a sidestream withdrawal. c) A step of separating the bottom flow from the first distillation column into a flow that essentially contains unreacted acrylic acid and is recycled to the esterification reactor, and a flow that essentially contains heavy ester by-products sent to the fourth distillation column, thereby enabling the concentration of the latter, the heavy bottom material, and the return of the light material to the reaction section. d) A step of thermally decomposing these ester heavy substances, which may or may not be hydrolyzed beforehand, either alone or together with acrylic heavy substances, in a cracking reactor and releasing a stream of recyclable, high-grade products, e) A step of hydrothermally gasifying the residue from the crackers as a mixture with water, f) A step that enables the separation of an organic phase essentially containing alkyl acrylate from an aqueous phase by liquid / liquid extraction of the top flow from the first distillation column using an aqueous flow, wherein the aqueous phase is distilled to recover, on the one hand, an alcohol-rich fraction that can be recycled to an esterification reactor, and on the other hand, a water-rich fraction that can be used as an aqueous flow in the liquid / liquid extraction step or for supply to a hydrothermal gasification unit. g) A step that enables the purification of the organic phase in a second distillation column and the recovery of purified alkyl acrylate, h) A process of bleeding the bottom of the purification column (second distillation column) and supplying a portion of the bled-off material to a hydrothermal gasification unit. Includes.

[0074] The present invention makes it possible to reduce the loss of high-grade products caused by the formation of heavy by-products at the bottom of the azeotropic column due to the bleeding operation imposed by the accumulation of alkyl alkoxypropionates in the purification line, and makes it possible to treat the organic matter in the aqueous liquid of the process by, on the one hand, regenerating monomers by cracking, and on the other hand, upgrading them to the form of methane and hydrogen.

[0075] Therefore, the present invention provides a simplified method for producing high-purity methyl or ethyl acrylate (i.e., having a purity exceeding 99.5% by mass, and in fact exceeding 99.8% by mass), and optimizes the material balance of the process. [Brief explanation of the drawing]

[0076] [Figure 1] This figure shows a plant for producing methyl acrylate, including the recycling of various products in the process and a combination of cracking and hydrothermal gasification. [Figure 2] This figure shows a plant that produces methyl acrylate, which involves recycling heavy acrylic acid material originating from an adjacent unit for acrylic acid production, recycling of various products in the process, and a combination of cracking and hydrothermal gasification. [Figure 3] This diagram shows a plant for producing methyl acrylate, originating from an adjacent unit for acrylic acid production, where pre-hydrolyzed heavy acrylic acid material is recycled, various products in the process are recycled, and a combination of cracking and hydrothermal gasification is involved. [Modes for carrying out the invention]

[0077] The present invention will be described in more detail and in no way in the following description.

[0078] For simplicity, the explanation is based on the example of methyl acrylate obtained by esterification of acrylic acid with methanol. The solutions proposed by the present invention are also applicable to the use of ethanol or methacrylic acid in esterification reactions, and to other configurations of the purification line (processes using azeotropic distillation without sidestream withdrawal, tailing columns or rectification columns for final purification).

[0079] The plant for the production of methyl acrylate is shown in Figure 1.

[0080] The reaction section includes an esterification reactor R. Reactor R is supplied by an acrylic acid supply pipe 1 and a methanol supply pipe 2. The reactor preferentially contains an acidic cation exchange resin type heterogeneous catalyst. In the case of a homogeneous catalyst, the reactor is further supplied by a catalyst supply line (not shown). The esterification reaction can be carried out with excess methanol or excess acrylic acid. 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.

[0081] At the outlet of reactor R, the reaction mixture 3 is sent to the azeotropic distillation unit C8 (first distillation column). The configuration of distillation column C8 allows for the separation of a stream 11 at the top, consisting of the azeotropic mixture containing the formed methyl acrylate, unreacted methanol, and water generated by the reaction, as well as light and heavy impurities; a stream 6 at the bottom, containing essentially unreacted acrylic acid, trace amounts of light and heavy products; and a stream 19 withdrawn as a by-stream.

[0082] Stream 19 contains a significant fraction of MMP formed as a by-product during esterification. Stream 19, rich in MMP (30-35%), water (40%), and 25% methyl acrylate, acrylic acid, and methanol, is supplied directly to hydrothermal gasification.

[0083] Alternatively, flow 19 can be purified before gasification to recover concentrated methyl methoxypropionate and high-grade compounds such as methyl acrylate, methanol, and acrylic acid.

[0084] The top flow 11 from the azeotropic distillation unit is sent to the liquid / liquid extraction unit L / L (sedimentation tank or contact device), where it generates an aqueous phase 17 that essentially contains methanol on one side and an organic phase 12 rich in methyl acrylate on the other. The flow 11 consists of the formed methyl acrylate, unreacted methanol, water generated by the reaction, and an azeotropic mixture also containing light and heavy impurities.

[0085] The aqueous phase 17 is subjected to distillation in distillation column C5 (third distillation column) to separate methanol which is recycled to the reactor (flow 5), and the aqueous flow 18, with the methanol reduced, is partially recycled to the liquid / liquid extraction phase or sent to flow 22 for hydrothermal gasification.

[0086] The organic phase 12 is subjected to a purification line including at least one split-wall column C9 (second distillation column) to recover methyl acrylate 15 with the purity required for subsequent use. Generally, a purity exceeding 99.5% by mass is desired, and in fact, a purity exceeding 99.8% by mass is preferred.

[0087] Flow 16 can be partially bleed off and also supplied to the hydrothermal gasification unit.

[0088] The first distillation column C8 separates a stream 6 containing essentially unreacted acrylic acid at the bottom, trace amounts of light products (with boiling points lower than that of acrylic acid), and heavy products (oligomers and Michael adducts of acrylic acid) with boiling points higher than that of acrylic acid.

[0089] Stream 6, in whole or in part, is sent to the fourth distillation column and / or film evaporator C2, where it separates at the top into stream 7, containing residual acrylic acid and lighter products, and at the bottom into stream 8, consisting essentially of heavier products. Stream 7 is advantageously recycled to reactor R.

[0090] Flow 8 can be subjected to pyrolysis C11, allowing for the recycling of valuable products 20 (starting compounds or final products) that are potentially recoverable from the heavy product fraction. Pyrolysis is generally carried out at a temperature that may be in the range of, for example, 120°C to 220°C, in the presence of an acid catalyst such as sulfuric acid or sulfonic acid, optionally. The final residue 21 from this cracker, and also flow 19, bottom flow 22 (99.9% water, 0.1% methanol) from the alcohol distillation column (third distillation column), possible contributions of water 23, and the recycling of all or part of the water from gasification are sent to the gasifier G12.

[0091] Hydrothermal gasification is carried out at a temperature range of 350-450°C and a pressure of 25 MPa. The residue concentration in the salt separator (21+16) / water + residue is between 10 g / l and 400 g / l. The resulting gas from gasification 24 consists of 40-70 vol% methane, 5-20 vol% hydrogen, and 20-40 vol% carbon dioxide. The obtained and separated salt 24 can be processed to a high grade for use as fertilizer.

[0092] In Figure 2, if the plant for acrylic acid production is located near the unit for methyl ester synthesis, the heavy by-products obtained from this production can be refined in flow 26 and simultaneously introduced into the cracker as flow 8.

[0093] Ultimately, as shown in Figure 3, if the acrylic acid equipment includes a hydrolysis apparatus HYD as described in reference FR2206330, the heavy acrylic acid material 27 can be supplied to column C2, while flows 19 and 22 can be improved in quality upstream of this hydrolysis apparatus.

[0094] The following embodiments illustrate the present invention and are not intended to limit the scope of the invention as defined by the appended claims. [Examples]

[0095] In the examples, unless otherwise specified, percentages are expressed in terms of mass, and the following abbreviations were used. PTZ: Phenothiazine AA: Acrylic acid MaA: Maleic acid H2O: Water AADi: Acrylate dimer AA3: Trimer of acrylic acid Heavy substances: Oligomers with a larger mass than AA3 HQ: Hydroquinone Acetic acid (TOH) AAHS: Acrylic Acid Heavy Substance MA: Methyl acrylate MeOH: methanol MAHS: Methyl Acrylate Heavy Substance MMP: Methyl Methoxypropionate

[0096] Thermal decomposition of heavy acrylic acid substances with or without prior hydrolysis This example corresponds to Examples 1 and 2 of application FR2206330 and demonstrates the advantage of treating AA heavy material before cracking by performing prior hydrolysis according to the method of the present invention. The results obtained are shown in [Table 1].

[0097] [Table 1]

[0098] Laboratory cracking of methyl acrylate heavy substance alone The apparatus consists of a glass thermal siphon boiler with an effective capacity of 100 ml. MAHS is continuously supplied from the storage tank to the boiler at room temperature via a diaphragm pump. The supply flow rate is adjusted and continuously measured. The boiler is heated using three heating tapes, each with a power of 160 W. Temperature measurements are taken at the base of the thermal siphon and at the top of the device.

[0099] The operating conditions are as follows: supply flow rate: 14.3 g / hour; top flow rate: 8.45 g / hour; T°: 175°C; residence time: 6.9 hours.

[0100] The results obtained are shown in [Table 2].

[0101] [Table 2]

[0102] It was found that MMP was only slightly improved in quality. The two types of improveable substances (AA and MA) generated by cracking represent approximately 32.6% of the top product. The viscosity of the bottom product was 15.3 cP, measured at 100°C.

[0103] Cracking of a mixture of heavy MAHS and AAHS at a pilot plant In the following embodiment, column C2 (see Figure 2) is a column with a diameter of 180 mm equipped with 24 bubble trays, and the boiler is 0.1 m 2This is a column with a horizontal film evaporator. It is operated under reduced pressure of 140 mmHg and stabilized with a 1940 g / hour (AA + 2% HQ) solution using a fixed reflux ratio of 1. This column is fed in tray 14 by a flow 6 originating from column C8 and also by a top flow 20 from cracker C11. Most of the top flow 7 from C2 is returned to reactor R, but the bottom product from C2 is fed into cracker C11, which has a volume of 12 l, after a 13% bleed-off. This is 5 m 3 Includes a forced recirculation loop with a centrifugal pump at / hour and an electrical exchanger with 5kW of power.

[0104] The top product 20 from the cracker is sent to C2, while the heavy product 21 is collected at the bottom.

[0105] Table 3 shows the revenue and expenses of the operation.

[0106] [Table 3]

[0107] Hydrothermal gasification A very similar example of a Michael adduct, namely a Michael adduct of butyl acrylate heavy material, explains hydrothermal gasification. The BuA heavy material mixture consists of: - Butanol: <0.1% - Butyl acrylate (5-10%) - Butyl hydroxypropionate (BHP): 1-3% - Butyl butoxypropionate (BBP): 70-80% - Butyl acryloyloxypropionate (AA / BuA): 4-6% - Dibutyl maleate: 2-5% - Phenothiazine: 1-3%.

[0108] The heavy BuA material and water were introduced at a rate of 33 g / hour and 970 g / hour respectively through two separate pipes into a separator and a catalytic reactor, both operated at 400°C and 25 MPa. After a 6-hour test period, under stable conditions, the heavy BuA material was converted into a gas mixture having 51% CH4, 34% CO2, and 19% H2 by volume. The energy of this gas was 7096 kWh / ton F, corresponding to BuA. The TOC (Total Organic Carbon) amount was <1 mg / l. [Explanation of Symbols]

[0109] 1. Acrylic acid supply pipe 2 methanol supply pipe 3. Reaction mixture 11 Flow 12 Organic phase 17 Aqueous phase 19 Flow 21 Final Residue 24 Salt C2 Film Evaporator C5 Distillation Column C8 Azeotropic Distillation Unit C9 Split Wall Column C11 pyrolysis G12 Gasification Unit R reactor HYD hydrolysis equipment

Claims

1. Acrylic acid C is obtained from a reaction mixture obtained from the esterification of acrylic acid with an alcohol selected from methanol and ethanol, carried out in the presence of a polymerization inhibitor. 1 ~C 2 A method for recovering / purifying alkyl, comprising at least the following steps: - Using the first distillation column, the reaction mixture is subjected to azeotropic distillation. - At the top, a stream containing alkyl acrylate, unreacted alcohol, and water, - At the bottom, a fraction containing unreacted acrylic acid and heavy products, - By-stream extraction yields aqueous fraction rich in alkyl alkoxypropionate by-products. The process that brings about the separation, - A step of treating the top flow from the first distillation column by liquid / liquid extraction to generate an aqueous phase essentially containing alcohol and an organic phase rich in alkyl acrylate, - In the second distillation column, the organic phase rich in alkyl acrylate is treated, - At the top, purified alkyl acrylate, - At the bottom, heavy products and polymerization inhibitors The process of separating and - In the third distillation column, the aqueous phase is treated by distillation. - At the top, the alcohol is recycled for the esterification reaction, and - At the bottom, a watery flow with reduced alcohol content. The process of separating and - A fourth distillation column and / or film evaporator is used to process the bottom flow from the first distillation column. - At the top, a flow containing residual acrylic acid and lighter products, and - At the bottom, a flow consisting of heavy products. The process of separating and - A step that allows the bottom flow from the fourth distillation column to be subjected to thermal decomposition to obtain valuable products such as alkyl acrylate and final residue. Includes, The method is characterized in that it includes a hydrothermal gasification step, which enhances the quality of the aqueous effluent containing methane and hydrogen, the final residue from cracking, and the side-flow extraction fraction from the first distillation column, the bottom flow from the third distillation column, and partly the bottom flow from the second column. method.

2. The method according to claim 1, wherein the thermal decomposition is performed on an acrylic acid ester adduct.

3. The method according to claim 1, wherein the thermal decomposition is performed on an acrylic acid ester adduct pretreated in a hydrolysis apparatus.

4. The method according to claim 1, wherein the thermal decomposition is performed on a mixture of an acrylic acid adduct and an acrylic acid ester adduct.

5. The method according to claim 1, wherein the thermal decomposition is performed on an acrylic acid adduct pretreated in a hydrolysis apparatus.

6. The method according to claim 1, wherein the thermal decomposition is performed on acrylic acid and acrylic acid ester adducts pretreated in a hydrolysis apparatus.

7. a) A step of carrying out the reaction using a fixed-bed esterification reactor containing an ion exchange resin, in which the alcohol and acrylic acid are supplied via a loop that recirculates the unreacted alcohol and acrylic acid, b) A step that enables azeotropic distillation of the reaction mixture using the first distillation column, separating the azeotropic mixture containing the alkyl acrylate, the unreacted alcohol and the water at the top, the fraction containing the unreacted acrylic acid and heavy by-products at the bottom, and the fraction rich in alkyl alkoxypropionate by-products, which is to be sent as the side stream to a purification line or otherwise to a hydrolysis apparatus, c) A step of separating the bottom flow from the first distillation column into a flow that essentially contains unreacted acrylic acid and is recycled to the esterification reactor, and a flow that essentially contains heavy by-products of ester sent to the fourth distillation column, thereby enabling the concentration of the latter, the heavy material at the bottom, and the return of the light material to the reaction section. d) A step of thermally decomposing these ester heavy substances, which may or may not be hydrolyzed beforehand, either alone or together with acrylic heavy substances, in a cracking reactor and releasing a stream of recyclable, high-grade products, e) A step of hydrothermally gasifying the residue from the crackers as a mixture with water, f) A step that enables the separation of the organic phase, which essentially contains alkyl acrylate, from the aqueous phase by liquid / liquid extraction of the top flow from the first distillation column using an aqueous flow, wherein the aqueous phase is distilled to recover, on the one hand, an alcohol-rich fraction that can be recycled to an esterification reactor, and on the other hand, a water-rich fraction that can be used as the aqueous flow by liquid / liquid extraction or supply to a hydrothermal gasification apparatus. g) A step that enables the purification of the organic phase in the second distillation column and the recovery of the purified alkyl acrylate, h) A process of bleeding the bottom of the purification column (second distillation column) and supplying a portion of the bled-off material to a hydrothermal gasification unit. The method according to claim 1, including the method described in claim 1.

8. The method according to claim 7, wherein the temperature of the hydrolysis apparatus fluctuates between 80°C and 200°C.

9. The method according to claim 7 or 8, wherein the water / addition substance ratio in the hydrolysis apparatus varies between 0.1 and 1.3, including a boundary.

10. The method according to any one of claims 1 to 9, wherein the concentration of residue / water + residue in the hydrothermal gasification supply is between 10 g / l and 400 g / l.

11. The method according to any one of claims 1 to 10, wherein the sidestream extraction flow is sent to the inlet of the hydrothermal gasification.

12. The method according to any one of claims 1 to 11, wherein a portion of the material bled off from the bottom of the second distillation column is sent to the inlet of the hydrothermal gasification.

13. The method according to any one of claims 1 to 12, wherein the material bleed off from the bottom of the liquid / liquid extraction column is sent to the inlet of the hydrothermal gasification.

14. The method according to any one of claims 1 to 13, wherein the gasification generates a gas consisting of a volume ratio of 40-70% methane, 5-20% hydrogen, and 20-40% carbon dioxide.

15. The method according to any one of claims 1 to 13, wherein the water at the outlet of the gasification device is free of organic compounds and is recycled to supply the salt separator, or to supply the hydrolysis device, or to the inlet of the liquid / liquid extraction unit.

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