Process for purifying light 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. The invention more particularly relates to a process for the recovery / purification of C1-C2 alkyl acrylate, comprising a step of thermal cracking of the ester adducts alone or in combination with the heavy products of an acrylic acid production facility, and a step of hydrothermal gasification of the bottom products of this cracker and of the wastewater from this process.

Description

[0001] Title: PROCESS FOR PURIFYING LIGHT 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 a step of thermal cracking of the ester adducts alone or in combination with the heavy products from an acrylic acid manufacturing workshop and a step of hydrothermal gasification of the bottom of this cracker and the waste water from this process.

[0005] PRIOR ART AND TECHNICAL PROBLEM

[0006] It is known to produce (meth)acrylic esters by carrying out an esterification reaction between an alcohol and a (meth)acrylic acid, in particular methyl acrylate or methacrylate and ethyl acrylate or methacrylate. This reaction is a balanced catalyzed reaction with generation of water. It is also accompanied by side reactions producing impurities, in particular heavy compounds, i.e. having a high boiling point, higher than that of the desired ester.

[0007] In such processes, for environmental and economic reasons, it is essential to recycle unconverted reagents to the reaction but also to recover the heavy products generated during the process, while seeking a high-purity finished product.

[0008] To this end, a set of distillations and / or extractions and decantations are generally carried out, which is relatively complex to implement, particularly due to the presence of azeotropic mixtures, which are costly in terms of energy and which have the disadvantage of generating a final residue that cannot be recovered and which may present a loss of raw materials.

[0009] The problems that arise during 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 on the one hand and methacrylic acid on the other hand in the esterification reaction. The operating conditions in temperature and pressure for the distillation train, and particularly for the azeotropic distillation column, are not critical in this process, and can be determined in accordance with distillation methods known from the state of the art.However, preferably, the azeotropic distillation column is operated at a pressure below atmospheric pressure, thus avoiding the polymerization of the unsaturated products present, minimizing the formation of heavy by-products. These compounds are heavy products that reduce the recovery efficiency by consuming the acrylic acid monomer.

[0010] It is essentially:

[0011] - addition derivatives of acrylic acid on the double bond of another acrylic acid molecule: 3-acryloxypropionic acid also called "dimeric acrylic acid" or "AA dimer";

[0012] - of acrylic acid addition derivatives on the double bond on an AA dimer molecule, to form the "AA trimer" and other oligomers formed by successive additions of acrylic acid on the double bonds of the preceding AA oligomers, and

[0013] - carboxylic acid addition derivatives formed as by-products of acrylic acid or water on the double bond of AA or the oligomers mentioned above.

[0014] As another side reaction, Michael addition can produce Michael adducts, particularly methyl methoxypropionate formed between methyl acrylate and methanol.

[0015] Methyl methoxy propionate (MPM) has a vapor pressure close to that of acrylic acid. Its boiling point is close to that of acrylic acid (144°C, atmospheric pressure). It will therefore concentrate like other heavy by-products in the recycling loop for unreacted acrylic acid. It can also interfere with the final purification of methyl acrylate and alter the quality of the finished product because it is the lightest of the by-products.

[0016] Like radical polymerization, this covalent reaction of formation of Michael derivatives is strongly favored by temperature. Consequently, the installation of columns with a high number of rectification plates to meet the quality requirements of the final ester leads to disadvantages in terms of product loss, which can only be compensated by an additional high-temperature cracking treatment of the Michael derivatives to regenerate the monomers or by a specific purge of methyl methoxy propionate which cracks only with great difficulty under the usual conditions of operation of a cracker. In order to limit the formation of methyl methoxy propionate, it has been proposed in document US 6,025,520, to carry out the esterification reaction under reduced pressure with an excess of acid.These conditions improve the yield and selectivity of the esterification reaction and significantly reduce the formation of heavy by-products such as methyl methoxy propionate, which is problematic for the purification train of the desired ester. The treatment of the acrylic acid recirculation loop is simply mentioned.

[0017] The process described in WO 2015 / 063388 makes it possible to significantly reduce the formation of alkyl alkoxy propionate during the synthesis of ethyl (meth)acrylate by carrying out the esterification reaction in a conventional fixed-bed reactor under atmospheric pressure and under conditions where the acid is in excess relative to the alcohol and where the hourly volumetric velocities are high. To recover the adducts, a partial treatment of the recirculation loop is carried out by first implementing a distillation column or an evaporator which first makes it possible to reconcentrate the heavy by-products at the bottom of the column and then to send them to a thermal or thermal and catalytic cracker to essentially release the acrylic acid and the little transformed ethyl ethoxy propionate to the reactor and a heavy residue intended for incineration. The fate of the purges from the columns of the separation train is not addressed.

[0018] In its patent FR3083233, the applicant company has shown that it is possible to partially remove methyl methoxy propionate by side draw-off during the azeotropic distillation of the reaction mixture carried out in a single distillation column equipped with a side draw-off. 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. The heavy by-products of the recirculation loop are treated by thermal or thermal and catalytic cracking. The fate of the purges from the columns of the separation train as well as the cracker residue is not addressed.

[0019] Document EP2334633 also explains that a stream of heavy by-products from an acrylic acid plant can be recycled to an ester plant such as butyl acrylate, especially if the latter is equipped with a cracker to regenerate acrylic acid from the dimer of this acid.

[0020] In the case where there is a production of light esters (methyl acrylate (MA) or ethyl acrylate (EA)) close to the acrylic acid (AA) production unit, co-cracking of the respective heavy products improves the monomer recovery performance. Thus, in document EP 717 031, it has been shown that it is possible to improve the efficiency of the recovery of these valuable noble products, if the cracking is carried out from a mixture of heavy products coming from an AA production unit and an acrylic ester (EA) production unit, compared to the individual cracking of the heavy streams from these units. The effect of the addition of heavy products coming from the ester units (LEA) to the heavy products coming from an AA unit (LAA) is to decrease the viscosity of the final residue.The cracking reaction is carried out using mixtures with a ratio of heavy AA / heavy ester of 9 / 1 to 1 / 9, at a temperature of 180 to 220°C, under atmospheric pressure, for a residence time of 0.5 to 3 hours. The installation to carry out the process must therefore be equipped with a reactor and a condenser at the top, operated at the same pressure, and a distillation column operated at reduced pressure, fed by the condensed product, and comprising a boiler at the bottom, and at the top a condenser, reflux equipment and an inhibitor feed. This device is complicated and expensive.

[0021] Patent ER3110571, by combining partial condensation with the cracking reactor, makes it possible to increase the cracking yield without any significant effect on the viscosity of the residue.

[0022] Application ER 2206330 applied to acrylic acid heavy products alone makes it possible to improve the regeneration efficiency in a continuous process, without a significant increase in the dynamic viscosity close to 1 Pa.s, by implementing a hydrolysis of the heavy by-products with a water: acrylic acid heavy product mass ratio ranging from 0.1 to 1.3 before implementing thermal cracking at a pressure higher than atmospheric pressure in order to maintain the liquid mixture. This improvement is however not described in the case of a mixture of heavy ester and heavy acrylic acid.

[0023] More generally, the vaporization of light compounds during cracking leads to a concentration of heavy products in the residue stream, and an increase in the viscosity of this stream. The residue must remain sufficiently fluid after cooling to be transported and then treated for destruction while allowing maximum recovery of noble products.

[0024] In the case of treatment of heavy acrylic acid (LAA) alone, it has also been considered to add a solvent to the residue.

[0025] However, these solutions have several disadvantages, such as the generation of waste to be burned, the provision of additional equipment for the production of the mixture or the energy consumption if we assume that water is chosen as the solvent to be vaporized. In addition, most of these solvents generate nitrogen or sulfur derivatives during burning. None of these solutions recover the wastewater from the process, which is intended for the biological station. On the other hand, it is desirable to be able to recover the final residue from the manufacture of (meth)acrylic acid into exportable methane gas, instead of transforming it into CO2 by combustion.

[0026] The oxidation of organic matter (incineration) to carbon dioxide and water is often used to treat organic residues and produce heating steam. In the conventional process, rapid oxidation of organic fuels is used to produce heat, which is then transferred in a heat exchanger to a fluid such as water. A heat loss of 10-15% is expected due to the losses necessarily occurring in the exhaust stack of conventional boilers. In addition to possible blockage due to solids feeding the boiler, hot spots due to salt deposits on the boiler tubes, or ash deposits on the tube faces exposed to the flame or hot gases, reduce good heat transmission and therefore the heat transfer efficiency, or even cause very costly time losses due to rupture of the tube walls.

[0027] Consequently, there is a need to eliminate heavy by-products and to recover the ultimate residues from the manufacture of light alkyl acrylates (C1-C2).

[0028] One of the objectives of the present invention is therefore to provide an improved process for the recovery / purification of C1-C2 alkyl acrylate, making it possible to optimize the recovery of the various resulting residues.

[0029] SUMMARY OF THE INVENTION

[0030] The present invention relates to 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 carried out in the presence of polymerization inhibitor(s), said process comprising at least the following steps: azeotropic distillation of said reaction mixture using a first distillation column, leading to the separation of: o at the top, a stream comprising alkyl acrylate, unreacted alcohol and water; o at the bottom, a fraction comprising unreacted acrylic acid and heavy products, and o in side draw-off, an aqueous fraction rich in alkyl alkoxypropionate by-products; treatment of the top stream of the first distillation column by liquid / liquid extraction generating an aqueous phase containing essentially alcohol, and an organic phase rich in alkyl acrylate;the treatment of said organic phase rich in alkyl acrylate in a second distillation column to separate: o at the top, the purified alkyl acrylate, o at the bottom, the heavy products and the polymerization inhibitors, the treatment by distillation of said aqueous phase in a third distillation column to separate: o at the top, alcohol, which will be recycled in the esterification reaction, and o at the bottom, an aqueous stream depleted in alcohol; the treatment of the bottom stream of the first distillation column using a fourth distillation column and / or a film evaporator, which separates: o at the top, a stream comprising the residual acrylic acid and lighter products, and o at the bottom, a stream consisting of heavy products;subjecting said bottom flow of the fourth distillation column to thermal cracking making it possible to obtain noble products such as alkyl acrylate, and an ultimate residue, characterized in that said process comprises a hydrothermal gasification step upgrading the ultimate residue of the cracking to methane and hydrogen, as well as the aqueous effluents comprising said fraction withdrawn laterally from the first distillation column, the bottom flow of the third distillation column, and partially the bottom flow of the second column.;

[0031] In one embodiment, the alcohol is methanol, the alkyl acrylate is methyl acrylate, and the alkyl alkoxy propionate is methyl methoxy propionate (MPM).

[0032] In one embodiment, the alcohol is ethanol, the alkyl acrylate is ethyl acrylate, and the alkyl alkoxy propionate is ethyl ethoxy propionate (EPE).

[0033] According to one embodiment, the acid is methacrylic acid.

[0034] According to one embodiment, the heavy AAs produced in an Acrylic Acid unit are essentially: - addition derivatives of acrylic acid on the double bond of another acrylic acid molecule: 3-acryloxypropionic acid also called "dimeric acrylic acid" or "AA dimer";

[0035] - of acrylic acid addition derivatives on the double bond on an AA dimer molecule, to form the "AA trimer" and other oligomers formed by successive additions of acrylic acid on the double bonds of the preceding AA oligomers,

[0036] - carboxylic acid addition derivatives formed as by-products of acrylic acid or water on the double bond of AA or the oligomers mentioned above.

[0037] The contents indicated are expressed by weight, unless otherwise indicated. The limits are included in the ranges of values ​​indicated.

[0038] According to one embodiment, the final purification to obtain commercial grade methyl acrylate can be carried out by using two columns but also a DWC partition column.

[0039] According to one embodiment, only the heavy methyl acrylate feeds the cracker.

[0040] According to one embodiment, only the heavy ethyl acrylate feeds the cracker.

[0041] According to one embodiment, the acrylic acid heavyweights are mixed as such with the ester heavyweights.

[0042] According to one embodiment, the acrylic acid heavy products are hydrolyzed beforehand in a hydrolysis reactor (hydrolyzer), before being mixed with the ester heavy products.

[0043] According to one embodiment, the ester and acrylic acid heavy metals are hydrolyzed beforehand in a hydrolysis reactor (hydrolyzer), before entering the cracker.

[0044] According to one embodiment, the pressure in the hydrolyser varies between 0.1 and 2 MPa, preferably between 0.5 and 1.5 MPa.

[0045] According to one embodiment, the water / adduct mass ratio in the hydrolyser varies from 0.1 to 1.3 inclusive.

[0046] According to one embodiment, the temperature in the hydrolyser varies between 80 and 200°C, preferably between 150 and 200°C.

[0047] According to one embodiment, the method according to the invention is a method for manufacturing high-purity technical (meth)acrylic ester, namely having a purity greater than 99.5%, or even greater than 99.8% by weight. According to one embodiment, the reaction mixture is obtained from the esterification of acrylic acid with a stoichiometric excess of alcohol.

[0048] 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.

[0049] According to one embodiment, the thermal cracking reaction takes place in the absence of a catalyst.

[0050] According to one embodiment, the cracking temperature is between 140 and 260°C, preferably between 160 and 210°C.

[0051] According to one embodiment, the thermal cracking is carried out on (heavy) ester adducts.

[0052] According to one embodiment, the thermal cracking is carried out on a mixture of (heavy) acrylic acid adducts and esters.

[0053] According to one embodiment, the residence time of the reaction mixture in the cracking reactor is between 0.5 h and 10 h, preferably between 4 h and 10 h.

[0054] According to one embodiment, the thermal cracking reaction takes place at atmospheric pressure or under slight pressure (maximum 0.2 MPa).

[0055] According to one embodiment, the product at the top of the cracker is recycled to the esterification reaction.

[0056] According to one embodiment, the cracker overhead product is partially mixed with the bottom flow of the azeotropic column.

[0057] According to one embodiment, the reactor bottom flow (residue) obtained at the end of the thermal cracking operation has a dynamic viscosity of less than 1 Pa.s, preferably less than 10 Pa.s, measured at a temperature of 100°C, for example using a Brookfield "CAP 1000+" cone-plate type viscometer.

[0058] According to one embodiment, said hydrothermal gasification equipment comprises a first reactor, a second reactor and a gas-liquid separator.

[0059] According to one embodiment, the residue is injected as is into the gasification and the water necessary for the hydrothermal treatment is injected elsewhere.

[0060] According to one embodiment, the residue is mixed with the water necessary for the hydrothermal treatment before introduction into the gasification.

[0061] Depending on the method, hydrothermal gasification is carried out at a temperature of 350-450°C and a pressure of 25 MPa.

[0062] According to the embodiment, the hydrothermal gasification comprises a gasifier for separating the salt at the bottom, and a gas and liquid mixture at the top. According to one embodiment, the hydrothermal gasification comprises a separator for separating the salt under critical conditions, a gasifier and a gas-liquid separator.

[0063] According to one embodiment, the hydrothermal gasification comprises a salt separator, a gasifier comprising a catalyst, and a gas-liquid separator.

[0064] According to one embodiment, the concentration of residue / water + residue, in the feed of the hydrothermal gasification, is between 10g / l and 400g / l.

[0065] According to one embodiment, the water used to carry out the hydrothermal gasification may be demineralized water, water from drilling, or weakly mineralized water.

[0066] According to one embodiment, the water used to carry out the hydrothermal gasification is taken in part from the bottom of the alcohol recovery column (the third distillation column).

[0067] According to one embodiment, the product obtained from the side draw-off of the azeotropic column is mixed with the acrylic acid heavyweights before hydrolysis.

[0068] According to one embodiment, the product obtained from the side withdrawal of the azeotropic column is sent directly to hydrothermal gasification.

[0069] According to one embodiment, the purge at the bottom of the methyl acrylate purification column (the second distillation column) is partially sent directly to the hydrothermal gasification.

[0070] According to one embodiment, the water leaving the gasifier, free of organic compounds, can be advantageously recycled to the separator feed, to the hydrolyser feed or to the liquid / liquid extraction column.

[0071] According to one embodiment, the salts obtained and separated can be used as fertilizers.

[0072] According to one embodiment, a proportion of 94% to 99% of the carbon introduced into the gasification is recovered in the form of gas.

[0073] According to one embodiment, the gas resulting from gasification is composed of 40-70% methane, 5-20% hydrogen and 20-40% carbon dioxide.

[0074] In one embodiment, the gases may be further fractionated to isolate methane from other compounds.

[0075] According to one embodiment, the process according to the invention comprises the following steps: a) Carrying out the reaction using a fixed-bed esterification reactor containing ion exchange resins fed with alcohol, acrylic acid, via the recirculation loops of acrylic acid and unreacted alcohol. b) 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, at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, and in side draw-off a fraction rich in alkyl alkoxy propionate by-product sent to the purification train or to the hydrolyser.c) Separation of the bottom stream of the first distillation column into a stream comprising essentially unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream comprising essentially heavy ester by-products sent to a fourth distillation column to concentrate the heavy esters at the bottom of the latter and return the light ones to the reaction section. d) Thermal cracking of these heavy ester products alone or with acrylic acid heavy products which may or may not have been previously hydrolyzed, carried out in a cracking reactor, releasing a stream of recoverable products which may be recycled. e) Hydrothermal gasification of the cracker residue mixed with water.f) Liquid / liquid extraction of the top 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 esterification reactor and, on the other hand, a water-rich fraction which can be used as an aqueous stream in the liquid / liquid extraction step or as feed to the hydrothermal gasifier. g) Purification of said organic phase in the second distillation column making it possible to recover the purified alkyl acrylate. h) A purge of the bottom of the purification column (second distillation column) partially feeding the hydrothermal gasifier.

[0076] The invention makes it possible to reduce the losses of recoverable products caused by the purges imposed by the accumulation of alkyl alkoxy propionate in the purification train, by the formation of heavy by-products in the bottom of the azeotropic column, to treat the organics of the process water by regenerating monomers by cracking on the one hand and by recovering them in the form of methane and hydrogen on the other hand.

[0077] Thus, the invention provides a simplified process for producing high-purity methyl or ethyl acrylate (i.e. having a purity greater than 99.5%, or even greater than 99.8% by mass), and optimizes the material balance of the process. BRIEF DESCRIPTION OF THE FIGURES

[0078] Figure 1 schematically represents a plant for producing methyl acrylate including the recycling of the different products in the process and the association of the cracker with hydrothermal gasification.

[0079] Figure 2 schematically represents a plant for producing methyl acrylate in which acrylic acid heavys from a neighboring acrylic acid manufacturing unit are recycled, including the recycling of the different products in the process and the association of the cracker with hydrothermal gasification.

[0080] Figure 3 schematically represents a plant for producing methyl acrylate in which previously hydrolyzed acrylic acid heavy products from a neighboring acrylic acid manufacturing unit are recycled, including the recycling of the various products in the process and the association of the cracker with hydrothermal gasification.

[0081] DETAILED DESCRIPTION OF THE INVENTION

[0082] The invention is now described in more detail and in a non-limiting manner in the following description.

[0083] 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 or methacrylic acid 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 for the final purification).

[0084] A methyl acrylate production facility is shown in Figure 1.

[0085] The reaction section comprises an esterification reactor R. The reactor R is fed by an acrylic acid feed line 1, a methanol feed line 2. The reactor preferably contains a heterogeneous catalyst of the acid cation exchange resin type. In the case of homogeneous catalysis, the reactor is further fed by a catalyst feed line (not shown). The esterification reaction can be carried out in excess methanol or in 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.

[0086] At the outlet of reactor R, the reaction mixture 3 is sent to an azeotropic distillation unit C8 (first distillation column). 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.

[0087] Stream 19 comprises a significant fraction of the MPM formed as a by-product during esterification. Stream 19, rich in MPM (30-35%), water (40%), and 25% methyl acrylate, acrylic acid, and methanol, directly feeds the hydrothermal gasification.

[0088] Alternatively, stream 19 may be subjected to purification prior to gasification in order to recover concentrated methyl methoxy propionate, and recoverable compounds such as methyl acrylate, methanol and acrylic acid on the other hand.

[0089] The overhead stream 11 from the azeotropic distillation unit is sent to a liquid / liquid L / L extraction section (decanter or contactor) which generates, on the one hand, an aqueous phase 17 containing essentially methanol and on the other hand, an organic phase 12 rich in methyl acrylate. The stream 11 consists 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.

[0090] The aqueous phase 17 is subjected to distillation on a distillation column C5 (third distillation column) to separate the methanol which is recycled into the reactor (stream 5), the aqueous stream 18 depleted in methanol being able to be recycled in part for the liquid / liquid extraction phase or sent stream 22 to hydrothermal gasification.

[0091] The organic phase 12 is subjected to a purification train comprising at least one partition column C9 (second distillation column) in order to recover the methyl acrylate 15 with the purity necessary for its subsequent use. Generally, a mass purity greater than 99.5%, or even greater than 99.8%, is sought.

[0092] Stream 16 is partially purged and can also feed the hydrothermal gasifier.

[0093] The first 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).

[0094] Stream 6 is sent in whole or in part to a fourth distillation column and / or a film evaporator C2 which separates at the top a stream 7 comprising the residual acrylic acid and the lighter products, and at the bottom a stream 8 consisting essentially of the heavy products. Stream 7 is advantageously recycled into reactor R.

[0095] Stream 8 can be subjected to thermal cracking Ci l allowing the recycling of noble products 20 (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 ultimate residue 21 from this cracker is sent to the gasifier G12 as well as stream 19, the bottom stream 22 of the alcohol distillation column (the third distillation column) (99.9% water, 0.1% methanol), a possible water make-up 23 and the recycling of all or part of the water leaving the gasification.

[0096] Hydrothermal gasification is carried out in a temperature range of 350-450°C and a pressure of 25 MPa. The concentration of residue (21+16) / water + residue in the salt separator is between 10g / l and 400 g / l. The gas from gasification 24 is composed of 40-70% methane, 5-20% hydrogen and 20-40% carbon dioxide (volume percentages). The obtained and separated salts 24 can be used as fertilizers.

[0097] When an acrylic acid production facility is located near the methyl ester synthesis unit Figure 2, the heavy by-products from this production can be recovered in a stream 26 which can be introduced at the same time as stream 8 into the cracker.

[0098] Finally, as shown in Figure 3, if the acrylic acid workshop includes a HYD hydrolyser as described in document FR2206330, then the acrylic acid heavys 27 can feed column C2, while streams 19 and 22 can be used upstream of this hydrolyser.

[0099] The following examples illustrate the present invention and are not intended to limit the scope of the invention as defined by the appended claims.

[0100] EXPERIMENTAL PART

[0101] In the examples, percentages are given by weight unless otherwise stated and the following abbreviations have been used:

[0102] PTZ: Phenothiazine

[0103] AA: Acrylic acid

[0104] MA: Maleic Acid

[0105] H20: Water Di AA: Dimer of acrylic acid

[0106] AA3: Trimer of acrylic acid

[0107] Heavy: Oligomers with a mass greater than AA3

[0108] HQ: Hydroquinone

[0109] ACOH: Acetic Acid

[0110] LAA: heavy acrylic acid

[0111] AM: Methyl Acrylate

[0112] MeOH: Methanol

[0113] LAM: Heavy Methyl Acrylate MPM: Methyl Methoxypropionate

[0114] Thermal cracking of heavy acrylic acids with or without prior hydrolysis

[0115] This example corresponds to examples 1 and 2 of application FR 2206330 and presents the advantage of treating heavy AA before cracking by implementing a preliminary hydrolysis according to the process of the invention. The results obtained are indicated in Table 1.

[0116] [Table 1]

[0117] Cracking of heavy methyl acrylates alone in the laboratory

[0118] The setup consists of a glass thermosiphon boiler with a useful capacity of 100 ml. The LAMs are continuously fed at room temperature into the boiler from a container via a diaphragm pump. The feed rate is regulated and measured continuously. The boiler is heated using 3 heating bands with a power of 160 W each. Temperature measurements are made in the leg of the thermosiphon and at the head of this device.

[0119] The operating conditions are as follows: feed rate: 14.3 g / h; head rate: 8.45 g / h; T°: 175°C; Residence time: 6.9 h.

[0120] The results obtained are shown in Table 2.

[0121] [Table 2]

[0122] It is noted that MPM is not highly valued. The two valuable species generated by cracking (AA) and (AM) represent approximately 32.6% of the top product. The viscosity of the bottom product measured at 100°C is 15.3 cP.

[0123] Cracking a mixture of heavy LAM and LAA to the pilot

[0124] In the example below, column C2 (see Figure 2) is a 180 mm diameter column equipped with 24 bell trays and a 0.1 m horizontal film evaporator 2as a boiler. It operates under a reduced pressure of 140mmHg and is stabilized by a solution (AA+2%HQ) of 1940g / h with a fixed reflux rate of 1. This column is fed to plate 14 by stream 6 from column C8 as well as overhead stream 20 from cracker Cl 1. The overhead stream 7 from C2 is returned largely to reactor R while the bottom of C2 after a 13% purge feeds cracker Ci l with a volume of 121. This includes a forced recirculation loop with a 5m3 / h centrifugal pump and an electric exchanger with a power of 5 kW.

[0125] The top product 20 of the cracker is sent to C2 while the heavy products 21 at the bottom are collected.

[0126] Table 3 shows the results of the operation.

[0127] [Table 3]

[0128] Hydrothermal gasification

[0129] Hydrothermal gasification will be illustrated by a very similar case of Michael adducts, namely those of heavy butyl acrylate adducts. The mixture of heavy ABU is composed of:

[0130] - Butanol < 0.1%

[0131] - Butyl acrylate (5-10%)

[0132] - Butyl hydroxypropionate (HPB): 1-3%

[0133] - Butyl butoxypropionate (BPB) 70-80%

[0134] - Butyl acryloxypropionate (AA / ABU) 4-6%

[0135] - Dibutylmaleate: 2-5%

[0136] - Phenothiazine: 1-3%.

[0137] A 33g / h ratio of heavy ABU and 970g / h of water are introduced through two different pipes into a separator and a catalytic reactor both operating at 400°C and 25 MPa. After 6 hours of testing under stabilized conditions, the heavy ABU are transformed into a gaseous mixture having the following volume composition: 51% CH4; 34% CO2 and 19% H2. The energy content of this gas corresponds to 7096 kWh / Tonne ABU. The TOC (total organic carbon) content is < 1mg / l.

Claims

CLAIMS 1. 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 carried out in the presence of polymerization inhibitor(s), said process comprising at least the following steps: azeotropic distillation of said reaction mixture using a first distillation column, leading to the separation of: o at the top, a stream comprising alkyl acrylate, unreacted alcohol and water; o at the bottom, a fraction comprising unreacted acrylic acid and heavy products, and o in side draw-off, an aqueous fraction rich in alkyl alkoxypropionate by-products; treatment of the top stream of the first distillation column by liquid / liquid extraction generating an aqueous phase containing essentially alcohol, and an organic phase rich in alkyl acrylate;the treatment of said organic phase rich in alkyl acrylate in a second distillation column to separate: o at the top, the purified alkyl acrylate, o at the bottom, the heavy products and the polymerization inhibitors, the treatment by distillation of said aqueous phase in a third distillation column to separate: o at the top, alcohol, which will be recycled in the esterification reaction, and o at the bottom, an aqueous stream depleted in alcohol; the treatment of the bottom stream of the first distillation column using a fourth distillation column and / or a film evaporator, which separates: o at the top, a stream comprising the residual acrylic acid and lighter products, and o at the bottom, a stream consisting of heavy products; subjecting said bottom stream of the fourth distillation column to thermal cracking making it possible to obtain noble products such as alkyl acrylate, and an ultimate residue; characterized in that said process comprises a hydrothermal gasification step recovering methane and hydrogen from the ultimate residue of the cracking, as well as the aqueous effluents comprising said fraction withdrawn laterally from the first distillation column, the bottom flow from the third distillation column, and partially the bottom flow from the second column.

2. The method of claim 1, wherein the thermal cracking is carried out on acrylic ester adducts.

3. A process according to claim 1, wherein the thermal cracking is carried out on acrylic ester adducts previously treated in a hydrolyzer.

4. The method of claim 1, wherein the thermal cracking is carried out on a mixture of acrylic acid adducts and acrylic esters.

5. Process according to claim 1, in which the thermal cracking is carried out on acrylic acid adducts previously treated in a hydrolyzer.

6. Process according to claim 1, in which the thermal cracking is carried out on adducts of acrylic acid and acrylic esters previously treated in a hydrolyzer.

7. Process according to any one of claims 1 to 6, comprising the following steps: a) Carrying out the reaction using a fixed-bed esterification reactor containing ion exchange resins fed with alcohol, acrylic acid, via the recirculation loops of acrylic acid and unreacted alcohol. b) 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, at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, and in side draw-off a fraction rich in alkyl alkoxy propionate by-product sent to the purification train or to the hydrolyser. c) Separation of the bottom stream of the first distillation column into a stream comprising essentially unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream comprising essentially heavy ester by-products sent to a fourth distillation column to concentrate the heavy esters at the bottom of the latter and return the light ones to the reaction section. d) Thermal cracking of these heavy ester products alone or with acrylic acid heavy products which may or may not have been previously hydrolyzed, carried out in a cracking reactor, releasing a stream of recoverable products which may be recycled. e) Hydrothermal gasification of the cracker residue mixed with water.f) Liquid / liquid extraction of the top 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 esterification reactor and, on the other hand, a water-rich fraction which can be used as an aqueous stream in the liquid / liquid extraction step or as feed to the hydrothermal gasifier. g) Purification of said organic phase in the second distillation column making it possible to recover the purified alkyl acrylate. h) A purge of the bottom of the purification column (second distillation column) partially feeding the hydrothermal gasifier.

8. Method according to claim 7, in which the temperature of the hydrolyser varies between 80 and 200°C.

9. Method according to one of claims 7 and 8, in which the water / adduct mass ratio in the hydrolyser varies from 0.1 to 1.3 limits inclusive.

10. Process according to claim 1 to 9, wherein the residue / water + residue concentration in the hydrothermal gasification feed is between 10g / l and 400g / l.

11. Method according to one of claims 1 to 10, in which the side draw-off stream is sent to the inlet of the hydrothermal gasification.

12. Method according to one of claims 1 to 11, in which the purge from the bottom of the second distillation column is partially sent to the inlet of the hydrothermal gasification.

13. Method according to one of claims 1 to 12, in which the purge from the bottom of the liquid / liquid extraction column is sent to the inlet of the hydrothermal gasification.

14. Method according to one of claims 1 to 13, in which the gasification generates a gas composed in volume ratio of 40 to 70% methane, 5-20% hydrogen and 20-40% carbon dioxide.

15. Method according to one of claims 1 to 13, in which the water leaving the gasifier, free of organic compounds, is recycled to the salt separator feed or to the hydrolyser feed or to the inlet of the liquid / liquid extraction section.

Images