PROCEDE DE PURIFICATION D’ACRYLATES LEGERS

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. More particularly, the invention relates to a process for recovering / purifying C1-C2 alkyl acrylate, comprising a step of thermal cracking of the ester adducts alone or in combination with heavy materials from an acrylic acid manufacturing plant, and a step of hydrothermal gasification of the cracker footing and the wastewater from this process.

Description

Title of the invention: METHOD FOR PURIFYING LIGHT ACRYLATES technical field

[0001] 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.

[0002] The invention relates more particularly to a process for recovering / purifying alkyl acrylate in Ci-C2 comprising a step of thermal cracking of ester adducts alone or in combination with heavy materials from an acrylic acid manufacturing plant and a step of hydrothermal gasification of the foot of this cracker and of the wastewater from this process. PREVIOUS ART AND TECHNICAL PROBLEM

[0003] 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 catalyzed, equilibrium reaction with the generation of water. It is also accompanied by secondary reactions producing impurities, in particular heavy compounds, i.e., compounds with a high boiling point, higher than that of the desired ester.

[0004] In such processes, for environmental and economic reasons, it is essential to recycle the unconverted reactants in the reaction but also to valorize the heavy products generated during the process, while seeking a finished product of high purity.

[0005] To this end, a series of distillations and / or extractions, decantations are generally carried out, which is both relatively complex to implement, in particular due to the presence of azeotropic mixtures, costly in terms of energy and which has the disadvantage of generating a final non-valuable residue which may present a loss of raw materials.

[0006] The problems that arise during the manufacture of light (meth)acrylic esters, in particular Ci-C2 alkyl acrylic esters, will now be explained, for convenience, using 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 in the esterification reaction.

[0007] The operating conditions in temperature and pressure for the train of dis The distillation parameters, particularly for the azeotropic distillation column, are not critical in this process and can be determined according to known state-of-the-art distillation methods. However, preferably, the azeotropic distillation column is operated at a pressure below atmospheric pressure, thus avoiding the polymerization of unsaturated products present and minimizing the formation of heavy byproducts. These compounds are heavy products that reduce the recovery yield by consuming the monomeric acrylic acid.

[0008] This essentially involves:

[0009] - of derivatives of the addition of acrylic acid to the double bond of another molecule acrylic acid: 3-acryloxypropionic acid also called "acrylic acid dimer" or "AA dimer";

[0010] - of derivatives of acrylic acid addition to the double bond on a molecule of AA dimer, to form the "AA trimer" and other oligomers formed by successive additions of acrylic acid to the double bonds of the preceding AA oligomers, and

[0011] - of carboxylic acid addition derivatives formed as by-products of the acid acrylic or water on the double bond of the AA or the oligomers mentioned above.

[0012] As another side reaction, a Michael addition can produce Michael adducts, in particular methyl methoxypropionate formed between methyl acrylate and methanol.

[0013] Methyl methoxy propionate (MPM) has a vapor pressure close to that of acrylic acid. Its boiling point is also close to that of acrylic acid (144°C, atmospheric pressure). Consequently, like other heavy by-products, it will concentrate in the unreacted acrylic acid recycling loop. It can also interfere with the final purification of methyl acrylate and impair the quality of the finished product because it is the lightest of the by-products.

[0014] Like radical polymerization, this covalent reaction for the formation of Michael derivatives is strongly favored by temperature. Consequently, the use of columns with a high number of rectification trays to meet the quality requirements of the final ester leads to drawbacks in terms of product loss, which can only be compensated for by additional high-temperature cracking treatment of the Michael derivatives to regenerate the monomers or by specific purging of the methyl methoxy propionate, which is very difficult to crack under normal cracker operating conditions.

[0015] In order to limit the formation of methyl methoxypropionate, it was proposed in US patent 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 methoxypropionate, which is problematic for the train purification of the desired ester. The treatment of the acrylic acid recirculation loop is simply mentioned.

[0016] The process described in document WO 2015 / 063388 significantly reduces the formation of alkyl alkoxypropionate during the synthesis of ethyl (meth)acrylate by carrying out the esterification reaction in a conventional fixed-bed reactor under atmospheric pressure and conditions where the acid is in excess relative to the alcohol and the hourly volumetric velocities are high. To recover value from the adducts, a partial treatment of the recirculation loop is performed by first using a distillation column or an evaporator, which initially reconcentrates the heavy by-products at the bottom of the column and then sends them to a thermal or thermal-catalytic cracker to release primarily acrylic acid and minimally transformed ethyl ethoxypropionate back into the reactor, along with a heavy residue destined for incineration. The fate of the purges from the separation train columns is not addressed.

[0017] In its patent FR3083233, the applicant company demonstrated 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 / EAU azeotrope but has no effect on the MPM present at the bottom of this azeotropic column in a stream consisting mainly 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 separation train columns and the cracker residue is not addressed.

[0018] Document EP2334633 also explains that a heavy by-product stream from an acrylic acid plant can be recycled to an ester plant such as a butyl acrylate plant, especially if the latter is equipped with a cracker that allows the acrylic acid to be regenerated from the dimer of this acid.

[0019] In the case where there is a production of light esters (methyl acrylate (AM) or ethyl acrylate (EA)) near the acrylic acid (AA) production unit, a co-cracking of the respective heavy ones improves the monomer recovery performance.

[0020] Thus, in document EP 717 031, it was shown that it is possible to improve the efficiency of recovering these valuable, high-quality products if cracking is carried out using a mixture of heavy materials from an AA production unit and an acrylic ester (AE) production unit, compared to cracking the heavy materials individually from these units. The effect of adding heavy materials from the ester units (AE) to the heavy materials from an AA unit (AE) 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 compounds with a 9:1 to 1:9 ratio are distilled at a temperature of 180 to 220°C, under atmospheric pressure, for a residence time of 0.5 to 3 hours. The installation for this 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 including a boiler at the bottom, and at the top a condenser, reflux equipment, and an inhibitor feed. This setup is complex and expensive.

[0021] Patent FR3110571, by associating partial condensation with the cracking reactor, makes it possible to increase the cracking yield without any noticeable effect on the viscosity of the residue.

[0022] French patent application FR 2206330, applied to heavy acrylic acids alone, improves regeneration efficiency in a continuous process without a significant increase in dynamic viscosity close to 1 Pa·s. This is achieved by hydrolyzing the heavy by-products with a water:heavy acrylic acid mass ratio ranging from 0.1 to 1.3 before thermal cracking at a pressure above atmospheric pressure to maintain the liquid mixture. However, this improvement is not described for a mixture of heavy esters and heavy acrylic acids.

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

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

[0025] However, these solutions have several disadvantages, such as the generation of waste to be burned, the need for additional equipment to prepare the mixture, and energy consumption if water is chosen as the solvent that must be vaporized. Furthermore, most of these solvents generate nitrogen or sulfur compounds during combustion.

[0026] None of these solutions utilizes the wastewater from the process, which is destined for the biological treatment plant. Furthermore, it is desirable to be able to recover the final residue from the (meth)acrylic acid production as exportable methane gas, instead of converting it into CO2 by combustion.

[0027] The oxidation of organic matter (incineration) into carbon dioxide and water is often used to treat organic waste and produce heating steam. In the conventional process, rapid oxidation of organic fuels is used to produce heat, which is then transferred to a heat exchanger. Heat is transferred to a fluid such as water. A heat loss of 10-15% is expected due to losses that inevitably occur in the exhaust column of conventional boilers. In addition to possible blockages caused by 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 efficient heat transfer and consequently the heat transfer efficiency, and can even lead to very costly downtime due to tube wall ruptures.

[0028] Consequently, there is a need to eliminate heavy by-products and to valorize the ultimate residues from the manufacture of light alkyl acrylates.

[0029] One of the objectives of the present invention is therefore to provide an improved process for the recovery / purification of alkyl acrylate in Ci-C2, allowing for the optimization of the valorization of the various resulting residues. Summary of the invention

[0030] The present invention relates to a process for recovering / purifying alkyl acrylate as Ci-C2 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 polymerization inhibitor(s), said process comprising the azeotropic distillation of said reaction mixture using a distillation column, and the purification of the alkyl acrylate using a separation assembly comprising at least one alkyl acrylate purification column, characterized in that it comprises a cracking treatment enabling the continuous transformation of heavy by-products into valuable monomers and a hydrothermal gasification valorizing the ultimate residues of the cracking as well as the aqueous effluents of the alcohol distillation column into methane and hydrogen.

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

[0032] According to 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 AA produced in an Acid unit Acrylics are essentially:

[0035] - of derivatives of the addition of acrylic acid to the double bond of another molecule acrylic acid: 3-acryloxypropionic acid also called "acrylic acid dimer" or "AA dimer";

[0036] - of derivatives of acrylic acid addition to the double bond on a molecule of AA dimer, to form the "AA trimer" and other oligomers formed by successive additions of acrylic acid to the double bonds of the preceding AA oligomers,

[0037] - of carboxylic acid addition derivatives formed as by-products of the acid acrylic or water on the double bond of the AA or the oligomers mentioned above.

[0038] According to one embodiment, the azeotropic column is equipped with a lateral draw-off

[0039] According to one embodiment, the final purification to obtain commercial grade methyl acrylate can be carried out by implementing two columns but also a DWC partition column.

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

[0041] According to one embodiment, only the heavy ethyl acrylate feeds the cracker.

[0042] According to one embodiment, the acrylic acid heavy compounds are mixed as such with the ester heavy compounds.

[0043] According to one embodiment, the acrylic acid heavys are hydrolyzed beforehand in a hydrolysis reactor (hydrolyzer), before being mixed with the ester heavys.

[0044] According to one embodiment, the ester heavy and the acrylic acid heavy are hydrolyzed beforehand in a hydrolysis reactor (hydrolyzer), before entering the cracker.

[0045] According to one embodiment, the pressure in the hydrolyzer varies between 0.1 and 2 MPa, preferably between 0.5 and 1.5 MPa.

[0046] According to one embodiment, the water / adduct mass ratio in the hydrolyzer varies from 0.1 to 1.3 inclusive.

[0047] According to one embodiment, the temperature in the hydrolyzer varies between 80 and 200°C, preferably between 150 and 200°C.

[0048] According to one embodiment, the process according to the invention is a process for manufacturing high-purity technical acrylic (meth) ester.

[0049] According to one embodiment, the reaction mixture is obtained from the esterification of acrylic acid with a stoichiometric excess of alcohol.

[0050] According to one embodiment, the reaction mixture is obtained from the esterification of acrylic acid with an alcohol under stoichiometric excess acid conditions.

[0051] According to one embodiment, the thermal cracking reaction takes place in the absence of a catalyst.

[0052] According to one embodiment, the cracking temperature is between 140 and 260°C, preferably between 160 and 210°C.

[0053] According to one embodiment, thermal cracking is carried out on adducts (heavy) with ester.

[0054] According to one embodiment, thermal cracking is carried out on a mixture of (heavy) acrylic acid and ester adducts.

[0055] According to one embodiment, the residence time of the reaction mixture in the cracking reactor is between 0.5h and 100, preferably between 4h and 100.

[0056] According to one embodiment, the thermal cracking reaction takes place at atmospheric pressure or under slight pressure (maximum 0.2 MPa).

[0057] According to one embodiment, the product at the top of the cracker is recycled to the esterification reaction.

[0058] According to one embodiment, the cracker head product is partially mixed with the flow from the foot of the azeotropic column.

[0059] According to one embodiment, the reactor bottom flux (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.

[0060] According to one embodiment, said hydrothermal gasification equipment comprises a first reactor, a second reactor and a gas-liquid separator.

[0061] According to one embodiment, the residue is injected as such into the gasification and the water required for the hydrothermal treatment is injected separately.

[0062] According to one embodiment, the residue is mixed with the water required for hydrothermal treatment before introduction into the gasification.

[0063] According to the embodiment, hydrothermal gasification is carried out at a temperature of 350-450°C and a pressure of 25 MPa.

[0064] According to the embodiment, hydrothermal gasification includes a gasifier allowing the salt to be separated at the bottom, and a gas and liquid mixture at the top.

[0065] According to one embodiment, hydrothermal gasification includes a separator for separating salt under critical conditions, a gasifier and a gas-liquid separator.

[0066] According to one embodiment, the hydrothermal gasification includes a salt separator, a gasifier comprising a catalyst, and a gas-liquid separator.

[0067] According to one embodiment, the concentration of residue / water + residue in the salt separator is between 10g / l and 400g / l.

[0068] According to one embodiment, the water used to carry out hydrothermal gasification can be demineralized water, well water, or low-mineralized water.

[0069] According to one embodiment, the water used to carry out the hydrothermal gasification is taken partly from the bottom of the alcohol recovery column.

[0070] According to one embodiment, the product obtained by lateral withdrawal from the column azeotropic is mixed with heavy acrylic acid before hydrolysis.

[0071] According to one embodiment, the product obtained by lateral withdrawal from the azeotropic column is sent directly to hydrothermal gasification.

[0072] According to one embodiment, the purge at the bottom of the methyl acrylate purification column is sent directly to hydrothermal gasification.

[0073] According to one embodiment, the purge from the foot of the purification column is sent before the hydrolyzer fed by the heavy acrylic acid.

[0074] According to one embodiment, the water exiting the gasifier, free of organic compounds, can advantageously be recycled to feed the separator, to feed the hydrolyzer or to the liquid / liquid extraction column.

[0075] According to one embodiment, the salts obtained and separated can be used as fertilizers.

[0076] According to one embodiment, a proportion of 94% to 99% of the carbon introduced into the gasification is recovered in the form of gas.

[0077] According to one embodiment, the gas from the gasification is composed of 40-70% methane, 5-20% hydrogen and 20-40% carbon dioxide.

[0078] According to one embodiment, the gases can be further fractionated to isolate the methane from the other compounds.

[0079] According to one embodiment, the process according to the invention comprises the following steps:

[0080] a) The implementation of the reaction using a fixed bed esterification reactor containing ion exchange resins fed with alcohol, acrylic acid, through recirculation loops of acrylic acid and unreacted alcohol.

[0081] b) The azeotropic distillation of the reaction mixture using a first distillation column allowing the separation at the top of an azeotropic mixture comprising alkyl acrylate, unreacted alcohol and water, at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, and by lateral withdrawal a fraction rich in alkyl alkoxy propionate by-product sent to the purification train or to the hydrolyzer.

[0082] c) Separating the bottom stream from the first distillation column into a stream consisting essentially of unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream consisting essentially of heavy ester by-products sent to a column allowing the heavy ones to be concentrated at the bottom of the column and the light ones sent back to the reaction section.

[0083] d) Thermal cracking of these ester heavys alone or with acrylic acid heavys, whether or not previously hydrolyzed, carried out in a cracking reactor, releasing a stream of valuable products which can be recycled.

[0084] e) Hydrothermal gasification of the cracker residue mixed with water.

[0085] f) Liquid / liquid extraction of the headstream of the first distillation column by an aqueous stream allowing separation of an organic phase comprising essentially 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.

[0086] g) The purification of said organic phase allowing the recovery of the purified alkyl acrylate.

[0087] h) A purge of the foot of the purification column feeding the hydrothermal gasifier.

[0088] The invention makes it possible to reduce the losses of valuable 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 foot of the azeotropic column, to treat the organics of the process water by regenerating monomers on the one hand by cracking and on the other hand by valorizing them in the form of methane and hydrogen.

[0089] Thus the invention provides a simplified process for the production of high-purity methyl or ethyl acrylate, and optimizes the material balance of the process. BRIEF DESCRIPTION OF THE FIGURES

[0090] Fig. 1 schematically represents an installation for producing methyl acrylate including the recycling of the various products in the process and the association of the cracker with hydrothermal gasification.

[0091] Figure 2 schematically represents an installation for producing methyl acrylate in which heavy acrylic acid from a nearby acrylic acid manufacturing unit is recycled, including the recycling of the various products in the process and the association of the cracker with hydro-thermal gasification.

[0092] Fig. 3 schematically represents an installation 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. DETAILED DESCRIPTION OF THE INVENTION

[0093] The invention is now described in more detail and in a non-limiting manner in the following description.

[0094] For simplicity, 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 implementation of ethanol or methacrylic acid in the esterification reaction, as well as to other configurations of the purification train (process with azeotropic distillation without lateral withdrawal, stemming column and rectification column for final purification).

[0095] A methyl acrylate production plant is shown in [Fig. 1].

[0096] The reaction section includes an esterification reactor R. Reactor R is fed by an acrylic acid supply line 1 and a methanol supply 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 also fed by a catalyst supply line (not shown). The esterification reaction can be carried out in excess of methanol or in excess of 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 concentration of 500 to 5000 ppm relative to the crude reaction mixture.

[0097] At the outlet of reactor R, the reaction mixture 3 is sent to an azeotropic distillation unit C8. The configuration of the distillation column C8 allows the separation, at the top, of a stream 11 consisting of an azeotropic mixture comprising the methyl acrylate formed, unreacted methanol and water generated by the reaction, as well as light and heavy impurities, at the bottom of a stream 6 consisting essentially of unreacted acrylic acid, traces of light products and heavy products, and a stream 19 drawn off laterally.

[0098] 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.

[0099] Alternatively, the stream 19 can be subjected to pre-gasification purification in order to recover concentrated methyl methoxy propionate, and valuable compounds such as methyl acrylate, methanol and acrylic acid on the other hand.

[0100] The head stream 11 of 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. The stream 11 consists of an azeotropic mixture comprising the methyl acrylate formed, unreacted methanol and water generated by the reaction, as well as light impurities and heavy impurities.

[0101] 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), the aqueous stream 18 depleted in methanol, which can be partially recycled for the liquid / liquid extraction phase or sent as stream 22 to hydrothermal gasification

[0102] The organic phase 12 is subjected to a purification train comprising at least one C9 partition column in order to recover the methyl acrylate 15 with the purity required for its subsequent use. Generally, a purity greater than 99.5%, or even greater than 99.8%, is sought.

[0103] The stream 16 is partially purged and can also supply the hydrothermal gasifier.

[0104] The distillation column C8 separates, at the bottom, a stream 6 consisting essentially of 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 (acrylic acid oligomers and Michael adducts).

[0105] The stream 6 is sent in whole or in part to a distillation column and / or a film evaporator C2 which separates a stream 7 comprising residual acrylic acid and lighter products, and a stream 8 consisting essentially of the heavier products. The stream 7 is advantageously recycled to reactor R.

[0106] The stream 8 can be subjected to thermal cracking C11, allowing the recycling of potentially recoverable valuable products 20 (starting compounds or finished product) 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 21 is sent to the gasifier G12, along with stream 19, the bottom stream 22 from the alcohol distillation column (99.9% water, 0.1% methanol), optional water 23, and the recycling of all or part of the water exiting the gasification process.

[0107] Hydrothermal gasification is carried out in a temperature range of 350-450°C and a pressure of 25 MPa. The residue concentration (21+16) / water + residue in the salt separator is between 10 g / l and 400 g / l. The gas from the gasification 24 is composed of 40-70% methane, 5-20% hydrogen, and 20-40% carbon dioxide. The salts 24 obtained and separated can be used as fertilizers.

[0108] When an acrylic acid production facility is located near the methyl ester synthesis unit [Fig.2], the heavy by-products from this production can be valorized in a stream 26 which can be introduced at the same time as stream 8 into the cracker.

[0109] Finally, as shown in [Fig. 3], if the acrylic acid plant includes a HYD hydrolyzer as described in document FR2206330, then the heavy acid acrylic 27 will be able to feed column C2, while the flows 19 and 22 upstream of this hydrolyzer can be utilized.

[0110] The following examples illustrate the present invention and are not intended to limit the scope of the invention as defined by the attached claims. [YES] EXPERIMENTAL SECTION

[0112] In the examples, percentages are given by weight unless otherwise indicated and the following abbreviations have been used:

[0113] PTZ: Phenothiazine

[0114] AA: Acrylic acid

[0115] MA: Maleic Acid

[0116] H2O: Water

[0117] Di AA: Acrylic acid dimer

[0118] AA3: Acrylic acid trimer

[0119] Heavy: Oligomers with a Mass Greater than AA3

[0120] HQ: Hydroquinone

[0121] ACOH: Acetic Acid

[0122] LAA: acrylic acid heavy

[0123] AM: Methyl Acrylate

[0124] MeOH: Methanol

[0125] LAM: heavy Methyl Acrylate

[0126] MPM: methyl methoxypropionate

[0127] Thermal cracking of acrylic acid heavy with or without prior hydrolysis

[0128] This example corresponds to examples 1 and 2 of French patent application FR 2206330 and has the advantage of treating AA heavys before cracking by implementing a preliminary hydrolysis according to the process of the invention. The results obtained are shown in Table 1.

[0129] [Tables 1] With hydrolysis Without hydrolysis Test No. 1 2 Hydrolysis - Temperature 150°C - Hydrolysis residence time 1h - Water / LAA ratio 0.5 - Cracking temperature 173°C 183°C Cracking residence time 100°C Useful Recovery Rate 68.95% 29.2% Overall Cracking Rate 94.85% 45.1% Residual viscosity Pa.s @ 100°C 0.785 1.034

[0130] Cracking of heavy methyl acrylate alone in the laboratory

[0131] The assembly consists of a glass thermosiphon boiler with a usable capacity of 100 ml. The LAMs are continuously fed into the boiler from a reservoir at room temperature via a diaphragm pump. The feed rate is regulated and continuously measured. The boiler is heated using three heating collars, each with a power rating of 160 W. Temperature measurements are taken at the base and the top of the thermosiphon.

[0132] The operating conditions are as follows: feed rate: 14.3 g / h; head flow rate: 8.45 g / h; T°: 175°C; residence time: 6.9 h.

[0133] The results obtained are shown in Table 2.

[0134] [Tables2] Composition Feed (%) Cracker Head (%) AA 15.7 57.9 AM 0.14 2.75 MeOH 0.07 0.12 MA 6.5 5.48 MPM 3.7 5.55 H2O 0.07 0.84 (AA)3 12.1 0.012 DiAA 12.3 1.9 Heavy 49.4 25.4

[0135] It is observed that the MPM is not highly valued. The two valuable species generated by cracking (AA) and (AM) represent approximately 32.6% of the head product. The viscosity of the foot measured at 100°C is 15.3 cP.

[0136] Cracking of a mixture of heavy LAM and LAA at the pilot

[0137] In the example below, column C2 (see [Fig. 2]) is a 180 mm diameter column equipped with 24 bell-shaped trays and a 0.1 m² horizontal film evaporator as a boiler. It operates at a reduced pressure of 140 mmHg and is stabilized by a (AA+2%HQ) solution of 1940 g / h with a fixed reflux ratio of 1. This column is fed at tray 14 by the flow 6 from column C8 as well as the overhead flow 20 from cracker Cl 1. The overhead flow 7 from C2 is largely returned to reactor R, while the bottom of C2, after a 13% purge, feeds cracker C1, which has a volume of 121. This cracker has a forced recirculation loop with a 5 m³ / h centrifugal pump and a 5 kW electric heat exchanger.

[0138] The head product 20 from the cracker is sent to C2 while the heavy 21 at the foot are collected.

[0139] Table 3 presents the results of the operation.

[0140] [Tables3] 6 (g) 8 (g) 7 (g) 20 (g) 21 (g) MeOH 55 0 112 24 AM 807 241 1103 108 4 H20 980 31 1126 14 MPM 255 604 33 394 41 AA 2991 1210 6840 3187 459 DiAA 2625 2607 124 174 632 AA3 1110 1104 416 Hydrothermal gasification

[0141] Hydrothermal gasification will be illustrated by a very similar case of Michael adducts, namely those of heavy butyl acrylate. The ABU heavy mixture is composed of:

[0142] - Butanol < 0.1%

[0143] - Butyl acrylate (5-10%)

[0144] - Butyl hydroxypropionate (HPB): 1-3%

[0145] - Butyl butoxypropionate (BPB) 70-80%

[0146] - Butyl acryloxypropionate (AA / ABU) 4-6%

[0147] - Dibutyl maleate: 2-5%

[0148] - Phenothiazine: 1-3%.

[0149] Heavy ABU and 970 g / h of water are introduced at a rate of 33 g / h through two separate 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 volumetric 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 < 1 mg / L.

Claims

Demands

1. A process for recovering / purifying alkyl acrylate as Ci-C2 from a reaction mixture obtained by esterifying acrylic acid with an alcohol selected from methanol and ethanol in the presence of polymerization inhibitor(s), said process comprising azeotropic distillation of said reaction mixture using a distillation column, and purification of the alkyl acrylate using a separation assembly comprising at least one alkyl acrylate purification column, characterized in that it comprises a cracking treatment enabling the continuous transformation of heavy by-products into valuable monomers and a hydrothermal gasification valorizing the ultimate residues of the cracking as well as the aqueous effluents from the alcohol distillation column into methane and hydrogen.

2. A method according to any one of claim 1, wherein thermal cracking is carried out on acrylic ester adducts.

3. A method according to any one of claims 1, wherein thermal cracking is carried out on acrylic ester adducts previously treated in a hydrolyzer.

4. A method according to any one of claims 1, wherein thermal cracking is carried out on a mixture of acrylic acid adducts and acrylic esters.

5. A process according to any one of claims 1, wherein thermal cracking is carried out on acrylic acid adducts previously treated in a hydrolyzer.

6. A process according to any one of claims 1, wherein thermal cracking is carried out on acrylic acid and acrylic ester adducts previously treated in a hydrolyzer.

7. A 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, through recirculating loops of acrylic acid and unreacted alcohol. b) Azeotropic distillation of the reaction mixture using a first distillation column enabling the separation at the top of the column of an azeotropic mixture comprising alkyl acrylate and unreacted alcohol.

8.

9.

10.

11.

12. and water, at the bottom a fraction comprising unreacted acrylic acid and heavy by-products, and by side withdrawal a fraction rich in alkyl alkoxy propionate by-product sent to the purification train or to a hydrolyzer. c) The separation of the bottom stream of the first distillation column into a stream consisting essentially of unreacted acrylic acid, this stream being recycled into the esterification reactor, and a stream consisting essentially of heavy ester by-products sent to a column allowing the heavy ones to be concentrated at the bottom of this column and the light ones sent back to the reaction section. d) Thermal cracking of these ester heavys alone or with acrylic acid heavys, whether or not previously hydrolyzed, carried out in a cracking reactor, releasing a stream of valuable products which can be recycled. e) Hydrothermal gasification of the cracker residue mixed with water. f) Liquid / liquid extraction of the headstream of the first distillation column by an aqueous stream allowing separation of an organic phase consisting essentially of 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) The purification of said organic phase allowing the recovery of the purified alkyl acrylate. h) A purge of the foot of the purification column feeding the hydrothermal gasifier. A process according to claim 7, wherein the temperature of the hydrolyzer varies between 80 and 200°C. A process according to claim 7, wherein the water / adduct mass ratio in the hydrolyzer varies from 0.1 to 1.3 inclusive. A process according to claim 1 to 9, wherein the concentration of residue / water + residue in the hydrothermal gasification feed is between 10g / l and 400g / l. A method according to any one of claims 1 to 10, wherein the lateral drawdown flow is sent to the inlet of the hydrothermal gasification. A method according to any one of claims 1 to 11, wherein the purging of the The bottom of the finishing column is sent to the inlet of the hydrothermal gasification.

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

14. A process according to any one of claims 1 to 13, wherein the gasification generates a gas composed of 40 to 70% methane, 5-20% hydrogen and 20-40% carbon dioxide.

15. A process according to any one of claims 1 to 13, wherein the water exiting the gasifier, free from organic compounds, is recycled to the feed of the separator or to the feed of the hydrolyzer or to the inlet of the liquid / liquid extraction column.

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