Improved process for producing high purity butyl acrylate

Abstract

The present invention relates to the production of butyl acrylate by direct esterification of acrylic acid with butanol, the reaction being catalyzed by sulfuric acid. More particularly, the subject of the present invention is an improved process for the production of butyl acrylate, which makes it possible to obtain high-purity butyl acrylate by upgrading both the Michael adducts formed during this process, by thermal and catalytic decomposition, in the form of reactants and esters that can be recycled in the process, and the final residues, by hydrothermal gasification, in the form of methane and inorganic salts.

Description

[Technical Field]

[0001] The present invention relates to the production of butyl acrylate by direct esterification of acrylic acid with butanol, the reaction being catalyzed by sulfuric acid. More specifically, the subject of the present invention is an improved process for producing butyl acrylate, which makes it possible to obtain high-purity butyl acrylate by upgrading both the Michael adducts formed during this process, by thermal and catalytic decomposition, in the form of reactants and esters that can be recycled in the process, and the final residues, by hydrothermal gasification, in the form of methane and inorganic salts. [Background technology]

[0002] The esterification of acrylic acid is an equilibrium reaction with the production of water that must be removed during the reaction to shift the equilibrium towards the production of acrylic esters.

[0003] The problems presented during the production of butyl acrylate by direct esterification of acrylic acid, generally in the presence of sulfuric acid as a catalyst, are mostly related to the complexity of the purification steps required after the reaction step to obtain a high purity product, which impairs the productive output of the process.

[0004] The industrial process described in the applicant's patent EP 0609127 involves the esterification of acrylic acid (AA) with excess butanol in the presence of sulfuric acid. At the end of the reaction, the reaction mixture contains butyl acrylate, residual acrylic acid, butyl hydrogen sulfate, traces of sulfuric acid, and various impurities resulting from side reactions. The reaction mixture is subsequently subjected to neutralization and water washing steps, the purpose of which is to remove the "acidic" impurities, i.e., residual sulfuric acid, butyl hydrogen sulfate, and acrylic acid. The mixture, now free of acidic impurities, is then subjected to various purification steps, resulting in the recovery of purified butyl acrylate. One of the "topping" steps consists in distilling, in particular, butanol and light by-products. The butanol can then be recycled to the esterification reaction.

[0005] The final step in the purification of butyl acrylate is to send the mixture containing the ester, freed from light products, to a final distillation column, from which the ester leaves at the top and the purified heavy by-products, for that matter, are found at the bottom of the distillation column and subsequently concentrated in an evaporator. The overhead product from this evaporator, i.e., butyl acrylate (BuA), is returned to the bottom of the rectification column, which not only allows it to be recovered as a final product, but also makes it possible to keep the temperature at the bottom of the column low enough to avoid contamination problems associated with the heat sensitivity of this monomer.

[0006] The residue from the evaporator contains, in addition to Michael derivatives and a few percent of free monomers, a few percent of polymerization inhibitors (which accumulate during all purification steps) (e.g., mainly phenothiazine in its free form or in the form of adducts with AA or BuA, and also heavy polymeric compounds that are more or less soluble in the medium). Generally, this residue is removed by incineration, which results in a significant loss of yield.

[0007] Among the by-products formed following side reactions, mention may be made of light products such as butyl acetate, butyl propionate, dibutyl ether or isobutyl acrylate, or heavy products such as dibutyl maleate.

[0008] "Heavy" compounds resulting from the Michael addition reaction are naturally formed in the units for the production of butyl acrylate. These parasitic reactions are promoted by the high temperatures encountered, especially at the bottom of the distillation columns of these units. This leads to the addition of acrylic acid, unreacted butanol or water of reaction to the double bond of butyl acrylate, mainly forming: - butyl acryloxypropionate (AA / BuA) by addition of acrylic acid (AA) to butyl acrylate (BuA), - butyl hydroxypropionate (BHP) by addition of water to butyl acrylate; -Butyl butoxypropionate (BBP) from the addition of butanol to butyl acrylate.

[0009] Polyaddition or the formation of mixed compounds may also occur.

[0010] One of the properties of the heavy by-products is that their boiling point is higher than that of acrylic acid, butanol and butyl acrylate. Due to their low volatility, the heavy by-products accumulate at the bottom of the last distillation column and at the bottom of the evaporator used to concentrate this residue.

[0011] Various solutions have been proposed for the upgrading of these heavy by-products, which still contain polymerization inhibitors.

[0012] Document CN1063678 proposes a method for treating oxyesters formed during the synthesis of butyl acrylate using protonic acid catalysts, such as sulfuric acid or paratoluenesulfonic acid. Compounds such as phthalates can also be added, as described in document US4293347.

[0013] The drawback of these cracking methods is that the residual product is viscous and contains solids. US6617470 proposes using an arylsulfonic acid, such as dodecylsulfonic acid, as a catalyst to suppress the formation of solids in the bottom residue. US2011 / 0230675 proposes continuously adding water when the cracking is carried out with an acid catalyst to avoid the formation of solid deposits. CN102173990 proposes adding copper salts to the feed of the thermal cracker to facilitate subsequent processing of the final cracking residue.

[0014] Without wishing to be bound by any explanation, the applicant company believes that it is the interaction between phenothiazine and the acid catalyst during catalytic cracking and thermal cracking that is the primary cause of the formation of solids in the final residue of the thermal cracker.

[0015] Application FR2108885 employs a thermal cracking device without a catalyst, which can successfully suppress this interaction, but the cracking yield remains lower than that obtained during thermal and catalytic cracking.

[0016] Application FR2111319 finally provides a simplified process that allows thermal and catalytic cracking to be carried out while preserving the integrity of the plant by pre-evaporating the bottom stream from the last distillation column and subjecting the top stream from the last distillation column to two successive condensations. The bottom of this evaporator therefore contains heavy residues and inhibitors, as well as more or less soluble heavy products of polymeric nature. The residue from the thermal cracker essentially consists of unreacted Michael adduct and the acid catalyst used during the cracking.

[0017] While solid deposits in the pyrolyzer are suppressed, the process of treating the residues, which is usually carried out by incineration to upgrade them in the form of superheated steam, has still proven problematic.

[0018] In effect, it is possible to choose between two solutions, namely the two residues from the bottom of the evaporator and the bottom of the pyrolyzer, which can be treated separately, resulting in two operations, or the two residue streams can be mixed, in fact combining, on the one hand, phenothiazine and, on the other hand, the catalyst used during decomposition, resulting in the formation of solids.

[0019] The oxidation (incineration) of organic matter to obtain carbon dioxide and water is a process that has always been known and is very frequently used to treat organic residues and generate heating steam. In conventional steam-form energy processes, the rapid oxidation of organic fuels is often used to generate heat, which is then transferred to a fluid such as water in a heat exchanger. Heat losses of 10% to 15% can be expected as a result of the inevitable losses in the exhaust stack of a conventional boiler. In addition to possible blockages due to solids fed into the boiler, hot spots due to salt deposits on boiler tubes or ash deposits on tube faces exposed to the flame or hot gases reduce good heat transfer and therefore heat transfer efficiency, and in fact can even cause very costly losses over time as a result of tube wall failure.

[0020] From 1981, document FR 2 481 949 describes oxidation in a supercritical medium, whereby an aqueous stream with a low organic loading is converted into CO2 and water by the addition of oxygen in a mixture composed of water and organic input, thus making the first incinerator more efficient in supercritical conditions, since the combustion energy is carried by water under pressure and critical temperature, without the need for exchangers, as in conventional boilers.

[0021] The article "Gasification of Biomass in Supercritical Water" by O. Boutin and J.C. Ruiz, published in Techniques de l'ingenieur [Techniques of the Engineer] J7010 on October 5, 2013, describes the implementation of hydrothermal gasification for the treatment of certain organic effluents on a pilot scale. This conversion technology allows for the conversion of wet biomass (>70% moisture) into syngas (a mixture of methane, hydrogen, and carbon dioxide) and the separation of inorganic salts present in the input. It has been used, for example, in the gasification of algae for the production of hydrogen, the treatment of primary sludge from sewage treatment plants, or the catalytic gasification of pig manure, possibly mixed with eucalyptus wood. [Prior art documents] [Patent documents]

[0022] [Patent Document 1] European Patent Application Publication No. 0609127 [Patent Document 2] Chinese Patent Application Publication No. 1063678 [Patent Document 3] U.S. Patent No. 4,293,347 [Patent Document 4] U.S. Patent No. 6,617,470 [Patent Document 5] US Patent Application Publication No. 2011 / 0230675 [Patent Document 6] Chinese Patent Application Publication No. 102173990 [Patent Document 7] French Patent Invention No. 2108885 [Patent Document 8] French Patent Invention No. 2111319 [Patent Document 9] French Patent Invention No. 2481949 [Non-patent literature]

[0023] [Non-Patent Document 1] The article "Gazeification de biomasse en eau supercritique [Gasification of Biomass in Supercritical Water]" by O. Boutin and J.C. Ruiz, appeared on October 5, 2013, in Techniques de l'ingenieur [Techniques of the Engineer] J7010. Summary of the Invention [Problem to be solved by the invention]

[0024] Processes need to be available that allow for the energy upgrading of final waste while preventing the formation of solids in the residue that would clog incinerators.

[0025] It has been found that by replacing the evaporator at the bottom of the rectification column and the distillation under reduced pressure and inert atmosphere with a single evaporator and its staged condensation system, the formation of solids in the residue from the pyrolysis unit is significantly reduced while simplifying the items of equipment used in a process that allows the production of high-purity butyl acrylate. In addition, the combination of the hydrothermal gasification process with the evaporator makes it possible to upgrade the final residue in the form of a gas with a high calorific value, in particular to give transportable methane gas, instead of converting it to CO2 by combustion.

[0026] The present invention makes it possible to meet the above requirements. More specifically, the present invention provides an improved process for the production of butyl acrylate by direct esterification of acrylic acid with butanol, which allows for better upgrading of the end product, which is usually sent for incineration, by regenerating the starting material by decomposition and converting the residue into fuel gas. The process according to the present invention makes it possible to improve the energy balance of the process while improving the material balance.

[0027] The present invention consists in carrying out a hydrothermal gasification in combination with a thermal and catalytic cracking unit used to upgrade Michael adducts. The aim of the invention is to upgrade these adducts as much as possible, with or without the presence of solid products, on the one hand to obtain an upgradeable starting material that is recycled in the distillation line, and on the other hand to produce, in the presence of solids and salts, a gas phase composed of methane, hydrogen and carbon dioxide, which makes it possible to meet the minimum energy requirements of the process and which can be upgraded in the natural gas system of the industrial site or discharged.

[0028] The present invention also applies to organic products that do not contain moisture and have not previously been upgraded by hydrothermal gasification. [Means for solving the problem]

[0029] The present invention describes an evaporation system that allows the recycling of butyl acrylate to maintain a temperature at the bottom of the rectification column that is compatible with the heat sensitivity of butyl acrylate, and sends the Michael adduct to a thermal and catalytic cracking unit, while simultaneously releasing very heavy compounds and polymerization inhibitors at the bottom of this evaporator.The process that allows high-purity butyl acrylate to be obtained is described in the reaction section of patent EP0609127.

[0030] It also complements the purification scheme described in the patent, on the one hand, by combining an evaporator placed at the foot of the column with its stepwise condensation system for the purification of butyl acrylate, and describes the recycling of the overhead product resulting from the decomposition in the process, and on the other hand, describes a hydrothermal gasification that makes it possible to convert the residues from the decomposition into upgradeable gases (methane, hydrogen, CO2) and, at a minimum, to provide energy for the process or to upgrade in the gas system.

[0031] The subject of the present invention is a process for the manufacture of butyl acrylate by direct esterification of acrylic acid with an excess of butanol in the presence of sulfuric acid as a catalyst and at least one polymerization inhibitor, resulting in a crude reaction mixture containing butyl acrylate, residual acrylic acid, residual butanol, butyl hydrogen sulfate, traces of sulfuric acid and impurities resulting from side reactions, the process comprising a neutralization step and a water washing step to obtain a reaction mixture free from "acidic" impurities, the reaction mixture from which the acidic impurities have been washed being subjected to at least the following steps: a) a topping step in a first distillation column known as a topping column, - at the top, a stream consisting essentially of unreacted reactants, at the bottom, a stream comprising the desired ester and heavy by-products A topping step that allows obtaining b) rectifying the bottoms stream from the topping column by tailing it in a second distillation column, at the top, the purified desired ester, at the bottom, a stream comprising heavy by-products, allowing the separation of c) concentrating the bottoms stream from the rectification column in an evaporator, recycling any light compounds present to the rectification column and providing a top stream cooled in two steps to concentrate the Michael adduct; d) decomposing said concentrate of Michael adducts in a thermal decomposition device, - at the top, inert products resulting from the decomposition which are recycled to the feed of said topping column, - At the bottom, the final residue a step of obtaining e) A step of hydrothermal treatment of said residue carried out in an item of hydrothermal gasification equipment in the presence of water, resulting in methane, hydrogen and CO2 type gases obtained at the top, and solid residue and water obtained at the bottom.

[0032] The present invention makes it possible to overcome the drawbacks of the prior art. More specifically, the present invention provides a process that incorporates an optimized process for the removal of polymerization inhibitors, decomposition of the Michael adduct to obtain reactants (acrylic acid and alcohol), and the final product, thereby increasing the productive output of the process by upgrading the residues to be removed, improving the energy balance and making it possible to obtain high-purity butyl acrylate with an ester purity of more than 99.5% as a specification.

[0033] Other features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying FIG. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is an overall diagram of a process for the synthesis of butyl acrylate according to the present invention, including a combination of thermal and catalytic cracking units and items of hydrothermal gasification equipment. DETAILED DESCRIPTION OF THE INVENTION

[0035] The subject of the present invention is a process for the preparation of butyl acrylate by direct esterification of acrylic acid with an excess of butanol in the presence of sulfuric acid as a catalyst and at least one polymerization inhibitor, resulting in a crude reaction mixture containing butyl acrylate, residual acrylic acid, residual butanol, butyl hydrogen sulfate, traces of sulfuric acid and impurities resulting from side reactions.

[0036] According to various embodiments, the method comprises the following features, combined where appropriate:

[0037] After the esterification step, the process according to the invention comprises a neutralization step and a water washing step which results in a reaction mixture free from "acidic" impurities, i.e., sulfuric acid, butyl hydrogen sulfate, acrylic acid dimer and residual acrylic acid.

[0038] Characteristically, the reaction mixture from which acidic impurities have been washed as described above is subjected to at least the following steps. a) a topping step in a first distillation column known as a topping column, - at the top, a stream consisting essentially of unreacted reactants, at the bottom, a stream comprising the desired ester and heavy by-products A topping step that allows obtaining b) the bottom stream from the topping column is fed to a tailings fractionator; at the top, the purified desired ester, at the bottom, a stream comprising heavy by-products, allows for the separation of c) concentrating the bottom stream from the rectification column in an evaporator, in particular a thin-film evaporator, to recycle the light compounds present to the rectification column and to provide a top stream cooled in two steps to concentrate the Michael adduct with a very low inhibitor content, d) decomposing said concentrate of Michael adducts in a thermal decomposition device, - at the top, inert products resulting from the decomposition which are recycled to the feed of said topping column, - At the bottom, the final residue a step of obtaining e) A step of hydrothermal treatment of said residue carried out in an item of hydrothermal gasification equipment in the presence of water, resulting in methane, hydrogen and CO2 type gases obtained at the top, and solid residue and water obtained at the bottom.

[0039] According to one embodiment, the pyrolysis may or may not be catalytic.

[0040] According to one embodiment, the two residues, namely the bottoms of the evaporator and the residue from the pyrolyzer, are treated separately.

[0041] According to one embodiment, the two residues, namely the residue from the bottom of the evaporator and the residue from the pyrolyzer, are mixed and treated in the same gasification operation.

[0042] According to one embodiment, the items of the hydrothermal gasification facility include a first reactor, a second reactor and a gas-liquid separator.

[0043] According to one embodiment, the residue is injected directly into the gasification, together with the water required for the hydrothermal treatment.

[0044] According to one embodiment, the residue is mixed with the water necessary for the hydrothermal treatment before being introduced into the gasification.

[0045] According to the embodiment, the hydrothermal gasification is carried out at a temperature of 350°C to 450°C and a pressure of 25 MPa.

[0046] According to said embodiment, the hydrothermal gasification comprises a gasifier making it possible to separate the salt at the bottom and the mixture of gas and liquid at the top.

[0047] According to one embodiment, the hydrothermal gasification comprises a separator, a gasifier and a gas-liquid separator that allow the separation of salts under critical conditions.

[0048] According to one embodiment, the concentration of retentate / water+retentate in the salt separator is between 10 g / l and 400 g / l.

[0049] According to one embodiment, the water used to carry out the hydrothermal gasification may be demineralized water, water resulting from drilling, or weak mineral water.

[0050] According to one embodiment, the outlet water of the gasifier, free of organic compounds, can advantageously be recycled to the feed of the separator.

[0051] According to one embodiment, the obtained and separated salt can be upgraded as a fertilizer.

[0052] According to one embodiment, a proportion of 94% to 99% of the carbon introduced into the gasification is upgraded in the form of gas.

[0053] According to one embodiment, the gas resulting from the gasification is composed of 40% to 70% methane, 5% to 20% hydrogen and 20% to 40% carbon dioxide.

[0054] According to one embodiment, the gas can be further fractionated to isolate the methane from other compounds.

[0055] According to one embodiment, the composition by weight of the main compounds of the residue from the bottom of the pyrolysis unit is as follows: - Butyl butoxypropionate (BBP): 65-90% - Para-toluenesulfonic acid (PTSA): 0.1-4% - Phenothiazine: 100-1000 ppm - Heavy products (molecular weight >264g / mol): >1%

[0056] According to one embodiment, the composition by weight of the bottom product from the evaporator is as follows: - Butyl butoxypropionate (BBP): 65-85% - Para-toluenesulfonic acid: 0% - Phenothiazine: 1-10% - Heavy products (molecular weight >264g / mol): >10%

[0057] Referring to Figure 1, which represents a preferred mode of the invention, the topping section comprises a distillation column having the equivalent of 10 to 30 theoretical plates, preferably 10 to 15. The internals used in the column can be valve trays or perforated trays with weirs, crossflow trays such as dual flow trays, tripple trays or Shell Turbogrid trays, or laminated packing, such as structured packing, e.g., Mellapack 250X manufactured by Sulzer.

[0058] The topping column is fed into the upper third of the column, preferably between theoretical plates 3 and 10 from the top of the column. The top stream of the column essentially contains unreacted reactants. This upgradeable stream is recycled to the reaction.

[0059] The column operates at a reflux ratio (flow rate of condensate returned to the column / flow rate recycled to the reaction) of 4 / 1 to 1 / 1, preferably 3 / 1. Advantageously, 50 to 5000 ppm of a polymerization inhibitor is introduced into the purification system according to the process of the invention.

[0060] Examples of polymerization inhibitors that can be used include phenothiazine (PTZ), hydroquinone (HQ), hydroquinone monomethyl ether (HQME), di(tert-butyl)-para-cresol (BHT), para-phenylenediamine, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), di(tert-butyl)catechol, or TEMPO derivatives such as OH-TEMPO, either alone or in any proportion, in a reaction medium content of 50 ppm to 5000 ppm, generally 150 ppm to 1000 ppm, optionally in the presence of depleted air. The addition of the polymerization inhibitor can be carried out at different points along with the introduction of the reactants or at the top of the distillation column.

[0061] To make the inhibitor more effective, it is advisable to inject oxygen, air, or "depleted" air with 7% O2 into the bottom of the column. Preferably, the amount of oxygen injected corresponds to a content of 0.2% to 0.5% of the organic vapor in the column.

[0062] The column can be operated under vacuum to minimize heat exposure of heat-sensitive compounds within the column. Advantageously, the topping column operates under vacuum in the range of 1000 Pa to 30000 Pa.

[0063] The bottom stream is preferably fed to a column, making it possible to obtain purified ester at the bottom of the column at theoretical plates 6 to 9.

[0064] The column for the distillation of the pure product contains the equivalent of 2 to 15 theoretical plates, preferably 6 to 12. The internals used in the column can be perforated trays with valve trays or weirs, cross-flow trays, such as dual-flow trays, ripple trays or shell turbogrid trays, or laminated packing, such as structured packing, for example Mellapack 250X from Sulzer.

[0065] The overhead stream from the column consists of high purity butyl acrylate with an ester purity of greater than 99.5% as specified.

[0066] The column operates at a reflux ratio (returned condensate flow rate / pure product flow rate) of 1 / 8 to 1 / 1, preferably 1 / 4. Similar to the topping column, the latter is stabilized and air or depleted air (7% O2) is injected into the column foot. The column can be operated under vacuum to minimize the heat exposure of heat-sensitive compounds within the column. Advantageously, the pure product column operates under vacuum in the range of 1000 Pa to 20000 Pa.

[0067] Advantageously, the operating temperature is between 50°C and 160°C.

[0068] The bottom stream is concentrated in a thin-film evaporator, which is well suited for viscous fouling products and contaminated liquids. Evaporation is carried out at temperatures between 80°C and 100°C, more particularly between 90°C and 100°C, and at pressures between 800 Pa and 2000 Pa. The top stream from this evaporator is cooled in two successive steps: partial condensation at a temperature range of 50°C to 80°C, more particularly 60°C to 70°C, at a pressure equal to that of the evaporator, in order to obtain, on the one hand, a liquid stream of Michael adduct which is fed to the decomposition reactor, and, on the other hand, a vapor stream; - After condensing this vapor stream at a temperature range of 20°C to 40°C, more specifically 20°C to 30°C, this liquid stream is pumped and mixed with the bottom product from the topping column to feed the rectification column.

[0069] The bottom residue, either alone or as a mixture, is subjected to hydrothermal gasification.

[0070] The overhead feed stream and para-toluenesulfonic acid catalyst (PTSA) dissolved in water or pre-dissolved in the Michael adduct are also continuously introduced into a forced recycle pyrolysis unit equipped with an external exchanger at a temperature range of 160°C to 210°C, with a residence time of about 2 to 10 hours, and under a pressure of 200 kPa to atmospheric pressure.

[0071] According to one embodiment, the decomposition is carried out at atmospheric pressure and at a temperature between 160°C and 180°C.

[0072] The catalyst content is, for example, 0.5% to 3% of the amount of adduct fed to the pyrolysis unit, as in FR 2901272. The reactants produced by this decomposition, essentially butanol and butyl acrylate, are returned to the process purification line. The residue, for its part, is treated by hydrothermal gasification, either alone or preferably as a mixture.

[0073] The residue and water are injected into the hydrothermal gasification equipment via two circuits through a high-pressure pump at a temperature range of 350°C to 450°C and a pressure of 25 MPa.

[0074] The first reactor makes it possible to separate the salt at the bottom of the latter from the aqueous organic solution.

[0075] The second gasification reactor contains a catalyst that allows for the conversion of the organic products to gas to be completed.

[0076] The gas-liquid separator makes it possible to recover, at the bottom, an aqueous phase that can be recycled to the inlet of the separator, and a gas phase rich in methane, which can be upgraded to produce a stream that can carry the energy necessary for the operation of the gasification, as well as energy for the operation of the reaction and purification lines of the process, or that can be further discharged. This hydrothermal gasification can be carried out in batch mode or, preferably, in continuous mode.

[0077] The following examples illustrate the present invention without, however, limiting its scope. [Example]

[0078] In the examples, unless otherwise indicated, percentages are given by weight and the following abbreviations are used: PTZ: Phenothiazine BuA: butyl acrylate BuOH: butanol BBP: butyl butoxypropionate DBE: Dibutyl ether BAP: butyl acryloxypropionate Heavy products: molecular weight>264g / mol PTSA: para-toluenesulfonic acid BPTS: butyl para-toluenesulfonate

[0079] Example 1: Obtaining residue from a thin film evaporator A commercial DV210 / 1m2 thin film evaporator heated with steam at 0.4 MPa and operated at a pressure of 130 Pa is fed at a rate of 50 kg / h with a mixture, i.e., BuA: 9%, BuOH: 3.5%, BBP: 67%, BAP: 5.7%, PTZ: 1.8%, residual to 100%: heavy residue.

[0080] The top product (40 kg / h) was 2 The resulting mixture is condensed at 20°C in a tubular exchanger. It is stabilized by the addition of 250 g / h of a butyl acrylate solution containing 2% phenothiazine. The overhead product, which is fed to the pyrolysis unit, contains 12.5% ​​BuA, 75% BBP, 3% butanol and 900 ppm phenothiazine.

[0081] The bottom product from the evaporator contains PTZ (6%), approximately 10% heavy products and BBP as the balance to 100%.

[0082] [Example 2] Thermal and catalytic cracking tests A forced recirculation boiler with a capacity of 40 liters was used, to which a diaphragm pump was used to continuously feed a balance of heavy products / BuA, to which 1% by weight of para-toluenesulfonic acid was added. The feed flow rate was measured using a mass flow meter placed in the feed line and also by the change in weight indicated by the balance over time. The operation was carried out at a pressure adjusted to prevent the butyl butoxypropionate from vaporizing. The temperature of the reaction medium and the temperatures at the inlet and outlet of the exchanger were continuously measured. The heat transfer fluid that provided heat to the exchanger came from an oil boiler. The heating power was fixed to keep the test temperature constant.

[0083] The heavy product / BuA is pre-distilled under vacuum and contains approximately 600 ppm phenothiazine.

[0084] After decomposition at 180°C under a pressure of 40 kPa (300 mmHg) with a residence time of 9 hours, the overhead / feed ratio, defined as the reactor volume to the feed flow rate by weight of Michael adduct, was 76%, and the overhead composition comprised 48% butyl acrylate and 15% butanol.

[0085] The residue, for its part, contains, inter alia, 0.6% PTSA, 2.5% BPTS, 80% BBP and 10% heavy products.

[0086] [Example 3] Hydrothermal gasification The heavy ends / BuA mixture consists of: - Butanol: <0.1% - Butyl acrylate: 5-10% - Butyl hydroxypropionate (BHP): 1-3% - Butyl butoxypropionate (BBP): 70-80% - Butyl acryloxypropionate (BAP): 4-6% - Dibutyl maleate: 2-5% - Phenothiazine: 1-3%

[0087] 33 g / h of heavy products / BuA and also 970 g / h of water are introduced into the separator and catalytic reactor via two different pipes, both of which are operated at 400 °C and 250 bar. After a 6-hour test under stabilization conditions, the heavy products / BuA are converted into a gas mixture with the following composition by volume: 51% CH4, 34% CO2 and 19% H2. The energy content of this gas corresponds to 7096 kWh / tBuA. The amount of TOC (total organic carbon) is <1 mg / l.

Claims

1. A process for producing butyl acrylate by direct esterification of acrylic acid with butanol in the presence of sulfuric acid as a catalyst and at least one polymerization inhibitor, which produces a crude reaction mixture containing butyl acrylate, residual acrylic acid, residual butanol, butyl hydrogen sulfate, a trace amount of sulfuric acid, and impurities resulting from side reactions, the process comprising a neutralization step and a water-washing step to obtain a reaction mixture free of acidic impurities, wherein the reaction mixture from which the acidic impurities have been washed away is subjected to at least the following steps: a) a topping step in a first distillation column known as a topping column, at the top, a stream essentially consisting of unreacted reactants, at the bottom, a stream comprising the desired ester and heavy by-products A topping step that allows obtaining b) rectifying the bottoms stream from the topping column by tailing it in a second distillation column, at the top, the purified desired ester, at the bottom, a stream comprising heavy by-products, allowing the separation of c) concentrating the bottoms stream from the rectification column in an evaporator, recycling any light compounds present to the rectification column and providing a top stream cooled in two steps to concentrate the Michael adduct; d) decomposing said concentrate of Michael adducts in a thermal decomposition device, at the top, inert products resulting from the cracking which are recycled to the feed of the topping column, - at the bottom, the final residue a step of obtaining e) a step of hydrothermal treatment of said residue carried out in an item of hydrothermal gasification equipment in the presence of water, with methane, hydrogen and CO obtained overhead; ２ This process results in a gas of the type obtained at the bottom, as well as a solid residue and water.

2. 2. The process of claim 1, wherein the acidic impurities are sulfuric acid, butyl hydrogen sulfate, acrylic acid dimer, and residual acrylic acid.

3. 3. The process of any of claims 1 and 2, wherein the polymerization inhibitor is selected from phenothiazine (PTZ), hydroquinone (HQ), hydroquinone monomethyl ether (HQME), di(tert-butyl)-para-cresol (BHT), para-phenylenediamine, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), di(tert-butyl)catechol, OH-TEMPO, or mixtures thereof in any proportion.

4. A process according to any of claims 1 to 3, wherein the polymerization inhibitor is used in the reaction medium or in the purification step at a content of from 50 ppm to 5000 ppm, preferably from 150 ppm to 1000 ppm.

5. 5. The process of any of claims 1 to 4, wherein the polymerization inhibitor is added at a different location along with the reactants or at the top of the distillation column.

6. A process according to any of claims 1 to 5, wherein the evaporation is carried out at a temperature ranging from 80°C to 100°C, preferably from 90°C to 100°C, and at a pressure ranging from 800 Pa to 2000 Pa.

7. A process according to any one of claims 1 to 6, wherein the overhead stream from the evaporator is cooled in two successive steps: a. partial condensation at a temperature range of 50°C to 80°C, more particularly 60°C to 70°C, at the same pressure as the evaporator pressure, to obtain, on the one hand, a liquid stream of Michael adduct that is fed to the decomposer, and, on the other hand, a vapor stream; b) After condensing this vapor stream at a temperature in the range of 20°C to 40°C, more specifically 20°C to 30°C, the liquid stream is pumped and fed to the rectification column.

8. 7. The process of any one of claims 1 to 6, wherein the decomposition is carried out at atmospheric pressure and at a temperature of from 160°C to 180°C.

9. The process of any one of claims 1 to 8, wherein the obtained butyl acrylate has a purity of more than 99.5%.

10. The process according to any one of claims 1 to 9, wherein the hydrothermal gasification comprises a separator, a gasifier and a gas-liquid separator that allows separating salts under supercritical conditions.

11. 11. The process of claim 10, wherein the concentration of residue / water+residue in the separator is between 10 g / l and 400 g / l.

12. 12. The process of any preceding claim, wherein the gasification produces a gas composed of 40% to 70% methane, 5% to 20% hydrogen, and 20% to 40% carbon dioxide.

13. A process according to any one of claims 10 to 12, wherein the gasifier outlet water free of organic compounds is recycled to the separator feed.

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