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, this reaction being catalyzed by sulfuric acid. More specifically, it relates to an improved process for producing butyl acrylate, enabling high-purity butyl acrylate to be obtained, by upgrading both the Michael adducts formed during this process, by thermal and catalytic cracking, in the form of reactants and ester which can be recycled in the process, and the final residue, by hydrothermal gasification in the form of methane and mineral salts.

Description

[0001] IMPROVED PROCESS FOR THE MANUFACTURE OF HIGH PURITY BUTYL ACRYLATE

[0002] TECHNICAL FIELD

[0003] The present invention relates to the manufacture of butyl acrylate by direct esterification of acrylic acid with butanol, this reaction being catalyzed by sulfuric acid. More specifically, it relates to an improved process for the manufacture of butyl acrylate, making it possible to obtain high-purity butyl acrylate, by recovering both the Michael adducts formed during this process, by thermal and catalytic cracking, in the form of reactants and ester which can be recycled in the process, and the final residue, by hydrothermal gasification in the form of methane and mineral salts.

[0004] TECHNICAL BACKGROUND AND TECHNICAL PROBLEM

[0005] The esterification of acrylic acid is a balanced reaction with generation of water which must be eliminated during the reaction to shift the equilibrium in the direction of production of the acrylic ester.

[0006] The problems that arise when manufacturing butyl acrylate by direct esterification of acrylic acid, usually in the presence of sulfuric acid as a catalyst, are most often related to the complexity of the purification steps required after the reaction step to obtain a high-purity product, to the detriment of the productivity of the process.

[0007] The industrial process, as described in the applicant's patent EP 0609127, consists of esterifying acrylic acid (AA) with excess butanol, in the presence of sulfuric acid. The reaction mixture at the end of the reaction comprises butyl acrylate, residual acrylic acid, butyl acid sulfate, traces of sulfuric acid and various impurities resulting from side reactions. This reaction mixture is then subjected to a neutralization and water washing step which aims to eliminate the so-called acid impurities: residual sulfuric acid, butanol acid sulfate and acrylic acid. This mixture, free of acid impurities, is subjected to various purification steps, which lead to the recovery of purified butyl acrylate. One of the so-called topping steps consists in particular of distilling the butanol and the light by-products. The butanol can thus be recycled to the esterification reaction.

[0008] The final stage of purification of butyl acrylate consists of sending the mixture containing the ester, freed from light products, into a final distillation column from which it emerges at the top, purified of the heavy by-products which are found at the bottom of the distillation column and are then concentrated in an evaporator. The top product of this evaporator, namely butyl acrylate (ABU), is returned to the bottom of the rectification column, which allows it to be recovered as a finished product but also to maintain the temperature at the bottom of the column low enough to avoid fouling problems linked to the heat-sensitive nature of this monomer.

[0009] The evaporator residue contains, in addition to Michael derivatives and a few percent of free monomers, a few percent of polymerization inhibitors, accumulated over the course of all the purification steps, such as mainly phenothiazine in its free form or as an adduct of AA or ABU, as well as heavy compounds of a polymeric nature that are more or less soluble in the medium. In general, this residue is eliminated by incineration, which results in a significant loss of yield.

[0010] By-products generated by secondary reactions include light products such as butyl acetate, butyl propionate, dibutyl ether, isobutyl acrylate, or heavy products such as dibutyl maleate.

[0011] "Heavy" compounds resulting from Michael addition reactions form spontaneously in butyl acrylate production units. These side reactions are favored by high temperatures encountered particularly in the distillation column bottoms of these units. Thus, acrylic acid, unreacted butanol, or water of reaction are added to the double bond of butyl acrylate to form mainly:

[0012] - butyl acryloxypropionate (AA / ABU) by addition of acrylic acid (AA) to butyl acrylate (ABU);

[0013] - butyl hydroxypropionate (BHP) by addition of water to butyl acrylate;

[0014] - butyl butoxypropionate (BPB) by addition of butanol to butyl acrylate.

[0015] Polyaddition or the formation of mixed compounds is also possible.

[0016] One of the characteristics of heavy by-products is that their boiling point is above the boiling points of acrylic acid, butanol and butyl acrylate. As their volatility is low, they accumulate at the bottom of the last distillation column, at the bottom of the evaporator used to concentrate this residue. Various solutions have been proposed for the recovery of these heavy by-products still containing polymerization inhibitors.

[0017] CN 1063678 provides methods for treating oxy-esters formed during the synthesis of butyl acrylate using protic acid catalysts such as sulfuric acid or para-toluenesulfonic acid. Compounds such as phthalates may also be added, as described in US 4293347.

[0018] The disadvantage of these cracking methods is that the residual product is viscous and contains solids. US 6617470 proposes using arylsulfonic acids such as dodecylsulfonic acid as catalysts, which eliminates the formation of solids in the bottom residue. US 2011 / 0230675 proposes adding water continuously when cracking is carried out by acid catalysis, in order to avoid the formation of solid deposits. CN 102173990 proposes adding copper salts to the cracker feed in order to facilitate the subsequent treatment of the final cracking residue.

[0019] Without the applicant being required to provide any explanation, it believes that it is the interaction between the phenothiazine and the acid catalyst during catalytic and thermal cracking which is largely responsible for the formation of solids in the final residue of the cracker.

[0020] Application FR 2108885 uses a thermal cracker without a catalyst, which successfully eliminates this interaction. However, the cracking efficiency remains lower than that obtained during thermal and catalytic cracking.

[0021] Finally, application FR 2111319 provides a simplified process for carrying out thermal and catalytic cracking while preserving the integrity of the installation by first subjecting the bottom flow of the last column to evaporation and the top flow of the latter to two successive condensations. The bottom of this evaporator then contains the heavy residues and the inhibitors as well as heavy products of a more or less soluble polymeric nature. The cracker residue will be essentially composed of unreacted Michael adducts and the acid catalyst used during cracking.

[0022] If the solid deposits in the cracker have been removed, it turns out that the residue treatment step, usually carried out by incineration which recovers them in the form of heating steam, remains problematic. Two solutions can be chosen: the two residues from the bottom of the evaporator and that from the bottom of the cracker can be treated separately, which leads to carrying out two operations, or the two residue streams can be mixed and in fact the phenothiazine and the catalyst used during cracking will be brought together, resulting in the formation of solids.

[0023] The oxidation of organic matter (incineration) to carbon dioxide and water is a well-known and widely used process for treating organic waste and producing heating steam. In the conventional steam energy process, rapid oxidation of organic fuels is often used to produce heat, which is then transferred to a fluid such as water in a heat exchanger. A heat loss of 10-15% is expected due to the losses that necessarily occur 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 heat transfer efficiency or even cause very costly losses of time due to rupture of the tube walls.

[0024] As early as 1981, document FR 2481949 described oxidation in a supercritical environment, with an additional supply of oxygen in a mixture composed of water and organic inputs, to transform an aqueous flow with a low organic content into CO2 and water, thus creating the first incinerator in supercritical conditions, more efficient because the combustion energy is carried by water under pressure and critical temperature without requiring exchangers as in traditional boilers.

[0025] The document "Gasification of biomass in supercritical water" by O. Boutin and JC Ruiz, published on 10.05.2013 in Techniques de l'ingénieur J7010, describes the implementation of hydrothermal gasification to treat certain organic effluents on a pilot scale. This conversion technology makes it possible to convert wet biomass (>70% humidity) into synthesis gas (mixture of methane, hydrogen and carbon dioxide), and to separate the mineral salts present in the input. It has been implemented, for example, in the gasification of algae for the production of hydrogen, the treatment of primary sludge from a wastewater treatment plant or the catalytic gasification of pig manure possibly mixed with eucalyptus wood. There remains a need for a process allowing the energy recovery of final waste, while preventing the formation of solids in the residue clogging the incinerators.

[0026] It has now been found that by replacing the evaporator at the bottom of the rectification column and the distillation under reduced pressure and in an inert atmosphere, with a single evaporator and its staged condensation system, the formation of solids in the cracker residue is significantly reduced, while simplifying the equipment used, in a process allowing the production of high-purity butyl acrylate. In addition, the association of a hydrothermal gasification process with said evaporator makes it possible to recover the ultimate residues in the form of gas with a high calorific value, in particular exportable methane gas, instead of transforming it into CO2 by combustion.

[0027] SUMMARY OF THE INVENTION

[0028] The present invention makes it possible to meet the above-mentioned needs. More particularly, the invention provides an improved process for producing butyl acrylate by direct esterification of acrylic acid with butanol, which makes it possible to better recover the final products usually sent to incineration, by regenerating the raw materials by cracking and transforming the residue into combustible gas. The process according to the invention makes it possible to improve the energy balance of the process while improving the material balance.

[0029] The invention consists of implementing hydrothermal gasification in association with the thermal and catalytic cracker used to recover Michael adducts. Its purpose is to recover these adducts as best as possible, in the presence or absence of solid products, on the one hand, into raw materials that can be recovered and recycled in the distillation train, and on the other hand to generate in the presence of solids and salts a gaseous phase composed of methane, hydrogen and carbon dioxide which makes it possible to meet at least the energy needs of the process and which can be recovered in the Natural Gas network of an industrial site or exported.

[0030] The invention also applies to an organic product without moisture and not recovered by hydrothermal gasification until now.

[0031] The present invention describes an evaporation system which, by recycling butyl acrylate, allows a rectification column bottom temperature to be maintained which is compatible with the heat-sensitive nature of butyl acrylate and to send the Michael adducts to the thermal and catalytic cracker, while purging the very heavy compounds and polymerization inhibitors at the bottom of this evaporator, for a process allowing the production of high-purity butyl acrylate, as described in patent EP 0609127 for the reaction part.

[0032] It also completes the purification scheme described in this patent by associating, on the one hand, an evaporator placed at the bottom of the butyl acrylate purification column with its staged condensation system and describes the recycling of the overhead products from cracking in the process, and on the other hand, a hydrothermal gasification which makes it possible to transform the cracking residue into recoverable gas (methane, hydrogen, CO2) which makes it possible at least to supply energy to the process or to recover it in a gas network.

[0033] The subject of the invention is a process for the manufacture of butyl acrylate by direct esterification of acrylic acid with excess butanol in the presence of sulfuric acid as catalyst and at least one polymerization inhibitor, leading to the production of a crude reaction mixture containing butyl acrylate, residual acrylic acid and butanol, butyl acid sulfate, traces of sulfuric acid and impurities resulting from the secondary reactions, said process comprising steps of neutralization and washing with water leading to the production of a reaction mixture free of so-called acid impurities, characterized in that said reaction mixture washed of acid impurities is subjected to at least the following steps: a) a topping step in a first distillation column called a topping column, making it possible to obtain:

[0034] - at the head a flow composed essentially of unreacted reagents;

[0035] - at the bottom a stream comprising the desired ester and heavy by-products; b) a rectification step by tailing said bottom stream from the topping column in a second distillation column making it possible to separate:

[0036] - at the top the purified desired ester;

[0037] - at the bottom a stream containing heavy by-products; c) a step of concentrating said stream from the bottom of the rectification column in an evaporator leading to a head stream, cooled in two stages in order to recycle the light compounds present to the rectification column, and to concentrate the Michael adducts; d) a step of cracking said concentrate into Michael adducts, in a thermal cracker making it possible to obtain:

[0038] - at the top the noble products from cracking which are recycled to feed the topping column,

[0039] - at the bottom the ultimate residue, e) a hydrothermal treatment step of said residue, in the presence of water, carried out in hydrothermal gasification equipment leading to the production at the top of gases of the methane, hydrogen and CO2 type, and at the bottom of solid residues and water.

[0040] The present invention overcomes the disadvantages of the state of the art. More specifically, it provides a process for obtaining a high-purity butyl acrylate having as specifications an ester purity greater than 99.5%, integrating an optimized process for removing polymerization inhibitors allowing cracking of the Michael adducts into reactants (acrylic acid and alcohol) and into a finished product, thus increasing the productivity of the process and improving the energy balance by recovering the residue to be eliminated.

[0041] Other characteristics and advantages of the invention will become more apparent upon reading the detailed description which follows, with reference to the attached Figure 1.

[0042] [Fig. 1]: overall diagram of the butyl acrylate synthesis process according to the invention, with the association of a thermal and catalytic cracker with hydrothermal gasification equipment.

[0043] DETAILED DESCRIPTION OF THE INVENTION

[0044] The subject of the invention is a process for the manufacture of butyl acrylate by direct esterification of acrylic acid with excess butanol, in the presence of sulfuric acid as catalyst and at least one polymerization inhibitor, leading to the production of a crude reaction mixture containing butyl acrylate, residual acrylic acid and butanol, butyl acid sulfate, traces of sulfuric acid and impurities resulting from the secondary reactions.

[0045] According to various embodiments, said method comprises the following characteristics, possibly combined.

[0046] After the esterification step, the process according to the invention comprises steps of neutralization and washing with water leading to the production of a reaction mixture freed from so-called acid impurities: sulfuric acid, butyl acid sulfate, acrylic acid dimer and residual acrylic acid.

[0047] Typically, the reaction mixture washed of acid impurities as described above is subjected to at least the following steps: a) a topping step in a first distillation column called a topping column, making it possible to obtain:

[0048] - at the head a flow composed essentially of unreacted reagents;

[0049] - at the bottom a flow comprising the desired ester and heavy by-products; b) the bottom flow of the topping column is subjected to a tailing rectification column allowing the separation of:

[0050] - at the top the purified desired ester;

[0051] - at the bottom a stream containing heavy by-products; c) a step of concentrating said stream from the bottom of the rectification column in an evaporator, in particular a thin-film evaporator, leading to a top stream, cooled in two stages in order to recycle the light compounds present to the rectification column, and concentrating the Michael adducts having a very low inhibitor content; d) a step of cracking said top stream from the evaporator, in a thermal cracker making it possible to obtain:

[0052] - at the top the noble products from cracking which are recycled to feed the topping column,

[0053] - at the bottom the ultimate residue, e) a hydrothermal treatment step of said residue, in the presence of water, carried out in hydrothermal gasification equipment leading to the production at the top of gases of the methane, hydrogen and CO2 type, and at the bottom of solid residues and water.

[0054] According to one embodiment, the thermal cracking may be catalytic or not.

[0055] According to one embodiment, the two residues: from the bottom of the evaporator and the residue from the cracker, are treated separately.

[0056] According to one embodiment, the two residues: from the bottom of the evaporator and the residue from the cracker, are mixed and treated in the same gasification operation.

[0057] According to one embodiment, said hydrothermal gasification equipment comprises a first reactor, a second reactor and a gas-liquid separator.

[0058] According to one embodiment, the residue is injected as is into the gasification and the water necessary for the hydrothermal treatment is injected elsewhere.

[0059] According to one embodiment, the residue is mixed with the water necessary for the hydrothermal treatment before introduction into the gasification.

[0060] According to the embodiment, hydrothermal gasification is carried out at a temperature of 350-450°C and a pressure of 25 MPa. According to the embodiment, hydrothermal gasification comprises a gasifier for separating the salt at the bottom, and a gas and liquid mixture at the top.

[0061] According to one embodiment, the hydrothermal gasification comprises a separator for separating the salt under critical conditions, a gasifier and a gas-liquid separator.

[0062] According to one embodiment, the concentration of residue / water + residue in the salt separator is between 10g / l and 400g / l.

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

[0064] According to one embodiment, the water leaving the gasifier, free of organic compounds, can be advantageously recycled to feed the separator.

[0065] According to one embodiment, the salts obtained and separated can be used as fertilizers.

[0066] According to one embodiment, a proportion of 94% to 99% of the carbon introduced into the gasification is recovered in the form of gas.

[0067] According to one embodiment, the gas resulting from gasification is composed of 40-70% methane, 5-20% hydrogen and 20-40% carbon dioxide.

[0068] In one embodiment, the gases may be further fractionated to isolate methane from other compounds.

[0069] Depending on the method of implementation, the mass composition of the main compounds of the residue from the foot of the cracker is as follows:

[0070] - Butyl butoxypropionate (BPB) 65-90%

[0071] - Para-toluene sulfonic acid (PTSA): 0.1-4%

[0072] - Phenothiazine: 100-1000 ppm

[0073] - heavy (Molecular mass > 264 g / mol); > 1%.

[0074] Depending on the embodiment, the mass composition of the evaporator base is as follows:

[0075] - Butyl butoxypropionate (BPB) 65-85%

[0076] - Para-toluene sulfonic acid: 0

[0077] - Phenothiazine: 1-10%

[0078] - heavy (Molecular mass > 264 g / mol): > 10%.

[0079] Referring to Figure 1, which represents the preferred embodiment, the topping section comprises a distillation column having an equivalent of 10 and 30 theoretical stages, preferably 10 to 15 theoretical stages. The internals used for the column may be valve trays or perforated weir trays, cross-flow trays such as Dual Flow, Ripple Trays, Turbo Grid Shell, or ordered packing such as structured packing such as Sulzer's Mellapack 25 OX.

[0080] The topping column is fed in the upper third of the column, preferably between theoretical plates 3 to 10, counting from the top of the column. The column top flow mainly comprises unreacted reactants. This recoverable flow is recycled to the reaction.

[0081] The column operates with a reflux ratio (flow rate of condensed liquid returned to the column / flow rate recycled to the reaction) of between 4 / 1 and 1 / 1, preferably 3 / 1. Advantageously, 50 to 5000 ppm of polymerization inhibitor are introduced into the purification system according to the process of the invention.

[0082] Examples of polymerization inhibitors that can be used include phenothiazine (PTZ), hydroquinone (HQ), hydroquinone monomethyl ether (EMHQ), di-tert-butyl para-cresol (BHT), paraphenylenediamine, TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy), di-tert-butylcatechol, or TEMPO derivatives, such as OH-TEMPO, alone or mixtures thereof in all proportions, at levels in the reaction medium that may be between 50 ppm and 5000 ppm, possibly in the presence of depleted air, but generally at levels between 150 ppm and 1000 ppm. The addition of polymerization inhibitors can be done at different locations, with the introduction of the reactants or at the top of the distillation column.

[0083] To make the inhibitors more effective, oxygen, air or air said to be depleted to 7% O2 should be injected at the bottom of the column. Preferably, the quantity of oxygen injected corresponds to a content of 0.2% to 0.5% relative to the quantity of organic vapor in the column.

[0084] The column can operate under vacuum, in order to minimize thermal exposure of the heat-sensitive compounds within the column. Advantageously, the topping column operates under a vacuum ranging from 1000 Pa to 30000 Pa.

[0085] The bottom flow preferably feeds the column allowing the purified ester to be obtained at the bottom of the column between theoretical plate 6 to 9.

[0086] The pure distillation column has an equivalent of 2 to 15 theoretical trays, preferably 6 to 12 theoretical stages. The internals used for the column can be valve trays or perforated weir trays, cross-flow trays such as Dual Flow, Ripple Trays, Turbo Grid Shell, or ordered packing such as structured packing such as Sulzer's Mellapack 25 OX. The column overhead stream consists of high purity butyl acrylate with specifications of an ester purity greater than 99.5%.

[0087] The column operates with a reflux ratio (flow rate of condensed liquid returned to the column / flow rate of pure liquid) between a ratio of 1 / 8 to 1 / 1, preferably 1 / 4. Like the topping column, it is stabilized and air or depleted air (7% O2) is injected at the bottom of the column. The column can operate under vacuum, in order to minimize thermal exposure of the heat-sensitive compounds within the column. Advantageously, the pure liquid column operates under a vacuum ranging from 1000 Pascal to 20000 Pascal.

[0088] Advantageously, the operating temperature is between 50°C and 160°C.

[0089] The bottom flow is concentrated on a thin-film evaporator very well suited to viscous, fouling products and dirty liquids. Evaporation is carried out in a temperature range of 80°C to 100°C and more specifically between 90°C and 100°C, in a pressure range of between 800 Pa and 2000 Pa. The top flow of this evaporator is cooled in two successive stages:

[0090] Partial condensation in a temperature range of 50 to 80°C and more specifically 60°C-70°C at the same pressure as that of the reactor to obtain on the one hand a liquid flow of Michael adducts to feed the cracker and on the other hand a flow of steam

[0091] Condensation of this vapor flow in a temperature range of 20°C to 40°C and more specifically 20°C-30°C before recovery of this liquid flow by a pump and mixing with the bottom of the topping column to feed the rectification column.

[0092] The foot residue is subjected alone or in mixture to hydrothermal gasification.

[0093] The overhead adduct stream, as well as the para-toluene sulfonic acid (PTSA) catalyst in solution in water or previously dissolved in Michael adducts, are continuously introduced into a forced recirculation cracker equipped with an external exchanger in a temperature range of 160-210°C, a residence time of the order of 2 to 10 hours, under a pressure of 200 kPa at atmospheric pressure.

[0094] According to one embodiment, the cracking is carried out at a temperature of 160°C to 180°C at atmospheric pressure.

[0095] The catalyst content relative to the quantity of adducts feeding the cracker is between 0.5 and 3% as for example in FR 2901272. The reactants generated by this cracking, essentially butanol and butyl acrylate, are returned to the purification train of the process. The residue is treated alone or preferably in a mixture by hydrothermal gasification. The residue is injected and water is injected by two circuits via high-pressure pumps into hydrothermal gasification equipment in a temperature range between 350°C and 450°C and a pressure of 25 MPa.

[0096] A first reactor allowing the salt at the bottom to be separated from the water and organic solution.

[0097] A second gasification reactor comprising a catalyst which completes the conversion of organic products into gas.

[0098] A gas-liquid separator that allows the recovery of an aqueous phase at the bottom that can be recycled to the inlet of the separator and a gaseous phase rich in methane that can be used to produce current that can provide the energy necessary for the operation of the gasification but also for that of the reaction and the purification train of this process or be exported elsewhere. This hydrothermal gasification can be carried out in batch mode or preferably in continuous mode.

[0099] The following examples illustrate the present invention without, however, limiting its scope.

[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] ABU: butyl acrylate

[0104] BuOH: butanol

[0105] BPB: butyl butoxypropionate

[0106] DBE: dibutyl ether

[0107] PDB: Butyl acryloxypropionate

[0108] Heavy Molecular mass > 264 g / mol

[0109] APTS: para-toluene sulfonic acid

[0110] BPTS: butyl para-toluene sulfononate

[0111] Example 1. Obtaining the residue from the thin-film evaporator

[0112] A commercially available DV210 / lm2 thin-film evaporator heated by 0.4 MPa steam, operating at a pressure of 130 Pa, is fed at a rate of 50 kg / h with a mixture: ABU: 9%; BuOH: 3.5%; BPB: 67%; APB: 5.7%; PTZ: 1.8%; balance to 100%: heavy residue. The overhead product (40 kg / h) is condensed at 20°C in a 4m tubular exchanger. 2. It is stabilized by adding a 250 g / h solution of butyl acrylate containing 2% phenothiazine. This overhead product feeding the cracker comprises 12.5% ​​ABU; 75% BPB; 3% Butanol and 900 ppm Phenothiazine.

[0113] The evaporator bottom product contains PTZ (6%), approximately 10% heavy and BPB as a 100% supplement.

[0114] Example 2. Thermal and catalytic cracking test

[0115] A forced recirculation boiler with a volume of 40 L is used, continuously fed using a membrane pump by heavy ABU placed on a balance, to which 1% by mass of para-toluenesulfonic acid has been added. The feed rate is measured using a mass flow meter placed on the feed line and also by the variation of the mass indicated by the balance over time. The operation is carried out at a pressure that is adjusted so as not to vaporize the butyl butoxypropionate. The temperature of the reaction medium as well as that at the inlet and outlet of the exchanger are continuously measured. The heat transfer fluid to bring the calories to the exchanger comes from an oil boiler. The heating power is fixed in order to maintain the fixed test temperature.

[0116] The heavy ABUs have been pre-distilled under vacuum and contain approximately 600 ppm of Phenothiazine.

[0117] After cracking at 180°C under a pressure of 40 kPa (300 mmHg) and a residence time of 9H defined as the reactor volume relative to the mass flow rate of Michael adduct feed, the overhead flow rate / feed rate ratio is 76% and the overhead composition comprises 48% butyl acrylate and 15% butanol.

[0118] The residue includes 0.6% APTS, 2.5% BPTS, 80% BPB, 10% heavy metals.

[0119] Example 3 Hydrothermal gasification

[0120] The ABU heavy mixture is composed of:

[0121] - Butanol < 0.1%

[0122] - Butyl acrylate: 5-10%

[0123] - Butyl hydroxypropionate (HPB): 1-3%

[0124] - Butyl butoxypropionate (BPB): 70-80% - Butyl acryloxypropionate (AA / ABU): 4-6%

[0125] - Dibutylmaleate: 2-5%

[0126] - Phenothiazine: 1-3%. 33g / h 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 250 bar. After 6 hours of testing under stabilized conditions, the heavy ABU are transformed into a gas mixture with the following volume composition: 51% EEC; 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 Process for the manufacture of butyl acrylate by direct esterification of acrylic acid with butanol in the presence of sulfuric acid as catalyst, and at least one polymerization inhibitor, leading to the production of a crude reaction mixture containing butyl acrylate, residual acrylic acid and butanol, butyl acid sulfate, traces of sulfuric acid and impurities resulting from the secondary reactions, said process comprising steps of neutralization and washing with water leading to the production of a reaction mixture free from acid impurities, characterized in that said reaction mixture washed of acid impurities is subjected to the following steps: a) a topping step in a first distillation column called a topping column, making it possible to obtain: - at the head a flow composed essentially of unreacted reagents; - at the bottom a stream comprising the desired ester and heavy by-products; b) a rectification step by tailing said bottom stream from the topping column in a second distillation column making it possible to separate: - at the top the purified desired ester; - at the bottom a stream containing heavy by-products; c) a step of concentrating said stream from the bottom of the rectification column in an evaporator leading to a head stream, cooled in two stages in order to recycle the light compounds present to the rectification column, and to concentrate the Michael adducts; d) a step of cracking said concentrate into Michael adducts, in a thermal cracker making it possible to obtain: - at the top the noble products from cracking which are recycled to feed the topping column, - at the bottom the ultimate residue, e) a hydrothermal treatment step of said residue, in the presence of water, carried out in hydrothermal gasification equipment leading to the production at the top of gases of the methane, hydrogen and CO2 type, and at the bottom of solid residues and water. The method of claim 1, wherein said acidic impurities are sulfuric acid, butyl acid sulfate, acrylic acid dimer, and residual acrylic acid. The method of any one of claims 1 and 2, wherein the polymerization inhibitor is selected from: phenothiazine (PTZ), hydroquinone (HQ), hydroquinone monomethyl ether (EMHQ), di-tert-butyl para-cresol (BHT), paraphenylenediamine, TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy), di-tert-butylcatechol, OH-TEMPO, or mixtures thereof in any proportion. Process according to any one of claims 1 to 3, in which the polymerization inhibitor is used in the reaction medium or in the purification steps at contents of between 50 ppm and 5000 ppm, preferably between 150 ppm and 1000 ppm.Process according to any one of claims 1 to 4, wherein the polymerization inhibitor is added at different locations, with the reactants or at the top of the distillation column. Process according to any one of claims 1 to 5, wherein the evaporation is carried out in a temperature range of 80°C to 100°C, preferably between 90°C and 100°C, and at a pressure of between 800 Pa and 2000 Pa. Process according to any one of claims 1 to 6, wherein the evaporator top stream is cooled in two successive stages: a. partial condensation in a temperature range of 50 to 80°C and more specifically 60°C-70°C at the same pressure as that of the evaporator to obtain on the one hand, a liquid flow of Michael adducts, having an inhibitor content of less than 1000 ppm, going to feed the cracker, and on the other hand, a flow of vapor, and. b. condensation of this vapor stream in a temperature range of 20°C to 40°C and more especially 20°C-30°C before taking up this liquid stream by a pump and feeding the rectification column. Process according to any one of claims 1 to 6, wherein the cracking is carried out at a temperature of 160°C to 180°C at atmospheric pressure. Process according to any one of claims 1 to 8, wherein the butyl acrylate obtained has a purity greater than 99.5%. Process according to any one of claims 1 to 9, wherein the hydrothermal gasification comprises a separator for separating the salt under critical conditions, a gasifier and a gas-liquid separator. Process according to claim 10, wherein the concentration of residue / water + residue in said separator is between 10g / l and 400g / l.Process according to one of claims 1 to 11, in which the gasification generates a gas composed of 40 to 70% methane, 5-20% hydrogen and 20-40% carbon dioxide. Process according to one of claims 10 to 12, in which the water leaving the gasifier, free of organic compounds, is recycled to the feed of the separator.