Method for producing biobased alpha-beta-unsaturated carboxylic acids from poly(3-hydroxyalkanoate) contained in biomass

Abstract

The present invention relates to a method for producing biobased α-β-unsaturated carboxylic acids from a biomass containing a poly(3-hydroxyalkanoate), comprising the extraction of the poly(3-hydroxyalkanoate), followed by thermolysis of the polymer in the solid or melt state, in the presence of polymerisation inhibitors and in the absence of catalyst, resulting in the production of biobased α-β-unsaturated carboxylic acids.

Description

[0001]PROCESS FOR PRODUCING BIOSOURCED α-β UNSATURATED CARBOXYLIC ACIDS FROM POLY(3-HYDROXYALKANOATE) CONTAINED IN BIOMASS Technical field The present invention relates to a process for producing biosourced ^- ^ unsaturated carboxylic acids from a biomass containing a poly(3-hydroxyalkanoate), comprising the extraction of said poly(3-hydroxyalkanoate) in the presence of polymerization inhibitors, followed by thermolysis of said polymer in the solid or molten state, in the absence of a catalyst, leading to the production of biosourced ^- ^ unsaturated carboxylic acids. Prior art and technical problem The industrial production of ^- ^ unsaturated carboxylic acids is currently mainly carried out from raw materials of fossil origin. For example, acrylic acid is obtained by oxidation of propylene, or methacrylic acid can be obtained by oxidation of isobutylene.One possible way to obtain these ^- ^ unsaturated carboxylic acids is the thermolysis at temperatures of 150 to 300 °C of the corresponding poly(3-hydroxyalkanoates) (P3HA), according to the following reaction: [Chem 1]. R1= H or alkyl and R2= H or alkyl; n is a number greater than 30 If R1=R2= H: - Poly(3-hydroxyalkanoate) = poly(3-hydroxypropionate) (P3HP); - Unsaturated carboxylic acid = propenoic acid (acrylic acid). If R1= methyl and R2= H: - Poly(3-hydroxyalkanoate) = poly(3-hydroxyisobutyrate) (P3HiB); - Unsaturated carboxylic acid = isobutenoic acid (methacrylic acid). If R1= H and R2= methyl: - Poly(3-hydroxyalkanoate) = poly(3-hydroxybutyrate) (P3HB); - Unsaturated carboxylic acid = but-2-enoic acid (crotonic acid). If R1=H and R2 = ethyl: - Poly(3-hydroxyalkanoate) is poly(3-hydroxyvalerate) (P3HV); - Unsaturated carboxylic acid = pent-2-enoic acid These poly(3-hydroxyalkanoates) can themselves be previously obtained by chemical transformations of raw materials of fossil origin, but also by fermentation of biomass.There is a strong market demand for these ^-^ unsaturated carboxylic acids, used as monomers in many applications, to be obtained from bio-based raw materials. These bio-based raw materials are derived from renewable organic matter (biomass) of biological origin (microorganisms, plants or animals). A potential problem with such a process is that the P3HA obtained by fermentation is present inside the cell. Thermolysis is therefore carried out in the presence of the cell membrane, which poses problems of reactor fouling or the presence of impurities in the final product. Several solutions have been proposed to solve this problem.US 9850192 describes a process for the production of acrylic acid from genetically modified microbial biomass metabolizing glucose or any other renewable raw material, to produce a homopolymer or copolymer of poly(3-hydroxypropionate) (P3HP) inside the microbial cells. Said process comprises a step of thermolysis of the washed / dried / ground biomass containing P3HP, in the presence of a catalyst. This process effectively makes it possible to produce acrylic acid while limiting the formation of oligomers of the latter, such as the dimer of acrylic acid which is spontaneously formed during the production of acrylic acid. The acrylic acid is recovered in gaseous form and then condensed, while the catalyst as well as the residual mass of biomass can be recycled in the process or subjected to thermal regeneration.However, there is a risk that the residue present in the reactor after thermolysis will be pasty and sticky, which could make it difficult to scale up to industrial scale. Example 5 and Figure 7 describe how to implement this invention on an industrial scale. After fermentation, the biomass is washed and dried using either an atomizer or a double-drum dryer. After adding the catalyst, the product is pyrolyzed in a FAST reactor. TMat 250-350 °C with a residence time of between 0.25- 1 hour using an inert gas such as nitrogen to send the vapors formed to the purification equipment. The vapor phase is composed of 90% organic / water and 10% inert gas. The gas is then purified, following the process described in document US 6646161 or in document US 20120006673, to obtain acrylic acid still containing many impurities. Complete purification is carried out using distillation columns, as described in documents US 7332624 and US 7179875, and may also require crystallization operations, as described in documents US 6482981 and US 71798750. Another solution consists of first extracting the P3HA from the biomass using an organic solvent before carrying out its thermolysis. Document US 20150376152 describes in Example 6 the extraction of P3HP from biomass, using an organic solvent, such as 2-butanone, thenobtaining acrylic acid in three stages: evaporation of the solvent and condensation of the latter in a receiving pot; thermal degradation of the P3HP in the absence of an inhibitor leading to the production of acrylic acid vapor, and finally distillation and condensation of the acrylic acid in a receiving pot containing hydroquinone to prevent polymerization of the acrylic acid. In its application FR 2208914, the applicant company proposes to carry out the thermolysis of P3HA in the absence of a catalyst and in the presence of a polymerization inhibitor; typically, the vapor pressure of at least one of the inhibitors at the thermolysis temperature is at least twice the pressure at which the thermolysis is carried out, which has the effect of preventing the formation of polymers in the reactor as well as the gaseous phase in the event of accidental condensation or at the time of condensation of the acrylic acid vapors at the top of the column. In its application FR 2208916,the applicant company describes a process using a solvent which makes it possible to selectively solubilize the P3HA from the biomass, separate the insoluble organic detritus in said solvent, and then carry out a thermolysis treatment of the P3HA and solvent medium in the liquid phase in the presence of polymerization inhibitors. Document WO 2016 / 039618 describes the thermal degradation of a dry biomass containing poly(3-hydroxybutyrate) in order to produce crotonic acid. In Example 1, it is shown that crotonic acid can be obtained with comparable yields of less than 60% from wet or dry biomass, in the absence of a catalyst. It has now been discovered that it is possible to simplify the procedure for manufacturing unsaturated ^- ^ carboxylic acids, by carrying out the thermolysis of P3HA in the absence of solvent, after prior extraction of the P3HA from the cell membrane, and in a mixture with at least one polymerization inhibitor insolid phase, without the use of a catalyst and without injecting inert gas to drive the vapors out of the reaction zone. More precisely, "in the absence of a catalyst" means that the thermolysis of PHA in the presence of at least one polymerization inhibitor takes place in the absence of another chemical species that accelerates or redirects the kinetics of the reaction. Thermolysis as envisaged is only induced by operating conditions such as temperature, pressure and residence time. Chemical species that lead to different types of catalysis depending on the nature of the species are excluded: - homogeneous catalysis, if the catalyst and the reactants form only one phase (often liquid); - heterogeneous catalysis, if the catalyst and the reactants form several phases (generally a solid catalyst for reactants in the gaseous or liquid phase); - enzymatic catalysis, if the catalyst is an enzyme, i.e. a protein.Consequently, the invention proposes to provide a simple and easy-to-implement solution for reducing fouling phenomena and the presence of impurities in the final product, and thus maintaining high reliability and high productivity in processes for manufacturing unsaturated carboxylic acids from poly(3-hydroxyalkanoates) obtained by fermentation. Summary of the invention The subject of the present invention is a process for manufacturing a bio-sourced unsaturated carboxylic acid from a biomass containing a poly(3-hydroxyalkanoate) (P3HA) in the absence of a catalyst, said process comprising the following steps: - extracting the poly(3-hydroxyalkanoate) from the biomass using a solvent capable of solubilizing the P3HA; - evaporating the solvent to yield a solid P3HA having a purity of at least 95% by weight; - mixing the extracted P3HA with at least one polymerization inhibitor in the solid state; - submit said solid mixture P3HA -inhibitor in a thermolysis step leading to obtaining on the one hand, said ^- ^ unsaturated carboxylic acid in vapor phase, and on the other hand, a molten residue; - separating the two phases formed into a gaseous phase and a solid phase; - purifying said gaseous phase to obtain a purified ^- ^ unsaturated carboxylic acid; - treating the residue in solid phase. According to various embodiments, said method comprises the following characteristics, where appropriate combined. The contents indicated are expressed by weight, unless otherwise indicated. Within the ranges of values ​​indicated, the limits are included. According to one embodiment, the poly(3-hydroxyalkanoate) used in the method comprises a single type of 3-hydroxyalkanoate unit and the product formed is therefore composed of a single ^- ^ unsaturated carboxylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the ^- ^ unsaturated carboxylic acid produced is acrylic acid. According to one embodimentembodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutyrate) and the unsaturated carboxylic acid produced is methacrylic acid. In one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) and the unsaturated carboxylic acid produced is crotonic acid. In one embodiment, the poly(3-hydroxyalkanoate) used in the method comprises several different 3-hydroxyalkanoate units and the product formed is therefore composed of a mixture of different unsaturated carboxylic acids. Examples of P3HA copolymers are poly-3-hydroxybutyrate-co-3-hydroxypropionate (poly-3HB-co-3HP) or poly-3-hydroxybutyrate-co-3-hydroxyvalerate (poly-3HB-co-3HV). In one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxypropionate unit and at least one of the ^- ^ unsaturated carboxylic acids produced is acrylic acid. In one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxyisobutyrate and at least one of the ^- ^ unsaturated carboxylic acids produced is methacrylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxybutyrate unit and at least one of the ^- ^ unsaturated carboxylic acids produced is crotonic acid. According to one embodiment, the host of the biomass is a bacterium, a yeast, a fungus, an algae, a cyanobacterium or a mixture of two or more of these elements. According to the embodiment, the P3HA used is extracted beforehand from the biomass, to result in a solid P3HA having a purity of at least 95%. According to one embodiment, the method according to the invention comprises a step of condensation of the vapors of the ^- ^ unsaturated carboxylic acid(s) obtained by the thermolysis reaction of poly(3-hydroxyalkanoate), followed by one or more purification steps. Purification operations may generally include distillations, extractionsliquid / liquid, separations using a film evaporator, or crystallizations. According to one embodiment, the process according to the invention comprises a step of treating said molten residue obtained at the end of thermolysis, for example by upgrading the latter by hydrothermal gasification into methane. The present invention meets the need expressed in the state of the art. It makes it possible to prevent the risks of fouling of the thermolysis reactor and / or the presence of impurities in the final product of unsaturated carboxylic acids, originating from cell membranes, by making it possible to obtain a gaseous phase rich in unsaturated carboxylic acid and also containing polymerization inhibitors as well as a molten or slightly pasty residue which can be upgraded. This solution has the advantage of carrying out the thermolysis of P3HA in the solid or molten state, which reduces the energy and environmental cost of the process. The invention will now be describedin more detail in the description which follows. Detailed description of the invention The invention aims to produce biosourced ^- ^ unsaturated carboxylic acids on an industrial scale by thermolysis of poly(3-hydroxyalkanoates) contained in biomass, while limiting the problems of fouling of the thermolysis reactor and / or the presence of impurities in the final product. The term "thermolysis" of poly(3-hydroxyalkanoate) (P3HA) means its chemical decomposition into ^- ^ unsaturated carboxylic acid obtained under the effect of temperature. This term is synonymous with pyrolysis. The subject of the present invention is a process for manufacturing a biosourced ^- ^ unsaturated carboxylic acid from a biomass containing a poly(3-hydroxyalkanoate) (P3HA) and in the absence of a catalyst, said process comprising the following steps: - extracting the poly(3-hydroxyalkanoate) from the biomass using a solvent capable of solubilizing the P3HA; - evaporating the solvent to produce a solid P3HA havinga purity of at least 95% by weight; - mixing the extracted P3HA with at least one polymerization inhibitor in the solid state; - subjecting said solid P3HA-inhibitor mixture to a thermolysis step leading to obtaining on the one hand said ^- ^ unsaturated carboxylic acid in the vapor phase and on the other hand a molten residue; - separating the two phases formed into a gas phase and a solid phase; - purifying said gas phase to obtain a purified ^- ^ unsaturated carboxylic acid; - treating the residue in the solid phase. According to one embodiment, said method for manufacturing a biosourced ^- ^ unsaturated carboxylic acid from a biomass containing a poly(3-hydroxyalkanoate) (P3HA) comprises the following steps: - extracting the poly(3-hydroxyalkanoate) from the biomass using a solvent capable of solubilizing the P3HA in a solvolysis reactor; - removing the cell membrane by liquid-solid separation; - evaporation of the solvent to produce a P3HAsolid having a purity of at least 95% by weight in this same reactor; - introduction of the P3HA and at least one polymerization inhibitor into a thermolysis reactor; - mixing of the P3HA and at least one polymerization inhibitor in said reactor; - thermolysis of this mixture stirred at a given temperature and at a controlled pressure in this same reactor in order to generate a vapor phase and a viscous phase; - separation of the two phases formed in a gas-liquid separator leading to the production of a gaseous phase and a residue; - treatment of said residue; - condensation of the gaseous phase; - treatment of the condensed phase to obtain the unsaturated carboxylic acid by the use of one or more distillation columns making it possible, on the one hand, to separate the unsaturated carboxylic acid from products heavier than the latter and, on the other hand, to obtain products lighter than the latter. According to one embodiment, said solvolysis reactoris stirred and heated to a temperature between 20°C and 170°C, preferably 50°C to 140°C. According to one embodiment, the cell membrane is removed by filtration or centrifugation. According to one embodiment, the solvent is evaporated by heating under reduced pressure between 3 kPa and 101 kPa, preferably 20 kPa and 60 kPa, in a temperature range between 50°C and 140°C. According to one embodiment, the introduction of P3HA and at least one polymerization inhibitor into said thermolysis reactor is carried out by means of a pipe or by a conveyor of the screw type. Advantageously, said thermolysis reactor is suitable for the treatment of solid, molten or pasty mixtures. According to one embodiment, the mixing of P3HA and at least one polymerization inhibitor in said thermolysis reactor is carried out by means of several endless screws operated in a sheath allowing the mixing of P3HA and at least one polymerization inhibitor.less one inhibitor. According to one embodiment, said residue is treated by valorization by spreading, by combustion or by hydrothermal gasification. According to one embodiment, the condensation of the gaseous phase is carried out by a system of at least one condenser of the tubular condenser type at the pressure of the thermolysis, by cooling it and by collecting the liquid phase obtained in a stirred storage tank, with optionally an addition of one or more additional inhibitors. According to one embodiment, said products heavier than the unsaturated carboxylic acid are recycled upstream of the thermolysis reactor, or are mixed with the solid residue resulting from the thermolysis. According to one embodiment, said products lighter than the unsaturated carboxylic acid are valorized by combustion or hydrothermal gasification. According to one embodiment, the unsaturated carboxylic acid obtained is purified by a crystallization operationfractionated comprising several separation stages to obtain high-purity unsaturated carboxylic acid ^- ^ and a residue to be recovered as energy or recycled. According to one embodiment, the process according to the invention allows the production of several bio-sourced α-β unsaturated carboxylic acids from the poly(3-hydroxyalkanoate) contained in the biomass. The invention is based on the use of a mixture of P3HA and at least one polymerization inhibitor by implementing a technology for mixing solids and thermal treatment of the latter. The term "biomass" means organic matter of plant (including microalgae), animal, bacterial or fungal (fungi) origin, usable as a source of bio-sourced raw materials, as opposed to raw materials of fossil origin. In the process according to the invention, the first stage uses genetically modified host biomass, resulting from genetic engineering. According to one embodimentembodiment, the biomass host is a bacterium, a yeast, a fungus, an algae, a cyanobacterium or a mixture of two or more of these elements. The biomass is obtained by a prior step of culturing a recombinant host with a renewable raw material. According to one embodiment, the renewable raw material is chosen from glucose, fructose, sucrose, arabinose, maltose, lactose, xylose, ethanol, methanol, glycerol, fatty acids, vegetable oils and syngas derived from the biomass or a combination thereof. According to one embodiment, the biomass used in the method according to the invention comes from a bacterial fermentation process of sugars or lipids. Depending on the culture conditions and the variety of the microorganism used, poly(3-hydroxyalkanoates) (P3HA) homo- or co-polymers with different 3-hydroxyalkanoic acid units are formed. The biomass used ispretreated by washing, drying and grinding operations, to result in a biomass containing at least 30% by weight of P3HA, preferably at least 50% by weight of P3HA. The step of extracting P3HA from the biomass by a solvent comprises a separation of organic detritus insoluble in said solvent, for example cell membranes, from the P3HA-solvent mixture, which is carried out by filtration or by centrifugation. The step of extracting P3HA from the biomass by a solvent takes place at a temperature of 20 to 130°C. According to one embodiment, the step of extracting P3HA from the biomass by a solvent takes place in batch mode. According to a preferred embodiment, the step of extracting P3HA from the biomass by a solvent takes place continuously. According to one embodiment, the solvent used to extract the P3HA present in the biomass at atmospheric pressure is chosen from polar solvents having a boiling temperature higher than the extraction temperature.but lower than the thermolysis temperature. These solvents may be linear or branched alcohols having a carbon number less than or equal to 7, for example heptanol or n-butanol, linear or branched aldehydes or ketones having a carbon number less than or equal to 7, such as hexanal or butanone, or carboxylic acids having a carbon number less than C4, such as butyric acid. The solvent used in the process must be capable of solubilizing the P3HAs at a content greater than 5% by weight of the solution, preferably greater than 20%, at the temperature used during the extraction step. Then, the solvent is evaporated to yield a solid P3HA having a purity of at least 95% by weight. Depending on the embodiment, the evaporation can be carried out under a pressure of 20 kPa to 100 kPa at a temperature between 20°C and 150°C. The solid P3HA is then mixed with at least one polymerization inhibitor chosenamong the inhibitors conventionally used in existing industrial processes for the production of ^- ^ unsaturated carboxylic acids. These include phenolic derivatives such as hydroquinone (HQ) and its derivatives such as hydroquinone methyl ether (EMHQ), 2,6-di-terbutyl-4-methyl phenol (BHT) or 2,4-dimethyl-6-terbutyl phenol (Topanol A); phenothiazine and its derivatives; nitroxide compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-OH-TEMPO); and amine compounds such as paraphenylenediamine derivatives. According to a preferred embodiment, at least one of said polymerization inhibitors is hydroquinone methyl ether (EMHQ). According to one embodiment, the mass content of inhibitor in the mixture with the P3HA is between 0.1% and 10%, preferably from 0.4% to 5%. According to the invention, the system for feeding P3HA and at least one polymerization inhibitor into the thermolysis reactor may be apipe, a screw conveyor, a conveyor belt or a hopper, a pneumatic transport, a vibrating conveyor, an extruder. In addition, they can be coupled to a dosing device. The mixture of P3HA and at least one polymerization inhibitor is then subjected to thermolysis in the solid or molten state. The step of mixing the P3HA and at least one polymerization inhibitor can be carried out in a conveyor mixer comprising several screw conveyors operated in a barrel or directly in the thermolysis reactor. According to one embodiment, the mixing and thermolysis steps are carried out continuously by successively operating the conveyor mixture and the thermolysis reactor or by carrying out these two operations in the thermolysis reactor. Preferably, the thermolysis reactor carries out the mixing as well as the thermolysis reaction. The heating of the mixture can be carried out at a temperature between 100 °C and a temperature belowthe auto-ignition temperature of the monomer formed. For acrylic acid this temperature is 438°C at atmospheric pressure (Standard NF T 20037). Preferably, the heating temperature is between 150°C and 400°C, advantageously between 200 and 350°C. The heating can be staged, with a first temperature zone of the order of 100°C-200°C, which makes it possible to liquefy all or part of the mixture while avoiding the polymerization of the acrylic acid. According to one embodiment, the pressure in the thermolysis reactor is between 3 kPa and 101 kPa, preferably between 15 kPa and 40 kPa. According to one embodiment, the residence time in the thermolysis reactor is between 0.05 h and 1 h, preferably between 0.15 and 0.5 h. According to one embodiment, the installation allowing the implementation of the method also comprises a reactor adapted for heating for thermolysis. For example, the heating can be carried out by exposing themixing with microwaves, pulsed electric fields or water vapor or a preheated inert gas, by a solid such as preheated sand, by contact with a hot surface such as in an extruder, a screw conveyor, a rotating drum, a tray. The hot surface can be heated by different means: direct electric heating, heating by heat transfer fluid (water vapor, oil, molten salts). According to one embodiment, the heat supply is made through a hot surface heated by a heat transfer fluid and in particular molten salts. The thermolysis reactor according to the invention can be an extruder or conveyor, a reactor suitable for pyrolysis, for high-temperature pyrolysis, or a fluidized reactor or a reactor suitable for solvolysis or a reactor consisting of hollow plates heated by a heat transfer fluid circulating in the plates. Nevertheless, reactors have been identified which allowhigher yield gains in unsaturated ^- ^ carboxylic acid such as: a conveyor, an extruder, an extruder-conveyor and / or a set of heating plates. According to the invention, the extruder-conveyor is a reactor comprising one or more endless screws each actuated in a barrel, allowing in particular the mixing of the elements introduced into said barrel. The use of an extruder-conveyor for the implementation of this P3HA thermolysis process is advantageous from an environmental, safety and process security point of view. Indeed, an extruder-conveyor makes it possible to treat molten media without resorting to the addition of a solvent to reduce the viscosity of the molten medium. The extruder-conveyor has the advantage of allowing efficient heat transfer from the barrel to the P3HA - inhibitor medium. The extruder can be advantageously replaced by a screw conveyor system in all or part of its length.Advantageously, the system may comprise the combination of a conveyor-type device in the first part, followed by an extruder-type device and a conveyor configured to transport the residue to the outlet. For example, the conveyor may be of the “Archimedes screw” type (endless screw). A thermolysis system according to the invention may comprise an extruder, such as the twin-screw extruder 200, comprising an inlet for the P3HA mixture - solid or pre-melted inhibitor. A twin-screw extruder may be a Cletrax-type extruder. The twin-screw extruder comprises two screws, most often parallel, rotating inside a barrel. Advantageously, the extruder has a modular nature, that is to say that the screw and the barrel are modules assembled in series and whose assembly can be modified. In the extruder, an external heating means regulating the temperature of the barrel is advantageously configured to, on the one hand, bring theP3HA - inhibitor mixture in the molten state, and on the other hand, to carry out the thermolysis of the P3HA. According to one embodiment, the thermolysis system comprises a device consisting of hollow plates, heated by a heat transfer fluid circuit (pressurized steam, oil, molten salts). During its treatment, the article advances on the plates of increasing temperatures initially. The residue finishes its passage in the reactor by passing on plates which are at a lower temperature and where the heat exchange takes place from the residue to the heat transfer fluid. The heat transfer fluid thus heated can then be used to preheat the P3HA - inhibitor mixture feeding the thermolysis reactor. According to one embodiment, the thermolysis system is a conveyor mixer type device, for example of the screw conveyor type. This device comprises a reactor in which two endless screws operate in opposition. The heating of the mixture is done through the wallhot using a heat transfer fluid such as water vapor. The movement of the two screws makes it possible to mix and homogenize the P3HA and polymerization inhibitor feeds. According to one embodiment, the method according to the invention carries out the thermolysis of the P3HA-inhibitor mixture by means of an extruder at a temperature of the order of 150-400 °C. In the thermolysis reactor, the P3HA - inhibitor mixture is, under the action of heat, transformed into gaseous compounds comprising an unsaturated carboxylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) (P3HP), and the unsaturated carboxylic acid obtained by the method according to the invention is acrylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutanoate) (P3HiB), and the unsaturated carboxylic acid obtained by the method according to the invention is methacrylic acid. According to one embodiment, thepoly(3-hydroxyalkanoate) is poly(3-hydroxybutanoate) (P3HB), and the unsaturated carboxylic acid obtained by the process according to the invention is crotonic acid. According to one embodiment, the invention relates to a process for manufacturing a mixture of α-β unsaturated carboxylic acids from a P3HA contained in biomass comprising several different 3-hydroxyalkanoate units. The gases containing the unsaturated carboxylic acid(s) can be directed to a cooling system in order to be condensed. The condensate obtained can then be collected in a chamber provided for this purpose. The reactor enclosure and the chamber are preferably under negative pressure. The condensation system can be equipped with an injection of one or more inhibitors. In order to enable the recovery of a purified ^- ^ unsaturated carboxylic acid the system may comprise a purification device, for example one or more distillation columns, one or moreliquid extraction, crystallization or membrane separation equipment. The solid residue is then recovered, for example by hydrothermal gasification or in the form of fuel. According to one embodiment, the condensation is carried out by using one or more tubular or spiral exchangers in series. According to one embodiment, the condensation is carried out by successive pressure adjustment and separation of the gaseous and liquid phases obtained containing unsaturated carboxylic acid and contaminants which can be recycled back into the reactor. According to the invention, the condensation is carried out by successive condensation temperature adjustment carried out by placing one or more condensers in series and separation of the gaseous and liquid phases obtained containing unsaturated carboxylic acid and contaminants which can be recycled back into the reactor or sent to the purification system. According to oneembodiment, one or more polymerization inhibitors are added to the condenser. According to one embodiment, this condensation can be carried out by bringing the ^- ^ unsaturated carboxylic acid in the gaseous state into contact with the ^- ^ unsaturated carboxylic acid in the liquid state. This contacting can for example be carried out in a shower-type device, by spraying the liquid ^- ^ unsaturated carboxylic acid into an enclosure collecting the ^- ^ unsaturated carboxylic acid in the gaseous state. According to one embodiment, no inhibitor is added to the condenser. According to one embodiment, the residue obtained after the thermolysis step is recovered by hydrothermal gasification. According to the embodiment, the hydrothermal gasification is carried out at a temperature of 350-450 °C and a pressure of 25 MPa. The examples below illustrate the present invention without, however, limiting its scope. EXPERIMENTAL PART The examples arecarried out on biomass containing 60% by weight of poly(3-hydroxypropionate) (P3HP). The ^- ^ unsaturated carboxylic acid obtained after thermolysis is acrylic acid (AA). The biomass containing P3HP is brought into contact with a solvent solubilizing the P3HP, then this mixture is treated by centrifugation to separate the insolubles (such as the cell membrane) from the P3HP-solvent mixture. The solvent is then evaporated under vacuum to recover the solid P3HP. Thermolysis is carried out by placing the solid P3HP (2 g) as well as the inhibitor (0 or 20 mg of EMHQ or PTZ) in a 50 mL two-necked flask equipped with a magnetic bar. The medium is stirred using a magnetic stirrer to distribute the inhibitor in the solid. This 50 mL two-necked flask containing the medium is equipped on the side neck with a thermometer to monitor the temperature of the thermolysis medium and on the upper neck with a separation bridge leading to a water-cooled side condenser. The condenser leads toa recipe consisting of a 25 mL single-necked flask. A tapping allows the experiment to be carried out under partial vacuum. At the beginning of the experiment, the system is placed under the desired pressure and then the flask containing the P3HP-Inhibitor mixture is placed in a heating system to establish the desired thermolysis temperature (oil bath or electric heating mantle). The recipe is cooled by an ice bath. As soon as the thermolysis reactor reaches more than 170 °C, the formation of AA vapors is observed, which condense mainly in the lateral condenser. After 4 h of heating, the formation of AA vapors in the thermolysis reactor decreases and the experiment is then stopped. The consistency of the thermolysis residue is judged visually at the end of the experiment. The results obtained are presented in Table 1. [Table 1] Test Inhibitor Vapor Pressure Operating Pressure Inhibitor Thermolysis Residue (kPa) at 200°C (kPa) 1 No - 100 Hard Solidsticky 2 No - 55 Sticky hard solid 3 No - 20 Sticky hard solid 4 EMHQ 28.5 100 Viscous pasty solid 5 EMHQ 28.5 55 Viscous pasty solid 6 EMHQ 28.5 20 Viscous pasty solid 7 PTZ 0.7 100 Sticky pasty solid 8 PTZ 0.7 55 Sticky pasty solid 9 PTZ 0.7 200 Sticky pasty solid The results in Table 1 highlight that the physical state of the residue is dependent on the presence of the inhibitor, particularly EMHQ. The addition of inhibitor allows the residue to become pasty and viscous whereas it was sticky without the addition of the latter. This change in consistency of the residue allows easier extraction of the latter when it is necessary to carry out continuous thermolysis. The tests of the following examples 10-12 are carried out in the same laboratory setup. - using P3HP purified from biomass as described previously. EXAMPLE 10 (comparative): Use of pure P3HP without catalyst and without inhibitor 2.05 g of purified P3HP areplaced in a 25 ml two-necked flask equipped with magnetic stirring. The flask is placed at 20 kPa pressure using a membrane vacuum pump and then heated to 200°C for 4 hours. The vapors generated are condensed using a water-cooled side condenser to obtain 1.41 g of acrylic acid, which corresponds to a 68% yield. The solid obtained after cracking forms a thin layer that remains stuck to the walls of the two-necked flask. The layer formed is very difficult to remove from the two-necked flask. Solid particles are found in the head of the flask and on the side condenser. In the absence of a catalyst, the recovery yield of acrylic acid is low, around 68%. This low value is consistent with that cited in document WO 2016 / 039618 example 1 in which the thermolysis of PHB leads to the production of 57% crotonic acid. In addition to this low yield, there is the presence of solid particles which is detrimental to the development of this process. EXAMPLE 11(according to the invention): Use of pure P3HP with the addition of 1% 4-methoxyphenol (EMHQ) without catalyst 2.12 g of purified P3HP are placed in a 25 ml two-necked flask equipped with magnetic stirring. 0.021 g of EMHQ are added to the flask and mixed with PH3P. The flask equipped with a separation bridge is placed at 20 kPa pressure using a membrane vacuum pump. The flask is heated to 200°C for 4 hours. The vapors generated are condensed using a water-cooled side condenser to obtain 1.99 g of acrylic acid, which corresponds to a 94% yield. After cracking, very little solid remains in the flask; this solid is easily removed from the flask by simple scraping. EXAMPLE 12 (according to the invention): Use of pure P3HP with the addition of 5% 4-methoxyphenol (EMHQ) without catalyst 2.12 g of purified P3HP are placed in a 25 ml two-necked flask equipped with magnetic stirring. 0.117 g of EMHQ are added to the flask and mixed with the PH3P. The flaskequipped with a separation bridge is placed at 20 kPa pressure using a membrane vacuum pump. The flask is heated to 200°C for 4 hours. The generated vapors are condensed using a water-cooled side condenser to obtain 1.85 g of acrylic acid, which corresponds to an 87% yield. After cracking, very little solid remains in the flask; this solid is easily removed from the flask with simple scraping. The yield obtained in Examples 11 and 12 is therefore significantly higher than that reported in Example 1 of document WO 2016 / 039618, where thermal degradation also occurs in the absence of a catalyst. Only when thermolysis occurs in the presence of a catalyst does the yield increase to 86 or 89% respectively (for Examples 2 and 3 of said document). These examples also show that in the presence of an inhibitor, in the process according to the invention, the thermolysis yields are very high in the absence of catalyst and even in thermal conditionsmore moderate since this thermolysis is carried out at 200°C (290°C with catalyst in W02016 / 039618 example 1).

Claims

CLAIMS 1. Process for manufacturing a biosourced ^- ^ unsaturated carboxylic acid from a biomass containing a poly(3-hydroxyalkanoate) (P3HA) and in the absence of a catalyst, said process comprising the following steps: - extracting the poly(3-hydroxyalkanoate) from the biomass using a solvent capable of solubilizing the P3HA; - evaporating the solvent to yield a solid P3HA having a purity of at least 95% by weight; - mixing the extracted P3HA with at least one polymerization inhibitor in the solid state; - subjecting said solid P3HA-inhibitor mixture to a thermolysis step leading to obtaining, on the one hand, said ^- ^ unsaturated carboxylic acid in the vapor phase, and on the other hand, a molten residue; - separating the two phases formed into a gas phase and a solid phase; - purifying said gas phase to obtain a purified ^- ^ unsaturated carboxylic acid; - treating the residue in the solid phase. 2.Method according to claim 1, comprising the following steps: - extraction of the poly(3-hydroxyalkanoate) from the biomass using a solvent capable of solubilizing the P3HA in a solvolysis reactor; - elimination of the cell membrane by liquid-solid separation; - evaporation of the solvent to produce a solid P3HA having a purity of at least 95% by weight in this same reactor; - introduction of the P3HA and at least one polymerization inhibitor into a thermolysis reactor; - mixing of the P3HA and at least one polymerization inhibitor in said reactor; - thermolysis of this mixture stirred at a given temperature and at a controlled pressure in this same reactor or in another of the same type in order to generate a vapor phase and a viscous phase;. - separation of the two phases formed in a gas-liquid separator, leading to the production of a gaseous phase and a residue; - treatment of said residue; - condensation of said gaseous phase; - treatment of the condensed phase to obtain the unsaturated α-β carboxylic acid by using one or more distillation columns making it possible, on the one hand, to separate the unsaturated α-β carboxylic acid from products heavier than the latter, and on the other hand to obtain products lighter than the latter.

3. Method according to one of claims 1 or 2, in which the biomass used is treated beforehand by washing, drying or grinding operations, to produce a biomass containing at least 30% by weight of P3HA, preferably at least 50% by weight of P3HA. 4.A method according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxypropionate unit and at least one of the α-β unsaturated carboxylic acids produced is acrylic acid.

5. A method according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the α-β unsaturated carboxylic acid produced is acrylic acid.

6. A method according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxybutyrate unit and at least one of the α-β unsaturated carboxylic acids produced is crotonic acid.

7. A process according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) and the α-β unsaturated carboxylic acid produced is crotonic acid. 8.A method according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxyisobutyrate unit and at least one of the α-β unsaturated carboxylic acids produced is methacrylic acid.

9. A process according to any one of claims 1 to 3, wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutyrate) and the α-β unsaturated carboxylic acid produced is methacrylic acid.

10. A process according to any one of the preceding claims, wherein the polymerization inhibitor(s) are compounds selected from phenolic derivatives, phenothiazine derivatives, nitroxide derivatives or paraphenylenediamine derivatives.

11. A process according to any one of the preceding claims, wherein at least one of said polymerization inhibitors is hydroquinone methyl ether.

12. A process according to any one of the preceding claims, wherein the solvent used to extract the P3HA present in the biomass is selected from polar solvents having a boiling temperature higher than the extraction temperature but lower than the thermolysis temperature. 13.Method according to any one of the preceding claims, in which the thermolysis reactor is chosen from: a conveyor, a conveyor mixer, an extruder, an extruder-conveyor and / or a set of heating plates.

14. Method according to claim 13, in which the thermolysis reactor is an extruder-conveyor comprising one or more endless screws each actuated in a barrel.

15. Method according to claim 13, in which the thermolysis reactor is a twin-screw extruder.

16. Method according to claim 13, in which the thermolysis reactor is a device consisting of hollow plates, heated by a heat transfer fluid circuit.

17. Method according to claim 13, in which the thermolysis reactor is a screw conveyor.

18. A method according to any one of the preceding claims, wherein the thermolysis is carried out between 150°C and 400°C with a residence time of between 0.05 h and 1 h.

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