Process for producing biobased alpha, beta-unsaturated carboxylic acids from poly(3-hydroxyalkanoate)

Abstract

The present invention relates to a process for producing biobased α,β-unsaturated carboxylic acids from biomass containing a poly(3-hydroxyalkanoate), or from a solid poly(3-hydroxyalkanoate) previously extracted from this biomass in the presence of polymerization inhibitors, by thermolysis of said polymer, in the absence of a catalyst, predominantly to α,β-unsaturated carboxylic acid in gaseous form without using an inert gas to facilitate the evaporation of this acid. This invention more precisely describes the step of thermolysis of the biomass or of P3HA, then the purification steps making it possible to obtain the α,β-unsaturated carboxylic acid and the recycling of the intermediate products.

Description

[0001]Title: 352&('(^'(^)$%5,&$7,21^'¶$&,'(6^&$5%2; < / ,48(6^Į-ȕ^ INSATURES BIOSOURCES A PARTIR DE POLY(3-HYDROXYALCANOATE) Domaine technique La présente invention concerne un procédé de fabrication d’acides carboxyliques D-E insaturés biosourcés à partir de la biomasse contenant un poly(3-hydroxyalcanoate), ou d’un poly(3-hydroxyalcanoate) solide préalablement extrait de cette biomasse en présence d’inhibiteurs de polymérisation, par thermolyse dudit polymère, en absence de catalyseur majoritairement en acide carboxylique D-E insaturé sous forme gazeuse sans utiliser un gaz inerte pour faciliter l’évaporation de cet acide, Cette invention décrit plus précisément l’étape de thermolyse de la biomasse ou du P3HA, puis les étapes de purification permettant d’obtenir l’acide carboxylique D-E insaturé et le recyclage des produits intermédiaires.Prior art and technical problem The industrial production of unsaturated DE 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 of the possible ways to obtain these unsaturated DE 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 DE carboxylic acid = propenoic acid (acrylic acid). If R1= methyl and R2= H: - Poly(3-hydroxyalkanoate) = poly(3-hydroxyisobutyrate) (P3HiB); - Unsaturated DE carboxylic acid = isobutenoic acid (methacrylic acid). If R1= H and R2= methyl: - Poly(3-hydroxyalkanoate) = poly(3-hydroxybutyrate) (P3HB); - Unsaturated DE carboxylic acid = but-2-enoic acid (crotonic acid). If R1=H and R2 = ethyl: - Poly(3-hydroxyalkanoate) is poly(3-hydroxyvalerate) (P3HV); - Unsaturated DE 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 DE 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). 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.The acrylic acid is recovered in gaseous form and then condensed, while the catalyst and the residual mass of biomass can be recycled in the process or subjected to thermal regeneration. However, the risk is that the residue present in the reactor after thermolysis is pasty and sticky, which could make its transfer to industrial scale complex. Example 5 and Figure 7 describe how to implement this invention on an industrial scale. After fermentation, the biomass is washed and dried using an atomizer or a double-drum dryer. After adding the catalyst, the product is pyrolyzed in a FAST reactor. TMat 250°C-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 US 6646161 or in US 20120006673, to obtain acrylic acid still containing many impurities. Complete purification is achieved using distillation columns, as described in US 7332624 and US 7179875, and may also require crystallization operations, as described in US 6482981 and US 71798750. These documents describe techniques commonly used to obtain acrylic acid by oxidation of propylene. Document US2014 / 0018574 describes a process for thermolysis of P3HA in the presence of a compound comprising a tertiary amine which acts as a catalyst, present in aconcentration of the order of 0.5% to 4% by weight relative to P3HA. Optionally, one or more inhibitors may be added to the P3HA before carrying out the thermolysis, preferably in a proportion of 150 ppm to 350 ppm relative to P3HA in the presence of depleted air (<6% O2) (0107-0108). Furthermore, with regard to the acrylic acid formed during this thermolysis, no inhibitor (0111) is added during its condensation. Finally, this document highlights that at a temperature of 175°C (00143) and in the absence of a catalyst, the thermolysis was ineffective. When the thermolysis of P3HA is carried out in the liquid phase as in document JP 2015067567, in the absence or presence of catalyst and in the absence of inhibitor, this reaction is preferably carried out in the presence of an inert gas to evaporate the acrylic acid formed (0031). Another solution consists of previously extracting the P3HA from the biomass using an organic solvent before carrying out its thermolysis. TheDocument US 20150376152 describes in Example 6 the extraction of P3HP from biomass, using an organic solvent, such as 2-butanone, then obtaining 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 inhibitor leading to obtaining 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 carrying out the thermolysis of P3HA in the absence of 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 inthe gas phase in the event of accidental condensation or at the time of condensation of 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 P3HA from the biomass, separate the insoluble organic detritus from said solvent, to carry out a thermolysis treatment 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 obtain high purity acrylic acid by combining the thermolysis of biomass containing P3HA, or the thermolysis of P3HAsolid and at least one polymerization inhibitor, a system of staged condensation of the thermolysis gases, fractional distillation and possibly crystallization, in the absence of a catalyst and without using an inert gas to promote the evaporation of the unsaturated carboxylic acid formed. More precisely, "in the absence of a catalyst" means that the thermolysis of the PHA in the presence of at least one polymerization inhibitor takes place in the absence of another chemical species which accelerates or reorients the kinetics of the reaction. Thermolysis as envisaged is only induced by operating conditions such as temperature, pressure and residence time. Chemical species which 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 severalphases (generally a solid catalyst for gaseous or liquid phase reagents); - enzymatic catalysis, if the catalyst is an enzyme, i.e. a protein. By the expression "in the absence of inert gas" is meant that the thermolysis of the PHA and in the presence of at least one polymerization inhibitor is carried out in the absence of gas injection such as for example depleted air (<6% O2) which facilitate the evaporation of the acid formed and also facilitate the activation of the inhibitors in the reaction medium. Consequently, the invention proposes to provide a simple and easy-to-implement solution for obtaining Į-ȕ^unsaturated carboxylic acids from biomass containing P3HA, or from solid PH3HA, by implementing a thermolysis reactor coupled with an optimized purification process. Summary of the invention The subject of the present invention is a process for manufacturing a biosourced unsaturated DE carboxylic acid, said process comprisingthe following steps: - mixing a biomass containing a poly(3-hydroxyalkanoate) (P3HA), or solid P3HA, with at least one polymerization inhibitor in the absence of a catalyst; - subjecting said biomass - inhibitor or P3HA - inhibitor mixture to a thermolysis step leading to obtaining, on the one hand, said unsaturated DE carboxylic acid in vapor phase, and on the other hand, a molten or solid residue, without adding an inert gas; - condensing in one or more steps, the gases resulting from the thermolysis, then feeding a distillation column with the thermolysis gases obtained, - fractionating the thermolysis gases into recovered light products, into heavy products recycled to the thermolysis reactor and into unsaturated Į-ȕ^carboxylic acid having a purity greater than 98% which can be crystallized to achieve a purity > 99.5%, - treating the residue in solid phase. According to various embodiments, said process comprises the following characteristics, where appropriate combined. The contents indicatedare expressed by weight, unless otherwise indicated. Within the ranges of values ​​indicated, the limits are included. The term "thermolysis" of poly(3-hydroxyalkanoate) (P3HA) means its chemical decomposition into unsaturated DE carboxylic acid obtained under the effect of temperature. This term is synonymous with pyrolysis. According to one embodiment, the poly(3-hydroxyalkanoate) used in the process comprises a single type of 3-hydroxyalkanoate unit and the product formed is therefore composed of a single unsaturated DE carboxylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the unsaturated DE carboxylic acid produced is acrylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutyrate) and the unsaturated DE carboxylic acid produced is methacrylic acid. According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) and the unsaturated DE carboxylic acid producedis crotonic acid. In one embodiment, the poly(3-hydroxyalkanoate) used in the process comprises several different 3-hydroxyalkanoate units and the product formed is therefore composed of a mixture of different unsaturated DE 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 DE carboxylic acids produced is acrylic acid. In one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxyisobutyrate unit and at least one of the unsaturated DE carboxylic acids produced is methacrylic acid. In one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxybutyrate unit and at least one of the unsaturated DE 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 cyanobacteria or a mixture of two or more of these elements. According to one embodiment, the biomass used is pretreated by washing, drying and grinding operations, to produce a biomass containing from 30% to 90% by weight of PHA, the remainder consisting of the cell membrane. According to one embodiment, the biomass is subjected to a thermolysis reaction, which takes place in the presence of one or more polymerization inhibitors. According to one embodiment, the P3HA with a purity greater than 95% by weight, used in the method according to the invention, comes from the extraction of the P3HA by a solvent, evaporation of the latter and removal of the cell membrane by filtration and centrifugation. According to one embodiment, the thermolysis reaction takes place in the presence of one or more polymerization inhibitors. According to one embodimentof embodiment, mixing, and thermolysis are carried out continuously in successive stages or simultaneously. According to one embodiment, the mixture comprising the biomass comprises at least 0.01% of one or more polymerization inhibitors up to 5% and preferably less than 1% of one or more polymerization inhibitors (mass contents). According to one embodiment, the mixture comprising the P3HA comprises at least 0.5% of one or more polymerization inhibitors up to 90% of one or more polymerization inhibitors (mass contents) and preferably between 20% and 70% of one or more polymerization inhibitors. According to one embodiment, the process according to the invention comprises one to several stages of condensation of the vapors of the unsaturated DE carboxylic acid(s) obtained by the thermolysis reaction of poly(3-hydroxyalkanoate). According to one embodiment, the condensates obtained can be recycled into the thermolysis reactor and to theseparation column. According to one embodiment, one or more inhibitors are also injected into the condensers. According to one embodiment, no inhibitors are injected into the condensers. According to one embodiment, one or more distillation columns may be used to purify the unsaturated DE carboxylic acid. According to one embodiment, the condensates obtained may be subjected to a rectification or crystallization treatment before being recycled to the thermolysis reactor. According to one embodiment, the separation column is fed in the gas phase. According to one embodiment, the bottom of the distillation column is recycled to the thermolysis reactor. According to one embodiment, the bottom of the separation column is subjected to a rectification or a crystallization operation before being recycled to the thermolysis reactor. According to one embodiment, the unsaturated DE carboxylic acid obtained at the top orside draw-off at a purity of at least 98% by weight. According to one embodiment, this unsaturated DE carboxylic acid can be further purified in a subsequent crystallization step. According to one embodiment, the purity of the unsaturated DE carboxylic acid after crystallization is greater than 99.5% by weight. According to one embodiment, the column top products are sent to a biological treatment plant. According to one embodiment, these column top products are upgraded to methane by hydrothermal gasification. According to one embodiment, the process according to the invention comprises a step of treating the solid or molten residue at the end of thermolysis by upgrading the latter by recycling upstream of the thermolysis reactor or by external treatment such as gasification. Other characteristics and advantages of the invention will become more apparent upon reading the detailed description which follows, with reference to the appended figures 1 and 2. TheFigure 1 represents the schematic diagram of an installation for implementing the method according to the invention, when applied to a P3HA – inhibitor mixture. Figure 2 represents the schematic diagram of an installation for implementing the method according to the invention, when applied to a biomass – inhibitor mixture. Detailed description of the invention By way of example, the illustration of the invention will be carried out by describing the method applied to poly(3-hydroxypropionate) (P3HP) extracted from the cell membrane, or to biomass still containing P3HP, making it possible to obtain unsaturated D-E carboxylic acid (in this case acrylic acid) having a purity greater than 99.5% by weight. The invention aims to produce acrylic acid on an industrial scale by thermolysis of poly(3-hydroxypropionate), while limiting the problems of fouling of the thermolysis reactor and making it possible to obtain this acid with a purity >98% or even >99.5% by weight. According toan embodiment, said method for obtaining bio-sourced acrylic acid comprising the following steps which can be carried out sequentially or simultaneously: - Introduction of the biomass (in powder form) or P3HP and at least one polymerization inhibitor, in the absence of a catalyst, into a mixer (in solid phase) by means of a pipe or by a conveyor of the screw type. - Mixing of the P3HP or the biomass and at least one polymerization inhibitor in a conveyor mixer comprising several screw screws operated in a barrel or directly in a reactor called a thermolysis reactor. - Thermolysis of this mixture at a given temperature and at a controlled pressure in a system adapted to the treatment of the molten or pasty residue, in order to generate a vapor phase and a viscous or even solid phase without injection of an inert gas. - Separation of the two phases formed in a gas-liquid separator. - Treatment of the residue forvalorization by spreading, by combustion or by hydrothermal gasification or by recycling upstream of the thermolysis reactor - Staged condensation of the gaseous phase carried out by an adjustment of successive condensation temperatures by placing in series one or more condensers and separation of the gaseous and liquid phases obtained containing acrylic acid and contaminants which can be recycled again in the reactor or sent to the purification system. - Treatment of the condensed phase to obtain acrylic acid by the implementation of one or more distillation columns allowing, on the one hand, to separate the acrylic acid from products heavier than the latter, and on the other hand to obtain products lighter than the latter. - Purification of the acrylic acid obtained by a liquid / solid separation method such as crystallization or by a gas / liquid separation method such as distillation. The invention is based onthe use of a mixture of biomass containing a P3HA, or solid P3HA, and at least one polymerization inhibitor by implementing a technology for mixing solids and heat treatment of this mixture. The term "biomass" means an organic matter of plant (including microalgae), animal, bacterial or fungal (fungi) origin, usable as a source of biosourced raw materials, as opposed to raw materials of fossil origin. In the method according to the invention, the first step uses genetically modified host biomass, resulting from genetic engineering. According to one embodiment, the host of the biomass is a bacterium, a yeast, a fungus, an algae, a cyanobacteria 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 theglucose, fructose, sucrose, arabinose, maltose, lactose, xylose, ethanol, methanol, glycerol, fatty acids, vegetable oils and syngas derived from biomass or a combination thereof. According to one embodiment, the biomass used in the process 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-hydroxyalkanoate) (P3HA) homo- or copolymers with different 3-hydroxyalkanoic acids are formed. The process according to the invention advantageously comprises a preliminary step of preparing the biomass, where it is treated by washing, drying and grinding operations, to produce a solid biomass (for example in powder form) containing at least 30% by weight of P3HA, preferably at least 50% by weight of P3HA. According to a first embodiment of the invention shown in theFigure 1, Stream 1 represents the supply of one or more inhibitors to the thermolysis reactor. The polymerization inhibitors used in the process according to the invention are chosen from the inhibitors conventionally used in existing industrial processes for the production of unsaturated DE 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. Stream 2 consists of P3HA previously extracted from the biomass. It feeds the thermolysis reactor via a pipe. Stream 1 and stream 2 are brought into the thermolysis reactor via a pipe, a screw conveyor, and a conveyor belt.or a hopper, a pneumatic conveyor, a vibrating conveyor, an extruder. In addition, they can be coupled to a dosing device. According to a preferred embodiment, at least one of said polymerization inhibitors is hydroquinone methyl ether (HMEQ). The mass proportion of inhibitor in the mixture with P3HA or with the biomass is at least 0.01% and can reach 90%; preferably the inhibitor content in said mixture is from 1% to 70%. When stream 2 is P3HA extracted from its cell membrane, the thermolysis reactor is a solvolysis reactor also used to depolymerize composites or a molten polycondensation type reactor. This reactor is equipped with a heating system and stirring by a pump and external recirculation through an exchanger or a magnetically driven shaft of the double helical ribbon type. According to one embodiment, the temperature in the thermolysis reactor isbetween 20°C and 250°C, preferably between 150°C and 200°C. This temperature can also be controlled using temperature sensors placed in the reactor. Such moderate heating makes it possible to liquefy all or part of the mixture while avoiding the polymerization of the unsaturated DE carboxylic 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 0.5 h and 5 h, preferably between 2 h and 4 h. The stream 3 leaving the thermolysis reactor is sent in whole or in part to a recovery unit or recycled upstream of the thermolysis reactor. Stream 5 feeds a first condenser C1 which will cool the gases to a temperature at least 20°C lower than the temperature of the thermolysis reactor and generate a liquid stream 12 which is recycled to the thermolysis reactor or whichcan be purified by crystallization (not shown) before recycling to the thermolysis reactor. The non-condensed gases leaving this condenser C1 by stream 8 are condensed in a condenser C2 at a temperature at least 20 °C lower than that of condenser C1. This temperature is adjusted so that the mass content of inhibitor in stream 11 is less than 3%. Stream 11 can be gaseous or liquid after condensation (not shown) before entering the separation column (COL) which will make it possible to recover unsaturated carboxylic acid DE with a purity greater than 98.5% at a temperature 5 °C lower, preferably 10 °C below the bubble point of the feed to this separation column. Streams 9 and 12 can be fully or partially recycled to the thermolysis reactor or sent to a crystallizer (not shown) to be separated and purified so as to obtain, on the one hand, part of the heavy impurities and the inhibitor that can berecycle to the thermolysis reactor and on the other hand acrylic acid which can be sent to the feed of the separation column (COL). Condensers C1 and C2 can also be fed with a solution of at least one inhibitor in solution in unsaturated DE carboxylic acid (streams 6 and 7). The separation column is equipped with a side draw-off and has a number of theoretical plates between 10 and 30, preferably between 20 and 25. This single column operates under a reduced pressure generally between 3 kPa and 30 kPa, preferably between 9 kPa and 20 kPa. The separation column is made up of any type of plates and / or bulk internals and / or structured packings available for the rectification of mixtures and suitable for the distillation of polymerizable compounds. It can be a conventional distillation column which can include at least one packing, such as for example a bulk packing and / or a combination ofsections equipped with loose and structured packings, and / or trays such as, for example, perforated trays, fixed valve trays, movable valve trays, cap trays, or combinations thereof. Preferably, the column is equipped with perforated trays. Stabilization of the column (stream 17) is generally carried out using stabilizers well known to those skilled in the art, possibly with injection of air or oxygen-depleted air (stream 16). The column is fed in the first quarter of the bottom of the column, preferably at a tray ranging from trays 1 to 7, preferably trays 3 to 5. Stream 4, rich in light compounds, is distilled at the top of the column and recovered by hydrothermal gasification or at a biological treatment station after condensation. Unsaturated DE carboxylic acid having a purity > 98% withdrawn in liquid or gas phase, preferably in the first third from the top of the columnseparation, in particular between the theoretical plates 1 to 5 plates located below the column head. Preferably, the polymer-grade unsaturated DE carboxylic acid is withdrawn in the liquid phase (stream 18). This stream 18 can be further purified by a crystallization operation carried out in the crystallizer (CRIS), to achieve a purity of unsaturated DE carboxylic acid > 99.5% and compatible with commercial specifications. According to one embodiment, this latter operation making it possible to obtain unsaturated DE carboxylic acid of very high purity is carried out by fractional crystallization. This can be implemented in different forms: dynamic crystallization, static crystallization or suspension crystallization. According to one embodiment, the crystallization is in falling film, carried out in a multi-tubular exchanger; in practice, each tube is continuously supplied by the stream 18 at the head, a fluid flowheat transfer fluid. This operation actually comprises 3 stages: first crystallization at a controlled temperature of around 14°C for example for acrylic acid, then sweating by a gradual increase in temperature of the heat transfer fluid to eliminate the impurities included in the crystals, and finally melting by a rapid increase in temperature beyond the controlled melting temperature of the unsaturated DE carboxylic acid (around 14°C for acrylic acid), but preferably below 35-40°C. The bottom of the separation column (COL) is a flow of unsaturated DE carboxylic acid comprising most of the heavy impurities and a large proportion of the inhibitor is recycled in whole or in part to the thermolysis reactor. According to one embodiment, the mass ratio between the flow withdrawn laterally and the flow fed to the column is between 60 and 95%, preferably between 75% and 90%. According to one embodiment, the mass ratio between theflow withdrawn at the bottom and the feed flow to the column is between 5% and 30%, preferably between 5% and 10%. According to a particular embodiment, the column is equipped with a condenser and a liquid feed at the top (not shown), which ensures liquid reflux in the column. The reflux ratio, which can be defined as the recycle flow rate from the column top to the separation column (COL) relative to that of the side withdrawal, is between 1 and 3, preferably between 1 and 2, for example is equal to 1.2. These conditions make it possible to achieve the best compromise between the size of the column / number of separation stages to be used and the energy to be implemented to ensure efficient distillation. According to a second embodiment of the invention shown in Figure 2, flow 1 represents the supply of one or more inhibitors to the thermolysis reactor, as described above. Flow 2 consists of biomass. Healso feeds the pyrolysis reactor which in this case is a conveyor mixer of the propeller dryer type (Paddle Dryer). Streams 1 and 2 are brought into the thermolysis reactor by a pipe, a screw, a conveyor belt or a hopper, a pneumatic transport, a vibrating conveyor, an extruder. In addition, they can be coupled to a metering device. According to a preferred embodiment, at least one of said polymerization inhibitors is hydroquinone methyl ether (HMEQ). The mass proportion of inhibitor in the mixture with the biomass is less than 1%. According to one embodiment, the temperature in the thermolysis reactor is between 20 °C and 250 °C, preferably 150 °C-200 °C and the pressure in the reactor is between 3 kPa and 101 kPa, preferably between 15 kPa and 40 kPa. According to one embodiment, the residence time in the reactor is between 0.5 h and 5 h, preferably between 2 h and 4 h. The flow 3 outletfrom the thermolysis reactor is sent in whole or in part to a recovery unit, by combustion, spreading or gasification. Depending on the embodiment, the residue is mixed with the necessary water and recovered by hydrothermal gasification. Stream 5 feeds a first condenser C1 which will cool the gases to a lower temperature below the temperature of the feed tray in the separation column (COL). The liquid stream 11 enters the separation column at a temperature below 5 °C, preferably 10 °C, below the bubble point of the column feed. The condensers C1 can also be fed with a solution of at least one inhibitor in solution in unsaturated DE carboxylic acid (stream 6). The separation column is equipped with a side draw-off and has a number of theoretical trays between 10 and 30, preferably between 20 and 25. This single column operates under a generally reduced pressurebetween 3 kPa and 30 kPa, preferably between 9 kPa and 20 kPa. The separation column consists of any type of trays and / or bulk internals and / or structured packings available for the rectification of mixtures and suitable for the distillation of polymerizable compounds. Preferably, the column is equipped with perforated trays. Stabilization of the column (stream 17) is generally carried out using stabilizers well known to those skilled in the art, possibly with injection of air or oxygen-depleted air (stream 16). The side draw stream may also be stabilized (not shown). The column is fed in the first quarter of the bottom of the column, preferably at a tray ranging from trays 3 to 10, preferably trays 4 to 8. Stream 4, rich in light compounds, is distilled at the top of the column and recovered by hydrothermal gasification or at the biological station after condensation. The carboxylic acid DEunsaturated DE having a purity > 98% withdrawn in the liquid phase or in the gas phase, preferably in the first quarter of the bottom of the separation column, in particular between the theoretical plates 10 to 20 plates located below the column head. Preferably, the polymer grade unsaturated DE carboxylic acid is withdrawn in the liquid phase (stream 18). After additional cooling, this stream 18 can be further purified by a crystallization operation in a crystallizer (CRIS) to achieve a purity of unsaturated DE carboxylic acid > 99.5% and compatible with commercial specifications. This last operation, making it possible to obtain unsaturated DE carboxylic acid of very high purity, is carried out by fractional crystallization. At the bottom of the separation column (COL), a stream of unsaturated DE carboxylic acid comprising most of the heavy impurities and a large proportion of the inhibitor is recycled in whole or in part to the separation reactor.thermolysis. According to the embodiment, the mass ratio between the flow withdrawn laterally and the flow fed to the column is between 60 and 95%, preferably between 75% and 90%. According to the embodiment, the mass ratio between the flow withdrawn at the bottom and the flow fed to the column is between 5% and 30%, preferably between 5% and 10%. According to a particular embodiment, COL is equipped with a condenser and a liquid feed at the top (not shown), which ensures liquid reflux in the column. The reflux ratio, which can be defined as the recycling flow rate from the column top to the separation column (COL) relative to that of the lateral withdrawal, is between 1 and 3, preferably between 1 and 2, for example is equal to 1.2. The examples below illustrate the present invention without, however, limiting its scope. EXPERIMENTAL SECTION The following abbreviations are used in the tables: AA: acrylic acidACOH: acetic acid H2O: water PTZ: phenothiazine EMHQ: hydroquinone methyl ether ACETAL: Acetaldehyde PROH: propanoic acid Examples 1-4: This laboratory-scale experiment aims to observe the consistency of the residue after a thermolysis operation to determine whether it can be handled after leaving the thermolysis reactor. Examples 1-4 are carried out on biomass containing 60% by weight of P3HP. The unsaturated carboxylic acid obtained after thermolysis is acrylic acid (AA). The step of mixing the biomass containing P3HP with the inhibitor is carried out by introducing 2 g of this biomass and 0 or 20 mg of EMHQ or in a 50 mL two-necked flask equipped with a magnetic bar. The medium is stirred using a magnetic stirrer in order to distribute the inhibitor in the solid. At the beginning of the experiment, the system is placed under the desired pressure and then the balloon containing the biomass is placed in a heating system allowingto establish the desired thermolysis temperature (oil bath or electric heating mantle). 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 hours of heating, the formation of AA vapors in the thermolysis reactor diminishes and the experiment is then stopped. The fouling state as well as the consistency of the thermolysis residue are judged visually at the end of the experiment. It is noted that the addition of the inhibitor makes it possible to transform a very hard solid into a viscous pasty solid which can be used in the invention. The operating conditions for tests 1-4 are shown in Table 1. [Table 1] Test Inhibitor Operating Pressure (kPa) Thermolysis Residue 1 EMHQ 100 Viscous pasty solid 2 EMHQ 55 Viscous pasty solid 3 EMHQ 20 Viscous pasty solid 4 NON 100 Very hard and sticky solid The results in Table 1 highlight that the physical state of theresidue is dependent on the presence of the inhibitor. The addition of inhibitor allows the residue to become pasty and viscous whereas it was very hard and sticky without the addition of the latter. This change in consistency of the residue allows for easier extraction of the latter when it comes to carrying out continuous thermolysis. Thermogravimetric Analysis Test This test aims to provide information on the operating conditions necessary to carry out the thermolysis of P3HA contained in the biomass. In order to best evaluate the thermolysis rate, this test is carried out with P3HP extracted from the biomass. 10 g of pure P3HP were subjected to thermogravimetric analysis. This thermogravimetric analysis is a technique which consists of measuring the variation in mass of a sample as a function of time, for a given temperature. To do this, for each temperature condition, 1 g of P3HP is placed on the balance of the device under nitrogen flushing and the loss ofweight over time is then recorded. It can be seen that the mass loss becomes significant and rapid from 170°C. From a thermolysis point of view, the least severe operating conditions would be: T° of 180°C for a residence time of 3 hours, to obtain a cracking rate greater than 95%. Table 2 shows the temperature conditions and times required to obtain different cracking rates, from 10% to complete cracking. [Table 2] Time required for: T 10% cracking 50% cracking Complete cracking (>95%) 120°C >24h >24h >24h 130°C 14h >24h >24h 140°C 6h 24h >24h 150°C 2h 8h 15h 160°C 1h30 6h 10h 170°C 1h 4h 8h 180°C 45min 2h 3h 190°C 30min 1h15 1h45 200°C <30min 45min 1h 210°C <30min 40min 50min 220°C <30min 35min 40min The temperature of the thermolysis reaction around 180°C in the process according to the invention is significantly smaller than that used in Example 1 of document WO2016 / 039618. The tests of the following Examples 5-7 arecarried out in a laboratory setup. A two-necked flask equipped with magnetic stirring was used. The side neck of the flask is equipped with a thermometer to monitor the reaction temperature. The upper neck of the flask is equipped with a separation bridge leading to a water-cooled side condenser, which in turn leads to a recipe consisting of a second 50 mL flask. An additional tapping allows the setup to be put under reduced pressure using a membrane vacuum pump. EXAMPLE 5 (comparative): Use of a biomass containing 60% P3HP without the addition of inhibitor, without catalyst, and in the absence of inert gas. 2.02 g of biomass containing 60% P3HP are placed in a 25 mL two-necked flask equipped with magnetic stirring. 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 generated vapors are condensed using a water-cooled side condenser to obtain 1.06 gof acrylic acid which corresponds to 87% yield. The solid obtained after cracking remains stuck to the walls of the two-necked flask. It 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. EXAMPLE 6 (according to the invention): Use of a biomass containing 60% P3HP with the addition of 5% 4-methoxyphenol (EMHQ) 2.19 g of biomass containing 60% 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 biomass. 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 generated vapors are condensed using a water-cooled side condenser to obtain 1.27 g of acrylic acid, which corresponds to a 96% yield. The solid obtained after cracking remains compact and easily detaches from the walls of the two-necked flask.and breaks easily with a spatula. The results of Example 6 show that, when the process according to the invention is implemented (in the presence of an inhibitor, without a catalyst, without the addition of an inert gas), the yield of acrylic acid reaches 95%, higher than that obtained in Comparative Example 5. In addition, the presence of the inhibitor makes it possible to easily remove the residue. Example 7: Processes according to the invention The simulations were carried out on the case of the thermolysis of P3HA poly(3-hydroxypropionate) (P3HP) giving acrylic acid (AA) as unsaturated DE carboxylic acid, using the Aspen Tech V12.1 software and Arkema thermodynamic databases. The compounds taken into account to represent the gas phase resulting from the thermolysis, without the addition of an inert gas, are listed below. The percentages are expressed as mass percentages. Condensation process outlet according to Figure 1 Table 3 shows the incoming and outgoing flowsof condensers C1 and C2 when the feed of C1 stream 5 is composed of 30% AA and 70% EMHQ at 200 °C and 26.7 kPa. C1 partially condenses the gases at 150 °C and C2 at 125 °C. The use of two staged condensers makes it possible to obtain an acrylic acid (stream 11) with an inhibitor content of 3%. In the case studied, streams 6 and 7 were zero. [Table 3] FLOW 5 12 8 9 11 Temperature °C 200.00 150.00 150.00 125.00 125.00 Pressure kPa 27 27 27 27 27 Total Mass Flow kg / h 100.00 79.50 20.50 4.96 15.54 AA Flow kg / h 30.00 12.99 17.01 1.97 15.04 EMHQ Flow kg / h 70.00 66.52 3.48 2.98 0.50 AA Mass Fraction 0.30 0.16 0.83 0.40 0.97 EMHQ 0.70 0.84 0.17 0.60 0.03 Distillation Process according to Figure 1 in the absence of an inert gas. Table 4 shows the flows entering and leaving the separation column. This has 25 theoretical stages. The feed is carried out at tray 20, the acrylic acid is withdrawn at tray 17 and the light products areeliminated at the top of the column. In this simulation, streams 16 and 17 were zero. As shown by the composition of withdrawal stream 18, the acrylic acid has a purity greater than 98%. The recovery balance of acrylic acid for purification is 98%. In fact, only the acrylic acid present in stream 4 will be used in hydrothermal gasification. [Table 4] Flow 11 15 4 18 Temperature C 50 110 30 90 Pressure kPa 200.00 20.00 20.00 20.00 Mass Flow kg / h 100.00 6.00 10.00 84.00 FORMOL kg / h 1.32 0.00 1.31 0.01 ACETAL kg / h 0.04 0.00 0.03 0.00 ACRO kg / h 0.00 0.00 0.00 0.00 H2O kg / h 4.87 0.00 4.56 0.31 ACOH kg / h 3.15 0.00 2.19 0.95 AA kg / h 87.42 3.06 1.90 82.46 PROH kg / h 0.28 0.02 0.00 0.26 EMHQ kg / h 2.92 2.92 0.00 0.00 Mass Fractions FORMOL 0.01 0.00 0.13 0.000 ACETAL 0.00 0.00 0.00 0.000 H2O 0.05 0.00 0.46 0.004 ACOH 0.03 0.00 0.22 0.011 AA 0.87 0.51 0.19 0.982 PROH 0.00 0.00 0.00 0.003 EMHQ 0.03 0.49 0.00 0.000 Condensation process according to figure 2in the absence of an inert gas. Table 5 shows the flows entering and leaving condenser C1 when the feed of C1 stream 5 is composed of 99% AA and 1% EMHQ at 200 °C and 26.7 kPa. C1 partially condenses the gases at 80 °C. Condensation is complete at 80 °C, i.e. at a temperature below the bubble point of the column feed tray. [Table 5] Stream 5 11 Temperature C 200 80 Pressure kPa 27 27 Mass Flow kg / h 100 100 AA kg / h 99 99 EMHQ kg / h 1 1 Mass Fractions AA 0.99 0.99 EMHQ 0.01 0.01 Distillation process according to Figure 2 Table 6 shows the flows entering and leaving the separation column. This column has 25 theoretical stages. The feed is carried out at tray 20, the acrylic acid is withdrawn at tray 17 and the light products are eliminated at the top of the column. In this simulation, streams 16 and 17 were zero. As shown by the composition of the withdrawal stream 18, the acrylic acid has a purity greater than98%. The recovery rate of acrylic acid for purification is 98.3%. In fact, only the acrylic acid present in stream 4 will be used in hydrothermal gasification. [Table 6] Flow Units 11 4 15 18 Temperature C 50 30 98 90 Pressure kPa 200 20 20 20 Mass Flow kg / h 100.00 10.00 6.00 84.00 FORMOL kg / h 1.35 1.34 0.00 0.01 ACETAL kg / h 0.04 0.04 0.00 0.00 H2O kg / h 4.97 4.65 0.00 0.31 ACOH kg / h 3.21 2.24 0.00 0.97 AA kg / h 89.15 1.73 4.98 82.45 PROH kg / h 0.29 0.00 0.03 0.26 EMHQ kg / h 0.99 0.00 0.99 0.00 Mass Fractions FORMOL 0.014 0.134 0.000 0.000 ACETAL 0.000 0.004 0.000 0.000 H2O 0.050 0.465 0.000 0.004 ACOH 0.032 0.224 0.000 0.011 AA 0.892 0.173 0.829 0.982 PROH 0.003 0.000 0.005 0.003 EMHQ 0.010 0.000 0.166 0.000 Distillation process according to Figure 2: Effect of a side draw in gaseous phase 5 or liquid Table 7 shows the draw-off streams lateral in gas or liquid phase. The column has 25 theoretical stages.The feed is carried out at tray 20, the acrylic acid is withdrawn at tray 17 and the light products are eliminated at the top of the column. In this simulation, streams 16 and 17 were zero. The most favorable configuration0 for recovering acrylic acid with a purity > 98% is the one with a lateral withdrawal in the liquid phase. [Table 7] Flow Units LIQUID PHASE GAS PHASE Temperature C 90 91 Pressure kPa 20 20 Mass Flow kg / h 84.00 84.00 FORMOL kg / h 0.01 0.44 ACETAL kg / h 0.00 0.01 H2O kg / h 0.31 1.78 ACOH kg / h 0.97 1.58 AA kg / h 82.45 79.93 PROH kg / h 0.26 0.26 EMHQ kg / h 0.00 0.00 Mass Fractions FORMOL 0.000 0.01 ACETAL 0.000 0.00 H2O 0.004 0.02 ACOH 0.011 0.02 AA 0.982 0.95 PROH 0.003 0.00 EMHQ 0.000 0.00

Claims

CLAIMS 1. Process for manufacturing a biosourced Į-ȕ^unsaturated carboxylic acid, said process comprising the following steps: - mixing a biomass containing a poly(3-hydroxyalkanoate) (P3HA), or solid P3HA, with at least one polymerization inhibitor; - subjecting said biomass - inhibitor or P3HA - inhibitor mixture without adding a catalyst and without adding an inert gas, to a thermolysis step leading to obtaining, on the one hand, said Į-ȕ unsaturated carboxylic acid in vapor phase, and on the other hand, a molten or solid residue; - condensing, in one or more stages, the gases resulting from thermolysis, then feeding a distillation column with the condensed thermolysis gases obtained, - fractionating the thermolysis gases into light products, heavy products recycled to the thermolysis reactor and unsaturated carboxylic acid having a purity greater than 98% which can be crystallized to achieve a purity greater than 99.5%,- treat the residue in solid phase or recycle it at the inlet of the thermolysis reactor.

2. Method according to claim 1, for obtaining biosourced acrylic acid comprising the following steps which can be carried out sequentially or simultaneously: - Introduction of the biomass (in powder form) or P3HP and at least one polymerization inhibitor into a mixer (in solid phase) by means of a pipe or by a conveyor of the endless screw type. - Mixing of the P3HP or the biomass and at least one polymerization inhibitor in a conveyor mixer comprising several endless screws operated in a barrel or directly in a reactor called a thermolysis reactor. - Thermolysis of this mixture at a given temperature and at a controlled pressure in a system adapted to the treatment of the molten or pasty residue,in order to generate a vapor phase and a viscous or even solid phase. - Separation of the two phases formed in a gas-liquid separator. - Treatment of the residue for recovery by spreading, by combustion, by hydrothermal gasification or recycling upstream of the pyrolysis reactor., - Staged condensation of the gas phase carried out by successive condensation temperature adjustment by placing one or more condensers in series and separation of the gaseous and liquid phases obtained containing acrylic acid and contaminants which can be recycled back into the reactor or sent to the purification system. - Treatment of the condensed phase to obtain acrylic acid by using one or more distillation columns allowing, on the one hand, to separate acrylic acid from products heavier than the latter, and on the other hand to obtain products lighter than the latter. - Purification of the acrylic acid obtained by a liquid / solid separation method such as crystallization or by a gas / liquid separation method such as distillation. 3.Process according to one of claims 1 or 2, in which the biomass used is pretreated by washing, drying or grinding operations, to result in a biomass containing at least 30% by weight of P3HA, preferably at least 50% by weight of P3HA.

4. Process according to one of claims 1 to 3, in which the poly(3-hydroxyalkanoate) contains the 3-hydroxypropionate unit and at least one of the unsaturated carboxylic acids produced is acrylic acid.

5. Process according to any one of claims 1 to 3, in which the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the 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 Į-ȕ 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 Į-ȕ unsaturated carboxylic acid produced is crotonic acid.

8. A process 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 Į-ȕ 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 Į-ȕ 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 method according to any one of the preceding claims, wherein the thermolysis reactor is selected from: a conveyor, a conveyor mixer, a dryer, a rotating drum and / or a set of heating plates.

13. A method according to any one of the preceding claims, wherein the thermolysis reactor is a solvolysis reactor also used to depolymerize composites or a melt polycondensation type reactor.

14. A method according to any one of the preceding claims, wherein the thermolysis reaction is carried out at a temperature between 150°C and 200°C.

15. A method according to any one of the preceding claims, wherein the thermolysis reaction is carried out for two to four hours.

16. A method according to any one of the preceding claims, wherein the thermolysis reaction is carried out at a pressure between 15 kPa and 40 kPa.

17. Process according to claims 1 to 3 in which the separation column is equipped with a side withdrawal and comprises a number of theoretical plates of between 10 and 30, preferably between 20 and 25.

18. Process according to claims 1 to 3 in which the separation column operates under a reduced pressure generally of between 3 kPa and 30 kPa, preferably between 9 kPa and 20 kPa.

19. Process according to claims 1 to 3 in which the withdrawal from the separation column is carried out in the liquid phase.

20. Process according to claim 12, in which the mixing between the biomass and the inhibitor and the thermolysis can be carried out consecutively or simultaneously.

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