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 poly(3-hydroxyalkanoate) (P3HA) contained in biomass by extraction of the P3HA using a solvent, followed by separation of insoluble organic waste and then thermolysis of the P3HA-solvent mixture in the presence of the solvent. The solvent is selected such that it provides good dissolution of the P3HA and does not boil under the thermolysis conditions.

Description

[0001] PROCESS FOR THE PRODUCTION OF BIOSOURCED aP UNSATURATED CARBOXYLIC ACIDS FROM POLY(3-HYDROXYALKANOATE) CONTAINED IN BIOMASS

[0002] Domain

[0003] The present invention relates to a process for manufacturing bio-sourced unsaturated aP carboxylic acids by extraction, from biomass, of a poly(3-hydroxyalkanoate) using a solvent, followed by thermolysis of said polymer in the presence of said solvent.

[0004] Prior art and

[0005] The industrial production of unsaturated carboxylic acids (aP) 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.

[0006] One possible way to obtain these unsaturated aP carboxylic acids is the thermolysis at temperatures of 150 to 300 °C of the corresponding poly(3-hydroxy alkanoates) (P3HA), according to the following reaction:

[0007] Ri= H or alkyl and R2= H or alkyl; n is a number greater than 30

[0008] If RI=R2= H:

[0009] Poly(3-hydroxyalkanoate) = poly(3-hydroxypropionate) (P3HP);

[0010] Unsaturated carboxylic acid aP = propenoic acid (acrylic acid).

[0011] If Ri= methyl and R2= H:

[0012] Poly(3-hydroxyalkanoate) = poly(3-hydroxyisobutyrate) (P3HiB);

[0013] Unsaturated carboxylic acid aP = isobutenoic acid (methacrylic acid).

[0014] If Ri= H and R2= methyl: Poly(3-hydroxyalkanoate) = poly(3-hydroxybutyrate) (P3HB);

[0015] Unsaturated α-P carboxylic acid = 2-butenoic acid (crotonic acid).

[0016] If R1=H and R2 = ethyl:

[0017] - Poly(3-hydroxyalkanoate) is poly(3-hydroxy valerate) (P3HV);

[0018] - Unsaturated carboxylic acid aP = pent-2-enoic acid

[0019] These poly(3-hydroxyalkanoates) can themselves be previously obtained by chemical transformations of raw materials of fossil origin, but also by fermentation of biomass.

[0020] There is a strong market demand for these unsaturated aD 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).

[0021] 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, or requires a prior P3HA extraction step, which can be complex and expensive.

[0022] Several solutions have been proposed to solve this problem.

[0023] US 9850192 describes a process for the production of acrylic acid from a genetically modified microbial biomass metabolizing glucose or any other renewable raw material, to produce a homopolymer or copolymer of poly-3-hydroxy propionate (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, but a risk is that the residue present in the reactor after thermolysis is pasty and sticky, which could make its conversion to industrial scale complex.

[0024] Another solution is to first extract P3HA from the biomass using an organic solvent before carrying out its thermolysis. Document US20150376152, describes in Example 6 the extraction of P3HP from biomass, using an organic solvent, such as 2-butanone. The solvent is then removed by distillation before carrying out the thermolysis of P3HP into acrylic acid.

[0025] The inventors have now surprisingly discovered that it is possible to simplify the procedure of extraction from biomass, followed by thermolysis of P3HA, without carrying out an additional step of separation of the solvent used for the extraction of P3HA.

[0026] Accordingly, 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 aP carboxylic acids from poly(3-hydroxyalkanoates) obtained by fermentation.

[0027] Summary of the invention

[0028] The proposed technical solution consists of using for the extraction of P3HA from biomass an organic solvent in which P3HA is very soluble, but which also has a boiling point high enough so that the thermolysis step can be carried out directly on this P3HA-solvent mixture, without having to first remove the extraction solvent.

[0029] The subject of the present invention is a process for manufacturing a bio-sourced unsaturated carboxylic acid aP, said process comprising the following steps:

[0030] - mixing a biomass comprising the poly(3-hydroxyalkanoate) with a solvent capable of solubilizing the P3HA,

[0031] - separating organic detritus insoluble in said solvent, including cell membranes, from the P3HA-solvent mixture,

[0032] - subjecting said PHA-solvent mixture to a thermolysis step leading to obtaining, on the one hand, said unsaturated carboxylic acid aP, and on the other hand, said solvent.

[0033] According to various embodiments, said method comprises the following characteristics, possibly combined. The contents indicated are expressed by weight, unless otherwise indicated. Within the ranges of values ​​indicated, the limits are included.

[0034] According to one embodiment, the poly(3-hydroxyalkanoate) used in the method comprises a single type of 3-hydroxyalkanoate units and the product formed is therefore composed of a single unsaturated carboxylic acid aP. According to one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxypropionate unit and at least one of the unsaturated carboxylic acids aP produced is acrylic acid.

[0035] According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the unsaturated carboxylic acid aP produced is acrylic acid.

[0036] According to one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxybutyrate unit and at least one of the unsaturated aP carboxylic acids produced is crotonic acid.

[0037] According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) and the unsaturated carboxylic acid aP produced is crotonic acid.

[0038] According to one embodiment, the poly(3-hydroxyalkanoate) contains the 3-hydroxyisobutyrate unit and at least one of the unsaturated aP carboxylic acids produced is methacrylic acid.

[0039] According to one embodiment, the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutyrate) and the unsaturated carboxylic acid aP produced is methacrylic acid.

[0040] According to 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 aP carboxylic acids. Examples of P3HA copolymers are poly-3-hydroxybutyrate-co-3-hydroxypropionate, poly-3-hydroxybutyrate-co-3-hydroxy val erate (poly-3-HB-co-3HV).

[0041] According to one embodiment, the biomass host is a bacterium, a yeast, a fungus, an algae, a cyanobacterium or a mixture of two or more of these elements.

[0042] According to one embodiment, the biomass used is pretreated by washing, drying and grinding operations, to produce a biomass containing at least 50% by weight of P3HA.

[0043] According to one embodiment, 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. According to one embodiment, the step of extracting P3HA from the biomass by a solvent takes place at a temperature of 20 to 130°C.

[0044] According to one embodiment, the step of extracting P3HA from the biomass using a solvent takes place in batch.

[0045] According to one embodiment, the step of extracting P3HA from the biomass by a solvent takes place continuously.

[0046] According to one embodiment, the thermolysis reaction of P3HA in solution in the solvent takes place at a temperature of 130 to 300°C, and at a pressure of 1 to 101 kPa (atmospheric pressure).

[0047] According to one embodiment, the solvent used to extract the P3HA present in the biomass has a boiling point such that it does not boil under the temperature and pressure conditions of the thermolysis reaction.

[0048] According to one embodiment, the thermolysis reaction takes place in the presence of one or more polymerization inhibitors.

[0049] 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 aP 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.

[0050] According to a preferred embodiment, at least one of said polymerization inhibitors is hydroquinone methyl ether (HMEQ).

[0051] According to one embodiment, the thermolysis reaction of the poly(3-hydroxyalkanoate) takes place in batch.

[0052] According to one embodiment, the thermolysis reaction of the poly(3-hydroxyalkanoate) takes place continuously.

[0053] According to one embodiment, the method according to the invention comprises a step of condensation of the vapors of the unsaturated carboxylic acid(s) aP obtained by the thermolysis reaction of poly(3-hydroxy alkanoate), followed by one or more purification steps. The purification operations may generally comprise distillations, liquid / liquid extractions, separations using a film evaporator, or crystallizations.

[0054] According to one embodiment, the method according to the invention comprises a step of recycling the solvent used to extract the P3HA from the biomass, at the end of the thermolysis step. Advantageously, the solvent can be recycled to the extraction step without having to be distilled.

[0055] 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 aP carboxylic acids, originating from cell membranes, without carrying out a step of separation of the solvent used for the extraction of P3HA.

[0056] This solution has two advantages: it saves the distillation of the solvent, which is energy-intensive, and the thermolysis of P3HA is carried out not in bulk, but in solution, which reduces the risk of fouling the thermolysis reactor.

[0057] The invention will now be described in more detail in the following description.

[0058] Detailed description of the invention

[0059] The invention aims to produce bio-sourced unsaturated aP 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.

[0060] The invention proposes to provide a method for reducing or eliminating this risk of fouling.

[0061] The invention is based on the use of an organic solvent for extracting P3HA from biomass, in which P3HA is highly soluble but which also has a boiling point high enough that the thermolysis step can be carried out directly on this P3HA-solvent mixture, without having to first remove the extraction solvent.

[0062] 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 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.

[0063] 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 selected 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.

[0064] According to one embodiment, the biomass used in the method according to the invention comes from a process of bacterial fermentation of sugars or lipids.

[0065] Depending on the cultivation conditions and the variety of the microorganism used, homo- or copolymers of poly(3-hydroxyalkanoates) (P3HA) with different 3-hydroxyalkanoic acids are formed.

[0066] According to one embodiment, the biomass used is pretreated by washing, drying and grinding operations, to produce a biomass containing at least 50% by weight of P3HA.

[0067] According to one embodiment, the solvent used to extract the P3HA present in the biomass is chosen from polar organic solvents with a high boiling point, so that it does not boil during the thermolysis step. Such solvents are, for example, glycol diethers (glymes), such as tetraglyme, sulfur sulfoxide or sulfone solvents, such as sulfolane or dimethyl sulfone, carbonate solvents, such as propylene carbonate, or phenol derivatives, such as para-methoxyphenol (also called hydroquinone methyl ether or EMHQ).

[0068] According to one embodiment, the extraction of the P3HA present in the biomass takes place at a temperature of 20 to 130°C.

[0069] According to one embodiment of the invention, 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.

[0070] According to one embodiment, the extraction is followed by a step of separating the P3HA-solvent mixture from the organic detritus insoluble in said solvent, for example cell membranes. Possible methods are filtration or centrifugation.

[0071] According to one embodiment of the invention, the steps of extracting P3HA from the biomass using a solvent and separating the P3HA-solvent mixture from the organic detritus insoluble in said solvent can be carried out in batch mode.

[0072] According to one embodiment of the invention, the steps of extracting P3HA from the biomass using a solvent and separating the P3HA-solvent mixture from the organic detritus insoluble in said solvent can be carried out continuously.

[0073] The term "thermolysis" of poly(3-hydroxyalkanoate) (P3HA) means its chemical decomposition into unsaturated carboxylic acid aP obtained under the effect of temperature. This term is synonymous with pyrolysis.

[0074] In the process according to the invention, the thermolysis reaction of the poly(3-hydroxyalkanoate)-solvent mixture takes place at a temperature of 130 to 300°C, preferably 170 to 230°C and at a pressure of 1 to 101 kPa (atmospheric pressure).

[0075] According to one embodiment of the invention, the step of thermolysis of the P3HA-solvent mixture can be carried out in batch.

[0076] According to one embodiment of the invention, the step of thermolysis of the P3HA-solvent mixture can be carried out continuously.

[0077] Advantageously, the solvent recovered at the end of thermolysis is recycled to the extraction stage.

[0078] According to one embodiment of the invention, the solvent used in the process has a boiling temperature greater than 230°C under atmospheric pressure.

[0079] According to one embodiment, the thermolysis of the poly(3-hydroxyalkanoate) takes place in the absence of a catalyst. The use of catalysts makes it possible to accelerate the kinetics of thermolysis and / or to reduce its temperature. However, the use of a catalyst makes the process more complex and more difficult to implement on an industrial scale.

[0080] According to one embodiment, the reaction medium in the thermolysis reactor comprises at least one polymerization inhibitor, in particular in an amount of 50 ppm to 5% by weight, in particular 0.01% to 3% by weight, relative to the weight of the poly(3-hydroxyalkanoate).

[0081] The polymerization inhibitors are selected from the inhibitors conventionally used in existing industrial processes for the production of unsaturated aP carboxylic acids. These include phenolic derivatives such as hydroquinone (HQ) and its derivatives such as hydroquinone methyl ether (EMHQ), 2,6-di-terbutyl-4-methylphenol (BHT) or 2,4-dimethyl-6-terbutylphenol (Topanol A); phenothiazine and its derivatives; nitroxide compounds such as 4-hydroxy-2,2,6,6-tetramethylpiperidin-l-oxyl (4-OH-TEMPO); amino compounds such as paraphenylenediamine derivatives.

[0082] According to one embodiment, said polymerization inhibitor is hydroquinone methyl ether (HMEQ).

[0083] According to a particular embodiment, the solvent used to extract the P3HA present in the biomass is hydroquinone methyl ether (HMEQ) used in molten form. After the step of separating the P3HA-HMEQ mixture from the insoluble organic detritus, the P3HA in solution in the molten HMEQ is then thermolyzed under conditions where the HMEQ is partially volatile without being boiling, without additional addition of HMEQ. The HMEQ then simultaneously plays the roles of extraction and thermolysis solvent but also of partially volatile polymerization inhibitor.

[0084] According to one embodiment, the temperature and pressure conditions in the thermolysis reactor are chosen so that the unsaturated aP carboxylic acid(s) formed are in the form of vapors.

[0085] According to one embodiment, the invention relates to a method for manufacturing bio-sourced acrylic acid from P3HP contained in biomass.

[0086] According to one embodiment, the invention relates to a method for manufacturing bio-sourced methacrylic acid from P3HiB contained in biomass.

[0087] According to one embodiment, the invention relates to a method for manufacturing bio-sourced crotonic acid from P3HB contained in biomass.

[0088] According to one embodiment, the invention relates to a method for manufacturing a mixture of unsaturated aP carboxylic acids from a P3HA, contained in biomass, comprising several different 3-hydroxyalkanoate units.

[0089] According to one embodiment, the method according to the invention comprises a step of condensation of the vapors of the unsaturated carboxylic acid(s) aP obtained by the thermolysis reaction of poly(3-hydroxy alkanoate), followed by one or more purification steps. The purification operations may generally comprise distillations, liquid / liquid extractions, separations using a film evaporator, or crystallizations.

[0090] According to a preferred embodiment, the P3HA contained in the biomass is P3HP, the extraction is carried out with a sulfone-type solvent, such as sulfolane or dimethylsulfone and the thermolysis step of the P3HP-sulfone solvent mixture is carried out in the presence of hydroquinone methyl ether.

[0091] The following examples illustrate the present invention without, however, limiting its scope.

[0092] EXPERIMENTAL PART

[0093] The examples are carried out on biomass containing 60% by weight of P3HP. The unsaturated carboxylic acid aP obtained after thermolysis is acrylic acid (AA).

[0094] The P3HP solvent extraction step is carried out by introducing 2 g of this biomass and 20 g of solvent into a glass test tube equipped with a magnetic stir bar. The medium is placed in an oil bath at 100 °C and stirred using a magnetic stirrer for 2 h. The insoluble organic detritus is then separated from the P3HP-solvent mixture by centrifugation.

[0095] The thermolysis step of P3HP in solution in the solvent is carried out by placing the medium obtained after the extraction and separation step of the organic detritus in a 50 mL two-necked flask; an addition of EMHQ inhibitor can be made. This 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 lateral condenser. The condenser leads to a recipe consisting of a 25 mL single-necked flask cooled by an ice bath. A tapping allows the experiment to be carried out under partial vacuum.

[0096] Thermolysis of biomass in a solvent medium without prior extraction and separation of organic detritus

[0097] Test 1.

[0098] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) and 20 g of sulfolane are introduced directly into the thermolysis assembly. 0.02 g of EMHQ are added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.1 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is difficult to handle (liquid loaded with sticky solids).

[0099] Test 2.

[0100] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) and 20 g of tetraglyme are introduced directly into the thermolysis assembly. 0.02 g of EMHQ are added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.1 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is difficult to handle (liquid loaded with sticky solids).

[0101] Test 3.

[0102] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) and 20 g of EMHQ are introduced directly into the thermolysis assembly. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 0.9 g of AA with a purity greater than 90% is recovered in the top recipe. The residue from the thermolysis reactor is difficult to handle (liquid loaded with sticky solids).

[0103] Test 4.

[0104] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) and 20 g of dimethylsulfone are introduced directly into the thermolysis assembly. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.0 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is difficult to handle (liquid loaded with sticky solids).

[0105] Test 5.

[0106] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) and 20 g of propylene carbonate are introduced directly into the thermolysis assembly. The thermolysis reaction is carried out at 200°C and 70 kPa for 4 h. 0.8 g of AA with a purity greater than 90% is recovered in the top recipe. The residue from the thermolysis reactor is difficult to handle (liquid loaded with sticky solids).

[0107] Thermolysis after prior extraction of biomass with methyl isobutyl ketone (MIBK) and separation of organic detritus

[0108] Test 6.

[0109] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) are extracted with 20 g of MIBK at 100°C for 2 h.

[0110] The insoluble organic detritus was separated by centrifugation and weighed 1.2 g. A maximum of 0.8 g of P3HP was therefore extracted in the MIBK, i.e. two-thirds of the P3HP contained in the biomass.

[0111] The homogeneous P3HP-MIBK mixture is introduced directly into the thermolysis assembly. 0.02 g EMHQ is added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 20.3 g of a homogeneous organic medium comprising 3% (i.e. 0.6 g) of AA in solution in MIBK are recovered at the top. The residue from the thermolysis reactor is a sticky solid.

[0112] Thermolysis after prior extraction of the biomass with a solvent according to the invention (good solvent for P3HP and which does not boil under thermolysis conditions)

[0113] Test 7.

[0114] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) are extracted with 20 g of sulfolane at 100°C for 2 h.

[0115] The insoluble organic detritus was separated by centrifugation and weighed 0.8 g. A maximum of 1.2 g of P3HP was therefore extracted in sulfolane, potentially all of the P3HP contained in the biomass.

[0116] The homogeneous P3HP-sulfolane mixture is introduced directly into the thermolysis assembly. 0.02 g EMHQ is added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.1 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is a clear liquid consisting mainly of sulfolane and can be recycled to the extraction step.

[0117] Test 8.

[0118] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) are extracted with 20 g of tetraglyme at 100°C for 2 h.

[0119] The insoluble organic detritus was separated by centrifugation and weighed 0.8 g. A maximum of 1.2 g of P3HP was therefore extracted in the tetraglyme, potentially all the P3HP contained in the biomass.

[0120] The homogeneous P3HP-tetraglyme mixture is introduced directly into the thermolysis assembly. 0.02 g EMHQ is added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.1 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is a clear liquid consisting mainly of tetraglyme which can be recycled to the extraction step.

[0121] Test 9.

[0122] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) are extracted with 20 g of EMHQ at 100°C for 2 h.

[0123] The insoluble organic detritus is separated by centrifugation and weighs 0.8 g. A maximum of 1.2 g of P3HP was therefore extracted in the EMHQ, potentially all the P3HP contained in the biomass.

[0124] The homogeneous P3HP-EMHQ mixture is introduced directly into the thermolysis assembly. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 0.9 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is a clear liquid consisting essentially of EMHQ which can be recycled to the extraction step.

[0125] Test 10.

[0126] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) were extracted with 20 g of dimethyl sulfone at 115°C for 2 h. The insoluble organic detritus was separated by centrifugation and weighed 0.8 g. A maximum of 1.2 g of P3HP was therefore extracted in dimethyl sulfone, potentially representing all of the P3HP contained in the biomass.

[0127] The homogeneous P3HP-dimethylsulfone mixture is introduced directly into the thermolysis assembly. 0.02 g EMHQ is added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.1 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is a clear liquid consisting essentially of dimethyl sulfone which can be recycled to the extraction step.

[0128] Test 11.

[0129] 2 g of biomass containing 60% P3HP (i.e. 1.2 g of P3HP) are extracted with 20 g of propylene carbonate at 100°C for 2 h.

[0130] The insoluble organic detritus was separated by centrifugation and weighed 0.8 g. A maximum of 1.2 g of P3HP was therefore extracted into the propylene carbonate, potentially all of the P3HP contained in the biomass.

[0131] The homogeneous P3HP-propylene carbonate mixture is introduced directly into the thermolysis setup. 0.02 g EMHQ is added as a polymerization inhibitor. The thermolysis reaction is carried out at 200°C and 20 kPa for 4 h. 1.0 g of AA with a purity greater than 90% is recovered in the overhead recipe. The residue from the thermolysis reactor is a clear liquid consisting mainly of propylene carbonate which can be recycled to the extraction step.

Claims

CLAIMS 1. A process for the production of unsaturated aP carboxylic acids from biomass containing a poly(3-hydroxyalkanoate) (P3HA), said process comprising the following steps: - extract the P3HA from the biomass with a solvent capable of solubilizing the P3HA, to form a P3HA-solvent mixture, - separate the organic detritus insoluble in said solvent from the P3HA-solvent mixture, - thermolyzing said P3HA-solvent mixture to obtain, on the one hand, said unsaturated carboxylic acid aP, and on the other hand, said solvent.

2. Method according to claim 1, 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.

3. Method according to one of claims 1 and 2, in which the extraction is carried out at a temperature between 20 and 130°C.

4. Process according to any one of the preceding claims, in which the thermolysis is carried out at a temperature between 130 and 300°C, preferably between 170 and 230°C, and at a pressure between 1 and 101 kPa (atmospheric pressure), preferably between 10 and 101 kPa (atmospheric pressure).

5. A process according to any preceding claim wherein the solvent has a boiling point under atmospheric pressure above 230°C.

6. Process according to any one of the preceding claims in which the solubility of P3HA in the solvent in the extraction step is greater than 5% by weight, preferably greater than 20% by weight.

7. Method according to any one of the preceding claims in which the extraction, separation and thermolysis steps are each carried out in batch or continuous mode.

8. Process according to any one of the preceding claims in which the thermolysis reaction takes place in the presence of one or more polymerization inhibitors.

9. Method according to claim 8, wherein the inhibitor content varies from 50 ppm to 5% by weight, in particular from 0.01% to 3% by weight, relative to the weight of the poly(3-hydroxyalkanoate).

10. Method according to one of claims 8 or 9, in which the polymerization inhibitor(s) are compounds chosen from phenolic derivatives, phenothiazine derivatives, nitroxide derivatives or paraphenylenediamine derivatives.

11. A method according to any one of claims 8 to 10, wherein one of the polymerization inhibitors is hydroquinone methyl ether (HMEQ).

12. Process according to any one of claims 1 to 11, in which the solvent is chosen from glycol diethers (glymes) such as tetraglyme, organic sulfur solvents such as sulfolane or dimethyl sulfone, or organic carbonates such as propylene carbonate.

13. Process according to claim 8, in which the solvent is itself a polymerization inhibitor, preferably the solvent is hydroquinone methyl ether (HMEQ) in molten form.

14. Process according to any one of the preceding claims in which the solvent recovered at the end of the thermolysis is recycled to the extraction step. A process according to any preceding claim wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxypropionate unit and at least one of the unsaturated aP carboxylic acids produced is acrylic acid. A process according to any preceding claim wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxypropionate) and the unsaturated aP carboxylic acid produced is acrylic acid. A process according to any one of claims 1 to 14 wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxybutyrate unit and at least one of the unsaturated aP carboxylic acids produced is crotonic acid. A process according to any one of claims 1 to 14 and 17 wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxybutyrate) and the unsaturated aP carboxylic acid produced is crotonic acid.A process according to any one of claims 1 to 14 wherein the poly(3-hydroxyalkanoate) contains the 3-hydroxyisobutyrate unit and at least one of the unsaturated aP carboxylic acids produced is methacrylic acid. A process according to any one of claims 1 to 14 and 19 wherein the poly(3-hydroxyalkanoate) is poly(3-hydroxyisobutyrate) and the unsaturated aP carboxylic acid produced is methacrylic acid. A process for the manufacture of unsaturated aP carboxylic acids obtained by the process according to any one of the preceding claims, characterized in that it comprises a step of condensation of the products thus obtained, followed by one or more purification steps chosen from distillation, liquid / liquid extraction, separation using a film evaporator, or crystallization or a combination of these techniques.

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