WO2026008302A1 - Method for producing esters by reaction between an alcohol and a carboxylic acid in the presence of an enzymatic catalyst in a two-phase medium in the form of a pickering emulsion - Google Patents

Abstract

The invention relates to a method for producing esters by reaction between a first reagent chosen from an alcohol or a carboxylic acid, contained in an aqueous solution, and at least one second reagent chosen from a carboxylic acid or an alcohol, in the presence of an enzymatic catalyst. The invention is characterised in that the reaction mixture is in the form of a Pickering emulsion comprising at least one water phase and one oil phase, said oil phase comprising at least one extraction solvent.

Description

PROCESS FOR THE MANUFACTURE OF ESTERS BY REACTION BETWEEN AN ALCOHOL AND A CARBOXYLIC ACID IN THE PRESENCE OF AN ENZYMATIC CATALYST IN A BIPHASIC MEDIUM IN THE FORM OF A PICKERING EMULSION

technical field

The present invention relates to the field of manufacturing esters preferably bio-based used in particular in the field of cosmetics, fragrances, lubricants, emulsifiers, glues, varnishes and biofuels by reaction between an alcohol and a carboxylic acid in the presence of an enzymatic catalyst in a biphasic medium in the form of a Pickering emulsion.

State of the art

The market for esters is very vast since these compounds are used in many fields such as biofuels, lubricants, emulsifiers, fragrances, complexing agents, synthesis intermediates, particularly for biodegradable polymers, adhesives, printing inks, paints, varnishes...

In a context of strong demand for bio-based products with a low environmental impact, ester manufacturers are increasingly seeking to source bio-based reagents, derived from renewable resources, for their production. It is well known that an ester can be manufactured from an alcohol and a carboxylic acid. Therefore, at least one of the two reagents must be bio-based to meet this demand.

These compounds can be obtained from biomass by fermentation, by oxidation (for carboxylic acids) of carbohydrates derived from biomass (cellulose, glucose, and glycerol), or by any process known to those skilled in the art. However, unlike the petrochemical industry, the processes used result in solutions that are dilute or even highly dilute in water. Yet, conventional ester manufacturing processes employ highly concentrated or pure reagents containing as little water as possible. Indeed, it is known to those skilled in the art that the presence of water is strongly detrimental to the esterification reaction. Therefore, it is necessary to use processes to separate these reagents in order to purify them. However, these processes have an energy cost that significantly increases the carbon footprint of the final product. Examples include vaporization, distillation, or membrane separation processes (see patents US8906204B2, US11471786B2, and US10961489B2). There are also liquid-liquid extraction processes, but these do not allow for the extraction of 100% of the compound of interest (see patent application LIS2013/0149757) especially if the compound is very diluted in water.

Van Den Berg et al. (Van Den Berg, C., et al. Biotechnol Bioeng (2013), 110(1), 137-142) propose reacting butanol formed by fermentation with butyric acid, both diluted in water, using an enzymatic catalyst in aqueous solution and extracting the resulting ester, butyl butyrate, into an oil phase such as hexadecane. However, the contact surface area between the oil and water phases is small in this implementation, which significantly slows ester extraction and thus the esterification reaction.

Patent CN 114606222 describes a process for reacting methanol in aqueous solution with lauric acid in an oil phase, in the presence of a biocatalyst. A Pickering emulsion is prepared to stabilize the emulsion and facilitate the exchange between the two phases. In this case, the methanol is present in very high excess to maximize the conversion of lauric acid. The methanol is therefore highly concentrated in the water (15% to 50% wt.). Since this concentration is problematic for the enzyme used, the enzyme must be encapsulated beforehand, and the capsules containing the enzyme are used to prepare the Pickering emulsion. Given the size of the capsules, the size of the water phase droplets dispersed in the oil phase is particularly large (150 µm to 650 µm), one to two orders of magnitude larger than what could be achieved with a Pickering emulsion not constrained by enzyme encapsulation. Since the exchange surface between the two phases is inversely proportional to the size of the drops, the exchange surface is reduced in this case and therefore penalizes the transfer of molecules between the phases.

Object of the invention

The applicant has developed a process for manufacturing esters by reacting an alcohol with a carboxylic acid in the presence of an enzymatic catalyst in a two-phase medium in the form of a Pickering emulsion. This process allows for the synthesis of esters with optimized yields and rates from alcohols and/or carboxylic acids present in dilute aqueous solutions. This is particularly relevant when the alcohols and/or carboxylic acids are bio-based.

The present invention therefore offers the advantage of implementing a process for manufacturing esters from reagents diluted in water without requiring prior purification or concentration of the reagents. The biocatalyst (enzymatic catalyst) used in the invention also allows the carboxylic acid to react with the alcohol in a dilute medium where a chemical catalyst would not have been sufficient to carry out the esterification reaction. Furthermore, in the process of manufacturing a bio-ester, replacing a chemical catalyst with a biocatalyst represents an additional advantage, especially as temperatures Implementation costs are much lower in this case, thus reducing the carbon footprint of the process.

The use of an emulsion according to the invention also allows the ester to be extracted from the oil phase as it is formed. Since the esterification reaction is an equilibrium reaction, that is, one that is not complete, the transfer of the ester into the oil phase shifts the equilibrium in the direction favorable to ester production.

The use of a Pickering emulsion according to the invention allows the emulsion to be optimized by developing a large exchange surface between the two phases, which greatly promotes the extraction of the ester.

This large exchange surface area offers an additional advantage if one of the two reactants is introduced into the oil phase to facilitate its transfer from the oil phase to the water phase, where the reaction takes place in the presence of the biocatalyst. This is the case, for example, with fatty carboxylic acids and fatty alcohols, which have sufficiently long carbon chains to significantly reduce their water solubility. They are then solubilized in the oil phase. The Pickering emulsion allows their reaction in water despite their low water solubility. The large exchange surface area generated between the two liquid phases compensates for this low solubility, and the microreactors created by the Pickering emulsion promote the reaction kinetics.

The Pickering emulsion also eliminates the need for vigorous agitation, which is traditionally required to transfer a molecule between two liquid phases, thus reducing the energy demand of the process. The Pickering emulsion produces an emulsion that remains stable after its creation; no additional energy is needed to maintain contact between the two liquid phases.

Pickering emulsions therefore also allow for continuous implementation with, for example, continuous reagent addition in the continuous phase and/or continuous withdrawal of the continuous phase to separate the reaction products.

Pickering emulsions have the added advantage over a surfactant-stabilized emulsion of not using products that may have an impact on the environment and of using solids that are easily separable from liquids. The present invention relates to a process for manufacturing an ester from a first reagent selected from an alcohol or a carboxylic acid in aqueous solution, comprising the following steps: a) an esterification reaction is carried out on a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion to form an ester in the oil phase, said reaction mixture being obtained according to the following steps: a1) a biphasic mixture is formed comprising at least a water phase and an oil phase, by contacting an aqueous solution comprising said first reagent with at least one second reagent selected from a carboxylic acid or an alcohol, at least one enzymatic catalyst, at least one organic extraction solvent, and solid particles; a2) said biphasic mixture obtained in step a1) is emulsified to form a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion; said reaction mixture comprising:

-either droplets of said oil phase stabilized by said solid particles in said water phase;

-either droplets of said water phase stabilized by said solid particles in said oil phase; b) the ester formed in step a) is recovered in the oil phase.

Advantageously, the first reactant contained in said aqueous solution is an alcohol, and the second reactant is a carboxylic acid.

Advantageously, the first reactant contained in said aqueous solution is a carboxylic acid and the second reactant is an alcohol.

Advantageously, the concentration of first reactant in said aqueous solution is between 0.001 mol/L and 0.4 mol/L when said first reactant is an alcohol, and between 0.001 mol/L and 2 mol/L when said first reactant is a carboxylic acid.

Advantageously, the molar ratio between said second reactant and said first reactant is between 1 and 10.

Advantageously, said first reagent chosen from said alcohol or said carboxylic acid is of bio-based origin.

Advantageously, the enzymatic catalyst added in step a 1) is chosen from lipases of microbial or plant origin. Preferably, the enzymatic catalyst added in step a1) is chosen from Candida antarctica lipase B, Candida rugosa lipase, or Rhizomucor miehei lipase.

Advantageously, the pH of the water phase is less than 7.

Advantageously, the solid particles added in step a1) are chosen from solid particles of silica, clay, or natural or synthetic polymers.

Advantageously, the droplet size of the Pickering emulsion obtained at the end of step a) is between 1 pm and 140 pm.

Advantageously, the temperature of the esterification reaction in step a) is between 10°C and 90°C.

Advantageously, the mass concentration of solid particles added in step a1) is between 0.1 wt% and 10 wt% relative to the total weight of said two-phase mixture.

Advantageously, the reaction mixture obtained at the end of step a) is a Pickering water-in-oil emulsion.

Advantageously, a step a’) of production of said first reagent chosen from said alcohol or said carboxylic acid in aqueous solution is carried out in combination with step a).

Detailed description of the invention

Definitions

The term “biomass” refers to all organic matter of plant or animal origin, but also to any by-product or liquid effluent resulting from its mechanical, thermochemical, enzymatic or fermentation processes, as well as mixtures thereof.

The term "bio-based" or "renewable" means that the material/product/compound it describes is derived from biomass. In the text, the prefix "Bio" can also be used before the type of compound to characterize its bio-based nature: for example, bio-methanol, bio-ethanol, bio-butanol, bio-isobutanol, bio-acrylic acid, bio-ester.

Emulsion and Pickering's emulsion:

An emulsion is a heterogeneous medium formed by the dispersion of one liquid in another. Emulsions are generally stabilized by surfactants due to their amphiphilic properties.

Emulsions can also be stabilized with solid particles; this is called a Pickering emulsion. Pickering emulsions are liquid-liquid dispersions stabilized by solid nanoparticles or nanoparticle aggregates that accumulate at the interface between two immiscible liquids (usually water and oil) and prevent coalescence (see, for example, Pickering, SU (1907). J. Chem. Soc. Trans. 91, 2001-2021). In fact, the solid particles used to make Pickering emulsions are capable of adhering irreversibly to the interface between the two liquids, resulting in much more effective emulsion stabilization than surfactant adsorption (see, for example, Aveyard, R., Binks, B. P., and Clint, JH (2003); Adv. Colloid Interface Sci. 100, 503-546). The direction of the emulsion (water in oil or oil in water) is determined by the preferential wettability of the solid particles towards one or the other phase. In fact, the liquid that is more wetting towards the solid particles will constitute the continuous phase of the emulsion, and the one that is less wetting will constitute the dispersed phase (see, for example, the publication Binks, B., and Lumsdon, S. (2000. Langmuir 16, 8622-8631).

Pickering emulsions have the advantage of promoting mass transfer between the two liquid phases. Indeed, to ensure the transfer of a molecule between two liquid phases, it is necessary to create a large exchange surface between the two liquids.

An "emulsifier" is a compound or substance that acts as a stabilizer for emulsions, preventing liquids from separating.

A "hydrophobic" molecule or part of a molecule is a molecule that is repelled by a mass of water and other polar substances.

A "hydrophilic" molecule or part of a molecule is a molecule that tends to interact with or be dissolved by water and other polar substances.

"Amphiphile" is a term describing a chemical compound that includes both hydrophilic and hydrophobic properties.

Sizes of solid particles and droplets:

Solid particle size: The solid particles according to the invention can be of various shapes and sizes, for example from a few nanometers to a few microns, or even tens of microns, in the form of substantially spherical or non-spherical beads (FB de Carvalho-Guimarães, K Leal Correa, T Pereira de Souza, JR Rodriguez Amado, RM Ribeiro-Costa and JO Carréra Silva-Júnior (2022) A Review of Pickering Emulsions: Perspectives and Applications, Pharmaceuticals, 15, 1413. https://doi.org/10.3390/ph15111413). The shape can They can be substantially spherical, or shaped like a rod, ellipsoid, needle, spindle, nanofibril, nanocage, plate, nanotube, nanocube, etc. (Li W, Jiao B, Li S, Faisal S, Shi A, Fu W, Chen Y and Wang Q (2022) Recent Advances on Pickering Emulsions Stabilized by Diverse Edible Particles: Stability Mechanism and Applications. Front. Nutr. 9:864943. doi: 10.3389/fnut.2022.864943). The size can vary enormously, from a few nanometers to a few tens of microns. The size obviously depends on the morphology of the solid particles involved. It is generally determined by scanning and transmission electron microscopy analyses. Defining size is easy for spherical particles (diameter) and more difficult for solid particles whose shape deviates from sphericity (plates, rods, ellipsoids, needles, etc.). In such cases, two characteristic sizes are generally specified: the smallest and the longest. Another difficulty arises from the spontaneous formation of aggregates between elementary solid particles. A distinction is then made between the size of the elementary solid particles and the size of the aggregates. For example, the commercial silica Aerosil R972 is a mixture of elementary solid particles between 5 nm and 50 nm with aggregates of average size on the order of 250 nm.

Droplet size: Droplet size refers to the largest dimension of the droplets measured by optical microscopy (notably by Olympus BX51 with analysIS software for image analysis).

Solubility

Solubility refers to the ability of a substance, called the solute, to dissolve in another substance, called the solvent. Depending on the solubility value, a certain percentage (mass fraction) of the substance is dissolved in the solvent.

In the case of a liquid/liquid biphasic medium, we speak of the affinity of a substance for a phase, when this substance solubilizes with a mass fraction greater than 50% in this phase, the remainder to 100% is found in the other phase.

The invention relates to a process for manufacturing an ester from a first reagent selected from an alcohol or a carboxylic acid in aqueous solution, comprising the following steps: a) an esterification reaction is carried out on a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion to form an ester in the oil phase, said reaction mixture being obtained according to the following steps: a1) a two-phase mixture comprising at least a water phase and an oil phase is formed by contacting an aqueous solution comprising said first reagent, at least one second reagent selected from a carboxylic acid or an alcohol, at least one enzymatic catalyst, at least one organic extraction solvent, and solid particles; a2) said biphasic mixture obtained in step a1 is emulsified to form a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion; said reaction mixture comprising:

-either droplets of said oil phase stabilized by said solid particles in said water phase;

-either droplets of said water phase stabilized by said solid particles in said oil phase; b) the ester formed in step a) is recovered in the oil phase.

Step a”) (optional) Step for producing the first reagent chosen from an alcohol or a carboxylic acid in aqueous solution

The first reagent chosen from an alcohol or a carboxylic acid can be obtained from biomass by fermentation and/or chemically using several processes.

Examples include the biorefinery processes aimed at producing alcohols and carboxylic acids, which are described by Laurent, P. et al., Biorefining, a promising alternative to petrochemistry, Biotechnology, Agronomy, Society and Environment, 2022, 15(4), 597-610; and by Takkellapati, S. et al., An overview of biorefinery-derived platform chemicals from a cellulose and hemicellulose biorefinery, Clean Technologies and Environmental Policy, 2018, 20(7), 1615-1630 or as described in patent FR2923840.

We can also mention the biomass transformation processes described by Straathof, A. J. J. et al., Transformation of biomass into commodity chemicals using enzymes or cells, Chem. Rev, 2014, 114, 1871-1908.

In particular, alcohols produced by fermentation processes (e.g., isopropanol and n-butanol) are among the most promising substitutes for petrochemical derivatives. ABE (Acetone-Butanol-Ethanol) fermentation, carried out by microorganisms of the genus Clostridium, is one of the oldest fermentations to have been industrialized and has since been extensively studied. More recently, IBE (Isopropanol-Butanol-Ethanol) fermentation, which produces a mixture of isopropanol, butanol, and ethanol and is also carried out by microorganisms of the genus Clostridium, has been the subject of relatively recent studies (Dos Santos Vieira et al., Acetone-free biobutanol production: Past and recent advances in the Isopropanol-Butanol-Ethanol (IBE) fermentation, Bioresource Technology, 2019, 287, 121425). Regarding the fermentation method used in this type of process, batch production has been studied for ABE and IBE fermentations (see, for example, Jones DT, Woods DR, Acetone-Butanol Fermentation Revisited, Microbiol. Rew., 1986, 50(4), 484-524). Continuous processes have also been studied, initially with cells suspended in a homogeneous reactor. Improvements to continuous processes were then proposed by increasing the retention of microbial biomass in the bioreactor, notably by using cells immobilized on a substrate, and/or by using cell recycling with retention by means of filter membranes (Dos Santos Vieira et al., Acetone-free biobutanol production: Past and recent advances in the Isopropanol-Butanol-Ethanol (IBE) fermentation, Bioresource Technology, 2019, 287,121425).

Carboxylic acids can be produced through fermentation processes using different types of biomass.

One example is the conversion of carbohydrates (sugars, glucose, fructose, sucrose...) by fermentation which leads to acetic, succinic, lactic, itaconic, citric and gluconic acids as described by Lopez-Garzon C.S. (Lopez-Garzon, C.S. et al, Recovery of carboxylic acids produced by fermentation, Biotechnology Advances, 2014, 32, 873-904).

We can also cite Abrodo P.A. et al., Fatty acid composition of cider obtained either by traditional or controlled fermentation, Food Chemistry, 2005, 92, 183-187; and Serra, S. et al., Microbial Fermentation of the Water-Soluble Fraction of Brewers’ Spent Grain for the Production of High-Value Fatty Acids, Fermentation, 2023, 9, 1008.

Carboxylic acids can also be obtained chemically from biomass. These can be carbohydrates derived from lignocellulosic biomass, including cellulose, glucose, fructose, or glycerol. The various pathways for producing acids from biomass are well described by Deng W et al., Production of organic acids from biomass resources, Current Opinion in Green and Sustainable Chemistry, 2016, 2, 54-58; and Li S. et al., Catalytic transformation of cellulose and its derivatives into functionalized organic acids, ChemSusChem, 2018, 11(13), 1995-2028; and Wang M. et al., Sustainable productions of organic acids and their derivatives from biomass via selective oxidation cleavage of C-C bond, ACS Catalysis, 2018, 8(3), 2129-2165.

We can also cite in particular the oxidation of cellulose according to Wang F. et al., One-pot hydrothermal conversion of cellulose into organic acids with CuO as an oxidant, Industrial & Engineering Chemistry Research, 2014, 53(19), 7939-7946; and Jiang, Z. et al., Metal-oxide- catalyzed efficient conversion of cellulose to oxalic acid in alkaline solution under low oxygen pressure, ACS Sustainable Chemistry & Engineering, 2016, 4(1), 305-311.

We can cite the case of glucose oxidation, as for example according to Tang Z. et al., Transformation of cellulose and its derived carbohydrates into formic and lactic acids catalyzed by vanadyl cations, ChemSusChem, 2014, 7(6), 1557-1567.

We can also cite the case of the oxidation of glycerol, as described in patent application WO2014199256, which leads to oxalic acid, formic acid and alpha-hydroxy acids such as lactic acid, glycolic acid, glyceric acid and tartronic acid.

Carboxylic acids can also be obtained by hydrolysis or saponification of vegetable or animal oils following a process described by BANCOURT, H., Saponification, Tech. Ingé., 1991, J5810, 1-6 or SPITZ, L., Soap Technology for the 1990s, ed. SPITZ, L. AOCS Press, Champaign, Illinois. 1991, or SPITZ, L., Soaps and Detergents: A Theoretical and Practical Review, ed. SPITZ, L. AOCS Press. 1996, or WOOLLATT, E., The Manufacture of Soaps, Other Detergents and Glycerin. Ellis Horwood Limited. 1985.

Step a) a reaction mixture is prepared in the form of a Pickering emulsion.

The invention aims to form an ester from a first reagent chosen from an alcohol or a carboxylic acid diluted in an aqueous solution, by adding to this aqueous solution a second reagent chosen from a carboxylic acid or an alcohol and an enzymatic catalyst. Since the ester is insoluble in the aqueous solution, the invention uses the immiscibility between the aqueous solution containing the first reagent and the ester produced to promote the shift of the reaction towards ester formation by preparing a biphasic mixture, notably with the addition of an organic solvent, in the form of a Pickering emulsion.

Pickering emulsions are liquid-liquid (water-oil phase) dispersions stabilized by solid particles or aggregates of solid particles that accumulate at the interface between the two immiscible liquids and prevent coalescence. The direction of the emulsion (water-in-oil or oil-in-water) is determined by the preferential wettability of the solid particles toward one phase or the other. In fact, the liquid with the highest wetting ability toward the solid particles will constitute the continuous phase of the emulsion, and the one with the lowest wetting ability will constitute the dispersed phase. The direction of the emulsion will therefore depend on the nature of the solid particles, the organic extraction solvent, the water phase, and the reactants (alcohol and carboxylic acid). Step a1) preparation of a two-phase mixture.

The aqueous solution comprising the first reagent chosen from the alcohol or the carboxylic acid, at least one second reagent chosen from a carboxylic acid or an alcohol, at least one enzymatic catalyst, at least one organic extraction solvent and solid particles are brought into contact.

When all these species are brought into contact, a two-phase mixture is formed, comprising a water phase and an oil phase. The different species distribute themselves between these two phases according to their affinity for one or the other. The exact composition of the different phases depends on the properties of each species present in the mixture.

Aqueous solution comprising the first reactant:

Said aqueous solution comprises at least the first reagent chosen from said alcohol or said carboxylic acid.

According to one embodiment of the invention, the aqueous solution comprises the first reactant in the form of micelles. This is then referred to as a micellar aqueous solution. This is the case, for example, with micellar solutions obtained by hydrolysis or saponification of vegetable oils. The fatty acid molecules thus obtained form micelles in solution in water.

If the first reactant is an alcohol, its concentration in the aqueous solution is between 0.001 mol/L and 3 mol/L, preferably between 0.001 mol/L and 2 mol/L, preferably between 0.001 and 1 mol/L and preferably between 0.001 and 0.4 mol/L.

If the first reactant is a carboxylic acid, its concentration in the aqueous solution is between 0.001 mol/L and 3 mol/L, preferably between 0.001 mol/L and 2 mol/L.

The said alcohol and carboxylic acid are described below.

Second reagent:

The second reagent is chosen from a carboxylic acid or an alcohol. Said alcohol and carboxylic acid are described below. It can be soluble in water or oil.

The molar ratio between the second reagent chosen from said carboxylic acid or said alcohol and the first reagent chosen from said alcohol or said carboxylic acid contained in the aqueous solution is greater than or equal to 1, preferably between 1 and 10 and most preferably between 1 and 5. According to a variant of the invention, said alcohol comprises several alcohol and/or carboxylic acid groups contain multiple carboxylic acid groups. In this case, the molar ratio between the alcohol and the carboxylic acid will be adjusted by a person skilled in the art according to the number of groups they wish to react.

When the first reactant in the aqueous solution is an alcohol, a carboxylic acid will be added as the second reactant to carry out the esterification reaction.

According to one embodiment of the invention, the second reactant is already present in the aqueous solution. This can be the case, for example, when the second reactant is formed at the same time as the first reactant. This can occur in a fermentation process.

Alcohol :

Depending on the circumstances, the alcohol in question is either the first reactant contained in the aqueous solution or the second reactant added to the aqueous solution to carry out the esterification reaction.

The alcohol according to the invention is any hydrocarbon compound comprising at least one alcohol functional group. The alcohol according to the invention preferably comprises a linear or non-linear, saturated or unsaturated, cyclic or non-cyclic, aromatic or non-aromatic carbon chain, comprising or not heteroatoms, preferably comprising 1 to 40 carbon atoms and possibly comprising other chemical functional groups. It may or may not be bio-based, derived from biomass such as cellulose, a sugar, a sterol, an alcohol formed by fermentation, or obtained by processing a bio-based product.

Without being exhaustive, the alcohol can be chosen from at least one of the following compounds: methanol, ethanol, 1-propanol, 2-propanol (or isopropanol), 1-butanol, 2-butanol, 2-methyl-1-propanol, tert-butanol, 3-hydroxybutanone (or acetoin), 1-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 1-heptanol (or n-heptanol), 2-octanol, 1-dodecanol (or lauryl alcohol), 1-tetradecanol (or myristyl alcohol), 1-hexadecanol (or cetyl alcohol), 1-octadecanol (or stearic alcohol), cis-9-octadecen-1-ol (or octadecenol or oleyl alcohol), 1,2-ethanediol (or ethylene glycol), 1,2-propanediol (or propylene glycol), 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, glycerol, trimethylolproprane, pentaerythritol, the sorbitol, xylitol, glucose, fructose, 5-hydroxymethylfurfural (5-HMF), furfuryl alcohol, a phenol, a polyphenol.

According to one embodiment of the invention, the molecule carries both a carboxylic acid function and an alcohol function and can be selected from lactic acid, glycolic acid, glyceric acid, tartronic acid, malic acid, citric acid, gluconic acid, 3-hydroxypropionic acid, 3-hydroxybutyric acid, 5-hydroxypentanoic acid, glyceric acid, ascorbic acid, 2-keto-L-gulonic acid, 2-hydroxyisobutyric acid, and glucosaminic acid. In this case, the molecule can be said first reactant and/or said second reactant.

Alcohols can be used alone or in mixtures.

According to a particular embodiment of the invention, said alcohol is of bio-based origin.

According to a particular embodiment of the invention, the alcohol is derived from an aqueous fermentation juice. In this case, the alcohols are used purified or unpurified. Thus, the fermentation alcohols are diluted in water with a concentration that varies according to their formation process.

Carboxylic acid:

Depending on the circumstances, the carboxylic acid is either the first reactant contained in the aqueous solution or the second reactant added to the aqueous solution to carry out the esterification reaction.

The carboxylic acid according to the invention is any hydrocarbon compound comprising at least one carboxylic acid functional group. The carboxylic acid according to the invention preferably comprises a linear or non-linear, saturated or unsaturated, cyclic or non-cyclic, aromatic or non-aromatic carbon chain, comprising or not heteroatoms, preferably comprising 1 to 40 carbon atoms, and possibly comprising other chemical functional groups. It may or may not be bio-based, derived from biomass, from the processing of vegetable or animal oil, from fermentation, particularly of sugars, obtained by pressing biomass, or obtained by processing a bio-based product, for example, by the oxidation of an alcohol. It may be in its acidic (or protonated) form or as a salt, for example, an alkali or alkaline earth metal salt or an ammonium salt. Without being exhaustive, the carboxylic acid can be chosen from at least one of the following compounds: formic acid, acetic acid, propanoic acid (or propionic acid), acid butanoic acid (or butyric acid), isobutyric acid, pentanoic acid (or valeric acid), isovaleric acid, hexanoic acid (or caproic acid), n-heptanoic acid, myristic acid, levulinic acid, behenic acid, gadoleic acid, succinic acid, adipic acid, glutaric acid, citric acid, aconitic acid, itaconic acid, palmitic acid, oleic acid, fumaric acid, glycolic acid, glyceric acid, tartronic acid, stearic acid, palmitoleic acid, linoleic acid, alinolenic acid, erucic acid, petroselinic acid, gondoic acid, sterculic acid, dihydrosterculic acid, acid calendic acid, α-eleostearic acid, punicic acid, eicosapentaenoic acid, docosahexaenoic acid, 10-undecenoic acid, ricinoleic acid, malic acid, gluconic acid, 3-hydroxypropionic acid, glyceric acid, ascorbic acid, glucosaminic acid, pyruvic acid, lactic acid, glycolic acid, glyceric acid, tartronic acid, malic acid, citric acid, 3-hydroxypropionic acid, 3-hydroxybutyric acid, 5-hydroxypentanoic acid, glyceric acid, ascorbic acid, acrylic acid, methacrylic acid, 2,5-furandicarboxylic acid, 2-keto-L-gulonic acid, 2-Hydroxyisobutyric acid, benzoic acid and glucosamine acid.

According to one embodiment of the invention, the molecule carries both a carboxylic acid function and an alcohol function and can be selected from lactic acid, glycolic acid, glyceric acid, tartronic acid, malic acid, citric acid, gluconic acid, 3-hydroxypropionic acid, 3-hydroxybutyric acid, 5-hydroxypentanoic acid, glyceric acid, ascorbic acid, 2-keto-L-gulonic acid, 2-hydroxyisobutyric acid, and glucosaminic acid. In this case, the molecule can be said first reactant and/or said second reactant.

According to a particular embodiment of the invention, said carboxylic acid is of bio-based origin.

Solid particles

Solid particles can be hydrophilic, hydrophobic, or amphiphilic. Preferably, solid particles are amphiphilic.

They can be modified to change their surface properties (in particular to modify their wettability). They can be of a single type, or be used in a mixture of several types of solid particles (in terms of size, shape and wettability). Optionally, at least one surfactant can be added to the solid particles. This surfactant (or each of them if a mixture of surfactants is used) can be anionic, cationic, non-ionic, or amphoteric.

According to the invention, the solid particles can thus be chosen from: solid silica particles, preferably at least partially functionalized by hydrophobic hydrocarbon groups, solid clay particles, preferably at least partially modified with organic or amphiphilic molecules, magnetic particles, in particular FesCU, carbon nanotubes, solid graphene oxide particles, solid synthetic polymer particles, such as polyethylene glycol (PEG), polystyrene (PS), polylactic acid (PLA), polycaprolactone (PCL), or solid latex particles, solid particles of material of natural origin preferably chosen from hydroxyapatite, chitosan, cyclodextrin, dextran, solid particles in the form of cellulose nanocrystals or nanofibers, solid particles of biological material, in particular food grade, preferably chosen from starch, zein, soy proteins, bacteria and yeasts.

The size can vary enormously, from a few nanometers to a few tens of microns. The size obviously depends on the morphology of the solid particles involved. It is generally determined by scanning and transmission electron microscopy. It is easy to define for spherical solid particles (diameter), and more difficult for solid particles whose shape deviates from sphericity (plates, rods, ellipsoids, needles, etc.). In these cases, we generally distinguish between two characteristic sizes: the smallest and the longest. Another difficulty is related to the spontaneous formation of aggregates between the elementary solid particles. We then distinguish between the size of the elementary solid particles and the size of the aggregates. For example, the commercial silica Aerosil R972 is a mixture of elementary solid particles between 5 nm and 50 nm with aggregates of average size on the order of 250 nm.

In a particular embodiment of the invention, the solid particles are nanometric, with an average size between 1 nm and 500 nm, preferably between 5 nm and 300 nm.

The content of solid particles relative to the weight of the two-phase reaction mixture obtained at the end of step a) is between 0.1% by weight and 10% by weight, in particular between 1% by weight and 5% by weight, and preferably between 0.5% by weight and 2% by weight of solid particles relative to the weight of said two-phase reaction mixture obtained at the end of step a). The ratio between the largest dimension of the droplets and the largest dimension of the solid particles is preferably at least 100. (The largest dimension is understood to be the diameter when the solid particles are approximately spherical). They are located at the interface of the water/oil emulsion droplets.

The enzymatic catalyst

The enzymatic catalyst is chosen from among lipases of animal, microbial or plant origin.

Different types of lipases can be used according to the invention. Without this being exhaustive, we will cite the lipases produced by Humicola lanuginosa, Rhizopus delemar, Geotrichum candidum, Rhizomucor miehei (Mucor miehei), Pseudomonas glumae, Candida rugosa (C. cylindraceae), Candida antarctica, Chromobacterium viscosum, Rhizopus arrhizus, Yarrowia lipolytica, Pseudomonas, Hansenula, Bacillus, Aspergillus, wheat germ, horse or bovine pancreas.

Preferably, the enzymatic catalyst is Candida antarctica lipase B, Candida rugosa lipase, or Rhizomucor miehei lipase. Preferably, Candida antarctica lipase B.

Enzymes can be commercially available or manufactured using techniques known to those skilled in the art. They are presented either as a dilute solution or immobilized by grafting or adsorption onto solid particles to facilitate their recovery. Those skilled in the art will adjust the quantity of enzyme according to its nature, reactivity, and dilution ratio if the enzyme is in solution, or the percentage of immobilized enzyme if it is supported on solid particles.

According to one variant of the invention, the enzyme is immobilized on the solid particles, which makes it easy to recover the enzyme by filtration and reuse it (Yin, Chengmei, et al. "Pickering emulsion biocatalysis: Bridging interfacial design with enzymatic reactions." Biotechnology Advances (2024): 108338).

Enzyme immobilization can be achieved by any method known to those skilled in the art. Classically, enzyme immobilization can be physical (adsorption, trapping) or chemical (chemical grafting).

In the so-called physical method, there can be different types of interaction between the enzyme and the solid particle: hydrogen bonds, electrostatic forces, or hydrophobic interactions. The enzyme is immobilized simply by contact with the solid particle. Preferably, the solid particle is rich in hydrophobic groups to immobilize the enzyme. In the so-called chemical method, a chemical bond is formed between the enzyme and the solid particle. To achieve this, the surface of the solid particles can be modified by agents. Bifunctional agents allow a bridge to be formed between the enzyme and the solid particle by reacting on one side with the enzyme and on the other with the solid particle. These bifunctional agents can be any compound well-known to those skilled in the art, such as epichlorohydrin, glutaraldehyde, glyoxal, paraformaldehyde, carbodiimide, or ethylenediamine. Bifunctional agents can react with the chemical functional groups of the enzyme, such as an alcohol, thiol, or amine group. The most common method is to react with an amine group of the enzyme. In this case, it is common to also introduce an amine group onto the surface of the solid particle and to use glutaraldehyde, which will create a bridge between an amine group of the enzyme and an amine group of the solid particle.

According to a particular embodiment of the invention, the solid particles on which the enzyme is immobilized are amphiphilic solid particles, that is to say, comprising on their surface at least one hydrophilic function and at least one hydrophobic function.

Organic extraction solvent:

The organic extraction solvent constitutes at least one of the components of the oil phase of the emulsion. It allows the extraction of the ester produced by the esterification reaction.

The organic extraction solvent can be any liquid that is immiscible with the aqueous solution.

A person skilled in the art may preferentially choose an organic solvent with a high partition coefficient for the ester produced and which does not present toxicity to the enzyme.

In one or more particular embodiments of the invention, the organic solvent can be chosen from vegetable or animal oils, fatty acid esters of natural or non-natural origin, ethers, alkyl glycerol ethers, glycol ethers and hydrocarbons or mixtures of hydrocarbons, branched or unbranched, aromatic or non-aromatic, which may contain other compounds (for example in the case of petroleum cuts or any mixture of hydrocarbons from petroleum refining).

Without being exhaustive, the organic solvent may be chosen from at least one of the following compounds: hexane, heptane, octane, decane, dodecane, hexadecane, cyclohexane, methylcyclohexane, toluene, paraxylene, metaxylene, orthoxylene, ethylbenzene, limonene, cyclopentyl methyl ether, diphenyl ether, methyl soyate, methyl or ethyl esters of rapeseed oil, palm oil, jatropha oil, olive oil, sesame oil, peanut oil, corn oil, poppy seed oil, safflower oil, soybean oil, sunflower seed oil, used oils or animal fats.

In one or more particular embodiments of the invention, the organic solvent may be the same compound as the product of the esterification reaction according to the invention.

In one or more particular embodiments of the invention, the solvent is one of the reactants of the esterification reaction (either said alcohol or said carboxylic acid) if it is liquid under the conditions of implementation of the invention and is not miscible with the aqueous solution.

In one or more particular embodiments of the invention, the organic solvent has a higher boiling point than the ester formed in order to promote the separation of the ester from the organic extraction solvent by distillation.

In one or more particular embodiments of the invention, the organic solvent has a lower boiling point than the ester formed in order to promote the separation of the solvent by distillation and recovery of the ester in the distillation residue.

In one or more particular embodiments of the invention, the organic solvent is chosen to be used in a mixture with the ester formed according to the invention, thus not requiring any further separation step of the ester and the organic solvent.

The phases present at stage a)

At least the aqueous solution comprising the first reagent chosen from the alcohol or the carboxylic acid, the second reagent chosen from a carboxylic acid or an alcohol, the enzymatic catalyst, the organic extraction solvent, and solid particles are brought into contact.

When all these species are brought into contact, a two-phase mixture is formed, comprising at least a water phase and an oil phase. The different species distribute themselves between these two phases according to their affinity for one or the other phase.

The exact composition of the different phases depends on the properties of each species present in the mixture and evolves during the process. After all species have been brought into contact, the water phase comprises at least water and at least a fraction of the first reactant chosen from the aforementioned alcohol or carboxylic acid. Depending on the affinity of the first reactant initially in the aqueous solution for the oil phase, a portion may dissolve in the oil phase upon contact. The water phase comprises between 40% and 100% by mass of the first reactant, and the oil phase comprises between 0% and 60% by mass of the first reactant. It is understood that the mass fraction of the first reactant dissolved in the water phase and the mass fraction of the first reactant dissolved in the oil phase each represent 100% of the mass of the first reactant.

Preferably, the first reagent has a greater affinity for the water phase. The water phase comprises a mass fraction greater than or equal to 50% of the first reagent. The oil phase comprises a mass fraction less than 50% of the first reagent.

Depending on the affinity of the second reactant for the water phase, the water phase also comprises a mass fraction of said second reactant ranging from 0 to 100% relative to the total mass of the second reactant chosen from said carboxylic acid or said alcohol, and the oil phase comprises between 0 and 100% of the second reactant relative to its total mass. It is understood that the mass fraction of the second reactant dissolved in the water phase and the mass fraction of the second reactant dissolved in the oil phase each represent 100% of the total mass of the second reactant.

The oil phase includes at least the organic extraction solvent.

During the esterification reaction, the composition of the oil phase changes; in particular, the ester produced by the esterification reaction passes into the oil phase.

At the end of the esterification reaction (step a), the water phase has become depleted in first reactant and the oil phase has become enriched in ester.

The solid particles are at the interface between the two phases.

If the enzymatic catalyst is not immobilized on the solid particles, the water phase also contains the enzymatic catalyst.

The volume fraction of the water phase in the two-phase reaction mixture prepared in step a1) is between 10% by volume and 90% by volume, preferably between 40% by volume and 60% by volume of the water phase relative to the total volume of said reaction mixture. This volume fraction changes during the process.

The pH of the water phase depends on the nature of the enzymatic catalyst, the solid particles, and the nature of the reagents and extraction solvent. A person skilled in the art can adjust the pH. by acidifying or alkalizing the environment to ensure optimal enzyme function. Preferably the pH is less than 7 or greater than 8, preferably the pH is less than 7.

The process according to the invention can be implemented in several embodiments depending on the method of obtaining the reagents and their hydrophilic or hydrophobic nature.

According to a first embodiment of the invention, solid particles, an enzymatic catalyst, and an oil phase comprising an organic extraction solvent are brought into contact with a water phase comprising an alcohol (first reactant) in aqueous solution, to which a carboxylic acid (second reactant) is added, having a greater affinity for the water phase than for the oil phase. In this case, the mass fraction of the carboxylic acid in the water phase is greater than 50% relative to the total mass of carboxylic acid. The mass fraction of the carboxylic acid in the oil phase is less than 50% relative to the total mass of carboxylic acid.

According to a second embodiment of the invention, solid particles, an enzymatic catalyst and an oil phase comprising an organic extraction solvent are brought into the presence of a water phase, comprising a carboxylic acid (first reactant) in aqueous solution, and to which is added an alcohol (second reactant) having a greater affinity for the water phase than for the oil phase.

In this case, the mass fraction of alcohol in the water phase is greater than 50% relative to the total mass of alcohol. The mass fraction of alcohol in the oil phase is less than 50% relative to the total mass of alcohol.

According to a third embodiment of the invention, solid particles, an enzymatic catalyst, and an oil phase comprising an organic extraction solvent are brought into contact with a water phase comprising an alcohol (first reactant) in aqueous solution. A carboxylic acid (second reactant) having a greater affinity for the oil phase than for the water phase is added. In this case, the mass fraction of the carboxylic acid in the oil phase is greater than 50% relative to the total mass of carboxylic acid. The mass fraction of the carboxylic acid in the water phase is less than 50% relative to the total mass of carboxylic acid. In this embodiment of the invention, the carboxylic acid is preferably dissolved in the oil phase before the two phases are brought into contact.

According to a fourth embodiment of the invention, solid particles, an enzymatic catalyst, and an oil phase comprising an organic extraction solvent are placed in The reaction involves the presence of a water phase, comprising a carboxylic acid (first reactant) in aqueous solution. An alcohol (second reactant) with a greater affinity for the oil phase than for the water phase is added. In this case, the mass fraction of the alcohol in the oil phase is greater than 50% relative to the total mass of alcohol. The mass fraction of the alcohol in the water phase is less than 50% relative to the total mass of alcohol. In this embodiment of the invention, the alcohol is preferably dissolved in the oil phase before the two phases are brought into contact.

Step a2) formation of a Pickering emulsion.

The biphasic mixture obtained in step a1) is emulsified to form a reaction mixture in the form of a Pickering oil-in-water or water-in-oil emulsion; the reaction mixture comprising at least droplets stabilized by the solid particles in the water phase or the oil phase.

Emulsification transforms the biphasic mixture obtained in step a1) into droplets dispersed in the continuous phase, forming a Pickering emulsion. The largest droplet size is between 1 pm and 1000 pm, preferably between 1 pm and 140 pm, preferably between 2 pm and 100 pm, and particularly between 10 pm and 50 pm. Note that the droplet size is measured by optical microscopy (specifically using an Olympus BX51 with AnalySIS software for image analysis).

The emulsification of a two-phase medium is achieved using any type of system that provides energy to generate the emulsification known to those skilled in the art. While not exhaustive, examples include rotor-stator type tools, propeller agitators, static mixers, colloid mills, membrane systems, ultrasonic stirring, and microfluidic systems. The principle of these mixers is described, for example, in the Techniques de l’ingénieur (Engineering Techniques) publication J2153V1: Emulsification Processes - Equipment Techniques, by M. Poux and JP Canselier, June 10, 2004. A microfluidic system is described, for example, in the Techniques de l’ingénieur publication J8010V1: Microfluidics and Formulation - Emulsions and Complex Colloidal Systems, by V. Nardello-Rataj and JF Ontiveros, May 10, 2019.

In a particular embodiment of the invention, emulsification is carried out using a rotor-stator system of the type of the system marketed under the name Ultra-Turrax.

The direction of the emulsion depends on the nature of the particles, the solvent, the water phase, and the reactants (alcohol and carboxylic acid). In a particular embodiment of the invention, the Pickering emulsion is a water-in-oil emulsion. The droplets, which comprise the water phase including at least water and at least a fraction of the first reagent selected from said alcohol or said carboxylic acid, are stabilized by solid particles in the oil phase including at least the extraction solvent and the ester formed by the esterification reaction. The second reagent is partitioned between the oil and water phases according to its affinity for these phases. The enzymatic catalyst is either in the water phase or immobilized on the solid particles, depending on its nature.

In another particular embodiment of the invention, the Pickering emulsion is an oil-in-water emulsion. The droplets, which comprise the oil phase including at least the extraction solvent and the ester formed by the esterification reaction, are stabilized by solid particles in the water phase, which includes at least water and at least a fraction of the first reagent selected from said alcohol or said carboxylic acid. The second reagent is distributed between the oil and water phases according to its affinity for these phases. The enzymatic catalyst is either in the water phase or immobilized on the solid particles, depending on its nature.

Esterification reaction

The esterification reaction in step a) is carried out at a temperature between 10°C and 90°C to form said ester. Preferably, the temperature is between 20°C and 60°C, most preferably between 25°C and 50°C, and most preferably between 35°C and 45°C.

The pressure is between atmospheric pressure and 0.3 MPa absolute.

The esterification reaction is written as:

R1-OH+ R2-COOH R2-COO-R1 + H2O

The reaction is in equilibrium and releases water. The ester, being sparingly soluble in water, is extracted into the oil phase, while the water formed is extracted into the water phase. The removal of one of the reaction products, by transfer from one phase to another, shifts the reaction towards the formation of ester.

At the end of step a) of esterification, the water phase has become depleted in first reactant and the oil phase has become enriched in ester.

A person skilled in the art will be able to use different implementations of this reaction. The reaction can be carried out with or without agitation. In a particular embodiment of the invention the reaction is conducted in a closed system (or batch).

In another particular embodiment of the invention, the reaction is conducted in an open (or continuous) system with continuous withdrawal of a fraction of the oil phase from the water-in-oil Pickering emulsion. The withdrawal of a fraction of the oil phase is sent to an ester separation step from the oil phase (step b2), and then the withdrawal of the ester-depleted oil phase is returned to step a).

In another particular embodiment of the invention, the reaction is carried out in an open (or continuous) system with additions of aqueous solution containing the first reagent chosen from said alcohol or said carboxylic acid, to the Pickering oil-in-water emulsion. According to this embodiment of the invention, a portion of the water phase can be withdrawn to control the ratio between the water and oil phases. According to this embodiment of the invention, an enzymatic catalyst can be added. This embodiment of the invention can be implemented in combination with the process for producing said first reagent chosen from said alcohol or said carboxylic acid in the aqueous solution (step a'), with or without withdrawal and reinjection of the water phase depleted of the first reagent in the production step a') of said first reagent. This embodiment of the invention is particularly suited to the use of an enzymatic catalyst immobilized on the solid particles.

In one or more particular embodiments of the invention, additions of a second reagent chosen from said alcohol or said carboxylic acid can be made, continuously or not, preferably via the continuous phase.

The reaction time in closed mode or the liquid flow rate in open mode depends on the operating conditions and the reactivity of the enzymatic catalyst. It will be adjusted by a person skilled in the art to obtain the desired ester yield within a desired timeframe.

In one or more particular embodiments of the invention, the optional step a’) of producing said first reagent chosen from said alcohol or said carboxylic acid, may be carried out in combination with step a).

This implementation has the advantage of promoting the production of said alcohol or carboxylic acid by extracting it as it is produced. This is particularly true when said alcohol or carboxylic acid is produced by fermentation or by an equilibrium reaction such as the hydrolysis of an ester, for example, the esters contained in vegetable and animal oils. Indeed, it is known to those skilled in the art that fermentation slows down as the content of the products increases. Fermentation in the medium occurs in the case of alcohol production (Lim, J. et al., Mathematical Modeling of Acetone-Butanol-Ethanol Fermentation with Simultaneous Utilization of Glucose and Xylose by Recombinant Clostridium acetobutylicum, Energy Fuels, 2019, 33, 8620-8631) and in the case of carboxylic acid production (Joglekar, HG et al., Comparative assessment of downstream processing options for lactic acid, Separation and Purification Technology, 2006, 52(1), 1-17). Therefore, their extraction as they are produced prevents the fermentation from being slowed down. Similarly, it is known to those skilled in the art that extracting a product from an equilibrium reaction, such as the hydrolysis of an ester, shifts the equilibrium towards the formation of that product. The combination of step a') with steps a) and b) can be carried out in various ways such as those described in US patents 2014/0178529 A1, US 9517985 B2, US 2010/0143993 A1, and US 8614077 B2 as well as by Woodley JM et al. Future directions for in-situ product removal (ISPR), J Chem Technol Biotechnol., 2008, 83,121-123.

Step b) Recovery of the ester formed in the oil phase

The recovery of the ester formed in the oil phase is advantageously carried out in two stages:

-Step b1) Separation of said oil phase from said water phase;

-Step b2) Separation of the ester in said oil phase;

Step b1) Separation of said oil phase from said water phase;

The two phases, oil and water, are separated. To achieve this, the Pickering emulsion is broken to separate the two liquid phases. The Pickering emulsion can be broken using various mechanical or physicochemical methods. The principles used to destabilize these systems are very well described in the journal article by C. P. Whitby and E. J. Wanless (2016), "Controlling Pickering Emulsion Destabilization: A Route to Fabricating New Materials by Phase Inversion," Materials, 9, 626; doi:10.3390/ma9080626. It is possible to break the emulsion by applying an external force that causes the interfacial film to rupture and the droplets to coalesce, such as a shear, compression, or centrifugal force. Another method involves adding a chemical that, through transfer from the continuous phase to the dispersed phase, destabilizes the interfacial film formed by the particles and causes the droplets to coalesce, thus breaking the emulsion. In the specific case of magnetic particles, a magnetic field can be used to destabilize the emulsion. It is also possible to break the emulsion by modifying the wettability of the particles. Detaching them from the interface and carrying them into the continuous or dispersed phase can be achieved by adding a surfactant, which will adsorb onto the particles and change their wettability, or by modifying the pH in the case of pH-sensitive particles (such as proteins), or by modifying the temperature in the case of heat-sensitive particles. It is also possible to combine all the different mechanisms described above (addition of a surfactant and shearing, modification of pH and centrifugation, these two examples being non-limiting).

In a particular embodiment of the invention, solid particles are removed from the reaction mixture using any solid/liquid separation technique such as filtration, centrifugation, or a combination of separation methods.

Once the emulsion has broken, the two phases can be recovered separately, for example in a decanter.

According to one embodiment of the invention, the oil phase is washed with salt water to extract any compounds other than the ester, thereby facilitating the separation of the ester from the oil phase and its constituents. The nature and salt concentration of the salt water will be adjusted by those skilled in the art to optimize the efficiency and selectivity of this washing. For example, saturated alkali or alkaline earth metal chlorides may be chosen.

According to one embodiment of the invention, any compounds in the oil phase other than the ester are adsorbed onto a solid by contacting the oil phase with that solid. Those skilled in the art will choose the adsorbent solid based on the nature of the compounds to be extracted.

According to one variant of the invention, the water phase is returned to step a).

According to one variant of the invention, the water phase is returned to step a’).

Step b2) Separation of the ester in said oil phase;

The ester is then separated from the oil phase recovered in step b1) to recover the ester and an oil phase depleted in ester. This depleted oil phase includes at least the organic solvent.

Any method known to a person skilled in the art can then be used to separate the ester dissolved in the oil phase. The ester can be separated by liquid-liquid extraction, precipitation, membrane separation, or distillation. Preferably, the ester is separated by distillation. According to one embodiment of the invention, the organic solvent has a higher boiling point than the ester formed in order to promote the separation of the ester from the organic extraction solvent by distillation.

According to one variant of the invention, the organic solvent has a lower boiling point than the ester formed in order to promote the separation of the solvent by distillation and recovery of the ester in the distillation residue.

According to one embodiment of the invention, the organic solvent is chosen to be used in mixture with the ester formed according to the invention, thus requiring no further separation step of the ester and the organic solvent.

According to one embodiment of the invention, the organic solvent is the same molecule as the ester formed according to the invention, thus requiring no further separation step of the ester and the organic solvent.

According to one embodiment of the invention, the ester-depleted oil phase is returned to step a).

Examples:

Examples 1 to 11 describe the esterification reaction between two reactants (alcohol and carboxylic acid) present in the water phase under different conditions. Examples 12 to 15 describe the esterification reaction between two reactants, one present in the water phase (alcohol) and the other in the oil phase (carboxylic acid). In all examples, the amount of ester formed is determined by analyzing a sample of the supernatant oil phase by gas chromatography on an Agilent 7890 instrument equipped with a 1ms H₂P column and using hexadecane as an internal standard. The conversion rate of 1-butanol after one hour and six hours is given in Table 1. It is calculated by dividing the amount of ester formed by the initial amount of 1-butanol.

Example 1 (not in accordance with the invention): biphasic mixture without biocatalyst (no Pickering emulsion)

600 mL of water containing 0.1 mol/L of 1-butanol and 0.1 mol/L of butyric acid, and 600 mL of n-dodecane, are stirred at 40°C at 500 rpm for 6 hours using a magnetic stir bar. The initial pH of the water phase is 2.7. The 1-butanol reacts with the butyric acid to form an ester, butyl butyrate, which is extracted in the oil phase containing n-dodecane.

Example 2 (not in accordance with the invention): biphasic mixture with biocatalyst (no Pickering emulsion) The protocol is the same as in example 1 with the addition of 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution reference L3170-50ML supplied by Sigma-Aldrich.

Example 3 (not in accordance with the invention): biphasic mixture with biocatalyst and with adjustment of the initial pH to 4 (no Pickering emulsion)

The protocol is the same as in example 2 with adjustment of the initial pH of the water phase to 4 by adding potassium.

Example 4 (not in accordance with the invention): biphasic mixture with biocatalyst and with adjustment of the initial pH to 4.5 (no Pickering emulsion)

The protocol is the same as in example 2 with adjustment of the initial pH of the water phase to 4.5 by adding potassium.

Example 5 (not in accordance with the invention): Pickering water-in-oil emulsion without biocatalyst

10.5 g of Aerosil® R972 supplied by Evonik, 600 mL of water containing 0.1 mol/L 1-butanol and 0.1 mol/L butyric acid, and 600 mL of n-dodecane are emulsified using an Ultra-Turrax for 10 minutes at 13,500 rpm to form a Pickering emulsion. The droplet size is between 10 and 50 µm. The Pickering emulsion is heated to 40°C and stirred at 500 rpm for 6 hours using a magnetic stir bar. The initial pH of the water phase is 2.7. The 1-butanol reacts with the butyric acid to form an ester, butyl butyrate, which is extracted into the oil phase containing n-dodecane.

Example 6 (according to the invention): Pickering water-in-oil emulsion with biocatalyst

10.5 g of Aerosil® R972 supplied by Evonik, 600 mL of water containing 0.1 mol/L 1-butanol and 0.1 mol/L butyric acid, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50ML, supplied by Sigma-Aldrich, and 600 mL of n-dodecane are emulsified using an Ultra-Turrax for 10 minutes at 13,500 rpm to form the Pickering emulsion. The droplet size is between 10 and 50 µm. The initial pH of the water phase is 2.7. The 1-butanol reacts with the butyric acid to form an ester, butyl butyrate, which is extracted into the oil phase containing n-dodecane.

Example 7 (according to the invention): Pickering water-in-oil emulsion with biocatalyst and with initial pH adjustment to 4

The protocol is the same as in example 6 with adjustment of the initial pH of the water phase to 4 by adding potassium. Example 8 (according to the invention): Pickering water-in-oil emulsion with biocatalyst and with initial pH adjustment to 4.5

The protocol is the same as in example 6 with adjustment of the initial pH of the water phase to 4.5 by adding potassium.

Example 9 (according to the invention): Pickering oil-in-water emulsion with biocatalyst and with initial pH adjustment to 4.5

10.5 g of Aerosil® R816 supplied by Evonik, 600 mL of water containing 0.1 mol/L 1-butanol and 0.1 mol/L butyric acid, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50ML, supplied by Sigma-Aldrich, and 600 mL of n-dodecane are emulsified using an Ultra-Turrax for 10 minutes at 13,500 rpm to form the Pickering emulsion. The droplet size is between 10 and 40 µm. The initial pH of the water phase is adjusted to 4.5 by adding potassium hydroxide. The 1-butanol reacts with the butyric acid to form an ester, butyl butyrate, which is extracted into the oil phase containing n-dodecane. To collect the oil phase and determine the amount of ester formed, the oil phase and the water phase are separated by centrifugation at 5000 revolutions per minute for 30 minutes.

Example 10 (not in accordance with the invention): biphasic mixture with biocatalyst, excess butyric acid and with adjustment of the initial pH to 4 (no Pickering emulsion)

The protocol is the same as in example 3, introducing 0.3 mol/L of butyric acid into the water phase instead of 0.1 mol/L.

Example 11 (according to the invention): Pickering water-in-oil emulsion with biocatalyst, excess butyric acid and with initial pH adjustment to 4

The protocol is the same as in example 7, introducing 0.3 mol/L of butyric acid into the water phase instead of 0.1 mol/L.

Example 12 (not in accordance with the invention): biphasic mixture containing hexanoic acid with biocatalyst (not Pickering emulsion)

600 mL of water containing 0.1 mol/L 1-butanol, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50ML, supplied by Sigma-Aldrich, and 600 mL of n-dodecane containing 0.1 mol/L hexanoic acid are stirred at 40°C at 500 rpm for 6 hours using a magnetic stir bar. The initial pH of the water phase is 6. The 1-butanol reacts with the hexanoic acid to form an ester, butyl hexanoate, which is extracted in the oil phase containing n-dodecane. Example 13 (according to the invention): Pickering water-in-oil emulsion containing hexanoic acid with biocatalyst

10.5 g of Aerosil® R972 supplied by Evonik, 600 mL of water containing 0.1 mol/L 1-butanol, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50 mL, supplied by Sigma-Aldrich, and 600 mL of n-dodecane containing 0.1 mol/L hexanoic acid are emulsified using an Ultra-Turrax for 10 minutes at 13,500 rpm to form the Pickering emulsion. The droplet size is between 10 and 50 µm. The initial pH of the water phase is 6. The 1-butanol reacts with the hexanoic acid to form an ester, butyl hexanoate, which is extracted into the oil phase containing n-dodecane.

Example 14 (not in accordance with the invention): biphasic mixture containing palmitic acid with biocatalyst (not Pickering emulsion)

600 mL of water containing 0.1 mol/L of 1-butanol, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50ML, supplied by Sigma-Aldrich, and 600 mL of n-dodecane containing 0.1 mol/L of palmitic acid are stirred at 40°C at 500 rpm for 6 hours using a magnetic stir bar. The initial pH of the water phase is 6. The 1-butanol reacts with the palmitic acid to form an ester, butyl palmitate, which is extracted in the oil phase containing n-dodecane.

Example 15 (according to the invention): Pickering water-in-oil emulsion containing palmitic acid with biocatalyst

10.5 g of Aerosil® R972 supplied by Evonik, 600 mL of water containing 0.1 mol/L 1-butanol, 1.8 mL of the commercial Lipase B Candida antarctica (CaLB) solution, reference L3170-50 mL, supplied by Sigma-Aldrich, and 600 mL of n-dodecane containing 0.1 mol/L palmitic acid are emulsified using an Ultra-Turrax for 10 minutes at 13,500 rpm, followed by Pickering emulsification. The droplet size is between 10 and 50 µm. The initial pH of the water phase is 6. The 1-butanol reacts with the palmitic acid to form an ester, butyl palmitate, which is extracted in the oil phase containing n-dodecane. Table 1

Examples 1 to 11 describe the esterification reaction between two reactants present in the water phase under different conditions. Example 1 shows first that without the biocatalyst, there is no reaction between the alcohol and the carboxylic acid under the conditions of the study, even in the case of the Pickering emulsion (comparative example 5). Comparative examples 2, 3, and 4 show that in the presence of a biocatalyst in a stirred two-phase medium without a Pickering emulsion, the conversions of the alcohol and the carboxylic acid to ester are low after one hour of reaction. Conversely, examples 6, 7, and 8 according to the invention show ester conversion rates in water-in-oil Pickering emulsion after one hour that are much higher than those obtained in the two-phase medium (there is a gain of approximately a factor of 4) and are still higher after 6 hours. Examples 1 through 8 clearly demonstrate that the combination of a biocatalyst and a Pickering emulsion enables the fastest conversion kinetics of alcohol and carboxylic acid to ester for a given pH. These examples also show that performance increases as the pH becomes increasingly acidic within the studied range. Example 9 according to the invention confirms that the advantage of the invention is maintained in the case of an oil-in-water Pickering emulsion. Example 11 according to the invention shows that an excess of carboxylic acid relative to alcohol increases the conversion to ester and the kinetics, which are significantly higher than in comparative example 10 in a stirred two-phase medium without a Pickering emulsion.

Examples 13 and 15 according to the invention and comparative examples 12 and 14 employ carboxylic acids, which are introduced into the oil phase due to their significantly greater solubility in the oil phase than in the water phase. It is clear once again that the implementation according to the invention allows for a considerable gain in the conversion to ester, as evidenced by the values obtained after 1 hour of reaction. This confirms that the invention works equally well whether both reactants are in the water phase or whether one reactant is in the water phase and the other in the oil phase.

The examples also show that ester conversions can be excellent at pH levels below 7.

Claims

DEMANDS 1. A process for manufacturing an ester from a first reagent selected from an alcohol or a carboxylic acid in aqueous solution, comprising the following steps: a) an esterification reaction is carried out on a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion to form an ester in the oil phase, said reaction mixture being obtained by the following steps: a1) a two-phase mixture comprising at least a water phase and an oil phase is formed by contacting an aqueous solution comprising said first reagent with at least one second reagent selected from a carboxylic acid or an alcohol, at least one enzymatic catalyst, at least one organic extraction solvent, and solid particles; a2) said two-phase mixture obtained in step a1 is emulsified to form a reaction mixture in the form of an oil-in-water or water-in-oil Pickering emulsion; said reaction mixture comprising: -either droplets of said oil phase stabilized by said solid particles in said water phase; -either droplets of said water phase stabilized by said solid particles in said oil phase; b) the ester formed in step a) is recovered in the oil phase. 2. A process according to claim 1, wherein the first reactant contained in said aqueous solution is an alcohol, and the second reactant is a carboxylic acid. 3. A process according to claim 1, wherein the first reactant contained in said aqueous solution is a carboxylic acid and the second reactant is an alcohol. 4. A process according to any one of the preceding claims, wherein the concentration of first reactant in said aqueous solution is between 0.001 mol/L and 0.4 mol/L when said first reactant is an alcohol, and between 0.001 mol/L and 2 mol/L when said first reactant is a carboxylic acid. 5. A method according to any one of the preceding claims, wherein the molar ratio between said second reactant and said first reactant is between 1 and 10. 6. A process according to any one of the preceding claims, wherein said first reagent selected from said alcohol or said carboxylic acid is of bio-based origin. 7. A method according to any one of the preceding claims, wherein the enzymatic catalyst added in step a1) is selected from lipases of microbial or plant origin. 8. A method according to any one of the preceding claims, wherein the enzymatic catalyst added in step a1) is selected from lipase B of Candida antarctica, lipase of Candida rugosa, or lipase of Rhizomucor miehei. 9. A process according to any one of the preceding claims, wherein the pH of the water phase is less than 7. 10. A method according to any one of the preceding claims, wherein the solid particles added in step a1) are selected from particles of silica, clay, or natural or synthetic polymers. 11. A method according to any one of the preceding claims, wherein the droplet size of the Pickering emulsion obtained at the end of step a) is between 1 pm and 140 pm. 12. A process according to any one of the preceding claims, wherein the temperature of the esterification reaction in step a) is between 10°C and 90°C. 13. A process according to any one of the preceding claims, wherein the mass concentration of solid particles added in step a1) is between 0.1% weight and 10% weight relative to the total weight of said two-phase mixture. 14. A process according to claim 1, wherein the reaction mixture obtained at the end of step a) is a Pickering water-in-oil emulsion. 15. A process according to any one of the preceding claims, wherein a step a') of producing said first reagent selected from said alcohol or said carboxylic acid in aqueous solution is carried out in combination with step a).