Process for producing an aqueous solution of 5-hydroxymethylfurfural comprising a liquid-liquid extraction step incorporated into or prior to filtration

Abstract

The method for producing an aqueous solution of hydroxymethylfurfural (5-HMF) comprises step a) of contacting a feedstock (1) containing 5-HMF and a polar aprotic synthetic solvent with an aqueous stream (21), step b) of liquid-liquid extraction with an organic extract (6), followed by step c) of backwashing with an aqueous solvent (7) to obtain an organic raffinate enriched in an aqueous solution of 5-HMF (12) and the organic solvent. The optionally concentrated organic raffinate (10) is then subjected to step e) of hydrodistillation to obtain an aqueous solution of 5-HMF. Step f) of liquid-solid separation of the aqueous raffinate (5) obtained in step b) and / or the solid particle fraction formed by precipitated humins in the intermediate stream (19) obtained in step b) is then carried out. The aqueous raffinate obtained in step b), from which precipitated humins have been removed, is then treated in step g) with a water-polar aprotic synthetic solvent mixture.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aqueous solution of 5-hydroxymethylfurfural (5-HMF). [Background technology]

[0002] 5-HMF is a biomass-derived compound of interest that can be beneficially utilized in many fields, particularly in pharmaceuticals, agrochemicals, and specialty chemicals. The production of 5-HMF by dehydration of sugars has been known for many years and has been the subject of numerous research studies.

[0003] There are many dehydration conditions, and the following methods can be mentioned as examples.

[0004] 5-HMF can be obtained in aqueous media, generally in the presence of an acid catalyst, which allows the dehydration of C6 sugars (especially fructose) to give 5-HMF, but also catalyzes the rehydration of 5-HMF to give formic acid and levulinic acid, which is very detrimental to the yield.

[0005] 5-HMF can also be obtained in non-aqueous polar protic media using solvents such as methanol, ethanol, or acetic acid in the presence of an acid catalyst. Under these conditions, 5-HMF is obtained as a mixture with its ether or ester derivatives, depending on the reaction medium used. The formation of these by-products results from the reaction of 5-HMF with the reaction solvent in an acidic medium.

[0006] WO 2007 / 104514 describes the synthesis of 5-HMF by dehydration of sugars using methanol or ethanol as a solvent in the presence of an acid catalyst, which also catalyzes the etherification reaction of 5-HMF with alcohol, giving a mixture of 5-HMF and its methyl or ethyl ether forms, depending on the alcohol used as the solvent.

[0007] 5-HMF can also be produced in polar aprotic media, with or without an acid catalyst. More specifically, the use of dimethyl sulfoxide (DMSO) can be mentioned, which allows the production of 5-HMF in very good yields, with or without an acid catalyst, without the undesired reactions listed above.

[0008] Furthermore, whatever the synthesis medium (water, methanol, DMSO, etc.), polymeric by-products called humins are formed during the production of 5-HMF (van Dam, HE; ​​Kieboom, APG; van Bekkum, H. (1986), The Conversion of Fructose and Glucose in Acidic Media Formation of Hydroxymethylfurfural, In Starch-Starke, Vol. 38, No. 3, pages 95-101).

[0009] The synthesis of 5-HMF in a medium such as DMSO is particularly advantageous because it allows obtaining 5-HMF in its alcohol form (rather than in its ether form) in very good yield. Nevertheless, the physicochemical properties of DMSO (or any other polar aprotic solvent) make it very difficult to separate from 5-HMF by conventional methods known to those skilled in the art.

[0010] One known method for isolating 5-HMF from DMSO is liquid-liquid extraction followed by crystallization of the extract, as described in French Patent No. 2669635. The applicant has already proposed an improvement to the process described in French Patent No. 2669635, which was the subject of French Patent No. 3071172. This improvement is based on modifying the liquid-liquid extraction step, in particular by adding a backwashing step with water and by recycling the backwash water upstream of the liquid-liquid extraction and mixing it with the 5-HMF / DMSO feedstock, the mixture optionally being filtered prior to the liquid-liquid extraction. This improvement makes it possible to increase the purity of 5-HMF without compromising the yield of the desired product and allows the 5-HMF crystallization step to be carried out under more favorable conditions.

[0011] Nevertheless, despite the improvements provided by French Patent No. 3071172, the crystallization of 5-HMF remains an expensive operation. The high production costs of 5-HMF limit its use, and the development of processes that allow for cost reduction is needed.

[0012] In this regard, French patent application No. 2114335 filed by the applicant discloses a method for recovering 5-HMF in aqueous solution rather than in crystallized form, in particular by concentrating the organic raffinate obtained in the backwashing step of the 5-HMF-containing extract resulting from liquid-liquid extraction, and by hydrodistilling the concentrate resulting from the concentrating step, in order to recover 5-HMF in the form of an aqueous solution of 5-HMF. The disclosed method advantageously includes a filtration step upstream of the liquid-liquid extraction to remove humins (solid particles) precipitated during the addition of water to the feedstock (mixing the feedstock with the backwash water), which is then sent to the liquid-liquid extraction. This is because adding water to the 5-HMF feedstock sent to the liquid-liquid extraction can cause precipitation of humins present in the feedstock, which can lead to operational problems during the liquid-liquid extraction, such as clogging of equipment. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2007 / 104514 [Patent Document 2] French Patent No. 2669635 [Patent Document 3] French Patent No. 3071172 [Patent Document 4] French Patent No. 2114335 Summary of the Invention [Problem to be solved by the invention]

[0014] The Applicant has demonstrated an alternative method that makes it possible to recover 5-HMF in aqueous solution rather than in crystalline form, which, in relation to the method according to French patent application filed under number 2114335, opens new possibilities for the utilization of 5-HMF in various applications or for subsequent transformations that could not be carried out either in DMSO or in the extracting solvent.

[0015] Furthermore, the method according to the invention allows for the recovery of 5-HMF in aqueous solution, while simultaneously limiting operational costs, wastewater, and therefore the environmental impact of the process. The method according to the invention also allows for improved removal of precipitated humins, particularly to protect equipment used during liquid-liquid extraction or downstream processes. This is because the problem of humin precipitation also occurs during the liquid-liquid extraction process and can adversely affect the liquid-liquid extraction operation as well as downstream operations that receive streams that may contain these precipitated humins, typically the treatment of water-DMSO mixtures resulting from the process. [Means for solving the problem]

[0016] One subject of the present invention relates to a method for producing an aqueous solution of 5-HMF.

[0017] More specifically, the present invention relates to a method for producing an aqueous solution of 5-hydroxymethylfurfural (5-HMF), the method comprising: a) contacting a feedstock comprising 5-HMF and a polar aprotic synthesis solvent with an aqueous stream to obtain at least one aqueous mixture; - step b) of liquid-liquid extraction of the aqueous mixture obtained at the end of step a) in the presence of an extraction solvent to produce an aqueous raffinate comprising the polar aprotic synthesis solvent, the organic extract, a solid particle fraction and optionally an intermediate liquid stream, wherein the aqueous raffinate and / or the intermediate liquid stream comprises the solid particle fraction, and then - step c) backwashing the organic extract with an aqueous solvent to produce an intermediate aqueous back extract and an organic raffinate comprising 5-HMF and an organic solvent; - an optional step d) of concentrating the organic raffinate resulting from step c) by removing at least a portion of the organic solvent to produce a concentrated organic raffinate comprising 5-HMF and residual organic solvent, producing a first stream comprising organic solvent; - a hydrodistillation step e) carried out by distilling the organic raffinate resulting from step c) or the concentrated organic raffinate resulting from step d) in the presence of water to produce an aqueous solution of 5-HMF and a second stream comprising an organic solvent; - step f) performing a liquid-solid separation of the solid fraction in the aqueous raffinate resulting from step b) and / or the intermediate liquid stream resulting from step b) to produce a solid particle stream and a solid particle-depleted aqueous raffinate and / or a particle-depleted intermediate liquid stream that is sent to step b); - step g) of treating at least one water-polar aprotic synthesis solvent mixture produced in the process, the mixture consisting of a particle-depleted aqueous raffinate resulting from step f) or consisting of an aqueous raffinate resulting from step b) without a solid particle fraction, to produce at least one aqueous effluent that can be recycled to the process.

[0018] According to one or more embodiments, step b) produces an intermediate liquid stream comprising a solid particle fraction, which is fed to step f) for separating the solid particle fraction from the intermediate liquid stream, a particle-depleted intermediate liquid stream is formed and fed to step b), and the at least water-polar aprotic synthesis solvent mixture consisting of an aqueous raffinate resulting from step b) without the solid particle fraction is fed to step g).

[0019] According to one or more embodiments, the intermediate liquid stream sent to step f) is an intermediate aqueous raffinate comprising a solid particle fraction, which is produced in liquid-liquid extraction step b) by separation of the extraction solvent and the water-polar aprotic synthesis solvent mixture.

[0020] According to one or more embodiments, the intermediate liquid stream sent to step f) is a three-phase mixture comprising a first liquid phase comprising 5-HMF and the extraction solvent, a second liquid phase comprising water and the polar aprotic synthesis solvent, and a solid phase comprising the solid particle fraction.

[0021] According to one or more embodiments, the aqueous raffinate produced in step b) comprises a solid particle fraction, and this aqueous raffinate is sent to step f) for separation of the solid particle fraction from the aqueous raffinate, forming a solid particle-depleted aqueous raffinate which is sent to step g) as a water-polar aprotic synthesis solvent mixture.

[0022] According to one or more embodiments, step f) is carried out at a temperature between 0 and 60° C. and preferably involves filtration, preferably carried out by a filter press.

[0023] According to one or more embodiments, step d) of concentrating the organic raffinate resulting from step c) comprises vaporizing the organic solvent under atmospheric pressure or under vacuum, preferably at a pressure of 0.01-0.1 MPa, and at a liquid temperature maintained at or below 130°C, such that the concentrated organic raffinate contains a 5-HMF content of at least 40% by weight and a residual organic solvent content of at most 60% by weight.

[0024] According to one or more embodiments, step e) is carried out at atmospheric pressure or under vacuum, preferably at a pressure of 0.001 to 0.1 MPa, preferably under vacuum at a pressure of 0.005 to 0.08 MPa.

[0025] According to one or more embodiments, step e) is carried out in a distillation column, preferably at a bottom temperature of 140° C. or less.

[0026] According to one or more embodiments, the extraction solvent is selected from dichloromethane, diethyl ether, diisopropyl ether, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, thiophene, anisole and toluene, preferably methyl isobutyl ketone.

[0027] According to one or more embodiments, the weight ratio (wt / wt) of aqueous solvent to organic extract in backwashing step c) is 0.04-5, preferably 0.07-3, preferably 0.1-1.

[0028] According to one or more embodiments, the method preferably comprises a step of dehydrating sugars to 5-HMF upstream of step a) by contacting a sugar feedstock comprising one or more sugars with a polar aprotic synthesis solvent and a dehydrating acid catalyst, preferably at a temperature of 30-200°C, preferably 50-180°C, preferably 70-150°C, preferably 90-130°C, and at a pressure of 0.001-10 MPa, preferably 0.001-5 MPa, preferably 0.01-1 MPa.

[0029] According to one or more embodiments, the aqueous effluent produced in step g) is used in whole or in part in step a) and / or step c) and / or step e).

[0030] According to one or more embodiments, in step a), the aqueous stream comprises all or part of the intermediate aqueous back-extract resulting from step c).

[0031] According to one or more embodiments, the polar aprotic synthesis solvent is selected from pyridine, butan-2-one, acetone, acetic anhydride, N,N,N',N'-tetramethylurea, benzonitrile, acetonitrile, methyl ethyl ketone, propionitrile, hexamethylphosphoramide, nitrobenzene, nitromethane, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate and γ-valerolactone, used alone or in mixtures, preferably dimethyl sulfoxide.

[0032] According to one or more embodiments, the concentrated organic raffinate obtained at the end of concentration step d) has a 5-HMF content of 40 to 95 wt. % and a residual organic solvent content of 5 to 60 wt. %, expressed relative to the weight of the concentrated organic raffinate.

[0033] According to one or more embodiments, the aqueous stream is fed to a hydrodistillation step e).

[0034] According to one or more embodiments, step g) comprises treating one or more other water-polar aprotic synthesis solvent mixtures produced in the process.

[0035] Other objects and advantages of the present invention will become apparent on reading the following description of particular exemplary embodiments of the invention, given by way of non-limiting example, the description being made with reference to the accompanying drawings, which are described below. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows an embodiment of the process according to the invention, in which the liquid-solid separation step f) is carried out during liquid-liquid extraction on the intermediate liquid stream removed in the liquid-liquid extraction step b). [Figure 2] FIG. 2 shows another embodiment of the process according to the invention, in which a liquid-solid separation step f) is carried out downstream of the liquid-liquid extraction step b) on the aqueous raffinate obtained at the end of the liquid-liquid extraction step b). [Figure 3]Figure 3 shows another embodiment of the process according to the invention, which, with respect to the embodiment shown in Figure 1, comprises a liquid-solid separation step f) carried out downstream of the liquid-liquid extraction step b), and also comprises an additional liquid-solid separation step in the mixing step a) and various recycles of the aqueous stream to the process. DETAILED DESCRIPTION OF THE INVENTION

[0037] In the drawings, the same reference numbers represent the same or similar elements.

[0038] In the following detailed description, numerous specific details are disclosed to provide a deeper understanding of the method. However, it will be apparent to those skilled in the art that the method may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0039] It is noted that throughout this specification, the phrase "between" is to be understood as including the stated boundaries, unless otherwise specified.

[0040] As used herein, the term "to comprise" is synonymous with (meaning the same as) "to include" and "to contain" and is inclusive or open-ended and does not exclude other elements not recited. The term "to comprise" is understood to include the exclusive and closed term "to consist of."

[0041] For the purposes of the present invention, the various embodiments presented can be used separately or in combination with one another, without any restriction to their combination, where this is technically feasible.

[0042] For purposes of the present invention, various ranges of parameters of a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for purposes of the present invention, a preferred range of pressure values ​​may be combined with a more preferred range of temperature values.

[0043] In the present specification, an aprotic solvent is understood to mean a molecule which acts as a solvent and in which all its hydrogen atoms are carried by carbon atoms.

[0044] In the present specification, polar solvent is understood to mean a molecule that acts as a solvent, the dipole moment μ, expressed in Debye units, having a value greater than or equal to 2.00 measured at 25°C.

[0045] Thus, in the present specification, a polar aprotic solvent is understood to mean a molecule acting as a solvent, all of whose hydrogen atoms are carried by carbon atoms, and whose dipole moment μ, expressed in Debye units, has a value greater than or equal to 2.00 measured at 25°C.

[0046] To better understand the present invention, reference will be made below to numerical references appearing in the figures to indicate the various elements of the method, but this does not constitute a limitation to the specific embodiment shown in Figures 1, 2 and 3.

[0047] Optional step of dehydrating sugars to 5-HMF Advantageously, the feedstock 1 comprising 5-HMF and a polar aprotic synthesis solvent introduced in step a) according to the invention can be obtained during a step of dehydrating sugars to 5-HMF, which is very advantageously located upstream of step a) according to the invention, by contacting a sugar feedstock comprising one or more sugars with a polar aprotic synthesis solvent and a dehydration acid catalyst to produce an effluent containing at least 5-HMF and a polar aprotic synthesis solvent, also referred to herein as synthesis effluent, which advantageously corresponds to the feedstock 1 of the process according to the invention introduced in mixing step a).

[0048] Therefore, the process according to the invention may optionally comprise a step upstream of step a) of dehydrating sugars to 5-HMF.

[0049] The polar aprotic synthesis solvents are advantageously chosen from all polar aprotic solvents whose dipole moment, expressed in Debye (D), is greater than or equal to 2.00.Preferably, the polar aprotic synthesis solvents are pyridine (2.37), butan-2-one (5.22), acetone (2.86), acetic anhydride (2.82), N,N,N',N'-tetramethylurea (3.48), benzonitrile (4.05), acetonitrile (3.45), methyl ethyl ketone (2.76), propionitrile (3.57), hexamethylphosphoramide (5.55), nitrobenzene. (4.02), nitromethane (3.57), N,N-dimethylformamide (3.87), N,N-dimethylacetamide (3.72), sulfolane (4.80), N-methylpyrrolidone (4.09) (denoted as NMP), dimethyl sulfoxide (3.90) (denoted as DMSO), propylene carbonate (4.94), and γ-valerolactone (4.71), either alone or in mixtures.

[0050] Preferably, the polar aprotic solvent is advantageously chosen from acetone, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, NMP, DMSO, propylene carbonate and γ-valerolactone, alone or in mixture.

[0051] Preferably, the polar aprotic solvent is advantageously chosen from N,N-dimethylacetamide, NMP, DMSO and γ-valerolactone, either alone or as a mixture.

[0052] Highly preferably, the polar aprotic solvent is DMSO.

[0053] The term "dehydration acid catalyst" is understood to mean any Brønsted acid catalyst selected from organic or inorganic homogeneous or heterogeneous Brønsted acids capable of inducing the dehydration of sugars to 5-HMF.

[0054] Preferably, the dehydration acid catalyst is a Bronsted acid having a pKa of 0 to 5.0, preferably 0.5 to 4.0, preferably 1.0 to 3.0 in a polar aprotic synthesis solvent, preferably DMSO, as defined in the paper by F.G. Bordwell et al. (J. Am. Chem. Soc., 1991, 113, 8398-8401).

[0055] Preferably, the dehydration acid catalyst is HF, HCl, HBr, HI, H2SO3, H2SO4, H3PO2, H3PO4, HNO2, HNO3, H2WO4, H4SiW 12 O 40 , H3PW 12 O 40 , (NH4)6(W 12 O 40 ).xH2O, H4SiMo 12 O 40 , H3PMo 12 O 40 , (NH4)6Mo7O 24 xH2O, H2MoO4, HReO4, H2CrO4, H2SnO3, H4SiO4, H3BO3, HClO4, HBF4, HSbF5, HPF6, H2FO3P, ClSO3H, FSO3H, HN(SO2F)2, HIO3, BF3, AlCl3, Al(OTf)3, FeCl3, ZnCl2, SnCl2, CrCl3, CeCl3, ErCl3, formic acid, acetic acid, trifluoroacetic acid, lactic acid, levulinic acid, methanesulfinic acid, methanesulfonic acid, trifluoromethanesulfonic acid, bis(trifluoromethanesulfonyl)amine, benzoic acid, para-toluenesulfonic acid, 4-biphenylsulfonic acid, diphenyl phosphate, and 1,1'-binaphthyl-2,2'-diylhydrogen phosphate.

[0056] Preferably, the dehydration acid catalyst is selected from HCl, H2SO4, H3PO2, H3PO4, HNO3, AlCl3, acetic acid, trifluoroacetic acid, methanesulfinic acid, methanesulfonic acid, and trifluoromethanesulfonic acid.

[0057] The term "sugar" refers to sugars containing six carbon atoms (hexoses), but this does not exclude the presence in the feedstock of sugars containing five carbon atoms (pentoses) in the form of oligosaccharides and monosaccharides. In particular, the term "sugar" refers to glucose or fructose, sucrose, either alone or in mixtures, but also to oligosaccharides such as cellobiose, maltose, cellulose or inulin.

[0058] The sugar raw material used may be sugar in solid form or an aqueous solution of sugar known as syrup, preferably containing at least 30% by weight of sugar, more preferentially at least 50% by weight of sugar, even more preferentially at least 70% by weight of sugar. By way of example, sucrose is generally produced in solid form, while glucose or fructose, alone or as a mixture, are generally produced in the form of an aqueous solution (syrup), for example with 70% by weight of sugar.

[0059] The optional dehydration step is carried out at a temperature of 30 to 200°C, preferably 50 to 180°C, preferably 70 to 150°C, preferably 90 to 130°C, for example at 120°C. Preferably, the optional dehydration step is carried out at a pressure of 0.001 to 10 MPa, preferably 0.001 to 5 MPa, preferably 0.01 to 1 MPa. Depending on the pressure and temperature conditions, the reaction medium is above or below the bubble point of the mixture. The term "bubble point" refers to the pressure and temperature conditions at which the first gas bubbles appear in the liquid. If the reaction medium is above the bubble point of the mixture, the vapor phase can be removed from the reactor, optionally rectified, and condensed to form a condensate, which can be sent to step g) for treating the water-polar aprotic synthesis solvent mixture.

[0060] Preferably, the dehydration acid catalyst is introduced into the dehydration step in a molar ratio of catalyst to sugar feedstock (expressed as acid / sugar) expressed as mole percent (mol%) of 0.01 to 10 mol%, preferably 0.05 to 8 mol%, preferably 0.1 to 6 mol%, preferably 0.2 to 5 mol%, preferably 0.3 to 4 mol%, and very preferably 0.5 to 3 mol%.

[0061] The optional dehydration step can be carried out according to various embodiments. Advantageously, the step can therefore be carried out discontinuously or continuously (discontinuous mode is called "batch mode"). The addition of the sugar feedstock can be staged (fed-batch) in the case of batch operation, or staged in series in different CSTR reactors (continuous stirred tank reactors) in the case of continuous operation. The process can be carried out in a closed reaction chamber or in a semi-open reactor.

[0062] Advantageously, the synthesis effluent obtained at the end of the optional dehydration step comprises 5-HMF and a polar aprotic synthesis solvent, preferably DMSO. The polar aprotic synthesis solvent, typically DMSO, generally represents from 30 to 95% by weight, preferably from 40 to 90% by weight, preferably from 50 to 90% by weight, preferably from 55 to 85% by weight of the synthesis effluent resulting from the dehydration step and treated in step a) of the process according to the invention.

[0063] 5-HMF represents more than 1% by weight, preferably more than 10% by weight, preferably more than 15% by weight, preferably less than 50% by weight, preferably less than 40% by weight, preferably less than 30% by weight of the synthesis effluent resulting from the optional dewatering step and treated in step a) of the process according to the invention.

[0064] Furthermore, the synthesis effluent resulting from the optional dehydration step may contain water even before it is mixed with the aqueous stream 21 in step a). Water may originate from the dehydration step. For example, water is formed during the dehydration reaction of sugars to 5-HMF (3 moles of water are produced per mole of 5-HMF produced). For practical reasons, for example, when using approximately 70% by weight of starch syrup in water, sugar may also be introduced into this water. Advantageously, during the optional dehydration step, the water-polar aprotic synthesis solvent (e.g., DMSO) mixture can be recovered in the gas phase. The water-polar aprotic synthesis solvent (e.g., DMSO) mixture can be advantageously sent to step g). Thus, the synthesis effluent resulting from the optional dehydration step and introduced into step a) as feedstock 1 may generally contain water in a proportion of 0.1 to 30% by weight, preferably 0.1 to 15% by weight, more preferably 0.1 to 10% by weight.

[0065] To reduce the water content in the reaction medium and thus improve the selectivity of the reaction, it may be advantageous to simultaneously extract water from the reaction medium during the optional dehydration step. 5-HMF selectivity is understood to mean the ratio of the number of moles of 5-HMF produced to the number of moles of fructose converted contained in the sugar feedstock introduced into the process. In polar aprotic media, the presence of water significantly reduces the selectivity of sugar conversion, the higher the sugar concentration in DMSO. Therefore, such continuous water extraction during the synthesis of 5-HMF is advantageous in this respect and also makes it possible to manage the extraction of water that may be present in the sugar feedstock, if it is in the form of a syrup, in a single step. During such extraction of water from the reaction medium, the reaction medium is above the bubble point of the mixture. The vapor phase can be removed from the reactor, rectified, and condensed to form a water condensate containing less than 10% by weight, preferably less than 5% by weight, or even less than 1% by weight, of the polar aprotic synthesis solvent. The extracted water may result from dehydration, if for practical reasons a feedstock in the form of a syrup is used, and / or may be introduced together with the sugar feedstock. Advantageously, at least 50% by weight, preferably at least 80% by weight, or even 90% by weight of the water present in the reaction medium is extracted. The water extracted from the reaction medium may correspond to at least 50% by weight, preferably at least 80% by weight, or even 90% by weight of the water produced during dehydration. Water can be extracted by various methods, such as evaporation, adsorption (e.g., in molecular sieves), membrane separation, or permeation, and is advantageously extracted by distillation, which requires that the polar aprotic synthesis solvent be less volatile than water. Advantageously, water is extracted under conditions that allow at least 90% by weight, preferably at least 95% by weight, or even 99% by weight, of the polar aprotic synthesis solvent used in the dehydration step to be recovered in the synthesis effluent obtained at the end of the optional dehydration step.The water extracted in this way, like the aqueous effluent 15 resulting from step g) of treating the water-polar aprotic synthesis solvent mixture, may be recycled to one or more steps of the process requiring the supply of an aqueous stream, or may be mixed with the reusable aqueous effluent 15, or may otherwise be treated to produce, in particular, a reusable aqueous effluent 15, and sent to step g) to remove any polar aprotic synthesis solvent it may still contain.

[0066] If the sugar raw material is in the form of a syrup, it may be advantageous to optionally reduce the water content present upstream of the optional step of dehydrating the sugar raw material by extracting the water resulting from the dehydration reaction during the dehydration step, as already mentioned above but not repeated here. Thus, it is possible to extract the water from the sugar raw material in the form of a syrup and exchange it with a polar aprotic synthesis solvent to obtain a mixture that is sent to the dehydration step. The water in the syrup may be at least partially extracted after mixing the syrup with the polar aprotic synthesis solvent. The solvent retains the sugar in a diluent medium, allowing the diluent to be replaced by water upon dilution with the synthesis solvent. Water can be extracted by various methods, such as evaporation, adsorption (e.g., in molecular sieves), membrane separation, and is advantageously extracted by distillation, which requires that the polar aprotic synthesis solvent be less volatile than water. Advantageously, the extracted water represents at least 50% by weight, preferably at least 80% by weight, or even at least 90% by weight, of the water present in the syrup. The extracted water may represent 90-99% by weight of the water in the syrup. Advantageously, the extracted water contains less than 10% by weight, preferably less than 5% by weight, or even less than 1% by weight, of synthesis solvent. The water thus extracted may be recycled to one or more steps of the process requiring the supply of an aqueous stream, such as the aqueous effluent 15 resulting from step g) of treating the water-polar aprotic synthesis solvent mixture, or may be mixed with the reusable aqueous effluent 15, or may otherwise be treated, in particular to produce a reusable aqueous effluent 15, and sent to step g) to remove any polar aprotic synthesis solvent it may still contain.

[0067] The synthesis effluent resulting from the optional dehydration step and introduced into step a) as feedstock 1 may also contain impurities, in particular humins. The term "humins" refers to all undesired polymeric compounds formed during the synthesis of 5-HMF. In particular, humins represent less than 30% by weight, preferably less than 20% by weight, of the converted sugar feedstock.

[0068] An optional neutralization step may be performed on the synthesis effluent resulting from the optional dehydration step before it is introduced into step a) as feedstock 1, the synthesis effluent containing the dehydration acid catalyst. This reduces the reactivity of the medium, thus avoiding the decomposition mechanism of 5-HMF or reducing corrosion of materials in equipment downstream of the optional dehydration step. Since the dehydration reaction may produce a small number of organic acids, the amount of neutralizing agent may advantageously be sufficient to neutralize all acids present in the synthesis effluent resulting from the dehydration step. Such a neutralization step is advantageously carried out at a minimum stoichiometric ratio relative to the amount of catalyst used. Since the dehydration reaction may produce a small number of organic acids, neutralization is generally carried out slightly superstoichiometrically relative to the catalyst used, preferentially at 1 to 2 times the stoichiometric ratio, and preferentially at 1 to 1.5 times the stoichiometric ratio. The neutralizing agent may be a basic compound selected from NaOH, KOH, NH4OH, Na2CO3, K2CO3, NaHCO3, KHCO3, Mg(OH)2, Ca(OH)2, Ba(OH)2.

[0069] Mixing process a) The process according to the invention comprises a step a) of contacting (or mixing) a feedstock 1 comprising 5-HMF and a polar aprotic synthesis solvent, optionally resulting from a dehydration step, with an aqueous stream 21 to obtain at least one aqueous mixture 3.

[0070] Aqueous stream 21 may consist of pure water external to the process or water recycled from the process, for example aqueous stream 21 may advantageously comprise all or part of the intermediate aqueous back extract 9 resulting from step c) and / or the water 15 produced in step g) of treating the water-polar aprotic synthesis solvent mixture.

[0071] Preferably, 5-HMF represents more than 1% by weight, preferably more than 10% by weight, preferably more than 15% by weight, preferably less than 50% by weight, preferably less than 40% by weight, preferably less than 30% by weight of feedstock 1 introduced in step a) of the process according to the invention.

[0072] Preferably, the polar aprotic synthesis solvent (for example DMSO) represents 30 to 95% by weight, preferably 40 to 90% by weight, preferably 50 to 90% by weight, preferably 55 to 85% by weight of the feedstock 1 introduced in step a).

[0073] The feedstock 1 introduced in step a) may also contain water in a proportion of preferably 0.1 to 30% by weight, preferably 0.1 to 15% by weight, more preferably 0.1 to 10% by weight.

[0074] Feedstock 1 may optionally comprise humins, in particular representing less than 30% by weight of Feedstock 1, preferably less than 20% by weight.

[0075] Thus, aqueous stream 21 may comprise or consist of water. If aqueous stream 21 comprises a fraction of recycled process water, this fraction may comprise at least 60% by weight of water, preferably at least 70% by weight, more preferentially at least 80% by weight, more preferentially even at least 95% by weight, or even 98% by weight of water. Aqueous stream 21 may comprise all or part of the intermediate aqueous back-extract 9 resulting from step c). Intermediate aqueous back-extract 9 comprises water, a polar aprotic synthesis solvent (e.g., DMSO) and optionally 5-HMF. Advantageously, intermediate aqueous back-extract 9 contains more than 60% by weight of water, preferably more than 70% by weight, preferably more than 80% by weight of water.

[0076] Advantageously, the aqueous mixture 3 obtained at the end of step a) contains between 10 and 90% by weight of water, preferably between 20 and 80% by weight of water, preferably between 40 and 75% by weight of water.

[0077] Preferably, step a) is carried out at a temperature between 0 and 60°C, preferably between 5 and 40°C, generally at ambient temperature, ie between 10 and 40°C.

[0078] Increasing the water content of feedstock 1 during step a) can lead to the precipitation of some of the humins present in feedstock 1. Therefore, the mixture resulting from the contact of feedstock 1 with aqueous stream 21 can advantageously be subjected to a liquid-solid separation step before being sent to liquid-liquid extraction step b), so as to obtain a liquid separated from the suspended solid particles and a solid residue containing humins, which is preferably removed from the process in the form of solids stream 2. Such an optional liquid-solid separation step therefore makes it possible to remove the humins precipitated in step a) or upstream. At least a portion of the liquid obtained is then advantageously sent to liquid-liquid extraction step b), and part or preferably all of the liquid is advantageously sent to step b), corresponding to aqueous mixture 3. Such a liquid-solid separation step in step a) can advantageously be carried out when the amount of humins precipitated in the mixture formed by feedstock 1 and aqueous stream 21 in step a) exceeds, for example, 1% by weight. This optional liquid-solid separation step is preferably carried out at a temperature between 0 and 60°C, preferably between 5 and 40°C, generally at ambient temperature (i.e., between 10 and 40°C). The optional liquid-solid separation step prior to step b) is a simple solid-liquid separation and can be carried out by any method known to those skilled in the art, such as using a filter press, a belt filter, a clarifier, a settler, a centrifuge, e.g. a plate centrifuge, these techniques being used alone or in combination in any order. Preferably, the liquid-solid separation step is a filtration, preferably carried out using a filter press.

[0079] Liquid-liquid extraction process b) The process according to the invention comprises a step b) of liquid-liquid extraction of the aqueous mixture 3 obtained at the end of step a) in the presence of an extraction solvent 4 to produce an aqueous raffinate 5 and an organic extract 6.

[0080] The liquid-liquid extraction carried out in step b) advantageously corresponds to washing the aqueous mixture with an organic extraction solvent. Preferably, the liquid-liquid extraction carried out in step b) is a countercurrent extraction of the aqueous mixture 3 obtained in step a) with an extraction solvent 4. This technique is well known to those skilled in the art. It can be carried out, for example, in a mixer-decanter array, in a column filled with random or structured packing, in a pulse column or even in a stirred column.

[0081] Liquid-liquid extraction may involve the performance of at least two theoretical separation stages. This is the case, for example, when the intermediate liquid stream 19 resulting from liquid-liquid extraction step b) is subjected to a liquid-solid separation step f), which returns to step b) once the solid particles have been removed, as further detailed in step f). A first liquid-liquid separation step is then performed to produce an intermediate liquid stream 19 which is sent to liquid-solid separation step f) to form a particle-depleted intermediate liquid stream 20 which may be sent to a second liquid-liquid extraction step of step b).

[0082] The liquid-liquid extraction step b) is advantageously carried out at a temperature between 0 and 60°C, preferably between 5 and 40°C, generally at ambient temperature (ie between 10 and 40°C).

[0083] The weight ratio (weight / weight) of the extraction solvent 4 to the aqueous mixture 3 is preferably 0.2 to 5, preferably 1 to 3, and preferably 1.5 to 2.5.

[0084] The extraction solvent 4 introduced in step b) is selected from water-immiscible organic solvents so as to form two liquid phases in step b) and in backwash step c), the characteristics of which depend largely on the relative proportions of the feedstock, back-extraction water and extraction solvent flow rates used in the process.

[0085] The extraction solvent is preferably selected from chlorinated organic solvents, ethers, esters, ketones, and aromatic compounds. Preferably, the extraction solvent is a chlorinated solvent having 1 to 10 carbon atoms (hereinafter referred to as C1-C10), an ether having 2 to 10 carbon atoms (C2-C10), an ester having 4 to 10 carbon atoms (C4-C10), a ketone having 3 to 10 carbon atoms (C3-C10), an aldehyde having 1 to 10 carbon atoms (C1-C10), or a C4-C10 aromatic compound. Preferably, the extraction solvent is selected from dichloromethane, diethyl ether, diisopropyl ether, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, thiophene, anisole, and toluene. Most preferably, the extraction solvent is methyl isobutyl ketone.

[0086] Advantageously, the extraction solvent is selected as follows:

[0087] - a very large difference in volatility from 5-HMF, in particular facilitating its removal in optional step d) and limiting the decomposition of 5-HMF, i.e. having a vaporization rate that avoids the decomposition of 5-HMF in step d) and minimizes the amount of residual solvent removed in step e), while at the same time ensuring that there is no liquid phase separation when the concentrated organic raffinate 10 is contacted with water in step e); - forming a heterogeneous azeotrope with water in step e), which is preferably solvent-rich, i.e. comprises more than 50% by weight of solvent, preferably more than 60% by weight of solvent, preferably more than 70% by weight of solvent. Advantageously, the azeotrope of the water / extraction solvent mixture has a boiling point significantly below the boiling point of water, preferably at least 5°C below the boiling point of water, preferably at least 8°C below the boiling point of water, preferably at least 10°C below the boiling point of water.

[0088] Advantageously, the organic solvent streams produced in the subsequent steps can be recycled to extraction step b) as extraction solvents. These organic solvent streams may contain impurities that may have been produced during the process. Advantageously, the organic solvent streams produced in the subsequent steps can be, for example, periodically distilled to avoid the accumulation of impurities.

[0089] Step b) thus makes it possible to obtain, firstly, an aqueous stream depleted in 5-HMF, called aqueous raffinate 5, which contains most of the polar aprotic synthetic solvent (e.g., DMSO) originally contained in feedstock 1; secondly, an organic stream enriched in 5-HMF, called organic extract 6, which contains most of the 5-HMF originally contained in feedstock 1; and extraction solvent 4. This organic extract 6 may also contain a polar aprotic synthetic solvent (e.g., DMSO). Preferably, the organic extract contains 5-HMF and a polar aprotic synthetic solvent (e.g., DMSO) in a weight ratio of 5-HMF / polar aprotic synthetic solvent (e.g., DMSO) of 50 / 50 to 99 / 01, preferably 50 / 50 to 95 / 05, preferably 55 / 45 to 90 / 10, more preferably 60 / 40 to 85 / 15, preferably 65 / 35 to 80 / 20.

[0090] Advantageously, the organic extract 6 is sent directly to the backwashing step c).

[0091] In step b), there is also present a solid particle fraction formed by precipitated humins, which may be humins precipitated in the upstream mixing step a) still present in the aqueous mixture 3 sent to step b), or humins precipitated in step b) or in the backwash step c).

[0092] The solid particle fraction may be suspended in the intermediate liquid stream 19 optionally formed in step b) and / or in the aqueous stream 15. When aqueous stream 15 contains a solid particle fraction, aqueous stream 15 is sent to a liquid-solid separation step f), further described below.

[0093] Backwash process c) The process according to the invention comprises a step c) of backwashing the organic extract 6 with an aqueous solvent 7 to produce an intermediate aqueous back-extract 9 comprising 5-HMF and an organic solvent and an organic raffinate 8. The intermediate aqueous back-extract 9 is advantageously passed partly or entirely to step a). The organic solvent is in particular at least partly composed of the extraction solvent, which may preferably also contain small amounts of a polar aprotic synthesis solvent (e.g. DMSO).

[0094] The introduction of aqueous solvent 7 in step c) is carried out in accordance with the general knowledge of the person skilled in the art so as to carry out backwashing.

[0095] The introduction of aqueous solvent 7 is carried out so that the amount of aqueous solvent is as small as possible to reduce costs, but sufficient to ensure a low weight content of polar aprotic synthesis solvent (e.g. DMSO) in the organic raffinate 8, preferably not more than 20.0% by weight relative to the weight of 5-HMF, preferably not more than 15.0% by weight relative to the weight of 5-HMF, preferably between 0.01 and 15.0% by weight relative to the weight of 5-HMF, very preferably between 0.01 and 10.0% by weight relative to the weight of 5-HMF.

[0096] Advantageously, the aqueous backwash solvent 7 introduced in step c) comprises at least 95% by weight of water (out of a maximum of 100%), preferably at least 98% by weight of water.

[0097] The aqueous solvent may contain a polar aprotic synthetic solvent (e.g., DMSO). The backwash effectiveness is generally higher the lower the amount of polar aprotic synthetic solvent (e.g., DMSO) present in the aqueous backwash solvent. The aqueous solvent may contain at most 1.0% by weight, preferably at most 0.1% by weight, of a polar aprotic synthetic solvent (e.g., DMSO). Advantageously, the aqueous backwash solvent 7 originates from step g) of treating the water-polar aprotic synthetic solvent mixture produced in the process and thus comprises at least a portion of the reusable effluent 15. In a preferred embodiment of the present invention, the aqueous raffinate 5 composed of water and polar aprotic synthetic solvent (e.g., DMSO) produced in step b) or the particle-depleted aqueous raffinate 5' produced in step f) is treated in step g), which advantageously involves distillation. The water-rich distillate thus obtained at the end of this step g) is also called aqueous effluent 15 reusable in the process and is advantageously used in step c) to form the aqueous backwash solvent 7, optionally in admixture with makeup water 22, or in the mixing step a), optionally together with at least one intermediate aqueous back-extract 7 fraction and / or makeup water, to form aqueous stream 21. The reusable effluent 15, e.g., the water-rich distillate, may also contain residual amounts of polar aprotic synthesis solvents (e.g., DMSO), preferably not more than 1% by weight, preferably not more than 0.1% by weight. The residual amount of polar aprotic synthesis solvents (e.g., DMSO) in the aqueous effluent 15 (distillate) is proportionally less the more efficiently the distillation of step g) is carried out, in particular with a number of distillation stages greater than 5, advantageously with suitable boil-up rates and reflux ratios.

[0098] The backwashing step c) is advantageously a liquid-liquid extraction of an organic stream, in particular the organic extract 6 obtained in step b), in countercurrent to the aqueous solvent 7. This technique is well known to those skilled in the art. The extraction can be carried out, for example, in a mixer-decanter array, in a column filled with random or structured packing, in a pulse column or even in a stirred column.

[0099] Step c) is preferably carried out at a temperature between 0 and 60°C, preferably between 5 and 40°C, generally at ambient temperature (ie between 10 and 40°C).

[0100] The weight ratio (wt / wt) of the aqueous solvent 7 to the organic extract 6 is preferably 0.04-5, preferably 0.07-3, and preferably 0.1-1.

[0101] Step c) makes it possible to obtain an aqueous stream advantageously enriched in polar aprotic synthetic solvents (e.g., DMSO), called intermediate aqueous back extract 9, which preferably contains at least 60% by weight of water, preferably at least 80% by weight of water, and an organic raffinate 8 advantageously depleted in polar aprotic synthetic solvents (e.g., DMSO). Intermediate aqueous back extract 9 is advantageously sent partially or preferably entirely to step a). The weight content of polar aprotic synthetic solvents in the organic raffinate 8 obtained is preferably at most 20.0% by weight, preferably at most 15.0% by weight, more preferentially at most 5.0% by weight, even more preferentially at most 4.0% by weight, more preferably at most 3.0% by weight, relative to the weight of 5-HMF.

[0102] According to the invention, the organic raffinate 8 produced in step c) is sent to an optional concentration step d) or directly to a hydrodistillation step e).

[0103] Humins may still be present in the organic extract 6 sent to backwash step c). If they precipitate in this step and subsequently form undesirable solid particles, they may be removed in liquid-solid separation step f) by sending the intermediate aqueous back extract 9, wholly or partly, to step b), which may contain the precipitated humins and be sent to liquid-solid separation step f) together with the intermediate liquid stream 19 and / or the aqueous raffinate 5. If the intermediate aqueous back extract 9 is sent partly or totally to step a) to enter the composition or to constitute the aqueous stream 21, the precipitated humins may also be separated during the optional liquid-solid separation of step a) or in step f) as already described above and in further detail below.

[0104] Optional concentration step d) The process according to the invention preferentially comprises a step d) in which the organic raffinate 8 resulting from step c) is concentrated by removing part of the organic solvent to produce a concentrated organic raffinate 10 comprising 5-HMF and residual organic solvent, and a first stream 11 comprising, preferably consisting of, organic solvent, advantageously constituted completely or partly by the extraction solvent and optionally by a polar aprotic synthesis solvent (for example DMSO).

[0105] Preferably, the first stream 11 comprising the organic solvent is totally or partly recycled to the extraction step b), for example to form at least part of the organic solvent stream 4.

[0106] Preferably, in step d), removal of part of the organic solvent is carried out by evaporation, for example in an atmospheric or vacuum distillation column, an evaporator, or by any method known to those skilled in the art.

[0107] According to this preferred embodiment, the evaporation of the organic solvent is advantageously carried out under atmospheric pressure or vacuum, preferably at a pressure of 0.01 to 0.1 MPa, preferentially at a pressure of 0.01 to 0.09 MPa, so as to limit the temperature of the liquid and thus the decomposition of 5-HMF. Preferably, the temperature of the liquid is maintained below 130°C, preferably below 100°C, and preferably below 70°C. The pressure level, particularly the vacuum level, applied to reach these temperatures naturally depends on the organic solvent, more specifically the extraction solvent used, and the rate of evaporation of the organic solvent.

[0108] In a preferred embodiment, to reduce the operating costs associated with solvent evaporation while limiting the risk of decomposition of the desired product, i.e., 5-HMF, the solvent is evaporated by multiple-effect evaporation or mechanical vapor recompression, or any other method known to those skilled in the art. For example, in the case of a triple-effect evaporator, the liquid temperature is kept below 130°C in the first effect, below 100°C in the second effect, and below 70°C in the third effect. Thus, the temperature of the liquid phase gradually decreases as 5-HMF is concentrated in the organic solvent, limiting the risk of decomposition.

[0109] Optional step d) is carried out with a vaporization mass rate (or evaporation rate) corresponding to the mass of vaporized organic solvent relative to the mass of organic raffinate 8 resulting from step c) (more specifically, the mass of stream 11 relative to the mass of organic raffinate 8) of at least 50%, preferably at least 60%, preferably at least 70%, preferably at least 75%, preferably at least 80%, preferably at least 85%, preferably at least 90%, preferably at most 99%. Advantageously, the vaporization rate is defined depending on the extraction solvent so as to minimize the amount of residual solvent that does not decompose 5-HMF but is removed in step e) and at the same time ensure that there is no liquid phase separation when the concentrated organic raffinate 10 is contacted with water in step e) (i.e. ensure that the liquid phase remains single-phase).

[0110] Due to the combination of all the operating conditions of steps a), b) and c) described above, as well as optional step d), the concentrated organic raffinate 10 obtained at the end of step d) very advantageously has a 5-HMF content, relative to the weight of the concentrated organic raffinate, of at least 40 wt.%, preferably at least 50 wt.%, preferably at least 60 wt.%, preferably at most 95 wt.%, preferably at most 90 wt.%, preferably at most 85 wt.% relative to the weight of the concentrated organic raffinate. In other words, the concentrated organic raffinate 10 preferably has a residual organic solvent content, relative to the weight of the concentrated organic raffinate, of at least 5 wt.%, preferably at least 10 wt.%, preferably at most 60 wt.%, preferably at most 50 wt.%, preferably at most 40 wt.% relative to the weight of the concentrated organic raffinate.

[0111] Advantageously, the organic solvent vaporized during optional step d) forms a first stream 11 comprising, preferably consisting of, organic solvent, which is preferably recycled to extraction step b).

[0112] Advantageously, the concentrated organic raffinate 10 is sent to a hydrodistillation step e).

[0113] Hydrodistillation process e) The process according to the invention comprises a hydrodistillation step e) carried out by distilling the concentrated organic raffinate 10 resulting from optional step d) or the organic raffinate 8 resulting from step c) in the presence of water to produce an aqueous solution of 5-HMF 12 and a second stream 13 comprising, preferably consisting of, an organic solvent.

[0114] Hydrodistillation step e) advantageously makes it possible to at least partially remove the residual organic solvent not removed during optional step d). The residual organic solvent removed during step e), i.e. the second stream 13 comprising the organic solvent, can be advantageously recycled to extraction step b), either alone or in a mixture with the first stream 11 resulting from optional step d).

[0115] Advantageously, the aqueous liquid 14 is fed to a hydrodistillation step e). The aqueous liquid 14 introduced into step e) preferably contains more than 95% by weight of water, preferably more than 98% by weight of water.

[0116] In one particular embodiment of the present invention, the aqueous liquid 14 is pure water, possibly external to the process, which can further minimize the content of residual polar aprotic synthesis solvents (e.g., DMSO) in the aqueous 5-HMF solution 12 produced in step e).

[0117] In another particular embodiment of the present invention, water isolated within the process is used to feed step e), limiting the operational costs of the process and its environmental impact. Typically, if the process integrates the preparation of feedstock 1 and the sugar raw material for the dehydration step is 70% by weight of starch syrup in water, approximately 1 ton of water is present at the end of the dehydration step (water in the sugar raw material and water produced during the dehydration reaction) per ton of 5-HMF produced. This water, which is advantageously recovered, must be treated before being discharged into the environment. Thus, the method according to the present invention advantageously uses the water resulting from the sugar raw material and / or the dehydration step to produce an aqueous 5-HMF solution concentrated at the end of step e), preferably at a concentration of 30% by weight or more, preferentially 40% by weight or more, thus reducing the reprocessing costs of the process and its environmental impact.

[0118] Advantageously, the aqueous liquid 14 introduced in step e) may correspond to at least part, and possibly all, of the aqueous effluent 15 (distillate) produced in step g), which may optionally contain residual amounts of polar aprotic synthesis solvent (for example DMSO).

[0119] Advantageously, during step e), the extraction solvent used in the process forms a heterogeneous azeotrope with water, which azeotrope is preferably rich in the extraction solvent, preferably comprising more than 50% by weight of the extraction solvent, preferably more than 60% by weight of the extraction solvent, preferably more than 70% by weight of the extraction solvent. Advantageously, the water / extraction solvent azeotrope has a boiling point significantly lower than that of water, preferably at least 5° C. lower than that of water, preferably at least 8° C. lower than that of water, preferably at least 10° C. lower than that of water.

[0120] This allows the residual organic solvent to be easily removed without decomposing 5-HMF after the concentrated organic raffinate 10 or the organic raffinate 8 is brought into contact with the aqueous liquid 14.

[0121] The hydrodistillation step e) can be carried out under atmospheric pressure or under vacuum, in particular under a pressure of 0.001 to 0.1 MPa, preferably under vacuum at a pressure of 0.005 to 0.08 MPa. Advantageously, the hydrodistillation step is carried out under vacuum, in particular under a pressure of 0.001 to 0.1 MPa, preferably 0.005 to 0.08 MPa, in order to facilitate the removal of residual organic solvents without decomposing the 5-HMF.

[0122] Advantageously, the hydrodistillation step e) is carried out in a distillation column at a bottom temperature of preferably at most 140°C, preferably at most 130°C, preferably at most 120°C, preferably at most 110°C, preferably at most 100°C, in order to facilitate the removal of residual organic solvents without decomposing the 5-HMF.

[0123] In one particular embodiment, concentrated organic raffinate 10 or otherwise organic raffinate 8 and aqueous liquid 14 are mixed prior to introduction into the distillation column, with the mixture being introduced at an intermediate point in the distillation column.

[0124] In another particular embodiment, the concentrated organic raffinate 10 or organic raffinate 8 is introduced into the upper portion of the distillation column, preferably into the upper half of the column, and an aqueous liquid is also introduced into the distillation column, after which mixing with the aqueous liquid occurs within the distillation column.

[0125] Considering the formation of a heterogeneous azeotrope of water and extraction solvent, condensation of the overhead vapor of the distillation column produces two liquid phases: a water-rich phase which can advantageously be returned to the column as reflux, and an organic solvent-rich phase 13 which can advantageously be recycled to the extraction step b).

[0126] According to the invention, the aqueous 5-HMF solution 12 obtained at the end of step e) has a 5-HMF content of at least 30% by weight, preferably at least 40% by weight, preferably less than 90% by weight, preferably less than 85% by weight, preferably less than 80% by weight, the percentages being given by the weight of 5-HMF relative to the weight of the aqueous 5-HMF solution obtained at the end of step e).

[0127] The process according to the invention therefore very advantageously allows the production of aqueous 5-HMF solutions having a weight content of polar aprotic synthesis solvents (for example DMSO) of not more than 10% by weight relative to the weight of 5-HMF, preferably not more than 5% by weight relative to the weight of 5-HMF, preferably not more than 3% by weight relative to the weight of 5-HMF.

[0128] Liquid-solid separation processf) According to the invention, the process comprises a liquid-solid separation step f) making it possible to reduce the content of solid particles formed by precipitated humins in at least one of the intermediate liquid stream 19 resulting from the liquid extraction step b) or in the (final) aqueous raffinate 5.

[0129] The liquid-liquid extraction step b), independently of what may occur in step a) or upstream of step a), can induce the precipitation of solids, i.e. precipitated humins, and the solid particle fractions generated during the liquid-liquid extraction or not removed by the liquid-solid separation possible in step a) can cause the problems already described. In order to maintain the equipment downstream of the liquid-liquid extraction step, in particular the equipment used in step g) for processing the water-polar aprotic synthetic solvent mixture, it can prove necessary in some cases to separate the precipitated solids at the end of the liquid-liquid extraction.

[0130] The separation is carried out on the intermediate stream 19 if produced in step b) or on the (final) aqueous raffinate 5 produced in the liquid-liquid extraction step b), or on both.

[0131] This liquid-solid separation step f) is preferably carried out at a temperature of 0 to 60°C, preferably 5 to 40°C, generally at ambient temperature (ie, 10 to 40°C).

[0132] The liquid-solid separation step is preferably a simple liquid-solid separation and can be carried out by any method known to those skilled in the art, for example using a filter press, a belt filter, a clarifier, a settler, a centrifuge, such as a plate centrifuge, and the separation techniques can be used alone or in any combination in any order. Preferably, the liquid-solid separation step is filtration, preferably carried out using a filter press.

[0133] The liquid-solid separation in step b) may involve the addition of additives to facilitate liquid-solid separation, for example the addition of diatomaceous earth in the case of filtration to facilitate or improve filtration if the solid particles are too sticky.

[0134] According to one or more embodiments, such as those shown in Figure 1 or 3, step b) produces an intermediate liquid stream 19 comprising a solid particle fraction, which is fed to step f) to separate the solid particle fraction from 19 and to form a particle-depleted intermediate liquid stream 20 which is fed to step b), typically to a second liquid-liquid extraction stage. The final aqueous raffinate 5 resulting from step b) and fed to step g) does not comprise the solid particle fraction resulting from step b). The precipitated humins have in fact been removed by subjecting intermediate liquid stream 19 to a separation.

[0135] According to one or more embodiments, the intermediate liquid stream 19 sent to step f) is an intermediate aqueous raffinate comprising a solid particle fraction, which is produced in liquid-liquid extraction step b) by separation of the extraction solvent and the water-polar aprotic synthesis solvent mixture.

[0136] Alternatively, the intermediate liquid stream 19 sent to step f) is a three-phase mixture comprising a first liquid phase comprising 5-HMF and the extraction solvent (which may be designated as intermediate extract), a second liquid phase comprising water and the polar aprotic synthesis solvent (which may be designated as intermediate raffinate), and a solid phase comprising the solid particle fraction.

[0137] A three-phase centrifuge may then be advantageously used to separate the three phases, i.e., intermediate raffinate, intermediate extract, and solid phase containing precipitated humics (solid particle stream 18), in a single device. Such a device used in step f) may also be the one used in stage b) of liquid-liquid extraction. The intermediate raffinate and intermediate extract will form aqueous raffinate 5 and organic extract 6, respectively.

[0138] According to one or more embodiments, the aqueous raffinate 5 produced in step b) contains a solid particle fraction, and the aqueous raffinate 5 is sent to step f) to separate the solid particle fraction from the aqueous raffinate 5, forming a solid particle-depleted aqueous raffinate 5', which is sent to step g) as a water-polar aprotic synthesis solvent mixture, as shown in FIG. According to one or more embodiments, step f) is carried out separately on both the intermediate liquid stream 19 and the final aqueous raffinate 5 produced in step b) if these two effluents each contain solid particles formed by precipitated humics. In this case, a solid particle-depleted aqueous raffinate is produced and sent to step g) as a water-polar aprotic synthesis solvent mixture.

[0139] An intermediate liquid raffinate / intermediate aqueous raffinate / aqueous raffinate depleted of solid particles (precipitated humins) is understood to mean a raffinate which contains less than 10% by weight, preferably less than 5% by weight and more preferentially less than 1% by weight of solid particles formed by precipitated humins.

[0140] Step g) Treating the water-polar aprotic synthesis solvent mixture The process according to the invention comprises a step g) of treating the water-polar aprotic synthetic solvent (e.g., DMSO) mixture produced by the steps of the process according to the invention to produce an aqueous effluent (also called distillate), which can be used in whole or in part in the backwashing step c) and / or step a) and / or step e). This step can also produce a polar aprotic synthetic solvent (e.g., DMSO)-rich stream 16 and an impurity stream 17. Thus, at least one water-polar aprotic synthetic solvent mixture produced in this way is treated in step g). This mixture can be a particle-depleted aqueous raffinate 5' resulting from step f) or an aqueous raffinate 5 free of solid particle fractions resulting from step b).

[0141] This step in particular makes it possible to separate, in a particle-depleted aqueous raffinate 5' resulting from at least one mixture (step f) or in an aqueous raffinate 5) free of solid particle fractions resulting from step b), the water, the polar aprotic synthesis solvent and the reaction products extracted in the raffinate, such as unconverted sugars, sugar oligomers, residual 5-HMF, etc.

[0142] One or more other water-polar aprotic synthesis solvent mixtures produced in the process may be sent to step g).

[0143] If the process integrates a step of synthesizing feedstock 1, i.e., a step of dehydrating the sugar feedstock as described above, either (i) this step involves the simultaneous extraction of water from the reaction medium, or (ii) this reaction step of dehydrating the sugar feedstock is preceded by a step of separating the water contained in the sugar feedstock, which, if the sugar feedstock is initially in the form of a syrup, involves extracting the water of the syrup and replacing it with a polar aprotic synthesis solvent, and synthesis solvent-rich stream 16 can be purged of that water simultaneously with the extraction of water in these two scenarios (i) and (ii).

[0144] The residual amount of polar aprotic synthesis solvent (for example DMSO) in the aqueous effluent produced at the end of step g) will be proportionally lower the more efficiently the distillation is carried out according to the knowledge of those skilled in the art.

[0145] The water-polar aprotic synthesis solvent (e.g., DMSO) mixture produced by the present process refers in particular to the aqueous raffinate 5 produced in step b) and depleted of solid particles in step f), and optionally the water-polar aprotic synthesis solvent (e.g., DMSO) mixture resulting from the optional step of dehydrating sugars to 5-HMF (if the present process integrates such a step).

[0146] Step g) of treating the water-polar aprotic synthesis solvent (e.g. DMSO) mixture preferably uses a section in which the water-polar aprotic synthesis solvent (e.g. DMSO) mixture is evaporated to remove any impurities, in particular heavy impurities, such as humics or unconverted sugars, in the form of stream 17, followed by a distillation section.

[0147] The evaporation section is preferably operated at a temperature of 80 to 120°C, preferably 100 to 110°C, and at a pressure of preferably 0.002 to 0.020 MPa, preferably 0.005 to 0.010 MPa. Preferably, the evaporation section uses a wiped film type (thin film evaporator, TFE) evaporator.

[0148] The distillation section of that part advantageously uses a distillation column or several separate pieces of equipment. Preferably, the distillation section of step g) is advantageously carried out in a distillation column, the temperature at the top of the column is preferably between 25 and 60°C, preferentially between 45 and 55°C, for example about 50°C, the temperature at the bottom of the column is preferably between 80 and 140°C, preferentially between 100 and 130°C, for example about 120°C, the pressure is preferably between 0.001 and 0.05 MPa, preferentially between 0.005 and 0.02 MPa, preferably between 0.008 and 0.012 MPa, and the reflux ratio is preferably between 0.01 and 0.50, preferably between 0.05 and 0.10.

[0149] Thus, the aqueous raffinate 5 produced in step b) and containing water and a polar aprotic synthetic solvent (e.g., DMSO), optionally containing a water-polar aprotic synthetic solvent (e.g., DMSO) mixture recovered in the optional dehydration step, is evaporated, and the gas phase is then recovered and distilled, preferably under vacuum, to produce a residue 16 rich in the polar aprotic synthetic solvent (e.g., DMSO), a water-rich distillate 15 (corresponding to the aqueous effluent), and finally a stream 17 containing heavy fractions such as humic substances and unconverted sugars of humic substances that have not been removed by filtration. The term "rich" in this context is understood to mean at least 95% by weight, preferably at least 98% by weight. Part or all of the water-rich distillate or aqueous effluent can advantageously be recycled to step c) as aqueous solvent for carrying out the backwash step and / or to the hydrodistillation step e) as aqueous stream. The water-rich distillate can also be completely or partially recycled as the water introduced into step a).

[0150] The residue, rich in polar aprotic synthesis solvent (for example DMSO), is advantageously introduced into an optional dehydration step, either directly or after distillation, allowing the discharge of any heavy products that may accumulate.

[0151] The examples and figures detailed below illustrate the invention without limiting its scope.

[0152] FIG. 1 shows one particular embodiment of the process according to the invention. A feedstock 1 containing 5-HMF, a polar aprotic synthetic solvent (e.g., DMSO), and humins is sent to step a) and contacted with an aqueous stream 21. The aqueous mixture 3 obtained at the end of step a) is sent to extraction step b) and placed in the presence of an extraction solvent 4 to extract 5-HMF from the aqueous mixture with the extraction solvent, obtaining an aqueous raffinate 5 and an organic extract 6. The organic extract 6 is placed in the presence of an aqueous solvent 7 in backwash step c). The organic raffinate 8 obtained at the end of step c) can be concentrated in an optional concentration step d) by removing stream 11, which can be recycled to step b). The organic raffinate 8 obtained at the end of step c), or, if performed, the concentrated organic raffinate 10 obtained at the end of step d), is treated in a hydrodistillation step e) to remove the residual organic solvent 13 and obtain an aqueous 5-HMF solution 12.

[0153] In this embodiment, a liquid-solid separation step f) is carried out during liquid-liquid extraction on the intermediate liquid stream removed in liquid-liquid extraction step b). The intermediate aqueous raffinate 19 produced in step b) is treated in liquid-solid separation step f). This liquid-solid separation makes it possible to extract the solids precipitated in the upstream phase, i.e. the precipitated humins, in the form of a stream of solid particles 18, to produce a clarified intermediate aqueous raffinate 20 that is reintroduced into extraction step b).

[0154] The aqueous raffinate 5 resulting from the liquid-liquid extraction step b) is sent to step g) for treating the water-polar aprotic synthesis solvent mixture, which produces an aqueous effluent 15, an enriched polar aprotic synthesis solvent stream 16, and a heavy end stream 17 containing humins and unconverted sugars that are not removed by filtration (humins and sugars are in a liquid, albeit very viscous, form at the treatment temperature of the mixture).

[0155] Figure 2 shows another particular embodiment of the process according to the invention, which is identical to the one shown in Figure 1, with the exception that a liquid-solid separation step f) is carried out downstream of the liquid-liquid extraction step b) on the aqueous raffinate obtained at the end of step b). In the embodiment shown, precipitated humins forming solid particles are present in the aqueous raffinate obtained at the end of step b), which is sent to a liquid-solid separation step f) to separate the solid particles from the remainder of the aqueous raffinate, generating a stream 18 of solid particles and a particle-depleted aqueous raffinate 5'. The latter is sent to step g) for the treatment of the water-polar aprotic synthesis solvent mixture, which works in the same way as described for Figure 1.

[0156] FIG. 3 shows another particular embodiment of the method according to the invention, which is identical to the one depicted in FIG. 1, except that it includes the following particular features:

[0157] - The mixture 3 formed in step a) is subjected to a liquid-solid separation step to separate the humins (solid particles) precipitated in step a) from the remainder of the mixture, and to produce a solids stream 2.

[0158] The method comprises a step d) of concentrating the organic raffinate 8 produced in the backwashing step c) to produce a concentrated organic raffinate 10 and a stream 11 of extractant, the latter being advantageously recycled to step b) and introduced together with the extractant 4.

[0159] The aqueous stream 21 used in the mixing step a) comprises recycled water resulting from the process, in particular the aqueous stream 21 consisting of the backwash extract 9 and a fraction of the aqueous effluent 15 produced in step g) of treating the water-polar aprotic synthesis solvent mixture.

[0160] The aqueous solvent 7 used in backwash step c) consists of the water-polar aprotic synthesis solvent mixture and a fraction of the aqueous effluent 15 produced in step g) of treating make-up water 22 (i.e., external to the process, in other words, not produced within the process and not resulting from recycle within the process). Alternatively, the aqueous solvent 7 used in backwash step c) consists of the fraction of the aqueous effluent 15 produced in step g) without make-up water. In this case, make-up water may be sent to step a) to form an aqueous stream 21 comprising the fraction of the aqueous effluent 15 produced in step g). Despite the water recycle carried out, a supply of make-up water during the process may be necessary.

[0161] The aqueous stream 14 used in the hydrodistillation step e) consists of a fraction of the aqueous stream 15 produced in step g) of treating the water-polar aprotic synthesis solvent mixture.

[0162] The extraction solvent 4 used in extraction step b) consists of the solvent streams produced in steps d) and e). In other words, the organic solvent streams 11 and 13 produced in steps d) and e), respectively, are recycled to step b) and form in particular part of the composition of the extraction solvent 4.

[0163] This embodiment therefore comprises the recycling of the aqueous effluent 15 resulting from step g) of treating the water-polar aprotic synthesis solvent mixture into steps a), c) and e), as well as the recycling of the organic solvent streams 11 and 13 into the liquid-liquid extraction step b), which firstly allows for an optimal management of water in the process, integrating the treatments within the process and avoiding excess make-up water, and secondly minimizes the consumption of extraction solvent, a combination of which ultimately has a favorable impact on the operating costs and environmental impact of the process.

[0164] Example Preparation of aqueous 5-HMF solution 12 according to the present invention The following examples are intended to illustrate some of the advantages of the method according to the invention carried out according to the embodiment shown in FIG.

[0165] DMSO, used as a polar aprotic synthesis solvent, is mixed with the acid catalyst methanesulfonic acid at a molar ratio (catalyst / sugar feedstock) of 1 mol % and the temperature is brought to 120 °C. Fructose is introduced in the form of an aqueous solution at a DMSO / fructose mass ratio of 2.3 and 70% by weight of the sugar (syrup). The pressure is maintained at 0.035 MPa. Under these pressure and temperature conditions, the reaction medium is above the bubble point of the mixture, so the gas phase can be withdrawn from the reactor and condensed to form a condensate. The sugar dehydration step is carried out batchwise, with the feedstock being added gradually over a period of 2 hours. The reaction medium is maintained at the above temperature and pressure for a further 2 hours after the end of the addition.

[0166] The liquid effluent resulting from the dehydration step contains 74% by weight of DMSO, 21% by weight of 5-HMF, and 3% by weight of water, i.e., a molar yield of 5-HMF relative to the fructose used is 81%. Polymeric compounds soluble in the reaction medium (called humins) are formed in an amount of 5% by weight. During this dehydration step, a water-DMSO mixture is recovered in the gas phase. The water-DMSO mixture has a composition of 32% by weight of DMSO and 68% water. This water-DMSO mixture is distilled under vacuum to produce water containing only traces of DMSO.

[0167] The liquid effluent resulting from the dehydration step corresponding to feedstock 1 is used in step a) for contacting with a water-containing stream at ambient temperature to obtain a mixture containing a DMSO / water mass ratio equal to 1.

[0168] The mixture from step a) is subjected to a liquid-solid separation step in a Buchner filter equipped with a 10 μm pore size polypropylene cloth filter. This liquid-solid separation step is carried out at room temperature. During the liquid-solid separation step, 7.5 g of "humic compounds" solid residue / kg of the filtered mixture is recovered along with a homogeneous liquid phase corresponding to aqueous mixture 3. Aqueous mixture 3 is composed of 43 wt% DMSO, 12 wt% 5-HMF, and 43 wt% water, containing impurities (approximately 2 wt% humic compounds).

[0169] The aqueous mixture 3 resulting from step a) is subjected to countercurrent liquid-liquid extraction step b) in a stirred glass column (Kuhni or ECR type) with eight sections, each 32 mm in internal diameter and 225 mm in height, as well as a lower decanter and an upper decanter. The effective height is approximately 1.8 m, and the total column height is 2.60 m. The total volume is approximately 3 liters. The organic extraction solvent is methyl isobutyl ketone (MIBK). The aqueous mixture 3 is introduced into the top of the apparatus and dispersed in the ascending organic phase. The column inlet flow rates are set at 2.2 kg / h for the DMSO-aqueous phase and 4.1 kg / h for the MIBK. The ratio (wt / wt) of the MIBK solvent to the aqueous mixture 3 resulting from step a) is 1.9. In this step b), the temperature is 20°C and the stirring speed is 300 rpm.

[0170] The aqueous raffinate obtained from the liquid-liquid extraction column enters step f), which is here filtration on a Büchner funnel equipped with a polypropylene cloth filter with a pore size of 1 μm. This liquid-solid separation step f) is carried out at ambient temperature. During the liquid-solid separation step f), a filtered mixture of 7.0 g of "humic" solid residue / kg is recovered together with a homogeneous liquid phase corresponding to the aqueous raffinate depleted of solid particles, also called clarified aqueous raffinate 20.

[0171] In this particular embodiment, clarified aqueous raffinate 20 forms the aqueous raffinate 5 produced at the end of step b).

[0172] At the end of step b), a 5-HMF-depleted aqueous raffinate 5 containing approximately 48% by weight of water, 48.5% by weight of DMSO, 0.4% by weight of 5-HMF, 1.8% by weight of MIBK, and humic impurities, and an organic extract 6 enriched in furan compounds containing 2.8% by weight of DMSO, 5.9% by weight of 5-HMF (i.e., a 5-HMF / DMSO weight ratio of approximately 68 / 32), and 91.3% by weight of MIBK are recovered. The extraction yields are 97% for 5-HMF and 13% for DMSO.

[0173] The aqueous raffinate 5 is treated in step g) for treating a water-DMSO mixture. The evaporation of water and DMSO is carried out sequentially in a batch distillation system, the first stage operating at a pressure of 0.008 MPa and 80°C, making it possible to recover the MIBK and almost all of the water present in the aqueous raffinate 5 as well as most of the DMSO until the DMSO content in the residue reaches 50% by weight, i.e., an evaporation rate of approximately 93%. The second stage, carried out at 0.0005 MPa, is stopped when the temperature of the medium reaches 90°C. At this stage, the heavy product contains only 20% by weight of DMSO, and approximately 95% of the DMSO present in the aqueous raffinate 5 is recovered.

[0174] The organic extract 6 resulting from the liquid-liquid extraction step b) is subjected to a backwash step c) in the same extraction apparatus (ECR or Kuhni-type stirred column). The organic extract is dispersed in a pure aqueous phase at 21.5°C. The column inlet flow rates are set at 5 kg / h for the organic extract and 1.5 kg / h for the aqueous phase. The ratio (wt / wt) of water introduced as aqueous backwash solvent to the organic extract is 0.3.

[0175] At the end of backwash step c) a DMSO-enriched intermediate aqueous back extract 9 containing 86% by weight of water, 7% by weight of DMSO, 5% by weight of 5-HMF and 2% by weight of MIBK and an organic raffinate 8 containing 4.3% by weight of 5-HMF, 0.092% by weight of DMSO (i.e. 2.1% by weight of DMSO relative to the weight of 5-HMF) and 88% by weight of MIBK are recovered, giving backwash yields of 27% by weight for 5-HMF and 95% by weight for DMSO.

[0176] The organic raffinate 8 produced is sent to the concentration step d). The solvent is evaporated under vacuum. The liquid temperature is set to 60°C, and the vacuum pressure is set to 0.02 MPa.

[0177] Step d) is carried out with a vaporization mass ratio of 95%, which corresponds to the mass of the vaporized organic solvent relative to the mass of the organic raffinate resulting from step c). The mass content of the concentrated organic raffinate obtained at the end of step d) is 84% ​​by weight of 5-HMF, 2% by weight of DMSO, and 9% by weight of MIBK. The 5-HMF content of the concentrated organic raffinate (84% by weight) is in line with the expected value (at least 40% by weight and at most 95% by weight), and its residual solvent content is 11% (the sum of 9% MIBK and 2% DMSO), which is in line with the expected value (at least 5% by weight and at most 60% by weight). The concentrated organic raffinate obtained at the end of step d) also contains humic impurities (5% by weight). The recovered distillate essentially contains MIBK and water, which is removed in the form of an azeotrope with MIBK, which separates into two immiscible phases upon condensation.

[0178] The concentrated organic raffinate obtained from step d) is contacted with purified water in a water / concentrated extract mass ratio of 0.95 and then sent to hydrodistillation step e), which is carried out by distillation. To facilitate the removal of the residual MIBK organic solvent in the form of a water / MIBK azeotrope without decomposing 5-HMF, hydrodistillation step e) is carried out at a column bottom temperature of 35°C and under a vacuum of 0.01 MPa. The composition of the aqueous 5-HMF solution obtained at the end of step e) is 45% by weight of 5-HMF, 53.3% by weight of water, 1% by weight of DMSO (i.e., 2.2% by weight of DMSO relative to the weight of 5-HMF), and 0.7% by weight of MIBK. [Explanation of symbols]

[0179] 1: Feed material 2: Solid flow 3: Aqueous mixture 4: Extraction solvent 5: Aqueous raffinate 6:Organic extract 7: Aqueous solvent 8: Organic raffinate 9: Intermediate aqueous back extract 10: Concentrated organic raffinate 11: First flow containing organic solvent 12:5-HMF aqueous solution 13: Second stream containing organic solvent 14:Aqueous liquid 15:Aqueous effluent 16: Polar aprotic synthesis solvent-rich stream (or "residue"-rich...) 17: Impurity stream (or heavy fraction stream) 18: Solid particle flow 19: Intermediate liquid flow 20: Particle-depleted intermediate liquid flow 21:Aqueous flow 22:Supplementary water

Claims

1. 1. A process for producing an aqueous solution of hydroxymethylfurfural (5-HMF), said process comprising: a) contacting a feedstock (1) comprising 5-HMF and a polar aprotic synthesis solvent with an aqueous stream (21) to obtain at least one aqueous mixture (3); step b) of liquid-liquid extraction of the aqueous mixture (3) obtained at the end of step a) in the presence of an extraction solvent (4) to produce an aqueous raffinate (5) comprising the polar aprotic synthesis solvent, the organic extract (6), a solid particle fraction and optionally an intermediate liquid stream (19), wherein the aqueous raffinate (5) and / or the intermediate liquid stream (19) comprises the solid particle fraction, and then - step c) back-washing the organic extract (6) with an aqueous solvent (7) to produce an intermediate aqueous back-extract (9) containing 5-HMF and an organic solvent and an organic raffinate (8); an optional step d) of concentrating the organic raffinate (8) resulting from step c) by removing at least a portion of the organic solvent to produce a concentrated organic raffinate (10) comprising 5-HMF and residual organic solvent, and a first stream (11) comprising organic solvent; a hydrodistillation step e) carried out by distilling the organic raffinate (8) resulting from step c) or the concentrated organic raffinate (10) resulting from step d) in the presence of water to produce an aqueous solution of 5-HMF (12) and a second stream (13) comprising an organic solvent; - step f) of liquid-solid separation of the aqueous raffinate (5) resulting from step b) and / or the solid fraction in the intermediate liquid stream (19) resulting from step b) to produce a solid particle stream (18) and a solid particle-depleted aqueous raffinate (5') and / or a particle-depleted intermediate liquid stream (20) which is sent to step b), - step g) of treating at least one water-polar aprotic synthesis solvent mixture produced in said process, said mixture consisting of said particle-depleted aqueous raffinate (5') resulting from step f) or consisting of said aqueous raffinate (5) resulting from step b) free of said solid particle fraction, to produce at least one aqueous effluent (15) which can be recycled to said process.

2. 2. The process according to claim 1, wherein step b) produces an intermediate liquid stream (19) comprising the solid particle fraction, which is fed to step f) for separating the solid particle fraction from the intermediate liquid stream (19), a particle-depleted intermediate liquid stream (20) is formed and fed to step b), and the at least the water-polar aprotic synthesis solvent mixture consisting of the aqueous raffinate (5) resulting from step b) without the solid particle fraction is fed to step g).

3. 3. The process according to claim 2, wherein the intermediate liquid stream (19) sent to step f) is an intermediate aqueous raffinate comprising the solid particle fraction, which is produced in liquid-liquid extraction step b) by separation of the extraction solvent from the water-polar aprotic synthesis solvent mixture.

4. 3. The method of claim 2, wherein the intermediate liquid stream (19) sent to step f) is a three-phase mixture comprising a first liquid phase comprising 5-HMF and an extraction solvent, a second liquid phase comprising water and a polar aprotic synthesis solvent, and a solid phase comprising the solid particle fraction.

5. 2. The process according to claim 1, wherein the aqueous raffinate (5) produced in step b) comprises the solid particle fraction, and the aqueous raffinate (5) is sent to step f) for separating the solid particle fraction from the aqueous raffinate (5), forming a solid particle-depleted aqueous raffinate (5') which is sent to step g) as a water-polar aprotic synthesis solvent mixture.

6. 6. The method according to any one of claims 1 to 5, wherein step f) is carried out at a temperature between 0 and 60°C and preferably comprises filtration, preferably carried out by means of a filter press.

7. 7. The method according to claim 1, wherein step d) of concentrating the organic raffinate (8) resulting from step c) comprises vaporizing the organic solvent under atmospheric pressure or under vacuum, preferably at a pressure of 0.01 to 0.1 MPa, and at a liquid temperature maintained at or below 130°C, so that the concentrated organic raffinate (10) has a 5-HMF content of at least 40% by weight and a residual organic solvent content of at most 60% by weight.

8. The method according to any one of claims 1 to 7, wherein step e) is carried out at atmospheric pressure or under vacuum, preferably at a pressure of 0.001 to 0.1 MPa, preferably under vacuum at a pressure of 0.005 to 0.08 MPa.

9. 9. The process according to claim 1, wherein step e) is carried out in a distillation column, preferably at a bottom temperature of 140° C. or less.

10. 10. The method according to any one of claims 1 to 9, wherein the extraction solvent (4) is selected from dichloromethane, diethyl ether, diisopropyl ether, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, thiophene, anisole and toluene, preferably methyl isobutyl ketone.

11. 11. The method according to claim 1, wherein the weight ratio (wt / wt) of aqueous solvent (7) to organic extract (6) in backwashing step c) is between 0.04 and 5.

12. 12. The method of any one of claims 1 to 11, comprising a step of dehydrating sugars to 5-HMF upstream of step a) by contacting a sugar feedstock comprising one or more sugars with said polar aprotic synthesis solvent and a dehydrating acid catalyst, preferably at a temperature of from 30 to 200°C and a pressure of from 0.001 to 10 MPa.

13. 13. The method according to any one of claims 1 to 12, wherein the aqueous effluent produced in step g) is used in whole or in part in step a) and / or step c) and / or step e).

14. 14. The method according to any one of claims 1 to 13, wherein in step a) the aqueous stream (21) comprises all or part of the intermediate aqueous back extract (9) resulting from step c).

15. 15. The method according to any one of claims 1 to 14, wherein the polar aprotic synthesis solvent is selected from pyridine, butan-2-one, acetone, acetic anhydride, N,N,N',N'-tetramethylurea, benzonitrile, acetonitrile, methyl ethyl ketone, propionitrile, hexamethylphosphoramide, nitrobenzene, nitromethane, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane, N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate and γ-valerolactone, used alone or in mixtures, preferably dimethyl sulfoxide.

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