Method for producing aqueous solution of 5-hydroxymethylfurfural comprising liquid-liquid extraction step incorporating or followed by filtration

Abstract

The invention relates to a method for producing an aqueous solution of 5-hydroxymethylfurfural (5-HMF), which successively comprises a) bringing a raw material (1) containing 5-HMF and a polar aprotic synthetic solvent into contact with an aqueous stream, b) a step c) of liquid-liquid extraction with an organic extraction solvent followed by backwashing with an aqueous solvent to obtain an organic raffinate rich in 5-HMF and solvent. The concentratable organic raffinate is then subjected to a water distillation step e) to obtain an aqueous solution of 5-HMF. A liquid-solid separation step f) of a solid particle fraction formed from the precipitated humus and present in the aqueous raffinate (5) obtained from step b) and / or the intermediate liquid stream (19) obtained from step b) is carried out. The aqueous raffinate obtained from the liquid-liquid extraction step b), from which the precipitated humus is removed, is treated in a step g), which treats the 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). Prior Art

[0002] 5-HMF is an interesting compound derived from biomass and can be profitably used in many fields, especially in pharmaceuticals, agrochemicals or specialty chemicals. The production of 5-HMF by dehydration of sugars has been known for many years and has been the subject of numerous investigations.

[0003] There are many dehydration conditions, and in particular, the following methods may be mentioned, for example: - 5-HMF can be obtained in an aqueous medium, usually in the presence of an acid catalyst. This acid catalyst enables the dehydration of C6 sugars (especially fructose) to produce 5-HMF, but also catalyzes the rehydration of 5-HMF to produce formic acid and levulinic acid, which is very harmful to the yield.

[0004] - 5-HMF can also be obtained in a non-aqueous polar proton medium, using a solvent such as methanol, ethanol or acetic acid and in the presence of an acid catalyst. Under these conditions, 5-HMF is obtained as a mixture with ether or ester derivatives of 5-HMF, depending on the reaction medium used. The formation of these by-products is attributed to the reaction of 5-HMF with the reaction solvent in an acidic medium.

[0005] - Patent application 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. In this case, the presence of the catalyst also catalyzes the etherification reaction of 5-HMF with the alcohol to produce a mixture of 5-HMF and its methyl or ethyl ether forms, depending on the alcohol used as the solvent.

[0006] - 5-HMF can also be produced in a polar aprotic medium, with or without an acid catalyst. The use of dimethyl sulfoxide (DMSO) may be mentioned more particularly, which enables the production of 5-HMF in very good yields and without the above-mentioned undesirable reactions, in the presence or absence of an acid catalyst.

[0007] In addition, regardless of the synthesis medium (water, methanol, DMSO, etc.), polymeric by-products called humins are formed during the production of 5-HMF (van Dam, H.E.; Kieboom, A.P.G.; van Bekkum, H. (1986), The Conversion of Fructose and Glucose in Acidic Media: Formation of Hydroxymethylfurfural, In: Starch - Stärke, Vol. 38, No. 3, pp. 95-101).

[0008] The synthesis of 5-HMF in a medium such as DMSO is particularly advantageous because it allows 5-HMF in its alcohol form (rather than its ether form) to be obtained in very good yields. Nevertheless, the physico-chemical properties of DMSO (or any other polar aprotic solvent) make it difficult to separate it from 5-HMF by conventional methods known to those skilled in the art.

[0009] A known method for separating 5-HMF from DMSO is liquid-liquid extraction as described in patent FR2669635, followed by crystallization of the extract. The applicant has proposed an improvement to the method described in patent FR2669635, which is the subject of patent FR3071172. This improvement is based on a modification of the liquid-liquid extraction step, in particular by adding a step of backwashing with water and by recycling the backwash water upstream of the liquid-liquid extraction to mix it with the 5-HMF / DMSO feedstock, which mixture is optionally filtered before the liquid-liquid extraction. This improvement makes it possible to increase the purity of 5-HMF without loss of the yield of the product of interest and enables the 5-HMF crystallization step to be carried out under more favorable conditions.

[0010] However, despite the improvements provided by patent FR3071172, the crystallization of 5-HMF remains an expensive operation. The high production cost of 5-HMF limits its use and there is a need to develop methods that can reduce the cost.

[0011] In this regard, the French patent application No. 2114335 filed by the present applicant discloses a method for recovering 5-HMF not in crystalline form but in an aqueous solution, in particular by implementing a step of concentrating the organic raffinate obtained in the step of backwashing the extract containing 5-HMF obtained from liquid-liquid extraction, and a step of hydrodistilling the concentrated stream obtained from the said concentration step, so as 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 humic substances (solid particles) precipitated during the addition of water to the raw material (the step of mixing the raw material with the backwashing water) before sending the raw material to the liquid-liquid extraction. This is because the addition of water to the 5-HMF raw material sent to the liquid-liquid extraction can cause the precipitation of humic substances present in the raw material, which can cause operating problems during the liquid-liquid extraction process, such as clogging of equipment.

[0012] The applicant has demonstrated another method capable of recovering 5-HMF not in crystalline form but in an aqueous solution, which, like the method according to the French patent application No. 2114335 filed, opens up new possibilities for the utilization of 5-HMF in various applications or for subsequent conversions that cannot be carried out in DMSO or in the extraction solvent.

[0013] Furthermore, the method according to the present invention thus allows 5-HMF to be recovered in an aqueous solution while limiting the operating costs, water discharges and thus the environmental impact of the said method. The method according to the present invention also makes it possible to improve the removal of precipitated humic substances, in particular in order to protect the equipment used during the liquid-liquid extraction process or during downstream steps. This is because problems of humic substance precipitation may also occur during the liquid-liquid extraction step and adversely affect the liquid-liquid extraction operation as well as downstream operations receiving streams that may contain these precipitated humic substances, typically the treatment of the water-DMSO mixture obtained from the method. Summary of the Invention One subject of the present invention relates to a method for producing an aqueous solution of 5-HMF.

[0015] More particularly, the present invention relates to a method for producing an aqueous solution of 5-hydroxymethylfurfural (5-HMF), the method comprising the following steps: - Step a), contacting a raw material containing 5-HMF and a polar aprotic synthetic solvent with an aqueous stream to obtain at least one aqueous mixture; - Step b), performing liquid-liquid extraction on the aqueous mixture obtained at the end of step a) in the presence of an extraction solvent to produce an aqueous raffinate containing the said polar aprotic synthetic solvent, an organic extract, a solid particle fraction and an optional intermediate liquid stream, the aqueous raffinate and / or the intermediate liquid stream containing the solid particle fraction; then - Step c), backwashing the organic extract with an aqueous solvent to produce an intermediate aqueous back-extract and an organic raffinate containing 5-HMF and an organic solvent; - Optionally step d), concentrating the organic raffinate obtained from step c) by removing at least a portion of the organic solvent to produce a concentrated organic raffinate containing 5-HMF and a residual organic solvent, and producing a first stream containing the organic solvent; - A water distillation step e), which is carried out by distilling the organic raffinate obtained from step c) or the concentrated organic raffinate obtained from step d) in the presence of water to produce an aqueous solution of 5-HMF and a second stream containing the organic solvent; - Step f), liquid-solid separation of the solid fraction within the aqueous raffinate obtained from step b) and / or the intermediate liquid stream obtained from step b) to produce a solid particle stream and an aqueous raffinate depleted in solid particles and / or an intermediate liquid stream depleted in particles sent to step b); - Step g), treating at least one water-polar aprotic solvent mixture produced in the method, the mixture consisting of the aqueous raffinate depleted in particles and obtained from step f) or the aqueous raffinate not containing a solid particle fraction and obtained from step b), to produce at least one aqueous effluent recyclable to the method.

[0016] According to one or more embodiments, step b) produces an intermediate liquid stream containing a solid particle fraction, and the intermediate liquid stream is sent to step f) to separate the solid particle fraction from the intermediate liquid stream to form an intermediate liquid stream depleted in particles sent to step b), and at least the water-polar aprotic solvent mixture consisting of the aqueous raffinate not containing a solid particle fraction and obtained from step b) is sent to step g).

[0017] According to one or more embodiments, the intermediate liquid stream sent to step f) is an intermediate aqueous raffinate, which contains a solid particle fraction and is produced by separation between the extraction solvent and the water-polar aprotic solvent mixture in the liquid-liquid extraction step b).

[0018] According to one or more embodiments, the intermediate liquid stream sent to step f) is a three-phase mixture, which contains a first liquid phase containing 5-HMF and an extraction solvent, a second liquid phase containing water and a polar aprotic solvent, and a solid phase containing a solid particle fraction.

[0019] According to one or more embodiments, the aqueous raffinate produced in step b) contains a solid particle fraction, and the aqueous raffinate is sent to step f) to separate the solid particle fraction from the aqueous raffinate to form a solid particle-depleted aqueous raffinate, which is sent as a water-polar aprotic solvent mixture to step g).

[0020] According to one or more embodiments, step f) is carried out at a temperature between 0 and 60 °C and preferably comprises filtration, preferably by means of a filter press.

[0021] According to one or more embodiments, step d) of concentrating the organic raffinate obtained from step c) comprises vaporizing the organic solvent at atmospheric pressure or under vacuum, preferably at a pressure between 0.01 MPa and 0.1 MPa, and at a liquid temperature maintained at less than or equal to 130 °C, the concentrated organic raffinate containing a content of 5-HMF of greater than or equal to 40% by weight and a content of residual organic solvent of less than or equal to 60% by weight.

[0022] According to one or more embodiments, step e) is carried out at atmospheric pressure or under vacuum, preferably at a pressure between 0.001 MPa and 0.1 MPa, and preferably under a vacuum with a pressure of 0.005 MPa to 0.08 MPa.

[0023] According to one or more embodiments, step e) is carried out in a distillation column, preferably at a bottom temperature of less than or equal to 140 °C.

[0024] 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, and is preferably methyl isobutyl ketone.

[0025] According to one or more embodiments, in the backwashing step c), the weight ratio (weight / weight) of the aqueous solvent to the organic extract is between 0.04 and 5, preferably between 0.07 and 3, and preferably between 0.1 and 1.

[0026] According to one or more embodiments, the method comprises a step of dehydrating sugar to 5-HMF upstream of step a), preferably by contacting a sugar feedstock containing one or more sugars with the polar aprotic solvent and a dehydration acid catalyst, preferably at a temperature between 30 °C and 200 °C, preferably between 50 °C and 180 °C, preferably between 70 °C and 150 °C, preferably between 90 °C and 130 °C, and at a pressure between 0.001 MPa and 10 MPa, preferably between 0.001 MPa and 5 MPa, preferably between 0.01 MPa and 1 MPa.

[0027] According to one or more embodiments, all or part of the aqueous effluent produced in step g) is used in step a) and / or step c) and / or step e).

[0028] According to one or more embodiments, in step a), the aqueous stream comprises all or part of the intermediate aqueous back-extract obtained from step c).

[0029] 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, alone or as a mixture, and is preferably dimethyl sulfoxide.

[0030] According to one or more embodiments, the concentrated organic raffinate obtained at the end of the concentration step d) has a 5-HMF content between 40 wt% and 95 wt% and a residual organic solvent content between 5 wt% and 60 wt%, expressed relative to the weight of the concentrated organic raffinate.

[0031] According to one or more embodiments, the aqueous stream is fed to the water distillation step e).

[0032] According to one or more embodiments, step g) comprises treating one or more other water-polar aprotic synthesis solvent mixtures produced within the process.

[0033] Other subjects and advantages of the present invention will become apparent upon reading the following description of specific exemplary embodiments of the invention given as non-limiting examples, which description is made with reference to the drawings described below.

[0034] List of Drawings Figure 1 Illustrates an embodiment of the method according to the invention, in which a liquid-solid separation step f) is carried out on the intermediate liquid stream withdrawn in the liquid-liquid extraction step b) during the liquid-liquid extraction process.

[0035] Figure 2 Illustrates another embodiment of the method according to the invention, in which a liquid-solid separation step f) is carried out on the aqueous raffinate obtained at the end of the liquid-liquid extraction step b) downstream of the liquid-liquid extraction step b).

[0036] Figure 3 Illustrates another embodiment of the method according to the invention, which is as Figure 1The embodiments shown include a liquid-solid separation step f) carried out downstream of the liquid-liquid extraction step b), and include an additional liquid-solid separation step in the mixing step a) and various recycles of the aqueous stream into the process.

[0037] In the drawings, like reference numerals denote like or similar elements.

[0038] Description of Embodiments In the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the method. However, it will be apparent to one skilled in the art that the method may be practiced without necessarily using all of these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0039] It should be noted that throughout this specification, unless otherwise specified, the expression "between... and..." should be understood to include the recited limits.

[0040] In this specification, the term "comprising" is synonymous with "including" and "containing" (having the same meaning), and is inclusive or open-ended and does not exclude other unrecited elements. It is to be understood that the term "comprising" includes the exclusive and closed term "consisting of".

[0041] For the present invention, the various embodiments given may be used alone or in combination with each other, and there is no restriction on their combination where technically feasible.

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

[0043] In this specification, an aprotic solvent is understood to mean a molecule that acts as a solvent and all of whose hydrogen atoms are carried by carbon atoms.

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

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

[0046] For a better understanding of the present invention, reference numerals appearing in the drawings are hereinafter referred to in order to denote the various elements of the method, which does not constitute a limitation on Figure 1 、 2and the limitations of the specific embodiments shown in 3.

[0047] Optional step of dehydrating sugar 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 the step of dehydrating sugar to 5-HMF, which step is very advantageously 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 dehydrating acid catalyst to produce an effluent containing at least 5-HMF and a polar aprotic synthesis solvent, also referred to herein as the synthesis effluent, and advantageously corresponding to the feedstock 1 of the process according to the invention introduced in the mixing step a).

[0048] The process according to the invention can thus optionally comprise such a step of dehydrating sugar to 5-HMF located upstream of step a).

[0049] The polar aprotic synthesis solvent is advantageously selected from all polar aprotic solvents having a dipole moment greater than or equal to 2.00 expressed in Debye (D). Preferably, the polar aprotic solvent is selected from 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), alone or as a mixture.

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

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

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

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

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

[0055] Preferably, the dehydrating acid catalyst is selected from 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, p - toluenesulfonic acid, 4 - biphenylsulfonic acid, diphenyl phosphate, and 1,1'-binaphthalene - 2,2'-diyl hydrogen phosphate.

[0056] Preferably, the dehydrating 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 6 carbon atoms (hexoses), but this does not exclude the presence of sugars containing 5 carbon atoms (pentoses) in the form of oligosaccharides and monosaccharides in the raw materials. In particular, the term "sugar" refers to glucose or fructose, sucrose, alone or as a mixture, and oligosaccharides such as cellobiose, maltose, cellulose, or even inulin.

[0058] The sugar raw material used can be sugar in solid form, or an aqueous solution of sugar known as syrup, which preferably contains at least 30% by weight of sugar, more preferably at least 50% by weight, and even more preferably at least 70% by weight of sugar. For example, sucrose is usually produced in solid form, while glucose or fructose, alone or as a mixture, is usually produced in the form of an aqueous solution (syrup), such as having 70% by weight of sugar.

[0059] The optional dehydration step is carried out at a temperature between 30 and 200 °C, preferably between 50 and 180 °C, preferably between 70 and 150 °C, and preferably between 90 and 130 °C, for example, at a temperature of 120 °C. Preferably, the optional dehydration step is carried out at a pressure between 0.001 MPa and 10 MPa, preferably between 0.001 MPa and 5 MPa, preferably between 0.01 MPa and 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 when the first bubble appears in the liquid. When the reaction medium is above the bubble point of the mixture, the gas 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 at a molar ratio of the catalyst to the sugar raw material (expressed as acid / sugar and represented as mole percentage (mol%)) between 0.01 and 10 mol%, preferably between 0.05 and 8 mol%, preferably between 0.1 and 6 mol%, preferably between 0.2 and 5 mol%, preferably between 0.3 and 4 mol%, and very preferably between 0.5 and 3 mol%.

[0061] The optional dehydration step can be carried out according to various embodiments. Thus, this step can be advantageously carried out discontinuously or continuously (the discontinuous mode is called the "batch mode"). The addition of the sugar raw material can be gradual in the case of batch implementation (fed-batch), or staged in different CSTR reactors (continuous stirred tank reactors) in series in the case of continuous implementation. The method can be carried out in a closed reaction chamber or in a semi-open reactor.

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

[0063] The 5-HMF constitutes more than 1% by weight, preferably more than 10% by weight, preferably more than 15% by weight, and preferably less than 50% by weight, preferably less than 40% by weight, preferably less than 30% by weight of the synthetic effluent obtained from an optional dehydration step and treated in step a) of the process according to the invention.

[0064] Furthermore, the synthetic effluent obtained from the optional dehydration step may contain water even before being mixed with the aqueous stream 21 in step a). The water may originate from the dehydration step: for example, water is formed during the dehydration reaction of sugar to 5-HMF (producing 3 moles of water per mole of 5-HMF). In the case where syrup (e.g., about 70% by weight in water) is used for practical reasons, this water may also be introduced together with the sugar. Advantageously, during the optional dehydration step, a water-polar aprotic synthetic solvent (e.g., DMSO) mixture can be recovered in the gas phase. The water-polar aprotic synthetic solvent (e.g., DMSO) mixture can be advantageously sent to step g). Thus, the synthetic effluent obtained from the optional dehydration step and introduced as feedstock 1 into step a) may contain water in a proportion generally between 0.1% by weight and 30% by weight, preferably between 0.1% by weight and 15% by weight, more preferably between 0.1% by weight and 10% by weight.

[0065] It may be advantageous to simultaneously extract water from the reaction medium during an optional dehydration step to reduce the water content in the reaction medium and thereby improve the selectivity of the reaction. The 5-HMF selectivity is understood to be the ratio of the number of moles of 5-HMF produced to the number of moles of fructose converted in the sugar feedstock introduced into the process. In a polar aprotic medium, the presence of water reduces the selectivity of sugar conversion in such a way that the higher the sugar concentration in DMSO, the more notable this is. Thus, this continuous water extraction during 5-HMF synthesis is advantageous in this regard and also enables the extraction of water that may be present in the sugar feedstock (in syrup form if there is water). During this extraction of water from the reaction medium, the reaction medium is above the bubble point of the mixture. The gas phase can be removed from the reactor, rectified, and condensed to form a water condensate containing less than 10 wt%, preferably less than 5 wt% or even less than 1 wt% of the polar aprotic synthesis solvent. The extracted water can be derived from dehydration and / or introduced with the sugar feedstock in cases where syrup-form feedstock is used for practical reasons. Advantageously, at least 50 wt%, preferably at least 80 wt% or even 90 wt% of the water present in the reaction medium is extracted. The water extracted from the reaction medium can constitute at least 50 wt%, preferably at least 80 wt% or even 90 wt% 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 advantageously by distillation, which requires the polar aprotic synthesis solvent to be less volatile than water. Advantageously, water is extracted under conditions such that at least 90 wt%, preferably at least 95 wt% or even 99 wt% of the polar aprotic synthesis solvent used in the dehydration step can be recovered in the synthesis effluent obtained at the end of the optional dehydration step. The water thus extracted can be recycled to one or more steps of the process that require an aqueous feed stream, like the aqueous effluent 15 obtained from step g) of treating the water - polar aprotic synthesis solvent mixture, or mixed with said recyclable aqueous effluent 15, or sent to step g) for treatment to remove any polar aprotic synthesis solvent it may still contain, in particular to produce said recyclable aqueous effluent 15.

[0066] When the sugar raw material is in the form of syrup, it may be advantageous to reduce the water content present upstream of the optional step of dehydrating the sugar raw material and optionally by extraction of the water generated by the dehydration reaction during the dehydration step as already described above and not repeated here. Thus, the water of the sugar raw material in syrup form can be extracted and replaced with a polar aprotic synthetic solvent, and a mixture sent to the dehydration step is obtained. The water in the syrup can be extracted at least partially after mixing the syrup with the polar aprotic synthetic solvent. The solvent enables the sugar to be maintained in a dilution medium and dilution with the synthetic solvent replaces dilution with water. The water can be extracted by various methods such as evaporation, adsorption (e.g., in molecular sieves), membrane separation, and advantageously by distillation, which requires that the polar aprotic synthetic solvent be less volatile than water. Advantageously, the extracted water constitutes 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 can constitute 90% to 99% by weight of the water of 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 the synthetic solvent. The water thus extracted can be recycled to one or more steps of the process that require an aqueous stream to be supplied, or mixed with the recyclable aqueous effluent 15, or sent to step g) for treatment and removal of the polar aprotic synthetic solvent that it may still contain, in particular to produce the recyclable aqueous effluent 15.

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

[0068] Before introducing the synthetic effluent obtained from an optional dehydration step as feedstock 1 into step a), an optional neutralization step can be carried out, and the synthetic effluent contains a dehydrated acid catalyst. This makes it possible to reduce the reactivity of the medium and thus avoid the degradation mechanism of 5-HMF or reduce the corrosion of the equipment materials downstream of the optional dehydration step. Since several organic acids may be produced in the dehydration reaction, the amount of the neutralizing agent can advantageously enable the neutralization of all the acids present in the synthetic effluent obtained from the dehydration step. Such a neutralization step is advantageously carried out at least in a stoichiometric ratio of the amount of the catalyst used. Since several organic acids may be produced in the dehydration reaction, this neutralization is usually carried out slightly supra-stoichiometrically with respect to the catalyst used, preferably between 1 and 2 times the stoichiometric ratio, preferably between 1 and 1.5 times the stoichiometric ratio. The neutralizing agent can be a basic compound selected from NaOH, KOH, NH4OH, Na2CO3, K2CO3, NaHCO3, KHCO3, Mg(OH)2, Ca(OH)2, Ba(OH)2.

[0069] Mixing step a) The method according to the invention comprises bringing into contact (or mixing) feedstock 1 optionally obtained from a dehydration step and containing 5-HMF and a polar aprotic synthetic solvent with an aqueous stream 21 to obtain at least one aqueous mixture 3.

[0070] The aqueous stream 21 can consist of pure water external to the method or water recycled from the method. For example, the aqueous stream 21 can advantageously contain all or part of the intermediate aqueous back-extract 9 obtained from step c) and / or all or part of the water 15 produced in step g) of treating the water-polar aprotic synthetic solvent mixture.

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

[0072] Preferably, the polar aprotic synthetic solvent (such as DMSO) constitutes 30% to 95% by weight, preferably 40% to 90% by weight, preferably 50% to 90% by weight, and preferably 55% to 85% by weight of the feedstock 1 introduced into step a).

[0073] The feedstock 1 introduced into step a) can also contain water, and its proportion is preferably between 0.1% and 30% by weight, preferably between 0.1% and 15% by weight, and more preferably between 0.1% and 10% by weight.

[0074] The feedstock 1 can also optionally contain humus. The humus particularly constitutes less than 30% by weight, preferably less than 20% by weight of the feedstock 1.

[0075] The aqueous stream 21 thus contains water and can consist of water. When the aqueous stream 21 contains a portion of recycled process water, said portion can contain at least 60 wt% water, preferably at least 70 wt%, more preferably at least 80 wt%, still more preferably at least 95 wt% or even 98 wt% water. The aqueous stream 21 can contain all or a portion of the intermediate aqueous anti-extract 9 obtained from step c). The intermediate aqueous anti-extract 9 contains water, a polar aprotic synthetic solvent (such as DMSO), and optionally 5-HMF. Advantageously, the intermediate aqueous anti-extract 9 contains greater than 60 wt% water, preferably greater than 70 wt% water, and preferably greater than 80 wt% water.

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

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

[0078] By increasing the water content of feedstock 1 during step a), a portion of the humus present in feedstock 1 can precipitate. The mixture resulting from the contact of said feedstock 1 with the aqueous stream 21 can thus advantageously undergo a liquid-solid separation step before being sent to the liquid-liquid extraction step b) to obtain a liquid separated from suspended solid particles and a solid residue containing humus and preferably removed from the process in the form of solid stream 2. This optional liquid-solid separation step thus enables the removal of humus that has precipitated in step a) or upstream. Then, at least a portion of the resulting liquid is advantageously sent to the liquid-liquid extraction step b), and the portion (or preferably all) of the liquid advantageously sent to step b) corresponds to the aqueous mixture 3. When the amount of humus precipitated in the mixture formed by feedstock 1 and the aqueous stream 21 in step a) is, for example, greater than 1 wt%, this liquid-solid separation step in step a) can be advantageously implemented. This optional liquid-solid separation step is preferably carried out at a temperature between 0 and 60 °C, preferably between 5 and 40 °C, and typically at ambient temperature (i.e., between 10 and 40 °C). This optional liquid-solid separation step before 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 by using a filter press, belt filter, clarifier, settler, centrifuge, such as a disc stack centrifuge, and said techniques can be used alone or in any combination in any order. Preferably, this liquid-solid separation step is filtration, preferably carried out using a filter press.

[0079] Liquid-liquid extraction step b) The method according to the invention comprises step b) of subjecting the aqueous mixture 3 obtained at the end of step a) to a liquid-liquid extraction 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 the extraction solvent 4. This technique is well known to those skilled in the art. It can be carried out, for example, in an array of mixer-settlers, in a column filled with random packing or structured packing, in a pulsed column or even in a stirred column.

[0081] The liquid-liquid extraction may comprise implementing at least two theoretical separation stages. For example, this is the case when carrying out a liquid-solid separation step f) on an intermediate liquid stream 19 obtained from the liquid-liquid extraction step b), as described in further detail below in step f), which, once the solid particles have been removed, is sent back to step b). Thus, a first liquid-liquid separation stage can be carried out to produce said intermediate liquid stream 19, which is sent to the liquid-solid separation step f) to form a particle-depleted intermediate liquid stream 20, which is sent to a second liquid-liquid extraction stage 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, and generally at ambient temperature (i.e., between 10 and 40 °C).

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

[0084] The extraction solvent introduced into step b) is selected from water-immiscible organic solvents to form two liquid phases in steps b) and the backwashing step c). This property highly depends on the relative proportions of the raw materials used in the method, the flow rates of the stripping water and the extraction solvent.

[0085] Without limitation, 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 denoted 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. Very preferably, the extraction solvent is methyl isobutyl ketone.

[0086] Advantageously, the extraction solvent is selected to: - Have a very large volatility difference with 5-HMF, especially to facilitate its removal in optional step d) and limit the degradation of 5-HMF, i.e., have a vaporization rate in step d) to avoid the degradation of 5-HMF and minimize the amount of residual solvent to be removed in step e), while ensuring no liquid phase separation when the concentrated organic raffinate 10 contacts water in step e), and - Form a heterogeneous azeotrope with water in step e), which preferably is rich in the solvent, i.e., has more than 50 wt% of the solvent, preferably has more than 60 wt% of the solvent, and preferably has more than 70 wt% of the solvent. Advantageously, the boiling point temperature of the azeotrope of the water / extraction solvent mixture is significantly lower than the boiling point temperature of water, preferably at least 5 °C lower than the boiling point temperature of water, preferably at least 8 °C lower than the boiling point temperature of water, and preferably at least 10 °C lower than the boiling point temperature of water.

[0087] Advantageously, the organic solvent stream produced in subsequent steps can be recycled as the extraction solvent to extraction step b). These organic solvent streams may contain impurities that may have been generated during the implementation of the method. Advantageously, the organic solvent stream produced in subsequent steps can be, for example, periodically distilled to avoid the accumulation of said impurities.

[0088] Step b) thus makes it possible to first obtain an aqueous stream poor in 5-HMF, called aqueous raffinate 5, which contains most of the polar aprotic synthetic solvents (such as DMSO) initially contained in feedstock 1, and secondly obtain an organic stream rich in 5-HMF, called organic extract 6, which contains most of the 5-HMF and the extraction solvent 4 initially contained in feedstock 1. This organic extract 6 may also contain polar aprotic synthetic solvents (such as DMSO). Preferably, the organic extract preferably contains 5-HMF and a polar aprotic synthetic solvent (such as DMSO) in a 5-HMF / polar aprotic synthetic solvent (such as DMSO) weight ratio between 50 / 50 and 99 / 01, preferably between 50 / 50 and 95 / 05, preferably between 55 / 45 and 90 / 10, more preferably between 60 / 40 and 85 / 15, and preferably between 65 / 35 and 80 / 20.

[0089] Advantageously, the organic extract 6 is directly sent to backwashing step c).

[0090] There is also a solid particle fraction formed by precipitated humic substances in step b). These can be humic substances precipitated in the upstream mixing step a) and still present in the aqueous mixture 3 sent to step b), or humic substances precipitated in step b) or in backwashing step c).

[0091] The solid particle fraction can be suspended in the optional intermediate liquid stream 19 formed in step b) and / or in the aqueous stream 15. When the aqueous stream 15 contains the solid particle fraction, the aqueous stream 15 is sent to the liquid-solid separation step f) further described below.

[0092] Backwashing step 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 and an organic raffinate 8 comprising 5-HMF and the organic solvent. Advantageously, part or all of the intermediate aqueous back-extract 9 is sent to step a). The organic solvent consists in particular at least in part of the extraction solvent and may optionally contain a polar aprotic synthetic solvent (such as DMSO), preferably in small amounts.

[0093] The introduction of the aqueous solvent 7 in step c) is carried out according to the general knowledge of a person skilled in the art for backwashing.

[0094] The introduction of the aqueous solvent 7 is carried out so that the amount of the aqueous solvent is as low as possible to reduce costs, but sufficient to ensure a low weight content of the polar aprotic synthetic solvent (such as DMSO) in the organic raffinate 8, and preferably less than or equal to 20.0% by weight, preferably less than or equal to 15.0% by weight, preferably between 0.01% by weight and 15.0% by weight, very preferably between 0.01% by weight and 10.0% by weight, based on the weight of 5-HMF.

[0095] Advantageously, the aqueous backwashing solvent 7 introduced in step c) contains at least 95% by weight of water, preferably at least 98% by weight of water (100% being the maximum).

[0096] The aqueous solvent may optionally comprise a polar aprotic synthetic solvent (e.g., DMSO). The lower the amount of the polar aprotic synthetic solvent (e.g., DMSO) present in the aqueous backwashing solvent, the higher the backwashing efficiency. The aqueous solvent may comprise up to 1.0 wt%, and preferably up to 0.1 wt% of the polar aprotic synthetic solvent (e.g., DMSO). Advantageously, the aqueous backwashing solvent is derived from step g) of treating the water-polar aprotic synthetic solvent mixture generated in the process, and thus comprises at least a portion of the recyclable effluent 15. In a preferred embodiment of the present invention, the aqueous raffinate 5 composed of water and a polar aprotic synthetic solvent (e.g., DMSO) generated in step b), or the particle-depleted aqueous raffinate 5' generated in step f), is treated in step g) advantageously comprising distillation. The water-rich distillate obtained at the end of this step g), also referred to as the aqueous effluent 15 recyclable to the process, is advantageously used to form the aqueous backwashing solvent 7 in step c), optionally as a mixture with makeup water 22, or for mixing step a) to form the aqueous stream 21, optionally together with at least one intermediate aqueous back-extraction fraction 7 and / or makeup water. The recyclable effluent 15, such as the water-rich distillate, may also contain residual amounts of the polar aprotic synthetic solvent (e.g., DMSO), preferably less than or equal to 1 wt% and preferably less than or equal to 0.1 wt%. The more efficiently the distillation in step g) is carried out, the proportionally lower the residual amount of the polar aprotic synthetic solvent (e.g., DMSO) in the aqueous effluent 15 (distillate), especially at a distillation stage number greater than 5 and with an advantageously suitable reboil rate and reflux ratio.

[0097] The backwashing step c) is advantageously a liquid-liquid extraction of the organic stream countercurrent to the aqueous solvent 7, in particular the organic extract 6 obtained in step b). This technique is well known to those skilled in the art. The extraction can be carried out, for example, in a mixer-settler array, in a column filled with random packing or structured packing, in a pulsed column or even in a stirred column.

[0098] Step c) is preferably carried out at a temperature between 0 and 60 °C, preferably between 5 and 40 °C, and typically at ambient temperature (i.e., between 10 and 40 °C).

[0099] The weight ratio (weight / weight) of the aqueous solvent 7 to the organic extract 6 is preferably between 0.04 and 5, preferably between 0.07 and 3, and preferably between 0.1 and 1.

[0100] Step c) enables an aqueous stream (referred to as intermediate aqueous anti-extract 9, which preferably contains at least 60% by weight of water, preferably at least 80% by weight of water) that is advantageously rich in polar aprotic synthesis solvents (such as DMSO) and an organic raffinate 8 that is advantageously poor in polar aprotic synthesis solvents (such as DMSO) to be obtained. The intermediate aqueous anti-extract 9 is advantageously partially or preferably entirely sent to step a). The resulting organic raffinate 8 has a weight content of polar aprotic synthesis solvents that is preferably less than or equal to 20.0% by weight, preferably less than or equal to 15.0% by weight, more preferably less than or equal to 5.0% by weight, even more preferably less than or equal to 4.0% by weight, and more preferably less than or equal to 3.0% by weight based on the weight of 5-HMF.

[0101] According to the invention, the organic raffinate 8 produced in step c) is sent to an optional concentration step d) or directly to a water distillation step e).

[0102] Humic substances may still be present in the organic extract 6 sent to the backwashing step c). If they precipitate in this step and then form undesirable solid particles, these can be removed in the liquid-solid separation step f) by sending all or part of the intermediate aqueous anti-extract 9 containing the precipitated humic substances to step b), and then it can be sent to the liquid-solid separation step f) together with the intermediate liquid stream 19 and / or the aqueous raffinate 5. If all or part of the intermediate aqueous anti-extract 9 is sent to step a) to enter the composition or form the aqueous stream 21, the precipitated humic substances can also be separated during the optional liquid-solid separation in step a) or in step f) as already described above and further detailed below.

[0103] Optional concentration step d) The method according to the invention preferably includes a step d) of concentrating the organic raffinate 8 obtained from step c) by removing a part of the organic solvent to produce a concentrated organic raffinate 10 containing 5-HMF and the residual organic solvent, and a first stream 11 containing the organic solvent and preferably consisting of the organic solvent, and the organic solvent is advantageously composed of all or part of the extraction solvent and an optional polar aprotic synthesis solvent (such as DMSO).

[0104] Preferably, the first stream 11 containing the organic solvent is recycled in whole or in part to the extraction step b), for example, to form at least a part of the organic solvent stream 4.

[0105] Preferably, in step d), the removal of a part of the organic solvent is carried out by vaporization (such as in an atmospheric or vacuum distillation column, in an evaporator) or by any method known to those skilled in the art.

[0106] According to this preferred embodiment, the vaporization of the organic solvent advantageously takes place at atmospheric pressure or under vacuum, preferably under a pressure between 0.01 MPa and 0.1 MPa, preferably under a vacuum with a pressure between 0.01 MPa and 0.09 MPa, to limit the temperature of the liquid and thus limit the degradation of 5-HMF. Preferably, the temperature of the liquid is maintained at less than or equal to 130 °C, preferably at less than or equal to 100 °C, preferably at less than or equal to 70 °C. The pressure level, especially the vacuum level, to be applied to reach these temperatures depends of course on the organic solvent and more particularly on the extraction solvent used and the vaporization rate of the organic solvent.

[0107] In a preferred embodiment, the vaporization of the solvent is carried out by multi-effect evaporation or mechanical vapor recompression or any other method known to those skilled in the art, to reduce the operating costs associated with the evaporation of the solvent while limiting the risk of degradation of the product of interest (i.e., 5-HMF). For example, in the case of a triple-effect evaporator, the liquid temperature is maintained below 130 °C in the first effect, below 100 °C in the second effect, and below 70 °C in the third effect. Thus, as 5-HMF is concentrated in the organic solvent, the temperature of the liquid phase is gradually reduced, thereby limiting any risk of degradation.

[0108] Optional step d) is carried out at a vaporization mass ratio (or evaporation rate) 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%, and preferably at most 99%, which corresponds to the mass of the vaporized organic solvent / the mass of the organic raffinate 8 obtained from step c) (more particularly, the mass-based quantity of stream 11 / the mass-based quantity of organic raffinate 8). Advantageously, the vaporization rate is defined according to the extraction solvent so as not to degrade 5-HMF but also to minimize the amount of residual solvent to be removed in step e), while ensuring that there is no liquid phase separation when the concentrated organic raffinate 10 comes into contact with water in step e) (i.e., ensuring that the liquid phase remains single-phase).

[0109] By means of the combination of all operating conditions of the aforementioned steps a), b) and c) and optionally step d), the concentrated organic raffinate 10 obtained at the end of step d) very advantageously has a 5-HMF content of at least 40% by weight, preferably at least 50% by weight, preferably at least 60% by weight, and preferably at most 95% by weight, preferably at most 90% by weight and preferably at most 85% by weight, based on the weight of the concentrated organic raffinate. In other words, the concentrated organic raffinate 10 preferably has a residual organic solvent content of at least 5% by weight, preferably at least 10% by weight, and preferably at most 60% by weight, preferably at most 50% by weight, preferably at most 40% by weight, based on the weight of the concentrated organic raffinate.

[0110] Advantageously, the organic solvent vaporized during the optional step d) forms a first stream 11, which contains the organic solvent, preferably consists of the organic solvent, and is preferably recycled to the extraction step b).

[0111] Advantageously, the concentrated organic raffinate 10 is sent to a water distillation step e).

[0112] Water distillation step e) The method according to the invention includes a water distillation step e), which is carried out by distilling the concentrated organic raffinate 10 obtained from the optional step d) or the organic raffinate 8 obtained from step c) in the presence of water to produce an aqueous solution of 5-HMF and a second stream 13 containing the organic solvent, preferably consisting of the organic solvent.

[0113] The water distillation step e) can advantageously at least partially remove the residual organic solvent that was not removed during the optional step d). The residual organic solvent removed during step e), i.e., the second stream 13 containing the organic solvent, can advantageously be recycled to the extraction step b) either alone or as a mixture with the first stream 11 obtained from the optional step d).

[0114] Advantageously, an aqueous liquid 14 is fed into the water distillation step e). The aqueous liquid 14 introduced in step e) preferably contains more than 95% by weight of water, preferably more than 98% by weight of water.

[0115] In a particular embodiment of the invention, the aqueous liquid 14 is pure water, possibly from outside the process, which can further minimize the content of residual polar aprotic synthetic solvents (such as DMSO) in the aqueous 5-HMF solution 12 produced in step e).

[0116] In another specific embodiment of the present invention, the water separated in the method is used for feeding step e) so as to be able to limit the operating costs of the method and its environmental impact. Generally, if the method integrates the preparation of raw material 1 and the sugar raw material used for the dehydration step is a syrup at 70% by weight in water, there is approximately 1 ton of water (the water in the sugar raw material and the water generated during the dehydration reaction) at the end of the dehydration step for every 1 ton of 5-HMF produced. This water, which is advantageously recovered, needs to be treated before being discharged into the environment. The method according to the present invention can then advantageously use the water obtained from the sugar raw material and / or the dehydration step to produce an aqueous solution of 5-HMF concentrated to preferably 30% by weight or more, preferably concentrated to 40% by weight or more, at the end of step e), and thus reduce the reprocessing costs of the method and its environmental impact.

[0117] Advantageously, the aqueous liquid 14 introduced into step e) can correspond to at least a part, optionally all, of the aqueous effluent 15 (distillate) generated in step g). The distillate may optionally contain a residual amount of a polar aprotic synthetic solvent (such as DMSO).

[0118] Advantageously, during step e), the extraction solvent used in the method forms a heterogeneous azeotrope with water, which azeotrope is preferably rich in the extraction solvent, preferably contains more than 50% by weight of the extraction solvent, preferably more than 60% by weight of the extraction solvent, and preferably more than 70% by weight of the extraction solvent. Advantageously, the boiling temperature of the water / extraction solvent azeotrope is significantly lower than the boiling temperature of water, preferably at least 5 °C lower than the boiling temperature of water, preferably at least 8 °C lower than the boiling temperature of water, and preferably at least 10 °C lower than the boiling temperature of water.

[0119] Therefore, after bringing the concentrated organic raffinate 10 or the organic raffinate 8 into contact with the aqueous liquid 14, the residual organic solvent can be easily removed without degrading 5-HMF.

[0120] The water distillation step e) can be carried out at atmospheric pressure or under vacuum, and in particular under a pressure between 0.001 MPa and 0.1 MPa, and preferably under a vacuum at a pressure between 0.005 MPa and 0.08 MPa. Advantageously, the water distillation step is carried out under vacuum, in particular between 0.001 MPa and 0.1 MPa, preferably between 0.005 MPa and 0.08 MPa, to facilitate the removal of the residual organic solvent without degrading 5-HMF.

[0121] Advantageously, the water distillation step e) is carried out in a distillation column at a bottom temperature of preferably less than or equal to 140 °C, preferably less than or equal to 130 °C, preferably less than or equal to 120 °C, preferably less than or equal to 110 °C, and preferably less than or equal to 100 °C to promote the removal of residual organic solvents without degrading 5-HMF.

[0122] In a particular embodiment, the concentrated organic raffinate 10 or the additional organic raffinate 8 and the aqueous liquid 14 are mixed before being introduced into the distillation column, and the mixture is introduced at an intermediate point of the distillation column.

[0123] In another particular embodiment, the concentrated organic raffinate 10 or the organic raffinate 8 is introduced into the upper part of the distillation column, preferably into the upper half of the distillation column, while the aqueous liquid is also introduced into the distillation column. Then the mixing with the aqueous liquid is carried out inside the distillation column.

[0124] Taking into account the formation of a heterogeneous azeotrope between water and the extraction solvent, the condensation of the overhead vapor of the distillation column produces two liquid phases: a water-rich phase, which can advantageously be returned as reflux to the column, and an organic solvent-rich phase, which can advantageously be recycled to the extraction step b).

[0125] According to the invention, the aqueous solution 12 of 5-HMF obtained at the end of step e) has an amount of 5-HMF of at least 30% by weight, preferably at least 40% by weight, and preferably less than 90% by weight, preferably less than 85% by weight, and preferably less than 80% by weight, said percentages being given by the weight of 5-HMF relative to the weight of the aqueous solution of 5-HMF obtained at the end of step e).

[0126] The process according to the invention is thus capable of very advantageously producing an aqueous solution of 5-HMF having a weight content of polar aprotic synthesis solvent (such as DMSO) of less than or equal to 10% by weight, preferably less than or equal to 5% by weight, and preferably less than or equal to 3% by weight relative to the weight of 5-HMF.

[0127] Liquid-solid separation step f) According to the invention, the process comprises a liquid-solid separation step f) of at least one of the intermediate liquid stream 19 or the (final) aqueous raffinate 5 obtained from the liquid-liquid extraction step b) so as to be able to reduce the content of solid particles formed by precipitated humic substances.

[0128] Irrespective of precipitation that may occur in or upstream of step a), the liquid-liquid extraction step b) can induce solid precipitation, namely precipitated humus, and the solid particle fraction generated during the liquid-liquid extraction or not removed by possible liquid-solid separation in step a) can cause the problems already described. To protect the equipment downstream of the liquid-liquid extraction step, and in particular in step g) of treating the water-polar aprotic solvent mixture and the equipment that may be used at the end of the liquid-liquid extraction, the separation of the precipitated solids proves necessary.

[0129] This separation is carried out on the intermediate liquid stream 19 (if this is produced in step b)), or on the (final) aqueous raffinate 5 produced in the liquid-liquid extraction step b), or on both.

[0130] This liquid-solid separation step f) is preferably carried out at a temperature between 0 and 60 °C, preferably between 5 and 40 °C, and generally at ambient temperature (i.e., between 10 and 40 °C).

[0131] This 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, such as using a filter press, belt filter, clarifier, settler, centrifuge, such as a disc stack centrifuge, and the separation techniques are used alone or in any order in combination. Preferably, this liquid-solid separation step is filtration, preferably carried out using a filter press.

[0132] The liquid-solid separation in step b) can include adding additives that promote liquid-solid separation, such as adding diatomaceous earth in the case of filtration, in order to, for example, accelerate filtration or improve filtration in the case where the solid particles are too sticky.

[0133] According to one or more embodiments, such as, for example Figure 1 or Figure 3 as shown in, step b) produces an intermediate liquid stream 19 containing the solid particle fraction, and the intermediate liquid stream 19 is sent to step f) to separate the solid particle fraction from the 19 and form a particle-depleted intermediate liquid stream 20, which is sent to step b), usually to a second liquid-liquid extraction stage. The final aqueous raffinate 5 obtained from step b) and sent to step g) does not contain the solid particle fraction obtained from step b); in fact, the precipitated humus has been removed by separating the intermediate liquid stream 19.

[0134] According to one or more embodiments, the intermediate liquid stream 19 sent to step f) is an intermediate aqueous raffinate containing a solid particle fraction, which is produced by the separation between the extraction solvent and the water-polar aprotic solvent mixture in the liquid-liquid extraction step b).

[0135] Alternatively, the intermediate liquid stream 19 sent to step f) is a three-phase mixture comprising a first liquid phase containing 5-HMF and an extraction solvent (which may be referred to as the intermediate extract), a second liquid phase containing water and a polar aprotic synthetic solvent (which may be referred to as the intermediate raffinate), and a solid phase containing a solid particle fraction.

[0136] A three-phase centrifuge can then advantageously be used to separate the three phases in a single piece of equipment: the intermediate raffinate, the intermediate extract, and the solid phase containing the precipitated humus (solid particle stream 18). Such an apparatus for step f) can be an apparatus used in the stage of liquid-liquid extraction b). The intermediate raffinate and the intermediate extract are used to form the aqueous raffinate 5 and the organic extract 6, respectively.

[0137] According to one or more embodiments, as for example Figure 2 shown, the aqueous raffinate 5 produced in step b) contains the solid particle fraction, and the aqueous raffinate 5 is sent to step f) to separate the solid particle fraction from the aqueous raffinate 5 and form a solid particle-depleted aqueous raffinate 5', which is sent as a water-polar aprotic synthetic solvent mixture to step g).

[0138] According to one or more embodiments, if the intermediate liquid stream 19 and the final aqueous raffinate 5 produced in step b) each contain solid particles formed from precipitated humus, then step f) is carried out separately on both of these effluents. In this case, a solid particle-depleted aqueous raffinate is produced and sent as a water-polar aprotic synthetic solvent mixture to step g).

[0139] The intermediate liquid raffinate / intermediate aqueous raffinate / aqueous raffinate depleted in solid particles (precipitated humus) is understood to mean a raffinate containing less than 10% by weight, preferably less than 5% by weight, and more preferably less than 1% by weight of solid particles formed from precipitated humus.

[0140] Step g) of treating the water-polar aprotic synthetic solvent mixture The method according to the invention comprises step g) of treating a water-polar aprotic synthetic solvent (such as DMSO) mixture produced by the steps of the method according to the invention to produce an aqueous effluent (also referred to as a distillate), which can be used in whole or in part for backwashing step c) and / or for step a) and / or for step e). This step can also produce a stream 16 rich in polar aprotic synthetic solvent (such as DMSO) and an impurity stream 17. At least one water-polar aprotic synthetic solvent mixture produced in the method is thus treated in step g). The mixture can be the solid particle-depleted aqueous raffinate 5' obtained from step f) or the aqueous raffinate 5 not containing a solid particle fraction obtained from step b).

[0141] This step in particular enables the separation of water, polar aprotic synthetic solvent and reaction products extracted in the raffinate, such as unconverted sugars, sugar oligomers, residual 5-HMF, in said at least one mixture (aqueous raffinate 5' poor in particles obtained from step f) or aqueous raffinate 5 not containing a solid particle fraction obtained from step b)).

[0142] One or more other water-polar aprotic synthetic solvent mixtures generated within the process can be sent to step g).

[0143] If the process integrates the step of synthesizing feedstock 1, i.e., the step of dehydrating the sugar feedstock as described above, and (i) this step includes simultaneously extracting water from the reaction medium or (ii) in the case where the sugar feedstock is initially in syrup form, a step of separating the water contained in the sugar feedstock (which includes extracting the water of the syrup and replacing it with a polar aprotic synthetic solvent) is carried out before this reaction step of dehydrating the sugar feedstock, then the stream 16 rich in synthetic solvent can remove its water while extracting water in both cases (i) and (ii).

[0144] According to the knowledge of those skilled in the art, the more efficiently the distillation is carried out, the lower the residual amount of polar aprotic synthetic solvent (such as DMSO) in the aqueous effluent generated at the end of step g) proportionally.

[0145] The water-polar aprotic synthetic solvent (such as DMSO) mixture generated by the process particularly refers to the aqueous raffinate 5 generated in step b) and poor in solid particles in step f), and optionally, the water-polar aprotic synthetic solvent (such as DMSO) mixture obtained from an optional step of dehydrating sugar to 5-HMF (when the process integrates such a step).

[0146] The step g) of treating the water-polar aprotic synthetic solvent (such as DMSO) mixture preferably uses an evaporation section of the water-polar aprotic synthetic solvent (such as DMSO) mixture to remove any impurities in the form of stream 17, particularly heavy impurities such as humus or unconverted sugars, followed by a distillation section.

[0147] The evaporation section operates at a temperature preferably between 80 and 120 °C, more preferably between 100 and 110 °C and at a pressure preferably between 0.002 MPa and 0.020 MPa, more preferably between 0.005 MPa and 0.010 MPa. Preferably, the evaporation section uses a wiped-film evaporator (thin-film evaporator, TFE).

[0148] The distillation section itself 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 at a top temperature preferably between 25 and 60 °C, preferably between 45 and 55 °C, for example about 50 °C, at a bottom temperature preferably between 80 and 140 °C, preferably between 100 and 130 °C, for example about 120 °C, at a pressure preferably between 0.001 MPa and 0.05 MPa, preferably between 0.005 MPa and 0.02 MPa, and preferably between 0.008 MPa and 0.012 MPa, and preferably at a reflux ratio between 0.01 and 0.50, preferably between 0.05 and 0.10.

[0149] Accordingly, the aqueous raffinate 5 produced in step b) and containing water and a polar aprotic synthesis solvent (such as DMSO) and optionally the water - polar aprotic synthesis solvent (such as DMSO) mixture recovered in an optional dehydration step are evaporated, and then the gas phase is recovered and distilled, preferably under vacuum, to produce on the one hand a residue 16 rich in polar aprotic synthesis solvent (such as DMSO), on the other hand a water - rich distillate 15 (corresponding to the aqueous effluent), and finally a stream 17 containing heavy fractions such as humus and unreacted sugars not removed by filtration. The term "rich" is understood herein 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 as the aqueous solvent for carrying out the back - washing step to step c) and / or as an aqueous stream to the water distillation step e). The water - rich distillate can also be recycled in whole or in part as the water introduced into step a).

[0150] The residue rich in polar aprotic synthesis solvent (such as DMSO) can advantageously be introduced directly or after distillation into an optional dehydration step in order to remove any heavy products that may have accumulated.

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

[0152] Figure 1Figure 0 shows a specific embodiment of the method according to the present invention. A feedstock 1 containing 5-HMF, a polar aprotic synthesis solvent (such as DMSO) and humic substances is sent to step a) and brought into contact with an aqueous stream 21. The aqueous mixture 3 obtained at the end of step a) is sent to an extraction step b) and brought into contact with an extraction solvent 4 to extract 5-HMF from the aqueous mixture using the extraction solvent, and an aqueous raffinate 5 and an organic extract 6 are obtained. The organic extract 6 is brought into contact with an aqueous solvent 7 in a backwashing step c). The organic raffinate 8 obtained at the end of step c) can be concentrated in an optional concentration step d) by removing a stream 11, which can be recycled to step b). The organic raffinate 8 obtained at the end of step c), or if step d) is carried out, the concentrated organic raffinate 10 obtained at the end of step d) is treated in a water distillation step e) to remove the residual organic solvent 13 and obtain an aqueous solution 12 of 5-HMF.

[0153] In this embodiment, a liquid-solid separation step f) is carried out on the intermediate liquid stream taken out in the liquid-liquid extraction step b) during the liquid-liquid extraction process: the intermediate aqueous raffinate 19 generated in step b) is treated in the liquid-solid separation step f). This liquid-solid separation enables the extraction of the solids precipitated in the upstream phase, i.e., the precipitated humic substances, in the form of a solid particle stream 18, and a clarified intermediate aqueous raffinate 20 is produced, which is re-introduced into the extraction step b).

[0154] The aqueous raffinate 5 obtained from the liquid-liquid extraction step b) is sent to a step g) for treating the water-polar aprotic synthesis solvent mixture. Step g) produces an aqueous effluent 15, a polar aprotic synthesis solvent-rich stream 16, and a heavy fraction stream 17 containing humic substances and unreacted sugars that have not been removed by filtration (the humic substances and sugars are in a liquid but very viscous form at the processing temperature of the mixture).

[0155] Figure 2 Figure 10 shows another specific embodiment of the method according to the present invention, which is the same as that shown in Figure 1 except that a liquid-solid separation step f) is carried out on the aqueous raffinate obtained at the end of step b) downstream of the liquid-liquid extraction step b). In the shown embodiment, precipitated humic substances forming solid particles are present in the aqueous raffinate obtained at the end of step b), which is sent to the liquid-solid separation step f) to separate the solid particles from the rest of the aqueous raffinate and produce a solid particle stream 18 and the particle-poor aqueous raffinate 5'. The latter is sent to a step g) for treating the water-polar aprotic synthesis solvent mixture, which operates in the same manner as that for Figure 1 described above.

[0156] Figure 3Shows another specific embodiment of the method according to the invention, which, in addition to including the following specific features, is the same as that shown in Figure 1 : - A liquid-solid separation step is performed on the mixture 3 formed in step a) to separate the precipitated humus (solid particles) in step a) from the rest of the mixture, to produce a solid stream 2; - The method includes a step d) of concentrating the organic raffinate 8 produced in the backwashing step c) to produce a concentrated organic raffinate 10 and an extraction solvent stream 11, and the extraction solvent stream 11 is advantageously recycled to step b) and introduced together with the extraction solvent 4; - The aqueous stream 21 used in the mixing step a) contains recycled water obtained from the method. In particular, the aqueous stream 21 consists of the backwashed extract 9 and a part of the aqueous effluent 15 produced in the step g) of treating the water-polar aprotic synthetic solvent mixture; - The aqueous solvent 7 used in the backwashing step c) consists of a part of the aqueous effluent 15 produced in the step g) of treating the water-polar aprotic synthetic solvent mixture and makeup water 22 (i.e., from outside the method, in other words, neither produced in the method nor recycled from the method). Alternatively, the aqueous solvent 7 used in the backwashing step c) consists of a part of the aqueous effluent 15 produced in the step g), without makeup water. In this case, the makeup water can be sent to step a) to form an aqueous stream 21 containing a part of the aqueous effluent 15 produced in the step g). Although water recycling is carried out, it may be necessary to supply makeup water in the method; - The aqueous stream 14 used in the water distillation step e) consists of a part of the aqueous stream 15 produced in the step g) of treating the water-polar aprotic synthetic solvent mixture; - The extraction solvent 4 used in the 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 particularly form a part of the composition of the extraction solvent 4.

[0157] This embodiment thus includes recycling the aqueous effluent 15 obtained from the step g) of treating the water-polar aprotic synthetic solvent mixture to steps a), c) and e), and recycling the organic solvent streams 11 and 13 to the liquid-liquid extraction step b), which can first optimize the water management in the method by integrating water treatment within the method and avoiding excessive makeup water, and secondly minimize the consumption of the extraction solvent. The combination of these ultimately favorably affects the operating cost and environmental impact of the method.

[0158] List of reference numerals used in the drawings: 1: Raw materials 2: Solid material stream 3: Aqueous mixture 4: Extraction solvent 5: Aqueous raffinate 6: Organic extract 7: Aqueous solvent 8: Organic raffinate 9: Intermediate aqueous stripping extract 10: Concentrated organic raffinate 11: First stream containing organic solvent 12: 5 - HMF aqueous solution 13: Second stream containing organic solvent 14: Aqueous liquid 15: Aqueous effluent 16: Stream rich in polar aprotic synthetic solvent (or stream rich in "residue") 17: Impurity stream (or heavy fraction stream) 18: Solid particle stream 19: Intermediate liquid stream 20: Intermediate liquid stream poor in particles 21: Aqueous stream 22: Make - up water. Examples

[0159] Preparation of 5 - HMF aqueous solution 12 according to the present invention The following examples are intended to show some advantages of the method according to the present invention carried out according to the embodiments shown in Figure 1 the present invention.

[0160] The acid catalyst methanesulfonic acid was mixed with DMSO used as a polar aprotic synthetic solvent so that the molar ratio to the sugar raw material (catalyst / sugar raw material) was 1 mol%, and they were brought to a temperature of 120 °C. Fructose was introduced in the form of an aqueous solution (syrup) containing 70 wt% sugar, and the DMSO / fructose mass ratio was 2.3. The pressure was maintained at 0.035 MPa. Under these pressure and temperature conditions, the reaction medium was above the bubble point of the mixture, so the gas phase could be withdrawn from the reactor and condensed to form condensate. The sugar dehydration step was carried out batchwise, with the raw materials being gradually added over 2 hours. After the addition was complete, the reaction medium was maintained at the above temperature and pressure for another 2 hours.

[0161] The liquid effluent obtained from the dehydration step contains 74 wt% DMSO, 21 wt% 5-HMF, and 3 wt% water, i.e., the molar yield of 5-HMF relative to the fructose used is 81%. A polymeric compound (referred to as humus) that is soluble in the reaction medium is formed in an amount of 5 wt%. During this dehydration step, a water-DMSO mixture is recovered in the gas phase. The water-DMSO mixture has a composition of 32 wt% DMSO and 68 wt% water. This water-DMSO mixture is distilled under vacuum to produce water containing only trace amounts of DMSO.

[0162] The liquid effluent obtained from the dehydration step corresponding to Feedstock 1 is used in step a) of contacting with an aqueous stream under ambient conditions to obtain a mixture having a DMSO / water mass ratio equal to 1.

[0163] The mixture from step a) is subjected to a liquid-solid separation step on a Büchner filter equipped with a polypropylene cloth filter with a pore size of 10 µm. This liquid-solid separation step is carried out at ambient temperature. During the liquid-solid separation step, 7.5 g of "humus" solid residue / kg of filtered mixture is recovered, as well as a homogeneous liquid phase corresponding to aqueous mixture 3. Aqueous mixture 3 consists of 43 wt% DMSO, 12 wt% 5-HMF, and 43 wt% water, and contains impurities (about 2 wt% humus).

[0164] The aqueous mixture 3 obtained from step a) is subjected to a countercurrent liquid-liquid extraction step b) in a glass stirred column (Kühni or ECR type), which includes 8 sections with a height of 225 mm and an inner diameter of 32 mm, as well as a lower decanter and an upper decanter. The effective height is about 1.8 m, and the total column height is 2.60 m. The total volume is about 3 liters. The organic extraction solvent is methyl isobutyl ketone (MIBK). The aqueous mixture 3 is introduced into the upper part of the device and dispersed in the rising organic phase. The column inlet flow rate is set to 2.2 kg / h for the DMSO-water phase and 4.1 kg / h for MIBK. The ratio (weight / weight) of the MIBK solvent relative to the aqueous mixture 3 obtained from step a) is 1.9. In this step b), the temperature is 20 °C and the stirring speed is 300 rpm.

[0165] The aqueous raffinate obtained from the liquid-liquid extraction column enters step f), which here is 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), 7.0 g of "humus" solid residue / kg of filtered mixture is recovered, as well as a homogeneous liquid phase corresponding to the aqueous raffinate with few solid particles (also referred to as clarified aqueous raffinate 20).

[0166] In this specific embodiment, clarified aqueous raffinate 20 forms aqueous raffinate 5 produced at the end of step b).

[0167] At the end of step b), aqueous raffinate 5 poor in 5-HMF containing about 48 wt% water, 48.5 wt% DMSO, 0.4 wt% 5-HMF, 1.8 wt% MIBK and humic impurities, and organic extract 6 rich in furan compounds containing 2.8 wt% DMSO, 5.9 wt% 5-HMF (i.e., 5-HMF / DMSO weight ratio of about 68 / 32) and 91.3 wt% MIBK are recovered. The extraction yield is 97% for 5-HMF and 13% for DMSO.

[0168] Aqueous raffinate 5 is treated in step g) for treating the water-DMSO mixture. Evaporation of water and DMSO is carried out successively in a batch distillation system, where the first stage operates at a pressure of 0.008 MPa and a temperature of 80 °C to enable recovery of MIBK present in aqueous raffinate 5, and almost all of the water and most of the DMSO until the DMSO content in the residue reaches 50 wt%, i.e., an evaporation rate of about 93%. The second stage operating at 0.0005 MPa stops when the medium temperature reaches 90 °C. In this stage, the heavy product contains only 20 wt% DMSO, and about 95% of the DMSO present in aqueous raffinate 5 is recovered.

[0169] Organic extract 6 obtained from the liquid-liquid extraction step b) is subjected to a backwashing step c) in the same extraction device (ECR or Kühni type stirred column). The organic extract is dispersed in the pure aqueous phase at 21.5 °C. The tower inlet flow rate is set to 5 kg / h for the organic extract and 1.5 kg / h for the aqueous phase. The ratio (weight / weight) of water introduced as the aqueous backwashing solvent to the organic extract is 0.3.

[0170] At the end of the backwashing step c), intermediate aqueous back-extract 9 rich in DMSO containing 86 wt% water, 7 wt% DMSO, 5 wt% 5-HMF and 2 wt% MIBK, and organic raffinate 8 containing 4.3 wt% 5-HMF, 0.092 wt% DMSO (i.e., 2.1 wt% DMSO based on the weight of 5-HMF) and 88 wt% MIBK are recovered, so that the backwashing yield is 27 wt% for 5-HMF and 95 wt% for DMSO.

[0171] The resulting organic raffinate 8 is sent to a concentration step d). The solvent is vaporized under vacuum. The temperature of the liquid is set at 60 °C, and the vacuum pressure is set at 0.02 MPa.

[0172] Step d) is carried out at a vaporization mass ratio of 95%, which corresponds to the mass of the vaporized organic solvent / the mass of the organic raffinate used obtained from step c). The concentrated organic raffinate obtained at the end of step d) has a mass content of 84 wt% 5-HMF, 2 wt% DMSO, and 9 wt% MIBK. The 5-HMF content (84 wt%) of this concentrated organic raffinate meets the expected value (at least 40 wt% and at most 95 wt%), and its residual solvent content of 11 wt% (the sum of 9% MIBK + 2% DMSO) also meets the expected value (at least 5 wt% and at most 60 wt%). The concentrated organic raffinate obtained at the end of step d) also contains humic impurities (5 wt%). The recovered distillate mainly contains MIBK and water, which are removed in the form of an azeotrope with MIBK and separate into two immiscible phases upon condensation.

[0173] The concentrated organic raffinate obtained from step d) is contacted with pure water, where the water / concentrated extract mass ratio is 0.95, and then sent to a water distillation step e) by distillation. The water distillation step e) is carried out at a bottom temperature of 35 °C and a vacuum of 0.01 MPa to promote the removal of the residual MIBK organic solvent in the form of a water / MIBK azeotrope without degrading 5-HMF. The 5-HMF aqueous solution obtained at the end of step e) has a composition of 45 wt% 5-HMF, 53.3 wt% water, 1 wt% DMSO (i.e., 2.2 wt% DMSO based on the weight of 5-HMF), and 0.7 wt% MIBK.

Claims

1. A method for producing an aqueous solution of hydroxymethylfurfural (5-HMF), the method comprising the following steps: - Step a), contacting a feedstock (1) comprising 5-HMF and a polar aprotic synthetic solvent with an aqueous stream (21) to obtain at least one aqueous mixture (3); - Step b), subjecting the aqueous mixture (3) obtained at the end of step a) to liquid-liquid extraction in the presence of an extraction solvent (4) to produce an aqueous raffinate (5) comprising the polar aprotic synthetic solvent, an organic extract (6), a solid particle fraction and an optional 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), backwashing the organic extract (6) with an aqueous solvent (7) to produce an intermediate aqueous back-extract (9) and an organic raffinate (8) comprising 5-HMF and an organic solvent; - Optional step d), concentrating the organic raffinate (8) obtained from step c) by removing at least a portion of the organic solvent to produce a concentrated organic raffinate (10) comprising 5-HMF and a residual organic solvent, and producing a first stream (11) comprising the organic solvent; - Water distillation step e), which is carried out by distilling the organic raffinate (8) obtained from step c) or the concentrated organic raffinate (10) obtained from step d) in the presence of water to produce an aqueous solution (12) of 5-HMF and a second stream (13) comprising the organic solvent; - Step f), subjecting the solid fraction in the aqueous raffinate (5) obtained from step b) and / or the intermediate liquid stream (19) obtained from step b) to liquid-solid separation to produce a solid particle stream (18) and an aqueous raffinate (5') depleted in solid particles and / or a particle-depleted intermediate liquid stream (20) sent to step b); - Step g), treating at least one water-polar aprotic synthetic solvent mixture produced in the method, the mixture consisting of the particle-depleted aqueous raffinate (5') obtained from step f) or the aqueous raffinate (5) obtained from step b) that does not contain a solid particle fraction, to produce at least one aqueous effluent (15) that can be recycled to the method.

2. The method according to claim 1, wherein step b) produces an intermediate liquid stream (19) comprising the solid particle fraction, and the intermediate liquid stream (19) is sent to step f) to separate the solid particle fraction from the intermediate liquid stream (19) to form the particle-depleted intermediate liquid stream (20) sent to step b), and at least the water-polar aprotic synthetic solvent mixture consisting of the aqueous raffinate (5) obtained from step b) that does not contain a solid particle fraction is sent to step g).

3. The method according to claim 2, wherein the intermediate liquid stream (19) fed to step f) is an intermediate aqueous raffinate containing the solid particle fraction and produced by separation between the extraction solvent and the water-polar aprotic solvent mixture in the liquid-liquid extraction step b).

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

5. The method according to claim 1, wherein the aqueous raffinate (5) produced in step b) contains the solid particle fraction, and the aqueous raffinate (5) is fed to step f) to separate the solid particle fraction from the aqueous raffinate (5) to form the solid particle-depleted aqueous raffinate (5'), which is fed as a water-polar aprotic solvent mixture to step g).

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

7. The method according to any one of the preceding claims, which comprises a step d) of concentrating the organic raffinate (8) obtained from step c), which comprises vaporizing the organic solvent at atmospheric pressure or under vacuum, preferably at a pressure between 0.01 MPa and 0.1 MPa and at a liquid temperature maintained at less than or equal to 130 °C, the concentrated organic raffinate (10) containing a content of 5-HMF of greater than or equal to 40% by weight and a content of residual organic solvent of less than or equal to 60% by weight.

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

9. The method according to any one of the preceding claims, wherein step e) is carried out in a distillation column, preferably at a bottom temperature of less than or equal to 140 °C.

10. The method according to any one of the preceding claims, 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, and is preferably methyl isobutyl ketone.

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

12. The method according to any one of the preceding claims, which comprises a step of dehydrating the sugar to 5-HMF upstream of step a), preferably by contacting a sugar raw material containing one or more sugars with the polar aprotic solvent and a dehydration acid catalyst, preferably at a temperature between 30 °C and 200 °C and at a pressure between 0.001 MPa and 10 MPa.

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

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

15. The method according to any one of the preceding claims, 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, alone or as a mixture, and preferably dimethyl sulfoxide.

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