Method for producing a furan derivative containing 5-hydroxymethylfurfural (5-HMF), and methods for producing a furan derivative, a solution containing the furan derivative, and a furandicarboxylic acid or a furandicarboxylic acid ester

Abstract

The present invention addresses the problem of providing a method that enables, at a low cost, production of 5-hydroxymethylfurfural from glucose with a high yield and high selectivity. Said problem is solved by a method that is for producing 5-hydroxymethylfurfural and that comprises a step for bringing glucose into contact with an isomerization catalyst and a dehydration catalyst, in a two phase solvent containing water and an organic solvent that does not blend with water.

Description

[Technical Field]

[0001] The present invention relates to a method for producing 5-hydroxymethylfurfural (hereinafter also referred to as 5-HMF) by contacting glucose with a mixed catalyst comprising an isomerization catalyst and a dehydration catalyst in a two-phase solvent system consisting of water and a water-immiscible organic solvent. The present invention also relates to a method for producing formylfurancarboxylic acid acetal, which is an intermediate in producing a dicarboxylic acid ester or dicarboxylic acid having a furan skeleton derived from a biomass feedstock, as well as to formylfurancarboxylic acid acetal and a solution containing the acetal. The present invention also relates to a method for producing a furan derivative, which is an intermediate in producing furandicarboxylic acid or a furandicarboxylic acid ester derived from a biomass feedstock, as well as the furan derivative and a solution containing the furan derivative. The present invention also relates to a method for producing furandicarboxylic acid or furandicarboxylic acid esters derived from biomass feedstocks. [Background technology]

[0002] In recent years, measures to address the global environmental burden of fossil fuel depletion and the increase in atmospheric carbon dioxide have become necessary. In response to these societal demands, attention has been focused on the development of processes for producing fuels and various useful chemicals from biomass materials grown under the current global atmospheric environment, and this work is being actively pursued. Such methods of utilizing biomass materials are expected to be an alternative to petroleum-based materials. For example, because plant-based production can be dispersed and diversified across various regions, it has the advantage of providing a very stable supply of raw materials. Furthermore, because fuel is produced and consumed within the atmosphere without consuming fossil fuels, the difference in the mass balance between carbon dioxide absorption and emission is relatively balanced. Therefore, it has the advantage of potentially enabling the realization of a recycling-oriented society, something that cannot be expected from fossil fuels, and its industrial value is extremely great.

[0003] 5-Hydroxymethylfurfural (5-HMF) is a key intermediate in a series of catalytic reactions that convert biomass feedstocks into starting materials for fuels and chemicals. 5-HMF is generally produced by the intramolecular dehydration of fructose, a hexose sugar, using an acid catalyst. 5-HMF is used as a raw material for 2,5-dimethylfuran (DMF) and 2,5-furandicarboxylic acid (FDCA). DMF has recently attracted attention as a biofuel alternative to fossil fuels, and FDCA can be used as a substitute for terephthalic acid in polyethylene terephthalate (PEF) by condensation polymerization with ethylene glycol.

[0004] Patent Document 1 discloses a method for producing 5-HMF from hexose. Specifically, 5-HMF is obtained by contacting glucose with a water-soluble complex catalyst, Poly(styrenesulfonic acid)AlCl3 (PSSA-AlCl3), in a two-phase solvent system consisting of water and a polar organic solvent (methyl isobutyl ketone (MIBK) / 2-BuOH) at 150°C. The conversion rate of this method is 95%, and the yield is 45%. Meanwhile, Non-Patent Document 1 describes a method for obtaining 5-HMF by dissolving fructose in a solvent of N-methylpyrrolidone:water=70:30 and then passing the resulting solution through a flow reactor packed with a cationic ion exchange resin (DIAION RCP160M) catalyst. This method has a conversion rate of 91% and a yield of 91%. Here, fructose is typically produced by isomerizing glucose. Non-Patent Document 2 describes a method for isomerizing glucose using glucose isomerase. Because this isomerization reaction is an equilibrium reaction, this method achieves a yield of 57%. The fructose thus distributed is produced by separating and recovering slightly more than 50% of the fructose produced from glucose. Non-Patent Document 3 describes a method for obtaining 5-HMF by contacting glucose with sodium chloride and a cation exchange resin (DIAION RCP160M) catalyst in a two-phase solvent of water, N-methylpyrrolidone, and methyl isobutyl ketone. The yield and selectivity of this method are described as 84% ​​and 90%, respectively.

[0005] On the other hand, among a series of catalytic reactions that derive useful chemicals from biomass feedstocks, processes via compounds having a furan ring have been proposed as particularly important processes from the viewpoints of functionality, diversity of applications, environmental impact, and economic efficiency. For example, the following reaction method has been proposed as a method for producing furandicarboxylic acid and its esters, which are the target of the present invention. [ka]

[0006] Specific production methods include, for example, Patent Document 2, which proposes the production of hydroxymethylfurfural (HMF) from monosaccharides such as glucose and fructose in the presence of hydrous niobic acid, and Patent Documents 3 and 4, which propose methods for producing furandicarboxylic acid (FDCA) or its esters by oxidation of HMF. However, in the methods described in Patent Documents 3 and 4 for producing furandicarboxylic acid or its esters by direct oxidation from HMF, HMF has low thermal stability due to reactive functional groups such as aldehyde and hydroxyl groups, leading to the occurrence of side reactions such as polymerization and ring-opening reactions. These side reactions result in the formation of oligomers such as humins, polymers, and levulinic acid, resulting in reduced reaction yields. Furthermore, the deposition of oligomers and polymers within the reactor and piping reduces the reactor's heat transfer efficiency and causes blockages in the piping, making stable long-term operation difficult. These problems are particularly pronounced when producing furandicarboxylic acid or its esters under high HMF concentrations, posing a significant challenge in industrial processes where production under low HMF concentrations is essential and economic efficiency is required.

[0007] Meanwhile, Patent Document 5 proposes a method for producing furandicarboxylic acid (FDCA) or its esters using a cyclic acetal of HMF as an intermediate, as a highly productive process capable of efficiently producing FDCA or its esters even under high HMF concentrations. However, this production method still suffers from the problem that the yield of FDCA decreases when the concentration of the cyclic acetal of HMF is increased. This is because the oxidation reaction of the acetal group of the cyclic acetal is difficult to occur in the production method described in Patent Document 5. To promote the oxidation reaction of the acetal group, it is necessary to increase the amount of catalyst used or to carry out the reaction under high-pressure conditions using a gas with a high oxygen concentration. Reactions under such harsh oxidation conditions require the use of high-pressure equipment using gas with a high oxygen concentration, which increases the construction costs of the production equipment. In addition, there are problems with the production costs increasing because a portion of the diol required to obtain the cyclic acetal of HMF is oxidized and consumed. Furthermore, a complex purification process is required to prevent the diol decomposition products from contaminating the final product or the recovered diol, further increasing the production costs. [ka] [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2019 / 089448 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-215172 [Patent Document 3] Patent No. 5217142 [Patent Document 4] International Publication No. 2015 / 155784 [Patent Document 5] Japanese Patent Application Publication No. 2018-39778 [Non-patent literature]

[0009] [Non-Patent Document 1] Chemical Engineering & Processing,Process Intensification,138,2019,65-72 [Non-patent document 2] Yoshiyuki Takasaki, "Development of isomerized sugars using glucose isomerase," Organic Synthetic Chemistry, Vol. 38, No. 6, pp. 538-545, 1980 [Non-patent document 3] Royal Society of Chemistry Advances,2020,10,9492-9498 Summary of the Invention [Problem to be solved by the invention]

[0010] A method for producing 5-HMF from fructose with high yield has been reported, as in Non-Patent Document 1. However, this production method requires a step of isomerizing glucose to fructose. For example, when fructose is obtained from glucose by the method in Non-Patent Document 2 or the like, and then 5-HMF is produced by the method in Non-Patent Document 1, the cumulative yield is only slightly more than 50%.

[0011] When 5-HMF is produced from glucose using the method described in Patent Document 1, the yield is approximately 45%. Furthermore, when 5-HMF is produced from glucose using the method described in Non-Patent Document 3, the yield is improved. However, side reactions result in the formation of condensates and oligomers of humins, as well as decomposition products such as formic acid and levulinic acid, resulting in a low 5-HMF selectivity of approximately 90%. Furthermore, these by-products and decomposition products can cause discoloration. If discoloration occurs, complex purification processes, such as an adsorption decolorization process, are required to remove the discoloration, which increases production costs. Furthermore, if these by-products and decomposition products adhere to the inside of the reactor, it will cause a decrease in the heat transfer efficiency of the reactor and blockage of the inside of the piping, making stable long-term operation difficult.

[0012] When 5-HMF is produced from glucose by the method described in Non-Patent Document 3, the sodium chloride used therein leads to the deactivation (capping) of the acidic groups of the cation ion exchange resin, resulting in a shortened catalyst life. Furthermore, this accelerates corrosion of the reactor, necessitating the use of a reactor made of a more corrosion-resistant material, such as a glass-lined reactor or a Hastelloy reactor. In other words, the method described in Non-Patent Document 3 has the problem of high construction costs for the reaction equipment.

[0013] Thus, when producing 5-HMF directly from glucose, the reaction yield and selectivity are still insufficient, and many issues remain to be resolved in terms of productivity and long-term stable operation. In contrast, the present invention aims to provide a method for producing 5-HMF from glucose in high yield and high selectivity at low cost. More specifically, the process for producing 5-HMF from glucose involves contacting glucose with a mixed catalyst, consisting of an isomerization catalyst and a dehydration catalyst, in a two-phase solvent system consisting of water and a water-immiscible organic solvent. The process (1) involves isomerizing glucose to fructose with the isomerization catalyst, while the partially produced fructose is rapidly and selectively converted to 5-HMF with the dehydration catalyst. The process also (2) involves partitioning the 5-HMF produced during the reaction into the organic solvent phase, which separates from water, so as to prevent the produced 5-HMF from undergoing decomposition reactions, such as by-products like formic acid and levulinic acid, or polymerization reactions, such as huminization and oligomerization, which can cause coloration (the first objective of the present invention).

[0014] Furthermore, although Patent Documents 3 to 5 have proposed methods for producing FDCA or its esters by oxidation of HMF, there remain problems in terms of productivity and production costs from an industrial perspective. An object of the present invention is to solve the above-mentioned problems in a method for producing FDCA or an ester thereof by the oxidation reaction of HMF, and to provide a new intermediate that can be used in a method for producing FDCA or an ester thereof in high yield under reaction conditions that are more advantageous in terms of production cost (the second object of the present invention). [Means for solving the problem]

[0015] The present inventors have conducted extensive research into the first problem described above and have found that by reacting glucose with a mixed catalyst of an isomerization catalyst and a dehydration catalyst and then distributing the resulting 5-HMF into an organic solvent (hereinafter also referred to as organic solvent) that separates into two phases from water, side reactions such as the decomposition reaction and polymerization reaction described above can be prevented, and 5-HMF can be produced with high yield and high selectivity (94-95%). That is, the first gist of the present invention is as follows.

[0016] [1] A method for producing 5-hydroxymethylfurfural, comprising the step of contacting glucose with a mixed catalyst comprising an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and an organic solvent that is immiscible with water, to cause a reaction. [2] A method for producing 5-hydroxymethylfurfural, comprising a contacting step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and a water-immiscible organic solvent, A method for producing 5-hydroxymethylfurfural, characterized in that the two-phase solvent contains 80 parts by mass or less of an alkali metal salt or an alkaline earth metal salt per 100 parts by mass of glucose. [3] The method for producing 5-hydroxymethylfurfural according to [1] or [2], wherein the isomerization catalyst is a metal oxide. [4] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [3], wherein the dehydration catalyst is a solid acid. [5] The specific surface area of ​​the isomerization catalyst is 100 m 2 / g or more, and the specific surface area of ​​the dehydration catalyst is 40m 2 / g or more, [1] to [4]. [6] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [5], characterized in that the ratio of the specific surface area of ​​the isomerization catalyst multiplied by the catalyst amount to the specific surface area of ​​the dehydration catalyst multiplied by the catalyst amount is 1:20 to 20:1. [7] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [6], characterized in that the mixing ratio (mass ratio) of the isomerization catalyst to the dehydration catalyst is 1:3 to 3:1. [8] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [7], characterized in that the isomerization catalyst is aluminum oxide and the dehydration catalyst is an ion exchange resin. [9] A method for producing 5-hydroxymethylfurfural described in any one of [1] to [8], characterized in that the organic solvent is hydrophobic and is one or more selected from the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons.

[10] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [9], characterized in that the boiling point of the organic solvent under atmospheric pressure is 70°C or higher.

[11] A method for producing 5-hydroxymethylfurfural described in any one of [1] to

[10] , characterized in that the organic solvent has an inorganic value / organic value ratio of 0.10 or more and 1.00 or less.

[12] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[11] , characterized in that the organic solvent is one or more selected from the group consisting of methyltetrahydropyran (MTHP), methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK).

[13] The method for producing 5-hydroxymethylfurfural according to any one of [1] to

[12] , characterized in that the mass ratio of the organic solvent to water is 1:1 to 4:1.

[14] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[13] , characterized in that the temperature in the reaction is 120°C or higher.

[0017] <ii>[1] A method for producing 5-hydroxymethylfurfural, comprising: a step of contacting glucose with a mixed catalyst, which is a mixture of an isomerization catalyst and a dehydration catalyst, in a two-phase solvent system of water and an organic solvent that is immiscible with water, to cause a reaction; and an oil-water separation step of separating the reaction solution obtained by the reaction into an organic solvent phase containing 5-hydroxymethylfurfural produced by the reaction and an aqueous phase containing sugars contained in the solution after the reaction and the mixed catalyst. [2] A method for producing 5-hydroxymethylfurfural, comprising: a contacting step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system of water and a water-immiscible organic solvent; and an oil-water separation step of separating the reaction solution obtained by the reaction into an organic solvent phase containing 5-hydroxymethylfurfural produced by the reaction and an aqueous phase containing sugars contained in the solution after the reaction and the mixed catalyst, A method for producing 5-hydroxymethylfurfural, characterized in that the two-phase solvent contains 80 parts by mass or less of an alkali metal salt or an alkaline earth metal salt per 100 parts by mass of glucose. [3] The method for producing 5-hydroxymethylfurfural according to [1] or [2], wherein the isomerization catalyst is a metal oxide and the dehydration catalyst is a solid acid. [4] The specific surface area of ​​the isomerization catalyst is 100 m 2 / g or more, and the specific surface area of ​​the dehydration catalyst is 40m 2 / g or more, [1] to [3]. [5] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [4], characterized in that the ratio of the specific surface area of ​​the isomerization catalyst multiplied by the catalyst amount to the specific surface area of ​​the dehydration catalyst multiplied by the catalyst amount is 1:20 to 20:1. [6] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [5], characterized in that the mixing ratio (mass ratio) of the isomerization catalyst to the dehydration catalyst is 1:3 to 3:1. [7] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [6], characterized in that the isomerization catalyst is aluminum oxide and the dehydration catalyst is an ion exchange resin. [8] A method for producing 5-hydroxymethylfurfural described in any one of [1] to [7], characterized in that the organic solvent is hydrophobic and is one or more selected from the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons. [9] A method for producing 5-hydroxymethylfurfural according to any one of [1] to [8], characterized in that the boiling point of the organic solvent under atmospheric pressure is 70°C or higher.

[10] The method for producing 5-hydroxymethylfurfural according to any one of [1] to [9], characterized in that the organic solvent has an inorganic value / organic value ratio of 0.10 to 1.00.

[11] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[10] , characterized in that the organic solvent is one or more selected from the group consisting of methyltetrahydropyran (MTHP), methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK).

[12] A method for producing 5-hydroxymethylfurfural described in any one of [1] to

[11] , which includes a step of dissolving (distributing) the 5-hydroxymethylfurfural produced by the reaction in the organic solvent phase obtained by the oil-aqueous separation step and recovering it.

[13] A method for producing 5-hydroxymethylfurfural described in any of [1] to

[12] , which includes a step of recovering the sugar and the mixed catalyst contained in the solution after the reaction together with the aqueous phase obtained by the oil-aqueous separation step.

[14] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[13] , characterized in that the mass ratio of the organic solvent to water is 1:1 to 4:1.

[15] A method for producing 5-hydroxymethylfurfural according to any one of [1] to

[14] , characterized in that the temperature in the reaction is 120°C or higher.

[0018] Furthermore, the present inventors conducted extensive research into the second problem described above and discovered a new method for producing an intermediate that can be used in the production method of FDCA or its esters, thereby completing the present invention. Furthermore, they discovered that the above problem can also be solved by using a method including specific production steps, thereby completing the present invention. By using the intermediates and specific steps according to the present invention, not only FDCA or its esters but also diformylfuran and formylfurancarboxylic acids having asymmetric substituents can be produced with high yield and high selectivity.

[0019] That is, the second gist of the present invention is as follows. <iii>[1] A method for producing a furan derivative having an acetal group and a carbonyl group, comprising an oxidation step of contacting hydroxymethylfurfural acetal with an oxidation catalyst. [2] The method according to [1], wherein the furan derivative is a compound represented by formula (1): [ka] (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. [3] The method according to [1] or [2], wherein the concentration of the furan derivative in all compounds having a furan skeleton in the product after the oxidation step is 70 mol % or more. [4] The method according to any one of [1] to [3], wherein the oxidation catalyst is a metal catalyst. [5] A furan derivative represented by formula (1). [ka] (In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. [6] A solution containing the furan derivative according to [5], wherein the concentration of the furan derivative in all compounds having a furan skeleton is 70 mol % or more. [7] The solution according to [6], wherein the furan derivative is a compound represented by formula (2): [ka] (In formula (2), R 2 and R 3 are independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent.)

[0020] <iv>[1] A method for producing a furan derivative, comprising a deprotection step of synthesizing a furan derivative by deprotecting formyl furancarboxylic acid acetal or an ester thereof, The production method, wherein the furan derivative is at least one selected from the group consisting of formylfurancarboxylic acid and its esters. [2] The method according to [1], wherein the formyl furancarboxylic acid acetal or its ester is a compound represented by formula (3): [ka] (In formula (3), X, R 4 and R 5 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. [3] The production method according to [1] or [2], wherein the concentration of formylfurancarboxylic acid and its ester in all compounds having a furan skeleton in the product after the deprotection step is 70 mol % or more. [4] The method according to any one of [1] to [3], further comprising a recovery step of recovering the diol from the reaction mixture after the deprotection step. [5] The method according to [4], wherein the diol is a diol having 2 to 10 carbon atoms. [6] A solution containing a compound having a furan skeleton, wherein the concentration of formylfurancarboxylic acid and its esters in all compounds having a furan skeleton is 70 mol % or more.

[0021] <v>[1] A method for producing furandicarboxylic acid or an ester thereof, comprising an oxidation step of contacting a composition containing a furan derivative with an oxidation catalyst, the furan derivative is at least one selected from the group consisting of diformylfuran and formylfurancarboxylic acid and its esters, The production method, wherein the concentration of the furan derivative in all compounds having a furan skeleton contained in the composition containing the furan derivative is 70 mass % or more. [2] The method according to [1], wherein the oxidation catalyst is a metal catalyst. [3] The method according to [1] or [2], wherein the reaction temperature in the oxidation step is 50°C or lower.

[0022] <vi>[1] A method for producing furandicarboxylic acid or a furandicarboxylic acid ester from hydroxymethylfurfural, the method comprising the following production steps (i) to (iv): (i) An acetalization step in which hydroxymethylfurfural is acetalized to synthesize hydroxymethylfurfural acetal. (ii) A first oxidation step in which hydroxymethylfurfural acetal is oxidized to synthesize formylfurancarboxylic acid acetal or its ester. (iii) A deprotection step of synthesizing formylfurancarboxylic acid or its ester by deprotecting formylfurancarboxylic acid acetal or its ester. (iv) a second oxidation step in which formylfurancarboxylic acid or its ester is oxidized. [2] The method for producing furandicarboxylic acid or a furandicarboxylic acid ester according to [1], wherein the formylfurancarboxylic acid acetal or the ester thereof is a compound represented by formula (3): [ka] (In formula (1), X, R 4 and R 5 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. [3] The method for producing furandicarboxylic acid or a furandicarboxylic acid ester according to [1] or [2], wherein an organic solvent selected from toluene and methyltetrahydropyran is used in the step (i). [4] The method for producing furandicarboxylic acid or a furandicarboxylic acid ester according to any one of [1] to [3], further comprising a recovery step of recovering the diol from the reaction solution after the step (iii). [5] The method for producing furandicarboxylic acid or a furandicarboxylic acid ester according to [4], wherein the diol is a diol having 2 to 10 carbon atoms. [Effects of the Invention]

[0023] According to the first aspect of the present invention, glucose is contacted with a mixed catalyst containing an isomerization catalyst and a dehydration catalyst to isomerize glucose to fructose, while the partially produced fructose is rapidly and selectively converted to 5-HMF by the dehydration catalyst. Furthermore, by rapidly partitioning the produced 5-HMF into an organic solvent, deterioration of the product is prevented, enabling 5-HMF to be produced from glucose at a higher yield and with higher selectivity than conventional methods, at a lower cost. In other words, this method allows 5-HMF to be produced directly from glucose as a raw material with high yield and high selectivity, without the need for a preparatory step to produce a fructose intermediate from the glucose raw material. This reduces the construction costs of the production facility and avoids the need for complicated operational management.

[0024] Furthermore, according to the second aspect of the present invention, a new intermediate can be provided that can be used in the process for producing FDCA or an ester thereof by the oxidation reaction of HMF. Furthermore, by using this intermediate, it is possible to reduce the reaction pressure and temperature during the oxidation reaction, and it is not necessary to use high-pressure equipment that uses gas with a high oxygen concentration, which contributes to reducing production costs. Furthermore, it is possible to produce FDCA or an ester thereof with a high yield. DETAILED DESCRIPTION OF THE INVENTION

[0025] Representative embodiments for carrying out the present invention will be specifically described below. The present invention is not limited to the following embodiments as long as it does not exceed the scope of the present invention. In this specification, "~" is used to express numerical values ​​or physical properties. In this case, the values ​​before and after the value will be used as well.

[0026] <First summary> One embodiment of the present invention (first aspect) is a method for producing 5-hydroxymethylfurfural, which includes a contacting step of contacting glucose with an isomerization catalyst and a dehydration catalyst in a two-phase solvent system consisting of water and a water-immiscible organic solvent.

[0027] <Reaction method> The reaction method according to this embodiment is carried out by a batch method in which a substrate, a solvent, and a catalyst are charged into a reactor, or a flow method in which a solution is circulated through a reactor (such as a fluidized bed or fixed bed) charged with a catalyst. A CSTR continuous stirred tank reaction method is also preferably used. The liquid-contacting materials of the reactor, flow path, etc. are not particularly limited, but examples include glass, stainless steel (SUS), iron, and other metals. Glass or stainless steel (SUS) are preferably used because of their corrosion resistance and high energy transfer efficiency. Furthermore, stainless steel (SUS) is preferably used from the viewpoint of the cost of the production equipment.

[0028] <Organic solvents> The organic solvent used in this embodiment is not particularly limited as long as it is hydrophobic and immiscible with water, and may be a mixture, i.e., it may be any solvent that separates into two phases when mixed with water. The boiling point of the organic solvent used in this embodiment under atmospheric pressure is not particularly limited. It is usually 70°C or higher, preferably 75°C or higher, and more preferably 80°C or higher. On the other hand, the upper limit is usually 250°C or lower, preferably 200°C or lower, and more preferably 150°C or lower. By using an organic solvent within this range, the reaction conversion rate can be improved. Furthermore, the load during distillation purification of the recovered organic solvent can be reduced.

[0029] The organic solvent used in the present embodiment is not particularly limited. Examples thereof include ethers having 4 to 20 carbon atoms, such as tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, and 3-pentanone. 2-hexanone, 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-hexadecanone Ketones having 4 to 20 carbon atoms, such as butadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, and acetophenone; esters, such as ethyl acetate, propyl acetate, and butyl acetate; 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, and 1-heptanol; Monoalcohols having 4 to 20 carbon atoms, such as 2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecen-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecen-1-ol, nonadecyl alcohol, and arachidyl alcohol;Examples of such hydrocarbons include saturated aliphatic hydrocarbons having 3 to 12 carbon atoms, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, and isododecane; aromatic hydrocarbons, such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones, such as γ-butyrolactone and γ-valerolactone; and halogenated hydrocarbons, such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane.

[0030] Among these, the organic solvent is preferably at least one selected from the group consisting of ethers, ketones, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons, more preferably at least one selected from the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons, and even more preferably an ether or a ketone.

[0031] As the ether, a cyclic ether is more preferred. Specific examples of the cyclic ether include methyltetrahydropyran (MTHP) and tetrahydropyran (THP). Among them, methyltetrahydropyran (MTHP) is more preferred because it has a high boiling point under atmospheric pressure, improves the reaction conversion rate in a short time, and provides high reaction selectivity.

[0032] As the ketone, methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), and diethyl ketone are more preferred, with methyl isobutyl ketone (MIBK) and methyl ethyl ketone (MEK) being even more preferred because they have high boiling points at atmospheric pressure, improve reaction conversion in a short time, and provide high reaction selectivity.

[0033] As the aromatic compound, xylene, toluene, and benzene are more preferred, with toluene being even more preferred because it has a high boiling point under atmospheric pressure, improves the reaction conversion rate in a short time, and provides high reaction selectivity. These organic solvents may be used alone or in any combination of two or more kinds in any ratio.

[0034] In this embodiment, the use of the organic solvent having the above boiling point improves the reaction conversion rate in a short time and produces 5-HMF with high reaction selectivity. Furthermore, the resulting 5-HMF can be efficiently extracted, thereby increasing the recovery rate of 5-HMF in the subsequent oil-water separation.

[0035] The Organic Concept Diagram Theory ("Systematic Organic Qualitative Analysis" by Fujita Atsushi, Kazama Shobo, 1974) proposes inorganic and organic values ​​for solvents. This calculates organic and inorganic values ​​based on preset values ​​for the functional groups that make up an organic compound, and characterizes the properties of the organic compound based on the ratio of these values. The organic solvents used in this embodiment preferably have an inorganic / organic ratio, as defined in Organic Conceptual Diagrams ("Systematic Organic Qualitative Analysis," by Fujita Atsushi, published by Kazama Shobo in 1974), of 0.10 or more and 1.00 or less. The lower limit is more preferably 0.20 or more, and the upper limit is more preferably 0.90 or less. By selecting a solvent within this range, affinity is increased not only for hydrocarbon groups but also for hydroxyl groups and aldehyde groups, enabling efficient extraction of 5-HMF. Table 1 below shows the inorganic value (I), organic value (O), and ratio (I / O) of major organic solvents.

[0036] [Table 1]

[0037] The organic solvent is mixed with water and used as a two-phase solvent for the reaction. In this embodiment, the two-phase solvent of water and an organic solvent that is immiscible with water includes a solvent in which water and an organic solvent form two layers, a solvent in which an organic solvent is dispersed in an aqueous solvent, and a solvent in which water is dispersed in an organic solvent. In the present invention, a two-phase solvent consisting of a combination of water and an organic solvent that is immiscible with water is one of the preferred embodiments because it reduces the load during solvent recovery. The mass ratio of the organic solvent to water is not particularly limited, but is usually 1:1 to 4:1, preferably 2:1 to 4:1, within this range, which is preferable because 5-HMF can be efficiently extracted from the aqueous phase and deterioration of 5-HMF can be reduced. The above mass ratios are those at atmospheric pressure and 25°C.

[0038] <Isomerization catalyst> The isomerization catalyst used in this embodiment is a catalyst that isomerizes glucose to fructose. The isomerization catalyst is preferably a metal oxide, and examples thereof include metal oxides such as aluminum oxide, magnesium oxide, calcium oxide, zirconium oxide, Nb2O5, YNbO4, Ta2O5, Nb2O5-WO3, Nb2O5-MoO3, TiO2-WO3, TiO2-MoO3, SiO2-Nb2O5, and SiO2-Ta2O5, metal composite oxides, and immobilized catalysts such as clay. Among these, aluminum oxide, magnesium oxide, calcium oxide, and zirconium oxide are preferred, and aluminum oxide is particularly preferred. These isomerization catalysts may be used either alone or as a mixture of two or more kinds in any ratio and combination.

[0039] When aluminum oxide is used as the isomerization catalyst, the specific surface area of ​​the aluminum oxide is preferably 100 m 2 / g or more, more preferably 150m 2 / g or more. There is no particular upper limit, but it is usually 500m 2 / g or less, preferably 300m 2 Within the above range, the probability of contact between glucose and aluminum oxide is sufficient, and the isomerization rate can be increased. The specific surface area of ​​aluminum can be measured by a permeation method or a gas adsorption method. The specific surface area value will be the same whether the permeation method or the gas adsorption method is used.

[0040] <Dehydration catalyst> The dehydration catalyst used in this embodiment catalyzes the intramolecular dehydration reaction of glucose or fructose. The dehydration catalyst is preferably a solid acid. A solid acid is a solid that chemically adsorbs a base and either donates a proton to a reactant or accepts an electron pair from the reactant. The solid acid is preferably a solid acid that is solid at 25°C and exhibits acidity. Specifically, heteropolyacid, phosphate diatomaceous earth, activated carbon, steam activated carbon, phosphoric acid activated carbon, acid-modified silica gel, acid-modified silica alumina, zeolite, ion exchange resin, sulfated ZrO 2 Examples of suitable catalysts include sulfuric acid-immobilized catalysts such as those mentioned above, and phosphoric acid-immobilized catalysts such as titania or niobia treated with phosphoric acid. Among these, ion exchange resins are preferred. The ion exchange resin is not particularly limited as long as it has Bronsted acid sites on the surface of the carrier, and examples include those having carboxyl groups and / or sulfonic acid groups. From the viewpoint of reactivity, strongly acidic cation exchange resins having sulfonic acid groups are preferred. From the viewpoint of catalyst recovery, sparingly soluble catalysts (also called heterogeneous catalysts) are preferred rather than water-soluble catalysts. These dehydration catalysts may be used alone or in any combination of two or more kinds in any ratio.

[0041] The specific surface area of ​​the dehydration catalyst is 40m 2 / g or more, and 2 / g or more is more preferable. The upper limit is not particularly limited, but is usually 200 m 2 / g or less, preferably 100m 2 Within the above range, the probability of contact between the fructose produced from glucose and the dehydration catalyst is sufficient, and the efficiency of the dehydration reaction can be increased. The specific surface area of ​​the dehydration catalyst can be measured by a permeation method or a gas adsorption method.

[0042] <Mixed catalyst> The isomerization catalyst and the dehydration catalyst are brought into contact as a mixed catalyst with glucose, which is the raw material. The specific manner in which the mixed catalyst is brought into contact with glucose is not particularly limited. The mixed catalyst may be a substantially uniform mixture of an isomerization catalyst and a dehydration catalyst, or the glucose may be contacted by filling a column with a catalyst in which the isomerization catalyst and the dehydration catalyst are alternately layered, and passing a solution containing an organic solvent and glucose through the column. For passing the liquids, an embodiment may be employed in which separate lines for passing the organic solvent and the glucose solution are prepared, and the lines merge before contacting the catalyst. Alternatively, the two-phase solvent, the mixed catalyst, and glucose may be charged into a reactor and reacted while stirring.

[0043] The use of a mixed catalyst facilitates the isomerization and dehydration reactions compared to contacting the feedstock with a single catalyst. Furthermore, compared to a method in which the feedstock is sequentially contacted with an isomerization catalyst tank and a dehydration catalyst tank, this method has the advantage of requiring only one reaction tank, thereby shortening the reaction process.

[0044] In this embodiment, the mixing ratio of the isomerization catalyst to the dehydration catalyst is not particularly limited and is determined taking into consideration the specific surface area of ​​each catalyst. The mass ratio is usually 1:3 to 3:1, and preferably 1:3 to 1:2. When the ratio is within this range, fructose partially produced by the isomerization reaction of glucose can be rapidly dehydrated.

[0045] The ratio of the specific surface area of ​​the isomerization catalyst multiplied by the catalyst amount to the specific surface area of ​​the dehydration catalyst multiplied by the catalyst amount is not particularly limited. The ratio is preferably 1:20 to 20:1, more preferably 1:10 to 10:1, and particularly preferably 1:1 to 10:1. Within the above range, it is possible to promote the glucose isomerization reaction, which tends to be rate-limiting, and to rapidly dehydrate the partially produced fructose.

[0046] The amount of the mixed catalyst used in this embodiment is not particularly limited. It is usually 0.01 g or more, preferably 0.1 g or more, and more preferably 0.5 g or more per 1 g of glucose. It is also usually 10 g or less, preferably 5 g or less, and more preferably 3 g or less. When the amount of catalyst is above the lower limit, the reaction can proceed efficiently. When the amount is below the upper limit, costs can be reduced by reducing excess catalyst.

[0047] <Glucose> The method for producing 5-HMF according to this embodiment is characterized by contacting the mixed catalyst with glucose to cause a reaction. The glucose source may be glucose itself (monosaccharide) or a glycopolymer (oligosaccharide or polysaccharide) containing glucose as a constituent sugar. Furthermore, a glucose derivative may also be used as the glucose source. The sugar polymer containing glucose as a constituent sugar is not particularly limited. Examples include sucrose, maltose, trehalose, turanose, isomaltulose, cellobiose, isomaltulose, nigerose, maltulose, isomaltulose, gentiobiose, maltotriose, 1-kestose, maltooligosaccharide, dextrin, dextran, starch, cellulose, lactose, lactulose, mannan, and xyloglucan. Among these, sucrose and starch are preferred. When a sugar polymer containing glucose as a constituent sugar is used as a glucose source, the sugar polymer can be decomposed by a heating reaction while glucose is being supplied, and then further converted to 5-HMF by an isomerization reaction and an intramolecular dehydration reaction using a mixed catalyst.

[0048] Glucose derivatives are not particularly limited as long as they have a functional group, such as a hydroxyl group, that can be subjected to a dehydration reaction, and examples include modified sugars such as amino sugars, etherified sugars, halogenated sugars, and phosphorylated sugars. Examples of such derivatives include glucosamine and glucose-6-phosphate. These derivatives can be pretreated with hydroxylation or reduction, and then converted to 5-HMF by isomerization and intramolecular dehydration using a mixed catalyst while supplying glucose.

[0049] The glucose source may also contain a hexose other than glucose as a sugar polymer or monosaccharide. The hexose other than glucose is not particularly limited, but fructose is preferred in terms of reactivity, availability, cost, etc. The glucose source preferably contains 10% by mass or more of glucose relative to the total sugar content, more preferably 50% by mass or more, and particularly preferably 90% by mass or more in terms of raw material cost and availability. According to the production method of this embodiment, even when a raw material containing glucose within the above range is used, 5-HMF can be obtained in high yield and with high selectivity, thereby reducing production costs compared to when fructose is used as the raw material.

[0050] In this embodiment, the glucose content in the glucose solution obtained by dissolving a glucose source in the two-phase solvent is preferably 1% to 90% by mass, more preferably 3% to 80% by mass, and particularly preferably 5% to 70% by mass, relative to the amount of water. The glucose solution may also contain solids consisting of undissolved sugars. The solids concentration of the solution is preferably 1% to 85% by mass, more preferably 5% to 80% by mass, and particularly preferably 20% to 75% by mass. Using a solution with a solids concentration below a certain level can further suppress the production of sugar condensates as by-products, while using a solution with a solids concentration above a certain level can efficiently promote the reaction.

[0051] The conditions for contacting the mixed catalyst with glucose are not particularly limited. The reaction temperature is preferably 80°C or higher, more preferably 100°C or higher. It is also preferably 200°C or lower, more preferably 150°C or lower. When the reaction temperature is above the lower limit, the reaction can proceed efficiently. When the reaction temperature is below the upper limit, the production of by-products can be suppressed, and catalyst deterioration can be suppressed. The reaction time is not particularly limited, but is preferably 1 to 24 hours, more preferably 2 to 10 hours. The reaction time can be set appropriately depending on the reaction temperature. For example, increasing the reaction temperature increases the reaction rate, thereby shortening the reaction time.

[0052] The pressure during the reaction is not particularly limited, but is preferably 0.01 MPa or more, more preferably 0.1 MPa or more, and is preferably 10 MPa or less, more preferably 1 MPa or less. Within the above range, the production of by-products can be suppressed.

[0053] <Alkali metal salts or alkaline earth metal salts> In this embodiment, the two-phase solvent preferably contains 80 parts by mass or less of an alkali metal salt or alkaline earth metal salt per 100 parts by mass of glucose, usually 80 parts by mass or less, and more preferably 50 parts by mass or less. The lower limit is not particularly limited, but is usually 1 part by mass or more, more preferably 0.01 part by mass or more. It is not necessary to contain an alkali metal salt or alkaline earth metal salt. It is preferable that the above-mentioned amount of alkali metal salt or alkaline earth metal salt is contained in the two-phase solvent, since this may facilitate oil-water separation, which will be described later. The alkali metal salt or alkaline earth metal salt is not particularly limited, and known salts can be used, such as sodium chloride and potassium chloride.

[0054] <Oil / water separation> The production method of this embodiment may further include an oil-water separation step. The oil-water separation step is a step of separating an organic solvent phase from an aqueous phase, and is carried out for the purpose of separating the target compound 5-HMF from other components from the reaction solution obtained by the above reaction. Specifically, the organic solvent phase contains oil-soluble components, primarily 5-HMF produced by the above reaction, while the aqueous phase contains water-soluble components such as raw sugars and catalysts. The oil-water separation method is not particularly limited as long as it utilizes the difference in specific gravity between the organic solvent phase and the aqueous phase. For example, the reaction solution is placed in a separation tank and allowed to stand until the organic solvent phase and the aqueous phase separate. The specific standing time is not particularly limited, but is typically 0.1 hours or more, preferably 1 hour or more. It is also typically 48 hours or less, preferably 24 hours or less.

[0055] When oil-water separation is performed, the temperature is preferably from room temperature to 90°C, with the lower limit being more preferably 30°C. The upper limit is more preferably 60°C, and even more preferably 40°C. By controlling the reaction temperature within this range, the extraction efficiency during recovery is improved and the operation time can be shortened.

[0056] In the production method of this embodiment, the reaction is carried out in a two-phase solvent system consisting of water and a water-immiscible organic solvent, thereby shortening the time required for oil-water separation after the reaction. This allows the produced 5-HMF to be separated from the catalyst, preventing its deterioration and enabling 5-HMF to be produced in a higher yield than conventional methods. 5-HMF can be further separated and purified by distilling off the organic solvent from the organic solvent phase recovered by oil-water separation. Purification may involve processes such as centrifugation, drying, and extraction. The distilled organic solvent may be reused.

[0057] In the oil-water separation, only the organic solvent phase may be recovered, and the aqueous phase may be discarded. The production method of this embodiment may also include a step of recovering the aqueous phase. The aqueous phase contains water-soluble components such as sugar raw materials and catalysts. Examples of sugars contained in the aqueous phase include the glucose sources and the hexoses other than glucose listed above, as well as sugars produced by their isomerization reactions and / or by-reactions such as sugar condensation reactions. Specific examples include glucose and fructose. The aqueous phase may be recovered, and the raw sugar may be added to the recovered aqueous phase, after which it may be reintroduced into the reactor for 5-HMF production. This process is preferable from the standpoint of production unit consumption, as it allows for efficient use of unreacted raw sugar and allows the recovered catalyst to be used as is. The recovered sugar and mixed catalyst may be further purified by treatment such as centrifugation, drying, extraction, etc. The recovered sugar and mixed catalyst can be reused in the reaction for producing 5-HMF.

[0058] The 5-HMF obtained by the production method of this embodiment can be converted into derivatives as needed and then used as a raw material for biofuels, synthetic resins, aroma-imparting components, physiologically active components, foods, medicines, etc. Examples of derivatives include 2,5-dimethylfuran (DMF), 2,5-furandicarboxylic acid (FDCA), and 5-methoxymethylfurfural. Known methods can be used to produce the above derivatives.

[0059] The method of the present embodiment can also be used to produce compounds produced from hexoses other than glucose through isomerization and dehydration reactions. The catalysts and reaction conditions used can be the same as those described above.

[0060] <Second summary> Another embodiment (second aspect) of the present invention is a method for producing a furan derivative having an acetal group and a carbonyl group, comprising a first oxidation step of contacting HMF acetal with an oxidation catalyst. Methods for producing FDCA or furandicarboxylic acid esters from HMF are disclosed in Patent Documents 3 and 4, etc., but we have found that FDCA or furandicarboxylic acid esters can be produced in high yield from HMF by a production method that goes through a furan derivative having an acetal group and a carbonyl group. When the method for producing FDCA or furandicarboxylic acid esters from HMF goes through the furan derivative, the method may include the following steps. Acetalization process for acetalizing HMF a deprotection step of a furan derivative having an acetal group and a carbonyl group; a recovery step of recovering the diol from the reaction solution after the deprotection step; a second oxidation step of oxidizing the compound obtained in the deprotection step; The following explains each in order.

[0061] <Acetalization process> The acetalization process acetalizes HMF. HMF can be obtained by deriving it from biomass feedstock. For example, HMF can be obtained using known methods such as those disclosed in Green Chemistry 16 (2014) 4816-4838, but is not limited to these. In one example, biomass feedstock is subjected to known pretreatment and saccharification processes such as chemical treatment with acids or alkalis, biological treatment using microorganisms, and physical treatment, thereby decomposing (saccharifying) the polysaccharides contained in the biomass feedstock into their constituent sugars, thereby obtaining a sugar solution containing oligosaccharides, disaccharides, and monosaccharides, and HMF can be obtained from this sugar solution.

[0062] Biomass raw materials include those in which solar light energy is converted and stored in the form of starch, cellulose, hemicellulose, etc. through the photosynthetic action of plants, as well as products made by processing plants. Examples of biomass raw materials include wood, rice straw, rice husks, rice bran, old rice, corn, sugarcane, cassava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, soybean pulp, corn cob, corn stover, corn fiber, tapioca, bagasse, vegetable oil cakes, potatoes, buckwheat, soybeans, waste paper, papermaking residues, fishery residues, livestock excrement, sewage sludge, and food waste. Among these, plant resources such as wood, rice straw, rice husks, rice bran, old rice, corn, sugarcane, cassava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, soybean pulp, corn cob, corn stover, corn fiber, tapioca, bagasse, vegetable oil cake, potato, buckwheat, soybean, waste paper, papermaking residue, and food waste are preferred, and wood, rice straw, rice husks, old rice, corn, sugarcane, cassava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, soybean pulp, corn cob, corn stover, corn fiber, tapioca, bagasse, vegetable oil cake, potato, buckwheat, soybean, waste paper, papermaking residue, and food waste are more preferred. The raw materials are sava, sago palm, cardoon, switchgrass, pine wood, poplar wood, maple wood, corn cob, corn stover, corn fiber, bagasse, potatoes, waste paper, papermaking residue, and food waste, and most preferably corn, sugarcane, cassava, sago palm, bagasse, cardoon, switchgrass, pine wood, poplar wood, maple wood, corn cob, corn stover, corn fiber, waste paper, papermaking residue, and food waste.

[0063] The sugars derived from the biomass materials mentioned above usually include hexoses such as glucose, mannose, galactose, fructose, sorbose, and tagatose, and disaccharides, oligosaccharides, and polysaccharides such as saccharose, starch, cellulose, and hemicellulose. Among these, glucose and fructose are preferred because of their high reaction yield. On the other hand, cellulose and hemicellulose are preferred as sugars derived from plant resources in a broader sense.

[0064] Acetalization is typically carried out in a solvent. A catalyst may be contained in the solvent. To allow the reaction to proceed in a short time, it is preferable to use an insoluble solid catalyst in the solvent and carry out the reaction in a heterogeneous system. Preferred catalysts include acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion; zeolites; metal oxides and composite metal oxides such as Nb2O5, YNbO4, Ta2O5, Nb2O5-WO3, Nb2O5-MoO3, TiO2-WO3, TiO2-MoO3, SiO2-Nb2O5, and SiO2-Ta2O5; clays; sulfuric acid-immobilized catalysts such as sulfated ZrO2; and phosphoric acid-immobilized catalysts such as titania or niobia treated with phosphoric acid. Among these, acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion, zeolite, Nb2O5, Nb2O5-WO3, and Nb2O5-MoO3 are more preferred because they selectively allow only the acetalization reaction of HMF to proceed, and acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion are particularly preferred.

[0065] These catalysts may be used alone or in combination of two or more. When two or more catalysts are used, the combination is not particularly limited, and the catalyst to be combined may be a co-catalyst whose metal has catalytic activity, or a promoter that improves the catalytic activity of another metal.

[0066] As the solvent, water or an organic solvent is usually used, but it may be preferable to use a mixed solvent of water and an organic solvent. From the viewpoint of cost advantage, it is preferable to use a single solvent as the reaction solvent.

[0067] The organic solvent to be used is not particularly limited, and examples thereof include ethers having 4 to 20 carbon atoms such as diethyl ether, tetrahydrofuran (THF), tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone, and 3-hexanone. Ketones having 4 to 20 carbon atoms, such as cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, and acetophenone; esters, such as ethyl acetate, propyl acetate, and butyl acetate;Methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecen-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecen-1-ol, nonadecyl alcohol, arachidyl alcohol, etc. monoalcohols having 1 to 20 carbon atoms; diols having 1 to 6 carbon atoms such as ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,3-pentanediol, 1,2-propanediol, 1,2-butanediol, and 1,2-pentanediol; phenols having 6 to 12 carbon atoms such as phenol, methylphenol, ethylphenol, propylphenol, and butylphenol; saturated aliphatic hydrocarbon compounds having 3 to 12 carbon atoms such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, and isododecane; aromatic hydrocarbons such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones such as γ-butyrolactone and γ-valerolactone; halogenated hydrocarbons such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane;Other examples include dimethylacetamide, N,N-dimethylformamide, N-methylmorpholine, N-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoric triamide, tetramethylurea, dimethyl sulfoxide, sulfolane, isosorbide, isosorbide dimethyl ether, propylene carbonate, and mixtures thereof. Other ionic liquids that may be used include pyrrolidinium salts such as 1-butyl-1-methylpyrrolidinium bromide; piperidinium salts such as 1-butyl-1-methylpiperidinium triflate; pyridinium salts such as 1-butylpyridinium tetrafluoroborate; imidazolium salts such as 1-ethyl-3-methylimidazolium chloride; ammonium salts such as tetrabutylammonium chloride; phosphonium salts such as tetrabutylphosphonium bromide; and sulfonium salts such as triethylsulfonium bis(trifluoromethanesulfonyl)imide.

[0068] Among these, the organic solvent is preferably selected from at least one of the group consisting of ethers, ketones, diols, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons, more preferably from at least one of the group consisting of ethers, ketones, diols, aromatic hydrocarbons, and saturated aliphatic hydrocarbons, and even more preferably from at least one of the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons. Specifically, methyltetrahydropyran, 2-butanone (methyl ethyl ketone), 4-methyl-2-pentanone (methyl isobutyl ketone), and toluene are preferred.

[0069] In the acetalization step, a diol is usually added to acetalize HMF, but any alcohol having two or more hydroxyl groups may be used, including trihydric alcohols such as glycerin and tetrahydric alcohols such as erythritol. Catechol is also preferably used. The diol to be added is appropriately determined depending on the type of acetal intermediate to be produced, and is preferably a diol having 2 to 10 carbon atoms, such as ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,3-pentanediol, 1-phenyl-1,3-propanediol, 2-phenyl-1,3-propanediol, 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, and 1-phenyl-ethylene glycol. Among these diols, diols that form a 6-membered ring structure are preferred because they improve the stability of the acetal intermediate, and specific examples include 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,3-pentanediol, 1-phenyl-1,3-propanediol, 2-phenyl-1,3-propanediol, etc. Two or more diols can be used, but typically one type is used.

[0070] A diol may be used as the organic solvent. When a diol is used as the organic solvent, it is preferably in a liquid state at room temperature. In this case, acetalization of HMF can be carried out without adding a diol to the organic solvent. Specific examples of the diol used as the organic solvent include ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,3-pentanediol, 1,2-propanediol, 1,2-butanediol, and 1,2-pentanediol.

[0071] The reaction method in the acetalization step can be a batch method, a flow method, or the like. The materials of the reactor, flow path, and other components that come into contact with the liquid are not particularly limited, and may be glass, stainless steel (SUS), iron, or other metals. However, glass or stainless steel (SUS) reactors are preferred because they are corrosion-resistant and have high energy transfer efficiency. Furthermore, stainless steel (SUS) reactors are preferred from the viewpoint of industrial production equipment costs.

[0072] In the acetalization step, a membrane may be installed in the reaction system, and the acetalization reaction may be carried out while dehydrating the reaction system using reactive separation. There are no limitations on the membrane installed in the reaction system, but examples include zeolite membranes, silica membranes, and carbon membranes. To selectively remove water, it is preferable to use a hydrophilic zeolite membrane with a pore size consistent with the diameter of water molecules. Zeolite membranes include FAU, BEA, MOR, MFI, FER, LTA, CHA, and DDR types. LTA (pore size: approximately 4 Å), CHA (pore size: approximately 3.8 Å), and DDR (pore size: approximately 3.2 Å), which have pore sizes close to the diameter of water molecules (approximately 2.7 Å), are preferred for dehydration. The silica (SiO2) / alumina (Al2O3) ratio of the zeolite membrane is preferably in the range of 2 to 40, more preferably 2 to 20. It is preferable to select a membrane having a silica / alumina ratio in this range, since it has good membrane stability (acid resistance), is hydrophilic, and has a high dehydration ability.

[0073] The reaction temperature in the acetalization step is preferably from room temperature to 120° C., with the lower limit being more preferably 30° C., and even more preferably 40° C. The upper limit being more preferably 100° C., and even more preferably 80° C. By controlling the reaction temperature within this range, it is possible to prevent the reaction from taking a long time, side reactions from occurring simultaneously, runaway reactions, coloration of the product, and the like. In the case of a batch system, the reaction time in the acetalization step is usually 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 30 minutes to 15 hours, starting from the time when stirring begins. By controlling the reaction time within this range, the occurrence of side reactions and coloration of the product can be suppressed. However, when a flow system is used, the reaction time is not limited to this. The reaction pressure in the acetalization step is not particularly limited, but is usually atmospheric pressure.

[0074] <First oxidation step> In the first oxidation step, HMF acetal is oxidized to synthesize a furan derivative having an acetal group and a carbonyl group. The oxidation in this step includes oxidative esterification. In this embodiment, in the first oxidation step, HMF acetal is contacted with an oxidation catalyst to synthesize a furan derivative having an acetal group and a carbonyl group. The furan derivative is preferably a compound represented by the following formula (1), more preferably a compound represented by the following formula (2), and even more preferably a compound represented by the following formula (4). [ka]

[0075] In formula (1), Z is a hydrogen atom or a hydroxyl group, and R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. Examples of the alkyl substituent include an alkyl group having 1 to 6 carbon atoms. [ka] In formula (2), R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. [ka]

[0076] The oxidation of HMF acetal is carried out in the presence of a catalyst, and examples of the catalyst include metals of Groups 8 to 10 of the periodic table, such as platinum, palladium, nickel, iron, ruthenium, and cobalt, and compounds thereof; metals of Group 11 of the periodic table, such as copper, silver, and gold, and compounds thereof; metals of Group 12 of the periodic table, such as zinc, and compounds thereof; metals of Group 13 of the periodic table, such as indium, and compounds thereof; metals of Group 14 of the periodic table, such as tin and lead, and compounds thereof; metals of Group 7 of the periodic table, such as manganese and rhenium, and compounds thereof; metals of Group 6 of the periodic table, such as chromium and molybdenum, and compounds thereof; metals of Group 5 of the periodic table, such as niobium and tantalum, and compounds thereof; metals of Group 4 of the periodic table, such as zirconium, and compounds thereof; metals of Group 3 of the periodic table, such as scandium, and compounds thereof; metals of Group 2 of the periodic table, such as magnesium and calcium, and compounds thereof; metals of Group 1 of the periodic table, such as cesium, and compounds thereof; and mixtures (including alloys) of these metals. Particularly preferred are metals from Groups 6 to 12 of the periodic table, their compounds, and mixtures (including alloys) of these, with metals from Groups 7 to 11 of the periodic table and their compounds being even more preferred. Among these, platinum, palladium, rhenium, magnesium, copper, silver, gold, zinc, manganese, cobalt, and their compounds are particularly preferred, with platinum, palladium, rhenium, copper, silver, gold, cobalt, manganese, and their compounds being most preferred. Examples of compounds include oxides, alkoxy compounds, alkyl compounds, and organic acid salts of these metals, with metals and their oxides or organic acid salts being preferred. These metals and their compounds may be mixed, and may be, for example, a catalyst consisting of a combination of a cobalt compound, a manganese compound, and a bromine compound.

[0077] These metal catalysts are preferably used as metal-supported catalysts supported on various supports. Examples of supports include natural minerals such as carbon, silica, alumina, titania, zirconia, niobia, ceria, tungsten oxide, silicon carbide, boron carbide, titanium carbide, diatomaceous earth, and layered silicates. Among these, carbon, titania, and ceria are preferred in terms of ease of catalyst preparation and activity. These catalysts may be used alone or in combination of two or more, or may be added later.

[0078] In this step, the oxidation reaction of HMF acetal in the presence of a metal catalyst can be carried out by a batch method, a flow method, or the like, but it is preferable to use the flow method because of its high production efficiency.

[0079] When the oxidation reaction is carried out in a batch system, the amount of the catalyst used is preferably 0.002 ppm by mass or more and 100,000 ppm by mass or less in terms of metal relative to the raw materials. The lower limit of the amount of catalyst used is more preferably 0.02 ppm by mass, even more preferably 0.2 ppm by mass, and particularly preferably 2 ppm by mass, in terms of metal relative to the raw materials. The upper limit of the amount of catalyst used is more preferably 50,000 ppm by mass, even more preferably 20,000 ppm by mass, and particularly preferably 10,000 ppm by mass, in terms of metal relative to the raw materials. By using such an amount of catalyst, the furan derivative can be produced efficiently in a reasonable reaction time, and an increase in catalyst costs and coloration of the product can be suppressed. However, the amount of catalyst used when a flow system is used is not limited to this.

[0080] In this step, the oxidation reaction may be carried out in the presence of a base, since the presence of a base can improve the stability of the acetal, suppress side reactions, and may also improve the yield of the target product. Examples of such bases include inorganic bases such as sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, and potassium bicarbonate, and organic bases such as triethylamine. Among these, inorganic bases are preferred because of their efficient removal from the product.

[0081] The amount of base used when carrying out the oxidation reaction in the presence of a base is not particularly limited, but the lower limit relative to the HMF acetal is 0.01 equivalents or more, preferably 0.1 equivalents or more, and the upper limit is 10 equivalents or less, preferably 5 equivalents or less, more preferably 3 equivalents or less. By adopting such an amount, the stability of the HMF acetal can be improved, side reactions can be suppressed, and the yield of the target product can be improved. The reaction temperature in this step is preferably from room temperature to 200° C., with the lower limit of the reaction temperature more preferably 30° C., even more preferably 40° C., and particularly preferably 60° C. The upper limit is more preferably 180° C., even more preferably 150° C., particularly preferably 130° C., and most preferably 80° C. Controlling the reaction temperature within this range can prevent prolonged reaction times, concurrent occurrence of side reactions, decomposition of the diol that serves as the acetalizing agent, runaway reaction, coloration of the product, and the like.

[0082] The oxygen source used in the oxidation reaction is not particularly limited, and may be an oxygen-containing organic compound, an inorganic peroxide, an oxygen-containing gas, or the like, but usually an oxygen-containing gas such as oxygen gas or air that does not require separation and purification after the reaction is completed is used. In a batch system, the oxygen-containing gas is confined in a reactor, and in a flow system, the oxygen-containing gas is flowed through the reactor to carry out the oxidation reaction, and the flow system is preferred.

[0083] When an oxygen-containing gas is used, the oxygen content in the oxygen-containing gas is usually 20% by volume or more, and may be 50% by volume or more. Pure oxygen (99% or more) may also be used. From the viewpoint of reducing the risk of explosion and ensuring reaction safety, it is preferable to use air containing approximately 21% by volume of oxygen, or an oxygen-containing gas having almost the same composition as air. The use of such an oxygen-containing gas not only improves reaction selectivity but also suppresses the oxidative decomposition reaction of the diol, which is necessary to obtain a cyclic acetal of HMF.

[0084] The reaction time in this step is not particularly limited when the oxidation reaction is carried out in a flow system. When the oxidation reaction is carried out in a batch system, the reaction time is usually 10 minutes to 30 hours, preferably 30 minutes to 20 hours, more preferably 1 hour to 10 hours, and even more preferably 1 hour to 5 hours, starting from the time when the oxygen-containing gas is first introduced into the reactor. By controlling the reaction time within this range, the occurrence of side reactions and runaway reactions can be suppressed, and production costs can be reduced.

[0085] When the oxidation reaction is carried out by a flow method, the flow rate of the oxygen-containing gas through the reactor is usually 1 mL / min to 100 L / min, preferably 10 mL / min to 10 L / min, more preferably 100 mL / min to 5 L / min, and even more preferably 500 mL / min to 1 L / min. By controlling the flow rate within this range, the oxygen consumption efficiency and the production efficiency of the target product can be improved, the occurrence of side reactions and runaway reactions can be suppressed, and the production cost can be reduced.

[0086] Examples of a method for passing the oxygen-containing gas through the reactor include a method of blowing the oxygen-containing gas into the liquid layer of the reactor or a method of blowing the oxygen-containing gas into the gas layer of the reactor, but the method of blowing the oxygen-containing gas into the liquid layer of the reactor is preferred. The oxygen-containing gas may be passed continuously or intermittently, but is preferably passed continuously. When passing the gas intermittently, it is preferable to appropriately adjust the intervals of the intermittent passes so as not to cause a shortage of oxygen. The oxidation reaction may be carried out by supplying an oxygen-containing gas so that the pressure inside the reaction vessel is pressurized. The reaction pressure is usually 0.1 MPa or more, preferably 0.3 MPa or more, more preferably 0.4 MPa or more, and usually 15 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less, even more preferably 3 MPa or less, and particularly preferably 1 MPa or less. Controlling the pressure within this range eliminates the need for high-pressure reaction equipment and can suppress the occurrence of side reactions and the oxidative decomposition reaction of the diol required to obtain the cyclic acetal of HMF.

[0087] The reaction solvent used in this step is not particularly limited, but is preferably a solvent containing water that dissolves the starting HMF acetal. In this case, a mixed solvent of the reaction solvent used in the acetalization step and water, a mixed solvent of the diol and water, or water alone can be used. When oxidation is carried out after isolating the cyclic acetal intermediate, the solvent does not necessarily have to be a mixed solvent; an aqueous solvent can also be used. Here, when using a mixed solvent with water, the water content is not particularly limited as long as it is 1 equivalent or more relative to the cyclic acetal intermediate. However, the lower limit in terms of volume ratio is usually 1 vol% or more, preferably 10 vol% or more, and more preferably 50 vol% or more, and there is no upper limit.

[0088] The concentration of HMF acetal in the reaction solvent introduced into the reactor usually has a lower limit of 1% by mass, preferably 5% by mass, more preferably 10% by mass, even more preferably 20% by mass, and particularly preferably 30% by mass, and an upper limit of usually 60% by mass, preferably 50% by mass. By controlling the concentration within this range, it is not necessary to use an excessively large reaction vessel, and the reaction can proceed in a short time with high production efficiency. In addition, side reactions such as the decomposition reaction of the HMF acetal can be suppressed.

[0089] When the oxidation in this step is oxidative esterification, the presence of an alcohol in the reaction system produces an ester of formylfurancarboxylic acid (FFCA) acetal. If the alcohol is a diol added in the acetalization step, a hydroxyalkyl ester of FFCA acetal is produced; if it is a monool, an alkyl ester of acetal is produced. The alcohol to be coexisted is not particularly limited, but examples thereof include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-ethyl-1-hexanol, 1-nonanol, and 1-decanol. The alcohol may be an aliphatic monoalcohol having 1 to 20 carbon atoms, such as 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecen-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecen-1-ol, nonadecyl alcohol, or arachidyl alcohol; or an aliphatic diol having 2 to 8 carbon atoms, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, or 1,4-cyclohexanedimethanol.

[0090] The reaction solution obtained after oxidation of the HMF acetal contains a furan derivative having an acetal group and a carbonyl group. In the reaction solution, the concentration of the furan derivative is preferably 70 mol % or more, more preferably 90 mol % or more, based on all compounds having a furan skeleton. That is, another embodiment of the present invention is a solution containing a furan derivative having an acetal group and a carbonyl group, wherein the concentration of the furan derivative is 70 mol % or more based on all compounds having a furan skeleton. Since the furan derivative is a compound with high thermal stability, by controlling the temperature within this range, it is possible to suppress decomposition of the compound containing a furan skeleton in the reaction solution in the deprotection step and second oxidation step described below.

[0091] <Deprotection process> The deprotection step is a step in which the furan derivative having an acetal group and a carbonyl group obtained in the oxidation step is deprotected by hydrolysis to synthesize diformylfuran, FDCA, or an ester thereof. The deprotection step makes it possible to easily produce FDCA and FDCA esters even under mild conditions. The deprotection of the furan derivative can be carried out by hydrolysis under acidic conditions. Another aspect of the present embodiment is a method for producing a furan derivative, including a deprotection step of synthesizing a furan derivative by deprotecting FFCA (formylfurancarboxylic acid) acetal or its ester, in which a formyl group is acetal-protected, wherein the furan derivative is one or more selected from the group consisting of formylfurancarboxylic acid and its esters. Methods for producing FDCA or furandicarboxylic acid esters from HMF are disclosed in Patent Documents 3 and 4, etc., but the present inventors have found that FDCA or its esters, i.e., furandicarboxylic acid esters, can be produced in high yield from HMF by a production method in which FDCA acetal or its esters are deprotected.

[0092] The deprotection step is a step in which FFCA acetal or its ester is deprotected by hydrolysis to synthesize FFCA or its ester. This step makes it possible to easily produce FDCA and FDCA esters even under mild conditions. Here, the deprotection of FFCA acetal or its ester can be carried out by hydrolysis under acidic conditions.

[0093] In this embodiment, in the deprotection step, FFCA or its ester is synthesized by deprotecting FFCA acetal or its ester. The FFCA acetal or its ester used in the deprotection step is not particularly limited, but is preferably a compound having a cyclic acetal structure of a 5-membered or 6-membered ring. The FFCA acetal is preferably a compound represented by the following formula (3). [ka] In formula (3), X, R 4 and R 5 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. Examples of the alkyl substituent include an alkyl group having 1 to 6 carbon atoms.

[0094] The reaction method in the deprotection step can be a batch method, a flow method, or the like. The materials of the reactor, flow path, and other components that come into contact with the liquid are not particularly limited, and may be glass, stainless steel (SUS), iron, or other metals. However, glass or stainless steel (SUS) reactors are preferred because they are corrosion-resistant and have high energy transfer efficiency. Furthermore, stainless steel (SUS) reactors are preferred from the viewpoint of industrial production equipment costs. The hydrolysis conditions are not particularly limited as long as they allow the hydrolysis of the furan derivative to proceed.

[0095] The reaction temperature in the hydrolysis is preferably from room temperature to 120° C., with the lower limit of the reaction temperature being more preferably 30° C., and even more preferably 40° C. The upper limit of the reaction temperature is more preferably 100° C., and even more preferably 80° C. By controlling the reaction temperature within this range, it is possible to prevent the reaction from taking a long time, side reactions from occurring simultaneously, runaway reactions, coloration of the product, and the like. In the case of a batch system, the reaction time for hydrolysis is usually 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 30 minutes to 15 hours, starting from the time when stirring begins. By controlling the reaction time within this range, the occurrence of side reactions and coloration of the product can be suppressed. However, this does not apply when the reaction is carried out in a flow system. The reaction pressure for the hydrolysis is not particularly limited, but is usually atmospheric pressure.

[0096] As a solvent for the hydrolysis, water is usually used, but a mixed solvent of water and an organic solvent may also be used. From the viewpoint of hydrolysis efficiency and cost advantage, it is preferable to use water as a reaction solvent. When a mixed solvent of water and an organic solvent is used, the organic solvent is not particularly limited, and examples thereof include ethers having 4 to 20 carbon atoms such as diethyl ether, tetrahydrofuran (THF), tetrahydropyran, methyltetrahydropyran, dipropyl ether, diisopropyl ether, methyl-tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, and 2-hexanone. Ketones having 4 to 20 carbon atoms, such as 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, 3-dodecanone, 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, and acetophenone; esters, such as ethyl acetate, propyl acetate, and butyl acetate;Methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 3-pentanol, 3-methyl-1-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 2-octanol, 3-octanol monoalcohols having 1 to 20 carbon atoms, such as ethanol, 2-ethyl-1-hexanol, 1-nonanol, 1-decanol, 1-undecyl alcohol, 1-lauryl alcohol, 1-tridecyl alcohol, 1-tetradecanol, 1-pentadecyl alcohol, 1-hexadecanol, cis-9-hexadecen-1-ol, 1-heptadecanol, 1-octadecanol, 16-methylheptadecen-1-ol, nonadecyl alcohol, and arachidyl alcohol; phenol, methyl Phenols having 6 to 12 carbon atoms, such as phenol, ethylphenol, propylphenol, and butylphenol; saturated aliphatic hydrocarbon compounds having 3 to 12 carbon atoms, such as pentane, hexane, cyclohexane, heptane, octane, nonane, decane, dodecane, and isododecane; aromatic hydrocarbons, such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones, such as γ-butyrolactone and γ-valerolactone; dichloromethane, Examples of suitable solvents include halogenated hydrocarbons such as chloroform, dichloroethane, tetrachloroethane, and hexachloroethane; dimethylacetamide, N,N-dimethylformamide, N-methylmorpholine, N-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoric triamide, tetramethylurea, dimethyl sulfoxide, sulfolane, isosorbide, isosorbide dimethyl ether, propylene carbonate, and mixtures thereof; pyrrolidinium salts such as 1-butyl-1-methylpyrrolidinium bromide; piperidinium salts such as 1-butyl-1-methylpiperidinium triflate; and pyridinium salts such as 1-butylpyridinium tetrafluoroborate.Ionic liquids such as imidazolium salts such as 1-ethyl-3-methylimidazolium chloride; ammonium salts such as tetrabutylammonium chloride; phosphonium salts such as tetrabutylphosphonium bromide; and sulfonium salts such as triethylsulfonium bis(trifluoromethanesulfonyl)imide may also be used.

[0097] Preferred catalysts for hydrolysis include acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion, zeolites, metal oxides or composite metal oxides such as NbO, YNbO, TaO, NbO-WO, NbO-MoO, TiO-WO, TiO-MoO, SiO-NbO, and SiO-TaO, clay, immobilized sulfuric acid catalysts such as sulfated ZrO, and immobilized phosphoric acid catalysts such as titania or niobia treated with phosphoric acid. Among these, acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion, and zeolites are more preferred, with acidic cation exchange resins such as Amberlyst, Amberlite, and Diaion being particularly preferred, as they selectively promote deprotection of HMF acetal in a solvent containing water.

[0098] The reaction solution obtained by hydrolyzing the furan derivative contains diformylfuran, FFCA, or an ester thereof. In the reaction solution, the concentration of diformylfuran, FFCA, and its ester is preferably 70 mol% or more, and more preferably 90 mol% or more, of all compounds having a furan skeleton. FFCA and its ester are particularly thermally stable compounds, so by controlling the concentration within this range, decomposition of compounds containing a furan skeleton in the reaction solution can be suppressed in the second oxidation step described below.

[0099] <Recovery process> In the deprotection step, a furan derivative having an acetal group and a carbonyl group is deprotected to synthesize diformylfuran, FFCA, or its ester, and the resulting reaction solution may be subjected to a recovery step to recover a diol from the reaction solution. The recovered diol is the diol added in the acetalization step. The method for recovering the diol from the reaction solution is not particularly limited, and the diol can be recovered by extraction, distillation, or the like. When extraction is performed in the recovery step, the temperature is preferably from room temperature to 90° C., with the lower limit being more preferably 30° C. The upper limit is more preferably 60° C., and even more preferably 40° C. By controlling the reaction temperature within this range, the extraction efficiency during recovery is improved and the operation time can be shortened.

[0100] As the extraction solvent, an organic solvent is usually used, but a mixed solvent of water and an organic solvent may also be used. From the viewpoint of cost advantage, it is preferable to use a single solvent as the extraction solvent. The organic solvent is not particularly limited, and examples thereof include ethers having 4 to 20 carbon atoms such as diethyl ether, tetrahydropyran, methyl tetrahydropyran, dipropyl ether, diisopropyl ether, methyl tert-butyl ether, butyl ether, pentyl ether, hexyl ether, octyl ether, nonyl ether, decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, and triethylene glycol dimethyl ether; 2-butanone (methyl ethyl ketone), 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, cyclohexanone, 4-methyl-2-pentanone (methyl isobutyl ketone), 2-heptanone, 5-methyl-2-hexanone, 2,4-dimethylpentanone, 5-nonanone, 4-decanone, 5-decanone, 2-undecanone, 4-undecanone, and 3-dodecanone. Ketones having 4 to 20 carbon atoms such as 2-tridecanone, 2-tetradecanone, 4-tetradecanone, 2-pentadecanone, 3-pentadecanone, 7-pentadecanone, 2-hexadecanone, 3-hexadecanone, 4-hexadecanone, 6-hexadecanone, 2-heptadecanone, 4-heptadecanone, 9-heptadecanone, 3-octadecanone, and acetophenone; esters such as ethyl acetate, propyl acetate, and butyl acetate; pentane, hexane, cyclohexanone, etc. Saturated aliphatic hydrocarbon compounds having 3 to 12 carbon atoms, such as toluene, xylene, trimethylbenzene, 1,2,3,4-tetrahydronaphthalene, and 1-methylnaphthalene; lactones, such as γ-butyrolactone and γ-valerolactone; and halogenated hydrocarbons, such as dichloromethane, chloroform, dichloroethane, tetrachloroethane, and hexachloroethane, may also be used. Among these, the organic solvent is preferably selected from at least one of the group consisting of ethers, ketones, esters, lactones, aromatic hydrocarbons, halogenated hydrocarbons, and saturated aliphatic hydrocarbons, more preferably selected from at least one of the group consisting of esters, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons, and even more preferably selected from at least one of the group consisting of esters, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons.As the ester, specifically, ethyl acetate is preferred.

[0101] The recovery process is carried out by a batch method, a flow method, or the like. The materials of the reactor, flow path, and other components that come into contact with the liquid are not particularly limited, and may be made of glass, stainless steel (SUS), iron, or other metals. However, glass or stainless steel (SUS) reactors are preferred because they are corrosion-resistant and have high energy transfer efficiency. Furthermore, stainless steel (SUS) reactors are preferred from the viewpoint of industrial production equipment costs.

[0102] <Second oxidation step> The second oxidation step involves oxidizing the diformylfuran, FFCA, or its ester obtained in the deprotection step. The oxidation in this step includes oxidative esterification. FDCA is obtained by oxidation of these compounds, and FDCA esters are obtained by oxidative esterification. Another aspect of the present embodiment is a method for producing furandicarboxylic acid or an ester thereof, comprising a second oxidation step of contacting a composition containing a furan derivative with an oxidation catalyst, wherein the furan derivative is at least one selected from the group consisting of diformylfuran, and formylfurancarboxylic acid and esters thereof, and the concentration of the furan derivative is 70 mass% or more of all compounds having a furan skeleton contained in the composition containing the furan derivative. Methods for producing FDCA or furandicarboxylic acid esters from HMF are disclosed in Patent Documents 2 and 3, etc., but the present inventors have found that FDCA or furandicarboxylic acid esters can be produced in high yield from HMF by a production method including a production step of oxidizing a high concentration of the furan derivative. Among the compositions to be subjected to the second oxidation step, it is preferable that the concentration of diformylfuran, FFCA and its esters in all the compounds having a furan skeleton is 70 mol% or more, and more preferably 90 mol% or more. Among these compounds having a furan skeleton, particularly, FFCA and its esters are compounds with high thermal stability. By controlling within this range, the effect of suppressing the decomposition of the compounds containing a furan skeleton in the reaction solution can be achieved.

[0103] In the second oxidation step, since the oxidation of the formyl group proceeds easily, from the viewpoint of suppressing the concurrent occurrence of side reactions, the reaction can be carried out at a temperature lower than the reaction temperature in the second oxidation step. Specifically, it may be 80°C or lower, or may be 60°C or lower. Also, the lower limit value of the reaction temperature in the second oxidation step may be the same as the lower limit value of the reaction temperature in the oxidation step. Thus, the second oxidation step can carry out the oxidation reaction under milder conditions compared to the oxidation step. Regarding the reaction conditions other than the reaction temperature in the second oxidation step, they are the same as the conditions described in the first oxidation step.

[0104] <Method for recovering FDCA and FDCA esters> The recovery of FDCA and FDCA esters obtained in the above second oxidation step is not particularly limited, and the product can be recovered by a solvent evaporation method, an extraction method with an organic solvent after solvent evaporation, a distillation method, a sublimation method, a crystallization method, or a chromatography method. Among these, a method of recovering the product while purifying it by a distillation method is preferable.

[0105] Also, as another aspect of this embodiment, the following production method can also be mentioned. That is, a method for producing a furandicarboxylic acid or a furandicarboxylic acid ester from hydroxymethylfurfural, which has the following production steps (i) to (iv). (i) Acetalize hydroxymethylfurfural to synthesize hydroxymethylfurfural acetal in an acetalization step, (ii) Hydroxymethylfurfural acetal is oxidized to formylfurancarboxylic acid a first oxidation step to synthesize an acetal or an ester thereof; (iii) deprotecting formyl furancarboxylic acid acetal or its ester to give formyl a deprotection step to synthesize sulfuric acid or its ester; and (iv) a second oxidation step in which formylfurancarboxylic acid or its ester is oxidized. After the step (iii), a recovery step as described below may be further included.

[0106] The formylfurancarboxylic acid acetal or its ester is preferably a compound represented by formula (3). [ka] In formula (3), X, R 2 and R 3 are independently selected from a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 12 carbon atoms which may have an alkyl substituent. In the step (i), it is preferable to use an organic solvent selected from 2-butanone (methyl ethyl ketone), 4-methyl-2-pentanone (methyl isobutyl ketone), toluene, and methyltetrahydropyran. It is preferable to have a recovery step of recovering a diol from the reaction solution after the step (iii), and it is preferable that the diol is a diol having 2 to 10 carbon atoms. [Example]

[0107] The present invention will be explained in more detail below with reference to examples, but the present invention does not go beyond the gist of the invention. However, the present invention is not limited to these examples.

[0108] <<Example A>> The yield of the product was measured by diluting the solution after the reaction and quantitatively analyzing the product using a liquid chromatography (Shimadzu Corporation: LC-2010, column: ULTRON PS-80H) with an absolute calibration curve method. The detector was a differential refractive index detector (RI detector), and the developing solvent was water. The yield of 5-hydroxymethylfurfural (5-HMF) was calculated using the following formula. Selectivity of 5-HMF (%) = moles of 5-HMF produced / moles of glucose consumed in the reaction × 100 5-HMF yield (%) = moles of 5-HMF produced / moles of glucose used in the reaction × 100

[0109] [Example A1] Glucose (0.3 g, 1.7 mmol), aluminum oxide (Al2O3) (0.3 g, 100 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM RCP160M (0.6 g, 200 wt % based on the substrate) was placed in a pressure vessel, to which methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added, and the vessel was sealed. The vessel was heated to 120°C and heated under a pressure of 0.2 MPa with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction, the catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0110] [Example A2] Glucose (0.3 g, 1.7 mmol), aluminum oxide (Al2O3) (0.3 g, 100 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM RCP160M (0.6 g, 200 wt % based on the substrate) was placed in a pressure vessel, to which methyl isobutyl ketone (MIBK) (7 g) and water (3 g) were added, and the vessel was sealed. The vessel was heated to 120°C and heated under a pressure of 0.2 MPa with stirring for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction, the catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0111] [Example A3] Glucose (1.0 g, 5.7 mmol) and aluminum oxide (Al) were used as an isomerization catalyst. 2 O 3 A pressure vessel was charged with 1.0 g (100 wt% relative to the substrate) of methyl tetrahydropyran (MTHP) (7 g) and 3 g of water as a dehydration catalyst (Diaion TMRCP160M) (2.0 g, 200 wt% relative to the substrate), followed by sealing. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0112] [Example A4] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and porous, strongly acidic cation exchange resin (Amberlyst® 15) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were then added and sealed. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0113] [Example A5] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion TMRCP160M) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and the vessel was sealed. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0114] [Example A6] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and phosphoric acid-activated carbon (1.0 g, 100 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were then added and sealed. The vessel was heated to 140 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0115] [Example A7] Glucose (1.0 g, 5.7 mmol), magnesium oxide (MgO) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and phosphoric acid-modified silica gel (1.0 g, 100 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel. Methyltetrahydropyran (MTHP) (7 g) and water (3 g) were then added and sealed. The vessel was heated to 140 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0116] [Comparative Example A1] Glucose (0.3 g, 1.7 mmol) and phosphoric acid (15 mg, 5 wt% relative to the substrate) as a catalyst were placed in a pressure vessel, to which methyl isobutyl ketone (MIBK) (7 g) and water (3 g) were added and sealed. The vessel was heated to 140°C and stirred for 4 hours. After 4 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction, the catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0117] [Comparative example A2] Glucose (0.3 g, 1.7 mmol) and phosphoric acid (15 mg, 5 wt% relative to the substrate) as a catalyst were placed in a pressure vessel, to which methyltetrahydropyran (MTHP) (7 g) and water (3 g) were added and sealed. The vessel was heated to 140 °C and stirred for 4 hours. After 4 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction, the catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0118] [Comparative example A3] Glucose (1.0 g, 5.7 mmol) and highly porous, strongly acidic cation exchange resin (Diaion) were used as a dehydration catalyst. TM A pressure vessel was charged with 2.0 g (200 wt% relative to the substrate) of RCP160M and 1.0 g (100 wt% relative to the substrate) of sodium chloride (NaCl) as an additive, followed by 7 g of methyl isobutyl ketone (MIBK) and 3 g of water, and then sealed. The vessel was heated to 120°C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0119] [Comparative example A4] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, highly porous, strongly acidic cation exchange resin (Diaion TMRCP160M) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst, and sodium chloride (NaCl) (1.0 g, 100 wt% relative to the substrate) as an additive were placed in a pressure vessel, and dimethyl sulfoxide (DMSO) (10 g) was added and sealed. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0120] [Comparative Example A5] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM RCP160M (2.0 g, 200 wt % based on the substrate) was placed in a pressure vessel, to which dimethyl sulfoxide (DMSO) (10 g) was added and sealed. The vessel was heated to 120°C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to stop the reaction, the catalyst was separated by filtration, and the organic phase was recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0121] [Comparative example A6] Glucose (1.0 g, 5.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% relative to the substrate) as an isomerization catalyst, and porous, strongly acidic cation exchange resin (Amberlyst® 15) (2.0 g, 200 wt% relative to the substrate) as a dehydration catalyst were placed in a pressure vessel, to which dimethyl sulfoxide (DMSO) (10 g) was added and sealed. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0122] [Comparative example A7] Glucose (0.3 g, 1.7 mmol), aluminum oxide (Al2O3) (1.0 g, 100 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM A pressure vessel was charged with 2.0 g (200 wt% relative to the substrate) of methyl tetrahydropyran (RCP160M) and 4.0 g (400 wt% relative to the substrate) of sodium chloride (NaCl) as an additive, followed by 7 g of methyl tetrahydropyran (MTHP) and 3 g of water, and then sealed. The vessel was heated to 120°C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was placed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0123] [Comparative example A8] Glucose (0.1 g, 0.5 mmol), aluminum oxide (Al2O3) (2.0 g, 200 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM A pressure vessel was charged with 2.0 g (200 wt% relative to the substrate) of 5-hydroxymethylfurfural (RCP160M) and 4.0 g (400 wt% relative to the substrate) of sodium chloride (NaCl) as an additive. 7 g of methyl isobutyl ketone (MIBK), 2.4 g of N-methylpyrrolidone (NMP), and 0.6 g of water were added and sealed. The vessel was heated to 120 °C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0124] [Comparative example A9] Glucose (0.1 g, 0.5 mmol), aluminum oxide (Al2O3) (2.0 g, 200 wt% of the substrate) as an isomerization catalyst, and highly porous, strongly acidic cation exchange resin (Diaion) as a dehydration catalyst were used. TM A pressure vessel was charged with 2.0 g (200 wt% relative to the substrate) of RCP160M and 1.0 g (100 wt% relative to the substrate) of sodium chloride (NaCl) as an additive, followed by 7 g of methyl isobutyl ketone (MIBK), 2.4 g of N-methylpyrrolidone (NMP), and 0.6 g of water, and then sealed. The vessel was heated to 120°C and stirred for 8 hours. After 8 hours of heating and stirring, the vessel was immersed in cold water to terminate the reaction. The catalyst was separated by filtration, and the organic phase was separated and recovered. The organic solvent was then distilled off to obtain 5-hydroxymethylfurfural (5-HMF). The reaction conditions, selectivity, and yield of 5-HMF are shown in Table 2.

[0125] [Table 2] *The catalyst and additive amounts in the table represent the mass ratio (wt%) to glucose (substrate).

[0126] As shown in Table 2, in the process for producing 5-HMF from glucose, Examples A1 to A7, which used a biphasic solvent and a mixed catalyst containing an isomerization catalyst and a dehydration catalyst, produced 5-HMF with high yield and selectivity. On the other hand, Comparative Examples A1 to A9, which used a conventional method using only a biphasic solvent or only a mixed catalyst, resulted in lower 5-HMF yield and selectivity, especially selectivity, compared to the Examples. Furthermore, Comparative Examples A7 to A9, similar to the prior art, were investigated by adding 100 to 400 wt% NaCl relative to the substrate, but also resulted in lower 5-HMF yield and selectivity. As claimed in the present technology, the addition of Na salt promotes the distribution of the product into the oil phase, but it also has a significant adverse effect on the isomerization catalyst and dehydration catalyst, especially the dehydration catalyst (reducing acid strength).

[0127] <<Example B>> The yield of the product was measured by adding trioxane as an internal standard to the solution after the reaction and quantifying the product using a nuclear magnetic resonance (NMR) spectrometer (JOEL-JNM-ECX400, manufactured by JOEL Electronics Co., Ltd.). The measurement frequency was 400 MHz and the measurement solvent was deuterated dimethyl sulfoxide. The yield of FDCA was calculated using the following formula. Yield (%) of HMF acetal in the acetalization step = number of moles of HMF acetal produced in the acetalization step / number of moles of HMF used in the reaction in the acetalization step × 100 Yield (%) of FFCA acetal in the oxidation step = number of moles of FFCA acetal produced in the oxidation step / number of moles of HMF acetal used in the reaction in the oxidation step × 100 Yield (%) of FFCA in the deprotection step = number of moles of FFCA produced in the deprotection step / number of moles of FFCA acetal used in the reaction in the deprotection step × 100 Yield (%) of FDCA in the second oxidation step = number of moles of FDCA produced in the second oxidation step / number of moles of FDCA used in the reaction in the second oxidation step × 100 Overall yield of FDCA (%) through all steps = (Yield of HMF acetal in the acetalization step (%) / 100) × (Yield of FFCA acetal in the oxidation step (%) / 100) × (Yield of FFCA in the deprotection step (%) / 100) × (Yield of FDCA in the second oxidation step (%) / 100) × 100

[0128] [Example B1] <Acetalization process> HMF (10.0 g, 79.3 mmol), neopentyl glycol (12.4 g, 119.0 mmol) as a diol, porous strongly acidic cation exchange resin (Amberlyst 15) (1.0 g, 10 wt% relative to the substrate) as a catalyst, and toluene (40.0 g) as a solvent were added and stirred at 30 °C for 1 hour. The reaction mixture was then cooled to room temperature and the catalyst was separated by filtration. After washing with water, the toluene was distilled off, yielding HMF acetal in 97% yield. The reaction conditions for the acetalization step and the yield of HMF acetal are shown in Table 3.

[0129] <First oxidation step> The resulting HMF acetal (4.0 g, 18.8 mmol), potassium carbonate (5.2 g, 37.6 mmol) as a base, 5% palladium-on-carbon (Pd / C) (4.0 g, 100 wt % relative to the substrate) as a catalyst, and water (16.0 g) as a solvent were added. Air was introduced to a pressure of 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction solution was then cooled to room temperature, and the reactor was depressurized. The catalyst was then separated by filtration, yielding an aqueous solution containing the FFCA acetal represented by formula (4). The yield was 97%. No decomposition of neopentyl glycol diol was observed during this process. The reaction conditions for the oxidation step and the yield of FFCA acetal are shown in Table 4. [ka]

[0130] <Deprotection process> The FFCA acetal (4.0 g, 17.7 mmol) obtained in the above example and a highly acidic cation exchange resin (Diaion TMRCP160M) (0.4 g, 10 wt % relative to the substrate) as a catalyst were added to water (16.0 g) as a solvent and stirred at 60°C for 1 hour. The reaction solution was then cooled to room temperature, and the catalyst was separated by filtration. The mixture was then washed with ethyl acetate to obtain FFCA in a 96% yield. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 5.

[0131] <Second oxidation step> The resulting FFCA (2.4 g, 17.0 mmol), potassium carbonate (4.7 g, 34.0 mmol) as a base, 5% palladium-on-carbon (Pd / C) (2.4 g, 100 wt % relative to the substrate) as a catalyst, and water (9.6 g) as a solvent were added. Air was introduced to a pressure of 0.9 MPa, and the mixture was stirred at 80°C for 8 hours. The reaction solution was then cooled to room temperature, and the reactor was depressurized. The catalyst was then separated by filtration, and sulfuric acid was poured into the filtrate, and the resulting precipitate was collected by filtration. The resulting solid was washed with water, yielding FDCA in 96% yield. The overall yield of FDCA was 87%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0132] [Example B2] <Acetalization process> HMF acetal was obtained in 97% yield by the same method as in Example B1, except that the amounts of HMF (40.0 g, 317.2 mmol), neopentyl glycol (49.6 g, 475.8 mmol), porous strongly acidic cation exchange resin (Amberlyst 15) (4.0 g, 10 wt% based on the substrate), and toluene (60.0 g) were changed. The reaction conditions for the acetalization step and the yield of HMF acetal are shown in Table 3.

[0133] <First oxidation step> FFCA acetal was obtained in 97% yield in the same manner as in Example B1, except that the amounts of HMF acetal (8.0 g, 37.7 mmol), potassium carbonate (10.4 g, 75.4 mmol), 5% palladium-on-carbon (Pd / C) (0.8 g, 10 wt % relative to the substrate), and water (12.0 g) were changed. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for this oxidation step and the yield of FFCA acetal are shown in Table 4.

[0134] <Deprotection process> FFCA was obtained in a yield of 95% in the same manner as in Example B1, except that the amount of water was changed to 6.0 g. In this step, decomposition of neopentyl glycol was not confirmed. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 53.

[0135] <Second oxidation step> FDCA was obtained in a yield of 97% in the same manner as in Example B1, except that the amounts of FFCA (1.2 g, 8.6 mmol), potassium carbonate (2.4 g, 17.2 mmol), 5% palladium-on-carbon (Pd / C) (0.12 g, 10 wt% relative to the substrate), and water (1.8 g) were changed. The overall yield of FDCA was 87%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0136] [Example B3] <Acetalization process> The reaction conditions for the acetalization step and the yield of HMF acetal are shown in Table 3.

[0137] <First oxidation step> FFCA acetal was obtained in a yield of 97% in the same manner as in Example B2, except that 5% platinum-supported carbon (Pt / C) (0.8 g, 10 wt% relative to the substrate) was used as the catalyst. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for this oxidation step and the yield of FFCA acetal are shown in Table 4.

[0138] <Deprotection process> FFCA was obtained in a yield of 96% in the same manner as in Example B2, except that the reaction time was changed to 2 hours. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for the deprotection step and the yield of FFCA are shown in Table 5.

[0139] <Second oxidation step> FDCA was obtained in a yield of 98% in the same manner as in Reference Example 2, except that 5% platinum-supported carbon (Pt / C) (0.1 g, 10 wt% relative to the substrate) was used as the catalyst. The overall yield of FDCA was 88%. The reaction conditions for the second oxidation step and the yield of FDCA are shown in Table 6.

[0140] [Comparative reference example B1] HMF (0.3 g, 2.4 mmol) and 5% platinum-loaded carbon (Pt / C) (0.03 g, 10 wt% relative to the substrate) as a catalyst were added to water (2.7 g) as a solvent, and air was introduced to a pressure of 0.9 MPa. The mixture was stirred at 80°C for 16 hours. The reaction solution was then cooled to room temperature, and the pressure in the reaction vessel was reduced. The catalyst was then separated by filtration, and sulfuric acid was poured into the filtrate, and the resulting precipitate was collected by filtration. The resulting solid was washed with water, yielding FDCA in a 22% yield. The reaction conditions and the yield of FDCA are shown in Table 7.

[0141] [Comparison reference example B2] FDCA was obtained in a 45% yield in the same manner as in Comparative Reference Example B1, except that HMF (1.2 g, 9.6 mmol), 5% platinum-supported carbon (Pt / C) (0.12 g, 10 wt% relative to the substrate) as a catalyst, potassium carbonate (2.65 g, 19.2 mmol) and water (1.8 g) as a solvent were added. The reaction conditions and the yield of FDCA are shown in Table 7.

[0142] [Table 3]

[0143] [Table 4]

[0144] [Table 5]

[0145] [Table 6]

[0146] [Table 7]

[0147] As shown in Table 3, Examples B1 to B3, which had an oxidation step of contacting HMF acetal with an oxidation catalyst in the production of FFCA acetal, produced FFCA acetal in high yield. Furthermore, as shown in Table 4, Examples B1 to B3, which had a deprotection step of deprotecting FFCA acetal in the production of FFCA, produced FFCA in high yield. Furthermore, as shown in Tables 5 and 6, Examples B1 to B3, which used the obtained FFCA acetal, produced FDCA in high yield. Furthermore, as shown in Table 6, Examples B1 to B3, which had a second oxidation step of contacting FFCA with an oxidation catalyst in the production of FDCA, produced FDCA in high yield. On the other hand, as shown in Table 7, Comparative Reference Examples B1 and B2, which used the conventional method of producing FDCA by direct oxidation of HMF, resulted in a lower FDCA yield than Examples B1 to B3. In addition, the FFCA obtained in the deprotection step of this example is oxidatively esterified in the second oxidation step to obtain an FDCA ester.

[0148] <<Example C>> [Example C1] <Step (i): Acetalization Step> HMF (10.0 g, 79.3 mmol), neopentyl glycol (12.4 g, 119.0 mmol) as a diol, and porous strongly acidic cation exchange resin (Amberlyst 15) (1.0 g, 10 wt % relative to the substrate) as a catalyst were added to toluene (40.0 g) as a solvent and stirred at 30°C for 1 hour. The reaction mixture was then cooled to room temperature and the catalyst was separated by filtration. After washing with water, the toluene was distilled off, yielding HMF acetal in 97% yield. The reaction conditions for step (i) are shown in Table 8.

[0149] <Step (ii): First oxidation step> The resulting HMF acetal (4.0 g, 18.8 mmol), potassium carbonate (5.2 g, 37.6 mmol) as a base, 5% palladium-on-carbon (Pd / C) (4.0 g, 100 wt % relative to the substrate) as a catalyst, and water (16.0 g) as a solvent were added, and the mixture was stirred at 80°C for 8 hours under an air pressure of 0.9 MPa. The reaction mixture was then cooled to room temperature and the reactor pressure was released. The catalyst was then separated by filtration, and FFCA acetal was obtained in a 97% yield. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0150] <Step (iii): Deprotection step> The obtained FFCA acetal (4.0 g, 17.7 mmol) was mixed with a highly acidic cation exchange resin (Diaion) as a catalyst. TM RCP160M (0.4 g, 10 wt % based on the substrate) was added to water (16.0 g) as a solvent and stirred at 60°C for 1 hour. The reaction mixture was then cooled to room temperature, and the catalyst was separated by filtration. FFCA was then obtained in a 96% yield by washing with ethyl acetate. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (iii) are shown in Table 10.

[0151] <Step (iv): Second oxidation step> The resulting FFCA (2.4 g, 17.0 mmol), potassium carbonate (4.7 g, 34.0 mmol) as a base, 5% palladium-on-carbon (Pd / C) (2.4 g, 100 wt % relative to the substrate) as a catalyst, and water (9.6 g) as a solvent were added, and the mixture was stirred at 80°C for 8 hours under an air pressure of 0.9 MPa. The reaction solution was then cooled to room temperature, and the pressure in the reaction vessel was released. The catalyst was then separated by filtration, and sulfuric acid was poured into the filtrate, and the resulting precipitate was collected by filtration. The resulting solid was washed with water to obtain FDCA in a yield of 96%. The overall yield of FDCA was 87%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0152] [Example C2] <Step (i): Acetal step> Except for changing the amount of neopentyl glycol to 9.9 g and 95.2 mmol, HMF acetal was obtained in a yield of 97% in the same manner as in Example 1. The reaction conditions are shown in Table 8. <Step (ii): First oxidation step> FFCA acetal was obtained in 98% yield by the same method as in Example 1, except that 5% platinum-supported carbon (Pt / C) (4.0 g, 100 wt% based on the substrate) was used as the catalyst. No decomposition of neopentyl glycol diol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0153] <Step (iii): Deprotection step> FFCA was obtained in a yield of 96% in the same manner as in Example 1. In this step, decomposition of neopentyl glycol diol was not confirmed. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in a yield of 97% in the same manner as in Example 1, except that 5% platinum-supported carbon (Pt / C) (2.4 g, 100 wt% relative to the substrate) was used as the catalyst. The overall yield of FDCA was 89%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0154] [Example C3] <Step (i): Acetalization Step> HMF (40.0 g, 317.2 mmol) was added to propanediol (60.0 g, 788.5 mmol) as a solvent and stirred at 80°C for 12 hours. Propanediol also acts as a diol for acetalization. A zeolite membrane ZX2 (CHA type, SiO2 / Al2O3 = 6-8, vacuum degree 12 Pa) was immersed in the reaction solution, and the reaction solution was stirred while dehydrating. The reaction solution was then cooled to room temperature, and the propanediol was distilled off, yielding HMF acetal in a 96% yield. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> The resulting HMF acetal (8.0 g, 37.7 mmol), potassium carbonate (10.4 g, 75.4 mmol) as a base, 2% gold-loaded hydroxyapatite (Au / HAP) (0.8 g, 10 wt% relative to the substrate) as a catalyst, and water (12.0 g) as a solvent were added, and the mixture was stirred at 80°C for 8 hours under an air pressure of 0.9 MPa. The reaction solution was then cooled to room temperature, and the reactor was depressurized. The catalyst was then separated by filtration, yielding FFCA acetal in a 95% yield. No decomposition of propanediol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0155] <Step (iii): Deprotection step> FFCA was obtained in a yield of 96% in the same manner as in Example 1, except that the amount of water was changed to 6.0 g and the reaction time was changed to 2 hours. No decomposition of propanediol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> The resulting FFCA (1.2 g, 8.6 mmol), potassium carbonate (2.4 g, 17.2 mmol) as a base, and 2% gold-loaded hydroxyapatite (Au / HAP) (0.12 g, 10 wt% relative to the substrate) as a catalyst were added to water (1.8 g) as a solvent, and the mixture was stirred at 80°C for 8 hours under an air pressure of 0.9 MPa. The reaction solution was then cooled to room temperature, and the reactor was depressurized. The catalyst was then separated by filtration, and sulfuric acid was poured into the filtrate, and the resulting precipitate was collected by filtration. The resulting solid was washed with water to obtain FDCA in a yield of 91%. The overall yield of FDCA was 80%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0156] [Example C4] <Step (i): Acetalization Step> HMF (40.0 g, 317.2 mmol), neopentyl glycol (49.6 g, 475.8 mmol) as a diol, and porous strongly acidic cation exchange resin (Amberlyst 15) (4.0 g, 10 wt % relative to the substrate) as a catalyst were added to toluene (60.0 g) as a solvent and stirred at 30°C for 1 hour. The reaction mixture was then cooled to room temperature and the catalyst was separated by filtration. After washing with water, the toluene was distilled off, yielding HMF acetal in 97% yield. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> FFCA acetal was obtained in 97% yield in the same manner as in Example 3, except that 5% palladium-supported carbon (Pd / C) (0.8 g, 10 wt% based on the substrate) was used as the catalyst. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0157] <Step (iii): Deprotection step> FFCA was obtained in a yield of 95% in the same manner as in Example 1, except that the amount of water was changed to 6.0 g. In this step, decomposition of neopentyl glycol was not confirmed. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in a yield of 97% in the same manner as in Example 3, except that 5% palladium-supported carbon (Pd / C) (0.12 g, 10 wt% based on the substrate) was used as the catalyst. The overall yield of FDCA was 87%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0158] [Example C5] <Step (i): Acetalization Step> Except for changing the amount of neopentyl glycol to 39.6 g and 380.6 mmol, HMF acetal was obtained in a yield of 96% in the same manner as in Example 4. The reaction conditions for step (i) are shown in Table 8. <Step (ii): First oxidation step> FFCA acetal was obtained in 97% yield by the same method as in Example 3, except that 5% platinum-supported carbon (Pt / C) (0.8 g, 10 wt% based on the substrate) was used as the catalyst. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (ii) are shown in Table 9.

[0159] <Step (iii): Deprotection step> FFCA was obtained in a yield of 96% in the same manner as in Example 1, except that the amount of water was changed to 6.0 g and the reaction time was changed to 2 hours. No decomposition of neopentyl glycol was observed in this step. The reaction conditions for step (iii) are shown in Table 10. <Step (iv): Second oxidation step> FDCA was obtained in a yield of 98% in the same manner as in Example 3, except that 5% platinum-supported carbon (Pt / C) (0.1 g, 10 wt% relative to the substrate) was used as the catalyst. The overall yield of FDCA through all steps was 88%. The reaction conditions for step (iv) and the yield of FDCA are shown in Table 11.

[0160] [Comparative Example C1] HMF (0.3 g, 2.4 mmol), 5% platinum-supported carbon (Pt / C) (0.03 g, 10 wt% relative to the substrate) as a catalyst, and water (2.7 g) as a solvent were added, and air was introduced at 0.9 MPa and stirred at 80°C for 16 hours. The reaction solution was then cooled to room temperature, and the reactor was depressurized. The catalyst was then separated by filtration, and sulfuric acid was poured into the resulting filtrate, and the resulting precipitate was collected by filtration. The resulting solid was washed with water, yielding FDCA in a 22% yield. The reaction conditions and FDCA yield are shown in Table 12. [Comparative Example C2] FDCA was obtained in a 57% yield in the same manner as in Comparative Example C1, except that HMF (0.9 g, 7.2 mmol), 5% platinum-supported carbon (Pt / C) (0.09 g, 10 wt% relative to the substrate) as a catalyst, potassium carbonate (2.0 g, 14.4 mmol) and water (2.1 g) as a solvent were added. The reaction conditions and the yield of FDCA are shown in Table 12. [Comparative Example C3] FDCA was obtained in a 45% yield in the same manner as in Comparative Example C1, except that HMF (1.2 g, 9.6 mmol), 5% platinum-supported carbon (Pt / C) (0.12 g, 10 wt% relative to the substrate) as a catalyst, potassium carbonate (2.65 g, 19.2 mmol) and water (1.8 g) as a solvent were added. The reaction conditions and the yield of FDCA are shown in Table 12.

[0161] [Table 8]

[0162] [Table 9]

[0163] [Table 10]

[0164] [Table 11]

[0165] [Table 12]

[0166] As shown in Table 11, in Examples C1 to C5, in which a method including steps (i) to (iv) was used in the process of producing FDCA from HMF, FDCA was obtained in high yield. On the other hand, as shown in Table 12, in Comparative Examples C1 to C3, in which a conventional method of producing FDCA by direct oxidation of HMF was used, the FDCA yield was lower than that of Examples C1 to C5.< / vi> < / v> < / iv> < / iii> < / ii>

Claims

1. 1. A method for producing 5-hydroxymethylfurfural, comprising a contacting step of contacting glucose with an isomerization catalyst and a dehydration catalyst as a mixed catalyst in a two-phase solvent system of water and a water-immiscible organic solvent, A method for producing 5-hydroxymethylfurfural, characterized in that the two-phase solvent contains 80 parts by mass or less of an alkali metal salt or an alkaline earth metal salt per 100 parts by mass of glucose.

2. The method for producing 5-hydroxymethylfurfural according to claim 1, wherein the isomerization catalyst is a metal oxide.

3. 3. The method for producing 5-hydroxymethylfurfural according to claim 1, wherein the dehydration catalyst is a solid acid.

4. The method for producing 5-hydroxymethylfurfural according to any one of claims 1 to 3, wherein the isomerization catalyst is aluminum oxide and the dehydration catalyst is an ion exchange resin.

5. The method for producing 5-hydroxymethylfurfural according to any one of claims 1 to 4, characterized in that the organic solvent is hydrophobic and is at least one selected from the group consisting of ethers, ketones, aromatic hydrocarbons, and saturated aliphatic hydrocarbons.

6. The method for producing 5-hydroxymethylfurfural according to any one of claims 1 to 5, wherein the organic solvent is at least one selected from the group consisting of methyl tetrahydropyran (MTHP), methyl isobutyl ketone (MIBK), and methyl ethyl ketone (MEK).

7. Furthermore, the reaction solution obtained in the contacting step is treated with 5-hydroxybenzoates produced in the contacting step. an oil-water separation step of separating the solution into an organic solvent phase containing hydroxymethylfurfural and an aqueous phase containing the sugars contained in the solution after the contact step and the mixed catalyst, The method for producing 5-hydroxymethylfurfural according to claim 1.

8. The method for producing 5-hydroxymethylfurfural according to claim 7, further comprising a recovery step of dissolving (distributing) the 5-hydroxymethylfurfural produced in the contact step in the organic solvent phase obtained in the oil-aqueous separation step and recovering the 5-hydroxymethylfurfural.

9. The method for producing 5-hydroxymethylfurfural according to claim 7 or 8, further comprising a step of recovering the sugar and the mixed catalyst contained in the solution after the contact step together with the aqueous phase obtained in the oil-aqueous separation step.

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