Method for synthesizing 2,5-diformylfuran

Abstract

To efficiently synthesize 2,5-diformylfuran via 5-hydroxymethyl-2-furfural from a raw material derived from biomass.SOLUTION: A method for synthesizing 2,5-diformylfuran includes: a hydrothermal treatment step of producing a reaction liquid containing 5-hydroxymethyl-2-furfural by subjecting a raw material containing carbohydrate derived from biomass to hydrothermal treatment using a mixed liquid of an organic liquid and water as a medium in the presence of one or more salts of alkali metal salts and alkali earth metal salts; a water removal step of removing water from an organic liquid layer of the reaction liquid to yield a crude product containing 5-hydroxymethyl-2-furfural; and an oxidation step of oxidizing 5-hydroxymethyl-2-furfural in the crude product to yield 2,5-diformylfuran.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for synthesizing 5-hydroxymethyl-2-furfural from a biomass-derived raw material, and a method for synthesizing 2,5-diformylfuran from 5-hydroxymethyl-2-furfural. [Background technology]

[0002] Various biomass such as wood, grass, straw, bamboo, or cotton, and chips, pulp, thread, or paper products derived from these biomass are used as raw materials. When the cellulose or hemicellulose contained in these materials is treated under hydrothermal conditions, sugars such as oligosaccharides, glucomannan, glucose, mannose, xylose, and fructose are obtained. When these sugars are further treated, various hydrocarbon derivatives with 1 to 6 carbon atoms are obtained. Among these hydrocarbon derivatives, 2,5-diformylfuran (hereinafter sometimes referred to as "DFF") is obtained via the intermediate 5-hydroxymethyl-2-furfural (hereinafter sometimes referred to as "HMF") (chemical reaction formula below). DFF is obtained by oxidation or dehydrogenation of HMF. Currently, DFF is expensive, costing about 10,000 yen / kg on a pharmaceutical raw material price basis, due to the low distribution volume.

[0003] [ka]

[0004] Methods have been reported in which HMF is synthesized from these biomass and the like, and then this HMF is oxidized to produce DFF (Patent Documents 1 to 3 and Non-Patent Documents 1 to 4). In recent years, a method has also been reported in which DFF is directly synthesized from glucose or fructose via HMF (Patent Documents 4 and 5). However, when considering the synthesis of DFF from biomass and the purification of the products obtained at each stage, the method of synthesizing DFF via HMF and then oxidizing it is more reliable.

[0005] In recent years, HMF is one of the important compounds obtained from biomass, and is expected to be used as a raw material for various compounds. For example, it has already been reported that HMF itself has physiological activity. By blending HMF with medicines, functional foods, cosmetics, bath products, or quasi-drugs, new anti-allergy and anti-inflammatory agents with high safety can be easily produced (Patent Document 6). In addition, HMF can be used to produce mold-making binders, bioplastic monomers, medicines, agricultural chemicals, insecticides, antibacterial agents, fragrances, polymer materials, and the like (Patent Documents 7 to 10). In addition, HMF has utility as a fuel modifier, etc., and there is a very large potential demand.

[0006] However, HMF obtained from biomass is formed from aldehyde groups, hydromethyl groups, and furan rings, and is therefore more reactive than general aromatic compounds, easily forming oligomers and turning into brown insoluble matter (solid waste) called humic substances, which is a major obstacle to practical mass production. For this reason, it is important to purify HMF while preventing it from turning into humic substances. A wide variety of methods have been proposed for purifying HMF. Purifying HMF is difficult.

[0007] For example, when distillation, which is a physical purification method of HMF, is performed, if HMF is exposed for a long time at a temperature at which distillation is possible, the above-mentioned solid waste or tar-like products are generated. For this reason, methods have been reported in which HMF is distilled under ultra-high vacuum, HMF is purified by a falling thin film reduced pressure, HMF is distilled at a lower temperature, and HMF is further purified by recrystallization after distillation (Patent Document 11). Even with these purification methods, it is difficult to suppress the decrease in the yield of HMF.

[0008] Furthermore, a well-known method for chemically purifying HMF is to introduce a protecting group to an active aldehyde group or hydroxymethyl group, convert it to an acetal or ester, distill it, remove the protecting group, and purify it by recrystallization (Non-Patent Documents 5 to 8). In addition, a method has been reported in which HMF is converted into an ester using an enzyme and then purified. However, even with these purification methods, about 23% of HMF is lost in the process of purifying HMF from the ester. For this reason, purified HMF is expensive. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Special Publication No. 2017-518386 [Patent Document 2] Japanese Patent Application Publication No. 54-9260 [Patent Document 3] Japanese Patent Application Publication No. 55-49368 [Patent Document 4] Special Publication No. 2011-506478 [Patent Document 5] JP 2013-231061 A [Patent Document 6] JP 2010-248107 A [Patent Document 7] JP 2013-212536 A [Patent Document 8] JP 2009-057345 A [Patent Document 9] JP 2007-145736 A [Patent Document 10] JP 2005-200321 A [Patent Document 11] JP 2005-232116 A [Non-patent literature]

[0010] [Non-Patent Document 1] William Francis Cooper, Walter Harold Nutall, Journal of the Chemical Society, Transactions, 1921, 101, 1074-1081.

Non-licensed Document 2

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

Non-licensed Document 7

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide a method for efficiently synthesizing HMF from various biomass-derived raw materials, and a method for efficiently synthesizing DFF from HMF. [Means for solving the problem]

[0012] As a result of intensive research into achieving the above-mentioned object, the inventors have found that HMF can be obtained with high selectivity by hydrothermal treatment, in a mixed liquid obtained by mixing an organic liquid such as tetrahydrofuran with water, of a mixture of an inexpensive alkali metal salt or alkaline earth metal salt and a base metal salt such as iron chloride, of a raw material containing cellulose derived from various biomass, a hexose such as glucose or fructose, or an oligosaccharide composed of hexose, or a sugar liquid containing sugars such as glucose or fructose obtained by further saccharifying the raw material containing these oligosaccharides.

[0013] Furthermore, the obtained HMF is unstable in the reaction solution, and the presence of water in particular affects its stability. Therefore, it was discovered that by cooling the reaction solution containing HMF and removing the water in the reaction solution as a solid (ice), it is possible to obtain an HMF-containing solution in which the conversion of HMF to humic substances is minimized. On the other hand, it was discovered that HMF produced using a sugar solution containing glucose or fructose as a raw material, without containing aromatic compounds, is stable in the reaction solution. Therefore, by handling HMF in a solvent, the loss of HMF can be minimized.

[0014] Furthermore, it was found that DFF can be easily synthesized by oxidizing this HMF-containing liquid, and that DFF with a purity of 95% or more can be obtained by various simple purification procedures such as recrystallization, as shown in subsequent previous reports. The present invention was completed based on these findings. The method for synthesizing HMF of the present invention includes a hydrothermal step in which a raw material containing carbohydrates derived from biomass is hydrothermally treated in the presence of one or more salts of an alkali metal salt and an alkaline earth metal salt, using a mixed liquid of an organic liquid and water as a medium, to obtain a reaction liquid containing HMF.

[0015] A method for synthesizing DFF in one embodiment of the present invention includes a hydrothermal step in which a raw material containing biomass-derived carbohydrates is hydrothermally treated in the presence of a mixture of one or more salts of alkali metal salts and alkaline earth metal salts and a base metal salt, using a mixed liquid of organic liquid and water as a medium, to obtain a reaction liquid containing HMF; a water removal step in which water is removed from the organic liquid layer of the reaction liquid to efficiently obtain a crude product containing HMF; and an oxidation step in which HMF in the crude product is oxidized to obtain DFF.

[0016] Another embodiment of the method for synthesizing DFF of the present invention includes a hydrothermal step in which a raw material containing sugars is hydrothermally treated in the presence of one or more types of alkali metal salts and alkaline earth metal salts using a mixed liquid of an organic liquid and water as a medium to obtain a reaction liquid containing HMF, a substitution step in which a high-boiling point organic liquid having a boiling point higher than the boiling points of the organic liquid and water is added to the reaction liquid, and then the organic liquid and at least a portion of the water are distilled off to obtain a solution containing HMF, and an oxidation step in which the HMF in the solution is oxidized to obtain DFF. Effect of the Invention

[0017] According to the present invention, HMF can be efficiently produced by hydrothermal treatment using water-soluble sugars as well as water-insoluble biomass as raw materials. In addition, by removing water from the reaction solution containing the obtained HMF, the stability of HMF is improved, and DFF can be efficiently produced by oxidizing HMF as it is without highly purifying it. Furthermore, HMF obtained by hydrothermal treatment using sugars as raw materials is stable in organic solvents. Therefore, if a high-boiling organic liquid is added to the reaction solution containing HMF and then at least a part of the organic liquid and water is distilled off, HMF can be oxidized directly in the high-boiling organic liquid. Therefore, DFF can be obtained while suppressing the loss of HMF. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The method for synthesizing HMF according to an embodiment of the present invention includes a hydrothermal step. In the hydrothermal step, a raw material is hydrothermally treated in the presence of a salt to obtain a reaction liquid containing HMF. The salt used in this embodiment is one or more of an alkali metal salt and an alkaline earth metal salt. The presence of this salt improves the reaction yield of HMF. The salt is preferably a lithium salt, a sodium salt, or a calcium salt. The anion of the salt is preferably F. - , Cl - , Br - , I - , HSO4 - , SO4 2- , CF3SO3 - , NO3 - , (CF3SO2)2N - , BF4 - , PF6 - , CH3COO - , CF3COO - , HPO4 - , and PO4 2- etc.

[0019] The reaction yield of HMF is further improved by carrying out hydrothermal treatment in the presence of one or more salts of alkali metal salts and alkaline earth metal salts, and base metal salts other than alkali metal salts and alkaline earth metal salts, such as iron chloride and zinc chloride. Cations of the base metal salts include iron, steel, copper, aluminum, lead, zinc, tin, tungsten, indium, molybdenum, chromium, germanium, tantalum, magnesium, cobalt, cadmium, titanium, zirconium, vanadium, gallium, antimony, manganese, nickel, hafnium, niobium, bismuth, rhenium, and thallium. Anions of the base metal salts include F - , Cl - , Br - , I - , HSO4 - , SO4 2- , CF3SO3 - , NO3 - , (CF3SO2)2N - , BF4 - , PO4 3- , PF6 - , CH3COO - , CF3COO - , HPO4 - , and PO4 2- etc.

[0020] The raw material contains carbohydrates derived from biomass. More specifically, the raw material contains, for example, grass biomass such as rice straw or cedar chips, pulp derived from these biomasses, paper and recycled paper, cellulose obtained by saccharifying these, and sugar liquid containing hexose and oligosaccharides composed of hexose obtained by saccharifying these. In addition, the raw material includes sugars such as hexoses such as glucose or fructose that are soluble in water and oligosaccharides composed of these hexoses, as well as various pulps such as soda pulp, kraft pulp, sulfite pulp, chemi-ground pulp, refiner ground pulp, thermomechanical pulp, and digested pulp, biomass containing cellulose that is not soluble in water, and paper such as cardboard, newspapers, paper containers, and recycled paper.

[0021] Biomass containing insoluble cellulose includes woods such as pine, cedar, beech, maple, and eucalyptus, grasses such as rice straw, wheat straw, rice husk, and bagasse, and non-woods such as cotton, hemp, flax, palm husk, and bamboo. The carbohydrates contained in the raw material include one or more types of sugars obtained by saccharifying cellulose contained in a biomass-derived substance, such as cellulose, hexoses such as glucose or fructose, and oligosaccharides composed of hexoses.

[0022] The biomass that is the source of the carbohydrates contained in the raw material is not particularly limited, and food biomass including potato or sugarcane starch can also be used. However, in consideration of the recent food situation, etc., it is preferable to use raw materials derived from herbaceous biomass such as rice straw, wheat straw, rice husks, palm husks, bagasse, corn cobs, and other residues that have no or only a small impact on food, raw materials derived from woody biomass such as firewood such as eucalyptus, bamboo, cedar, sawtooth oak, red carpinus, and pine, chips, pellets, briquettes, wood chips, and lumber scraps, as well as sugar solutions containing sugars obtained by saccharifying these materials.

[0023] Among these, the raw materials are preferably chips derived from eucalyptus, bamboo, and cedar, various pulps obtained from these, and sugar liquids containing sugars obtained by saccharifying various pulps, and more preferably chips derived from eucalyptus, bamboo, and cedar, digested pulp obtained from these, and sugar liquids containing sugars obtained by saccharifying cedar or eucalyptus pulp. In addition to using biomass directly as a raw material, waste paper containing cellulose, hexose, and oligosaccharides composed of hexose can also be used as a raw material in recent years. In addition, carbohydrate-containing substances such as glucose, fructose, fruit sugar, starch, and cellulose that are widely available can also be used as raw materials.

[0024] In this embodiment, the raw material is hydrothermally treated using a mixture of organic liquid and water as a medium. The hydrothermal treatment can be performed by a batch type, a flow type, or a percolation type. The hydrothermal treatment can be performed at a temperature of 100°C to 250°C. The hydrothermal treatment can be performed for a residence time of 1 hour to 60 hours in the case of a batch type, and for a residence time of 10 minutes or more in the case of a flow type and a percolation type. The hydrothermal treatment can be performed at a pressure of 0.1 MPa to 20 MPa. A mixture of organic liquid and water can be used as a medium for the hydrothermal treatment. This is because cellulose, glucose, and fructose are easily reactive. The organic liquid can be selected from those that do not react with and do not decompose cellulose, glucose, and fructose at a temperature of 100°C to 250°C and a pressure of 0.1 MPa to 20 MPa.

[0025] Such organic liquids include tetrahydrofuran, methyltetrahydrofuran, 1,4-dioxane, diethyl ether, dimethyl ether, dimethylimidazolidinone, acetonitrile, methanol, ethanol, butanol, methyl isobutyl ketone, hexafluoroisopropanol, ethyl acetate, hexane, dimethylformamide, dimethyl sulfide, acetone, methyl ethyl ketone, Hmm Among these, preferred organic liquids are tetrahydrofuran, dioxane, butanol, methyl isobutyl ketone, ethyl acetate, dimethylformamide, dimethyl sulfide, methyl ethyl ketone, and the like, which are slightly soluble in water and can be phase-separated from water.

[0026] If hydrothermal treatment at high pressure is not possible due to the pressure resistance of the reaction vessel, the desired HMF can be obtained by replacing part of the organic liquid with an organic liquid having a higher boiling point. For example, if about 75% by mass of the organic liquid tetrahydrofuran is replaced with an aromatic hydrocarbon such as toluene, which is an organic liquid having a higher boiling point, the hydrothermal reaction can be carried out at a pressure of 1 MPa or less while suppressing a decrease in the yield of HMF.

[0027] There is no particular restriction on the form of the raw material, but it is preferable that the raw material is uniformly dissolved or uniformly dispersed in the mixed liquid. This is because the selectivity of the raw material to HMF is improved. When a sugar solution containing sugars is used as the raw material, the raw material dissolves in the mixed liquid, so the solution obtained by dissolving the sugar solution in the mixed liquid can be directly subjected to hydrothermal treatment. On the other hand, raw materials containing cellulose that is poorly soluble in various media including water, such as woody biomass or herbaceous biomass, are preferably crushed in advance and the dispersion uniformly dispersed in the mixed liquid is preferably subjected to hydrothermal treatment. During the reaction, the amount of carbohydrate contained in the raw material in the mixed liquid is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 10% by mass or more, and most preferably 25% by mass or more.

[0028] In the batch-type hydrothermal treatment, the particle size of the raw material after pulverization does not affect the hydrothermal treatment, so the particle size of the raw material after pulverization is not particularly limited. However, in the case of the flow-type hydrothermal treatment, the particle size of the raw material after pulverization is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and most preferably 20 μm or less. This is because the dispersion of the mixed liquid in which the raw material is dispersed becomes stable.

[0029] The method for synthesizing DFF according to the embodiment of the present invention includes a hydrothermal step, a water removal step, and an oxidation step. In the hydrothermal step, a reaction liquid containing HMF is obtained, similar to the hydrothermal step of the method for synthesizing HMF according to the present embodiment. If the reaction liquid is left to stand after removing the remaining raw materials by filtration as necessary, it separates into a water layer and an organic liquid layer. The generated HMF is dissolved in a larger amount in the organic liquid layer.

[0030] Therefore, the organic liquid layer is collected from the reaction solution and used in the next oxidation step. In order to oxidize the HMF contained in the organic liquid layer to produce DFF, it is necessary to remove as much water as possible from the organic liquid layer containing water. In the water removal step, water is removed from the organic liquid layer of the reaction solution to obtain a crude product containing HMF.

[0031] However, when the reaction solution containing HMF is heated, HMF is easily converted into an insoluble solid consisting of humic substances, which cannot be regenerated into HMF. For this reason, it is not preferable to remove water from the organic liquid layer of the reaction solution by a method that requires heating, such as distillation. Therefore, the reaction solution is cooled to freeze the water in the organic liquid layer, and the ice is then filtered to remove the water in the organic liquid layer, thereby obtaining a crude product containing HMF. The cooling temperature of the reaction solution at this time is preferably from the freezing point of the organic liquid to 0°C. For example, when the organic liquid is tetrahydrofuran (hereinafter sometimes referred to as "THF"), the water in the reaction solution can be suitably removed as ice by cooling the reaction solution to from -108°C to 0°C.

[0032] In addition, when replacing the organic liquid of the reaction solution containing HMF with another organic liquid to be used in the oxidation step before the next oxidation step, in the past, the organic liquid was removed from the reaction solution and then the other organic liquid was added. In this conventional method, the HMF was significantly converted into humic substances due to the HMF concentrated when the organic liquid was removed and the trace amounts of water remaining. This resulted in a large loss of HMF and a decrease in the yield of the final product, DFF.

[0033] However, when sugars containing glucose or fructose, but not aromatic compounds such as lignin, were used as the raw material, HMF remained stable for a long time in the reaction liquid obtained in the hydrothermal process. Therefore, the next oxidation process can be carried out by simply removing the water by liquid-liquid separation, without having to remove the water in the reaction liquid as ice. Furthermore, if a high-boiling organic liquid, which has a boiling point higher than that of the organic liquid and water in the reaction liquid obtained in the hydrothermal process and is used in the oxidation process, is added to the reaction liquid, and the organic liquid is distilled off while the water contained in the organic liquid is distilled off using the azeotropic phenomenon, the organic medium can be replaced while the liquid is in solution, and a liquid containing HMF can be obtained.

[0034] That is, when a raw material containing sugars is used in the hydrothermal step, a substitution step can be applied instead of the water removal step of this embodiment. In addition, the "sugars" of this application include not only monosaccharides and disaccharides, but also oligosaccharides such as oligosaccharides, and polysaccharides such as starch. In this substitution step, an organic liquid and a high-boiling organic liquid having a boiling point higher than that of water are added to the reaction liquid, and then the organic liquid is distilled off while at least a part of the water contained in the organic liquid is distilled off using the azeotropic phenomenon to obtain a liquid containing HMF. The larger the amount of organic liquid and water to be distilled off, the more preferable it is. This is because the content of the high-boiling organic liquid suitable for the oxidation step can be increased as much as possible, and water, which is one of the causes of destabilization of HMF, can be reduced. It is most preferable to replace the organic liquid and water other than the organic liquid and water that are inevitably contained with the high-boiling organic liquid.

[0035] When the organic liquid is THF, the high-boiling organic liquid used in the oxidation step includes an organic medium having a boiling point of 66°C or higher at normal pressure. Examples of such organic media include aliphatic solvents such as hexane, ethyl acetate, acetonitrile, dimethylformamide, dimethyl sulfoxide, or trichlorobenzene, and aromatic solvents such as toluene, ethylbenzene, cumene, xylene, anisole, benzaldehyde, acetophenone, benzophenone, or pyridine. Among these, toluene, ethylbenzene, cumene, xylene, or anisole are preferred, as they are suitable for synthesizing DFF from HMF by a catalytic reaction using oxygen or air as an oxidizing agent. Furthermore, toluene or anisole is preferred. This is because the THF used in the hydrothermal step can be easily replaced, and at the same time, these organic media form an azeotrope with water, so that the water dissolved in the organic medium can also be removed.

[0036] In the oxidation step, HMF in the crude product obtained in the water removal step is oxidized to obtain DFF. More specifically, for example, after removing organic liquid from the crude product containing HMF, the HMF is dissolved in a solvent used for the oxidation reaction to carry out the oxidation reaction. There are no particular limitations on the method for oxidizing HMF. However, the crude product contains several tens of mass percent of biomass-derived impurities, and if a solid catalyst or the like is used to oxidize HMF, catalyst poisoning is likely to occur, making it difficult to efficiently proceed with the oxidation reaction.

[0037] For this reason, in the oxidation step, it is preferable to use a homogeneous oxidation catalyst or a strong oxidizing agent, but a heterogeneous oxidizing agent such as manganese oxide is also preferable. Examples of the oxidation catalyst include copper chloride, copper iodide, nitroxy radical (R2N-O·), and vanadium complexes, and examples of the oxidizing agent include manganese oxide, permanganic acid, chromic acid, dichromate, chromium oxide, nitric acid, chloric acid, hypochlorous acid, halogen, ozone, oxygen, hydrogen peroxide, peroxide, and oxygen. In the oxidation step, oxidation can also be performed by combining these oxidizing agents with the various oxidation catalysts described above. In addition, in the oxidation step, the HMF in the HMF-containing liquid obtained in the substitution step may be oxidized to obtain DFF. EXAMPLES

[0038] The method for synthesizing HMF and the method for synthesizing DFF of the present invention will be specifically described below based on examples, but the present invention is not limited in any way to the following examples.

[0039] The yield of HMF was expressed as a percentage (raw material %) of the amount of substance of the obtained HMF relative to the amount of substance (so-called molar amount) equivalent to glucose contained in the raw material eucalyptus chips, cedar chips, moso bamboo chips, pulp, cellulose, or sugar solution. The yield of DFF was expressed as a percentage (HMF%) of the amount of substance of the obtained DFF relative to the amount of substance of the HMF used, or as a percentage (raw material %) of the amount of substance of the obtained DFF relative to the amount of substance equivalent to glucose contained in the raw material eucalyptus chips, cedar chips, moso bamboo chips, pulp, cellulose, or sugar solution. The conversion rate was expressed as a percentage (%) of the amount of substance or mass of the reacted raw material relative to the amount of substance or mass equivalent to glucose in the raw material.

[0040] (Example 1: Synthesis of HMF from sugar solution) 10.5g (0.24mol) of lithium chloride, which is a salt, and 6.7g (0.024mol) of iron chloride hexahydrate, which is a base metal salt, were added to 35g of sugar solution containing 7.84g of glucose and 1.35g of xylose, and after stirring well to completely dissolve, the solution was filled into an autoclave with a volume of 300mL. After adding 200mL of THF to the autoclave, the autoclave was sealed and nitrogen purged. The autoclave was then heated in a heating furnace, and the reaction was started when the reaction temperature reached 150°C, after which the reaction was carried out for 20 hours. The pressure inside the autoclave during the reaction was 4MPa. The reaction solution was then cooled to room temperature. After cooling, the organic layer (THF layer) and aqueous layer of the resulting reaction solution were collected separately. The yield of HMF contained in the organic layer and aqueous layer from the sugar solution was 46% of the raw material.

[0041] Example 2: Synthesis of DFF from HMF The organic layer separated from the reaction solution obtained in Example 1 was cooled to -30°C, and the precipitated ice was filtered to remove moisture from the organic layer. If the moisture in the filtrate (organic layer) was not sufficiently removed, the cooling temperature was further lowered or the ice was removed by cooling again, as necessary, to remove as much moisture as possible from the filtrate. The obtained filtrate (THF solution containing HMF) was distilled under reduced pressure at a low temperature of 60°C or less. 100 mL of dichloromethane, the solvent used in the oxidation reaction, was added to the obtained highly viscous reaction product containing HMF. Solids insoluble in dichloromethane were removed by filtration. Humic substances and other impurities were removed using alumina as necessary.

[0042] To the dichloromethane solution of the obtained HMF, about 20 mg to 30 mg of manganese dioxide as an oxidizing agent was added in several portions, and the reaction was carried out at room temperature. During the reaction, the remaining amount of HMF was confirmed using gas chromatography, and if HMF remained, further manganese dioxide was added to proceed with the reaction. After confirming that the HMF had almost disappeared, the manganese dioxide was collected by filtration. The used manganese dioxide was washed with sulfuric acid and reused. Alumina was added to the obtained filtrate to adsorb impurities and then filtered. The solvent was distilled off from the obtained filtrate under reduced pressure. After that, a solution of dichloromethane and hexane mixed in an appropriate ratio was added to carry out recrystallization, and 2.50 g of the target substance DFF (46% yield from the sugar solution) was obtained.

[0043] (Example 3: Synthesis of HMF from sugar solution using various salts) Using the salts shown in Table 1 below, the reaction time was set to 2 hours, and HMF was synthesized from the sugar solution in the same manner as in Example 1, without using iron chloride. The results are shown in Table 1. The ratio of the yield to the conversion rate (yield / conversion rate) was greatest when lithium chloride was used as the salt.

[0044] [Table 1]

[0045] (Example 4: Synthesis of HMF from sugar solution under various conditions) Under the conditions shown in Table 2 below, HMF was synthesized from sugar solution in the same manner as in Example 1 using only lithium chloride or lithium chloride and iron chloride in the substance amount ratio shown in the table. The results are shown in Table 2. Furthermore, it was found that the use of iron chloride increases the conversion rate and yield. It was also found that when the substance amount ratio of iron chloride to the substance amount of lithium chloride is 0.1 or more, there is an effect of increasing the conversion rate and yield. Furthermore, it was found that by lowering the reaction temperature to 150°C, although the reaction time is longer, the production of by-products is minimized and HMF can be obtained in high yield.

[0046] [Table 2]

[0047] (Example 5: Synthesis of HMF from sugar solution under various conditions) Under the conditions shown in Table 3 below, HMF was synthesized from sugar solution in the same manner as in Example 1 using only calcium chloride, which is cheaper and more readily available than lithium chloride, or calcium chloride and iron chloride in the substance amount ratio shown in the table. The results are shown in Table 3. It was found that when calcium chloride and iron chloride were used, the yield increased compared to when only calcium chloride was used, although the conversion rate was the same.

[0048] [Table 3]

[0049] In addition, when the reaction temperature was 190°C, the pressure inside the autoclave was about 3 MPa, but by lowering the reaction temperature to 150°C, the pressure inside the autoclave became about 1 MPa, and it was found that HMF could be produced using a more general-purpose reaction device. Furthermore, when HMF was produced at reaction temperatures of 130°C to 160°C, the conversion rate and yield were roughly equivalent when the reaction temperature was 145°C to 155°C. In other words, it was found that HMF can be obtained with a stable yield if the reaction can be carried out at a reaction temperature of 145°C to 155°C, even in an environment where the reaction temperature is uneven.

[0050] (Example 6: Synthesis of HMF with partial replacement of the solvent) In order to reduce the reaction pressure, a part of the organic liquid THF was replaced with toluene, an organic liquid having a boiling point higher than that of THF, and HMF was synthesized from the sugar solution in the same manner as in Example 5. 1.2 g of calcium chloride, a salt, and 0.12 g of iron chloride, a base metal salt, were placed in a 30 mL autoclave, and 2.0 g of sugar solution and 3.0 g of water were further added. THF and toluene were further added in the amounts shown in Table 4 below, and the reaction was carried out at a reaction temperature of 150° C. for 24 hours.

[0051] After the reaction, the products were analyzed by liquid chromatography to examine the components contained in the organic and aqueous phases, and the conversion and yield were calculated. Table 4 shows the pressure inside the autoclave during the reaction, and the conversion and yield of HMF. As a result, it was found that the reaction pressure could be reduced by increasing the amount of toluene replaced, although the yield decreased by about 10%. This demonstrated that HMF can be synthesized using a reaction vessel with low pressure resistance.

[0052] [Table 4]

[0053] (Example 7: Synthesis of HMF from cedar-derived pulp) Under the conditions shown in Table 5 below, HMF was synthesized in the same manner as in Example 1 using 0.5 g of cedar-derived pulp as the raw material. The results are shown in Table 5. It was found that HMF can be synthesized using pulp as the raw material. When only lithium chloride was used, the yield was 19% (No. 1), but by adding iron chloride to lithium chloride, the conversion rate and yield improved (68% and 40% in No. 2).

[0054] It was also found that when only zinc chloride was used, the solubility of pulp improved and the HMF yield increased by 28% compared to when only lithium chloride or only iron chloride was used (No. 4). In addition, the addition of zinc chloride to lithium chloride improved the conversion rate and yield (84% and 45% in No. 5). Furthermore, when calcium chloride and iron chloride or zinc chloride (No. 6 and No. 7) were used instead of lithium chloride and iron chloride or zinc chloride (No. 2 and No. 5), a slight decrease in the conversion rate and yield was observed, but generally good results were obtained.

[0055] [Table 5]

[0056] Example 8: Synthesis of DFF from HMF DFF was synthesized in the same manner as in Example 2 using the oxidation catalyst and oxidizing agent shown in Table 6 below, and an HMF solution obtained from pulp. The results are shown in Table 6. The reaction solution containing HMF obtained from pulp contains small amounts of lignin-derived components, etc., although water and solids unnecessary for THF have been removed. For this reason, it tends to be difficult to use solid catalysts (No. 1 to No. 4) in the synthesis of DFF. On the other hand, the homogeneous vanadium catalyst (No. 5) tended to have a high yield.

[0057] [Table 6]

[0058] (Example 9: Synthesis of DFF from cedar-derived pulp) DFF was synthesized via HMF in the same manner as in Example 2, except that 1.16 g of cedar-derived pulp was used as the raw material. The yield of DFF was 36.2 mg, and the yield of DFF was 17.9% of the raw material, calculated as cellulose contained in the pulp.

[0059] (Example 10: Synthesis of DFF from eucalyptus-derived pulp) Except for using 1.06 g of eucalyptus-derived pulp as the raw material, DFF was synthesized via HMF in the same manner as in Example 2. The yield of DFF was 45.4 mg, and the yield of DFF was 7.47% in terms of cellulose contained in the pulp.

[0060] (Example 11: Synthesis of DFF from Moso bamboo chips) DFF was synthesized via HMF in the same manner as in Example 2, except that 1.5 g of Moso bamboo chips was used as the raw material. The yield of DFF was 60.2 mg, and the yield of DFF was 10.7% of the raw material, calculated as cellulose contained in the chips.

[0061] Example 12: Synthesis of DFF using cellulose, glucose, and fructose as reagents As raw materials, 1.0 g of cellulose (Avicel) with a purity of 95% or more purchased as a reagent, 1.0 g of glucose, and 1.0 g of fructose were used to synthesize DFF via HMF in the same manner as in Examples 1 and 2. The yields of DFF were 121.5 mg (15.8%), 215.1 mg (31.2%), and 306.4 mg (44.5%), respectively.

[0062] (Example 13: Reuse of manganese dioxide) The manganese dioxide used in Examples 8 to 12 was recovered, concentrated sulfuric acid was added at room temperature and stirred, then filtered, washed with water, and dried in an oven at 60°C for one day to be regenerated. The obtained manganese dioxide was added in several portions of about 20 g to 30 g to the HMF solution of Example 8, and DFF was synthesized at room temperature. During the reaction, the remaining amount of HMF was confirmed using gas chromatography, and if any remained, further manganese dioxide was added to proceed with the reaction.

[0063] After confirming that the HMF had almost completely disappeared, the manganese dioxide was recovered by filtration. The used manganese dioxide was further washed with sulfuric acid and reused. Alumina was added to the obtained filtrate to adsorb impurities and then filtered again. The solvent of the obtained filtrate was distilled off under reduced pressure. After that, a solution of dichloromethane-hexane mixed in an appropriate ratio was added to carry out recrystallization, and the target substance DFF (2.50 g, 46% raw material yield from the sugar solution) was obtained.

[0064] (Example 14: Synthesis of HMF from sugar solution 2) 2 g of the sugar solution used in Example 1 (glucose content 0.82 g), 1.2 g of calcium chloride (salt), 0.12 g of iron chloride (base metal salt), 2 mL of water, and 20 mL of THF were added to a 30 mL autoclave, and the mixture was reacted at a reaction temperature of 150° C. for 24 hours. After the reaction, the product was analyzed by liquid chromatography, and the yield of HMF was 62%. Only the THF phase was collected using a separatory funnel, and insoluble matter was removed by filtration.

[0065] A portion of this THF solution containing HMF was sampled and left to stand at room temperature and pressure for 15 days. The ratio of the HMF content after time to the HMF content immediately after sampling (HMF content after time / HMF content immediately after sampling (hereinafter sometimes referred to as "HMF content ratio")) was 0.98 after 1 day, 1.10 after 4 days, 0.95 after 5 days, 1.02 after 6 days, and 1.01 after 15 days. Even after 15 days had passed since the THF solution containing HMF was sampled, the HMF content ratio hardly changed, and no tendency for HMF to change into humic substances or the like was observed.

[0066] On the other hand, when a part of the THF solution containing HMF was taken, and immediately after distilling off the THF for 20 minutes, the same amount of toluene as that of THF was added and the HMF content was measured, the HMF content ratio was 0.65. Furthermore, when a part of the THF solution containing HMF was taken, toluene with a boiling point higher than that of THF was added in an amount 1.5 times that of THF, the THF and water were distilled off, and the HMF content was measured, the HMF content ratio was 0.9. From these results, it was found that HMF is stable in organic liquids, and that solvent replacement with reduced loss of HMF is possible by using an organic liquid with a boiling point higher than that of THF.

[0067] (Example 15: Synthesis of DFF from HMF 2) As shown in Table 7 below, the reaction solution containing HMF obtained by the method of Example 14 was replaced with aromatic toluene and anisole, and 200 mg of 5 mass% ruthenium-supported alumina catalyst (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the HMF-containing solution, and oxygen was further introduced to carry out the oxidation process. The boiling points of toluene and anisole are higher than those of THF and water. The results are shown in Table 7.

[0068] [Table 7]

[0069] In Example 8, when HMF obtained from pulp was oxidized with oxygen using a ruthenium-supported alumina catalyst, DFF was not obtained due to catalyst poisoning (No. 1 in Table 6). For this reason, it was necessary to carry out the oxidation process using manganese oxide. However, it was found that HMF obtained from a sugar liquid that does not contain aromatic compounds such as lignin as a raw material can be oxidized with oxygen using a ruthenium-supported alumina catalyst. As shown in Table 7, DFF was obtained with a yield of 90% or more. Furthermore, while air was used as the oxidizing agent in Example 6, in this example, oxygen other than air was used as the oxidizing agent, and DFF was obtained in a short time.

[0070] When the reaction temperature was examined when the high-boiling organic liquid was toluene, the yield decreased when the reaction temperature significantly exceeded the boiling point of toluene. This is thought to be because the produced DFF volatilizes. 0.89 g of crude DFF with a purity of 75% and containing impurities was heated to 200°C and purified by sublimation. 0.45 g of colorless, transparent, needle-shaped crystals were obtained (yield 67%). NMR measurement of these crystals showed that the purity was nearly 100%. In other words, it was found that DFF is sublimable and that extremely high-purity DFF can be obtained by sublimation purification.

Claims

1. a hydrothermal step of hydrothermally treating a raw material containing carbohydrates derived from biomass in the presence of one or more salts of an alkali metal salt and an alkaline earth metal salt, using a mixed liquid of an organic liquid and water as a medium, to obtain a reaction liquid containing 5-hydroxymethyl-2-furfural; a water removal step of separating the reaction solution into an organic liquid layer and an aqueous layer, collecting the organic liquid layer, and then removing water from the organic liquid layer as ice to obtain a crude product containing 5-hydroxymethyl-2-furfural; an oxidation step of oxidizing 5-hydroxymethyl-2-furfural in the crude product to obtain 2,5-diformylfuran; having The organic liquid is at least one of tetrahydrofuran, methyltetrahydrofuran, diethyl ether, acetonitrile, methanol, ethanol, n-butanol, 2-butanol, isobutanol, methyl isobutyl ketone, hexafluoroisopropanol, ethyl acetate, hexane, dimethylformamide, dimethyl sulfide, acetone, methyl ethyl ketone, and toluene.

2. In claim 1, In the water removing step, the organic liquid layer is cooled to a temperature equal to or higher than the freezing point of the organic liquid and equal to or lower than 0° C., and water is removed from the organic liquid layer in the form of ice.

3. In claim 1 or 2, In the oxidation step, the organic liquid is removed from the crude product, a solvent is added, and then 5-hydroxymethyl-2-furfural in the crude product is oxidized.

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