A method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid

Abstract

The present invention relates to a method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid. The method of the present invention starts from fructose-based carbohydrates, continuously produces important biomass-based platform compound 5-hydroxymethylfurfural and functional polymer material monomer 2,5-furandicarboxylic acid, and in the process of producing 2,5-furandicarboxylic acid, avoids the separation and purification process of 5-hydroxymethylfurfural, and has the advantages of simple process, low generation and emission of three wastes, environmental friendliness, etc.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and in particular relates to a method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid through fructose-based carbohydrates. Background Art

[0002] Since biomass is renewable and widely available, the research on using it as raw material to prepare fuels and fine chemicals through chemical catalysis is an important research route for various biomass utilization and transformation. Sugar compounds represented by glucose and fructose are important components of biomass resources. Starting from sugar compounds, new platform compounds and intermediates are prepared by chemical methods. Through further transformation, they can effectively replace chemical products obtained from fossil resources, thereby effectively alleviating the energy crisis and environmental problems caused by the current large-scale use of fossil resources. In recent years, 5-hydroxymethylfurfural (HMF), a product obtained by dehydration of hexose as a raw material, has been considered to be an important bio-based furan compound. This compound and its derivatives can be further transformed into a variety of fine chemicals, and have potential applications in polymer monomers, furan pharmaceutical intermediates, pesticide chemicals, etc. Therefore, developing a method for efficiently utilizing sugar compounds to prepare HMF is a key issue for the effective utilization of bioresources. At the same time, 2,5-furandicarboxylic acid (FDCA) is obtained by catalytic oxidation of HMF. FDCA can be used to synthesize bio-based polymer materials to effectively improve their heat resistance and mechanical properties. It is considered to be an ideal substitute for petroleum-based monomer terephthalic acid (PTA) and can be widely used in the synthesis of bio-based polymers such as polyester, polyamide, and epoxy resin. Therefore, the development of a synthetic method for 2,5-furandicarboxylic acid has important application value and significance for the sustainable utilization of biomass.

[0003] HMF can be prepared from glucose or fructose. Compared with glucose, the fructose route does not require an isomerization process. The target product can be obtained by dehydrating the fructose molecule catalyzed by proton acid. The reaction rate is faster and the product yield is higher. It is currently a hot topic in the preparation of HMF. Studies have shown that in order to improve the production yield of HMF and realize the large-scale production of HMF as soon as possible, we urgently need to establish a two-liquid phase solvent system suitable for liquid acid catalysts to realize the continuous production technology of HMF. However, common liquid acid catalysts have a large solubility in water and organic solvents, and are difficult to separate from the reaction medium and products. Therefore, while improving the yield and purity of the target product, it is necessary to establish an effective liquid acid catalyst recovery method through appropriate means, and strengthen the effective separation and comprehensive utilization of other by-products and impurities to reduce the pressure on the environment. In addition, we also need to pay attention to the reaction factors other than catalysts and organic solvents, such as the role of salt compounds in improving the yield of HMF, and break the inhibition of the existing reaction factors on the yield of HMF.

[0004] On the other hand, in the process of preparing FDCA by selective oxidation of HMF, due to the low solubility of FDCA in water (<1g / 100mL water, 100°C), researchers often increase the single-pass processing capacity of the process by adding alkaline compounds to the product FDCA during the reaction to generate soluble salt compounds of FDCA. However, the salt compounds of FDCA obtained by these methods cannot be directly used in processes such as the production of polymers, but must be acidified (pH≈1) to be converted back into FDCA products, which undoubtedly increases the complexity of the overall production process of FDCA and reduces its environmental friendliness. CN108779088A discloses a method for preparing FDCA by one-step or two-step oxidation of HMF without the introduction of alkaline compounds. The method effectively improves the solubility of FDCA by using a mixed solvent of water and an organic solvent. The catalyst used in the method is a supported metal catalyst, in which the metal components are Pt and Au, and the specific surface area of ​​the carrier is limited to 20m 2 / g to 500m 2 / g. Since the prices of Pt and Au are relatively expensive (about 300-400 yuan / g), the overall process cost is relatively high, which is difficult to be applied in practice. CN111039906A also realizes the method of preparing FDCA by oxidizing HMF in a mixed solvent of water and organic solvent by doping N element on the surface of carbon-based carrier, but the carrier nitrogen doping process of this method is relatively complicated, which increases the preparation cost of the catalyst accordingly and is also difficult to be applied in practice.

[0005] Therefore, it is urgent to provide a simple, inexpensive and green method for synthesizing 2,5-furandicarboxylic acid to solve the above-mentioned problems existing in the prior art. The present method unexpectedly found that using a high specific surface area (1000m 2 / g~1500m 2 / g) of carbon-containing materials (such as activated carbon, etc.), under alkali-free conditions, the organic phase containing 5-hydroxymethylfurfural obtained by the above method is used as a raw material, and a certain proportion of water is added to achieve the reaction process of HMF oxidation to prepare FDCA. The price of the metal Ru used in this method (about 70 yuan / gram) is significantly lower than that of metals such as Pt or Au. At the same time, the catalyst can be prepared by a simple method from commercially purchased activated carbon and metal precursors, and the FDCA yield is high (>90%). Compared with the disclosed methods, this method greatly simplifies the process flow and reduces the cost, and is a method for preparing FDCA with great industrial potential.

[0006] It should be noted that the information disclosed in the aforementioned background technology section is only used to enhance the background understanding of the present invention, and therefore it may include information of the prior art known to ordinary technicians in this field. Summary of the invention

[0007] In a first aspect, the object of the present invention is to overcome the above-mentioned disadvantages of the prior art and to provide a method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid from fructosyl carbohydrates.

[0008] In the step of producing 5-hydroxymethylfurfural, the present invention utilizes the difference in solubility of a liquid acid catalyst in an aqueous solution of an organic ammonium halide and an organic solvent to establish a method for directly separating and recovering the liquid acid, thereby solving the problem of separating the liquid acid catalyst from the target product and achieving continuous production of 5-hydroxymethylfurfural.

[0009] In the step of producing 2,5-furandicarboxylic acid, the present invention uses the organic solution of 5-hydroxymethylfurfural obtained in the previous step without separation and purification directly as a raw material, which simplifies the process flow, and improves the solubility of 2,5-furandicarboxylic acid by adding water to form a mixed solvent, thereby avoiding the introduction of alkaline compounds in the traditional method and the complicated processes such as acidification treatment brought about by it; at the same time, the present invention uses a Ru-based catalyst supported by a carbon-containing carrier with a high specific surface area as an oxidation catalyst, the catalyst preparation method is simple and inexpensive, the reaction process is green and concise, and the FDCA yield is high.

[0010] The present invention provides a method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid from fructose-based carbohydrates, comprising:

[0011] (1) In a binary two-phase reaction system consisting of a low-boiling point polar organic solvent and an aqueous solution of an organic ammonium halide, a fructose-based carbohydrate undergoes an intramolecular dehydration reaction in a reactor under the catalytic action of a strongly acidic liquid acid catalyst containing a sulfonic acid group; after the reaction is completed, the reaction system is divided into an aqueous phase and an organic phase containing 5-hydroxymethylfurfural;

[0012] (2) using the organic phase containing 5-hydroxymethylfurfural in step (1) as a raw material, adding a certain proportion of water, and subjecting the 5-hydroxymethylfurfural to an oxidation reaction in a reactor in the presence of an oxidation catalyst and oxygen to obtain a solution containing 2,5-furandicarboxylic acid.

[0013] Wherein, the oxidation catalyst is a supported metal catalyst, which includes a carrier and a metal supported on the carrier, and the metal is Ru, or a combination of Ru and one or more of Pt, Pd or Au.

[0014] In step (1), the fructosyl carbohydrate is selected from one of purified fructose, crude fructose, polyfructose, fructose syrup and fructose-glucose syrup.

[0015] In step (1), the strong acidic liquid acid catalyst containing a sulfonic acid group is selected from one or more of sulfuric acid, methanesulfonic acid, and aminosulfonic acid, preferably one of sulfuric acid and methanesulfonic acid.

[0016] In step (1), the organic ammonium halide is selected from C1-C 12 Hydrocarbon, hydroxyl or halogen substituted C1-C 12 The hydrocarbon organic ammonium halide is preferably one or more of C1-C6 hydrocarbon and hydroxyl or halogen substituted C1-C6 hydrocarbon trimethyl quaternary ammonium salt halides, further preferably one or more of C1-C4 hydrocarbon and hydroxyl or halogen substituted C1-C4 hydrocarbon trimethyl quaternary ammonium salt chlorides or bromides, most preferably one of tetramethylammonium chloride, tetramethylammonium bromide, choline chloride, choline chloride (chlormequat), allyltrimethylammonium chloride, and butyltrimethylammonium chloride.

[0017] In step (1), the low boiling point polar organic solvent is selected from one or two of acetone, tetrahydrofuran, 1,4-dioxane, and acetonitrile, preferably 1,4-dioxane.

[0018] In step (1), the process conditions for the intramolecular dehydration reaction of the fructose-based carbohydrate include:

[0019] The mass ratio of the fructose-based carbohydrate to the reaction system is 1:1-1000, preferably 1:2-100, more preferably 1:5-20, wherein the reaction system refers to the sum of the low-boiling polar organic solvent and the organic ammonium halide aqueous solution.

[0020] The volume proportion of the organic ammonium halide aqueous solution in the total reaction system is 5%-50%, preferably 10%-35%.

[0021] The concentration of the liquid acid catalyst in the aqueous phase is 0.02-0.5 g / mL, preferably 0.03-0.1 g / mL.

[0022] The mass ratio of the fructosyl carbohydrate to the organic ammonium halide is 1:0.1-10, preferably 1:1-5.

[0023] The temperature of the dehydration reaction is 80°C-200°C, preferably 100°C-150°C; the time of the dehydration reaction is 0.1-12 hours, preferably 0.1-1 hour.

[0024] In step (1), the reactor can be a thick-walled pressure-resistant bottle, a stainless steel reactor with a polytetrafluoroethylene liner, and a reactor that can be easily thought of by a person skilled in the art. In order to facilitate the observation of the interface between the aqueous phase and the organic phase and further facilitate the two-phase separation operation, the reactor is preferably a thick-walled pressure-resistant bottle.

[0025] In step (1), according to the method of the present invention, the phase separation process of the two-liquid phase reaction system is specifically manifested as follows: after the reaction is completed and stirring is stopped, due to the salting-out effect of the organic ammonium halide, the organic solvent and the organic ammonium halide aqueous solution will immediately separate into an upper and lower phase, wherein the upper layer is the organic solvent and the lower layer is the organic ammonium halide aqueous solution, and there is a clear phase interface between the two phases. The two phases can be separated by conventional methods, such as extraction by a syringe, separation by a separating funnel, or other methods that can be easily thought of by personnel in the field to separate and remove the two phases.

[0026] In step (1), according to the method of the present invention, during the process of preparing the target product by dehydrating fructose-based carbohydrates, 5-hydroxymethylfurfural is extracted into the organic solvent in real time, so after the reaction is completed and the organic solvent and the organic ammonium halide aqueous solution are separated, 5-hydroxymethylfurfural is located in the upper organic solvent. At the same time, by-products and impurities such as humin produced during the reaction are retained in the organic phase, so the upper organic solvent is brown. The organic phase containing 5-hydroxymethylfurfural can be decolorized and separated and purified to obtain 5-hydroxymethylfurfural.

[0027] Wherein, the decolorization method can adopt activated carbon adsorption.

[0028] The separation and purification method comprises distilling the decolorized 5-hydroxymethylfurfural solution under reduced pressure, crystallizing or recrystallizing the solution, and then freeze-drying the solution.

[0029] Among them, the conversion rate of the reaction substrate during the reaction, the selectivity, yield and purity of the target product can be analyzed and calculated by high performance liquid chromatography.

[0030] According to the inventive method, the liquid acid catalyst containing sulfonic acid group can establish a stronger hydrogen bond network with water in the presence of some specific organic solvents, so that the catalyst is dissolved in the organic ammonium halide aqueous solution but insoluble in the organic solvent, so after the reaction is terminated and the organic solvent and the organic ammonium halide aqueous solution are phase-separated, the liquid acid catalyst is substantially retained in the lower organic ammonium halide aqueous solution, and the upper target product is separated in situ. Now the aqueous phase solution is a mixed aqueous solution of organic ammonium halide and liquid acid, which can be directly separated and recovered, without further separation of organic ammonium halide and liquid acid catalyst, and can be directly reused after decolorization. A small amount of acid catalyst remaining in the organic phase can be neutralized by adding an equal amount of alkali, and the generated salt can be precipitated from the organic phase, and directly filtered, without affecting solvent recovery.

[0031] According to the method of the present invention, the organic phase containing 5-hydroxymethylfurfural obtained in step (1) can be directly used as a raw material for producing 2,5-furandicarboxylic acid without going through a separation and purification process because the organic phase has a high 5-hydroxymethylfurfural content and a low impurity content, and can be subjected to the oxidation reaction described in step (2) in the presence of an oxidation catalyst and oxygen.

[0032] In step (2), in the supported metal catalyst, in the combination of Ru and one or more of Pt, Pd or Au, the mass content of Ru is 5% to 95%, preferably 20% to 90%, more preferably 40% to 80%.

[0033] In step (2), in the supported metal catalyst, based on the total mass of the carrier, the loading amount of the metal is 0.25% to 30%, preferably 1% to 20%, and more preferably 5% to 15%.

[0034] In step (2), the carrier is selected from carbonaceous materials, including one or more of activated carbon, carbon nanotubes, graphene or graphene oxide, preferably activated carbon. Wherein, when the carrier is activated carbon, the specific surface area of ​​the activated carbon is 1000m2 / g to 1500m2 / g.

[0035] In step (2), the mass ratio of the organic phase containing 5-hydroxymethylfurfural to water is 5:1 to 0.5:1, preferably 3:1 to 1:1.

[0036] In step (2), the process conditions for the oxidation reaction of 5-hydroxymethylfurfural include:

[0037] The molar ratio of the metal in the supported metal catalyst to the 5-hydroxymethylfurfural is 1:1-1000, preferably 1:5-500, and more preferably 1:5-250.

[0038] The oxygen may come from pure oxygen, air or a mixed gas consisting of oxygen and nitrogen. The partial pressure of the oxygen is 0.2 MPa to 4 MPa, preferably 1 to 3 MPa.

[0039] The reaction temperature of the oxidation reaction is 50°C to 170°C, preferably 90°C to 150°C.

[0040] In step (2), according to the method of the present invention, the mixed solvent formed by the organic solvent in the raw material and the added water can improve the solubility of 2,5-furandicarboxylic acid, thereby avoiding the introduction of alkaline compounds and the formation of salt products, and directly obtaining a solution containing 2,5-furandicarboxylic acid. After the solution is separated and purified, 2,5-furandicarboxylic acid can be obtained.

[0041] The separation and purification method comprises distilling the solution containing 2,5-furandicarboxylic acid under reduced pressure at a distillation temperature of 30°C-100°C, preferably 30°C-50°C, and a distillation time of 1-10 hours, preferably 2-4 hours.

[0042] The separation and purification method further comprises crystallizing or recrystallizing the solution containing 2,5-furandicarboxylic acid at a crystallization temperature of -10°C to 30°C, preferably 0°C to 20°C, and a crystallization time of 1 to 24 hours, preferably 5 to 10 hours.

[0043] The purification method further comprises a process of drying the product after distillation or crystallization. The drying method is preferably freeze drying. The drying time is 3-24 hours, preferably 18-24 hours.

[0044] Among them, the conversion rate of the reaction substrate during the reaction, the selectivity, yield and purity of the target product can be analyzed and calculated by high performance liquid chromatography.

[0045] In step (2), the supported metal catalyst can be prepared according to existing methods, such as isochoric impregnation, incipient wetness impregnation, ion exchange, deposition-precipitation or vacuum impregnation. In the specific preparation, after metal deposition, the solid powder is placed in an oven at 100-140°C and dried for about 6-24 hours. The supported catalyst precursor is first calcined in nitrogen at 300-800°C for a period of time, and then reduced in a reducing atmosphere (such as H2 or a mixed atmosphere of H2 and N2) at 200-500°C for about 6-24 hours to obtain a supported metal catalyst.

[0046] In step (2), the method of the present invention increases the solubility of the product 2,5-furandicarboxylic acid by using a mixed solution of water and an organic solvent in an appropriate proportion as a solvent, thereby avoiding the introduction of alkaline compounds, simplifying the post-treatment steps of the product, and avoiding the situation where a large amount of waste acid and waste water are generated in the subsequent acidification process; at the same time, the Ru-based catalyst supported by the high specific surface area carbonaceous material used in the present invention has a simple preparation method, is more inexpensive, is easy to scale up for production, and has a good industrial application prospect.

[0047] The method of the present invention can also perform activated carbon adsorption on the aqueous phase and the organic phase obtained in step (1), and calcine the activated carbon adsorbed with impurities at high temperature to restore the adsorption capacity of the activated carbon.

[0048] In a second aspect, the present invention provides a reaction system for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid, which includes: a dehydration reaction unit, a phase separation unit, an oxidation reaction unit, a separation and purification unit, a drying unit, etc.

[0049] In the dehydration reaction unit, a dehydration reaction to prepare 5-hydroxymethylfurfural is carried out in a fructose-based carbohydrate reactor, wherein the reactor may be a slurry bed, a bubbling bed or a tube reactor, etc. After the reaction is completed, the two-liquid phase reaction system enters a phase separation unit for automatic phase separation.

[0050] The organic phase containing 5-hydroxymethylfurfural separated from the phase separation unit enters the reactor of the oxidation reaction unit for oxidation to prepare 2,5-furandicarboxylic acid, wherein the reactor can be a slurry bed, a fixed bed, a bubbling bed, etc. The aqueous phase containing the acid catalyst separated from the phase separation unit can be recycled to the inlet of the dehydration reactor.

[0051] The reaction liquid containing 2,5-furandicarboxylic acid obtained from the oxidation reaction unit can be subjected to a separation and purification unit and a drying unit to obtain a 2,5-furandicarboxylic acid product. The separation and purification unit can be a distillation separation, in which the reactor can be a vacuum distillation tower or a molecular distiller; or a crystallization separation, in which the reactor can be a fluidized bed, a tubular continuous crystallizer or a precipitation crystallizer.

[0052] The organic phase containing 5-hydroxymethylfurfural separated from the phase separation unit can also be partially directly fed into a decolorization and purification unit and a freeze drying unit to obtain a 5-hydroxymethylfurfural product. The decolorization and purification unit includes an activated carbon adsorption tower, a vacuum distillation tower, and a crystallizer, and the freeze drying unit includes a freeze dryer.

[0053] The reaction system of the present invention may also include an activated carbon calcining furnace and a corresponding tail gas absorption device.

[0054] In summary, the present invention has the following advantages:

[0055] 1. The catalyst and organic solvent used in the present invention are both conducive to large-scale production of HMF.

[0056] 2. The present invention regulates the solubility of HMF and the catalyst in the two-phase solution, and retains HMF and the liquid acid catalyst in the organic phase and the aqueous phase respectively after the reaction is completed, thereby solving the problem of separating the liquid acid catalyst from the reaction medium and the target product, greatly simplifying the catalyst separation operation, and thus realizing the continuous reaction.

[0057] 3. The present invention realizes in-situ separation of HMF and the acid catalyst during the reaction process, reduces the acid amount of HMF in the organic phase, and avoids the decomposition of HMF due to the presence of the acid catalyst during high-temperature in-situ extraction of HMF.

[0058] 4. The present invention can use the organic phase containing HMF directly as a raw material to produce FDCA, avoiding intermediate separation and purification processes and simplifying the process of producing FDCA.

[0059] 5. The present invention increases the solubility of FDCA by using a method of forming a mixed solution with organic solution and water, avoids the introduction of alkaline compounds, and also avoids the generation of FDCA salt products, and directly obtains a solution containing FDCA. After the solution is separated and purified, FDCA can be obtained, which greatly simplifies the process flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic flow diagram of the reaction system of the present invention. DETAILED DESCRIPTION

[0061] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0062] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0063] Example 1

[0064] This example illustrates the method for synthesizing HMF of the present invention using sulfuric acid as a catalyst.

[0065] Add 0.5g of fructose, 0.06g of sulfuric acid, 1.5g of water, 8.5g of 1,4-dioxane, and 0.5g of tetramethylammonium chloride to a 15mL pressure bottle. When the temperature of the multichannel heater is heated to 110°C, place the pressure bottle in the multichannel heater and stir the reaction at a speed of 600r / min for 10-30 minutes. After the reaction is completed, take out the pressure bottle from the multichannel heater and cool it naturally to room temperature. The reaction liquid is separated by a liquid separator to obtain an aqueous phase and an organic phase containing 5-hydroxymethylfurfural. The two phases are analyzed by high performance liquid chromatography to determine the conversion rate of fructose and the yield of HMF. The optimal yield of HMF obtained during the reaction time period and the corresponding fructose conversion rate and the retention rate of HMF in the upper organic phase are listed in Table 1.

[0066] After the reaction is completed, the reaction solution is rapidly separated into two phases, and the lower organic quaternary ammonium salt aqueous solution is taken out by a liquid separator. The organic quaternary ammonium salt aqueous solution contains a liquid acid catalyst, and the content of the liquid acid catalyst in the aqueous phase is determined by a basic titration method, and the retention rate of the liquid acid catalyst in the aqueous phase is further calculated in combination with the catalyst feed amount, and the results are listed in Table 1.

[0067] Example 2

[0068] This example illustrates the method for synthesizing HMF of the present invention using sulfuric acid as a catalyst.

[0069] The reaction was carried out according to Example 1, except that the amount of tetramethylammonium chloride added was increased to 1.5 g. The corresponding reaction results are listed in Table 1.

[0070] Example 3

[0071] This example illustrates the method for synthesizing HMF of the present invention using sulfuric acid as a catalyst.

[0072] The reaction was carried out according to Example 1, except that the amount of tetramethylammonium chloride added was increased to 2.5 g. The corresponding reaction results are listed in Table 1.

[0073] After the reaction was completed, the reaction liquid was quickly separated into two phases, and the lower aqueous phase solution was taken out by a liquid separator and directly put into the next cycle test. The results of the cycle experiment are listed in Table 2.

[0074] Example 4

[0075] This example illustrates the method for synthesizing HMF of the present invention using methanesulfonic acid as a catalyst.

[0076] The reaction was carried out according to Example 1, except that the sulfuric acid catalyst was replaced by a methanesulfonic acid catalyst and the catalyst feed amount was increased to 0.2 g. The corresponding reaction results are listed in Table 1.

[0077] Example 5

[0078] This example illustrates the method for synthesizing HMF of the present invention using methanesulfonic acid as a catalyst.

[0079] The reaction was carried out according to Example 2, except that the sulfuric acid catalyst was replaced by a methanesulfonic acid catalyst and the catalyst feed amount was increased to 0.2 g. The corresponding reaction results are listed in Table 1.

[0080] Example 6

[0081] This example illustrates the method for synthesizing HMF of the present invention using methanesulfonic acid as a catalyst.

[0082] The reaction was carried out according to Example 3, except that the sulfuric acid catalyst was replaced by a methanesulfonic acid catalyst and the catalyst feed amount was increased to 0.2 g. The corresponding reaction results are listed in Table 1.

[0083] Example 7

[0084] The reaction was carried out according to Example 1, except that the amount of tetramethylammonium chloride added was increased to 3.0 g. The corresponding reaction results are listed in Table 1.

[0085] Example 8

[0086] The reaction was carried out according to Example 6, except that the amount of tetramethylammonium chloride added was increased to 3.0 g. The corresponding reaction results are listed in Table 1.

[0087] Comparative Example 1

[0088] The reaction was carried out according to Example 1, except that tetramethylammonium chloride was replaced with sodium chloride in an equal molar ratio. The corresponding reaction results are listed in Table 1.

[0089] Comparative Example 2

[0090] The reaction was carried out according to Example 2, except that tetramethylammonium chloride was replaced with sodium chloride in an equal molar ratio. The corresponding reaction results are listed in Table 1.

[0091] Comparative Example 3

[0092] The reaction was carried out according to Example 3, except that tetramethylammonium chloride was replaced with sodium chloride in an equal molar ratio. The corresponding reaction results are listed in Table 1.

[0093] Table 1 Experimental results in Examples 1-8 and Comparative Examples 1-3

[0094]

[0095] Table 2 Results of recycling of aqueous solvent in the two-liquid system in Example 3

[0096]

[0097] Comparing the results of Examples 1-3 and 7, it can be seen that after adding tetramethylammonium chloride into the reaction system, the optimal yield of HMF gradually increases with the increase in the feeding amount of tetramethylammonium chloride. When the feeding amount increases from 2.5g to 3.0g, the optimal yield of HMF remains basically unchanged. Considering the HMF yield and production cost, the preferred mass ratio of fructose to tetramethylammonium chloride is 1:1-5.

[0098] Comparing the results of Examples 4-6 and Example 8, it can be seen that after the catalyst was replaced with methanesulfonic acid, the optimal yield of HMF changed with the feeding amount of tetramethylammonium chloride, and the preferred mass ratio of fructose to tetramethylammonium chloride did not change.

[0099] From the results of Example 3, it can be seen that after the reaction, the lower aqueous phase solvent of the two-liquid phase system was taken out and directly put into the next cycle test. After 6 consecutive cycles, the fructose conversion rate was maintained at more than 99.0%, without a significant decrease. The optimal yield of HMF decreased slightly after 4 cycles, and dropped to 87.2% in the 5th cycle reaction and 86.8% in the 6th cycle reaction, indicating that the aqueous phase solution after phase separation has excellent recovery performance.

[0100] Comparing the results of Comparative Examples 1-3, it can be seen that when the salt compound used in the reaction system is changed to inorganic salt sodium chloride, although a two-liquid phase system can still be formed, the optimal yield of HMF no longer increases with the increase in the amount of sodium chloride, which means that unlike organic quaternary ammonium chloride salts, ordinary inorganic chloride salts have no promoting effect on the formation of HMF. And at the same salt concentration, the HMF yield of organic quaternary ammonium salts is higher than that of inorganic chloride salts, indicating that the cations of organic quaternary ammonium salts have a promoting effect on the formation of HMF compared with metal cations.

[0101] Example 9

[0102] This example is used to illustrate the use of the initial impregnation method in the present invention to prepare an oxidation catalyst 10% Ru / C:

[0103] Mix 5.4 mL of 0.05 g / mL RuCl3 solution and 10.0 mL of deionized water, stir evenly, then add 0.9 g of activated carbon carrier to the mixture, stir and immerse for 10 hours at room temperature, evaporate the water, and then dry in an oven at 110°C for 12 hours to obtain a catalyst precursor. The Ru loading is 10% (mass percentage). The precursor prepared in the above steps is placed in a quartz tube, first calcined at 500°C in nitrogen for 4 hours, and then reduced at 500°C in 20% H2+N2 for 3 hours to obtain a loaded 10% Ru / C catalyst.

[0104] Different catalysts with various Ru loadings on various commercial activated carbon powders or granules were prepared in a similar manner. The compositions and specific surface areas of these catalysts are listed in Table 3 below.

[0105] Example 10

[0106] This example is used to illustrate the use of the initial impregnation method in the present invention to prepare an oxidation catalyst 10% Ru-5% Pt / C:

[0107] Mix 5.4 mL of 0.05 g / mL RuCl3 solution, 2.7 mL of 0.05 g / mL H2PtCl6 solution and 10.0 mL of deionized water, stir evenly, then add 0.9 g of activated carbon carrier to the mixture, stir and immerse for 10 hours at room temperature, evaporate the water, and then dry in an oven at 110°C for 12 hours to obtain a catalyst precursor. The loading amount of Ru is 10% (mass percentage), and the loading amount of Pt is 5% (mass percentage). The precursor prepared in the above steps is placed in a quartz tube, first calcined at 500°C in nitrogen for 4 hours, and then reduced at 500°C in 20% H2+N2 for 3 hours to obtain a loaded 10% Ru-5% Pt / C catalyst.

[0108] Different catalysts with various loadings of Ru and Pt, Pd and Au on various commercial activated carbon powders or granules were prepared in a similar manner. The compositions and specific surface areas of these catalysts are listed in Table 3 below.

[0109] Embodiment 11

[0110] This example is used to illustrate the method for synthesizing 2,5-furandicarboxylic acid of the present invention.

[0111] In a 50mL high-pressure reactor, 5g of the organic phase containing 5-hydroxymethylfurfural obtained in Example 1, 0.2g of several 10% Ru / C oxidation catalysts prepared in Example 9, and 5g of water (the mass ratio of water to organic phase is 1:1) are added. After the reactor is sealed, 1MPa of oxygen is filled to replace the residual air in the reactor. After repeating three times, 1MPa of oxygen is filled into the reactor, and the reactor is placed on a heating furnace to heat to a reaction temperature of 100°C, and stirred at a speed of 700rpm for 10 hours. After the reaction is completed, the reactor is taken out from the heating furnace, cooled to room temperature, filtered, and the filter cake is washed with a mixed solvent that is the same as the reaction solvent, and finally the volume is fixed to 100mL, and a liquid sample is taken for high-performance liquid chromatography analysis. The reaction results are listed in Table 3.

[0112] Example 12

[0113] The method of Example 11 was followed, except that the oxidation catalyst was a 10% Ru / C catalyst supported on activated carbon from Dali Hongye, and the Ru loading in the oxidation catalyst was 5% or 15%. The reaction results are listed in Table 3.

[0114] Embodiment 13

[0115] The method of Example 11 was followed, except that the oxidation catalyst was a 10% Ru / C catalyst supported on activated carbon from Dali Hongye, and the oxygen pressure was 2 MPa or 3 MPa. The reaction results are listed in Table 3.

[0116] Embodiment 14

[0117] The method of Example 11 was followed, except that the oxidation catalyst was only a 10% Ru / C catalyst supported on activated carbon from Dali Hongye, and the reaction temperature was 120° C. or 140° C. The reaction results are listed in Table 3.

[0118] Embodiment 15

[0119] The method of Example 11 was followed, except that the oxidation catalyst was a catalyst with different loading amounts of Ru, Pt, Pd and Au prepared in Example 10, wherein the carrier activated carbon was from Dali Hongye. The reaction results are listed in Table 3.

[0120] Table 3. Catalyst compositions and properties in Examples 11-15

[0121]

[0122]

[0123] Comparative Example 4

[0124] Different catalysts with various Pt, Pd or Au loadings on various commercially available activated carbon powders or granules were prepared according to the method of Example 9. The compositions and specific surface areas of these catalysts are listed in Table 4 below.

[0125] The method of Example 11 was followed, except that the oxidation catalyst was selected from the activated carbon supported Pt, Pd or Au catalyst prepared by the above method. The reaction results are listed in Table 4.

[0126] Table 4. Composition and performance of the catalyst in Comparative Example 4

[0127]

[0128] Comparative Example 5

[0129] The method of Example 11 was followed, except that the oxidation catalyst was only a 10% Ru / C catalyst supported on activated carbon from Dali Hongye, and no water was added. After the reaction, the conversion rate of HMF was 14%, and the yield of FDCA was 3%.

[0130] From the data in Table 3, it can be seen that 1. The specific surface area of ​​the activated carbon support in the Ru / C oxidation catalyst has a significant effect on the activity of the catalyst and the yield of FDCA. 2 / g, the yield of FDCA reaches more than 90%; 2. The loading amount of Ru in the Ru / C oxidation catalyst will affect the performance of the catalyst, but in the loading range of 5% to 15%, the FDCA yield is greater than 90%; 3. The oxygen partial pressure and reaction temperature will also affect the performance of the Ru / C oxidation catalyst. Excessive oxygen partial pressure and reaction temperature will cause a decrease in the FDCA yield; 4. The oxidation catalyst composed of Ru and Pt, Pd or Au supported on activated carbon also has good catalytic performance under the investigation conditions of the present invention.

[0131] It can be seen from the data in Table 4 that the single Pt, Pd or Au oxidation catalyst supported by activated carbon, within the specified range of the present invention, all exhibit catalytic performance significantly lower than that of the Ru / C oxidation catalyst, indicating that the Ru / C oxidation catalyst supported by the high specific surface area carbon-containing material involved in the present invention has a special catalytic effect on the reaction of HMF oxidation to FDCA.

[0132] It can be seen from Comparative Example 5 that, without the addition of water, the organic solvent alone cannot effectively dissolve the FDCA generated in the reaction, causing a small amount of FDCA generated in the reaction to adhere to the surface of the oxidation catalyst and poison the catalytic active center, resulting in a significant decrease in the activity of the oxidation catalyst and the FDCA yield.

[0133] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0134] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0135] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid, comprising: (1) In a binary two-phase reaction system consisting of a low-boiling point polar organic solvent and an aqueous solution of an organic ammonium halide, under the catalytic action of a strongly acidic liquid acid catalyst containing a sulfonic acid group, a fructose-based carbohydrate is subjected to an intramolecular dehydration reaction in a reactor; after the reaction is completed, the reaction system is divided into an aqueous phase and an organic phase containing 5-hydroxymethylfurfural, wherein the low-boiling point polar organic solvent is selected from one or two of acetone, tetrahydrofuran, 1,4-dioxane, and acetonitrile, and the organic ammonium halide is selected from C1-C12 hydrocarbon organic ammonium halide and hydroxyl- or halogen-substituted C1-C12 hydrocarbon organic ammonium halide; (2) using the organic phase containing 5-hydroxymethylfurfural in step (1) as a raw material, adding water, and subjecting the 5-hydroxymethylfurfural to an oxidation reaction in a reactor in the presence of an oxidation catalyst and oxygen to obtain a solution containing 2,5-furandicarboxylic acid, and obtaining the 2,5-furandicarboxylic acid after separation and purification; wherein the oxidation catalyst is a supported metal catalyst, the supported metal catalyst comprises a carrier and a metal supported on the carrier, the metal is Ru or a combination of Ru and one or more of Pt, Pd or Au, and the carrier is a catalyst with a specific surface area of ​​1000 m 2 / g~1500m 2 / g of activated carbon.

2. The method according to claim 1, wherein: The fructosyl carbohydrate in step (1) is selected from one of purified fructose, crude fructose, polyfructose, fructose syrup and fructose-glucose syrup.

3. The method according to claim 1, wherein: The strong acidic liquid acid catalyst containing a sulfonic acid group in step (1) is selected from sulfuric acid and methanesulfonic acid.

4. The method according to claim 1, wherein: The organic ammonium halide in step (1) is selected from one or more of C1-C6 hydrocarbon groups and hydroxyl or halogen-substituted C1-C6 hydrocarbon trimethyl quaternary ammonium salt halides.

5. The method according to claim 1, wherein: The organic ammonium halide in step (1) is selected from the chloride or bromide of C1-C4 hydrocarbon group and hydroxyl or halogen substituted C1-C4 hydrocarbon trimethyl quaternary ammonium salt.

6. The method according to claim 1, wherein: The organic ammonium halide described in step (1) is selected from one of tetramethylammonium chloride, choline chloride and choline chloride.

7. The method according to claim 1, wherein: The low boiling point polar organic solvent described in step (1) is 1,4-dioxane.

8. The method according to claim 1, wherein: The mass ratio of the fructose-based carbohydrate to the reaction system in step (1) is 1:1-1000, wherein the reaction system refers to the sum of the low-boiling point polar organic solvent and the organic ammonium halide aqueous solution.

9. The method according to claim 1, wherein: The mass ratio of the fructose-based carbohydrate to the reaction system in step (1) is 1:2-100.

10. The method according to claim 1, wherein: The mass ratio of the fructose-based carbohydrate to the reaction system in step (1) is 1:5-20.

11. The method according to claim 1, wherein: The volume proportion of the organic ammonium halide aqueous solution in the total reaction system is 5%-50%.

12. The method according to claim 1, wherein: The volume proportion of the organic ammonium halide aqueous solution in the total reaction system is 10%-35%.

13. The method according to claim 1, wherein: The concentration of the liquid acid catalyst in the aqueous phase in step (1) is 0.02-0.5 g / mL.

14. The method according to claim 1, wherein: The concentration of the liquid acid catalyst in the aqueous phase in step (1) is 0.03-0.1 g / mL.

15. The method according to claim 1, wherein: The temperature of the dehydration reaction in step (1) is 80°C-200°C, and the time of the dehydration reaction is 0.1-12 hours.

16. The method according to claim 1, wherein: The temperature of the dehydration reaction in step (1) is 100° C.-150° C., and the time of the dehydration reaction is 0.1-1 hour.

17. The method according to claim 1, wherein: In the combination of Ru and one or more of Pt, Pd or Au in step (2), the mass content of Ru is 5% to 95%.

18. The method according to claim 1, wherein: In the combination of Ru and one or more of Pt, Pd or Au in step (2), the mass content of Ru is 20% to 90%.

19. The method according to claim 1, wherein: In the combination of Ru and one or more of Pt, Pd or Au in step (2), the mass content of Ru is 40% to 80%.

20. The method according to claim 1, wherein: In the supported metal catalyst in step (2), the loading amount of the metal is 0.25% to 30% based on the total mass of the carrier.

21. The method according to claim 1, wherein: In the supported metal catalyst in step (2), the supported amount of the metal is 1-20% based on the total mass of the carrier.

22. The method according to claim 1, wherein: In the supported metal catalyst in step (2), the loading amount of the metal is 5% to 15% based on the total mass of the carrier.

23. The method according to claim 1, wherein: The mass ratio of the organic phase containing 5-hydroxymethylfurfural to water in step (2) is 5:1 to 0.5:

1.

24. The method according to claim 1, wherein: The mass ratio of the organic phase containing 5-hydroxymethylfurfural to water in step (2) is 3:1 to 1:

1.

25. The method according to claim 1, wherein: The molar ratio of the metal in the supported metal catalyst to the 5-hydroxymethylfurfural in step (2) is 1:1-1000.

26. The method according to claim 1, wherein: The molar ratio of the metal in the supported metal catalyst to the 5-hydroxymethylfurfural in step (2) is 1:5-500.

27. The method according to claim 1, wherein: The molar ratio of the metal in the supported metal catalyst to the 5-hydroxymethylfurfural in step (2) is 1:5-250.

28. The method of claim 1, wherein: The oxygen in step (2) comes from pure oxygen, air or a mixed gas consisting of oxygen and nitrogen, and the partial pressure of the oxygen is 0.2MPa to 4MPa.

29. The method according to claim 1, wherein: The oxygen in step (2) comes from pure oxygen, air or a mixed gas consisting of oxygen and nitrogen, and the partial pressure of the oxygen is 1 to 3 MPa.

30. The method of claim 1, wherein: The reaction temperature of the oxidation reaction in step (2) is 50°C to 170°C.

31. The method of claim 1, wherein: The reaction temperature of the oxidation reaction in step (2) is 90°C to 150°C.

32. A reaction system for continuously producing 5-hydroxymethylfurfural and 2,5-furandicarboxylic acid used in the method of claim 1, comprising: A dehydration reaction unit, a phase separation unit, an oxidation reaction unit, a separation and purification unit and a drying unit, wherein the reactor of the dehydration reaction unit is a slurry bed, a bubbling bed or a tube reactor, after the reaction is completed, the two-liquid phase reaction system enters the phase separation unit for automatic phase separation, and the organic phase containing 5-hydroxymethylfurfural separated from the phase separation unit enters the reactor of the oxidation reaction unit, the oxidation reactor is a slurry bed, a fixed bed or a bubbling bed, and the reactor of the separation and purification unit is selected from a vacuum distillation tower, a molecular distiller, a fluidized bed, a tubular continuous crystallizer or a precipitation crystallizer.

33. The reaction system according to claim 32, wherein: Part of the organic phase containing 5-hydroxymethylfurfural separated from the phase separation unit enters a decolorization and purification unit and a freeze-drying unit to obtain a 5-hydroxymethylfurfural product.

34. The reaction system according to claim 33, wherein: The decolorization and purification unit comprises an activated carbon adsorption tower, a vacuum distillation tower, and a crystallizer, and the freeze-drying unit comprises a freeze-dryer.

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