A method for preparing 2,5-furandicarboxylic acid from biomass sugars via continuous reaction

Abstract

This invention relates to the field of 2,5-furandicarboxylic acid (FDCA) preparation technology, and more particularly to a method for the continuous reaction preparation of FDCA from biomass sugar. The method includes the following steps: Under the action of a homogeneous metal salt catalyst, biomass sugar is used as a raw material for a dehydration reaction to generate 5-hydroxymethylfurfural. A co-oxidant and acetic acid are added to the dehydrated reaction solution obtained after the reaction. The co-oxidant is one or more of acetaldehyde, trimetaldehyde, and methyl ethyl ketone. An oxidation reaction is carried out under an oxidizing gas atmosphere under the action of an oxidation catalyst, and then 2,5-furandicarboxylic acid is separated. Using the method of this invention, the yield and product purity of the continuous reaction preparation of FDCA from biomass sugar can be improved, while the use of hydrogen bromide in the oxidation reaction can be reduced or even avoided, thus reducing the corrosion of equipment by hydrogen bromide.

Description

Technical Field

[0001] This invention relates to the field of 2,5-furandicarboxylic acid preparation technology, and more particularly to a method for preparing 2,5-furandicarboxylic acid from biomass sugar through continuous reaction. Background Technology

[0002] The development of biodegradable plastics is urgent. Among them, PET alternative PEF (polyethylene furanoate) has attracted much attention due to its excellent heat resistance and barrier properties. However, its industrialization is still constrained by the high price of the biomass-based monomer 2,5-furandicarboxylic acid (FDCA).

[0003] In the preparation of FDCA, a common route involves the dehydration of fructose to produce 5-hydroxymethylfurfural (HMF), followed by oxidation to FDCA. However, fructose is currently quite expensive. Some biomass sugars with high yields and low prices are more suitable as raw materials for large-scale industrial production of FDCA. For example, glucose can be isomerized to fructose, which can then undergo dehydration to produce HMF, followed by further oxidation to prepare FDCA.

[0004] Lewis acids typically exhibit good catalytic effects on the conversion of biomass sugars to HMF (hydrogen methyl sulfoxide). However, HMF is relatively unstable and easily undergoes hydrolysis in high-temperature, acidic aqueous phases, generating byproducts such as levulinic acid. Furthermore, under high-temperature reaction conditions, it may undergo dehydration condensation to form humin. These side reactions result in low purity of the obtained HMF. If a continuous reaction method is used (i.e., after the dehydration reaction, the HMF product is not separated and purified before proceeding directly to the oxidation reaction), the byproducts contained in the dehydration product will affect the subsequent oxidation reaction, resulting in low yield and purity of FDCA prepared from biomass sugars. For example, in patent CN115028608A, the intermediate product HMF was not separated and purified; FDCA was directly prepared from glucose, with a yield of only 44.1%. Summary of the Invention

[0005] To address the technical problem of low yield and purity of FDCA produced from biomass sugars via continuous reaction, this invention provides a method for preparing 2,5-furandicarboxylic acid from biomass sugars via continuous reaction. This method can improve the yield and purity of FDCA produced from biomass sugars via continuous reaction, while also reducing or even eliminating the use of hydrogen bromide in the oxidation reaction, thus minimizing the corrosion of equipment by hydrogen bromide.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for preparing 2,5-furandicarboxylic acid from biomass sugars via a continuous reaction includes the following steps:

[0008] Under the action of a homogeneous metal salt catalyst, biomass sugar is used as raw material to carry out a dehydration reaction to produce 5-hydroxymethylfurfural. A co-oxidant and acetic acid are added to the dehydrated reaction solution obtained after the reaction is completed. The co-oxidant is one or more of acetaldehyde, trimetaldehyde and methyl ethyl ketone. Under the action of an oxidation catalyst, an oxidation reaction is carried out in an oxidizing gas atmosphere, and then 2,5-furandicarboxylic acid is separated.

[0009] This invention employs a continuous reaction method to prepare FDCA. Since the dehydration product HMF is not separated and purified before the oxidation reaction, production efficiency is improved and the cost of HMF separation and purification is reduced. To address the low yield and purity of FDCA in continuous reaction methods, this invention uses a specific co-oxidant that undergoes an oxidation reaction with HMF. HMF is converted to FDCA, and the co-oxidant is converted to acetic acid. This reduces the impact of byproducts from the dehydration reaction on the final product and promotes the HMF→FDCA oxidation reaction. Thus, high FDCA yield and purity can be achieved while minimizing or even eliminating the use of hydrogen bromide in the oxidation reaction to reduce equipment corrosion.

[0010] The three co-oxidants used in this invention (acetaldehyde, triacetaldehyde, and methyl ethyl ketone) can effectively reduce the impact of byproducts in the dehydration reaction on the final product and promote the oxidation reaction of HMF→FDCA. In addition, the product after their oxidation reaction is acetic acid, which is easy to separate from FDCA. Furthermore, when acetic acid is used as the reaction solvent, there is no need to separate it from the reaction solvent, thus avoiding complicating the product separation and purification process.

[0011] Preferably, the method specifically includes the following steps:

[0012] (1) After preparing a mixture containing biomass sugar, homogeneous metal salt catalyst, organic bromide and water, a dehydration reaction is carried out to obtain a dehydration reaction solution;

[0013] (2) Add a co-oxidant and a portion of acetic acid to the dehydration reaction solution and mix to obtain the initial solution;

[0014] (3) Add an oxidation catalyst and another part of acetic acid to the reaction vessel, heat to the oxidation reaction temperature, add the initial solution to the reaction vessel under an oxidizing gas atmosphere, carry out the oxidation reaction, and then separate 2,5-furandicarboxylic acid.

[0015] Preferably, the biomass sugar includes one or more of glucose, high fructose syrup, mannose, galactose, sucrose, maltose, and lactose.

[0016] Furthermore, the biomass sugar is one or more of glucose, sucrose, and high fructose syrup with a fructose content of 42-90% in the solid components.

[0017] Preferably, the homogeneous metal salt catalyst includes one or more of chromium salts, aluminum salts, nickel salts, iron salts, tin salts, and cobalt salts.

[0018] The aforementioned homogeneous metal salt catalyst can effectively catalyze the conversion of biomass sugar into HMF, and when it remains in the dehydration reaction solution, it will not have a significant adverse effect on the subsequent oxidation reaction. Therefore, after the dehydration reaction is completed, the subsequent oxidation reaction can be carried out directly without separating it from the reaction system.

[0019] Furthermore, the homogeneous metal salt catalyst includes one or more of tetravalent chromium salts, trivalent aluminum salts, divalent nickel salts, trivalent iron salts, divalent tin salts, and divalent cobalt salts.

[0020] Preferably, the organic bromide includes one or more of choline bromide, bromine-containing quaternary ammonium salts, and bromine-containing imidazole ionic liquids.

[0021] Further, the organic bromide includes one or more of the following: choline bromide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, tetrabutylammonium bromide, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-hexyl-3-methylimidazolium bromide, 1-octyl-3-methylimidazolium bromide, and 1-butyl-2,3-dimethylimidazolium bromide.

[0022] Preferably, the mass ratio between the homogeneous metal salt catalyst and the biomass sugar is 0.02 to 0.5:1; the temperature of the dehydration reaction is 100 to 150°C, and the time is 20 min to 5 h.

[0023] Furthermore, the dehydration reaction is carried out at a temperature of 110–140°C for a time of 1–4 hours.

[0024] Preferably, the mass ratio of the biomass sugar to the organic bromide is 1:0.5 to 10.

[0025] Preferably, the oxidation catalyst includes a main catalyst, or includes a main catalyst and a co-catalyst; the main catalyst contains cobalt and manganese; and the co-catalyst contains at least one of iron, zirconium, zinc, copper and nickel.

[0026] Furthermore, the main catalyst includes divalent cobalt salt and divalent manganese salt; the co-catalyst includes one or more of trivalent iron salt, tetravalent zirconium salt, divalent copper salt, divalent zinc salt and divalent nickel salt.

[0027] Furthermore, the oxidation catalyst is a homogeneous metal salt catalyst.

[0028] Furthermore, the homogeneous metal salt catalyst includes one or more of acetate, halide, carbonate, sulfate, nitrate and phosphate.

[0029] Furthermore, the molar ratio of cobalt to manganese in the main catalyst is 1:0.015 to 0.15.

[0030] Furthermore, based on metal elements, the molar ratio between the main catalyst and the co-catalyst is 1:0.07 to 0.10.

[0031] Preferably, the mass ratio of the co-oxidant to the biomass sugar is 0.2 to 1.5:1, and more preferably 0.4 to 1.1:1.

[0032] In the process of preparing HMF from biomass sugar, a side reaction can easily occur, producing humin, resulting in low purity of HMF in the dehydrated reaction solution. Increasing the amount of co-oxidant can help reduce the impact of HMF purity on the yield and purity of FDCA to a greater extent. However, if the amount of co-oxidant is too large, it can cause excessive oxidation reaction and generate byproducts. This invention, by introducing a co-oxidant and controlling the mass ratio of co-oxidant to biomass sugar within the above-mentioned range, can further improve the yield and purity of FDCA prepared from biomass sugar through continuous reaction.

[0033] Preferably, the total mass of the dehydration reaction solution, co-oxidant, acetic acid, and oxidation catalyst contains 1000–6000 ppm of oxidation catalyst (calculated as metal element); the oxidation reaction is carried out at a temperature of 120–200°C for 10 min–1 h.

[0034] Furthermore, the oxidation reaction is carried out at a temperature of 130–180°C.

[0035] Preferably, the oxidizing gas is air, or a mixture of air and CO2; the pressure of the oxidizing gas atmosphere is 0.4 to 5 MPa.

[0036] Furthermore, the oxidizing gas is a mixture of air and CO2 in a volume ratio of 1:0.125 to 4, and more preferably a volume ratio of 1:0.15 to 2.

[0037] Preferably, the method for separating 2,5-furandicarboxylic acid is crystallization.

[0038] Preferably, in step (1), the biomass sugar, organic bromide, and water contain 30-60% by mass.

[0039] As the concentration of biomass sugar increases, the purity of the dehydration product HMF decreases, which in turn reduces the yield and purity of the subsequent oxidation product FDCA. This invention, by using a co-oxidant during the oxidation reaction, can reduce the impact of HMF purity on the yield and purity of FDCA. Therefore, the decrease in FDCA yield and purity is smaller when the biomass sugar concentration increases, thus achieving relatively high FDCA yield and purity even at higher biomass sugar concentrations.

[0040] Preferably, in step (2), during the preparation of the initial solution, the mass ratio between the dehydration reaction solution and the portion of acetic acid is 1:3 to 10, and more preferably 1:4 to 8.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] (1) In the process of preparing 2,5-furandicarboxylic acid by continuous reaction of biomass sugar, the present invention can achieve a high product FDCA yield and purity, and the reaction raw materials can be inexpensive biomass sugars such as glucose, which gives the continuous reaction method a better industrial application prospect, which is conducive to reducing production costs and improving production efficiency.

[0043] (2) The present invention can reduce or even avoid the use of hydrogen bromide in the oxidation reaction process while ensuring the yield and purity of FDCA, thereby reducing the corrosion of equipment. Detailed Implementation

[0044] The present invention will be further described below with reference to embodiments.

[0045] General Implementation Examples

[0046] A method for preparing 2,5-furandicarboxylic acid from biomass sugars via a continuous reaction includes the following steps:

[0047] Under the action of a homogeneous metal salt catalyst, biomass sugar is used as raw material to carry out a dehydration reaction to produce 5-hydroxymethylfurfural. A co-oxidant and acetic acid are added to the dehydrated reaction solution obtained after the reaction is completed. The co-oxidant is one or more of acetaldehyde, trimetaldehyde and methyl ethyl ketone. Under the action of an oxidation catalyst, an oxidation reaction is carried out in an oxidizing gas atmosphere, and then 2,5-furandicarboxylic acid is separated.

[0048] As one specific implementation method, the method specifically includes the following steps:

[0049] (1) After preparing a mixture containing biomass sugar, homogeneous metal salt catalyst, organic bromide and water, a dehydration reaction is carried out to obtain a dehydration reaction solution;

[0050] Optionally: the organic bromide includes one or more of choline bromide, bromine-containing quaternary ammonium salts, and bromine-containing imidazole ionic liquids; the mass ratio between the biomass sugar and the organic bromide is 1:0.5-10; and the biomass sugar accounts for 30-60% of the mass of the biomass sugar, organic bromide, and water.

[0051] (2) Add a co-oxidant and a portion of acetic acid to the dehydration reaction solution and mix to obtain the initial solution;

[0052] Optionally, the mass ratio between the dehydration reaction solution and the portion of acetic acid is 1:3 to 10;

[0053] (3) Add an oxidation catalyst and another part of acetic acid to the reaction vessel, heat to the oxidation reaction temperature, add the initial solution to the reaction vessel under an oxidizing gas atmosphere, carry out the oxidation reaction, and then separate 2,5-furandicarboxylic acid.

[0054] In one specific embodiment, the biomass sugar includes one or more of glucose, high fructose syrup, mannose, galactose, sucrose, maltose, and lactose.

[0055] In one specific embodiment, the homogeneous metal salt catalyst includes one or more of chromium salt, aluminum salt, nickel salt, iron salt, tin salt and cobalt salt; the mass ratio between the homogeneous metal salt catalyst and biomass sugar is 0.02 to 0.5:1; the dehydration reaction is carried out at a temperature of 100 to 150°C for a time of 20 min to 5 h.

[0056] In one specific embodiment, the oxidation catalyst includes a main catalyst, or includes a main catalyst and a co-catalyst; the main catalyst contains cobalt and manganese; the co-catalyst contains at least one of iron, zirconium, zinc, copper, and nickel; the molar ratio of cobalt to manganese in the main catalyst is 1:0.015 to 0.15; and the molar ratio of the main catalyst to the co-catalyst, calculated by metal element, is 1:0.07 to 0.10.

[0057] In one specific embodiment, the mass ratio between the co-oxidant and the biomass sugar is 0.2–1.5:0.05–0.6:1; the total mass of the dehydration reaction solution, co-oxidant, acetic acid, and oxidation catalyst contains 1000–6000 ppm of the oxidation catalyst as a metal element; the oxidation reaction temperature is 120–200°C, and the time is 10 min–1 h.

[0058] In one specific embodiment, the oxidizing gas is air, or a mixture of air and CO2 in a volume ratio of 1:0.125 to 4; the pressure of the oxidizing gas atmosphere is 0.4 to 5 MPa.

[0059] As one specific implementation method, the method for separating 2,5-furandicarboxylic acid is crystallization. Specific Implementation

[0061] The present invention will now be described through specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Variations and advantages that can be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0062] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. Unless otherwise specified, the raw materials and equipment used in this invention are conventional in the art and can be obtained through conventional commercial means; unless otherwise specified, the methods used in this invention are conventional methods in the art.

[0063] The detection and analysis methods used in the following embodiments are as follows:

[0064] (1) High-performance liquid chromatography (HPLC) detection methods for each component:

[0065] Biomass sugars: The instrument was an Agilent 1260, the column was a Hi-Plex H, the column temperature was 65℃, the detector was differential, the mobile phase was 5mM sulfuric acid aqueous solution, and the flow rate was 0.4mL / min.

[0066] HMF: The instrument was an Agilent 1260, the column was an Eclipse XDB-C18, the column temperature was 40℃, the detector was UV, the mobile phase was a mixture of methanol and water with a volume ratio of 9:1, the flow rate was 1mL / min, and the detection wavelength was 283nm.

[0067] FDCA: The instrument was an Agilent 1260, the column was an Eclipse XDB-C18, the column temperature was 35℃, the detector was UV, the mobile phase was a mixture of trifluoroacetic acid aqueous solution (mass fraction of 0.1%) and methanol with a volume ratio of 2:3, the flow rate was 1 mL / min, and the detection wavelength was 260 nm.

[0068] (2) Formula for calculating the conversion rate of biomass sugar and HMF:

[0069] Biomass sugar conversion rate = (molar amount of converted biomass sugar / molar amount of added biomass sugar) × 100%;

[0070] HMF conversion rate = (molar amount of HMF converted / molar amount of HMF in the added fructose dehydration reaction solution) × 100%.

[0071] (3) Formulas for calculating the yields of HMF and FDCA when using glucose, mannose, fructose syrup, or galactose as raw materials:

[0072] HMF yield = (molar amount of HMF generated / molar amount of added biomass sugar) × 100%;

[0073] FDCA yield = (molar amount of FDCA generated / molar amount of HMF entering the oxidation reactor) × HMF yield.

[0074] (4) Formulas for calculating the yields of HMF and FDCA when using sucrose, maltose, or lactose as raw materials:

[0075] HMF yield = (molar amount of HMF generated / (molar amount of added biomass sugar × 2) × 100%)

[0076] FDCA yield = (molar amount of FDCA generated / molar amount of HMF entering the oxidation reactor) × HMF yield.

[0077] The above-mentioned "molar amount of converted biomass sugar", "molar amount of generated HMF" and "molar amount of generated FDCA" were calculated using high performance liquid chromatography.

[0078] Examples 1-8: The effect of the choice of organic bromide on the reaction

[0079] The preparation of 2,5-furandicarboxylic acid from glucose via a continuous reaction is as follows:

[0080] S1: Glucose → 5-Hydroxymethylfurfural:

[0081] A certain amount of glucose, 500g of organic bromide, 100g of water, and a certain amount of homogeneous metal salt catalyst were added to a 2L reactor. Stirring was started, and the mixture was heated to the dehydration reaction temperature and reacted for a certain period of time to obtain a dehydrated reaction solution. Samples were taken, analyzed by high-performance liquid chromatography (HPLC), and the yield of 5-hydroxymethylfurfural was calculated.

[0082] S2: 5-Hydroxymethylfurfural → 2,5-Furfurandicarboxylic acid

[0083] A certain amount of co-oxidant was added to the dehydration reaction solution, and then mixed with a certain amount of acetic acid to obtain a preliminary solution. 6000g of acetic acid and a certain amount of oxidation catalyst were added to a 20L reactor. After heating to the oxidation reaction temperature, 6000g of the preliminary solution was introduced under an oxidizing gas atmosphere (feeding rate 60g / min, time 100min) to carry out the oxidation reaction to produce 2,5-furandicarboxylic acid. After the reaction, 2,5-furandicarboxylic acid was separated by crystallization, detected by high-performance liquid chromatography, and the fructose conversion rate, purity, and yield of 2,5-furandicarboxylic acid were calculated. The glucose conversion rates in Examples 1-8 were all >99.9%.

[0084] The detailed design of the preparation process in Examples 1 to 8, as well as the calculation results of product purity and yield, are shown in Tables 1 and 2.

[0085] Table 1. Details of the preparation process and experimental results of Examples 1-4

[0086]

[0087] 1 Glucose mass fraction: refers to the percentage of glucose in the total mass of glucose, organic bromide, and water in step S1, i.e., glucose mass fraction = glucose mass / (glucose mass + organic bromide mass + water mass) × 100%; the "glucose mass fraction" in the tables below has the same meaning.

[0088] 2 Added amount: refers to the mass of glucose added in step S1; the same meaning applies to "added amount" in the tables below.

[0089] 3 Dehydration reaction solution: Acetic acid (m:m): Here, "acetic acid" refers to the acetic acid added when preparing the "initial solution"; the same meaning applies to "dehydration reaction solution: acetic acid (m:m)" in the tables below.

[0090] 4 Oxidation reaction temperature and time: The oxidation reaction time here is started from the time the initial solution is added; the same meaning applies to the "oxidation reaction temperature and time" in the tables below.

[0091] Table 2. Preparation process details and experimental results of Examples 5-8

[0092]

[0093]

[0094] Analysis of Examples 1-8 yields the following conclusions:

[0095] Under conditions where the reaction proceeds fully (glucose conversion rate > 99.9%), the use of choline bromide or tetraethylammonium bromide can improve the yield of HMF compared to other organic bromides, thereby increasing the purity and yield of the final product FDCA.

[0096] Examples 9-15: Effects of different dehydration catalysts (homogeneous metal salt catalysts) on the reaction

[0097] In Examples 9-15, the steps for preparing 2,5-furandicarboxylic acid from glucose via a continuous reaction were the same as in Examples 1-8. The glucose conversion rate in Examples 9-15 was measured to be >99.9%.

[0098] The detailed design of the preparation process in Examples 9-15, as well as the calculation results of product purity and yield, are shown in Tables 3 and 4.

[0099] Table 3. Details of the preparation process and experimental results of Examples 9-12

[0100]

[0101]

[0102] Table 4. Details of the preparation process and experimental results of Examples 13-15

[0103]

[0104] Analysis of Examples 9-15 yields the following conclusions:

[0105] Under the condition that the reaction proceeds fully (glucose conversion rate > 99.9%), compared with other homogeneous metal salt catalysts, the use of chromium salts (such as chromium bromide and chromium chloride) as the dehydration reaction catalyst can improve the yield of HMF, and thus improve the purity and yield of the final product FDCA.

[0106] Examples 16-21: Effect of Dehydration Catalyst (Homogeneous Metal Salt Catalyst) Addition on the Reaction

[0107] In Examples 16-21, the steps for preparing 2,5-furandicarboxylic acid from glucose via a continuous reaction were the same as in Examples 1-8. The glucose conversion rate in Examples 16-21 was measured to be >99.9%.

[0108] The detailed design of the preparation process in Examples 16-21, as well as the calculation results of product purity and yield, are shown in Table 5.

[0109] Table 5. Details of the preparation process and experimental results of Examples 16-21

[0110] Analysis of Examples 16-21 yields the following conclusions:

[0111] Under the condition that the reaction proceeds fully (glucose conversion rate > 99.9%), as the amount of catalyst added to the dehydration reaction increases, the yield of HMF and the purity and yield of FDCA first increase and then decrease.

[0112] Examples 22-29: Effect of the ratio of dehydration reaction solution to acetic acid on the reaction

[0113] In Examples 22-29, the steps for preparing 2,5-furandicarboxylic acid from glucose via a continuous reaction were the same as in Examples 1-8. The glucose conversion rate in Examples 22-29 was measured to be >99.9%.

[0114] The detailed design of the preparation process in Examples 22–29, as well as the calculation results of product purity and yield, are shown in Tables 6 and 7.

[0115] Table 6. Details of the preparation process and experimental results of Examples 22-25

[0116]

[0117] Table 7. Details of the preparation process and experimental results of Examples 26-29

[0118]

[0119]

[0120] Analysis of Examples 22-29 yields the following conclusions:

[0121] Within a certain range, the purity of the product FDCA can be improved by increasing the mass ratio between the dehydration reaction solution and acetic acid.

[0122] Examples 30-37: Effects of different biomass sugars on the reaction

[0123] The steps for preparing 2,5-furandicarboxylic acid from biomass sugar via a continuous reaction are as follows:

[0124] S1: Biomass sugar → 5-hydroxymethylfurfural:

[0125] A certain amount of biomass sugar, 500g of organic bromide, 100g of water, and a certain amount of homogeneous metal salt catalyst were added to a 2L reactor. Stirring was started, and the mixture was heated to the dehydration reaction temperature and reacted for a certain period of time to obtain a dehydrated reaction solution. Samples were taken, analyzed by high-performance liquid chromatography (HPLC), and the yield of 5-hydroxymethylfurfural was calculated.

[0126] S2: 5-Hydroxymethylfurfural → 2,5-Furfurandicarboxylic acid

[0127] A certain amount of co-oxidant was added to the dehydration reaction solution, and then mixed with a certain amount of acetic acid to obtain a preliminary solution. 6000g of acetic acid and a certain amount of oxidation catalyst were added to a 20L reactor. After heating to the oxidation reaction temperature, 6000g of the preliminary solution was introduced under an oxidizing gas atmosphere (feeding rate 60g / min, time 100min) to carry out the oxidation reaction to produce 2,5-furandicarboxylic acid. After the reaction, 2,5-furandicarboxylic acid was separated by crystallization, detected by high-performance liquid chromatography, and the fructose conversion rate, purity, and yield of 2,5-furandicarboxylic acid were calculated. The glucose conversion rates in Examples 30–37 were all >99.9%.

[0128] The detailed design of the preparation process in Examples 30-37, as well as the calculation results of product purity and yield, are shown in Tables 8 and 9.

[0129] Table 8. Details of the preparation process and experimental results of Examples 30-33

[0130]

[0131]

[0132] 1 Mass fraction: refers to the mass percentage of biomass sugar, organic bromide and biomass sugar in water in step S1, that is, biomass sugar mass fraction = biomass sugar mass / (biomass sugar mass + organic bromide mass + water mass) × 100%; the "mass fraction" in Table 9 has the same meaning.

[0133] 2 Added amount: refers to the mass of biomass sugar added in step S1; the same meaning is given for "added amount" in Table 9.

[0134] Table 9. Details of the preparation process and experimental results of Examples 34-37

[0135]

[0136]

[0137] Analysis of Examples 30-37 yields the following conclusions:

[0138] (1) When high fructose syrup is used as the reaction raw material, the yield of HMF and the yield and purity of FDCA can be improved by increasing the fructose content.

[0139] (2) Compared with other biomass sugars, using high fructose syrup or sucrose can achieve higher FDCA yield and purity.

[0140] Examples 38-40: Effects of different co-oxidants on the reaction

[0141] In Examples 38-40, the steps for preparing 2,5-furandicarboxylic acid from glucose via a continuous reaction were the same as in Examples 1-8. The glucose conversion rate and HMF conversion rate in Examples 38-40 were both >99.9%.

[0142] The detailed design of the preparation process in Examples 38-40, as well as the calculation results of product purity and yield, are shown in Table 10.

[0143] Table 10. Details of the preparation process and experimental results of Examples 38-40

[0144]

[0145] Analysis of Examples 38-40 yields the following conclusions:

[0146] Compared to acetaldehyde and methyl ethyl ketone, using paraldehyde as a co-oxidant achieves higher FDCA yields and purity. This is because the co-oxidant is first oxidized in acetic acid solvent to form peroxides, which then change the valence state of the metal elements in the catalyst through oxidation, promoting HMF oxidation. While acetaldehyde and methyl ethyl ketone have similar structures, their peroxide formation mechanism differs from that of paraldehyde. The higher activity of paraldehyde may be due to the higher oxidative activity of the peroxides formed from paraldehyde compared to acetaldehyde and methyl ethyl ketone.

[0147] Examples 41-50: Effect of Co-oxidant Dosage on the Reaction

[0148] In Examples 41-50, the steps for preparing 2,5-furandicarboxylic acid from glucose via a continuous reaction were the same as in Examples 1-8. The glucose conversion rate in Examples 41-50 was measured to be >99.9%.

[0149] The detailed design of the preparation process in Examples 41-50, as well as the calculation results of product purity and yield, are shown in Tables 11 and 12.

[0150] Table 11. Details of the preparation process and experimental results of Examples 41-45

[0151] Table 12 Details of the preparation process and experimental results of Examples 46-50

[0152]

[0153] Analysis of Examples 41-50 yields the following conclusions:

[0154] Within a certain range, increasing the amount of co-oxidant can improve the yield and purity of FDCA; however, excessive amounts of co-oxidant can negatively impact the yield and purity of FDCA. This is because co-oxidants can promote the HMF→FDCA reaction and reduce the influence of HMF purity on the yield and purity of the FDCA product. However, excessive amounts of co-oxidant can lead to over-oxidation, generating byproducts.

[0155] Comparative Examples 1-2: Effect of not using a co-oxidizing agent on the reaction. 2,5-furandicarboxylic acid was prepared from glucose by a continuous reaction, as follows:

[0156] S1: Glucose → 5-Hydroxymethylfurfural:

[0157] A certain amount of glucose, 500g of organic bromide, 100g of water, and a certain amount of homogeneous metal salt catalyst were added to a 2L reactor. Stirring was started, and the mixture was heated to the dehydration reaction temperature and reacted for a certain period of time to obtain a dehydrated reaction solution. Samples were taken, analyzed by high-performance liquid chromatography (HPLC), and the yield of 5-hydroxymethylfurfural was calculated.

[0158] S2: 5-Hydroxymethylfurfural → 2,5-Furfurandicarboxylic acid

[0159] The dehydrated reaction solution was mixed with a certain amount of acetic acid to obtain a preliminary solution. 6000g of acetic acid and a certain amount of oxidation catalyst were added to a 20L reactor. After heating to the oxidation reaction temperature, 6000g of the preliminary solution was introduced under an oxidizing gas atmosphere (feeding rate 60g / min, time 100min) to carry out the oxidation reaction to produce 2,5-furandicarboxylic acid. After the reaction, 2,5-furandicarboxylic acid was separated by crystallization, detected by high-performance liquid chromatography (HPLC), and the fructose conversion rate, purity, and yield of 2,5-furandicarboxylic acid were calculated.

[0160] The glucose conversion rate and HMF conversion rate of Comparative Examples 1 and 2 were both >99.9%. The detailed design of the preparation process in Comparative Examples 1 and 2, as well as the calculation results of product purity and yield, are shown in Table 13.

[0161] Table 13. Details of the preparation process and experimental results of Comparative Examples 1-2

[0162]

[0163] Analysis of Examples 38-40 and Comparative Examples 1-2 yields the following conclusions:

[0164] By using co-oxidizing agents such as acetaldehyde, triacetaldehyde, or methyl ethyl ketone, it is possible to improve the yield and purity of FDCA while reducing the use of hydrobromic acid and lowering the reaction temperature.

[0165] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing 2,5-furandicarboxylic acid from biomass sugars via a continuous reaction, characterized in that, Includes the following steps: Under the action of a homogeneous metal salt catalyst, biomass sugar is used as raw material to carry out a dehydration reaction to produce 5-hydroxymethylfurfural. A co-oxidant and acetic acid are added to the dehydrated reaction solution obtained after the reaction is completed. The co-oxidant is triacetaldehyde. Under the action of an oxidation catalyst, an oxidation reaction is carried out in an oxidizing gas atmosphere, and then 2,5-furandicarboxylic acid is separated.

2. The method according to claim 1, characterized in that, Specifically, the following steps are included: (1) After preparing a mixture containing biomass sugar, homogeneous metal salt catalyst, organic bromide and water, a dehydration reaction is carried out to obtain a dehydration reaction solution; (2) Add a co-oxidant and a portion of acetic acid to the dehydration reaction solution and mix to obtain the initial solution; (3) Add an oxidation catalyst and another part of acetic acid to the reaction vessel, heat to the oxidation reaction temperature, add the initial solution to the reaction vessel under an oxidizing gas atmosphere, carry out the oxidation reaction, and then separate 2,5-furandicarboxylic acid.

3. The method according to claim 1 or 2, characterized in that, The biomass sugars include one or more of glucose, high fructose syrup, mannose, galactose, sucrose, maltose, and lactose.

4. The method according to claim 3, characterized in that, The biomass sugar is one or more of glucose, sucrose, and high fructose syrup with a fructose content of 42-90% in the solid components.

5. The method according to claim 1 or 2, characterized in that, The homogeneous metal salt catalyst includes one or more of chromium salts, aluminum salts, nickel salts, iron salts, tin salts, and cobalt salts.

6. The method according to claim 1 or 2, characterized in that, The mass ratio between the homogeneous metal salt catalyst and the biomass sugar is 0.02~0.5:1; the dehydration reaction is carried out at a temperature of 100~150℃ for 20 min~5 h.

7. The method according to claim 1 or 2, characterized in that, The oxidation catalyst includes a main catalyst, or includes a main catalyst and a co-catalyst; the main catalyst contains cobalt and manganese; the co-catalyst contains at least one of iron, zirconium, zinc, copper and nickel.

8. The method according to claim 1 or 2, characterized in that, The mass ratio of the co-oxidant to biomass sugar is 0.2~1.5:

1.

9. The method according to claim 2, characterized in that, In step (1), the biomass sugar, organic bromide and water contain 30-60% biomass sugar by mass.

10. The method according to claim 2, characterized in that, In step (2), during the preparation of the initial solution, the mass ratio between the dehydration reaction solution and the portion of acetic acid is 1:3~10.

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