A method for photocatalytic preparation of fructose

Abstract

The application belongs to the technical field of biomass resource utilization, and specifically discloses a method for preparing fructose through photocatalysis. The method for preparing fructose through photocatalysis provided by the application is to use a six-carbon sugar as a raw material, and to perform an isomerization reaction under the action of a photocatalyst and illumination to obtain fructose. The method provided by the application has mild reaction conditions, and the photocatalyst used has low cost and high energy utilization rate, and the catalytic effect of the photocatalyst basically does not change after multiple cycles, so that the method can provide high-quality raw materials for the stable production of a high-value-added biomass derivative HMF.

Description

Technical Field

[0001] This invention belongs to the field of biomass resource utilization technology, specifically relating to a method for photocatalytic preparation of fructose. Background Technology

[0002] Converting carbohydrates from renewable agricultural biomass and lignocellulosic waste into high-value-added chemicals is fundamental to modern biorefining. Typical high-value-added chemicals include furfuryl alcohol (FA), furfural (FF), levulinic acid (LA), γ-valerate (GVL), and 5-hydroxymethylfurfural (HMF). Among these, HMF has a wide range of applications and has received considerable attention from both industry and academia. Compared to glucose and other pyranoses, fructose's furanulose structure allows for a faster and more selective HMF production rate, but fructose has significant disadvantages in terms of yield and price. Currently, intramolecular hydride transfer under the influence of Lewis acids is the common method for fructose formation. However, the mainstream homogeneous Lewis acid isomerization method produces a large volume of waste liquid, has low selectivity, and generally requires energy such as heat to initiate the reaction.

[0003] Reducing the use of fossil fuels, improving their utilization rate, finding alternatives to fossil fuels, and recycling energy have become important research directions in the scientific community in recent years. Currently, most reactions still rely on energy converted from fossil fuels, and the large-scale use of fossil fuels and the multi-stage energy conversion process lead to low energy utilization efficiency. From a reaction perspective, some researchers have attempted to improve reactions using catalysis. While conventional chemical catalysis has a wide range of applications, the emission of waste liquids and gases cannot be ignored. Biocatalysis, on the other hand, typically suffers from demanding enzyme cultivation conditions and high overall costs.

[0004] Therefore, the present invention aims to provide a method for photocatalytic preparation of fructose, so as to achieve fructose preparation under high selectivity and mild conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a method for photocatalytic preparation of fructose, which has the advantages of high selectivity, mild reaction conditions, low cost of photocatalyst, and reusability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] In a first aspect, the present invention provides a method for photocatalytic preparation of fructose, using hexose as raw material, and isomerizing under light irradiation in the presence of a photocatalyst to prepare fructose.

[0008] The photocatalyst comprises at least one of the following: a non-precious metal element, a non-precious metal oxide, or a non-precious metal chloride; or, the photocatalyst further comprises at least one of the following: a non-metal element element, a non-metal element polymer, or a non-metal element oxide.

[0009] The photocatalyst is a multiphase composite material comprising at least two phases, wherein the phases in the multiphase composite material may be the same or different. Specifically, the photocatalyst may be, for example, a multiphase composite material composed of at least one of a non-precious metal element, a non-precious metal oxide, and a non-precious metal chloride, and at least one of a non-metal element, a non-metal element polymer, and a non-metal element oxide; or it may be a multiphase composite material composed of any two or more of a non-precious metal element, a non-precious metal oxide, and a non-precious metal chloride; or it may be a multiphase composite material composed of any two or more of a non-metal element, a non-metal element polymer, and a non-metal element oxide.

[0010] In one embodiment of the present invention, the non-precious metal in the photocatalyst is selected from magnesium, aluminum, calcium, barium, scandium, titanium, chromium, copper, manganese, iron, cobalt, nickel, gallium, cerium, lanthanum, zinc, niobium, cadmium, lead, zirconium, and tin.

[0011] Preferably, the non-precious metal is selected from magnesium, aluminum, calcium, titanium, copper, iron, cerium, zinc, and tin.

[0012] In one embodiment of the present invention, the non-metallic element in the photocatalyst is selected from boron, carbon, nitrogen, silicon, and phosphorus.

[0013] Preferably, the non-metallic element is selected from carbon and nitrogen.

[0014] As one embodiment of the present invention, the photocatalyst is selected from any one of Ti / ZnCl2, Sn / Si, Cu / AlCl3 / g-C3N4, Ce / AlCl3 / g-C3N4, and MgO / CaO / Fe / g-C3N4.

[0015] As one embodiment of the present invention, the illumination described in the present invention uses one or more of the following as light sources: natural light, LED, ultraviolet xenon lamp, and ultraviolet mercury lamp.

[0016] Preferably, the illumination uses an ultraviolet xenon lamp and / or an ultraviolet mercury lamp as the light source, with an ultraviolet wavelength of 280–400 nm and an irradiance of 0.3–18 W / m². 2 .

[0017] As one embodiment of the present invention, the hexose is selected from one or more of glucose, galactose, mannose, sorbitol, sucrose, inulin, hydrolyzed starch, and cellulose.

[0018] Preferably, the hexose is selected from one or more of glucose, galactose, mannose, and sorbitol.

[0019] As one embodiment of the present invention, the reaction solvent used in the isomerization reaction of the present invention is water and / or an organic solvent, preferably a mixed solvent composed of water and an organic solvent.

[0020] Preferably, the volume ratio of water to organic solvent in the mixed solvent is 1:(2-5), more preferably the volume ratio of water to organic solvent in the mixed solvent is 1:3.

[0021] As one embodiment of the present invention, the organic solvent is selected from one or more of ethylene glycol, methanol, ethanol, acetone, 4-methyl-2-pentanone, N,N-dimethylformamide, acetonitrile, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, dimethyl sulfoxide, ethylene glycol dimethyl ether, diethyl ether, methyl tert-butyl ether, ethyl acetate, pyridine, benzene, isopropanol, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0022] Preferably, the organic solvent is selected from at least one of dimethyl sulfoxide, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0023] Preferably, when 2-methyltetrahydrofuran is used as the organic solvent, acetic acid or citric acid can be added to the reaction system to promote the reaction. Preferably, the amount of acetic acid or citric acid used is 1.0–5.0% of the mass of the hexose raw material, and more preferably, the amount of acetic acid or citric acid used is 1.5–4.5% of the mass of the hexose raw material.

[0024] In one embodiment of the present invention, the concentration of hexose in the mixed solvent is 0.05–0.25 g / mL.

[0025] In one embodiment of the present invention, the amount of photocatalyst used is 1 to 15% of the mass of the hexose raw material.

[0026] Preferably, the amount of photocatalyst used is 5-15% of the mass of the hexose raw material; more preferably, the amount of photocatalyst used is 7.5-13.5% of the mass of the hexose raw material.

[0027] In one embodiment of the present invention, the reaction temperature of the isomerization reaction is 20-35°C, preferably 25-30°C.

[0028] In one embodiment of the present invention, the reaction time of the isomerization reaction is 0.5 to 24 hours, preferably 5 to 20 hours.

[0029] As one embodiment of the present invention, the photocatalytic method for preparing fructose further includes the following steps: after the isomerization reaction is completed, the photocatalyst in the reaction solution is recovered and then subjected to an activity regeneration treatment to obtain a regenerated photocatalyst; the regenerated photocatalyst is recycled and, according to experiments, can be recycled at least ten times.

[0030] The active regeneration process includes drying and high-temperature calcination; preferably, the drying temperature is 75°C and the high-temperature calcination temperature is 500°C.

[0031] This invention utilizes a photocatalyst to catalyze the isomerization reaction of hexoses (such as hexoses with a pyran structure). Under light-driven conditions, the efficient charge separation of the photocatalyst causes a transient rearrangement of the electron cloud, thereby triggering the generation of Lewis acid-base sites. Photocatalysts doped with specific elements can effectively separate charge carriers and specific active sites, thus enabling the isomerization of hexoses such as glucose to fructose under light irradiation. From a reaction perspective, compared to biological enzyme catalysis, photocatalysis has lower requirements for reaction conditions and lowers overall costs. Compared to chemical catalysis, photocatalysis further increases reaction selectivity and provides milder reaction conditions. From an energy perspective, photocatalysis not only converts solar energy into energy usable for chemical reactions but also reduces atmospheric and water pollution, thus aligning with the "dual carbon" concept proposed by the state in recent years. The method for preparing fructose using a photocatalyst-catalyzed hexose isomerization reaction provided by this invention offers a new direction for the high-value utilization and conversion of biomass.

[0032] The photocatalytic method for preparing fructose provided by this invention features a simple reaction system and mild reaction conditions. The photocatalyst used is doped with non-precious metal elements, as well as non-metallic elements and polymers, resulting in low cost and high energy utilization. The photocatalyst's catalytic effect remains essentially unchanged after multiple cycles, allowing for repeated use. The reaction is stable, and wastewater treatment consumes low energy. This invention provides a stable, high-quality raw material for the production of high-value-added biomass derivatives, HMF. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below. Those skilled in the art should understand that the specific embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof.

[0034] It should be noted that, unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available conventional products.

[0035] The photocatalyst provided by this invention uses the following reagents in its preparation method: concentrated sulfuric acid, formic acid, acetic acid, concentrated hydrochloric acid, phosphoric acid, citric acid, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium bisulfate, metal chloride, 2,4-pentanedione, tetraethylammonium hydroxide, tetraethyl orthosilicate, tetrabutyl titanate, polymer g-C3N4, etc. During the preparation of the photocatalyst, it needs to be calcined at 300-700℃ for 1-6 hours, or reacted in a microwave reactor at 180-300℃ for 0.5-2.5 hours.

[0036] Specifically, the present invention provides the following photocatalysts and their preparation processes.

[0037] Preparation Example 1

[0038] This preparation example provides a photocatalyst doped with metallic Ti, and the preparation process is as follows:

[0039] Weigh out 8g of tetrabutyl titanate, 1.5g of 2,4-pentanedione, 0.5g of Zn3(PO4)2, 0.1g of concentrated hydrochloric acid, 2g of acetic acid, 30mL of 2-propanol, and 20mL of deionized water. Mix them, sonicate at room temperature for 30min, and then react them in an oil bath at 75℃ for 8h. After that, dry the gel at 100℃ for 8h, take out the dried particles, grind them, and then calcine them in a muffle furnace at 500℃ for 2h. After cooling to room temperature, take out the remaining solid, wash it with deionized water, and dry it at 75℃ under nitrogen for 16h to obtain the photocatalyst, denoted as 1-Ti / ZnCl2.

[0040] Preparation Example 2

[0041] This preparation example provides a photocatalyst doped with metal Sn and non-metal Si. The preparation process is as follows:

[0042] Weigh out 8g of tetraethylammonium hydroxide, 7g of tetraethyl orthosilicate, 0.3g of SnCl4, 2g of acetic acid, 40mL of ethanol and 10mL of deionized water, mix them, sonicate at room temperature for 30min, then heat in an oil bath at 150℃ for 4h. After grinding the particles, add them to a muffle furnace and calcine at 550℃ for 4h. After cooling to room temperature, take out the remaining solid, wash it with deionized water, and dry it at 75℃ under nitrogen for 16h to obtain the photocatalyst, denoted as 2-Sn / Si.

[0043] Preparation Example 3

[0044] This preparation example provides a photocatalyst doped with metallic Cu, and the preparation process is as follows:

[0045] Weigh out 1.5g CuCl2, 0.1g AlCl3, 0.2g concentrated hydrochloric acid, 4g polycarbon nitride g-C3N4, 25mL DMF, and 25mL deionized water, mix them, and sonicate at room temperature for 120min. Then, take out the lower layer of precipitated solid, grind the particles, and put them into a microwave reactor to react at 200℃ for 0.5h. After that, wash with deionized water and dry under nitrogen at 75℃ for 16h to obtain the photocatalyst, denoted as 3-Cu / AlCl3 / g-C3N4.

[0046] Preparation Example 4

[0047] This preparation example provides a photocatalyst doped with metal Ce, and the preparation process is as follows:

[0048] Weigh 2g of CeO2, 0.7g of AlCl3, 3.6g of polycarbon nitride g-C3N4, and 0.4g of NaH2PO4, mix them with 40mL of ethylene glycol and 10mL of deionized water, and sonicate at room temperature for 30min. Then transfer the suspension to a 100mL hydrothermal reactor, place the reactor in a muffle furnace for calcination, and react at 700℃ for 3h under nitrogen protection. After cooling to room temperature, remove the remaining solid, wash with deionized water, and dry at 75℃ under nitrogen for 16h to obtain the photocatalyst, denoted as 4-Ce / AlCl3 / g-C3N4.

[0049] Preparation Example 5

[0050] This preparation example provides a photocatalyst doped with metals Mg and Ca, and the preparation process is as follows:

[0051] Weigh out 1.5g of MgO, 1.5g of CaO, 0.1g of H3PO4, 4g of polycarbon nitride g-C3N4, and 1.5g of FeCl3. Mix them with 10mL of DMF, 20mL of MeOH, and 20mL of deionized water. Sonicate at room temperature for 30min. Then transfer the suspension to a 100mL hydrothermal reactor. Place the hydrothermal reactor in a muffle furnace for calcination. React at 600℃ for 6h under nitrogen protection. After cooling to room temperature, remove the remaining solid, wash with deionized water, and dry at 75℃ under nitrogen for 16h to obtain the photocatalyst, denoted as 5-MgO / CaO / Fe / g-C3N4.

[0052] Using the specific photocatalysts prepared above, experiments were conducted on the photocatalytic preparation of fructose, and the examples are as follows.

[0053] Example 1

[0054] This embodiment provides a method for preparing fructose by glucose isomerization, which is carried out according to the following steps:

[0055] Take 0.5 g of the photocatalyst 1-Ti / ZnCl2 obtained in Preparation Example 1, 6 g of glucose, 20 mL of water, 20 mL of THF (tetrahydrofuran), and 40 mL of DMSO (dimethyl sulfoxide), and add them together into a light-transmitting conical flask; first sonicate for 30 min, then irradiate with an intensity of 0.35 W / m 2 The isomerization reaction was carried out under ultraviolet xenon lamp irradiation with an ultraviolet wavelength of 310 nm for 16 h; the reaction was carried out using a magnetic stirrer at a stirring speed of 1600 r / min at 25–30 °C.

[0056] After the reaction was completed, the total mass of the contents of the conical flask, the mass of the remaining solid, and the mass of the liquid were recorded. The solution was sampled and diluted to volume, and the concentrations of the remaining glucose and fructose were determined by HPLC.

[0057] In this application, fructose and total sugar content were detected using an Agilent 1260Ⅱ liquid chromatograph, and quantification was performed using the external standard method. The calculation formulas for sugar conversion rate (C), selectivity (S), and fructose yield (Y) are as follows (the detection and calculation methods in the following embodiments are the same as in this embodiment):

[0058]

[0059]

[0060]

[0061] Calculations show that in this embodiment, the fructose yield (Y) is 22.17%, the glucose conversion rate (C) is 42.68%, and the fructose selection rate (S) reaches 51.94%.

[0062] Example 2

[0063] This embodiment provides a method for preparing fructose by glucose isomerization, which is carried out according to the following steps:

[0064] Take 1 g of the photocatalyst 2-Sn / Si obtained in Preparation Example 2, 9 g of glucose, 0.4 g of acetic acid, 20 mL of water, and 60 mL of 2-methyltetrahydrofuran, and add them together into a transparent conical flask; first sonicate for 30 min, then irradiate with an intensity of 0.76 W / m 2 The isomerization reaction was carried out under ultraviolet xenon lamp irradiation with an ultraviolet wavelength of 340 nm for 8 hours. The reaction was carried out using a magnetic stirrer at a stirring speed of 1600 r / min at 25–30 °C.

[0065] After the reaction was completed, the total mass of the contents of the conical flask, the mass of the remaining solid, and the mass of the liquid were recorded. The solution was sampled and diluted to volume, and the concentrations of the remaining glucose and fructose were determined by HPLC.

[0066] Calculations show that in this embodiment, the fructose yield (Y) is 32.44%, the glucose conversion rate (C) is 46.92%, and the fructose selection rate (S) reaches 69.14%.

[0067] Example 3

[0068] This embodiment provides a method for preparing fructose by galactose isomerization, which is carried out according to the following steps:

[0069] Take 1.2 g of the photocatalyst 3-Cu / AlCl3 / g-C3N4 obtained in Preparation Example 3, 9 g of galactose, 0.15 g of citric acid, 20 mL of water, and 60 mL of 2-methyltetrahydrofuran, and add them together into a light-transmitting conical flask; first sonicate for 30 min, then irradiate with an intensity of 10 W / m 2 The isomerization reaction was carried out under ultraviolet xenon lamp irradiation with an ultraviolet wavelength of 290 nm for 10 h; the reaction was carried out using a magnetic stirrer at a stirring speed of 1600 r / min at 25–30 °C.

[0070] After the reaction was completed, the total mass of the contents of the conical flask, the mass of the remaining solid, and the mass of the liquid were recorded. The solution was sampled and diluted to volume, and the concentrations of the remaining galactose and fructose were determined by HPLC.

[0071] Calculations show that in this embodiment, the fructose yield (Y) is 14.26%, the galactose conversion rate (C) is 31.62%, and the fructose selection rate (S) reaches 45.09%.

[0072] Example 4

[0073] This embodiment provides a method for preparing fructose by isomerization of mannose, which is carried out according to the following steps:

[0074] Take 0.7 g of the photocatalyst 4-Ce / AlCl3 / g-C3N4 obtained in Preparation Example 4, 9 g of mannose, 0.2 g of acetic acid, 10 mL of water, and 30 mL of 2-methyltetrahydrofuran, and add them together into a light-transmitting conical flask; first sonicate for 30 min, then irradiate with an intensity of 10 W / m 2 The isomerization reaction was carried out under ultraviolet xenon lamp irradiation with an ultraviolet wavelength of 290 nm for 10 h; the reaction was carried out using a magnetic stirrer at a stirring speed of 1600 r / min at 25–30 °C.

[0075] After the reaction was completed, the total mass of the contents of the conical flask, the mass of the remaining solid, and the mass of the liquid were recorded. The solution was sampled and diluted to volume, and the concentrations of the remaining mannose and fructose were determined by HPLC.

[0076] Calculations show that in this embodiment, the fructose yield (Y) is 13.59%, the mannose conversion rate (C) is 33.51%, and the fructose selection rate (S) reaches 40.56%.

[0077] Example 5

[0078] This embodiment provides a method for preparing fructose by isomerization of sorbitol, which is carried out according to the following steps:

[0079] Take 0.5 g of the photocatalyst 5-MgO / CaO / Fe / g-C3N4 obtained in Preparation Example 5, 5 g of sorbitol, 20 mL of water, and 60 mL of 2-methyltetrahydrofuran, and add them together into a light-transmitting conical flask; first sonicate for 30 min, then irradiate with an intensity of 18 W / m 2 The isomerization reaction was carried out under ultraviolet xenon lamp irradiation with an ultraviolet wavelength of 300 nm for 5 hours. The reaction was carried out using a magnetic stirrer at a stirring speed of 1600 r / min at 25–30 °C.

[0080] After the reaction was completed, the total mass of the contents of the conical flask, the mass of the remaining solid, and the mass of the liquid were recorded. The solution was sampled and diluted to volume, and the concentrations of the remaining sorbitol and fructose were determined by HPLC.

[0081] Calculations show that in this embodiment, the fructose yield (Y) is 20.25%, the sorbitol conversion rate (C) is 41.92%, and the fructose selection rate (S) reaches 48.31%.

[0082] In Examples 1-5, after the reaction was completed, the photocatalyst in the reaction solution was recovered and its activity was regenerated. Then, the catalyst activity and the number of cycles were evaluated. See Examples 6-10 below for details.

[0083] Example 6

[0084] In this embodiment, the recovered photocatalyst 1-Ti / ZnCl2 was used to conduct an experiment on the isomerization of glucose to produce fructose, and the following steps were taken:

[0085] The photocatalyst 1-Ti / ZnCl2 after the first photocatalytic reaction was recovered, washed repeatedly with water and acetone, dried at 75°C for 16 hours, and then calcined in a muffle furnace under a nitrogen atmosphere at 500°C for 1 hour. The regenerated photocatalyst was denoted as 1-Ti / ZnCl2(R).

[0086] The experiment of Example 1 was repeated 10 times using this 1-Ti / ZnCl2(R). The average yield of fructose was calculated to be 21.86%, the average conversion rate of glucose was 42.35%, and the average selectivity of fructose was 51.62%. The catalytic performance of the photocatalyst remained basically unchanged after multiple cycles of use.

[0087] Example 7

[0088] In this embodiment, the recovered photocatalyst 2-Sn / Si was used to conduct an experiment on the isomerization of glucose to produce fructose, and the following steps were taken:

[0089] The photocatalyst 2-Sn / Si after the first photocatalytic reaction was recovered, washed repeatedly with alternating water and ethanol, dried at 75°C for 16 hours, and then calcined in a muffle furnace under a nitrogen atmosphere at 500°C for 1 hour. The regenerated photocatalyst was denoted as 2-Sn / Si(R).

[0090] The experiment of Example 2 was repeated 12 times using the 2-Sn / Si(R) catalyst. The average yield of fructose was calculated to be 32.07%, the average conversion rate of glucose was 46.59%, and the average selectivity of fructose was 68.82%. The catalytic performance of the photocatalyst remained basically unchanged after multiple cycles of use.

[0091] Example 8

[0092] In this embodiment, the recovered photocatalyst 3-Cu / AlCl3 / g-C3N4 was used to conduct an experiment on the isomerization of galactose to produce fructose, and the following steps were taken:

[0093] The photocatalyst 3-Cu / AlCl3 / g-C3N4 after the first photocatalytic reaction was recovered, washed repeatedly with alternating water and ethanol, dried at 75℃ for 16h, and then calcined in a muffle furnace under nitrogen atmosphere at 500℃ for 1h. The regenerated photocatalyst was denoted as 3-Cu / AlCl3 / g-C3N4(R).

[0094] The experiment of Example 3 was repeated 10 times using the 3-Cu / AlCl3 / g-C3N4(R). The average fructose yield was calculated to be 13.47%, the average galactose conversion rate was 30.39%, and the average fructose selectivity was 44.32%. The catalytic performance of the photocatalyst remained basically unchanged after multiple cycles of recycling.

[0095] Example 9

[0096] In this embodiment, the isomerization of mannose to fructose was carried out using the recovered photocatalyst 4-Ce / AlCl3 / g-C3N4, and the following steps were followed:

[0097] The photocatalyst 4-Ce / AlCl3 / g-C3N4 after the first photocatalytic reaction was recovered, washed repeatedly with water and acetone, dried at 75°C for 16 h, and then calcined in a muffle furnace under a nitrogen atmosphere at 500°C for 1 h. The regenerated photocatalyst was named 4-Ce / AlCl3 / g-C3N4(R).

[0098] The experiment of Example 4 was repeated 10 times using the 4-Ce / AlCl3 / g-C3N4(R). The average yield of fructose was calculated to be 12.37%, the average conversion rate of mannose was 30.92%, and the average selectivity of fructose was 40.01%. The catalytic performance of the photocatalyst remained basically unchanged after multiple cycles of use.

[0099] Example 10

[0100] In this embodiment, the recovered photocatalyst 5-MgO / CaO / Fe / g-C3N4 was used to conduct an experiment on the isomerization of sorbitol to produce fructose, and the following steps were taken:

[0101] The photocatalyst 5-MgO / CaO / Fe / g-C3N4 after the first photocatalytic reaction was recovered, washed repeatedly with water and acetone, dried at 75°C for 16 h, and then calcined in a muffle furnace at 500°C under a nitrogen atmosphere for 1 h. The regenerated photocatalyst was denoted as 5-MgO / CaO / Fe / g-C3N4(R).

[0102] The experiment of Example 5 was repeated 10 times using the 5-MgO / CaO / Fe / g-C3N4(R). The average yield of fructose was calculated to be 19.02%, the average conversion rate of sorbitol was 39.64%, and the average selectivity of fructose was 47.98%. The catalytic performance of the photocatalyst remained basically unchanged after multiple cycles of recycling.

[0103] The experimental results above show that the method of this invention achieves a high yield of fructose from the isomerization of hexoses, reaching up to 32% or more. Compared with traditional chemical catalysis, this invention converts light energy into chemical energy, causing glucose and other sugars to isomerize into fructose, which readily generates 5-HMF (a certain amount of 5-HMF is generated during the isomerization of hexoses into fructose). This further increases reaction selectivity and provides milder reaction conditions. Compared with biocatalysis, photocatalysis is less expensive and has lower reaction condition requirements. Photocatalysis not only converts solar energy into energy usable for chemical reactions but also reduces atmospheric and water pollution, thus aligning with the "dual carbon" concept proposed by the state in recent years and providing a new direction for the high-value utilization and conversion of biomass.

[0104] This invention employs photocatalysis to isomerize non-fructose pyranose into fructose. The reaction conditions are easy to achieve, and the reaction system is simple. The photocatalyst used is doped with non-precious metal elements, as well as non-metallic elements and polymers, further reducing costs and increasing energy utilization. At the same time, the catalytic effect of the photocatalyst remains basically unchanged after multiple cycles, ensuring stable operation and low energy consumption for wastewater treatment. This provides a stable and high-quality raw material for the production of high-value-added biomass derivatives 5-HMF.

[0105] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for photocatalytic preparation of fructose, characterized in that, Fructose was prepared by isomerization reaction of hexose as raw material under light irradiation in the presence of a photocatalyst. The photocatalyst is selected from any one of Ti / ZnCl2, Sn / Si, Cu / AlCl3 / g-C3N4, Ce / AlCl3 / g-C3N4, and MgO / CaO / Fe / g-C3N4; The hexose is selected from one or more of glucose, galactose, mannose, sorbitol, sucrose, inulin, hydrolyzed starch, and cellulose.

2. The method according to claim 1, characterized in that, The illumination uses one or more of the following as light sources: natural light, LED, ultraviolet xenon lamp, and ultraviolet mercury lamp.

3. The method according to claim 2, characterized in that, The illumination uses ultraviolet xenon lamps and / or ultraviolet mercury lamps as the light source, with ultraviolet wavelengths of 280~400nm and irradiance of 0.3~18W / m². 2 .

4. The method according to claim 1, characterized in that, The hexose is selected from one or more of glucose, galactose, mannose, and sorbitol.

5. The method according to claim 4, characterized in that, The isomerization reaction uses a mixed solvent consisting of water and an organic solvent, wherein the volume ratio of water to organic solvent in the mixed solvent is 1:(2~5). The organic solvent is selected from at least one of dimethyl sulfoxide, tetrahydrofuran, and 2-methyltetrahydrofuran.

6. The method according to claim 5, characterized in that, The concentration of hexose in the mixed solvent is 0.05~0.25 g / mL.

7. The method according to claim 1, characterized in that, The amount of photocatalyst used is 5-15% of the mass of the hexose raw material.

8. The method according to claim 1, characterized in that, The reaction temperature for the isomerization reaction is 25~30℃.

9. The method according to any one of claims 1-8, characterized in that, The photocatalytic method for preparing fructose further includes the following steps: after the isomerization reaction is completed, the photocatalyst in the reaction solution is recovered, and then an active regeneration treatment is performed to obtain a regenerated photocatalyst; the regenerated photocatalyst is recycled. The active regeneration process includes drying and high-temperature calcination, wherein the drying process is carried out at a temperature of 75°C and the high-temperature calcination process is carried out at a temperature of 500°C.

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