A method for the continuous production of fructose by glucose isomerization in a microchannel reactor

Abstract

The application provides a method for continuously preparing fructose from glucose in a microchannel reactor. First, a vanadium-containing heteropoly acid catalyst and a substrate glucose are dissolved in deionized water, and then the mixture is injected into the microchannel through a continuous feeding pump. High-purity argon is used as a gas phase, and the flow rate is adjusted through a gas mass flow controller, and the microchannel is continuously input. Compared with the existing traditional intermittent tank process, the method introduces inert gas in the microchannel reactor to form a gas-liquid two-phase plug flow, which strengthens the internal heat and mass transfer of the reaction liquid, improves the reaction rate and selectivity, realizes the continuous process, and has a broad practical application prospect.

Description

Technical Field

[0001] This invention relates to a method for the continuous preparation of fructose by glucose isomerization in a microchannel reactor, belonging to the field of organic synthesis. Background Technology

[0002] Glucose is the most common carbohydrate we encounter in our daily lives. The cellulose and starch we ingest through our diet are broken down by digestive enzymes in the body and converted into glucose, which then participates in biochemical reactions that maintain the normal functioning of the human body. Due to its wide availability, glucose is also used as a raw material to produce high-value-added chemicals. For example, glucose is used to produce formic acid through oxidation, ethanol and lactic acid through fermentation, and the bio-based platform compound 5-hydroxymethylfurfural through dehydration. Research on glucose-based conversion reactions has become a hot topic in both academia and industry.

[0003] In the process of preparing high-value-added chemicals from glucose, the isomerization of glucose to fructose is usually involved. The rate and selectivity of this isomerization process affect the overall rate and selectivity of the reaction. To improve the rate and selectivity of glucose isomerization to fructose, researchers have developed various catalysts. Among them, immobilized bio-enzyme catalysis has become the main commercial method for glucose isomerization to fructose due to its high selectivity. However, the investment cost of using bio-enzymes as catalysts is too high, and the reaction conditions are demanding, requiring specific temperatures and pH levels to maintain their activity. Enzyme inactivation is also an unavoidable problem, and microbial contamination of the enzymes must be prevented, making it difficult to maintain long-term stable production. Based on the above shortcomings of bio-enzyme-catalyzed glucose to fructose conversion methods, researchers have focused on developing chemical catalytic methods for glucose isomerization to fructose. According to the catalytic system, the glucose isomerization to fructose reaction mainly includes inorganic base catalytic systems, organic base catalytic systems, Bronsted acid catalytic systems, and Lewis acid catalytic systems. Under the catalysis of strong bases, glucose and its isomerization product fructose readily decompose to produce various byproducts such as lactic acid, glycolic acid, or formic acid. Glucose also readily undergoes epimerization to produce mannose, thus reducing the selectivity of the reaction and the yield of fructose (Journal of Catalysis, 2015, 330, 474-484). Using Bronsted acid as a catalyst, the fructose yield from glucose isomerization is low. Although adding metal salts to the system can improve the catalytic effect (ACS Catalysis, 2015, 5(9): 5097-5103), the reaction time is long, the amount of catalyst required is large, and the addition of metal salts increases the difficulty of product separation. Compared with Bronsted acid catalysts, using metal chlorides such as CrCl3, AlCl3, and SnCl4 as Lewis acids has higher catalytic activity for the isomerization of glucose to fructose (Catalysis Today, 2014, 234: 83-90.). However, metal chlorides are also ideal catalysts for the dehydration of fructose to 5-hydroxymethylfurfural, which causes further dehydration of the generated fructose, resulting in a decrease in the fructose yield.

[0004] Therefore, there is an urgent need to find a highly efficient catalyst for the isomerization of glucose to fructose, which has no or weak catalytic effect on the further conversion of fructose. Furthermore, current reaction processes for the isomerization of glucose to fructose are all batch processes, characterized by slow heat and mass transfer rates, severe backmixing, and wide and long residence times, resulting in reduced reaction rates and selectivity. In summary, there is an urgent need to develop a new method for the isomerization of glucose to fructose that offers a fast glucose conversion rate, high fructose yield, and a continuous reaction process. Summary of the Invention

[0005] This invention aims to address the shortcomings of current glucose-to-fructose catalytic technologies and processes, providing a novel method for the continuous preparation of fructose via glucose isomerization using a microchannel reactor. Leveraging the highly efficient transport properties of the microchannel reactor, rapid glucose conversion can be achieved under relatively mild conditions, significantly shortening the reaction residence time and thus greatly suppressing further fructose decomposition. This method represents a cost-effective, green, efficient, and continuous fructose preparation approach.

[0006] To achieve the above objectives, this invention provides a method for preparing fructose by glucose isomerization in a microchannel reactor, the specific technical solution of which is as follows: The catalyst (H5PV2Mo) 10 O 40 A glucose aqueous solution and argon gas are mixed and dispersed using a micromixer. The resulting gas-liquid two-phase flow is injected into a microchannel reactor through the outlet of the micromixer. The reaction then proceeds at a preset temperature and pressure. After the reaction is complete, the products flow into a gas-liquid separator for gas-liquid separation. The gas phase is discharged into the atmosphere from the top of the gas-liquid separator through a back pressure valve, while the liquid phase reaction liquid is placed into a sample collector from the bottom.

[0007] The microchannel reactor system includes a raw material storage tank, an argon cylinder, a gas mass flow controller, a continuous feed pump, a microchannel mixer, a microchannel reactor, a reaction temperature control device, a gas-liquid separator, a back pressure valve, a product collection tank, and a waste liquid tank.

[0008] The raw material storage tank, continuous feed pump, microchannel mixer, microchannel reactor, gas-liquid separator, back pressure valve, and gas-liquid separator (waste tank and sample tank) are connected in series. The argon cylinder, gas mass flow controller, and microchannel mixer in the gas phase branch are connected in series. The gas phase branch and liquid phase branch are connected in parallel through the micro-mixer. The waste tank and sample tank are connected in parallel.

[0009] The microchannel reactor is placed in a reaction temperature control device, while the other components are not subject to temperature control.

[0010] In the method provided by the present invention, the temperature range of the microchannel reactor is controlled between 120 and 180°C. o C, preferably in the range of 140~180 o C, more preferably 140~160 o C.

[0011] The pressure of the reaction system is regulated by a back pressure valve connected to the gas phase outlet pipeline at the top of the gas-liquid separator. The reaction pressure is between 0.5 and 4.0 MPa, preferably between 1.5 and 4.0 MPa, and more preferably between 1.5 and 3.5 MPa. The pressure regulation is intended to enhance mixing and maintain the liquid phase state of the reaction liquid.

[0012] The amount of glucose added is 0.4 to 8.0 wt% by mass, based on the amount of solvent used. The solvent used is deionized water, preferably in the range of 1.0 to 7.2 wt%, more preferably in the range of 1.0 to 4.8 wt%.

[0013] The catalyst H5V2Mo 10 O 40 The amount added is 0.1 to 0.6 wt% by mass, preferably 0.2 to 0.6 wt%, and more preferably 0.2 to 0.5 wt%.

[0014] The residence time of the reactants in the microchannel reactor is 1-10 min, preferably 2-4 min, and more preferably 2-3 min. The residence time is controlled by changing the inner diameter of the microchannel reactor, adjusting the flow rates of the glucose aqueous solution and argon gas, and changing the tube length.

[0015] The internal hydrodynamic diameter of the microchannel reactor is 0.1~1.5 mm, preferably 0.25~0.60 mm, and more preferably 0.30-0.50 mm; the length of the microreactor is 2000~20000 mm, preferably 2000~15000 mm, and more preferably 2000~10000 mm.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] (1) The present invention provides a chemical catalytic method for the isomerization of glucose to produce fructose, wherein the catalyst used is a vanadium-containing heteropolyacid H5PV2Mo. 10 O 40 This catalyst is a highly efficient catalyst for the isomerization of glucose to fructose, and has a weak catalytic effect on the further conversion of fructose, which can greatly improve the reaction rate and selectivity.

[0018] (2) In the method provided by the present invention, the glucose reaction solution can be rapidly heated to the required temperature by utilizing the high specific surface area of ​​the microchannel reactor. The temperature of the system is uniform and controllable during the reaction process, which can effectively avoid the problem of low reaction selectivity caused by local overheating in traditional batch reactors.

[0019] (3) In the method provided by the present invention, inert gas argon is introduced into the microchannel reactor to form a gas-liquid two-phase slug flow system, which effectively breaks the boundary layer effect in the laminar flow state of the single-phase system and enhances the mixing and heat transfer effect inside the reaction liquid. The microchannel reactor can be regarded as a microtube plug flow reactor, which effectively solves the problems of wide reaction residence time distribution and reduced selectivity caused by material backmixing, and realizes the continuous process of glucose isomerization to prepare fructose.

[0020] Compared with the existing traditional batch reactor process, this method introduces inert gas into the microchannel reactor, forming a gas-liquid two-phase slug flow, which enhances the heat and mass transfer inside the reaction liquid, improves the reaction rate and selectivity, and realizes the continuous process, and has broad prospects for practical application. Attached Figure Description

[0021] Figure 1 A flowchart illustrating the method of the present invention is provided, in which: 1 is a glucose aqueous solution raw material storage tank; 2 is a liquid phase co-current pump; 3 is an argon cylinder; 4 is a first gas pressure reducing valve; 5 is a gas filter; 6 is a second gas pressure reducing valve; 7 is a gas phase check valve; 8 is a first pressure sensor; 9 is a gas mass flow controller; 10 is a gas phase check valve; 11 is a liquid phase check valve; 12 is a micro mixer; 13 is a temperature control device; 14 is a microchannel reactor; 15 is a three-way ball valve; 16 is a waste liquid tank (first gas-liquid separator); 17 is a product tank (second gas-liquid separator); 18 is a second pressure sensor; 19 is a back pressure valve; 20 is a liquid phase product collection container; 21 is a waste liquid collection container.

[0022] Figure 2 This is a schematic diagram of the steady-state Taylor flow pattern for bubbles and droplets. In the diagram: 22 is the inner diameter; 23 is the bubble; 24 is the liquid film; 25 is the droplet. The figure is taken from the steady flow pattern at the reactor inlet in Example 1 below (taken at room temperature of 25°C by a Phantom R311 high-speed camera, manufactured by Vision Research). The flow pattern is a gas-liquid Taylor flow.

[0023] Among them, the liquid phase advection pump is from Beijing Xingda Technology Development Co., Ltd.; the gas pressure reducing valve is from Shanghai Dunyang Fluid Equipment Co., Ltd.; the gas filter is from CIR-LOK (China) Co., Ltd. (with inlet and outlet); the one-way valve, two-way, three-way ball valve and back pressure valve are all from Beijing Xiongchuan Technology Co., Ltd.; the microchannel mixer is from Yijia (Beijing) Technology Co., Ltd.; the temperature control device (DF-101S heat-collecting constant temperature heating magnetic stirrer) is from Shanghai Lichen Bangxi Instrument Technology Co., Ltd., the heat transfer oil is dimethyl silicone oil from Dow Corning (China) Silicone Co., Ltd.; the pressure sensor is from Siemens (China) Co., Ltd., and the digital display used is from Yudian Automation Technology Co., Ltd.

[0024] Figure 3 This is a schematic diagram illustrating the principle of the method for producing fructose by catalytic isomerization of glucose provided by the present invention.

[0025] With heteropoly acid (H5V2Mo) 10 O 40 (This is a catalyst in which vanadium combines with oxygen bridged by itself to form VO2.) + VO2 + In aqueous solution, it forms a vanadium-water complex 1 with water. Then, 1 combines with the hydroxyl group at the β-carbon position of glucose to form process product 2. Under the action of the catalyst, the hydroxyl group attached to vanadium combines with the hydroxyl hydrogen at the β-carbon position of glucose to form water, which then detaches from glucose. The catalyst potential then increases, allowing it to combine with the aldehyde oxygen at the α-carbon position of glucose to form intermediate 3. At this point, the potential at the α-carbon position of glucose increases, thus pulling the hydrogen at the β-carbon position of glucose. When the hydrogen at the β-carbon position of glucose is "pulled apart," the catalyst also detaches from the hydrogen at the β-carbon position of glucose, resulting in the formation of a ketone carbonyl group at the β-carbon position of glucose (intermediate 4). Conversely, at the α-carbon position of glucose, the oxygen attached to it has a higher potential, so the hydroxyl hydrogen attached to vanadium is pulled together to form intermediate 5. Then, the catalyst reacts with VO2. + The form of fructose is separated, and the target product is formed.

[0026] However, this process is also accompanied by another process involving the catalyst, namely: ; The presence of oxygen in the system promotes fructose decomposition, making the presence of argon crucial. Argon acts as a protective gas, inhibiting fructose decomposition to a certain extent and maximizing fructose yield. For the reduced catalyst VO... 2+ It can be placed in the air for natural oxidation, based on the fact that VOCs... 2+ It can undergo re-oxidation with molecular oxygen in the air at room temperature and pressure, causing it to re-form VO2. + . Detailed Implementation

[0027] A T-type micromixer is used: a microchannel mixer (T-junction) with two inlets and one outlet; one inlet and outlet are located on the same axis as the mixing microchannels, serving as the main inlet; the other inlet forms a 90-degree angle with the axis of the mixing microchannels, serving as the side inlet. The microchannel mixer is placed at ambient room temperature.

[0028] The process used to achieve glucose isomerization to fructose production within a microchannel reactor, such as... Figure 1 As shown, an aqueous solution (raw material solution) containing catalyst and glucose is stored in raw material storage tank 1. The raw material solution is continuously pumped into one inlet (side inlet) of microchannel mixer 12 via a liquid phase check valve 11 through a horizontal flow pump 2. High-pressure argon gas is released from argon cylinder 3 through a first pressure reducing valve 4, passes through a gas filter 5, and then comes to another second pressure reducing valve 6. After being depressurized twice, the argon gas flows stably through a gas phase check valve 7 and a pressure sensor 8 into a gas mass flow controller 9. At this time, the pressure sensor 8 displays the pressure in the gas phase branch. Then, the gas mass flow controller adjusts the argon gas flow rate required for the reaction, and then flows into the other inlet (main channel inlet) of microchannel mixer 12 through the pipeline. After the gas and liquid phases are mixed and dispersed in the microchannel mixer, they enter the microchannel reactor 14, which is connected to the outlet of the microchannel mixer and is placed in the reaction temperature control device 13. The temperature of the microchannel reactor is regulated by the reaction temperature control device 13, and the pressure of the reaction system is controlled by a back pressure valve 19.

[0029] The outlet of the microchannel reactor 14 is connected to the waste liquid tank 16 and the product tank 17 via a three-way ball valve 15. The gas phase outlet at the top of the waste liquid tank 16 and the gas phase outlet at the top of the product tank 17 are connected to the gas collection container or the atmosphere via a three-way valve or a pressure sensor 18 and a back pressure valve 19, respectively. The liquid phase outlet valve at the bottom of the waste liquid tank 16 is connected to the waste liquid collection container 21. The liquid phase outlet valve at the bottom of the product tank 17 is connected to the liquid phase product collector 20.

[0030] During the pressure stabilization, flow pattern stabilization, and temperature rise stages, the three-way ball valve points towards the waste liquid tank 16. Waste liquid from the reaction can be collected by the waste liquid collector 21. When the pressure, flow pattern, and temperature are stable, the three-way ball valve points towards the sample tube 17. The system pressure is observed through the second pressure sensor 18. To maintain a stable gas input, the reading of the first pressure sensor 8 must be greater than the reading of the second pressure sensor 18, and the pressure difference must be controlled within the normal operating range of the gas mass flow controller. One-way valves 7 and 10 protect the gas mass flow controller. After the material completes the reaction process in the microchannel reactor, the reacted material enters the gas-liquid separator 17 for gas-liquid separation. The gas phase is discharged into the atmosphere from the top of the gas-liquid separator through the back pressure valve, while the liquid phase reaction liquid is placed into the liquid phase sample collection tank 20 from the bottom.

[0031] The above H5PV2Mo 10 O 40 The preparation method mainly refers to the literature (Inorg. Chem, 1968, 7, 437-441.), and its specific preparation and improvement process is as follows: First, weigh 4.88 g of NaVO3 using an analytical balance, mix it with 20 mL of deionized water in a beaker, and then... o In a water bath at C, heat to boiling while stirring. After all NaVO3 is dissolved, mix the NaVO3 aqueous solution with 1.42 g of weighed Na2HPO4·2H2O and 20 mL of deionized water. After the solution cools to room temperature, add 1 mL of concentrated H2SO4 (98 wt%) dropwise. The solution turns deep red. Then, weigh 24.2 g of Na2MoO4·H2O and dissolve it in 40 mL of deionized water. Mix the NaMoO4 aqueous solution with the above solution containing NaVO3, Na2HPO4, and H2SO4 and stir vigorously. Then, slowly add 17 mL of concentrated H2SO4 (98 wt%). (Note: Catalyst formation requires an acidic environment of pH=2. The synthesis of heteropoly compounds is very sensitive to pH; sometimes a pH difference of 0.01 can cause significant changes in the structure of the reaction products.) The solution turns bright red. After the solution cools to room temperature, pour it into a separatory funnel, add an equal volume of diethyl ether, shake thoroughly, and let stand for 4 hours. Then, take the lower layer of red H5PV2Mo. 10 O 40 The mixture with ether was placed in an oven at 95°C. o Dry at C for 0.25 hours until crystals form. Remove and shake to allow crystal growth. Then place in a fume hood (or place directly in a ventilated area to crystallize naturally) until crystals are fully formed. Add 10 mL of water to completely dissolve the crystals and place in an oven (purpose: to remove residual ether <90°C). o C, then heated to 95°C oC recrystallize the sample. When crystals form (0.5 hours), remove the sample, gently shake, and filter while hot (using a Buchner funnel and ordinary filter paper; do not stir the unfiltered sample) (purpose: to remove residual unreacted metal ions). Collect the orange-red crystals in a petri dish, spread them thinly, and place them in a vacuum drying oven at 65°C. o C. Drying (function: removes organic solvents or water molecules from the pores (activates the material). For porous materials, vacuum drying removes residual substances from the pores, preserving the original structure of the material. A vacuum oven avoids damage to the material structure or loss of pore structure due to temperature or solvent changes. It improves the usability of the material's pores and increases the specific surface area and pore volume.) Finally, 10 g of the heteropolyacid H5PV2Mo is obtained. 10 O 40 Crystal.

[0032] The present invention has been described above, and specific embodiments thereof are given below. These specific embodiments are only used to further illustrate the present invention and do not limit the scope of protection of the claims of this application.

[0033] Example 1 Deionized water was used as the reaction solvent to prepare the required glucose aqueous solution. Based on a solvent mass of 100%, the mass fraction of glucose in the aqueous solution (relative to the mass of the solvent, hereinafter the same) was 1.0 wt%. The catalyst was H5PV2Mo. 10 O 40 The mass fraction was 0.4 wt% (based on a mass ratio of 100% to the solvent, the same below); high-purity argon was used as a protective gas during the reaction. Figure 1 The process flow shown describes the isomerization of glucose to prepare fructose. In this process, a T-type micromixer is used to mix the reaction raw material liquid and the protective gas. The internal through-hole diameter of the micromixer is 0.50 mm; the inner diameter of the microchannel reactor is 0.50 mm, and the microchannel length is 10000 mm.

[0034] At a reaction pressure of 3.0 MPa (read by the second pressure sensor 18) and a reaction temperature of 150°C... o C. The volumetric flow rate ratio of the gas phase to the liquid phase is 15 ml / min : 0.075 ml / min (its flow pattern is as follows). Figure 2 Under the conditions shown (as indicated), and a residence time of 2.25 min, glucose isomerization to fructose was carried out, and the liquid products after the reaction were analyzed by liquid chromatography. The results showed that the glucose conversion rate was 71.33%, the fructose yield was 65.31%, and the selectivity was 91.56%.

[0035] Comparative Example 1 Change the catalyst to H3PW 12 O40 (Provided by Shanghai Maclean Biochemical Technology Co., Ltd.), with other conditions the same as in Example 1. The results showed that the glucose conversion rate was 27.42%, the fructose yield was 9.41%, and the selectivity was 34.32%.

[0036] Comparative Example 2 The catalyst was changed to NaVO3 (provided by Shanghai E. En Chemical Technology Co., Ltd.), while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 50.22%, the fructose yield was 31.57%, and the selectivity was 62.86%.

[0037] Example 2 The glucose content in the aqueous phase was changed to 3.2 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 67.42%, the fructose yield was 60.57%, and the selectivity was 89.84%.

[0038] Example 3 The glucose content in the aqueous phase was changed to 4.8 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 64.98%, the fructose yield was 56.47%, and the selectivity was 86.90%.

[0039] Example 4 The glucose content in the aqueous phase was changed to 7.2 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 61.75%, the fructose yield was 53.06%, and the selectivity was 85.93%.

[0040] Example 5 The glucose content in the aqueous phase was changed to 8.0 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 60.85%, the fructose yield was 51.77%, and the selectivity was 85.08%.

[0041] Comparative Example 3 The process was the same as in Example 1, except that the glucose content in the aqueous phase was changed to 0.1 wt%, and the other conditions were the same as in Example 1. The results showed that the glucose conversion rate was 98.89%, the fructose yield was 15.33%, and the selectivity was 15.50%.

[0042] Example 6 The glucose content in the aqueous phase was changed to 0.4 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 89.32%, the fructose yield was 71.37%, and the selectivity was 79.90%.

[0043] Example 7 The catalyst content in the aqueous phase was changed to 0.1 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 63.83%, the fructose yield was 55.35%, and the selectivity was 86.71%.

[0044] Example 8 The catalyst content in the aqueous phase was changed to 0.2 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 66.17%, the fructose yield was 57.85%, and the selectivity was 87.43%.

[0045] Example 9 The catalyst content in the aqueous phase was changed to 0.3 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 68.37%, the fructose yield was 60.39%, and the selectivity was 88.33%.

[0046] Example 10 The catalyst content in the aqueous phase was changed to 0.5 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 74.38%, the fructose yield was 65.48%, and the selectivity was 88.03%.

[0047] Example 11 The catalyst content in the aqueous phase was changed to 0.6 wt%, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 80.04%, the fructose yield was 66.58%, and the selectivity was 84.24%.

[0048] Example 12 The length of the microchannel reactor was changed to 2000 mm, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 58.77%, the fructose yield was 50.37%, and the selectivity was 85.71%.

[0049] Example 13 The length of the microchannel reactor was changed to 6000 mm, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 64.95%, the fructose yield was 58.69%, and the selectivity was 90.36%.

[0050] Comparative Example 4 The process was the same as in Example 1, except that the length of the microchannel reactor was changed to 1000 mm and the inner diameter of the micromixer was changed to 0.45 mm, while all other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 24.89%, the fructose yield was 17.97%, and the selectivity was 72.20%.

[0051] Example 14 The pressure of the reaction system was changed to 1.5 MPa, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 70.97%, the fructose yield was 64.47%, and the selectivity was 90.84%.

[0052] Example 15 The pressure of the reaction system was changed to 3.5 MPa, while other conditions remained the same as in Example 1. The results showed that the glucose conversion rate was 71.27%, the fructose yield was 65.35%, and the selectivity was 91.69%.

[0053] Example 16 The process is the same as in Example 1, except the reaction temperature is changed to 140°C. o C, with the remaining conditions the same as in Example 1. The results showed that the glucose conversion rate was 63.04%, the fructose yield was 59.37%, and the selectivity was 94.18%.

[0054] Example 17 Change the reaction temperature to 160 o C, with the remaining conditions the same as in Example 15. The results showed that the glucose conversion rate was 76.62%, the fructose yield was 61.47%, and the selectivity was 80.23%.

[0055] Comparative Example 5 Change the reaction temperature to 185 o C, with the remaining conditions the same as in Example 15. The results showed that the glucose conversion rate was 86.18%, the fructose yield was 40.31%, and the selectivity was 46.77%.

[0056] Comparative Example 6 Change the reaction temperature to 100 o C, with the remaining conditions the same as in Example 1. The results showed that the glucose conversion rate was 40.07%, the fructose yield was 18.05%, and the selectivity was 45.05%.

[0057] Comparative Example 7 Change the reaction temperature to 110 o C, with the remaining conditions the same as in Example 1. The results showed that the glucose conversion rate was 46.39%, the fructose yield was 34.33%, and the selectivity was 74.00%.

[0058] Example 18 The gas-liquid two-phase flow rate ratio was changed to 10 ml / min : 0.075 ml / min, with other conditions remaining the same as in Example 15. The results showed that the glucose conversion rate was 81.61%, the fructose yield was 70.60%, and the selectivity was 86.51%.

[0059] Example 19 The gas-liquid two-phase flow rate ratio was changed to 25 ml / min : 0.075 ml / min, with other conditions remaining the same as in Example 15. The results showed that the glucose conversion rate was 60.39%, the fructose yield was 51.79%, and the selectivity was 85.76%.

[0060] Comparative Example 8 The gas-liquid two-phase flow rate ratio was changed to 5 ml / min : 0.10 ml / min, with other conditions remaining the same as in Example 15. The results showed that the glucose conversion rate was 83.33%, the fructose yield was 37.47%, and the selectivity was 44.97%.

[0061] Example 20 The diameter of the microchannel reactor was changed by 1 mm, while other conditions remained the same as in Example 15. The results showed that the glucose conversion rate was 66.38%, the fructose yield was 57.25%, and the selectivity was 86.25%.

[0062] Example 21 The diameter of the microchannel reactor was changed by 1.5 mm, while other conditions remained the same as in Example 15. The results showed that the glucose conversion rate was 58.09%, the fructose yield was 49.79%, and the selectivity was 85.71%.

[0063] Example 22 The process is the same as in Example 1, except the reaction temperature is changed to 180°C. o C. The microchannel reactor tube length was 4000 mm, and other conditions were the same as in Example 1. The results showed that the glucose conversion rate was 79.34%, the fructose yield was 52.87%, and the selectivity was 66.64%.

[0064] Example 23 The length of the microchannel reactor tube was changed to 8000 mm, while other conditions remained the same as in Example 22. The results showed that the glucose conversion rate was 83.39%, the fructose yield was 55.39%, and the selectivity was 66.42%.

[0065] Comparative Example 9 The glucose aqueous solution required for the reaction was prepared as in Example 1. It was placed in a batch reactor, and to purge air from the reactor, it was purged three times with high-purity argon gas, and finally purged with argon gas at 3.0 MPa. During the reaction, magnetic stirring was used to maintain the homogeneity of the materials, and the reaction temperature was 150°C. o The reaction time was 5 min. The results showed that the glucose conversion rate was 7.32%, the fructose yield was 5.47%, and the selectivity was 74.73%.

[0066] Comparative Example 10 The process was the same as in Comparative Example 6, except that the reaction time was changed to 30 min, and all other conditions were the same as in Comparative Example 6. The results showed that the glucose conversion rate was 50.37%, the fructose yield was 28.47%, and the selectivity was 56.52%.

[0067] Comparative Example 11 The process was the same as in Comparative Example 6, except that the reaction time was changed to 60 min, and all other conditions were the same as in Comparative Example 6. The results showed that the glucose conversion rate was 88.57%, the fructose yield was 38.44%, and the selectivity was 43.40%.

[0068] By comparing Examples 1-5 with Comparative Example 3, it can be seen that when the content of the substrate glucose is low, the content of the catalyst is relatively excessive. While increasing the rate of the catalytic reaction, it also leads to a stronger oxidizing property of the reaction system. Although the conversion rate will increase, the target product fructose will undergo further oxidation and bond breaking. Therefore, the experimental results show that the glucose conversion rate is high and the fructose yield is low. By comparing the above Examples 12 and 13 with Comparative Example 4, it can be seen that the change in tube length directly affects the residence time of the reaction. Increasing the residence time of the reaction can improve the reaction conversion rate to a certain extent. By comparing the above Examples 15-17 with Comparative Example 5, it can be seen that when the reaction temperature is too high, the activation energy will decrease, the molecular dynamics will be enhanced, the reaction rate constant will increase, and while improving the glucose conversion rate, it will also lead to the decomposition of fructose. By comparing Examples 15-17 with Comparative Example 6, it can be seen that when the reaction temperature is too low, the rate constant decreases, the reactant activity decreases, the effective collisions and the overcoming of the energy barrier are reduced, resulting in a decrease in the conversion rate. By comparing Example 1 with Comparative Examples 9-11, it can be seen that microreactors have significant advantages over traditional batch reactors. Microreactors can significantly shorten reaction time, greatly improve reaction efficiency, and achieve high yields and high selectivity of glucose to fructose. The essential reason for this result lies in the inherent characteristics of each type of reactor. Due to the small size of microreactors, they allow for more precise and high-quality control of temperature, pressure, and component distribution. In contrast, traditional batch reactors suffer from disadvantages such as large volume, difficulty in temperature and concentration control, and safety issues. Therefore, microreactors can complete the reaction more efficiently, improve selectivity and yield, and reduce safety hazards.

[0069] Although the invention and its implementation results have been described in detail above, any modifications or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the invention should be included within the scope of the invention. Therefore, the scope of protection of the invention should be determined by the scope of the claims.

Claims

1. A method for the continuous preparation of fructose by glucose isomerization in a microchannel reactor, characterized in that, The method includes the following steps: (1) Dissolve the catalyst and glucose in water to obtain a glucose aqueous solution; The catalyst is a vanadium-containing heteropolyacid H5PV2Mo. 10 O 40 The glucose content in the glucose aqueous solution described in step (1) is between 0.4% and 8.0 wt%, relative to the mass of the solvent, i.e., with the mass of water as 100%. The mass fraction of the catalyst ranges from 0.1% to 0.6% wt%. (2) The inert gas and glucose aqueous solution are transported to a microchannel mixer for mixing, and then enter the microchannel reactor for reaction; The microchannel reactor reaction is carried out at a pressure range of 1.5~3.5 MPa. The temperature of the microchannel reactor was maintained at 140~160°C. o C; The reaction residence time is 2~4 min; The volumetric flow ratio of the liquid glucose aqueous solution to the gaseous inert gas is 1:120 to 1:

350. The pore size range of the microchannel reactor is 0.4~1.5 mm; The length of the microchannel reactor is 2000~10000 mm; (3) After the reaction is completed, the gas-liquid two-phase fluid enters the gas-liquid separator for gas-liquid separation.

2. The method according to claim 1, characterized in that: The glucose content in the glucose aqueous solution described in step (1) is between 1.0 and 7.2 wt%.

3. The method according to claim 2, characterized in that: The glucose content in the glucose aqueous solution described in step (1) is between 1.0 and 4.8 wt%.

4. The method according to claim 1, characterized in that: The mass fraction of the catalyst ranges from 0.2 to 0.6 wt%.

5. The method according to claim 4, characterized in that: The mass fraction of the catalyst ranges from 0.2 to 0.5 wt%.

6. The method according to claim 1, characterized in that: In step (2), the microchannel mixer is placed at 10~40 o At temperature C, the reaction residence time is 2-3 minutes.

7. The method according to claim 6, characterized in that: In step (2), the microchannel mixer is placed at 20~30°C. o At temperature C.

8. The method according to any one of claims 1-7, characterized in that: The pore size range of the microchannel reactor in step (2) is 0.4~0.8 mm; the pore size range of the microchannel mixer is 0.1~1.5 mm.

9. The method according to claim 8, characterized in that: The pore size range of the microchannel reactor in step (2) is 0.4~0.6 mm; the pore size range of the microchannel mixer is 0.4~0.8 mm.

10. The method according to any one of claims 1-4, characterized in that: The volumetric flow rate of the gaseous inert gas ranges from 10 to 25 ml / min, and the volumetric flow rate of the liquid phase ranges from 0.05 to 0.10 ml / min.

11. The method according to claim 1, characterized in that: The mixing process described in step (2) is as follows: First, the inert gas and glucose aqueous solution are mixed and dispersed through a microchannel mixer. The gas phase enters through the main channel inlet of the T-type micro mixer, and the liquid phase enters through one side inlet of the T-type mixer. During this process, the gas phase is dispersed into small bubbles of uniform size and spacing. Then, the dispersed gas-liquid two-phase fluid is introduced into the microchannel reactor through the other side port of the T-type mixer for reaction. The T-type micromixer is a microchannel mixer with two inlets and one outlet; one inlet and outlet are located on the same axis as the mixing microchannel, serving as the main channel inlet; the other inlet forms an angle greater than 0 to 90 degrees with the axis of the mixing microchannel, serving as the side inlet.

12. The method according to claim 1 or 11, characterized in that: After gas-liquid separation, the gas phase in the gas-liquid separator is discharged into the atmosphere from the top of the gas-liquid separator through the back pressure valve, while the liquid phase reaction liquid is put into the sample collector from the bottom. Two gas-liquid separation tanks are connected in parallel at the outlet of the microchannel reactor. These two separation tanks serve as waste liquid tank and sample tank, respectively. For product solutions that have not reached the reaction conditions of the microchannel reactor at the beginning of the reaction, they are allowed to flow into the waste liquid tank. Once the gas and liquid form a stable gas-liquid Taylor flow pattern with water phases distributed in the confined space, and the reaction pressure and temperature reach the required reaction conditions and stabilize, the product is then sent to the sample tank. Place the microchannel mixer at ambient temperature (10-40°C). o C. The microchannel reactor is placed inside the reaction temperature control device.

13. The method according to claim 12, characterized in that: Place the microchannel mixer at ambient temperature for 20-30 degrees Celsius. o C. The microchannel reactor is placed inside the reaction temperature control device.

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