Device and method for synthesizing glyoxylic acid through Fenton oxidation in microreactor

Abstract

The invention discloses a device and a method for synthesizing glyoxylic acid through Fenton oxidation in a microreactor. According to the device, a first liquid storage bottle is connected with a first metering pump, the first metering pump is connected to a first micro heat exchanger, and the first micro heat exchanger is connected to a micro mixer; the second liquid storage bottle is connected with a second metering pump, the second metering pump is connected to a second micro heat exchanger, and the second micro heat exchanger is connected to the micro mixer; the micro mixer is connected to the micro reactor, the micro reactor is connected to the back pressure valve, and the back pressure valve is connected to the collecting bottle. According to the invention, the problems of low reaction efficiency and unstable yield of glyoxylic acid synthesized by a traditional tank reactor in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of microchemical technology, and in particular to an apparatus and method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor. Background Technology

[0002] Glyoxylic acid (CHO-COOH), as the simplest α-keto acid, possesses both aldehyde and carboxyl functional groups, exhibiting the chemical properties of both aldehydes and carboxylic acids. It is widely used in pharmaceuticals, pesticides, fragrances, and polymer materials, and has become an indispensable key synthetic intermediate. For example, glyoxylic acid plays a crucial role in the synthesis of vanillin, vitamin B5, and various antibiotics. Furthermore, it is an ideal choice for environmentally friendly metal chelating agents and polyester resin crosslinking agents. With the increasing demand for green chemicals and the rapid development of the fine chemical industry, the market demand for glyoxylic acid continues to rise, placing higher demands on its production efficiency and product quality.

[0003] Currently, mainstream glyoxylic acid production processes, such as the nitric acid oxidation of glyoxal, oxygen / air oxidation, oxalic acid electrolytic reduction, and maleic anhydride ozone oxidation, generally suffer from high energy consumption, heavy pollution, and limited process efficiency. The nitric acid oxidation method involves adding nitric acid and sodium nitrite to an aqueous solution of glyoxal. The nitric acid reacts with the initiator sodium nitrite to generate nitrous acid, which then oxidizes glyoxal to glyoxylic acid. This method is widely used due to its high yield, but it produces a large amount of nitrogen oxides (NOx) as byproducts, leading to equipment corrosion and increasing the difficulty of waste gas treatment. The oxalic acid electrolytic reduction method synthesizes glyoxylic acid by electrolytic reduction of oxalic acid in an aqueous solution on a cathode made of materials such as platinum, graphite, and lead. Although this method can achieve the electrochemical synthesis of glyoxylic acid, it suffers from high energy consumption, poor economic efficiency, numerous side reactions, and low product purity. The oxygen oxidation method utilizes catalysts such as gold, silver, platinum, bismuth, palladium, and ruthenium supported on a modified carbon matrix to oxidize glyoxal aqueous solution to glyoxylic acid aqueous solution by the presence of oxygen in the air. While possessing certain environmental advantages due to its use of green oxidants, this method suffers from high catalyst costs, susceptibility to deactivation, and a slow reaction rate requiring high temperature and pressure conditions to accelerate the reaction, leading to a significant increase in energy consumption. Therefore, developing a glyoxylic acid synthesis process that combines high efficiency and environmental friendliness has become a pressing technical challenge for the chemical industry. In recent years, the oxidation of glyoxal with Fenton's reagent to synthesize glyoxylic acid has been proposed as an emerging method, offering advantages such as high synthesis efficiency, good safety, and low environmental impact, demonstrating promising application prospects.

[0004] Currently, the synthesis of glyoxylic acid using the Fenton oxidation method typically employs a traditional batch reactor. The raw material glyoxal and the catalyst ferrous sulfate heptahydrate are added to the reactor, and the reaction rate is controlled by the dropwise addition of hydrogen peroxide. Continuous stirring is required during the reaction to ensure sufficient contact between the reactants. However, this process has several problems. First, stirring within the batch reactor makes it difficult to achieve ideal liquid-liquid mixing, and the low liquid-liquid mass transfer efficiency leads to easy backmixing of materials, hindering a rapid and uniform oxidation process and affecting the yield and selectivity of glyoxylic acid. Second, the dropwise addition of hydrogen peroxide suffers from response lag and imprecise control, easily triggering violent local reactions, rapid temperature rises, or even boiling over, posing safety risks and affecting product stability. Furthermore, because the Fenton reaction is highly sensitive to conditions, the delayed heat and mass transfer in the batch reactor can exacerbate side reactions, such as further oxidation of glyoxylic acid to oxalic acid, reducing product purity. Simultaneously, the decomposition of hydrogen peroxide generates a large number of oxygen bubbles during the reaction, and the generation and accumulation of these gases further exacerbate the uneven mixing within the batch reactor. The retention of gas bubbles in the liquid phase can lead to decreased local stirring efficiency and uneven heat transfer, easily forming gas-liquid stratification or dead zones, resulting in unstable reaction rates and conversion rates. Furthermore, the instantaneous release of gas can cause liquid splashing or localized boiling, increasing equipment operating risks and making it difficult to stably control reaction temperature and pressure. Overall, traditional batch reactor processes suffer from unstable temperature control, difficulty in adjusting the reaction path, safety hazards caused by gas generation, and numerous byproducts, increasing the burden on subsequent separation processes and limiting their industrial application.

[0005] Therefore, the technical problems of low reaction efficiency and unstable yield in the traditional batch reactor synthesis of glyoxylic acid have not yet been solved in related technologies. Summary of the Invention

[0006] The purpose of this invention is to provide an apparatus and method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor, so as to solve the problems of low reaction efficiency and unstable yield in the traditional batch reactor for synthesizing glyoxylic acid in related technologies.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: an apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor, comprising: a first storage bottle connected to a first metering pump, the first metering pump connected to a first micro heat exchanger, and the first micro heat exchanger connected to a micro mixer; a second storage bottle connected to a second metering pump, the second metering pump connected to a second micro heat exchanger, and the second micro heat exchanger connected to a micro mixer; the micro mixer connected to a microreactor, the microreactor connected to a back pressure valve, and the back pressure valve connected to a collection bottle.

[0008] Further configuration: the first micro heat exchanger, the second micro heat exchanger, the micro mixer, and the micro reactor are placed in a thermostat.

[0009] A further setting is made: the collection bottle is placed in a water tank containing an ice-water mixture.

[0010] The configuration is further defined as follows: the first storage bottle contains glyoxal and ferrous sulfate; the second storage bottle contains hydrogen peroxide.

[0011] To achieve the above objectives, another aspect of the present invention provides a method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor, comprising: dissolving ferrous sulfate in glyoxal and storing it in a first storage bottle; storing hydrogen peroxide in a second storage bottle; conveying glyoxal and ferrous sulfate to a first micro heat exchanger via a first metering pump; conveying hydrogen peroxide to a second micro heat exchanger via a second metering pump; thoroughly mixing the glyoxal and ferrous sulfate output from the first micro heat exchanger and the hydrogen peroxide output from the second micro heat exchanger via a micro mixer, and then inputting the mixture into the microreactor; and discharging the product from the microreactor into a collection bottle.

[0012] Further, after the product in the collection bottle is cooled, it enters the post-processing system to remove waste acid and the byproduct formic acid. The crystals are dissolved and precipitated, and after oxalic acid is removed, glyoxylic acid is obtained.

[0013] Furthermore, the mass fraction of the glyoxal aqueous solution is 5wt%~20wt%, and the initial pH value is 2-4.5; the mass fraction of the hydrogen peroxide aqueous solution is 0.1wt%~30wt%, and the initial pH value is 2-4.5; the reaction temperature in the microreactor is 0℃~40℃, and the reaction pressure is 0bar~20bar.

[0014] Furthermore, the total flow rate in the microreactor is 1 mL / min to 7 mL / min; the flow ratio of glyoxal to hydrogen peroxide in the metering pump in the microreactor is 0.13:1.87 to 1.15:1.87.

[0015] Furthermore, the molar ratio of hydrogen peroxide to glyoxal in the microreactor is 0.6:1 to 2:1; the molar ratio of ferrous sulfate to glyoxal in the microreactor is 0.05:1 to 0.25:1; and the reaction residence time in the microreactor is 1 min to 15 min.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] 1. This invention employs a continuous flow microreactor, which, compared to the traditional batch reactor process, improves the reaction conversion rate, shortens the reaction time, reduces hydrogen peroxide consumption, eliminates gas generation, and avoids the dangers of the synthesis process. At the same time, the continuous flow microreactor, due to its relatively closed reaction system and efficient mass and heat transfer performance, can meet the high requirements of this step based on environmental protection, safety, and stable process parameters.

[0018] 2. By investigating the effects of factors such as the molar ratio of materials, the molar ratio of ferrous sulfate to glyoxal, the reaction residence time, the reaction temperature, the reaction pressure, the mass fraction of glyoxal, and the mass fraction of hydrogen peroxide on the conversion rate of glyoxal, the yield of glyoxylic acid, and its purity, the optimal process conditions were optimized and determined. The optimized process features fast reaction rate, high conversion efficiency, few side reactions, strong safety, no gas release, no waste generation, low energy consumption and labor costs, and strong controllability of the reaction process, making it suitable for continuous and industrial production. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of an apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor.

[0021] Figure 2 The chemical reaction formula for preparing glyoxylic acid according to this invention is shown below.

[0022] Reference numerals in the attached drawings: 1. First storage bottle; 2. Second storage bottle; 3. First metering pump; 4. Second metering pump; 5. First micro heat exchanger; 6. Second micro heat exchanger; 7. Micro mixer; 8. Microreactor; 9. Thermostat; 10. Back pressure valve; 11. Collection bottle; 12. Water tank. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0025] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] Example 1

[0027] Reference Figure 1 This invention discloses an apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor. The invention includes: a first storage bottle 1 connected to a first metering pump 3, the first metering pump 3 connected to a first micro heat exchanger 5, and the first micro heat exchanger 5 connected to a micro mixer 7; a second storage bottle 2 connected to a second metering pump 4, the second metering pump 4 connected to a second micro heat exchanger 6, and the second micro heat exchanger 6 connected to the micro mixer 7; the micro mixer 7 connected to a microreactor 8, the microreactor 8 connected to a back pressure valve 10, and the back pressure valve 10 connected to a collection bottle 11.

[0028] Specifically, the microreactor 8 is made of polytetrafluoroethylene (PTFE), stainless steel, silicon carbide, polyetheretherketone (PEEK), or soluble polytetrafluoroethylene (PFA), exhibiting excellent corrosion resistance and thermal stability. It is suitable for oxidation reaction systems containing hydrogen peroxide, ensuring the safety and continuous stable operation of the reaction process. The micromixer 7 adopts common T-type or focusing type designs with an inner diameter of 0.5mm–3.0mm. The microchannel reactor uses readily available capillary tubes with an inner diameter of 0.5mm–3.0mm.

[0029] The pressure of the internal reaction system is controlled by the back pressure valve 10.

[0030] Optionally, the first micro heat exchanger 5, the second micro heat exchanger 6, the micro mixer 7, and the microreactor 8 are placed in the thermostat 9 to ensure that the reaction takes place under constant temperature conditions.

[0031] Optionally, the collection bottle 11 is placed in a water tank 12 containing an ice-water mixture. The ice-water mixture is used to rapidly cool and crystallize the generated product.

[0032] Optionally, the first storage bottle 1 contains glyoxal and ferrous sulfate; the second storage bottle 2 contains hydrogen peroxide.

[0033] To address the problems of long reaction time, inaccurate temperature control, numerous side reactions, high safety risks, and unstable product selectivity and yield in the traditional Fenton oxidation process for glyoxylic acid synthesis in a batch reactor, this invention, after in-depth research, successfully developed a method for synthesizing glyoxylic acid via Fenton oxidation in a microreactor. This method enhances the reaction process by introducing a capillary microreactor 8. Compared to the batch operation of traditional batch reactors, the continuous flow system employed in this invention offers significant advantages such as strong process controllability, high selectivity, stable yield, low energy consumption, high operational safety, and high automation. Due to its high specific surface area and microscale reaction channels, the capillary microreactor 8 exhibits superior performance in mass and heat transfer, enabling precise temperature control and rapid dispersion of reaction heat, effectively avoiding local overheating, violent exothermic reactions, and free radical side reactions, thereby improving the selectivity of the target product, glyoxylic acid. Simultaneously, the microreactor 8 has a small reaction liquid holdup and controllable reactant residence time, avoiding reactant accumulation, bubble aggregation, and over-reaction, significantly improving the system's safety and stability. Compared to traditional processes, this method allows for rapid and efficient glyoxal oxidation at lower temperatures, reducing hydrogen peroxide consumption, improving atom economy, and lowering environmental impact. Furthermore, the capillary microreactor 8 in this invention has a simple structure, is easy to scale up in parallel, and possesses good potential for industrial expansion, making it suitable for high-throughput, continuous production of glyoxylic acid. In summary, this invention has significant advantages in enhancing reaction heat and mass transfer, suppressing the adverse effects of gas generation, improving reaction efficiency and safety, and reducing environmental impact. Currently, there are no publicly available reports or patent applications, either domestically or internationally, regarding the combination of Fenton oxidation and capillary microreactor 8 technology for continuous glyoxylic acid synthesis, demonstrating outstanding novelty and broad application prospects.

[0034] This invention discloses a method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor. The method includes: dissolving ferrous sulfate in glyoxal and storing it in a first storage bottle 1; storing hydrogen peroxide in a second storage bottle 2; transporting glyoxal and ferrous sulfate to a first micro heat exchanger 5 via a first metering pump 3; transporting hydrogen peroxide to a second micro heat exchanger 6 via a second metering pump 4; thoroughly mixing the glyoxal and ferrous sulfate output from the first micro heat exchanger 5 and the hydrogen peroxide output from the second micro heat exchanger 6 via a micro mixer 7, and then inputting the mixture into a microreactor 8; the product output from the microreactor 8 is then collected in a collection bottle 11.

[0035] Reference Figure 2 , Figure 2 The chemical reaction formula for preparing glyoxylic acid according to this invention is shown below.

[0036] Optionally, after cooling, the product in collection bottle 11 enters a post-treatment system to remove waste acid and the byproduct formic acid. The crystals are dissolved and precipitated, and after removing oxalic acid, glyoxylic acid is obtained. Other post-treatment methods can also be used.

[0037] Optionally, the mass fraction of the glyoxal aqueous solution is 5wt%~20wt%, and the initial pH value is 2-4.5; the mass fraction of the hydrogen peroxide aqueous solution is 0.1wt%~30wt%, and the initial pH value is 2-4.5; the reaction temperature in the microreactor 8 is 0℃~40℃, and the reaction pressure is 0bar~20bar.

[0038] Optionally, the total flow rate in the microreactor 8 is 1 mL / min to 7 mL / min; the flow ratio of glyoxal to hydrogen peroxide in the metering pump of the microreactor 8 is 0.13:1.87 to 1.15:1.87.

[0039] Optionally, the molar ratio of hydrogen peroxide to glyoxal in microreactor 8 is 0.6:1 to 2:1; the molar ratio of ferrous sulfate to glyoxal in microreactor 8 is 0.05:1 to 0.25:1; and the reaction residence time in microreactor 8 is 1 min to 15 min.

[0040] In this invention, min represents minutes; h represents hours; g represents grams; mL represents milliliters; kg represents kilograms; wt% represents mass fraction; bar represents bar; kPa represents kilopascals. HPLC represents high-performance liquid chromatography.

[0041] Example 2

[0042] 1 mol of 20 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1 mol of 3 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to adjust the pH to 3.25. The reactor temperature was set to 4 °C, the back pressure valve 10 pressure to 0 bar, the inner diameter of the microreactor 8 to 0.8 mm, and the inner diameter of the micromixer 7 to 0.5 mm. The materials in the storage bottle were pumped into the microchannel reactor using two plunger metering pumps at a flow ratio of 0.15:1.85, with a total flow rate of 2.0 mL / min and a residence time of 9.0 min. The liquid product was collected and cooled with an ice-water mixture to achieve quenching. The reaction was monitored by HPLC to ensure complete reaction. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain the compound glyoxylic acid with a purity of 95% and a yield of 45%.

[0043] Example 3

[0044] 1 mol of 2.5 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1 mol of 3 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to make the pH 3.25. The temperature of microreactor 8 was set to 8℃, the pressure of back pressure valve 10 was set to 0 bar, the inner diameter of microreactor 8 was 0.5 mm, and the inner diameter of micromixer 7 was 3 mm. The materials in the storage bottles were pumped into the microchannel reactor at a flow ratio of 0.8:1.2 using two plunger metering pumps, with a total flow rate of 2.0 mL / min and a residence time of 9.0 min. The liquid product was collected, and the reaction was monitored by HPLC until complete. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain glyoxylic acid with a purity of 96% and a yield of 48.1%.

[0045] Example 4

[0046] 1 mol of 20 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1 mol of 3 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to make the pH 3.25. The temperature of microreactor 8 was set to 4 °C, the pressure of back pressure valve 10 was set to 0 bar, the inner diameter of microreactor 8 was 1 mm, and the inner diameter of micromixer 7 was 1 mm. The materials in the storage bottles were pumped into the microchannel reactor at a flow ratio of 0.2:2.8 using two plunger metering pumps, with a total flow rate of 3.0 mL / min and a residence time of 5 min. The liquid products were collected, and the reaction was monitored by HPLC to ensure complete reaction. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain the compound glyoxylic acid with a purity of 93% and a yield of 35.6%.

[0047] Example 5

[0048] 1 mol of 20 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1 mol of 1 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to make the pH 3.25. The temperature of microreactor 8 was set to 4℃, the pressure of back pressure valve 10 was set to 0 bar, the inner diameter of microreactor 8 was 0.8 mm, and the inner diameter of micromixer 7 was 0.5 mm. The materials in the storage bottles were pumped into the microchannel reactor at a flow ratio of 0.14:1.86 using two plunger metering pumps, with a total flow rate of 2.0 mL / min and a residence time of 3 min. The liquid product was collected, and the reaction was monitored by HPLC to ensure complete reaction. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain the compound glyoxylic acid with a purity of 98% and a yield of 38.2%.

[0049] Example 6

[0050] 1 mol of 2.5 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1 mol of 5.6 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to make the pH 3.25. The temperature of microreactor 8 was set to 8℃, the pressure of back pressure valve 10 was set to 15 bar, the inner diameter of microreactor 8 was 3 mm, and the inner diameter of micromixer 7 was 0.5 mm. The materials in the storage bottles were pumped into the microchannel reactor at a flow ratio of 0.45:1.55 using two plunger metering pumps, with a total flow rate of 2.0 mL / min and a residence time of 7 min. The liquid product was collected, and the reaction was monitored by HPLC to ensure complete reaction. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain the compound glyoxylic acid with a purity of 97% and a yield of 39.7%.

[0051] Example 7

[0052] 1 mol of 20 wt% glyoxal was placed in a storage bottle (1) containing glyoxal and ferrous sulfate, and 0.15 mol of ferrous sulfate was dissolved in glyoxal. 1.2 mol of 10 wt% hydrogen peroxide aqueous solution was placed in a storage bottle (2) containing hydrogen peroxide, and H2SO4 was added to make the pH 3.25. The temperature of microreactor 8 was set to 4℃, the pressure of back pressure valve 10 to 10 bar, the inner diameter of microreactor 8 to 0.5 mm, and the inner diameter of micromixer 7 to 0.5 mm. The materials in the storage bottles were pumped into the microchannel reactor at a flow ratio of 0.9:1.1 using two plunger metering pumps, with a total flow rate of 2.0 mL / min and a residence time of 10 min. The liquid product was collected, and the reaction was monitored by HPLC until it was complete. After the reaction liquid flowed out, it entered the post-processing system, where it was cooled and crystallized to remove waste acid and the byproduct formic acid. After the crystals dissolved and precipitated, oxalic acid was removed to obtain glyoxylic acid with a purity of 93% and a yield of 22.2%.

[0053] The working principle and beneficial effects of this invention are as follows: This invention employs a continuous flow microreactor 8, which, compared to the traditional batch reactor process, improves the reaction conversion rate, shortens the reaction time, reduces hydrogen peroxide consumption, eliminates gas generation, and avoids the dangers of the synthesis process. Simultaneously, the continuous flow microreactor 8, due to its relatively closed reaction system and highly efficient mass and heat transfer performance, can meet the high requirements of environmental safety and stable process parameters for this step. By investigating the effects of factors such as the molar ratio of materials, the molar ratio of ferrous sulfate to glyoxal, the reaction residence time, the reaction temperature, the reaction pressure, the mass fraction of glyoxal, and the mass fraction of hydrogen peroxide on the conversion rate of glyoxal, the yield of glyoxylic acid, and its purity, the optimal process conditions were optimized and determined. The optimized process features fast reaction rate, high conversion efficiency, few side reactions, strong safety, no gas release, no waste generation, low energy consumption and labor costs, and strong controllability of the reaction process, making it suitable for continuous and industrial production.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor, characterized in that, include: The first storage bottle (1) is connected to the first metering pump (3), the first metering pump (3) is connected to the first micro heat exchanger (5), and the first micro heat exchanger (5) is connected to the micro mixer (7). The second storage bottle (2) is connected to the second metering pump (4), the second metering pump (4) is connected to the second micro heat exchanger (6), and the second micro heat exchanger (6) is connected to the micro mixer (7). The micro mixer (7) is connected to the microreactor (8), the microreactor (8) is connected to the back pressure valve (10), and the back pressure valve (10) is connected to the collection bottle (11).

2. The apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor according to claim 1, characterized in that, include: The first micro heat exchanger (5), the second micro heat exchanger (6), the micro mixer (7) and the micro reactor (8) are placed in a thermostat (9).

3. The apparatus for Fenton oxidation synthesis of glyoxylic acid in a microreactor according to claim 1, characterized in that, include: The collection bottle (11) is placed in a water tank (12) containing an ice-water mixture.

4. The apparatus for Fenton oxidation synthesis of glyoxylic acid in a microreactor according to claim 1, characterized in that, include: The first storage bottle (1) contains glyoxal and ferrous sulfate; The second storage bottle (2) contains hydrogen peroxide.

5. A method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor, applied to the apparatus for synthesizing glyoxylic acid by Fenton oxidation in a microreactor as described in any one of claims 1-4, characterized in that, include: Ferrous sulfate is dissolved in glyoxal and stored in the first storage bottle (1). Hydrogen peroxide is stored in the second storage bottle (2); Glyoxal and ferrous sulfate are delivered to the first micro heat exchanger (5) via the first metering pump (3); Hydrogen peroxide is delivered to the second micro heat exchanger (6) via the second metering pump (4); The glyoxal and ferrous sulfate output from the first micro heat exchanger (5) and the hydrogen peroxide output from the second micro heat exchanger (6) are thoroughly mixed by the micro mixer (7) and then fed into the micro reactor (8). The micro reactor (8) outputs the product into the collection bottle (11).

6. The method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor according to claim 5, characterized in that, include: After the product in the collection bottle (11) is cooled, it enters the post-processing system to remove waste acid and by-product formic acid. The crystals are dissolved and precipitated, and after removing oxalic acid, glyoxylic acid is obtained.

7. The method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor according to claim 5, characterized in that, include: The mass fraction of glyoxal aqueous solution is 5wt%~20wt%, and the initial pH value is 2-4.5; The mass fraction of the hydrogen peroxide aqueous solution is 0.1wt%~30wt%, and the initial pH value is 2-4.5; The reaction temperature in the microreactor (8) is 0℃~40℃ and the reaction pressure is 0bar~20bar.

8. The method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor according to claim 5, characterized in that, include: The total flow rate in the microreactor (8) is 1 mL / min to 7 mL / min; The flow ratio of glyoxal to hydrogen peroxide in the metering pump of the microreactor (8) is 0.13:1.87 to 1.15:1.

87.

9. The method for synthesizing glyoxylic acid by Fenton oxidation in a microreactor according to claim 5, characterized in that, include: The molar ratio of hydrogen peroxide to glyoxal in the microreactor (8) is 0.6:1 to 2:1; The molar ratio of ferrous sulfate to glyoxal in the microreactor (8) is 0.05:1 to 0.25:1; The reaction residence time in the microreactor (8) is 1 min to 15 min.

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