A flow-mode switchable microreactor and its application in controlled synthesis and selective oxidation of catalysts

Abstract

This invention discloses a flow-mode switchable microreactor and its application in controlled synthesis and selective oxidation reactions. The microreactor comprises a multi-layered structure consisting of a top plate, a gasket plate, a channel plate, and a barrier plate arranged sequentially from top to bottom. The position of the barrier plate is adjusted via a "click-to-switch" mechanism using a mechanical adjustment mechanism, enabling rapid switching between laminar and turbulent flow modes. In laminar flow mode, α, β, δ, or γ-phase MnO₂ catalysts can be controllably prepared, reducing energy consumption by more than 60% compared to batch methods. In turbulent flow mode, photocatalytic selective oxidation of HMF using α-phase MnO₂ achieves a space-time yield of 23.8 mmol / g / h. This invention overcomes the limitations of "single reactor - single function," providing an integrated platform for intelligent, large-scale catalyst material preparation and bio-based DFF production.

Description

Technical Field

[0001] This invention belongs to the field of microchemical technology and multiphase catalysis, specifically relating to a microreactor device that can rapidly switch between laminar and turbulent flow modes, and a method for the controllable synthesis of manganese dioxide catalyst and the selective oxidation of 5-hydroxymethylfurfural to prepare 2,5-diformylfuran using this device. Background Technology

[0002] Microchannel reactors, as a key representative of process intensification technology, have shown broad application prospects in fine chemicals, pharmaceuticals, and materials synthesis due to their continuous operation, excellent heat and mass transfer performance, precise process control, and inherent safety. Compared with traditional batch reactors, microreactors can effectively solve the scale-up effects of complex fluid dynamics and heat transfer, and have significant advantages in large-scale catalyst synthesis and the production of high-value-added chemicals.

[0003] Existing microreactor technology mainly suffers from the following technical shortcomings:

[0004] (i) Fixed flow pattern and single function: The fluid state within a microreactor is usually determined by a fixed channel geometry. Laminar flow microreactors (Re < 2300) are suitable for the precise synthesis of nanomaterials and the control of interfacial reactions, but their mass transfer efficiency is limited; turbulent flow microreactors can enhance mass transfer, but are not conducive to the precise control of material morphology. This unadjustability of the flow pattern results in a single device having a single function, making it impossible to integrate catalyst synthesis and catalytic reaction. (ii) Disconnection between catalyst synthesis and catalytic reaction: In traditional processes, catalyst preparation and catalytic reaction are usually carried out in separate devices, involving intermediate steps such as material transfer, storage, and redispersion, which increases energy consumption, material consumption, and operational complexity, and may lead to changes in active components due to catalyst exposure to the environment. (iii) Difficulty in balancing energy consumption and efficiency: Batch reactors for synthesizing nanocatalysts have high energy consumption, long reaction times, and poor batch-to-batch consistency; while continuous flow reactors with a fixed flow pattern cannot simultaneously meet the high precision requirements of material synthesis and the high efficiency requirements of catalytic reaction.

[0005] Therefore, developing an integrated microreactor platform with dynamically switchable flow regimes and combined catalyst synthesis and catalytic reaction functions is of great significance for realizing intelligent and large-scale chemical manufacturing. Summary of the Invention

[0006] One of the objectives of this invention is to provide an integrated microreactor platform with dynamically switchable flow modes and functions for both catalyst synthesis and catalytic reaction, enabling controllable switching of the reaction stream between laminar and turbulent flow modes.

[0007] Specifically, as an embodiment of a flow-mode switchable microreactor, it includes a mechanical adjustment mechanism and a top plate, a gasket plate, a channel plate, and a barrier plate arranged sequentially from top to bottom. The channel plate has microchannels for the flow of the reactant material, and the bottom of each microchannel has multiple circular through-holes of diameter c distributed along its extension path. The upper surface of the barrier plate has cylindrical barriers of diameter d distributed thereon, with each cylindrical barrier corresponding to one of the circular through-holes, where (cd) ≤ 0.1 mm, and the height of the cylindrical barriers is greater than or equal to the height of the channel plate. The mechanical adjustment mechanism is used to adjust the vertical distance between the channel plate and the barrier plate to adjust the length of the cylindrical barriers inserted into the microchannels through the circular through-holes, thereby enabling the flow mode of the reactant material within the microchannels to switch between laminar and turbulent flow modes.

[0008] Alternatively, in combination with any of the above aspects, in another implementation of this aspect, the top plate is a light-transmitting plate, so that external light can pass through the top plate and irradiate the microchannel, inducing the catalyst in the microchannel to carry out a photocatalytic reaction.

[0009] Optionally, in combination with any of the above aspects, in another implementation of this aspect, the mechanical adjustment mechanism is a screw lifting mechanism or a cam pressing mechanism; the barrier plate position is quickly repositioned by the operator's "click" operation, thereby realizing one-click switching of the reactive material between laminar flow mode and turbulent flow mode in the microchannel.

[0010] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, in the laminar flow mode, the cylindrical barrier is embedded in the circular through-hole, and the upper surface of the cylindrical barrier is completely attached to the lower surface of the microchannel, thereby forming a planar flow channel, in which the reactant fluid is in a stable laminar flow state; optionally, the cross-sectional shape of the planar flow channel is rectangular, the fluid is in a stable laminar flow state in the planar flow channel, the Reynolds number Re < 10, and the mass transfer is mainly molecular diffusion.

[0011] In the turbulent flow mode, the cylindrical barrier is at least partially inserted into the microchannel to disturb the reactant fluid and form turbulence; optionally, the cylindrical barrier is partially inserted into the microchannel, and the barrier disturbs the fluid to form a periodic vortex structure with a Reynolds number Re of 900-1100, and mass transfer is mainly by convection and diffusion.

[0012] Alternatively, in combination with any of the above aspects, in another implementation of this aspect, the hydraulic diameter of the microchannel is 0.8-4.8 mm and the total length of the channel is 100-500 mm.

[0013] Another objective of this invention is to utilize the aforementioned microreactor for the controllable synthesis of manganese dioxide catalysts, thereby achieving the selective preparation of MnO2 with different crystalline phases through precise parameter control in laminar flow mode.

[0014] Specifically, as an embodiment of a controllable synthesis method for manganese dioxide catalyst, a continuous co-precipitation reaction is carried out in laminar flow mode using a microreactor as described in any of the above aspects, and α, β, δ or γ crystalline phases of MnO2 are selectively synthesized by controlling the type, concentration, flow rate and temperature of the reactants.

[0015] Optionally, in combination with any of the above aspects, in another implementation of this aspect, the controllable synthesis method of the manganese dioxide catalyst in the laminar flow mode includes the following steps: (1) Solution preparation: Prepare solution A: Dissolve the oxidant in deionized water at a concentration of 0.1-0.4 mol / L; Prepare solution B: Dissolve the manganese salt in deionized water at a concentration of 0.05-0.25 mol / L; (2) Continuous co-precipitation: Pump solution A and solution B into the two inlets of the microreactor at the same flow rate using an injection pump, and mix and react in the microchannel in laminar flow mode. Control the reaction temperature of solution A and solution B to 40-80°C, and the residence time of the reaction stream in the microchannel to 2-10 minutes; (3) Post-treatment: Collect the reaction precipitate, wash it with deionized water and anhydrous ethanol, dry it at 60-80°C, and calcine it in a muffle furnace at 300-400°C for 1-3 hours to obtain the target crystalline phase MnO2.

[0016] Alternatively, in combination with any of the above aspects, in another implementation of this aspect, the selective synthesis of MnO2 with different crystalline phases is achieved by controlling the types, concentration ratios, flow rates, and temperatures of reactants. The specific crystalline phases and their characteristics are shown in Table 1 below:

[0017] <![CDATA[α-MnO2]]> potassium permanganate manganese sulfate 500 80 2×2 tunnel structure, nanorod-shaped <![CDATA[β-MnO2]]> ammonium persulfate manganese sulfate 200 70 1×1 tunnel structure, nanorod-shaped <![CDATA[δ-MnO2]]> potassium permanganate manganese sulfate 400 80 1×1 tunnel structure, nanorod-shaped <![CDATA[δ-MnO2]]> ammonium persulfate manganese sulfate 450 50 1×1 tunnel structure, nanorod-shaped

[0018] It should be noted that the flow rates described in the table above specifically refer to the set flow rates at which solution A or solution B enters the microreactor as reactants.

[0019] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, the synthesis conditions of the α-crystalline MnO2 are as follows: solution A is a 3.125 g / 100 mL KMnO4 aqueous solution, solution B is a 1.313 g / 100 mL MnSO4·H2O aqueous solution, the flow rates of solutions A and B are set to 500 μL / min, and the reaction temperature is 80°C. Under these reaction conditions, the obtained α-crystalline MnO2 has the largest specific surface area (>150 m² / g) and the highest Mn³⁺ / Mn 4The ⁺ ratio (>1.0) and the highest adsorbed oxygen / lattice oxygen ratio (Oads / Olatt > 0.75).

[0020] Another objective of this invention is to provide a method for the selective oxidation of 5-hydroxymethylfurfural to prepare 2,5-dicarboxyfuran using the aforementioned microreactor, achieving a space-time yield exceeding the limits of existing technologies through enhanced mass transfer in turbulent mode.

[0021] Specifically, as an embodiment of a method for preparing 2,5-diformylfuran (DFF) based on the selective oxidation of 5-hydroxymethylfurfural, a gas-liquid-solid three-phase catalytic oxidation reaction is carried out using the microreactor described in the first aspect above, in the turbulent mode, with the α-crystalline phase MnO2 synthesized in the second aspect above as a catalyst.

[0022] Optionally, in conjunction with any of the above aspects, in another implementation of this aspect, a method for selective oxidation of 5-hydroxymethylfurfural (HMF) using the above-mentioned microreactor and the synthesized α-crystalline MnO2 catalyst, employing a turbulent flow mode, includes the following steps: (1) Catalyst dispersion: adding the α-crystalline MnO2 catalyst to an acetonitrile solution containing HMF to form a mixture, wherein the concentration of the α-crystalline MnO2 catalyst is 1-7 mg / mL and the concentration of HMF is 5 mg / mL. mg / mL, ultrasonically dispersed for 10-30 minutes; (2) Gas-liquid-solid three-phase reaction: the catalyst mixture containing HMF is pumped into the liquid inlet of the microreactor through an injection pump, and oxygen is controlled to enter the gas inlet of the microreactor through a mass flow meter, and the liquid-gas flow ratio is adjusted to 1:4 to 4:1; (3) Turbulent enhanced reaction: the microreactor is switched to turbulent mode, the reaction temperature is set to 60-80°C, the residence time is 0.5-2 hours, and selective oxidation reaction is carried out under the action of eddy enhanced mass transfer; (4) Product collection: the reaction solution is filtered through a 0.22 μm membrane to remove the catalyst, and the filtrate is analyzed by HPLC.

[0023] Preferably, the liquid-to-gas flow ratio of the mixture and the oxygen is 2:1, the hydraulic diameter of the channel is 0.8 mm, the reaction temperature is 70°C, and the residence time is 1 hour.

[0024] Preferably, the α-MnO2 catalyst has an average particle size of 10-15 μm and a Zeta potential of -15 to -25 mV to ensure dispersion stability in acetonitrile.

[0025] Another objective of this invention is to provide a method for catalyst regeneration and recycling, comprising: collecting the catalyst after the above-mentioned selective oxidation reaction, washing it with acetonitrile, drying it at 60-80°C, and then heat-treating it at 200°C for 8-12 hours to completely desorb the adsorbed organic species and restore the catalyst activity. The regenerated catalyst can be recycled at least 16 times with an activity retention rate >80%.

[0026] Compared with the prior art, the present invention has the following significant technical effects:

[0027] This invention creatively designs a microreactor capable of switching between laminar and turbulent flow modes. Through a "click-to-switch" mechanism, the same microreactor platform can perform both controlled catalyst synthesis and highly efficient catalytic reaction, achieving multifunctional integration of the equipment, reducing intermediate transfer steps, and improving the atom economy and operational safety of the reaction process.

[0028] Compared with the traditional batch method, the microreactor used in the synthesis of MnO2 according to the present invention reduces the reaction temperature by 20-40°C, shortens the reaction time by more than 90%, and reduces the energy consumption per unit yield by 60-72%. Specifically, the energy consumption is reduced by 68.6% for α-MnO2, 71.6% for β-MnO2, 60.4% for δ-MnO2, and 67.2% for γ-MnO2.

[0029] In turbulent flow mode, the space-time yield of HMF oxidation to DFF reached 23.8 mmol / g / h, which is 50% higher than that in laminar flow mode (15.8 mmol / g / h) and significantly higher than that of previously reported thermocatalytic systems (typically <10 mmol / g / h).

[0030] The synthesized α-MnO2 exhibits the largest specific surface area, the highest oxygen vacancy concentration, and the strongest low-temperature reducing power, demonstrating a 70% conversion rate and >99% DFF selectivity in HMF oxidation. The catalyst can be regenerated with simple heat treatment and exhibits excellent cycle stability.

[0031] The continuous flow operation and precise parameter control of the microreactor ensure consistent product quality. 24-hour continuous operation verification shows that the system has good stability and has the potential for industrial scale-up.

[0032] The above summary provides a simplified overview of some concepts, which will be further described in detail in the following specific embodiments. The above summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter. The claimed subject matter is not limited to embodiments that address any or all the shortcomings pointed out in the background art.

[0033] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments thereof. Attached Figure Description

[0034] The accompanying drawings, incorporated in and forming part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without any creative effort. These drawings and textual descriptions are not intended to limit the scope of the concept of this application in any way, but rather to illustrate the concepts of this application to those skilled in the art by referring to specific embodiments.

[0035] Figure 1 This is a schematic diagram of the flow-mode switchable microreactor of the present invention and a schematic diagram of the internal structure of the reaction chamber;

[0036] Figure 2 This is a schematic diagram illustrating the working principle of the switchable microreactor of the present invention.

[0037] Figure 3 This is the SEM image of α-MnO2 in Example 2 of the present invention;

[0038] Figure 4 This is the SEM image of β-MnO2 in Example 3 of the present invention;

[0039] Figure 5 This is the SEM image of δ-MnO2 in Example 4 of the present invention;

[0040] Figure 6 This is the SEM image of γ-MnO2 in Example 5 of the present invention;

[0041] Figure 7 The XRD patterns of different crystal forms of MnO2 in Examples 2-5 of this invention;

[0042] Figure 8 Raman diagrams of different crystal forms of MnO2 in Examples 2-5 of this invention;

[0043] Figure 9 This describes the fluid simulation under different manifold modes and the process of converting HMF to DFF in Embodiments 6 and 7 of the present invention. Detailed Implementation

[0044] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0045] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. It should be further understood that, as used herein, the singular forms "a," "an," and "the" are intended to also include the plural forms, unless the context indicates otherwise. Furthermore, the terms "or," "and / or," "including at least one of the following," etc., as used herein, can be interpreted as inclusive, or mean any one or any combination thereof. Exceptions to this definition only arise when combinations of elements, functions, steps, or operations are inherently mutually exclusive in some manner.

[0046] It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0047] Example 1: Assembly of a flow-mode switchable microreactor

[0048] The components of the microreactor are manufactured using polymethyl methacrylate (PMMA) or polytetrafluoroethylene (PTFE).

[0049] Channel plate: The serpentine microchannel is machined by CNC micro-milling. The channel cross-section is rectangular, with a width of 1.0 mm, a depth of 0.5 mm (hydraulic diameter of 0.8 mm), and a total length of 300 mm. Circular through holes with a diameter of c = 0.6 mm are machined at 5 mm intervals at the bottom of the channel.

[0050] Barrier plate: A cylindrical barrier with a diameter of d = 0.55 mm and a height of h = 0.5 mm is machined, with an array spacing of 5 mm, corresponding to the hole positions of the channel plate.

[0051] Gasket plate: 0.2 mm thick, to ensure the flow channel is level after assembly.

[0052] Assemble the components from bottom to top: barrier plate → channel plate → gasket plate → top plate, and fasten them with bolts. A structural diagram is shown below. Figure 1 As shown, a spiral lifting mechanism is connected to the bottom of the barrier plate, which allows for precise adjustment of the distance between the barrier plate and the channel plate by rotation, switching between laminar and turbulent flow modes.

[0053] Example 2: Synthesis of α-MnO2 catalyst

[0054] Solution preparation: Solution A: 3.125 g KMnO4 dissolved in 100 mL deionized water, concentration 0.198 mol / L; Solution B: 1.313 g MnSO4·H2O dissolved in 100 mL deionized water, concentration 0.078 mol / L. Continuous synthesis: The microreactor was set to laminar flow mode (barrier plate completely attached to channel plate). Solutions A and B were pumped into the two inlets of the microreactor at a flow rate of 500 μL / min using two syringe pumps, converging at the Y-type mixer before entering the microchannel. The reactor was placed in an 80°C constant temperature water bath for approximately 3.6 minutes. Post-treatment: The brown suspension at the outlet was collected, the precipitate was separated by centrifugation, washed three times with deionized water, washed twice with anhydrous ethanol, and vacuum dried at 80°C for 12 hours. The dried solid was placed in a muffle furnace and heated to 360°C at a rate of 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature to obtain the α-MnO2 catalyst.

[0055] Characterization results: SEM ( Figure 3 XRD showed that α-MnO2 exhibited a nanorod morphology, with a length of 0.5-1.2 μm and a width of 30-70 nm. Figure 7 The results show that all diffraction peaks correspond to the JCPDS 44-0141 standard card, which is pure phase α-MnO2 (2×2 tunnel structure).

[0056] Example 3: Synthesis of β-MnO2 catalyst

[0057] Solution preparation: Solution A: 5.7 g (NH4)2S2O8 dissolved in 100 mL deionized water, concentration 0.25 mol / L; Solution B: 4.23 g MnSO4·H2O dissolved in 100 mL deionized water, concentration 0.25 mol / L. Continuous synthesis: laminar flow mode in a microreactor, flow rate 200 μL / min, temperature 70°C, other operations are the same as in Example 2.

[0058] Characterization results: SEM ( Figure 4 XRD showed that β-MnO2 exhibited a nanorod morphology with a length of 0.5-1.2 μm and a width of 30-70 nm; Figure 7 It is shown as a pure phase β-MnO2 (JCPDS 24-0735, 1×1 tunnel structure) crystal form.

[0059] Example 4: Synthesis of δ-MnO2 catalyst

[0060] Solution preparation: Solution A: 3.75 g KMnO4 dissolved in 100 mL deionized water; Solution B: 0.7 g MnSO4·H2O dissolved in 100 mL deionized water. The microreactor was operated in laminar flow mode at a flow rate of 400 μL / min and a temperature of 80°C. All other operations were the same as in Example 2.

[0061] Characterization results: SEM ( Figure 5 XRD showed that δ-MnO2 exhibited a flower-like nanosheet structure with a sheet thickness of 10-20 nm and a flower diameter of 10-12 μm; Figure 7 It is shown as a pure phase δ-MnO2 (JCPDS 80-1098, layered structure) crystal form.

[0062] Example 5: Synthesis of γ-MnO2 catalyst

[0063] Solution preparation: Solution A: 5.7 g (NH4)2S2O8 dissolved in 100 mL deionized water; Solution B: 4.225 g MnSO4·H2O dissolved in 100 mL deionized water. Continuous synthesis: laminar flow mode in a microreactor, flow rate 450 μL / min, temperature 50°C, and other operations were the same as in Example 2.

[0064] Characterization results: SEM ( Figure 6 XRD showed that γ-MnO2 exhibited a sea urchin-like structure composed of radially arranged nanoneedles; Figure 7 It is shown as a pure phase γ-MnO2 (JCPDS 14-0644, 1×2 / 1×1 mixed tunnel structure) crystal phase.

[0065] Example 6: HMF oxidation reaction in laminar flow mode

[0066] Catalyst dispersion: 50 mg of α-MnO2 prepared in Example 2 was added to 50 mL of acetonitrile solution containing 250 mg HMF and ultrasonically dispersed for 20 minutes. The microreactor was set to laminar flow mode (with the barrier plate fully attached) with a channel diameter of 0.8 mm. The catalyst suspension was pumped into the reactor at a specific flow rate using a syringe pump, while the oxygen flow rate was controlled by a mass flow meter to adjust the liquid-to-gas ratio. The reaction temperature was 70°C, and the residence time was 2 hours. Condition optimization: Channel diameter optimization: 0.8, 1.6, 2.4, and 4.8 mm were tested, with 0.8 mm yielding the highest DFF yield (72%). Liquid-to-gas ratio optimization: Liquid-to-gas ratios of 4:1, 3:1, 2:1, 1:1, 1:2, and 1:4 were tested, with a 2:1 liquid-to-gas ratio showing the best space-time yield (15.8 mmol / g / h).

[0067] Results analysis: Smaller channel diameter enhances heat transfer efficiency, and appropriate gas phase ratio promotes gas-liquid mass transfer, but excessively high gas phase ratio reduces space-time yield and leads to excessive oxidation of DFF.

[0068] Example 7: HMF oxidation reaction in turbulent mode

[0069] Switching operation: The microreactor in Example 7 is switched to turbulent mode via a "click switching" mechanism: the rotating spiral lifting mechanism lowers the barrier plate by 0.3 mm, and the cylindrical barrier portion is inserted into the microchannel. Reaction conditions: channel diameter 0.8 mm, liquid-to-gas ratio 2:1, temperature 70°C, residence time 1 hour, the rest are the same as in Example 6.

[0070] Reaction results: DFF yield: 90% (significantly higher than 72% in laminar flow mode); residence time: reduced to 1 hour (2 hours in laminar flow mode); space-time yield: 23.8 mmol / g / h (50% higher than 15.8 mmol / g / h in laminar flow mode). In turbulent flow mode, the eddies generated by the barrier significantly enhanced mass transfer at the gas-liquid-solid interface, allowing oxygen to reach the catalyst surface more quickly, while the product DFF detached from the active site in a timely manner, inhibiting over-oxidation.

[0071] Example 8: Catalyst Cyclic Stability Test

[0072] Following the conditions of Example 7, a 24-hour continuous operation experiment was conducted, with product collected every 2 hours. A total of 39.9 mmol of DFF was produced over 24 hours, with an average selectivity of 81.83%. The system operated stably without significant catalyst deposition. The catalyst after reaction was collected, washed with acetonitrile, dried at 80°C, and regenerated by heat treatment at 200°C for 10 hours. The regenerated catalyst was used in the next round of reaction, for a total of 18 cycles. In cycles 1-18, the activity gradually decreased to 70% of its initial value; after regeneration, the activity recovered to over 95% of its initial value; after another 16 cycles following regeneration, the activity retention rate was >80%.

[0073] Example 9: Comparison of catalytic performance of MnO2 with different crystal phases

[0074] Following the conditions of Example 7, the catalytic performance of the four crystalline phases of MnO2 prepared in Examples 2-5 was tested (as shown in Table 2 below). α-MnO2 exhibited the best performance, which was closely related to its largest specific surface area, highest oxygen vacancy concentration, and strongest surface oxygen migration ability. Product images are shown below. Figure 9 As shown.

[0075] <![CDATA[α-MnO2]]> 70% >99% 23.8 <![CDATA[β-MnO2]]> 45% 85% 12.5 <![CDATA[δ-MnO2]]> 55% 90% 15.2 <![CDATA[γ-MnO2]]> 38% 78% 9.8

[0076] Comparative Example 1

[0077] To demonstrate the mass transfer enhancement effect of the microreactor turbulence mode in catalytic reactions, a conventional batch reactor was used as a comparative example, employing the same α-MnO2 catalyst as in this invention.

[0078] The selective oxidation of HMF was carried out in a 100 mL transparent reactor. The prepared α-MnO2 (50 mg) was added to 50 mL of acetonitrile solution containing 250 mg HMF and ultrasonically dispersed for 20 minutes. The suspension was transferred to the reactor and a magnetic stir bar (Φ8 mm × 25 mm) was added. The remaining conditions were the same as in Example 7. After the reaction was complete, the reaction solution was cooled to room temperature, filtered through a 0.22 μm membrane to remove the catalyst, and the filtrate was analyzed by HPLC.

[0079] Table 3 below compares the catalytic performance of the batch reactor and the microreactor of this invention in turbulent flow mode:

[0080] DFF Yield (%) 68 90 +32% HMF conversion rate (%) 72 92 +28% DFF selectivity (%) 94 ＞99 +5% Byproduct FFCA (%) 4.5 ＜1 -78% Byproduct HMFCA (%) 1.2 ＜1 -17% Spacetime yield (mmol / g / h) 8.2 23.8 +190% Oxygen utilization rate (%) 35 68 +94% Catalyst recovery rate (%) 82 95 +16%

[0081] In a stirred tank reactor, even with mechanical stirring at 600 rpm, the shear force generated by stirring is insufficient to effectively break up oxygen bubbles due to the reactor's large size (80 mm in diameter). Since the bubble diameter is typically >2 mm, the rapid rise speed, and short gas-liquid contact time make oxygen mass transfer the rate-limiting step.

[0082] In the turbulent mode of the microreactor, the eddies generated by the barrier structure break the bubbles to <0.5 mm, increasing the gas-liquid contact area by more than 4 times; at the same time, the eddies promote the uniform suspension of catalyst particles, avoid sedimentation, and significantly improve the catalyst utilization rate.

[0083] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0084] In this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions are generally described in detail only when they appear for the first time. When they appear again, they are generally not repeated for the sake of brevity. When understanding the technical solutions and other contents of this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions that are not described in detail later can be referred to their previous relevant detailed descriptions.

[0085] In this application, the descriptions of the various embodiments have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0086] The technical features of the present application can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0087] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A microreactor with switchable flow regime, characterized in that, The system includes a mechanical adjustment mechanism and, from top to bottom, a top plate, a gasket plate, a channel plate, and a barrier plate. The channel plate contains microchannels for the flow of the reactant material, and the bottom of each microchannel has multiple circular through-holes of diameter c distributed along its extension path. The barrier plate has cylindrical barriers of diameter d distributed on its upper surface, each corresponding to one of the circular through-holes, where (cd) ≤ 0.1 mm, and the height of each cylindrical barrier is greater than or equal to the height of the channel plate. The mechanical adjustment mechanism adjusts the vertical distance between the channel plate and the barrier plate to adjust the length of the cylindrical barriers inserted into the microchannels through the circular through-holes, thereby switching the flow state of the reactant material within the microchannels between laminar and turbulent modes.

2. The microreactor according to claim 1, characterized in that, The mechanical adjustment mechanism is a screw lifting mechanism or a cam pressing mechanism.

3. The microreactor according to claim 1 or 2, characterized in that, In the laminar flow mode, the cylindrical barrier is embedded in the circular through-hole, and the upper surface of the cylindrical barrier is completely attached to the lower surface of the microchannel, thereby forming a planar flow channel, and the reactant material is in a stable laminar flow state in the microchannel; in the turbulent flow mode, the cylindrical barrier is at least partially inserted into the microchannel to disturb the reactant material and form turbulence.

4. A controllable synthesis method for a manganese dioxide catalyst, characterized in that, Using the microreactor according to any one of claims 1-3, a continuous co-precipitation reaction is carried out in the laminar flow mode, and α, β, δ or γ crystalline phase MnO2 is selectively synthesized by controlling the type, concentration, flow rate and temperature of reactants.

5. The method according to claim 4, characterized in that, The conditions for synthesizing α-crystalline MnO2 are as follows: KMnO4 is used as the oxidant and MnSO4 is used as the manganese source. The aqueous solutions of both are pumped into the microchannel of the microreactor at a flow rate of 500 μL / min, and the reaction temperature is controlled at 80°C.

6. The method according to claim 4, characterized in that, The conditions for synthesizing β-phase MnO2 are as follows: (NH4)2S2O8 is used as the oxidant and MnSO4 is used as the manganese source. The aqueous solutions of both are pumped into the microchannel of the microreactor at a flow rate of 200 μL / min, and the reaction temperature is controlled at 70°C.

7. The method according to claim 4, characterized in that, The conditions for synthesizing δ-phase MnO2 are as follows: KMnO4 is used as the oxidant and MnSO4 is used as the manganese source. The aqueous solutions of both are pumped into the microchannel of the microreactor at a flow rate of 400 μL / min, and the reaction temperature is controlled at 80°C.

8. The method according to claim 4, characterized in that, The conditions for synthesizing γ-crystalline MnO2 are as follows: (NH4)2S2O8 is used as the oxidant and MnSO4 is used as the manganese source. The aqueous solutions of both are pumped into the microchannel of the microreactor at a flow rate of 450 μL / min, and the reaction temperature is controlled at 50°C.

9. The method according to any one of claims 4-8, characterized in that, Following the continuous coprecipitation reaction, the process also includes post-treatment steps such as collecting the precipitate, washing, drying, and calcining at 300-400°C for 1-3 hours.

10. A method for preparing 2,5-dicarboxyfuran based on the selective oxidation of 5-hydroxymethylfurfural, characterized in that, Using the microreactor according to any one of claims 1-3, in the turbulent mode, a gas-liquid-solid three-phase catalytic oxidation reaction is carried out with the α-crystalline phase MnO2 synthesized according to claim 4 or 5 as a catalyst.

11. The method according to claim 10, characterized in that, The reaction raw materials for the gas-liquid-solid three-phase catalytic oxidation reaction are: acetonitrile as solvent, with 5 mg of the catalyst and 5 mg of 5-hydroxymethylfurfural added per milliliter of acetonitrile solvent to form a mixture, while oxygen is introduced simultaneously, and the liquid-to-gas flow ratio of the mixture to the oxygen is 2:1; the reaction conditions are: reaction temperature 60-80°C, residence time 0.5-2 hours.

12. The method according to claim 10, characterized in that, The average particle size of the α-phase MnO2 catalyst is 10-15 μm, and the Zeta potential is -15 to -25 mV.

13. The method according to claim 10, characterized in that, The yield of the 2,5-dicarboxyfuran reached 90%, and the space-time yield reached 23.8 mmol / g / h.

14. The application of the microreactor according to any one of claims 1-3 in a combined process of catalyst synthesis and catalytic reaction.

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