A nano-bubble reinforced micro-channel catalytic reactor and a hydrogen peroxide synthesis method thereof

Abstract

The application belongs to the technical field of chemical reactor and hydrogen peroxide preparation, and particularly relates to a micro-channel catalytic reactor reinforced by nano-bubbles and a hydrogen peroxide synthesis method. The reactor comprises a micro-channel reactor main body, at least one nano-bubble generating unit, a gas-liquid mixing unit and a product collecting unit. The nano-bubble generating unit breaks hydrogen-containing or oxygen-containing gas into 50-300 nm nano-bubbles dispersed in liquid phase, and the nano-bubbles are mixed with another reaction gas stream and then introduced into the micro-channel. The hydrogen peroxide is catalytically generated under the conditions of 0.1-1.0 MPa, 0-35 DEG C and 1-30 seconds of residence. The gas-liquid mass transfer rate is increased by more than 5 times, the selectivity of the hydrogen peroxide can reach more than 92%, the selectivity of the 80-120 nm particle size interval is more than 94%, the volume fraction of free hydrogen in the system is less than 1.0% throughout the process, the operation safety is significantly improved, and the system is suitable for continuous and distributed on-site preparation of hydrogen peroxide.

Description

Technical Field

[0001] This invention belongs to the field of chemical reactor and hydrogen peroxide preparation technology, specifically relating to a nanobubble-enhanced microchannel catalytic reactor and its hydrogen peroxide synthesis method. Background Technology

[0002] Hydrogen peroxide (H2O2) is an environmentally friendly green oxidant that is widely used in papermaking, textiles, electronics, and wastewater treatment, and is an important basic chemical in the chemical industry.

[0003] Currently, the anthraquinone process is the main method for producing hydrogen peroxide in industry. Although this process has achieved large-scale industrial application, it has many inherent drawbacks that are difficult to overcome: the production process is long, the overall energy consumption is high, and the organic waste generated during production causes serious pollution; at the same time, the finished hydrogen peroxide needs to go through transportation and storage before it can be used, making it impossible to achieve on-site production and difficult to adapt to the application requirements of distributed on-site preparation. Therefore, developing a clean and efficient new hydrogen peroxide production process is an important research direction in this field.

[0004] The direct synthesis of hydrogen peroxide from hydrogen and oxygen using a catalyst is the most ideal atom-economic route and is considered a green alternative to the anthraquinone process. However, the direct synthesis of hydrogen peroxide is a gas-liquid-solid three-phase catalytic reaction, requiring the gas to be passed into a solvent and reacted under the action of a catalyst. Its reaction performance is limited by the mass transfer efficiency between the three phases. On the one hand, hydrogen has extremely low solubility and slow diffusion rate in the liquid phase. Traditional methods involve passing hydrogen and oxygen into a high-pressure reactor to increase gas solubility through high pressure. However, high-pressure reaction conditions are harsh and can only be carried out in batch or one-pot production, making it difficult for hydrogen peroxide to meet the application needs of the end market. On the other hand, insufficiently dispersed hydrogen easily accumulates inside the reactor, posing significant safety hazards under high-pressure reaction conditions, thus limiting the industrial-scale promotion of this technology.

[0005] Microchannel reactors, with their small channel size and large specific surface area, can enhance heat and mass transfer in reaction processes to a certain extent, especially in suppressing the risk of explosion of hydrogen-oxygen mixtures. Therefore, they have been applied in the direct catalytic synthesis of hydrogen peroxide in recent years. However, existing microchannel reaction technologies still cannot fundamentally solve the mass transfer bottleneck caused by the low gas solubility, and there is a clear upper limit to their mass transfer enhancement effect and reaction performance improvement.

[0006] In recent years, nanobubbles with a diameter of less than 1 micrometer have shown great application potential in the field of gas-liquid reactions due to their advantages such as huge specific surface area, high stability, extremely fast gas-liquid mass transfer rate, and excellent solubilization properties. However, to date, there are no reports on the technology of integrating nanobubble generating units with microchannel catalytic reactors for the direct synthesis of hydrogen peroxide, and it is impossible to further improve the reaction efficiency and operational safety of direct hydrogen peroxide synthesis through the synergistic effect of the two.

[0007] In addition, existing microchannel reactors face the following technical challenges in actual operation: nanobubbles tend to aggregate and grow within the channel as the reaction proceeds, and existing technologies cannot restore the bubble size in situ during the reaction; the catalyst gradually loses activity due to the adsorption of byproducts during long-term operation, requiring shutdown for replacement or offline regeneration, leading to production interruptions; the liquid phase fluctuates in volume due to evaporation or consumption during the reaction, and existing technologies lack effective automatic compensation methods; a single reaction channel cannot achieve online catalyst replacement, making it difficult to meet the needs of continuous industrial production; and existing microchannel reactors are all open-loop operations, lacking real-time adaptive control capabilities based on product quality. Summary of the Invention

[0008] The purpose of this invention is to provide a nanobubble-enhanced microchannel catalytic reactor and its hydrogen peroxide synthesis method, which effectively improves the problem of low reaction efficiency caused by low hydrogen liquid phase solubility and slow diffusion rate in the existing direct synthesis process. At the same time, it solves the technical problems such as nanobubble aggregation failure during the reaction, inability to regenerate the catalyst online, inability to operate the reactor continuously and without interruption, and lack of intelligent adaptive control.

[0009] The objective of this invention is achieved through the following technical solution: The present invention provides a nanobubble-enhanced microchannel catalytic reactor, comprising a microchannel reactor body, at least one nanobubble generating unit, a gas-liquid mixing unit, and a product collection unit; The microchannel reactor body is equipped with microchannels inside, with a hydraulic diameter of 0.5~3mm. The inner wall of the channel is loaded with a noble metal catalyst for the direct synthesis of hydrogen peroxide from hydrogen and oxygen, forming a wall-supported catalyst coating. The nanobubble generating unit is located before the microchannel inlet or inside the microchannel, and is used to break hydrogen-containing gas or oxygen-containing gas into nanobubbles with a diameter of 50~300nm and disperse them in the liquid phase. The gas-liquid mixing unit is used to uniformly mix hydrogen-containing nanobubble dispersion with oxygen-containing gas flow, or oxygen-containing nanobubble dispersion with hydrogen-containing gas flow, and then send it into the microchannel. The product collection unit is connected to the microchannel outlet and is used to collect the reaction mixture and perform gas-liquid separation to obtain hydrogen peroxide solution. Unreacted gas can be recycled.

[0010] Furthermore, the reactor is also equipped with at least one of the following: a nanobubble particle size classification and screening unit, a shrinkage and expansion structure unit, a multi-temperature zone pulse heating and regeneration unit, a compensation liquid self-water replenishment unit, a multi-module parallel switching unit, and a closed-loop adaptive control unit. The nanobubble particle size classification and screening unit is disposed between the nanobubble generating unit and the microchannel reactor body, and includes at least two levels of microporous sieve plates arranged in series. The first level sieve plate has a pore size of 300~400nm, and the second level sieve plate has a pore size of 120~180nm. The shrinkage-expansion structural unit consists of 3 to 20 alternating shrinkage-expansion structures spaced at intervals along the microchannel axis. Each shrinkage-expansion structural unit is composed of a channel hydraulic diameter that gradually shrinks from 1.5 to 3.0 mm to 0.3 to 0.8 mm and then expands back to its original size. The multi-temperature zone pulse heating regeneration unit consists of at least two temperature control zones arranged along the length of the microchannel reactor body, with an inlet temperature of 20~35℃ and an outlet temperature of 5~10℃. The noble metal catalyst is mounted on the inner wall of the microchannel in the form of a coating to form a wall-mounted catalyst coating. The conductive heating layer is disposed on the back side of the channel wall where the wall-mounted catalyst coating is located and connected to a pulse power supply. The pulse heating time is 0.5~5 seconds and the interval is 30~300 seconds. The self-watering unit of the compensating liquid is a compensating liquid channel parallel to the reaction microchannel. The compensating liquid channel and the reaction microchannel are separated by a microporous membrane with a pore size of 0.2~0.5μm. Deionized water is introduced into the compensating liquid channel. The multi-module parallel switching unit consists of at least two parallel microchannel reactor main modules. The inlet end of each module is connected to an independent nanobubble generating unit and an independent flow regulating valve, and the outlet ends of each module are connected to the same product collection unit. The closed-loop adaptive control unit is an online hydrogen peroxide concentration monitoring sensor connected to the outlet end of the microchannel reactor body. The signal output end of the online concentration sensor is connected to the control module of the nanobubble generating unit and the flow regulating valve on the hydrogen supply pipeline.

[0011] Furthermore, the nanobubble generating unit is selected from any one of hydraulic cavitation, microporous membrane foaming, or ultrasonic cavitation nanobubble generators, or is a series combination structure of hydraulic cavitation component and ultrasonic cavitation component.

[0012] Furthermore, the inner wall of the microchannel is provided with spiral microgrooves, the depth of which is 20~100μm, the width of which is 30~150μm, the spacing between adjacent grooves is 100~500μm, and the helix angle is 15°~45°.

[0013] The present invention also provides a method for synthesizing hydrogen peroxide using the aforementioned nanobubble-enhanced microchannel catalytic reactor, comprising the following steps: (1) Hydrogen-containing gas is made into nanobubbles and dispersed in the liquid phase through a nanobubble generating unit to form a hydrogen-containing nanobubble dispersion; or oxygen-containing gas is made into nanobubbles and dispersed in the liquid phase to form an oxygen-containing nanobubble dispersion. (2) The hydrogen-containing nanobubble dispersion and the oxygen-containing gas flow, or the oxygen-containing nanobubble dispersion and the hydrogen-containing gas flow, are introduced into the microchannel reactor separately or mixed together; (3) The reactants undergo a catalytic reaction in the microchannel reactor to generate hydrogen peroxide; (4) The reaction outlet material is separated into hydrogen peroxide aqueous solution by gas-liquid separation, and the unreacted gas is dried, pressurized and recycled.

[0014] Furthermore, in step (3), the reaction pressure is 0.1~1.0MPa, the reaction temperature is 0~35℃, and the residence time of the reactants in the microchannel is 1~30 seconds; and / or, the oxygen-containing gas is oxygen, air or oxygen-enriched air, and the liquid phase is deionized water.

[0015] Furthermore, in step (3), the mass transfer flux at the gas-liquid interface in the reaction system is increased by more than 5 times compared with the traditional micron bubble system, and the hydrogen peroxide selectivity can reach more than 92%; when the nanobubble particle size is in the range of 80~120nm, the hydrogen peroxide selectivity can reach more than 94%; and during the reaction process, the free hydrogen gas integral number at each point in the microchannel is less than 1.0%, which is lower than the lower explosive limit of hydrogen in air.

[0016] The beneficial effects of this invention are as follows: This invention organically integrates a nanobubble generating unit with a microchannel catalytic reactor, fully combining the solubilizing and efficient mass transfer characteristics of nanobubbles with the high specific surface area advantage of the microchannel reactor. This fundamentally overcomes the mass transfer bottleneck caused by low gas solubility in traditional gas-liquid reaction systems. The nanobubbles generated in the system can increase the gas-liquid specific surface area by 2-3 orders of magnitude compared to traditional micron-bubble systems, and increase the gas-liquid interface mass transfer flux by more than 5 times. Simultaneously, by employing a feeding method that pre-disperses the reactant gas in the form of nanobubbles in the liquid phase, local accumulation of gaseous hydrogen inside the reactor is effectively avoided. The free hydrogen gas fraction along the process is consistently below 1.0%, far below the lower explosive limit of 4 vol% for hydrogen in air, significantly improving the operational safety of the reaction process.

[0017] This invention creatively integrates six innovative functions into a single microchannel reactor: nanobubble size classification and screening, in-situ bubble regeneration via a shrinking-expansion structure, in-situ catalyst regeneration via pulse heating, osmotic pressure self-replenishment, multi-module parallel switching, and closed-loop adaptive control of product concentration, forming a multi-level synergistic enhancement system. Specifically: size classification and screening allows for gradient utilization of bubbles of different sizes within their respective suitable channels, avoiding aggregation losses caused by wide particle size distributions; the shrinking-expansion structure unit achieves in-situ renewal of bubble size during the reaction process through compression-expansion cycles, maintaining a high specific surface area throughout; pulse heating removes adsorbed byproducts from the catalyst surface in situ through periodic thermal oscillation, extending catalyst lifespan by 50%–200%; osmotic pressure self-replenishment automatically maintains water balance without external power; multi-module parallel operation enables continuous production with online catalyst regeneration without shutdown; and closed-loop feedback allows the reactor to self-optimize its operation based on product quality. Under these synergistic effects, hydrogen peroxide selectivity can reach over 92%, and over 94% in the 80–120 nm particle size range, with a significantly extended catalyst lifespan, making it suitable for continuous, distributed on-site hydrogen peroxide production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall structure and process flow of the nanobubble-enhanced microchannel catalytic reactor of the present invention.

[0020] Figure 2 This is a partial axonometric sectional view of the main body of the microchannel reactor of the present invention, and a partial enlarged view of the wall-supported catalytic interface is given (point A in the figure). Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used herein is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, regarding numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention.

[0023] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0024] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0025] The microchannel reactors used in the following embodiments have the following common structures: a particle size classification screening unit composed of two-stage microporous sieves is provided before the inlet of the reaction microchannel, with the first-stage sieve having a pore size of 350 nm and the second-stage sieve having a pore size of 150 nm; the inner wall of the reaction microchannel is provided with spiral microgrooves, 50 μm deep, 80 μm wide, 200 μm apart, and with a spiral angle of 30°; five contraction and expansion structural units are provided along the flow path, with the hydraulic diameter shrinking from 1.5 mm to 0.5 mm and then recovering; three temperature control zones of 30°C, 20°C, and 5°C are provided along the length direction; a conductive heating layer is provided on the back side of the channel wall where the catalyst coating is located, with pulse heating for two seconds and an interval of 120 seconds; a compensation liquid channel separated by a 0.3 μm microporous membrane is provided next to the reaction microchannel; an online hydrogen peroxide concentration sensor is provided at the outlet to provide feedback control of the power of the nanobubble generating unit and the hydrogen flow rate; when two parallel reaction modules are used, each module is adjusted independently, and the deactivated module can be regenerated and switched online.

[0026] I. Reactor Structure and Working Principle like Figure 1 As shown, the nanobubble-enhanced microchannel catalytic reactor of the present invention includes, along the material flow direction, a nanobubble generating unit (1), a particle size classification and screening unit (2), a gas-liquid mixing unit (3), a microchannel reactor body (4), and a product collection unit (6) connected in sequence. The nanobubble generating unit (1) can be set before the inlet of the reaction microchannel or integrated inside the reaction microchannel, and its number is at least one; one stream of reaction gas and liquid phase enters the nanobubble generating unit (1), and another stream of reaction gas is directly sent to the gas-liquid mixing unit (3), and a hydrogen flow regulating valve (9) is set on the hydrogen supply pipeline.

[0027] like Figure 1 As shown, the particle size classification and screening unit (2) is located between the nanobubble generating unit (1) and the microchannel reactor body (4), and includes a first-stage microporous sieve plate (21) and a second-stage microporous sieve plate (22) connected in series. The dispersion containing nanobubbles flows through the two sieve plates in sequence: bubbles with a particle size larger than the pore size of the first-stage microporous sieve plate (21) are intercepted and returned to the nanobubble generating unit (1) through the return pipe (25) to be broken up again; bubbles with a particle size between the pore sizes of the two sieve plates enter the auxiliary reaction channel (24); bubbles with a particle size smaller than the pore size of the second-stage microporous sieve plate (22) enter the main reaction channel (23); the main reaction channel (23) and the auxiliary reaction channel (24) merge before the microchannel outlet, so that bubbles of different particle sizes can be utilized in a gradient manner.

[0028] like Figure 2 As shown, a reaction microchannel (41) is set inside the main body (4) of the microchannel reactor. The hydraulic diameter of the reaction microchannel (41) is 0.5~3mm. The inner wall is coated with a noble metal catalyst (47) to form a continuous wall-supported catalyst coating. The noble metal catalyst (47) includes, but is not limited to, supported palladium-based catalysts such as Pd / TS-1, Pd / TiO2, and Pd / Al2O3. The main body (4) of the microchannel reactor can be made of corrosion-resistant and pressure-resistant materials such as 316L stainless steel and plexiglass. The length of the reaction microchannel (41) can be adjusted according to the residence time requirements.

[0029] like Figure 2 As shown, the inner wall of the reaction microchannel (41) is provided with spiral microgrooves (42) distributed in a spiral shape along the axial direction. The depth is 20~100μm, the width is 30~150μm, the spacing between adjacent grooves is 100~500μm, and the spiral angle is 15°~45°. These grooves are used to induce local turbulence and enhance the contact between the material and the catalyst on the wall.

[0030] like Figure 2 As shown, 3 to 20 alternating contraction and expansion structural units (43) are arranged axially within the reaction microchannel (41). Each contraction and expansion structural unit (43) includes a contraction section (431) and an expansion section (432). The hydraulic diameter gradually shrinks from 1.5 to 3.0 mm along the contraction section (431) to 0.3 to 0.8 mm, and then gradually returns to its original size through the expansion section (432). The length ratio of the contraction section (431) to the expansion section (432) is 1.0:1.2 to 1.0:2.5. The nanobubbles are compressed in the contraction section (431), causing some gas to dissolve into the liquid phase. They are then re-precipitated in the expansion section (432) to form secondary nanobubbles with smaller particle sizes, thereby achieving in-situ renewal of bubble particle size during the reaction.

[0031] like Figure 2As shown, the main body (4) of the microchannel reactor is divided into at least two temperature control zones along its length. The inlet temperature is 20~35℃ and the outlet temperature is 5~10℃, forming a temperature decreasing distribution along the process. This allows the material to react rapidly at a relatively high temperature first and then suppress the decomposition of hydrogen peroxide at a lower temperature. The noble metal catalyst (47) is coated on the inner wall of the reaction microchannel (41) to form a wall-mounted catalyst coating. A conductive heating layer (44) is set on the back side of the channel wall where the wall-mounted catalyst coating is located and connected to a pulse power supply. The pulse heating time is 0.5~5 seconds and the interval is 30~300 seconds, so that the surface of the wall-mounted catalyst coating is instantly heated by 20~50℃ and then recovers, realizing the in-situ thermal regeneration of the catalyst.

[0032] like Figure 2 As shown, the main body (4) of the microchannel reactor is provided with a compensation liquid channel (45) parallel to the reaction microchannel (41). The two are separated by a microporous membrane (46) with a pore size of 0.2~0.5μm. Deionized water is introduced into the compensation liquid channel (45). When the water in the reaction microchannel (41) is consumed due to reaction and evaporation and an osmotic pressure difference is formed on both sides, the deionized water automatically seeps into the reaction microchannel (41) through the microporous membrane (46) to replenish it without the need for external power.

[0033] like Figure 1 As shown, the reactor contains at least two parallel reaction modules, namely the first reaction module (11) and the second reaction module (12). The inlet end of each reaction module is connected to an independent nanobubble generating unit (1) and an independent flow regulating valve, and the outlet ends are connected to the same product collection unit (6). Each reaction module independently adjusts the feed flow rate according to its own catalyst activity state. The deactivated module can be shut down and regenerated online, while the other modules continue to operate.

[0034] like Figure 1 As shown, the outlet end of the microchannel reactor body (4) is connected to an online hydrogen peroxide concentration sensor (7), and its signal output end is connected to a control module (8). The output end of the control module (8) is connected to the power control end of the nanobubble generating unit (1) and the hydrogen flow regulating valve (9) on the hydrogen supply pipeline. When the concentration is lower than the set lower limit, the control module (8) automatically increases the power of the nanobubble generating unit (1) or increases the opening of the hydrogen flow regulating valve (9). When the concentration is higher than the set upper limit, it reverses the adjustment, thereby forming a closed-loop adaptive control.

[0035] The nanobubble generating unit (1) can be selected from any one of hydraulic cavitation, microporous membrane foaming, or ultrasonic cavitation nanobubble generators, preferably a combination structure of hydraulic cavitation component and ultrasonic cavitation component connected in series. The obtained nanobubbles can maintain good dispersion stability within 60 minutes: in deionized water at 25℃ and normal pressure, the initial bubble number concentration is 1.2 × 10⁻⁶. 8The average particle size was 120 nm, and after standing for 30 minutes, the average particle size was 130 nm and the number concentration was 1.1 × 10⁻⁶. 8 The number concentration remained at 1.0 × 10⁶ cells / mL after 60 minutes, with an average particle size of 140 nm. 8 A concentration of 1 or more per mL can meet the requirement of residence time of several seconds to tens of seconds within the reaction microchannel.

[0036] The gas-liquid mixing unit (3) is used to uniformly mix the hydrogen-containing nanobubble dispersion with an oxygen-containing gas stream, or the oxygen-containing nanobubble dispersion with a hydrogen-containing gas stream, and then send it into the main body of the microchannel reactor (4). The oxygen-containing gas can be pure oxygen, air, or oxygen-enriched air. The product collection unit (6) is equipped with a gas-liquid separation component (61). After the reaction mixture is separated by the gas-liquid separation component (61), the hydrogen peroxide aqueous solution is output as the product, and the unreacted gas is dried, pressurized, and returned to the reaction system for recycling through the circulation pipeline (10).

[0037] The overall working process of the reactor is as follows: After hydrogen-containing gas forms a nanobubble dispersion through the nanobubble generating unit (1), it flows through the particle size classification and screening unit (2) and is divided into the main reaction channel (23) or auxiliary reaction channel (24) according to the particle size. Then, it is pre-mixed with oxygen-containing gas through the gas-liquid mixing unit (3) and enters the main body (4) of the microchannel reactor. In the reaction microchannel (41), the material comes into contact with the noble metal catalyst (47) under the turbulence enhancement induced by the spiral microgroove (42). When flowing through the shrinking and expanding structure unit (43), it undergoes multiple compression and expansion cycles to renew the bubble particle size in situ. The temperature field decreases along the way. The rapid reaction and low-temperature protection are completed sequentially. At the same time, the catalyst coating on the wall is periodically pulsed and regenerated in situ by the conductive heating layer (44) on the back side of the wall. The water consumed in the reaction is automatically replenished by the compensation liquid channel (45) through the microporous membrane (46). The outlet concentration signal is sent to the control module (8) through the online hydrogen peroxide concentration sensor (7) to adjust the power of the nanobubble generating unit (1) and the hydrogen flow regulating valve (9) in real time. After the mixed liquid flows out, it enters the product collection unit (6) and obtains hydrogen peroxide product through the gas-liquid separation component (61). The unreacted gas is recycled through the circulation pipeline (10). When the first reaction module (11) and the second reaction module (12) are connected in parallel, each module adjusts its operating parameters independently. The deactivated module is switched and regenerated online without affecting the total output.

[0038] II. Hydrogen peroxide synthesis method The method for synthesizing hydrogen peroxide using the above-mentioned reactor specifically includes the following steps: (I) Preparation of nanobubble dispersion: Hydrogen-containing nanobubble dispersion is prepared by dispersing hydrogen-containing gas in a liquid medium through a nanobubble generating unit (1), or oxygen-containing nanobubble dispersion is prepared by dispersing oxygen-containing gas (oxygen, air or oxygen-enriched air) in a liquid medium, wherein the liquid medium is a reaction solvent such as deionized water.

[0039] (II) Nanobubble particle size classification and diversion: The dispersion obtained in step (1) is passed into the particle size classification and screening unit (2). Bubbles with a particle size larger than the pore size (300~400nm) of the first-stage microporous sieve plate (21) are refluxed and crushed through the reflux pipeline (25). Bubbles with a particle size between the pore sizes of the two-stage sieve plates enter the auxiliary reaction channel (24). Bubbles with a particle size smaller than the pore size (120~180nm) of the second-stage microporous sieve plate (22) enter the main reaction channel (23). The materials in the two channels react with the catalyst and merge before the outlet.

[0040] (III) Gas-liquid mixing and catalytic reaction: The hydrogen-containing nanobubble dispersion and the oxygen-containing stream are fed into the gas-liquid mixing unit (3) and then into the main body (4) of the microchannel reactor. In the reaction microchannel (41), the material strengthens the contact with the catalyst on the wall under the turbulence induced by the spiral microgroove (42). When flowing through the shrinking and expanding structure unit (43), it is repeatedly compressed and expanded to update the bubble particle size in situ. It reacts in the multi-temperature control zone with decreasing temperature along the process. At the same time, the catalyst is regenerated in situ by pulse heating by the conductive heating layer (44). Water is automatically replenished by the compensation liquid channel (45) through the microporous membrane (46). The operating parameters are optimized in real time by the online hydrogen peroxide concentration sensor (7) through the control module (8). The reaction pressure is 0.1~1.0MPa, the reaction temperature is 0~35℃, and the residence time is 1~30 seconds. Under the action of the noble metal catalyst (47), hydrogen and oxygen react to generate hydrogen peroxide.

[0041] (iv) Product separation and gas circulation: The material exiting the reaction microchannel (41) enters the product collection unit (6), and hydrogen peroxide aqueous solution is obtained through the gas-liquid separation component (61). The separated unreacted gas is dried, pressurized, and then returned to the reaction system for recycling through the circulation pipeline (10).

[0042] (v) Continuous operation of multiple modules in parallel: When at least two parallel reaction modules are used, the catalyst activity status of each module is determined based on the outlet concentration or pressure drop, and the feed flow rate is adjusted independently. When the catalyst activity of any module drops to the set threshold, the feed of that module is shut off and online regeneration is started, while the remaining modules maintain normal reaction operation, so as to achieve uninterrupted continuous production of the system.

[0043] To investigate the effect of nanobubble particle size on reaction performance, multiple particle size gradient experiments confirmed that when the nanobubble particle size is in the range of 50~300nm, the hydrogen peroxide selectivity and product concentration are better than those of the traditional non-bubble system; the reaction performance is better when the particle size is less than 150nm, and the reaction effect is best in the range of 80~120nm. This particle size range can provide a larger gas-liquid specific surface area and a higher interfacial mass transfer rate.

[0044] To investigate the in-situ renewal effect of the shrinkage-expansion structural unit (43) on bubble particle size, a nanoparticle tracking analyzer was used to detect the average particle size at the outlet before entering the shrinkage-expansion structural unit, after passing through three shrinkage-expansion structural units, and after passing through all shrinkage-expansion structural units. The results showed that the average particle size before entering was 145 nm, after passing through three shrinkage-expansion structural units it was 125 nm, a decrease of about 14% compared to before entering, and the outlet size after passing through all shrinkage-expansion structural units was 118 nm. This indicates that the compression and expansion cycle can break up the agglomerated and grown bubbles, achieving in-situ recovery and renewal of particle size.

[0045] To investigate the effect of pulse heating on catalyst lifespan, comparative experiments were conducted under the same reaction conditions with and without pulse heating regeneration. The results showed that without pulse heating, the catalyst activity decreased to 65% of its initial value after 48 hours of continuous operation; with pulse heating (pulse duration of two seconds, interval of 120 seconds), the activity remained above 82% of its initial value after 72 hours of continuous operation.

[0046] To investigate the self-replenishment effect of the compensation liquid channel (45), the change in liquid volume in the reaction microchannel (41) was monitored during six hours of continuous operation. The results showed that the liquid volume decreased by about 12% without the compensation liquid channel. After setting the compensation liquid channel (45), the liquid volume was automatically replenished by relying on the osmotic pressure difference on both sides of the microporous membrane (46), and the decrease in liquid volume was controlled within 2%.

[0047] To investigate operational safety, hydrogen concentration distribution was tested under the same reaction conditions (1.0 MPa, 25 °C, hydrogen flow rate 20 mL / min, oxygen flow rate 40 mL / min, deionized water flow rate 10 mL / min) using a nanobubble system with an average particle size of 120 nm and a traditional microbubble system with an average particle size of 80 μm. Three detection points were set along the axial direction of the reaction microchannel: the inlet section, the middle section, and the outlet section. Online sampling was performed using a micro gas chromatograph, and the concentration of dissolved hydrogen in the liquid phase and the integral number of free hydrogen in the gas phase were detected simultaneously. The results are shown in Table 1.

[0048] Table 1 Test Results

[0049] Test results show that the lower limit of the explosive volume fraction of hydrogen in air is 4 vol%. In the traditional micron bubble system, the free hydrogen gas fraction at the inlet reaches 4.2%, which exceeds the lower limit of hydrogen explosion and poses a risk of local combustion and explosion. In contrast, in the nanobubble system of this invention, the free hydrogen gas fraction at all three detection points is less than 1.0 vol%, far below the lower limit of explosion. At the same time, the concentration of dissolved hydrogen in the liquid phase in the nanobubble system is 2.5 to 3 times that in the micron bubble system, indicating that hydrogen is more efficiently dispersed and dissolved in the liquid phase, effectively avoiding the local accumulation of gaseous hydrogen and significantly improving the operational safety of the reaction process.

[0050] To verify the continuous operation effect of parallel multi-module differentiated operation and online switching regeneration, a 72-hour continuous operation test was conducted using two parallel modules. Initially, both modules operated at full load. After 48 hours, the catalyst activity in module A decreased to 70% of its initial value. The feed to module A was then shut off, and hot nitrogen was introduced for online regeneration (2 hours), during which time module B maintained full-load production. After module A's regeneration was completed, the feed was restored, and module B continued operation. The total output fluctuation during the entire 72-hour test was less than 5%, achieving truly uninterrupted continuous production.

[0051] To verify the response performance of the closed-loop adaptive control system, the outlet hydrogen peroxide concentration setpoint was manually adjusted from 2.2 wt% to 2.8 wt%. Within 30 seconds, the control system automatically increased the power of the nanobubble generator unit by 20% and simultaneously increased the hydrogen flow rate from 20 mL / min to 25 mL / min. The outlet concentration recovered to near the new setpoint of 2.8 wt% within 2 minutes and remained stable, demonstrating that the feedback control system has good response speed and adjustment accuracy.

[0052] Under the synergistic effect of the above structure and operation, the introduction of nanobubbles increases the gas-liquid specific surface area by 2 to 3 orders of magnitude compared with traditional micron bubbles, significantly improving the gas-liquid mass transfer rate and increasing the reaction rate by more than 5 times compared with traditional microchannel reactors. With the combined effect of multi-level synergistic enhancement methods such as particle size classification and screening, in-situ renewal of shrinkage and expansion structures, in-situ regeneration by pulse heating, osmotic pressure self-replenishment, multi-module parallel switching and closed-loop adaptive control, the selectivity of hydrogen peroxide can reach more than 92%, and the selectivity in the 80-120nm nanobubble range can reach more than 94%. The catalyst life is extended by 50% to 200%. The reactor can operate continuously and without interruption. It can realize the continuous, miniaturized and safe production of hydrogen peroxide, and is suitable for distributed on-site hydrogen peroxide production application scenarios.

[0053] Example 1 This embodiment uses a hydraulic cavitation nanobubble generator to construct the reaction system, and the specific operation is as follows: Using deionized water as the liquid medium, with a hydrogen flow rate of 20 mL / min and a deionized water flow rate of 10 mL / min, a hydrogen-containing nanobubble dispersion was prepared using a hydraulic cavitation nanobubble generator. The initial average particle size of the nanobubbles was characterized by a nanoparticle tracking analyzer, revealing a particle size distribution of 120 nm. The hydrogen-containing nanobubble dispersion was then passed through a nanobubble particle size classification and sieving unit. This unit consisted of two stages of microporous sieves connected in series: the first stage had a pore size of 350 nm, and the second stage had a pore size of 150 nm. After classification, approximately 65% ​​of the nanobubbles were smaller than 150 nm. Approximately 30% of the nanobubbles (with a particle size between 150 and 350 nm) enter the main reaction channel, while about 5% of the large bubbles are retained and returned to the nanobubble generating unit for re-breaking. The oxygen flow rate is controlled at 40 mL / min, and the oxygen and the above-mentioned hydrogen-containing nanobubble dispersion are sent to the gas-liquid mixing unit for pre-mixing. The mixed material is then sent to a microchannel reactor made of 316L stainless steel. The microchannel adopts the aforementioned common structure (including spiral microgrooves, 5 shrinkage and expansion structural units, three temperature zones, pulse heating layer, and compensation liquid channel), and the inner wall of the channel is loaded with 1 wt% Pd / TS-1 catalyst.

[0054] The reaction system pressure was controlled at 1.0 MPa, the reaction temperature at 25°C, and the residence time of the reactants in the microchannel was 5 seconds. Under the action of the catalyst, hydrogen and oxygen underwent a catalytic reaction to produce hydrogen peroxide.

[0055] After the reaction, the material flows out of the microchannel outlet into the product collection unit, where it undergoes gas-liquid separation to obtain a hydrogen peroxide aqueous solution. Testing showed that the hydrogen peroxide concentration in the outlet liquid phase was 2.2 wt%, and the reaction selectivity was 94.1%. During continuous operation for 72 hours, the catalyst activity remained stable; the automatic water replenishment rate of the compensation liquid channel was approximately 1.5 mL / h; and the outlet concentration fluctuation was controlled within ±0.1 wt%.

[0056] Example 2 Using deionized water as the liquid medium and oxygen-enriched air with an oxygen volume fraction of 40 vol% as the reaction gas source, with the oxygen-enriched air flow rate controlled at 40 mL / min and the deionized water flow rate at 10 mL / min, an oxygen-containing nanobubble dispersion was prepared using a microporous membrane foaming nanobubble generator. Dynamic light scattering instrumentation showed that the initial average particle size of the nanobubbles was 80 nm. The oxygen-containing nanobubble dispersion was then passed through a nanobubble particle size classification and screening unit (first-stage sieve aperture 300 nm, second-stage sieve aperture 130 nm). Nanobubbles with a particle size smaller than 130 nm entered the main reaction channel, while those with a particle size between 130 and 300 nm entered the auxiliary reaction channel. Hydrogen flow rate was controlled at 20 mL / min, and the hydrogen was uniformly mixed with the above-split oxygen-containing nanobubble dispersion in a gas-liquid mixing unit before the microchannel inlet. The mixed material was then fed into a 316L stainless steel microchannel reactor with the same structure as in Example 1, loaded with 1 wt% Pd / TS-1 catalyst.

[0057] The reaction system pressure was controlled at 1.2 MPa, the reaction temperature at 25°C, the residence time of the reactants in the microchannel was 5 seconds, and the pulse heating parameters were: pulse time 1.5 seconds, interval 100 seconds, pulse power density 4 W / cm². Under the action of the catalyst, hydrogen and oxygen reacted to produce hydrogen peroxide.

[0058] After the reaction, the material was separated into gas and liquid phases to obtain an aqueous hydrogen peroxide solution. Testing showed that the hydrogen peroxide concentration in the outlet liquid phase was 2.8 wt%, and the reaction selectivity was 95.5%. After 72 hours of continuous operation, the catalyst activity retention rate was 83% of the initial value, while the activity retention rate of the control group without pulse heating was only 62% under the same conditions.

[0059] Example 3 This embodiment is a verification experiment of nanobubble particle size gradient. The specific operation is as follows: Hydrogen-containing nanobubble dispersions with average particle sizes of 200 nm and 300 nm were prepared by adjusting the hydrocavitation intensity and liquid flow rate using a hydraulic cavitation nanobubble generator. These dispersions were then processed by a nanobubble particle size classification and screening unit before entering their respective reaction channels. The hydrogen flow rate was controlled at 20 mL / min and the oxygen flow rate at 40 mL / min. The oxygen was premixed with the hydrogen-containing nanobubble dispersions and then fed into a microchannel reactor loaded with 1 wt% Pd / TS-1 catalyst, identical to that used in Example 1.

[0060] The reaction system pressure was controlled at 1.0 MPa, the reaction temperature at 25°C, and the residence time of the reactants in the microchannel was 5 seconds to carry out the catalytic reaction.

[0061] The reaction results are as follows: When the average particle size of the hydrogen-containing nanobubbles is 200 nm, the hydrogen peroxide concentration in the outlet liquid phase is 1.6 wt%, and the reaction selectivity is 89.5%. When the average particle size of hydrogen-containing nanobubbles is 300 nm, the hydrogen peroxide concentration in the outlet liquid phase is 1.1 wt%, and the reaction selectivity is 84.0%.

[0062] The above results show that within the particle size range of 50~300 nm, the smaller the nanobubble particle size, the better the reaction performance; even the nanobubble system with a particle size of 300 nm still has significantly better reaction performance than the traditional micron bubble reaction system.

[0063] Example 4 This example is a reaction safety comparison and verification experiment, and the specific operation is as follows: The reaction conditions were exactly the same as in Example 1: a hydro-cavitation nanobubble generator, hydrogen flow rate of 20 mL / min, oxygen flow rate of 40 mL / min, deionized water flow rate of 10 mL / min, a 316L stainless steel microchannel reactor loaded with 1 wt% Pd / TS-1 catalyst, reaction pressure of 1.0 MPa, reaction temperature of 25 °C, and residence time of 5 seconds; parallel experiments were conducted using a nanobubble system with an average particle size of 120 nm and a conventional microbubble system with an average particle size of 80 μm.

[0064] Three detection points were set along the axial direction inside the microchannel reactor: the inlet section, the middle section, and the outlet section. Online sampling was performed using a micro gas chromatograph to detect the integral number of free hydrogen gas in the gas phase at each point.

[0065] The test results show that in the nanobubble system, the free hydrogen gas fraction at the inlet, middle, and outlet points is all below 1.0 vol%, far below the lower explosive limit of 4 vol% for hydrogen in air. In contrast, in the traditional microbubble system, the free hydrogen gas fraction at the inlet reaches 4.2 vol%, exceeding the lower explosive limit and posing a risk of localized combustion and explosion. These results demonstrate that the reaction system using nanobubble dispersion in this invention has significant advantages in terms of operational safety.

[0066] Example 5 This embodiment uses two parallel microchannel reactor modules to verify the effect of uninterrupted continuous production. The specific operation is as follows: Both Module A and Module B adopted the exact same reactor structure as in Example 1, and were loaded with the same 1 wt% Pd / TS-1 catalyst. In the initial stage, both modules were operated at full load under the following conditions: hydrogen flow rate of 20 mL / min, oxygen flow rate of 40 mL / min, deionized water flow rate of 10 mL / min, pressure of 1.0 MPa, temperature of 25 °C, and residence time of 5 seconds.

[0067] After 48 hours of operation, the hydrogen peroxide concentration at the outlet of module A decreased from the initial 2.2 wt% to 1.6 wt%. The hydrogen feed to module A was shut off, and nitrogen (flow rate 50 mL / min, temperature 80℃) was introduced for online regeneration, which took 2 hours. During this period, module B continued to operate at full capacity under the original conditions.

[0068] After module A completes regeneration, feeding resumes, and the outlet concentration recovers to 2.1 wt% within 15 minutes. During the entire 72-hour continuous operation test, the total output of both modules fluctuates by less than 5%.

[0069] Example 6 This embodiment verifies the closed-loop control effect of product concentration feedback to the nanobubble generating unit. The specific operation is as follows: Using the same reactor structure and operating conditions as in Example 1, the outlet hydrogen peroxide concentration was stabilized at 2.2 wt%.

[0070] The concentration setpoint was increased from 2.2wt% to 2.8wt% in a step. The control system detected the deviation within 10 seconds and then automatically executed: (1) within 15 seconds, the ultrasonic power of the nanobubble generating unit was increased from 50W to 75W, so that the average particle size of the nanobubbles was reduced from 120nm to 95nm; (2) within 20 seconds, the hydrogen flow rate was gradually increased from 20mL / min to 28mL / min.

[0071] The outlet concentration stabilized at 2.75 wt% (deviation <2%) at t=120 seconds, and the free hydrogen gas integral was always below 0.9 vol throughout the process.

[0072] Comparative Example 1 This comparative example uses a traditional micron-bubble reaction system that does not employ nanobubbles. The specific operation is as follows: Hydrogen-containing microbubbles were generated using a conventional microporous aeration method. The average particle size of the microbubbles was 80 μm. The remaining reaction conditions were exactly the same as in Example 1: hydrogen flow rate of 20 mL / min, oxygen flow rate of 40 mL / min, deionized water flow rate of 10 mL / min, a 316L stainless steel microchannel reactor loaded with 1 wt% Pd / TS-1 catalyst, reaction pressure of 1.0 MPa, reaction temperature of 25 °C, and material residence time of 5 seconds.

[0073] After the reaction, the concentration of hydrogen peroxide in the outlet liquid phase was only 0.6 wt%, and the reaction selectivity was only 78%, which is far lower than the reaction performance of the nanobubble system of this invention. This proves that the introduction of nanobubbles plays a decisive role in improving the efficiency of the direct synthesis reaction of hydrogen peroxide.

[0074] Comparative Example 2 This comparative example uses the exact same reactor structure and operating conditions as Example 1, but the pulse power supply to the conductive heating layer is turned off, i.e., pulse heating regeneration is not performed, while the other conditions remain unchanged.

[0075] The reaction results showed that after 48 hours of continuous operation, the hydrogen peroxide concentration at the outlet of the catalyst without pulse heating regeneration decreased from the initial 2.2 wt% to 1.4 wt% (activity retention rate of about 64%), and further decreased to 0.9 wt% (activity retention rate of about 41%) after 72 hours, with an obvious byproduct adsorption layer detected on the catalyst surface; while after 72 hours of operation, the outlet concentration of the catalyst with pulse heating regeneration in Example 1 was still 2.1 wt% (activity retention rate of about 95%), and there was no obvious accumulation of byproducts on the catalyst surface.

[0076] This comparative example demonstrates that the pulse heating in-situ regeneration mechanism employed in this invention can effectively extend the service life of the catalyst in continuous reactions, playing an important role in maintaining the long-term stable operation of the reactor.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A nanobubble-reinforced microchannel catalytic reactor, characterized in that, It includes a microchannel reactor body, at least one nanobubble generating unit, a gas-liquid mixing unit, and a product collection unit; The microchannel reactor body is equipped with microchannels inside, with a hydraulic diameter of 0.5~3mm. The inner wall of the channel is loaded with a noble metal catalyst for the direct synthesis of hydrogen peroxide from hydrogen and oxygen, forming a wall-supported catalyst coating. The nanobubble generating unit is located before the microchannel inlet or inside the microchannel, and is used to break hydrogen-containing gas or oxygen-containing gas into nanobubbles with a diameter of 50~300nm and disperse them in the liquid phase. The gas-liquid mixing unit is used to uniformly mix hydrogen-containing nanobubble dispersion with oxygen-containing gas flow, or oxygen-containing nanobubble dispersion with hydrogen-containing gas flow, and then send it into the microchannel. The product collection unit is connected to the microchannel outlet and is used to collect the reaction mixture and perform gas-liquid separation to obtain hydrogen peroxide solution. Unreacted gas can be recycled.

2. The nanobubble-reinforced microchannel catalytic reactor according to claim 1, characterized in that, The reactor is also equipped with at least one of the following: a nanobubble particle size classification and screening unit, a shrinkage and expansion structure unit, a multi-temperature zone pulse heating and regeneration unit, a self-water replenishment unit for compensating liquid, a multi-module parallel switching unit, and a closed-loop adaptive control unit. The nanobubble particle size classification and screening unit is disposed between the nanobubble generating unit and the microchannel reactor body, and includes at least two levels of microporous sieve plates arranged in series. The first level sieve plate has a pore size of 300~400nm, and the second level sieve plate has a pore size of 120~180nm. The shrinkage-expansion structural unit consists of 3 to 20 alternating shrinkage-expansion structures spaced at intervals along the microchannel axis. Each shrinkage-expansion structural unit is composed of a channel hydraulic diameter that gradually shrinks from 1.5 to 3.0 mm to 0.3 to 0.8 mm and then expands back to its original size. The multi-temperature zone pulse heating regeneration unit consists of at least two temperature control zones arranged along the length of the microchannel reactor body, with an inlet temperature of 20~35℃ and an outlet temperature of 5~10℃. The noble metal catalyst is mounted on the inner wall of the microchannel in the form of a coating to form a wall-mounted catalyst coating. The conductive heating layer is disposed on the back side of the channel wall where the wall-mounted catalyst coating is located and connected to a pulse power supply. The pulse heating time is 0.5~5 seconds and the interval is 30~300 seconds. The self-watering unit of the compensating liquid is a compensating liquid channel parallel to the reaction microchannel. The compensating liquid channel and the reaction microchannel are separated by a microporous membrane with a pore size of 0.2~0.5μm. Deionized water is introduced into the compensating liquid channel. The multi-module parallel switching unit consists of at least two parallel microchannel reactor main modules. The inlet end of each module is connected to an independent nanobubble generating unit and an independent flow regulating valve, and the outlet ends of each module are connected to the same product collection unit. The closed-loop adaptive control unit is an online hydrogen peroxide concentration monitoring sensor connected to the outlet end of the microchannel reactor body. The signal output end of the online concentration sensor is connected to the control module of the nanobubble generating unit and the flow regulating valve on the hydrogen supply pipeline.

3. The nanobubble-reinforced microchannel catalytic reactor according to claim 1, characterized in that, The nanobubble generating unit is selected from any one of the hydraulic cavitation type, microporous membrane foaming type, or ultrasonic cavitation type nanobubble generators, or is a series combination structure of hydraulic cavitation component and ultrasonic cavitation component.

4. The nanobubble-reinforced microchannel catalytic reactor according to claim 1, characterized in that, The inner wall of the microchannel is provided with spiral microgrooves, the depth of which is 20~100μm, the width of which is 30~150μm, the spacing between adjacent grooves is 100~500μm, and the helix angle is 15°~45°.

5. A method for synthesizing hydrogen peroxide using a nanobubble-enhanced microchannel catalytic reactor according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Hydrogen-containing gas is made into nanobubbles and dispersed in the liquid phase through a nanobubble generating unit to form a hydrogen-containing nanobubble dispersion; or oxygen-containing gas is made into nanobubbles and dispersed in the liquid phase to form an oxygen-containing nanobubble dispersion. (2) The hydrogen-containing nanobubble dispersion and the oxygen-containing gas flow, or the oxygen-containing nanobubble dispersion and the hydrogen-containing gas flow, are introduced into the microchannel reactor separately or mixed together; (3) The reactants undergo a catalytic reaction in the microchannel reactor to generate hydrogen peroxide; (4) The reaction outlet material is separated into hydrogen peroxide aqueous solution by gas-liquid separation, and the unreacted gas is dried, pressurized and recycled.

6. The method for synthesizing hydrogen peroxide according to claim 5, characterized in that, In step (3), the reaction pressure is 0.1~1.0MPa, the reaction temperature is 0~35℃, and the residence time of the reactants in the microchannel is 1~30 seconds; and / or, the oxygen-containing gas is oxygen, air or oxygen-enriched air, and the liquid phase is deionized water.

7. The method for synthesizing hydrogen peroxide according to claim 5, characterized in that, In step (3), the mass transfer flux at the gas-liquid interface in the reaction system is increased by more than 5 times compared with the traditional micron bubble system, and the hydrogen peroxide selectivity can reach more than 92%; when the nanobubble particle size is in the range of 80~120nm, the hydrogen peroxide selectivity can reach more than 94%; and the free hydrogen gas integral number at each point in the microchannel during the reaction process is less than 1.0%, which is lower than the lower explosive limit of hydrogen in air.

Images