Microchannel multitubular reactor and process for the preparation of propylene carbonate

Abstract

The present application relates to the field of propylene carbonate synthesis, discloses a kind of microchannel array tube reactor and the method for preparing propylene carbonate.The microchannel array tube reactor includes outer tube, inner tube is arranged in outer tube, and the annular gap is formed between the inner tube and outer tube;Along the direction of flow, the inner tube of the microchannel array tube reactor includes alternately arranged venturi and gas-liquid reaction tube, forms flow field;Wherein, the gas-liquid reaction tube is provided with component, for the mixing reaction of fluid.The microchannel array tube reactor of the present application realizes the effective control of thermal risk, and the propylene carbonate is prepared by the microchannel array tube reactor, improves the selectivity of propylene carbonate, greatly improves reaction efficiency.

Description

Technical Field

[0001] This invention relates to the field of propylene carbonate synthesis, and more specifically to a microchannel tubular reactor and a method for preparing propylene carbonate. Background Technology

[0002] Since the Industrial Revolution, rapid advancements in technology and the massive use of fossil fuels have led to the emission of large amounts of industrial waste gas into the atmosphere, causing a sharp rise in atmospheric CO2 concentration. Since the beginning of the 21st century, CO2 concentration has increased at an average rate of 2.5 ppm per year. The large-scale emission of CO2 into the atmosphere has caused serious ecological and environmental problems. As countries around the world increasingly recognize its importance, CO2 capture, storage, and recycling technologies have become a global focus. Achieving both energy conservation and emission reduction, while simultaneously capturing and utilizing CO2 resources, has become the best solution for the current dual-carbon development strategy.

[0003] Synthesizing corresponding cyclic carbonates using CO2 and epoxides as raw materials is one of the few routes that have been industrialized using CO2 as a raw material. Cyclic carbonates are high-performance organic solvents and organic synthesis intermediates with advantages such as high boiling point, high polarity, low toxicity and low corrosivity. They are widely used in organic synthesis, gas separation, plastics, battery dielectrics and textile printing and dyeing.

[0004] CO2 is the highest oxidation state of carbon, and its molecules are quite stable, making it difficult to activate. Even its addition reaction with highly reactive epoxides requires specific temperature, pressure, and catalyst conditions. Catalysts for cycloaddition reactions mainly include quaternary ammonium salts, quaternary phosphonium salts, alkali metal salts, alkaline earth metal salts, transition metal complexes, ionic liquids, metal oxides, and functional resins. Early industrial production used quaternary ammonium salt catalysts, such as tetraethylammonium bromide, achieving a cycloaddition reaction yield of 98% after approximately 120 minutes at 150-200℃ and 8.0 MPa. However, these catalysts are prone to decomposition at high temperatures, and long-term use can generate other polymers. Therefore, industrial production catalysts for cyclic carbonates have gradually been replaced by metal complex ionic liquid systems. CN104492488A discloses a cycloaddition reaction yield of 99% after approximately 60 minutes at 80-120℃ and 2.5-4.0 MPa.

[0005] As can be seen from the above, thanks to the efforts of researchers, the technology for preparing cyclic carbonates by CO2 cycloaddition reactions has been greatly developed. However, the single-unit capacity of cyclic carbonates has increased from 500 t / a, 1500 t / a, 5000 t / a, 30 kt / a, 40 kt / a to the current 50 kt / a. The cycloaddition reaction always adopts a two-tower process, and the tower diameters have also increased from DN273, DN450, DN600, DN700, DN800 and DN1000, with a height of 20 meters. The industrial-scale production capacity towers are large and tall, with a single tower capacity reaching 15 m³. 3 The inherent safety risks are relatively high.

[0006] In recent years, research on microreactor technology has deepened. Microreactors mainly refer to small, multi-channel microstructure reactors manufactured using surface science and microfabrication technology through microprocessing and precision techniques. The channel sizes of microreactors are only at the submicron and submillimeter levels, giving them heat / mass transfer characteristics that are 1 to 3 orders of magnitude better than traditional chemical equipment. Therefore, they are particularly suitable for high-exothermic and rapid gas-liquid phase catalytic reactions. CN106928120A discloses a method for the continuous preparation of dicarbonylindole compounds using a microchannel reaction device. Using phenylacetaldehyde and indole compounds as raw materials, dicarbonylindole compounds are prepared in a microchannel reaction device with an inner diameter of 0.5–1 mm, shortening the reaction time and offering simple and safe operation. CN115960071A discloses a method for synthesizing cyclic carbonates using a eutectic ionic liquid under mild conditions in a microchannel reactor. In the microchannel reactor with an inner diameter of 2 mm, CO2 and propylene oxide are reacted with an ionic liquid to produce propylene carbonate, with a yield of 94.23% and a selectivity of 99%.

[0007] As can be seen from the above background, the technology for preparing cyclic carbonates via CO2 cycloaddition reactions has developed rapidly over the years, but large-scale production still relies on tower-type equipment, which has a large capacity and high risk. Meanwhile, with the continuous advancement of microreactor technology research, some researchers have developed CO2 cycloaddition processes in microreactors, but current microchannel technology still suffers from low reaction throughput, low production capacity, and low yields of cyclic carbonates. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of high risk in existing tower-type equipment and low production capacity in microchannel technology, and to provide a microchannel tubular reactor and a method for preparing propylene carbonate. The microchannel tubular reactor of this invention constructs microchannels within a tubular reactor, effectively controlling thermal risks. The preparation of propylene carbonate using this microchannel tubular reactor improves the selectivity of propylene carbonate and greatly enhances reaction efficiency.

[0009] To achieve the above objectives, the first aspect of the present invention provides a microchannel tubular reactor, the microchannel tubular reactor comprising an outer tube and an inner tube disposed inside the outer tube, wherein an annular gap is formed between the inner tube and the outer tube;

[0010] Along the flow direction, the inner tube of the microchannel tubular reactor includes alternating Venturi tubes and gas-liquid reaction tubes to form a flow field; wherein, the gas-liquid reaction tube is provided with components for the mixing reaction of fluids.

[0011] A second aspect of the present invention provides a method for preparing propylene carbonate, the method comprising: passing CO2, propylene oxide and a catalyst into the microchannel tubular reactor described in the first aspect above to carry out a cycloaddition reaction.

[0012] Through the above technical solution, the present invention has the following beneficial effects:

[0013] (1) The microchannel tubular reactor provided by the present invention has the advantages of thermal control, high-speed mixing, high-efficiency heat transfer, mass transfer and good repeatability by constructing specific microchannels in the tubular reactor, thereby enhancing the mixing, heat transfer and mass transfer effect of the reaction system; it effectively avoids the problem of uneven temperature distribution in traditional batch reactors, avoids the occurrence of local hot spots and strong exothermic decomposition reactions, achieves effective control of thermal risks, and improves the stability and reliability of the reaction; at the same time, the reactor provided by the present invention has a larger reaction throughput than typical microchannel reactors, and can realize large-scale industrial production step by step, and the reaction process is safe and reliable.

[0014] (2) The microchannel tubular reactor provided by the present invention can prepare propylene carbonate without the need for additional catalyst preparation. The raw materials for catalyst preparation (preferably including metal halides and ligands) can be added to the reaction system to exert catalytic performance, eliminating the catalyst preparation process, greatly shortening the reaction time, enabling reactions with large material throughput, increasing the reaction rate by 1-2 orders of magnitude, and the catalyst can still maintain good catalytic activity under high temperature conditions.

[0015] (3) The method for preparing propylene carbonate provided by the present invention introduces CO2, propylene oxide and catalyst into a microchannel tubular reactor, which has excellent catalytic effect and significantly improves the reaction efficiency of CO2 cycloaddition to prepare propylene carbonate. The conversion rate of propylene oxide and the selectivity of propylene carbonate in the reaction are both improved. Attached Figure Description

[0016] Figure 1 This is a partial structural schematic diagram of the microchannel tubular reactor provided by the present invention;

[0017] Figure 2This is a partially enlarged structural schematic diagram of the microchannel tubular reactor provided by the present invention;

[0018] Figure 3 This is a flowchart of the catalytic synthesis of propylene carbonate using a microchannel tubular reaction system provided by the present invention.

[0019] Explanation of reference numerals in the attached figures

[0020] 1. CO2 Inlet I 2. CO2 Injection Port I 3. Gas-Liquid Reaction Pipe 4. CO2 Injection Port II 5. Feed Pipe 6. CO2 Inlet II

[0021] 7. CO2 inlet III 8. Gas-liquid separator 9. Back pressure valve

[0022] 10. Tail gas absorption tank; 11. Flow control valve; 12. Catalyst separator; 13. Product tank; D1. Outer pipe; D2. Inner pipe; A0. Throat; A1. First inlet section; A2. Diffusion section outlet. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of the present invention provides a microchannel tubular reactor, the microchannel tubular reactor comprising an outer tube and an inner tube disposed inside the outer tube, wherein an annular gap is formed between the inner tube and the outer tube;

[0025] Along the flow direction, the inner tube of the microchannel tubular reactor includes alternating Venturi tubes and gas-liquid reaction tubes to form a flow field; wherein, the gas-liquid reaction tube is provided with components for the mixing reaction of fluids.

[0026] The microchannel tubular reactor provided by this invention enhances the mixing, heat transfer, and mass transfer of the reaction system by constructing specific microchannels within the tubular reactor. It effectively avoids the uneven temperature distribution problem inherent in traditional batch reactors, prevents localized hot spots and strongly exothermic decomposition reactions, achieves effective control of thermal risks, and improves the stability and reliability of the reaction. The reactor provided by this invention has a larger reaction throughput than typical microchannel reactors, enabling large-scale industrial production in stages, and the reaction process is safe and reliable. The preparation of propylene carbonate using this microchannel tubular reactor eliminates the need for catalyst preparation, significantly shortens the reaction time, and effectively improves the yield of propylene carbonate.

[0027] In some embodiments of the present invention, preferably, the venturi tube includes an inlet section and a constriction section, wherein the length of the inlet section is 2-5 times the diameter of the inlet section; the length of the constriction section is 0.5-5 times the diameter of the inlet section, the cone angle of the constriction section is 23°-27°, the diameter of the throat is 1 / 5-1 / 3 times the diameter of the inlet section, and the cone angle of the diffuser section is 8°-12°.

[0028] In this invention, the inlet section of the Venturi tube refers to the starting portion of the Venturi tube. The length of the inlet section can be 2, 2.5, 3, 3.5, 4, 4.5, or 5 times the diameter of the Venturi tube, or any value within the range of any two of these values, preferably 4-5 times. Using this preferred length of the inlet section is more conducive to guiding the fluid smoothly into the Venturi tube.

[0029] In this invention, the throat refers to the narrowest part of the venturi tube. Using a throat diameter within the aforementioned range is beneficial for fluid mixing and reaction.

[0030] In this invention, the constriction section of the Venturi tube refers to the portion of the Venturi tube connecting the inlet section and the throat. In this invention, the length of the constriction section is 0.5-5 times the diameter of the Venturi tube; for example, it can be 0.5 times, 1 time, 2 times, 3 times, 4 times, 5 times, or any value within the range of any two of the above values, preferably 1-2 times. Using a constriction section length within the above-mentioned preferred range is more conducive to gradually accelerating the fluid and reducing pressure, which is beneficial to subsequent mixing and reaction processes.

[0031] In this invention, the cone angle of the contraction section refers to the angle formed as the pipe wall gradually slopes inward during the transition from the inlet section to the throat. Using the preferred cone angle of the contraction section described above is more conducive to promoting fluid mixing.

[0032] In this invention, the cone angle of the diffuser section refers to the angle formed as the tube wall gradually slopes outward during the transition from the throat to other parts of the reactor. Using the aforementioned preferred cone angle of the diffuser section is more conducive to promoting stable fluid flow in the reactor.

[0033] In this invention, the geometry of the component is not particularly limited and can be any combined shape of micro-component constructed using 3D printing technology. Preferably, the geometry of the component is selected from at least one of Y-shaped, T-shaped, serpentine, and mesh-shaped, and more preferably from at least one of T-shaped, serpentine, and mesh-shaped. Using components with the above-mentioned preferred geometries is more conducive to promoting efficient mixing and reaction of fluids within the reactor.

[0034] In some embodiments of the present invention, preferably, the number of Venturi tubes n in the inner tubes of the microchannel tubular reactor is less than or equal to the number of components m. Adopting the above-described preferred embodiments helps to ensure sufficient mixing of the fluid within the reactor and guarantees sufficient residence time for the reaction.

[0035] In this invention, the number of Venturi tubes n and the number of components m are not particularly limited. Researchers can set them according to actual production needs, as long as the number of Venturi tubes n is not higher than the number of components m. Preferably, the number of Venturi tubes n is 1-5. In this invention, the number of Venturi tubes n and the number of components m refer to the number of Venturi tubes and components in a microchannel tubular reactor.

[0036] In some embodiments of the present invention, preferably, the inner tube of the microchannel tubular reactor further includes a feed pipe connected to a Venturi tube. Along the flow direction, the feed pipe is positioned upstream of the Venturi tube to deliver the raw materials and catalyst into the Venturi tube. In this invention, the number of feed pipes is not particularly limited; there can be one or more. It is understood that when multiple feed pipes are provided, the reaction raw materials can be fed into the microchannel reactor through different feed pipes and Venturi tubes.

[0037] In this invention, preferably, the diameter of the Venturi inlet section is the same as the diameter of the feed pipe. More preferably, the diameter of the Venturi inlet section, the diameter of the gas-liquid reaction tube, and the diameter of the feed pipe are the same.

[0038] In this invention, the length of the venturi tube diffusion section is not particularly limited. Preferably, along the material flow direction, the ratio of the length of the diffusion section of the venturi tube connected to the feed pipe to that of its downstream adjacent venturi tube satisfies the condition that the length of the diffusion section of the downstream adjacent venturi tube is more than twice the length of the diffusion section of the venturi tube connected to the feed pipe.

[0039] In this invention, the length of the gas-liquid reaction tube is not particularly limited. Preferably, along the flow direction, the length ratio between the gas-liquid reaction tube connected to the feed pipe and its downstream adjacent gas-liquid reaction tube satisfies the condition that the length of the downstream adjacent gas-liquid reaction tube is more than twice the length of the gas-liquid reaction tube connected to the feed pipe. Using the above-described preferred embodiment, good mixing effect can still be maintained even when the pressure is gradually reduced.

[0040] In this invention, the microchannel tubular reactor is divided into three regions along the material flow direction based on the difference in reaction temperature. Preferably, the microchannel tubular reactor is provided with a preheating mixing region, a reaction region, and a cooling region along the material flow direction. By adopting the above embodiment, the heat control, high-speed mixing, efficient heat and mass transfer performance of the reaction can be enhanced, effectively preventing the problem of uneven temperature distribution, avoiding local hot spots and strong exothermic decomposition reactions, and achieving effective control of thermal risks.

[0041] In some embodiments of the present invention, preferably, the lengths of the preheating mixing region, the reaction region, and the cooling region are each independently a multiple of the step length L. In this invention, the step length is a fixed length, and the present invention does not limit the specific value of the fixed length. Researchers can adjust the length according to actual reaction needs, as long as the lengths of the preheating mixing region, the reaction region, and the cooling region are all multiples of the same step length.

[0042] In this invention, preferably, the step length L is 1-6m, for example, it can be 1m, 2m, 3m, 4m, 5m, 6m, or any value within the range of any two of the above values. By adopting the above preferred embodiment, the material throughput in the reaction can be increased, which is beneficial for large-scale industrial applications.

[0043] In some embodiments of the present invention, preferably, the length of the preheating mixing zone is αL, the length of the reaction zone is βL, and the length of the cooling zone is γL, where α, β, and γ are integers.

[0044] In this invention, αL, βL, and γL have a wide range of selection. Preferably, βL > αL and βL > γL. In this invention, when the lengths of the preheating mixing zone, reaction zone, and cooling zone meet the above ranges, it can ensure sufficient reaction of the materials while avoiding energy waste.

[0045] In this invention, the specific lengths of the preheating mixing zone, reaction zone, and cooling zone are not particularly limited. Researchers can set them according to actual production needs, as long as the lengths of the three parts meet the above-mentioned requirements. Preferably, the length of the preheating mixing zone is 1-48m; the length of the reaction zone is 1-240m; and the length of the cooling zone is 1-24m. More preferably, the length of the preheating mixing zone is 12-48m; the length of the reaction zone is 30-240m; and the length of the cooling zone is 6-24m.

[0046] In this invention, the diameter of the inner tube has a wide range of selection. Preferably, the diameter of the inner tube is selected from any one of DN4, DN8, DN14, DN19, DN25, and DN32, and more preferably from at least one of DN4, DN8, and DN19. In this invention, DN4 refers to an inner tube diameter of 4 mm. In this invention, unless otherwise specified, the diameter of the inner tube refers to the diameter of the feed pipe, the diameter of the Venturi inlet section, and the diameter of the gas-liquid reaction pipe.

[0047] In this invention, the diameter of the outer tube has a wide range of selection. Preferably, the diameter of the outer tube is selected from any one of DN80, DN108, DN125 and DN150, and more preferably from DN80 and / or DN108.

[0048] In this invention, when the diameters of the inner and outer tubes meet the above-mentioned range, it is beneficial to increase the interface contact area, improve the mass and heat transfer efficiency and reaction rate, enhance the mixing, heat transfer and mass transfer effects of the reaction system, and at the same time increase the amount of material that the reaction system can handle.

[0049] In a preferred embodiment of the present invention, a schematic diagram of the microchannel tubular reactor is shown below. Figure 1 As shown: The microchannel tubular reactor includes an outer tube D1 and an inner tube D2 disposed inside the outer tube, with an annular gap formed between the inner tube D2 and the outer tube D1; along the material flow direction, the inner tube D2 of the microchannel tubular reactor includes alternating Venturi tubes and gas-liquid reaction tubes 3, forming a material flow field; wherein, the gas-liquid reaction tubes 3 are provided with components for the mixing reaction of fluids; the microchannel tubular reactor also includes a CO2 inlet I1, a feed pipe 5, and a CO2 injection port I2; along the material flow direction, the CO2 inlet I1 is connected to the CO2 injection port I2 and CO2 injection port II4 disposed on the Venturi tube, and the feed pipe 5 is connected to the inlet section of the Venturi tube.

[0050] In a preferred embodiment of the present invention, a partially enlarged structural schematic diagram of the microchannel tubular reactor is shown below. Figure 2 As shown: Figure 2In the reactor, along the flow direction, the (n-1)th Venturi tube, the gas-liquid reaction tube 3, and the nth Venturi tube are sequentially arranged. The Venturi tube includes a first inlet section A1, a throat A0, and a diffuser outlet A2. The raw material liquid (raw material and catalyst) is fed into the reactor through the feed pipe 5. At this time, the flow velocity at A1 is less than that at A0. Due to the Venturi principle, the pressure at A0 is less than that at A1. CO2 is input into the Venturi tube in the microfluidic reactor by the high-pressure system, and then undergoes forced mixing at A2. It is further reacted through the gas-liquid reaction tube 3. The temperature inside the gas-liquid reaction tube 3 is high, the reaction is exothermic, and the gas expands due to heat. The CO2, which was originally in a liquid and gas state, will form microbubbles as the pressure is released. At this time, the components set in the gas-liquid reaction tube 3 force the CO2 microbubbles to mix with the reaction liquid and continuously renew the gas-liquid mixture on the inner wall of the tube to avoid the formation of a stagnant gas film that hinders heat transfer, so that the heat exchange between the inner and outer fields of the microchannel can be carried out rapidly. Therefore, the process can be viewed as follows: the raw material liquid (reactants and catalyst) is mixed and reacted with subcritical CO2, and then the raw material liquid is mixed and reacted with CO2 micro-nano bubbles.

[0051] A second aspect of the present invention provides a method for preparing propylene carbonate, the method comprising: passing CO2, propylene oxide and a catalyst into the microchannel tubular reactor described in the first aspect above to carry out a cycloaddition reaction.

[0052] In this invention, propylene carbonate is prepared using the microchannel tubular reactor described in the first aspect above. No additional catalyst preparation is required; the raw materials for catalyst preparation are simply added to the reaction system to exert catalytic performance, eliminating the catalyst preparation process. This significantly shortens the reaction time, enabling reactions with large material throughputs and increasing the reaction rate by 1-2 orders of magnitude. Simultaneously, the catalyst maintains good catalytic activity even at high temperatures. It exhibits excellent catalytic effects, significantly improving the reaction efficiency of CO2 cycloaddition to propylene carbonate, and enhancing both the conversion rate of propylene oxide and the selectivity of propylene carbonate in the reaction.

[0053] In some embodiments of the present invention, preferably, the catalyst comprises a metal halide and a ligand.

[0054] In this invention, the types of metal halides and ligands can be selected from a wide range. Preferably, based on the total amount of catalyst, the molar ratio of the metal halide to the ligand is 1:4-9, more preferably 1:5-7, for example, it can be 1:5, 1:5.5, 1:6, 1:6.5, 1:7, or any value within the range of any two of the above values. Using the above-mentioned preferred molar ratio can maximize the synergistic effect between the metal halide and the ligand, further enhancing the catalytic activity of the catalyst.

[0055] In this invention, the catalyst can be a catalyst material composed of a mixture of metal halide and ligand. This invention does not specifically limit the mixing state of the active component and ligand, which can be a uniform mixture or an arbitrary non-uniform mixture, as long as the metal halide and ligand exist simultaneously in the reaction system in the above molar ratio.

[0056] In this invention, the metal halide has a wide range of metal selection options. Preferably, the metal halide is selected from at least one of zinc, copper, manganese, and potassium, more preferably zinc and / or potassium, and even more preferably zinc.

[0057] In this invention, the types of halogen atoms in the metal halide have a wide range of selection. Preferably, the halogen atoms in the metal halide are selected from bromine and / or iodine, with bromine being the most preferred.

[0058] In this invention, the use of the above-mentioned preferred metal halides is beneficial for obtaining highly active catalysts.

[0059] In this invention, the type of ligand is not particularly limited, and ligands of various catalysts conventionally used in the art for the catalytic synthesis of propylene carbonate can be used in this invention. Preferably, the ligand is selected from at least one of 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, tetraethylammonium bromide, tetraphenylammonium bromide, methyltriphenylphosphine bromide, 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, preferably 1-ethyl-3-methylimidazolium bromide and / or 1-butyl-3-methylimidazolium bromide, more preferably 1-ethyl-3-methylimidazolium bromide.

[0060] In this invention, the use of the above-mentioned preferred metal halides and ligands is beneficial to forming a highly efficient catalytic system and further improving catalytic performance.

[0061] In some embodiments of the present invention, preferably, the catalyst is fed in the form of a propylene carbonate solution. Using the above embodiments is beneficial for improving the dispersibility and uniformity of the catalyst, increasing the yield and selectivity of propylene carbonate, and improving reaction efficiency.

[0062] In some embodiments of the present invention, preferably, at least a portion of the propylene carbonate solution containing the catalyst is derived from the reaction products. By employing the above embodiments, the catalyst can be recycled without introducing additional propylene carbonate solution, effectively reducing reaction costs.

[0063] In some embodiments of the present invention, preferably, the molar ratio of CO2 to propylene oxide is 1-2:1, for example, it can be 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1, or any value within the range of any two of the above values, preferably 1.2-1.5:1. Using a molar ratio within the above preferred range is beneficial for increasing the effective collision probability between CO2 and propylene oxide, accelerating the reaction, reducing side reactions, and increasing the selectivity of propylene carbonate.

[0064] In this invention, the CO2 in the method for preparing propylene carbonate can be added together or added in stages. Preferably, the CO2 is added in stages. There is no particular limitation on the amount of CO2 added in stages, as long as the total amount meets the aforementioned range.

[0065] In some embodiments of the present invention, preferably, the mass fraction of the catalyst is 0.5-2 wt% based on the total feed mass, for example, it can be 0.5 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, or any value within any range of two of the above values, preferably 1-2 wt%. In the present invention, the total feed mass refers to the total mass of propylene oxide and propylene carbonate. Using the above-preferred range of catalyst dosage is more conducive to providing sufficient catalytic active sites, increasing the reaction rate, and reducing reaction costs and resource consumption.

[0066] In this invention, preferably, the method includes: introducing a heat exchange medium into the annular gap to regulate the reaction temperature. This implementation method facilitates real-time temperature control of all parts of the microchannel tubular reactor, improving the reactor's heat and mass transfer capabilities, and enhancing its production capacity and safety performance.

[0067] In this invention, the type of heat exchange medium is not specifically limited. It can be any heat exchange material commonly used in the art that can achieve a heat exchange effect on the material in the reactor. Specifically, it can be selected from at least one of heat transfer oil, steam, molten salt and water.

[0068] In this invention, the amount of heat exchange medium introduced is not specifically limited. Researchers can make adjustments based on the actual reaction conditions to ensure that the temperature of each part of the reactor meets the actual production requirements.

[0069] In this invention, preferably, the method includes: introducing reactants and catalyst into the inner tube disposed inside the outer tube. In this invention, the reactants and catalyst can be introduced into the inner tube from the same inlet or from different inlets, as long as the amount of reactants and catalyst in the microchannel tubular reactor meets the aforementioned range. Preferably, the reactants and catalyst can be introduced into the inner tube from the same inlet. More preferably, the microchannel tubular reactor includes a reactant and catalyst mixture inlet 5, through which the reactants and catalyst are introduced into the inner tube disposed inside the outer tube.

[0070] In this invention, the flow rates of the reactants and catalyst have a wide range of selection. Preferably, the flow rates of the reactants and catalyst are 0.1-0.6 m / s, for example, 0.1 m / s, 0.2 m / s, 0.3 m / s, 0.4 m / s, 0.5 m / s, 0.6 m / s, and any value within any range of two of the above values. In this invention, unless otherwise specified, the flow rates of the reactants and catalyst refer to the feed flow rates of propylene oxide, catalyst, and propylene carbonate. Using the above-mentioned preferred flow rates is beneficial for ensuring sufficient reaction while increasing the amount of reactants, thereby improving the reaction rate and the selectivity of propylene carbonate.

[0071] In this invention, the preheating and mixing conditions have a wide range of selection. Preferably, the preheating and mixing temperature is 80-120°C; the pressure is 2.5-4.5 MPa, more preferably 3-4.5 MPa. When the preheating and mixing conditions in this invention meet the above-mentioned preferred ranges, the materials can be fully mixed while maintaining a suitable temperature, thereby enhancing the reaction rate and safety performance of the reaction system.

[0072] In this invention, the reaction conditions have a wide range of selectability. Preferably, the reaction temperature is 120-160°C and the pressure is 2.5-4.5 MPa. More preferably, the reaction temperature is 140-150°C and the pressure is 3-4.5 MPa. When the reaction conditions meet the above preferred ranges, the effective collision probability between reactants can be increased, the catalytic activity of the catalyst material can be enhanced, and thus the reaction rate and selectivity can be increased.

[0073] In this invention, the total time for preheating, mixing, and reaction has a wide range of selection. Preferably, the total time for preheating, mixing, and reaction is 180-600 s, more preferably 400-600 s. For example, it can be 400 s, 425 s, 450 s, 475 s, 500 s, 525 s, 550 s, 575 s, 600 s, or any value within the range of any two of the above values. Using the above-mentioned preferred time is beneficial for the reaction to proceed fully, while avoiding energy waste caused by excessively long reaction times.

[0074] In this invention, preferably, the method further includes: performing gas-liquid separation on the crude carbonate obtained from the cycloaddition reaction. The apparatus for gas-liquid separation in this invention is not particularly limited, but a gas-liquid separator is preferred.

[0075] In this invention, preferably, the method further includes: performing catalyst separation on the separated liquid. The apparatus for catalyst separation in this invention is not particularly limited, but a catalyst separation tank is preferred. In this invention, the method for catalyst separation is not particularly limited; various conventional catalyst separation methods used in the art can be employed, as long as the catalyst can be separated from the liquid.

[0076] In this invention, preferably, the catalyst obtained from catalyst separation is recycled along with a portion of the propylene carbonate as a catalyst solvent in the reaction process; the remaining liquid (propylene carbonate) obtained from catalyst separation is collected. The apparatus for collecting propylene carbonate described in this invention is not particularly limited, but a product tank is preferred.

[0077] In this invention, preferably, the method further includes: absorbing the separated gas as exhaust gas. The exhaust gas handwashing device of this invention is not particularly limited, but is preferably an exhaust gas absorption tank. The method of exhaust gas absorption is not particularly limited, and various exhaust gas absorption methods conventionally used in the art can be employed.

[0078] In this invention, the mixture of raw materials and catalyst can be added together or in stages in the method for preparing propylene carbonate. Preferably, the mixture of raw materials and catalyst is added in stages. There is no particular limitation on the amount of the mixture of raw materials and catalyst added in stages, as long as the total amount meets the aforementioned range.

[0079] In this invention, the number of microchannel tubular reactors in the method for preparing propylene carbonate is not particularly limited, and those skilled in the art can choose according to actual reaction requirements.

[0080] In some embodiments of the present invention, the propylene carbonate is prepared in a manner such as... Figure 3The system shown includes: the microchannel tubular reactor described in the first aspect above, a gas-liquid separator 8, a catalyst separator 12, a tail gas absorption tank 10, and a product tank 13; the outlet of the microchannel tubular reactor is connected to the inlet of the gas-liquid separator 8; the liquid outlet of the gas-liquid separator 8 is connected to the catalyst separator 12, and the outlet of the catalyst separator 12 is connected to the inlet of the product tank 13; the gas outlet of the gas-liquid separator 8 is connected to the tail gas absorption tank 10.

[0081] In a preferred embodiment of the present invention, the method for preparing propylene carbonate is as follows: Figure 3 As shown:

[0082] CO2 is introduced through CO2 inlet I1, CO2 inlet II6, and CO2 inlet III7, and enters the Venturi tube through CO2 injection port I2 and CO2 injection port II4. The mixture of raw materials and catalyst is introduced through feed pipe 5, and a cycloaddition reaction takes place in the Venturi tube and gas-liquid reaction tube 3. The reactants further react in the gas-liquid reaction tube 3 to obtain crude propylene carbonate. The crude propylene carbonate enters the gas-liquid separator 8, and the system pressure is controlled by the back pressure valve 9. The flow rate of the material entering the reactor is adjusted by the flow regulating valve 11. The gas obtained from the gas-liquid separation enters the tail gas absorption tank 10, and the liquid obtained from the gas-liquid separation enters the catalyst separation tank 12. The separated catalyst, along with part of the propylene carbonate, is recycled as a catalyst solvent in the reaction process, and the remaining separated liquid is stored in the product tank 13.

[0083] The present invention will be described in detail below through embodiments.

[0084] The propylene carbonate in the product was determined by gas chromatography.

[0085] The conversion rate of propylene oxide (%) = the amount of propylene oxide reacted × 100% / the amount of propylene oxide fed.

[0086] Example 1

[0087] CO2 epoxidation was carried out in a microchannel tubular reactor with an internal pipe diameter of DN4 and an external pipe diameter of DN80. The Venturi tube inlet section had a diameter of DN4 (4 mm) and a length of 16 mm. The constriction section was 6 mm long with a cone angle of 25°. The throat diameter was 1 mm, and the diffusion section had a cone angle of 10°. The reactor components were mesh-like. Each microchannel tubular reactor contained three Venturi tubes in its inner tube and three components. The step length was 6 m, the preheating and mixing section was 12 m long, the reaction section was 30 m long, and the cooling section was 6 m long. Zinc bromide and 1-ethyl-3-methylimidazolium bromide were dissolved in propylene carbonate at a molar ratio of 1:6. The total feed mass (propylene oxide and propylene carbonate) was used as the feed ratio. Based on propylene carbonate, the mass fractions of zinc bromide and 1-ethyl-3-methylimidazolium bromide were 2%, the molar ratio of CO2 to propylene oxide was 1.2:1, the feed flow rate of the materials (zinc bromide, 1-ethyl-3-methylimidazolium bromide, propylene carbonate, and propylene oxide) was 0.1 m / s, the temperature of the preheating mixing section was 100℃, the pressure of the preheating mixing section was 4.5 MPa, the temperature of the reaction section was 150℃, the pressure of the reaction section was 4.5 MPa, and the total time for preheating mixing and heating reaction was 480 s. The obtained crude propylene carbonate was subjected to gas-liquid separation. The separated gas was recovered as tail gas, and the separated liquid was subjected to catalyst separation. The catalyst obtained from catalyst separation was recycled along with part of the propylene carbonate as a catalyst solvent in the reaction process, and the remaining product from catalyst separation was collected.

[0088] Tests showed that the conversion rate of propylene oxide was 99.8%, and the selectivity of propylene carbonate was 99.5%.

[0089] Example 2

[0090] The method described in Example 1 is different except that the molar ratio of zinc bromide to 1-ethyl-3-methylimidazolium bromide is 1:4.

[0091] Tests showed that the conversion rate of propylene oxide was 97.5%, and the selectivity of propylene carbonate was 99.6%.

[0092] Example 3

[0093] The method is the same as described in Example 1, except that the molar ratio of zinc bromide to 1-ethyl-3-methylimidazolium bromide is 1:9; and the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 1% based on the total mass of the feed.

[0094] Tests showed that the conversion rate of propylene oxide was 98.2% and the selectivity of propylene carbonate was 99.6%.

[0095] Example 4

[0096] The method described in Example 1 is different in that, based on the total mass of the feed, the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 1.5%; the pressure of the preheating mixing section is 4 MPa; and the pressure of the reaction section is 4 MPa.

[0097] Tests showed that the conversion rate of propylene oxide was 98.9% and the selectivity of propylene carbonate was 99.5%.

[0098] Example 5

[0099] The method described in Example 1 is different in that, based on the total mass of the feed, the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 1%; and the temperature of the reaction section is 130°C.

[0100] Tests showed that the conversion rate of propylene oxide was 97.4%, and the selectivity of propylene carbonate was 99.5%.

[0101] Example 6

[0102] The method described in Example 1 is different in that, based on the total mass of the feed, the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 0.5%; and the temperature of the reaction section is 130°C.

[0103] Tests showed that the conversion rate of propylene oxide was 93.4%, and the selectivity of propylene carbonate was 99.5%.

[0104] Example 7

[0105] The method described in Example 1 is different except that the molar ratio of CO2 to propylene oxide is 1:1; the pressure of the preheating mixing section is 4 MPa; and the pressure of the reaction section is 4 MPa.

[0106] Tests showed that the conversion rate of propylene oxide was 97.9% and the selectivity of propylene carbonate was 99.5%.

[0107] Example 8

[0108] The method described in Example 1 is different except that the molar ratio of CO2 to propylene oxide is 2:1.

[0109] Tests showed that the conversion rate of propylene oxide was 98.2% and the selectivity of propylene carbonate was 99.6%.

[0110] Example 9

[0111] The method described in Example 1 is different in that, based on the total mass of the feed, the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 1.5%; the feed flow rate of the material is 0.12 m / s; and the total time for preheating mixing and heating reaction is 400 s.

[0112] Tests showed that the conversion rate of propylene oxide was 99.5%, and the selectivity of propylene carbonate was 99.4%.

[0113] Example 10

[0114] The method described in Example 1 is different in that the feed flow rate of the material is 0.16 m / s; the temperature of the reaction section is 160°C; and the total time for preheating mixing and heating reaction is 300 s.

[0115] Tests showed that the conversion rate of propylene oxide was 99.0%, and the selectivity of propylene carbonate was 99.5%.

[0116] Example 11

[0117] The method described in Example 1 is different except that the feed flow rate of the material is 0.12 m / s, the total time for preheating mixing and heating reaction is 400 s, and the temperature of the reaction section is 140°C.

[0118] Tests showed that the conversion rate of propylene oxide was 99.7%, and the selectivity of propylene carbonate was 99.5%.

[0119] Example 12

[0120] The method described in Example 1 is different in that, based on the total mass of the feed, the mass fraction of zinc bromide and 1-ethyl-3-methylimidazolium bromide is 1.5%; the feed flow rate of the material is 0.08 m / s; the total time for preheating mixing and heating reaction is 600 s; the pressure of the preheating mixing section is 3 MPa; and the pressure of the reaction section is 3 MPa.

[0121] Tests showed that the conversion rate of propylene oxide was 99.3% and the selectivity of propylene carbonate was 99.5%.

[0122] Example 13

[0123] The method described in Example 1 is different except that the temperature of the reaction section is 120°C; the pressure of the preheating mixing section is 4 MPa; and the pressure of the reaction section is 4 MPa.

[0124] Tests showed that the conversion rate of propylene oxide was 98.2% and the selectivity of propylene carbonate was 99.6%.

[0125] Example 14

[0126] The method described in Example 1 is different in that the feed flow rate of the material is 0.08 m / s; the total time for preheating mixing and heating reaction is 600 s; the pressure of the preheating mixing section is 4 MPa; and the pressure of the reaction section is 4 MPa.

[0127] Tests showed that the conversion rate of propylene oxide was 99.6%, and the selectivity of propylene carbonate was 99.5%.

[0128] Example 15

[0129] The method described in Example 1 is different in that the ligand is tetraethylammonium bromide; the molar ratio of zinc bromide to tetraethylammonium bromide is 1:9; and the mass fraction of zinc bromide and tetraethylammonium bromide is 1.5% based on the total mass of the feed.

[0130] The test results showed that the conversion rate of propylene oxide was 98.1% and the selectivity of propylene carbonate was 99.4%.

[0131] Example 16

[0132] The method described in Example 1 is different in that the ligand is tetraethylammonium bromide; the feed flow rate of the material is 0.12 m / s; the total time for preheating mixing and heating reaction is 400 s; the pressure of the preheating mixing section is 4 MPa; and the pressure of the reaction section is 4 MPa.

[0133] Tests showed that the conversion rate of propylene oxide was 99.4%, and the selectivity of propylene carbonate was 99.4%.

[0134] Example 17

[0135] The method described in Example 1 is different except that the ligand is 1-butyl-3-methylimidazolium bromide.

[0136] Tests showed that the conversion rate of propylene oxide was 99.7%, and the selectivity of propylene carbonate was 99.4%.

[0137] Example 18

[0138] The method described in Example 1 is different except that the ligand is 1-butyl-3-methylimidazolium bromide and the molar ratio of CO2 to propylene oxide is 1.5:1.

[0139] Tests showed that the conversion rate of propylene oxide was 98.6% and the selectivity of propylene carbonate was 99.5%.

[0140] Example 19

[0141] The method described in Example 1 is different except that the ligand is 1,8-diazabicyclo[5.4.0]undec-7-ene; the feed flow rate of the material is 0.16 m / s; and the total time for preheating mixing and heating reaction is 300 s.

[0142] The test results showed that the conversion rate of propylene oxide was 97.1% and the selectivity of propylene carbonate was 99.4%.

[0143] Example 20

[0144] The method described in Example 1 is different in that the step length is 6m, the length of the preheating and mixing section is 48m, the length of the reaction section is 120m, and the length of the cooling section is 24m; the material feed flow rate is 0.4m / s.

[0145] Tests showed that the conversion rate of propylene oxide was 99.6%, and the selectivity of propylene carbonate was 99.4%.

[0146] Example 21

[0147] The method described in Example 1 is different in that the step length is 6m, the length of the preheating and mixing section is 48m, the length of the reaction section is 240m, and the length of the cooling section is 24m; the mass fraction of zinc bromide and tetraethylammonium bromide is 1.5% based on the total mass of the feed; the feed flow rate of the material is 0.6m / s; and the total time for preheating and mixing and heating reaction is 520s.

[0148] Tests showed that the conversion rate of propylene oxide was 99.8%, and the selectivity of propylene carbonate was 99.5%.

[0149] Example 22

[0150] The method described in Example 1 differs in that the internal diameter of the microchannel tubular reactor is DN8 and the external diameter is DN108; the inlet diameter of the Venturi tube is DN8 (8mm), the length of the inlet section is 32mm, the length of the contraction section is 12mm, the cone angle of the contraction section is 25°, the diameter of the throat is 2mm, and the cone angle of the diffusion section is 10°; the step length is 6m, the length of the preheating and mixing section is 24m, the length of the reaction section is 60m, and the length of the cooling section is 12m; the feed velocity of the material is 0.2m / s.

[0151] Tests showed that the conversion rate of propylene oxide was 99.8%, and the selectivity of propylene carbonate was 99.5%.

[0152] Example 23

[0153] The method described in Example 1 differs in that the internal diameter of the microchannel tubular reactor is DN19 and the external diameter is DN108; the inlet diameter of the Venturi tube is DN19 (19mm), the length of the inlet section is 76mm, the length of the contraction section is 28.5mm, the cone angle of the contraction section is 25°, the diameter of the throat is 4.8mm, and the cone angle of the diffusion section is 10°; the step length is 6m, the length of the preheating and mixing section is 48m, the length of the reaction section is 120m, and the length of the cooling section is 24m; the feed velocity of the material is 0.35m / s; and the total time for preheating, mixing, and heating reaction is 550s.

[0154] Tests showed that the conversion rate of propylene oxide was 99.8%, and the selectivity of propylene carbonate was 99.5%.

[0155] The data above shows that using the microchannel tubular reactor and the method for preparing propylene carbonate provided by this invention effectively improves the conversion rate of propylene oxide and the selectivity of propylene carbonate, and the catalyst can still maintain good catalytic activity under high temperature conditions.

[0156] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A microchannel tubular reactor, characterized in that, The microchannel tubular reactor includes an outer tube and an inner tube disposed inside the outer tube, with an annular gap formed between the inner tube and the outer tube; Along the flow direction, the inner tube of the microchannel tubular reactor includes alternating Venturi tubes and gas-liquid reaction tubes to form a flow field; wherein, the gas-liquid reaction tubes are provided with components for the mixing reaction of fluids.

2. The reactor according to claim 1, wherein, The length of the venturi tube inlet section is 2-5 times the diameter of the inlet section; the length of the contraction section is 0.5-5 times the diameter of the inlet section, the cone angle of the contraction section is 23°-27°, the diameter of the throat is 1 / 5-1 / 3 times the diameter of the inlet section, and the cone angle of the diffuser section is 8°-12°. Preferably, the geometry of the component is selected from at least one of Y-shaped, T-shaped, serpentine, and mesh-shaped; Preferably, in the inner tube of the microchannel tubular reactor, the number of Venturi tubes n ≤ the number of components m.

3. The reactor according to claim 1 or 2, wherein, The microchannel tubular reactor is provided with a preheating mixing zone, a reaction zone, and a cooling zone along the material flow direction; Preferably, the lengths of the preheating mixing zone, the reaction zone, and the cooling zone are each independently multiples of the step size L; Preferably, the length of the preheating mixing zone is αL, the length of the reaction zone is βL, and the length of the cooling zone is γL, where α, β, and γ are integers; Preferably, βL>αL and βL>γL.

4. The reactor according to any one of claims 1-3, wherein, The diameter of the inner tube is selected from any one of DN4, DN8, DN14, DN19, DN25 and DN32; Preferably, the diameter of the outer tube is selected from any one of DN80, DN108, DN125 and DN150.

5. A method for preparing propylene carbonate, the method comprising: CO2, propylene oxide, and a catalyst are introduced into the microchannel tubular reactor according to any one of claims 1-4 to carry out a cycloaddition reaction.

6. The method according to claim 5, wherein, The catalyst comprises a metal halide and a ligand; Preferably, based on the total amount of catalyst, the molar ratio of the metal halide to the ligand is 1:4-9, more preferably 1:5-7; Preferably, the metal in the metal halide is selected from at least one of zinc, copper, manganese and potassium, preferably zinc and / or potassium, and more preferably zinc; Preferably, the halogen atom in the metal halide is selected from bromine and / or iodine, with bromine being the most preferred.

7. The method according to claim 5 or 6, wherein, The ligand is selected from at least one of 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, tetraethylammonium bromide, tetraphenylammonium bromide, methyltriphenylphosphine bromide, 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diazabicyclo[4.3.0]non-5-ene, preferably 1-ethyl-3-methylimidazolium bromide and / or 1-butyl-3-methylimidazolium bromide, more preferably 1-ethyl-3-methylimidazolium bromide.

8. The method according to any one of claims 5-7, wherein, The catalyst is fed in the form of a propylene carbonate solution; Preferably, the propylene carbonate solution containing at least a portion of the catalyst is derived from the reactants.

9. The method according to any one of claims 5-8, wherein, The molar ratio of CO2 to propylene oxide is 1-2:1; Preferably, the mass fraction of the catalyst is 0.5-2 wt%, based on the total mass of the feed.

10. The method according to any one of claims 5-9, wherein, A heat exchange medium is introduced into the annular gap to regulate the reaction temperature; Preferably, the flow rate of the raw materials and catalyst is 0.1-0.9 m / s; Preferably, the temperature of the preheating mixture is 80-120℃; the pressure is 2.5-4.5MPa, preferably 3-4.5MPa; Preferably, the reaction temperature is 120-160℃, more preferably 140-150℃, and the pressure is 2.5-4.5MPa, more preferably 3-4.5MPa; Preferably, the total time for preheating, mixing, and reaction is 180-600 s, more preferably 400-600 s.

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