A catalyst recovery system and method in a cyclic carbonate preparation process

Abstract

The present invention provides a catalyst recovery system and method in the process of preparing cyclic carbonate, relates to the technical field of fine chemical industry, solves the technical problem that the existing carbonization crystallization system of sodium methoxide has a local supersaturation reaction and generates fine crystal blockage when carbon dioxide is introduced. The aspect ratio of the reaction section pipeline of the present invention is ≥500:1, and the reaction section includes a first static mixer for introducing water into a crude propylene glycol solution and a plurality of groups of second static mixers vertically arranged for introducing carbon dioxide, and the lower end of the second static mixer is provided with an air inlet for introducing carbon dioxide into the reaction section and supplementing pressure. The present invention avoids the aggregation of fine crystals to form scaling, has a small pressure drop loss, reduces the maintenance frequency and cost of equipment, improves the conversion rate of sodium methoxide, reduces the unreacted sodium methoxide residue, and improves the overall reaction efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemicals, and in particular to a catalyst recovery system and method in a cyclic carbonate preparation process. Background Art

[0002] In the process of producing dimethyl carbonate by transesterification, sodium methoxide is often used as a catalyst. Dimethyl carbonate is synthesized by reactive distillation. The bottom of the tower is a crude propylene glycol solution containing sodium methoxide. Sodium methoxide needs to be removed to recycle propylene glycol. In the industrial device put into production, the method adopted is to pass carbon dioxide and water into the crude propylene glycol solution to carry out carbonization reaction, so that sodium methoxide reacts to produce sodium carbonate and methanol. The solubility of sodium carbonate in propylene glycol is very low, and it will precipitate in the form of crystals. The solid can be removed after filtration.

[0003] In current practical applications, the carbonization equipment is a kettle reactor. Carbon dioxide is introduced from below the liquid surface, and stirring is used to achieve uniform distribution of gas and suspension of solids. In order to enhance the carbonization effect, two-stage carbonization kettles are often connected in series to ensure the complete reaction of sodium methoxide, such as the device provided by patent CN201848238U. However, after actual operation, it was found that this carbonization system has many problems, which seriously restricts the long-term stable operation of production: 1. The carbonization reaction is essentially a reaction crystallization with a very high degree of supersaturation. Once the stirring effect of the kettle is not good, it is easy to explode fine crystals, which are easy to agglomerate and adhere to the stirring paddle and the wall to form a scale layer, requiring personnel to stop and clean periodically. The by-product allyl alcohol contained in the crude propylene glycol solution is a highly toxic substance, which brings great difficulties to the cleaning of personnel; 2. It is difficult to achieve accurate addition of carbon dioxide in the two-stage carbonization process. The carbonization kettle is large in size and it is difficult to achieve uniform distribution of concentration in the kettle. The precipitated sodium carbonate is easy to continue to react with carbon dioxide and water to form sodium bicarbonate, and the solubility of sodium bicarbonate in propylene glycol is much greater, resulting in a decrease in the efficiency of the subsequent filtration system. When propylene glycol containing sodium bicarbonate enters the distillation tower, sodium bicarbonate is extremely unstable when heated, and sodium carbonate will be precipitated, causing the distillation tower to be blocked and production to be interrupted.

[0004] Therefore, the patent with publication number CN116173885A proposes a carbonization crystallization system and method for sodium methoxide, which realizes precise control of the amount of carbon dioxide gas added during the carbonization process through a tubular crystallizer with an annular plate, thereby regulating the supersaturation of the carbonization process, obtaining uniformly distributed sodium carbonate crystals, avoiding scaling caused by fine crystal agglomeration, and reducing the equipment footprint. However, in this way, carbon dioxide is introduced through the small holes of the annular plate, although the uniformity of carbon dioxide distribution is increased, the annular plate is set in the pipeline reactor, and the small holes of the annular plate are easy to penetrate into the reaction solution when the carbon dioxide pressure is insufficient. In the annular plate, a local supersaturation reaction occurs to generate fine crystals, which are easy to agglomerate to form scaling, and the annular plate is more easily blocked by scaling, which further causes supersaturation of the reaction. Summary of the invention

[0005] The invention provides a catalyst recovery system and method in the preparation process of cyclic carbonate, so as to solve the technical problem that the existing carbonization crystallization system of sodium methoxide still has the problem of local supersaturation reaction and fine crystal blockage caused by the introduction of carbon dioxide.

[0006] The embodiments of the present invention are implemented by the following technical solutions:

[0007] A catalyst recovery system in a cyclic carbonate preparation process comprises a reaction section for reacting sodium methoxide to generate sodium carbonate, a precipitation device for cooling and precipitating the sodium carbonate, and a separation device for separating the sodium carbonate. The length-to-diameter ratio of the reaction section pipeline is ≥500:1. The reaction section comprises a first static mixer for introducing water into a crude propylene glycol solution and a plurality of groups of second static mixers vertically arranged for introducing carbon dioxide, which are connected in sequence. The lower end of the second static mixer is provided with an air inlet for introducing carbon dioxide into the reaction section and supplementing the pressure.

[0008] Preferably, the reaction section comprises a mixing pipe connected to the first static mixer and the second static mixer, a reaction pipe connected to a plurality of groups of second static mixers, and an output pipe connected to the precipitation device.

[0009] Preferably, the reaction pipe is further provided with a cooling jacket for controlling the reaction temperature to 20°C-40°C.

[0010] Preferably, the output pipeline is provided with a heating jacket for heating the propylene glycol solution after the reaction to 150° C.-200° C. to decompose sodium bicarbonate.

[0011] Preferably, the ratio of the sum of the lengths of the first static mixer and the mixing pipe, the sum of the lengths of the reaction pipe and the second static mixer, and the length of the output pipe is 2-3:4-5:1.

[0012] Preferably, the air inlet is also provided with a circulating compression pump for introducing pressurized nitrogen and a mixing box for mixing nitrogen and carbon dioxide.

[0013] Preferably, a collecting hood for collecting nitrogen is provided on the top of the second static mixer, and the collecting hood is connected to the circulating compression pump.

[0014] Preferably, the first static mixer and the second static mixer are spiral mixers.

[0015] A method for recovering a catalyst in a cyclic carbonate preparation process comprises the following steps:

[0016] S1: Dispersion: Mix the crude propylene glycol solution and water;

[0017] S2: Ventilation reaction: carbon dioxide is introduced for reaction;

[0018] S3: Gas supplement and pressurization: Add carbon dioxide and nitrogen to increase the pressure and further react:

[0019] S4: Thermal decomposition: Thermal decomposition produces sodium bicarbonate as a byproduct:

[0020] S5: Precipitation and separation: Sodium carbonate is precipitated by cooling and solid-liquid separation of sodium carbonate.

[0021] Preferably, in step S3, carbon dioxide and nitrogen are additionally introduced to maintain the pressure at the discharge end at 1 barG-1.5 barG, and the flow rate of the material is 1.8 m / s-2.1 m / s.

[0022] By adopting the technical solution, the crude propylene glycol solution can be effectively mixed with water and carbon dioxide by using the first static mixer and the second static mixer. This helps to improve the reaction efficiency, ensure that the reactants are fully contacted, and thus accelerate the catalytic process. The reaction pipeline is provided with a cooling jacket, which can control the reaction temperature between 20°C and 40°C, in order to maintain the best reaction conditions to promote the formation of the target product and reduce by-products. By setting the heating jacket on the output pipeline, the propylene glycol solution after the reaction can be heated to 150°C-200°C in the thermal decomposition stage to decompose sodium bicarbonate. The advantage of this is that the heating process can be controlled more accurately, excessive energy consumption can be avoided, and it also helps environmental protection. The system is specially designed with a precipitation device and a separation device for separating sodium carbonate from the solution after the reaction, which is crucial for the recovery of the catalyst, can reduce production costs, reduce resource waste, and is environmentally friendly. The air inlet can not only pass carbon dioxide, but also supplement nitrogen through a circulating compression pump and a mixing box, and the gas composition can be adjusted according to actual needs. Collecting nitrogen through the top collection hood and reintroducing it into the system not only improves the utilization rate of the gas, but also reduces possible safety hazards. By setting the length ratio of each part at a specific ratio and accurately controlling the reaction parameters, it is beneficial to achieve continuous production and improve production efficiency. In summary, this system can not only effectively promote the preparation of cyclic carbonates, but also show significant advantages in catalyst recovery, energy conservation and emission reduction, and safety.

[0023] Mixing the crude propylene glycol solution and water first can ensure that the two liquids are fully mixed to form a uniform mixed solution. This helps the carbon dioxide to contact the sodium methoxide in the solution more evenly when the carbon dioxide is added later, thereby improving the uniformity and efficiency of the reaction. By mixing water first, the crude propylene glycol solution can be diluted to reduce the concentration of sodium methoxide, thereby slowing down the reaction rate of carbon dioxide and sodium methoxide. This helps to better control the reaction process and avoid excessively violent reactions, resulting in uncontrollable supersaturation. The addition of water can absorb part of the reaction heat, help control the reaction temperature, and prevent side reactions or equipment damage caused by excessive temperature. By mixing water first, the supersaturation of the solution can be better controlled, which is conducive to nucleation and crystal growth. In a uniform solution environment, the nucleation and growth processes are more controllable, which helps to form crystals with uniform particle size distribution and larger size, and improve the quality and yield of the product. Avoid fine crystals from agglomerating to form scaling, and reduce the maintenance frequency and cost of equipment. Improve the conversion rate of sodium methoxide, reduce the unreacted sodium methoxide residue, and improve the overall reaction efficiency.

[0024] In the carbonization crystallization process of sodium methoxide, the method of adding carbon dioxide and pressurized nitrogen in stages for supplementary pressurization has several advantages. These methods can significantly improve the efficiency of the reaction, control the reaction conditions, and reduce the generation of by-products. By adding carbon dioxide in stages in different reaction zones, the supersaturation and reaction rate of each zone can be controlled more accurately. This can avoid the local supersaturation caused by adding a large amount of carbon dioxide at one time, thereby reducing the formation of fine crystals and improving the quality and uniformity of the crystals. The use of pressurized nitrogen can maintain the pressure of the system without increasing the total amount of carbon dioxide, ensuring that the reaction is carried out under the required high pressure conditions. This helps to increase the solubility of carbon dioxide and promote its full reaction with sodium methoxide. The segmented addition of carbon dioxide can make the gas more evenly distributed in the liquid, increase the gas-liquid contact area, and thus improve the reaction efficiency. The evenly distributed carbon dioxide can better react with sodium methoxide and reduce the unreacted sodium methoxide residue. By supplementing the pressurization with pressurized nitrogen, the pressure of the system can be kept stable to avoid reaction instability caused by pressure fluctuations. A stable reaction environment helps to improve the consistency and repeatability of the reaction. By accurately controlling the amount and distribution of carbon dioxide added, the generation of the by-product sodium bicarbonate can be reduced. Sodium bicarbonate has a high solubility in propylene glycol and is easily precipitated during the subsequent distillation process, causing blockage. The segmented addition of carbon dioxide can better control the reaction conditions and reduce the generation of sodium bicarbonate. In the thermal decomposition zone, maintaining a high pressure by pressurized nitrogen can improve the thermal decomposition efficiency of sodium bicarbonate, further reduce its content, and avoid problems in subsequent processes. Equipment wear caused by pressure fluctuations and local supersaturation can be reduced by adding carbon dioxide and pressurized nitrogen in segments. It helps to extend the service life of the equipment and reduce maintenance costs. The segmented addition of carbon dioxide and pressurized nitrogen can optimize operating conditions, reduce unnecessary energy consumption, and improve the operating efficiency of the equipment. It can better control the temperature and pressure during the reaction and reduce safety risks caused by local high temperature or high pressure. Pressurized nitrogen can help maintain a stable pressure in the system, reduce system instability caused by pressure fluctuations, and improve the safety and stability of the entire process. The segmented addition of carbon dioxide can flexibly adjust the carbon dioxide flow rate in each area according to the actual reaction situation to cope with changes in different batches of raw materials. This flexibility helps to optimize reaction conditions and improve product quality.

[0025] The method of adding carbon dioxide and pressurized nitrogen in stages for supplementary pressurization can significantly improve the reaction efficiency of the sodium methoxide carbonization crystallization process, control the reaction conditions, reduce the generation of by-products, improve equipment utilization, enhance safety and stability, and provide higher flexibility and adaptability.

[0026] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0027] 1. The present invention is conducive to realizing continuous production, reducing the generation of by-products, improving the utilization rate of gas, reducing possible safety hazards, and improving production efficiency;

[0028] 2. The method of adding carbon dioxide and pressurized nitrogen in stages for supplementary pressurization can significantly improve the reaction efficiency of the sodium methoxide carbonization crystallization process, control the reaction conditions, reduce the generation of by-products, improve equipment utilization, enhance safety and stability, and provide higher flexibility and adaptability;

[0029] 3. The present invention can avoid the formation of scaling due to the aggregation of fine crystals, reduce the maintenance frequency and cost of equipment, improve the conversion rate of sodium methoxide, reduce the pressure drop loss, reduce the unreacted sodium methoxide residue, and improve the overall reaction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 A schematic structural diagram of a catalyst recovery system in a cyclic carbonate preparation process provided in Example 1 of the present invention;

[0032] Figure 2 A schematic diagram of the specific structure of the second static mixer of the catalyst recovery system in the cyclic carbonate preparation process provided in Example 1 of the present invention;

[0033] Icons: 1. First static mixer; 2. Mixing pipe; 3. Second static mixer; 31. Air inlet; 32. Mixing box; 33. Circulation compression pump; 34. Collection hood; 4. Reaction pipe; 41. Cooling jacket; 5. Output pipe; 51. Heating jacket; 6. Precipitation device; 7. Separation device. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0037] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when used. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0038] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] Example 1

[0040] A catalyst recovery system in a cyclic carbonate preparation process comprises a reaction section for reacting sodium methoxide to generate sodium carbonate, a precipitation device 6 for cooling and precipitating the sodium carbonate, and a separation device 7 for separating the sodium carbonate. The length-to-diameter ratio of the reaction section pipeline is ≥500:1. The reaction section comprises a first static mixer 1 for introducing water into a crude propylene glycol solution and a plurality of groups of vertically arranged second static mixers 3 for introducing carbon dioxide, which are connected in sequence. The lower end of the second static mixer 3 is provided with an air inlet 31 for introducing carbon dioxide into the reaction section and supplementing the pressure.

[0041] In this embodiment, the reaction section includes a mixing pipe 2 connected to the first static mixer 1 and the second static mixer 3 , a reaction pipe 4 connected to a plurality of groups of second static mixers 3 , and an output pipe 5 connected to the precipitation device 6 .

[0042] In this embodiment, the reaction pipe 4 is further provided with a cooling jacket 41 for controlling the reaction temperature to be 30°C.

[0043] In this embodiment, the output pipeline 5 is provided with a heating jacket 51 for heating the propylene glycol solution after the reaction to 160° C. to decompose sodium bicarbonate.

[0044] In this embodiment, the air inlet 31 is further provided with a circulating compression pump 33 for introducing pressurized nitrogen and a mixing box 32 for mixing nitrogen and carbon dioxide.

[0045] In this embodiment, a collecting hood 34 for collecting nitrogen is provided on the top of the second static mixer 3 , and the collecting hood 34 is connected to the circulating compression pump 33 .

[0046] In this embodiment, the first static mixer 1 and the second static mixer 3 are spiral mixers.

[0047] In this embodiment, the total length of the reaction section is 75m, the inner diameter of the pipe is 0.15m, and the length-to-diameter ratio of the pipe is 500:1. Specifically, the sum of the lengths of the first static mixer 1 and the mixing pipe 2 is 24m, the sum of the lengths of the reaction pipe 4 and the second static mixer 3 is 40m, and the length of the output pipe 5 is 11m.

[0048] In this embodiment, the precipitation device 6 uses a condenser to condense and precipitate sodium carbonate, and the separation device 7 uses a plate and frame filter press to separate the sodium carbonate.

[0049] A method for recovering a catalyst in a cyclic carbonate preparation process comprises the following steps:

[0050] S1: Dispersion: Mix the crude propylene glycol solution and water in a ratio of 300:1;

[0051] S2: Ventilation reaction: carbon dioxide is introduced for reaction;

[0052] S3: Air supplement and pressurization: Add carbon dioxide and nitrogen to increase the pressure and further react, keep the pressure at the discharge end at 1barG-1.3barG, and the flow rate of the material is 1.8m / s-2m / s:

[0053] S4: Thermal decomposition: Thermal decomposition produces sodium bicarbonate as a byproduct:

[0054] S5: Precipitation and separation: Sodium carbonate is precipitated by cooling and solid-liquid separation of sodium carbonate.

[0055] In this embodiment, three groups of the second static mixers 3 are arranged in total and are evenly distributed in the reaction pipe 4 .

[0056] In this embodiment, the crude propylene glycol solution flow rate is 13 t / h, the mixed water flow rate is 43 kg / h, the carbon dioxide flow rates are 10 kg / h, 12 kg / h and 10 kg / h respectively, and the total carbon dioxide flow rate is 32 kg / h.

[0057] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 96.2 wt % propylene glycol, 2.66 wt % methanol, 0.7 wt % allyl alcohol, and 0.44 wt % sodium bicarbonate.

[0058] Example 2

[0059] The difference between this embodiment and embodiment 1 is that, in this embodiment, the heating jacket 51 is used to heat the propylene glycol solution after the reaction to 150° C. to decompose sodium bicarbonate.

[0060] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 96.5 wt % propylene glycol, 2.66 wt % methanol, 0.7 wt % allyl alcohol, and 0.74 wt % sodium bicarbonate.

[0061] Example 3

[0062] The only difference between this embodiment and embodiment 1 is that, in this embodiment, the heating jacket 51 is used to heat the propylene glycol solution after the reaction to 200° C. to decompose sodium bicarbonate.

[0063] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 96.3 wt % propylene glycol, 2.64 wt % methanol, 0.7 wt % allyl alcohol, and 0.36 wt % sodium bicarbonate.

[0064] Example 4

[0065] The only difference between this embodiment and embodiment 1 is that in this embodiment, in step S3, the pressure at the discharge end is maintained at 1.3 barG-1.5 barG, and the flow rate of the material is 2 m / s-2.1 m / s.

[0066] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 95.9 wt % propylene glycol, 2.86 wt % methanol, 0.8 wt % allyl alcohol, and 0.44 wt % sodium bicarbonate.

[0067] Example 5

[0068] The only difference between this embodiment and embodiment 1 is that, in this embodiment, the total length of the reaction section is 75 m, the inner diameter of the pipe is 0.15 m, and the length-to-diameter ratio of the pipe is 500:1. Specifically, the sum of the lengths of the first static mixer 1 and the mixing pipe 2 is 20 m, the sum of the lengths of the reaction pipe 4 and the second static mixer 3 is 40 m, and the length of the output pipe 5 is 15 m.

[0069] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 96.13 wt % propylene glycol, 2.66 wt % methanol, 0.7 wt % allyl alcohol, and 0.41 wt % sodium bicarbonate.

[0070] Example 6

[0071] The only difference between this embodiment and embodiment 1 is that, in this embodiment, the total length of the reaction section is 75 m, the inner diameter of the pipe is 0.15 m, and the length-to-diameter ratio of the pipe is 500:1. Specifically, the sum of the lengths of the first static mixer 1 and the mixing pipe 2 is 18 m, the sum of the lengths of the reaction pipe 4 and the second static mixer 3 is 45 m, and the length of the output pipe 5 is 12 m.

[0072] In this embodiment, the composition of the filtrate from the plate and frame filter press is analyzed as follows: 96.57 wt % propylene glycol, 2.28 wt % methanol, 0.7 wt % allyl alcohol, and 0.45 wt % sodium bicarbonate.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that in this comparative example, carbon dioxide is added and mixed at one time.

[0075] In this comparative example, the composition of the filtrate from the plate and frame filter press was analyzed as follows: 95.37 wt % propylene glycol, 3.18 wt % methanol, 0.9 wt % allyl alcohol, and 0.55 wt % sodium bicarbonate.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that in this comparative example, the total length of the reaction section is 30 m, the inner diameter of the pipe is 0.15 m, and the length-to-diameter ratio of the pipe is 200:1. Specifically, the sum of the lengths of the first static mixer 1 and the mixing pipe 2 is 3 m, the sum of the lengths of the reaction pipe 5 and the second static mixer 3 is 5 m, and the length of the output pipe 5 is 22 m.

[0078] In this comparative example, the composition of the filtrate from the plate and frame filter press was analyzed to be as follows: 93.6 wt % propylene glycol, 4.31 wt % methanol, 0.7 wt % allyl alcohol, and 1.39 wt % sodium bicarbonate.

[0079] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A catalyst recovery system in a cyclic carbonate preparation process, characterized in that: The invention comprises a reaction section for reacting sodium methoxide to generate sodium carbonate, a precipitation device (6) for cooling and precipitating the sodium carbonate, and a separation device (7) for separating the sodium carbonate. The length-to-diameter ratio of the pipeline of the reaction section is ≥500:

1. The reaction section comprises a first static mixer (1) for introducing water into a crude propylene glycol solution and a plurality of groups of vertically arranged second static mixers (3) for introducing carbon dioxide. The lower end of the second static mixer (3) is provided with an air inlet (31) for introducing carbon dioxide into the reaction section and supplementing the pressure.

2. The catalyst recovery system in the process of preparing cyclic carbonate according to claim 1, characterized in that: The reaction section comprises a mixing pipe (2) connected to the first static mixer (1) and the second static mixer, a reaction pipe (4) connected to a plurality of groups of second static mixers (3), and an output pipe (5) connected to the precipitation device (6).

3. The catalyst recovery system in the process of preparing cyclic carbonate according to claim 2, characterized in that: The reaction pipe (4) is also provided with a cooling jacket (41) for controlling the reaction temperature to be 20°C-40°C.

4. The catalyst recovery system in the process of preparing cyclic carbonate according to claim 2, characterized in that: The output pipeline (5) is provided with a heating jacket (51) for heating the propylene glycol solution after the reaction to 150°C-200°C to decompose the sodium bicarbonate.

5. A catalyst recovery system in a cyclic carbonate preparation process according to any one of claims 2 to 4, characterized in that: The ratio of the sum of the lengths of the first static mixer (1) and the mixing pipe (2), the sum of the lengths of the reaction pipe (4) and the second static mixer (3), and the length of the output pipe (5) is 2-3:4-5:

1.

6. A catalyst recovery system in a cyclic carbonate preparation process according to any one of claims 1 to 4, characterized in that: The air inlet (31) is also provided with a circulating compression pump (33) for introducing pressurized nitrogen and a mixing box (32) for mixing nitrogen and carbon dioxide.

7. The catalyst recovery system in the process of preparing cyclic carbonate according to claim 6, characterized in that: A collecting hood (34) for collecting nitrogen is provided on the top of the second static mixer (3), and the collecting hood (34) is connected to the circulating compression pump (33).

8. A catalyst recovery system in a cyclic carbonate preparation process according to any one of claims 1 to 4, characterized in that: The first static mixer (1) and the second static mixer (3) are spiral mixers.

9. A method for recovering a catalyst in a cyclic carbonate preparation process, characterized in that: The catalyst recovery system in the process of preparing the cyclic carbonate according to any one of claims 1 to 8 comprises the following steps: S1: Dispersion: Mix the crude propylene glycol solution and water; S2: Ventilation reaction: carbon dioxide is introduced for reaction; S3: Gas supplement and pressurization: Add carbon dioxide and nitrogen to increase the pressure and further react: S4: Thermal decomposition: Thermal decomposition produces sodium bicarbonate as a byproduct: S5: Precipitation and separation: Sodium carbonate is precipitated by cooling and solid-liquid separation of sodium carbonate.

10. The method for recovering a catalyst in a cyclic carbonate preparation process according to claim 1, characterized in that: In the step S3, carbon dioxide and nitrogen are additionally introduced to maintain the pressure at the discharge end at 1 barG-1.5 barG, and the flow rate of the material is 1.8 m / s-2.1 m / s.

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