Process method for synthesizing propylene carbonate in fixed bed reactor

Abstract

The invention discloses a process method for synthesizing propylene carbonate in a fixed bed reactor. The method comprises the following steps: in a reactor, CO2, epoxypropane and a catalyst are subjected to a contact reaction to obtain propylene carbonate; a heat exchange component is arranged in the reactor; the heat exchange part is arranged in the catalyst bed layer; the heat exchange component comprises a plurality of longitudinally arranged heat exchange tubes; the top end of the heat exchange component is flush with the top of the catalyst bed layer, and the bottom end is flush with the bottom of the catalyst bed layer; the heat exchange tube extends downwards along the axial direction of the reactor; and the heat exchange area of the heat exchange component is gradually reduced from top to bottom. The method provided by the invention solves the influence of reaction heat release on the catalyst in the fixed bed synthesis process of propylene carbonate, reduces the energy consumption in the production process, and significantly improves the yield of the target product propylene carbonate.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesizing propylene carbonate, and particularly relates to a process for synthesizing propylene carbonate in a fixed bed reactor. Background Art

[0002] Propylene carbonate is an excellent organic solvent and an important organic chemical product. It is widely used in textiles, printing and dyeing, batteries, polymer synthesis, and other fields. It also plays a key role in the synthesis of pharmaceuticals and fine chemical intermediates. In recent years, with the rapid development of electric vehicles, the demand for propylene carbonate, a key component of electric vehicle battery electrolytes, has increased dramatically.

[0003] The synthesis of propylene carbonate mostly uses homogeneous catalysts, and the reactors are mainly kettle type and shell-and-tube type reactors, which have problems such as complex products, difficult separation, low product purity and high energy consumption.

[0004] CN112851625A discloses a method for preparing cyclic carbonates. Using a halogen metal salt as a catalyst, the method involves mixing carbon dioxide and alkylene oxide in an internal circulation static mixer to produce a mixture. The mixture is then fed into a tubular reactor, where it reacts under the action of the catalyst to produce a reaction product. The product then enters a flash tank to separate the cyclic carbonate and catalyst. The reaction pressure is 0.3-3.5 MPa, the reaction temperature is 60-160°C, and the reaction time is 60-300 minutes.

[0005] CN110028483A discloses a method for preparing cyclic carbonates using an external circulation spray type gas-liquid contact process. The method uses a bifunctional catalyst containing an aluminum complex containing a quaternary ammonium salt as a catalyst. The method comprises adding the cyclic carbonate containing the catalyst to an external circulation spray reactor at a reaction pressure of 0.3 to 3.0 MPa and a reaction temperature of 60 to 150°C. The starting materials are heated to the reaction temperature via a heat exchanger, and carbon dioxide is introduced until the reaction system pressure reaches the reaction pressure. Alkylene oxide and carbon dioxide are then introduced into the external circulation spray reactor while maintaining the reaction pressure. After the addition of the materials is completed, the reaction is continued until the alkylene oxide is completely consumed. The reaction materials in the external circulation spray reactor are then transferred to a flash tank, the carbon dioxide is separated, and then vacuum distilled to obtain the cyclic carbonate. The residual liquid containing the catalyst is recycled as the starting material for the next batch of reactions.

[0006] Most existing technologies use homogeneous catalysts. While the contact methods for the working fluids in tubular reactors and circulating spray reactors differ, their goal is to increase the contact area between the reactants and remove the heat generated by the reaction. However, these methods often result in high product impurities and high energy consumption for subsequent separation. Furthermore, few existing processes utilize fixed-bed reactors for the synthesis of propylene carbonate. Therefore, developing a method for synthesizing propylene carbonate in a fixed-bed reactor is of great significance to the field of propylene carbonate synthesis technology. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention provides a process for synthesizing propylene carbonate using a fixed-bed reactor. This process utilizes a fixed-bed reactor to synthesize propylene carbonate, eliminating the effects of exothermic reaction on the catalyst, reducing energy consumption during the production process, and significantly increasing the yield of the target product, propylene carbonate.

[0008] The present invention provides a process for synthesizing propylene carbonate using a fixed-bed reactor. The process comprises the following steps:

[0009] In a fixed bed reactor, CO2, propylene oxide and catalyst react to produce propylene carbonate.

[0010] According to the present invention, the catalyst is an alkylimidazole-grafted resin microsphere catalyst. In the catalyst, the resin microspheres account for 80-90% by weight, and the alkylimidazole accounts for 10-20% by weight, based on the catalyst mass. Furthermore, the alkylimidazole includes at least one of 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, or 1-butylimidazole. The catalyst can be commercially available or prepared using conventional methods, such as surface chemical grafting.

[0011] According to the present invention, CO2 is compressed by a compressor and then mixed with propylene oxide, which is then introduced into a reactor, which is loaded with the catalyst; CO2 and propylene oxide are contacted with the catalyst to react and generate propylene carbonate.

[0012] According to the present invention, the reaction pressure is 0.1-3 MPa; the reaction temperature is 80-180°C, preferably 120-150°C; the volume space velocity of propylene oxide is 0.01-3 h -1 , preferably 0.2 to 3 hours -1 The molar ratio of CO2 to propylene oxide is 1.2 to 4, preferably 2 to 3.

[0013] According to the present invention, the reactor is a fixed-bed reactor. A heat exchange component is disposed within the reactor. The heat exchange component is disposed within the catalyst bed. The heat exchange component comprises a plurality of longitudinally arranged heat exchange tubes. The top end of the heat exchange component is flush with the top of the catalyst bed, and the bottom end is flush with the bottom of the catalyst bed. The heat exchange tubes extend downwardly along the axial direction of the reactor. The heat exchange area of ​​the heat exchange component decreases gradually from top to bottom.

[0014] According to the present invention, the heat exchange component comprises at least N heat exchange zones from top to bottom, in order of heat exchange area, namely, the first heat exchange zone, the second heat exchange zone, the third heat exchange zone, and finally the Nth heat exchange zone, where N is the number of heat exchange zones, and N is greater than or equal to 3, preferably 3 to 4. That is, from largest to smallest heat exchange area, the first heat exchange zone is the first heat exchange zone, and so on.

[0015] According to the present invention, in addition to the height ratio of the N-1th and Nth stage heat exchange zones, the height of the upper heat exchange zone accounts for 20% to 50% of the height of the adjacent lower heat exchange zone, preferably 38% to 50%.

[0016] According to the present invention, the height of the Nth stage heat exchange zone accounts for 5% to 50% of the height of the N-1th stage heat exchange zone, preferably 5% to 20%.

[0017] According to the present invention, the height of the first-stage heat exchange zone accounts for 5% to 13% of the total height of the catalyst bed.

[0018] According to the present invention, the total cross-sectional area of ​​the first stage heat exchange zone accounts for 50% to 80% of the cross-sectional area of ​​the reactor, and the cross-sectional area of ​​a single heat exchange tube accounts for 5% to 15% of the total cross-sectional area of ​​the first stage heat exchange zone.

[0019] According to the present invention, the total cross-sectional area of ​​the lower heat exchange zone accounts for 65% to 95%, preferably 77% to 95%, of the total cross-sectional area of ​​the adjacent upper heat exchange zone.

[0020] According to the present invention, preferably, the heat exchange tubes of the heat exchange component have the same diameter.

[0021] According to the present invention, the heat exchange component is provided with a gas phase outlet, which is located above the cavity at the top of the reactor connected to the refrigerant feed pipe.

[0022] According to the present invention, the refrigerant is liquid carbon dioxide. Furthermore, the refrigerant is liquid CO2 at a pressure of 6.0-7.3 MPa and a temperature of 20-31°C. The refrigerant enters the heat exchange tubes of the heat exchange component from the refrigerant feed pipe, flows downward, and after being vaporized by heat exchange on the tube walls, exits the reactor through the gas phase outlet. The heat exchange tubes contain a gas-liquid two-phase flow. The refrigerant exiting the reactor can be recycled after being pressurized and heat exchanged again. The refrigerant recycling equipment can utilize a heat exchanger and a compressor.

[0023] According to the present invention, the feed space velocity of the refrigerant is 20 to 28 kg refrigerant / (L catalyst·hour).

[0024] According to the present invention, the post-reaction stream in the reactor includes CO2 and the reaction product, propylene carbonate. The post-reaction stream flows out from the bottom of the reactor. The post-reaction stream undergoes gas-liquid separation to produce a gaseous stream and a liquid stream. The gaseous stream is CO2. The separated gaseous stream enters a propylene oxide recovery process. The liquid stream undergoes rectification to produce propylene carbonate. The gas-liquid separation device can be a high-pressure separator and a low-pressure separator.

[0025] According to the present invention, the aspect ratio of the catalyst bed is (7-20): 1. The aspect ratio is the ratio of the height to the diameter of the catalyst bed.

[0026] According to the present invention, the diameter of a single heat exchange tube is 12 to 40 mm, preferably 15 to 32 mm.

[0027] Compared with the prior art, the main advantages of the present invention are:

[0028] The present invention adopts a conventional fixed bed process. On this basis, a heat exchange component is provided in the reactor of the present invention, using liquid CO2 as a refrigerant, and the heat generated by the reaction is extracted by gasification of CO2, and then the liquid CO2 is cooled and compressed to enter the heat exchange tube by gravity. The heat extraction tubes at different positions have different evaporation effects on the low-temperature CO2 in the tube due to their different temperatures. The flow length of CO2 in the tube bundle of the secondary heat exchange zone depends on its surface temperature after heat exchange in the primary heat exchange zone. If the surface temperature is high, the gasification and cooling are accelerated. If the surface temperature is low, it flows into the next heat exchange zone. Due to the reduction in the heat exchange area of ​​the next heat exchange zone, the overall heat exchange will also decrease. The hierarchical heat exchange method can better deal with the problem that the heat release is huge in the early stage of the reaction, while the heat release decreases in the middle and late stages. The heat exchange component adopts hierarchical control according to the heat exchange area. The present invention solves the problem that the reaction heat is large when the raw material concentration at the reactor inlet is high, and the heat release decreases as the reactants decrease, thereby improving the yield of the target product propylene carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a process flow chart for synthesizing propylene carbonate in Examples 1 to 4.

[0030] Figure 2 Schematic diagram of the structure of the heat exchange component of Examples 1 to 4.

[0031] Figure 3 Schematic side views of the heat exchange components of Examples 1 to 4.

[0032] Figure 4 Schematic top view of the top of the heat exchange component of Examples 1 to 4.

[0033] Description of main reference numerals:

[0034] 1-liquid CO2, 2-propylene oxide, 3-fixed bed reactor, 4-liquid-phase logistics after reaction, 5-high-pressure separator, 6-liquid-phase logistics of high-pressure separator, 7-low-pressure separator, 8-gas-phase logistics at the top of low-pressure separator, 9-liquid-phase logistics of low-pressure separator, 10-distillation tower, 11-propylene carbonate product, 12-light component recovery, 13-CO2 circulation, 14-carbon dioxide circulation compressor, 15-circulating refrigerant, 16-refrigerant heat exchanger, 17-refrigerant compressor, 18-CO2 supplementary gas, 31-heat exchange component, 30-refrigerant feed pipe, 301-gas phase outlet, 310-heat exchange pipe, 311-first-stage heat exchange zone, 312-second-stage heat exchange zone, 313-third-stage heat exchange zone, 314-fourth-stage heat exchange zone. DETAILED DESCRIPTION

[0035] The preparation effects of the present invention are further illustrated below through examples and comparative examples. It should be understood that the specific embodiments described are only intended to illustrate and explain the present invention and are not intended to limit the present invention.

[0036] In the present invention, % refers to mass percentage unless otherwise specified.

[0037] In the present invention, the yield of propylene carbonate is expressed in mass percentage.

[0038] In the present invention, the liquid CO2 in each case is liquid CO2 at 6.1 MPa and 23°C.

[0039] In the present invention, each catalyst is prepared by chemical grafting.

[0040] In the present invention, the heat exchange component in each embodiment is described with the number of heat exchange zones being 4.

[0041] In the present invention, each embodiment adopts Figure 1 The process flow diagram of the synthesis of propylene carbonate shown in FIG. Figure 2 、 Figure 3 、 Figure 4 Heat exchange components shown.

[0042] like Figure 1 As shown, the workflow of this embodiment is as follows:

[0043] System recirculating CO2 13 and CO2 make-up gas 18 are combined and then mixed with propylene oxide 2 before entering fixed-bed reactor 3. A reaction occurs under the action of a catalyst to produce a post-reaction liquid stream 4, which flows out from the bottom of the reactor and enters a high-pressure separator 5 to separate out unreacted CO2, which is then recycled as system recirculating CO2 13. The unreacted CO2 is then recycled through a carbon dioxide recycle compressor 14. Liquid stream 6 released from the bottom of the high-pressure separator 5 is separated by a low-pressure separator 7 to remove a small amount of unreacted CO2. The liquid stream 9 separated by the low-pressure separator is then refined by a distillation tower 10 to produce propylene carbonate product 11.

[0044] Liquid CO21, acting as a refrigerant, enters the heat exchange tubes 310 of the heat exchange component 31 through the refrigerant feed pipe 30 at the top of the reactor. After evaporating within the heat exchange tubes, the refrigerant removes heat from the vapor phase outlet 301. The remaining refrigerant continues to flow downward, exchanging heat with the tube walls of the next-level region, extracting heat from the next-level region. After evaporation, the refrigerant exits the reactor through the vapor phase outlet 301. The evaporated portion of CO2 can be used as CO2 supplementary gas 18 as a reaction feedstock, or as circulating refrigerant 15, after being cooled by the refrigerant heat exchanger 16 and refrigerant compressor 17 and then circulated back into the system.

[0045] like Figure 1 、 2 As shown in Figures 3 and 4, according to a specific embodiment of the present invention, a heat exchange component is provided in the reactor. The heat exchange component is provided in the catalyst bed. The heat exchange component includes several heat exchange tubes arranged longitudinally. The top of the heat exchange component is flush with the top of the catalyst bed, and the bottom end is flush with the bottom of the catalyst bed; the heat exchange tube extends downward along the axial direction of the reactor. The heat exchange area of ​​the heat exchange component gradually decreases from top to bottom. In order of heat exchange area from large to small, they are the first-stage heat exchange zone 311, the second-stage heat exchange zone 312, the third-stage heat exchange zone 313, and the fourth-stage heat exchange zone 314. Among them, heat exchange tubes of the same diameter are used, and the multiple heat exchange tubes are evenly arranged in the reactor from the top cross-section. The heat exchange areas of the first-stage heat exchange zone 311, the second-stage heat exchange zone 312, the third-stage heat exchange zone 313, and the fourth-stage heat exchange zone 314 gradually decrease, which is achieved by using multiple heat exchange tubes of different heights. That is, the number of heat exchange tubes in the next-stage heat exchange zone is reduced compared with the adjacent upper-stage heat exchange zone, and in each stage of the heat exchange zone, the heat exchange tubes are evenly arranged in the reactor to facilitate uniform temperature distribution in the reactor.

[0046] In the present invention, Figures 1 to 4 The schematic diagram of the heat exchange component only represents the height change diagram of the heat exchange tube, and does not represent the radial distribution arrangement of the heat exchange tube in the reactor.

[0047] In the present invention, the propylene carbonate yield in the examples and comparative examples is the propylene carbonate yield after 8 hours of reaction.

[0048] In the present invention, the catalyst bed height in the examples and comparative examples was 2000 mm, the diameter was 182 mm, and the catalyst was fully loaded.

[0049] Example 1

[0050] In the heat exchange component of this example, the height of the first-stage heat exchange zone accounts for 36% of the height of the second-stage heat exchange zone. The height of the second-stage heat exchange zone accounts for 47% of the height of the third-stage heat exchange zone. The height of the fourth-stage heat exchange zone accounts for 31% of the height of the third-stage heat exchange zone. The height of the first-stage heat exchange zone accounts for 8.8% of the total height of the catalyst bed. The total cross-sectional area of ​​the first-stage heat exchange zone accounts for 51.9% of the cross-sectional area of ​​the reactor. The cross-sectional area of ​​a single heat exchange tube accounts for 5.3% of the total cross-sectional area of ​​the first-stage heat exchange zone. The total cross-sectional area of ​​the second-stage heat exchange zone accounts for 84.2% of the total cross-sectional area of ​​the first-stage heat exchange zone, the total cross-sectional area of ​​the third-stage heat exchange zone accounts for 81.3% of the total cross-sectional area of ​​the second-stage heat exchange zone, and the total cross-sectional area of ​​the fourth-stage heat exchange zone accounts for 92.3% of the total cross-sectional area of ​​the third-stage heat exchange zone.

[0051] A fixed-bed reactor is used to react CO2, propylene oxide, and a catalyst to produce propylene carbonate. The catalyst is an alkylimidazole compound grafted onto resin microspheres. The resin microspheres account for 86.8% by weight of the catalyst, and the alkylimidazole compound accounts for 13.2% by weight. The alkylimidazole compound is 1-methylimidazole.

[0052] The refrigerant fed into the heat exchange component is liquid CO2. The refrigerant feed space velocity is 22 kg refrigerant / (L catalyst·hour). The reaction pressure is 2.5 MPa; the reaction temperature is 120°C. The volume space velocity of propylene oxide is 0.2 h -1 The molar ratio of CO2 to propylene oxide was 2. The yield of propylene carbonate was 80 wt%.

[0053] Example 2

[0054] In the heat exchange components of this example, the height of the first-stage heat exchange zone accounts for 50% of the height of the second-stage heat exchange zone. The height of the second-stage heat exchange zone accounts for 50% of the height of the third-stage heat exchange zone. The height of the fourth-stage heat exchange zone accounts for 16.7% of the height of the third-stage heat exchange zone, and the height of the first-stage heat exchange zone accounts for 12% of the total height of the catalyst bed. The total cross-sectional area of ​​the first-stage heat exchange zone accounts for 51.9% of the cross-sectional area of ​​the reactor. The cross-sectional area of ​​a single heat exchange tube accounts for 5.3% of the total cross-sectional area of ​​the first-stage heat exchange zone. The total cross-sectional area of ​​the second-stage heat exchange zone accounts for 84.2% of the total cross-sectional area of ​​the first-stage heat exchange zone, the total cross-sectional area of ​​the third-stage heat exchange zone accounts for 81.3% of the total cross-sectional area of ​​the second-stage heat exchange zone, and the total cross-sectional area of ​​the fourth-stage heat exchange zone accounts for 92.3% of the total cross-sectional area of ​​the third-stage heat exchange zone.

[0055] A fixed-bed reactor is used to react CO2, propylene oxide, and a catalyst to produce propylene carbonate. The catalyst is an alkylimidazole compound grafted onto resin microspheres. The resin microspheres account for 86.8% by weight of the catalyst, and the alkylimidazole compound accounts for 13.2% by weight. The alkylimidazole compound is 1-methylimidazole.

[0056] The refrigerant fed into the heat exchange component is liquid CO2. The refrigerant feed space velocity is 26 kg refrigerant / (L catalyst·hour). The reaction pressure is 2.5 MPa; the reaction temperature is 120°C. The volume space velocity of propylene oxide is 0.2 h -1 The molar ratio of CO2 to propylene oxide was 2. The yield of propylene carbonate was 91.3 wt%.

[0057] Example 3

[0058] In this example, the height of the first-stage heat exchange section accounts for 48% of the height of the second-stage heat exchange section. The height of the second-stage heat exchange section accounts for 47% of the height of the third-stage heat exchange section. The height of the fourth-stage heat exchange section accounts for 6% of the height of the third-stage heat exchange section, and the height of the first-stage heat exchange section accounts for 12.5% ​​of the total height of the catalyst bed. The total cross-sectional area of ​​the first-stage heat exchange section accounts for 78.1% of the cross-sectional area of ​​the reactor. The cross-sectional area of ​​a single heat exchange tube accounts for 5.3% of the total cross-sectional area of ​​the first-stage heat exchange section. The total cross-sectional area of ​​the second-stage heat exchange section accounts for 85.1% of the total cross-sectional area of ​​the first-stage heat exchange section, the total cross-sectional area of ​​the third-stage heat exchange section accounts for 82.4% of the total cross-sectional area of ​​the second-stage heat exchange section, and the total cross-sectional area of ​​the fourth-stage heat exchange section accounts for 91.0% of the total cross-sectional area of ​​the third-stage heat exchange section.

[0059] A fixed-bed reactor is used to react CO2, propylene oxide, and a catalyst to produce propylene carbonate. The catalyst is an alkylimidazole compound grafted onto resin microspheres. The resin microspheres account for 86.8% by weight of the catalyst, and the alkylimidazole compound accounts for 13.2% by weight. The alkylimidazole compound is 1-methylimidazole.

[0060] The refrigerant fed into the heat exchange component is liquid CO2. The refrigerant feed space velocity is 24 kg refrigerant / (L catalyst·hour). The reaction pressure is 2.5 MPa; the reaction temperature is 110°C. The volume space velocity of propylene oxide is 0.2 h -1 The molar ratio of CO2 to propylene oxide was 3. The yield of propylene carbonate was 89.7 wt%.

[0061] Example 4

[0062] In the heat exchange component of this example, the height of the first-stage heat exchange zone accounts for 48% of the height of the second-stage heat exchange zone. The height of the second-stage heat exchange zone accounts for 47% of the height of the third-stage heat exchange zone. The height of the fourth-stage heat exchange zone accounts for 6% of the height of the third-stage heat exchange zone, and the height of the first-stage heat exchange zone accounts for 12.5% ​​of the total height of the catalyst bed. The total cross-sectional area of ​​the first-stage heat exchange zone accounts for 77.5% of the cross-sectional area of ​​the reactor. The cross-sectional area of ​​a single heat exchange tube accounts for 10.3% of the total cross-sectional area of ​​the first-stage heat exchange zone. The total cross-sectional area of ​​the second-stage heat exchange zone accounts for 87.6% of the total cross-sectional area of ​​the first-stage heat exchange zone, the total cross-sectional area of ​​the third-stage heat exchange zone accounts for 85.0% of the total cross-sectional area of ​​the second-stage heat exchange zone, and the total cross-sectional area of ​​the fourth-stage heat exchange zone accounts for 92.3% of the total cross-sectional area of ​​the third-stage heat exchange zone.

[0063] A fixed-bed reactor is used to react CO2, propylene oxide, and a catalyst to produce propylene carbonate. The catalyst is an alkylimidazole compound grafted onto resin microspheres. The resin microspheres account for 86.8% by weight of the catalyst, and the alkylimidazole compound accounts for 13.2% by weight. The alkylimidazole compound is 1-methylimidazole.

[0064] The refrigerant fed into the heat exchange component is liquid CO2. The refrigerant feed space velocity is 24 kg refrigerant / (L catalyst·hour). The reaction pressure is 2.5 MPa; the reaction temperature is 130°C. The volume space velocity of propylene oxide is 0.2 h -1 The molar ratio of CO2 to propylene oxide was 2.5. The yield of propylene carbonate was 89.3 wt%.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that the heat exchange area of ​​the heat exchange components is not controlled in stages. That is, all heat exchange tubes are of the same height. In this example, the height of the heat exchange tubes in the heat exchange zone accounts for 100% of the total height of the catalyst bed. The top ends of the heat exchange tubes are flush with the top of the catalyst bed, and the bottom ends are flush with the bottom of the catalyst bed. The total cross-sectional area of ​​the heat exchange tubes in the heat exchange zone accounts for 51.9% of the cross-sectional area of ​​the reactor, and the cross-sectional area of ​​a single heat exchange tube accounts for 5.3% of the total cross-sectional area of ​​the heat exchange tubes.

[0067] The test was conducted under the same conditions as in Example 1. That is, a fixed bed reactor was used in this example, and CO2, propylene oxide and the catalyst were contacted to react to obtain propylene carbonate. The catalyst is an alkyl imidazole compound grafted resin microsphere catalyst. In the catalyst, based on the mass of the catalyst, the resin microspheres accounted for 86.8wt%, and the alkyl imidazole compound accounted for 13.2wt%. The alkyl imidazole compound is 1-methylimidazole. The refrigerant introduced into the heat exchange component is liquid CO2. The feed air velocity of the refrigerant is 22kg refrigerant / (L catalyst·hour). The pressure of the reaction is 2.5MPa; the temperature of the reaction is 120°C. The volume air velocity of propylene oxide is 0.2h -1 The molar ratio of CO2 to propylene oxide was 2. The yield of propylene carbonate was 58.2 wt%.

Claims

1. A process for synthesizing propylene carbonate using a fixed-bed reactor, comprising: In a fixed bed reactor, CO2, propylene oxide and catalyst react to produce propylene carbonate; A heat exchange component is provided in the reactor; the heat exchange component is provided in the catalyst bed; the heat exchange component includes several longitudinally arranged heat exchange tubes; the top of the heat exchange component is flush with the top of the catalyst bed, and the bottom end is flush with the bottom of the catalyst bed; the heat exchange tube extends downward along the axial direction of the reactor; the heat exchange area of ​​the heat exchange component gradually decreases from top to bottom.

2. The method according to claim 1, characterized in that According to the size of the heat exchange area, the heat exchange component contains at least N heat exchange zones from top to bottom, namely the first heat exchange zone to the Nth heat exchange zone, N is greater than or equal to 3, and preferably N is 3-4.

3. The method according to claim 2, characterized in that In addition to the height ratio of the N-1th and Nth stage heat exchange zones, the height of the upper heat exchange zone accounts for 20% to 50%, preferably 38% to 50%, of the height of the adjacent lower heat exchange zone.

4. The method according to claim 2 or 3, characterized in that The height of the Nth stage heat exchange zone accounts for 5% to 50% of the height of the N-1th stage heat exchange zone, preferably 5% to 20%.

5. The method according to any one of claims 2 to 4, characterized in that: The height of the first-stage heat exchange zone accounts for 5% to 13% of the total height of the catalyst bed.

6. The method according to claim 2, characterized in that: The total cross-sectional area of ​​the first-stage heat exchange zone accounts for 50% to 80% of the cross-sectional area of ​​the reactor.

7. The method according to claim 2 or 6, characterized in that: The cross-sectional area of ​​a single heat exchange tube accounts for 5% to 15% of the total cross-sectional area of ​​the first-stage heat exchange zone.

8. The method according to any one of claims 2 to 7, characterized in that: The total cross-sectional area of ​​the lower heat exchange zone accounts for 65% to 95%, preferably 77% to 95%, of the total cross-sectional area of ​​the adjacent upper heat exchange zone.

9. The method according to claim 1, characterized in that: The refrigerant used is liquid carbon dioxide.

10. The method according to claim 9, characterized in that: The feed space velocity of the refrigerant is 20 to 28 kg refrigerant / (L catalyst·hour).

11. The method according to claim 1, characterized in that: The height-to-diameter ratio of the catalyst bed is (7-20):

1.

12. The method according to claim 1, characterized in that: The diameter of a single heat exchange tube is 12 to 40 mm, preferably 15 to 32 mm.

13. The method according to claim 1, characterized in that: The catalyst is an alkyl imidazole grafted resin microsphere catalyst.

14. The method according to claim 1, wherein: The reaction pressure is 0.1-3 MPa; and / or the reaction temperature is 80-180°C; and / or the volume space velocity of propylene oxide is 0.01-3 h -1 ; and / or, the molar ratio of CO2 to propylene oxide is 1.2 to 4.

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