Method for synthesizing propylene carbonate by tubular reactor

Abstract

The invention discloses a method for synthesizing propylene carbonate by a tubular reactor. The method comprises the following steps: carrying out contact reaction on CO2, epoxypropane and a catalyst by adopting a tubular reactor to obtain propylene carbonate, the tubular reactor comprises a shell pass and a tube pass; the reaction of synthesizing the propylene carbonate is carried out in a tube pass; a heat exchange medium is introduced into the shell side; the heat exchange medium comprises propylene carbonate and CO2. According to the method, the content of propylene carbonate in the product is increased, the energy consumption in the production process is reduced, and the economic benefit is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesizing propylene carbonate, and particularly relates to a method for synthesizing propylene carbonate using a tubular 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 primarily utilizes homogeneous catalysts, primarily in kettle and shell-and-tube reactors. These processes present challenges such as complex product formation, difficult separation, low product purity, and high energy consumption. While some continuous reactions have been reported, these have typically employed homogeneous catalysts such as ionic liquids.

[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] CN114761390A discloses a kind of method that prepares cyclic carbonate product continuously by making epoxide and carbon dioxide reaction under the heterogeneous catalyst that is activated by activating compound.This method is carried out in first reactor, second reactor, the 3rd reactor, and each reactor comprises the suspension of heterogeneous catalyst and the cyclic carbonate product that exists in liquid form.To the first reactor continuous supply carbon dioxide and epoxide, liquid cyclic carbonate is discharged and unreacted carbon dioxide and epoxide are discharged to the second reactor as the first gaseous effluent stream, and substantially all heterogeneous catalysts remain in the first reactor.In the 3rd reactor, add activating compound.Then, the 3rd reactor becomes the second reactor, and the second reactor becomes the first reactor and the first reactor becomes the 3rd reactor, reacts successively and produces cyclic carbonate continuously.

[0006] Although CN112851625A also uses a shell-and-tube reactor to increase the contact area of ​​the reactants, it is inefficient in removing the heat generated by the reaction. Although CN114761390A can produce continuously, it has problems with catalyst filtration and impurity separation, and this will result in high separation energy consumption. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention provides a method for synthesizing propylene carbonate using a tubular reactor. The method of the present invention increases the propylene carbonate content in the product, reduces energy consumption in the production process, and improves economic benefits.

[0008] The present invention provides a method for synthesizing propylene carbonate using a tubular reactor. The method comprises the following steps:

[0009] Using a shell-and-tube reactor, CO2, propylene oxide and a catalyst are contacted and reacted to produce propylene carbonate;

[0010] The shell-and-tube reactor comprises a shell side and a tube side; the reaction of synthesizing propylene carbonate is carried out in the tube side; a heat exchange medium is introduced into the shell side; the heat exchange medium comprises propylene carbonate and CO2.

[0011] 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.

[0012] According to the present invention, the shell-and-tube reactor comprises a shell side and a tube side. The tube side is loaded with a catalyst; the reaction for synthesizing propylene carbonate occurs in the tube side. The reaction is exothermic. A heat exchange medium is introduced into the shell side. The heat exchange medium comprises propylene carbonate and CO2. The mass ratio of propylene carbonate to CO2 is (0.5-2):1.

[0013] According to the present invention, preferably, the heat exchange medium further contains propylene oxide, and the mass ratio of propylene oxide to CO2 is (0.1-0.7):1, preferably (0.4-0.7):1.

[0014] According to the present invention, the CO2 in the heat exchange medium is low-temperature CO2, which is -20 to -5°C, preferably -10 to -5°C.

[0015] According to the present invention, a heat exchange medium is introduced into the reactor through the bottom inlet of the shell side and exits the reactor through the top outlet of the shell side. The effluent of the heat exchange medium can be subjected to gas-liquid separation to produce propylene oxide and CO2. The gaseous propylene oxide and CO2 are cooled and frozen to separate the propylene oxide, producing low-temperature CO2. This CO2 can then be mixed with the separated liquid stream and recycled as the heat exchange medium.

[0016] According to the present invention, the reaction raw materials can be preheated before being introduced into the reactor. The preheating temperature of the reaction raw materials propylene oxide and CO2 is 100-170°C.

[0017] According to the present invention, the reaction pressure is 0.1 to 3.0 MPa, the tube-side inlet temperature is 100 to 180°C, preferably 120 to 150°C. The tube-side outlet temperature is ≤ 190°C, preferably 140 to 190°C. The feeding method of the tubular reactor is upflow. Propylene oxide and CO2 are introduced into the reactor through the bottom tube-side inlet, and the post-reaction stream flows out of the reactor through the top tube-side outlet.

[0018] According to the present invention, the tube diameter of the tubular reactor is 10-200 mm, preferably 20-100 mm, more preferably 35-80 mm, and the aspect ratio is 30-200, preferably 80-160, more preferably 100-150.

[0019] According to the present invention, the number of tubes in the tubular reactor is greater than or equal to 2, preferably 7 to 2000.

[0020] According to the present invention, the feed volume space velocity of the reaction raw material propylene oxide is 0.01 to 3.0 h -1 , preferably 0.08~1.2h -1 ; The molar ratio of CO2 and propylene oxide is 1.2 to 4, preferably 2 to 3.

[0021] According to the present invention, the feed space velocity of the heat exchange medium is 10 to 50 kg heat exchange medium / (kg propylene oxide·hour).

[0022] Compared with the prior art, the main advantages of the present invention are:

[0023] The present invention uses propylene carbonate that has absorbed CO2 as a heat exchange medium. By absorbing the low-temperature CO2 in the system, the system comprehensively utilizes the cold source, and heat is removed by separating the CO2 through heat exchange. This reduces the energy consumption required for cooling and achieves comprehensive energy utilization. Due to the high boiling point of propylene carbonate, the amount of propylene carbonate required for the same heat exchange capacity is only 25% of that of water. At the same time, the propylene carbonate content in the product is increased.

[0024] Preferably, the present invention also incorporates propylene oxide into the heat exchange medium. One advantage of adding propylene oxide is that it facilitates the separation of the gaseous CO₂ after heat exchange, allowing the separated liquid phase to absorb more low-temperature CO₂ (compared to without propylene oxide) to form new heat exchange medium for recycling. A second advantage is that the addition of propylene oxide to the heat exchange medium reduces the gaseous partial pressure of CO₂, regulates the composition of the heat exchange medium in the tube side, prevents localized temperature fluctuations, and achieves a uniform reaction temperature within the tube, facilitating the reaction in the tube side and increasing the propylene carbonate content in the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The process flow chart of synthesizing propylene carbonate in Examples 1 to 3 is shown.

[0026] Main reference numerals:

[0027] 1-propylene carbonate; 2-propylene oxide; 3-a mixture of reaction raw materials propylene oxide and carbon dioxide; 4-shell side inlet logistics; 5-shell side outlet logistics; 6-light components rich in CO2; 7-materials at the outlet of the tubular reactor after reaction; 8-bottom logistics of the high-pressure separator; 9-circulating CO2; 10-light components at the top of the low-pressure separator; 11-bottom logistics of the low-pressure separator; 12-light components at the top of the distillation tower; 13-propylene carbonate-rich logistics; 14-impurities and water; 15-low-temperature CO2; 16-propylene carbonate product; 17-tubular reactor; 18-flash separator; 19-high-pressure separator; 20-low-pressure separator; 21-distillation tower; 22-refrigerator. DETAILED DESCRIPTION

[0028] 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.

[0029] In the present invention, % refers to mass percentage unless otherwise specified.

[0030] In the present invention, nCO2:nPO in each example is the molar ratio of CO2 to propylene oxide.

[0031] In the present invention, each example adopts Figure 1 The process flow of synthesizing propylene carbonate is shown.

[0032] The catalysts used in the Examples and Comparative Examples are identical, consisting of alkylimidazole-grafted resin microspheres. The catalysts comprise 86.8% by weight of the resin microspheres and 13.2% by weight of the alkylimidazole, based on the catalyst mass. The alkylimidazole is 1-methylimidazole. The catalysts were prepared using a surface chemical grafting method.

[0033] In the present invention, the diameter of each tubular reactor is 40 mm, the aspect ratio is 100, and the number of tubes in the tubular reactor is 7.

[0034] In the present invention, the low-temperature CO2 temperature in each embodiment is -10°C.

[0035] In the present invention, the raw materials in each embodiment were preheated before being introduced into the reactor. The preheating temperature of propylene oxide and CO2 was 120°C.

[0036] In the present invention, the reaction product is analyzed by chromatography to determine the content of the product.

[0037] In the present invention, the gas-liquid separation conditions of the heat exchange medium effluent in each embodiment in the flash separator are: temperature 156° C., pressure 2.0 MPa.

[0038] like Figure 1 As shown, a mixture of propylene oxide and carbon dioxide (CO2) 3, the raw materials, is mixed and preheated, and then flows into the bottom inlet of a tubular reactor 17. The outlet stream 7 enters a high-pressure separator 19 to separate excess CO2, which is then recycled back to the bottom inlet of the tubular reactor 17. The bottom stream 8 of the high-pressure separator enters a low-pressure separator 20 to separate lighter components 10, including CO2, propylene oxide, and water. The heavier component 11, propylene carbonate, flows into a distillation column 21 for purification to produce propylene carbonate product 16. The light component 10 at the top of the low-pressure separator 20 and the light component 12 at the top of the distillation column enter a freezer 22 for freezing and impurity removal 14, yielding low-temperature CO2 15. The heat exchange medium 4, formed by mixing low-temperature CO2 15, propylene oxide 2, and propylene carbonate 1, enters the shell side of the tubular reactor, exchanges heat, and flows out of the shell side outlet. The shell side outlet stream 5 is then separated from the CO2 in a flash separator 18. The liquid stream of propylene carbonate is returned to the shell side inlet of the tubular reactor or sent to a distillation tower to be refined into a product.

[0039] Example 1

[0040] Analytically pure 99.7wt% propylene oxide and carbon dioxide were used as raw materials. Propylene carbonate, CO2 and propylene oxide were used as heat exchange media, wherein the mass ratio of propylene carbonate to CO2 was 0.83:1, and the mass ratio of propylene oxide to CO2 was 0.1:1. The feed space velocity of the heat exchange medium was 22.1kg heat exchange medium / (kg propylene oxide·hour). Under the conditions of tube inlet temperature of 140℃, tube outlet temperature of 162℃, reaction pressure of 2.0MPa and nCO2:nPO=2.5, the feed volume space velocity of propylene oxide was 0.08h in the tubular reactor. -1 Feed reaction.

[0041] The shell-side inlet temperature of the heat exchange medium is 65°C, the shell-side outlet temperature is 152°C, and the maximum reaction temperature in the tube side is 170°C.

[0042] The heat exchange medium effluent from the reactor at the shell-side outlet was subjected to gas-liquid separation to separate CO2. The CO2 mass content in the liquid phase stream after heat exchange medium separation was 2.7%.

[0043] After 18 hours of reaction, the collected reaction products were analyzed and found to have a propylene carbonate content of 91.1 wt% and a propylene oxide content of 8.9 wt%.

[0044] Example 2

[0045] Analytically pure 99.7wt% propylene oxide and carbon dioxide were used as raw materials. Propylene carbonate, CO2 and propylene oxide were used as heat exchange media. The mass ratio of propylene carbonate and CO2 was 1.2:1, and the mass ratio of propylene oxide and CO2 was 0.6:1. The feed space velocity of the heat exchange medium was 18.6kg heat exchange medium / (kg propylene oxide·hour). Under the conditions of tube inlet temperature of 140℃, tube outlet temperature of 140℃, reaction pressure of 2.0MPa and nCO2:nPO=2.5, the feed volume space velocity of propylene oxide was 0.08h in the tubular reactor. -1 Feed reaction.

[0046] The heat exchange medium inlet temperature is 65°C, the shell side outlet temperature is 130°C, and the maximum reaction temperature in the tube side is 162°C.

[0047] The heat exchange medium effluent from the reactor at the shell-side outlet was subjected to gas-liquid separation to separate CO2. The CO2 mass content in the liquid phase stream after heat exchange medium separation was 2.1%.

[0048] After 18 hours of reaction, the collected reaction products were analyzed and found to have a propylene carbonate content of 94.4 wt% and a propylene oxide content of 5.6 wt%.

[0049] Example 3

[0050] Analytically pure 99.7wt% propylene oxide and carbon dioxide were used as raw materials. Propylene carbonate, CO2 and propylene oxide were used as heat exchange media, wherein the mass ratio of propylene carbonate and CO2 was 1:1, and the mass ratio of propylene oxide and CO2 was 0.3:1. The feed space velocity of the heat exchange medium was 19.3kg heat exchange medium / (kg propylene oxide·hour). Under the conditions of tube inlet temperature of 140℃, tube outlet temperature of 147℃, reaction pressure of 2.0MPa and nCO2:nPO=2.5, the feed volume space velocity of propylene oxide was 0.08h in the tubular reactor. -1 Feed reaction.

[0051] The shell-side inlet temperature of the heat exchange medium is 65°C, and the shell-side outlet temperature is 164°C. The maximum reaction temperature in the tube side is 173°C.

[0052] The heat exchange medium effluent from the reactor at the shell-side outlet was subjected to gas-liquid separation to separate CO2. The CO2 content in the liquid phase after heat exchange medium separation was 1.8% by mass.

[0053] After 18 hours of reaction, the collected reaction products were analyzed and found to have a propylene carbonate content of 91.2 wt% and a propylene oxide content of 8.8 wt%.

[0054] Example 4

[0055] The main difference between this example and Example 1 is that propylene oxide is not introduced into the heat exchange medium.

[0056] Analytically pure 99.7wt% propylene oxide and carbon dioxide were used as raw materials. Propylene carbonate and CO2 were used as heat exchange media, wherein the mass ratio of propylene carbonate to CO2 was 0.83:1. The feed space velocity of the heat exchange medium was 25.7kg heat exchange medium / (kg propylene oxide·hour). Under the conditions of tube inlet temperature of 140℃, tube outlet temperature of 167℃, reaction pressure of 2.0MPa and nCO2:nPO=2.5, the feed volume space velocity of propylene oxide was 0.08h in the tubular reactor. -1 Feed reaction.

[0057] The shell-side inlet temperature of the heat exchange medium is 65°C, and the shell-side outlet temperature is 157°C. The highest reaction temperature in the tube side is 171°C.

[0058] The heat exchange medium effluent from the reactor at the shell-side outlet was subjected to gas-liquid separation to separate CO2. The CO2 mass content in the liquid phase stream after heat exchange medium separation was 3.8%.

[0059] After 18 hours of reaction, the collected reaction products were analyzed and found to have a propylene carbonate content of 85.7 wt% and a propylene oxide content of 14.3 wt%.

[0060] Comparative Example 1

[0061] The main difference between this example and Examples 1-4 is that the heat exchange medium is water.

[0062] Analytically pure 99.7 wt% propylene oxide and carbon dioxide were used as raw materials. Water was used as the heat exchange medium. The water feed space velocity was 66.7 kg heat exchange medium / (kg propylene oxide·hour). Under the conditions of tube side inlet temperature of 140°C, tube side outlet temperature of 134°C, reaction pressure of 2.0 MPa and nCO2:nPO=2.5, the propylene oxide feed volume space velocity was 0.08 h in the tubular reactor. -1 Feed reaction.

[0063] In the tube side of Comparative Example 1, the difference between the highest and lowest reaction temperatures was 60°C, a significant difference (the temperature differences in the examples were all within 33°C). Furthermore, the highest reaction temperature in the tube side of Comparative Example 1 reached 196°C, exceeding the maximum temperature allowed by the catalyst.

[0064] After 18 hours of reaction, the collected reaction products were analyzed. The mass content of propylene carbonate in Comparative Example 1 was 80.3 wt %; the mass content of propylene oxide was 19.7 wt %.

[0065] Comparison of Examples 1-4 and Comparative Example 1 shows that using water as the medium results in a high and uneven temperature rise in the heat exchange section. Using the heat exchange medium of the present invention results in a smaller temperature rise and no temperature spike within the reactor. Product analysis also demonstrates a significant increase in the propylene carbonate content of the present invention.

Claims

1. A method for synthesizing propylene carbonate using a tubular reactor, comprising the following steps: Using a shell-and-tube reactor, CO2, propylene oxide and a catalyst are contacted and reacted to produce propylene carbonate; The shell-and-tube reactor comprises a shell side and a tube side; the reaction of synthesizing propylene carbonate is carried out in the tube side; a heat exchange medium is introduced into the shell side; The heat exchange medium includes propylene carbonate and CO2.

2. The method according to claim 1, characterized in that The heat exchange medium also contains propylene oxide; further, the mass ratio of propylene oxide to CO2 is (0.1-0.7):1, preferably (0.4-0.7):

1.

3. The method according to claim 1 or 2, characterized in that The mass ratio of propylene carbonate and CO2 in the heat exchange medium is (0.5-2):

1.

4. The method according to claim 1, characterized in that The CO2 in the heat exchange medium is low-temperature CO2, and the low temperature is preferably -20 to -5°C, preferably -10 to -5°C.

5. The method according to claim 1, characterized in that: The reaction pressure is 0.1~3.0MPa.

6. The method according to claim 1 or 5, characterized in that The tube side inlet temperature is 100-180°C, preferably 120-150°C; the tube side outlet temperature is ≤190°C, preferably 140-190°C.

7. The method according to claim 1, characterized in that: The feed volume space velocity of the reaction raw material propylene oxide is 0.01~3.0h -1 , preferably 0.08~1.2h -1 .

8. The method according to claim 1, characterized in that: The molar ratio of CO2 to propylene oxide is 1.2 to 4, preferably 2 to 3.

9. The method according to claim 1, characterized in that: The catalyst is an alkylimidazole-grafted resin microsphere catalyst. The resin microspheres comprise 80-90 wt% of the catalyst by weight, and the alkylimidazole comprises 10-20 wt% of the catalyst by weight. Furthermore, the alkylimidazole comprises at least one of 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, or 1-butylimidazole.

10. The method according to claim 1, characterized in that: The tube diameter of the tubular reactor is 10 to 200 mm.

11. The method according to claim 1, characterized in that: The feed space velocity of the heat exchange medium is 10 to 50 kg heat exchange medium / (kg propylene oxide·hour); wherein propylene oxide is the reaction raw material propylene oxide.

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