Reaction system and reaction process for preparing propylene carbonate by urea method

Abstract

The invention discloses a reaction system and a reaction process for preparing propylene carbonate by a urea method, and relates to the technical field of chemistry and chemical engineering. The reaction system comprises a primary reaction system, a secondary reaction system and a final reaction system which are sequentially connected, the primary reaction system comprises a first reaction kettle and a first flash tank, the secondary reaction system comprises a second reaction kettle and a second flash tank, and the final reaction system comprises a third reaction kettle and a third flash tank; a baffle plate is arranged in the first reaction kettle, a spray nozzle is arranged in the second reaction kettle, a rotating plate is arranged in the third reaction kettle, and the rotating plate is coaxially connected with a stirrer in the third reaction kettle. The reaction process comprises the steps of primary reaction, secondary reaction and final reaction. The method can effectively remove ammonia gas generated in the process reaction, realizes continuous production of propylene carbonate, and is high in process yield, simple in equipment, clear in process and beneficial to large-scale production.

Description

Technical Field

[0001] This application relates to the field of chemical engineering technology, specifically to a reaction system and process for preparing propylene carbonate using the urea method. Background Technology

[0002] In existing technologies for the production of propylene carbonate using the urea process, the timely removal of ammonia generated during the reaction significantly impacts the final yield. Furthermore, the state of materials, including the catalyst, changes depending on the reaction progress and temperature conditions. These changes affect the operation of the reaction equipment and indirectly influence the ammonia removal efficiency and final yield. While some existing technologies and equipment exist for the urea process, they often focus solely on ammonia removal, neglecting the impact of material state changes, or they struggle to ensure continuous production, failing to simultaneously meet the requirements for ammonia removal, continuity, and high yield. Summary of the Invention

[0003] The purpose of this application is to provide a reaction system and process for preparing propylene carbonate using the urea method, which can effectively remove ammonia generated in the process reaction and realize the continuous production of propylene carbonate. The process has a high yield, simple equipment and clear process, which is conducive to large-scale production.

[0004] The technical solution of this application is as follows:

[0005] On one hand, embodiments of this application provide a reaction system for preparing propylene carbonate by urea method, comprising a primary reaction system, a secondary reaction system and a final reaction system connected in sequence. The primary reaction system includes a first reactor and a first flash tank, the secondary reaction system includes a second reactor and a second flash tank, and the final reaction system includes a third reactor and a third flash tank. The liquid outlet of the first reactor is connected to the inlet of the first flash tank, and the liquid outlet of the first flash tank is connected to the inlet of the first reactor and the inlet of the second reactor, respectively. The liquid outlet of the second reactor is connected to the inlet of the second flash tank, and the liquid outlet of the second flash tank is connected to the inlet of the second reactor and the inlet of the third reactor, respectively. The liquid outlet of the third reactor is connected to the inlet of the third flash tank, and the liquid outlet of the third flash tank is connected to the inlet of the third reactor and the subsequent separation process, respectively. It also includes an exhaust system, which is connected to the primary reaction system, the secondary reaction system and the final reaction system, respectively. The first reactor is equipped with a baffle plate, the second reactor is equipped with a spray nozzle, and the third reactor is equipped with a rotating plate. The rotating plate is coaxially connected to the agitator inside the third reactor.

[0006] On the other hand, this application also provides a reaction process for preparing propylene carbonate using the urea method, which is implemented through the above-mentioned reaction system and includes the following steps: Primary reaction: Take urea, 1,2-propanediol and catalyst, mix and preheat them and send them to the first reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged and the reaction products are sent to the first flash tank for flash evaporation to obtain flash products and waste gas. The waste gas is discharged and part of the flash products are sent back to the first reactor. The remaining part is sent to the subsequent process steps. Secondary reaction: A portion of the flash product obtained in the primary reaction step is fed into the second reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged, and the reaction products are sent to the second flash tank for flash evaporation. Flash products and waste gas are obtained, and the waste gas is discharged. A portion of the flash product is returned to the second reactor, and the remaining portion is sent to the subsequent process steps. Final stage reaction: A portion of the flash product obtained in the secondary reaction step is fed into the third reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged, and the reaction products are sent to the third flash tank for flash evaporation to obtain flash products and waste gas. The waste gas is discharged, a portion of the flash products is returned to the third reactor, and the remaining portion is sent to the subsequent separation process to obtain the product.

[0007] Compared with the prior art, the embodiments of this application have at least the following advantages or beneficial effects: To address the above aspects, this application provides a reaction system and process for preparing propylene carbonate using a urea method. The system uses urea, 1,2-propanediol (PG), and a catalyst as raw materials. First, a primary reaction is carried out in a primary reaction system. The main purpose of the primary reaction is to obtain the intermediate product hydroxypropyl carbamate (HPC), and the ammonia gas produced is discharged. The reactants are then flash-evaporated in a first flash tank to further remove ammonia. After flash evaporation, a portion of the material is returned to the first reactor for further reaction to ensure complete reaction and conserve resources, while the remaining material is sent to a secondary reaction system for subsequent process steps.

[0008] The materials further enter the secondary reaction system. At this stage, the second reactor mainly contains urea, PG, catalyst, and HPC, undergoing a secondary reaction. The primary purpose of this secondary reaction is to simultaneously deammonize HPC to form propylene carbonate (PC), while the resulting ammonia gas is discharged. The reactants are then flash-evaporated in a second flash tank to further remove ammonia. After flash evaporation, a portion of the material is returned to the second reactor for further reaction to ensure complete reaction and conserve resources, while the remaining material is sent to the final reaction system for subsequent process steps.

[0009] The materials further enter the final stage reaction system. At this point, the materials in the third reactor mainly consist of HPC, PC, catalyst, and PG, undergoing a final stage reaction. The primary purpose of this final stage reaction is to deammoniate HPC to obtain PC, and the resulting ammonia gas is discharged. PG is recovered via a third flash tank, and the waste gas (ammonia) generated within the system is discharged through the exhaust system. The ammonia gas in the materials is further removed by flash evaporation in the third flash tank. After flash evaporation, some of the material is returned to the third reactor for further reaction to ensure complete reaction and conserve resources. The remaining material can be sent to subsequent separation processes for further separation and refining, ultimately yielding the final product.

[0010] In the entire reaction system, during the primary reaction, the materials in the primary reaction system are mainly in a solid-liquid mixed state. The first reaction vessel is equipped with baffles to ensure thorough mixing of the materials. During the secondary reaction, the materials in the secondary reaction system are mainly in a liquid state. The ammonia gas generated during the reaction is better removed by spraying the feed through nozzles in the second reaction vessel. During the final reaction, the materials in the final reaction system become more viscous due to the solid-liquid mixed state. If nozzle spraying is still used at this time, it is easy to clog the equipment. If baffles are used, it is easy to cause sticking. However, the rotating plate in the third reaction vessel is used to assist stirring to avoid the above situations and also help improve the ammonia removal effect in the system.

[0011] Through the above reaction system, continuous production of propylene carbonate by urea method can be achieved. The system equipment can be better adapted to the reaction process and can remove ammonia generated during the reaction in a timely and effective manner, thereby avoiding unnecessary side reactions, improving the final yield of the process, and facilitating large-scale production. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a flowchart illustrating the reaction system and process flow for the preparation of propylene carbonate using the urea method in this application. Figure 2 This is a schematic diagram of the structure of the first reaction vessel in the embodiments of this application; Figure 3 This is a schematic diagram of the structure of the second reactor in the embodiments of this application; Figure 4 This is a schematic diagram of the structure of the third reactor in the embodiments of this application.

[0014] Reference numerals in the attached drawings: 1-First reaction vessel, 11-Baffle plate, 2-First flash tank, 3-Second reaction vessel, 31-Spray nozzle, 4-Second flash tank, 5-Third reaction vessel, 51-Rotating plate, 6-Third flash tank, 7-First vacuum pump, 8-Second vacuum pump, 9-First condenser, 10-Second condenser. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations; without conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0016] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0017] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0018] It should be noted that relational terms such as "first," "second," and "third" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the term "comprising," or any other variation thereof, is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes it.

[0019] It should be noted that, unless otherwise specified in the examples, the conditions should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0020] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0021] Example 1 Please see Figures 1-4 This application provides a reaction system for preparing propylene carbonate by urea method, including a primary reaction system, a secondary reaction system and a final reaction system connected in sequence. The primary reaction system includes a first reactor 1 and a first flash tank 2. The secondary reaction system includes a second reactor 3 and a second flash tank 4. The final reaction system includes a third reactor 5 and a third flash tank 6. The liquid outlet of the first reactor 1 is connected to the inlet of the first flash tank 2. The liquid outlet of the first flash tank 2 is connected to the inlet of the first reactor 1 and the inlet of the second reactor 3. The liquid outlet of the second reactor 3 is connected to the inlet of the second flash tank 4. The liquid outlet of the second flash tank 4 is connected to the inlet of the second reactor 3 and the inlet of the third reactor 5. The liquid outlet of the third reactor 5 is connected to the inlet of the third flash tank 6. The liquid outlet of the third flash tank 6 is connected to the inlet of the third reactor 5 and the subsequent separation process. It also includes an exhaust system, which is connected to the primary reaction system, the secondary reaction system and the final reaction system, respectively. The first reactor 1 is provided with a baffle plate 11, the second reactor 3 is provided with a spray nozzle 31, and the third reactor 5 is provided with a rotating plate 51. The rotating plate 51 is coaxially connected to the stirrer in the third reactor 5.

[0022] Furthermore, the exhaust system includes a first vacuum pump 7 and a second vacuum pump 8; the gas outlets of the first reactor 1, the second reactor 3 and the third reactor 5 are all connected to the first vacuum pump 7; the gas outlets of the first flash tank 2, the second flash tank 4 and the third flash tank 6 are all connected to the second vacuum pump 8.

[0023] Furthermore, the gas outlets of the first reactor 1, the second reactor 3, and the third reactor 5 are all connected to a first condenser 9, and the outlet of any one of the first condensers 9 is connected to the first vacuum pump 7; the gas outlets of the first flash tank 2, the second flash tank 4, and the third flash tank 6 are all connected to a second condenser 10, and the outlet of any one of the second condensers 10 is connected to the second vacuum pump 8.

[0024] Example 2 This application provides a reaction process for preparing propylene carbonate using the urea method, which is implemented using the reaction system provided in Example 1, and the process flow is as follows: Figure 1 As shown, it includes the following steps: Primary reaction: Urea and 1,2-propanediol (PG) are mixed at a molar ratio of 1:1.5, and a catalyst of 2% by weight of urea is added. The mixture is preheated to 80°C and then fed into the first reactor 1. The temperature inside the first reactor 1 is controlled below 144°C, and the reaction is carried out under a vacuum of -60 kPa to obtain the reaction products (mainly hydroxypropyl carbamate (HPC)) and waste gas (ammonia and gaseous PG). The waste gas is condensed by the first condenser 9 to recover the PG and is fed back into the first reactor 1. The ammonia is discharged through the first vacuum pump 7. The reacted material in the first reactor 1 (mainly composed of unreacted urea, PG, catalyst, intermediate product HPC, and residual ammonia) is sent to the first flash tank 2 for flash evaporation to remove ammonia. After flash evaporation, flash products (mainly composed of urea, PG, catalyst, and HPC) and waste gas (ammonia and gaseous PG) are obtained. The waste gas is condensed and PG is recovered by the second condenser 10, and the ammonia is discharged by the second vacuum pump 8. Part of the flash products are sent back to the first reactor 1 for re-reaction, and part is sent to the second reactor 3 for subsequent secondary reaction steps.

[0025] Secondary reaction: Part of the flash products obtained in the primary reaction step (mainly urea, PG, catalyst and HPC) are fed into the second reactor 3 and reacted under vacuum of -60 kPa and 145-168°C to obtain reaction products (mainly HPC and propylene carbonate (PC) obtained by removing ammonia from HPC) and waste gas (ammonia and gaseous PG). The waste gas is condensed by the first condenser 9 to recover the PG and is fed back into the second reactor 3, while the ammonia is discharged by the first vacuum pump 7. The reacted material in the second reactor 3 (mainly composed of unreacted PG, as well as catalyst, HPC, PC and residual ammonia) is sent to the second flash tank 4 for flash evaporation to remove ammonia. After flash evaporation, flash products (mainly composed of PG, catalyst, HPC and PC) and waste gas (ammonia and gaseous PG) are obtained. The waste gas is condensed and PG is recovered by the second condenser 10, and the ammonia is discharged by the second vacuum pump 8. Part of the flash products are sent back to the second reactor 3 for re-reaction, and part is sent to the third reactor 5 for subsequent final reaction steps.

[0026] Final stage reaction: Part of the flash products obtained in the secondary reaction step (mainly composed of PG, catalyst, HPC and PC) are sent to the third reactor 5 and reacted under vacuum of -60 kPa and 168-170 °C to obtain reaction products (mainly PC) and waste gas (ammonia and gaseous PG). The waste gas is condensed by the first condenser 9 to recover the PG and is sent back to the third reactor 5, while the ammonia is discharged by the first vacuum pump 7. The reacted material (mainly composed of PG, catalyst, PC, and residual ammonia) in the third reactor 5 is sent to the third flash tank 6 for flash evaporation to remove ammonia. After flash evaporation, flash products (mainly composed of PG, catalyst, and PC) and waste gas (ammonia and gaseous PG) are obtained. The waste gas is condensed and PG is recovered by the second condenser 10, and the ammonia is discharged by the second vacuum pump 8. Part of the flash products are sent back to the third reactor 5 for re-reaction (there may be a small amount of unreacted HPC remaining), and part is sent to the subsequent separation process to finally obtain the product.

[0027] Comparative Example 1 Based on the reaction process provided in Example 2, the flash tanks (i.e., the first flash tank 2, the second flash tank 4, and the third flash tank 6) in the system are removed. In each process step, the material obtained after the reaction in the reactor is no longer subjected to flash evaporation to remove ammonia, but is directly sent to the subsequent system for subsequent process steps.

[0028] Test case The urea method for preparing propylene carbonate was carried out according to the processes of Example 2 and Comparative Example 1, respectively. After stable and continuous production, the products were collected, and their ammonia content and PC yield were tested. The results are shown in Table 1.

[0029] Table 1

[0030] As can be seen from the results, the reaction system and reaction process provided in this application embodiment have better ammonia removal effect and higher product yield.

[0031] In summary, the embodiments of this application provide a reaction system and process for preparing propylene carbonate using the urea method, which enables continuous production of propylene carbonate using the urea method. The system equipment can be better adapted to the reaction process and can remove ammonia generated during the reaction in a timely and effective manner, thereby avoiding unnecessary side reactions and improving the final yield of the process, which is conducive to large-scale production.

[0032] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A reaction system for preparing propylene carbonate using the urea process, characterized in that, It includes a primary reaction system, a secondary reaction system and a final reaction system connected in sequence. The primary reaction system includes a first reactor and a first flash tank. The secondary reaction system includes a second reactor and a second flash tank. The final reaction system includes a third reactor and a third flash tank. The liquid outlet of the first reactor is connected to the inlet of the first flash tank, and the liquid outlet of the first flash tank is connected to the inlet of the first reactor and the inlet of the second reactor, respectively; the liquid outlet of the second reactor is connected to the inlet of the second flash tank, and the liquid outlet of the second flash tank is connected to the inlet of the second reactor and the inlet of the third reactor, respectively; the liquid outlet of the third reactor is connected to the inlet of the third flash tank, and the liquid outlet of the third flash tank is connected to the inlet of the third reactor and the subsequent separation process, respectively. It also includes an exhaust system, which is connected to the primary reaction system, the secondary reaction system and the final reaction system respectively; The first reactor is equipped with a baffle plate, the second reactor is equipped with a spray nozzle, and the third reactor is equipped with a rotating plate, which is coaxially connected to the stirrer inside the third reactor.

2. The reaction system and process for preparing propylene carbonate using the urea method according to claim 1, characterized in that, The exhaust system includes a first vacuum pump and a second vacuum pump; the gas outlets of the first reaction vessel, the second reaction vessel, and the third reaction vessel are all connected to the first vacuum pump; the gas outlets of the first flash tank, the second flash tank, and the third flash tank are all connected to the second vacuum pump.

3. The reaction system for preparing propylene carbonate by the urea method according to claim 2, characterized in that, The gas outlets of the first reactor, the second reactor, and the third reactor are all connected to a first condenser, and the outlet of any one of the first condensers is connected to the first vacuum pump; the gas outlets of the first flash tank, the second flash tank, and the third flash tank are all connected to a second condenser, and the outlet of any one of the second condensers is connected to the second vacuum pump.

4. A reaction process for preparing propylene carbonate using the urea method, characterized in that, It is achieved through a reaction system as described in any one of claims 1 to 3, comprising the following steps: Primary reaction: Take urea, 1,2-propanediol and catalyst, mix and preheat them and send them to the first reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged and the reaction products are sent to the first flash tank for flash evaporation to obtain flash products and waste gas. The waste gas is discharged and part of the flash products are sent back to the first reactor. The remaining part is sent to the subsequent process steps. Secondary reaction: A portion of the flash product obtained in the primary reaction step is fed into the second reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged, and the reaction products are sent to the second flash tank for flash evaporation. Flash products and waste gas are obtained, and the waste gas is discharged. A portion of the flash product is returned to the second reactor, and the remaining portion is sent to the subsequent process steps. Final stage reaction: A portion of the flash product obtained in the secondary reaction step is fed into the third reactor. After the reaction, reaction products and waste gas are obtained. The waste gas is discharged, and the reaction products are sent to the third flash tank for flash evaporation to obtain flash products and waste gas. The waste gas is discharged, a portion of the flash products is returned to the third reactor, and the remaining portion is sent to the subsequent separation process to obtain the product.

5. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the primary reaction step, the waste gas obtained from the reaction in the first reactor is condensed, the condensed liquid material is recovered back to the first reactor, and then the waste gas is discharged. The waste gas obtained from the first flash tank is condensed, the condensed liquid material is recovered back into the first flash tank, and then the waste gas is discharged.

6. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the secondary reaction step, the waste gas obtained from the reaction in the second reactor is condensed, the condensed liquid material is recovered into the second reactor, and then the waste gas is discharged. The waste gas obtained from the first flash tank is condensed, and the liquid material obtained from the condensation is recovered into the second flash tank before the waste gas is discharged.

7. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the final reaction step, the waste gas obtained from the reaction in the third reactor is condensed, the condensed liquid material is recovered back to the third reactor, and then the waste gas is discharged. The waste gas obtained from the third flash tank is condensed, and the condensed liquid material is recovered back into the third flash tank before the waste gas is discharged.

8. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the primary reaction step, the molar ratio of urea to 1,2-propanediol is 1:(1.5-2), and the amount of catalyst used is 2-3% of the mass of urea.

9. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the primary reaction step, urea, 1,2-propanediol and catalyst are mixed, preheated to 70-80°C, and then fed into the first reaction vessel for reaction.

10. The reaction process for preparing propylene carbonate using the urea method according to claim 4, characterized in that, In the primary reaction step, the reaction temperature inside the first reaction vessel is controlled to be below 144°C. In the secondary reaction step, the reaction temperature inside the second reactor is controlled to be 145–165°C. In the final stage reaction step, the reaction temperature inside the third reactor is controlled at 168–170°C.

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