A separation and purification system and method for preparing propylene carbonate by urea process

Abstract

The present invention provides a separation and purification system and method for preparing propylene carbonate by a urea process, relates to the technical field of fine chemical industry, and solves the technical problem that the existing direct evaporation separation of catalysts easily reduces the product yield. The present invention includes an evaporator for evaporating and separating light components and catalysts containing product PC, and also includes a solid-liquid separator for pre-separating PC synthetic liquid and a gas-liquid-solid separator for secondary separation of the gas phase separated from the upper part of the evaporator; the evaporator is also provided with a liquid phase buffer tank for collecting the residual liquid phase and solid phase after evaporation; the liquid phase buffer tank is also connected to a filtering device for filtering the catalyst; the liquid phase buffer tank, the filtering device, the solid-liquid separator and the gas-liquid-solid separator are all connected to a catalyst storage tank for collecting the catalyst. The present invention effectively avoids the problem that the PC yield and purity are easily reduced by relying solely on evaporation separation.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical industry, and in particular to a separation and purification system and method for preparing propylene carbonate by a urea process. Background Art

[0002] Cyclic carbonates (ethylene carbonate, propylene carbonate, glycerol carbonate, etc.) are a new type of "green" organic compound that is widely used and highly valued both at home and abroad. Specifically, they can be used in the fields of extraction and separation of mixtures, organic synthesis (synthesis of polycarbonate resins, phenolic resins, and biodegradable medical polymer materials), high-energy-density battery electrolytes, cosmetic additives, and supercritical fluid separation technology.

[0003] The process of preparing propylene carbonate (PC) by reacting urea with propylene glycol is an important chemical conversion process. This process is an intermediate product in the two-step synthesis of DMC by urea and is also the product of the first step. In order to improve the selectivity and yield of the reaction, the process usually requires the use of a catalyst to promote this conversion. The selection of catalysts and their effective recovery and reuse are one of the important factors in realizing the industrialization of this process. In this reaction, commonly used catalysts include but are not limited to acidic solid catalysts, alkaline solid catalysts, metal salts, and biocatalysts such as enzymes. Among them, acidic solid catalysts such as sodium bisulfate, solid acids, etc. can effectively promote the decomposition of urea to produce ammonia and carbon dioxide, and then react with propylene glycol to produce propylene carbonate. Alkaline solid catalysts such as zinc oxide, magnesium oxide, potassium hydroxide, etc. accelerate the reaction through different mechanisms. For solid catalysts, the most direct method is to separate the catalyst from the reaction mixture by filtration.

[0004] The effective separation and recovery of catalysts is crucial to reducing production costs, reducing environmental pollution, and improving the overall economic benefits of the process. In addition, by optimizing the catalyst recovery method, the service life of the catalyst can be extended, further improving the sustainability of the entire production process. Therefore, researching and developing efficient and economical catalyst recovery technology is an important aspect of promoting the industrialization of the process of preparing propylene carbonate from urea and propylene glycol.

[0005] Therefore, the method for recovering the catalyst for preparing cyclic carbonate by reacting urea with polyols, as proposed in the patent with publication number CN110339867A, is to use the mixed liquid after the reaction of urea with polyols as the separation raw material, directly enter the evaporator to separate the light component without filtering step; the remaining catalyst and heavy component are calcined at high temperature to achieve a catalyst recovery rate of more than 99.0%. The recovery method has the advantages of high economic benefits, convenience for large-scale industrial application, and low catalyst loss rate. However, directly through high-temperature evaporation, the catalyst is easy to induce side reactions in the evaporator, resulting in a decrease in the yield of the product and an increase in the proportion of by-products. In addition, if the evaporation is thorough, the energy consumption is high, and the light component will contain more impurity gases. If it is not completely evaporated, the separation is not thorough, and some PC is discharged and wasted with the catalyst in the liquid phase, further reducing the product yield. Summary of the invention

[0006] The invention provides a separation and purification system and method for preparing propylene carbonate by a urea process, so as to solve the technical problem that the product yield is easily reduced by directly evaporating and separating the catalyst in the prior art.

[0007] The embodiments of the present invention are implemented by the following technical solutions:

[0008] A separation and purification system for preparing propylene carbonate by a urea process comprises an evaporator for evaporating and separating light components and catalysts including a product PC, a solid-liquid separator for preliminarily performing a primary separation on a PC synthesis liquid, and a gas-liquid-solid separator for performing a secondary separation on a gas phase separated from the upper portion of the evaporator; the evaporator is also provided with a liquid phase buffer tank for collecting residual liquid and solid phases after evaporation; the liquid phase buffer tank is also connected to a filtering device for filtering catalysts; the liquid phase buffer tank, the filtering device, the solid-liquid separator and the gas-liquid-solid separator are all connected to a catalyst storage tank for collecting catalysts.

[0009] Preferably, the filtering device is also connected to a PC recovery tower for recovering unevaporated products in the filtrate; the PC recovery tower is provided with a top condenser for condensing gaseous PC and a condensate tank for storing condensate at the top, and the condensate tank is connected to the product tower.

[0010] Preferably, a reboiler for heating the filtrate obtained by the filtering device, a drain tank for discharging the PC recovery tower and separating water from the filtrate are provided at the lower part of the PC recovery tower.

[0011] Preferably, the PC recovery tower is further provided with a tail cooler for cooling the condensed tail gas and a tail condensate buffer tank for storing tail gas condensate, and the tail condensate buffer tank is connected to the condensate tank.

[0012] Preferably, the gas-liquid-solid separator is connected to a distillation tower for further purifying the light components in the gas phase.

[0013] Preferably, the method further comprises an ammonia removal device connected to the solid-liquid separator for removing ammonia from the PC synthetic liquid.

[0014] A separation and purification method for preparing propylene carbonate by a urea process comprises the following steps:

[0015] S1: primary separation: solid-liquid separation of PC synthetic liquid;

[0016] S2: Evaporation separation: evaporating the PC synthetic liquid after solid-liquid separation;

[0017] S3: Secondary separation: Evaporation separation obtains the gas phase for gas-liquid-solid separation;

[0018] S4: Distillation: The gas phase after secondary separation is sent to a distillation tower for distillation.

[0019] Preferably, the method further comprises the following steps:

[0020] S5: Catalyst collection and recycling: The catalyst in the solid phase separated in step S1, the solid phase and the liquid phase obtained by evaporation in step S2, and the liquid phase and the solid phase obtained by secondary separation in step S3 are recycled into the propylene carbonate reactor;

[0021] S6: Catalyst regeneration: After the catalyst is recycled for 5-50 times, it is calcined and regenerated.

[0022] Preferably, in the step S5, after the solid phase and the liquid phase obtained by evaporation in the step S2 are filtered to separate the catalyst, the remaining liquid phase is reboiled to recover the PC product therein.

[0023] Preferably, in step S2, the vacuum degree of the evaporator is -0.08 to -0.095 MPa, the temperature is 120 to 180° C., and the evaporation time is 20 to 30 min.

[0024] Preferably, the catalyst can be a metal oxide catalyst, such as ZnO, MgO, Al2O3, etc.; it can be an acidic catalyst, such as molecular sieve, sodium bisulfate, etc.; it can be a composite catalyst, such as ZnO-Al2O3, MgO-Al2O3, etc.

[0025] Preferably, in step S5, the reboiling recovery temperature is 160-180°C.

[0026] Preferably, in step S6, the roasting regeneration comprises the following steps:

[0027] Pretreatment: First, clean the catalyst with a solvent (such as water, ethanol, etc.) to remove organic matter and impurities on the surface. Dry the cleaned catalyst at 100-120°C for 2-4 hours to remove moisture.

[0028] Calcination: Calcinate at 300-600℃ for 2-6h in air or inert gas (such as nitrogen) atmosphere. The specific temperature depends on the type of catalyst and active components. For example, ZnO: 400-500℃; MgO: 350-450℃; Al2O3: 500-600℃. The specific calcination time depends on the degree of deactivation and regeneration effect of the catalyst. Air atmosphere helps to oxidize and remove carbon deposits on the catalyst surface, while inert gas atmosphere can prevent further oxidation of the catalyst.

[0029] Cooling: Allow the calcined catalyst to cool naturally to room temperature in air.

[0030] By adopting the technical scheme, impurities can be effectively removed, and the purity and yield of propylene carbonate can be improved through multi-stage separation of solid-liquid separator, evaporator, gas-liquid-solid separator and distillation tower. After solid-liquid separation is first performed to remove most of the catalyst, evaporation separation is performed to ensure that the side reaction will not be promoted due to the action of the catalyst at high temperature during evaporation separation, thereby improving the yield of propylene carbonate. After evaporation separation, the upper gas phase is further subjected to gas-liquid-solid separation to prevent the partial liquid phase and solid phase carried out with the gas phase from being mixed into the subsequent processing process in actual production. The top condenser and reboiler in the PC recovery tower can further separate and recover gaseous PC to avoid the waste of PC that has not been completely evaporated; effectively avoiding the problem of reducing the yield and purity of PC by relying solely on evaporation separation.

[0031] It can also realize the continuous recovery and reuse of catalysts, reduce downtime and improve production efficiency. The design of scraper evaporator can improve heat transfer efficiency, shorten evaporation time, and thus increase production speed. The catalyst is collected and reused, which reduces catalyst consumption and reduces production costs. Through the PC recovery tower and drain tank, the product and water that are not completely evaporated can be recovered to reduce resource waste. The ammonia removal device removes ammonia from the PC synthetic liquid to prevent ammonia from increasing side reactions in the subsequent treatment process, while reducing the emission of harmful gases and protecting the environment. The liquid phase buffer tank and filter device can effectively separate the catalyst and unreacted raw materials, reducing the generation of waste liquid and the cost of treatment.

[0032] By adjusting the vacuum, temperature and time of the evaporator, the properties and process requirements of different materials can be flexibly responded to. The activity of the catalyst can be restored through roasting and regeneration, extending its service life and reducing the cost of frequent catalyst replacement. The steps of pretreatment, roasting and cooling can effectively remove impurities and carbon deposits on the catalyst surface and ensure the regeneration effect of the catalyst. Solid impurities in PC synthetic liquid are removed to improve the efficiency of subsequent treatment.

[0033] The separation and purification system and method for preparing propylene carbonate by the urea process of the present application significantly improves the production efficiency and product quality of propylene carbonate through measures such as multi-stage separation, catalyst recovery and regeneration, while reducing resource waste and environmental pollution.

[0034] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0035] 1. The present invention effectively avoids the problem that the PC yield and purity are easily reduced by simply relying on evaporation separation;

[0036] 2. The present invention reduces the consumption and treatment process of the catalyst and reduces the production cost;

[0037] 3. The present invention improves the production efficiency and product quality of propylene carbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] 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.

[0039] Figure 1 A schematic diagram of the structure of a separation and purification system for preparing propylene carbonate by the urea process provided in Example 1 of the present invention;

[0040] Figure 2 A process flow chart of the separation and purification method for preparing propylene carbonate by the urea process provided in Example 2 of the present invention;

[0041] Figure 3 A structural diagram related to PC recovery in a separation and purification system for preparing propylene carbonate by a urea process provided in Example 3 of the present invention;

[0042] Icons: 1. Ammonia removal device; 2. Solid-liquid separator; 3. Evaporator; 4. Liquid phase buffer tank; 5. Gas-liquid-solid separator; 6. Catalyst storage tank; 7. Filtration device; 8. Distillation tower; 9. PC recovery tower; 91. Top condenser; 92. Tail cooler; 93. Tail condensate buffer tank; 94. Condensate tank; 95. Reboiler; 96. Drain tank. DETAILED DESCRIPTION

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] Example 1

[0049] A separation and purification system for preparing propylene carbonate by a urea process comprises an evaporator 3 for evaporating and separating light components and catalysts including a product PC, a solid-liquid separator 2 for preliminarily performing a primary separation on a PC synthetic liquid, and a gas-liquid-solid separator 5 for performing a secondary separation on a gas phase separated from the upper portion of the evaporator 3; the evaporator 3 is also provided with a liquid phase buffer tank 4 for collecting a liquid phase and a solid phase remaining after evaporation; the liquid phase buffer tank 4 is also connected to a filtering device 7 for filtering a catalyst; the liquid phase buffer tank 4, the filtering device 7, the solid-liquid separator 2 and the gas-liquid-solid separator 5 are all connected to a catalyst storage tank 6 for collecting a catalyst.

[0050] In this embodiment, the gas-liquid-solid separator 5 is connected to a distillation tower 8 for further purifying the light components in the gas phase.

[0051] In this embodiment, an ammonia removal device 1 connected to the solid-liquid separator 2 for removing ammonia from the PC synthetic liquid is also included.

[0052] In this embodiment, the recovery rate of the catalyst is 100%. The catalyst is reused 40 times and then regenerated and put into use. It can be reused 200-300 times. The yield of propylene carbonate is 95%.

[0053] Example 2

[0054] A separation and purification method for preparing propylene carbonate by a urea process comprises the following steps:

[0055] S1: primary separation: solid-liquid separation of PC synthetic liquid;

[0056] S2: Evaporation separation: evaporating the PC synthetic liquid after solid-liquid separation;

[0057] S3: Secondary separation: Evaporation separation obtains the gas phase for gas-liquid-solid separation;

[0058] S4: Distillation: The gas phase after the secondary separation is sent to the distillation tower 8 for distillation.

[0059] In this embodiment, the following steps are also included:

[0060] S5: Catalyst collection and recycling: The catalyst in the solid phase separated in step S1, the solid phase and the liquid phase obtained by evaporation in step S2, and the liquid phase and the solid phase obtained by secondary separation in step S3 are recycled into the propylene carbonate reactor;

[0061] S6: Catalyst regeneration: After the catalyst is recycled for 5-50 times, it is calcined and regenerated.

[0062] In this embodiment, in the step S5, after the solid phase and the liquid phase obtained by evaporation in the step S2 are filtered to separate the catalyst, the remaining liquid phase is reboiled to recover the PC product therein.

[0063] In this embodiment, in step S2, the vacuum degree of the evaporator 3 is -0.095 MPa, the temperature is 160° C., and the evaporation time is 30 min.

[0064] In this embodiment, the catalyst is a metal oxide catalyst ZnO.

[0065] In this embodiment, in step S5, the reboiling recovery temperature is 180°C.

[0066] In this embodiment, in step S6, the roasting regeneration includes the following steps:

[0067] Pretreatment: First, clean the catalyst with a solvent (water) to remove organic matter and impurities on the surface. Dry the cleaned catalyst at 100-120°C for 2-4 hours to remove moisture.

[0068] Calcination: Calcinate at 400-500°C for 4 hours in air or inert gas (such as nitrogen) atmosphere.

[0069] Cooling: Allow the calcined catalyst to cool naturally to room temperature in air.

[0070] Example 3

[0071] In this embodiment, the filtering device 7 is also connected to a PC recovery tower 9 for recovering the unevaporated product in the filtrate; the PC recovery tower 9 is provided with a top condenser 91 for condensing gaseous PC and a condensate tank 94 for storing condensate at the top, and the condensate tank 94 is connected to the product tower.

[0072] In this embodiment, the lower part of the PC recovery tower 9 is provided with a reboiler 95 for heating the filtrate obtained by the filtering device 7, and a drain tank 96 for discharging the PC recovery tower 9 and separating the water in the filtrate.

[0073] In this embodiment, the PC recovery tower 9 is further provided with a tail cooler 92 for cooling the condensed tail gas and a tail condensate buffer tank 93 for storing tail gas condensate, and the tail condensate buffer tank 93 is connected to the condensate tank 94 .

[0074] In this embodiment, the yield of propylene carbonate is 96%.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that the catalyst and the gas phase light component are separated only by evaporation. After separation, the catalyst carries more components, and direct reuse is likely to cause side reactions. It can be reused after roasting and regeneration, and can be reused 10-20 times. The catalyst recovery rate is 100%, and the propylene carbonate yield is 72%.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 1 is that in this comparative example, solid-liquid separation is performed before evaporation separation to separate the catalyst, and gas-liquid-solid separation and PC recovery are not performed after evaporation separation. The catalyst recovery rate is 100%, and the propylene carbonate yield is 78%.

[0079] Comparative Example 3

[0080] The only difference between this comparative example and Example 1 is that in this comparative example, PC recovery is not performed, the catalyst recovery rate is 100%, and the propylene carbonate yield is 79%.

[0081] 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 separation and purification system for preparing propylene carbonate by a urea process, comprising an evaporator (3) for evaporating and separating light components including product PC and a catalyst, characterized in that: The invention also comprises a solid-liquid separator (2) for preliminarily performing a primary separation on the PC synthetic liquid and a gas-liquid-solid separator (5) for performing a secondary separation on the gas phase separated from the upper part of the evaporator (3); the evaporator (3) is also provided with a liquid phase buffer tank (4) for collecting the residual liquid phase and solid phase after evaporation; the liquid phase buffer tank (4) is also connected to a filtering device (7) for filtering the catalyst; the liquid phase buffer tank (4), the filtering device (7), the solid-liquid separator (2) and the gas-liquid-solid separator (5) are all connected to a catalyst storage tank (6) for collecting the catalyst.

2. The separation and purification system for preparing propylene carbonate by urea process according to claim 1, characterized in that: The filtering device (7) is also connected to a PC recovery tower (9) for recovering the unevaporated product in the filtrate; the PC recovery tower (9) is provided with a top condenser (91) for condensing gaseous PC and a condensate tank (94) for storing condensate at the top, and the condensate tank (94) is connected to the product tower.

3. The separation and purification system for preparing propylene carbonate by urea process according to claim 2, characterized in that: The lower part of the PC recovery tower (9) is provided with a reboiler (95) for heating the filtrate obtained by the filtering device (7), and a drain tank (96) for discharging the PC recovery tower (9) and separating water from the filtrate.

4. The separation and purification system for preparing propylene carbonate by urea process according to claim 2, characterized in that: The PC recovery tower (9) is further provided with a tail cooler (92) for cooling the condensed tail gas and a tail condensate buffer tank (93) for storing tail gas condensate, and the tail condensate buffer tank (93) is connected to the condensate tank (94).

5. A separation and purification system for preparing propylene carbonate by urea process according to any one of claims 1 to 4, characterized in that: The gas-liquid-solid separator (5) is connected to a distillation tower (8) for further purifying the light components in the gas phase.

6. A separation and purification system for preparing propylene carbonate by urea process according to any one of claims 1 to 4, characterized in that: It also includes an ammonia removal device (1) connected to the solid-liquid separator (2) for removing ammonia from the PC synthetic liquid.

7. A separation and purification method for preparing propylene carbonate by urea process, characterized in that: The separation and purification system for preparing propylene carbonate by the urea method according to any one of claims 1 to 6 comprises the following steps: S1: primary separation: solid-liquid separation of PC synthetic liquid; S2: Evaporation separation: evaporating the PC synthetic liquid after solid-liquid separation; S3: Secondary separation: Evaporation separation obtains the gas phase for gas-liquid-solid separation; S4: Distillation: The gas phase after secondary separation is sent to a distillation tower for distillation.

8. The separation and purification method for preparing propylene carbonate by urea process according to claim 7, characterized in that: The following steps are also included: S5: Catalyst collection and recycling: The catalyst in the solid phase separated in step S1, the solid phase and the liquid phase obtained by evaporation in step S2, and the liquid phase and the solid phase obtained by secondary separation in step S3 are recycled into the propylene carbonate reactor; S6: Catalyst regeneration: After the catalyst is recycled for 5-50 times, it is calcined and regenerated.

9. The separation and purification method for preparing propylene carbonate by urea process according to claim 8, characterized in that: In the step S5, after the solid phase and liquid phase obtained by evaporation in the step S2 are filtered to separate the catalyst, the remaining liquid phase is reboiled to recover the PC product therein.

10. The separation and purification method for preparing propylene carbonate by urea process according to claim 8, characterized in that: In step S6, the catalyst calcination regeneration comprises the following steps: Pretreatment: After cleaning the catalyst, dry it to remove moisture; Calcination: Calcination at 300-600°C for 2-6h in air or inert gas atmosphere; Cooling: Allow the calcined catalyst to cool naturally to room temperature in air.

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