Recovery device and recovery method of bdo in production of pbat

Abstract

The application discloses a BDO recovery device and method in PBAT production, the recovery device comprises a process column and a BDO vacuum system, the pipeline at the bottom of the process column is divided into two routes after a shielding pump, one route is connected with an intermediate BDO storage tank, and the other route is connected with a BDO evaporator and a liquid seal groove through a heat exchanger to form a hot fluid passage; the coolant inlet of the heat exchanger is connected with a BDO collecting tank, and the coolant outlet is connected with the process column to form a cold fluid passage, thereby reducing production energy consumption and improving the stability of the vacuum system. The recovery method exchanges heat between the hot fluid of the process column and the cold fluid of the BDO collecting tank, the hot fluid is branched into the BDO evaporator and the liquid seal groove of the vacuum system to supplement working liquid, and the cold fluid enters the process column to supplement the column liquid, thereby reducing the oligomer content in the BDO in the liquid seal groove and the amount of fresh BDO, solving the BDO balance problem. At the same time, the water content of the intermediate BDO storage tank is reduced, the esterification rate of the esterification system is improved, and the full recovery and cyclic use of high-quality BDO are realized.

Description

Technical Field

[0001] This invention relates to polyester production equipment and processes, and more particularly to a BDO recovery device and method in PBAT production. Background Technology

[0002] PBAT has excellent biodegradability and is mainly used in film products such as packaging, mulch films, shopping bags, garbage bags, roll bags, express delivery bags, and takeout bags, reducing the environmental pollution problems caused by the use of traditional films. During production, BDO (1,4-butanediol) is collected from the bottom of the process tower and stored in an intermediate BDO storage tank for slurry preparation. The temperature of the BDO from the bottom of the process tower is relatively high, normally between 170 and 200°C, while THF has a boiling point of 66°C. To reduce THF volatilization, the temperature of the intermediate BDO storage tank is usually controlled by circulating water, resulting in some wasted heat. During PBAT production, the large volume of gas generated in the polycondensation reactor can easily carry oligomers into the BDO circulating working fluid in the vacuum system's liquid seal tank, thus affecting the performance of the vacuum system. Chinese patent CN2015200506850 discloses a BDO vacuum system for PBT production, including a scraped condenser connected to a vacuum pump and a polycondensation reaction device. A BDO spraying device is located at the upper part of the scraped condenser. The liquid BDO outlet at the bottom of the scraped condenser is connected sequentially to a buffer tank, a BDO circulation pump, a heat exchanger, and the BDO spraying device via a BDO circulation pipeline. The heat exchanger is connected to a cooling circulating water pipeline. The inlet of the circulating water pump near the cooling circulating water pipeline is connected to the main circulating water inlet pipe. The cooling circulating water pipeline, located above the main circulating water inlet pipe, is connected to the main circulating water outlet pipe. By introducing lower-temperature main circulating water, the temperature of the cooling circulating water flowing through the heat exchanger is adjusted, thereby achieving precise control of the liquid BDO temperature within the BDO circulation pipeline at 45℃±0.5℃, ensuring stable system operation. Furthermore, to improve the quality of the BDO sprayed in the vacuum system, it is necessary to replace the BDO in the vacuum system's liquid seal tank with higher-quality BDO (such as fresh BDO or refined BDO). If fresh BDO is used for replacement, it is difficult to recycle all of the BDO; if a BDO recycling unit is set up for BDO recycling and refining, it will increase the energy consumption of production. Summary of the Invention

[0003] Objective of the Invention: This invention aims to provide a BDO recovery device that reduces production energy consumption and improves the stability of vacuum systems. This invention also provides a method for the complete recycling and reuse of BDO.

[0004] Technical Solution: The BDO recovery device in PBAT production according to the present invention includes a process tower and a BDO vacuum system. The pipeline at the bottom of the process tower is divided into two paths after passing through a shielded pump. One path connects to an intermediate BDO storage tank, and the other path connects to the BDO evaporator and liquid seal tank of the BDO vacuum system through a heat exchanger, forming a hot fluid passage. The heat medium outlet of the heat exchanger is connected to the BDO evaporator and liquid seal tank. The cold medium inlet of the heat exchanger is connected to the BDO collection tank of the BDO vacuum system, and the cold medium outlet is connected to the process tower, forming a cold fluid passage.

[0005] Preferably, the liquid seal tank is divided into a BDO liquid seal tank for a polycondensation spray system and a BDO liquid seal tank for a polycondensation jet system.

[0006] Preferably, a filter is provided at the inlet of the heat exchanger.

[0007] Preferably, the pipeline is equipped with a manual valve, a regulating valve, and a flow meter.

[0008] Working Principle: After being pressurized by a shielded pump at the bottom of the process tower, the hot fluid flows successively through a filter and a heat exchanger, connecting to the BDO evaporator, the BDO liquid seal tank of the polycondensation spray system, and the BDO liquid seal tank of the polycondensation jet system. This effectively reduces the amount of recycled BDO used, reduces coking at the jet pump nozzles, and improves the vacuum stability of the polycondensation system. It also reduces the amount of fresh BDO needed to replace the BDO in these systems during PBAT production due to the large gas volume and heavy vacuum load of the polycondensation system, thus solving the problem of continuously rising liquid levels in the intermediate BDO storage tank. Simultaneously, the high-temperature BDO (hot fluid) extracted from the process tower is used to replenish the BDO evaporator, potentially saving heating energy. After the cold and hot fluids exchange heat in the heat exchanger in a counter-current or co-current manner, they enter the process tower. The cold fluid is used to replenish the bottom liquid of the process tower, while removing water and tetrahydrofuran, reducing the THF and H2O content in the intermediate BDO storage tank and increasing the esterification rate. The BDO liquid seal tank of the polycondensation spray system is connected to the BDO liquid seal tank of the polycondensation spray system via a shielded pump and pipeline, reducing the amount of fresh BDO used in the liquid seal tank. By reducing the return flow rate at the top of the process tower, the process tower can additionally heat and purify a certain amount of cold fluid for reuse as BDO, and then exit as hot fluid, achieving effective energy recovery.

[0009] The method for recovering BDO in PBAT production using the above-mentioned device is as follows: The hot fluid purified by the process tower is used as the heat medium of the heat exchanger, and the cold fluid in the BDO collection tank is used as the coolant of the heat exchanger. After heat exchange in the heat exchanger, the hot fluid flows into the BDO evaporator and the vacuum system liquid seal tank to replenish the working fluid, and the cold fluid enters the process tower to replenish the bottom liquid of the process tower.

[0010] Preferably, a filtration process is added before the hot fluid enters the heat exchanger.

[0011] Preferably, the cold fluid is a liquid mixture of BDO and water after being replaced by the liquid ring pump of the esterification and polycondensation system.

[0012] Beneficial Effects: Compared with the prior art, the significant advantages of this invention are: 1. This device realizes heat exchange between the hot fluid of the process tower and the cold fluid of the BDO collection tank, reducing production energy consumption; 2. This device realizes effective recovery of BDO produced by the process tower, reduces coking phenomenon in the jet pump nozzle, and improves the vacuum stability and vacuum capacity of the polycondensation system; 3. This method realizes the full recovery and recycling of high-quality BDO; 4. This method reduces the amount of BDO reused, solves the BDO balance problem during production, improves system operability, and solves potential production problems; 5. This method reduces the water content of the intermediate BDO storage tank and increases the esterification rate of the esterification system by recovering the BDO displaced by the liquid ring pump. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the device structure of the present invention. Detailed Implementation

[0014] The invention will now be further described with reference to the accompanying drawings.

[0015] This invention relates to a BDO recovery device in PBAT production, comprising a process tower 1 and a BDO vacuum system. The pipeline at the bottom of the process tower 1 is split into two paths after passing through a shielded pump. One path connects to an intermediate BDO storage tank 3, and the other path connects to a BDO evaporator 6, a BDO liquid seal tank 7 in a polycondensation spray system, and a BDO liquid seal tank 8 in a polycondensation jet system via a heat exchanger 5, forming a hot fluid passage. The heat medium outlet of the heat exchanger 5 connects to the BDO evaporator 6 and the liquid seal tank. The cold medium inlet of the heat exchanger 5 connects to the BDO collection tank 4 of the BDO vacuum system, and the cold medium outlet connects to the process tower 1, forming a cold fluid passage. A filter is installed at the inlet of the heat exchanger 5, and a manual valve, a regulating valve, and a flow meter are installed on the pipeline.

[0016] The method for recovering BDO in PBAT production using the above-mentioned apparatus is as follows: The hot fluid purified from process tower 1 is collected. This hot fluid is a liquid mixture of BDO and water, with a water content of 0.5% and a temperature of 190°C. After filtration, the hot fluid enters heat exchanger 5. The working fluid in heat exchanger 5 is the cold fluid from BDO collection tank 4. The cold fluid is a liquid mixture of BDO and water after being replaced by the liquid ring pump in the esterification and polycondensation system, with a water content of 2.5% and a temperature of 45°C. The flow rates of both the hot and cold fluids are 1 t / h. The hot and cold fluids exchange heat in the plate heat exchanger 5 in a counter-current or co-current manner. After heat exchange, the hot fluid flows into the BDO evaporator 6 and the vacuum system liquid seal tank to replenish the working fluid; the cold fluid enters process tower 1 to replenish the bottom liquid of process tower 1.

[0017] The cold fluid with a high water content enters the process tower for purification, and a hot fluid with a low water content is extracted. This hot fluid is used to replenish the BDO evaporator, reducing the amount of fresh BDO used by 1 t / h. The temperature of the fresh BDO is 40℃, and the temperature of the hot fluid after heat exchange is 181℃. The energy-saving BDO evaporator heating capacity is 0.0498 GJ / h.

[0018] The BDO energy recovery method and apparatus described in this invention can be used in relevant polyester plants, wherein the polyester plants are not limited to polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polypropylene terephthalate (PTT), poly(butylene terephthalate-co-butylene adipate) (PBAT), poly(butylene terephthalate-co-butylene succinate) (PBST), polybutylene adipate succinate (PBSA), polybutylene succinate (PBS), and thermoplastic polyester elastomer (TPEE).

Claims

1. A method for recovering BDO in PBAT production, comprising using a BDO recovery device for PBAT production, characterized in that, The device includes a process tower (1) and a BDO vacuum system. The pipeline at the bottom of the process tower (1) is divided into two paths after passing through a shielded pump. One path connects to the intermediate BDO storage tank (3), and the other path connects to the BDO evaporator (6) and liquid seal tank of the BDO vacuum system through a heat exchanger (5), forming a hot fluid passage. The heat medium outlet of the heat exchanger (5) is connected to the BDO evaporator (6) and liquid seal tank. The cold medium inlet of the heat exchanger (5) is connected to the BDO collection tank (4) of the BDO vacuum system, and the cold medium outlet is connected to the process tower (1), forming a cold fluid passage. The recovery method is as follows: the hot fluid refined in the process tower (1) is used as the heat medium of the heat exchanger, and the cold fluid in the BDO collection tank (4) is used as the cold medium of the heat exchanger (5). After heat exchange in the heat exchanger (5), the hot fluid flows into the BDO evaporator (6) and the vacuum system liquid seal tank to replenish the working fluid, and the cold fluid enters the process tower (1) to replenish the bottom liquid of the process tower (1).

2. The method for recovering BDO in PBAT production according to claim 1, characterized in that, Before the hot fluid enters the heat exchanger (5), a filtration process is added.

3. The method for recovering BDO in PBAT production according to claim 1, characterized in that, The cold fluid is a liquid mixture of BDO and water after being replaced by the liquid ring pump of the esterification and polycondensation system.

4. The method for recovering BDO in PBAT production according to claim 1, characterized in that, The liquid seal tank is divided into a BDO liquid seal tank for a polycondensation spray system (7) and a BDO liquid seal tank for a polycondensation jet system (8).

5. The method for recovering BDO in PBAT production according to claim 1, characterized in that, A filter is provided at the inlet of the heat exchanger (5).

6. The method for recovering BDO in PBAT production according to claim 1, characterized in that, The pipeline is equipped with a manual valve, a regulating valve, and a flow meter.

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