Thermal cleaning method for polycarbonate polycondensation reactor

Abstract

The invention relates to the technical field of reactor cleaning, and particularly discloses a thermal cleaning method for a polycarbonate polycondensation reactor, which is characterized by comprising the following operation steps: (1) discharging polycarbonate melt in the polycondensation reactor, and then adding the polycarbonate melt into the polycondensation reactor; depressurizing and then pressurizing the polycondensation reactor, and repeating the depressurizing and pressurizing processes for two or more times; (2) cooling the polycondensation reactor; (3) adding phenol into the polycondensation reactor; (4) carrying out hot boiling on the polycondensation reactor by using phenol, observing the liquid level of the phenol, and supplementing the phenol; (5) after hot boiling is completed, phenol is recycled through a phenol recycling system; and (6) phenol discharged from the outlet of the polycondensation reactor in the step (5) is detected, whether hot boiling is qualified or not is judged, if yes, the cleaning process is ended, and if not, the steps (4)-(5) are repeated once. According to the thermal cleaning method for the polycarbonate polycondensation reactor, the polycarbonate polycondensation reactor can be cleaned more efficiently.

Description

Technical Field

[0001] The invention relates to the technical field of reactor cleaning, and in particular to a thermal cleaning method for a polycarbonate polycondensation reactor. Background Art

[0002] Polycarbonate (PC) is a thermoplastic engineering plastic with excellent comprehensive performance, mainly represented by bisphenol A polycarbonate. Due to its special structure, polycarbonate has excellent light transmittance, impact toughness, electrical insulation, weather resistance and other characteristics, and is widely used in aerospace, electrical lighting, light-transmitting building materials and other industries. Industrial production mainly adopts interfacial polycondensation method or melt ester exchange method.

[0003] The production process of polycarbonate by melt transesterification needs to go through two stages: prepolymerization and gradual polycondensation. The polycondensation reaction is first carried out in a multi-stage falling film evaporator and then continues in a multi-stage polycondensation reactor. As the reaction progresses, higher and higher temperatures and vacuum degrees are required to gradually polycondense to obtain a polycarbonate melt of the corresponding molecular weight. After the reaction, the polycarbonate melt is mixed with additives, filtered through a melt filter to remove impurities, and then pelletized to obtain a polycarbonate product in the form of particles.

[0004] In the production process of polycarbonate by melt transesterification, the polycondensation reactor is mainly implemented by a horizontal reactor with a disc stirrer. The operating temperature of the polycondensation reactor is about 280-310°C and the operating pressure is about 100-1000 Pa.A.

[0005] During the production process, some of the oligomers in the liquid phase of the condensation reactor are attached to the inner wall of the reactor gas phase while being carried out by the gas phase. These oligomers are further cross-linked and polymerized under long-term high temperature and high vacuum to form brown-brown polymers. Due to vacuum pressure fluctuations and other reasons, they fall into the liquid phase and cannot melt. They can only swell and break into small particles. The extremely fine parts of these small particles cannot be intercepted by the filtering device and enter the polycarbonate product, appearing as "black spots" in downstream applications, affecting the appearance and spraying, etc. Summary of the invention

[0006] The object of the present invention is to provide a method for thermally cleaning a polycarbonate polycondensation reactor, which can more efficiently clean the polycarbonate polycondensation reactor.

[0007] The present invention is achieved by the following technical solution: The thermal cleaning method of the polycarbonate polycondensation reactor of the present invention comprises the following operating steps:

[0008] (1) After the polycarbonate melt in the polycondensation reactor is discharged, the temperature of the polycondensation reactor is adjusted to 275-285°C; the polycondensation reactor is depressurized and then increased, and the depressurization and increase process are repeated 2 times or more; wherein the depressurization parameters are: depressurization to 50-1000 Pa.A, depressurization rate ≥1.25 kPa / h; and the increase parameters are: increase to 100-200 kPa.A, and increase rate ≥5 kPa / h. Through the pressure change, the polymer on the inner wall of the gas phase can be initially stripped.

[0009] (2) Cooling the polycondensation reactor to 180-190°C at a rate of 5-10°C / h. The polymer on the inner wall of the gas phase is further stripped off by temperature change.

[0010] (3) Add phenol to the polycondensation reactor; when adding phenol, the temperature of the polycondensation reactor is controlled to be 180-190°C, the pressure is greater than 5 kPa.G, and the injection amount of phenol is 20-60% of the liquid level of the polycondensation reactor. The purity of the phenol used is greater than 99.5%, and the color is ≤20 Hazen.

[0011] (4) Using phenol to heat-boil the polycondensation reactor, observing the liquid level of phenol, and adding phenol; during the heat-boiling process, the temperature of the polycondensation reactor is controlled to be 183-200°C, the pressure is 5-60kPa.G, and the heat-boiling time is 2-4 hours. During the heat-boiling process, the vaporization rate of the liquid phenol in the polycondensation reactor is controlled to be less than 50% by pressure, and the liquid level of the polycondensation reactor is made greater than 20% by adding phenol. The gaseous phenol penetrates and peels off the brown-brown polymer on the inner wall of the polycondensation reactor, and the peeled brown-brown polymer further swells and melts in the liquid phenol, and the color of the phenol deepens accordingly.

[0012] (5) After the hot boiling is completed, the phenol is recovered by using a phenol recovery system; the phenol recovery system includes a phenol evaporator, a crude phenol collection tower, and a phenol distillation tower connected in sequence; the temperature of the phenol evaporator is 185-200°C; the top pressure of the phenol distillation tower is 1.5-2.5 kPa.A, the top reflux is 6000-10000 kg / h, the bottom temperature is 175-190°C, and the bottom circulation volume is 100-150 t / h. The heavy component waste liquid remaining in the phenol evaporator and the bottom of the phenol distillation tower is sent for incineration treatment.

[0013] (6) Detect the phenol discharged from the outlet of the polycondensation reactor in step (5) and determine whether the hot boiling is qualified. If it is qualified, the cleaning process is terminated; if it is unqualified, steps (4)-(5) are repeated once. The standard for determining whether the hot boiling is qualified is: if the purity of the phenol discharged from the outlet of the polycondensation reactor is less than 98.5% or the color is greater than 200 Hazen, it is unqualified; if the purity of the phenol discharged from the outlet of the polycondensation reactor is greater than 98.5% and the color is less than 200 Hazen, it is qualified.

[0014] The technical solution of the present invention has at least the following advantages and beneficial effects: The thermal cleaning method of the polycarbonate polycondensation reactor of the present invention can clean the brown polymer on the inner wall of the reactor gas phase space, reduce the risk of black spots entering the product, and greatly improve the quality of the polycarbonate product. The residual melt in the reactor can be cleaned to achieve the purpose of cold-state rotating agitator, which is convenient for the agitator maintenance project. DETAILED DESCRIPTION

[0015] Example 1

[0016] This embodiment provides a method for thermal cleaning of a polycarbonate polycondensation reactor, comprising the following steps:

[0017] (1) After the residual polycarbonate melt in the polycondensation reactor is discharged, the melt valve in front of the melt pump is closed, the temperature of the polycondensation reactor is maintained at 280°C, and the pressure of the polycondensation reactor is evacuated to 100 Pa.A by a vacuum system at a pressure reduction rate of 1.3 kPa / h. The vacuum valve is closed, and the vacuum is broken to 160 kPa.A by nitrogen at a pressure increase rate of 5.3 kPa / h. This process is repeated twice. The polymer attached to the gas phase inner wall of the polycondensation reactor is initially stripped by the rapid pressure change.

[0018] (2) The temperature of the polycondensation reactor was reduced to 180°C at a rate of 7°C / h, and the polymer on the inner wall of the gas phase of the polycondensation reactor was further stripped by the temperature change.

[0019] (3) The pressure of the polycondensation reactor was adjusted to 110 kPa.A, a phenol inlet was preset at the feed end, phenol (purity 99.6%, chroma ≤ 20 Hazen) was pumped into the polycondensation reactor, and the liquid level of the polycondensation reactor was established to 30%.

[0020] (4) Raise the temperature of the polycondensation reactor to 184-186°C and control the pressure at 110 kPa.A to vaporize part of the phenol in the polycondensation reactor. Boil the phenol for 2 hours until the liquid level drops to 18%. Continue to add phenol to 30% and continue boiling for 2 hours. During this period, manually turn the agitator of the polycondensation reactor. After it can be turned, turn it once every half an hour.

[0021] (5) After the hot boiling is completed, the manual valve of the outlet pipeline of the polycondensation reactor to the phenol evaporation tank is opened, and the materials in the polycondensation reactor are discharged to the outlet pipeline of the polycondensation reactor to the phenol evaporation tank. At the same time, samples are taken at the sampling point. The purity of phenol is 96% and the chromaticity is greater than 400 Hazen. The phenol evaporation tank is heated by a heat transfer oil coil and continuously stirred by an agitator. The temperature is controlled at 190°C and the pressure is controlled at 3kPa.G. After phenol evaporates, it is condensed and recovered in the phenol condenser to the crude phenol collection tank. When the liquid level of the crude phenol collection tank reaches more than 50%, it is sent to the phenol distillation tower by the crude phenol delivery pump. The tower pressure of the phenol distillation tower is controlled at 1.6kPa.A, the top reflux is 7000kg / h, the tower bottom temperature is 180°C, and the tower bottom circulation volume is 120t / h. After purification at the top of the tower, part of the phenol is refluxed, and part of it is recycled and used in places with high requirements for phenol purity, such as catalyst configuration and working medium of the phenol vacuum system. Part of the bottom liquid of the phenol distillation tower is extracted and sent to incineration. After phenol recovery, the remaining material in the phenol evaporation tank is sent to incineration as waste liquid.

[0022] (6) Steps (4) and (5) are repeated to perform phenol hot boiling and phenol recovery. When discharged to the phenol evaporation tank, another sample is taken at the sampling point. The analysis results show that the phenol purity is 98.8%, the chromaticity is 150 Hazen, and the cleaning is qualified. The amount of phenol added to the polycondensation reactor is counted, and 10.8 tons of phenol is used and 9.9 tons of phenol is recovered by the phenol distillation tower, with a recovery rate of 92%.

[0023] Example 2

[0024] This embodiment provides a method for thermal cleaning of a polycarbonate polycondensation reactor, comprising the following steps:

[0025] (1) After the residual polycarbonate melt in the polycondensation reactor is discharged, the melt valve in front of the melt pump is closed, the temperature of the polycondensation reactor is maintained at 280°C, and the pressure of the polycondensation reactor is evacuated to 200 Pa.A by a vacuum system at a pressure reduction rate of 1.3 kPa / h. The vacuum valve is closed, and the vacuum is broken to 150 kPa.A by nitrogen at a pressure increase rate of 5.1 kPa / h. This is repeated three times. The polymer attached to the gas phase inner wall of the polycondensation reactor is initially stripped by the rapid pressure change.

[0026] (2) The temperature of the polycondensation reactor was reduced to 180°C at a rate of 5°C / h, and the polymer on the inner wall of the gas phase of the polycondensation reactor was further stripped by the temperature change.

[0027] (3) The pressure of the polycondensation reactor was adjusted to 115 kPa.A, a phenol inlet was preset at the feed end, phenol (purity 99.6%, chroma ≤ 20 Hazen) was pumped into the polycondensation reactor, and the liquid level of the polycondensation reactor was established to 30%.

[0028] (4) Raise the temperature of the polycondensation reactor to 186-187°C and control the pressure at 115 kPa.A to vaporize part of the phenol in the polycondensation reactor. Boil the phenol for 2 hours until the liquid level drops to 20%. Continue to add phenol to 30% and continue boiling for 2 hours. During this period, manually turn the agitator of the polycondensation reactor. After it can be turned, turn it once every half an hour.

[0029] (5) After the hot boiling is completed, the manual valve of the outlet pipeline of the polycondensation reactor to the phenol evaporation tank is opened, and the materials in the polycondensation reactor are discharged to the outlet pipeline of the polycondensation reactor to the phenol evaporation tank. At the same time, samples are taken at the sampling point. The purity of phenol is 97% and the chromaticity is greater than 400 Hazen. The phenol evaporation tank is heated by a heat transfer oil coil and continuously stirred by an agitator. The temperature is controlled at 195°C and the pressure is controlled at 2kPa.G. After phenol evaporates, it is condensed and recovered in the phenol condenser to the crude phenol collection tank. When the liquid level of the crude phenol collection tank reaches more than 50%, it is sent to the phenol distillation tower by the crude phenol delivery pump. The tower pressure of the phenol distillation tower is controlled at 2.0kPa.A, the top reflux is 8000kg / h, the tower bottom temperature is 185°C, and the tower bottom circulation volume is 120t / h. After the phenol is purified at the top of the tower, part of it is refluxed, and part of it is recycled and used in places with high requirements for phenol purity, such as catalyst configuration and working medium of the phenol vacuum system. Part of the bottom liquid of the phenol distillation tower is extracted and sent to incineration. After phenol recovery, the remaining material in the phenol evaporation tank is sent to incineration as waste liquid.

[0030] (6) Repeat steps (4) and (5) twice to perform phenol hot boiling and phenol recovery. When the latter is discharged to the phenol evaporator, a sample is taken at the sampling point. The analysis results show that the phenol purity is 98.9%, the color is 150 Hazen, and the cleaning is qualified. The amount of phenol added to the polycondensation reactor is counted, and 18.4 tons of phenol is used and 16.7 tons of phenol is recovered by the phenol distillation tower, with a recovery rate of 91%.

[0031] (7) The temperature of the polycondensation reactor is raised to 200°C, the polycondensation reactor is evacuated to 100 Pa.A, and then the vacuum is broken by nitrogen to 100 kPa.A, and this is repeated 4 times, and then the temperature is lowered to room temperature. During the cooling process, positive pressure is charged and nitrogen is used to replace the residual phenol. After the temperature is lowered to room temperature, the blind plate is used to isolate the system, the factory air is replaced, and the analysis is qualified, and the maintenance personnel are allowed to enter the polycondensation reactor for maintenance.

[0032] 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 method for thermal cleaning of a polycarbonate polycondensation reactor, characterized in that: The steps are as follows: (1) After the polycarbonate melt in the polycondensation reactor is discharged, the pressure of the polycondensation reactor is reduced and then increased, and the pressure reduction and pressure increase process is repeated 2 times or more; (2) cooling the polycondensation reactor; (3) adding phenol into the polycondensation reactor; (4) using phenol to heat the polycondensation reactor, observing the liquid level of phenol, and adding phenol; (5) After the hot cooking is completed, the phenol recovery system is used to recover the phenol; (6) Detect the phenol discharged from the outlet of the polycondensation reactor in step (5) and determine whether the hot boiling is qualified. If it is qualified, end the cleaning process; if it is unqualified, repeat steps (4)-(5) once.

2. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: In step (1), the temperature of the polycondensation reactor is 275-285°C; The depressurization parameters are: depressurization to 50-1000Pa.A, depressurization rate ≥1.25kPa / h; The boost parameters are: boost to 100-200kPa.A, boost rate ≥5kPa / h.

3. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: In step (2), the polycondensation reactor is cooled to 180-190°C at a cooling rate of 5-10°C / h.

4. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: In step (3), when phenol is added, the temperature of the polycondensation reactor is controlled to be 180-190° C., the pressure is greater than 5 kPa.G, and the injection amount of phenol is 20-60% of the liquid level of the polycondensation reactor.

5. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 4, characterized in that: The purity of the phenol used in step (3) is greater than 99.5%, and the chromaticity is ≤20 Hazen.

6. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: During the hot cooking process of step (4), the temperature of the polycondensation reactor is controlled to be 183-200° C., the pressure is 5-60 kPa.G, and the hot cooking time is 2-4 hours.

7. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 6, characterized in that: In step (4), the vaporization rate of the liquid phenol in the polycondensation reactor is controlled to be less than 50% by pressure, and the liquid level in the polycondensation reactor is made greater than 20% by adding phenol.

8. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: In step (5), the phenol recovery system comprises a phenol evaporation tank, a crude phenol collection tower, and a phenol distillation tower which are connected in sequence; The temperature of the phenol evaporation tank is 185-200°C; The top pressure of the phenol distillation tower is 1.5-2.5 kPa.A, the top reflux is 6000-10000 kg / h, the bottom temperature is 175-190°C, and the bottom circulation volume is 100-150 t / h.

9. The method for thermal cleaning of a polycarbonate polycondensation reactor according to claim 1, characterized in that: In step (6), the criteria for determining whether the hot boiling is qualified are: if the purity of phenol discharged from the outlet of the polycondensation reactor is less than 98.5% or the chromaticity is greater than 200 Hazen, it is unqualified; if the purity of phenol discharged from the outlet of the polycondensation reactor is greater than 98.5% and the chromaticity is less than 200 Hazen, it is qualified.