A method for rapid devolatilization of color-stable polycarbonate pellets

Abstract

The invention relates to a method for rapid devolatilization of polycarbonate particles with stable color. A crude polycarbonate slurry enters a devolatilization tank, and nitrogen containing a compounding agent of isopropyl mercaptan and n-butylamine is added from a distributor to perform nitrogen attachment devolatilization. The devolatilized polycarbonate slurry enters a filter blowing tank, and high-temperature gas is blown and filtered to remove water and dichloromethane, thereby obtaining target polycarbonate particles. The invention combines nitrogen attachment devolatilization and high-efficiency filter blowing to effectively solve the problems of product yellowing and color fluctuation in the production process of polycarbonate, and improves the quality of polycarbonate products, wherein the dichloromethane content of the polycarbonate particles is less than 6000ppm, the water content is less than 10000ppm, the hydrochloric acid content is less than 0.3ppm, and the product color number is less than 3.6.

Description

Technical Field

[0001] The invention belongs to the field of polycarbonate, and in particular relates to a method for quickly devolatilizing polycarbonate particles with stable color. Background Art

[0002] Polycarbonate (PC) is a colorless and transparent thermoplastic material with excellent strength characteristics of high strength, high elastic modulus and high impact strength. It also has excellent properties such as colorless transparency, good fatigue resistance and good weather resistance, and has a very wide range of applications. However, aromatic polycarbonate is prone to yellowing during the production process and has poor color stability, which affects the stability of downstream products and seriously restricts its application in downstream.

[0003] Patent CN103640108 B discloses using hot nitrogen as a carrier gas to dry polycarbonate powder through a two-stage drying process, recycling the nitrogen to solve the problem of recovering dichloromethane solvent during the drying process of polycarbonate powder, and avoiding the potential accident hazards of flammable and explosive dust in the polycarbonate drying system.

[0004] In the production process of polycarbonate, the removal of solvent dichloromethane has always been a bottleneck restricting production efficiency. Effectively improving the removal efficiency of dichloromethane in polycarbonate particles can effectively reduce production costs. Polycarbonate particles are very easy to decompose under long-term high temperature conditions, resulting in color fluctuations, which in turn affects product quality.

[0005] The polycarbonate drying methods provided by the above patents have improved the quality of polycarbonate products to a certain extent, but have failed to effectively solve the problems of yellowing and color fluctuations of polycarbonate in the production process. Summary of the invention

[0006] The purpose of the present invention is to provide a method for rapid devolatilization of polycarbonate particles with stable color in view of the above-mentioned problems existing in the prior art, which can effectively solve the problems of yellowing and color deterioration existing in the existing polycarbonate production process and improve the devolatilization rate of polycarbonate.

[0007] In the process of studying the production process of polycarbonate, the inventor found that the dichloromethane content in the polycarbonate particles is high before they enter the drying process. Dichloromethane will decompose at high temperature and react with water to generate aldehydes, which will lead to oxidation and decomposition of the polycarbonate end groups, resulting in color fluctuations. Controlling the dichloromethane content of the polycarbonate entering the dryer to about 6000ppm can effectively reduce the decomposition rate of dichloromethane. Controlling the water content to about 10000ppm can effectively reduce the generation of aldehydes by the reaction of dichloromethane decomposition products and water. Studies have found that by increasing the devolatilization temperature or extending the devolatilization time, polycarbonate will be hydrolyzed at high temperature in water, the molecular weight distribution will be broadened, and the product color will decrease. In addition, in the conventional devolatilization process, dichloromethane will decompose to produce acidic substances and form acid solution with water. Polycarbonate will decompose under acidic conditions to produce small molecular phenols, causing the product to turn yellow. At the same time, acidic substances will also cause equipment corrosion. Therefore, how to overcome the thermodynamic diffusion limitation of dichloromethane removal under low temperature conditions, remove the dichloromethane content to the target content, and reduce the water content to the target content, avoid the production of aldehydes in the drying process that lead to product degradation, and avoid the acidic decomposition of polycarbonate produced in the devolatilization process to produce phenols, is the key to solving the color problem of polycarbonate products and an important means to improve production efficiency.

[0008] In order to solve the above problems, the inventors conducted in-depth research and found that by introducing nitrogen containing a compound of isopropyl mercaptan and n-butylamine during the devolatilization process, the removal rate and removal limit of dichloromethane in polycarbonate particles can be improved without heating, and the hydrogen chloride produced by the decomposition of dichloromethane can be effectively controlled below 0.3ppm; at the same time, a filter blowing tank is used to blow the slurry under high pressure with medium-temperature nitrogen to control the water content below 1%, and the dichloromethane removal effect is further enhanced in a medium-temperature anhydrous environment, thereby solving the problem of color deterioration of carbonate products during the devolatilization and drying process.

[0009] The biggest difference between the present invention and other devolatilization processes for producing polycarbonate is that a gas distributor is arranged in the liquid phase material of the devolatilization tank, and nitrogen containing a compounding agent of isopropyl mercaptan and n-butylamine with a specific content is introduced through the gas distributor. Nitrogen bubbles containing a compounding agent of isopropyl mercaptan and n-butylamine generated after passing through the gas distributor are attached to the surface of polycarbonate particles, thereby reducing the vapor pressure of dichloromethane on the surface of the particles and accelerating the devolatilization rate. Meanwhile, isopropyl mercaptan has an extraction effect on the residual solvent dichloromethane in the polycarbonate particles, thereby increasing the removal limit of dichloromethane. Moreover, the addition of n-butylamine has a significant promoting effect on the extraction rate of isopropyl mercaptan. At the same time, the compounding agent of isopropyl mercaptan and n-butylamine eliminates the hydrochloric acid produced by the system online through the reaction, thereby preventing the polycarbonate from decomposing and producing colored phenolic substances under acidic conditions; and in the dehydration unit, high-temperature gas is used to blow the polycarbonate particles at high speed to replace the traditional centrifugal dehydration, thereby reducing the water content in the particles to less than 1%, solving the problem of high water content after traditional centrifugal dehydration, and further improving the removal effect of dichloromethane in a medium-temperature water-free environment.

[0010] In order to achieve the above-mentioned invention object, the specific technical solution adopted by the present invention is:

[0011] A method for rapid devolatilization of color-stable polycarbonate particles, the method comprising the following steps:

[0012] S1: The crude polycarbonate slurry enters the devolatilization tank, and nitrogen containing isopropyl mercaptan and n-butylamine compounding agent is added from the distributor to carry out nitrogen attachment devolatilization;

[0013] S2: The devolatilized polycarbonate slurry enters a filter blowing tank, where it is blown by high-temperature gas to remove water and dichloromethane, thereby obtaining target polycarbonate particles.

[0014] In the present invention, the solid content of the crude polycarbonate slurry in S1 is 10-40%, and the mass content of dichloromethane in the polycarbonate particles is 20-50%; preferably, the particle size of the polycarbonate particles in the crude polycarbonate slurry is 10-1000 μm.

[0015] In the present invention, the number of the distributors in S1 is 1-4, the shape of the distributor is cylindrical, the diameter of the distributor is 20-300 mm, the length of the distributor is 500-2000 mm, the aperture of the distributor is 0.1-3 mm, and the opening rate is 10-30% based on the surface area of ​​the distributor. The gas distributor can disperse a certain volume of non-condensable gas into a large number of bubbles with small diameters, increase the probability of collision between non-condensable gas bubbles and polycarbonate particles, and increase the contact area between gas and liquid phases.

[0016] In the present invention, the residence time of S1 in the devolatilizer is 0.3-5h, the temperature of the polycarbonate slurry is 40-100°C, and the discharge mode of the devolatilizer is overflow.

[0017] In the present invention, the nitrogen gas volume of the compounding agent containing isopropyl mercaptan and n-butylamine in S1 is 1-100Nm 3 / h, the mass of the compounding agent is 0.1-2wt% of the mass of nitrogen; preferably, n-butylamine accounts for 0.1-30wt% of the mass content of the compounding agent in the compounding agent. Nitrogen containing isopropyl mercaptan and n-butylamine compounding agents adheres to the surface of polycarbonate particles in the liquid phase, reduces the dichloromethane partial pressure in the bubbles on the surface of the polycarbonate particles, accelerates the volatilization of dichloromethane, and at the same time, due to the increase in bubble volume after the fusion of bubbles, the surface tension of the gas-solid two-phase on the surface of the polycarbonate changes, and the bubble shedding rate increases, further increasing the diffusion and volatilization of dichloromethane. Through the extraction of dichloromethane by isopropyl mercaptan and n-butylamine compounding agents, the thermodynamic limitation of dichloromethane volatilization is overcome, and the limit of solvent removal in polycarbonate particles is increased. At the same time, isopropyl mercaptan and n-butylamine compounding agents eliminate the acidic substances produced by the decomposition of dichloromethane online through reaction, avoid the decomposition of polycarbonate under acidic conditions, produce phenolic substances with color, and affect the background color of the product.

[0018] In the present invention, the high temperature gas in S2 is nitrogen with a gas volume of 1-100 Nm 3 / h; the temperature is 100-140℃, preferably 110-130℃; the filtration pressure difference is 1-5kPa, preferably 1-10kPa. The high-temperature gas first heats the polycarbonate particles. After heating, in an anhydrous environment, the dichloromethane inside the polycarbonate particles accelerates diffusion and volatilization. The gas phase of the filter blowing tank can be reused for a second time and passed into the devolatilization tank as a non-condensable gas for bubbling devolatilization. Since the gas phase outlet of the filter blowing tank has waste heat, it can be used in the devolatilization tank to avoid the consumption of heat energy during the bubbling devolatilization process and reduce the amount of non-condensable tail gas.

[0019] In the present invention, the residence time of S2 in the filter blowing tank is 3-15 minutes, the temperature of the polycarbonate slurry is 40-120° C.; the discharge mode of the filter blowing tank is automatic downflow feeding and discharging.

[0020] In the present invention, the number of the distributors in S2 is 1-4, the shape of the distributor is cylindrical, the diameter of the distributor is 200-300 mm, the length of the distributor is 500-2000 mm, the aperture of the distributor is 10-50 mm, and the opening rate is 20-40% based on the outer surface area of ​​the distributor.

[0021] Another object of the present invention is to provide a polycarbonate pellet with stable color.

[0022] A color-stable polycarbonate particle is devolatilized by the devolatilization method. The dichloromethane content of the polycarbonate particle is less than 6000 ppm, the water content is less than 10000 ppm, the hydrochloric acid content is less than 0.3 ppm, and the product color number is less than 3.6.

[0023] Compared with the prior art, the positive effects of the present invention are:

[0024] (1) The present invention performs nitrogen gas attachment coupling extraction and devolatilization of isopropyl mercaptan and n-butylamine compound in the devolatilization unit, and performs high-temperature gas high-pressure purge dehydration and further devolatilization in the filtration unit to obtain polycarbonate particles with stable color (color number less than 3.6) and low dichloromethane content (less than 6000 ppm);

[0025] (2) The present invention has high devolatilization efficiency, low energy consumption, and can prevent equipment corrosion and extend the service life of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a process flow chart for removing dichloromethane from a polycarbonate slurry, in which: 1, slurry feed to a devolatilizer, 2, slurry overflow discharge from a devolatilizer (slurry feed to a filter blowing tank), 3, polycarbonate particle discharge from a filter blowing tank, 4, high-temperature nitrogen inlet for a filter blowing tank, 5, high-temperature nitrogen outlet for a filter blowing tank (nitrogen inlet for a devolatilizer), 6, steam inlet for a devolatilizer, 7, water phase outlet for a filter blowing tank, 8, gas phase outlet for a devolatilizer, 9, an attached devolatilizer gas distributor, and 10, a filter blowing gas distributor.

[0027] Figure 2 The present invention is a schematic diagram of the gas distributor structure of the devolatilizer tank. In the figure: 1, distributor main pipe, 2, distributor air hole, 3, fixing part, 4, connecting flange, 5, gas main pipe, 6, gas main pipe connecting flange.

[0028] Figure 3 This is a schematic diagram of the structure of the gas distributor of the filter blowing tank of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

[0030] Crude polycarbonate slurry: a polycarbonate dichloromethane solution produced by an interfacial polycondensation process, obtained by a kneading machine to obtain a crude polycarbonate slurry, wherein the dichloromethane content in the polycarbonate particles is 20-50%

[0031] The slurry bed devolatilizer (abbreviated as devolatilizer) has a gas distributor at the bottom. The parameters of the distributor are as follows:

[0032] Distributor 1: The distributor is annular with a diameter of 1000mm and a cross-sectional diameter of 60mm. The distributor is anti-particle clogging shaped and has truncated cone-shaped holes. The outer surface diameter of the distributor is 1mm, the inner surface diameter of the distributor is 0.5mm, and the opening rate is 10% based on the outer surface area of ​​the distributor.

[0033] Distributor 2: The distributor is annular with a diameter of 3000 mm and a cross-sectional diameter of 60 mm. The surface diameter of the distributor is 3 mm, and the opening rate is 30% based on the surface area of ​​the distributor.

[0034] A high-temperature gas distributor is set in the cavity of the filter blowing tank (referred to as the filter blowing tank), and the parameters of the distributor are as follows:

[0035] Distributor 1: 3 distributors are evenly spaced with a spacing of 200mm. The distributor is cylindrical in shape, with a diameter of 200mm, a length of 600mm, an aperture of 15mm, and an opening rate of 30% based on the surface area of ​​the distributor. The gas enters from the side of the material and is extracted from the back of the material.

[0036] Distributor 2: 3 distributors are evenly spaced with a spacing of 200mm. The distributor is cylindrical in shape, with a diameter of 300mm, a length of 1000mm, an aperture of 10mm, and an opening rate of 40% based on the surface area of ​​the distributor. The gas enters from the side of the material and is extracted from the back of the material.

[0037] Polycarbonate powder product test method:

[0038] Equipment and instrument information:

[0039] Cassette furnace: Xiamen Lesde Scientific Instrument Co., Ltd., / KSQL-S-310;

[0040] Ion chromatography: Thermo Fisher Scientific (China) Co., Ltd., CIC-D100;

[0041] Injection molding machine: Ningbo Haitian Group Co., Ltd., MA8000;

[0042] Colorimeter: Shenzhen Aikerui Instruments Co., Ltd., CS-600.

[0043] Water content test in polycarbonate: Take 2.5g of powder and accurately record the weight. Put the powder into the bottle for Karl Fischer furnace and press the bottle cap tightly. Connect the Karl Fischer furnace to the coulometric moisture meter. Set the Karl Fischer furnace heating temperature to 120℃, measure the blank and accurately enter the sample weight to measure the water content.

[0044] Determination of dichloromethane content in polycarbonate: Take 5.0g of powder in a 15ml glass bottle and accurately record the sample mass. Thereafter, add isopropyl mercaptan and n-butylamine compounding agent to the glass bottle to 10.0g, and accurately record the dilution multiple. Cover the bottle cap, ultrasonically treat for ten minutes, and let it stand for 20h. Thereafter, use a disposable syringe to absorb the liquid in the bottle and filter it into a 1.5ml gas phase vial for gas chromatography detection. Use an external standard curve for quantification.

[0045] Determination of hydrogen chloride content in polycarbonate: Take 2.0g of powder in a 40ml disposable filter tube, use a pipette to accurately transfer 15ml of dichloromethane, and let it stand. After the powder is completely dissolved, use a pipette to accurately transfer 15ml of pure water into the filter tube. Shake well for 30 minutes, let it stand to separate, draw the upper aqueous phase with a disposable syringe, filter it, and perform ion chromatography to detect the chloride ion content, and perform a blank dichloromethane extraction test.

[0046] Determination of polycarbonate color number: Take 3kg of polycarbonate powder, dry it at 130℃ for 3h, and use a continuous injection molding machine to make samples. The first 9 samples are heated to 200℃ without staying in the injection molding machine. The 10-14 samples are kept in the injection molding machine for 9min. The samples are placed in a colorimeter to read the color number.

[0047] Raw material polycarbonate: Wanhua Chemical Group Co., Ltd., WH1225;

[0048] Isopropyl mercaptan: China National Pharmaceutical Group Corporation, analytical grade;

[0049] n-Butylamine: China National Pharmaceutical Group Corporation, analytical grade.

[0050] In the following examples, the process flow used is as follows Figure 1 shown.

[0051] Example 1

[0052] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0053] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 1wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 10wt%, nitrogen and compound are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0054] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 3kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0055] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 4185 ppm, the water content was 0.89%, and the hydrogen chloride content was 0.21 ppm.

[0056] In addition, the base color of the dried powder was measured, and the color number value was 2.91.

[0057] Example 2

[0058] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0059] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 2wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 10wt%, nitrogen and compound are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0060] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 3kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0061] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 4473 ppm, the water content was 0.89%, and the hydrogen chloride content was 0.23 ppm.

[0062] In addition, the base color of the dried powder was measured, and the color number value was 3.18.

[0063] Example 3

[0064] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0065] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 0.1wt% of isopropyl mercaptan and n-butylamine compounding agent, the concentration of n-butylamine in the compounding agent is 10wt%, nitrogen and compounding agent are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0066] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 3kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0067] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 5793 ppm, the water content was 0.90%, and the hydrogen chloride content was 0.22 ppm.

[0068] In addition, the base color of the dried powder was measured, and the color number value was 3.89.

[0069] Example 4

[0070] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0071] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 1wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 20wt%, nitrogen and compound are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0072] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 3kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0073] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 4598 ppm, the water content was 0.88%, and the hydrogen chloride content was 0.22 ppm.

[0074] In addition, the base color of the dried powder was measured, and the color number value was 3.21.

[0075] Example 5

[0076] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0077] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 1wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 1wt%, nitrogen and compound are mixed for 5min by static mixer, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0078] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 3kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0079] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The content of dichloromethane in the polycarbonate particles was 4921 ppm, the content of water was 0.91%, and the content of hydrogen chloride was 1.97 ppm.

[0080] In addition, the base color of the dried powder was measured, and the color number value was 3.59.

[0081] Example 6

[0082] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0083] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 1wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 10wt%, nitrogen and compound are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0084] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain a pressure difference of 5kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0085] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 4532 ppm, the water content was 0.78%, and the hydrogen chloride content was 0.25 ppm.

[0086] In addition, the base color of the dried powder was measured, and the color number value was 3.33.

[0087] Example 7

[0088] The polycarbonate slurry produced in the previous process, wherein the solid content of the polycarbonate particles is 20%, the dichloromethane content in the polycarbonate particles is 40%, and the particle size distribution is 200-500 μm, is devolatilized in the following manner.

[0089] S1: Polycarbonate slurry at 10Nm 3 / h flow rate into the devolatilization tank from the bottom, and 60kPa steam is continuously introduced into the slurry to heat the slurry to 90°C. The devolatilization tank adopts overflow discharge, and the residence time is 90min. Nitrogen is introduced from the bottom of the devolatilization tank for nitrogen attachment devolatilization, and the nitrogen flow rate is 50Nm 3 / h, add 1wt% of isopropyl mercaptan and n-butylamine compound, the concentration of n-butylamine in the compound is 10wt%, nitrogen and compound are mixed by static mixer for 5min, and bubbles with a diameter of 100um are generated through the gas distributor at the bottom of the tank. The bubbles and polycarbonate particles are mixed, contacted and attached to enhance the removal rate and removal limit of dichloromethane. After the bubbles fall off, they enter the gas recovery system from the top of the devolatilization tank. The slurry after devolatilization is discharged from the overflow port at the top of the devolatilization tank.

[0090] S2: The treated polycarbonate slurry enters the filter tank from the top of the filter tank, and the polycarbonate slurry is filtered and dehydrated, 10Nm 3 / h 130℃ high-temperature nitrogen is introduced from the powder side cavity of the filter blowing tank, and the gas is distributed through two distributors to maintain the pressure difference of 1kPa on both sides of the slurry. The high-temperature nitrogen dilutes and promptly carries out the water, dichloromethane, isopropyl mercaptan and n-butylamine compounding agent volatilized from the filter cake particles. The residence time of the filtration process is 5min. The outlet gas phase enters the tail gas treatment unit, and the water obtained by the filtration enters the hot water system for heat recovery and water reuse. The polycarbonate particles obtained by the filtration are discharged intermittently and enter the subsequent drying process.

[0091] The polycarbonate particles flowed out from the overflow weir of the filter blowing tank. The dichloromethane content in the polycarbonate particles was 4729 ppm, the water content was 1.90%, and the hydrogen chloride content was 0.27 ppm.

[0092] In addition, the base color of the dried powder was measured, and the color number value was 3.51.

[0093] Comparative Example 1

[0094] Isobutane was used to replace isopropyl mercaptan, butadiene was used to replace n-butylamine, and the rest was the same as in Example 1.

[0095] The content of dichloromethane in the polycarbonate particles was 22982 ppm, the content of water was 0.88%, and the content of hydrogen chloride was 4.35 ppm.

[0096] In addition, the base color of the dried powder was measured and the color number value was 4.93.

[0097] Comparative Example 2

[0098] In step S1, isopropyl mercaptan and n-butylamine are not added, and the rest is the same as in Example 1.

[0099] The content of dichloromethane in the polycarbonate particles was 23141 ppm, the content of water was 0.83%, and the content of hydrogen chloride was 5.83 ppm. In addition, the base color of the dried powder was measured, and the color number value was 5.18.

[0100] Comparative Example 3

[0101] The centrifugal process was used to replace the S2 filtration process, and the rest was the same as in Example 1.

[0102] The content of dichloromethane in the polycarbonate particles was 7173 ppm, the content of water was 8.10%, and the content of hydrogen chloride was 0.22 ppm. In addition, the base color of the dried powder was measured, and the color number value was 3.81.

Claims

1. A method for rapid devolatilization of color-stable polycarbonate particles, characterized in that: The method comprises the following steps: S1: The crude polycarbonate slurry enters the devolatilization tank, and nitrogen containing isopropyl mercaptan and n-butylamine compounding agent is added from the distributor to carry out nitrogen attachment devolatilization; S2: The devolatilized polycarbonate slurry enters a filter blowing tank, where it is blown by high-temperature gas to remove water and dichloromethane, thereby obtaining target polycarbonate particles.

2. The devolatilization method according to claim 1, characterized in that the solid content of the crude polycarbonate slurry in S1 is 10-40%, and the mass content of dichloromethane in the polycarbonate particles is 20-50%; And / or, the number of the distributors in S1 is 1-4, the shape of the distributor is annular, the diameter of the distributor is 200-3000mm, the cross-sectional diameter of the distributor is 50-100mm, the pore size of the distributor is 0.1-3mm, and the opening rate is 10-30% based on the outer surface area of ​​the distributor; and / or, the residence time of S1 in the devolatilizer is 0.3-5h, the temperature of the polycarbonate slurry is 40-100°C, and the discharge mode of the devolatilizer is overflow; And / or, the nitrogen gas volume containing isopropyl mercaptan and n-butylamine compound described in S1 is 1-100Nm 3 / h, and the mass content of the compounding agent is 0.1%-2% of the nitrogen mass flow rate.

3. The devolatilization method according to claim 2, characterized in that the particle size of the polycarbonate particles in the crude polycarbonate slurry in S1 is 10-1000 μm; In the compound described in S1, n-butylamine accounts for 0.1%-30% of the mass ratio of the compound.

4. The devolatilization method according to claim 1, characterized in that the high temperature gas in S2 is nitrogen with a gas volume of 1-100 Nm 3 / h; temperature is 100-140℃; filtration pressure difference is 1-5kPa; And / or, the residence time of S2 in the filter blowing tank is 3-15 min, the temperature of the polycarbonate slurry is 40-120° C.; the discharge mode of the filter blowing tank is automatic downflow feeding and discharging; And / or, the number of the distributors in S2 is 1-4, the shape of the distributor is cylindrical, the diameter of the distributor is 200-300 mm, the length of the distributor is 500-2000 mm, the aperture of the distributor is 10-15 mm, and the opening rate is 20-40% based on the outer surface area of ​​the distributor.

5. The devolatilization method according to claim 4, characterized in that the temperature in S2 is 110-130°C.

6. A color-stable polycarbonate particle, devolatilized by the devolatilization method according to any one of claims 1 to 5, characterized in that: The polycarbonate particles have a dichloromethane content of less than 6000 ppm, a water content of less than 10000 ppm, a hydrochloric acid content of less than 0.3 ppm, and a product color number of less than 3.6.

Images