Cleaning method and cleaning system for polymeric kettle

Abstract

The invention provides a cleaning method and a cleaning system for a polymeric kettle. The cleaning method comprises the following steps: (1) adding a cleaning solvent into a to-be-cleaned polymerization kettle until the kettle is full, and carrying out stirring type cleaning; the cleaning solvent comprises a recovery solvent and / or a fresh solvent; the stirring type cleaning comprises the steps of continuously discharging and filtering liquid in the kettle while stirring the liquid, and returning filtrate into the kettle for recycling; and (2) after the cleaning is finished, taking liquid in the kettle as a recovery solvent, taking a part of the recovery solvent as a reaction solvent for the next polymerization reaction, and returning the rest of the recovery solvent to the step (1) for the next cleaning. The method and system are simple and easy to operate and good in cleaning efficiency and effect, the solvent utilization rate is greatly increased, and cost is saved.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber technology, and more specifically to a cleaning method and system for a polymerization reactor. Background Technology

[0002] Carbon fiber is a high-strength, high-modulus fiber with a carbon content of over 90%. It has properties such as high temperature resistance, friction resistance, electrical conductivity, thermal conductivity, and corrosion resistance. It is widely used in aerospace, marine engineering, new energy equipment, engineering machinery, transportation facilities, and other fields, and is a strategic new material with very broad application prospects.

[0003] The preparation process of polyacrylonitrile-based carbon fiber is time-consuming and complex, mainly consisting of three stages: polymerization of polyacrylonitrile copolymer, spinning of polyacrylonitrile precursor fibers, and oxidative carbonization treatment of the fibers. Among these, the polymerization process, as the starting point of production, requires particularly strict quality control. During acrylonitrile polymerization, uneven heating, poor stirring, or even inadequate polishing or scratches on the reactor walls can all lead to the formation of gel particles to varying degrees. If not cleaned promptly, these particles will deposit into larger gels later, significantly impacting production stability.

[0004] Currently, the most commonly used methods for cleaning polymerization reactors in the carbon fiber production industry include: (1) high-pressure spray cleaning. Although this method is highly efficient, the complex heat exchange components inside the reactor, such as coils and supports, cannot be 100% cleaned by the spray, especially the lower surface of the reactor; (2) solvent washing. This method requires a large amount of solvent, and the solution needs to be separated after washing. In addition, there is another method that does not clean but relies on long-term evacuation to minimize the amount of material adhering to the reactor. This method is time-consuming, cannot completely remove the original solution, and is more likely to generate gel. In view of this, the present invention proposes an improved polymerization reactor cleaning method and system. Summary of the Invention

[0005] In order to solve one of the above-mentioned technical problems in the prior art, the present invention provides a cleaning method and cleaning system for a polymerization reactor, which can solve the problems of difficult cleaning of the polymerization reactor, low solvent utilization efficiency, and a large number of carbon fiber spinneret breakages caused by incomplete cleaning.

[0006] In a first aspect, the present invention provides a method for cleaning a polymerization reactor, the cleaning method comprising the following steps:

[0007] (1) Add cleaning solvent to the polymerization reactor to be cleaned until the reactor is full, and perform stirring cleaning;

[0008] The cleaning solvent includes recycled solvent and / or fresh solvent; the stirring cleaning includes continuously discharging and filtering the liquid in the vessel while stirring it, and returning the filtrate to the vessel for recycling.

[0009] (2) After cleaning, the liquid in the reactor is used as a recycled solvent. Part of the recycled solvent is used as the reaction solvent for the next polymerization reaction, and the rest of the recycled solvent is returned to step (1) for the next cleaning.

[0010] According to some embodiments of the present invention, in step (2), a portion of the recovered solvent is directly used as the reaction solvent for the next polymerization reaction (without adding fresh solvent).

[0011] According to some embodiments of the present invention, in step (2), the reaction solvent for the next polymerization reaction also includes a fresh solvent.

[0012] According to some embodiments of the present invention, in step (2), the volume percentage of the recovered solvent in the cleaning solvent and the reaction solvent of the next polymerization reaction is 5% to 100%, for example, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or any value between them, preferably 50% to 100%, more preferably 80% to 100%, and even more preferably 100%.

[0013] According to some embodiments of the present invention, the stirring rate is 20-200 r / min, for example, 20 r / min, 50 r / min, 80 r / min, 100 r / min, 120 r / min, 150 r / min, 180 r / min, 200 r / min or any value between them.

[0014] According to some embodiments of the present invention, the cleaning time is 2-48 hours, preferably 5-34 hours.

[0015] According to some embodiments of the present invention, the agitation-type cleaning further includes heating the liquid in the vessel while agitating it. In some embodiments, the heating temperature is 25-80°C. In some embodiments, the heating temperature is 25-60°C. In some embodiments, the heating temperature is 60-80°C.

[0016] According to some embodiments of the present invention, the fresh solvent is the same solvent used in the polymerization reaction in the reactor.

[0017] In this invention, the polymerization reactions that can occur in the polymerization reactor include, but are not limited to, the copolymerization reaction of acrylonitrile and itaconic acid.

[0018] According to some embodiments of the present invention, the fresh solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0019] According to some embodiments of the present invention, in the polymerization reaction, the mass percentage of acrylonitrile monomer is 96-98.7% based on the total mass of acrylonitrile monomer and itaconic acid monomer.

[0020] According to some embodiments of the present invention, the viscosity of the polyacrylonitrile copolymer stock solution obtained after the polymerization reaction is 30 to 130 Pa·s at 60°C, preferably 40 to 100 Pa·s.

[0021] According to some embodiments of the present invention, the number of particles in the polyacrylonitrile copolymer stock solution obtained after the polymerization reaction is 25,000-50,000 particles / mL, preferably 28,000-48,000 particles / mL.

[0022] A second aspect of the present invention provides a cleaning system for a polymerization reactor, the cleaning system comprising:

[0023] A polymerization reactor, wherein the polymerization reactor is provided with a recovered solvent inlet, a fresh solvent inlet and a stirring device, and the polymerization reactor is configured to perform stirring cleaning when the recovered solvent and / or fresh solvent are added to the full reactor;

[0024] A filtration device is connected to the polymerization reactor and is configured to filter the continuously discharged liquid from the reactor and return the filtrate to the reactor for recycling when the polymerization reactor is being stirred and cleaned.

[0025] A solvent recovery buffer tank is provided, with its two ends connected to the polymerization reactor and the filtration device, respectively. The tank is configured to store the recovered solvent discharged from the reactor after the polymerization reactor is cleaned, and to regulate the volume ratio of the recovered solvent in the reaction solvent during the next polymerization reaction by adjusting the volume of the recovered solvent stored in the buffer tank.

[0026] According to some embodiments of the present invention, the polymerization reactor is further provided with a heating device for heating the liquid inside the reactor during cleaning.

[0027] According to some embodiments of the present invention, the polymerization reactor is further provided with a raw material inlet and a product outlet.

[0028] According to some embodiments of the present invention, the polymerization reactor is further provided with a circulating solvent inlet and a circulating solvent outlet; the inlet of the filtration device is connected to the circulating solvent outlet of the polymerization reactor via a circulating pump, and the outlet of the filtration device is connected to the circulating solvent inlet of the polymerization reactor.

[0029] According to some embodiments of the present invention, the filtration device has an accuracy of 0.1 μm-10 μm, preferably 0.2 μm-1 μm.

[0030] According to some embodiments of the present invention, the recovered solvent buffer tank is provided with an adjustable overflow port, and the volume of recovered solvent stored in the buffer tank is adjusted by adjusting the position of the overflow port.

[0031] In some embodiments, the overflow port of the recovered solvent buffer tank is connected to the recovered solvent inlet of the polymerization reactor, and the inlet of the recovered solvent buffer tank is connected to the outlet of the filtration device.

[0032] According to some embodiments of the present invention, the recovered solvent buffer tank is further provided with a heat preservation device, which is used to maintain the recovered solvent in the buffer tank at a constant temperature, preferably maintaining the temperature of the recovered solvent in the buffer tank within the heating temperature range during the cleaning of the polymerization reactor.

[0033] In some embodiments, the insulation device is a jacket or a coil.

[0034] A third aspect of the present invention provides the application of the above-described cleaning system in cleaning a polymerization reactor for preparing carbon fibers.

[0035] In some embodiments, the carbon fiber includes polyacrylonitrile-based carbon fiber.

[0036] In some embodiments, the polyacrylonitrile-based carbon fiber comprises a copolymer of acrylonitrile and itaconic acid.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The method and system of the present invention can perform high-intensity cleaning of the polymerization reactor when it is full of liquid. There is no need to set up a complex rinsing component in the reactor or a high-pressure environment. This can greatly reduce the probability of the polymer adhering to the reactor forming gel. In particular, it can thoroughly clean various dead corner areas. Compared with the existing high-pressure spray cleaning method, the process equipment and operation method are simpler. While ensuring high cleaning efficiency, it improves the cleanliness of the polymerization reactor and saves a lot of costs.

[0039] (2) The method and system of the present invention can perform partial washing of the cleaning solvent without increasing the concentration of polymer dissolved therein. After multiple cycles of filtration, the cleaning solution can be directly used for the next polymerization reaction. Not only is there no need for additional separation and treatment of the cleaning solvent, but the overall amount of solvent used in the process can also be reduced, which greatly improves the efficiency of solvent use and is more green and environmentally friendly.

[0040] (3) The polymerization kettle is cleaned, which reduces the accumulation of gel and improves the stability of the polymerization liquid. There are fewer particles in the raw liquid, which solves the problem of a large number of broken filaments in the spinneret and improves the stability of carbon fiber production. Attached Figure Description

[0041] Figure 1 The diagram below shows a schematic of a polymerization reactor cleaning system according to a specific embodiment of the present invention, wherein R: reactor; S: stirring device; H: heating device; V-1: side wall plunger valve; V-2, V-3: three-way switching valves; P: circulating pump; T: high-level constant temperature and volume buffer tank; L: overflow pipeline; F: filter.

[0042] Figure 2 This is a schematic diagram of a conventional spray washing vessel device in the prior art, where R: reaction vessel; P: spray device; H: heating device. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0044] Unless otherwise specified, all reagents used in the following experiments of this invention are commercially available products or reagents prepared according to conventional methods. Unless otherwise specified, all methods used in the experiments are conventional experimental methods. Unless otherwise specified, all instruments used in the experiments are commercially available.

[0045] The term "fresh solvent" as used in this invention refers to the solvent used in the polymerization reaction in the polymerization reactor, i.e., the reaction solvent.

[0046] The term "recovered solvent" as used in this invention refers to the liquid discharged from the polymerization reactor after cleaning it with a cleaning solvent. For example, after the first polymerization reaction, fresh solvent is used as a cleaning agent for the first cleaning, and the liquid after cleaning is used as the recovered solvent. The reactor is then fed again for the polymerization reaction. After the reaction is completed, the reacted material is discharged, and the recovered solvent obtained after the first cleaning (or some fresh solvent can be added to the recovered solvent) is used as a cleaning agent for the second cleaning. The liquid after cleaning is used as the recovered solvent. This cycle is repeated.

[0047] The term "precision of the filtration device" or "precision of the filter" as used in this invention refers to the minimum size of particulate matter that the filtration device (or filter) can filter out.

[0048] According to a specific embodiment of the present invention, such as Figure 1As shown, a cleaning system for a polymerization reactor used to prepare polyacrylonitrile-based carbon fibers is provided. The cleaning system consists of a polymerization reactor (R) with a plunger valve (V-1) installed on the reactor wall, a circulation pump (P), a high-level thermostatic and volumetric buffer tank (T), a filter (F), an overflow line (L), a three-way switching valve V-2 connecting the plunger valve (V-1), the high-level thermostatic and volumetric buffer tank (T), and the circulation pump (P), and a three-way switching valve V-3 connecting the polymerization reactor (R), the high-level thermostatic and volumetric buffer tank (T), and the filter (F).

[0049] The polymerization reactor (R) is also equipped with a fresh solvent inlet, a monomer inlet (acrylonitrile, itaconic acid), an additive inlet, and a polyacrylonitrile-based carbon fiber solution outlet. The polymerization reactor (R) is connected to a stirring device (S) and a heating device.

[0050] The high-level thermostatic volumetric buffer tank (T) is equipped with different overflow ports to adjust the volume of recovered solvent entering the polymerization reactor (R). Furthermore, the high-level thermostatic volumetric buffer tank (T) is also equipped with an insulation medium, such as a jacket or coil, to maintain the temperature of the solvent in the high-level thermostatic volumetric buffer tank (T) within the cleaning temperature range inside the polymerization reactor (R). This saves time when heating the solvent inside the reactor during solvent recycling.

[0051] The cleaning method for the polymerization reactor using the above-mentioned cleaning system includes the following steps:

[0052] (1) After the polymerization reaction is completed, the reaction material is released, and the recovered solvent and / or fresh solvent in T is added to R for full-bottle cleaning.

[0053] (2) Turn on the heating device H and stirring device S connected to the polymerization reactor to raise the temperature and stir. Turn on V-1, set V-2 to connect R and P, set V-3 to connect F and R, and turn on P circulation to filter the gel generated in the reactor in F. The filtrate is circulated back to R.

[0054] (3) Cool down to room temperature and stop stirring; switch V-3 to connect F and T, adjust the position of the overflow port so that a certain volume of recycled solvent is retained in T, thereby controlling the ratio of recycled solvent and fresh solvent entering the polymerization reactor in the next polymerization reaction. When L overflows, stop P and close V-1.

[0055] (4) After cleaning, the polymerization reactor is re-fed, using the recovered solvent retained in the reactor as the reaction solvent or adding some new solvent (i.e., a mixture of recovered and fresh solvents) as the reaction solvent to obtain polyacrylonitrile-based carbon fiber raw material. The raw material in the reactor is released, and then wet spinning is performed to obtain carbon fiber precursor.

[0056] Repeat steps (1) to (4).

[0057] In some specific embodiments, the selected fresh solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide, preferably the same solvent as the polymerization solvent.

[0058] In some specific embodiments, when starting the RPFR cycle, the temperature is set to 25-80℃, preferably 25-60℃, the stirring rate is 20-200r / min, and the cleaning time is 2-48h, preferably 5-34h.

[0059] In some specific embodiments, the residence time t of the cleaning solvent in the reactor is 3-60 min, t = V R / R 流量 .

[0060] In some specific embodiments, the volume of the recovered solvent in T is adjusted by the overflow port position, thereby controlling the ratio of fresh solvent to recovered solvent in the polymerization reactor during the polymerization process. The volume percentage of the recovered solvent is preferably 5%-100%, more preferably 50%-100%, and even more preferably 80%-100%. In this invention, it is preferable to use the recovered solvent as the reaction solvent for the next polymerization reaction, that is, no fresh solvent is added in the next polymerization reaction, which can improve solvent utilization while ensuring good product performance.

[0061] In some specific embodiments, the insulation medium of the high-level constant temperature and volume buffer tank selected for the cleaning system is a jacket or coil, and the temperature is set at 25-80℃, preferably 25-60℃.

[0062] In some specific embodiments, the filter used in the cleaning system has a precision of 0.1-10μm, preferably 0.2-1μm.

[0063] The method of this invention can be used to prepare polyacrylonitrile-based carbon fiber materials by solution polymerization, using acrylonitrile and itaconic acid as monomers for copolymerization. Using the method and system of this invention to clean the polymerization reactor, in the subsequent wet spinning process, the viscosity of the polyacrylonitrile-based copolymer spinning solution at 60°C is 30–130 Pa·s, for example, 40–100 Pa·s. The particle number in the solution is 25,000–50,000 particles / mL, for example, 28,000–48,000 particles / mL. After filtering and extruding through a spinneret, the polyacrylonitrile copolymer solution is sequentially subjected to coagulation molding, water washing, hot water drawing, oiling, drying densification, and steam drawing to obtain polyacrylonitrile carbon fiber precursor. The fineness of the precursor is 0.70–1.32 dtex, preferably 0.80–1.10 dtex. The fiber count in the spinneret is 500–12K.

[0064] The testing instruments and conditions used in the following embodiments and comparative examples of this invention are as follows:

[0065] The viscosity of the spinning solution in this invention is measured using the following method: An Anton Paar Rheolab QC rheometer is used. The spinning solution is filled into a measuring cup, taking care to avoid air bubbles, and the filling amount is slightly higher than the graduation mark inside the cup. The measuring cup is then placed in the rheometer and allowed to stand for 5 minutes until the sample is leveled. The measuring cup is then removed, the rotor is pressed into the measuring cup, and the two are reassembled into the rheometer to begin the test.

[0066] In this invention, the number of filaments during the spinneret extrusion process is counted by using an online camera to monitor the number of filaments contained in the nascent fibers within a continuous 10,000-meter range at the spinneret extrusion outlet.

[0067] The method for testing particles in the spinning solution in this invention is as follows: The particle count is determined using a PSS AccuSizer A7000 SIS liquid particle counter (detection limit 10,000 particles / ml). The spinning solution is diluted 20-100 times and placed in the instrument for detection. The number of samples measured multiplied by the corresponding dilution factor is the number of particles per milliliter of the original solution.

[0068] The raw materials used in the examples are either directly available for purchase or prepared according to existing methods.

[0069] The polymerization reactions in the following examples and comparative examples of the present invention are all polymerization reactions to prepare polyacrylonitrile by copolymerization of acrylonitrile and itaconic acid as monomers.

[0070]

Example 1

[0071] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor (R) for full operation. The temperature is raised and maintained at 45°C, with stirring at 50 rpm. V-1 and V-2 are switched from R to P, and V-3 from F to R. P circulation is initiated, and the gel already formed in the reactor is filtered through F. The filtration device has a precision of 0.2 μm. The filtrate is circulated back to R and maintained for 34 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 10 minutes. Then, the temperature is lowered to room temperature and stirring is stopped. V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, cleaning is considered complete. The overflow port position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 40:60 (volume ratio). The polymerization reactor is again quantitatively fed with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 40,000 particles / ml. After being extruded through a 6K spinneret, the raw material undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretch ratio is 2.4 times, and the total stretch ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 17 filaments at the spinneret.

[0072]

Example 2

[0073] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor T to fill the reactor R. The temperature is raised and maintained at 25°C, with stirring at 200 rpm. V-1 and V-2 are switched from R to P, and V-3 from F to R. P circulation is initiated to filter the gel already formed in the reactor through F. The filtration device has a precision of 0.1 μm. The filtrate is circulated back to R and maintained for 48 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 15 minutes. Then, stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, cleaning is considered complete. The overflow port position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 20:80 (volume ratio). The polymerization reactor is again quantitatively filled with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 48,000 particles / ml. After being extruded through a 6K spinneret, the raw solution undergoes two coagulation baths for solidification, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretching ratio is 2.4 times, and the total stretching ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 20 filaments at the spinneret.

[0074]

Example 3

[0075] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor (R) for full operation. The temperature is raised and maintained at 80°C, with stirring at 120 rpm. V-1 and V-2 are switched from R to P, and V-3 from F to R. P circulation is initiated to filter the gel already formed in the reactor through F. The filtration device has a precision of 0.2 μm. The filtrate is circulated back to R and maintained for 24 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 60 minutes. Then, stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, cleaning is considered complete. The overflow position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 30:70 (volume ratio). The polymerization reactor is again quantitatively fed with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 36,000 particles / ml. After being extruded through a 6K spinneret, the raw solution undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretch ratio is 2.4 times, and the total stretch ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 16 filaments at the spinneret.

[0076]

Example 4

[0077] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor T to fill the reactor R. The temperature is raised and maintained at 60°C, with stirring at 120 rpm. V-1 and V-2 are switched from R to P, and V-3 is switched from F to R. P circulation is initiated to filter the gel already formed in the reactor through F. The filtration device has a precision of 0.2 μm. The filtrate is circulated back to R and maintained for 24 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 10 minutes. Then, stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, cleaning is considered complete. The overflow position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 40:60 (volume ratio). The polymerization reactor is again quantitatively fed with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 31,000 particles / ml. After being extruded through a 6K spinneret, the raw material undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretching ratio is 2.4 times, and the total stretching ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 15 filaments at the spinneret.

[0078]

Example 5

[0079] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor T to fill the reactor R. The temperature is raised and maintained at 80°C, and the stirrer is started at 120 rpm. V-1 and V-2 are switched from R to P, and V-3 is switched from F to R. The P circulation is activated to filter the gel already formed in the reactor through F. The filtration device has a precision of 1 μm. The filtrate is circulated back to R and maintained for 12 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 30 minutes. Then, the stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, the cleaning is considered complete. The overflow port position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 30:70 (volume ratio). The polymerization reactor is then quantitatively filled again with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution showed a particle count of 33,000 particles / ml. After being extruded through a 6K spinneret, the raw material undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretching ratio is 2.4 times, and the total stretching ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 15 filaments at the spinneret.

[0080]

Example 6

[0081] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor T to fill the reactor R. The temperature is raised and maintained at 80°C, and the stirrer is started at 120 rpm. V-1 and V-2 are switched from R to P, and V-3 is switched from F to R. The P circulation is activated to filter the gel already formed in the reactor through F. The filter precision is selected as 0.2 μm. The filtrate is circulated back to R and maintained for 5 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 20 minutes. Then, the stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, the cleaning is considered complete. The overflow port position is controlled, and the polymerization solvent in the next polymerization reactor is adjusted to a ratio of fresh solvent to recovered solvent of 30:70 (volume ratio). The polymerization reactor is again quantitatively fed with reactants and fresh solvent to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 43,000 particles / ml. After being extruded through a 6K spinneret, the raw material undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretching ratio is 2.4 times, and the total stretching ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 25 filaments at the spinneret.

[0082]

Example 7

[0083] After the polymerization reaction is completed, the following method is used: Figure 1The cleaning system shown involves quantitatively adding recovered solvent and fresh dimethyl sulfoxide (DMSO) to the reactor T to fill the reactor R. The temperature is raised and maintained at 80°C, and the stirrer is started at 120 rpm. V-1 and V-2 are switched from R to P, and V-3 is switched from F to R. The P circulation is initiated, and the gel already formed in the reactor is filtered in F. The filtration device has a precision of 0.2 μm. The filtrate is circulated back to R and maintained for 5 hours. During this period, the residence time of the cleaning solvent in the polymerization reactor is 20 minutes. Then, stirring is stopped, and V-3 is switched from F to T. When L overflows, P is stopped and V-1 is closed. At this point, cleaning is considered complete. The overflow port position is controlled, and the polymerization solvent ratio in the next polymerization reactor is adjusted to 0:100 (fresh solvent:recovered solvent). The polymerization reactor is then quantitatively filled with reactants and polymerization solvent again to prepare a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution shows a particle count of 42,000 particles / ml. After being extruded through a 6K spinneret, the raw solution undergoes two coagulation baths for curing, followed by water washing, hot water stretching, and oiling. The water washing temperature is 65℃ with a stretch ratio of 1.06, the hot water stretching temperature is 92℃ with a stretch ratio of 2.4, and oiling is carried out at room temperature. Subsequently, during the drying and densification process, the temperature is 110℃ without stretching. During steam stretching, the steam pressure is 2.5 MPa, the stretching ratio is 2.4 times, and the total stretching ratio is 8.7. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 0.74 dtex. Observations during spinning revealed 23 filaments at the spinneret.

[0084] Therefore, compared with the use of a mixture of fresh and recycled solvents as the reaction solvent for the next polymerization reaction in Examples 1-6, the use of recycled solvents only in Example 7 has little impact on the performance of the obtained polyacrylonitrile-based carbon fiber dope and the performance of the prepared precursor fiber. Polymerization using only recycled solvents can meet production requirements, and improves solvent utilization and saves costs.

[0085] Comparative Example 1

[0086] After the polymerization reaction is completed, the following method is used: Figure 2The polymerization reactor was cleaned using a conventional spray washing apparatus, with a cleaning time of approximately 24 hours. After cleaning, the polymerization reactor was re-fed for reaction, yielding a polyacrylonitrile copolymer stock solution with a viscosity of 65 Pa·s (at 60°C). Particle count analysis of this stock solution showed a particle count of 108,000 particles / ml. After extrusion through a 6K spinneret, this stock solution underwent two solidification baths, followed by water washing, hot water stretching, and oiling. The water washing temperature was 65°C with a stretch ratio of 1.06, the hot water stretching temperature was 92°C with a stretch ratio of 2.4, and oiling was performed at room temperature. Subsequently, during the drying and densification process, the temperature was 110°C, with no stretching applied. During steam stretching, the steam pressure was 2.5 MPa, the stretching ratio was 2.4 times, and the total stretching ratio was 8.7. The resulting polyacrylonitrile-based carbon fiber precursor had a fineness of 0.74 dtex. During spinning, 82 filaments were observed at the spinneret.

[0087] The cleaning process parameters and cleaning results in the above embodiments and comparative examples are shown in Table 1.

[0088] Table 1

[0089]

[0090]

[0091] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for cleaning a polymerization reactor, comprising the following steps: (1) Add cleaning solvent to the polymerization reactor to be cleaned until the reactor is full, and perform stirring cleaning; The cleaning solvent includes recycled solvent and / or fresh solvent; the stirring cleaning includes continuously discharging and filtering the liquid in the vessel while stirring it, and returning the filtrate to the vessel for recycling. (2) After cleaning, the liquid in the reactor is used as a recycled solvent. Part of the recycled solvent is used as the reaction solvent for the next polymerization reaction, and the rest of the recycled solvent is returned to step (1) for the next cleaning.

2. The method according to claim 1, characterized in that, In step (2), the reaction solvent for the next polymerization reaction may also include an optional fresh solvent; Preferably, in step (2), the volume percentage of the recovered solvent in the reaction solvent of the next polymerization reaction is 5% to 100%, more preferably 50% to 100%, more preferably 80% to 100%, and even more preferably 100%.

3. The method according to claim 1 or 2, characterized in that, The stirring rate is 20-200 r / min; and / or the cleaning time is 2-48 hours, preferably 5-34 hours; and / or the stirring cleaning also includes heating the liquid in the vessel while stirring it, preferably the heating temperature is 25-80℃, more preferably 25-60℃.

4. The method according to any one of claims 1-3, characterized in that, The fresh solvent and the reaction solvent used in the polymerization reaction in the reactor are the same solvent; Preferably, the fresh solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

5. The method according to claim 4, characterized in that, The polymerization reaction preferably includes a copolymerization reaction of acrylonitrile monomer and itaconic acid monomer; Preferably, in the polymerization reaction, based on the total mass of acrylonitrile monomer and itaconic acid monomer, the mass percentage of acrylonitrile monomer is 96-98.7%; Preferably, the viscosity of the polyacrylonitrile copolymer stock solution obtained after the polymerization reaction is 30-130 Pa·s at 60°C, and more preferably 40-100 Pa·s. Preferably, the number of particles in the polyacrylonitrile copolymer stock solution obtained after the polymerization reaction is 25,000-50,000 particles / mL, more preferably 28,000-48,000 particles / mL.

6. A cleaning system for a polymerization reactor, comprising: A polymerization reactor, wherein the polymerization reactor is provided with a recovered solvent inlet, a fresh solvent inlet and a stirring device, and the polymerization reactor is configured to perform stirring cleaning when the recovered solvent and / or fresh solvent are added to the full reactor; A filtration device is connected to the polymerization reactor and is configured to filter the continuously discharged liquid from the reactor and return the filtrate to the reactor for recycling when the polymerization reactor is being stirred and cleaned. A solvent recovery buffer tank is provided, with its two ends connected to the polymerization reactor and the filtration device, respectively. The tank is configured to store the recovered solvent discharged from the reactor after the polymerization reactor is cleaned, and to regulate the volume ratio of the recovered solvent in the reaction solvent during the next polymerization reaction by adjusting the volume of the recovered solvent stored in the buffer tank.

7. The system according to claim 6, characterized in that, The polymerization reactor is also equipped with a heating device for heating the liquid inside the reactor during cleaning; and / or, the polymerization reactor is also equipped with a reactant inlet and a product outlet; and / or, the polymerization reactor is also equipped with a circulating solvent inlet and a circulating solvent outlet; the inlet of the filter device is connected to the circulating solvent outlet of the polymerization reactor via a circulating pump, and the outlet of the filter device is connected to the circulating solvent inlet of the polymerization reactor. Preferably, the filtration device has an accuracy of 0.1μm-10μm, more preferably 0.2μm-1μm.

8. The system according to claim 6 or 7, characterized in that, The recovered solvent buffer tank is equipped with an adjustable overflow port, and the volume of recovered solvent stored in the buffer tank can be adjusted by adjusting the position of the overflow port. Preferably, the overflow port of the recovered solvent buffer tank is connected to the recovered solvent inlet of the polymerization reactor, and the inlet of the recovered solvent buffer tank is connected to the outlet of the filtration device.

9. The system according to any one of claims 6-8, characterized in that, The recovered solvent buffer tank is also equipped with a heat preservation device, which is used to maintain the recovered solvent in the buffer tank at a constant temperature, preferably maintaining the temperature of the recovered solvent in the buffer tank within the heating temperature range during the cleaning of the polymerization reactor. Preferably, the heat preservation device is a jacket or a coil.

10. The application of the system according to any one of claims 6-9 in cleaning a polymerization reactor for preparing carbon fibers; Preferably, the carbon fiber comprises polyacrylonitrile-based carbon fiber; More preferably, the polyacrylonitrile-based carbon fiber comprises a copolymer of acrylonitrile and itaconic acid.

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