Polyacrylonitrile spinning solution and preparation method and device therefor, and polyacrylonitrile carbon fiber precursor

Abstract

The present application provides a polyacrylonitrile spinning solution and a preparation method and device therefor, and a polyacrylonitrile carbon fiber precursor. The preparation method comprises the following steps: 1) dividing a comonomer into two parts, parts A and B, part A accounting for 50-70% of the total weight of the comonomer, and part B accounting for 30-50% of the total weight of the comonomer; 2) mixing part A of the comonomer, acrylonitrile, an initiator, and a solvent to obtain a mixed material; 3) continuously pumping the mixed material into a microchannel reactor for primary polymerization to obtain a prepolymerization product system; and 4) adding the prepolymerization product system and part B of the comonomer to a batch polymerization kettle for secondary polymerization to obtain a polyacrylonitrile spinning solution. The preparation method can realize rapid removal of the heat of polymerization reaction, improve the efficiency of polymerization reaction, inhibit the generation of a polymer gel, and improve the distribution uniformity of copolymerized units in a polymer.

Description

A polyacrylonitrile spinning solution, its preparation method and apparatus, and polyacrylonitrile carbon fiber precursor.

[0001] This application claims priority to Chinese Patent Application No. 202411665185.8, filed on November 20, 2024, entitled "A polyacrylonitrile spinning solution and its preparation method, apparatus, and polyacrylonitrile carbon fiber precursor", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of polyacrylonitrile spinning technology, and in particular to a polyacrylonitrile spinning solution and its preparation method, apparatus, and polyacrylonitrile carbon fiber precursor. Background Technology

[0003] Polymerization processes for manufacturing polyacrylonitrile spinning solutions include batch polymerization and continuous polymerization. Continuous polymerization offers a more stable reaction and theoretically can yield polyacrylonitrile polymers with a narrower distribution. However, in actual production, there are no reports of true plug flow continuous reactor applications; instead, semi-continuous polymerization processes using multiple reactors in series are employed. While this multi-reactor series approach distributes the reaction heat across multiple reactors and improves temperature control stability, monomers such as acrylonitrile readily react and form gels in the first polymerization reactor, limiting continuous production cycles and deteriorating the spinnability of the polyacrylonitrile spinning solution. Therefore, most manufacturers still use batch polymerization.

[0004] The batch polymerization process conforms to the characteristics of typical free radical solution polymerization. At a certain stage, the acrylonitrile conversion rate exhibits a significant self-acceleration effect as the system viscosity increases and the mass and heat transfer capacity decreases. During this stage, heat exchange is difficult, and temperature control is prone to fluctuations, resulting in uneven quality of the spinning solution.

[0005] Invention patent CN107556431A provides a continuous polymerization reactor stirrer and a continuous polymerization process. It adopts single-reactor continuous polymerization, but the conversion rate is only about 60%, and the monomer removal load is very large. Invention patents CN115772719A and CN107245117A respectively adopt a semi-continuous process of three reactors in series. In the first reactor, an external circulation is set to increase the heat exchange area of ​​the reactor. However, since the external circulation is a plug flow, gelation is easily generated during long-term operation.

[0006] Application content

[0007] This application provides a method for preparing polyacrylonitrile spinning solution. This method uses a microchannel reactor coupled with a batch polymerization reactor to achieve rapid removal of polymerization heat, improve polymerization efficiency, suppress the formation of polymerization gel, and improve the uniformity of copolymer unit distribution in the polymer.

[0008] This application also provides an apparatus for preparing polyacrylonitrile spinning solution, which can be used to prepare polyacrylonitrile spinning solution.

[0009] This application also provides a polyacrylonitrile spinning solution. Since the polyacrylonitrile spinning solution is prepared by the above-described method, it has a narrow molecular weight distribution, moderate viscosity, and high spinnability.

[0010] This application also provides a polyacrylonitrile carbon fiber precursor, which, since it is made from the aforementioned polyacrylonitrile spinning solution, has better strength and modulus.

[0011] In detail, firstly, this application provides a method for preparing a polyacrylonitrile spinning solution, comprising the following steps:

[0012] 1) Divide the comonomer into two parts, A and B. Part A contains 50%-70% of the total weight of the comonomer, and part B contains 30%-50% of the total weight of the comonomer.

[0013] 2) The comonomer A, acrylonitrile, initiator, and solvent are mixed to obtain a mixture.

[0014] 3) The mixture is continuously pumped into a microchannel reactor for one polymerization to obtain a prepolymer product system;

[0015] 4) The prepolymer product system and the B comonomer are added to a batch polymerization reactor for secondary polymerization to obtain a polyacrylonitrile spinning solution.

[0016] Furthermore, the microchannel reactor includes a mixer, a reaction tube, a back pressure valve, and a temperature control system; wherein the diameter of the reaction tube is 1-10 mm.

[0017] Furthermore, at least a portion of the inner wall surface of the reaction tube is coated with polytetrafluoroethylene; and / or, the surface roughness Ra of the inner wall of the reaction tube is 0.2 μm-0.8 μm.

[0018] Furthermore, the primary polymerization meets the following conditions: polymerization temperature is 60℃-120℃, polymerization pressure is 0.1Mpa-0.8Mpa, and polymerization time is 3min-30min.

[0019] Furthermore, the secondary polymerization meets the following conditions: polymerization temperature 60℃-80℃, polymerization pressure at atmospheric pressure, and polymerization time 3h-8h.

[0020] Furthermore, the conversion rate of the comonomer after the first polymerization is 40%-60%, and the conversion rate after the second polymerization is 80%-90%.

[0021] Furthermore, the comonomer includes at least one monomer containing a carboxyl group.

[0022] Furthermore, the comonomer accounts for 0.1%-10% of the mass of the acrylonitrile;

[0023] When the comonomer includes a carboxyl-containing monomer and a carboxyl-free monomer, the mass ratio of the carboxyl-containing monomer to the acrylonitrile is 0.1%-5%, preferably 0.2%-3%.

[0024] Furthermore, the initiator accounts for 0.4%-1.5% of the total mass of the comonomer and acrylonitrile, preferably 0.5%-1.2%.

[0025] Furthermore, the mixing process meets the following conditions: the mixing temperature is 20℃-30℃, and the mixing time is 20min-40min.

[0026] Secondly, this application provides an apparatus for preparing polyacrylonitrile spinning solution, the apparatus comprising: a comonomer storage unit; a mixing vessel, a microchannel reactor, a mixer, and a batch polymerization vessel connected in series via pipelines; wherein the outlet of the comonomer storage unit is connected to the inlet of the mixer, and the microchannel reactor comprises a mixer, a reaction tube, a back pressure valve, and a temperature control system; wherein the diameter of the reaction tube is 1-10 mm.

[0027] Fourthly, this application provides a polyacrylonitrile spinning solution prepared by the preparation method described in the first aspect, comprising: a copolymer obtained by polymerizing the comonomer and acrylonitrile, wherein the molecular weight distribution Mw / Mn of the copolymer is 1.6-2.5, the intrinsic viscosity of the polyacrylonitrile spinning solution is 1.4-4.6, and the rotational viscosity is 30-210 Pa·s.

[0028] Fourthly, this application provides a polyacrylonitrile carbon fiber precursor, which is prepared from the polyacrylonitrile spinning solution described in the third aspect.

[0029] The method for preparing polyacrylonitrile spinning solution provided in this application achieves rapid removal of polymerization heat, improves monomer polymerization efficiency, inhibits polymerization gel formation, and improves the uniformity of copolymer unit distribution in the polymer by coupling a microchannel reactor with a batch polymerization reactor. Moreover, it can reduce the molecular weight distribution of polyacrylonitrile copolymers compared with traditional batch polymerization. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments of this application or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 shows an apparatus for preparing polyacrylonitrile spinning solution according to a specific embodiment of this application;

[0032] In the diagram, 01: mixing vessel, 02: microchannel reactor, 03: mixer, 04: batch polymerization vessel, 05: comonomer storage unit, 06: filter, 07: metering pump, 08: mixer, 09: back pressure valve, 10: gear pump. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] High-performance polyacrylonitrile (PAN) carbon fibers are widely prepared by batch solution polymerization to produce spinning solutions. During batch polymerization, the gelation of the spinning solution can be well controlled. However, the disadvantage of batch polymerization is that the main reaction is exothermic and concentrated, resulting in large temperature fluctuations, which affects the stability and controllability of the polymerization reaction. Although continuous polymerization can improve polymerization efficiency and polymerization temperature control stability, the gelation problem has always been difficult to solve.

[0035] To address the above issues, this application adopts the following solution:

[0036] In a first aspect, this application provides a method for preparing a polyacrylonitrile spinning solution, comprising the following steps:

[0037] 1) Divide the comonomer into two parts, A and B. Part A contains 50%-70% of the total weight of the comonomer, and part B contains 30%-50% of the total weight of the comonomer.

[0038] 2) The comonomer A, acrylonitrile, initiator, and solvent are mixed to obtain a mixture.

[0039] 3) The mixture is continuously pumped into a microchannel reactor for one polymerization to obtain a prepolymer product system;

[0040] 4) The prepolymer product system and the B comonomer are added to a batch polymerization reactor for secondary polymerization to obtain a polyacrylonitrile spinning solution.

[0041] This application achieves rapid removal of polymerization heat by coupling a microchannel reactor with a batch polymerization reactor, thereby improving polymerization efficiency, suppressing the formation of polymer gel, and reducing the molecular weight distribution of polyacrylonitrile copolymers. Specifically: Firstly, the coupling of the microchannel reactor with the batch polymerization reactor significantly improves polymerization efficiency compared to conventional batch polymerization, and the reaction temperature is stable and controllable. This is because the most vigorous stage of the reaction takes place in the microreactor, where the heat of reaction can be efficiently removed, reducing the risk of overshoot and other runaway reactions. Furthermore, due to the micro-size effect of the microchannel reactor, the molecular weight distribution of the polymer in the pre-reaction stage is lower than that in conventional batch polymerization processes. Secondly, this application adds the comonomer in two stages at different polymerization stages, which is beneficial for obtaining copolymers with uniform composition. The uniform distribution of comonomer units on the polymer backbone promotes the smooth progress of the oxidation cyclization reaction and improves the efficiency of monomer utilization. If the comonomer is added all at once, the rapid consumption of the monomer will lead to uneven distribution of comonomer units in the polymer, and even the absence of comonomer units in the polymer generated in the later stages of the reaction.

[0042] In some embodiments, the coefficient of variation (CV) of the copolymer unit content in the polymer does not exceed 20%, and preferably, the CV value does not exceed 10%.

[0043] This application does not specifically limit the microchannel reactor used in the reaction. In some embodiments, the reaction tube of the microchannel reactor is made of materials such as inert fluoropolymers (e.g., PTFE, PFA, and FEP) or stainless steel (e.g., SST), and includes a mixer, reaction tube, back pressure valve, and temperature control system connected in series. The smaller diameter of the reaction tube can provide efficient heat transfer and ensure that the spinning solution maintains a uniform temperature during the preparation process. However, if the diameter of the reaction tube is too small and the pipeline is too long, it will increase the risk of pipe blockage. Therefore, in order to ensure reaction efficiency and further avoid pipeline blockage, in one specific embodiment, the diameter of the reaction tube is 1-10 mm.

[0044] It is understood that the above-mentioned mixing and secondary polymerization should be carried out under a protective atmosphere. In some embodiments, nitrogen purging should be used before mixing and secondary polymerization to remove oxygen from the container before processing. In some embodiments, a metering pump can also be connected before the mixer of the microchannel reactor to accurately measure the amount of raw material entering the microchannel continuous flow reactor.

[0045] The comonomer in part A accounts for 50%-70% of the total weight of the comonomer, and part B accounts for 30%-50% of the total weight of the comonomer, based on the total weight of the comonomer as 100%.

[0046] In some embodiments, the secondary polymerization process further includes a step of removing monomers and bubbles.

[0047] To further reduce the surface energy of the reaction tube wall and promote rapid and stable polymerization, in one specific embodiment, at least a portion of the inner wall surface of the reaction tube is coated with polytetrafluoroethylene; and / or, the surface roughness Ra of the inner wall of the reaction tube is 0.2 μm-0.8 μm.

[0048] In one specific embodiment, the primary polymerization meets the following conditions: polymerization temperature is 60℃-120℃, polymerization pressure is 0.1Mpa-0.8Mpa, and polymerization time is 3min-30min.

[0049] In conventional batch reactor polymerization, the reaction temperature is usually below 80°C and the pressure is atmospheric pressure. Since this application uses the above-mentioned microchannel reactor for one-time polymerization, the reaction deheating is rapid. Even if the reaction temperature exceeds 100°C and the system pressure reaches above 0.2 MPa, the polymer molecular weight distribution can still be maintained at a low level, but the polymerization efficiency can be greatly improved.

[0050] In one specific embodiment, the secondary polymerization meets the following conditions: polymerization temperature 60℃-80℃, polymerization pressure at atmospheric pressure, and polymerization time 3h-8h.

[0051] In one specific embodiment, the conversion rate of the comonomer after the first polymerization is 40%-60%, and the conversion rate after the second polymerization is 80%-90%.

[0052] Although theoretically, microchannel reactors can achieve higher conversion rates of the comonomers (the sum of all comonomers in the reactor) in a single polymerization, the applicant found that when the conversion rate of the added comonomers exceeds 60%, the increased viscosity of the material leads to the risk of blockage in the microchannel reactor. When the conversion rate of the added comonomers is below 40%, the monomer concentration in the system remains at a high level, resulting in poor reaction controllability after entering step 4) and affecting polymerization efficiency. The conversion rate of the comonomers (the sum of all comonomers in the batch polymerization reactor) in the secondary polymerization is controlled at 90% or below. If it exceeds 90%, the probability of bimolecular termination or branching between macromolecules increases in the later stages, resulting in an abnormally wide molecular weight distribution.

[0053] In one embodiment, the comonomer includes at least one monomer containing a carboxyl group.

[0054] In some embodiments, the comonomer is one or more of methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, acrylamide, methacrylamide, acrylic acid, methacrylic acid, itaconic acid, itaconic acid monomethyl ester, itaconic acid monoethyl ester, itaconic acid monon-propyl ester, itaconic acid monoisopropyl ester, itaconic acid monon-n-butyl ester, itaconic acid monoisobutyl ester, itaconic acid monotert-butyl ester, maleic acid, methylmaleic acid, maleic anhydride, fumaric acid, and methyl fumaric acid.

[0055] In some embodiments, the solvent is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, sodium thiocyanate aqueous solution, and zinc chloride aqueous solution.

[0056] In one specific embodiment, the comonomer accounts for 0.1%-10% of the mass of the acrylonitrile;

[0057] When the comonomer includes a carboxyl-containing monomer and a carboxyl-free monomer, the mass ratio of the carboxyl-containing monomer to the acrylonitrile is 0.1%-5%, preferably 0.2%-3%.

[0058] In one specific embodiment, the initiator accounts for 0.4%-1.5% of the total mass of the comonomer and acrylonitrile, preferably 0.5%-1.2%.

[0059] In some embodiments, the initiator is one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovalerate, and dimethyl azobisisobutyrate.

[0060] In one specific embodiment, the mixing process satisfies the following conditions: the mixing temperature is 20℃-30℃, and the mixing time is 20min-40min.

[0061] Secondly, this application provides an apparatus for preparing polyacrylonitrile spinning solution. Referring to Figure 1, the apparatus includes: a comonomer storage unit 05; a mixing vessel 01, a microchannel reactor 02, a mixer 03, and a batch polymerization vessel 04 connected in series via pipelines; wherein the outlet of the comonomer storage unit is connected to the inlet of the mixer, and the microchannel reactor includes a mixer 08, a reaction tube, a back pressure valve 09, and a temperature control system; wherein the diameter of the reaction tube is 1-10 mm.

[0062] In some embodiments of this application, the microchannel reactor comprises two parallel microchannel reactors 1 and 2. Furthermore, the device also includes three metering pumps 07, respectively positioned before the two mixers and after the comonomer storage unit 05.

[0063] In some embodiments of this application, the device further includes two filters 06, respectively disposed before the mixing tank 01 and after the batch polymerization tank 04.

[0064] In some embodiments of this application, the device further includes a gear pump 10 disposed between the intermittent polymerization reactor 04 and a filter 06 located near the intermittent polymerization reactor.

[0065] The preparation of polyacrylonitrile spinning solution using the apparatus shown in Figure 1 includes the following steps:

[0066] 1) Divide the comonomer into two parts, A and B. Part A contains 50%-70% of the total weight of the comonomer, and part B contains 30%-50% of the total weight of the comonomer.

[0067] 2) The comonomer A, acrylonitrile, initiator, and solvent are mixed in a mixing tank to obtain a mixture.

[0068] 3) The mixture is continuously pumped into microchannel reactor 1 and microchannel reactor 2 for one polymerization to obtain a prepolymer product system;

[0069] 4) The prepolymer product system and the B comonomer are added to the mixer, mixed, and then passed through the intermittent polymerization reactor 04 for secondary polymerization to remove monomers and bubbles, thereby obtaining polyacrylonitrile spinning solution.

[0070] Thirdly, this application provides a polyacrylonitrile spinning solution prepared by the preparation method described in the first aspect, comprising: a copolymer obtained by polymerizing the comonomer and acrylonitrile, wherein the molecular weight distribution Mw / Mn of the copolymer is 1.6-2.5, the intrinsic viscosity of the polyacrylonitrile spinning solution is 1.4-4.6, and the rotational viscosity is 30-210 Pa·s.

[0071] Fourthly, this application provides a polyacrylonitrile carbon fiber precursor, which is prepared from the polyacrylonitrile spinning solution described in the third aspect.

[0072] The present application is described in detail below with reference to specific embodiments:

[0073] The following experiments involve the testing methods for parameters:

[0074] Intrinsic viscosity

[0075] The polymer powder / film was dried at 120℃ for 2 hours to constant weight. 40-50 mg of the sample was dissolved in 50 mL of dimethylformamide solution, and the intrinsic viscosity was measured at 50℃ using an Ubbelohde viscometer.

[0076] Where η sp =(t / t0)-1; ηr = t / t0.

[0077] <Rotational viscosity>

[0078] The rotational viscosity of the spinning solution was measured using a Kinexus Jl009 rheometer at a shear rate of 10 s. -1 The test temperature was 60℃.

[0079] <Molecular weight distribution>

[0080] Analytical instrument: Agilent 1260 Infinity

[0081] Mobile phase: DMF (containing 1 g / L LiBr)

[0082] Columns: Waters Styragel HR5E and Waters Styragel HR2 in tandem

[0083] Detector: Agilent 1260 RID

[0084] Flow rate: 0.7 mL / min

[0085] Injection volume: 20 μL

[0086] Injection concentration: 10 mg / mL

[0087] Standard product: PS (polystyrene)

[0088] Column temperature: 55℃

[0089] Detector temperature: 55℃

[0090] Conversion Rate

[0091] Weigh approximately 1g of polymer solution and record its accurate mass as M1. After coating it into a film, precipitate it with deionized water and soak it for 30 minutes. Then rinse it three times with ethanol and dry it in a 105°C oven until constant weight. Record its mass as M2. The solid content C = M2 / M1 × 100%. The initial monomer concentration is recorded as C0. The conversion rate = C / C0 × 100%.

[0092] <Copolymer Composition>

[0093] The copolymer composition was determined using a Bruker AVANCE III 400MHz NMR spectrometer. Measurement frequencies were 400MHz for 1H-NMR and 100MHz for 13C-NMR. The solvent was DMSO-d6, and TMS was used as an internal standard. Sample concentrations were 5% for 1H-NMR and 10% for 13C-NMR. Samples were taken every 5 minutes during the first polymerization process and every hour during the second polymerization process.

[0094] Example 1

[0095] This example provides a method for preparing a polyacrylonitrile spinning solution, including the following steps:

[0096] 1) Weigh out itaconic acid and divide it into two parts, A and B; the mass ratio of parts A and B is 0.18:0.12;

[0097] 2) Add 22 parts acrylonitrile, 79 parts dimethyl sulfoxide, 0.18 parts itaconic acid (part A), and 0.126 parts azobisisobutyronitrile to a mixing tank and stir at 25°C for 30 minutes to obtain a mixture.

[0098] 3) The mixture is pumped into a microchannel reactor for one-time polymerization. The reaction temperature for the one-time polymerization is 105℃, the back pressure valve pressure is 0.3Mpa, the diameter of the microchannel reactor is 8mm, the roughness of the polytetrafluoroethylene coating on the inner wall of the tube is 0.4μm, the residence time of the material in the microchannel reactor is 10min, and the conversion rate of monomer after the one-time polymerization is 45%.

[0099] 4) After the first polymerization, the material was mixed with 0.12 parts of itaconic acid (part B, dissolved in DMSO solution, itaconic acid content 10 wt%) in a static mixer and simultaneously cooled to 75°C before entering a batch polymerization reactor. The stirring speed was 35 rpm, and the reactor temperature was controlled at 75°C. The second polymerization reaction was carried out for 8 hours, and the conversion rate of itaconic acid was 86%. The resulting polyacrylonitrile spinning solution had a copolymer solid content of 18.9%, an intrinsic viscosity of 2.1 dl / g, a rotational viscosity of 67 Pa·s, a molecular weight distribution of 1.92, and a CV value of 8.2% for the copolymer composition (itaconic acid unit content) determined by NMR.

[0100] Example 2

[0101] This example provides a method for preparing a polyacrylonitrile spinning solution, which differs from Example 1 in that: in step 3), the residence time of the material in the microchannel reactor is 20 min, the monomer conversion rate after the first polymerization is 54%, the conversion rate after the second polymerization is 89%, and the copolymer solid content of the obtained polyacrylonitrile spinning solution is 19.6%, the intrinsic viscosity is 2.05 dl / g, the rotational viscosity is 74 Pa·s, the molecular weight distribution of the copolymer is 1.89, and the CV value of the copolymer composition measured by NMR is 8.7%.

[0102] Example 3

[0103] This example provides a method for preparing a polyacrylonitrile spinning solution, which differs from Example 1 in that it includes the following steps: a primary polymerization temperature of 95°C, a pressure of 0.2 MPa, and a time of 30 min; the monomer conversion rate after the primary polymerization is 58%, and the conversion rate after the secondary polymerization is 90%. The resulting polyacrylonitrile spinning solution has a copolymer solid content of 19.8%, an intrinsic viscosity of 2.23 dl / g, a rotational viscosity of 82 Pa·s, a molecular weight distribution of 1.85, and a CV value of 8.3% for the copolymer composition determined by NMR.

[0104] Example 4

[0105] This example provides a method for preparing a polyacrylonitrile spinning solution, which differs from Example 3 in that: in step 3), the residence time of the material in the microchannel reactor is 20 min, the monomer conversion rate after the first polymerization is 40%, the second polymerization time is 6 h, the conversion rate of itaconic acid is 83%, and the copolymer solid content of the obtained polyacrylonitrile spinning solution is 18.3%, the intrinsic viscosity is 2.19 dl / g, the rotational viscosity is 55 Pa·s, the molecular weight distribution of the copolymer is 1.87, and the CV value of the copolymer composition measured by NMR is 8.5%.

[0106] Example 5

[0107] This example provides a method for preparing a polyacrylonitrile spinning solution, which differs from Example 4 in that: 1) Itaconic acid is weighed and divided into two parts, A and B, with a mass ratio of 1.5:1.5; 2) 1.5 parts of itaconic acid are added, and the monomer conversion rate after the first polymerization is 41%; 3) 1.5 parts of itaconic acid are added, and the itaconic acid conversion rate after the second polymerization is 84%; the obtained polyacrylonitrile spinning solution has a copolymer solid content of 18.5%, an intrinsic viscosity of 2.13 dl / g, a rotational viscosity of 56 Pa·s, a molecular weight distribution of 1.82, and a copolymer composition CV value of 11.4%.

[0108] Example 6

[0109] This example provides a method for preparing a polyacrylonitrile spinning solution, which differs from Example 4 in that: 1) Itaconic acid is weighed and divided into two parts, A and B, with a mass ratio of 2.1:0.9; 2) 2.1 parts of itaconic acid are added, and the monomer conversion rate after the first polymerization is 38%; 3) 0.9 parts of itaconic acid are added, and the itaconic acid conversion rate after the second polymerization is 83%; the obtained polyacrylonitrile spinning solution has a copolymer solid content of 18.3%, an intrinsic viscosity of 1.89 dl / g, a rotational viscosity of 53 Pa·s, a molecular weight distribution of 2.06, and a copolymer composition CV value of 10.6%.

[0110] Comparative Example 1

[0111] This example provides a method for preparing a polyacrylonitrile spinning solution, including the following steps:

[0112] 1) Add 22 parts acrylonitrile, 79 parts dimethyl sulfoxide, 0.3 parts itaconic acid, and 0.126 parts azobisisobutyronitrile to a mixing tank and stir at 25°C for 30 minutes to obtain a mixture.

[0113] 2) The mixture was pumped into a microchannel reactor for one-time polymerization. The reaction temperature was 105℃, the back pressure valve pressure was 0.3 MPa, the microchannel reactor tube diameter was 8 mm, the roughness of the polytetrafluoroethylene coating on the inner wall of the tube was 0.4 μm, the residence time of the material in the microchannel reactor was 30 min, the conversion rate of itaconic acid was 68%, and a polyacrylonitrile spinning solution was obtained. The copolymer solid content was 14.9%, the intrinsic viscosity was 1.98 dl / g, the rotational viscosity was 22 Pa·s, the molecular weight distribution of the copolymer was 1.73, and the CV value of the copolymer composition was 23.3%.

[0114] Comparative Example 2

[0115] This example provides a method for preparing a polyacrylonitrile spinning solution, including the following steps:

[0116] 1) Add 22 parts acrylonitrile, 79 parts dimethyl sulfoxide, 0.3 parts itaconic acid, and 0.126 parts azobisisobutyronitrile to a mixing tank and stir at 25°C for 30 minutes to obtain a mixture.

[0117] 2) The mixture was directly added to a batch polymerization reactor at a temperature of 65℃ and a stirring speed of 35 rpm. The reaction was carried out for 12 hours, and the conversion rate of itaconic acid was 90%. A polyacrylonitrile spinning solution was obtained with a copolymer solid content of 20.1%, an intrinsic viscosity of 2.34 dl / g, a rotational viscosity of 87 Pa·s, a molecular weight distribution of 3.05, and a copolymer composition CV value of 26.2%.

[0118] Comparative Example 3

[0119] 1) Add 22 parts acrylonitrile, 79 parts dimethyl sulfoxide, 0.3 parts itaconic acid (part A), and 0.126 parts azobisisobutyronitrile to a mixing tank and stir at 25°C for 30 minutes to obtain a mixture.

[0120] 2) The mixture is pumped into a microchannel reactor for one-time polymerization. The reaction temperature of the one-time polymerization is 105℃, the back pressure valve pressure is 0.3Mpa, the diameter of the microchannel reactor is 8mm, the roughness of the polytetrafluoroethylene coating on the inner wall of the tube is 0.4μm, the residence time of the material in the microchannel reactor is 10min, and the conversion rate of itaconic acid is 41%.

[0121] 3) After the first polymerization, the material was cooled to 75°C and fed into a batch polymerization reactor. The stirring speed was 35 rpm, and the temperature inside the reactor was controlled at 75°C. The second polymerization reaction was carried out for 8 hours, and the conversion rate of itaconic acid was 82%. A polyacrylonitrile spinning solution was obtained, in which the copolymer solid content was 18%, the intrinsic viscosity was 2.1 dl / g, the rotational viscosity was 59 Pa·s, the molecular weight distribution of the copolymer was 1.95, and the CV value of the copolymer composition was 24.7% according to NMR.

[0122] Table 1 summarizes some of the reaction conditions and parameters of the polyacrylonitrile spinning solution of the above examples and comparative examples.

[0123] Table 1:

[0124] As shown in Table 1, the polyacrylonitrile spinning solution of the examples has a more uniform distribution of copolymer units in the copolymer compared with the polyacrylonitrile spinning solutions of Comparative Examples 1-3. Furthermore, the polyacrylonitrile spinning solution of the examples has a narrower molecular weight distribution of copolymers and a shorter polymerization time compared with the polyacrylonitrile spinning solution of Comparative Example 2.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a polyacrylonitrile spinning solution, characterized in that, Includes the following steps: 1) Divide the comonomer into two parts, A and B. Part A contains 50%-70% of the total weight of the comonomer, and part B contains 30%-50% of the total weight of the comonomer. 2) The comonomer A, acrylonitrile, initiator, and solvent are mixed to obtain a mixture. 3) The mixture is continuously pumped into a microchannel reactor for one polymerization to obtain a prepolymer product system; 4) The prepolymer product system and the B comonomer are added to a batch polymerization reactor for secondary polymerization to obtain a polyacrylonitrile spinning solution.

2. The preparation method according to claim 1, characterized in that, The microchannel reactor includes a mixer, a reaction tube, a back pressure valve, and a temperature control system; wherein the diameter of the reaction tube is 1-10 mm.

3. The preparation method according to claim 2, characterized in that, At least a portion of the inner wall surface of the reaction tube is coated with polytetrafluoroethylene; and / or, the surface roughness Ra of the inner wall of the reaction tube is 0.2 μm-0.8 μm.

4. The preparation method according to claim 2 or 3, characterized in that, The polymerization process meets the following conditions: polymerization temperature is 60℃-120℃, polymerization pressure is 0.1Mpa-0.8Mpa, and polymerization time is 3min-30min.

5. The preparation method according to claim 4, characterized in that, The secondary polymerization meets the following conditions: polymerization temperature 60℃-80℃, polymerization pressure at atmospheric pressure, and polymerization time 3h-8h.

6. The preparation method according to claim 5, characterized in that, The conversion rate of the comonomer after the first polymerization is 40%-60%, and the conversion rate after the second polymerization is 80%-90%.

7. The preparation method according to claim 1, characterized in that, The comonomer includes at least one monomer containing a carboxyl group.

8. The preparation method according to claim 7, characterized in that, The comonomer accounts for 0.1%-10% of the mass of the acrylonitrile; When the comonomer includes a carboxyl-containing monomer and a carboxyl-free monomer, the mass ratio of the carboxyl-containing monomer to the acrylonitrile is 0.1%-5%, preferably 0.2%-3%.

9. The preparation method according to claim 1, characterized in that, The initiator accounts for 0.4%-1.5% of the total mass of the comonomer and acrylonitrile, preferably 0.5%-1.2%.

10. The preparation method according to claim 1, characterized in that, The mixing process meets the following conditions: the mixing temperature is 20℃-30℃, and the mixing time is 20min-40min.

11. A polyacrylonitrile spinning solution, characterized in that, The copolymer prepared by any one of claims 1-10 comprises the copolymer obtained by polymerization of the comonomer and acrylonitrile, wherein the molecular weight distribution Mw / Mn of the copolymer is 1.6-2.5, the intrinsic viscosity of the polyacrylonitrile spinning solution is 1.4-4.6, and the rotational viscosity is 30-210 Pa·s.

12. An apparatus for preparing polyacrylonitrile spinning solution by any one of the preparation methods according to claims 1-10, characterized in that, include: A comonomer storage unit; a mixing vessel, a microchannel reactor, a mixer, and a batch polymerization vessel connected in series via pipelines; wherein the outlet of the comonomer storage unit is connected to the inlet of the mixer, and the microchannel reactor includes a mixer, a reaction tube, a back pressure valve, and a temperature control system; wherein the diameter of the reaction tube is 1-10 mm.

13. A polyacrylonitrile carbon fiber precursor, characterized in that, It is prepared from the polyacrylonitrile spinning solution according to claim 11.

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