A method and system for preparing polyacrylonitrile spinning dope and applications thereof

Abstract

The application discloses a method and system for preparing polyacrylonitrile spinning dope and application. The method for preparing polyacrylonitrile spinning dope comprises the step of feeding a reaction feed stream into an m-stage reactor for reaction to obtain polyacrylonitrile spinning dope; wherein m is an integer greater than or equal to 2, and the reactor is a coil reactor. The method solves the problems of difficulty in enlarging the existing batch polymerization reactor, low polymerization efficiency, uneven internal temperature distribution of the reactor, frequent shutdown for cleaning due to gel formation in the reactor, wide average molecular weight distribution, large equipment investment, and the problems of the existing continuous polymerization reactor, such as inconvenient cleaning, reactor blockage, frequent equipment maintenance, large space occupation, large energy consumption, large equipment investment and the like. The method has the advantages of easy enlargement of the polymerization reactor, high continuous production efficiency, good internal temperature uniformity of the reactor, long maintenance cycle, narrow average molecular weight distribution and less equipment investment.

Description

Technical Field

[0001] This invention relates to the field of fiber preparation technology, specifically to a method, system, and application for preparing polyacrylonitrile spinning dope. Background Technology

[0002] The structure and properties of polyacrylonitrile precursor fibers directly affect the quality of polyacrylonitrile-based carbon fibers, while the properties of polyacrylonitrile precursor fibers are influenced by various factors such as the polymerization process and polymerization method of the polyacrylonitrile spinning solution. In the production of polyacrylonitrile-based carbon fibers, the polymerization process, as the initial step in the entire production process, is the key to determining the performance of the polyacrylonitrile-based carbon fiber product.

[0003] Chinese patent CN102041575A discloses a polyacrylonitrile precursor fiber and its production equipment, a polymerization reactor. The formulation of the polyacrylonitrile precursor fiber mainly includes monomers AN, MA, and IA, with DMSO as the solvent and azobisisobutyronitrile (AIBN) as the initiator. The weight percentages of each component are as follows: a mixture of AN, MA, and IA is 1%, DMSO content is 30-50%, and AIBN content is 6.5-9.5%. The production equipment reactor for polyacrylonitrile precursor fiber includes a reactor body and a reactor cover, which are connected by a flange. The reactor body contains a stirrer, and the reactor cover has an inlet and an outlet. The stirrer is a ribbon stirrer, and there are two or more ribbon stirrers.

[0004] Chinese patent CN103421141A discloses a polyacrylonitrile copolymer spinning solution and its preparation method. The method involves co-polymerizing acrylonitrile in a tubular reactor containing a static mixer assembly. The tubular reactor with the static mixer assembly leverages its advantages of high mass and heat transfer efficiency, continuous and stable reaction, and the elimination of the need for mechanical stirring. The polyacrylonitrile copolymer spinning solution is obtained by copolymerization of a reaction solution composed of monomers, a free radical initiator, and a solvent. The monomers in the reaction solution have a weight percentage concentration of 15-30%, the free radical initiator is 0.4-1% of the monomer weight, and the remainder is solvent. The monomers are acrylonitrile monomer and comonomer. The resulting polyacrylonitrile copolymer spinning solution has a dynamic viscosity of 200-800 Pa·s and a molecular weight distribution of 1.5-2.6.

[0005] Existing batch polymerization processes typically employ stirred tank reactors. As carbon fiber plants continue to expand in scale, the volume of stirred tank reactors is also increasing, with reactor volumes reaching 100m³ for thousand-ton-scale production lines. 3 The increasing size of reactors brings a series of engineering problems, such as lower mass transfer, heat transfer, temperature uniformity, concentration uniformity, and wider average molecular weight distribution within the reactor.

[0006] Current continuous polymerization processes typically employ tubular reactors with static mixers or multiple reactors in series. Tubular reactors with static mixers suffer from significant drawbacks. The static mixer itself has a large pressure drop, cannot be bent (including internal components), and its angle constantly reverses, resulting in high fluid resistance. Therefore, internal circulation pumps are required at intervals, leading to high energy consumption. Furthermore, because the reaction requires a certain residence time (generally over 14 hours), tubular reactors with static mixers typically occupy a large volumetric space. The constantly reversing angle of the static mixer creates low-pressure zones, which are dead zones for materials. If gel accumulates, cleaning is extremely difficult and can easily cause reactor blockage. Multiple reactors in series alleviate some of the problems of single-reactor batch polymerization, but they cannot fundamentally solve the issues unless numerous small reactors are connected in series. However, this would lead to an unlimited increase in both space requirements and energy consumption.

[0007] Therefore, existing polymerization processes and their reactors have problems such as difficulty in scale-up, low polymerization efficiency, uneven temperature distribution inside the reactor, frequent shutdowns for cleaning due to easy gel formation inside the reactor, wide average molecular weight distribution of products, large footprint, and high equipment investment. Continuous polymerization has problems such as inconvenient cleaning leading to reactor blockage, frequent equipment maintenance, large footprint, high energy consumption, and high equipment investment. Summary of the Invention

[0008] To address the problems of existing batch polymerization reactors in the acrylonitrile and carbon fiber industries, such as difficulty in scaling up, low polymerization efficiency, uneven temperature distribution inside the reactor, frequent shutdowns for cleaning due to easy gel formation inside the reactor, wide average molecular weight distribution, and large equipment investment, as well as the problems of existing continuous polymerization reactors, such as inconvenient cleaning leading to reactor blockage, frequent equipment maintenance, large footprint, high energy consumption, and large equipment investment, this invention provides a method, system, and application for preparing polyacrylonitrile spinning dope.

[0009] One objective of this invention is to provide a method for preparing polyacrylonitrile spinning solution, comprising the step of feeding a reaction feed stream into an m-segment reactor for reaction to obtain polyacrylonitrile spinning solution; wherein m is an integer greater than or equal to 2, and the reactor is a coil reactor.

[0010] The coil reactor described in this invention is based on the existing stirred tank reactor. Stirred tank reactors typically use coil heating, with the heat transfer medium flowing inside the coil and the material on the outside. This invention creatively combines the design principles of a plug flow reactor with the traditional coil-type stirred tank reactor, directing the material to flow inside the coil and the heat transfer medium to flow outside, thus transforming the material reaction from a completely mixed flow to a plug flow. The coil reactor described in this invention can be equipped with or without a stirrer.

[0011] In a preferred embodiment of the present invention,

[0012] m is an integer between 2 and 4; and / or,

[0013] The m-section reactors are connected in series; and / or,

[0014] In a single-stage coil reactor, the number of parallel coils is n1, where n1 is an integer less than or equal to 2, for example, n1 is 1 or n1 is 2; and / or,

[0015] In a two-stage or higher coil reactor, the number of parallel coils may be the same or different, each independently represented as n2, where n2 is an integer greater than or equal to 2, preferably an integer between 2 and 4; and / or,

[0016] The inner diameter of the coils in each section of the coiled reactor may be the same or different, and is independently 15-200 mm, preferably 40-150 mm, and more preferably 50-100 mm; preferably, the inner diameter of the coils in two or more sections of the coiled reactor is less than or equal to the inner diameter of the coils in a single section of the coiled reactor; more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is 0-50 mm smaller than the inner diameter of the coils in a single section of the coiled reactor, preferably 0-30 mm smaller, and more preferably 10-25 mm smaller; and / or,

[0017] The reaction feed stream enters the coil of the coil reactor, and a heat transfer medium is installed outside the coil of the reactor.

[0018] In the technical solution described in this invention, the number of parallel coils in the second and subsequent reactors is two or more. Under the same residence time, the coil diameter becomes smaller, which can enhance the heat transfer effect of the reactants. Moreover, due to the smaller coil diameter, the mixing effect is significantly improved, the reaction is more uniform, and the molecular weight distribution becomes narrower and more optimized.

[0019] In the technical solution described in this invention, the coils in the coil reactor can be of any form, such as a concentric spiral arrangement with the same diameter, a concentric spiral arrangement with different diameters, or a meandering arrangement without a center or diameter.

[0020] In the technical solution described in this invention, the material in the coil of the coil reactor is in the liquid phase within the reaction temperature range and will not vaporize; while in the traditional batch reactor, the reaction usually takes place under slightly positive pressure conditions, and there is a gas phase space inside the reactor. When the temperature rises, some of the material will vaporize, thus affecting the quality of the polymerization solution.

[0021] In the technical solution described in this invention, researchers discovered the intrinsic relationship between conversion rate, viscosity, and inner diameter of the coil reactor through extensive experimental data, and correlated this relationship into a mathematical formula to guide the selection of the coil reactor. Using the technical solution described in this invention, the interface temperature distribution of the coil reactor can be controlled within ±0.6℃, while the internal temperature distribution of a 10 cubic meter batch polymerization reactor is typically within ±2.0~2.5℃.

[0022] In the technical solution described in this invention, the inner diameter of the coil of each section of the coil reactor and its outlet conversion rate satisfy the following relationship (1):

[0023] 0.75%m≤D*X≤20%m Equation (1);

[0024] In equation (1), D is the inner diameter of the coil in the coil reactor, in meters; X is the outlet conversion rate of the coil reactor, in percentage; and / or,

[0025] The total length of the coil in each section of the coil reactor and the inner diameter of the coil satisfy the following relationship as shown in equation (2):

[0026] L=Fm*t / (0.785ρD 2 Equation (2);

[0027] In equation (2), L is the total length of the coils in the coil reactor (when there are two or more parallel coils in the reactor, L is the sum of the lengths of the parallel coils), in meters; Fm is the flow rate of the reaction feed, in kg / h; t is the residence time of the material, in hours; and ρ is the density of the reaction feed, in kg / m³. 3 D is the inner diameter of the coil of the coil reactor, in meters.

[0028] In the technical solution described in this invention, the coil volume of each section of the coil reactor satisfies the following relationship as shown in equation (3):

[0029] V = Fm*t / ρ (Equation 3);

[0030] In equation (3), V is the coil volume of the coil reactor, in m³. 3 Fm is the reaction feed flow rate, in kg / h; t is the residence time, in h; ρ is the density, in kg / m³. 3 .

[0031] In a preferred embodiment of the present invention,

[0032] The residence time of the reactants in the first-stage reactor is 4-12 hours, preferably 4-10 hours; and / or, the reaction temperature in the first-stage reactor is 55-70℃, preferably 60-68℃; and / or,

[0033] The residence time of the reactants in the two or more reactors may be the same or different, and is independently 6-14h, preferably 6-12h; and / or the reaction temperature of the two or more reactors may be the same or different, and is independently 60-75℃, preferably 64-72℃.

[0034] In a preferred embodiment of the present invention,

[0035] In each section of the coil reactor, the coils are immersed in a temperature-controlled medium (i.e., a heat transfer medium). Preferably, the specific heat capacity of the temperature-controlled medium is greater than or equal to 0.7 KJ / kg·℃. More preferably, the temperature-controlled medium is one or a mixture of several of water, brine, and liquid organic matter with a specific heat capacity greater than or equal to 0.7 KJ / kg·℃. Even more preferably, the temperature-controlled medium is one or a mixture of several of water, brine, heat transfer oil, and ethylene glycol with a specific heat capacity greater than or equal to 0.7 KJ / kg·℃; and / or,

[0036] The heat transfer area of ​​the coil reactor corresponding to the unit mass of reaction feed stream is greater than or equal to 100 cm². 2 / kg (i.e., greater than or equal to 0.01m) 2 / kg), preferably greater than or equal to 220cm 2 / kg (i.e., greater than or equal to 0.022m) 2 / kg), more preferably 250-500cm 2 / kg (i.e., 0.025-0.05m) 2 / kg).

[0037] In a preferred embodiment of the present invention,

[0038] The flow rate of the reaction feed stream is 500-2000 kg / h, preferably 1200-1800 kg / h; and / or,

[0039] The reaction feed stream can be any conventional polyacrylonitrile spinning solution reaction feed stream in the art. In this invention, the reaction feed stream preferably contains monomers, free radical initiators, and solvents; preferably,

[0040] The monomers include acrylonitrile monomers and comonomers, wherein the comonomers are preferably selected from at least one of itaconic acid, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, acrylamide, methacrylamide, dimethyl itaconic acid, and dibutyl itaconic acid; and / or,

[0041] The free radical initiator is selected from at least one of azo initiators and peroxide initiators, preferably from at least one of azobisisobutyronitrile and azobisisoheptanenitrile; and / or,

[0042] The solvent is selected from at least one of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide; more preferably,

[0043] By mass percentage, the acrylonitrile monomer accounts for 17-22%, the solvent accounts for 77-81%, the comonomer accounts for 0.15-1%, and the initiator accounts for 0.02-1%.

[0044] In the technical solution described in this invention, the viscosity of the reaction product before separation is 50-100 Pa·s (60°C).

[0045] In a preferred embodiment of the present invention,

[0046] The method includes:

[0047] The reaction feed stream is fed into a first-stage reactor for reaction. The resulting first-stage reaction product is fed into a second-stage reactor for reaction. The resulting second-stage reaction product is fed into a next-stage reactor for reaction. In sequence, the resulting first-stage reaction product is fed into the next-stage reactor for reaction. The resulting m-1 stage reaction product is fed into the m-stage reactor for reaction. Finally, after separating the unreacted monomers from the resulting m-stage reaction product, the polyacrylonitrile spinning dope is obtained.

[0048] In a preferred embodiment of the present invention,

[0049] The reaction products from each of the two stages (m-1) can be optionally divided into two streams: one stream is used as a recycle stream and mixed with the reaction products from the previous stage; the other stream is sent to the next stage reactor for further reaction; and / or,

[0050] The reaction products of segment m are divided into two streams. One stream is used as a circulating stream to mix with the reaction products of the previous segment, and the other stream is sent to the separation unit to separate unreacted monomers.

[0051] Preferably, the recycled streams from stage II to stage M each independently account for 0-50 wt% of the reaction products from stage II to stage M, more preferably 0-45 wt%.

[0052] In the technical solution described in this invention, the material from the outlet of the second-stage reactor is recycled back to the inlet of the second-stage reactor, mixed with the material from the outlet of the first-stage reactor, and then enters the second-stage reactor. This is mainly to increase the residence time and ensure the conversion rate. Similarly, recycling the material from the outlets of three or more stages back to their inlets also aims to increase the residence time and ensure the conversion rate.

[0053] The method for preparing polyacrylonitrile spinning solution according to the present invention can adopt the following specific technical solution (taking two reactors connected in series as an example):

[0054] After being heated, the reaction feed stream is fed into a first-stage reactor, where it reacts in a coil inside the reactor. The resulting first-stage reaction product is mixed with the second-stage reaction product circulating stream and fed into a second-stage reactor, where it reacts in a coil inside the reactor. The second-stage reaction product is pressurized and divided into two streams. One stream is used as a circulating stream and merges with the first-stage reaction product. The other stream is separated from unreacted monomers to obtain the polyacrylonitrile spinning dope.

[0055] In another specific technical solution of the present invention, the reactor is connected in series in three stages. The number of parallel coils in the third stage reactor is the same as that in the second stage. The reaction feed stream, after heating, is sent to the first stage reactor, where it reacts in the coils inside. The resulting first-stage reaction product is mixed with the second-stage reaction product circulating stream and sent to the second stage reactor, where it reacts in the coils inside. The second-stage reaction product is pressurized and divided into two streams. One stream is used as a circulating stream and merges with the first-stage reaction product before being sent to the second stage reactor. The other stream is mixed with the third-stage reaction product circulating stream and sent to the third stage reactor, where it reacts in the coils inside. The third-stage reaction product is pressurized and divided into two streams. One stream is used as a circulating stream and merges with the second-stage reaction product. The other stream, after separating unreacted monomers, yields the polyacrylonitrile spinning dope. In this case, the proportion of circulating material in the second and third stage reactors can be reduced; the more reactor stages connected in series, the smaller the proportion of circulating material, or even none at all.

[0056] In the technical solution described in this invention, the reactor is connected in series in two or more sections, each section of the reactor can be temperature controlled separately, and the residence time can also be flexibly adjusted.

[0057] In the technical solution described in this invention, the first stage reactor reacts violently, the material viscosity is low, and the temperature control medium needs to adopt a control method with a large flow rate and a small temperature difference.

[0058] In the technical solution described in this invention, the reaction in the second and subsequent reactor stages is relatively mild, with slightly higher viscosity and a lower heat transfer coefficient, requiring a longer residence time to ensure the conversion rate.

[0059] In the technical solution described in this invention, the reaction occurs inside the coil, and the space where the temperature control medium is located outside the coil does not bear pressure and has no special requirements for materials, which can greatly save equipment investment.

[0060] In the technical solution described in this invention, when the temperature control medium circulates in the temperature control system and each section of the reactor, it is extracted from the bottom and entered from the top, which plays a role in stirring and mixing the temperature control medium outside the coil. The stirrer is not a necessary option.

[0061] In the technical solution described in this invention, a coil reactor is used, with the coil immersed in a temperature-controlled medium. This not only facilitates temperature control and saves space, but also ensures thorough mixing and forced heat transfer due to the continuous change in the material flow direction within the coil.

[0062] In the technical solution described in this invention, the material in the coil reactor coil changes direction continuously within the coil, making it less prone to adhering to the coil wall and thus having a self-cleaning effect.

[0063] A second objective of this invention is to provide a system for preparing polyacrylonitrile spinning dope, preferably a method for performing one objective of this invention, comprising a reaction unit and a separation unit, wherein the reaction unit comprises an m-section coil reactor, where m is an integer greater than or equal to 2; preferably,

[0064] m is an integer between 2 and 4; and / or,

[0065] The m-section coil reactors are connected in series; and / or,

[0066] In a single-stage coil reactor, the number of parallel coils is n1, where n1 is an integer less than or equal to 2, for example, n1 is 1 or n1 is 2; and / or,

[0067] In a two-stage or higher coil reactor, the number of parallel coils may be the same or different, each independently represented by n2, where n2 is an integer greater than or equal to 2; and / or,

[0068] The inner diameter of the coils in each section of the coiled reactor may be the same or different, and is independently 15-200 mm, preferably 40-150 mm; more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is less than or equal to the inner diameter of the coils in a single section of the coiled reactor; even more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is 0-50 mm smaller than the inner diameter of the coils in a single section of the coiled reactor, preferably 0-30 mm smaller, more preferably 10-25 mm smaller; and / or,

[0069] The coil of the coiled reactor serves as a channel for the reactants, and the outside of the coil is the heat transfer medium.

[0070] In a preferred embodiment of the present invention,

[0071] Each section of the coil reactor is equipped with a reactant inlet and a product outlet. Sequentially, the product outlet of the previous section is connected to the material inlet of the next section of the coil reactor, the product outlet of section m-1 of the coil reactor is connected to the material inlet of section m of the coil reactor, and the product outlet of section m of the coil reactor is connected to the separation unit. Preferably, the reactant inlet is connected to the pipe inlet of the coil, and the product outlet is connected to the pipe outlet of the coil.

[0072] The separation unit includes any conventional gas-liquid separation equipment in the art. No special limitations are imposed in this invention, as long as it can separate unreacted monomers. Preferably, the separation unit in this invention includes a gas-liquid separation tank.

[0073] In a preferred embodiment of the present invention,

[0074] A feed heater is installed on the pipeline that sends the reaction feed stream into the reactant inlet of a section of the coil reactor; and / or,

[0075] A product transfer pump and a mixer are installed on the pipeline connecting the product outlet of the first to the m-1 section of the coiled reactor to the material inlet of the next section of the coiled reactor. Preferably, the product transfer pump is located before the mixer; and / or,

[0076] A final reaction product transfer pump is installed on the pipeline connecting the reaction product outlet of the m-section coil reactor to the separation unit.

[0077] In a preferred embodiment of the present invention,

[0078] Each section of the coil reactor is connected to a product delivery pump and a mixer via a pipeline that can optionally include a branch connecting to the previous section of the mixer.

[0079] In a preferred embodiment of the present invention,

[0080] Each section of the coil reactor is equipped with a reactor temperature control system. The temperature control medium circulates within the reactor temperature control system and each section of the reactor, and the temperature of the temperature control medium is regulated by the reactor temperature control system.

[0081] The system for preparing polyacrylonitrile spinning solution of the present invention can adopt the following specific technical solutions:

[0082] The reaction feed line is connected to the feed heater inlet, the feed heater outlet is connected to the reactant inlet of the first-stage coil reactor, the reaction product outlet of the first-stage coil reactor is connected to the inlet of the first-stage reaction product conveying pump, the discharge outlet of the first-stage reaction product conveying pump is connected to the first inlet of the first mixer, the discharge outlet of the first mixer is connected to the material inlet of the second-stage coil reactor, the reaction product outlet of the second-stage coil reactor is connected to the inlet of the second-stage reaction product conveying pump, and the discharge outlet of the second-stage reaction product conveying pump is connected to the second inlet of the first mixer and the inlet of the separation unit, respectively.

[0083] A third objective of this invention is to provide an application of a method for one objective of this invention or a system for another objective of this invention in liquid-phase polymerization reactions, preferably in the preparation of acrylonitrile and carbon fiber.

[0084] The liquid-phase polymerization reaction can be any liquid-phase polymerization reaction in the chemical field in the prior art, including but not limited to liquid-phase polymerization of polyacrylonitrile, etc.

[0085] Compared with the prior art, the present invention has the following beneficial effects:

[0086] (1) The system and process described in this invention mainly solve the problems of existing batch polymerization reactors in the acrylonitrile and carbon fiber industries, such as difficulty in scale-up, low polymerization efficiency, uneven temperature distribution inside the reactor, easy formation of gel inside the reactor requiring frequent shutdown and cleaning, wide average molecular weight distribution, and large equipment investment. Existing continuous polymerization reactors have problems such as inconvenient cleaning, easy to cause reactor blockage, frequent equipment maintenance, large footprint, high energy consumption, and large equipment investment.

[0087] (2) The system and process described in this invention solve the above problems well and can be used in the production process of acrylonitrile, carbon fiber, etc. It has the advantages of easy scale-up of polymerization reactor, high continuous production efficiency, good temperature uniformity inside the reactor, less tendency to generate gel inside the reactor, long maintenance cycle, narrow average molecular weight distribution, and low equipment investment. Attached Figure Description

[0088] Figure 1 This is a schematic diagram of the process flow for preparing polyacrylonitrile spinning solution using a two-stage reactor according to the present invention.

[0089] Figure 2 This is a schematic diagram of the process flow for preparing polyacrylonitrile spinning solution using another two-stage reactor according to the present invention.

[0090] Figure 3 This is a schematic diagram of the process flow for preparing polyacrylonitrile spinning solution using a three-stage reactor according to the present invention.

[0091] Figure 1 , Figure 2 , Figure 3 Explanation of Chinese markings:

[0092] 111 Reaction feed stream; 112 Reaction feed stream after heating; 113 First stage reaction product; 114 First stage reaction product after pressurization; 115 Second stage reaction feed stream; 116 Second stage reaction product; 117 Second stage reaction product after pressurization; 118 Second stage reaction product return stream; 119 Second stage reaction product discharge from the transfer pump; 120 Discharge from the separation unit (polyacrylonitrile spinning solution); 121 Third stage reaction feed stream; 122 Third stage reaction product; 123 Third stage reaction product after pressurization; 124 Third stage reaction product return stream. ; 125 Three-stage reaction product transfer pump discharge; E111 Feed heater; R111 First-stage coil reactor; P111 First-stage reaction product transfer pump; R112 Second-stage coil reactor; P112 Second-stage reaction product transfer pump; R113 Three-stage coil reactor; P113 Three-stage reaction product transfer pump; F111 First mixer; F112 Second mixer; Q111 First-stage reactor temperature control system; Q112 Second-stage reactor temperature control system; Q113 Third-stage reactor temperature control system; T111 Separation unit. Detailed Implementation

[0093] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0094] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0095] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0096] In this invention, such as Figure 1 or Figure 2 As shown ( Figure 1 and Figure 2 There is no significant difference; the only difference lies in the equipment combination, which will affect the floor space required. Figure 1 The two-stage reactor is arranged as a single unit, connected vertically. Figure 2The two-stage reactor is arranged in a split configuration. The reaction feed stream 111 is heated by the feed heater E111 to obtain the heated reaction feed stream 112, which is then fed into the first-stage coil reactor R111. The reaction takes place inside the coil of the reactor. The first-stage reaction product 113 is pressurized by the first-stage reaction product transfer pump P111 to obtain the pressurized first-stage reaction product 114, which is then sent to the first mixer F111. After mixing with the second-stage reaction product return stream 118, the second-stage reaction feed stream 115 is obtained and fed into the second-stage coil reactor R112. The reaction takes place inside the coil of the reactor. The second-stage reaction product 116 is pressurized by the second-stage reaction product transfer pump P112 to obtain the pressurized second-stage reaction product 117, which is divided into two streams. One stream is sent to the first mixer F111 as the second-stage reaction product return stream 118, and the other stream is sent to the separation unit T111 as the second-stage reaction product discharge 119, which is then sent to the separation unit discharge 120 (polyacrylonitrile spinning solution).

[0097] In this invention, such as Figure 3 As shown, the reaction feed stream 111 is heated by the feed heater E111 to obtain the heated reaction feed stream 112, which is then fed into the first-stage reactor R111. The reaction takes place in the coils inside the reactor. The first-stage reaction product 113 is pressurized by the first-stage reaction product transfer pump P111 to obtain the pressurized first-stage reaction product 114, which is then sent to the first mixer F111. There, it is mixed with the second-stage reaction product return stream 118 to obtain the second-stage reaction feed stream 115, which is fed into the second-stage reactor R112. The reaction takes place in the coils inside the reactor. The second-stage reaction product 116 is pressurized by the second-stage reaction product transfer pump P112 to obtain the pressurized second-stage reaction product 117, which is then divided into two streams. One stream serves as the second-stage reaction product return stream. The return stream 118 is sent to the first mixer F111, and another stream of the second-stage reaction product discharge 119 is sent to the second mixer F112. After mixing with the third-stage reaction product return stream 124, the third-stage reaction feed stream 121 is obtained and sent to the three-stage coil reactor R113. The reaction takes place in the coil inside the reactor. The third-stage reaction product 122 is pressurized by the third-stage reaction product discharge pump P113 to obtain the pressurized third-stage reaction product 123, which is divided into two streams. One stream is sent to the second mixer F112 as the third-stage reaction product return stream 124, and the other stream of the third-stage reaction product discharge 125 is sent to the separation unit T111 to obtain the separation unit discharge 120 (polyacrylonitrile spinning solution).

[0098] Taking a thousand-ton-level carbon fiber production unit as an example, the mass flow rate of the reaction feed stream is 1500 kg / h. The typical values ​​reported in Xu Lianghua, Cao Weiyu, and Hu Liangquan, *Polyacrylonitrile-based Carbon Fiber* [M]. Beijing: National Defense Industry Press, 2018, are as follows (by mass percentage): Acrylonitrile (AN) 20.5%, Itaconic acid (IA) 0.50%, Azobisisobutyronitrile (AIBN) 0.3%, and Dimethyl sulfoxide (DMSO) 78.7%. The density of the reaction feed stream is 1000 kg / m³. 3 count.

[0099] In this embodiment of the invention, the formula for calculating the heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is: 3.14*D*L / (Fm*t), where L is the total length of the coil reactor in m; Fm is the reaction feed stream flow rate in kg / h; t is the material residence time in h; and D is the inner diameter of the coil reactor coil in m.

[0100]

Example 1

[0101] like Figure 2 As shown, the temperature of the first coil reactor is 60℃, the residence time of the first coil reactor is 10h, the outlet conversion rate of the first coil reactor is 71.00%, and the cross-sectional temperature uniformity of the first coil reactor is ±0.25℃.

[0102] The volume of one section of the coiled reactor coil is 15.00 m³. 3 The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 1911 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.1% m.

[0103] The temperature of the two-stage coil reactor is 72℃, the residence time is 6h, the outlet conversion rate is 90.03%, and the interface temperature uniformity is ±0.3℃. The recycle material at the outlet of the two-stage reactor accounts for 0.1% (10wt%) of the total outlet material.

[0104] The two-stage coil reactor has a coil volume of 9.90 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 986 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 7.2% m.

[0105] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the viscosity of the material at the outlet of the first-stage coil reactor is 60.5 Pa·s (measured at 60℃); the heat transfer area of ​​the coil reactor corresponding to the unit mass of reaction feed stream in the second-stage coil reactor is 500 cm². 2 / kg, the viscosity of the material at the outlet of the two-stage coil reactor is 78.6 Pa·s (measured at 60℃); the residual amount of spinning solution at the exit of the separation zone is 500 PPM, the average molecular weight distribution is 1.44, and the continuous stable operation time is greater than 4000h.

[0106]

Example 2

[0107] like Figure 2 As shown, the temperature of the first-stage coil reactor is 62℃, the residence time of the first-stage coil reactor is 8h, the outlet conversion rate of the first-stage coil reactor is 72.5%, and the cross-sectional temperature uniformity of the first-stage coil reactor is ±0.25℃.

[0108] The volume of one section of the coiled reactor coil is 12.00 m³. 3 The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 1529 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.25% m.

[0109] The temperature of the two-stage coil reactor is 70℃, the residence time is 7.5h, the outlet conversion rate is 90.02%, and the interface temperature uniformity is ±0.3℃. The proportion of recycled material at the outlet of the two-stage reactor is 0.1% (i.e., 10wt%).

[0110] The two-stage coil reactor has a coil volume of 12.38 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 1232 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 7.2% m.

[0111] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 63.2 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor was 78.5 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone was 501 PPM, the average molecular weight distribution was 1.43, and the continuous stable operation time was greater than 4000h.

[0112]

Example 3

[0113] like Figure 1 As shown, the temperature of the first-stage coil reactor is 65℃, the residence time of the first-stage coil reactor is 6h, the outlet conversion rate of the first-stage coil reactor is 74.00%, and the cross-sectional temperature uniformity of the first-stage coil reactor is ±0.25℃.

[0114] The volume of the coil in a single section of the coiled reactor is 9.00 m³. 3 The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 1147 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.4% m.

[0115] The temperature of the two-stage coil reactor is 67℃, the residence time is 9.5h, the outlet conversion rate is 90.01%, and the interface temperature uniformity is ±0.3℃. The recycle material at the outlet of the two-stage reactor accounts for 0.1% (10wt%) of the total outlet material.

[0116] The two-stage coil reactor has a coil volume of 15.68 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 1561 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 7.2% m.

[0117] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 66.2 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor was 78.5 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone was 502 PPM, the average molecular weight distribution was 1.42, and the continuous stable operation time was greater than 4000h.

[0118]

Example 4

[0119] like Figure 1 As shown, the temperature of the first-stage coil reactor is 68℃, the residence time of the first-stage coil reactor is 4h, the outlet conversion rate of the first-stage coil reactor is 78.00%, and the cross-sectional temperature uniformity of the first-stage coil reactor is ±0.25℃.

[0120] The volume of a single coiled reactor coil is 6.00 m³. 3The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 765 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.8% m.

[0121] The temperature of the two-stage coil reactor is 64℃, the residence time is 12h, the outlet conversion rate is 90.01%, and the interface temperature uniformity of the one-stage coil reactor is ±0.3℃. The recycle material at the outlet of the two-stage reactor accounts for 0.1% (10wt%) of the total outlet material.

[0122] The two-stage coil reactor has a coil volume of 19.8 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 1971 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 7.2% m.

[0123] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 69.1 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor was 78.6 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone was 502 PPM, the average molecular weight distribution was 1.42, and the continuous stable operation time was greater than 4000h.

[0124]

Example 5

[0125] like Figure 1 As shown, the temperature of the first coil reactor is 60℃, the residence time of the first coil reactor is 10h, the outlet conversion rate of the first coil reactor is 71.00%, and the cross-sectional temperature uniformity of the first coil reactor is ±0.25℃.

[0126] The volume of one section of the coiled reactor coil is 15.00 m³. 3 The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 1911 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.1% m.

[0127] The temperature of the two-stage coil reactor is 72℃, the residence time is 6h, the outlet conversion rate is 90.10%, and the interface temperature uniformity is ±0.3℃. The recycle material at the outlet of the two-stage reactor accounts for 0.3% (30wt%) of the total outlet material.

[0128] The two-stage coil reactor has a coil volume of 11.70 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 1165 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 7.21% m.

[0129] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 60.6 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor is 80.1 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone is 495 PPM, the average molecular weight distribution is 1.44, and the continuous stable operation time is greater than 4000h.

[0130]

Example 6

[0131] like Figure 3 As shown, the first-stage coil reactor and the second-stage coil reactor are operated under the conditions of Example 4, with the second-stage coil reactor having no return flow.

[0132] The temperature of the first-stage coil reactor is 68℃, the residence time of the first-stage coil reactor is 4h, the outlet conversion rate of the first-stage coil reactor is 78.0%, and the cross-sectional temperature uniformity of the first-stage coil reactor is ±0.25℃.

[0133] The volume of a single coiled reactor coil is 6.00 m³. 3 The reactor uses a coil with an inner diameter of 100 mm (one coil in parallel) and a length of 765 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 7.8% m.

[0134] The temperature of the two-stage coil reactor is 64℃, the residence time is 6h, the outlet conversion rate is 86.6%, and the interface temperature uniformity is ±0.3℃. The proportion of recycled material at the outlet of the two-stage reactor is 0% by mass.

[0135] The two-stage coil reactor has a coil volume of 9.00 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 896 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 6.93% m.

[0136] The three-stage coil reactor operates at a temperature of 64℃, a residence time of 6 hours, an outlet conversion rate of 90.02%, and an interface temperature uniformity of ±0.3℃. By mass percentage, the recycle material at the three-stage reactor outlet accounts for 0% of the total outlet material.

[0137] The three-section coil reactor has a coil volume of 9.00 m³. 3 The reactor uses a double-layer coil with an inner diameter of 80mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 896m. The product of the inner diameter of the three-section coil reactor and the conversion rate is 7.2%m.

[0138] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 69.1 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor is 75.6 Pa·s (measured at 60℃), and the heat transfer area of ​​the three-stage coil reactor corresponding to a unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the three-stage coil reactor was 78.7 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone was 501 PPM, the average molecular weight distribution was 1.42, and the continuous stable operation time was greater than 4000h.

[0139]

Example 7

[0140] like Figure 2 As shown, the diameter of the coil and the number of parallel coils in the coil reactor were changed according to the process conditions of Example 1.

[0141] The temperature of the first-stage coil reactor is 60℃, the residence time of the first-stage coil reactor is 10h, the outlet conversion rate of the first-stage coil reactor is 74.8%, and the cross-sectional temperature uniformity of the first-stage coil reactor is ±0.35℃.

[0142] The volume of one section of the coiled reactor coil is 15.00 m³. 3The reactor uses a coil with an inner diameter of 80 mm (one coil in parallel) and a length of 2986 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 5.98% m.

[0143] The temperature of the two-stage coil reactor is 72℃, the residence time is 8h, the outlet conversion rate is 90.43%, and the interface temperature uniformity is ±0.20℃. The proportion of recycled material at the outlet of the two-stage reactor is 0.1% (10wt%).

[0144] The two-stage coil reactor has a coil volume of 13.2 m³. 3 The reactor uses a three-layer coil with an inner diameter of 50mm (3 coils in parallel, each coil with the same length), and each coil is 2242m long. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 4.52%m.

[0145] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 66.8 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 800 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor is 82.3 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone is 500 PPM, the average molecular weight distribution is 1.43, and the continuous stable operation time is greater than 4000h.

[0146]

Example 8

[0147] like Figure 1 As shown, the temperature of the first coil reactor is 60℃, the residence time of the first coil reactor is 10h, the outlet conversion rate of the first coil reactor is 74.8%, and the cross-sectional temperature uniformity of the first coil reactor is ±0.25℃.

[0148] The volume of one section of the coiled reactor coil is 15.00 m³. 3 The reactor uses a coil with an inner diameter of 80 mm (one coil in parallel) and a length of 2986 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 5.98% m.

[0149] The temperature of the two-stage coil reactor is 72℃, the residence time is 6h, the outlet conversion rate is 90.15%, and the interface temperature uniformity is ±0.2℃. The recycle material at the outlet of the two-stage reactor accounts for 0.3% (30wt%) of the total outlet material.

[0150] The two-stage coil reactor has a coil volume of 11.70 m³. 3 The reactor uses a double-layer coil with an inner diameter of 50 mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 2981 m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 4.51% m.

[0151] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 66.9 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 800 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor was 81.2 Pa·s (measured at 60℃); the residual amount of spinning solution at the separation zone was 498 PPM, the average molecular weight distribution was 1.43, and the continuous stable operation time was greater than 4000h.

[0152]

Example 9

[0153] like Figure 1 As shown, the temperature of the first coil reactor is 60℃, the residence time of the first coil reactor is 10h, the outlet conversion rate of the first coil reactor is 74.7%, and the cross-sectional temperature uniformity of the first coil reactor is ±0.25℃.

[0154] The volume of one section of the coiled reactor coil is 15.00 m³. 3 The reactor uses a coil with an inner diameter of 80 mm (one coil in parallel) and a length of 2986 m. The product of the inner diameter of the coil and the conversion rate of a single coil reactor is 5.98% m.

[0155] The temperature of the two-stage coil reactor is 72℃, the residence time is 6h, the outlet conversion rate is 89.98%, and the interface temperature uniformity is ±0.2℃. The recycle material at the outlet of the two-stage reactor accounts for 0.3% (30wt%) of the total outlet material.

[0156] The two-stage coil reactor has a coil volume of 11.70 m³. 3The reactor uses a double-layer coil with an inner diameter of 100mm (two coils are arranged in parallel, and each coil has the same length). The length of each coil is 745m. The product of the inner diameter of the coil and the conversion rate in the two-stage coil reactor is 9.0%m.

[0157] The temperature control medium is hot water with a specific heat capacity of 4.18 kJ / kg·℃. The heat transfer area of ​​the coil reactor corresponding to a unit mass of reaction feed stream is 500 cm². 2 / kg, the outlet viscosity of the first-stage coil reactor is 66.5 Pa·s (measured at 60℃); the heat transfer area of ​​the second-stage coil reactor corresponding to the unit mass of reaction feed stream is 400 cm². 2 / kg, the outlet viscosity of the two-stage coil reactor is 80.3 Pa·s (measured at 60℃); the residual amount of spinning solution at the exit of the separation zone is 505 PPM, the average molecular weight distribution is 1.47, and the continuous stable operation time is greater than 4000h.

[0158]

Comparative Example 1

[0159] Using the same reaction feed stream as in Example 1, and employing a batch reactor, the polymerization time required to achieve a conversion rate of 90% is 16–20 hours (excluding operations such as feeding, discharging, and cooling after reaction). The feed mass flow rate is 1500 kg / h, and the density is 1000 kg / m³. 3 The volume of a single reactor is 34–43 m³. 3 If the operation time for processes such as feeding, discharging, and cooling after reaction is considered, the volume of a single reactor reaches 77m³. 3 Due to the large volume of the polymerization reactor, the temperature uniformity inside the reactor can only be controlled within ±3 to 5℃. Furthermore, due to the uneven temperature, gelation is prone to occur, requiring periodic shutdowns (approximately 600 to 800 hours) for cleaning. Moreover, the average molecular weight distribution is also relatively wide, ranging from 3.5 to 4.0.

[0160] [Comparative Example 2]

[0161] Referring to Example 1 of Chinese Patent CN101215357A, 19.84 kg of acrylonitrile and 0.16 kg of itaconic acid were dissolved in 79.8 kg of dimethyl sulfoxide at room temperature. After stirring for one hour, 0.1 kg of azobisisobutyronitrile and 0.1 kg of azobisisobutyronitrile were added. After stirring for half an hour, the temperature was lowered to -10°C, and the solution was continuously added from the top of the polymerization reactor. Cooling water was circulated through the reactor jacket, and the temperature was controlled between 30°C and 70°C for a total of 36 hours. The polyacrylonitrile solution continuously discharged from the bottom outlet had a concentration of 19%, a viscosity of 45 Pa·s (measured at 45°C), and a molecular weight distribution coefficient of 2.4. After degassing and filtration, the spinning solution was obtained. The continuous polymerization process is carried out in 1-4 jacketed polymerization reactors connected in series. The molecular weight distribution of the product is above 2.4, which is too wide. The number of equipment is large, the total investment is large, and the footprint is large.

[0162] As can be seen from Examples 1-9 and Comparative Examples 1-2, the system and process described in this invention effectively solve the problems of existing batch polymerization reactors in the acrylonitrile and carbon fiber industries, such as difficulty in scaling up, low polymerization efficiency, uneven temperature distribution inside the reactor, easy formation of gel inside the reactor requiring frequent shutdowns for cleaning, wide average molecular weight distribution, and large equipment investment. Existing continuous polymerization reactors also suffer from problems such as inconvenient cleaning leading to reactor blockage, frequent equipment maintenance, large footprint, high energy consumption, and large equipment investment. The system and process have the advantages of easy scale-up of polymerization reactors, high continuous production efficiency, good temperature uniformity inside the reactor, less tendency to form gel inside the reactor, long maintenance cycle, narrow average molecular weight distribution, and low equipment investment.

[0163] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing polyacrylonitrile spinning dope, comprising the step of feeding a reaction feed stream into a m-stage reactor to react and obtain a polyacrylonitrile spinning dope; wherein, m is an integer greater than or equal to 2, and the reactor is a coil reactor.

2. The method as described in claim 1, characterized in that: m is an integer between 2 and 4; and / or, The m-section reactors are connected in series; and / or, In a single-stage coil reactor, the number of parallel coils is n1, where n1 is an integer less than or equal to 2; and / or, In a two-stage or higher coil reactor, the number of parallel coils may be the same or different, each independently represented as n2, where n2 is an integer greater than or equal to 2, preferably an integer between 2 and 4; and / or, The inner diameter of the coils in each section of the coiled reactor may be the same or different, and is independently 15-200 mm, preferably 40-150 mm; preferably, the inner diameter of the coils in two or more sections of the coiled reactor is less than or equal to the inner diameter of the coils in a single section of the coiled reactor; more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is 0-50 mm smaller than the inner diameter of the coils in a single section of the coiled reactor, preferably 0-30 mm smaller; and / or, The reaction feed stream enters the coil of the coil reactor, and a heat transfer medium is installed outside the coil of the reactor.

3. The method as described in claim 1, characterized in that: The inner diameter of the coil in each section of the coil reactor and its outlet conversion rate satisfy the following equation (1): 0.75%m≤D*X≤20%m Equation (1); In equation (1), D is the inner diameter of the coil in the coil reactor, in meters; X is the outlet conversion rate of the coil reactor, in percentage; and / or, The total length of the coil in each section of the coil reactor and the inner diameter of the coil satisfy the following relationship as shown in equation (2): L=Fm*t / (0.785ρD 2 Equation (2); In equation (2), L is the total length of the coil in the coil reactor, in meters; Fm is the flow rate of the reaction feed, in kg / h; t is the residence time of the material, in hours; and ρ is the density of the reaction feed, in kg / m³. 3 D is the inner diameter of the coil of the coil reactor, in meters.

4. The method as described in claim 1, characterized in that: The residence time of the reactants in the first-stage reactor is 4-12 hours, preferably 4-10 hours; and / or, the reaction temperature in the first-stage reactor is 55-70℃, preferably 60-68℃; and / or, The residence time of the reactants in the two or more reactors may be the same or different, and is independently 6-14h, preferably 6-12h; and / or the reaction temperature of the two or more reactors may be the same or different, and is independently 60-75℃, preferably 64-72℃.

5. The method as described in claim 1, characterized in that: In each section of the coil reactor, the coils are immersed in a temperature-controlled medium, preferably with a specific heat capacity greater than or equal to 0.7 KJ / kg·℃; and / or, The heat transfer area of ​​the coil reactor corresponding to the unit mass of reaction feed stream is greater than or equal to 100 cm². 2 / kg, preferably greater than or equal to 220cm 2 / kg.

6. The method as described in claim 1, characterized in that: The flow rate of the reaction feed stream is 500-2000 kg / h, preferably 1200-1800 kg / h; and / or, The reaction feed stream contains monomers, free radical initiators, and solvents; preferably, The monomers include acrylonitrile monomers and comonomers, wherein the comonomers are preferably selected from at least one of itaconic acid, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, acrylamide, methacrylamide, dimethyl itaconic acid, and dibutyl itaconic acid; and / or, The free radical initiator is selected from at least one of azo initiators and peroxide initiators, preferably from at least one of azobisisobutyronitrile and azobisisoheptanenitrile; and / or, The solvent is selected from at least one of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide; more preferably, By mass percentage, the acrylonitrile monomer accounts for 17-22%, the solvent accounts for 77-81%, the comonomer accounts for 0.15-1%, and the initiator accounts for 0.02-1%.

7. The method according to any one of claims 1-6, characterized in that... The method includes: The reaction feed stream is fed into a first-stage reactor for reaction. The resulting first-stage reaction product is fed into a second-stage reactor for reaction. The resulting second-stage reaction product is fed into a next-stage reactor for reaction. In sequence, the resulting first-stage reaction product is fed into the next-stage reactor for reaction. The resulting m-1 stage reaction product is fed into the m-stage reactor for reaction. Finally, after separating the unreacted monomers from the resulting m-stage reaction product, the polyacrylonitrile spinning dope is obtained.

8. The method as described in claim 7, characterized in that: The reaction products from each of the two stages (m-1) can be optionally divided into two streams: one stream is used as a recycle stream and mixed with the reaction products from the previous stage; the other stream is sent to the next stage reactor for further reaction; and / or, The reaction products of segment m are divided into two streams. One stream is used as a circulating stream to mix with the reaction products of the previous segment, and the other stream is sent to the separation unit to separate unreacted monomers. Preferably, the recycled streams from stage II to stage M each independently account for 0-50 wt% of the reaction products from stage II to stage M, more preferably 0-45 wt%.

9. A system for preparing polyacrylonitrile spinning solution, preferably used for performing the method according to any one of claims 1-8, comprising a reaction unit and a separation unit, wherein the reaction unit comprises an m-section coil reactor, wherein, m is an integer greater than or equal to 2; preferably, m is an integer between 2 and 4; and / or, The m-section coil reactors are connected in series; and / or, In a single-stage coil reactor, the number of parallel coils is n1, where n1 is an integer less than or equal to 2; and / or, In a two-stage or higher coil reactor, the number of parallel coils may be the same or different, each independently represented by n2, where n2 is an integer greater than or equal to 2; and / or, The inner diameter of the coils in each section of the coiled reactor may be the same or different, and is independently 15-200 mm, preferably 40-150 mm; more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is less than or equal to the inner diameter of the coils in a single section of the coiled reactor; even more preferably, the inner diameter of the coils in two or more sections of the coiled reactor is 0-50 mm smaller than the inner diameter of the coils in a single section of the coiled reactor, preferably 0-30 mm smaller; and / or, The coil of the coiled reactor serves as a channel for the reactants, and the outside of the coil is the heat transfer medium.

10. The system as described in claim 9, characterized in that: Each section of the coil reactor is equipped with a reactant inlet and a product outlet. Sequentially, the product outlet of the previous section is connected to the material inlet of the next section of the coil reactor, the product outlet of section m-1 of the coil reactor is connected to the material inlet of section m of the coil reactor, and the product outlet of section m of the coil reactor is connected to the separation unit. Preferably, the reactant inlet is connected to the pipe inlet of the coil, and the product outlet is connected to the pipe outlet of the coil.

11. The system as described in claim 10, characterized in that: A feed heater is installed on the pipeline that sends the reaction feed stream into the reactant inlet of a section of the coil reactor; and / or, A product transfer pump and a mixer are installed on the pipeline connecting the product outlet of the first to the m-1 section of the coiled reactor to the material inlet of the next section of the coiled reactor. Preferably, the product transfer pump is located before the mixer; and / or, A final reaction product transfer pump is installed on the pipeline connecting the reaction product outlet of the m-section coil reactor to the separation unit.

12. The system as described in claim 11, characterized in that: Each section of the coil reactor is connected to a product delivery pump and a mixer via a pipeline that can optionally include a branch connecting to the previous section of the mixer.

13. The system as described in any one of claims 9-12, characterized in that: Each section of the coil reactor is equipped with a reactor temperature control system.

14. The application of the method as described in any one of claims 1-8 or the system as described in any one of claims 9-13 in a liquid-phase polymerization reaction, preferably in the preparation of acrylonitrile and carbon fiber.

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