A continuous method of preparing a para-aramid polymer

Abstract

This invention provides a continuous preparation method for para-aramid polymers. The continuous preparation method includes the following steps: (a) mixing p-phenylenediamine and a polar solvent to obtain a p-phenylenediamine solution; (b) melting terephthaloyl chloride to obtain molten terephthaloyl chloride; (c) passing the p-phenylenediamine solution obtained in step (a) and a portion of the molten terephthaloyl chloride obtained in step (b) into a microchannel reactor for reaction to obtain a prepolymer; (d) mixing the prepolymer obtained in step (c) with the remaining molten terephthaloyl chloride obtained in step (b) and reacting to obtain the para-aramid polymer; wherein the microchannel reactor is a single-channel microreactor. The continuous preparation method provided by this invention ensures uniform material mixing, rapid removal of reaction heat, and effective control of side reactions. The resulting para-aramid polymer exhibits narrow molecular weight distribution, stable performance, and good particle size uniformity.

Description

Technical Field

[0001] This invention belongs to the field of aramid preparation technology, specifically relating to a continuous preparation method for para-aramid polymers. Background Technology

[0002] Poly(p-phenylene terephthalamide) fiber was synthesized by DuPont in 1965 using a low-temperature solution polycondensation reaction. Utilizing the liquid crystal behavior of PPTA / H₂SO₄ solution, a dry-jet wet spinning method was invented to obtain high-performance poly(p-phenylene terephthalamide) fiber, known in my country as para-aramid or aramid 1414. This high-performance aromatic polyamide fiber possesses excellent properties such as high strength, high modulus, high temperature resistance, acid and alkali resistance, and low density. Its specific tensile strength is 8 times that of steel wire (≥5 GPa), and its specific modulus is 3–4 times that of steel wire (≥148 GPa). Therefore, it has important applications in aerospace, defense, automotive industry, and sporting goods.

[0003] The industrial production of aramid 1414 fiber employs a two-step process: polymerization followed by spinning. Currently, the industrially available method for preparing poly(p-phenylene terephthalamide) is low-temperature solution polycondensation. The specific process involves dissolving calcium chloride (CaCl2) in N-methylpyrrolidone to prepare a CaCl2-NMP solvent, dissolving p-phenylenediamine (PPDA) in the CaCl2-NMP solvent, and then adding an equimolar ratio of terephthaloyl chloride (TPC). The polymer is then obtained under high-speed shear using low-temperature solution polycondensation. This process can be performed continuously or intermittently. The polymerization reaction is shown in the following equation:

[0004]

[0005] During low-temperature polycondensation, the viscosity of the mixture increases rapidly with increasing molecular weight, and the mixture gradually undergoes a phase transition from liquid to solid, making it very difficult to mix the reactants. Due to the high reactivity of the poly(p-phenylene terephthalamide) monomers, this process requires strict isolation from oxygen and water. Furthermore, because the polycondensation reaction is very rapid and exothermic (enthalpy of reaction is -107 kJ / mol), a highly efficient heat exchange system is needed when using traditional reactors to ensure that the mixture temperature is sufficiently low and uniform. This is necessary to obtain polymers with high weight-average molecular weight and narrow molecular weight distribution. However, uneven temperature distribution within the reactor is prone to occur, with localized high temperatures, leading to problems such as a wider molecular weight distribution, low weight-average molecular weight, and more byproducts, making it difficult to obtain high-performance aramid fibers. At the same time, polymerization is a hazardous chemical process under key national regulation and a major problem that urgently needs to be solved in the development of the industry.

[0006] Therefore, there is a need to develop a continuous preparation method for para-aramid polymers that can achieve uniform material mixing and solve the problem of uneven heat exchange leading to uneven temperature within the reactor. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a continuous preparation method for para-aramid polymers. In this continuous preparation method, the materials are mixed uniformly, the heat of reaction can be quickly removed, and the occurrence of side reactions can be effectively controlled. The prepared para-aramid polymers have the characteristics of narrow molecular weight distribution, stable performance, and good particle size uniformity.

[0008] To achieve this objective, the present invention employs the following technical solution:

[0009] This invention provides a continuous preparation method for para-aramid polymers, the continuous preparation method comprising the following steps:

[0010] (a) Mixing p-phenylenediamine with a polar solvent to obtain a p-phenylenediamine solution, wherein the mass concentration of water in the p-phenylenediamine solution is ≤200ppm, such as 40ppm, 60ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm or 180ppm.

[0011] (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride;

[0012] (c) The p-phenylenediamine solution obtained in step (a) and a portion of the molten terephthaloyl chloride obtained in step (b) are passed into a microchannel reactor to react and obtain a prepolymer;

[0013] (d) The prepolymer obtained in step (c) is mixed with the remaining molten terephthaloyl chloride obtained in step (b) and reacted to obtain the para-aramid polymer.

[0014] Steps (a) and (b) may be performed in any order, or simultaneously.

[0015] The microchannel reactor is a single-channel microreactor, comprising a first body 101, a second body 102, a microchannel inlet 201, a microchannel 202, a microchannel outlet 203, a conveying channel inlet 301, a conveying channel 302, and a conveying channel outlet 303, wherein the conveying channel 302 is an annular cavity surrounding the microchannel 202;

[0016] The discharge port 303 of the conveying channel is connected to the microchannel 202 and is located near the inlet 201 of the microchannel. In step (c), the molten terephthaloyl chloride flows into the microchannel reactor from the inlet 201 of the microchannel; the p-phenylenediamine solution flows into the microchannel reactor from the inlet 301 of the conveying channel, and the prepolymer flows out of the microchannel reactor from the discharge port 203 of the microchannel. The flow direction of the p-phenylenediamine solution in the conveying channel 302 is opposite to the flow direction of the fluid in the microchannel 202.

[0017] In this invention, a two-step polymerization method is employed. The prepolymerization stage utilizes a single-channel microreactor. The small diameter of the microchannels in this single-channel microreactor allows for sufficient contact between the material and the channel walls for heat dissipation. A cooler p-phenylenediamine solution surrounds the microchannels, rapidly removing heat generated during the reaction and achieving a more uniform heat distribution and equilibrium. This prevents heat accumulation within the microchannels, which could lead to runaway reactions and effectively controls the safety risks of the polymerization reaction. Compared to traditional reactors, the microchannel reactor described in this invention removes heat more rapidly, resulting in more uniform material temperature and eliminating large local temperature differences. Consequently, the obtained prepolymer exhibits consistent molecular weight and a narrower molecular weight distribution. A good prepolymer ensures consistent polymer molecular weight growth rates during final polymerization, resulting in a narrow final polymer molecular weight distribution without gelation or other phenomena. Furthermore, it avoids the complex structure and numerous dead zones associated with multi-stage parallel microreactors. This continuous preparation method for para-aramid polymers is a micro-unit polymerization reaction with small online reactant quantities, making it safer and more controllable.

[0018] Preferably, a guide channel is provided at the material outlet 303 of the material conveying channel.

[0019] In this invention, a guide channel is provided at the discharge port 303 of the conveying channel, which allows the p-phenylenediamine solution to enter the microchannel through the guide channel and form a swirling flow. This further increases the heat exchange between the mixture in the microchannel and the flow channel wall, avoiding the temperature unevenness phenomenon caused by uneven heat exchange in traditional reactors, where the internal material temperature is high and the external material temperature is low. This results in obtaining a para-aramid polymer with a high molecular weight and a narrow molecular weight distribution.

[0020] Preferably, the diameter of the microchannel 202 is ≤3mm, such as 0.5mm, 1mm, 1.5mm, 2mm or 2.5mm.

[0021] Preferably, the microchannel reactor is made of any one of glass, metal or polymer materials, and more preferably metal.

[0022] Preferably, the polar solvent in step (a) comprises N-methylpyrrolidone.

[0023] Preferably, the mixing in step (1) further includes mixing with a co-solvent.

[0024] Preferably, the co-solvent includes calcium chloride or lithium chloride.

[0025] Preferably, the co-solvent is calcium chloride, and the mass percentage of calcium chloride in the p-phenylenediamine solution is 7% to 10%, for example, 7.3%, 7.6%, 7.9%, 8.2%, 8.5%, 8.8%, 9.1%, 9.4%, or 9.7%.

[0026] Preferably, the co-solvent is lithium chloride, and the mass percentage of lithium chloride in the p-phenylenediamine solution is 2% to 3%, such as 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, or 2.9%.

[0027] Preferably, the mass percentage of p-phenylenediamine in the p-phenylenediamine solution in step (a) is 3% to 8%, for example, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% or 7.5%.

[0028] Preferably, the temperature of the p-phenylenediamine solution in step (a) is 0–15°C (e.g., 2°C, 4°C, 6°C, 8°C, 10°C, 12°C, or 14°C), and more preferably 4–6°C.

[0029] Preferably, the temperature of the molten terephthaloyl chloride in step (b) is 85–95°C (e.g., 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, or 94°C).

[0030] Preferably, the spray direction of the p-phenylenediamine solution at the outlet 303 of the feed channel in the microchannel reactor is at an angle of 15° to 75° with the microchannel 202.

[0031] In this invention, by making the spray direction of the p-phenylenediamine solution form an angle of 15° to 75° with the microchannel, the mixture formed by the p-phenylenediamine solution and the molten terephthaloyl chloride after entering the microchannel can flow along the microchannel towards the outlet. This enables uniform mixing and full contact between the p-phenylenediamine solution and the molten terephthaloyl chloride, increasing the reaction rate and enhancing heat exchange between the mixture and the flow channel wall of the microchannel. This avoids the temperature unevenness caused by uneven heat exchange in traditional reactors, where the internal material temperature is high and the external material temperature is low. As a result, a para-aramid polymer with high molecular weight and narrow molecular weight distribution is obtained.

[0032] Preferably, the injection velocity of the p-phenylenediamine solution into the microchannel 202 in step (c) is 0.3–2 m / s.

[0033] (e.g., 0.5m / s, 0.7m / s, 0.9m / s, 1.1m / s, 1.3m / s, 1.5m / s, 1.7m / s or 1.9m / s, etc.), more preferably 1.2m / s, with a flow rate of 0.45 to 3 tons / hour, such as 0.5 tons / hour, 1 ton / hour, 1.5 tons / hour, 2 tons / hour or 2.5 tons / hour, etc.

[0034] Preferably, the flow rate of the molten terephthaloyl chloride introduced into the microchannel 202 in step (c) is 0.8 to 1.6 m / s (e.g., 0.9 m / s, 1.0 m / s, 1.1 m / s, 1.2 m / s, 1.3 m / s, 1.4 m / s or 1.5 m / s, etc.).

[0035] Preferably, the length of the microchannel 202 is 20-50cm, such as 23cm, 26cm, 29cm, 32cm, 35cm, 38cm, 41cm, 44cm or 47cm.

[0036] Preferably, the molar ratio of the molten terephthaloyl chloride in step (c) to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution in step (c) is (0.3-0.7):1, for example, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1 or 0.65:1, etc.

[0037] Preferably, the temperature of the reaction in step (c) is 0 to 25°C, such as 3°C, 6°C, 9°C, 12°C, 15°C, 18°C, 21°C, or 24°C.

[0038] In step (c) of the continuous preparation method of the present invention, the heat generated by the reaction is absorbed by the p-phenylenediamine solution, which makes the heat distribution more uniform, reduces the accumulation of heat generated by the reaction in the microchannel, and can achieve temperature stability during the continuous preparation process. After the reaction, the heat and products are discharged from the microchannel outlet.

[0039] Preferably, the ratio of the total molar amount of molten terephthaloyl chloride in steps (c) and (d) to the molar amount of p-phenylenediamine in the p-phenylenediamine solution in step (c) is 0.99 to 1.01:1, for example, 0.992:1, 0.994:1, 0.996:1, 0.998:1, 1.000:1, 1.002:1, 1.004:1, 1.006:1, or 1.008:1, etc.

[0040] Preferably, the reaction in step (d) is carried out in a twin-screw reactor or a batch reactor.

[0041] Preferably, the length-to-diameter ratio of the twin-screw reactor is ≤10, for example, 5, 6, 7, 8 or 9.

[0042] Preferably, the gap between the inner wall of the cylinder and the screw element of the twin-screw reactor is ≤2mm, such as 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.4mm, 1.6mm or 1.8mm.

[0043] The screw element described in this invention includes threaded elements and / or meshing elements.

[0044] Preferably, the stirring rate of the batch reactor is ≥300 rpm (e.g., 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm or 700 rpm, etc.), and more preferably ≥500 rpm.

[0045] Preferably, the gap between the maximum outer diameter of the agitator of the batch reactor and the cylinder wall is ≤2mm, such as 0.2mm, 0.4mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.4mm, 1.6mm or 1.8mm.

[0046] Preferably, the temperature of the reaction in step (d) is ≤40℃, such as 5℃, 10℃, 15℃, 20℃, 25℃, 30℃ or 35℃, and the reaction time is 10 to 40 min, such as 13 min, 16 min, 19 min, 21 min, 23 min, 25 min, 28 min, 31 min, 34 min or 37 min.

[0047] Preferably, step (d) further includes neutralization, washing, and drying steps after the reaction.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The continuous preparation method of para-aramid polymer described in this invention is a micro-unit polymerization reaction, employing a two-step polymerization process. The prepolymerization stage utilizes a microchannel reactor, allowing for online polymerization with minimal reactant volume, effectively controlling heat release, and enhancing safety and controllability, thus mitigating the safety risks of the polymerization reaction. The microchannel reactor is a single-channel microreactor, which, compared to traditional reactors, removes heat more rapidly, resulting in a more uniform material temperature and eliminating the problem of large local temperature differences. Therefore, the obtained prepolymer has a consistent molecular weight and more uniform molecular weight distribution. A good prepolymer ensures consistent polymer molecular weight growth rate during final polymerization, resulting in a narrow final polymer molecular weight distribution without gelation or other phenomena, and exhibiting good particle size uniformity. It also avoids the problems of complex structures and numerous dead zones associated with multi-stage parallel microreactors. The continuous preparation method of para-aramid polymer described in this invention offers high yield, enabling the production of thousands of tons of para-aramid polymer per year on a single line. The para-aramid polymer prepared by this continuous preparation method is used for spinning, resulting in aramid fibers with stable properties. Attached Figure Description

[0050] Figure 1 This is a cross-sectional view of a microchannel reactor;

[0051] Among them, 101-first main body, 102-second main body, 201-microchannel inlet, 202-microchannel, 203-microchannel outlet, 301-material conveying channel inlet, 302-material conveying channel, 303-material conveying channel outlet;

[0052] Figure 2 This is a schematic diagram of a mixture flowing along a microchannel in a swirling manner. Detailed Implementation

[0053] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0054] Example 1

[0055] This embodiment provides a continuous preparation method for para-aramid polymers, the continuous preparation method comprising the following steps:

[0056] (a) p-phenylenediamine, a polar solvent (N-methylpyrrolidone) and calcium chloride are mixed to obtain a p-phenylenediamine solution, wherein the mass percentage of calcium chloride in the p-phenylenediamine solution is 7%, the mass concentration of water is 150 ppm, the mass percentage of p-phenylenediamine is 5%, and the temperature of the p-phenylenediamine solution is 5°C.

[0057] (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride at a temperature of 90°C.

[0058] (c) The p-phenylenediamine solution obtained in step (a) and a portion of the molten terephthaloyl chloride obtained in step (b) are introduced into a microchannel reactor for reaction, with the molar ratio of p-phenylenediamine to terephthaloyl chloride being 1:0.3, to obtain a prepolymer;

[0059] The aforementioned microchannel reactor is a single-channel microreactor made of 316 stainless steel. Figure 1 As shown, it includes a first body 101, a second body 102, a microchannel inlet 201, a microchannel 202, a microchannel outlet 203, a conveying channel inlet 301, a conveying channel 302, and a conveying channel outlet 303, wherein the conveying channel 302 is an annular cavity surrounding the microchannel 202;

[0060] The material conveying channel outlet 303 is connected to the microchannel 202 and is located near the microchannel inlet 201. A guide channel is provided at the material conveying channel outlet 303 to create a swirling flow of fluid. Figure 2 As shown; in step (c), molten terephthaloyl chloride flows into the microchannel reactor through the microchannel inlet 201; p-phenylenediamine solution flows into the microchannel reactor through the feed channel inlet 301; the prepolymer flows out of the microchannel reactor through the microchannel outlet 203; the flow direction of the p-phenylenediamine solution in the feed channel 302 is opposite to the flow direction of the molten terephthaloyl chloride in the microchannel 202.

[0061] The microchannel inlet 201, microchannel 202 and microchannel outlet 203 have the same diameter of 3 mm. The flow rate of molten terephthaloyl chloride into the microchannel 202 is 1.2 m / s. The length of the microchannel 202 is 50 cm.

[0062] In the microchannel reactor, the spray direction of the p-phenylenediamine solution at the outlet 303 of the feed channel forms a 30° angle with the microchannel 202. The spray velocity of the p-phenylenediamine solution entering the microchannel 202 is 0.8 m / s, and the flow rate is 2 tons / hour.

[0063] (d) The prepolymer obtained in step (c) and the remaining molten terephthaloyl chloride obtained in step (b) are fed into a twin-screw reactor for reaction. The total molar ratio of the molten terephthaloyl chloride in steps (c) and (d) to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution in step (c) is 1:1. The reaction temperature is 40°C, the reaction time is 20 min, the aspect ratio of the twin-screw reactor is 10, and the gap between the inner wall of the twin-screw reactor cylinder and the screw element is 2 mm. After neutralization, washing, and drying, the para-aramid polymer is obtained. 。

[0064] Example 2

[0065] This embodiment provides a continuous preparation method for para-aramid polymers. The only difference between this method and Example 1 is that in step (a), the temperature of the p-phenylenediamine solution is adjusted to 10°C; in step (c), the spray direction of the p-phenylenediamine solution at the outlet of the feed channel in the microchannel reactor is adjusted to be at a 15° angle with the microchannel; the flow rate of molten terephthaloyl chloride into the microchannel is 0.8 m / s; the spray velocity of the p-phenylenediamine solution into the microchannel 202 is 0.4 m / s; the flow rate is 1 ton / hour; and in step (c), the molar ratio of p-phenylenediamine to terephthaloyl chloride is changed to 1:0.4. Other conditions are the same as in Example 1.

[0066] Example 3

[0067] This embodiment provides a continuous preparation method for para-aramid polymers. The only difference between this method and Example 1 is that the flow rate of molten terephthaloyl chloride in step (3) is adjusted to 1.6 m / s, and the molar ratio of p-phenylenediamine to terephthaloyl chloride in step (c) is 1:0.4. Other conditions are the same as in Example 1.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing a para-aramid polymer, the preparation method specifically including the following steps:

[0070] (a) p-phenylenediamine, a polar solvent (N-methylpyrrolidone) and calcium chloride are mixed to obtain a p-phenylenediamine solution, wherein the mass percentage of calcium chloride in the p-phenylenediamine solution is 7%, the mass concentration of water is 150 ppm, the mass percentage of p-phenylenediamine is 5%, and the temperature of the p-phenylenediamine solution is 5°C.

[0071] (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride at a temperature of 90°C.

[0072] (c) The p-phenylenediamine solution obtained in step (a) and the molten terephthaloyl chloride obtained in step (b) are fed into a twin-screw reactor for reaction. The molar ratio of the molten terephthaloyl chloride to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution is 1:1. The reaction temperature is 40°C and the reaction time is 20 min. The length-to-diameter ratio of the twin-screw reactor is 10. The gap between the inner wall of the twin-screw reactor cylinder and the screw element is 1 mm. After neutralization, washing and drying, the para-aramid polymer is obtained.

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing a para-aramid polymer, the preparation method specifically including the following steps:

[0075] (a) p-phenylenediamine, a polar solvent (N-methylpyrrolidone) and calcium chloride are mixed to obtain a p-phenylenediamine solution, wherein the mass percentage of calcium chloride in the p-phenylenediamine solution is 7%, the mass concentration of water is 150 ppm, the mass percentage of p-phenylenediamine is 5%, and the temperature of the p-phenylenediamine solution is 5°C.

[0076] (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride at a temperature of 90°C.

[0077] (c) The p-phenylenediamine solution obtained in step (a) and the molten terephthaloyl chloride obtained in step (b) are transported to a conventional 10L small stirred tank reactor for reaction. The molar ratio of the molten terephthaloyl chloride to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution is 1:1. The reaction temperature is 40°C, the reaction time is 20 min, the stirring rate is 500 rpm, and the maximum outer diameter of the stirrer in the stirred tank reactor is 2 mm from the cylinder wall. After neutralization, washing and drying, the para-aramid polymer is obtained.

[0078] Comparative Example 3

[0079] (a) p-phenylenediamine, a polar solvent (N-methylpyrrolidone) and calcium chloride are mixed to obtain a p-phenylenediamine solution, wherein the mass percentage of calcium chloride in the p-phenylenediamine solution is 7%, the mass concentration of water is 150 ppm, the mass percentage of p-phenylenediamine is 5%, and the temperature of the p-phenylenediamine solution is 5°C.

[0080] (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride at a temperature of 90°C.

[0081] (c) The p-phenylenediamine solution obtained in step (a) and part of the molten terephthaloyl chloride obtained in step (b) are transported to a conventional 10L small stirred tank reactor for reaction, with the molar ratio of p-phenylenediamine to terephthaloyl chloride being 1:0.3, to obtain a prepolymer;

[0082] (d) The prepolymer obtained in step (c) is mixed with the remaining molten terephthaloyl chloride obtained in step (b), and reacted in a twin-screw reactor. The total molar ratio of the molten terephthaloyl chloride obtained in steps (c) and (d) to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution obtained in step (c) is 1:1. The reaction temperature is 40°C, the reaction time is 20 min, the aspect ratio of the twin-screw reactor is 10, and the gap between the inner wall of the twin-screw reactor cylinder and the screw element is 2 mm. After neutralization, washing, and drying, the para-aramid polymer is obtained. 。

[0083] The following performance tests were performed on the para-aramid polymers obtained in Examples 1-3 and Comparative Examples 1-3.

[0084] Logarithmic viscosity of specific concentration: The obtained para-aramid polymer was subjected to five logarithmic viscosity measurements, and the maximum and minimum values ​​were taken as the endpoints of the logarithmic viscosity range of specific concentration.

[0085] Particle size: The particle size distribution of the para-aramid polymer was measured using a particle size analyzer. The test results are shown in Table 1 below.

[0086] Table 1

[0087]

[0088]

[0089] In Table 1, " / " indicates that the test was not performed.

[0090] As shown in Table 1, the continuous preparation method of para-aramid polymer provided in Examples 1-3 yields para-aramid polymers with a specific viscosity of 5-8, a relatively small CV value, and good particle size uniformity.

[0091] Compared to Example 1, if a microchannel reactor is not used for the reaction (Comparative Example 1), but a twin-screw reactor is used for polymerization, the specific concentration logarithmic viscosity of the obtained para-aramid polymer fluctuates more, with a CV value reaching 20%, and a higher proportion of larger and smaller particles.

[0092] Compared with Example 1, if a microchannel reactor is not used for the reaction (Comparative Example 2), and a conventional stirred tank reactor is used for polymerization, the specific concentration logarithmic viscosity of the obtained para-aramid polymer fluctuates more, with a CV value of 30%, and a higher proportion of larger and smaller particles.

[0093] Compared with Example 1, if a conventional stirred reactor (Comparative Example 3) is used to prepare the prepolymer, the prepolymer is not uniform enough, the reaction is incomplete, and particulate matter is present. The final para-aramid polymer has a large fluctuation in specific viscosity logarithmic viscosity, with a CV value of up to 20%, and a high proportion of larger and smaller particles.

[0094] In summary, the para-aramid polymer prepared by the continuous preparation method of the present invention has a relatively small CV value and good particle uniformity.

[0095] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for the continuous production of a para-aramid polymer, characterized in that, The continuous preparation method includes the following steps: (a) p-phenylenediamine and a polar solvent are mixed to obtain a p-phenylenediamine solution, wherein the mass concentration of water in the p-phenylenediamine solution is ≤200 ppm; (b) Melt terephthaloyl chloride to obtain molten terephthaloyl chloride; (c) The p-phenylenediamine solution obtained in step (a) and a portion of the molten terephthaloyl chloride obtained in step (b) are passed into a microchannel reactor to react and obtain a prepolymer; (d) The prepolymer obtained in step (c) is mixed with the molten terephthaloyl chloride obtained in the remaining step (b) and reacted to obtain the para-aramid polymer; Steps (a) and (b) may be performed in any order, or simultaneously. The microchannel reactor is a single-channel microreactor, comprising a first body (101), a second body (102), a microchannel inlet (201), a microchannel (202), a microchannel outlet (203), a conveying channel inlet (301), a conveying channel (302), and a conveying channel outlet (303), wherein the conveying channel (302) is an annular cavity surrounding the microchannel (202); The discharge port (303) of the conveying channel is connected to the microchannel (202) and is located near the inlet (201) of the microchannel. In step (c), the molten terephthaloyl chloride flows into the microchannel reactor through the inlet (201) of the microchannel; the p-phenylenediamine solution flows into the microchannel reactor through the inlet (301) of the conveying channel, and the prepolymer flows out of the microchannel reactor through the discharge port (203). The flow direction of the p-phenylenediamine solution in the conveying channel (302) is opposite to the flow direction of the fluid in the microchannel (202). A guide channel is provided at the material outlet (303) of the material conveying channel; The direction of the spraying of p-phenylenediamine solution at the outlet (303) of the feed channel in the microchannel reactor is at an angle of 15° to 75° with the microchannel (202); The diameter of the microchannel (202) is ≤3mm; The length of the microchannel (202) is 20~50cm; The temperature of the p-phenylenediamine solution in step (a) is 0~15℃; The temperature of the molten terephthaloyl chloride in step (b) is 85~95℃; The reaction temperature in step (c) is 0~25℃; The injection velocity of the p-phenylenediamine solution into the microchannel (202) in step (c) is 0.7~2 m / s, and the flow rate is 1.5~3 tons / hour; The flow rate of the molten terephthaloyl chloride introduced into the microchannel (202) in step (c) is 0.9~1.6 m / s.

2. The continuous manufacturing process of claim 1, wherein, The microchannel reactor can be made of any one of glass, metal or polymer materials.

3. The continuous manufacturing process of claim 1, wherein, The polar solvent in step (a) includes N-methylpyrrolidone.

4. The continuous manufacturing process of claim 1, wherein, The mixing in step (1) also includes mixing with a co-solvent.

5. The continuous preparation method according to claim 4, characterized in that, The co-solvent includes calcium chloride or lithium chloride.

6. The continuous preparation method according to claim 4, characterized in that, The co-solvent is calcium chloride, and the mass percentage of calcium chloride in the p-phenylenediamine solution is 7% to 10%.

7. The continuous preparation method according to claim 4, characterized in that, The co-solvent is lithium chloride, and the mass percentage of lithium chloride in the p-phenylenediamine solution is 2% to 3%.

8. The continuous preparation method according to claim 1, characterized in that, The p-phenylenediamine in the p-phenylenediamine solution in step (a) has a mass percentage of 3% to 8%.

9. The continuous preparation method according to claim 1, characterized in that, The molar ratio of the molten terephthaloyl chloride in step (c) to the molar ratio of p-phenylenediamine in the p-phenylenediamine solution in step (c) is (0.3~0.7):

1.

10. The continuous preparation method according to claim 1, characterized in that, The ratio of the total molar amount of molten terephthaloyl chloride in steps (c) and (d) to the molar amount of p-phenylenediamine in the p-phenylenediamine solution in step (c) is 0.99~1.01:

1.

11. The continuous preparation method according to claim 1, characterized in that, The reaction described in step (d) is carried out in a twin-screw reactor or a batch reactor.

12. The continuous preparation method according to claim 11, characterized in that, The aspect ratio of the twin-screw reactor is ≤10.

13. The continuous preparation method according to claim 11, characterized in that, The gap between the inner wall of the cylinder and the screw element of the twin-screw reactor is ≤2mm.

14. The continuous preparation method according to claim 11, characterized in that, The stirring rate of the batch reactor is ≥300 rpm.

15. The continuous preparation method according to claim 11, characterized in that, The stirring rate of the batch reactor is ≥500 rpm.

16. The continuous preparation method according to claim 11, characterized in that, The maximum outer diameter of the agitator in the reactor has a gap of ≤2mm between it and the reactor wall.

17. The continuous preparation method according to claim 1, characterized in that, The temperature of the reaction in step (d) is ≤40℃ and the reaction time is 10~40min.

18. The continuous preparation method according to claim 1, characterized in that, Step (d) is followed by neutralization, washing and drying steps after the reaction.

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