A purification method for raw materials used in the preparation of polyacrylonitrile-based carbon fibers

Abstract

This application relates to a purification method for raw materials used in the preparation of polyacrylonitrile-based carbon fibers. The purification method includes: taking the raw material to be treated and, under preset conditions, sequentially passing it through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin to remove impurities from the raw material; wherein the first ion exchange resin is a first-type macroporous cation exchange resin, the second ion exchange resin is a gel-type anion exchange resin, and the first and second ion exchange resins are used to remove organic impurities from the raw material; the third ion exchange resin is a second-type macroporous cation exchange resin, and the fourth ion exchange resin is a gel-type cation exchange resin, and the third and fourth ion exchange resins are used to remove metal and / or metal compound impurities from the raw material. The method of this application can efficiently remove impurities from the raw material.

Description

Technical Field

[0001] This application relates to the field of carbon fiber production technology, and in particular to a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers. Background Technology

[0002] Polyacrylonitrile-based carbon fiber is carbon fiber made from polyacrylonitrile fiber. Due to its advantages such as high strength, high elastic modulus, and strong heat resistance, it is widely used in wind power generation, high pressure vessels, aerospace, and national defense.

[0003] Polyacrylonitrile-based carbon fibers are typically prepared using the following method: First, acrylonitrile and other small amounts of second and third monomers are polymerized to form polyacrylonitrile resin; then, the polyacrylonitrile resin is dissolved in an organic solvent to form a spinning solution; finally, the spinning solution is spun using a wet or dry-jet wet spinning method, and after being processed through drawing, washing and other processes, polyacrylonitrile-based carbon fibers are obtained.

[0004] Currently, the raw materials used to prepare polyacrylonitrile-based carbon fibers are mainly industrial-grade. These raw materials typically contain trace amounts of organic impurities such as acrolein, oxazole, acetone, propionitrile, polymerization inhibitors, methanethiol, dimethyl sulfide, and dimethyl disulfide. The highly electronegative groups in these organic impurities significantly affect the polymerization process and the properties of the precursor fibers. Furthermore, the presence of metal ions or their compounds such as potassium, sodium, calcium, magnesium, iron, zinc, and nickel in these raw materials can form eutectic or metal carbides with carbon at high temperatures, disrupting the continuity of fiber crystallization. Moreover, these impurities leave porosity defects during high-temperature treatment (pretreatment, carbonization), leading to a decrease in the mechanical properties of the carbon fibers and an increase in their dispersion.

[0005] Therefore, it is essential to purify the raw materials for preparing polyacrylonitrile-based carbon fibers to remove impurities. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers, which can efficiently remove organic impurities, metals, and metal compounds from the raw materials.

[0007] This application provides a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers, including:

[0008] Take the raw material to be treated and, under preset conditions, pass it sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin to remove impurities from the raw material to be treated.

[0009] Wherein, the first ion exchange resin is a macroporous cation exchange resin of the first type, and the second ion exchange resin is a gel-type anion exchange resin. The first ion exchange resin and the second ion exchange resin are used to remove organic impurities from the raw material to be treated.

[0010] The third ion exchange resin is a macroporous cation exchange resin of the second type, and the fourth ion exchange resin is a gel-type cation exchange resin. The third and fourth ion exchange resins are used to remove metal and / or metal compound impurities from the raw material to be treated.

[0011] In some embodiments of this application, the first type of macroporous cation exchange resin includes D001 macroporous styrene-based strong acid cation exchange resin, which is used to remove organic impurities, including oxazole, from the raw material to be treated.

[0012] In some embodiments of this application, the second ion-gel type anion exchange resin includes D201 gel type styrene-based strong base anion exchange resin, which is used to remove organic impurities including acrolein, acetone, methanethiol, propionitrile, dimethyl sulfide, and dimethyl disulfide from the raw material to be treated.

[0013] In some embodiments of this application, the macroporous cation exchange resin of the second type includes HD-8 macroporous strong acid cation exchange resin.

[0014] In some embodiments of this application, the macroporous cation exchange resin of the second type includes HD-8 macroporous strong acid cation exchange resin.

[0015] In some embodiments of this application, the gel-type cation exchange resin includes 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin.

[0016] In some embodiments of this application, the step of sequentially passing through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin under preset conditions includes:

[0017] At a temperature of 30–45°C, the raw material to be treated is passed sequentially through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin at a preset volume hourly space velocity, and is kept there for 2–4 hours.

[0018] In some embodiments of this application, the mass-to-volume ratio of the sum of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to the raw material to be treated is (3-5):100.

[0019] In some embodiments of this application, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:(0.8-1.5):(0.8-1.5):(0.8-1.5).

[0020] In some embodiments of this application, the mass ratio of the sum of the first ion exchange resin, the second ion exchange resin, and the third ion exchange resin to the fourth ion exchange resin is (2.85-3.65):1.

[0021] In some embodiments of this application, before the raw material to be processed passes sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin under preset conditions, the purification method further includes:

[0022] The first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin are respectively activated.

[0023] The activation treatment includes: drying and activating the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin under vacuum conditions at 20-70°C for 8-12 hours.

[0024] The technical solution provided in this application can include the following beneficial effects: By fixing the order of ion exchange resins, the raw material to be treated passes through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin in sequence, realizing the process of first adsorbing organic impurities and then adsorbing inorganic impurities, and the process of first macroporous adsorption and then gel adsorption. This can efficiently remove organic impurities and impurities such as metals and metal compounds from the raw material, thereby improving the quality of the precursor fiber, reducing the dispersion of polyacrylonitrile-based carbon fibers, and improving the strength of polyacrylonitrile-based carbon fibers.

[0025] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] Figure 1This is a flowchart illustrating a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers according to an exemplary embodiment.

[0028] Figure 2 This is a flowchart illustrating a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers according to an exemplary embodiment.

[0029] Figure 3 This is a flowchart illustrating a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers according to an exemplary embodiment.

[0030] Figure 4 This is a schematic diagram of the adsorption tower apparatus in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other.

[0032] The raw materials for preparing polyacrylonitrile-based carbon fibers typically include monomers such as acrylonitrile, itaconic acid, and methyl acrylate, as well as organic solvents such as dimethyl sulfoxide. In order to reduce the impact of impurities in the raw materials on fiber properties, the above raw materials need to be purified before polymerization and spinning to improve the uniformity of polyacrylonitrile precursor fibers, reduce the dispersion of polyacrylonitrile-based carbon fibers, and thus improve the overall performance of polyacrylonitrile-based carbon fibers.

[0033] Based on this, this application provides a purification method for the raw materials used to prepare polyacrylonitrile-based carbon fibers. By fixing the order of ion exchange resins, the raw materials to be treated are passed through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin in sequence. This achieves the process of first adsorbing organic impurities and then adsorbing inorganic impurities, as well as the process of first adsorbing macroporous impurities and then adsorbing gel impurities. This can efficiently improve the adsorption efficiency of impurities, thereby reducing the dispersion of carbon fibers and improving the strength and other properties of carbon fibers.

[0034] like Figure 1 As shown in an exemplary embodiment, a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers is provided, comprising:

[0035] S110. Take the raw material to be treated and, under preset conditions, pass it sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin to remove impurities from the raw material to be treated.

[0036] The first ion exchange resin is a macroporous cation exchange resin of the first type, and the second ion exchange resin is a gel-type anion exchange resin. The first and second ion exchange resins are used to remove organic impurities from the raw materials to be treated.

[0037] The third ion exchange resin is a macroporous cation exchange resin of the second type, and the fourth ion exchange resin is a gel-type cation exchange resin. The third and fourth ion exchange resins are used to remove metal and / or metal compound impurities from the raw materials to be treated.

[0038] In this embodiment, by fixing the order of the ion exchange resins, the raw material to be treated is passed through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin in sequence. This achieves the process of first adsorbing organic impurities and then adsorbing inorganic impurities, as well as the process of first adsorbing macroporous impurities and then adsorbing gel impurities. This can effectively improve the adsorption efficiency of impurities, thereby reducing the dispersion of carbon fibers and improving the strength and other properties of carbon fibers.

[0039] In an exemplary embodiment, the first type of macroporous cation exchange resin includes D001 macroporous styrene-based strong acid cation exchange resin, which is used to remove organic impurities, including oxazole, from the raw material to be treated.

[0040] In this embodiment, the D001 macroporous styrene-based strong acid cation exchange resin is a macroporous strong acid cation exchange resin with a polystyrene skeleton, which has a good adsorption effect on organic impurities such as oxazole in the raw materials.

[0041] In an exemplary embodiment, the gel-type anion exchange resin includes D201 gel-type styrene-based strong base anion exchange resin, which is used to remove organic impurities including acrolein, acetone, methanethiol, propionitrile, dimethyl sulfide, and dimethyl disulfide from the raw material to be treated.

[0042] In this embodiment, the D201 gel-type styrene-based strong base anion exchange resin effectively adsorbs organic impurities such as acrolein, acetone, methanethiol, propionitrile, dimethyl sulfide, and dimethyl disulfide from the raw material. By employing a macroporous adsorption followed by gel adsorption method, organic impurities in the raw material can be adsorbed more efficiently, thereby improving the removal efficiency of organic impurities.

[0043] In one exemplary embodiment, the second type of macroporous cation exchange resin includes HD-8 macroporous strong acid cation exchange resin.

[0044] In one exemplary embodiment, the gel-type cation exchange resin includes 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin.

[0045] In this embodiment, the method of first adsorbing macroporous structures and then gel adsorption can more efficiently adsorb metal and metal compound impurities in the raw materials, thereby improving the removal efficiency of metal and metal compound impurities.

[0046] like Figure 2 As shown in an exemplary embodiment, a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers is provided, comprising:

[0047] S210. At a temperature of 30-45°C, the raw material to be treated is passed sequentially through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin at a preset volume hourly space velocity, and is kept there for 2-4 hours.

[0048] Ion exchange resins can achieve better adsorption of impurities at suitable temperatures. If the adsorption temperature is too low, the expected impurity adsorption effect is difficult to achieve; if the adsorption temperature is too high, it may affect the performance and activity of the raw material. In this embodiment, controlling the temperature for impurity adsorption between 30 and 45°C can improve the adsorption efficiency of the ion exchange resin for the raw material, thereby shortening the time required for impurity adsorption.

[0049] Furthermore, the temperature at which the ion exchange resin adsorbs impurities is 35–40°C, and the residence time of the raw materials to be treated is 2–4 hours.

[0050] For example, the temperature at which the ion exchange resin adsorbs impurities is 30°C and the residence time of the raw material to be treated is 2 hours.

[0051] Understandably, the temperature at which the ion exchange resin adsorbs impurities and the residence time of the raw material to be treated can also be other values ​​within the above range. For example, the ion exchange resin adsorbs impurities at a temperature of 35°C and the residence time of the raw material to be treated is 3 hours. Alternatively, the ion exchange resin adsorbs impurities at a temperature of 40°C and the residence time of the raw material to be treated is 4 hours.

[0052] In an exemplary embodiment, the mass-volume ratio of the sum of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to the raw material to be treated is (3-5):100.

[0053] In this embodiment, by controlling the mass-to-volume ratio of the sum of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to the raw material to be treated, the adsorption effect of impurities in the raw material to be treated can be better achieved.

[0054] For example, the mass-volume ratio of the sum of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to the raw material to be treated is 3:100.

[0055] Understandably, the mass-to-volume ratio of the sum of the first, second, third, and fourth ion exchange resins to the raw material to be treated can also be other ratios within the aforementioned range. For example, the mass-to-volume ratio of the sum of the first, second, third, and fourth ion exchange resins to the raw material to be treated can be 3.5:100, 4:100, 4.5:100, or 5:100.

[0056] It should be noted that in the mass-volume ratio of this embodiment, the unit of mass is grams (g) and the unit of volume is milliliters (mL).

[0057] In an exemplary embodiment, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:(0.8-1.5):(0.8-1.5):(0.8-1.5).

[0058] In this embodiment, by limiting the amounts of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to 1:(0.8-1.5):(0.8-1.5):(0.8-1.5), various impurities in different raw materials to be treated can be fully removed, thereby improving the purification effect.

[0059] For example, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:0.8:0.8:0.8.

[0060] Understandably, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin can also be other ratios within the above range. For example, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:1:1:1. Alternatively, the mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:1.5:1.5:1.5.

[0061] In an exemplary embodiment, the mass ratio of the sum of the first ion exchange resin, the second ion exchange resin, and the third ion exchange resin to the fourth ion exchange resin is (2.85-3.65):1.

[0062] In this application, when using a first, second, third, and fourth ion exchange resin to adsorb organic impurities and metal and metal compound impurities in the raw material, the order of each ion exchange resin needs to be fixed to ensure that organic impurities are adsorbed first, followed by inorganic impurities. In this embodiment, by controlling the mass ratio of the sum of the first, second, and third ion exchange resins to the fourth ion exchange resin at (2.85-3.65):1, various impurities in the raw material can be removed as much as possible, and the removal efficiency can be improved.

[0063] Furthermore, the mass ratio of the sum of the first ion exchange resin, the second ion exchange resin, and the third ion exchange resin to the fourth ion exchange resin is (3.00-3.35):1.

[0064] For example, the mass ratio of the sum of the first, second, and third ion exchange resins to the fourth ion exchange resin is 2.85:1. It is understood that the mass ratio of the sum of the first, second, and third ion exchange resins to the fourth ion exchange resin can also be other ratios within the above range. For example, the mass ratio of the sum of the first, second, and third ion exchange resins to the fourth ion exchange resin can be 3.00:1, 3.35:1, or 3.65:1.

[0065] like Figure 3 As shown in an exemplary embodiment, a method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers is provided, comprising:

[0066] S310. The first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin are activated respectively; wherein, the activation treatment includes: drying and activating the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin under vacuum conditions of 20 to 70°C for 8 to 12 hours.

[0067] After a certain period of use or storage, the ability of ion exchange resin to adsorb impurities will decrease. In order to improve the adsorption effect of ion exchange resin on impurities, in this step, the first ion exchange resin, the second ion exchange resin, the third ion exchange resin and the fourth ion exchange resin are dried and activated under vacuum conditions of 20-70°C for 8-12 hours respectively, so as to restore the activation level of the ion exchange resin and improve its adsorption capacity for impurities.

[0068] The activation temperature and time can be adjusted according to the properties of the ion exchange resin. For example, the first, second, third, and fourth ion exchange resins can be dried and activated under vacuum at 30°C for 12 hours. Alternatively, the ion exchange resins can be dried and activated under vacuum at 50°C for 10 hours. Or, the ion exchange resins can be dried and activated under vacuum at 60°C for 8 hours.

[0069] To further prevent impurities from the ion exchange resin from being introduced into the raw material to be treated, thus causing contamination, the ion exchange resin can be pretreated, such as by cleaning, before the activation treatment of the ion exchange process described above.

[0070] For example, the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin are each cleaned to remove impurities from the ion exchange resins.

[0071] For example, taking the pretreatment process of the first ion exchange resin (cation exchange resin) as an example: the first ion exchange resin is placed in the exchange column and backwashed with pure water for 30 minutes to remove impurities; then the first ion exchange resin is treated with a hydrochloric acid solution with a concentration of 4wt% and a volume of 2 to 3 times that of the first ion exchange resin for 1 hour; after washing with water, the first ion exchange resin is treated with a sodium hydroxide solution with a concentration of 4wt% and a volume of 2 to 3 times that of the first ion exchange resin for 1 hour; after washing with water, the first ion exchange resin is treated again with a hydrochloric acid solution with a concentration of 4wt% and a volume of 2 to 3 times that of the first ion exchange resin for 1 hour; after washing with water, the cleaning process of the first ion exchange resin is completed.

[0072] Taking the pretreatment process of the second ion exchange resin (anion exchange resin) as an example: the second ion exchange resin is placed in the exchange column and backwashed with pure water for 30 minutes to remove impurities; then, the second ion exchange resin is treated with a sodium hydroxide solution with a concentration of 4wt% and a volume of 2-3 times that of the second ion exchange resin for 1 hour; after washing with water, the second ion exchange resin is treated with a hydrochloric acid solution with a concentration of 4wt% and a volume of 2-3 times that of the second ion exchange resin for 1 hour; after washing with water, the second ion exchange resin is treated again with a sodium hydroxide solution with a concentration of 4wt% and a volume of 2-3 times that of the second ion exchange resin for 1 hour; after washing with water, the cleaning process of the second ion exchange resin is completed.

[0073] S320. Take the raw material to be treated and, under preset conditions, pass it sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin to remove impurities from the raw material to be treated.

[0074] This step is the same as step S110 in the above embodiments, and will not be described again here.

[0075] To more clearly explain the technical solution of this application, this application provides a specific embodiment of a purification method for preparing polyacrylonitrile-based carbon fiber. The beneficial effects of selecting the above-mentioned range of process parameters will be explained through specific experimental data provided in the specific embodiment.

[0076] Example

[0077] Example 1: A method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers, comprising:

[0078] (1) Preprocessing:

[0079] The D001 macroporous styrene-based strong acid cation exchange resin, the D201 gel-type styrene-based strong base anion exchange resin, the HD-8 macroporous strong acid cation exchange resin, and the 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin were pretreated to clean and remove impurities from the ion exchange resins.

[0080] (2) Activation:

[0081] The pretreated D001 macroporous styrene-based strong acid cation exchange resin, D201 gel-type styrene-based strong base anion exchange resin, HD-8 macroporous strong acid cation exchange resin, and 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin were dried and activated under vacuum at 70°C for 8 hours to restore the activation level of the ion exchange resins.

[0082] (3)Loading:

[0083] like Figure 4As shown, the first, second, third, and fourth adsorption towers are connected in series via pipelines. The first adsorption tower is filled with D001 macroporous styrene-based strong acid cation exchange resin after pretreatment and activation. The second adsorption tower is filled with D201 gel-type styrene-based strong base anion exchange resin after pretreatment and activation, swollen with ethanol solvent. The third adsorption tower is filled with HD-8 macroporous strong acid cation exchange resin after pretreatment and activation. The fourth adsorption tower is filled with 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin after pretreatment and activation, swollen with ethanol solvent. The loading mass of ion exchange resin in each adsorption tower is set according to the volume of the raw material to be treated. For every 100 mL of raw material to be treated, 1 g of D001 macroporous styrene-based strong acid cation exchange resin, 1 g of D201 gel-type styrene-based strong base anion exchange resin, 1 g of HD-8 macroporous strong acid cation exchange resin, and 1 g of 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin are required. The mass-to-volume ratios are as follows: C1 = (First ion exchange resin + Second ion exchange resin + Third ion exchange resin + Fourth ion exchange resin) / Raw material to be treated = 4:100. C2 = First ion exchange resin : Second ion exchange resin : Third ion exchange resin : Fourth ion exchange resin = 1:1:1:1. C3 = (First ion exchange resin + Second ion exchange resin + Third ion exchange resin) / Fourth ion exchange resin = 3:1.

[0084] (4) Remove impurities:

[0085] The operating temperature of each adsorption tower was adjusted to 45℃. The raw material to be treated was pumped into each adsorption tower at a preset volume hourly space velocity using a metering pump. The raw material was then passed sequentially through D001 macroporous styrene-based strong acid cation exchange resin, D201 gel-type styrene-based strong base anion exchange resin, HD-8 macroporous strong acid cation exchange resin, and 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin. The residence time of the raw material in the adsorption tower was maintained at 4 hours to adsorb impurities. The raw material with impurities removed was then sealed and stored for later use.

[0086] After being treated by the above purification method, the raw materials can be freed from most of the organic impurities such as acrolein, oxazole, acetone, propionitrile, polymerization inhibitors, methanethiol, dimethyl sulfide, and dimethyl disulfide, as well as metal ions or their compounds such as potassium, sodium, calcium, magnesium, iron, zinc, and nickel. To verify the effectiveness of impurity removal, the content of remaining impurities in the raw materials can usually be tested. However, the uncertainty of the types of impurities that may be present in the raw materials increases the difficulty of testing the impurity content.

[0087] Studies have shown that impurities in the raw materials used to prepare polyacrylonitrile-based carbon fibers have a significant impact on the strength and dispersion of the resulting carbon fibers. Therefore, in order to more intuitively demonstrate the removal effect of the purification method of this application on the impurities in the raw materials to be treated, this application uses purified raw materials to prepare carbon fibers, and evaluates the removal effect of the purification method on the impurities in the raw materials used to prepare polyacrylonitrile-based carbon fibers by measuring the strength and dispersion of the carbon fibers.

[0088] Polyacrylonitrile-based carbon fibers can be prepared as follows: Acrylonitrile and itaconic acid, after impurity removal, are continuously added to the mixing zone of a tubular static mixer at a molar ratio of 98:2.0. Mixing is carried out at 40°C for 1.5 hours, followed by a heating zone. Once the temperature reaches 56°C, the mixture is transferred to the reaction zone and reacted at a constant temperature of 56°C for 40 minutes. The mixture is then transferred to a fully mixed polymerization reactor, where the reaction temperature is controlled at 58-60°C for 24 hours to obtain the polymer. After polymerization, the polymer is aged, filtered to remove impurities, and then transported to the spinning unit via pipeline. Dry-jet wet spinning is used. The spinning solution is extruded through a metering pump and spinneret, and then enters a coagulation bath, where it is drawn to obtain coagulated filaments. The resulting coagulated filaments are subjected to multi-stage water washing via guide rollers. After washing, the filaments are oiled, dried and densified at 120-160°C, steam-drawn, pre-oxidized, and carbonized at low and high temperatures to obtain carbon fibers.

[0089] Example 2-10

[0090] To verify the effects of the temperature at which the ion exchange resin adsorbs impurities and the residence time of the raw material on the impurity removal efficiency, the purification treatment of the raw material was carried out using the methods described in Examples 2-10. The main difference between Examples 2-10 and Example 1 lies in the temperature at which the ion exchange resin adsorbs impurities and the residence time of the raw material. The process conditions and carbon fiber properties of Examples 1-10 are recorded in Table 1.

[0091] The tensile strength and dispersion (dispersion coefficient) of carbon fiber were determined in accordance with GB / T3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament". The dispersion is the ratio of the standard deviation of the tensile strength to the average value.

[0092] Table 1. Process conditions and carbon fiber performance test results for Examples 1-10

[0093]

[0094] As can be seen from the data in Table 1, the carbon fibers prepared from the raw materials treated by the methods of Examples 1-10 all have a dispersion of less than 5%, and the strength of the carbon fibers is all above 6000 MPa. This indicates that the method of this application can remove most of the impurities in the raw materials to be treated. When preparing carbon fibers from the purified raw materials, the porosity defects of the carbon fibers can be reduced, which is beneficial to improving the mechanical properties of the carbon fibers and reducing the dispersion of the carbon fibers.

[0095] The data from Examples 1-10 show that the carbon fiber prepared from the raw material treated by the method of Example 4 has a dispersion of 1.7% and a strength of 6328 MPa; the carbon fiber prepared from the raw material treated by the method of Example 5 has a dispersion of 1.8% and a strength of 6342 MPa. This indicates that when the temperature at which the ion exchange resin adsorbs impurities is 40°C and the residence time of the raw material to be treated is 3-4 hours, it has a good removal effect on the impurities in the raw material to be treated.

[0096] Examples 11-18

[0097] To verify the effect of the mass ratio of each ion exchange resin on the removal efficiency of impurities, the raw materials to be treated were purified using the methods described in Examples 11-18. The main difference between Examples 11-18 and Example 4 is the amount and ratio of ion exchange resins used. The amount of ion exchange resin used and the performance of carbon fiber in Examples 11-18 are recorded in Table 2.

[0098] Table 2. Process conditions and carbon fiber performance test results for Examples 11-18

[0099]

[0100] As can be seen from the data in Table 2, compared with Example 4, the strength and dispersion of the carbon fibers prepared from the raw materials treated by the methods of Examples 11-18 changed to varying degrees. This indicates that changes in the mass-volume ratios C1 [(first ion exchange resin + second ion exchange resin + third ion exchange resin + fourth ion exchange resin) / raw material to be treated], C2 (first ion exchange resin: second ion exchange resin: third ion exchange resin: fourth ion exchange resin), and C3 [(first ion exchange resin + second ion exchange resin + third ion exchange resin) / fourth ion exchange resin] affect the removal of impurities from the raw materials.

[0101] Comparative Examples 1-5

[0102] To verify the effect of the order of ion exchange resins (i.e., the adsorption order of impurities in the raw material) on the removal efficiency of impurities, the raw materials were purified using the methods of Comparative Examples 1-5. The main difference between Comparative Examples 1-5 and Example 4 is the different order in which the ion exchange resins were placed in the adsorption tower. The order in which the ion exchange resins were placed in the adsorption tower and the performance of the carbon fiber in Comparative Examples 1-5 are recorded in Table 3.

[0103] Table 3. Placement order of ion exchange resins in the adsorption tower and carbon fiber performance test results.

[0104]

[0105] Based on the data in Table 3, and in conjunction with Example 4 and Comparative Examples 1-5, it can be seen that the different placement order of the ion exchange resin in the adsorption tower has a significant impact on the strength and dispersion of the carbon fibers. This indicates that the adsorption order of the ion exchange resin in the raw material to be treated has a significant impact on the removal effect of the impurities. When the method in Example 4 of this application is used, i.e., adsorbing organic impurities first and then inorganic impurities, and adsorbing macroporous impurities first and then gel adsorption, the method of this application has a better removal effect on the impurities in the raw material to be treated under the same conditions compared with other impurity adsorption methods.

[0106] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0107] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for purifying raw materials for preparing polyacrylonitrile-based carbon fibers, characterized in that, include: Take the raw material to be treated and, under preset conditions, pass it sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin to remove impurities from the raw material to be treated. Wherein, the first ion exchange resin is a macroporous cation exchange resin of the first type, and the second ion exchange resin is a gel-type anion exchange resin. The first ion exchange resin and the second ion exchange resin are used to remove organic impurities from the raw material to be treated. The third ion exchange resin is a macroporous cation exchange resin of the second type, and the fourth ion exchange resin is a gel-type cation exchange resin. The third and fourth ion exchange resins are used to remove metal and / or metal compound impurities from the raw material to be treated. The mass ratio of the sum of the first ion exchange resin, the second ion exchange resin, and the third ion exchange resin to the fourth ion exchange resin is (2.85-3.65):

1.

2. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The first type of macroporous cation exchange resin includes D001 macroporous styrene-based strong acid cation exchange resin, which is used to remove organic impurities, including oxazole, from the raw material to be treated.

3. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The gel-type anion exchange resin includes D201 gel-type styrene-based strong base anion exchange resin, which is used to remove organic impurities, including acrolein, acetone, methanethiol, propionitrile, dimethyl sulfide, and dimethyl disulfide, from the raw material to be treated.

4. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The second type of macroporous cation exchange resin includes HD-8 macroporous strong acid cation exchange resin.

5. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The gel-type cation exchange resin includes 732-H sulfonic acid-based gel-type styrene-based strong acid cation exchange resin.

6. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The process, under preset conditions, sequentially passes through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin, including: At a temperature of 30~45℃, the raw material to be treated is passed sequentially through the first ion exchange resin, the second ion exchange resin, the third ion exchange resin and the fourth ion exchange resin at a preset volume hourly space velocity, and is kept there for 2~4 hours.

7. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The mass-to-volume ratio of the sum of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin to the raw material to be treated is (3-5):

100.

8. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, The mass ratio of the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin is 1:(0.8-1.5):(0.8-1.5):(0.8-1.5).

9. The purification method for the raw materials used in the preparation of polyacrylonitrile-based carbon fibers according to claim 1, characterized in that, Before the raw material to be treated passes sequentially through a first ion exchange resin, a second ion exchange resin, a third ion exchange resin, and a fourth ion exchange resin under preset conditions, the purification method further includes: The first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin are respectively activated. The activation treatment includes drying and activating the first ion exchange resin, the second ion exchange resin, the third ion exchange resin, and the fourth ion exchange resin under vacuum conditions at 20-70°C for 8-12 hours.

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