Polyacrylonitrile-based activated carbon fibers and their preparation methods

Abstract

This invention discloses polyacrylonitrile-based activated carbon fibers and their preparation method. The method includes the following steps: S1, wet spinning or dry-jet-wet spinning of polyacrylonitrile spinning solution, controlling the solvent content inside the polyacrylonitrile fiber during the spinning process to obtain polyacrylonitrile precursor fibers containing solvent; S2, supercritical treatment of the polyacrylonitrile precursor fibers under a supercritical carbon dioxide atmosphere to obtain porous polyacrylonitrile fibers; S3, pre-oxidation treatment of the porous polyacrylonitrile fibers to obtain pre-oxidized fibers; S4, carbonization of the pre-oxidized fibers under inert gas protection to obtain polyacrylonitrile-based activated carbon fibers. The method of this invention has advantages such as being environmentally friendly, having controllable reactions, avoiding high temperatures, and avoiding the addition of additional chemical reagents. Activated carbon fibers with large surface areas and abundant pores can be obtained using this method.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber surface modification technology, specifically to polyacrylonitrile-based activated carbon fibers and their preparation methods. Background Technology

[0002] Activated carbon materials mainly include activated carbon, activated carbon fiber felt, and activated carbon fiber. Currently, activated carbon is widely used due to its simple preparation method and low price. The micropore diameter of activated carbon materials is generally less than 2 nm, the hollow pore diameter is generally 2-50 nm, and the macropore diameter is generally greater than 50 nm. In contrast, activated carbon fiber is mainly composed of micropores with a small amount of hollow pores and no macropores. Its pore size is uniformly distributed, generally between 0.8-1 nm, resulting in a very large specific surface area. Compared to activated carbon, its adsorption capacity for organic gases is several times, even tens of times, higher than that of activated carbon in adsorbing gases from air. Therefore, it is mainly used for the recovery of organic solvents and gas-phase separation, offering advantages such as fast adsorption-desorption rates, large processing capacity, and high-quality recovered solvents.

[0003] Activated carbon fibers, due to their large specific surface area, abundant microporous structure, and certain mechanical properties, are widely used in wastewater treatment, air purification, hydrogen storage, solvent recovery, pharmaceuticals, carriers, anti-toxic materials, and hydrometallurgy. Currently, the preparation methods for activated carbon fibers generally include chemical activation and gas activation. Gas activation methods typically include steam activation, CO2 activation, and air activation. Chemical activation methods generally utilize acids, alkalis, or other substances to react with disordered carbon, thereby forming a microporous structure inside and on the surface of the fiber to prepare activated carbon fibers.

[0004] CN106676676A discloses a method for preparing polyacrylonitrile-based activated carbon fibers and their applications. The method involves first subjecting polyacrylonitrile fibers to a three-stage heat treatment to obtain pre-oxidized fibers, then performing low-temperature carbonization at 600℃-900℃ in a nitrogen atmosphere, followed by activation at 700℃-1000℃ for 60-200 minutes to obtain the final activated carbon fibers. This activation method is cumbersome, and the specific surface area of ​​the prepared activated carbon fibers is not high.

[0005] CN103409853A discloses a method for preparing activated carbon fiber materials with energy storage characteristics from polyacrylonitrile-based pre-oxidized fibers and its application. The method involves washing and drying purchased pre-oxidized fibers, followed by activation treatment with a strong alkali. By controlling the water content and heating rate during this process, activated carbon fibers with different degrees of activation are obtained and applied to electrochemical capacitors. This method uses a strong alkali, requiring high-quality equipment and incurring additional costs such as wastewater treatment. The process is relatively complex, and the strong alkali activation process is difficult to control. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of cumbersome preparation processes and low specific surface area of ​​the prepared activated carbon fibers in existing technologies, and to provide polyacrylonitrile-based activated carbon fibers and their preparation method. This invention uses a supercritical carbon dioxide method to prepare polyacrylonitrile-based activated carbon fibers, which has advantages such as being environmentally friendly, having controllable reactions, avoiding high temperatures, and avoiding the addition of additional chemical reagents. The resulting activated carbon fibers have a large specific surface area.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing polyacrylonitrile-based activated carbon fibers, the method comprising the following steps:

[0008] S1. The polyacrylonitrile spinning solution is subjected to wet spinning or dry-jet-wet spinning. During the spinning process, the solvent content inside the polyacrylonitrile fiber is controlled to obtain polyacrylonitrile precursor fiber containing solvent.

[0009] S2. The polyacrylonitrile precursor fiber is subjected to supercritical treatment under a supercritical carbon dioxide atmosphere to obtain porous polyacrylonitrile fiber.

[0010] S3. The porous polyacrylonitrile fiber is subjected to pre-oxidation treatment to obtain pre-oxidized fiber;

[0011] S4. Under inert gas protection, the pre-oxidized fiber is carbonized to obtain polyacrylonitrile-based activated carbon fiber.

[0012] A second aspect of the present invention provides a polyacrylonitrile-based activated carbon fiber prepared by the method described in the first aspect above, wherein the specific surface area of ​​the polyacrylonitrile-based activated carbon fiber is 800-2400 m². 2 / g.

[0013] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0014] 1) The method for preparing polyacrylonitrile-based activated carbon fibers proposed in this invention involves controlling the solvent content within the polyacrylonitrile fibers during wet spinning or dry-jet-wet spinning of the polyacrylonitrile spinning solution to obtain solvent-containing polyacrylonitrile precursor fibers. These fibers are then treated with supercritical carbon dioxide to obtain porous polyacrylonitrile fibers, which are subsequently pre-oxidized and carbonized to obtain polyacrylonitrile-based activated carbon fibers. This preparation method offers advantages such as being environmentally friendly, having controllable reactions, avoiding high temperatures, and avoiding the addition of additional chemical reagents.

[0015] 2) The specific surface area and pore size of the activated carbon fibers prepared by this invention can be controlled by the solvent content within the fibers after spinning, resulting in activated carbon fibers with large surfaces and abundant pores. The specific surface area of ​​the obtained activated carbon fibers can reach 800-2400 m². 2 / g, with a pore volume of 0.53-0.8mL / g. Detailed Implementation

[0016] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0017] The first aspect of this invention provides a method for preparing polyacrylonitrile-based activated carbon fibers, the method comprising the following steps:

[0018] S1. The polyacrylonitrile spinning solution is subjected to wet spinning or dry-jet-wet spinning. During the spinning process, the solvent content inside the polyacrylonitrile fiber is controlled to obtain polyacrylonitrile precursor fiber containing solvent.

[0019] S2. The polyacrylonitrile precursor fiber is subjected to supercritical treatment under a supercritical carbon dioxide atmosphere to obtain porous polyacrylonitrile fiber.

[0020] S3. The porous polyacrylonitrile fiber is subjected to pre-oxidation treatment to obtain pre-oxidized fiber;

[0021] S4. Under inert gas protection, the pre-oxidized fiber is carbonized to obtain polyacrylonitrile-based activated carbon fiber.

[0022] In the process of wet spinning or dry-jet-wet spinning, this invention controls the specific surface area and pore size of activated carbon fibers by controlling the residual solvent in the polyacrylonitrile precursor fiber and combining it with supercritical carbon dioxide treatment, thereby obtaining activated carbon fibers with large surface area and abundant pores.

[0023] In step S1 of the present invention:

[0024] In some embodiments, the solvent content of the polyacrylonitrile precursor fiber is 0.1-2 wt%, preferably 0.2-1.5 wt%, based on the total weight of the polyacrylonitrile precursor fiber.

[0025] In some embodiments, during the wet spinning or dry-jet-wet spinning process, the solvent content inside the polyacrylonitrile fiber is controlled by adjusting the washing time.

[0026] In some preferred embodiments, the washing time is 1-8 minutes.

[0027] In some preferred embodiments, the washing time is determined by controlling the length of the washing tank and the number of washing tanks.

[0028] In some preferred embodiments, the effective immersion length L of the fiber in the washing tank is 1-3m, and the number of washing tanks is 1-6.

[0029] In this invention, the solvent content inside the polyacrylonitrile fiber is controlled by adjusting the washing time, which can be determined by controlling the length and number of washing tanks. The solvent content in the polyacrylonitrile precursor during the wet spinning process will affect the specific surface area, pore size and pore volume of the final activated carbon fiber.

[0030] This invention does not impose any special restrictions on the solvent used in wet spinning or dry-jet-wet spinning, and conventional wet spinning solvents can be used.

[0031] In some embodiments, the solid content of the polyacrylonitrile spinning solution is 11-28 wt%.

[0032] In this invention, the solid content mainly affects the mechanical properties of the fiber, but has little effect on the porosity. The appropriate solid content can be selected according to the required strength of the porous carbon fiber.

[0033] In some preferred embodiments, the solvent of the polyacrylonitrile spinning solution is at least one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAc).

[0034] The conditions for wet spinning include: spinneret orifice diameter of 0.055 mm, spinneret orifice number of 3000-50000, coagulation bath temperature of 0℃-50℃, coagulation bath concentration of 12-60 wt%, and hot water temperature during hot drawing of (Tg+1)℃-(Tg+6)℃, where Tg is the glass transition temperature of the fiber at the hot drawing point;

[0035] The conditions for the dry-jet-wet spinning process include: a spinneret orifice diameter of 0.055 mm, a spinneret orifice count of 3000-50000, an air section length of 5-60 mm, a coagulation bath temperature of 0℃-50℃, a coagulation bath concentration of 12-60 wt%, and a hot water temperature of (Tg+1)℃-(Tg+6)℃ during the hot drawing process, where Tg is the glass transition temperature of the fiber at the hot drawing point.

[0036] In this invention, the solvent of the polyacrylonitrile spinning solution is the same as the solvent of wet spinning or dry-jet-wet spinning, that is, the solvent contained in the polyacrylonitrile precursor fiber.

[0037] In step S2 of the present invention:

[0038] In some embodiments, the supercritical treatment is performed at a temperature of 50°C-140°C, a pressure of 8-20 MPa, and a time of 10-50 min.

[0039] In some implementations, air is purged 2-5 times with CO2 prior to the supercritical treatment.

[0040] In some embodiments, after the supercritical treatment, CO2 gas is released to depressurize and the porous polyacrylonitrile fiber is removed, and the depressurization time is 1-3 minutes.

[0041] Specifically, the supercritical reactor is heated to a certain temperature, and then polyacrylonitrile (PAN) precursor fibers containing solvent are placed into the supercritical carbon dioxide reactor. After the air in the reactor is removed by CO2 several times, CO2 is introduced to a certain pressure. After reacting for a period of time, CO2 gas is released to depressurize and the fibers are taken out to obtain porous polyacrylonitrile fibers.

[0042] This invention removes the solvent contained in polyacrylonitrile precursor fibers through supercritical carbon dioxide treatment, thereby forming a porous structure within the fibers.

[0043] In step S3 of the present invention:

[0044] In some embodiments, the pre-oxidation treatment includes: performing the pre-oxidation in an air atmosphere at a temperature range of 210°C-280°C in four temperature zones, with the temperature gradient increasing in the four zones, and each zone pre-oxidizing for 10-20 minutes.

[0045] In some preferred embodiments, the temperature of the first temperature zone is 210℃-220℃, and the time is 10-20 min; the temperature of the second temperature zone is 230℃-240℃, and the time is 10-20 min; the temperature of the third temperature zone is 250℃-260℃, and the time is 10-20 min; and the temperature of the fourth temperature zone is 270℃-280℃, and the time is 10-20 min.

[0046] In this invention, the atmosphere for the pre-oxidation treatment is air, and all four stages are carried out in air, with the oxygen content being the same as that of air oxygen.

[0047] More preferably, the four temperature zones are 220℃, 235℃, 255℃ and 275℃, respectively, and the total pre-oxidation time is 45 minutes.

[0048] In step S4 of the present invention:

[0049] In some embodiments, the carbonization includes low-temperature carbonization and high-temperature carbonization.

[0050] In some preferred embodiments, the low-temperature carbonization temperature is 300℃-800℃, and the carbonization time is 6-14 min.

[0051] In some preferred embodiments, the high-temperature carbonization temperature is 800℃-1600℃, and the carbonization time is 2-6 minutes.

[0052] In some preferred embodiments, the inert gas is N2 or Ar.

[0053] In some preferred embodiments, the heating rate during the carbonization process is 5-30°C / min.

[0054] Specifically, the carbonization process includes: under the protection of N2 or Ar inert gas, heating from 300℃ to 800℃ at a heating rate of 5-20℃ / min for low-temperature carbonization; and then heating from 800℃ to 1200℃-1600℃ at a heating rate of 20-30℃ / min for high-temperature carbonization.

[0055] A second aspect of the present invention provides a polyacrylonitrile-based activated carbon fiber prepared by the method described in the first aspect above, wherein the specific surface area of ​​the polyacrylonitrile-based activated carbon fiber is 800-2400 m². 2 / g.

[0056] In some embodiments, the pore volume of the polyacrylonitrile-based activated carbon fiber is 0.53-0.8 mL / g.

[0057] During use, you can select the appropriate specific surface area and pore volume as needed.

[0058] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Unless otherwise specified, all reagents involved in the embodiments of this invention are commercially available products and can be purchased through commercial channels.

[0060] In the following examples, the specific surface area and pore volume were determined by nitrogen adsorption / desorption testing of activated carbon fibers using a JW-BK222 fully automated physical adsorption instrument. Before testing, the samples were degassed under vacuum at 250°C for 2-3 hours to remove gases and impurities from the pores. Using nitrogen as the adsorbate, the amount of nitrogen adsorbed on the sample at 77K was measured within a relative pressure range (P / P0) of 0-1, yielding the adsorption / desorption isotherm of the activated carbon fibers. Based on this isotherm, the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The total pore volume (Vtot) was determined using the amount of N2 adsorbed when the relative pressure was close to 1 (P / P0 = 0.99).

[0061] Example 1

[0062] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of a DMSO / polyacrylonitrile spinning solution with a solid content of 21 wt%. The spinneret orifice diameter was 0.055 mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15 ℃ and 20% respectively. The fibers were then passed through 6 water washing tanks, each with a length of 1.3 m and a washing time of 8 min. The hot drawing process was carried out with hot water at 94 ℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 0.2 wt%.

[0063] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 60°C until the pressure is 10MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0064] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0065] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first carbonized at a low temperature in the temperature range of 300-800℃ at a heating rate of 10℃ / min, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high temperature carbonization. After cooling, activated carbon fiber I is obtained.

[0066] The specific surface area of ​​activated carbon fiber I was tested to be 739 m². 2 / g, pore volume is 0.53mL / g.

[0067] Example 2

[0068] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of a DMSO / polyacrylonitrile spinning solution with a solid content of 21%. The spinneret orifice diameter was 0.055 mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20% respectively. The fibers were then passed through three water washing tanks, each with a length of 1 m and a washing time of 3 min. The hot drawing process was carried out with hot water at 94℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.0 wt%.

[0069] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 60°C until the pressure is 10MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0070] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0071] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber II is obtained.

[0072] The specific surface area of ​​activated carbon fiber II was measured to be 1582 m². 2 / g, pore volume is 0.66mL / g.

[0073] Example 3

[0074] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of DMSO / polyacrylonitrile spinning solution with a solid content of 21wt%. The spinneret orifice diameter was 0.055mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20% respectively. The fibers were then passed through a water washing tank with a length of 1m and a washing time of 1min. The hot drawing process was carried out with hot water at 94℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.5wt%.

[0075] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 60°C until the pressure is 10MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0076] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0077] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber III is obtained.

[0078] The specific surface area of ​​activated carbon fiber III was measured to be 2091 m². 2 / g, pore volume is 0.72mL / g.

[0079] Example 4

[0080] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of a DMSO / polyacrylonitrile spinning solution with a solid content of 21 wt%. The spinneret orifice diameter was 0.055 mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15 ℃ and 20% respectively, and then through a water washing tank with a length of 1 m and a washing time of 1 min. The hot drawing process was carried out with hot water at 94 ℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.5 wt%.

[0081] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 90°C until the pressure is 10MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0082] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0083] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber IV is obtained.

[0084] The specific surface area of ​​activated carbon fiber IV was measured to be 2131 m². 2 / g, pore volume is 0.73mL / g.

[0085] Example 5

[0086] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of DMSO / polyacrylonitrile spinning solution with a solid content of 21wt%. The spinneret orifice diameter was 0.055mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20% respectively. The fibers were then passed through a water washing tank with a length of 1m and a washing time of 1min. The hot drawing process was carried out with hot water at 94℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.5wt%.

[0087] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 90°C until the pressure is 14MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0088] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0089] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber V is obtained.

[0090] The specific surface area of ​​activated carbon fiber V was tested to be 2283 m². 2 / g, pore volume is 0.74mL / g.

[0091] Example 6

[0092] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of DMSO / polyacrylonitrile spinning solution with a solid content of 21wt%. The spinneret orifice diameter was 0.055mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20% respectively. The fibers were then passed through a water washing tank with a length of 1m and a washing time of 1min. The hot drawing process was carried out with hot water at 94℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.5wt%.

[0093] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 90°C until the pressure is 20MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0094] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0095] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1200℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber VI is obtained.

[0096] The specific surface area of ​​activated carbon fiber VI was tested to be 2217 m². 2 / g, pore volume is 0.74mL / g.

[0097] Example 7

[0098] (1) Polyacrylonitrile precursor fibers were prepared by wet spinning of a DMSO / polyacrylonitrile spinning solution with a solid content of 21%. The spinneret orifice diameter was 0.055 mm and the number of spinneret orifices was 3000. The polyacrylonitrile fibers were passed through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20% respectively. The fibers were then passed through a water washing tank with a length of 1 m and a washing time of 1 min. The hot drawing process was carried out with hot water at 94℃. The solvent content in the obtained polyacrylonitrile precursor fibers was 1.5 wt%.

[0099] (2) Place the polyacrylonitrile precursor obtained in step (1) into a supercritical carbon dioxide reactor, introduce CO2 into the reactor at 90°C until the pressure is 20MPa, remove the air twice, treat the supercritical process for 20 minutes, and then slowly depressurize for 2 minutes to obtain porous fibers.

[0100] (3) The porous fibers obtained in step (2) are pre-oxidized in an oxidation furnace in four temperature zones, with temperature zones of 220℃, 235℃, 255℃ and 275℃ respectively, and the pre-oxidation time is 45 minutes to prepare pre-oxidized fibers.

[0101] (4) Under N2 atmosphere protection, the pre-oxidized fiber obtained in step (3) is first heated from 300℃ to 800℃ at a heating rate of 10℃ / min for low-temperature carbonization, and then heated from 800℃ to 1600℃ at a heating rate of 30℃ / min for high-temperature carbonization. After cooling, activated carbon fiber VII is obtained.

[0102] The specific surface area of ​​activated carbon fiber VII was tested to be 2295 m². 2 / g, pore volume is 0.75mL / g.

[0103] Comparative Example 1

[0104] Activated carbon fibers were prepared according to the method of Example 1. The only difference from Example 1 was in step (1). During the wet spinning fiber washing process, the solvent inside and on the surface of the fiber was completely removed through 8 washing tanks, and the solvent residue was less than 20 ppm, finally obtaining activated carbon fiber D1.

[0105] Step (1) specifically includes: preparing polyacrylonitrile precursor fibers by wet spinning of a DMSO / polyacrylonitrile spinning solution with a solid content of 21%, wherein the spinneret orifice diameter is 0.055 mm and the number of spinneret orifices is 3000. The polyacrylonitrile fibers pass through a coagulation bath with a coagulation bath temperature and concentration of 15℃ and 20%, respectively, and then through 8 water washing tanks, each with a length of 2 m and a water washing time of 16 min. The hot drawing process is carried out in 94℃ hot water.

[0106] The specific surface area of ​​activated carbon fiber D1 was measured to be 1.3 m². 2 / g, pore volume is 0.01mL / g.

[0107] Comparative Example 2

[0108] Activated carbon fibers were prepared according to the method of Example 1. The only difference from Example 1 is that the polyacrylonitrile precursor obtained in step (1) was not subjected to the supercritical treatment in step (2) but was directly pre-oxidized and carbonized; that is, only steps (1), (3) and (4) of Example 1 were included, and finally activated carbon fiber D2 was obtained.

[0109] The specific surface area of ​​activated carbon fiber D2 was tested to be 67 m². 2 / g, pore volume is 0.01mL / g.

[0110] As can be seen from Examples 1, 2 and 3, under the same conditions, when the number of water tanks in step (1) is 6, 3 and 1 respectively, the specific surface area and pore volume of the obtained activated carbon fiber increase as the number of water tanks decreases; that is, within a certain range of solvent content, the higher the solvent content of polyacrylonitrile precursor, the larger the specific surface area of ​​the obtained activated carbon fiber.

[0111] As can be seen from Examples 3 and 4, under the same conditions, increasing the temperature of supercritical carbon dioxide from 60°C to 90°C increases the specific surface area of ​​the obtained activated carbon fibers.

[0112] As can be seen from Examples 4, 5, and 6, under the same conditions, when the pressures in step (2) are 10 MPa, 14 MPa, and 20 MPa, respectively, the specific surface areas of the obtained activated carbon fibers are 2131 m². 2 / g、2283m 2 / g and 2217m 2 / g, the specific surface area of ​​activated carbon fibers increases and then decreases, indicating that the pressure of supercritical treatment is not necessarily better the higher it is.

[0113] As can be seen from Examples 6 and 7, under the same conditions, the high-temperature carbonization temperatures in step (4) were 1200℃ and 1600℃, respectively, and the specific surface areas of the obtained activated carbon fibers were 2217 m², respectively. 2 / g and 2295m 2 / g indicates that within a certain range, the specific surface area of ​​the obtained activated carbon fibers also increases with the increase of high-temperature carbonization temperature.

[0114] As can be seen from Example 1 and Comparative Examples 1-2, Comparative Example 1, through eight water washing tanks, completely removed the solvent from the interior and surface of the fibers, leaving less than 20 ppm of solvent residue, ultimately resulting in activated carbon fibers with a specific surface area of ​​only 1.3 m². 2 / g, indicating that the solvent content in the polyacrylonitrile precursor fiber has a significant impact on the specific surface area of ​​the final activated carbon fiber during the spinning process. Although Comparative Example 2 contains a small amount of solvent, it undergoes pre-oxidation and carbonization directly without the supercritical treatment in step (2), resulting in activated carbon fibers with a specific surface area of ​​only 67m². 2 / g, which shows that supercritical treatment has a significant impact on the specific surface area of ​​the final activated carbon fibers.

[0115] As can be seen from the above, the specific surface area of ​​activated carbon fibers can be increased by controlling the residual solvent content of polyacrylonitrile precursor fibers, supercritical treatment, pre-oxidation treatment, and carbonization, so that the specific surface area of ​​the obtained activated carbon fibers can reach 800 m². 2 / g or higher, even reaching 2400m 2 / g.

[0116] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile-based activated carbon fibers, characterized in that, The preparation method includes the following steps: S1. The polyacrylonitrile spinning solution is subjected to wet spinning or dry-jet-wet spinning. During the spinning process, the solvent content inside the polyacrylonitrile fiber is controlled to obtain polyacrylonitrile precursor fiber containing solvent. S2. The polyacrylonitrile precursor fiber is subjected to supercritical treatment under a supercritical carbon dioxide atmosphere to obtain porous polyacrylonitrile fiber. S3. The porous polyacrylonitrile fiber is subjected to pre-oxidation treatment to obtain pre-oxidized fiber; S4. Under inert gas protection, the pre-oxidized fiber is carbonized to obtain polyacrylonitrile-based activated carbon fiber. The solvent content of the polyacrylonitrile precursor fiber is 0.1-2 wt% based on its total weight; the supercritical treatment temperature is 50℃-140℃, the pressure is 8-20 MPa, and the time is 10-50 min; the pre-oxidation treatment includes: conducting the treatment in an air atmosphere at a temperature range of 210℃-280℃ in four temperature zones, with a temperature gradient increase in each zone, and pre-oxidation in each zone for 10-20 min; the carbonization includes low-temperature carbonization and high-temperature carbonization, with the low-temperature carbonization temperature being 300℃-800℃ and the carbonization time being 6-14 min; and the high-temperature carbonization temperature being 800℃-1600℃ and the carbonization time being 2-6 min.

2. The preparation method according to claim 1, wherein, In step S1, the solvent content of the polyacrylonitrile precursor fiber is 0.2-1.5 wt% based on the total weight of the polyacrylonitrile precursor fiber.

3. The preparation method according to claim 1 or 2, wherein, In step S1, during the wet spinning or dry-jet-wet spinning process, the solvent content inside the polyacrylonitrile fiber is controlled by adjusting the water washing time.

4. The preparation method according to claim 3, wherein, The washing time is 1-8 minutes; And / or, the washing time is determined by controlling the length of the washing tank and the number of washing tanks; And / or, the effective immersion length of the fiber in the washing tank is 1-3m, and the number of washing tanks is 1-6.

5. The preparation method according to claim 1 or 2, wherein, In step S1, the solid content of the polyacrylonitrile spinning solution is 11-28 wt%. And / or, the solvent of the polyacrylonitrile spinning solution is at least one of N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

6. The preparation method according to claim 1 or 2, wherein, In step S1, The conditions for wet spinning include: spinneret orifice diameter of 0.055 mm, spinneret orifice number of 3000-50000, coagulation bath temperature of 0℃-50℃, coagulation bath concentration of 12-60 wt%, and hot water temperature during hot drawing of (Tg+1)℃-(Tg+6)℃, where Tg is the glass transition temperature of the fiber at the hot drawing point; The conditions for the dry-jet-wet spinning process include: a spinneret orifice diameter of 0.055 mm, a spinneret orifice count of 3000-50000, an air section length of 5-60 mm, a coagulation bath temperature of 0℃-50℃, a coagulation bath concentration of 12-60 wt%, and a hot water temperature of (Tg+1)℃-(Tg+6)℃ during the hot drawing process, where Tg is the glass transition temperature of the fiber at the hot drawing point.

7. The preparation method according to claim 1 or 2, wherein, In step S2, before the supercritical treatment, the air is purged with CO2 2-5 times; And / or, after the supercritical treatment, CO2 gas is released to depressurize and the porous polyacrylonitrile fiber is removed, the depressurization time being 1-3 minutes.

8. The preparation method according to claim 1 or 2, wherein, In step S3, the temperature of the first temperature zone is 210℃-220℃, and the time is 10-20 min; the temperature of the second temperature zone is 230℃-240℃, and the time is 10-20 min; the temperature of the third temperature zone is 250℃-260℃, and the time is 10-20 min; the temperature of the fourth temperature zone is 270℃-280℃, and the time is 10-20 min.

9. The preparation method according to claim 1 or 2, wherein, The inert gas is N2 or Ar; And / or, during the carbonization process, the heating rate is 5-30°C / min; And / or, the carbonization process includes: heating from 300°C to 800°C at a heating rate of 5-20°C / min to perform low-temperature carbonization; Then, the temperature is increased from 800℃ to 1200℃-1600℃ at a heating rate of 20-30℃ / min for high-temperature carbonization.

10. A polyacrylonitrile-based activated carbon fiber prepared by the preparation method according to any one of claims 1-9, characterized in that, The specific surface area of ​​the polyacrylonitrile-based activated carbon fiber is 800-2400 m². 2 / g.

11. The polyacrylonitrile-based activated carbon fiber according to claim 10, wherein, The pore volume of the polyacrylonitrile-based activated carbon fiber is 0.53-0.8 mL / g.