A carbon nanotube acid bubbling purification process

Abstract

The application discloses a carbon nanotube acid bubble purification process and relates to the technical field of carbon nanotube purification. The process comprises the following steps: step S1, raw material pretreatment; step S2, multistage acid bubble purification; step S3, intensified water washing; step S4, drying treatment; and step S5, post-treatment. The complete process chain of raw material pretreatment, multistage acid bubble purification, intensified water washing, drying treatment and post-treatment is arranged, wherein the raw material pretreatment adopts a vacuum suction pump for feeding and combines with a bag dust collector for collecting dust, the multistage acid bubble purification is sequentially performed for primary, secondary and tertiary purification, and reaction conditions are accurately controlled, the intensified water washing starts to use an ultrasonic device to assist pressure filtration water washing, the drying treatment combines with a cyclone separator and a bag dust collector, and the post-treatment comprises screening, multistage magnetic removal and nitrogen filling packaging. Therefore, the problems of large product purity fluctuation and incomplete impurity removal caused by the incoherent process and rough parameter control in each link of the existing process can be solved.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube purification technology, specifically to an acid bubble purification process for carbon nanotubes. Background Technology

[0002] The acid bubble purification process for carbon nanotubes involves treating crude carbon nanotubes with strong acid. By utilizing the oxidation and dissolution effects of the acid, residual metal catalysts, amorphous carbon, and other impurities from the preparation process are removed. At the same time, the surface of the carbon nanotubes is moderately etched to improve their dispersibility and surface activity, ultimately yielding carbon nanotube products with higher purity, more regular structure, and more stable performance.

[0003] In existing technologies, the acid bubble purification process for carbon nanotubes suffers from poor process continuity and coarse parameter control at each stage, resulting in large fluctuations in product purity and incomplete impurity removal, which severely restricts the quality and efficiency of carbon nanotube purification. Therefore, this invention provides an acid bubble purification process for carbon nanotubes. Summary of the Invention

[0004] The purpose of this invention is to provide an acid foam purification process for carbon nanotubes. This invention establishes a complete process chain, including raw material pretreatment, multi-stage acid foam purification, enhanced water washing, drying, and post-treatment. Precise control of parameters at each stage enables refined purification of carbon nanotubes from raw materials to finished products. Simultaneously, a three-stage spray recovery acid mist recovery tower achieves synergistic treatment of acid mist resource utilization and harmlessness. A multi-stage demagnetization device deeply removes magnetic impurities, thereby significantly improving the purity and stability of carbon nanotubes, enhancing the resource recovery rate and environmental compliance rate of acid mist treatment, reducing the magnetic impurity content of the product, and solving the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A carbon nanotube acid bubble purification process includes the following steps:

[0007] Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter.

[0008] Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe.

[0009] Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities.

[0010] Step S4: Drying treatment. The washed wet cake is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter.

[0011] Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%.

[0012] Preferably, the purification in step S2 specifically involves: pumping a mixed acid solution of 40% HF, 30% HCl and 40% HNO3 into the paste material, introducing steam to control the material temperature at 50℃±1℃, using a pulsed steam introduction method with a steam pulse frequency of 6 to 9 times per minute, each pulse lasting 6 to 9 seconds, and stirring the reaction for 8.5 to 9.5 hours. The soluble substance H2SiF6 is generated by the reaction of HF with silicon oxide, while nitric acid is used to oxidize Fe2+ to soluble Fe3+, thus simultaneously removing silicon oxide and iron oxide impurities.

[0013] Preferably, the secondary purification in step S2 is as follows: after primary purification, the sample is washed with water by pressure filtration, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 6.5 to 7.5 hours to dissolve the residual iron oxide.

[0014] Preferably, the three purification steps in step S2 are as follows: after the second purification, the sample is washed with water by pressure filtration, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 4.5 to 5.5 hours to remove trace iron salt impurities.

[0015] Preferably, the volume ratio of the mixed acid solution purified in step S2 is 40%HF:30%HCl:40%HNO3 = (1.2~1.8):(3.5~4.5):(1.2~1.8).

[0016] Preferably, the acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals by calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, thereby realizing the synergistic treatment of acid mist resource utilization and harmlessness.

[0017] Preferably, the stirring in step S2 adopts an adaptive variable speed mode, which automatically adjusts according to the acid concentration and the reaction progress:

[0018] When a high acid concentration is detected, the stirring speed should be 280–320 r / min;

[0019] When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 180-220 r / min;

[0020] The reaction automatically accelerates to 320-380 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

[0021] Preferably, in step S3, the ultrasonic frequency of the ultrasonic device is 30-80kHz, the power is 150-450W, and segmented ultrasonic is used, with a 1-minute pause every 5 minutes of operation, and the total ultrasonic duration during a single pressure filtration and water washing process is 18-25 minutes.

[0022] Preferably, in step S4, the voltage of the electrostatic adsorption device is 6-9kV, and the electrode plate adopts a honeycomb structure with a pore size of 3-5mm.

[0023] Preferably, the pre-demagnetization unit of the multi-stage demagnetization device in step S5 uses rare-earth permanent magnets with a magnetic field gradient of 100-150 T / m;

[0024] The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled between 4.2 and 77 K, and a temperature difference of ±0.5 K.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. This invention establishes a complete process chain encompassing raw material pretreatment, multi-stage acid foam purification, enhanced water washing, drying, and post-treatment. Raw material pretreatment utilizes a vacuum pump for feeding combined with baghouse dust collection. Multi-stage acid foam purification involves primary, secondary, and tertiary purification with precise control of reaction conditions. Enhanced water washing employs ultrasonic-assisted pressure filtration. Drying combines a cyclone separator and baghouse dust collection. Post-treatment includes sieving, multi-stage demagnetization, and nitrogen-filled packaging. This series of operations achieves refined purification of carbon nanotubes from raw materials to finished products. Compared to existing technologies, this significantly improves the purity stability of carbon nanotubes and reduces batch-to-batch purity variations. Therefore, it solves the problems of large product purity fluctuations and incomplete impurity removal caused by discontinuous processes and coarse parameter control at each stage in existing processes.

[0027] 2. This invention employs a three-stage spray recovery acid mist recovery tower. HCl is purified to 30% using ion exchange resin and then reused for secondary and tertiary purification. HF is converted to calcium fluoride crystals through calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, achieving synergistic treatment of acid mist resource recovery and harmlessness. Compared with existing technologies, this invention significantly improves the resource recovery rate and environmental compliance rate of acid mist treatment by increasing the HCl reuse rate, the HF conversion rate to calcium fluoride, and the NOx removal rate. Therefore, it solves the problems of existing processes that often use a single absorption method for acid mist treatment, resulting in low resource recovery rates, easy exceedance of emission standards causing secondary pollution, and high treatment costs.

[0028] 3. This invention employs a multi-stage demagnetization device comprising a pre-demagnetization unit and a main demagnetization unit. The pre-demagnetization unit utilizes a rare-earth permanent magnet with a magnetic field gradient of 100–150 T / m, while the superconducting coil of the main demagnetization unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled between 4.2 and 77 K with a temperature difference of ±0.5 K. This achieves deep removal of magnetic impurities from carbon nanotubes. Compared to existing technologies, this reduces the magnetic impurity content of the product, thus solving the problem that existing demagnetization processes often use a single magnet, resulting in insufficient magnetic field strength and stability, making it difficult to remove trace amounts of magnetic impurities, which in turn affects the performance of carbon nanotubes during application. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention have been clearly and completely described. 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.

[0030] This embodiment provides a carbon nanotube acid bubble purification process, including the following steps:

[0031] Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter.

[0032] Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe.

[0033] Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities.

[0034] Step S4: Drying treatment. The washed wet cake is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter.

[0035] Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%.

[0036] In some embodiments, the purification in step S2 specifically involves: pumping a mixed acid solution of 40% HF, 30% HCl and 40% HNO3 into the paste material, introducing steam to control the material temperature at 50℃±1℃, using a pulsed steam introduction method with a steam pulse frequency of 6 to 9 times per minute and each pulse lasting 6 to 9 seconds, stirring the reaction for 8.5 to 9.5 hours, generating soluble H2SiF6 through the reaction of HF with silicon oxide, and simultaneously using nitric acid to oxidize Fe2+ to soluble Fe3+, thereby removing silicon oxide and iron oxide impurities simultaneously.

[0037] In some embodiments, the secondary purification in step S2 specifically involves: after primary purification, the sample is washed with water by pressure filtration, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 6.5 to 7.5 hours to dissolve the residual iron oxide.

[0038] In some embodiments, the three-stage purification in step S2 specifically involves: after secondary purification, the sample is washed with water by pressure filtration, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 4.5 to 5.5 hours to remove trace iron salt impurities.

[0039] In some embodiments, the volume ratio of the mixed acid solution purified in step S2 is 40%HF:30%HCl:40%HNO3 = (1.2~1.8):(3.5~4.5):(1.2~1.8).

[0040] In some embodiments, the acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals by calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, thereby realizing the synergistic treatment of acid mist resource utilization and harmlessness.

[0041] In some embodiments, the stirring in step S2 employs an adaptive variable speed mode, automatically adjusting according to the acid concentration and reaction progress:

[0042] When a high acid concentration is detected, the stirring speed should be 280–320 r / min;

[0043] When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 180-220 r / min;

[0044] The reaction automatically accelerates to 320-380 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

[0045] In some embodiments, the ultrasonic frequency of the ultrasonic device in step S3 is 30-80kHz, the power is 150-450W, and segmented ultrasonic is used, with a 1-minute pause every 5 minutes of operation, and the total ultrasonic duration during a single pressure filtration and washing process is 18-25 minutes.

[0046] In some embodiments, the voltage of the electrostatic adsorption device in step S4 is 6-9kV, and the electrode plate adopts a honeycomb structure with a pore size of 3-5mm.

[0047] In some embodiments, the pre-demagnetization unit of the multi-stage demagnetization device in step S5 uses rare-earth permanent magnets with a magnetic field gradient of 100-150T / m.

[0048] The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled between 4.2 and 77 K, and a temperature difference of ±0.5 K.

[0049] In this embodiment, by precisely setting and coordinating the process parameters of each step in the carbon nanotube purification process, the efficient removal of impurities and the stable improvement of product performance are achieved. The operational details and parameter coordination of each step form a complete purification system, ensuring the quality of the final carbon nanotube product.

[0050] Based on the foregoing embodiments, the following sets of experiments were conducted:

[0051] It should be noted that the raw materials used in the following embodiments are all commercially available.

[0052] Example 1: A carbon nanotube acid bubble purification process, comprising the following steps:

[0053] Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter.

[0054] Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe.

[0055] The purification process in step S2 is as follows: a mixed acid solution of 40% HF, 30% HCl and 40% HNO3 is pumped into the paste material, and steam is introduced to control the material temperature at 50℃±1℃. A pulsed steam introduction method is used, with a steam pulse frequency of 6 times per minute and each pulse lasting 6 seconds. The reaction is stirred for 8.5 hours. The soluble substance H2SiF6 is generated by the reaction of HF with silicon oxide. At the same time, nitric acid is used to oxidize Fe2+ to soluble Fe3+, and silicon oxide and iron oxide impurities are removed simultaneously.

[0056] In step S2, the volume ratio of the mixed acid solution purified once is 40%HF:30%HCl:40%HNO3 = 1.2:3.5:1.2.

[0057] The secondary purification in step S2 is as follows: after the first purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃+1℃, and the reaction is stirred for 6.5 hours to dissolve the residual iron oxide.

[0058] The three purification steps in step S2 are as follows: after the second purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃+1℃, and the mixture is stirred for 4.5 hours to remove trace iron salt impurities.

[0059] The acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals through calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, realizing the synergistic treatment of acid mist resource utilization and harmlessness.

[0060] In step S2, the stirring adopts an adaptive variable speed mode, which automatically adjusts according to the acid concentration and the reaction progress:

[0061] When a high acid concentration is detected, the stirring speed is 280 r / min;

[0062] When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 180 r / min;

[0063] The reaction automatically accelerates to 320 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

[0064] Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities.

[0065] In step S3, the ultrasonic device has an ultrasonic frequency of 30kHz and a power of 150W. It also uses segmented ultrasonic technology, pausing for 1 minute every 5 minutes of operation. The total ultrasonic duration during a single pressure filtration and water washing process is 18 minutes.

[0066] Step S4: Drying treatment. The washed wet cake is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter.

[0067] In step S4, the voltage of the electrostatic adsorption device is 6kV, and the electrode plate adopts a honeycomb structure with a pore size of 3mm.

[0068] Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%.

[0069] In step S5, the pre-demagnetization unit of the multi-stage demagnetization device uses rare-earth permanent magnets with a magnetic field gradient of 100T / m.

[0070] The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled at 4.2K and a temperature difference of ±0.5K.

[0071] Example 2: A carbon nanotube acid bubble purification process, comprising the following steps:

[0072] Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter.

[0073] Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe.

[0074] The purification process in step S2 specifically involves pumping a mixed acid solution of 40% HF, 30% HCl, and 40% HNO3 into the paste-like material, introducing steam to maintain the material temperature at 50°C, using a pulsed steam introduction method with a steam pulse frequency of 7 times per minute and each pulse lasting 7 seconds, stirring and reacting for 9 hours, generating soluble H2SiF6 through the reaction of HF with silica, and simultaneously using nitric acid to oxidize Fe2+ to soluble Fe3+, thus removing silica and iron oxide impurities at the same time.

[0075] In step S2, the volume ratio of the mixed acid solution purified once is 40%HF:30%HCl:40%HNO3=1.5:4:1.5.

[0076] The secondary purification in step S2 is as follows: after the first purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃, and the reaction is stirred for 7 hours to dissolve the residual iron oxide.

[0077] The three purification steps in step S2 are as follows: after the second purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃, and the mixture is stirred for 5 hours to remove trace iron salt impurities.

[0078] The acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals through calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, realizing the synergistic treatment of acid mist resource utilization and harmlessness.

[0079] In step S2, the stirring adopts an adaptive variable speed mode, which automatically adjusts according to the acid concentration and the reaction progress:

[0080] When a high acid concentration is detected, the stirring speed is 300 r / min;

[0081] When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 200 r / min;

[0082] The reaction automatically accelerates to 350 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

[0083] Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities.

[0084] In step S3, the ultrasonic device has an ultrasonic frequency of 50kHz and a power of 300W. It also uses segmented ultrasonic technology, pausing for 1 minute every 5 minutes of operation. The total ultrasonic duration during a single pressure filtration and water washing process is 22 minutes.

[0085] Step S4: Drying treatment. The wet material cake after washing is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter.

[0086] In step S4, the voltage of the electrostatic adsorption device is 7.5kV, and the electrode plate adopts a honeycomb structure with a pore size of 4mm.

[0087] Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%.

[0088] In step S5, the pre-demagnetization unit of the multi-stage demagnetization device uses rare-earth permanent magnets with a magnetic field gradient of 125T / m.

[0089] The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled at 40K and a temperature difference of ±0.5K.

[0090] Example 3: A carbon nanotube acid bubble purification process, comprising the following steps:

[0091] Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter.

[0092] Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe.

[0093] The purification process in step S2 is as follows: a mixed acid solution of 40% HF, 30% HCl and 40% HNO3 is pumped into the paste material, and steam is introduced to control the material temperature at 50℃±1℃. A pulsed steam introduction method is used, with a steam pulse frequency of 9 times per minute and each pulse lasting 9 seconds. The reaction is stirred for 9.5 hours. The soluble substance H2SiF6 is generated by the reaction of HF with silicon oxide. At the same time, nitric acid is used to oxidize Fe2+ to soluble Fe3+, and silicon oxide and iron oxide impurities are removed simultaneously.

[0094] In step S2, the volume ratio of the mixed acid solution purified once is 40%HF:30%HCl:40%HNO3=1.8:4.5:1.8.

[0095] The secondary purification in step S2 is as follows: after the first purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 7.5 hours to dissolve the residual iron oxide.

[0096] The three purification steps in step S2 are as follows: after the second purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the mixture is stirred for 5.5 hours to remove trace iron salt impurities.

[0097] The acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals through calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, realizing the synergistic treatment of acid mist resource utilization and harmlessness.

[0098] In step S2, the stirring adopts an adaptive variable speed mode, which automatically adjusts according to the acid concentration and the reaction progress:

[0099] When a high acid concentration is detected, the stirring speed is 320 r / min;

[0100] When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 220 r / min;

[0101] The reaction automatically accelerates to 380 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

[0102] Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities.

[0103] In step S3, the ultrasonic device has an ultrasonic frequency of 80kHz and a power of 450W. It also uses segmented ultrasonic technology, pausing for 1 minute every 5 minutes of operation. The total ultrasonic duration during a single pressure filtration and water washing process is 25 minutes.

[0104] Step S4: Drying treatment. The wet material cake after washing is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter.

[0105] In step S4, the voltage of the electrostatic adsorption device is 9kV, and the electrode plate adopts a honeycomb structure with a pore size of 5mm.

[0106] Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%.

[0107] In step S5, the pre-demagnetization unit of the multi-stage demagnetization device uses rare-earth permanent magnets with a magnetic field gradient of 150T / m.

[0108] The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled at 77K and a temperature difference of ±0.5K.

[0109] Comparative Example 1 differs from Example 1 in that: in step S2, the adaptive variable speed stirring mode is not used, and the stirring speed is maintained at 200 r / min throughout the process. The remaining steps are the same as in Example 1.

[0110] Comparative Example 2 differs from Example 1 in that the ultrasonic device is not activated in step S3, and only conventional pressure filtration and water washing are performed. The remaining steps are the same as in Example 1.

[0111] Comparative Example 3 differs from Example 1 in that: in step S5, only the pre-demagnetization unit is used for demagnetization, and the main demagnetization unit is not used; the remaining steps are the same as in Example 1.

[0112] Comparative Example 4 differs from Example 1 in that only one purification is performed in step S2, without secondary or tertiary purification; the remaining steps are the same as in Example 1.

[0113] Performance testing: Performance tests were conducted on the carbon nanotubes treated in Examples 1, 2, 3, Comparative Examples 1, 2, 3, and 4. The test items and corresponding standards are as follows:

[0114] Carbon nanotube purity: The purity was determined using the method specified in GB / T30544.13-2018 "Nanotechnology Terminology Part 13: Carbon Nanotubes". This standard provides clear specifications for the testing principle and operating procedures of carbon nanotube purity.

[0115] Batch-to-batch purity variation: Based on GB / T30544.13-2018, the purity test results of different batches of products using the same process are statistically analyzed to calculate the batch-to-batch variation value.

[0116] Magnetic impurity content: The test method for magnetic material content in GB / T38053-2019 "Nano-grade Carbonyl Iron Powder" was adjusted appropriately based on the characteristics of carbon nanotubes before determination. This standard provides detailed instructions on the detection methods and limits for magnetic impurities.

[0117] HCl reuse rate: Based on the method for determining the concentration of hydrochloric acid in GB / T11199-2006 "High Purity Hydrochloric Acid", the reuse rate is calculated by detecting the amount and concentration of HCl before and after recycling.

[0118] HF conversion rate: The HF content before and after the reaction was determined according to the relevant chemical analysis methods in GB / T620-2011 "Chemical Reagents Hydrofluoric Acid", and then the conversion rate was calculated.

[0119] NOx removal rate: Referring to HJ693-2014 "Determination of Nitrogen Oxides in Exhaust Gas from Stationary Sources by Constant Potential Electrolysis Method", the concentration of NOx in the exhaust gas before and after treatment was detected, and the removal rate was calculated accordingly.

[0120] Soluble salt residue: The extraction and determination methods for soluble salts in GB / T5009.167-2003 "Determination of macroelements in food" were used for testing, combined with the pretreatment requirements for carbon nanotube samples.

[0121] The obtained test data are recorded in Table 1 below:

[0122]

[0123] By comparing the data of each embodiment with the comparative example, it can be seen that Embodiments 1, 2 and 3 show better performance in terms of carbon nanotube purity, batch-to-batch stability, removal of magnetic impurities, acid mist recovery and utilization, and control of soluble salt residues.

[0124] Example 1 employs a complete multi-stage acid bubbling purification process. In the first purification stage, three acid solutions are mixed in a specific volume ratio and introduced via pulsed steam, coupled with adaptive variable-speed stirring. The stirring speed is adjusted according to the acid concentration and reaction progress to fully utilize the effects of each acid solution and simultaneously remove silicon oxide and iron oxide impurities. The second and third purification stages further remove residual impurities and improve the purity of carbon nanotubes. The water washing stage is enhanced by using an ultrasonic device, with segmented operation accumulating a specific time to effectively wash away soluble salts. In the multi-stage demagnetization device, the pre-demagnetization unit works in conjunction with the main demagnetization unit to effectively control the content of magnetic impurities. The three-stage spray design of the acid mist recovery tower improves the efficiency of acid mist recovery and utilization, and the purity difference between batches is small, demonstrating process stability.

[0125] Example 2 optimizes the parameters, adjusting the mixed acid volume ratio, steam pulse frequency and duration, reaction time, stirring speed, ultrasonic device parameters, and multi-stage demagnetizing device parameters. The combination of these parameters enhances the synergistic effect of each step, resulting in superior performance in carbon nanotube purity, magnetic impurity removal effect, and acid mist recovery efficiency compared to Example 1. This suggests that the intermediate parameters may be more suitable for this purification process.

[0126] In Example 3, the volume ratio of the mixed acid solution, the frequency and duration of the steam pulse, the reaction time, the stirring speed, the parameters of the ultrasonic device, and the parameters of the multi-stage demagnetizing device were further adjusted. It showed good performance in terms of carbon nanotube purity, control of magnetic impurity content, acid mist recovery efficiency, and batch-to-batch purity stability. Although some performance aspects were slightly inferior to Example 2, it was still superior to the comparative examples, indicating that within this parameter range, the process can still maintain a good purification effect.

[0127] Comparative Example 1 did not adopt an adaptive variable speed stirring mode, maintaining a fixed stirring speed throughout the process. This prevented adjustments based on acid concentration and reaction progress, resulting in uneven mixing of the acid and materials, incomplete reaction, decreased carbon nanotube purity, increased batch-to-batch purity differences, and a certain impact on acid mist recovery efficiency.

[0128] In Comparative Example 2, without using the ultrasonic device, only conventional pressure filtration and water washing were performed, which was insufficient to effectively remove soluble salts, resulting in an increase in the amount of soluble salt residues, which in turn affected the purity and performance of carbon nanotubes.

[0129] The three comparative examples used a pre-demagnetization unit for demagnetization but did not use a main demagnetization unit. The removal of magnetic impurities was not thorough enough, and the content of magnetic impurities increased, which affected the application of carbon nanotubes in fields sensitive to magnetic impurities.

[0130] Comparative Example 4 only underwent one purification, without secondary or tertiary purification, which failed to fully remove residual impurities, resulting in low purity of carbon nanotubes, high levels of soluble salt residue and magnetic impurities, large differences in purity between batches, and low efficiency in acid mist recovery and utilization.

[0131] By comparing and analyzing the relevant data in the table, it can be seen that this invention, through complete process chain design and precise parameter control at each stage, achieves highly efficient purification of carbon nanotubes, demonstrating significant advantages in improving purity, stability, impurity removal efficiency, and resource recycling efficiency. This indicates that the carbon nanotube acid bubbling purification process provided by this invention has a broader market prospect and is more suitable for widespread application.

[0132] In the description of this specification, references to terms such as "an experiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that experiment or example is included in at least one experiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same experiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more experiments or examples.

[0133] The preferred experiments disclosed above are merely illustrative of the invention. These preferred experiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these experiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize it. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A carbon nanotube acid bubble purification process, characterized in that, Includes the following steps: Step S1: Raw material pretreatment. Carbon nanotube powder with a purity of about 85% is sent into a mixing tank through a vacuum pump, while pure water is pumped in and stirred into a paste. The dust generated during the stirring process is collected by a bag filter. Step S2: Multi-stage acid bubble purification, which involves first-stage purification, second-stage purification and third-stage purification in sequence. The HCl, HF and NOx generated during the purification process enter the acid mist recovery tower through the exhaust pipe. The purification process is as follows: a mixed acid solution of 40% HF, 30% HCl and 40% HNO3 is pumped into the paste material, and steam is introduced to control the material temperature at 50℃±1℃. A pulsed steam introduction method is used, with a steam pulse frequency of 6 to 9 times per minute and each pulse lasting 6 to 9 seconds. The reaction is stirred for 8.5 to 9.5 hours. The soluble substance H2SiF6 is generated by the reaction of HF with silicon oxide, and at the same time, nitric acid is used to oxidize Fe2+ to soluble Fe3+, thus removing silicon oxide and iron oxide impurities simultaneously. The acid mist recovery tower adopts a three-stage spray recovery device. HCl is purified to 30% by ion exchange resin and then reused for secondary and tertiary purification. HF is converted into calcium fluoride crystals by calcium salt precipitation. NOx is selectively catalytically reduced to nitrogen gas under the action of a catalyst, realizing the synergistic treatment of acid mist resource utilization and harmlessness. Step S3: Enhanced water washing. After three purifications, pressure filtration and water washing are performed. During the pressure filtration process, the ultrasonic device installed on the filter plate group of the filter press is activated until the pH value of the washing solution is 6.5-7.5, so as to wash away soluble salt impurities. The ultrasonic device has an ultrasonic frequency of 30-80kHz and a power of 150-450W. It adopts segmented ultrasonication, pausing for 1 minute every 5 minutes of operation. The total ultrasonic time during a single pressure filtration and water washing process is 18-25 minutes. Step S4: Drying treatment. The wet material cake after washing is sent to a flash dryer and dried until the moisture content is <5%. The dust generated during drying is collected by a cyclone separator and a bag filter. An electrostatic adsorption device is installed between the cyclone separator and the bag filter. Step S5: Post-processing. The dried carbon nanotubes are conveyed under negative pressure to a screening machine for screening, and then conveyed under negative pressure to a multi-stage demagnetizing device containing a pre-demagnetizing unit and a main demagnetizing unit for demagnetization. Finally, they are packaged with nitrogen, with a nitrogen purity of ≥99.99%. The pre-demagnetization unit of the multi-stage demagnetizing device uses rare-earth permanent magnets with a magnetic field gradient of 100-150T / m. The superconducting coil of the main demagnetizing unit is cooled by a mixture of liquid nitrogen and helium, with the temperature controlled between 4.2 and 77 K, and a temperature difference of ±0.5 K.

2. The carbon nanotube acid bubble purification process according to claim 1, characterized in that, The secondary purification in step S2 is as follows: after the first purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the reaction is stirred for 6.5 to 7.5 hours to dissolve the residual iron oxide.

3. The carbon nanotube acid bubble purification process according to claim 1, characterized in that, The three purification steps in step S2 are as follows: after the second purification, the mixture is filtered and washed with water, pure water is added and stirred, 30% HCl vapor is introduced, the temperature is controlled at 50℃±1℃, and the mixture is stirred for 4.5 to 5.5 hours to remove trace iron salt impurities.

4. The carbon nanotube acid bubble purification process according to claim 1, characterized in that, In step S2, the volume ratio of the mixed acid solution purified once is 40%HF:30%HCl:40%HNO3 = (1.2~1.8):(3.5~4.5):(1.2~1.8).

5. The carbon nanotube acid bubble purification process according to claim 1, characterized in that, In step S2, the stirring adopts an adaptive variable speed mode, which automatically adjusts according to the acid concentration and the reaction progress: When a high acid concentration is detected, the stirring speed should be 280–320 r / min; When the concentration is appropriate in the middle stage of the reaction, the rate is automatically adjusted to 180-220 r / min; The reaction automatically accelerates to 320-380 r / min in the later stages, with a speed adjustment accuracy of ±5 r / min.

6. The carbon nanotube acid bubble purification process according to claim 1, characterized in that, In step S4, the voltage of the electrostatic adsorption device is 6-9kV, and the electrode plate adopts a honeycomb structure with a pore size of 3-5mm.

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