Method for continuous high yield production of carbon nanotube fibers

Abstract

The method for continuously preparing carbon nanotube fibers at a high yield breaks through the bottleneck of the inhibition of the catalyst activity by the concentration of the promoter by injecting a catalyst precursor solution and a sulfur-containing promoter solution into a floating catalytic chemical vapor deposition reactor respectively to realize the reconstruction of the spatial distribution and the local concentration dilution in the reactor; the method comprises at least a double-channel injection module, a thermal flow field regulation module, a concentration distribution regulation module, a process parameter optimization module and a yield evaluation function; the method prevents sulfur poisoning by spatially decoupling the injection of the catalyst precursor and the sulfur-containing promoter, combines the thermal flow field regulation to form a uniform cold zone, calculates the sulfur concentration distribution and optimizes the process parameters, and dynamically adjusts based on the closed loop iteration until the yield meets the standard, and finally realizes the production of carbon nanotube fibers at a high yield. The method for continuously preparing carbon nanotube fibers at a high yield solves the problem that the catalyst activity is inhibited due to the excessively high local concentration of the promoter in the prior art, thereby limiting the yield improvement of the carbon nanotube fibers.

Description

Technical Field

[0001] This invention relates to the fields of chemical engineering, materials, and nanomaterial preparation, and particularly to a method for the continuous high-yield preparation of carbon nanotube fibers. Background Technology

[0002] Floating catalytic chemical vapor deposition (FCCVD) is one of the most important industrial technologies for high-throughput production of carbon nanotube fibers (CNTFs). This method involves directly injecting a catalyst precursor, carbon source, and promoter solution into a high-temperature reactor to continuously form carbon nanotube aerogels in the gas phase, which are then collected as fibers. This process offers inherent advantages for continuous and large-scale production.

[0003] In the FCCVD process for preparing carbon nanotube fibers, the introduction of sulfur-containing compounds (such as thiophene) as growth promoters has been widely recognized as crucial for improving yield. Studies have shown that sulfur can effectively lower the activation energy of carbon nanotube synthesis, forming sulfides on the catalyst metal surface, promoting the diffusion of atomic carbon, and accelerating carbon nanotube growth. However, existing research has also found that the yield of carbon nanotubes exhibits a bell-shaped dependence on the amount of sulfur added. When using the traditional single-channel injection method, where all components are pre-mixed and introduced into the reactor through a single injection port, the amount of sulfur added is limited to a narrow threshold (typically 0.5-5 wt.%). Once this threshold is exceeded, excessive sulfur can clog the surface of the catalyst particles, leading to catalyst deactivation and severely restricting the high-yield preparation of carbon nanotube fibers. Simultaneously, it results in uneven carbon source concentration and reaction heat release, accelerating catalyst "poisoning" and deactivation, thus leading to low carbon nanotube yield and uneven fiber thickness.

[0004] Therefore, it is urgent and necessary to develop a method for the continuous high-yield preparation of carbon nanotube fibers that can achieve spatial decoupling between the promoter and the catalyst, construct a uniform thermal field distribution, dynamically optimize process parameters, and overcome the bottleneck of promoter concentration inhibition. Summary of the Invention

[0005] This invention provides a method for continuous high-yield preparation of carbon nanotube fibers, which solves the problem in the prior art where excessively high local concentration of promoter leads to inhibition of catalyst activity, thereby limiting the improvement of carbon nanotube fiber yield.

[0006] To solve the above-mentioned technical problems, the present invention is implemented as follows: This invention provides a method for the continuous high-yield preparation of carbon nanotube fibers. By injecting a catalyst precursor solution and a sulfur-containing promoter solution separately into a floating catalytic chemical vapor deposition reactor, the spatial distribution within the reactor is reconstructed and local concentration is diluted, thereby overcoming the bottleneck of promoter concentration inhibiting catalyst activity. The method includes at least a multi-channel injection module, a thermal flow field control module, a concentration distribution control module, a process parameter optimization module, and a yield evaluation function. The method includes at least the following steps: S1: The catalyst precursor solution and the sulfur-containing promoter solution are injected into the preheating zone of the reactor through the multi-channel injection module to form a spatially decoupled injection mode, so that the local concentration of the sulfur-containing promoter in the reactor is lower than the threshold concentration that causes poisoning of the catalyst active sites. S2: Input the injection parameters of the multi-channel injection module into the heat flow field control module, and control the temperature field distribution of the reactor through the heat flow field control module to form a uniform cold zone with a temperature gradient of less than 150°C in the injection port area. S3: Input the sulfur-iron ratio and catalyst precursor concentration data into the concentration distribution control module to calculate the local concentration distribution of sulfur atoms in the reactor and their contact probability with the active sites of the catalyst. S4: Input the obtained local concentration distribution data of sulfur atoms into the process parameter optimization module, and optimize the injection parameters based on the mapping relationship between sulfur-iron ratio and yield; S5: The yield evaluation function is based on the macroscopic yield of carbon nanotube fibers and the carbon source utilization rate to calculate the evaluation index. If the evaluation index does not reach the preset threshold, the process parameter optimization module dynamically adjusts at least one parameter of the injection rate, injection rate ratio, and carrier gas flow rate of the multi-channel injection module according to the deviation between the evaluation index and the target value, and feeds the adjusted parameter back to S1 to form a closed-loop iteration until the yield evaluation function reaches the target. If the yield evaluation function reaches the target, high-yield carbon nanotube fibers are output.

[0007] Optionally, the multi-channel injection module includes at least two independent injection channels; in the at least two independent injection channels of the multi-channel injection module, the axial distance between the outlets of adjacent injection channels is 30 to 150 mm, and the sum of the injection rates of each channel is equal to the total injection rate under the single-channel injection method; the single-channel injection method refers to the method of injecting the mixed solution using a single channel.

[0008] Optionally, the catalyst precursor solution is an ethanol solution of ferrocene, and the sulfur-containing promoter solution is an ethanol solution of thiophene; the catalyst precursor solution and the sulfur-containing promoter solution are not pre-mixed before entering the reactor, and are injected separately through different injection channels of the multi-channel injection module; the concentration of ferrocene in the catalyst precursor solution is 1.89 wt.% to 3.6 wt.%, and the concentration of thiophene in the sulfur-containing promoter solution is such that the molar ratio of sulfur to iron injected into the reactor is greater than 3.3:1.

[0009] Optionally, the thermal flow field control module includes at least one of a temperature gradient monitoring submodule and a cold zone range calculation submodule; the cold zone range calculation submodule is used to calculate the axial extension length of the uniform cold zone in the injection port area, and the axial extension length is greater than the cold zone length under the single-channel injection method.

[0010] Optionally, the temperature field distribution data in the heat flow field control module can be obtained by any of the following methods: (a) arranging high-temperature resistant temperature measuring devices at intervals along the reactor axis for in-situ monitoring; or (b) obtaining the data through calculation based on the mapping relationship between the reactor heating power, carrier gas flow rate and the preset temperature field model.

[0011] Optionally, the local concentration distribution data of sulfur atoms in the concentration distribution control module is calibrated by combining computational fluid dynamics simulation with reactor outlet tail gas analysis; the calculation formula for the local concentration distribution of sulfur atoms is determined based on the injection rate of sulfur-containing promoter, carrier gas flow rate, temperature distribution inside the reactor, and axial distance.

[0012] Optionally, the process parameter optimization module includes at least one of a sulfur-iron ratio optimization submodule and a precursor concentration optimization submodule; the sulfur-iron ratio optimization submodule is used to control the sulfur-iron ratio within the range described in claim 3; the precursor concentration optimization submodule is used to control the concentration of ferrocene in the catalyst precursor solution within the range described in claim 3.

[0013] Optionally, the yield evaluation function is constructed based on a multi-objective weighted evaluation method, and its evaluation indicators include at least two of the following: macroscopic yield of carbon nanotube fibers, carbon source utilization rate, and fiber resistivity; the macroscopic yield is determined by the fiber mass collected per unit time, the carbon source utilization rate is calculated based on the difference between the amount of carbon source injected at the reactor inlet and the amount of unreacted carbon source at the outlet, and the resistivity is measured using the four-probe method.

[0014] Optionally, the yield of carbon nanotube fibers is increased by more than 114% compared to the single-channel injection method, and the carbon source utilization rate is increased from 3.7% to more than 9.6%.

[0015] Optionally, the resistivity of the carbon nanotube fibers prepared by the method is lower than that of the carbon nanotube fibers prepared by the single-channel injection method, and the macroscopic yield of the carbon nanotube fibers is not less than 190 mg / h, and the spinning rate is not less than 116 m / h.

[0016] This invention addresses the problem of catalyst precursor and sulfur-containing promoter being spatially decoupled during injection by setting up a multi-channel injection module. This dilutes the local concentration of promoter within the reactor from the source, solving the problem of high-concentration promoter poisoning of catalyst active sites. By incorporating a thermal flow field control module, a wider and smaller uniform cold zone with a smaller temperature gradient is constructed in the injection port area, providing a mild thermal environment for the uniform decomposition of the catalyst precursor and preventing excessive iron atom aggregation caused by severe thermal shock. Furthermore, by setting up a concentration distribution control module and a process parameter optimization module, combined with a yield evaluation function to form a closed-loop iteration, precise optimization of key parameters such as the sulfur-to-iron ratio and injection rate is achieved, ensuring that the entire preparation process always operates in an optimal state. This invention solves the problems of limited promoter concentration, easy catalyst deactivation, and difficulty in increasing yield in existing technologies. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for preparing carbon nanotube fibers in continuous high yield according to an embodiment of the present invention; Figure 2 A composition diagram of the method for continuous high-yield preparation of carbon nanotube fibers provided in this embodiment of the invention; Figure 3 This is a fiber characterization diagram comparing the yield under single-channel and multi-channel injection methods in an embodiment of the present invention; Figure 4 This is a simulation comparison diagram of the internal thermal flow field of the reactor under single-channel and multi-channel injection methods in an embodiment of the present invention; Figure 5 This is a comparison diagram of the resistivity of carbon nanotube fibers prepared by single-channel and multi-channel methods in an embodiment of the present invention. Explanation of reference numerals in the attached figures: 10. Multi-channel injection module; 20. Heat flow field control module; 30. Concentration distribution control module; 40. Process parameter optimization module; 50. Yield evaluation function. Detailed Implementation

[0019] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive step are within the scope of protection of the present invention.

[0020] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of the invention. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification do not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0021] See Figures 1 to 5 This invention provides a method for the continuous high-yield preparation of carbon nanotube fibers, which solves the problem of catalyst activity inhibition and yield limitation caused by excessively high local concentration of promoter in the prior art. This method achieves spatial distribution reconstruction and local concentration dilution within the reactor by injecting the catalyst precursor solution and sulfur-containing promoter solution separately into a floating catalytic chemical vapor deposition reactor, thereby overcoming the bottleneck of promoter concentration inhibiting catalyst activity. The method includes at least a multi-channel injection module (10), a thermal flow field control module (20), a concentration distribution control module (30), a process parameter optimization module (40), and a yield evaluation function (50). The method includes at least the following steps: S1: The catalyst precursor solution and the sulfur-containing promoter solution are injected into the preheating zone of the reactor through the multi-channel injection module (10) to form a spatially decoupled injection mode, so that the local concentration of the sulfur-containing promoter in the reactor is lower than the threshold concentration that causes the catalyst active site to be poisoned. S2: Input the injection parameters of the multi-channel injection module (10) into the heat flow field control module (20), and control the temperature field distribution of the reactor through the heat flow field control module (20) so that a uniform cold zone with a temperature gradient of less than 150°C is formed in the injection port area. S3: Input the sulfur-iron ratio and catalyst precursor concentration data into the concentration distribution control module (30) to calculate the local concentration distribution of sulfur atoms in the reactor and their contact probability with the active sites of the catalyst; S4: Input the obtained local concentration distribution data of sulfur atoms into the process parameter optimization module (40) to optimize the injection parameters based on the mapping relationship between sulfur-iron ratio and yield; S5: The yield evaluation function (50) calculates the evaluation index based on the macroscopic yield of carbon nanotube fibers and the carbon source utilization rate; if the evaluation index does not reach the preset threshold, the process parameter optimization module (40) dynamically adjusts at least one parameter of the injection rate, injection rate ratio, and carrier gas flow rate of the multi-channel injection module (10) according to the deviation between the evaluation index and the target value, and feeds back the adjusted parameter to S1 to form a closed loop iteration until the yield evaluation function (50) reaches the target; if the yield evaluation function (50) reaches the target, high-yield carbon nanotube fibers are output.

[0022] In this invention, by injecting the catalyst and promoter through separate channels, the limitation of achieving high concentrations of both simultaneously in the injection port area under traditional single-channel injection is overcome. Taking ferrocene as the catalyst precursor, thiophene as the promoter, and ethanol as the carbon source and solvent as an example, in the reactor preheating zone, multi-channel injection makes the sulfur atoms generated by thiophene decomposition more spatially dispersed, and their local concentration can be controlled below the catalyst poisoning threshold, thus allowing the catalyst to maintain high activity even under conditions of higher overall sulfur-to-iron ratio. At the same time, multi-channel injection changes the heat and mass transfer characteristics of the injection port area. The heat flow field control module (20) monitors the temperature distribution in real time through high-temperature resistant temperature measuring devices (such as type B thermocouples) arranged at intervals along the reactor axis, and adjusts the reactor heating power in conjunction with the PID controller, so that a uniform cold zone with a longer axial extension is formed in the injection port area, and the axial temperature gradient in this area is less than 150°C. This mild thermal environment allows ferrocene to decompose more smoothly, forming uniformly sized and well-dispersed iron nanoparticles, avoiding excessive aggregation caused by severe thermal shock, and providing more active sites for the growth of carbon nanotubes.

[0023] The concentration distribution control module (30) establishes a computational fluid dynamics model based on parameters such as reactor geometry, carrier gas flow rate and composition, multi-channel injection rate, and temperature field distribution. It uses a coupled solution of component transport equations and a turbulence model to simulate the three-dimensional concentration distribution of sulfur atoms within the reactor. Simultaneously, the simulation model is calibrated using gas chromatography-mass spectrometry analysis of the reactor outlet exhaust gas to ensure the accuracy of the concentration distribution data. Furthermore, based on the coupling relationship between sulfur atom concentration distribution and catalyst particle spatial distribution, this module calculates the contact probability between sulfur atoms and catalyst active sites. This probability is defined as the collision frequency of sulfur atoms reaching the surface of iron nanoparticles through diffusion and convection, obtained through the superposition analysis of particle tracking model and sulfur component transport results.

[0024] The process parameter optimization module (40) utilizes the aforementioned concentration distribution and contact probability data, combined with feedback from the yield evaluation function (50), to form a closed-loop control. This module employs a multi-parameter iterative optimization algorithm, prioritizing the adjustment of the multi-channel injection rate ratio to change the local sulfur-iron ratio distribution within the reactor. Once the local sulfur-iron ratio approaches the preset optimization range, the module then coordinates the overall injection rate and carrier gas flow rate. For example, when the yield evaluation index fails to meet the target, the module adjusts the injection rate ratio according to the deviation direction between the evaluation index and the target value, and re-evaluates the updated sulfur atom distribution and contact probability through the concentration distribution control module (30) until the yield evaluation function (50) reaches the preset threshold and operates continuously and stably for more than the set time. This dynamic optimization mechanism enables the entire system to adaptively maintain the optimal yield state, achieving continuous, stable, and high-yield preparation of carbon nanotube fibers.

[0025] Optionally, the multi-channel injection module (10) includes at least two independent injection channels; in the at least two independent injection channels of the multi-channel injection module (10), the axial distance between the outlets of adjacent injection channels is 30 to 150 mm, and the sum of the injection rates of each channel is equal to the total injection rate under the single-channel injection mode; the single-channel injection mode refers to the method of injecting mixed solution using a single channel.

[0026] In this invention, the axial distance between the outlets of adjacent injection channels is controlled within the range of 30–150 mm to achieve effective spatial decoupling. If the distance is too small (less than 30 mm), the two solutions will mix before entering the high-temperature zone, failing to achieve the effect of local concentration dilution, equivalent to single-channel injection. If the distance is too large (greater than 150 mm), the two solutions may not be able to mix sufficiently within the effective reaction area in the reactor, resulting in a weakened synergistic effect between the catalyst and the accelerator, affecting the continuous growth of the fiber. Simultaneously, maintaining the sum of the injection rates of multiple channels equal to the total injection rate of a single channel allows for comparison under the same total material throughput conditions, thereby eliminating the impact of changes in total feed rate on yield and more accurately verifying the technical effectiveness of the multi-channel spatial decoupling strategy itself.

[0027] Optionally, the catalyst precursor solution is an ethanol solution of ferrocene, and the sulfur-containing promoter solution is an ethanol solution of thiophene; the catalyst precursor solution and the sulfur-containing promoter solution are not pre-mixed before entering the reactor, and are injected through different injection channels of the multi-channel injection module (10); the concentration of ferrocene in the catalyst precursor solution is 1.89 wt.% to 3.6 wt.%, and the concentration of thiophene in the sulfur-containing promoter solution makes the molar ratio of sulfur to iron injected into the reactor greater than 3.3:1.

[0028] In this invention, ferrocene serves as the iron source catalyst, decomposing at high temperatures to form iron nanoparticles, which catalyze the growth of carbon nanotubes. Thiophene, as the sulfur source promoter, generates sulfur atoms that lower the activation energy for carbon nanotube growth and accelerate carbon atom diffusion. The core premise of the spatial decoupling strategy is to prevent these two components from pre-mixing before entering the reactor, thus avoiding interaction during the injection stage. The key technological breakthrough of this invention lies in the ability to increase the sulfur-to-iron ratio to greater than 3.3:1 through multi-channel injection. In traditional single-channel processes, when the sulfur-to-iron ratio exceeds 3.3:1, excess sulfur atoms form an iron sulfide passivation layer on the surface of the iron nanoparticles, poisoning active sites and leading to a sharp drop in yield. This invention, through spatial decoupling, dilutes the local sulfur concentration, ensuring that even with an overall sulfur-to-iron ratio greater than 3.3:1, the surface of the iron nanoparticles retains sufficient active sites. Experimental data show that within this sulfur-to-iron ratio range, the yield of the multi-channel injection method is more than 50% higher than that of the single-channel method. Meanwhile, the ferrocene concentration is controlled between 1.89 wt.% and 3.6 wt.%. In the high concentration range (such as 3.6 wt.%), the advantages of the multi-channel strategy are more prominent, and the yield increase can reach 114.7%.

[0029] Optionally, the heat flow field control module (20) includes at least one of a temperature gradient monitoring submodule (21) and a cold zone range calculation submodule (22); the cold zone range calculation submodule (22) is used to calculate the axial extension length of the uniform cold zone in the injection port area, and the axial extension length is greater than the cold zone length under the single-channel injection method.

[0030] In this invention, the temperature gradient monitoring submodule (21) is used to monitor the temperature gradient change in the injection port area in real time, ensuring that it is always maintained within a range of less than 150°C. When an abnormal temperature gradient is detected, it can be corrected by adjusting the heating power or the carrier gas flow rate. The cold zone range calculation submodule (22) calculates the axial extension length of the uniform cold zone (i.e., the area with a temperature gradient of less than 150°C) in the injection port area based on the thermal flow field model. The computational fluid dynamics simulation results show that, under the multi-channel injection method, due to the spatial dispersion of the evaporation heat absorption of multiple solutions, the axial extension length of the formed cold zone is significantly greater than that under the single-channel injection method. This larger cold zone range provides a more sufficient buffer space for the uniform decomposition of the catalyst precursor, slows down the rapid aggregation of iron atoms, and makes the formed iron nanoparticles more uniform in size and better dispersed, thereby retaining more catalytic active sites, which is a key thermodynamic factor for improving yield.

[0031] Optionally, the temperature field distribution data in the heat flow field control module (20) can be obtained by any of the following methods: (a) arranging high-temperature resistant temperature measuring devices at intervals along the reactor axis for in-situ monitoring; or (b) obtaining the data through calculation based on the mapping relationship between the reactor heating power, carrier gas flow rate and the preset temperature field model.

[0032] In this invention, accurately obtaining the temperature field distribution within the reactor is fundamental to implementing heat flow field control. Method (a) employs in-situ monitoring, such as arranging type B or type S thermocouples at intervals along the reactor's axial direction, enabling real-time and accurate measurement of the actual temperature at each point. This method is suitable for experimental or production scenarios requiring high-precision control. Method (b) utilizes a mapping model established between heating power, carrier gas flow rate, and temperature field for calculation. This eliminates the need for drilling holes in the reactor to install sensors, making implementation more convenient and suitable for scenarios with high cost control requirements or where reactor structure is difficult to modify. Both methods provide reliable data input to the heat flow field control module, and those skilled in the art can choose the appropriate method based on actual conditions.

[0033] Optionally, the local concentration distribution data of sulfur atoms in the concentration distribution control module (30) is calibrated by combining computational fluid dynamics simulation with reactor outlet tail gas analysis; the calculation formula of the local concentration distribution of sulfur atoms is determined based on the sulfur-containing promoter injection rate, carrier gas flow rate, reactor temperature distribution and axial distance.

[0034] In this invention, accurately determining the local concentration distribution of sulfur atoms within the reactor is crucial for optimizing injection parameters and preventing catalyst poisoning. This invention employs a combination of CFD simulation and tail gas analysis: First, a CFD model is established based on parameters such as the sulfur-containing promoter injection rate, carrier gas flow rate, reactor temperature distribution, and axial distance to simulate the diffusion and distribution trends of sulfur atoms within the reactor. Then, by performing component analysis on the reactor outlet tail gas (e.g., using gas chromatography-mass spectrometry to detect unreacted sulfur-containing substances), the actual participation of sulfur atoms in the reactor reaction is inferred. Cross-validating and calibrating the simulation results with experimental data yields more accurate data on the local concentration distribution of sulfur atoms, providing a reliable basis for optimizing process parameters.

[0035] Optionally, the process parameter optimization module (40) includes at least one of a sulfur-iron ratio optimization submodule (41) and a precursor concentration optimization submodule (42); the sulfur-iron ratio optimization submodule (41) is used to control the sulfur-iron ratio within the range described in claim 3; the precursor concentration optimization submodule (42) is used to control the concentration of ferrocene in the catalyst precursor solution within the range described in claim 3.

[0036] In this invention, the sulfur-to-iron ratio optimization submodule (41) dynamically adjusts the injection rate of the sulfur-containing promoter solution based on the local sulfur atom concentration distribution data provided by the concentration distribution control module (30), so that the actual sulfur-to-iron ratio participating in the reaction in the reactor is stabilized within a range greater than 3.3:1. The core function of this module is that even if the overall injected sulfur-to-iron ratio is high, it can ensure that the local sulfur concentration does not exceed the catalyst poisoning threshold through spatial decoupling and distribution control. The precursor concentration optimization submodule (42) is used to control the concentration of ferrocene in the catalyst precursor solution within the range of 1.89 wt.% to 3.6 wt.%, and finds the optimal concentration point within this range based on the feedback of the yield evaluation function (50). Experiments show that when the ferrocene concentration increases from 1.89 wt.% to 3.6 wt.%, the yield of the multi-channel injection method shows a continuous upward trend, while the yield of the single-channel method decreases due to catalyst agglomeration. Through the synergistic optimization of these two submodules, the entire preparation process can always operate under the optimal combination of sulfur-to-iron ratio and catalyst concentration, thereby maximizing the yield.

[0037] Optionally, the yield evaluation function (50) is constructed based on a multi-objective weighted evaluation method, and its evaluation index includes at least two of the following: macroscopic yield of carbon nanotube fibers, carbon source utilization rate and fiber resistivity; the macroscopic yield is determined by the fiber mass collected per unit time, the carbon source utilization rate is calculated based on the difference between the amount of carbon source injected at the reactor inlet and the amount of unreacted carbon source at the outlet, and the resistivity is measured using the four-probe method.

[0038] In this invention, the industrial production of carbon nanotube fibers, solely pursuing output may lead to carbon source waste or decreased fiber performance. Therefore, this invention constructs a multi-objective weighted evaluation function that comprehensively considers multiple key indicators. Macroscopic output is a direct indicator of production efficiency, determined by the fiber mass collected per unit time (mg / h); carbon source utilization reflects the economic and environmental benefits of the process, calculated as (total inlet carbon source - amount of unreacted outlet carbon source) / total inlet carbon source × 100%; resistivity is a key parameter characterizing the fiber's conductivity, measured using the four-probe method. This method involves applying current and measuring voltage through four equally spaced probes contacting the fiber surface, thereby accurately calculating the resistivity. By setting reasonable weighting factors (e.g., output weight 0.5, carbon source utilization weight 0.3, resistivity weight 0.2), multiple objectives can be weighted and summed to form a comprehensive evaluation index, guiding closed-loop optimization of process parameters and ensuring that economic benefits and product performance are considered while increasing output.

[0039] Optionally, the yield of carbon nanotube fibers is increased by more than 114% compared to the single-channel injection method, and the carbon source utilization rate is increased from 3.7% to more than 9.6%.

[0040] In this invention, the multi-channel injection strategy brings significant improvements in technical performance. Experimental data shows that, under optimized conditions with a sulfur-to-iron ratio greater than 3.3:1, the macroscopic yield of carbon nanotube fibers using the multi-channel injection method of this invention is increased by more than 50% compared to the traditional single-channel injection method, reaching a maximum of 114.7%. Simultaneously, the carbon source utilization rate also increases from 3.7% in the traditional process to over 9.6%. This improved carbon source utilization rate means that more carbon source is effectively converted into carbon nanotube fibers, reducing the emission of unreacted carbon source in the exhaust gas. This lowers raw material costs and reduces the burden of exhaust gas treatment, demonstrating the economic and environmental advantages of this invention.

[0041] Optionally, the resistivity of carbon nanotube fibers prepared by the method is lower than that of carbon nanotube fibers prepared by single-channel injection. Figure 5 Furthermore, the macroscopic yield of the carbon nanotube fiber is not less than 190 mg / h, and the spinning rate is not less than 116 m / h.

[0042] In this invention, the carbon nanotube fibers prepared by the method of this invention not only have increased yield but also improved electrical conductivity. Measurements using the four-probe method show that the resistivity of fibers prepared by the multi-channel injection method is generally superior to that prepared by the single-channel injection method. This is because multi-channel injection promotes the formation of more uniform and stable catalyst nanoparticles, resulting in a more regular graphite structure in the grown carbon nanotubes, thereby reducing the fiber resistivity. Furthermore, under the optimized process conditions of this invention, the macroscopic yield of carbon nanotube fibers can stably reach no less than 190 mg / h, and the spinning rate can be no less than 116 m / h, indicating that this method has good continuous production capability and process stability, and can meet the needs of large-scale production.

[0043] 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 a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0044] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0045] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

[0046] Example 1 This embodiment takes a dual-channel approach as an example to verify the effect of the multi-channel injection strategy described in this invention on improving the yield of carbon nanotube fibers, and compares it with the traditional single-channel injection method to demonstrate the significant advantages of this invention in overcoming the bottleneck of promoter concentration inhibition and improving yield and carbon source utilization.

[0047] Experimental preparation: A vertical mullite tube reactor with an inner diameter of 80 mm and a length of 1400 mm was used as a floating catalytic chemical vapor deposition reactor. The bottom of the reactor was sealed by a water bath, and the synthesized hollow carbon nanotube socks were transformed into solidified fibers as they passed through the water bath. The total carrier gas flow rate was kept constant at 1400 sccm (800 sccm for hydrogen and 600 sccm for argon), and the reactor temperature was 1200 °C. All experiments were conducted under the same carrier gas flow rate and temperature conditions to eliminate interference from other variables.

[0048] Catalyst solution preparation: Single-channel injection method: Ferrocene, thiophene, deionized water, and anhydrous ethanol were mixed to prepare a catalyst solution. The ferrocene addition was 2 g / 100 g ethanol, and the thiophene addition was 0 g, 1 g, 2 g, 3 g, 5 g, and 10 g, corresponding to sulfur-to-iron ratios of 0:1, 1.1:1, 2.2:1, 3.3:1, 5.5:1, and 11:1, respectively. After the solution was heated to 30°C using an ultrasonic cleaner, it was injected into the top of the reactor through a single injection port at a rate of 8.7 ml / h using a syringe pump.

[0049] Dual-channel injection method: A catalyst precursor solution and a sulfur-containing promoter solution are prepared separately. The catalyst precursor solution is an ethanol solution of ferrocene (containing 1 g deionized water per 100 g ethanol), with the ferrocene concentration adjusted within the range of 0.48 wt.% to 3.6 wt.%. The sulfur-containing promoter solution is an ethanol solution of thiophene, with the thiophene concentration adjusted according to the target sulfur-to-iron ratio. The two solutions are not pre-mixed before entering the reactor and are injected into the high-temperature zone of the reactor through two independent injection channels of the dual-channel injection module. The axial distance between the outlets of the two injection channels is 50 mm, and the sum of the injection rates of the two channels is equal to the total injection rate of the single channel (both 8.7 ml / h). The total injection volume for both channels is 10 ml to eliminate the influence of variations in the total feed rate on the yield.

[0050] Experimental procedure: Single-channel injection experiment: The prepared mixed catalyst solution was injected into the reactor through a single channel. The solution evaporated upon heating at the injection port, forming a localized cold zone. The catalyst precursor and promoter decomposed simultaneously, and iron nanoparticles catalyzed the growth of carbon nanotubes in the presence of sulfur atoms. The formed carbon nanotube fibers were collected, washed with deionized water and ethanol, and then dried in an oven at 80°C for 180 minutes. The yield was obtained by weighing.

[0051] Dual-channel injection experiment: First, step S1 is performed, injecting the catalyst precursor solution and the sulfur-containing promoter solution into the reactor through two independent injection channels of the dual-channel injection module. During injection, the thermal flow field control module monitors and adjusts the temperature field distribution of the reactor in real time according to the injection parameters, ensuring that a uniform cold zone with a temperature gradient of less than 150℃ is formed in the injection port area. The concentration distribution control module calculates the local concentration distribution of sulfur atoms in the reactor based on the sulfur-containing promoter injection rate, carrier gas flow rate, reactor temperature distribution, and axial distance. The process parameter optimization module optimizes the injection parameters based on the local sulfur atom concentration distribution data and the mapping relationship between the sulfur-to-iron ratio and yield, controlling the sulfur-to-iron ratio within a range greater than 3.3:1. The yield evaluation function calculates evaluation indicators based on macroscopic yield and carbon source utilization. If the preset threshold is not reached, the injection rate, injection rate ratio, or carrier gas flow rate is dynamically adjusted to form a closed-loop iteration until the target is achieved.

[0052] Experimental results: (1) Yield comparison: Under the condition that the sulfur-iron ratio is greater than 3.3:1, the yield of carbon nanotube fibers prepared by dual-channel injection is significantly higher than that prepared by single-channel injection. When the sulfur-iron ratio is 3.3:1, the yield of dual-channel injection method is 52.7% higher than that of single-channel injection method; when the sulfur-iron ratio is increased to 5.5:1, the yield of single-channel injection method drops sharply to near zero due to severe catalyst poisoning, while dual-channel injection method can still maintain a high yield level. With a fixed sulfur-to-iron ratio of 3.3:1, as the ferrocene concentration in the catalyst precursor solution increased from 0.48 wt.% to 3.6 wt.%, the yield of the single-channel injection method showed a trend of first increasing and then decreasing, reaching a peak of 190 mg / h at a ferrocene concentration of 1.89 wt.%, and then decreasing to 173 mg / h. In contrast, the yield of the dual-channel injection method showed a continuous upward trend, reaching a peak at a ferrocene concentration of 3.6 wt.%, representing a 114.7% increase compared to the single-channel injection method. Furthermore, the spinning rate of the dual-channel injection method was not less than 116 m / h, and the macroscopic yield was not less than 190 mg / h.

[0053] (2) Carbon source utilization rate: The carbon source utilization rate is defined as the ratio of the number of moles of carbon atoms in the generated carbon nanotube fibers to the number of moles of carbon atoms in the ethanol input catalyst. The actual carbon yield was calculated by subtracting the residual mass of the catalyst through thermogravimetric analysis. The experimental results show that the carbon source utilization rate of the single-channel injection method under optimal conditions is 3.7%, while the carbon source utilization rate of the dual-channel injection method is increased to more than 9.6% under the condition that the sulfur-iron ratio is greater than 3.3:1, indicating that more carbon source is effectively converted into carbon nanotube fibers.

[0054] (3) Characterization of fiber properties: Raman spectroscopy was used to analyze the defect degree of the prepared carbon nanotube fibers. The results showed that the defect degree of fibers prepared by both methods increased with the increase of thiophene concentration, but the defect degree of fibers prepared by the dual-channel injection method was slightly higher than that of fibers prepared by the single-channel injection method. This is because the dual-channel injection method reduces the local concentration of catalyst nanoparticles, provides a larger range of activity, and the catalyst has more active sites. The concentration of carbon atoms provided by carbon source cracking remains unchanged. The active sites compete for carbon source, resulting in rapid growth of carbon nanotubes and generating more growth defects. The resistivity of the fibers was measured by the four-probe method. The results showed that the resistivity of fibers prepared by the dual-channel injection method was generally better than that of fibers prepared by the single-channel injection method. The resistivity showed a U-shaped curve with the increase of thiophene concentration and a linear increasing trend with the increase of precursor concentration. Thermogravimetric analysis showed that the purity of fibers prepared by the two methods was similar, and the impurity content decreased with the increase of thiophene addition.

[0055] (4) Thermal flow field simulation verification: To reveal the mechanism of the dual-channel injection method, computational fluid dynamics was used for numerical simulation. The simulation results show that the single-channel injection method disrupts the axisymmetric distribution of the internal temperature field of the reactor, with a temperature gradient of 291.67℃ in the injection port area; while under the dual-channel injection method, the internal temperature distribution of the reactor is well maintained, with a temperature gradient of only 102.14℃ in the injection port area, forming a more extensive and smaller uniform cold zone. This cold zone effectively regulates the decomposition kinetics of the catalyst precursor and thiophene, slows down the evolution of iron atoms into large-sized clusters, and allows the catalyst to retain more active sites. At the same time, the flow velocity inside the reactor is smaller under the dual-channel injection method, which prolongs the residence time of catalyst particles in the reaction zone and is conducive to the full growth of carbon nanotubes.

[0056] in conclusion: This embodiment verifies the technical effectiveness of the continuous high-yield carbon nanotube fiber preparation method described in this invention. By using a dual-channel injection module to achieve spatial decoupling of the catalyst precursor and sulfur-containing promoter injection, combined with closed-loop control through heat flow field regulation, concentration distribution regulation, and process parameter optimization modules, the bottleneck of promoter concentration inhibiting catalyst activity in traditional single-channel processes is successfully overcome. Experimental results show that, under conditions where the sulfur-to-iron ratio is greater than 3.3:1, the carbon nanotube fiber yield is increased by more than 50% compared to the single-channel injection method, reaching a maximum of 114.7%; the carbon source utilization rate is increased from 3.7% to over 9.6%; the fiber resistivity is optimized (below 100 mΩ·cm); the spinning rate is not less than 116 m / h, and the macroscopic yield is not less than 190 mg / h. This embodiment fully demonstrates the significant progress of this invention in achieving continuous, stable, and high-yield preparation of carbon nanotube fibers.

Claims

1. A method for continuous high-yield preparation of carbon nanotube fibers, characterized in that, By injecting the catalyst precursor solution and the sulfur-containing promoter solution into a floating catalytic chemical vapor deposition reactor, the spatial distribution within the reactor is reconstructed and the local concentration is diluted, thereby overcoming the bottleneck of promoter concentration inhibiting catalyst activity. The method includes at least a multi-channel injection module (10), a thermal flow field control module (20), a concentration distribution control module (30), a process parameter optimization module (40), and a yield evaluation function (50). The method includes at least the following steps: S1: The catalyst precursor solution and the sulfur-containing promoter solution are injected into the preheating zone of the reactor through the multi-channel injection module (10) to form a spatially decoupled injection mode, so that the local concentration of the sulfur-containing promoter in the reactor is lower than the threshold concentration that causes the catalyst active site to be poisoned. S2: Input the injection parameters of the multi-channel injection module (10) into the heat flow field control module (20), and control the temperature field distribution of the reactor through the heat flow field control module (20) so that a uniform cold zone with a temperature gradient of less than 150°C is formed in the injection port area. S3: Input the sulfur-iron ratio and catalyst precursor concentration data into the concentration distribution control module (30) to calculate the local concentration distribution of sulfur atoms in the reactor and their contact probability with the active sites of the catalyst; S4: Input the obtained local concentration distribution data of sulfur atoms into the process parameter optimization module (40) to optimize the injection parameters based on the mapping relationship between sulfur-iron ratio and yield; S5: The yield evaluation function (50) calculates the evaluation index based on the macroscopic yield of carbon nanotube fibers and the carbon source utilization rate; if the evaluation index does not reach the preset threshold, the process parameter optimization module (40) dynamically adjusts at least one parameter of the injection rate, injection rate ratio, and carrier gas flow rate of the multi-channel injection module (10) according to the deviation between the evaluation index and the target value, and feeds back the adjusted parameter to S1 to form a closed loop iteration until the yield evaluation function (50) reaches the target; if the yield evaluation function (50) reaches the target, high-yield carbon nanotube fibers are output.

2. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The multi-channel injection module (10) includes at least two independent injection channels; in the at least two independent injection channels of the multi-channel injection module (10), the axial distance between the outlets of adjacent injection channels is 30 to 150 mm, and the sum of the injection rates of each channel is equal to the total injection rate under the single-channel injection mode; the single-channel injection mode refers to the method of injecting mixed solution using a single channel.

3. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The catalyst precursor solution is an ethanol solution of ferrocene, and the sulfur-containing promoter solution is an ethanol solution of thiophene. The catalyst precursor solution and the sulfur-containing promoter solution are not premixed before entering the reactor, and are injected through different injection channels of the multi-channel injection module (10). The concentration of ferrocene in the catalyst precursor solution is 1.89 wt.% to 3.6 wt.%, and the concentration of thiophene in the sulfur-containing promoter solution makes the molar ratio of sulfur to iron in the reactor greater than 3.3:

1.

4. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The heat flow field control module (20) includes at least one of a temperature gradient monitoring submodule (21) and a cold zone range calculation submodule (22); the cold zone range calculation submodule (22) is used to calculate the axial extension length of the uniform cold zone in the injection port area, and the axial extension length is greater than the cold zone length under the single-channel injection method.

5. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The temperature field distribution data in the heat flow field control module (20) is obtained by any of the following methods: (a) arranging high-temperature resistant temperature measuring devices at intervals along the reactor axis for in-situ monitoring; (b) obtaining the data through calculation based on the mapping relationship between the reactor heating power, carrier gas flow rate and the preset temperature field model.

6. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The local concentration distribution data of sulfur atoms in the concentration distribution control module (30) is calibrated by combining computational fluid dynamics simulation with reactor outlet tail gas analysis; the calculation formula of the local concentration distribution of sulfur atoms is determined based on the injection rate of sulfur-containing promoter, carrier gas flow rate, temperature distribution in the reactor and axial distance.

7. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The process parameter optimization module (40) includes at least one of a sulfur-iron ratio optimization submodule (41) and a precursor concentration optimization submodule (42); the sulfur-iron ratio optimization submodule (41) is used to control the molar ratio of sulfur to iron; the precursor concentration optimization submodule (42) is used to control the concentration of ferrocene in the catalyst precursor solution.

8. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The yield evaluation function (50) is constructed based on a multi-objective weighted evaluation method. Its evaluation indicators include at least two of the following: macroscopic yield of carbon nanotube fibers, carbon source utilization rate, and fiber resistivity. The macroscopic yield is determined by the fiber mass collected per unit time. The carbon source utilization rate is calculated based on the difference between the amount of carbon source injected at the reactor inlet and the amount of unreacted carbon source at the outlet. The resistivity is measured using the four-probe method. The preset threshold range of the evaluation indicators is 2%-10%.

9. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The principle of high-yield carbon nanotube fiber preparation is based on a multi-field matching strategy of "entropy increase", which includes at least the concentration field, temperature field and flow field.

10. The method for continuous high-yield preparation of carbon nanotube fibers according to claim 1, characterized in that, The resistivity of the carbon nanotube fibers prepared by the method is less than 100 mΩ·cm.

Images