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CN-121974327-A - Preparation method of biochar based on staged pyrolysis and hetero atom co-doping

CN121974327ACN 121974327 ACN121974327 ACN 121974327ACN-121974327-A

Abstract

The invention discloses a preparation method of biological carbon based on staged pyrolysis and heteroatom codoping, which comprises the following steps of S1, crushing biomass raw materials, S2, carrying out low-temperature carbonization and high-temperature carbonization under inert atmosphere to obtain intermediate biological carbon, S3, mixing the intermediate biological carbon with a nitrogen source and a sulfur source, adding water to carry out hydrothermal reaction, and S4, washing and drying to obtain the heteroatom codoping biological carbon. Stable carbon frameworks and micropores are initially constructed through low-temperature carbonization, and then mesoporous/macroporous holes are formed through high-temperature carbonization and reaming, so that the pore canal sintering or collapse caused by single high temperature is effectively avoided through graded pyrolysis. The formed micropore-mesopore-macropore continuous multistage pore channel structure has the advantages that micropores provide high specific surface area and a large number of adsorption/reaction sites, mesopores serve as channels for rapid transmission of ions and molecules, macropores serve as buffer reservoirs of electrolyte or reactants, and the utilization rate of the specific surface area and the reaction mass transfer efficiency are obviously improved in a synergistic manner.

Inventors

  • ZHANG RAN
  • WANG PENG
  • HE XIANG
  • SHU JINHUA
  • XIONG XIN

Assignees

  • 中冶北方（大连）工程技术有限公司

Dates

Publication Date
20260505
Application Date
20260125

Claims (10)

  1. 1. The preparation method of the biochar based on the staged pyrolysis and the hetero atom co-doping is characterized by comprising the following steps of: S1, crushing a biomass raw material; S2, carrying out low-temperature carbonization and high-temperature carbonization in an inert atmosphere to obtain intermediate biochar; S3, mixing the intermediate biochar with a nitrogen source and a sulfur source, and adding water for hydrothermal reaction; S4, washing and drying to obtain the heteroatom co-doped biochar.
  2. 2. The preparation method of the biochar based on the staged pyrolysis and the hetero atom co-doping is characterized in that the low-temperature carbonization temperature is 300-450 ℃, the heating rate is 8-12 ℃ per minute, the heat preservation time is 2-4 hours, the high-temperature carbonization temperature is 600-800 ℃, the heating rate is 8-12 ℃ per minute, and the heat preservation time is 4-5 hours.
  3. 3. The method for preparing biochar based on staged pyrolysis and hetero atom co-doping according to claim 1, wherein the biomass raw material comprises at least one of walnut shells, rice husks, corncobs and crop straws, and sieving is needed to control particle size uniformity after crushing.
  4. 4. The method for preparing the biochar based on staged pyrolysis and heteroatom co-doping according to claim 1, wherein the inert atmosphere is nitrogen or argon, the airflow rate is controlled to be 50-200 mL/min, and the mass ratio of biomass to water is 1:2-5.
  5. 5. The method for preparing the biochar based on staged pyrolysis and heteroatom codoping according to claim 1, wherein the nitrogen source is urea, melamine or dicyandiamide, the sulfur source is one of thiourea or sulfate, and the purity of the nitrogen source and the sulfur source is more than or equal to 99%.
  6. 6. The preparation method of the biochar based on the staged pyrolysis and the hetero atom co-doping, which is characterized in that the hydrothermal reaction is carried out in a high-pressure reaction kettle, the biochar generated after the reaction has a multi-stage pore structure, wherein micropores (pore diameter <2 nm) account for 30% -50%, mesopores (pore diameter 2-50 nm) account for 40% -60%, macropores (pore diameter >50 nm) account for 5% -15%, and the specific surface area is more than or equal to 800m 2 /g.
  7. 7. The biochar prepared by the method for preparing the biochar based on staged pyrolysis and hetero atom co-doping according to any one of claims 1-6 is characterized in that the surface of the biochar contains active sites of graphite nitrogen, pyridine nitrogen and C-S-C structures, the doping total amount of hetero atoms accounts for 2% -8% of the mass of the material, the ash content is less than or equal to 5%, and the fixed carbon content is more than or equal to 80%.
  8. 8. The biochar according to claim 7, wherein the biochar has a specific capacitance of not less than 280F/g at a current density of 1A/g and a capacitance retention of not less than 95% after 5000 cycles when applied as an electrode material in an electrochemical energy storage device.
  9. 9. The biochar according to claim 7, wherein the removal rate of p-nitrophenol is not less than 95% within 30min and the catalytic activity can be maintained within a wide range of pH 3-11 when the biochar is used for catalytic degradation of organic pollutants in environmental remediation.
  10. 10. The biochar according to claim 7, wherein when the biochar is used as a cathode catalyst for a fuel cell, half-wave potential of an oxygen reduction reaction is shifted forward by 0.1 to 0.15v compared to a commercial Pt/C catalyst, and methanol poisoning resistance is improved by at least 3 times.

Description

Preparation method of biochar based on staged pyrolysis and hetero atom co-doping Technical Field The invention relates to the technical field of biochar preparation, in particular to a method for preparing biochar based on fractional pyrolysis and hetero atom co-doping. Background With the continuous growth of global energy demand, the development of efficient and clean energy storage and conversion technologies and environmental remediation materials has become the focus of scientific research and industry development. The biochar, which is a carbon-rich material generated by pyrolysis of biomass resources under anoxic or oxygen-limited conditions, has wide raw material sources (such as agricultural waste and forestry residues), low cost, environmental friendliness, certain pore structure and surface activity, and has great application potential in the fields of super capacitors, fuel cell catalysts, water body organic pollutant adsorption/catalytic degradation and the like. However, the traditional preparation method of the biochar, particularly a single and one-step carbonization process, has remarkable limitations and restricts the high-performance application of the biochar. These limitations are mainly manifested in the following two aspects: 1. The pore structure is difficult to precisely regulate and optimize. The performance of biochar, particularly its specific surface area and pore structure, largely determines its efficiency in specific application scenarios. If a lower carbonization temperature (for example, lower than 500 ℃) is adopted, although partial original structure of biomass can be reserved and a certain initial pore is formed, the carbonization degree is often insufficient, the conductivity of the material is poor, the micropore ratio is too high, the rapid transmission of ions or reactant molecules is not facilitated, and the application of the biomass is limited in occasions where rapid charge and discharge or mass transfer control is required. On the contrary, if high-temperature carbonization (for example, higher than 700 ℃) is directly adopted, the graphitization degree and conductivity of carbon can be improved, but severe precipitation of volatile matters in biomass and excessive shrinkage and sintering of a carbon skeleton are extremely easy to cause a large number of formed micropores, medium Kong Tanta and closure, the finally obtained biochar has limited specific surface area and single pore distribution, and a continuous multi-stage pore channel system which is beneficial to material transmission is difficult to construct. Therefore, how to construct a multi-level pore structure with high specific surface area (providing a large number of active sites) and proper pore size distribution (ensuring efficient mass transfer) in the biochar through ingenious process design is a primary technical problem for improving the comprehensive application performance of the biochar. 2. The chemical activity is insufficient. The biochar material consisting of pure carbon has relatively inert surface chemistry and lacks a high-activity catalytic center. This makes it often not as active as a noble metal-based or metal oxide-based material when used as an electrocatalyst (e.g., an oxygen reduction catalyst in a fuel cell) or as a heterogeneous catalyst in a higher oxidation process. Doping with heteroatoms (such as nitrogen, sulfur, boron, phosphorus, etc.) is an effective strategy for enhancing its chemical activity. The heteroatom doping can change the local electron cloud density of the carbon material and create charge asymmetry, so that the surface chemical property of the carbon material can be effectively regulated, and a large number of defect sites are introduced to serve as active centers of catalytic reaction. Although the heteroatom doping modification technology itself is mature, challenges remain in practical applications. First, if the doping process is separated from the carbonization process (e.g., carbonization followed by doping), it is often difficult for the dopant to enter the interior of the formed, possibly partially graphitized carbon skeleton uniformly and deeply, resulting in active sites being mainly distributed on the surface of the material and low utilization. Secondly, if a method of intense gas phase doping or expensive precursor is adopted, although efficient doping can be realized, the problems of complex process, high cost, secondary pollution or the like can be introduced, and the method is unfavorable for large-scale production and practical application. More importantly, the optimization of the pore structure and the improvement of the surface chemical activity are not independent, but closely related and mutually influenced. A developed pore structure is the physical basis for supporting a large number of active sites, and the manner and degree of surface chemical activity is introduced, which may in turn affect the stability and conductivity of the