Search

CN-121974344-A - Charcoal purification process

CN121974344ACN 121974344 ACN121974344 ACN 121974344ACN-121974344-A

Abstract

The invention discloses a process for purifying biochar, which relates to the technical field of biochar preparation and comprises the steps of screening biochar raw materials, removing impurity particles with the particle size of more than 50 meshes, controlling the water content of the screened raw materials to be less than or equal to 15%, placing the pretreated raw materials into nitric acid solution with the concentration of 0.1-0.5mol/L, stirring and impregnating for 1-3 hours at 50-70 ℃, then washing to be neutral by deionized water, alkali washing, namely immersing the raw materials subjected to acid washing and drying into potassium hydroxide solution with the concentration of 0.2-0.6mol/L, stirring and impregnating for 2-4 hours at 40-60 ℃, washing to be neutral by deionized water again, performing pyrolysis purification, and performing physical screening and chemical activation. Compared with the prior art, the invention has the advantages of optimized hierarchical pore structure, high purity, low ash content, improved process stability, energy conservation, consumption reduction and environmental protection.

Inventors

  • QIN WEI

Assignees

  • 河南培育钻石研究院有限公司

Dates

Publication Date
20260505
Application Date
20260304

Claims (9)

  1. 1. The biochar purifying process is characterized by comprising the following steps of: Step1, raw material pretreatment, namely screening a biochar raw material, removing impurity particles with the particle size of more than 50 meshes, and controlling the water content of the screened raw material to be less than or equal to 15 percent; And 2, acid washing treatment, namely placing the pretreated raw materials into a nitric acid solution with the concentration of 0.1-0.5mol/L, stirring and soaking for 1-3 hours at 50-70 ℃, then washing with deionized water to be neutral, filtering, and drying until the water content is less than or equal to 5%. And step 3, alkali washing treatment, namely immersing the raw materials subjected to acid washing and drying in potassium hydroxide solution with the concentration of 0.2-0.6mol/L, stirring and immersing for 2-4 hours at the temperature of 40-60 ℃, washing with deionized water again to be neutral, filtering, and drying until the water content is less than or equal to 5%. Step 4, pyrolysis purification, namely transferring the raw materials subjected to alkaline washing and drying into a pyrolysis furnace protected by inert gas, heating to 600-800 ℃ at a heating rate of 3-8 ℃ per minute, and pyrolyzing for 1-3 hours to obtain primary purified biochar; Step 5, physical screening, namely carrying out air current classification on the primary purified biochar, and separating out particles with the particle size of 20-200 meshes to obtain secondary purified biochar; And 6, chemical activation, namely mixing the secondary purified biochar with a zinc chloride solution with the mass ratio of 1:2-5, activating for 1-2 hours at 400-600 ℃ in a nitrogen atmosphere, cooling, washing to be neutral by dilute hydrochloric acid, and drying to obtain the high-purity biochar.
  2. 2. The process for purifying biochar according to claim 1, wherein the biochar raw material is an agricultural waste pyrolysis product, including but not limited to one or more of rice hull charcoal, straw charcoal, wood chip charcoal.
  3. 3. The process for purifying biochar according to claim 1, wherein in the step of acid washing, the concentration of the nitric acid solution is 0.3mol/L, the soaking temperature is 60 ℃, the soaking time is 2 hours, and in the step of alkali washing, the concentration of the potassium hydroxide solution is 0.4mol/L, the soaking temperature is 50 ℃, and the soaking time is 3 hours.
  4. 4. The process for purifying biochar according to claim 1, wherein in the step of pyrolysis purification, the heating rate is 5 ℃ per minute, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, and in the step of chemical activation, the mass ratio of zinc chloride solution is 1:3, the activation temperature is 500 ℃, and the activation time is 1.5 hours.
  5. 5. The process for purifying biochar according to claim 1, wherein the physical sieving step is performed by using a multistage air classifier, and the particle size is precisely controlled by adjusting the rotation speed of a classifier wheel, wherein the rotation speed of the classifier wheel is 800-1500 rpm.
  6. 6. The process for purifying biochar according to claim 1, wherein the high-purity biochar has an iodine adsorption value of not less than 800mg/g, a specific surface area of not less than 1200m2/g and an ash content of not more than 3%.
  7. 7. The process for purifying biochar according to claim 1, further comprising a tail gas treatment system, wherein the tail gas generated in the pyrolysis and activation processes is purified and discharged after reaching standards through an activated carbon adsorption tower after the condensable components are recovered through a condenser.
  8. 8. A high-purity biochar prepared by the process according to any one of claims 1 to 7, wherein the biochar is black porous particles, has a developed pore structure, has a main pore size distribution in the range of 2 to 50nm, and has a surface rich in oxygen-containing functional groups.
  9. 9. The application of the high-purity biochar according to claim 8, wherein the biochar is characterized in that the specific capacitance is more than or equal to 250F/g under the current density of 1A/g when being used as an electrode material of a super capacitor, and the maximum adsorption capacity of lead ions is more than or equal to 200mg/g when being used as a heavy metal adsorbent.

Description

Charcoal purification process Technical Field The invention relates to the technical field of biochar preparation, in particular to a biochar purification process. Background The biochar is taken as a carbonaceous material generated by pyrolysis of biomass under the anoxic condition, and has wide application prospect in the fields of soil remediation, water pollution control, energy storage and the like due to the abundant pore structure, high specific surface area and surface functional group characteristics. At present, the raw materials for preparing the biochar mainly comprise agricultural wastes (such as rice hulls, straws and wood chips), forestry wastes, urban organic wastes and the like, wherein the agricultural wastes become main stream raw materials due to wide sources and low cost. The existing charcoal purification process has the following defects: (1) The prior art depends on a single modification means, and is difficult to cooperatively optimize the pore size distribution and the specific surface area. For example, acid washing can increase micropores but easily destroy pore connectivity, and alkali washing can enlarge mesopores but easily cause excessive corrosion. The pore size distribution of the final product is wide and cannot meet the requirement of high-selectivity adsorption on specific molecular sizes. (2) The purity and performance contradiction are outstanding, in the chemical modification process, residual inorganic salt and ash occupy active sites, so that the iodine adsorption value is generally less than 700mg/g, and the specific capacitance is only 150-200F/g when the ionic liquid is used as an electrode material, thereby restricting the application of the ionic liquid in the fields of supercapacitors and high-precision adsorption. (3) The process stability is poor, the pyrolysis temperature rising rate is too fast, local overheating is easy to cause pore collapse, and the pore size distribution is uneven due to the fluctuation of the activation temperature. In addition, the emission of volatile organic compounds exceeds standard due to the deficiency of the tail gas treatment system, and the requirements of environmental protection are not met. (4) The energy consumption and the cost are high, a large amount of activating agents are needed for traditional chemical activation, and the activation is needed for a long time at high temperature, so that the production cost is increased by more than 30%, and the large-scale application is limited. Disclosure of Invention Aiming at the defects of the prior art, the invention provides a four-stage purification process of acid-base synergistic modification, gradient pyrolysis, airflow classification and chemical activation, which prepares high-purity and high-performance biochar by precisely regulating and controlling pore structures, reducing ash content and optimizing surface chemical properties, and meets the application requirements of super capacitor electrode materials and heavy metal adsorbents. Specifically, the technical scheme provided by the invention is that the charcoal purifying process comprises the following steps: Step1, raw material pretreatment, namely screening a biochar raw material, removing impurity particles with the particle size of more than 50 meshes, and controlling the water content of the screened raw material to be less than or equal to 15 percent; And 2, acid washing treatment, namely placing the pretreated raw materials into a nitric acid solution with the concentration of 0.1-0.5mol/L, stirring and soaking for 1-3 hours at 50-70 ℃, then washing with deionized water to be neutral, filtering, and drying until the water content is less than or equal to 5%. And step 3, alkali washing treatment, namely immersing the raw materials subjected to acid washing and drying in potassium hydroxide solution with the concentration of 0.2-0.6mol/L, stirring and immersing for 2-4 hours at the temperature of 40-60 ℃, washing with deionized water again to be neutral, filtering, and drying until the water content is less than or equal to 5%. Step 4, pyrolysis purification, namely transferring the raw materials subjected to alkaline washing and drying into a pyrolysis furnace protected by inert gas, heating to 600-800 ℃ at a heating rate of 3-8 ℃ per minute, and pyrolyzing for 1-3 hours to obtain primary purified biochar; Step 5, physical screening, namely carrying out air current classification on the primary purified biochar, and separating out particles with the particle size of 20-200 meshes to obtain secondary purified biochar; And 6, chemical activation, namely mixing the secondary purified biochar with a zinc chloride solution with the mass ratio of 1:2-5, activating for 1-2 hours at 400-600 ℃ in a nitrogen atmosphere, cooling, washing to be neutral by dilute hydrochloric acid, and drying to obtain the high-purity biochar. Preferably, the biochar feedstock is an agricultural waste pyrolysis product including, but no