A method for preparing coal-based activated carbon

Abstract

This invention relates to the technical field of activated carbon materials, specifically disclosing a method for preparing coal-based activated carbon. This method selects biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water as novel binders. Through steps such as grinding, kneading, carbonization, and activation, coal-based activated carbon with a large specific surface area and large total pore volume is produced. The carbonization and activation time of this coal-based activated carbon is shortened, the reaction temperature is lowered, and the production efficiency is increased.

Description

Technical Field

[0001] This invention relates to the technical field of activated carbon materials, and more specifically, to a method for preparing coal-based activated carbon. Background Technology

[0002] Activated carbon is a carbon-based adsorbent material produced by processing various carbon-containing materials as raw materials. It possesses a large specific surface area, stable physicochemical properties, and excellent adsorption performance, and is currently widely used in electronics, medicine, and defense industries. Based on the raw materials used, activated carbon can be classified into coal-based activated carbon, wood-based activated carbon, and coconut shell activated carbon.

[0003] The conventional production process of coal-based activated carbon includes grinding, kneading and molding, carbonization, and activation. During the kneading and molding process, a binder and coal powder are typically added. Coal tar is often chosen as the binder, but it is an extremely complex polymer compound and a hazardous chemical. Coal tar volatilizes during activated carbon preparation, causing serious air pollution. Simultaneously, coal tar easily produces colloidal substances during carbonization, leading to adhesion between the carbonized materials and clogging of their pore structure. This hinders activation and pore formation, ultimately reducing the specific surface area and total pore volume of the activated carbon. Summary of the Invention

[0004] To address the environmentally unfriendly production process and small specific surface area of ​​coal-based activated carbon, this application provides a method for preparing coal-based activated carbon.

[0005] This application provides a method for preparing coal-based activated carbon, using the following technical solution: A method for preparing coal-based activated carbon includes the following steps: Preparation of binder: Biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water are prepared in a weight ratio of (1.2-3.6):(2.5-4):(0.02-0.1):(0.005-0.01):1. First, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water are mixed in the same weight ratio. Then, biomass straw powder is added and stirred to obtain binder. Grinding; Kneading and molding: The binder and the pulverized coal powder are kneaded and mixed at a weight ratio of (0.78~0.92):1, and then extruded to obtain the pre-carbonized material; Carbonization; the pre-carbonized material is first heated to 300-450℃ under an inert gas atmosphere for primary carbonization, and held for 20-30 minutes. Then, it is heated to 550-600℃ for secondary carbonization, and held for 20-30 minutes to obtain carbonized material. Activation: The carbonized material and gas activator are kept at 700-800℃ for 45-60 minutes for activation. After cooling, the material is acid washed and dried to obtain coal-based activated carbon.

[0006] Furthermore, the weight ratio of the biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water is (2.4-3.0):(3.2-3.6):(0.05-0.06):(0.008-0.01):1.

[0007] Furthermore, the particle size range of the biomass straw powder is 50–100 μm.

[0008] Furthermore, in the grinding step, the particle size range of the coal powder obtained by grinding is 200–500 μm.

[0009] Furthermore, in the kneading and molding step, the weight ratio of binder to coal powder is 0.85:1.

[0010] Furthermore, in the carbonization step, the heating rate of the pre-carbonized material during the first carbonization is 5-6℃ / min.

[0011] Furthermore, in the carbonization step, the heating rate of the pre-carbonized material during the secondary carbonization is 6-10℃ / min.

[0012] Furthermore, in the activation step, the ratio of the activator amount to the weight of the carbonized material is 40-60 (m). 3 / h):1000kg.

[0013] This application has at least the following advantages: First, this application selects biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water as binders. Biomass straw powder itself contains a large number of porous structures, enabling it to absorb substances such as waste molasses, potassium hydroxide, and water. After absorption, the biomass straw powder exhibits a binding effect. The novel binder developed in this application utilizes biomass straw powder and waste molasses as its main components, replacing coal tar. It does not produce toxic gases during carbonization and activation stages, making it safe and environmentally friendly.

[0014] Biomass straw powder contains certain alkali metals, which, together with potassium hydroxide, promote the formation of a rich microporous network structure in the pre-carbonized material during the low-temperature carbonization stage. The viscosity of waste molasses decreases after dilution with potassium hydroxide aqueous solution; simultaneously, the long-chain alkyl quaternary ammonium salt surfactant, an amphiphilic substance, promotes the dispersion of the hydrophilic binder in the hydrophobic coal powder, resulting in uniform kneading of the binder and coal powder. During the carbonization stage, the waste molasses undergoes pyrolysis, generating small-molecule gases that can remove the volatile matter from the biomass straw powder, reducing the likelihood of volatile matter clogging the surface pores of coal-based activated carbon. At the same time, the waste molasses increases the fixed carbon content, and the pyrolysis products are rich in oxygen-containing functional groups, which helps in the later absorption of water vapor, potassium hydroxide, and other polar activators, thereby increasing the mesoporosity and specific surface area of ​​the coal-based activated carbon. With the replenishment of fixed carbon content, a well-developed pore structure forms within the coal-based activated carbon during the activation process. This pore structure is less prone to collapse, resulting in increased strength, specific surface area, and total pore volume, leading to excellent adsorption performance. Furthermore, the combined action of biomass straw powder, potassium hydroxide, and waste molasses assists in the activation of the pre-carbonized material, enhancing the reactivity of the coal powder and lowering the activation temperature. This reduces the original 4-hour carbonization activation time to less than 2 hours, resulting in high production efficiency.

[0015] Secondly, this application optimizes the composition ratio of each material in the binder and adjusts the overall viscosity of the binder. The viscosity and flowability of the binder are balanced, and the binder can fully wet the coal powder particles without affecting their bonding performance. This helps the pre-carbonized material that is pressed into shape to maintain a relatively complete structure during the carbonization and activation stages. Waste molasses, biomass straw powder and potassium hydroxide and other auxiliary activating substances can fully penetrate into the coal powder, and the pore structure of the coal-based activated carbon is well developed.

[0016] Third, this application optimizes the particle size range of biomass straw powder and coal powder, enabling biomass straw powder to enter the gaps in coal powder, which helps the alkali metals contained in the biomass straw powder to assist in activation and pore formation during the later carbonization and activation process.

[0017] Fourth, this application adopts a stepwise carbonization method, which helps to shorten the carbonization time, control the degree of decomposition of waste molasses, and allow some of the thermal decomposition products of waste molasses to enter the coal powder. At the same time, it can maintain the structural strength of the carbonized material, which is helpful for subsequent activation. Detailed Implementation

[0018] Unless otherwise specified, the sources of raw materials involved in the following embodiments and comparative examples are as follows: Coal: The type is Shanxi anthracite; Biomass straw powder: It comes from Hailun City, Heilongjiang Province, and is made from soybean straw. The harvested soybean straw is washed, dried and other processes. The crushing parameters are adjusted according to the required particle size range to obtain biomass straw powder. Waste molasses: recycled from a sugarcane manufacturer in Guangdong, with a viscosity of 4322 Pa·s and a specific gravity of 1.332 g / cm³. 3 ; Long-chain alkyl quaternary ammonium salt surfactant: octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, sourced from Jiangsu Bost Chemical Co., Ltd. Example Example 1

[0019] A method for preparing coal-based activated carbon, comprising the following steps: Preparation of adhesive: Prepare biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water in the following weight ratio: 3.0:3.6:0.06:0.01:1, wherein the particle size of the biomass straw powder is 50-100 μm; add the waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water into a mixer and stir at 100 rpm; then add the biomass straw powder and stir continuously at 100 rpm for 5 minutes to obtain a binder for later use; Grinding: Shanxi anthracite is fed into a grinding mill, the grinding speed and time are set, and after screening, coal powder with a particle size range of 200-500μm is obtained; Kneading and molding: The binder and the ground coal powder are added to the kneader at a weight ratio of 0.85:1 and mixed together. The mixture is then extruded and molded under a pressure of 20MPa to form a cylindrical pre-carbonized material with a diameter of 1cm and a height of 2cm. Carbonization: The pre-carbonized material is put into a rotary carbonization furnace, and nitrogen is introduced. Under the nitrogen atmosphere, the temperature is first raised to 400°C at a heating rate of 5°C / min for primary carbonization, and held for carbonization for 30 min; then the temperature is raised to 600°C at a heating rate of 5°C / min for secondary carbonization, and held for carbonization for 30 min to obtain carbonized material. Activation: Water vapor is used as the activating agent, and is introduced into the carbonized material at a rate of 50m³ per 1000kg of carbonized material. 3 The carbonized material is activated for 45 minutes under the condition of 800℃ in an activation furnace with water vapor per hour. After cooling to room temperature, it is then pickled in a hydrochloric acid pickling tank, followed by water washing and drying to obtain coal-based activated carbon.

[0020] Examples 2-4 A method for preparing coal-based activated carbon differs from Example 1 in that the weight ratios of biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water are different, as detailed below: In Example 2, the weight ratio of biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water was 2.4:3.2:0.05:0.008:1. In Example 3, the weight ratio of biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide, and water was 3.6:4:0.1:0.01:1. In Example 4, the weight ratio of biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water was 1.2:2.5:0.02:0.005:1.

[0021] Examples 5-6 A method for preparing coal-based activated carbon differs from Example 1 in that the weight ratio of binder to coal powder is different, as detailed below: In Example 5, the weight ratio of binder to coal powder was 0.78:1; In Example 6, the weight ratio of binder to coal powder was 0.92:1.

[0022] Examples 7-8 A method for preparing coal-based activated carbon differs from Example 1 in that the particle size ranges of the coal powder and biomass straw powder are different, as detailed below: In Example 7, the particle size range of biomass straw powder is 200–500 μm, and the particle size range of coal powder is 200–500 μm. In Example 8, the particle size range of biomass straw powder is 500–1500 μm, and the particle size range of coal powder is 200–500 μm.

[0023] Examples 9-10 A method for preparing coal-based activated carbon differs from Example 1 in that the temperature and heating rate of the carbonization step are different, as detailed below: In the carbonization step of Example 9, the pre-carbonized material is put into a rotary carbonization furnace, nitrogen is introduced, and under the nitrogen atmosphere, the temperature is first raised to 450°C at a heating rate of 6°C / min for primary carbonization, and held for carbonization for 20 min; then the temperature is raised to 600°C at a heating rate of 10°C / min for secondary carbonization, and held for carbonization for 20 min to obtain carbonized material. In the carbonization step of Example 10, the pre-carbonized material was put into a rotary carbonization furnace, and nitrogen gas was introduced. Under the nitrogen atmosphere, the temperature inside the furnace was first raised to 300°C at a heating rate of 10°C / min for primary carbonization, and held for carbonization for 30 min; then the temperature was raised to 600°C at a heating rate of 15°C / min for secondary carbonization, and held for carbonization for 20 min to obtain carbonized material.

[0024] Examples 11-12 A method for preparing coal-based activated carbon differs from Example 1 in that the parameters of the activation step are different, as detailed below: In the activation step of Example 11, steam was used as the activating agent, and 40m³ of steam was introduced per 1000kg of carbonized material. 3 / h water steam, the temperature in the activation furnace is raised to 700℃, and the carbonized material is activated for 60 minutes under the heat preservation state. After being taken out of the furnace and cooled to room temperature, it is put into the hydrochloric acid pickling tank for pickling, then washed with water, and dried to obtain coal-based activated carbon. In the activation step of Example 12, steam was used as the activating agent, and 60m³ of steam was introduced per 1000kg of carbonized material. 3 The carbonized material is activated for 50 minutes under the condition of 750℃ in an activation furnace with water vapor per hour. After cooling to room temperature, it is then placed in a hydrochloric acid pickling tank for pickling, followed by water washing and drying to obtain coal-based activated carbon. Comparative Example

[0025] Comparative Example 1 A method for preparing coal-based activated carbon differs from Example 1 in that the composition of the binder is different, as detailed below: The binder is composed of waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water, in the following weight ratio: 6.6:0.06:0.01:1.

[0026] Comparative Example 2 A method for preparing coal-based activated carbon differs from Example 1 in that the composition of the binder is different, as detailed below: The binder is composed of biomass straw powder, waste molasses, potassium hydroxide and water, with the following weight ratio: 3.0:3.6:0.07:1.

[0027] Comparative Example 3 A method for preparing coal-based activated carbon differs from Example 1 in that the carbonization step is a one-step carbonization process, and the specific carbonization steps are as follows: The pre-carbonized material is put into a rotary carbonization furnace, nitrogen is introduced, and under the nitrogen atmosphere, the temperature inside the furnace is raised to 450°C at a heating rate of 10°C / min for carbonization. The carbonization is held for 60 minutes to obtain the carbonized material.

[0028] Blank control group A coal-based activated carbon, purchased from Conno, catalog number 0103, is made from coal tar as a binder.

[0029] Performance testing

[0030] The coal-based activated carbon prepared in Examples 1-12 and Comparative Examples 1-3, as well as the blank control group, were tested.

[0031] Table 1. Detection data of Examples 1-12, Comparative Examples 1-3 and Blank Control Group Specific surface area m² / g 2276 2098 2047 1880 Total pore volume cm³ / g 0.9333 0.8603 0.8394 0.7710 Iodine value (mg / g) 1722 1587 1549 1423 Testing items Example 5 Example 6 Example 7 Example 8 Specific surface area m² / g 1916 2175 2217 1964 Total pore volume cm³ / g 0.7857 0.8920 0.9090 0.8055 Iodine value (mg / g) 1450 1646 1677 1486 Testing items Example 9 Example 10 Example 11 Example 12 Specific surface area m² / g 2196 1877 1790 2021 Total pore volume cm³ / g 0.9005 0.7698 0.7342 0.8287 Iodine value (mg / g) 1662 1420 1355 1529 Testing items Comparative Example 1 Comparative Example 2 Comparative Example 3 Blank control group Specific surface area m² / g 1010 1419 1303 1200 Total pore volume cm³ / g 0.4140 0.5688 0.5345 0.4921 Iodine value (mg / g) 564 1080 986 908

[0032] in conclusion

[0033] The test data shows that: First, Example 1 of this application forms a single comparison with Comparative Examples 1-2. In Comparative Example 1, the binder lacks biomass straw powder, and waste molasses is used instead of biomass straw powder. Due to the increase in the content of waste molasses, the viscosity of the binder increases linearly, resulting in a decrease in its fluidity. It can only partially wet the coal powder, and the coal powder is unevenly distributed during the kneading process. In the later carbonization and activation stages, the binder cannot fully play its auxiliary activation role, and the pore-forming effect of the binder and activator on the coal powder is weakened. At the same time, due to the low decomposition temperature of waste molasses, only a small amount of thermal decomposition products of waste molasses enter the coal powder. The coal powder lacks the replenishment of fixed carbon, and the pore structure of the coal powder is prone to collapse, resulting in a decrease in specific surface area and total pore volume. Finally, the iodine value drops to below 600 mg / g. In Comparative Example 2, the lack of long-chain alkyl quaternary ammonium salt surfactants prevented the binder from entering the coal powder and playing an auxiliary activation role on the surface of the coal powder. The pore structure of the carbonized material was restricted, and the specific surface area and total pore volume of the coal-based activated carbon decreased. Compared with Example 1, the iodine value decreased significantly.

[0034] Secondly, Example 1 of this application forms a single comparison with Comparative Example 3. Comparative Example 3 uses a one-step carbonization method, which prolongs the carbonization time, but the specific surface area and total pore volume of the final product still decrease. The reason is that a large amount of waste molasses decomposes at high temperature, and the thermal decomposition products volatilize along with the volatile matter of biomass straw, resulting in only a small amount of thermal decomposition products being added to the coal powder as fixed carbon. The carbonized material experiences pore collapse during the activation stage. At the same time, Example 1 of this application forms a comparison with the blank control group. The blank control group uses coal tar as a binder, but the specific surface area and total pore volume of the final product are lower than those of Example 1 of this application.

[0035] Third, by comparing Example 1 with Examples 2-12 of this application, it can be seen that the composition ratio of the binder, the particle size of the powder, the carbonization and activation parameters all have a significant impact on the specific surface area and total pore volume of coal-based activated carbon.

[0036] The various technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0037] Furthermore, the above-described embodiments merely illustrate several implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing coal-based activated carbon, characterized in that, Includes the following steps: Preparation of binder: Biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water are prepared in a weight ratio of (1.2-3.6):(2.5-4):(0.02-0.1):(0.005-0.01):

1. First, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water are mixed in the same weight ratio. Then, biomass straw powder is added and stirred to obtain binder. Grinding; Kneading and molding: The binder and the pulverized coal powder are kneaded and mixed at a weight ratio of (0.78~0.92):1, and then extruded to obtain the pre-carbonized material; Carbonization; the pre-carbonized material is first heated to 300-450℃ under an inert gas atmosphere for primary carbonization, and held for 20-30 minutes. Then, it is heated to 550-600℃ for secondary carbonization, and held for 20-30 minutes to obtain carbonized material. Activation: The carbonized material and gas activator are kept at 700-800℃ for 45-60 minutes for activation. After cooling, the material is acid washed and dried to obtain coal-based activated carbon.

2. The method for preparing coal-based activated carbon as described in claim 1, characterized in that: The weight ratio of the biomass straw powder, waste molasses, long-chain alkyl quaternary ammonium salt surfactant, potassium hydroxide and water is (2.4-3.0):(3.2-3.6):(0.05-0.06):(0.008-0.01):

1.

3. The method for preparing coal-based activated carbon as described in claim 1, characterized in that: The particle size range of the biomass straw powder is 50–100 μm.

4. The method for preparing coal-based activated carbon as described in claim 3, characterized in that: In the grinding step, the particle size range of the coal powder obtained by grinding is 200-500 μm.

5. The method for preparing coal-based activated carbon as described in claim 1, characterized in that: In the kneading and molding step, the weight ratio of binder to coal powder is 0.85:

1.

6. The method for preparing coal-based activated carbon as described in claim 1, characterized in that: In the carbonization step, the heating rate of the pre-carbonized material during the first carbonization is 5-6℃ / min.

7. The method for preparing coal-based activated carbon as described in claim 6, characterized in that: In the carbonization step, the heating rate of the pre-carbonized material during the secondary carbonization is 6-10℃ / min.

8. The method for preparing coal-based activated carbon as described in claim 7, characterized in that: In the activation step, the ratio of the activator amount to the weight of the carbonized material is 40–60 (m). 3 / h):1000kg.