Process for producing activated carbon by alkali activation

Abstract

The application discloses a production process of activated carbon by alkali activation method, which comprises the following steps: firstly, uniformly mixing raw materials and an activating agent and then performing a first-stage reaction in the presence of an inert atmosphere; after the first-stage reaction is completed, cooling and mixing the first-stage reaction product with a passivating agent, then heating and performing a second-stage reaction; and finally, washing and drying to obtain the activated carbon. The production process is simple, safe and reliable, and solves the problems of wall sticking and potassium explosion risk in the process of preparing the activated carbon by the alkali activation method.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials, and in particular relates to a process for preparing activated carbon by alkali activation. Background Technology

[0002] Activated carbon is the most widely used adsorbent material, with its production and use dating back to the 19th century. Activated carbon is widely used due to its high specific surface area and well-developed pore structure. Activated carbon materials with high specific surface area are excellent adsorption, catalysis, gas storage, and electrode materials, possessing high economic added value.

[0003] In the field of activated carbon preparation, the advantages of alkali activation technology are short activation time, low activation temperature, and relatively well-developed microporous structure of the product. However, the large-scale use of alkali increases production costs, has a strong corrosive effect on equipment at high temperatures, and the alkali reactants and carbonates generated during the reaction have high melting points. Cooling from the molten state to room temperature directly leads to material sticking to the walls, directly affecting the continuous operation of the overall process and mass and heat transfer during the reaction. Most importantly, the reaction produces large amounts of potassium and sodium as byproducts, and the presence of elemental potassium and sodium seriously endangers normal production. This has long been a key factor restricting the large-scale production of high specific surface area activated carbon in my country. How to solve this problem and break the foreign technological monopoly has become an urgent issue to be addressed in this field.

[0004] Chinese patent CN00104267.X discloses a method for preparing activated carbon for methane storage, using petroleum coke or pitch as raw material, KOH as activating agent, and an alkali-to-carbon ratio (KOH / petroleum coke mass ratio) of 4:1, to prepare activated carbon with a specific surface area as high as 2308 m². 2 / g of activated carbon. CN101428823 discloses a continuous alkali metal treatment method and apparatus for alkali-activated activated carbon production. The method involves discharging waste gas generated during alkali-activated activated carbon production into an oxidation tower through an exhaust pipe, which is then heated and insulated. The discharged gas is then oxidized into alkali metal oxides using air within the oxidation tower, and cooled in the gas flow. The cooled alkali metal oxide powder is then carried by the gas flow into a recovery chamber, where it is washed and recovered using water spraying. This invention also provides a continuous alkali metal treatment apparatus for alkali-activated activated carbon production, enabling the industrial-scale continuous production of high specific surface area activated carbon through alkali activation. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an alkali activation method for producing activated carbon. This process is simple, safe, and reliable, and solves the problems of wall adhesion and potassium explosion risks present in current alkali activation methods for activated carbon production.

[0006] This invention provides an alkali activation method for producing activated carbon, the process comprising the following steps:

[0007] (1) Under the presence of an inert atmosphere, the raw materials and activator are mixed evenly to carry out a reaction;

[0008] (2) After the first stage of reaction is completed, adjust the temperature to 20-190℃, preferably 80-150℃, and then mix the passivating agent with the material after the first stage of reaction. Then raise the temperature to carry out the second stage of reaction. After the reaction is completed, wash and dry to obtain activated carbon.

[0009] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the raw material in step (1) can be one or more of petroleum coke, coal, coal tar coke, coal pitch, petroleum pitch, and biomass, preferably petroleum coke. The biomass can be one or more of coconut shell carbonized material, hazelnut shell carbonized material, and rice husk carbonized material. When biomass is used as raw material, it needs to undergo pre-carbonization treatment before activation, and this pre-carbonization treatment is a method known in the art. Generally, the pre-carbonization treatment temperature for biomass raw materials such as coconut shell, hazelnut shell, and rice husk is 400–500℃, and the pre-treatment time is 0.5–12 h, under inert atmosphere conditions. The mixing method between the raw material and the alkali activator can be mechanical mixing or impregnation, preferably mechanical mixing.

[0010] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the activator in step (1) is at least one of sodium hydroxide and potassium hydroxide, preferably potassium hydroxide.

[0011] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the weight ratio of activator to raw material in step (1) is 0.1 to 20:1, preferably 1 to 6:1.

[0012] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the reaction temperature of the first stage reaction in step (1) is 200-600℃, preferably 300-450℃, and the reaction time is 5-720 min, preferably 20-90 min.

[0013] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the inert atmosphere in step (1) can be at least one of nitrogen, helium, neon, argon, krypton, and xenon, preferably nitrogen.

[0014] Furthermore, in the above-mentioned alkaline activation activated carbon production process, the passivating agent in step (2) is one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, and sodium sulfate. The weight ratio of the passivating agent to the material after the first stage of reaction is 10 to 500:1, and more preferably 50 to 200:1.

[0015] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the reaction temperature of the two-stage reaction in step (2) is 600-900℃, preferably 650-850℃; the reaction time is 20-420 min, preferably 80-240 min.

[0016] Furthermore, in the above-mentioned alkali activation method for activated carbon production, the activation reaction is preferably carried out in a rotary kiln, and the rotation speed of the rotary kiln is generally controlled at 0.5 to 60 r / min, preferably 0.5 to 15 r / min.

[0017] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the reaction in step (2) is carried out in the presence of an inert atmosphere, which can be at least one of nitrogen, helium, neon, argon, krypton, and xenon, preferably nitrogen.

[0018] Furthermore, in the above-mentioned alkaline activation activated carbon production process, the washing in step (2) includes acid washing and water washing. The acid washing is performed with an acidic solution, which can be any one of hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic acid, etc., preferably nitric acid; the mass concentration of the acidic solution is 1-70 wt%, preferably 10-30 wt%; the mass ratio of the sample obtained in step (2) to the acid solution is 1:1-1:100, preferably 1:1-1:20. The water washing continues until the filtrate is neutral.

[0019] Furthermore, in the above-mentioned alkali-activated activated carbon production process, the drying temperature in step (2) is 60-150℃, preferably 80-120℃, and the drying time is 2-10h, preferably 4-8h; the drying is preferably carried out under vacuum conditions.

[0020] A second aspect of the present invention provides activated carbon obtained using the above-described production process.

[0021] Compared with existing technologies, the alkali activation method for producing activated carbon provided by this invention has the following technical advantages:

[0022] 1. The alkali activation activated carbon production process provided by this invention fundamentally solves the problem of explosion caused by the generation of elemental alkali metals during alkali activation. Furthermore, the material does not clump or stick to the wall during the production process, but exists in a spherical shape, which not only makes mass and heat transfer more uniform, but also fundamentally solves the key problem that has long plagued the alkali activation device for long-term safe and stable operation.

[0023] 2. The alkali activation method for producing activated carbon provided by this invention involves using a passivating agent to encapsulate the material obtained in the first stage reaction after the first stage reaction. During the second stage reaction, the passivating agent further forms a bridge with the molecular clusters of the material obtained in the first stage reaction, thereby forming a coating. This prevents the elemental alkali metal generated in the reaction from escaping from the reaction system, thus sealing it inside the coating and preventing the explosion of the elemental alkali metal.

[0024] 3. The alkaline activation method for activated carbon production provided by this invention uses a passivating agent to form a coating, which can reduce the force between the material and the inner wall of the rotating furnace, thus avoiding the problem of the reacting material sticking to the wall during the rotation process. Detailed Implementation

[0025] The technical content and effects of the present invention are further illustrated below with reference to embodiments, but these embodiments do not limit the scope of the present invention.

[0026] The specific surface area and pore volume described in the embodiments and comparative examples of this invention were determined by the N2 physical adsorption-desorption method.

[0027] Example 1

[0028] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 450℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with a passivating agent NaCl (mass ratio of passivating agent to spherical product 100:1). After thorough contact, the mixture was loaded back into the rotary kiln and heated to 750℃ and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​2800 m². 2 / g, pore volume 1.25cm 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0029] Example 2

[0030] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 400℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with a passivating agent NaCl at a mass ratio of 50:1. After thorough contact, the mixture was loaded back into the rotary kiln and heated to 750℃ at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​2682 m².2 / g, pore volume 1.15cm 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0031] Example 3

[0032] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 400℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 150℃, and the spherical product was removed and mixed with a passivating agent NaCl (mass ratio of passivating agent to spherical product 200:1). After thorough contact, the mixture was loaded back into the rotary kiln and heated to 750℃ and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 30wt% nitric acid, then with deionized water until neutral. Under vacuum, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​3077 m². 2 / g, pore volume 1.35cm 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0033] Example 4

[0034] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 400℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 80℃, and the spherical product was removed and mixed with a passivating agent NaCl at a mass ratio of 80:1. After thorough contact, the mixture was loaded back into the rotary kiln and heated to 650℃ at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15% hydrochloric acid, then with deionized water until neutral. Under vacuum conditions, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​2100 m². 2 / g, pore volume 0.95 cm³ 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0035] Example 5

[0036] 100g of petroleum coke and 500g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 350℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with a passivating agent, NaCl, at a mass ratio of 200:1. After thorough contact, the mixture was loaded back into the rotary kiln and heated to 600℃ and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum, it was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​2516 m². 2 / g, pore volume 1.10cm 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0037] Example 6

[0038] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 450℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with potassium carbonate (a passivating agent at a mass ratio of 100:1). After thorough contact, the mixture was loaded back into the rotary kiln and heated to 850℃ and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​3019 m². 2 / g, pore volume 1.27cm 3 / g. No elemental potassium was observed at the gas outlet of the reaction, and no wall adhesion was found.

[0039] Example 7

[0040] 100g of petroleum coke and 100g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 450℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with potassium carbonate passivating agent (mass ratio of passivating agent to spherical product 100:1). After thorough contact, the mixture was loaded back into the rotary kiln, heated to 750℃, and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum conditions, the mixture was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​2169 m². 2 / g, pore volume 1.02cm 3 / g. No elemental potassium was observed at the gas outlet, and no wall adhesion was detected.

[0041] Comparative Example 1

[0042] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the temperature was raised to 450℃, the rotation speed was 5 r / min, and the treatment was carried out for 120 min. Then the temperature was lowered to 100℃, and then raised to 750℃, the rotation speed was 10 r / min, and the treatment was carried out for 60 min. After cooling to room temperature, it was found that the sample stuck to the wall and elemental potassium was generated, making it impossible to remove the sample smoothly.

[0043] Comparative Example 2

[0044] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 450℃ and rotated at 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed and mixed with sodium nitrate at a mass ratio of 100:1. After thorough contact, the mixture was loaded back into the rotary kiln, heated to 750℃, and rotated at 10 r / min for 60 min. After cooling to room temperature, the mixture was found to stick to the walls and elemental potassium was generated, making it impossible to remove the sample.

[0045] Comparative Example 3

[0046] 100g of petroleum coke and 300g of potassium hydroxide were mixed evenly and loaded into a rotary kiln. Under a nitrogen atmosphere, the mixture was heated to 450℃ at a rotation speed of 5 r / min for 120 min. The temperature was then lowered to 100℃, and the spherical product was removed. NaCl was used as a passivating agent (mass ratio of passivating agent to spherical product was 100:1). After thorough contact, the mixture was loaded back into the rotary kiln and heated to 950℃ at a rate of 5℃ / min at a rotation speed of 10 r / min for 60 min. After cooling to room temperature, the product was removed, washed first with 15wt% hydrochloric acid, then with deionized water until neutral. Under vacuum conditions, the product was dried at 120℃ for 8 h. The resulting activated carbon product had a specific surface area of ​​3050 m². 2 / g, pore volume 1.28cm 3 / g. Adhesion to the gas wall was observed, and elemental potassium was generated at the gas outlet.

Claims

1. A process for producing activated carbon using an alkali activation method, the process comprising the following: (1) Under the presence of an inert atmosphere, the raw material and the activator are mixed evenly to carry out a first-stage reaction; the raw material is petroleum coke; (2) After the first stage of reaction is completed, adjust the temperature to 20-190℃, and then mix the passivating agent with the material after the first stage of reaction. The passivating agent coats the material obtained from the first stage of reaction, and then the temperature is raised to carry out the second stage of reaction. After the reaction is completed, activated carbon is obtained by washing and drying. The passivating agent is one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, and sodium sulfate. The activator in step (1) is potassium hydroxide; the weight ratio of the activator to the raw material in step (1) is 0.1 to 20:1; the reaction temperature of the first stage reaction in step (1) is 350 to 450°C, and the reaction time is 5 to 720 min; The reaction temperature of the second stage reaction in step (2) is 600-850℃ and the reaction time is 20-420min; the weight ratio of the passivating agent to the material after the first stage reaction in step (2) is 10-500:1; The first and second stage reactions are carried out in a rotary kiln.

2. The alkali activation method for producing activated carbon according to claim 1, characterized in that: In step (2), after the first stage of reaction is completed, the temperature is adjusted to 80-150℃, and the passivating agent is mixed with the material after the first stage of reaction.

3. The alkali activation method for producing activated carbon according to claim 1, characterized in that: In step (1), the weight ratio of activator to raw material is 1 to 6:

1.

4. The alkali-activated activated carbon production process according to claim 1, characterized in that: The reaction time for one stage of the reaction in step (1) is 20 to 90 minutes.

5. The alkali-activated activated carbon production process according to claim 1, characterized in that: In step (1), the inert atmosphere is at least one of nitrogen, helium, neon, argon, krypton, and xenon.

6. The alkali-activated activated carbon production process according to claim 5, characterized in that: In step (1), the inert atmosphere is nitrogen.

7. The alkali activation method for producing activated carbon according to claim 1, characterized in that: The weight ratio of the passivating agent to the material after the first stage of reaction is 50 to 200:

1.

8. The alkali activation method for producing activated carbon according to claim 1, characterized in that: The reaction temperature of the two-stage reaction in step (2) is 650-850℃; the reaction time is 80-240 min.

9. The alkali activation method for producing activated carbon according to claim 1, characterized in that: The reaction in step (2) is carried out in the presence of an inert atmosphere, which is at least one of nitrogen, helium, neon, argon, krypton, and xenon.

10. The alkali activation method for producing activated carbon according to claim 9, characterized in that: The reaction in step (2) is carried out in the presence of an inert atmosphere, which is nitrogen.

11. The alkali-activated activated carbon production process according to claim 1, characterized in that: The washing in step (2) includes acid washing and water washing. The acid washing is washing with an acidic solution, which is any one of hydrochloric acid, nitric acid, sulfuric acid, formic acid, and acetic acid. The mass concentration of the acidic solution is 1 to 70 wt%. The mass ratio of the sample obtained in step (2) to the acidic solution is 1:1 to 1:

100.

12. The alkali activation method for producing activated carbon according to claim 11, characterized in that: The acidic solution mentioned in step (2) is nitric acid; the mass concentration of the acidic solution is 10-30 wt%; the mass ratio of the sample obtained in step (2) to the acidic solution is 1:1 to 1:

20.

13. The alkali-activated activated carbon production process according to claim 1, characterized in that: The drying temperature in step (2) is 60-150℃ and the drying time is 2-10h.

14. The alkali activation method for producing activated carbon according to claim 13, characterized in that: The drying temperature in step (2) is 80-120°C and the drying time is 4-8 hours; the drying is carried out under vacuum conditions.