Preparation method of biomass activated carbon with high specific surface area

Abstract

The invention relates to the field of preparation methods of activated carbon, in particular to a preparation method of biomass activated carbon with a high specific surface area. The method comprises the following steps: S1, cleaning and drying a biomass raw material, then crushing and sieving to obtain powder with uniform granularity, and then grinding and fully mixing the powder with an activator potassium hydroxide to obtain mixture powder; s2, putting the corundum crucible filled with the mixture powder into a tubular furnace, and carrying out two-stage uninterrupted programmed heating and heat preservation in a nitrogen atmosphere; then naturally cooling to room temperature to obtain a crude product of biomass activated carbon; and S3, carrying out acid pickling on the crude product of the biomass activated carbon until a cleaning solution is neutral, and finally drying a solid sample. According to the method, the technological process is simplified, the preparation time is shortened, and the biomass activated carbon with the high specific surface area can be synthesized on a large scale. The method can be applied to industrial production of natural gas or methane storage adsorbents of the ANG technology.

Description

Technical Field

[0001] The invention relates to the field of activated carbon preparation methods, in particular to a method for preparing biomass activated carbon with high specific surface area. Background Art

[0002] The main component of natural gas is methane, which has the advantages of being clean, environmentally friendly and economical. Natural gas is considered to be the most promising energy source in the next few decades. Its storage technologies mainly include compressed natural gas (CNG), liquefied natural gas (LNG) and adsorbed natural gas (ANG). Compared with LNG technology and CNG technology, ANG technology is a new technology that uses the high specific surface area and microporous structure of adsorbents to adsorb and store natural gas at room temperature 298 K and medium and low pressure (3-4 MPa). ANG technology has the advantages of low working pressure, large storage capacity, low cost, convenient and safe use, and is expected to achieve large-scale commercial application. The selection and development of adsorbents are key factors in determining the successful commercialization of ANG technology. Among many adsorbents, activated carbon is considered to be the most promising natural gas (or methane) storage adsorbent because of its high specific surface area and porosity, large natural gas adsorption capacity, reusability, long service life, low price and easy large-scale production.

[0003] The raw materials of activated carbon are quite abundant. Among them, agricultural and forestry waste biomass materials, such as straw, fruit shells, bamboo, etc., can usually produce activated carbon with large specific surface area and developed pores due to their natural characteristics such as porous capillary system and high carbon content. Agricultural and forestry waste biomass materials have a wide range of sources, abundant reserves and low prices. The preparation of biomass activated carbon is generally divided into four steps: pretreatment, carbonization, activation and post-treatment of raw materials. Among them, carbonization and activation are two very critical links in the process of preparing activated carbon as adsorbent material. After pretreatment, the biomass material is carbonized by high-temperature pyrolysis in an inert atmosphere. The carbonized product is mixed with an activator, such as zinc chloride, phosphoric acid and potassium hydroxide, and then calcined and activated at high temperature to prepare activated carbon with high specific surface area. The carbonization and activation of biomass raw materials are two independent processes. The two steps require cooling, sample processing and re-heating, etc. The process is time-consuming and seriously affects production efficiency. Summary of the invention

[0004] The technical problem to be solved by the present invention is: In order to solve the technical problem described in the background technology, the present invention provides a method for preparing biomass activated carbon with high specific surface area. The present application simplifies the process flow, shortens the preparation time, and can synthesize biomass activated carbon with high specific surface area on a large scale. It can be applied to the industrial production of natural gas or methane storage adsorbents of ANG technology.

[0005] The technical solution adopted by the present invention to solve its technical problem is: A method for preparing biomass activated carbon with high specific surface area comprises the following steps: S1, washing and drying the biomass raw material, then crushing and sieving to obtain a powder with uniform particle size, and then grinding and fully mixing with an activator potassium hydroxide to obtain a mixed powder; S2, placing the corundum crucible containing the mixture powder in a tube furnace, and performing two stages of uninterrupted programmed heating and heat preservation under a nitrogen atmosphere; the first stage is the carbonization process of the mixture powder, and the second stage is the activation process of the carbonization product; then naturally cooling to room temperature to obtain a crude product of biomass activated carbon; S3. The crude product of biomass activated carbon is acid-washed until the washing liquid is neutral, and finally the solid sample is dried to obtain biomass activated carbon with a high specific surface area.

[0006] Specifically, the biomass raw materials are corn stalks, coconut shells, and bamboo.

[0007] Specifically, in step S1, the drying temperature is 60-200°C, the heating rate is 5-10°C / min, and the insulation time is 6-24h.

[0008] Specifically, in step S1, the crushing time is 2 to 6 hours.

[0009] Specifically, in step S1, the sieve used for screening is 100-400 mesh.

[0010] Specifically, in step S1, the mass ratio of the sieved powder to potassium hydroxide solid is 1:1 to 1:4.

[0011] Specifically, in step S2, the flow rate of the nitrogen is 50-200 mL / min, the heating rate in the first stage is 5-10° C. / min, the temperature is 300-400° C., and the insulation time is 1-6 h.

[0012] Specifically, in step S2, the heating rate of the second stage is 5-10°C / min, the temperature is 700-900°C, and the insulation time is 0.5-2h.

[0013] Specifically, in step S3, the temperature of drying the solid sample is 60-200° C., and the insulation time is 6-24 hours.

[0014] Specifically, in step S3, the acid used for pickling is 1 mol / L nitric acid, hydrochloric acid or sulfuric acid.

[0015] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing biomass activated carbon with a high specific surface area. The present application simplifies the process flow, shortens the preparation time, and can synthesize biomass activated carbon with a high specific surface area on a large scale. It can be applied to the industrial production of natural gas or methane storage adsorbents of ANG technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0017] Figure 1 is a Raman spectrum of the target product obtained in Example 1 of the present invention; Figure 2 is a Raman spectrum of the target product obtained in Example 2 of the present invention; Figure 3 is a Raman spectrum of the target product obtained in Example 3 of the present invention; Figure 4 is a nitrogen adsorption-desorption curve diagram of the target product obtained in Example 1 of the present invention; Figure 5 is a nitrogen adsorption-desorption curve diagram of the target product obtained in Example 2 of the present invention; Figure 6 is a nitrogen adsorption-desorption curve diagram of the target product obtained in Example 3 of the present invention; Figure 7 is the pore size distribution diagram of the target product obtained in Example 1 of the present invention; Figure 8 This is the pore size distribution diagram of the target product obtained in Example 2 of the present invention; Fig. 9 This is the pore size distribution diagram of the target product obtained in Example 3 of the present invention; DETAILED DESCRIPTION

[0018] The technical solution adopted by the present invention to solve its technical problem is: A method for preparing biomass activated carbon with high specific surface area comprises the following steps: S1, washing and drying the biomass raw material, then crushing and sieving to obtain a powder with uniform particle size, and then grinding and fully mixing with an activator potassium hydroxide to obtain a mixed powder; S2, placing the corundum crucible containing the mixture powder in a tube furnace, and performing two stages of uninterrupted programmed heating and heat preservation under a nitrogen atmosphere; the first stage is the carbonization process of the mixture powder, and the second stage is the activation process of the carbonization product; then naturally cooling to room temperature to obtain a crude product of biomass activated carbon; S3. The crude product of biomass activated carbon is acid-washed until the washing liquid is neutral, and finally the solid sample is dried to obtain biomass activated carbon with a high specific surface area.

[0019] The biomass raw materials are corn stalks, coconut shells and bamboo.

[0020] In step S1, the drying temperature is 60-200°C, the heating rate is 5-10°C / min, and the insulation time is 6-24h.

[0021] In step S1, the crushing time is 2 to 6 hours.

[0022] In step S1, the sieve used for the screening is 100-400 mesh.

[0023] In step S1, the mass ratio of the sieved powder to potassium hydroxide solid is 1:1 to 1:4.

[0024] In step S2, the flow rate of the nitrogen is 50-200 mL / min, the heating rate in the first stage is 5-10° C. / min, the temperature is 300-400° C., and the insulation time is 1-6 h.

[0025] In step S2, the heating rate of the second stage is 5-10°C / min, the temperature is 700-900°C, and the insulation time is 0.5-2h.

[0026] In step S3, the temperature of drying the solid sample is 60-200° C., and the insulation time is 6-24 hours.

[0027] In step S3, the acid used for pickling is 1 mol / L nitric acid, hydrochloric acid or sulfuric acid. Example 1

[0028] The coconut shell raw material was washed with water and dried naturally, and then placed in an oven. The temperature of the oven was set to 60℃, the heating rate was 5℃ / min, and the holding time was 12h. After taking it out, it was placed in a crusher with a power of 550W, a speed of 32000 rpm, and a crushing time of 6h. Then it was passed through a 150-mesh sieve. The sieved powder was mixed with potassium hydroxide solid at a mass ratio of 1:3, and the resulting mixture was placed in a corundum crucible after grinding in an agate mortar for 2h. The corundum crucible containing the coconut shell raw material and sodium hydroxide mixture was placed in a tubular furnace, and nitrogen protection was passed through it at a nitrogen flow rate of 100mL / min. The heating rate of the first stage of the tubular furnace was set to 5℃ / min, the temperature was 400℃, and the holding time was 6h. The heating rate of the second stage was 5℃ / min, the temperature was 800℃, the holding time was 2h, and it was naturally cooled to room temperature after the end. The carbonized and activated product was washed with 1 mol / L hydrochloric acid until the pH of the washing solution was 7. The crucible containing the solid product was then placed in an oven and dried at 60° C. for 12 h to obtain biomass activated carbon. Example 2

[0029] The coconut shell raw material was washed with water and dried naturally, and then placed in an oven. The temperature of the oven was set to 60℃, the heating rate was 5℃ / min, and the holding time was 12h. After taking it out, it was placed in a crusher with a power of 550W, a speed of 32000 rpm, and a crushing time of 6h. Then it was passed through a 150-mesh sieve. The sieved powder was mixed with potassium hydroxide solid at a mass ratio of 1:4, and the resulting mixture was placed in a corundum crucible after grinding in an agate mortar for 2h. The corundum crucible containing the coconut shell raw material and sodium hydroxide mixture was placed in a tubular furnace, and nitrogen protection was passed through it at a nitrogen flow rate of 100mL / min. The heating rate of the first stage of the tubular furnace was set to 5℃ / min, the temperature was 400℃, and the holding time was 6h. The heating rate of the second stage was 5℃ / min, the temperature was 800℃, the holding time was 2h, and it was naturally cooled to room temperature after the end. The carbonized and activated product was washed with 1 mol / L hydrochloric acid until the pH of the washing solution was 7. The crucible containing the solid product was then placed in an oven and dried at 60° C. for 12 h to obtain biomass activated carbon. Example 3

[0030] The coconut shell raw material was washed with water and dried naturally, and then placed in an oven. The temperature of the oven was set to 60℃, the heating rate was 5℃ / min, and the holding time was 12h. After taking it out, it was placed in a crusher with a power of 550W, a speed of 32000 rpm, and a crushing time of 6h. Then it was passed through a 150-mesh sieve. The sieved powder was mixed with potassium hydroxide solid at a mass ratio of 1:4, and the resulting mixture was placed in a corundum crucible after grinding in an agate mortar for 2h. The corundum crucible containing the coconut shell raw material and sodium hydroxide mixture was placed in a tubular furnace, and nitrogen protection was passed through it at a nitrogen flow rate of 100mL / min. The heating rate of the first stage of the tubular furnace was set to 5℃ / min, the temperature was 400℃, and the holding time was 6h. The heating rate of the second stage was 5℃ / min, the temperature was 900℃, the holding time was 2h, and it was naturally cooled to room temperature after the end. The carbonized and activated product was washed with 1 mol / L hydrochloric acid until the pH of the washing solution was 7. The crucible containing the solid product was then placed in an oven and dried at 60° C. for 12 h to obtain biomass activated carbon.

[0031] The Raman spectrum, specific surface area and pore size of the biomass activated carbon prepared in this embodiment were tested. The Raman spectrum results showed that the graphitization degree of the biomass activated carbon prepared in Examples 1 to 3 was relatively high.

[0032] Combined with Figure 1 , Attachment Figure 4 , Attachment Figure 7As shown, the specific surface area and pore size of the biomass activated carbon prepared in Example 1 are 1831 m2 / g and 3.5 nm, respectively.

[0033] Combined with Figure 2 , Attachment Figure 5 , Attachment Figure 8 As shown, the specific surface area and pore size of the biomass activated carbon prepared in Example 2 are 2417 m2 / g and 3.3 nm, respectively.

[0034] Combined with Figure 3 , Attachment Figure 6 , Attachment Fig. 9 As shown, the specific surface area and pore size of the biomass activated carbon prepared in Example 3 are 2818 m2 / g and 3.1 nm, respectively.

[0035] In summary, compared with the prior art, the present invention greatly shortens the process time, greatly improves the processing efficiency, and the prepared biomass activated carbon has a high specific surface area and can be synthesized on a large scale. It is expected to realize the industrial production of natural gas or methane storage adsorbents of ANG technology.

[0036] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing biomass activated carbon with high specific surface area, characterized in that: The following steps are involved: S1, washing and drying the biomass raw material, then crushing and sieving to obtain a powder with uniform particle size, and then grinding and fully mixing with an activator potassium hydroxide to obtain a mixed powder; S2, placing the corundum crucible containing the mixture powder in a tube furnace, and performing two stages of uninterrupted programmed heating and heat preservation under a nitrogen atmosphere; the first stage is the carbonization process of the mixture powder, and the second stage is the activation process of the carbonization product; then naturally cooling to room temperature to obtain a crude product of biomass activated carbon; S3. The crude product of biomass activated carbon is acid-washed until the washing liquid is neutral, and finally the solid sample is dried to obtain biomass activated carbon with a high specific surface area.

2. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: The biomass raw materials are corn stalks, coconut shells and bamboo.

3. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S1, the drying temperature is 60-200°C, the heating rate is 5-10°C / min, and the insulation time is 6-24h.

4. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S1, the crushing time is 2 to 6 hours.

5. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S1, the sieve used for the screening is 100-400 mesh.

6. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S1, the mass ratio of the sieved powder to potassium hydroxide solid is 1:1 to 1:

4.

7. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S2, the flow rate of the nitrogen is 50-200 mL / min, the heating rate in the first stage is 5-10° C. / min, the temperature is 300-400° C., and the insulation time is 1-6 h.

8. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S2, the heating rate of the second stage is 5-10°C / min, the temperature is 700-900°C, and the insulation time is 0.5-2h.

9. The method for preparing high specific surface area biomass activated carbon according to claim 1, characterized in that: In step S3, the temperature of drying the solid sample is 60-200° C., and the insulation time is 6-24 hours.

10. The method for preparing biomass activated carbon with high specific surface area according to claim 1, characterized in that: In step S3, the acid used for pickling is 1 mol / L nitric acid, hydrochloric acid or sulfuric acid.

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