Preparation method of carbon aerogel for air purification

Abstract

The invention relates to the field of preparation of waste gas adsorption materials, in particular to a preparation method of carbon aerogel for air purification. Comprising the following steps: (1) uniformly mixing a natural polymer and deionized water to prepare a solution, then adding a cross-linking agent, stirring in a water bath, pouring the solution into a mold after the cross-linking reaction is finished, and standing; (2) putting the composite hydrogel obtained in the step (1) above a cuboid steel tank filled with liquid nitrogen, and directionally freezing the composite hydrogel; after complete freezing, demolding the sample, and performing freeze drying to obtain aerogel; (3) dipping the aerogel material obtained in the step (2) in an activating agent solution, and then drying in a vacuum drying oven; and then putting into a tubular furnace for heat treatment, and washing with water to obtain the carbon aerogel material with the graded porous structure. Compared with traditional activated carbon, the material is richer in pore structure and wider in application range; and heat accumulation is not easily caused to cause spontaneous combustion, so that the safety is greatly improved.

Description

Technical Field

[0001] The invention relates to the field of waste gas adsorption material preparation, and in particular to a method for preparing carbon aerogel for air purification. Background Art

[0002] "Triphenyl" waste gas refers to the gas containing benzene, toluene and xylene, three toxic, harmful, flammable and explosive aromatic hydrocarbons. It is usually produced in the shoemaking, paint, printing and other industries. Its treatment often adopts the activated carbon adsorption method. One is the activated carbon adsorption desorption recovery method. After the activated carbon is saturated with adsorption at room temperature, it is decomposed with water vapor below 110 ° C, and the solvent is recovered after condensation and separation. This process is suitable for treating a single component and has a large investment, which is not suitable for small factories. The other is the activated carbon adsorption catalytic combustion method. After the activated carbon adsorbs pollutants, it is desorbed with hot air, and then catalytic combustion is adopted. It is suitable for large-volume organic waste gas and has no secondary pollution. However, due to the thick activated carbon layer, it is easy to cause heat accumulation and spontaneous combustion, and the safety is poor. In addition, traditional activated carbon for air purification is mostly columnar or granular, which requires complicated processes such as bonding, granulation, and modification, and will pollute the environment. For example, CN 106000432 A discloses “Catalyst-loaded wood granular activated carbon for air purification and its preparation method”, in which powdered activated carbon is subjected to bonding, granulation, and modification to load the catalyst to obtain a granular carbon-based catalyst; CN110575813 A discloses “A method for preparing activated carbon for air purification with high adsorption properties”, in which the raw material is first activated to obtain powdered activated carbon, which is then bonded, granulated, and carbonized to obtain granular activated carbon, and finally immersed in an organic amine solution for modification and then heat-treated to obtain modified activated carbon.

[0003] Carbon aerogel materials have rich three-dimensional network structures and high continuous porosity, and have received widespread attention in gas adsorption and air purification. More importantly, their ultra-lightness, high elasticity, and thermal insulation properties make them suitable for complex components and not prone to heat accumulation and spontaneous combustion. Summary of the invention

[0004] The present invention provides a method for preparing carbon aerogel for air purification to solve the technical problem that the thick activated carbon layer easily causes heat accumulation and spontaneous combustion, and the safety is poor in the treatment of "triphenylbenzene" waste gas. In view of the single pore structure of the carbon aerogel material, the present invention uses phosphoric acid or magnesium oxide to improve the pore structure to further improve the adsorption performance of the material. The carbon aerogel prepared by the present invention exhibits excellent waste gas adsorption performance, is simple to prepare, is green and environmentally friendly, and has wide industrial application potential.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing carbon aerogel for air purification, comprising the following steps: (1) The natural polymer and deionized water are mixed evenly to prepare a solution, and then a cross-linking agent is added and stirred in a water bath at 70-80 °C. After the cross-linking reaction is completed, the solution is poured into a mold and allowed to stand to remove bubbles to obtain a composite hydrogel; (2) placing the composite hydrogel obtained in step (1) 1 to 2 cm above a rectangular steel tank filled with liquid nitrogen to allow it to be directionally frozen; after being completely frozen, demolding the sample and freeze-drying it for 24 to 48 hours to obtain an aerogel; (3) The aerogel material obtained in step (2) is impregnated in an activator solution and then dried in a vacuum drying oven at 110°C; subsequently, it is placed in a tubular furnace for heat treatment and washed with water to obtain a carbon aerogel material having a hierarchical porous structure.

[0006] The present invention uses natural polymer as raw material and adds a cross-linking agent to enhance the mechanical properties of the composite hydrogel; directional freezing can make the ice nucleus grow laterally and improve the stability of the material; appropriate activators and heat treatment can increase the mesoporosity of the carbon aerogel material, thereby improving the adsorption performance of the material.

[0007] As a further limitation of the technical solution of the present invention, the natural polymer described in step (1) is one or more of chitosan, cellulose and corn starch, and the cross-linking agent is one or an equal ratio mixture of sodium alginate and polyvinyl alcohol.

[0008] As a further limitation of the technical solution of the present invention, the mass ratio of the natural polymer, deionized water and cross-linking agent is 3-8:90-95:1-3.

[0009] As a further limitation of the technical solution of the present invention, the activator described in step (3) is phosphoric acid or magnesium oxide, the mass ratio of aerogel to activator is 1-2:1, the solvent of the activator solution is water or alcohol, and an appropriate amount of water or alcohol is added to make a solution for immersion, and the immersion time in the activator solution is ten minutes.

[0010] As a further limitation of the technical solution of the present invention, the heat treatment operation described in step (3) is specifically heating to 400-650°C at a heating rate of 5-10°C / min under argon flow conditions and maintaining the temperature for 1-3 hours.

[0011] As a further limitation of the technical solution of the present invention, the specific surface area of ​​the carbon aerogel material prepared in step (3) is 1000-1400 m 2 / g, pore volume 0.6~0.8 cm 3 / g, and the mesoporosity is 20%~30%.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention prepares a carbon aerogel material with excellent pore structure based on freeze drying and heat treatment process. The material prepared by the present invention has richer pore structure than traditional activated carbon, and does not require the addition of metal catalysts. The specific surface area is about 1000~1400 m 2 / g, pore volume is about 0.6~0.8 cm 3 / g, and the mesoporosity is 20%~30%.

[0013] 2. In the specific use process, the carbon aerogel material prepared by the present invention can handle both single components and complex components, and due to its elasticity, its desorption and recovery after adsorption saturation is simpler. Compared with the preparation process of traditional granular activated carbon, the process of the present invention is simple, avoiding the complicated processes such as traditional bonding, granulation, and modification, and the raw material source is wide, the equipment is simple, and it has the potential for mass production.

[0014] 3. The material of the present invention is ultra-light and heat-insulating, and is not prone to heat accumulation and spontaneous combustion, which greatly improves safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The present invention is a flow chart of the preparation method.

[0016] Figure 2 This is the nitrogen adsorption-desorption curve of the carbon aerogel material obtained in Example 1. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with specific embodiments. Example 1

[0018] A method for preparing carbon aerogel for air purification, the steps are as follows: Chitosan, cellulose and deionized water were mixed evenly to prepare a solution, and sodium alginate was added to stir in a water bath at 80 ℃ for cross-linking reaction. The mass ratio of chitosan, cellulose, deionized water and sodium alginate was 4:4:91:1. After the solution was finished, it was poured into a mold and allowed to stand to remove bubbles to obtain a composite hydrogel. The composite hydrogel was placed 1~2 cm above a rectangular steel tank filled with liquid nitrogen to freeze it in a directional manner; after complete freezing, the sample was demoulded and freeze-dried for 48 h to obtain an aerogel. The aerogel material was immersed in a phosphoric acid solution for ten minutes and dried in a vacuum drying oven at 110 ℃. The mass ratio of aerogel to activator was 2:1; it was then placed in a tubular furnace and heated to 550 ℃ at a heating rate of 5 ℃ / min under argon flow conditions and kept at a constant temperature for 2 h. After cooling, it was washed with water to obtain a carbon aerogel material.

[0019] In order to verify the performance of the prepared carbon aerogel material, the carbon aerogel material obtained in Example 1 was subjected to nitrogen adsorption and desorption experiments. The results are as follows: Figure 2 shown. Example 2

[0020] A method for preparing carbon aerogel for air purification, the steps are as follows: Chitosan, corn starch and deionized water were mixed evenly to prepare a solution, and sodium alginate was added and stirred in a water bath at 70 ℃ for cross-linking reaction. The mass ratio of chitosan, corn starch, deionized water and sodium alginate was 3:4:91:2. After the end, the solution was poured into a mold and allowed to stand to remove bubbles to obtain a composite hydrogel. The composite hydrogel was placed 1~2 cm above a rectangular steel tank filled with liquid nitrogen to freeze it in a directional manner; after complete freezing, the sample was demoulded and freeze-dried for 36 h to obtain an aerogel. The aerogel material was immersed in a phosphoric acid solution for ten minutes and dried in a vacuum drying oven at 110 ℃. The mass ratio of aerogel to activator was 1.5:1; it was then placed in a tubular furnace and heated to 550 ℃ at a heating rate of 5 ℃ / min under argon flow conditions and kept at a constant temperature for 2 h. After cooling, it was washed with water to obtain a carbon aerogel material. Example 3

[0021] A method for preparing carbon aerogel for air purification, the steps are as follows: Corn starch, cellulose and deionized water were mixed evenly to prepare a solution, and polyvinyl alcohol was added and stirred in a water bath at 80 ℃ for cross-linking reaction. The mass ratio of corn starch, cellulose, deionized water and polyvinyl alcohol was 4:4:90:2. After the solution was finished, it was poured into a mold and allowed to stand to remove bubbles to obtain a composite hydrogel. The composite hydrogel was placed 1~2 cm above a rectangular steel tank filled with liquid nitrogen to freeze it in a directional manner; after complete freezing, the sample was demoulded and freeze-dried for 48 h to obtain an aerogel. The aerogel material was immersed in a phosphoric acid solution for ten minutes and dried in a vacuum drying oven at 110 ℃. The mass ratio of aerogel to activator was 1.5:1; it was then placed in a tubular furnace and heated to 600 ℃ at a heating rate of 5 ℃ / min under argon flow conditions and kept at a constant temperature for 2 h. After cooling, it was washed with water to obtain a carbon aerogel material.

[0022] The above examples are only some preferred examples of the present invention and cannot limit the patent scope of the present invention. If the relevant contents are replaced by the same examples, they should all be included in the protection scope of the present invention.

Claims

1. A method for preparing carbon aerogel for air purification, characterized in that: The following steps are involved: (1) The natural polymer and deionized water are mixed evenly to prepare a solution, and then a cross-linking agent is added and stirred in a water bath at 70-80 °C. After the cross-linking reaction is completed, the solution is poured into a mold and allowed to stand to remove bubbles to obtain a composite hydrogel; (2) placing the composite hydrogel obtained in step (1) 1 to 2 cm above a rectangular steel tank filled with liquid nitrogen to allow it to be directionally frozen; after being completely frozen, demolding the sample and freeze-drying it for 24 to 48 hours to obtain an aerogel; (3) The aerogel material obtained in step (2) is impregnated in an activator solution and then dried in a vacuum drying oven at 110°C; subsequently, it is placed in a tubular furnace for heat treatment and washed with water to obtain a carbon aerogel material having a hierarchical porous structure.

2. The method for preparing carbon aerogel for air purification according to claim 1, characterized in that: The natural polymer described in step (1) is one or more of chitosan, cellulose and corn starch, and the cross-linking agent is one or an equal ratio mixture of sodium alginate and polyvinyl alcohol.

3. The method for preparing carbon aerogel for air purification according to claim 1, characterized in that: The mass ratio of the natural polymer, deionized water and cross-linking agent is 3-8:90-95:1-3.

4. The method for preparing carbon aerogel for air purification according to claim 1, characterized in that: The activator described in step (3) is phosphoric acid or magnesium oxide, the mass ratio of aerogel to activator is 1-2:1, the solvent of the activator solution is water or alcohol, and the immersion time in the activator solution is ten minutes.

5. The method for preparing carbon aerogel for air purification according to claim 1, characterized in that: The heat treatment operation described in step (3) is specifically to heat to 400-650°C at a heating rate of 5-10°C / min under argon flow conditions and keep the temperature constant for 1-3 hours.

6. The method for preparing carbon aerogel for air purification according to claim 1, characterized in that: The specific surface area of ​​the carbon aerogel material prepared in step (3) is 1000~1400 m 2 / g, pore volume 0.6~0.8 cm 3 / g, and the mesoporosity is 20%~30%.

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