Alkali metal modified waste plastic-based porous carbon and preparation method thereof

Abstract

The invention discloses waste-plastic-based porous carbon and a preparation method thereof.The preparation method comprises the steps that waste plastic and medical waste incineration slag serve as raw materials, the waste plastic and the medical waste incineration slag are crushed to obtain raw material particles of a certain mesh number, then the waste plastic particles are subjected to high-temperature carbonization to obtain waste-plastic-based pyrolytic carbon, the medical waste incineration slag particles are subjected to acid treatment, and the waste-plastic-based pyrolytic carbon is obtained; and then mixing, ball-milling and co-activating at high temperature, so that the alkali metal component in the slag is chemically loaded on the surfaces of the carbon particles, thereby obtaining the alkali metal modified waste plastic-based porous carbon. The solid waste is used as a basic raw material, the synthesis route is simple, expensive equipment / chemical reagents are not needed, the operation cost is greatly reduced, large-scale production is guaranteed, and the obtained porous carbon has good adsorption performance on volatile organic compounds.

Description

Technical Field

[0001] This invention belongs to the field of porous carbon material preparation technology, specifically relating to an alkali metal-modified waste plastic-based porous carbon and its preparation method. Background Technology

[0002] Volatile organic pollutants are a very important class of pollutants in the atmospheric environment, and are part of PM2.5. 2.5 Volatile organic pollutants (VOCs) are key precursors to ozone formation. Regarding their health hazards, VOCs have irritating odors that directly irritate the skin and eyes, damage the nervous and respiratory systems, and pose significant health risks. Therefore, VOC emission reduction has received increasing attention. VOCs have a wide range of sources, and many low-concentration emission sources exist in engineering practice, such as electronics manufacturing and small car repair shops, significantly increasing VOC emissions. There are many methods for removing VOCs, including absorption, adsorption, catalytic oxidation, membrane separation, catalytic combustion, and biodegradation. Among these, adsorption is the most promising method for the efficient removal of low-concentration organic pollutants.

[0003] Carbon-based adsorbents, especially activated carbon, are among the most widely used adsorbent materials. However, conventional commercial activated carbon, primarily composed of graphite surfaces, exhibits weak adsorption capacity for volatile organic compounds (VOCs), particularly limited adsorption performance for polar VOCs. Therefore, to improve adsorption performance, activated carbon surfaces are typically modified through acid treatment, metal ion modification, or heteroatom loading. However, most modification processes are complex, produce numerous byproducts, and are costly, hindering large-scale industrial production. Therefore, developing low-cost, high-adsorption-performance carbon-based adsorbent materials is crucial for ensuring the efficient removal of low-concentration VOCs. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an alkali metal-modified waste plastic-based porous carbon and its preparation method, which can be applied to the efficient adsorption and removal of low-concentration polar volatile organic pollutants, providing a new method to solve the problems of high preparation cost and low removal efficiency of organic pollutants in functionalized carbon materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: One objective of this invention is to protect a method for preparing alkali metal-modified waste plastic-based porous carbon, which includes the following steps: (1) Pre-treat waste plastics and medical waste incineration slag separately; (2) The waste plastics pretreated in step (1) are carbonized at high temperature to obtain waste plastic-based pyrolytic carbon; (3) Acid treatment is performed on the medical waste incineration slag after the pretreatment in step (1); (4) The waste plastic-based pyrolytic carbon obtained in step (2) is mixed with the medical waste incineration slag after acid treatment in step (3) and then ball-milled. Then it is co-activated at high temperature so that the alkali metal components in the medical waste incineration slag are chemically loaded on the surface of the waste plastic-based pyrolytic carbon particles. After that, the product is sequentially acid-washed, water-washed and dried to obtain the waste plastic-based porous carbon.

[0006] Furthermore, the waste plastics mentioned in step (1) mainly refer to high molecular polymers with oxygen-containing elements, including polyethylene terephthalate, polycarbonate, phenolic resin, polyurethane, etc.

[0007] Furthermore, in step (1), the pretreatment of waste plastics involves cooling and crushing them in liquid nitrogen to obtain waste plastic particles of 80-100 mesh.

[0008] Furthermore, the medical waste incineration slag mentioned in step (1) is the slag produced after incinerating incinerable medical waste, including infectious waste, sharps waste, pathological waste, pharmaceutical waste, and chemical waste, with a SiO2 content of less than 35% and a total Na2O and K2O content of more than 6%.

[0009] Furthermore, in step (1), the pretreatment of medical waste incineration slag involves crushing it into slag particles of 120-150 mesh.

[0010] Furthermore, the high-temperature carbonization described in step (2) is carried out under a nitrogen atmosphere, with a carbonization temperature of 400~500℃, a heating rate of 5~10℃ / min, a time of 30~120 min, and a nitrogen gas flow rate of 200~500 mL / min.

[0011] Furthermore, the acid treatment in step (3) is to impregnate with hydrofluoric acid solution; the volume concentration of the hydrofluoric acid solution is 5~10%, and its dosage is calculated based on the water content in the slag after impregnation being 25~45%, and the impregnation time is 2~4 h.

[0012] Furthermore, during the mixing process in step (4), the mass percentage of the acid-treated medical waste incinerator slag in the mixture is 15-25%.

[0013] Furthermore, the ball milling time in step (4) is 2 to 6 hours.

[0014] Further, in step (4), the high-temperature co-activation uses water vapor or CO2 as the activator and nitrogen as the carrier gas. The nitrogen gas flow rate is 200~500 mL / min, and the volume content of water vapor or CO2 is 5~25%. The activation temperature is 600~800 ℃, the heating rate is 5~10 ℃ / min, and the time is 30~120 min.

[0015] Furthermore, the acid washing in step (4) uses a hydrochloric acid solution of 0.2~1 mol / L.

[0016] Further, in step (4), the solution is washed with water until the pH of the washing solution is neutral.

[0017] Furthermore, the drying temperature in step (4) is 100~110 ℃ and the time is 12~24h.

[0018] A second objective of this invention is to protect the alkali metal-modified waste plastic-based porous carbon prepared by the method described above.

[0019] The beneficial effects of this invention are as follows: (1) The present invention selects waste plastic with a large annual output as carbon source and medical waste incineration slag with high alkaline component content as metal source, which can greatly reduce the material preparation cost. Moreover, the preparation method of porous carbon is simple, with few by-products, and has significant environmental protection advantages, making it suitable for large-scale industrial production.

[0020] (2) This invention fully utilizes the characteristics of medical waste incineration slag, which has low silicon content, high alkaline metal content, and unburned carbon. During the co-activation process, the alkaline components are converted into metal ion adsorption sites on the surface of waste plastic-based porous carbon. These sites can enhance the adsorption of volatile organic pollutants through the dual effects of electrostatic attraction and hydrogen bonding, thereby improving the capture efficiency of organic pollutants. At the same time, the alkaline metal components also have a catalytic effect on the formation of pores during carbon formation, which can further improve the activation efficiency. In addition, medical waste incineration slag also contains a small amount of copper, iron, nickel, and other metal components, which are also converted into metal active sites on the carbon surface during carbon formation. Therefore, they can enhance the adsorption of organic pollutants through electron transfer, greatly improving the adaptability and compatibility of plastic-based porous carbon to complex organic pollutant waste gas, and providing a guarantee for the engineering application of porous carbon.

[0021] In summary, this invention fully utilizes the organic components of waste plastics and the metal components in medical waste incineration slag, transforming the metal components into metal adsorption sites on the carbon surface through a co-activation method. This enhances the adsorption capacity of carbon materials for volatile organic pollutants and promotes their efficient capture of organic molecules. Furthermore, the porous carbon preparation process in this invention is simple, low-cost, and produces few byproducts, exhibiting strong adaptability to low-concentration waste gases. It broadens the ways to utilize solid waste at high value and has significant implications for the construction of "zero-waste cities" and the realization of carbon reduction and emission reduction. Attached Figure Description

[0022] Figure 1 The graph shows a comparison of the adsorption capacity of waste plastic-based porous carbon prepared in Examples (a) and Comparative Examples 1-2 (bc) with that of commercial activated carbon (d) for volatile organic compounds. Detailed Implementation

[0023] An alkali metal-modified waste plastic-based porous carbon, the preparation of which includes the following steps: (1) Cool and crush waste plastics in liquid nitrogen to obtain waste plastic particles of 80-100 mesh; (2) Crush the medical waste incineration slag into slag particles of 120-150 mesh; (3) The waste plastic particles obtained in step (1) are carbonized at high temperature under a nitrogen atmosphere. The carbonization temperature is 400~500 ℃, the heating rate is 5~10 ℃ / min, the time is 30~120 min, and the N2 flow rate is 200~500 mL / min to obtain waste plastic-based pyrolytic carbon. (4) Use a hydrofluoric acid solution with a volume concentration of 5-10% to acid-wet the slag particles obtained in step (2). The amount of hydrofluoric acid solution used is calculated based on the water content in the slag after wetting being 25-45%, and the wetting time is 2-4 hours. (5) The waste plastic-based pyrolytic carbon obtained in step (3) and the medical waste incineration slag after acid treatment in step (4) are mixed at a mass percentage ratio of 85~75:15~25 and ball-milled for 2~6 hours. Then, high-temperature co-activation is carried out using N2 as carrier gas and water vapor or CO2 as activator. The N2 flow rate is 200~500 mL / min, and the volume content of water vapor or CO2 is 5~25%. The activation temperature is 600~800 ℃, the heating rate is 5~10 ℃ / min, and the time is 30~120 min, so that the alkali metal components in the medical waste incineration slag are chemically loaded on the surface of the waste plastic-based pyrolytic carbon particles. Then, the product is acid-washed with 0.2~1 mol / L hydrochloric acid solution, and then washed with deionized water until the pH of the washing liquid is neutral. Finally, it is dried in hot air at 100~110 ℃ for 12~24 hours to obtain the waste plastic-based porous carbon.

[0024] The waste plastics mentioned mainly refer to high molecular polymers containing oxygen, including polyethylene terephthalate, polycarbonate, phenolic resin, and polyurethane. The medical waste incineration slag is the slag produced after incinerating incinerable medical waste, including infectious waste, sharps waste, pathological waste, pharmaceutical waste, and chemical waste, with a SiO2 content of less than 35% and a total Na2O and K2O content of more than 6%.

[0025] The carbon surface of the waste plastic-based porous carbon prepared in this invention is modified by alkaline metal ions and a small amount of copper, iron and nickel in medical waste incineration slag, forming metal adsorption sites. Therefore, it exhibits strong electrostatic and hydrogen bonding effects on volatile organic pollutants, which can promote the efficient capture of low-concentration organic molecules and improve the removal efficiency.

[0026] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto. Example

[0027] An alkali metal-modified porous carbon based on waste plastics is prepared by the following steps: S1: Select waste mineral water bottles made of polyethylene terephthalate as raw materials, cool them in liquid nitrogen, and then pulverize them by ball milling to obtain waste plastic particles of 80~100 mesh. S2: Collect slag from the outlet of the rotary kiln for medical waste incineration, ball mill and crush it to obtain slag particles of 120-150 mesh, the chemical composition of which is shown in Table 1. Table 1 Chemical composition of slag particles

[0028] S3: Weigh 15 g of the waste plastic granules obtained in step S1, put them into a porcelain crucible, and load them into a tube furnace for high-temperature carbonization at 400 ℃ for 60 min under N2 atmosphere (heating rate of 5 ℃ / min, N2 flow rate of 200 mL / min) to obtain waste plastic-based pyrolytic carbon. S4: Take 2 g of the slag particles obtained in step S2, add 0.8 g of hydrofluoric acid solution with a volume concentration of 5% dropwise, and soak for 3 h; S5: Mix the plastic-based pyrolytic carbon prepared in step S3 with the acid-wetted slag particles obtained in step S4, ball mill for 3 h, and then put it into a tube furnace. Use N2 as carrier gas and CO2 as activator (N2 flow rate is 300 mL / min, CO2 volume fraction is 15%), and activate at 700 ℃ for 60 min (heating rate is 10 ℃ / min). After activation, cool to room temperature under N2 atmosphere. S6: The porous carbon prepared in step S5 is washed with 0.5 mol / L hydrochloric acid and then washed with deionized water until the pH of the washing solution is neutral. Then it is dried in a drying oven at 105 °C for 24 h to obtain waste plastic-based porous carbon, in which the total loading of Na and K is about 6%.

[0029] Comparative Example 1 A porous carbon based on waste plastics, the preparation steps of which are as follows: S1: Select waste mineral water bottles made of polyethylene terephthalate as raw materials, cool them in liquid nitrogen, and then pulverize them by ball milling to obtain waste plastic particles of 80~100 mesh. S2: Place 15 g of waste plastic granules obtained in step S1 into a porcelain crucible, load it into a tube furnace, and carbonize it at 400 °C for 60 min under N2 atmosphere (heating rate of 5 °C / min, N2 flow rate of 200 mL / min) to obtain waste plastic-based pyrolytic carbon. S3: After ball milling the plastic-based pyrolytic carbon prepared in step S2 for 3 h, place it in a tube furnace, use N2 as carrier gas and CO2 as activator (N2 flow rate is 300 mL / min, CO2 volume fraction is 15%), activate at 700 ℃ for 60 min (heating rate is 10℃ / min), and after activation, cool to room temperature under N2 atmosphere. S4: The porous carbon prepared in step S3 is washed with 0.5 mol / L hydrochloric acid, then washed with deionized water until the pH of the washing solution is neutral, and then dried in a drying oven at 105 ℃ for 24 h to obtain waste plastic-based porous carbon.

[0030] Comparative Example 2 A potassium-modified porous carbon based on waste plastics is prepared by the following steps: S1: Select waste mineral water bottles made of polyethylene terephthalate as raw materials, cool them in liquid nitrogen, and then pulverize them by ball milling to obtain waste plastic particles of 80~100 mesh. S2: Place 15 g of the waste plastic granules obtained in step S1 into a porcelain crucible, load it into a tube furnace, and carbonize it at 400 ℃ for 60 min under N2 atmosphere (heating rate is 5 ℃ / min, N2 flow rate is 200 mL / min) to obtain waste plastic-based pyrolytic carbon. S3: Weigh 2.0 g of the plastic-based pyrolytic carbon prepared in step S2, impregnate it with 5.2 mL of a mixed solution of KCl and NaCl (where the mass concentration of KCl is 1.23% and the molar concentration of NaCl is 1.97%) for 2 h, then ball mill it for 3 h and place it in a tube furnace. Use N2 as the carrier gas and CO2 as the activator (N2 flow rate is 300 mL / min, CO2 volume fraction is 15%), and activate it at 700 ℃ for 60 min (heating rate is 10 ℃ / min). After activation, cool it to room temperature under N2 atmosphere. S4: The porous carbon prepared in step S3 is washed with 0.5 mol / L hydrochloric acid and then washed with deionized water until the pH of the washing solution is neutral. Then it is dried in a drying oven at 105 °C for 24 h to obtain Na and K modified waste plastic-based porous carbon, wherein the total loading of Na and K is about 6%.

[0031] The surface chemical composition of the waste plastic-based porous carbon prepared in the examples and comparative examples was detected by X-ray photoelectron spectroscopy, and the results are shown in Table 2.

[0032] Table 2 Chemical composition of porous carbon surface based on waste plastic (%)

[0033] As shown in Table 2, the Na and K elements on the surface of the porous carbon prepared in the examples are 4.21% and 1.86%, respectively, indicating that there is basically no loss of alkaline metal elements during the activation process after loading. In contrast, the waste plastic-based porous carbon prepared by KCl and NaCl mixture in Comparative Example 2 has a small amount of alkaline components lost during the thermal activation process.

[0034] The pore structure characteristics of the waste plastic-based porous carbon and coconut shell-based commercial activated carbon prepared in the examples and comparative examples were detected by N2 adsorption method, and the key parameters are shown in Table 3.

[0035] Table 3 Pore structure parameters of porous carbon based on different waste plastics

[0036] As shown in Table 3, the porous carbon prepared in the examples has a specific surface area as high as 1465.4 m². 2 / g, total pore volume is 0.6631 m³ 3 / g, with more micro-mesoporous structures. In contrast, the specific surface area and pore volume of the waste plastic-based porous carbon prepared by the comparative example without the addition of medical waste incineration slag or by directly using a mixed solution of metal ions were smaller than those of the porous carbon prepared in the example. This indicates that the added medical waste incineration slag did not block the pores of the carbon material and could even promote pore formation.

[0037] Performance testing: Commonly used propanol, ethyl acetate, and acetone were selected as target compounds to test the volatile organic compound adsorption performance of the waste plastic-based porous carbon prepared in the examples and comparative examples.

[0038] (1) The adsorption performance of volatile organic compounds was evaluated on a fixed-bed reactor with an inner diameter of 10 mm and a length of 400 mm. N2 was used as the balance gas. Adsorption conditions: Volatile organic compound concentration: 50 mg / m³ 3 The adsorption temperature was 40 °C, the total gas flow rate was 1 L / min, and the amount of porous carbon used was 100 mg. The adsorption breakthrough curve was tested using a portable volatile organic compound (VOC) detection device.

[0039] (2) The saturated adsorption capacity of the three volatile organic compounds on porous carbon was obtained by integration. The results are shown in the figure. Figure 1 .

[0040] from Figure 1It can be seen that the waste plastic-based porous carbon prepared in the examples exhibits saturated adsorption capacities of 125.6 mg / g, 160.7 mg / g, and 116.2 mg / g for propanol, ethyl acetate, and acetone, respectively. The adsorption capacity for acetone is 4.1 times that of commercial activated carbon (the adsorption capacities of commercial activated carbon are all below 50 mg / g). In contrast, the unmodified porous carbon in Comparative Example 1 exhibits saturated adsorption capacities of 88.3 mg / g, 90.7 mg / g, and 65.2 mg / g for propanol, ethyl acetate, and acetone, respectively, significantly lower than the adsorption performance of the porous carbon prepared in the examples. However, its adsorption capacity is higher than that of commercial activated carbon, mainly due to its larger specific surface area. The K and Na modified waste plastic-based porous carbon prepared in Comparative Example 2 showed an adsorption capacity of 6.12-9.33% higher for three volatile organic compounds than that in Comparative Example 1, indicating that the modification with alkali metal ions promoted the improvement of the material's adsorption performance. However, its adsorption effect was still significantly lower than that of the porous carbon prepared in the examples. This fully demonstrates that the doping and co-activation of medical waste incineration slag has multiple effects on the waste plastic-based porous carbon, such as multi-metal component chemical modification and pore expansion. It also proves that the porous carbon prepared by co-activation of waste plastic coupled with medical waste incineration slag has excellent adsorption performance and high potential for engineering applications.

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing alkali metal-modified waste plastic-based porous carbon, characterized in that, It includes the following steps: (1) Pre-treat waste plastics and medical waste incineration slag separately; (2) The waste plastics pretreated in step (1) are carbonized at high temperature to obtain waste plastic-based pyrolytic carbon; (3) Acid treatment is performed on the medical waste incineration slag after the pretreatment in step (1); (4) The waste plastic-based pyrolytic carbon obtained in step (2) is mixed with the medical waste incineration slag after acid treatment in step (3) and then ball-milled. Then it is co-activated at high temperature so that the alkali metal components in the medical waste incineration slag are chemically loaded on the surface of the waste plastic-based pyrolytic carbon particles. After that, the product is sequentially acid-washed, water-washed and dried to obtain the waste plastic-based porous carbon.

2. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, In step (1), the pretreatment of waste plastics involves cooling and crushing them in liquid nitrogen to obtain waste plastic particles of 80-100 mesh.

3. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, In step (1), the pretreatment of medical waste incineration slag involves crushing it into slag particles of 120-150 mesh; the SiO2 content in the medical waste incineration slag is less than 35%, and the total content of Na2O and K2O is greater than 6%.

4. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, The high-temperature carbonization described in step (2) is carried out under a nitrogen atmosphere, with a carbonization temperature of 400~500 ℃ and a time of 30~120 min.

5. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, The acid treatment in step (3) is to impregnate the slag with hydrofluoric acid solution. The volume concentration of the hydrofluoric acid solution is 5-10%, and the amount used is calculated based on the water content of 25-45% in the slag after impregnation. The impregnation time is 2-4 hours.

6. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, In step (4), the mass percentage of the acid-treated medical waste incinerator slag in the mixture is 15-25%.

7. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, The ball milling time in step (4) is 2 to 6 hours.

8. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, In step (4), the high-temperature co-activation uses water vapor or CO2 as the activator and N2 as the carrier gas, wherein the volume content of water vapor or CO2 is 5~25%; the activation temperature is 600~800 ℃ and the time is 30~120 min.

9. The method for preparing waste plastic-based porous carbon according to claim 1, characterized in that, The drying temperature in step (4) is 100~110 ℃ and the time is 12~24h.

10. An alkali metal-modified waste plastic-based porous carbon prepared by any one of claims 1 to 9.

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