Activated carbon for adsorbing dioxin and preparation method thereof

Abstract

The invention discloses activated carbon for adsorbing dioxin and a preparation method of the activated carbon, and belongs to the field of activated carbon preparation. The activated carbon is prepared by the following steps: firstly, mixing coconut shell charcoal with phosphoric acid, performing activating treatment in a microwave reactor, and then calcining to obtain coconut shell-based activated carbon; then soaking the coconut shell-based activated carbon in a ferrous chloride solution, adding an antioxidant, and drying after soaking; and dipping the coconut shell-based activated carbon in a ferrocene mixed solution, and drying after dipping to obtain the activated carbon for adsorbing dioxin. By constructing a micropore-mesopore structure, the dioxin containing capacity of the activated carbon is remarkably enhanced, ferrocene is loaded on the surface of the activated carbon, and the combining capacity of the activated carbon and the dioxin is further improved.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon preparation, specifically relating to an activated carbon for adsorbing dioxins and its preparation method. Background Technology

[0002] Dioxins are a class of highly toxic and persistent organic pollutants, mainly originating from processes such as waste incineration and chemical production. Due to their large molecular weight, stable structure, and tendency to accumulate in organisms, the development of highly efficient adsorption materials has become crucial for pollution control.

[0003] Activated carbon, due to its high specific surface area and abundant pore structure, is widely used for dioxin adsorption. Traditional activated carbon is predominantly microporous, but dioxin molecules are relatively large and often combine with fly ash particles to form even larger complexes, resulting in poor accessibility to micropores and limiting adsorption capacity. Conventional preparation processes offer limited control over the functional groups (such as carboxyl and phenolic hydroxyl groups) on the activated carbon surface, lacking specific adsorption sites targeting the hydrophobic and aromatic ring structures of dioxins, thus resulting in insufficient selective adsorption capacity. Summary of the Invention

[0004] Given the shortcomings of existing technologies, the purpose of this invention is to provide activated carbon for adsorbing dioxins and its preparation method, which enhances selective adsorption by introducing π-π interaction sites and hydrophobically modified surfaces.

[0005] The first aspect of this invention is to provide a method for preparing activated carbon for adsorbing dioxins, comprising the following steps: S1: Coconut shell charcoal and phosphoric acid are mixed at a mass ratio of 1:2-4, activated in a microwave reactor, and then calcined to obtain coconut shell-based activated carbon; S2: Coconut shell-based activated carbon is impregnated in ferrous chloride solution, an antioxidant is added, and then dried after impregnation; S3: The coconut shell-based activated carbon treated by S2 is impregnated in a ferrocene mixed solution, and dried after impregnation to obtain activated carbon for adsorbing dioxins; wherein, the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 2-8 wt%.

[0006] It should be noted that microwave heating works by directly applying electromagnetic waves to polar molecules. In a microwave field, the polar molecules of phosphate vibrate violently, generating local hot spots. High-concentration phosphate rapidly diffuses to form micropores (1-2 nm). As the penetration gradually deepens, the phosphate concentration decreases, leading to impeded migration and the slow formation of mesopores (2-5 nm). This creates a gradient structure that is dense on the outside and sparse on the inside, which is more suitable for the size of dioxin molecules and increases the range of absorbable particles.

[0007] In addition to the above technical points, the present application also dips the coconut shell-based activated carbon in a ferrous chloride solution, so that the ferrous ions form active sites on the surface of the activated carbon, facilitating the subsequent loading of ferrocene on the activated carbon. Then, the coconut shell-based activated carbon is dipped in a ferrocene mixed solution, so that the ferrocene is loaded on the activated carbon. The ferrocene not only has an aromatic ring similar to the aromatic ring of dioxin, which can form a pi-pi stacking effect with the aromatic ring of dioxin to attract each other, but also has ferrous ions which can form an ion-dipole effect with the electronegative chlorine atoms of dioxin, thereby improving the binding force with dioxin.

[0008] In some embodiments, the phosphoric acid concentration is 40-60 wt%.

[0009] In some embodiments, the microwave reactor power is 750-800 W, and the activation treatment time is 10-20 min.

[0010] In some embodiments, the calcination in S1 is calcination under inert gas protection at 500-600℃ for 2-3h.

[0011] In some embodiments, the inert gas is nitrogen.

[0012] The calcination under inert gas protection is to prevent the oxidation of the carbon skeleton.

[0013] In some embodiments, the ferrous chloride solution concentration is 8-10 wt%.

[0014] In some embodiments, the antioxidant is 0.1M citric acid.

[0015] In some embodiments, the dipping in S2 and S3 is carried out under ultrasonic conditions, the ultrasonic frequency is 20-40 kHz, and the dipping time is 30-60 min.

[0016] In some embodiments, the drying temperature in S2 and S3 is 60-80℃.

[0017] If the temperature is too high, the ferrocene will sublimate and be lost.

[0018] The second aspect of the present application provides a preparation method of activated carbon for adsorbing dioxin.

[0019] Compared with the prior art, the present application has the following beneficial effects: 1. The activated carbon for adsorbing dioxin provided by the present application has a microporous-mesoporous structure, which is highly matched with the size of dioxin molecules (0.5-1.5 nm) and fly ash compounds, significantly improves the adsorption capacity and diffusion efficiency, and significantly enhances the pollution capacity of the activated carbon.

[0020] 2、The application successfully loads ferrocene on the surface of activated carbon by successively immersing in ferrous chloride solution and ferrocene mixed solution, ferrocene can form π-π stacking effect with the aromatic ring of dioxin to attract each other, and can also form ion-dipole effect with the electronegative chlorine atom of dioxin, greatly improving the binding force of activated carbon and dioxin. DETAILED DESCRIPTION

[0021] The application will be further described in detail below with examples.

[0022] Example 1 A preparation method of activated carbon for adsorbing dioxin, comprising the following steps: S1: coconut shell carbon is mixed with 50 wt% phosphoric acid at a mass ratio of 1:3, activated in a microwave reactor at a power of 800 W for 15 min, then calcined at 550 DEG C for 3 h under nitrogen protection to obtain coconut shell-based activated carbon; S2: the coconut shell-based activated carbon is immersed in 9 wt% ferrous chloride solution at an ultrasonic frequency of 30 kHz for 40 min, 0.1M citric acid is added, and then dried at 70 DEG C after immersion; S3: the coconut shell-based activated carbon treated by S2 is immersed in a ferrocene mixed solution at an ultrasonic frequency of 30 kHz for 40 min, and then dried at 70 DEG C after immersion to obtain activated carbon for adsorbing dioxin; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 6 wt%.

[0023] Example 2 A preparation method of activated carbon for adsorbing dioxin, comprising the following steps: S1: coconut shell carbon is mixed with 60 wt% phosphoric acid at a mass ratio of 1:2, activated in a microwave reactor at a power of 750 W for 20 min, then calcined at 600 DEG C for 2 h under nitrogen protection to obtain coconut shell-based activated carbon; S2: the coconut shell-based activated carbon is immersed in 10 wt% ferrous chloride solution at an ultrasonic frequency of 40 kHz for 30-60 min, 0.1M citric acid is added, and then dried at 60-80 DEG C after immersion; S3: the coconut shell-based activated carbon treated by S2 is immersed in a ferrocene mixed solution at an ultrasonic frequency of 20-40 kHz for 50 min, and then dried at 60 DEG C after immersion to obtain activated carbon for adsorbing dioxin; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 8 wt%.

[0024] Example 3 A preparation method of activated carbon for adsorbing dioxin, comprising the following steps: S1: Coconut shell charcoal was mixed with 40 wt% phosphoric acid at a mass ratio of 1:2, activated in a microwave reactor at a power of 750 W for 10 min, and then calcined at 500°C for 2 h under nitrogen protection to obtain coconut shell-based activated carbon; S2: The coconut shell-based activated carbon was immersed in a 8 wt% ferrous chloride solution at an ultrasonic frequency of 20 kHz for 30 min, 0.1M citric acid was added, and then dried at 60°C after immersion; S3: The coconut shell-based activated carbon treated by S2 was immersed in a ferrocene mixed solution at an ultrasonic frequency of 20 kHz for 30 min, and then dried at 60°C after immersion to obtain activated carbon for adsorbing dioxins; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 2 wt%.

[0025] Example 4 A preparation method of activated carbon for adsorbing dioxins, comprising the following steps: S1: Coconut shell charcoal was mixed with 60 wt% phosphoric acid at a mass ratio of 1:2, activated in a microwave reactor at a power of 800 W for 20 min, and then calcined at 600°C for 3 h under nitrogen protection to obtain coconut shell-based activated carbon; S2: The coconut shell-based activated carbon was immersed in a 10 wt% ferrous chloride solution at an ultrasonic frequency of 40 kHz for 60 min, 0.1M citric acid was added, and then dried at 80°C after immersion; S3: The coconut shell-based activated carbon treated by S2 was immersed in a ferrocene mixed solution at an ultrasonic frequency of 40 kHz for 60 min, and then dried at 80°C after immersion to obtain activated carbon for adsorbing dioxins; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 8 wt%.

[0026] Example 5 A preparation method of activated carbon for adsorbing dioxins, comprising the following steps: S1: Coconut shell charcoal was mixed with 45 wt% phosphoric acid at a mass ratio of 1:3, activated in a microwave reactor at a power of 750 W for 15 min, and then calcined at 550°C for 2.5 h under nitrogen protection to obtain coconut shell-based activated carbon; S2: The coconut shell-based activated carbon was immersed in a 10 wt% ferrous chloride solution at an ultrasonic frequency of 30 kHz for 30 min, 0.1M citric acid was added, and then dried at 70°C after immersion; S3: The coconut shell-based activated carbon treated by S2 was immersed in a ferrocene mixed solution at an ultrasonic frequency of 30 kHz for 60 min, and then dried at 80°C after immersion to obtain activated carbon for adsorbing dioxins; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 7 wt%.

[0027] Comparative Example 1 On the basis of Example 1, S1 is omitted, that is, the coconut shell charcoal is not subjected to activation treatment.

[0028] Comparative Example 2 On the basis of Example 1, S3 is omitted, that is, the ferrocene is not loaded on the surface of the activated carbon.

[0029] Comparative Example 3 On the basis of Example 1, the ferrous chloride in S2 is replaced by ferric chloride.

[0030] The activated carbon obtained in the examples and comparative examples is subjected to pore size testing by using an ASAP 2020 full-automatic rapid specific surface area and mesopore micropore analyzer, and the testing results are shown in Table 1.

[0031] Table 1 As can be seen from Table 1, the micropore-mesopore ratio in Examples 1-5 of the present application is higher than 70%, and the micropore-mesopore ratio in Comparative Example 1 is greatly reduced because the coconut shell charcoal is not activated, which shows that after the coconut shell charcoal is mixed with phosphoric acid and subjected to microwave heating, the polar molecules of the phosphoric acid can be shaken violently to generate a large number of micropores and mesopores.

[0032] The activated carbon obtained in the examples and comparative examples is placed in an adsorption device, and flue gas containing dioxins with a concentration of 5.5 ng TEQ / m 3 is continuously introduced into the adsorption device, wherein the total adsorption time is 14 h, and a high-resolution mass spectrometer produced by Japan JEOL Company is used to detect the concentration of dioxins at the outlet of the adsorption device, and the testing results are shown in Table 2.

[0033] Table 2 As can be seen from Table 2, the activated carbon for adsorbing dioxins provided in the present application can effectively adsorb and remove dioxins, and the adsorption effect is much better than that of each comparative example; in combination with the comparative examples, it can be seen that the adsorption capacity of the activated carbon for dioxins is reduced in Comparative Example 1 due to the small micropore-mesopore ratio, which leads to poor adsorption effect, although the micropore-mesopore structure is formed in Comparative Example 2, the combination ability of the activated carbon and dioxins is reduced due to the absence of ferrocene loaded on the surface of the activated carbon, which leads to poor adsorption and removal effect of dioxins, and the impregnation effect of ferrocene is poor in Comparative Example 3 because the ferrous ions cannot form active sites on the surface of the activated carbon after the ferrous chloride is replaced by ferric chloride, which reduces the adsorption capacity of the activated carbon for dioxins, which shows that only the iron component consistent with ferrocene can improve the impregnation effect of ferrocene.

[0034] The above merely describes some embodiments of the present application. For those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A method for producing activated carbon for adsorbing dioxins, characterized by, The method comprises the following steps: S1: mixing coconut shell charcoal and phosphoric acid at a mass ratio of 1:2-4, carrying out activation treatment in a microwave reactor, and then calcining to obtain coconut shell-based activated carbon; S2: immersing the coconut shell-based activated carbon in a ferrous chloride solution, adding an antioxidant, drying after immersion; S3: immersing the coconut shell-based activated carbon treated in S2 in a ferrocene mixed solution, drying after immersion to obtain the activated carbon for adsorbing dioxins; wherein the ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the ferrocene concentration is 2-8 wt%.

2. The method for producing activated carbon for adsorbing dioxins according to claim 1, characterized by, The concentration of the phosphoric acid is 40-60 wt%.

3. The method for producing activated carbon for adsorbing dioxins according to claim 1, characterized by, The power of the microwave reactor is 750-800 W, and the activation treatment time is 10-20 min.

4. The method for producing activated carbon for adsorbing dioxins according to claim 1, characterized by, In S1, the calcination is calcination at 500-600 DEG C for 2-3 h under the protection of inert gas.

5. The method for producing activated carbon for adsorbing dioxins according to claim 4, wherein The inert gas is nitrogen.

6. The method for preparing activated carbon for adsorbing dioxins according to claim 1, characterized in that, The concentration of the ferrous chloride solution is 8-10 wt%.

7. The method of claim 1, wherein the activated carbon is prepared by the steps of: mixing 1 kg of coal with 1 kg of water; and heating the mixture to 400°C for 1 hour. The antioxidant is 0.1M citric acid.

8. The method for producing activated carbon for adsorbing dioxins according to claim 1, wherein The immersion in S2 and S3 is carried out under ultrasonic conditions, the ultrasonic frequency is 20-40 kHz, and the immersion time is 30-60 min.

9. The method for producing activated carbon for adsorbing dioxins according to claim 8, wherein The drying temperature in S2 and S3 is 60-80 DEG C.

10. The activated carbon for adsorbing dioxins prepared by the method for preparing the activated carbon for adsorbing dioxins according to any one of claims 1-9.

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