Activated carbon for adsorbing dioxin and a method for preparing the same

Abstract

The application discloses activated carbon for adsorbing dioxin and a preparation method thereof, and belongs to the field of activated carbon preparation. The activated carbon is prepared by the following steps: firstly, coconut shell carbon is mixed with phosphoric acid, and then is subjected to activation treatment in a microwave reactor, and then is calcined to obtain coconut shell-based activated carbon; then, the coconut shell-based activated carbon is immersed in a ferrous chloride solution, an antioxidant is added, and after immersion, the coconut shell-based activated carbon is dried; then, the coconut shell-based activated carbon is immersed in a ferrocene mixed solution, and after immersion, the coconut shell-based activated carbon is dried to obtain the activated carbon for adsorbing dioxin. The application significantly enhances the accommodation capacity of the activated carbon for dioxin by constructing micropore-mesopore structures, and further improves the combination capacity of the activated carbon for dioxin by loading ferrocene on the surface of the activated carbon.

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:

[0006] 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;

[0007] S2: Coconut shell-based activated carbon is impregnated in ferrous chloride solution, an antioxidant is added, and then dried after impregnation;

[0008] 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%.

[0009] 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.

[0010] In addition to the aforementioned technical points, this invention also impregnates coconut shell-based activated carbon in a ferrous chloride solution, allowing ferrous ions to form active sites on the activated carbon surface, facilitating the subsequent loading of ferrocene onto the activated carbon. Then, the coconut shell-based activated carbon is impregnated in a ferrocene mixed solution, allowing ferrocene to be loaded onto the activated carbon. Ferrocene not only possesses aromatic analog rings that can form π-π stacking interactions with the aromatic rings of dioxins, attracting them to each other; ferrocene also has ferrous ions that can form ion-dipole interactions with the electronegative chlorine atoms of dioxins, ultimately improving the binding force with dioxins.

[0011] In some implementations, the phosphoric acid concentration is 40-60 wt%.

[0012] In some implementations, the microwave reactor power is 750-800 W and the activation treatment time is 10-20 min.

[0013] In some embodiments, calcination in S1 is performed at 500-600°C for 2-3 hours under inert gas protection.

[0014] In some implementations, the inert gas is nitrogen.

[0015] Calcination under inert gas protection is to prevent the carbon skeleton from oxidizing.

[0016] In some embodiments, the concentration of the ferrous chloride solution is 8-10 wt%.

[0017] In some implementations, the antioxidant is 0.1M citric acid.

[0018] In some embodiments, the impregnation in S2 and S3 is carried out under ultrasonic conditions, with an ultrasonic frequency of 20-40 kHz and an impregnation time of 30-60 min.

[0019] In some implementations, the drying temperature in S2 and S3 is 60-80°C.

[0020] Excessive temperature will cause ferrocene to sublimate and be lost.

[0021] A second aspect of the present invention is to provide a method for preparing activated carbon for adsorbing dioxins, and the activated carbon prepared for adsorbing dioxins.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The activated carbon for adsorbing dioxins provided by this invention has a microporous-mesoporous structure, which is highly matched with the size of dioxin molecules (0.5-1.5 nm) and fly ash complex, significantly improving adsorption capacity and diffusion efficiency, and significantly enhancing the pollution-holding capacity of activated carbon.

[0024] 2. This invention successfully loads ferrocene onto the surface of activated carbon by sequentially immersing it in a ferrous chloride solution and a ferrocene mixed solution. Ferrocene can form π-π stacking interactions with the aromatic rings of dioxins and attract them to each other. It can also form ion-dipole interactions with the electronegative chlorine atoms of dioxins, which greatly improves the binding force between activated carbon and dioxins. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments.

[0026] Example 1

[0027] A method for preparing activated carbon for adsorbing dioxins includes the following steps:

[0028] S1: Coconut shell activated carbon is mixed with 50wt% phosphoric acid at a mass ratio of 1:3, activated in a microwave reactor at a power of 800 W for 15 min, and then calcined at 550℃ for 3 h under nitrogen protection to obtain coconut shell-based activated carbon.

[0029] S2: Coconut shell-based activated carbon was impregnated in a 9 wt% ferrous chloride solution for 40 min at an ultrasonic frequency of 30 kHz, 0.1 M citric acid was added, and the impregnation was dried at 70 °C.

[0030] 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. After immersion, it is dried at 70℃ to obtain activated carbon for adsorbing dioxins. The ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 6 wt%.

[0031] Example 2

[0032] A method for preparing activated carbon for adsorbing dioxins includes the following steps:

[0033] S1: Coconut shell activated 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, and then calcined at 600℃ for 2 h under nitrogen protection to obtain coconut shell-based activated carbon.

[0034] S2: Coconut shell-based activated carbon is immersed in a 10 wt% ferrous chloride solution at an ultrasonic frequency of 40 kHz for 30-60 min, 0.1 M citric acid is added, and then dried at 60-80℃ after immersion.

[0035] S3: The coconut shell-based activated carbon treated by S2 is immersed in a ferrocene mixed solution at an ultrasonic frequency of 20-40kHz for 50 min. After immersion, it is dried at 60℃ to obtain activated carbon for adsorbing dioxins. The ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 8 wt%.

[0036] Example 3

[0037] A method for preparing activated carbon for adsorbing dioxins includes the following steps:

[0038] S1: Coconut shell activated carbon is 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℃ for 2 h under nitrogen protection to obtain coconut shell-based activated carbon.

[0039] S2: Coconut shell-based activated carbon was immersed in an 8 wt% ferrous chloride solution for 30 min at an ultrasonic frequency of 20 kHz, 0.1 M citric acid was added, and the immersion was dried at 60 °C.

[0040] S3: The coconut shell-based activated carbon treated by S2 is immersed in a ferrocene mixed solution at an ultrasonic frequency of 20 kHz for 30 min. After immersion, it is dried at 60℃ to obtain activated carbon for adsorbing dioxins. The ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 2 wt%.

[0041] Example 4

[0042] A method for preparing activated carbon for adsorbing dioxins includes the following steps:

[0043] S1: Coconut shell charcoal and 60 wt% phosphoric acid are mixed 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℃ for 3 h under nitrogen protection to obtain coconut shell-based activated carbon.

[0044] S2: Coconut shell-based activated carbon was impregnated in a 10 wt% ferrous chloride solution for 60 min at an ultrasonic frequency of 40 kHz, 0.1 M citric acid was added, and the impregnation was dried at 80 °C.

[0045] S3: The coconut shell-based activated carbon treated by S2 is immersed in a ferrocene mixed solution at an ultrasonic frequency of 40 kHz for 60 min. After immersion, it is dried at 80 °C to obtain activated carbon for adsorbing dioxins. The ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 8 wt%.

[0046] Example 5

[0047] A method for preparing activated carbon for adsorbing dioxins includes the following steps:

[0048] S1: Coconut shell activated carbon is 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℃ for 2.5 h under nitrogen protection to obtain coconut shell-based activated carbon.

[0049] S2: Coconut shell-based activated carbon was immersed in a 10 wt% ferrous chloride solution for 30 min at an ultrasonic frequency of 30 kHz, 0.1 M citric acid was added, and the immersion was dried at 70 °C.

[0050] 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 60 min. After immersion, it is dried at 80 °C to obtain activated carbon for adsorbing dioxins. The ferrocene mixed solution is ferrocene dispersed in a mixture of ethanol and water, and the concentration of ferrocene is 7 wt%.

[0051] Comparative Example 1

[0052] Based on Example 1, S1 is omitted, that is, the coconut shell charcoal is not activated.

[0053] Comparative Example 2

[0054] Based on Example 1, S3 is omitted, i.e., ferrocene is not loaded on the surface of activated carbon.

[0055] Comparative Example 3

[0056] Based on Example 1, ferrous chloride in S2 was replaced with ferric chloride.

[0057] The activated carbon obtained in the examples and comparative examples was tested for pore size using an ASAP 2020 fully automated rapid specific surface area and mesopore / micropore analyzer. The test results are shown in Table 1.

[0058] Table 1

[0059]

[0060] As can be seen from Table 1, the proportion of micropores and mesopores in Examples 1-5 of the present invention is all higher than 70%. In Comparative Example 1, the coconut shell charcoal was not activated, resulting in a significant decrease in the proportion of micropores and mesopores. This indicates that after coconut shell charcoal is mixed with phosphoric acid, microwave heating can cause the polar molecules of phosphoric acid to vibrate violently, thereby generating a large number of micropores and mesopores.

[0061] The activated carbon obtained in the examples and comparative examples was placed in an adsorption device, and an adsorption solution containing 5.5 ng TEQ / m³ was continuously introduced. 3The dioxin in the flue gas was subjected to a total adsorption time of 14 hours. The concentration of dioxins at the outlet of the adsorption unit was detected using a high-resolution mass spectrometer manufactured by JEOL Corporation of Japan. The test results are shown in Table 2.

[0062] Table 2

[0063]

[0064] As shown in Table 2, the activated carbon provided in this embodiment for adsorbing dioxins can effectively adsorb and remove dioxins, and its adsorption effect is far superior to that of the comparative examples. Looking at the comparative examples, Comparative Example 1 has a smaller proportion of micropores and mesopores, resulting in a decreased adsorption capacity for dioxins and thus a poor adsorption effect. Comparative Example 2, although it formed a micropore-mesopore structure, did not load ferrocene onto the activated carbon surface, reducing the binding capacity between the activated carbon and dioxins, leading to a poor adsorption and removal effect. Comparative Example 3 replaced ferrous chloride with ferric chloride, failing to utilize ferrous ions to form active sites on the activated carbon surface, resulting in a poor ferrocene impregnation effect and reducing the activated carbon's adsorption capacity for dioxins. This demonstrates that only impregnation with an iron composition identical to ferrocene can improve the ferrocene impregnation effect.

[0065] The above descriptions are merely some embodiments of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and all such modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A method for preparing activated carbon for adsorbing dioxins, characterized in that, Includes 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: The coconut shell-based activated carbon is impregnated in a ferrous chloride solution, an antioxidant is added, and then dried after impregnation; S3: The coconut shell-based activated carbon treated in S2 is impregnated in a ferrocene mixed solution, and dried after impregnation to obtain the activated carbon used 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%.

2. The method for preparing activated carbon for adsorbing dioxins according to claim 1, characterized in that, The phosphoric acid concentration is 40-60 wt%.

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

4. The method for preparing activated carbon for adsorbing dioxins according to claim 1, characterized in that, In S1, calcination is performed at 500-600℃ for 2-3 hours under inert gas protection.

5. 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%.

6. The method for preparing activated carbon for adsorbing dioxins according to claim 1, characterized in that, The antioxidant is 0.1M citric acid.

7. The method for preparing activated carbon for adsorbing dioxins according to claim 1, characterized in that, The impregnation in S2 and S3 is carried out under ultrasonic conditions, with an ultrasonic frequency of 20-40 kHz and an impregnation time of 30-60 min.

8. The method for preparing activated carbon for adsorbing dioxins according to claim 7, characterized in that, The drying temperature in S2 and S3 is 60-80℃.

9. Activated carbon for adsorbing dioxins prepared by the method for preparing activated carbon for adsorbing dioxins according to any one of claims 1-8.

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