Carbon-based polycyclic aromatic hydrocarbon adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a carbon-based polycyclic aromatic hydrocarbon adsorbent and a preparation method and application thereof.The preparation method comprises the steps that firstly, a mixture of a pretreated coconut shell material and a modifier is subjected to high-temperature treatment to obtain a carbonized material, then the carbonized material is immersed in an activating solution to be subjected to low-temperature treatment, and then filtering, washing to be neutral and drying in the shade at the room temperature are conducted to obtain the carbon-based polycyclic aromatic hydrocarbon adsorbent. Carrying out secondary high-temperature treatment to obtain an activated material; and crushing and sieving the activated material to obtain the carbon-based polycyclic aromatic hydrocarbon adsorbent. The carbon-based polycyclic aromatic hydrocarbon adsorbent has obvious advantages in the selective adsorption and removal process of polycyclic aromatic hydrocarbon, silicon species are introduced in the carbonization process, a microporous structure in a carbon material is destroyed in a pillared mode, then the pore structure of the catalyst is regulated and controlled, the mesoporous structure is richer, and the adsorption selectivity of the polycyclic aromatic hydrocarbon is improved; the adsorbent has high adsorption capacity and adsorption selectivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of polycyclic aromatic hydrocarbon adsorption and separation, and particularly relates to a carbon-based polycyclic aromatic hydrocarbon adsorbent, a preparation method thereof, and an application thereof. Background Art

[0002] With the acceleration of the industrialization process and the increasing severity of environmental pollution problems, polycyclic aromatic hydrocarbons (PAHs), as a type of persistent organic pollutant (POPs), have attracted widespread attention due to their potential harm to the environment and human health. Polycyclic aromatic hydrocarbons are a class of persistent organic pollutants formed by the conjugation of two or more benzene rings, widely present in industrial processes such as petrochemical industry, coking, and automobile exhaust emissions, and can enter the soil and groundwater environment through atmospheric deposition, water body migration, and other pathways. Due to the high toxicity, carcinogenicity, mutagenicity, and bioaccumulation of PAHs, their environmental pollution problems have attracted global widespread attention. The World Health Organization (WHO) and environmental protection agencies of various countries have listed PAHs as priority control pollutants, and there is an urgent need to develop efficient, economical, and environmentally friendly treatment technologies.

[0003] Currently, the main methods for treating PAH pollution include physical adsorption, chemical oxidation, and biodegradation, etc. Among them, the physical adsorption method has become the mainstream technology in practical applications due to its advantages such as simple operation, controllable cost, and no secondary pollution. However, traditional adsorption materials (such as activated carbon, zeolite, silica gel, etc.) still have significant limitations in the field of PAH adsorption. Although activated carbon has a high specific surface area, its non-polar surface is easily interfered by competitive adsorption of coexisting substances such as humic acid and heavy metal ions in the environment, resulting in a decrease in the selective adsorption efficiency of PAHs. In addition, there is a mass transfer resistance for PAHs with larger molecular weights (such as benzo[a]pyrene) in the microporous structure (pore diameter < 2nm) of activated carbon, and the adsorption kinetics is slow. The adsorption performance of natural mineral materials (such as bentonite, zeolite) is easily affected by environmental pH, ionic strength, and temperature fluctuations, and their stability is insufficient in complex environmental media, making it difficult to meet the actual engineering requirements.

[0004] Patent CN105289466B discloses a method for adsorptive separation and removal of polycyclic aromatic hydrocarbons. The adsorbent used is metal-modified silica gel, and the treatment raw material is simulated diesel. The highest polycyclic aromatic hydrocarbon removal rate is 91.74%, and the removal efficiency is still insufficient.

[0005] Patent CN110586053B discloses a method for removing polycyclic aromatic hydrocarbons by solid-phase extraction. The adsorbent used is functionalized modified silica gel. By utilizing the hydrophobicity of the modified silica gel and the π-π interaction between the functional groups and polycyclic aromatic hydrocarbons, the removal of polycyclic aromatic hydrocarbons in water, soil and food is achieved. However, its adsorption capacity is low and it cannot handle polycyclic aromatic hydrocarbons in the industrial production process.

[0006] Currently, the adsorption capacity, removal depth and selectivity of polycyclic aromatic hydrocarbon adsorbents are still insufficient, and further regulation of the pore structure and composition of the adsorbent is required. Summary of the Invention

[0007] The present invention is proposed to solve the problems of low adsorption capacity, poor removal depth and insufficient selectivity of polycyclic aromatic hydrocarbon adsorbents in the prior art, and its purpose is to provide a carbon-based polycyclic aromatic hydrocarbon adsorbent, a preparation method thereof and an application.

[0008] The present invention is achieved through the following technical solutions:

[0009] A preparation method of a carbon-based polycyclic aromatic hydrocarbon adsorbent, comprising the following steps:

[0010] (Ⅰ) Pretreat the coconut shell material

[0011] (Ⅱ) Carbonize

[0012] Mix the coconut shell material pretreated in step (Ⅰ) with a modifier, and then perform high-temperature treatment under a nitrogen atmosphere;

[0013] (Ⅲ) Activate

[0014] Immerse the material carbonized in step (Ⅱ) in an activation solution for low-temperature treatment, then filter, wash with water until neutral, air-dry at room temperature, and then perform secondary high-temperature treatment;

[0015] (Ⅳ) Post-treatment

[0016] Crush and screen the material after the secondary high-temperature treatment in step (Ⅲ) to obtain the carbon-based polycyclic aromatic hydrocarbon adsorbent; the mesh number for screening is required to be 20 mesh to 60 mesh.

[0017] In the above technical solution, the pretreatment includes crushing, screening, cleaning and impurity removal, and drying, and the mesh number for screening is 10 mesh to 80 mesh.

[0018] In the above technical solution, the specific conditions for drying are: drying at 100°C to 130°C for 5h to 8h.

[0019] In the above technical solution, the specific conditions for the high-temperature treatment are: under a nitrogen atmosphere, heating at a heating rate of 1°C / min to 600°C to 1000°C, preferably 800°C, and holding for 5h to 7h.

[0020] In the above technical solution, the mass ratio of the coconut shell material to the modifier is 1:(0.5 - 1).

[0021] In the above technical solution, the modifier is an aqueous solution of SiO₂ with a mass fraction of 5% - 10%, and the pH value of the aqueous solution of SiO₂ is 1.5 - 3.5.

[0022] In the above technical solution, the preparation method of the modifier is: slowly add a liquid silicon source with a SiO₂ content of 15wt% - 22wt% to an aqueous solution of inorganic acid, and mix evenly to obtain the modifier; the pH value of the aqueous solution of inorganic acid is 1.3 - 2.0.

[0023] In the above technical solution, the liquid silicon source is any one of water glass, silica sol or tetraethyl orthosilicate.

[0024] In the above technical solution, the inorganic acid is any one of sulfuric acid or nitric acid.

[0025] In the above technical solution, the activation solution is an aqueous solution of an alkaline metal salt and / or an alkaline hydroxide with a mass fraction of 5% - 10%.

[0026] In the above technical solution, the alkaline metal salt is any one of sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate.

[0027] In the above technical solution, the alkaline hydroxide is sodium hydroxide or potassium hydroxide.

[0028] In the above technical solution, the mass ratio of the material after carbonization in step (Ⅱ) to the activation solution is 1:(1 - 2). Controlling the mass between the carbonized particles and the activation solution can make the pore structure of the prepared carbon-based polycyclic aromatic hydrocarbon adsorbent meet the corresponding requirements.

[0029] In the above technical solution, the specific conditions of the low-temperature treatment are: at 60°C - 100°C, treat for 3h - 5h.

[0030] In the above technical solution, the specific conditions of the secondary high-temperature treatment are: heat up to 400°C at a heating rate of 1°C / min, and keep the temperature for 1h - 2h.

[0031] A carbon-based polycyclic aromatic hydrocarbon adsorbent prepared by the aforementioned method, the pore volume of the adsorbent is 0.7 cm 3 / g - 1 cm 3 / g, the pore diameter is 4nm - 7nm, and there is no micropore specific surface area.

[0032] Application of a carbon-based polycyclic aromatic hydrocarbon adsorbent prepared by the foregoing method in the adsorption and separation of polycyclic aromatic hydrocarbons. The separation method is specifically as follows: After thoroughly mixing an alkane, a cycloalkane, a monocyclic aromatic hydrocarbon, and a polycyclic aromatic hydrocarbon, they are brought into contact with the carbon-based polycyclic aromatic hydrocarbon adsorbent for the adsorption and separation process; the specific conditions for the adsorption and separation of polycyclic aromatic hydrocarbons are as follows: the pressure is 0.5 MPa to 1 MPa, the temperature is 60 °C to 100 °C, and the desorbent is a toluene solution.

[0033] The beneficial effects of the present invention are as follows:

[0034] The present invention provides a carbon-based polycyclic aromatic hydrocarbon adsorbent, its preparation method and application. The carbon-based polycyclic aromatic hydrocarbon adsorbent of the present invention starts from coconut shells and related products of coconut shells, and a carbon-silicon-aluminum composite adsorbent material is prepared through processes such as pretreatment, carbonization, activation, and post-treatment. The carbon-based polycyclic aromatic hydrocarbon adsorbent has obvious advantages in the selective adsorption and removal of polycyclic aromatic hydrocarbons, and silicon species are introduced during the carbonization process to destroy the microporous structure in the carbon material in a pillared manner, thereby regulating the pore structure of the catalyst, making the mesoporous structure more abundant, and improving the adsorption selectivity of polycyclic aromatic hydrocarbons; the adsorbent has a high adsorption capacity and adsorption selectivity. Specific embodiments

[0035] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below through specific embodiments.

[0036] Example 1

[0037] A preparation method of a carbon-based polycyclic aromatic hydrocarbon adsorbent includes the following steps:

[0038] (Ⅰ) Pretreatment

[0039] 100 g of coconut shells are crushed and screened, and then the screened particles are dried at 120 °C for 7 h;

[0040] (Ⅱ) Carbonization

[0041] The dried particles in step (Ⅰ) are mixed with a modifier in a mass ratio of 1:0.5, and then, under a nitrogen atmosphere, the temperature is raised to 800 °C at a heating rate of 1 °C / min and held for 6 h;

[0042] The SiO2 content in the modifier is 5 wt%, and the pH of the modifier is 2;

[0043] The preparation method of the modifier is as follows: Sodium silicate is slowly added to an aqueous sulfuric acid solution and mixed evenly to obtain the modifier;

[0044] (Ⅲ) Activation

[0045] Immerse the particles carbonized in step (II) into the prepared activation solution for low-temperature treatment. The low-temperature treatment temperature is 80 °C, and the low-temperature treatment duration is 3 h. After the low-temperature treatment, wash repeatedly with deionized water until neutral, and air-dry in the shade at room temperature. Then, under a nitrogen atmosphere, heat to 400 °C at a heating rate of 1 °C / min and hold for 1 h.

[0046] The mass ratio of the particles carbonized in step (II) to the activation solution is 1:1. The activation solution is an aqueous sodium hydroxide solution with a mass fraction of 10%.

[0047] (IV) Post-treatment

[0048] Pulverize the particles activated in step (III) again, and sieve them through a 20-40 mesh standard sieve to obtain the carbon-based polycyclic aromatic hydrocarbon adsorbent A1.

[0049] Example 2

[0050] Implement according to the method of Example 1, the difference is that the liquid silicon source of the modifier in step (II) is silica sol, and the carbon-based polycyclic aromatic hydrocarbon adsorbent A2 is obtained.

[0051] Example 3

[0052] Implement according to the method of Example 1, the difference is that the liquid silicon source of the modifier in step (II) is tetraethyl orthosilicate, and the carbon-based polycyclic aromatic hydrocarbon adsorbent A3 is obtained.

[0053] Example 4

[0054] Implement according to the method of Example 1, the difference is that the activation solution in step (III) is an aqueous potassium hydroxide solution with a mass fraction of 10%, and the carbon-based polycyclic aromatic hydrocarbon adsorbent A4 is obtained.

[0055] Example 5

[0056] Implement according to the method of Example 1, the difference is that the activation solution in step (III) is an aqueous sodium carbonate solution with a mass fraction of 10%, and the carbon-based polycyclic aromatic hydrocarbon adsorbent A5 is obtained.

[0057] Example 6

[0058] Implement according to the method of Example 1, the difference is that the activation solution in step (III) is an aqueous potassium carbonate solution with a mass fraction of 10%, and the carbon-based polycyclic aromatic hydrocarbon adsorbent A6 is obtained.

[0059] Comparative Example 1

[0060] Implement according to the method of Example 1, the difference is that the modification solution in step (II) is a sulfuric acid aqueous solution with pH = 2, and the polycyclic aromatic hydrocarbon adsorbent D1 is obtained.

[0061] The pore volume and pore size of the adsorbents A1 - A6 and D1 prepared in Examples 1 - 6 and Comparative Example 1 were tested:

[0062] The pore volume, pore size and specific surface area of A1 - A6 and D1 were characterized by nitrogen adsorption / desorption. The instrument used was Micromeritics ASAP 2020Plus, the analysis temperature was 77K, and the degassing condition was treatment at 150°C for 10h under vacuum; the test results are shown in Table 1;

[0063] Table 1: Pore volume and pore size results of Examples 1 - 6 and Comparative Example 1

[0064]

[0065] The separation performance of the adsorbents A1 - A6 and D1 prepared in Examples 1 - 6 and Comparative Example 1 was evaluated:

[0066] The adsorption separation process was carried out using a fixed - bed reactor. Simulated diesel was introduced, and its specific composition is shown in Table 2; the contents of each component in the raw material and the effluent were determined by gas chromatography (GC) and gas chromatography - mass spectrometry (GC - MS); 100 mL of the polycyclic aromatic hydrocarbon adsorbent was loaded, the column temperature was 85°C, the pressure was 0.5 MPa, and the removal rate of polycyclic aromatic hydrocarbons during the adsorption separation process was detected. The performance evaluation results are shown in Table 3.

[0067] The calculation formula for the removal rate of polycyclic aromatic hydrocarbons is:

[0068] Removal rate of polycyclic aromatic hydrocarbons = (total amount of polycyclic aromatic hydrocarbons in the raw material - total amount of polycyclic aromatic hydrocarbons in the effluent) / total amount of polycyclic aromatic hydrocarbons in the raw material × 100%;

[0069] Table 2: Composition of simulated diesel

[0070] Monoaromatic hydrocarbons Polycyclic aromatic hydrocarbons Alkanes Cycloalkanes Content, wt% 25.7 14.3 35.4 24.6

[0071] Table 3: Evaluation results of polycyclic aromatic hydrocarbon adsorption separation

[0072] A1 A2 A3 A4 A5 A6 D1 Content of polycyclic aromatic hydrocarbons in the effluent, wt% 0.30 0.53 0.63 0.70 0.82 0.87 2.35 Removal rate of polycyclic aromatic hydrocarbons, % 97.9 96.3 95.6 95.1 94.3 93.9 83.6

[0073] The applicant declares that the above - mentioned is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a carbon-based polycyclic aromatic hydrocarbon adsorbent, characterized in that: It includes the following steps: (Ⅰ) Pretreat the coconut shell material (Ⅱ) Mix the pretreated coconut shell material in step (Ⅰ) with a modifier, and then conduct high-temperature treatment under a nitrogen atmosphere to obtain a carbonized material; (Ⅲ) Immerse the carbonized material in step (Ⅱ) in an activation solution for low-temperature treatment, then filter, wash with water until neutral, dry in the shade at room temperature, and then conduct secondary high-temperature treatment to obtain an activated material; (Ⅳ) Crush and screen the activated material obtained in step (Ⅲ) to obtain a carbon-based polycyclic aromatic hydrocarbon adsorbent.

2. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 1, wherein: The pretreatment in step (Ⅰ) includes crushing, screening, cleaning and removing impurities, and drying; the specific conditions for drying are: drying at 100°C to 130°C for 5h to 8h.

3. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 1, wherein: The specific conditions for the high-temperature treatment in step (Ⅱ) are: under a nitrogen atmosphere, heating at a heating rate of 1°C / min to 600°C to 1000°C, and holding for 5h to 7h; the mass ratio of the coconut shell material to the modifier is 1:(0.5 - 1).

4. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 1, characterized in that: The modifier is an aqueous solution of SiO2 with a mass fraction of 5% to 10%, and the pH value of the aqueous solution of SiO2 is 1.5 to 3.

5.

5. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 4, characterized in that: The preparation method of the modifier is: slowly add a liquid silicon source with a SiO2 content of 15wt% to 22wt% into an aqueous solution of inorganic acid, and mix evenly to obtain the modifier.

6. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 5, characterized in that: The liquid silicon source is any one of water glass, silica sol or tetraethyl orthosilicate; the inorganic acid is any one of sulfuric acid or nitric acid; the pH value of the aqueous solution of inorganic acid is 1.3 to 2.

0.

7. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 1, wherein: The activation solution in step (Ⅲ) is an aqueous solution of an alkaline metal salt and / or an alkaline hydroxide with a mass fraction of 5% to 10%; the alkaline metal salt is any one of sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate; the alkaline hydroxide is sodium hydroxide or potassium hydroxide.

8. The preparation method of the carbon-based polycyclic aromatic hydrocarbon adsorbent according to claim 1, wherein: The mass ratio of the carbonized material in step (Ⅱ) to the activation solution is 1:(1 - 2); the specific conditions for the low-temperature treatment are: treating at 60°C to 100°C for 3h to 5h; the specific conditions for the secondary high-temperature treatment are: heating at a heating rate of 1°C / min to 400°C and holding for 1h to 2h.

9. A carbon-based polycyclic aromatic hydrocarbon adsorbent prepared by the method according to any one of claims 1 to 8, characterized in that: The pore volume of the adsorbent is 0.7 cm 3 / g to 1 cm 3 / g, the pore diameter is 4 nm to 7 nm, and there is no micropore specific surface area.

10. Use of the carbon-based polycyclic aromatic hydrocarbon adsorbent prepared by the method according to any one of claims 1 to 8 in the adsorption and separation of polycyclic aromatic hydrocarbons, characterized in that: The separation method is specifically: fully mix alkanes, cycloalkanes, monocyclic aromatic hydrocarbons and polycyclic aromatic hydrocarbons, contact with the carbon-based polycyclic aromatic hydrocarbon adsorbent, and conduct an adsorption separation process; the specific conditions for the polycyclic aromatic hydrocarbon adsorption separation are: the pressure is 0.5MPa to 1MPa, the temperature is 60°C to 100°C, and the desorbent is a toluene solution.

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