Active carbon for purifying VOCs (volatile organic compounds) and preparation method of active carbon

Abstract

The invention discloses active carbon for purifying VOCs (volatile organic compounds) and a preparation method thereof, and the method comprises the following steps: dissolving a nitrogen-containing organic matter in water, adding a certain amount of active carbon raw carbon, and dipping for a preset time; washing, centrifuging and drying the impregnated activated carbon; placing the dried activated carbon in a high-temperature furnace protected by nitrogen, and carrying out heat treatment at a certain temperature and a certain heating rate; soaking the activated carbon subjected to heat treatment in a CTAB (Cetyltrimethyl Ammonium Bromide) solution for not less than 24 hours, and performing auxiliary oscillation in the soaking process; the activated carbon subjected to soaking and oscillation treatment is cleaned, centrifuged and dried in a vacuum environment. Hydrophobic nitrogen-containing functional groups are grafted on the surface of the activated carbon, specific chemical adsorption of non-polar VOCs is enhanced, meanwhile, pore size distribution of the activated carbon is regulated and controlled, the specific surface area of the activated carbon is remarkably increased, the modified activated carbon is excellent in VOCs gas treatment performance through synergistic cooperation of the two modes, the saturated adsorption capacity is large, and the adsorption efficiency is high. And the penetration time is long.

Description

Technical Field

[0001] The present invention relates to the technical field of air purification, and in particular to activated carbon for VOCs purification and a preparation method thereof. Background Art

[0002] Formaldehyde and benzene are the VOCs of particular concern in indoor environments. They have high concentration levels and reactivity, and are closely related to the indoor air quality. In addition, VOCs can also cause serious harm to human health. Most VOCs, such as aldehydes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons, alcohols and ketones, are toxic and carcinogenic. Among them, the most concerned VOCs in indoor environments are mainly formaldehyde and benzene. Long-term exposure to low-level formaldehyde concentrations can cause a series of respiratory problems, mainly including throat discomfort, eye irritation and dull breathing. Long-term exposure to high-concentration formaldehyde environments can increase the risk of acute poisoning and nasal tumors. Similarly, formaldehyde can also cause serious diseases such as nasopharyngeal cancer, lung damage, leukemia and sick building syndrome. Even if the indoor environment contains low concentrations of benzene pollutants, as long as the exposure time is long enough, it will cause certain harm to the human body, such as inability to concentrate, physical fatigue, anorexia, forgetfulness and blurred vision. Inhalation of high concentrations of benzene can cause coma, dizziness, and even death. In addition, my country has increasingly stringently formulated formaldehyde and benzene concentration limits in indoor environments. The formaldehyde concentration limit in indoor environments is 0.08 mg / m3. In the latest draft of the Indoor Air Quality Standard (GB / T 18883-2020), the benzene concentration limit is reduced to 0.03 mg·m-3, and the toluene concentration limit is 0.2 mg·m-3. In the new version of the indoor environment standard "Civil Construction Engineering Indoor Environmental Pollution Control Standard" (GB 50325-2020), toluene and xylene are added as indoor air pollutants, and the concentration limit stipulates that the toluene limit in a class of civil construction projects is 0.15 mg·m-3, and the xylene concentration limit is 0.2 mg·m-3. Therefore, the development of efficient VOCs control technology is of great significance to the control of air pollution in indoor environments.

[0003] Activated carbon usually has a large specific surface area and rich pore structure, and contains a variety of surface functional groups, which has good adsorption performance for VOCs molecules. The adsorption process is mainly affected by the hierarchical structure of macropores (>50nm), mesopores (2-50nm) and micropores (<2nm). The kinetic diameter of VOCs molecules determines the effective pore structure for them to enter the adsorbent. In theory, pore structures with pore sizes larger than the kinetic diameter of VOCs molecules can adsorb VOCs, but in fact, the adsorption is most effective when the pore size is close to the kinetic diameter of VOCs molecules, because when the pore diameter of activated carbon far exceeds the kinetic diameter of VOCs molecules, the adsorption effect of activated carbon on VOCs molecules is weakened, and it only serves as a channel for VOCs molecules to transport. Mesopores can promote the transport channel of benzene molecules from the outer surface to the inner surface of micropores, and micropores provide the main adsorption sites. Appropriate regulation of the pore size of activated carbon and auxiliary surface functional group modification can achieve large-capacity and persistent absorption of VOCs gas by activated carbon. However, existing activated carbon has a certain adsorption capacity for most organic pollutants, but for the removal of VOCs molecules, it mainly utilizes the porous structure rich in raw carbon to physically adsorb small molecules. The disadvantage of this porous structure for adsorbing VOCs gas is that the adsorption capacity is low (for example, the saturated adsorption capacity of 9 VOCs gas molecules is less than 100 mg / g), and the stability is poor, and the desorption effect is obvious (for example, after 48 hours of saturated adsorption of 9 VOCs molecules, there will be competitive adsorption between water molecules in the air and VOCs molecules, resulting in desorption of some VOCs molecules), thus resulting in insufficient adsorption capacity for VOCs molecules. Summary of the invention

[0004] In view of the problems existing in the prior art, the object of the present invention is to provide an activated carbon for VOCs purification, which increases the adsorption capacity of activated carbon for VOCs gas through the synergistic combination of chemical bonding and physical adsorption, and a preparation method thereof.

[0005] To achieve the above object, the first aspect of the present invention provides a method for preparing activated carbon for VOCs purification, comprising the following steps:

[0006] Step 1): dissolving nitrogen-containing organic matter in water, adding a certain amount of activated carbon raw carbon and impregnating for a predetermined time;

[0007] Step 2): washing, centrifuging and drying the impregnated activated carbon;

[0008] Step 3): placing the dried activated carbon in a high-temperature furnace protected by nitrogen and performing heat treatment at a certain temperature and heating rate;

[0009] Step 4): Soak the heat-treated activated carbon in a CTAB solution for no less than 24 hours, and perform auxiliary shaking during the soaking process;

[0010] Step 5): The activated carbon that has been soaked and shaken is washed, centrifuged and dried under vacuum.

[0011] Furthermore, the nitrogen-containing organic matter is one or a mixture of multiple organic amines, and the nitrogen content of the organic amines is 8% by mass.

[0012] Furthermore, the organic amine includes one or a mixture of ethanolamine, amide, and fatty amine.

[0013] Furthermore, the organic amine is weakly alkaline, and the pH of the mixed solution is ≤9.

[0014] Furthermore, the volume ratio of the nitrogen-containing organic matter mixed solution to the activated carbon raw carbon is ≥2:1.

[0015] Furthermore, in step 3), the heat treatment temperature is 450°C±10°C, and the heating rate is 10°C / min±1°C / min.

[0016] Furthermore, the concentration of the CTAB solution used in step 4) is 10 mg / mL to 35 mg / mL.

[0017] Furthermore, in step 4), the oscillation frequency range is 100 r / min to 150 r / min.

[0018] Furthermore, in step 5), the drying temperature range is 150° C. to 180° C., and the drying time is not less than 2 hours.

[0019] A second aspect of the present invention provides activated carbon for VOCs purification, which is prepared using the above-mentioned preparation method.

[0020] The present invention grafts hydrophobic nitrogen-containing functional groups on the surface of activated carbon to enhance the specific chemical adsorption of non-polar VOCs and at the same time regulates the pore size distribution of the activated carbon, so that the specific surface area of ​​the activated carbon is significantly increased. The two methods work together to make the modified activated carbon have excellent performance in treating VOCs gases, not only with a large saturated adsorption capacity but also a long penetration time.

[0021] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings in the specification, which constitute a part of this application, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] In the attached picture:

[0024] Figure 1This is a flow chart of a method for preparing activated carbon for VOCs purification according to an embodiment of the present invention;

[0025] Figure 2 for Figure 1 Schematic diagram of the dynamic adsorption performance test results of VOCs purification activated carbon prepared by the method. DETAILED DESCRIPTION

[0026] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the present invention will be more comprehensive and complete and fully convey the concept of the example embodiments to those skilled in the art.

[0027] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The first aspect of the present invention provides a method for preparing activated carbon for VOCs purification, comprising the following steps:

[0029] Step S100: dissolving nitrogen-containing organic matter in water, and adding a certain amount of activated carbon raw carbon to soak for a predetermined time;

[0030] Step S110: washing, centrifuging and drying the impregnated activated carbon;

[0031] Step S120: placing the dried activated carbon in a high-temperature furnace protected by nitrogen, and performing heat treatment at a certain temperature and heating rate;

[0032] Step S130: soaking the heat-treated activated carbon in a CTAB solution for no less than 24 hours, and performing auxiliary shaking during the soaking process;

[0033] Step S140: The activated carbon that has been soaked and shaken is washed, centrifuged and dried under a vacuum environment.

[0034] In one embodiment of the present invention, the nitrogen-containing organic matter is one or a mixture of multiple organic amines, and the nitrogen content of the organic amines is 8% by mass.

[0035] In one embodiment of the present invention, the organic amine includes one or a mixture of ethanolamine, amide, and fatty amine.

[0036] In one embodiment of the present invention, the organic amine is weakly alkaline, and the pH of the mixed solution is ≤9. The use of weakly alkaline organic amine can prevent the activated carbon from releasing ammonia smell due to residual organic amine after long-term storage.

[0037] In one embodiment of the present invention, the volume ratio of the nitrogen-containing organic matter mixed solution to the activated carbon raw carbon is ≥2:1, so that the activated carbon is fully in contact with the mixed solution, which increases the number of hydrophobic nitrogen functional groups grafted on the surface of the activated carbon to a certain extent, further enhances the specific chemical adsorption of non-polar VOCs, and regulates the pore size distribution of the activated carbon.

[0038] In one embodiment of the present invention, the heat treatment temperature in step S120 is 450° C.±10° C., and the heating rate is 10° C. / min±1° C. / min.

[0039] In one embodiment of the present invention, the concentration of the CTAB solution used in step S130 is 10 mg / mL to 35 mg / mL. CTAB is an amphiphilic surfactant. The surface of the activated carbon raw carbon also has hydrophilic groups. CTAB can be attached to the surface of the activated carbon with hydrophilic groups and the hydrophobic groups facing outward, making the activated carbon hydrophobic. Most VOCs molecules are hydrophobic molecules. The activated carbon with a hydrophobic surface can further improve the ability to adsorb hydrophobic VOCs molecules.

[0040] In one embodiment of the present invention, the oscillation frequency in step S140 is in the range of 100 r / min to 150 r / min. The oscillation frequency value in this range can ensure that the activated carbon does not fall off and the CTAB does not agglomerate.

[0041] In one embodiment of the present invention, the drying temperature in step S140 ranges from 150° C. to 180° C., and the drying time is not less than 2 hours, so as to remove small molecules remaining inside the activated carbon during the drying process.

[0042] The second aspect of the present invention provides an activated carbon for VOCs purification, which is prepared by the above-mentioned preparation method. In order to enable those skilled in the art to more clearly understand the adsorption performance of the activated carbon prepared in this application, the following specific examples are listed for illustration:

[0043] Example 1 (modified carbon 1): This example prepares activated carbon according to the preparation method of the above example

[0044] (1) Prepare 2 L of ethanolamine solution so that its nitrogen content is 8%;

[0045] (2) Add 1L of activated carbon and soak for 24 hours;

[0046] (3) Wash the impregnated activated carbon, centrifuge it, and dry it at 105°C for 12 hours;

[0047] (4) placing the dried activated carbon in a high-temperature furnace protected by N2, with a heat treatment temperature of 450°C ± 10°C and a heating rate of 10°C / min ± 1°C / min;

[0048] (5) preparing 2LCTAB solution to a concentration of 15 mg / ml;

[0049] (6) The activated carbon obtained in the previous step was immersed in a 2LCTAB solution, assisted by shaking at 120 r / min for 24 h;

[0050] (7) The product activated carbon is washed, centrifuged, and dried under vacuum at 150°C for 2 h to obtain the target product modified activated carbon.

[0051] Example 2 (modified carbon 2): This example prepares activated carbon according to the preparation method of the above example

[0052] (1) Prepare 2 L of acetamide solution so that its nitrogen content is 8%;

[0053] (2) Add 1L of activated carbon and soak for 24 hours;

[0054] (3) Wash the impregnated activated carbon, centrifuge it, and dry it at 105°C for 12 hours;

[0055] (4) placing the dried activated carbon in a high-temperature furnace protected by N2, with a heat treatment temperature of 450°C ± 10°C and a heating rate of 10°C / min ± 1°C / min;

[0056] (5) preparing a 2LCTAB solution to a concentration of 25 mg / ml;

[0057] (6) The activated carbon obtained in the previous step was immersed in a 2LCTAB solution, assisted by shaking at 120 r / min for 24 h;

[0058] (7) The product activated carbon is washed, centrifuged, and dried under vacuum at 150°C for 2 h to obtain the target product modified activated carbon.

[0059] from Figure 2 It can be seen that the modified carbon 1 and modified carbon 2 were prepared according to the above method, and the pore size distribution of the activated carbon was regulated, so that the specific surface area of ​​the activated carbon was significantly increased. The specific surface area tested by the BET multi-point method was greater than 1000m 2 / g; significantly increased pore volume, micropore volume greater than 0.5cm 3 / g, which makes the saturated adsorption capacity of activated carbon high. After testing, the dynamic toluene adsorption saturation capacity is greater than 400mg / g; at the same time, hydrophobic nitrogen-containing functional groups are grafted on the surface of the activated carbon to enhance the specific chemical adsorption of non-polar VOCs. Compared with the activated carbon prepared by the existing method, the ability to adsorb VOCs molecules and the stability are stronger. The synergistic combination of the two methods makes the modified activated carbon have excellent performance in treating VOCs gas. It not only has a large saturated adsorption capacity, but also a long penetration time. The performance test results of the modified activated carbon / original carbon on the dynamic adsorption of VOCs (benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, styrene, n-undecane, n-butyl acetate) under normal temperature and humidity conditions show that the saturated adsorption capacity and penetration time of the modified activated carbon are significantly improved to a great extent. For details, see Figure 2 (Toluene was used as the test gas).

[0060] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0061] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing activated carbon for VOCs purification, characterized in that: The steps include: Step 1): dissolving nitrogen-containing organic matter in water, adding a certain amount of activated carbon raw carbon and impregnating for a predetermined time; Step 2): washing, centrifuging and drying the impregnated activated carbon; Step 3): placing the dried activated carbon in a high-temperature furnace protected by nitrogen and performing heat treatment at a certain temperature and heating rate; Step 4): Soak the heat-treated activated carbon in a CTAB solution for no less than 24 hours, and perform auxiliary shaking during the soaking process; Step 5): The activated carbon that has been soaked and shaken is washed, centrifuged and dried under vacuum.

2. The preparation method according to claim 1, characterized in that The nitrogen-containing organic matter is one or a mixture of multiple organic amines, and the nitrogen content of the organic amines is 8% by mass.

3. The preparation method according to claim 2, characterized in that: The organic amine includes one or a mixture of ethanolamine, amide, and fatty amine.

4. The preparation method according to claim 2 or 3, characterized in that: The organic amine is weakly alkaline, and the pH of the mixed solution is ≤9.

5. The preparation method according to claim 1, characterized in that: The volume ratio of nitrogen-containing organic matter mixed solution to activated carbon raw carbon is ≥2:

1.

6. The preparation method according to claim 1, characterized in that: In step 3), the heat treatment temperature is 450°C ± 10°C, and the heating rate is 10°C / min ± 1°C / min.

7. The preparation method according to claim 1, characterized in that: The concentration of the CTAB solution used in step 4) is 10 mg / mL to 35 mg / mL.

8. The preparation method according to claim 1, characterized in that: In step 4), the oscillation frequency range is 100 r / min to 150 r / min.

9. The preparation method according to claim 1, characterized in that: In step 5), the drying temperature ranges from 150° C. to 180° C., and the drying time is not less than 2 hours.

10. An activated carbon for VOCs purification, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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