Method for modifying activated carbon and its application in adsorbing cvocs

Abstract

This invention discloses a method for modifying activated carbon and its application in the adsorption of CVOCs, belonging to the field of environmental protection technology. This invention prepares activated carbon through a multi-step modification process using low-pressure glow discharge plasma. The resulting activated carbon possesses high specific surface area, high adsorption capacity, and excellent hydrophobic properties. The adsorption system achieves fully automated integrated CVOCs adsorption-desorption-regeneration-wastewater treatment. The system of this invention can treat concentrations ≥10000 mg / m³. 3 The CVOCs waste gas, after purification, has a gas concentration ≤50mg / m³. 3 Simultaneously, it treats CVOCs wastewater with COD of 5000~7000mg / L to ≤50mg / L, all meeting national standards; the system reduces operating costs by over 77%, and after 7200 hours of continuous use, the activated carbon loss rate is ≤2%, and the purification efficiency is ≥99%, resulting in significant environmental and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for modifying activated carbon and its application in the adsorption of CVOCs. Background Technology

[0002] Chlorinated organic compounds (CVOCs) are organic compounds containing chlorine in their molecules and exhibiting high volatility at room temperature. They mainly include dichloromethane, trichloromethane, carbon tetrachloride, dichloroethane, trichloroethane, trichloroethylene, and tetrachloroethylene. These CVOCs are typically highly toxic, highly stable, and difficult to degrade, and possess carcinogenic, teratogenic, and mutagenic effects, posing a serious threat to human health. Some CVOCs (such as carbon tetrachloride) are ozone-depleting substances, capable of damaging stratospheric ozone and exacerbating global warming. Therefore, the control of CVOCs has become one of the most urgent environmental problems to be solved.

[0003] Commonly used CVOCs waste gas treatment technologies mainly include condensation, absorption, combustion, biological treatment, and adsorption. ① Condensation involves using temperatures below the boiling point to condense CVOCs in the waste gas into liquid, achieving a certain removal effect. The condensed liquid can often be reused in production. This method is generally suitable for waste gases with small volumes and high concentrations. However, the organic matter concentration in the condensed waste gas remains high, requiring further treatment to meet emission standards. ② Absorption can be divided into chemical absorption and physical absorption. Physical absorption is generally used for readily soluble organic pollutants, while chemical absorption includes acid absorption, alkali absorption, and redox absorption. In practical engineering applications, one or more chemical absorption methods are often used depending on the specific properties of the waste gas. If absorption is used alone for purification, the removal effect on poorly soluble CVOCs is not ideal. Even with oxidative absorption using oxidants, the ability to degrade CVOCs is not very strong, generally failing to achieve the expected treatment target, resulting in a low CVOCs degradation rate. ③ Thermal oxidation uses high temperatures to decompose organic pollutants into harmless substances. Incineration is a relatively effective method for treating organic pollutants, and generally achieves satisfactory treatment results. However, if the incineration temperature and residence time are not properly controlled, incomplete combustion can occur, producing more toxic substances, especially dioxins, which are highly toxic for chlorinated organic compounds. For CVOCs, the biggest obstacle to incineration is the high likelihood of producing highly toxic dioxins after combustion. Standards such as the "Safety Technical Requirements for Regenerative Thermal Oxidizer Systems" (DB32 / T 4700-2024) and the "Technical Specification for Industrial Organic Waste Gas Treatment Engineering by Regenerative Combustion Method" (HJ 1093-2020) do not recommend using regenerative thermal oxidizers (RTOs) to treat CVOCs. ④ Biological treatment utilizes microbial degradation to convert organic matter in waste gas into simple inorganic substances (CO2, water, etc.) and cellular components. CVOCs are highly biotoxic and insoluble in water, making them difficult for microorganisms to degrade. Therefore, biological treatment of CVOCs often requires a longer acclimatization period. ⑤ The adsorption method uses porous solid adsorbents as adsorbents to adsorb CVOCs onto the surface of the adsorbent, thereby achieving removal. After adsorption, heat treatment is generally used to remove the adsorbed CVOCs, allowing the adsorbent to be regenerated and reused. The adsorption method has advantages such as simple process, high adsorption efficiency, and low energy consumption.

[0004] Activated carbon, due to its large specific surface area, good chemical stability, and low cost, has a high adsorption capacity for CVOCs (Continuously Activated Carbon) waste gases, making it a widely used adsorbent. However, conventional activated carbon suffers from drawbacks in CVOC adsorption, such as low adsorption capacity, poor moisture resistance, and low mechanical strength, which limit its application in CVOC adsorption. In recent years, activated carbon modification has become a research hotspot, mainly focusing on chemical modification. This involves introducing carboxylic acid, lactone, phenolic, and amine functional groups through acid treatment, alkali treatment, and impregnation. While chemical modification can indeed increase the number of functional groups on the activated carbon surface, it inevitably consumes a large amount of energy, and the secondary pollutants generated during modification can also pollute the environment. Low-temperature plasma, as an emerging modification and regeneration technology, has advantages such as significant effects and no pollution. It has gained widespread recognition in the field of material surface modification research and is a hot direction for future in-depth research on adsorption theory.

[0005] Therefore, how to utilize low-temperature plasma to modify activated carbon, apply the modified activated carbon to specific processes to adsorb CVOCs waste gas, and meet national standards after adsorption treatment has become an urgent problem to be solved. Summary of the Invention

[0006] The first technical problem to be solved by this invention is to provide a method for modifying activated carbon, which utilizes low-temperature plasma to modify activated carbon. The second technical problem to be solved by this invention is to provide modified activated carbon, which is a green, efficient, and controllable surface treatment technology that requires no chemical reagents, produces no secondary pollution, is flexible in operation and short in time, and allows for precise and controllable surface modification, significantly improving the surface chemical properties and adsorption performance of activated carbon. The third technical problem to be solved by this invention is to provide the application of this modified activated carbon in the adsorption of CVOCs.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for modifying activated carbon involves using pretreated columnar activated carbon as the material. First, a nitrogen / ammonia plasma method is used to introduce basic nitrogen-containing functional groups into the activated carbon in the reaction chamber of a plasma treatment device to obtain GAC-NH2. Then, GAC-NH2 is treated with TMA / ammonia plasma vapor deposition to load metallic aluminum, resulting in GAC-NH2-AlN. Next, GAC-NH2-AlN is treated with a siloxane plasma-assisted hydrophobic modification method to obtain GAC-NH2-AlN-FDTS. Finally, GAC-NH2-AlN-FDTS is treated with an acetylene / hydrogen plasma method to enhance mechanical strength, yielding modified activated carbon GAC-NH2-AlN-FDTS-DLC. Each step is performed under plasma parameters of 20-100 Pa working pressure and 300-500 W discharge power, with each step lasting 10-30 minutes.

[0009] Furthermore, the preparation steps for introducing basic nitrogen-containing functional groups into nitrogen / ammonia plasma are as follows: a nitrogen / ammonia mixed gas is introduced into the reaction chamber of the plasma processing device, with a nitrogen to ammonia volume ratio of 1:2 to 1:3, and the mixture is processed for 10 to 30 minutes under the conditions of a chamber working pressure of 20 to 100 Pa and a discharge power of 300 to 500 W to obtain GAC-NH2.

[0010] Furthermore, the preparation steps of TMA / ammonia plasma vapor deposition loaded aluminum are as follows: TMA is bubbled with argon as the carrier gas and ammonia as the reactant gas, the volume flow ratio of NH3 to TMA is controlled at 5:1~10:1, and GAC-NH2 is treated for 10~30 min under the conditions of cavity working pressure of 20~100Pa and discharge power of 300~500W to obtain GAC-NH2-AlN.

[0011] Furthermore, the preparation steps of siloxane plasma-assisted hydrophobic modification are as follows: FDTS is bubbled with argon as the carrier gas and oxygen as the activation gas, the volume flow ratio of argon to oxygen is controlled at 2:1, and GAC-NH2-AlN is treated for 10-30 min under the conditions of cavity working pressure of 20~100Pa and discharge power of 300~500W to obtain GAC-NH2-AlN-FDTS.

[0012] Further, the preparation steps of acetylene / hydrogen plasma-enhanced mechanical strength are as follows: acetylene / hydrogen mixed gas is introduced into the reaction chamber of the plasma treatment device, wherein the volume ratio of acetylene is 1~10% and the volume ratio of hydrogen is 90~99%, and GAC-NH2-AlN-FDTS is treated for 10~30 min under the conditions of chamber working pressure 20~100Pa and discharge power 300~500W to obtain GAC-NH2-AlN-FDTS-DLC.

[0013] Furthermore, the specific surface area of ​​the GAC-NH2-AlN-FDTS-DLC modified activated carbon is 1369.39 m². 2 / g, micropore volume is 0.9321cm³ 3 / g, total pore volume is 1.4023cm³. 3 / g, abrasion strength of 98.49%, and carbon tetrachloride adsorption rate of 97.26%.

[0014] Furthermore, the modified activated carbon is prepared by the aforementioned method.

[0015] Furthermore, the modified activated carbon is used in the adsorption of CVOCs.

[0016] Furthermore, the application includes the following steps:

[0017] (1) After the CVOCs waste gas enters the surface cooler through the inlet valve to cool down and remove water, it is sent to the activated carbon adsorber by the waste gas exhaust fan. After being purified by modified activated carbon adsorption, the purified gas is discharged through the outlet valve.

[0018] (2) When the adsorber is saturated, close the inlet valve and outlet valve, open the saturated water vapor inlet valve, and introduce saturated water vapor to desorb CVOCs. The desorbed gas enters the desorbed gas recovery system through the desorbed gas discharge valve.

[0019] (3) After being condensed through multiple stages, the desorbed gas enters the condensate stratification tank, where CVOCs are separated from the aqueous phase. The CVOCs are then recycled in the solvent recovery tank, and the wastewater enters the wastewater receiving tank.

[0020] (4) Wastewater enters the activated carbon adsorber and is treated by modified activated carbon adsorption before being discharged in compliance with standards.

[0021] (5) After desorption, the activated carbon adsorber is evacuated and cooled by a water ring vacuum pump. The vacuum degree is ≤-0.08MPa and the residual water vapor content in the adsorber is ≤1% after drying.

[0022] Furthermore, the concentration of CVOCs in the exhaust gas before treatment shall not be less than 10,000 mg / m³. 3 The concentration of the purified gas after treatment is no higher than 50 mg / m³. 3 The regeneration rate of the modified activated carbon after desorption is ≥98%, and the loss rate after continuous use for 7200 hours is ≤2%.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The low-pressure glow discharge plasma modified activated carbon disclosed in this invention is a green, efficient and controllable surface treatment technology. It requires no chemical reagents, has no secondary pollution, is flexible in operation and short in time, and the surface modification is precise and controllable, which can significantly improve the surface chemical properties and adsorption performance of activated carbon.

[0025] (2) Compared with commercially available conventional columnar activated carbon, the modified activated carbon (GAC-NH2-AlN-FDTS-DLC) prepared in this invention has a BET specific surface area of ​​1369.39 m². 2 / g (increased by 22%), micropore volume 0.9321cm³ 3 / g (increased by 32%), total pore volume 1.4023cm³ 3 / g (27% increase), abrasion strength 98.49% (7% increase), carbon tetrachloride adsorption rate 97.26% (21% increase), significantly improving the adsorption performance and mechanical strength of activated carbon.

[0026] (3) Compared with commercially available conventional columnar activated carbon, the modified activated carbon (GAC-NH2-AlN-FDTS-DLC) prepared in this invention has a saturated adsorption capacity of 718.16 mg / g for dichloromethane (an increase of 95.32%), a saturated adsorption capacity of 791.10 mg / g for 1,2-dichloroethane (an increase of 115.16%), and a saturated adsorption capacity of 648.30 mg / g for trichloroethylene (an increase of 76.32%).

[0027] (4) In high humidity environments (relative humidity 80%), the saturated adsorption capacity of commercially available columnar activated carbon for CVOCs decreases by as much as 50% to 60%; the saturated adsorption capacity of the modified activated carbon (GAC-NH2-AlN-FDTS-DLC) prepared in this invention decreases by no more than 5%, which significantly improves the hydrophobic properties of activated carbon.

[0028] (5) The adsorption system realizes the fully automatic integrated operation of CVOCs waste gas adsorption-desorption-regeneration-wastewater treatment. After the device is used continuously for 7200 hours, the modified activated carbon loss rate is 2%, and the purification efficiency within one adsorption cycle (12 hours) is still not less than 99%.

[0029] (6) The modified activated carbon (GAC-NH2-AlN-FDTS-DLC) and its adsorption system disclosed in this invention can reduce the emission concentration to as high as 10,000 mg / m³. 3 The CVOCs waste gas was reduced to 60 mg / m³ after adsorption treatment. 3 The following meet the current "Jiangsu Province Integrated Emission Standard for Air Pollutants" (DB32 / 4041-2021) and require no further treatment.

[0030] (7) The modified activated carbon (GAC-NH2-AlN-FDTS-DLC) and its adsorption system disclosed in this invention can reduce the COD concentration of CVOCs waste gas, which is as high as 5000~7000mg / L, to 50mg / L after adsorption treatment, meeting the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB 18918-2002), without the need for further treatment.

[0031] (8) The operating cost of the adsorption system disclosed in this invention is reduced from RMB 8,494 / d for unmodified activated carbon and the original device to RMB 1,944 / d, saving more than 77% in operating costs, and achieving significant environmental and economic benefits. Attached Figure Description

[0032] Figure 1 This is a process flow diagram of the laboratory activated carbon adsorption CVOCs device used in this application.

[0033] Figure 2 This is a permeation curve of CVOCs adsorbing dichloromethane on modified activated carbon according to this application.

[0034] Figure 3 This is a permeation curve of CVOCs adsorbing 1,2-dichloroethane on modified activated carbon according to this application.

[0035] Figure 4 This is a permeation curve of CVOCs adsorbing trichloroethylene on modified activated carbon according to this application.

[0036] Figure 5 This is a diagram showing the concentrations of chloroform at the inlet and outlet of the modified activated carbon adsorption-desorption device in this application.

[0037] Figure 6 This is a continuous monitoring diagram showing the instantaneous purification efficiency of the modified activated carbon adsorption-desorption device in this application.

[0038] Figure 7 This is a diagram showing the concentrations of chloroform at the inlet and outlet of the unmodified activated carbon adsorption-desorption device in this application.

[0039] Figure 8 This is a continuous monitoring graph showing the instantaneous purification efficiency of the unmodified activated carbon adsorption-desorption device in this application.

[0040] Among them, 1. Air compressor; 2. Water vapor bubbling device; 6. COVCs bubbling device; 4. Gas mixing device; 7. Activated carbon adsorption column; Q1. Volumetric flow meter; Q2. Volumetric flow meter; Q3. Volumetric flow meter; Q4. Volumetric flow meter. Detailed Implementation

[0041] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] The activated carbon used in the following examples of modification was commercially available conventional columnar activated carbon, with the following main parameters: particle size φ4.0mm, BET specific surface area of ​​1120.45m². 2 / g, total pore volume is 1.1036cm³ 3 / g, micropore volume is 0.7035cm³ 3 The modified activated carbon exhibits the following properties: abrasion strength of 92.04%, iodine adsorption value of 1025 mg / g, and carbon tetrachloride adsorption rate of 80.05%. The plasma device used for modified activated carbon is a low-pressure glow discharge plasma device. Key parameters include: discharge positive and negative electrodes made of SUS304 stainless steel; electrode gap of 10-20 cm; discharge power of 300-500 W; chamber working pressure of 20-100 Pa; processing time of 10-30 min; and modified gas flow rate of 50-200 cm⁻¹. 3 / min.

[0043] Example 1

[0044] The method for modifying activated carbon includes the following steps:

[0045] (1) Nitrogen / ammonia plasma-induced modification of basic nitrogen-containing functional groups: ① Sample pretreatment: Take 5 kg of commercially available conventional columnar activated carbon in a glass container, add 0.1 mol / L hydrochloric acid solution, soak and stir for 15 min to remove impurities on the surface of the activated carbon powder, rinse the activated carbon several times with deionized water until the filtrate is neutral, filter with a circulating water vacuum pump to obtain a solid sample, and dry in an oven at 105℃ for 24 h for later use. ② Vacuuming of the reaction chamber: Place 5 kg of pretreated sample into the reaction chamber (between the electrodes) of the plasma treatment device and spread it evenly into a thin layer with a thickness of 5 cm and a length and width of 45 cm × 45 cm. Vacuum up to the base pressure (10 -1 ~10 -3 Pa), to eliminate interference from air (especially oxygen and water vapor). ③ Introduce modified gas: Introduce the modified gas into the reaction chamber at a predetermined flow rate (50~200 cm⁻¹). 3④ Establish stable pressure: By adjusting the inlet and outlet valves, stabilize the working pressure inside the chamber within the predetermined range (20~100Pa). ⑤ Sample processing: Adjust the power input to the predetermined range (300~500W), and start timing the sample processing time (10~30min) after a stable and uniform atomized glow discharge is formed between the electrodes. ⑥ Post-processing and sampling: After the predetermined time is reached, first turn off the power, the plasma glow is extinguished, then turn off the modified gas, introduce air into the chamber to restore the pressure to normal, and finally remove the sample to obtain nitrogen / ammonia plasma modified activated carbon, denoted as GAC-NH2.

[0046] (2) TMA / ammonia plasma vapor deposition loading of aluminum: 5 kg of GAC-NH2 was placed in the reaction chamber of the plasma treatment device (placement method as above) for loading aluminum modification. At this time, the modification gas was a mixture of carrier gas argon, TMA vapor and reaction gas NH3. Argon (Ar) was bubbled into a colorless and transparent liquid trimethylaluminum (C3H9Al, TMA) bubbled in a constant temperature (temperature controlled at 25℃) bubble bottle. The carrier gas flow rate was controlled at 10~20 cm. 3 The flow rate is adjusted to provide a stable TMA vapor pressure. NH3 is used as the reactant gas at a flow rate of 50–200 cm³ / min. 3 The flow rate was maintained at NH3 / min, with a volumetric flow ratio of NH3 to TMA between 5:1 and 10:1. The remaining argon gas was used as a dilution gas to stabilize the plasma. The remaining steps were the same as above, resulting in plasma-loaded aluminum-modified activated carbon, denoted as GAC-NH2-AlN.

[0047] (3) Siloxane plasma-assisted hydrophobic modification: 5 kg of GAC-NH2-AlN was placed in the reaction chamber of the plasma treatment device (placement method as above) for siloxane hydrophobic modification to obtain highly hydrophobic modified activated carbon. The modifying gas was a mixture of carrier gas argon, FDTS vapor and activation gas O2. The carrier gas argon (Ar) was bubbled in a colorless and transparent liquid perfluorodecyltrimethoxysilane (FDTS) bubbler at a constant temperature (temperature controlled at 25℃). The carrier gas flow rate was controlled at 20~50 cm³. 3 The flow rate is 10-100 cm³ / min to provide a stable FDTS vapor pressure. O₂ is used as the activation gas at a flow rate of 10-100 cm³ / min. 3 / min, with the remainder argon gas used as a dilution gas to stabilize the plasma. The remaining steps are the same as above, yielding siloxane-modified hydrophobic activated carbon, denoted as GAC-NH2-AlN-FDTS.

[0048] (4) Acetylene / hydrogen plasma enhanced mechanical strength modification of activated carbon: 5 kg of GAC-NH2-AlN-FDTS is placed in the reaction chamber of the plasma treatment device (placement method is the same as above) to enhance its mechanical strength, that is, to form a "diamond-like carbon" film on the surface of activated carbon. At this time, the modified gas is a mixture of C2H2 and H2, with a C2H2 volume ratio of 1~10% and an H2 volume ratio of 90~99%. The remaining steps are the same as above, and a modified activated carbon with better mechanical strength is obtained, which is denoted as GAC-NH2-AlN-FDTS-DLC.

[0049] The performance parameters of activated carbons GAC, GAC-NH2, GAC-NH2-AlN, GAC-NH2-AlN-FDTS and GAC-NH2-AlN-FDTS-DLC are shown in Table 1.

[0050] The test methods for BET specific surface area, micropore volume, and total pore volume of activated carbon refer to "Test Methods for Coal-based Granular Activated Carbon: Determination of Pore Volume and Specific Surface Area" (GB / T 7702.20-2008). The test method for abrasion strength refers to "Test Methods for Coal-based Granular Activated Carbon: Determination of Strength" (GB / T 7702.3-2008). The test method for iodine adsorption value refers to "Test Methods for Coal-based Granular Activated Carbon: Part VII: Determination of Iodine Adsorption Value" (GB / T 7702.7-2023). The test method for carbon tetrachloride adsorption rate refers to "Test Methods for Coal-based Granular Activated Carbon: Determination of Carbon Tetrachloride Adsorption Rate" (GB / T 7702.13-1997).

[0051] Table 1 Comparison of relevant parameters of activated carbon before and after modification

[0052]

[0053] Table 1 shows that activated carbon modified by low-pressure glow discharge plasma exhibits significantly higher BET specific surface area, micropore volume, and total pore volume compared to unmodified activated carbon. Specifically, the BET specific surface area increases by 18%–23%, micropore volume by 32%–40%, and total pore volume by 26%–30%. This is primarily because the low-pressure glow discharge plasma effectively removes blockages within the activated carbon pores through high-energy particle bombardment and active free radical etching, expanding existing micropores and even creating new ones. This synergistic physical and chemical action deeply cleans and optimizes the pore structure, thereby significantly improving its BET specific surface area, micropore volume, and total pore volume. Activated carbon modified by acetylene / hydrogen low-pressure glow discharge plasma also shows significantly higher mechanical strength than unmodified activated carbon or activated carbon modified by other methods, exhibiting a statistically significant difference. This is mainly because the acetylene / hydrogen plasma generates a robust "diamond-like" hydrocarbon film on the activated carbon surface and within the pores through chemical vapor deposition, effectively filling microcracks and defects and reinforcing the carbon skeleton. This "repair and reinforcement" mechanism enhances the structural integrity and pore wall strength of the particles, thereby improving the macroscopic mechanical strength of activated carbon.

[0054] Example 2

[0055] The laboratory activated carbon adsorption-desorption device used in this application is as follows: Figure 1 As shown, standard air from air compressor 1 is divided into three streams. One stream, controlled by volumetric flow meter Q1, enters the constant-temperature bubbling device 2 containing purified water from the top. Another stream, controlled by volumetric flow meter Q2, directly enters the gas mixing device 4. The third stream, controlled by volumetric flow meter Q3, enters the constant-temperature bubbling device 6 containing CVOCs from the top. The three streams of gas are thoroughly mixed in the gas mixing device 4, and then the gas flow is controlled by volumetric flow meter Q4 to directly enter the activated carbon adsorption column 7, finally passing through the exhaust gas after-treatment system. By adjusting Q1, Q2, and Q3, CVOCs gases of different concentrations and humidity levels can be obtained. The activated carbon adsorption column 5 used is a cylindrical structure with an inner diameter of 200 mm, a length of 1000 mm, an activated carbon layer filling length of 600 mm, and a cross-sectional area of ​​0.0314 m². 2 The activated carbon loading amount is 0.0188m³. 3 The activated carbon filling mass is approximately 8 kg, and the waste gas treatment flow rate is approximately 20 m³ / h. 3 The cross-sectional flow velocity is 0.20 m / s, the gas residence time is 3 s, and the CVOCs exhaust gas concentration is controlled within ±7000 mg / m³. 3 The relative humidity was controlled at 40%. The results were as follows: Figure 2-4 As shown in Table 2-3.

[0056] The CVOCs concentration (as C) at the inlet and outlet of the experimental apparatus was measured using a portable VOCs monitoring instrument. The adsorption efficiency at the inlet and outlet of the experimental apparatus was calculated using the following formula:

[0057]

[0058] In the formula: (mg / m 3 )and (mg / m 3 The concentrations of CVOCs at the inlet and outlet of the experimental setup are shown below. (Nm) 3 / h) and (Nm) 3 ( / h) represents the gas flow rate at the inlet and outlet of the experimental apparatus, respectively.

[0059] Depend on Figure 2-4 It can be seen that the adsorption and permeation times of CVOCs (dichloromethane, 1,2-dichloroethane, and trichloroethylene) on modified activated carbon changed significantly compared with those on unmodified activated carbon. The adsorption and permeation times of CVOCs on GAC-NH2 and GAC-NH2-AlN were significantly longer than those on unmodified activated carbon, showing statistically significant differences. The adsorption and permeation times of CVOCs on GAC-NH2-AlN-FDTS and GAC-NH2-AlN-FDTS-DLC modified activated carbon were also significantly longer than those on GAC-NH2 and GAC-NH2-AlN modified activated carbon, showing statistically significant differences, but there was no significant difference in adsorption and permeation times between these two types of modified activated carbon. The adsorption permeation time order of CVOCs (dichloromethane, 1,2-dichloroethane, trichloroethylene) on different modified activated carbons is as follows: GAC-NH2-AlN-FDTS~GAC-NH2-AlN-FDTS-DLC>GAC-NH2-AlN>GAC-NH2>GAC.

[0060] The saturated adsorption capacities of various modified activated carbons for CVOCs (dichloromethane, 1,2-dichloroethane, and trichloroethylene) calculated based on adsorption permeation curves are shown in Table 2 below. For example, compared with GAC, the saturated adsorption capacity of GAC-NH2 for dichloromethane increased by 37.35%, GAC-NH2-AlN by 69.97%, and GAC-NH2-AlN-FDTS and GAC-NH2-AlN-FDTS-DLC by 86.54%~95.32%.

[0061] Nitrogen / ammonia plasma modification introduces basic nitrogen-containing functional groups such as amine (-NH2), imine (-C=N-), pyridine nitrogen, and quaternary nitrogen into the surface of activated carbon through covalent bonding, altering its surface acidity, hardness, and thus changing the surface chemical properties of conventional activated carbon. By introducing nitrogen-containing functional groups, the activated carbon surface, which originally relied primarily on physical adsorption, is equipped with multiple "chemical grippers" (including enhanced Lewis acid-base interactions, dipole interactions, improved π-π interactions, and hydrogen bonds) targeting chlorinated organic molecules. These grippers work synergistically to significantly enhance the overall interaction force between the adsorbate and adsorbent, thereby achieving a higher saturation adsorption capacity and binding strength for target pollutants within the same (or even slightly reduced) physical pore space.

[0062] TMA (trimethylaluminum) / ammonia plasma modification mainly involves the in-situ deposition of highly dispersed aluminum nitride (AlN) nanoclusters on the surface of activated carbon, introducing extremely strong Lewis acid sites (Al... 3+ These sites can efficiently chemisorb chlorine-containing organic compounds through strong Lewis acid-base coordination (Cl→Al).

[0063] Consistent with the superior adsorption performance shown in the experimental results.

[0064] Table 2. Saturated adsorption capacity of CVOCs on modified activated carbon

[0065]

[0066] Based on the adsorption permeation curves, the saturated adsorption capacities of various modified activated carbons for CVOCs (dichloromethane, 1,2-dichloroethane, and trichloroethylene) under relative humidity conditions of 40% and 80% are shown in Table 3. When the relative humidity increases from 40% to 80%, the saturated adsorption capacity of GAC, GAC-NH2, and GAC-NH2-AlN activated carbons decreases by as much as 50%–60%; while the saturated adsorption capacity of the siloxane-modified activated carbons GAC-NH2-AlN-FDTS and GAC-NH2-AlN-FDTS-DLC decreases by no more than 5%. Siloxane plasma polymerizes on the activated carbon surface to form a superhydrophobic polysiloxane nanofilm. The abundant methyl groups and the micro / nano rough structure together constitute a low surface energy barrier. This barrier strongly repels water molecules from the environment, preventing them from condensing within the pores and competing for adsorption with the target organic matter. Meanwhile, the modified layer preferentially deposits at the pore openings and on the inner walls of the mesopores, reversing the surface polarity from hydrophilic to hydrophobic while basically preserving the microporous adsorption space, thus enhancing the affinity with non-polar organic matter.

[0067] Table 3. Saturated adsorption capacity of CVOCs on modified activated carbon under different relative humidity conditions

[0068]

[0069] Example 3

[0070] The adsorption system device used in this application is based on patent CN119113707A. The working principle of this system is the same as that of CN119113707A. Among them, 3 is CVOCs exhaust gas inlet valve a, 5 is CVOCs exhaust gas inlet valve b, and the rest of the device is the same.

[0071] The modified activated carbon (GAC-NH2-AlN-FDTS-DLC) prepared in Example 1 was used to treat trichloromethane waste gas from a fine chemical enterprise in Jiangsu Province by adsorption. The design parameters are as follows:

[0072] (1) Exhaust gas parameters: The main component is chloroform, and the exhaust gas flow rate is 5000 m³ / h. 3 / h, exhaust gas concentration (calculated as carbon) is 6000-7000 mg / m³ 3 The exhaust gas temperature is 30℃, and the relative humidity of the exhaust gas is 60%~70%.

[0073] (2) Adsorption system parameters: The adsorber adopts a vertical one-adsorption-one-desorption design, and is equipped with a special adsorber for the adsorption treatment of trichloromethane wastewater. The size of the adsorber tank is Φ2200mm. 2800mm (vertical), each adsorber is filled with 5m³ of modified activated carbon. 3 The tank size of the trichloromethane wastewater adsorber is Φ1500mm. 2000mm, the adsorber is filled with 1.5m of modified activated carbon. 3 The gas velocity at the adsorber cross section is 0.4 m / s, and the gas residence time is 3 s.

[0074] (3) Condensation system parameters: heat exchange area of ​​surface cooler 200m² 2 The heat exchange area of ​​the shell-and-tube condenser is 40m². 2 The heat exchange area of ​​the wound tube condenser is 10m². 2 Spiral plate condenser heat exchange area 5m² 2 ;

[0075] (4) Steam desorption system parameters: ≥0.6MPa, DN40, flow rate 1t / h;

[0076] (5) Other settings: The adsorption cycle is 12h, the drying method is vacuum drying, and various safety detection instruments are set.

[0077] The inlet and outlet were continuously monitored for 15 hours using an FID (Fiber Optic Identifier) ​​instrument, and the results were as follows: Figure 5-6 As shown, the concentration of imported chloroform (calculated as carbon) is 5509~7053 mg / m³. 3The average concentration (as carbon) was 6326 mg / m³. 3 The exported chloroform concentration (calculated as carbon) was 19.97~75.24 mg / m³. 3 The average concentration (as carbon) was 40.41 mg / m³. 3 The instantaneous purification efficiency is 98.83%~99.68%, with an average purification efficiency as high as 99.36%. Within 12 hours of adsorption, it meets the "NMHC emission concentration not exceeding 60 mg / m³" standard of the "Jiangsu Province Integrated Emission Standard for Air Pollutants" (DB32 / 4041-2021). 3 The technical requirement is that the modified activated carbon adsorption-desorption device can meet the emission standards. The raw COD of the wastewater generated by chloroform desorption is 5000~7000 mg / L. After the wastewater is treated with modified activated carbon, the COD of the effluent decreases to 50 mg / L. The COD index of the wastewater meets the acceptance standards of the wastewater treatment plant in the chemical industrial park or the water quality standards for sewage discharge into the urban sewer system, and no further treatment is required. Therefore, the company sets an adsorption cycle of 12 hours, performs saturated steam desorption twice a day, and consumes a total of 4 tons of saturated steam. The resulting 4 tons of chloroform wastewater are then treated again by modified activated carbon adsorption-desorption to meet the emission standards.

[0078] The operating costs of this device are as follows:

[0079] ① The cost of saturated steam consumption is 4 tons / day × 300 yuan / ton = 1200 yuan / day;

[0080] ② The electricity cost consumed by the electrical equipment is 18.5KW × 24h / d × 1 yuan / kWh = 444 yuan / d;

[0081] ③ The cost of low-temperature water consumed by the refrigeration system is 300 yuan / day;

[0082] ④ The total operating cost is RMB 1944 per day.

[0083] Comparative Example 1

[0084] Unmodified commercially available conventional columnar activated carbon was used to treat trichloromethane waste gas from a fine chemical enterprise in Jiangsu Province via adsorption. The design parameters are as follows:

[0085] (1) Exhaust gas parameters: The main component is chloroform, and the exhaust gas flow rate is 5000 m³ / h. 3 / h, exhaust gas concentration (calculated as carbon) is 6000-7000 mg / m³ 3 The exhaust gas temperature is 30℃, and the relative humidity of the exhaust gas is 60%~70%.

[0086] (2) Adsorption system parameters: The adsorber adopts a vertical one-adsorption-one-desorption design, and the adsorber tank size is Φ2200mm. 2800mm (vertical), each adsorber is filled with 5m³ of commercially available standard columnar activated carbon. 3 The gas velocity at the adsorber cross section is 0.4 m / s, and the gas residence time is 3 s.

[0087] (3) Condensation system parameters: heat exchange area of ​​surface cooler 200m² 2 The heat exchange area of ​​the shell-and-tube condenser is 40m². 2 The heat exchange area of ​​the wound tube condenser is 10m². 2 Spiral plate condenser heat exchange area 5m² 2 ;

[0088] (4) Steam desorption system parameters: ≥0.6MPa, DN40, flow rate 1t / h;

[0089] (5) Other settings: The adsorption cycle is 6 hours, no chloroform wastewater adsorption-desorption system is set, vacuum drying is adopted, and various safety detection instruments are set.

[0090] The inlet and outlet were continuously monitored using an FID detector for one complete adsorption cycle (6 hours). The results are as follows: Figure 7-8 As shown, the concentration of imported chloroform (calculated as carbon) is 5143~9207 mg / m³. 3 The average concentration (as carbon) was 6913 mg / m³. 3 Exported chloroform (calculated as carbon) is 399~1533 mg / m³. 3 The average concentration (as carbon) was 852 mg / m³. 3 The instantaneous purification efficiency ranges from 78.13% to 95.53%, with an average purification efficiency of only 87.30%, which fails to meet the requirement of "NMHC emission concentration not exceeding 60 mg / m³" in the "Jiangsu Province Integrated Emission Standard for Air Pollutants" (DB32 / 4041-2021). 3 "Technical requirements."

[0091] Because the pre-modification adsorption-desorption unit could not meet emission standards, the adsorbed and recovered trichloromethane waste gas needed to be connected to a subsequent RTO unit for further treatment. Due to some issues with RTO treatment of chlorinated organic waste gas, the company set one adsorption cycle to 6 hours, performing 4 saturated steam desorption cycles per day, consuming a total of 8 tons of saturated steam per day, and simultaneously generating 8 tons of trichloromethane wastewater. The operating cost of this unit is calculated as follows:

[0092] ① The cost of saturated steam consumption is 8 tons / day × 300 yuan / ton = 2400 yuan / day;

[0093] ② The cost of treating desorption wastewater is 8 tons / day × 200 yuan / ton = 1600 yuan / day;

[0094] ③ The electricity cost of the equipment used in the adsorption device is 18.5KW × 24h / d × 1 yuan / KWh = 444 yuan / d;

[0095] ④ The cost of low-temperature water consumed by the refrigeration system is 300 yuan / day;

[0096] ⑤ The cost of natural gas consumed by the RTO for further processing of chloroform tail gas is 25m. 3 / 10,000 m 3 air·h×5000m 3 ×3.5 yuan / m 3 ×24h / d = 1050 yuan / d;

[0097] ⑥ The high-temperature oxidation of chloroform to produce HCl consumes 300 yuan / day of liquid alkali, and the treatment cost of the high-salt wastewater generated is 2 tons / day × 600 yuan / ton = 1200 yuan / day;

[0098] ⑦ The induction of chloroform into the RTO for combustion produces a large amount of HCl gas, which causes severe corrosion to the furnace body, valves, pipelines, etc., increasing the cost of equipment replacement or maintenance by approximately 1,500 yuan / day.

[0099] The total operating cost is 8494 yuan / day.

[0100] Compared with the original process of Comparative Example 1, the device of this application in Example 3 eliminates wastewater treatment costs, natural gas costs, liquid alkali consumption costs, and equipment maintenance costs, resulting in a 77% reduction in operating costs while meeting emission standards. Furthermore, after 7200 hours of continuous use, the modified activated carbon loss rate is only 2%, and the purification efficiency within one adsorption cycle (12 hours) remains no less than 99%, indicating that it possesses excellent adsorption-desorption capacity and mechanical strength.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for modifying activated carbon, characterized in that, Using pretreated columnar activated carbon as material, GAC-NH2 was first treated in the reaction chamber of a plasma treatment device by introducing basic nitrogen-containing functional groups using nitrogen / ammonia plasma. Then, GAC-NH2 was treated with aluminum-loaded metal by TMA / ammonia plasma vapor deposition to obtain GAC-NH2-AlN. Next, GAC-NH2-AlN was treated with siloxane plasma in conjunction with hydrophobic modification to obtain GAC-NH2-AlN-FDTS. Finally, GAC-NH2-AlN-FDTS was treated with acetylene / hydrogen plasma to enhance mechanical strength, thus obtaining modified activated carbon GAC-NH2-AlN-FDTS-DLC. Each step of the treatment was carried out under plasma parameters of 20~100Pa working pressure and 300~500W discharge power, and the treatment time for each step was 10~30min.

2. The method for modifying activated carbon according to claim 1, characterized in that: The preparation steps for introducing basic nitrogen-containing functional groups into nitrogen / ammonia plasma are as follows: nitrogen / ammonia mixed gas is introduced into the reaction chamber of the plasma processing device, with a nitrogen to ammonia volume ratio of 1:2 to 1:

3. The mixture is processed for 10 to 30 minutes under the conditions of chamber working pressure of 20 to 100 Pa and discharge power of 300 to 500 W to obtain GAC-NH2.

3. The method for modifying activated carbon according to claim 1, characterized in that: The preparation steps of TMA / ammonia plasma vapor deposition loaded aluminum are as follows: TMA is bubbled with argon as carrier gas and ammonia as reactant gas. The volume flow ratio of NH3 to TMA is controlled at 5:1~10:

1. GAC-NH2 is treated for 10~30 min under the conditions of cavity working pressure of 20~100Pa and discharge power of 300~500W to obtain GAC-NH2-AlN.

4. The method for modifying activated carbon according to claim 1, characterized in that: The preparation steps of siloxane plasma-assisted hydrophobic modification are as follows: FDTS is bubbled with argon as carrier gas and oxygen as activation gas, and the volume flow ratio of argon to oxygen is controlled at 2:

1. GAC-NH2-AlN is treated for 10-30 min under the conditions of working pressure of 20~100Pa and discharge power of 300~500W to obtain GAC-NH2-AlN-FDTS.

5. The method for modifying activated carbon according to claim 1, characterized in that: The preparation steps of acetylene / hydrogen plasma-enhanced mechanical strength are as follows: acetylene / hydrogen mixed gas is introduced into the reaction chamber of the plasma treatment device, wherein the volume ratio of acetylene is 1~10% and the volume ratio of hydrogen is 90~99%. GAC-NH2-AlN-FDTS is treated for 10~30 min under the conditions of chamber working pressure 20~100Pa and discharge power 300~500W to obtain GAC-NH2-AlN-FDTS-DLC.

6. The method for modifying activated carbon according to claim 1, characterized in that: The specific surface area of ​​the GAC-NH2-AlN-FDTS-DLC modified activated carbon is 1369.39 m². 2 / g, micropore volume is 0.9321cm³ 3 / g, total pore volume is 1.4023cm³. 3 / g, abrasion strength of 98.49%, and carbon tetrachloride adsorption rate of 97.26%.

7. Modified activated carbon prepared by the modification method of activated carbon according to any one of claims 1 to 6.

8. The application of the modified activated carbon according to claim 7 in the adsorption of CVOCs.

9. The application according to claim 8, characterized in that, Includes the following steps: (1) After the CVOCs waste gas enters the surface cooler through the inlet valve to cool down and remove water, it is sent to the activated carbon adsorber by the waste gas exhaust fan. After being purified by modified activated carbon adsorption, the purified gas is discharged through the outlet valve. (2) When the adsorber is saturated, close the inlet valve and outlet valve, open the saturated water vapor inlet valve, and introduce saturated water vapor to desorb CVOCs. The desorbed gas enters the desorbed gas recovery system through the desorbed gas discharge valve. (3) After being condensed through multiple stages, the desorbed gas enters the condensate stratification tank, where CVOCs are separated from the aqueous phase. The CVOCs are then recycled in the solvent recovery tank, and the wastewater enters the wastewater receiving tank. (4) Wastewater enters the activated carbon adsorber and is treated by modified activated carbon adsorption before being discharged in compliance with standards. (5) After desorption, the activated carbon adsorber is evacuated and cooled by a water ring vacuum pump. The vacuum degree is ≤-0.08MPa and the residual water vapor content in the adsorber is ≤1% after drying.

10. The application according to claim 9, characterized in that: The concentration of CVOCs in the exhaust gas before treatment is not less than 10,000 mg / m³ 3 The concentration of the purified gas after treatment is no higher than 50 mg / m³. 3 The regeneration rate of the modified activated carbon after desorption is ≥98%, and the loss rate after continuous use for 7200 hours is ≤2%.

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