A method for preparing a hierarchical pore modified zeolite adsorbent with lithium silicon powder and application thereof

Abstract

The present application belongs to the technical field of waste gas treatment, and particularly relates to a method for preparing a multi-level pore modified zeolite adsorbent from lithium silicon powder and application thereof. The method comprises the following steps: grinding and sieving, acid pickling and impurity removal, gel crystallization, filtration and washing, and zeolite modification. The present application uses lithium silicon powder as the main raw material, and combines acid pickling, crystallization, washing and modification to obtain a multi-level pore modified zeolite adsorbent which has the characteristics of large specific surface area, high porosity, fast adsorption rate, high capacity, good thermal stability and strong regeneration capacity. The preparation method is simple and easy to operate, and has low cost. The multi-level pore modified zeolite prepared by the method has high adsorption efficiency for VOCs, and can be recycled and reused, thereby further reducing the cost of VOCs treatment.

Description

Technical Field

[0001] This invention belongs to the field of waste gas treatment technology, specifically relating to a method for preparing multi-level porous modified zeolite adsorbents using lithium silicon powder and its application. Background Technology

[0002] The industrial production of lithium carbonate generates a large amount of industrial waste, lithium silicon powder. This waste has extremely low utilization and simply accumulates, severely consuming land resources and negatively impacting the environment. Lithium silicon powder mainly contains Si and Al, providing the basic conditions for zeolite preparation. Chinese invention patent CN110270308A discloses a method for preparing an adsorbent for wastewater treatment using lithium silicon powder and nitrogen-doped mesoporous carbon. The adsorbent prepared by this method exhibits excellent ability to simultaneously reduce COD and efficiently remove ammonia nitrogen from wastewater.

[0003] Volatile organic compounds (VOCs) are a significant source of air and indoor environmental pollution, and their efficient treatment has become an urgent need in the environmental protection field. Adsorption methods are widely used for VOCs capture and recovery due to their simple operation and relatively low cost. Zeolite molecular sieves are considered one of the most promising VOCs adsorbents due to their regular micropores, high specific surface area, excellent thermal and chemical stability, and non-flammability. However, existing zeolite adsorbents generally suffer from drawbacks such as low VOCs adsorption capacity, low adsorption efficiency, low regeneration efficiency, and a significant decrease in adsorption capacity with increasing temperature. Furthermore, there are currently no patents related to the preparation of zeolite adsorbents for VOCs using lithium silicon powder. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing multi-level porous modified zeolite adsorbents using lithium silicon powder and its application. This preparation method is simple, easy to operate, and low in cost. The resulting multi-level porous modified zeolite is used to adsorb VOCs with high adsorption efficiency and can be regenerated and recycled, further reducing the cost of VOCs treatment.

[0005] The purpose of this invention is to provide a method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder, the method comprising the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and then sieve it to remove large particles. Take the sieve material and dry it for later use. (2) Acid washing to remove impurities: Take a certain amount of lithium silicon powder and mix it with HCl solution to react for 2-3 hours. Filter the reaction solution and wash the filter residue with deionized water for 10-15 minutes. Repeat the filtration-washing process until the filtrate is neutral. Dry the filter residue. (3) Gel crystallization: The dried filter residue and NaOH are poured into a container containing deionized water and reacted for 10-15 minutes to obtain the initial gel. The initial gel is then poured into a reaction vessel and placed in a vacuum drying oven for hydrothermal reaction. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a container. Deionized water is added and the mixture is stirred for 10-15 minutes. The filtration and washing process is repeated until the filtrate is neutral. The filter residue is dried to obtain the zeolite adsorbent. (5) Zeolite modification: After mixing NaOH solution and TPAOH solution evenly, pour them into a container, add zeolite adsorbent, place in a water bath and stir to react. After the reaction is completed, filter to obtain filter residue, repeat the filtration and washing with deionized water until the filtrate is neutral, dry the filter residue, and finally place it in a tube furnace and calcine under a nitrogen atmosphere to obtain multi-level porous modified zeolite adsorbent.

[0006] This invention uses lithium silicon powder as the main raw material. After crushing, it is activated by acid. The main reaction is Li4SiO4 + 4HCl → 4LiCl + SiO2•2H2O. The generated silicic acid can form a high specific surface area and porous network framework, while removing impurities such as lithium carbonate and lithium hydroxide. This ensures that the final silica framework has clean and unobstructed pores. Although the drying and washing after acidification and impurity removal complicates the process, it gives the adsorbent excellent regenerability. After preparing the gel with alkali, a hydrothermal reaction is carried out in a vacuum drying oven. The reaction temperature does not need to be too high to complete quickly, resulting in higher reaction efficiency and better product quality. Finally, the obtained zeolite is reacted in a water bath in a mixed solution of NaOH and TPAOH and nitrogen doped. The resulting adsorbent is a hierarchical porous modified zeolite with characteristics such as large specific surface area, high porosity, fast adsorption rate, high capacity, good thermal stability, and strong regeneration ability.

[0007] Preferably, in step (1) of the above technical solution, the sieving is performed through a 200-mesh sieve.

[0008] Preferably, in step (2) of the above technical solution, the concentration of the HCl solution is 2-3 mol / L; the solid-liquid ratio of the lithium silicon powder to the HCl solution is 1:6-8. In this technical solution, by controlling the concentration of hydrochloric acid, not only can impurities be effectively removed, but the voids left by the dissolved lithium also form abundant mesopores, preserving the basic silicon framework and forming a high surface area ratio and porous structure.

[0009] Preferably, in step (3) of the above technical solution, the mass ratio of the dried filter residue to NaOH is 2-3:1; the solid-liquid ratio of the total amount of dried filter residue and NaOH to deionized water is 1:4-6.

[0010] Preferably, in step (3) of the above technical solution, the temperature of the hydrothermal reaction is 100±5℃ and the time is 15-20h.

[0011] Preferably, in step (5) of the above technical solution, the molar ratio of NaOH and TPAOH is 1:1, the concentration of the NaOH solution is 0.004-0.006 mol / L, preferably 0.005 mol / L; the concentration of the TPAOH solution is 0.004-0.006 mol / L, preferably 0.005 mol / L. Previous research and experiments have shown that using high-concentration sodium hydroxide solution as a modifier easily leads to the preferential removal of silicon species from the zeolite crystal framework, resulting in framework collapse. In this technical solution, by controlling the concentration and ratio of NaOH solution and TPAOH solution, using low-concentration sodium hydroxide as an alkaline modifier, and simultaneously introducing TPAOH solution as a silicon species protectant and pore-forming agent, the coordination between the zeolite outer surface and pore size can be effectively adjusted, maximizing adsorption efficiency and capacity. This modification principle includes: TPA... + The ion is a relatively large organic cation with four propyl groups, possessing a certain size and hydrophobicity. In the early stages of synthesis, TPA... + It will be negatively charged silicate oligomers (due to OH) - (By attacking Si atoms to make them negatively charged), they are attracted and bonded together via electrostatic interactions, forming TPA. + Large organic groups form a "protective shield" around themselves, which physically prevents external OH groups from entering. - The ions randomly attack the internal silicon species, guiding the silicate species to undergo orderly and directional condensation around them. This process is like providing a "mold," and the silicon species can only build according to the shape of this mold, thus gradually forming the preformed unit of the MFI structure.

[0012] Preferably, in step (5) of the above technical solution, the temperature of the water bath reaction is 50-60℃, the time is 0.5-1h, and the solid-liquid ratio is 1:38-40.

[0013] Preferably, in step (5) of the above technical solution, the calcination process is as follows: the nitrogen flow rate is 100 mL / min, the temperature is raised to 550℃ at a heating rate of 5℃ / min, and then calcined for 6-8 hours. In this technical solution, nitrogen doping modification is achieved by further calcining the zeolite in a nitrogen atmosphere, which can further improve the thermal stability and adsorption performance of the product.

[0014] Preferably, in the above technical solution, the entire process of drying filter residue involves drying at 105°C in an oven for 20-24 hours.

[0015] The present invention also provides a multi-level porous modified zeolite adsorbent prepared by the above method.

[0016] The present invention also provides an application of the above-mentioned multi-level porous modified zeolite adsorbent in VOCs waste gas treatment.

[0017] Advantages compared to existing technologies: (1) The preparation method of the multi-level porous modified zeolite adsorbent provided by the present invention is simple and easy to operate, with low production cost, and is suitable for large-scale production.

[0018] (2) The multi-level porous modified zeolite adsorbent provided by the present invention has the advantages of high adsorption efficiency and good thermal stability in the field of VOCs treatment, and has regeneration characteristics. In the regeneration capacity test of the multi-level porous modified zeolite adsorbent after adsorbing toluene, after six adsorption-desorption cycles, the adsorption efficiency of toluene can still be maintained at more than 93% compared with the fresh adsorbent.

[0019] (3) The multi-level porous modified zeolite adsorbent provided by the present invention uses industrial solid waste lithium silicon powder as raw material, which improves the comprehensive utilization rate of resources and greatly reduces the cost of treating VOCs. Attached Figure Description

[0020] Figure 1 This is a thermogravimetric analysis (TGA) diagram of the adsorbent of the present invention. Detailed Implementation

[0021] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions. However, the present invention is not limited to these embodiments, nor are these embodiments limited in any way.

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the formulations involved in the following examples are all commercially available products that can be purchased from the market.

[0023] The present invention will be further described in detail below with reference to embodiments: Example 1 A method for preparing zeolite adsorbents using lithium silicon powder includes the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and pass it through a 200-mesh sieve to remove large particles. Take the sieve material and dry it in an oven at 105℃ for 24 hours for later use. (2) Acid washing to remove impurities: First, prepare a 3 mol / L HCl solution in a 1000 mL volumetric flask, take 800 mL and pour it into a beaker, then take 100 g of lithium silicon powder obtained in step (1) and pour it into the beaker and stir to react for 2 h. Filter the reaction solution and wash the filter residue with deionized water for 10 min. Repeat the filtration-washing step 6 times until the filtrate is neutral (pH around 7). Place the filter residue in an oven at 105℃ and dry for 24 h for later use. (3) Gel crystallization: 45 mL of deionized water was measured with a graduated cylinder and poured into a beaker. Then, 3 g of NaOH was weighed and poured into the beaker. After the NaOH dissolved, 6 g of dried filter residue was weighed and poured into the beaker. The mixture was stirred and reacted for 10 min to obtain the initial gel. The initial gel was poured into a polytetrafluoroethylene-lined stainless steel reactor and placed in a vacuum drying oven. The reactor was subjected to hydrothermal reaction at 100 °C for 18 h. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a beaker. Deionized water is added and the mixture is stirred for 10 min. The filtration-washing steps are repeated 6 times until the filtrate is neutral (pH around 7). The filter residue is placed in an oven at 105℃ and dried for 24 h to obtain the zeolite adsorbent.

[0024] Example 2 A method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder includes the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and pass it through a 200-mesh sieve to remove large particles. Take the sieve material and dry it in an oven at 105℃ for 24 hours for later use. (2) Acid washing to remove impurities: First, prepare a 3 mol / L HCl solution in a 1000 mL volumetric flask, take 800 mL and pour it into a beaker, then take 100 g of lithium silicon powder obtained in step (1) and pour it into the beaker and stir to react for 2 h. Filter the reaction solution and wash the filter residue with deionized water for 10 min. Repeat the filtration-washing step 6 times until the filtrate is neutral (pH around 7). Place the filter residue in an oven at 105℃ and dry for 24 h for later use. (3) Gel crystallization: 45 mL of deionized water was measured with a graduated cylinder and poured into a beaker. Then, 3 g of NaOH was weighed and poured into the beaker. After the NaOH dissolved, 6 g of dried filter residue was weighed and poured into the beaker. The mixture was stirred and reacted for 10 min to obtain the initial gel. The initial gel was poured into a polytetrafluoroethylene-lined stainless steel reactor and placed in a vacuum drying oven. The reactor was subjected to hydrothermal reaction at 100 °C for 18 h. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a beaker. Deionized water is added and the mixture is stirred for 10 min. The filtration-washing steps are repeated 6 times until the filtrate is neutral (pH around 7). The filter residue is placed in an oven at 105℃ and dried for 24 h to obtain zeolite adsorbent. (5) Zeolite modification: First, prepare 0.005mol / L NaOH solution and TPAOH solution in 500mL volumetric flasks respectively. Then, take 40mL of each solution and pour them into a beaker. Sonicate for 10min to disperse the mixed solution evenly. Then, weigh 2g of the zeolite adsorbent obtained in step (4) and add it to the beaker. Place the beaker in a water bath and heat it to 55℃. Stir and react for 0.5h. After the reaction is completed, filter to obtain the filter residue. Repeat the filtration-washing step 6 times with deionized water until the filtrate is neutral (pH around 7). Dry the filter residue and place it in an oven at 105℃ for 24h. Finally, place it in a tube furnace and calcine it at 550℃ for 6h under a nitrogen atmosphere (nitrogen flow rate 100mL / min) at a heating rate of 5℃ / min to obtain the multi-level porous modified zeolite adsorbent.

[0025] Example 3 A method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder includes the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and pass it through a 200-mesh sieve to remove large particles. Take the sieve material and dry it in an oven at 105℃ for 24 hours for later use. (2) Acid washing to remove impurities: First, prepare a 2 mol / L HCl solution in a 1000 mL volumetric flask, take 600 mL and pour it into a beaker, then take 100 g of lithium silicon powder obtained in step (1) and pour it into the beaker and stir for 3 h. Filter the reaction solution, wash the filter residue with deionized water for 15 min, repeat the filtration-washing step 5 times until the filtrate is neutral (pH around 7), place the filter residue in an oven at 105℃ and dry for 24 h for later use. (3) Gel crystallization: 40 mL of deionized water was measured with a graduated cylinder and poured into a beaker. Then, 2 g of NaOH was weighed and poured into the beaker. After the NaOH dissolved, 6 g of dried filter residue was weighed and poured into the beaker. The mixture was stirred and reacted for 15 min to obtain the initial gel. The initial gel was poured into a polytetrafluoroethylene-lined stainless steel reactor and placed in a vacuum drying oven. The reactor was subjected to hydrothermal reaction at 100 °C for 15 h. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a beaker. Deionized water is added and the mixture is stirred for 15 minutes. The filtration-washing steps are repeated 5 times until the filtrate is neutral (pH around 7). The filter residue is placed in an oven at 105°C and dried for 24 hours to obtain the zeolite adsorbent. (5) Zeolite modification: First, prepare 0.004mol / L NaOH solution and TPAOH solution in 500mL volumetric flasks respectively. Then, take 40mL of each solution and pour them into a beaker. Sonicate for 10min to disperse the mixed solution evenly. Then, weigh 2g of the zeolite adsorbent obtained in step (4) and add it to the beaker. Place the beaker in a water bath and heat it to 50℃. Stir and react for 1h. After the reaction is completed, filter to obtain the filter residue. Repeat the filtration-washing step 5 times with deionized water until the filtrate is neutral (pH around 7). Dry the filter residue and place it in an oven at 105℃ for 24h. Finally, place it in a tube furnace and calcine it at 550℃ for 6h under a nitrogen atmosphere (nitrogen flow rate 100mL / min) at a heating rate of 5℃ / min to obtain the multi-level porous modified zeolite adsorbent.

[0026] Example 4 A method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder includes the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and pass it through a 200-mesh sieve to remove large particles. Take the sieve material and dry it in an oven at 105℃ for 24 hours for later use. (2) Acid washing to remove impurities: First, prepare a 3 mol / L HCl solution in a 1000 mL volumetric flask, take 700 mL and pour it into a beaker, then take 100 g of the lithium silicon powder obtained in step (1) and pour it into the beaker and stir for 2.5 h. Filter the reaction solution, wash the filter residue with deionized water for 12 min, repeat the filtration-washing step 5 times until the filtrate is neutral (pH around 7), place the filter residue in an oven at 105℃ and dry for 24 h for later use. (3) Gel crystallization: 54 mL of deionized water was measured with a graduated cylinder and poured into a beaker. Then, 3 g of NaOH was weighed and poured into the beaker. After the NaOH dissolved, 6 g of dried filter residue was weighed and poured into the beaker. The mixture was stirred and reacted for 12 min to obtain the initial gel. The initial gel was poured into a polytetrafluoroethylene-lined stainless steel reactor and placed in a vacuum drying oven. The reactor was subjected to hydrothermal reaction at 100 °C for 20 h. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a beaker. Deionized water is added and the mixture is stirred for 12 minutes. The filtration-washing steps are repeated 5 times until the filtrate is neutral (pH around 7). The filter residue is placed in an oven at 105°C and dried for 24 hours to obtain the zeolite adsorbent. (5) Zeolite modification: First, prepare 0.006mol / L NaOH solution and TPAOH solution in 500mL volumetric flasks respectively. Then, take 40mL of each solution and pour them into a beaker. Sonicate for 10min to disperse the mixed solution evenly. Then, weigh 2g of the zeolite adsorbent obtained in step (4) and add it to the beaker. Place the beaker in a water bath and heat it to 60℃. Stir and react for 0.5h. After the reaction is completed, filter to obtain the filter residue. Repeat the filtration-washing step 6 times with deionized water until the filtrate is neutral (pH around 7). Dry the filter residue and place it in an oven at 105℃ for 24h. Finally, place it in a tube furnace and calcine it at 550℃ for 6h under a nitrogen atmosphere (nitrogen flow rate 100mL / min) at a heating rate of 5℃ / min to obtain the multi-level porous modified zeolite adsorbent.

[0027] Comparative Example 1 A method for preparing zeolite adsorbent using lithium silicon powder, differing from Example 1 in that the concentration of HCl in step (2) is 5 mol / L.

[0028] Comparative Example 2 A method for preparing zeolite adsorbent using lithium silicon powder differs from Example 1 in that, in step (2), the filter residue is washed with deionized water for 12 minutes and then directly dried.

[0029] Comparative Example 3 A method for preparing zeolite adsorbent using lithium silicon powder differs from Example 1 in that the hydrothermal reaction temperature in step (3) is 150°C.

[0030] Comparative Example 4 A method for preparing zeolite adsorbent using lithium silicon powder differs from Example 1 in that, in step (3), the mass of NaOH and dried filter residue is the same, both being 6g.

[0031] Comparative Example 5 A method for preparing multi-level porous modified zeolite adsorbent using lithium silicon powder differs from Example 2 in that the water bath temperature in step (5) is 45°C.

[0032] Comparative Example 6 A method for preparing multi-level porous modified zeolite adsorbent using lithium silicon powder differs from Example 2 in that the water bath temperature in step (5) is 65°C.

[0033] Comparative Example 7 A method for preparing multi-level porous modified zeolite adsorbent using lithium silicon powder differs from Example 2 in that, in step (5), the concentrations of NaOH solution and TPAOH solution are both 0.0025 mol / L.

[0034] Comparative Example 8 A method for preparing multi-level porous modified zeolite adsorbent using lithium silicon powder differs from Example 2 in that, in step (5), the concentrations of NaOH solution and TPAOH solution are both 0.0075 mol / L.

[0035] Test case 1. The adsorbent products obtained from Comparative Examples 1-4 and 1-8, as well as two commercially available zeolite adsorbents, were used to test the toluene adsorption performance. The results are shown in Table 1. The experimental method was as follows: The performance of the prepared adsorbents was tested using a laboratory toluene adsorption apparatus. The apparatus consisted of four systems: bubbling, gas mixing, detection, and tail gas absorption. N2 generated from a gas cylinder was divided into two streams: one stream was fed into the bubbling apparatus to purge toluene; the other stream was used to dilute the toluene concentration. All gases were precisely adjusted using a mass flow meter to achieve the required toluene concentration and flow rate, and the toluene concentration was prepared to 1000 mg / m³. 3 The total gas flow rate was 300 mL / min. The prepared mixed gas was introduced into a mixing tank for thorough mixing, and then into a reaction bed without adsorbent. The outlet concentration was detected by a gas chromatograph equipped with a flame ionization (FID) detector. After the entire gas path stabilized, 0.3 g of pre-dried adsorbent was loaded into the quartz tube bed. The prepared toluene gas was introduced into the adsorption bed to undergo the adsorption reaction. The tail gas was treated in an absorption bottle. Before the adsorption test began, the zeolite sample in the adsorption bed was pretreated with nitrogen (50 mL / min) at 150 °C for 20 min to remove water or other impurities. The point at which the outlet concentration reached 5% of the inlet concentration was recorded as the adsorbent breakthrough point, and the corresponding time was defined as the breakthrough time t. b The adsorbent saturation point is defined as the outlet concentration reaching 95% of the inlet concentration, and the corresponding adsorption capacity is taken as the saturated adsorption capacity q. s The corresponding time is the saturation time t. s .

[0036] Table 1 shows the performance test results.

[0037] As can be seen from the results in Table 1, the multi-level porous modified zeolite adsorbents prepared in Examples 2-4 have a large specific surface area and good micropore volume, resulting in a long toluene breakthrough time, large adsorption capacity, short adsorption time, and high adsorption efficiency, indicating that this method is feasible. However, the zeolite adsorbent prepared in Example 1, due to the lack of modification treatment, has a relatively small specific surface area and micropore volume, a short breakthrough time, and significantly reduced adsorption capacity and efficiency. In Comparative Example 1, the excessively high concentration of hydrochloric acid damaged the silicon framework to some extent, reducing its specific surface area and micropore volume compared to Example 1, thus affecting the adsorption capacity and effect. In Comparative Example 2, the use of only one wash with deionized water led to acid residue dissolving the silicon framework and causing structural collapse, resulting in a poorly performing adsorbent. In Comparative Example 3, the hydrothermal reaction temperature was too high; increasing the temperature accelerates crystal formation. The growth of the crystals leads to excessively large crystal grains, a decrease in specific surface area, and prolonged exposure to high temperatures and strong alkaline environments can damage the original silicon framework structure and cause pore collapse. In Comparative Example 4, the excessively high concentration of sodium hydroxide resulted in larger gel particles, affecting the specific surface area and thus the adsorption effect. In Comparative Examples 5 and 6, the excessively low or high temperature of the modified water bath reaction also affected the specific surface area and micropore volume, thus impacting the adsorption effect. In Comparative Examples 7 and 8, the excessively low or high concentration of the modifier both affected the crystallinity of the product to some extent, affecting the specific surface area and micropore volume, thus impacting the adsorption effect. Furthermore, although the multi-level porous modified zeolite adsorbent prepared by this invention is comparable to or less than that of 13-X zeolite and Y-type zeolite in terms of specific surface area and micropore volume, its adsorption capacity is greater than that of the two existing commercial zeolites mentioned above, further demonstrating the feasibility of the preparation method of this invention and its significant advantages.

[0038] 2. The thermal stability of Examples 1 and 2 was analyzed by thermogravimetric analysis (TG) in a temperature range of 30-600℃. The results are as follows: Figure 1 As shown.

[0039] Depend on Figure 1 It can be seen that Examples 1 and 2 only show one decomposition peak in the 30-600°C range. This is mainly due to the weight loss caused by the evaporation of adsorbed water and capillary water on the zeolite surface, further reflecting the good thermal stability of the zeolite adsorbent before and after modification. The curve of Example 1 starts to decline at 50°C and stabilizes after 370°C. In contrast, the weight loss temperature range of Example 2 is smaller, mainly occurring in the 70-310°C range, and the weight loss rate of Example 2 (22.9%) is smaller than that of Example 1 (25.1%), indicating that the thermal stability is enhanced after modification.

[0040] 3. After the adsorbent products obtained in Example 1 and the adsorbent obtained in Example 2 were regenerated 6 times by adsorption-desorption of toluene, the adsorption efficiency and regeneration rate were tested. The adsorption-desorption adopted the thermal regeneration method: the adsorbent that was saturated with adsorption was regenerated by raising the temperature and partially desorbing the adsorbed toluene molecules from the zeolite surface. Then, the desorbed adsorbate was transported out of the adsorbent by the help of the purging gas.

[0041] Test results show that, compared with fresh adsorbent, the adsorbents obtained in Examples 1 and 2 maintained an adsorption capacity of 94.6% and 93.1% for toluene after 6 cycles of regeneration, respectively, indicating that the two zeolites prepared in Examples 1 and 2 have good regeneration performance for toluene.

[0042] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder, characterized in that, The method includes the following steps: (1) Grinding and sieving: Grind the lithium silicon powder and then sieve it to remove large particles. Take the sieve material and dry it for later use. (2) Acid washing to remove impurities: Take a certain amount of lithium silicon powder and mix it with HCl solution to react for 2-3 hours. Filter the reaction solution and wash the filter residue with deionized water for 10-15 minutes. Repeat the filtration-washing process until the filtrate is neutral. Dry the filter residue. The concentration of the HCl solution is 2-3 mol / L. (3) Gel crystallization: The dried filter residue and NaOH are poured into a container containing deionized water and reacted for 10-15 min to obtain an initial gel. The initial gel is then poured into a reaction vessel and placed in a vacuum drying oven for hydrothermal reaction. The mass ratio of the dried filter residue to NaOH is 2-3:

1. The temperature of the hydrothermal reaction is 100±5℃. (4) Filtration and washing: After the hydrothermal reaction is completed, the crystals in the reactor are ground into powder and transferred to a container. Deionized water is added and the mixture is stirred for 10-15 minutes. The filtration and washing process is repeated until the filtrate is neutral. The filter residue is dried to obtain the zeolite adsorbent. (5) Zeolite modification: After mixing NaOH solution and TPAOH solution evenly, pour them into a container, add zeolite adsorbent, place in a water bath and stir to react. After the reaction is completed, filter to obtain filter residue, repeat the filtration and washing with deionized water until the filtrate is neutral, dry the filter residue, and finally place it in a tube furnace and calcine under a nitrogen atmosphere to obtain multi-level porous modified zeolite adsorbent.

2. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (1), the sieving is done through a 200-mesh sieve.

3. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the lithium silicon powder to the HCl solution is 1:6-8.

4. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (3), the total amount of dried filter residue and NaOH is in a solid-liquid ratio of 1:4-6 to deionized water.

5. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (3), the hydrothermal reaction takes 15-20 hours.

6. The method for preparing a hierarchical porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (5), the molar ratio of NaOH to TPAOH is 1:1, the concentration of the NaOH solution is 0.004-0.006 mol / L, and the concentration of the TPAOH solution is 0.004-0.006 mol / L.

7. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (5), the water bath reaction temperature is 50-60℃, the time is 0.5-1h, and the solid-liquid ratio is 1:38-40.

8. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, In step (5), the calcination process is as follows: the nitrogen flow rate is 100 mL / min, the temperature is raised to 550℃ at a rate of 5℃ / min, and then calcined for 6-8 hours.

9. The method for preparing a multi-level porous modified zeolite adsorbent using lithium silicon powder according to claim 1, characterized in that, The entire process of drying filter residue involves drying in an oven at 105℃ for 20-24 hours.

10. The application of a multi-level porous modified zeolite adsorbent prepared by the method of any one of claims 1-9 in the treatment of VOCs waste gas.

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