Method for preparing hierarchical pore modified zeolite adsorbent from lithium silicon powder and application of hierarchical pore modified zeolite adsorbent

Abstract

The invention belongs to the technical field of waste gas treatment, and particularly relates to a method for preparing a hierarchical pore modified zeolite adsorbent from lithium silicon powder and application of the hierarchical pore modified zeolite adsorbent. The method comprises the following steps: grinding and sieving, pickling and impurity removal, gel crystallization, filtering and washing, and zeolite modification. The lithium silicon powder is used as a main raw material, acid pickling, crystallization, washing and modification are combined, and the obtained hierarchical pore modified zeolite adsorbent has the advantages of being large in specific surface area, high in porosity, high in adsorption rate, high in capacity, good in thermal stability and high in regeneration capacity; the preparation method is simple in process, easy to operate and low in cost, and the prepared hierarchical porous modified zeolite is used for adsorbing VOCs, is high in adsorption efficiency and can be regenerated and recycled, so that the VOCs treatment cost is further reduced.

Description

TECHNICAL FIELD

[0001] The 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. BACKGROUND

[0002] With the rapid development of new energy vehicles in China, the demand for lithium carbonate has increased dramatically. However, a large amount of industrial waste lithium silicon powder is generated during the industrial production of lithium carbonate. This kind of industrial waste has very low utilization rate and can only be continuously accumulated, which not only seriously occupies land resources, but also causes adverse effects on the environment. Lithium silicon powder mainly contains Si and Al and has the basic conditions for preparing zeolite. Chinese Invention Patent CN110270308A discloses a method for preparing a sewage treatment adsorbent from lithium silicon powder and nitrogen-doped mesoporous carbon. The adsorbent prepared by the method has good ability to simultaneously reduce COD in sewage and high efficiency in removing ammonia nitrogen.

[0003] Volatile organic compounds (VOCs) are an important source of atmospheric pollution and indoor environmental pollution, and their efficient treatment has become an urgent demand in the current environmental protection field. Adsorption method is widely used in the capture and recovery of VOCs due to its simple operation and relatively low cost. Zeolite molecular sieve is considered as one of the most promising VOCs adsorbents due to its regular microporous channels, high specific surface area, excellent thermal and chemical stability, and non-flammability. However, the existing zeolite adsorbents usually have the disadvantages of low VOCs adsorption capacity, low adsorption efficiency, low regeneration efficiency, and significant reduction in adsorption capacity with increasing temperature. Currently, there is no related patent for preparing VOCs adsorbent zeolite from lithium silicon powder. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a method for preparing a multi-level pore modified zeolite adsorbent from lithium silicon powder and application thereof. The preparation method is simple, easy to operate, and low in cost. The multi-level pore modified zeolite prepared by the method has high adsorption efficiency for VOCs and can be regenerated and recycled, further reducing the cost of treating VOCs.

[0005] The purpose of the application is to provide a method for preparing a multi-level pore modified zeolite adsorbent from lithium silicon powder, which comprises the following steps: (1) Grinding and sieving: grind the lithium silicon powder and sieve to remove large particles, and take the undersize for drying; (2) Acid pickling and impurity removal: mix a certain amount of lithium silicon powder with HCl solution and react for 2-3 h, then perform suction filtration on the reaction liquid, stir-wash the filter residue with deionized water for 10-15 min, and repeat the filtration-washing until the filtrate is neutral, and then dry the filter residue; (3) Gel crystallization: the dried filter residue and NaOH are poured into a container with deionized water to react for 10-15 min to prepare an initial gel, and the prepared initial gel is poured into a reaction kettle and placed in a vacuum drying oven for hydrothermal reaction; (4) Filtration and washing: after the hydrothermal reaction is completed, the crystals in the reaction kettle are ground into powder and transferred to a container, deionized water is added and stirred and washed for 10-15 min, and the filtration and washing are repeated until the filtrate is neutral, and the filter residue is dried to obtain a zeolite adsorbent; (5) Zeolite modification: NaOH solution and TPAOH solution are uniformly mixed and poured into a container, the zeolite adsorbent is added and placed in a water bath for stirring and reaction, after the reaction is completed, the filter residue is obtained by suction filtration, and the suction filtration and washing are repeated with deionized water until the filtrate is neutral, the filter residue is dried, and finally it is calcined in a tube furnace under a nitrogen atmosphere to obtain a multi-pore modified zeolite adsorbent.

[0006] The present application uses lithium silicon powder as the main raw material, which is activated by acid after being crushed, and the main reaction is Li4SiO4+4HCl→4LiCl+SiO2•2H2O, the generated silicic acid can form a high specific surface area and porous network skeleton, and at the same time, impurities such as lithium carbonate and lithium hydroxide are removed, which can ensure that the final formed silica skeleton has clean and unobstructed voids, and although the drying and washing process after acidification and impurity removal complicates the process, it gives the adsorbent excellent regenerability; the gel prepared by using alkali is subjected to hydrothermal reaction in a vacuum drying oven, which can be quickly completed at a relatively low reaction temperature, has higher reaction efficiency, and produces better product quality; finally, the obtained zeolite is subjected to water bath reaction in a mixed solution of NaOH and TPAOH, and nitrogen doping, and the obtained adsorbent is a multi-pore modified zeolite, which has the characteristics of large specific surface area, high porosity, fast adsorption rate, high capacity, good thermal stability, strong regenerability, etc.

[0007] Preferably, in step (1) of the above technical solution, the sieving is sieving 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, and 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 also the voids left by the dissolved lithium form abundant mesopores, retaining the basic skeleton of silicon and forming a high surface 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, and the solid-liquid ratio of the total amount of the dried filter residue and NaOH to deionized water is 1:4-6.

[0010] Preferably, in the step (3), the hydrothermal reaction is carried out at a temperature of 100±5℃ for 15-20h.

[0011] Preferably, in the step (5), the molar ratio of NaOH to TPAOH is 1:1, the concentration of the NaOH solution is 0.004-0.006mol / L, preferably 0.005mol / L, and the concentration of the TPAOH solution is 0.004-0.006mol / L, preferably 0.005mol / L. Through preliminary research and experiments, it is found that using a high-concentration sodium hydroxide solution as a modifier can easily cause the preferential removal of framework silicon species in the zeolite crystal, resulting in the collapse of the framework. In the present technical solution, by controlling the concentration and ratio of the NaOH solution and the TPAOH solution, a low-concentration sodium hydroxide solution is used as an alkaline modifier, and a TPAOH solution is introduced as a silicon species protective agent and a pore-forming agent, which can effectively adjust the coordination of the outer surface and pore size of the zeolite, and greatly improve the adsorption efficiency and capacity. The modification principle includes: TPA + ions are large organic cations with four propyl chains, and have a certain volume and hydrophobicity. In the early stage of synthesis, TPA + ions are attracted by negatively charged silicate oligomers (OH - ions attack Si atoms to make them negatively charged) through electrostatic attraction, and after combination, the bulky organic groups of TPA + ions will form a "protective cover" around them, which physically hinders the random attack of external OH - ions on internal silicon species, and guides the silicate species to condense in an orderly and directional manner. This process is like providing a "mold", and the silicon species can only build according to the shape of the mold, thereby gradually forming preformed units of MFI structure.

[0012] Preferably, in the step (5), the water bath reaction is carried out at a temperature of 50-60℃ for 0.5-1h, and the solid-liquid ratio is 1:38-40.

[0013] Preferably, in the step (5), the calcination process is as follows: the nitrogen flow is 100mL / min, the temperature is raised to 550℃ at a rate of 5℃ / min, and then calcination is carried out for 6-8h. In the present technical solution, the zeolite is further calcined in a nitrogen atmosphere to realize nitrogen-doped modification, which can further improve the thermal stability and adsorption performance of the product.

[0014] Preferably, in the present technical solution, the entire process of filtering and drying the residue is carried out by drying in an oven at 105℃ for 20-24h.

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

[0016] The application also provides application of the above multi-level pore modified zeolite adsorbent in VOCs waste gas treatment.

[0017] The beneficial effects of the prior art are as follows: (1) The preparation method of the multi-level pore modified zeolite adsorbent provided by the application is simple and easy to operate, has low production cost, and is suitable for large-scale production.

[0018] (2) The multi-level pore modified zeolite adsorbent provided by the application has high adsorption efficiency and good high-temperature stability in the field of VOCs treatment, and has a regeneration property. In the regeneration capacity test after the multi-level pore modified zeolite adsorbent adsorbs toluene, the toluene adsorption efficiency can still be maintained at more than 93% after six adsorption-desorption cycles of regeneration compared with the fresh adsorbent.

[0019] (3) The multi-level pore modified zeolite adsorbent provided by the application uses industrial solid waste lithium silicon powder as raw material, improves the comprehensive utilization rate of resources, and greatly reduces the cost of VOCs treatment. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The thermogravimetric analysis diagram of the adsorbent of the application. DETAILED DESCRIPTION

[0021] The above technical features of the application and the technical features described in detail in the following (such as examples) can be combined with each other to form new or preferred technical solutions, but the application is not limited to only these examples, and these examples also do not limit the application in any way.

[0022] The experimental methods in the following examples are all conventional methods unless otherwise specified. The preparations involved in the following examples are all ordinary commercially available products unless otherwise specified, and can be purchased on the market.

[0023] The application will be further described in detail below in combination with examples: Example 1 A method for preparing a zeolite adsorbent from lithium silicon powder, comprising the following steps: (1) Grind and sieve: grind the lithium silicon powder and pass it through a 200-mesh sieve to remove large particles, and take the undersize and place it in an oven at 105℃ for drying for 24h, for standby 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. (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.

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 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.

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 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.

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 temperature of the hydrothermal reaction is 100±5℃ and the time is 15-20h.

6. 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 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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