A method for preparing ZSM-5 molecular sieve by microwave-assisted desilication liquid

Abstract

This invention discloses a method for preparing ZSM-5 molecular sieves using a microwave-assisted method with desilication solution, comprising the following steps: First, pretreatment of the desilication solution: the desilication solution is mixed with an oxyacid to adjust the pH to 9-11.5, a template agent is added and mixed evenly to obtain an initial gel; Second, preparation of the ZSM-5 molecular sieve: the initial gel obtained in the first step is placed in a microwave synthesizer for aging with high-speed stirring; the aged solution undergoes a crystallization reaction, followed by filtration, washing, drying, and high-temperature calcination to obtain the ZSM-5 molecular sieve. This invention uses desilication solution as a raw material to prepare ZSM-5 molecular sieves, saving material costs and providing a new approach for the high-value utilization of desilication solution. Furthermore, by utilizing microwave-assisted synthesis on the basis of the traditional hydrothermal method, the time cost is effectively shortened.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve technology, specifically, it relates to a method for preparing ZSM-5 molecular sieves using a microwave-assisted method with desilication liquid. Background Technology

[0002] Fly ash, one of the largest industrial wastes emitted in my country, is rich in silicon and aluminum resources, attracting widespread attention. There are two main ways to utilize fly ash: one is to directly synthesize materials from it or to utilize it through certain pretreatment processes; the other is to extract valuable elements from it. Compared to the former, extracting valuable elements from fly ash is a high-value utilization method.

[0003] Fly ash typically contains highly reactive amorphous SiO2, requiring selective extraction with a high-concentration NaOH solution to effectively reduce the generation of calcium silicate slag during the alumina extraction process from high-alumina fly ash. The synergistic utilization of alumina extraction from high-alumina fly ash and the co-utilization of silicon and aluminum has opened up new avenues for the coordinated use of high-alumina fly ash resources. However, the commonly used alkaline alumina extraction process generates highly alkaline wastewater, and its reuse has become a bottleneck restricting the development of the alumina extraction industry from high-alumina fly ash.

[0004] Elemental analysis of the desilication solution revealed that silicon and aluminum were abundant, with a silicon-to-aluminum ratio generally exceeding 40, making it suitable for the preparation of high-silica molecular sieves, such as ZSM-5. ZSM-5 molecular sieves have a wide range of applications in petrochemicals, chemical industry, and environmental protection. Furthermore, compared to other high-silica molecular sieves, ZSM-5 requires a relatively higher alkalinity of the initial solution, meaning that the amount of acid used can be reduced during the desilication solution pretreatment stage. Therefore, using desilication solution to prepare ZSM-5 molecular sieves allows for the high-value utilization of the desilication solution. However, the preparation of ZSM-5 molecular sieves also suffers from an excessively long production cycle. For example, in the study by Yin et al. [Yin, H., et al., An eco-friendly method for the scale-up synthesis of ZSM-5Zeolite. Microporous and Mesoporous Materials, 2024. 365: p. 112907], the crystallization of ZSM-5 required 24 hours. In the study by Yu et al. [Yu, L., J. Zhou, and W. Wang, Sub-micron sized hierarchical porous ZSM-5 particles with controllable mesoporous structures by changing the alkalinity in the synthesis using NaOH. Journal of Solid State Chemistry, 2023. 322: p. 123989], the crystallization time for preparing controllable mesoporous ZSM-5 was 96 hours. Summary of the Invention

[0005] To overcome the technical problem of excessively long synthesis cycle in the traditional hydrothermal method for preparing molecular sieves, the purpose of this invention is to provide a method for preparing ZSM-5 molecular sieves using a microwave-assisted method with desilication liquid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing ZSM-5 molecular sieves using a microwave-assisted method with a desilication solution, comprising the following steps:

[0008] The first step is the pretreatment of the desilication solution.

[0009] The desilication solution is mixed with an oxyacid to adjust the pH to 9-11.5 (preferably 10.5, 10.4, or 9), and the template agent is added and mixed evenly to obtain the initial gel.

[0010] The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution is (40-200):1:(120-1200):(1000-8000) (preferably 150:1:375:6600, 92:1:230:6600, 100:1:250:7200, 109.08:1:163.62:6170.29).

[0011] The oxyacid is selected from sulfuric acid, phosphoric acid, nitric acid, and hypochlorous acid;

[0012] The template agent is selected from tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-butylamine, and ethylamine;

[0013] The molar ratio of Al2O3 to template agent in the desilication solution is 1:(16-80) (preferably 1:60, 1:36.8, 1:40, or 1:46.6).

[0014] The second step is the preparation of ZSM-5 molecular sieves.

[0015] The initial gel obtained in the first step was placed in a microwave synthesizer for aging and high-speed stirring; the aged solution was subjected to a crystallization reaction, filtered, washed, dried, and calcined at high temperature to obtain ZSM-5 molecular sieve.

[0016] In the second step, the parameters of the microwave synthesizer are set to 100-300W (preferably 150W or 200W), temperature 20-180℃ (preferably 40℃, 80℃, 180℃ or 100℃), and time 20min-5h (preferably 60min, 40min, 4h or 30min).

[0017] The crystallization temperature in the second step is 160-200℃ (preferably 180℃), and the crystallization time is 2-24h (preferably 12h).

[0018] In the second step, the filtration and washing are carried out using deionized water and ethanol.

[0019] The drying temperature in the second step is 60-120℃ (preferably 110℃, 120℃, or 60℃), and the time is 4-12 hours (preferably 6 hours or 8 hours).

[0020] The high-temperature calcination temperature in the second step is 450-650℃ (preferably 550℃ or 500℃), and the time is 3-6h (preferably 5h, 3h, or 6h).

[0021] By adopting the above technical solution, the present invention has the following advantages and beneficial effects:

[0022] This invention prepares ZSM-5 molecular sieves using desilication liquid as raw material, saving material costs and providing a new approach for the high-value utilization of desilication liquid. At the same time, it utilizes microwave-assisted synthesis based on the traditional hydrothermal method, effectively shortening the time cost.

[0023] The present invention relates to a microwave-assisted method for preparing ZSM-5 molecular sieves from desilication liquor. This invention transforms the difficulty of reusing the high alkali content in the desilication liquor into a favorable factor for ZSM-5 molecular sieve preparation. The large amount of Na in the desilication liquor... + As alkali metal cations, they can maintain the electroneutrality of the framework. During the preparation of ZSM-5, if the molar ratio of Na₂O to SiO₂ is too low, the framework charge cannot be balanced, leading to a change in the crystal form of the resulting product and preventing the formation of ZSM-5 molecular sieves. Simultaneously, the OH⁻ in the desilication solution... - This invention can increase the dissolution rate of silica sol, accelerate the nucleation rate, and make the formation rate of crystal nuclei higher than the growth rate of crystals, thereby increasing the number of crystal nuclei and reducing the size of crystal particles. This invention utilizes microwave-assisted methods to achieve rapid synthesis of ZSM-5 molecular sieves. This invention requires no additional silicon or aluminum sources, only a small amount of template agent, has a simple and short operation time, and yields ZSM-5 molecular sieves with relatively high crystallinity, high yield, and low cost, making it easy to industrialize. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the ZSM-5 molecular sieve preparation process.

[0025] Figure 2 The image shows the XRD pattern of the sample obtained in Example 1.

[0026] Figure 3 This is a schematic diagram showing the XRD comparison results of C40J2 and C40J4 after microwave synthesis and aging for 40 minutes in Example 2.

[0027] Figure 4 This is a schematic diagram of the infrared spectra of the samples obtained from the two initial solutions in Example 4 (WD: desilication solution sample containing impurities, WP: desilication solution sample without impurities).

[0028] Figure 5 These are SEM images of two samples from Example 4. Detailed Implementation

[0029] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1

[0031] A method for preparing ZSM-5 molecular sieves using a microwave-assisted desilication solution, such as... Figure 1 As shown, Figure 1 A schematic diagram of the ZSM-5 molecular sieve preparation process, including the following steps:

[0032] The first step is the pretreatment of the desilication solution.

[0033] The desilication solution was mixed with an oxyacid to adjust the pH to 10.5, and the template agent was added and mixed evenly to obtain the initial gel.

[0034] The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution is 150:1:375:6600;

[0035] The oxyacid is sulfuric acid; the template agent is tetrapropylammonium bromide.

[0036] The molar ratio of Al2O3 to template agent in the desilication solution is 1:60;

[0037] The second step is the preparation of ZSM-5 molecular sieves.

[0038] The initial gel obtained in the first step was aged in a microwave synthesizer with parameters set to 150W, 40℃, and 60min, with high-speed stirring. The aged solution was then transferred to a polytetrafluoroethylene-lined reactor for crystallization at 180℃ for 12h. After crystallization, the solution was washed with deionized water and ethanol, dried at 110℃ for 6-8h, and then calcined in a muffle furnace at 550℃ for 5h to remove the template agent, yielding 0.5g of ZSM-5 molecular sieve sample (per 20g of initial solution). XRD analysis and comparison with ZSM-5 molecular sieve analysis were performed. Figure 2 As shown, Figure 2 The image shows the XRD pattern of the sample obtained in Example 1. The calculated relative crystallinity of the sample is 93%.

[0039] The obtained sample was modified with 0.4M sodium hydroxide for 4 hours, and the adsorption of lead-containing wastewater (200 mg / L) was investigated using the modified sample. The study found that the saturated adsorption capacity of the sample for lead could reach 137.76 mg / g.

[0040] Example 2

[0041] The first step is the pretreatment of the desilication solution.

[0042] The desilication solution was mixed with an oxyacid to adjust the pH to 10.4, and the template agent was added and mixed evenly to obtain the initial gel.

[0043] The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution is 92:1:230:6600;

[0044] The oxyacid is sulfuric acid; the template agent is tetrapropylammonium bromide.

[0045] The molar ratio of Al2O3 to template agent in the desilication solution is 1:36.8;

[0046] The second step is the preparation of ZSM-5 molecular sieves.

[0047] The initial gel obtained in the first step was aged in a microwave synthesizer with the parameters set to 200W, 80℃, and 40min, with high-speed stirring. After aging, the parameters were changed to 200W, 180℃, and 4h, with high-speed stirring. The aged solution was then transferred to a polytetrafluoroethylene-lined reactor for crystallization at 180℃ for 12h. After crystallization, the solution was washed with deionized water and ethanol, dried at 120℃ for 8h, and then calcined in a muffle furnace at 550℃ for 3h to obtain 0.45g of ZSM-5 molecular sieve sample (initial solution was 20g).

[0048] Figure 3 This is a schematic diagram comparing the XRD results of samples aged in a microwave synthesizer for 40 minutes followed by microwave synthesis and aging, then crystallized for 2 hours (C40J2) and 4 hours (C40J4) (C40J4). As can be seen from the figure, the sample remained amorphous after 2 hours of microwave-assisted aging, while pure-phase ZSM-5 molecular sieves were obtained after 4 hours of crystallization. Compared to the traditional hydrothermal method for preparing ZSM-5 molecular sieves, which requires 1-3 days, this method effectively shortens the crystallization synthesis cycle.

[0049] Example 3

[0050] The first step is the pretreatment of the desilication solution.

[0051] The desilication solution was mixed with an oxyacid to adjust the pH to 9, and the template agent was added and mixed evenly to obtain the initial gel.

[0052] The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution is 100:1:250:7200;

[0053] The desilication solution contains potassium impurities, with a potassium ion concentration of 723.8 mg / L;

[0054] The oxyacid is sulfuric acid; the template agent is tetrapropylammonium bromide.

[0055] The molar ratio of Al2O3 to template agent in the desilication solution is 1:40;

[0056] The second step is the preparation of ZSM-5 molecular sieves.

[0057] The initial gel obtained in the first step was placed in a microwave synthesizer for aging with high-speed stirring; the aged solution was subjected to a crystallization reaction, filtered, washed, dried, and calcined at high temperature to obtain 0.52g of ZSM-5 molecular sieve sample (initial solution was 20g), and the relative crystallinity of the sample was 114%.

[0058] In the second step, the parameters of the microwave synthesizer are set to 200W, 100℃, and 30min.

[0059] In the second step, the crystallization temperature is 180℃ and the crystallization time is 12h.

[0060] In the second step, the filtration and washing are carried out using deionized water and ethanol.

[0061] The drying temperature in the second step is 60℃, and the time is 8 hours.

[0062] The high-temperature calcination in the second step is 550℃ for 5 hours.

[0063] Example 4

[0064] The first step is the pretreatment of the desilication solution.

[0065] The desilication solution or desilication solution containing impurities is mixed with an oxyacid to adjust the pH to 10.5, and the template agent is added and mixed evenly to obtain the initial gel.

[0066] The desilication solution was prepared by dissolving 51.12 g of sodium silicate nonahydrate, 0.8 g of aluminum chloride hexahydrate, and 21.6 g of sodium hydroxide in 180 g of deionized water. The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution was 109.08:1:163.62:6170.29.

[0067] Preparation of the desilication solution containing impurities: Dissolve 51.12g sodium silicate nonahydrate, 0.8g aluminum chloride hexahydrate and 21.6g sodium hydroxide in 180g deionized water, and add trace impurity ions such as 0.13g calcium, 0.01g iron and 0.14g potassium to obtain the desilication solution containing impurities.

[0068] The oxyacid is sulfuric acid; the template agent is tetrapropylammonium bromide.

[0069] The molar ratio of Al2O3 to the template agent in the oxyacid is 1:46.6;

[0070] The second step is the preparation of ZSM-5 molecular sieves.

[0071] The initial gel obtained in the first step was placed in a microwave synthesizer for aging with high-speed stirring; the aged solution was subjected to a crystallization reaction, filtered, washed, dried, and calcined at high temperature to obtain a ZSM-5 molecular sieve sample.

[0072] The relative crystallinity of ZSM-5 molecular sieve prepared from desilication liquid without impurities was 86.53%, while the relative crystallinity of ZSM-5 molecular sieve prepared from desilication liquid containing impurities was 93.58%.

[0073] In the second step, the parameters of the microwave synthesizer are set to 200W, 100℃, and 30min.

[0074] In the second step, the crystallization temperature is 180℃ and the crystallization time is 12h.

[0075] In the second step, the filtration and washing are carried out using deionized water and ethanol.

[0076] The drying temperature in the second step is 60℃, and the time is 8 hours.

[0077] The high-temperature calcination in the second step is 500℃ for 6 hours.

[0078] Figure 4 This is a schematic diagram of the infrared spectra of the samples obtained from the two initial solutions in Example 4 (WD: desilication solution sample containing impurities, WP: desilication solution sample without impurities). As can be seen from the infrared spectra, the samples prepared using the two desilication solutions by the microwave-assisted method both exhibit typical MFI structures. Both samples show a peak density only at 1624 cm⁻¹. -1 (1634cm -1 The existence of slight deviations indicates that the influence of trace impurities in the desilication solution is not significant in a microwave-assisted uniformly heated system.

[0079] Figure 5 These are SEM images of two samples from Example 4. The images show that the ZSM-5 molecular sieve sample prepared using a microwave-assisted method with a desilication solution has small crystallites and is prone to aggregation.

[0080] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing ZSM-5 molecular sieves using a microwave-assisted desilication solution, characterized in that, Includes the following steps: The first step is the pretreatment of the desilication solution. The desilication solution was mixed with an oxyacid to adjust the pH to 9-11.5, and the template agent was added and mixed evenly to obtain the initial gel. The initial molar ratio of SiO2, Al2O3, Na2O, and H2O in the desilication solution is (40-200):1:(120-1200):(1000-8000). The oxyacid is selected from sulfuric acid, phosphoric acid, nitric acid, and hypochlorous acid; The template agent is selected from tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-butylamine, and ethylamine; The molar ratio of Al2O3 to template agent in the desilication solution is 1:(16-80). The second step is the preparation of ZSM-5 molecular sieves. The initial gel obtained in the first step was placed in a microwave synthesizer for aging and high-speed stirring; the aged solution was subjected to a crystallization reaction, filtered, washed, dried, and calcined at high temperature to obtain ZSM-5 molecular sieve. In the second step, the parameters of the microwave synthesizer are set to 100-300W, temperature 20-180℃, and time 20min-5h. The crystallization temperature in the second step is 160~200℃, and the crystallization time is 2~24h; The drying temperature in the second step is 60-120℃, and the time is 4-12 hours; The high-temperature calcination in the second step is at a temperature of 450-650℃ for 3-6 hours.

2. The method for preparing ZSM-5 molecular sieves using microwave-assisted desilication liquid according to claim 1, characterized in that, In the second step, the filtration and washing are carried out using deionized water and ethanol.

Images