Preparation method of hydrophobic molecular sieve carrier based on coal gangue and hydrophobic molecular sieve

Abstract

This invention relates to a method for preparing a hydrophobic molecular sieve carrier based on coal gangue and the hydrophobic molecular sieve itself, belonging to the field of molecular sieve material preparation technology. The preparation method includes: crushing and grinding coal gangue followed by activation treatment to obtain activated coal gangue; mixing the activated coal gangue with an alkali source and then performing alkali fusion treatment to obtain an alkali fusion product; mixing the alkali fusion product with water, subjecting it to ultrasonic dispersion treatment and aging to form a precursor gel; in-situ hydrophobication-crystallization: introducing a hydrophobic modifier during the precursor gel formation process, aging process, and / or before hydrothermal crystallization, and performing hydrothermal crystallization on the resulting system to ensure that molecular sieve crystallization and the construction of the hydrophobic outer surface layer occur simultaneously; performing solid-liquid separation, washing, and drying to directly obtain the hydrophobic molecular sieve carrier. This invention uses coal gangue as the main raw material, requires no template agent, has high crystallization efficiency, and can obtain a hydrophobic molecular sieve in one step, thereby increasing the added value of comprehensive utilization of coal gangue.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve material preparation technology, and in particular to a method for preparing a hydrophobic molecular sieve carrier based on coal gangue and the hydrophobic molecular sieve itself. Background Technology

[0002] Coal gangue is a typical coal-based solid waste generated during coal mining and washing. It is mainly composed of silica-alumina minerals such as kaolinite and quartz, rich in SiO2 and Al2O3, and contains certain amounts of impurities such as Fe, Ti, Ca, and Mg. Coal gangue stockpiles occupy land and pose environmental risks; therefore, developing high-value utilization methods for coal gangue is of great significance.

[0003] Zeolite molecular sieves are a class of three-dimensional aluminosilicate materials with regular microporous structures, possessing high specific surface area, ion exchange capacity, and selective adsorption properties. Existing technologies for preparing molecular sieves from coal gangue mostly employ thermal activation / alkali fusion activation followed by hydrothermal crystallization, yielding molecular sieves such as NaA, NaX, and NaY. While these methods can achieve high-value utilization of solid waste, several challenges remain in engineering and application expansion. (1) Impurities and unstable dissolution of silicon and aluminum: Impurities such as Fe and Ti in coal gangue can easily affect alkali consumption, crystal phase purity and product appearance during activation and crystallization. (2) The crystallization cycle is relatively long: Conventional hydrothermal crystallization often takes several hours to more than ten hours, which consumes a lot of energy and makes it difficult to control the crystal size distribution; (3) Hydrophilic material surface: Coal gangue-based molecular sieves usually contain a lot of surface hydroxyl groups, which are easy to absorb water, and their use is limited in scenarios such as oil-water separation and non-polar adsorption / separation; (4) Process and cost: Some routes require template agents or additional silicon and aluminum sources, which increases the cost of raw materials and post-processing burden.

[0004] Therefore, there is an urgent need for a method to prepare molecular sieves that use coal gangue as the main raw material, do not require template agents, have high crystallization efficiency, and can obtain hydrophobic surfaces in one step, so as to enhance the added value of comprehensive utilization of coal gangue and provide a support basis for subsequent construction of catalytic materials loaded with active components such as metals and / or metal oxides for catalytic oxidation of low-concentration gas. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a hydrophobic molecular sieve support based on coal gangue, and the hydrophobic molecular sieve itself. The technical solution of this invention is as follows: In a first aspect, a method for preparing a hydrophobic molecular sieve support based on coal gangue is provided, comprising: S1, Coal gangue activation and impurity removal: Coal gangue is crushed and ground and then activated to obtain activated coal gangue; S2, Alkali fusion treatment: Activated coal gangue is mixed with an alkali source and then subjected to alkali fusion treatment to obtain alkali fusion product; S3, Precursor gel - ultrasonic dispersion - aging: The alkali-fused product is mixed with water, ultrasonically dispersed and aged to form a precursor gel; S4, In-situ hydrophobication-crystallization: A hydrophobic modifier is introduced during the formation of the precursor gel, the aging process and / or before hydrothermal crystallization, and the resulting system is subjected to hydrothermal crystallization so that the molecular sieve crystallization and the construction of the hydrophobic layer on the outer surface are carried out simultaneously. S5 is used for solid-liquid separation, washing, and drying to directly obtain a hydrophobic molecular sieve carrier.

[0006] Preferably, S1 includes: The coal gangue is crushed and ground to 200-400 mesh, then acid-leached with acid solution to remove impurities, dried, and calcined at 650-850℃ for 1.5-3 hours to obtain activated coal gangue. The acid leaching process uses a 3-4 mol / L hydrochloric acid solution with a solid-liquid mass ratio of 1:15-20, an acid leaching temperature of 50-80℃, and a leaching time of 6-12 hours.

[0007] Preferably, S2 includes: After the activated coal gangue and the alkali source are ball-milled and mixed evenly, they are subjected to alkali fusion treatment to convert the silica-aluminate phase into an easily soluble silicate / aluminate active phase, thus obtaining the alkali fusion product. The alkali source is sodium hydroxide and / or sodium carbonate; the mass ratio of sodium hydroxide to activated coal gangue is 1.2 to 1.8:1, the alkali fusion treatment temperature is 600 to 750°C, and the alkali fusion treatment time is 1 to 3 hours.

[0008] Preferably, S3 includes: The alkali fusion product is mixed with water in a certain proportion, ultrasonically dispersed, and aged at room temperature or lower temperature to form a precursor gel containing silicon-aluminum species. The ultrasonic dispersion time is 30–90 min, and the aging time is 6–12 h; 0.1–5 wt% of FAU structure seed crystals are added during the aging process.

[0009] Preferably, S4 includes: The precursor gel is placed in a closed reaction vessel, and a hydrophobic modifier is introduced after gel formation, during aging, and / or into the crystallization-forward system. The gel is then crystallized at 80–110 °C for 120–240 min under microwave heating conditions, so that the molecular sieve crystallization and hydrophobic layer construction are carried out simultaneously.

[0010] Preferably, the hydrophobic modifier is one or more alkyl / fluoroalkyl silanes, including octadecyltrichlorosilane, hexadecyltrimethoxysilane, and dimethyldichlorosilane; the mass ratio of the hydrophobic modifier to the solid silicon-aluminum source in the system is 0.05 to 0.2:1.

[0011] Preferably, the hydrothermal crystallization temperature is 80–110°C, and the hydrothermal crystallization time is 120–240 min.

[0012] Preferably, after hydrothermal crystallization, the resulting product is subjected to a curing heat treatment at 200–350°C for 1–3 hours under an inert atmosphere or vacuum.

[0013] In a second aspect, a hydrophobic molecular sieve is provided, which is prepared by the preparation method of the hydrophobic molecular sieve carrier based on coal gangue as described in the first aspect, including a zeolite molecular sieve framework formed by the conversion of coal gangue, and a hydrophobic layer formed in situ on the outer surface of the zeolite molecular sieve framework; the hydrophobic layer is formed by the in-situ loading, condensation, grafting and / or coating of a hydrophobic modifier during the crystallization process of the hydrophobic molecular sieve.

[0014] Preferably, the zeolite molecular sieve framework is an FAU structure, the hydrophobic layer is an organosilicon hydrophobic layer, and the water contact angle of the hydrophobic molecular sieve is ≥90°.

[0015] All of the above-mentioned optional technical solutions can be combined arbitrarily, and the present invention will not provide a detailed description of the structure after each combination.

[0016] By means of the above solution, the beneficial effects of the present invention are as follows: (1) High-value utilization of solid waste: using coal gangue as the main source of silicon and aluminum, reducing the amount of external silicon and aluminum raw materials, and increasing the added value of resource utilization.

[0017] (2) High crystallization efficiency: Microwave-assisted crystallization can achieve rapid crystal formation in 2-4 hours at a lower temperature, and simultaneously complete the construction of hydrophobic layer, which is conducive to shortening the cycle and reducing energy consumption.

[0018] (3) One-step construction of hydrophobic surface: By introducing hydrophobic modifiers in situ during the gelation, aging and / or crystallization stages, the outer surface hydrophobic layer is constructed simultaneously during the molecular sieve formation process, avoiding the traditional independent post-processing steps of "first forming the sieve and then modifying", and improving the selective adsorption and separation capabilities of oil phase and hydrophobic organic matter.

[0019] (4) Structure retention and scalability: While maintaining the microporous structure, the surface is made hydrophobic, and the pore structure and surface properties can be synergistically controlled by adjusting the timing, amount and crystallization conditions of the hydrophobic modifier.

[0020] (5) Application prospects of low-concentration gas catalytic oxidation: Hydrophobic molecular sieve support can be used as a potential support for methane oxidation active components such as metals and / or metal oxides; due to the hydrophobic properties of its outer surface, it is beneficial to reduce the influence of water molecule competitive adsorption on active sites in a humid low-concentration gas system. Therefore, it has good application prospects in the field of low-concentration gas catalytic oxidation.

[0021] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0022] Figure 1 The image shows the XRD pattern of the hydrophobic molecular sieve sample prepared in an embodiment of the present invention.

[0023] Figure 2 This is a SEM image of the hydrophobic molecular sieve sample prepared in an embodiment of the present invention.

[0024] Figure 3 The graphs show the performance of the hydrophobic molecular sieve loaded with transition metal oxides before and after water resistance testing in the embodiments of the present invention. Detailed Implementation

[0025] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] The method for preparing a hydrophobic molecular sieve support based on coal gangue provided in this embodiment of the invention includes: S1, Coal gangue activation and impurity removal: Coal gangue is crushed and ground and then activated to obtain activated coal gangue.

[0027] In one specific embodiment, step S1 includes: crushing and grinding coal gangue to 200-400 mesh, leaching it with an acid solution to remove impurities, drying it, and then calcining it at 650-850°C for 1.5-3 hours to obtain activated coal gangue. The purpose of calcination is to destroy / transform the original crystal structure of the coal gangue and remove combustible components.

[0028] The acid leaching process uses a 3-4 mol / L hydrochloric acid solution with a solid-liquid mass ratio of 1:15-20, an acid leaching temperature of 50-80℃, and a leaching time of 6-12 hours.

[0029] S2, Alkali fusion treatment: Activated coal gangue is mixed with an alkali source and then subjected to alkali fusion treatment to obtain the alkali fusion product.

[0030] In one specific embodiment, step S2 includes: ball milling and mixing activated coal gangue with an alkali source until uniform, followed by alkali fusion treatment to convert the silica-aluminate phase into an easily soluble silicate / aluminate active phase, thereby obtaining an alkali fusion product. The alkali source is sodium hydroxide and / or sodium carbonate.

[0031] The mass ratio of sodium hydroxide to activated coal gangue is 1.2–1.8:1, the alkali fusion treatment temperature is 600–750℃, and the alkali fusion treatment time is 1–3 hours.

[0032] S3, Precursor Gel - Ultrasonic Dispersion - Aging: The alkali-melted product is mixed with water, ultrasonically dispersed, and aged to form a precursor gel.

[0033] In one specific embodiment, S3 includes: mixing the alkali-fused product with water in a certain proportion, ultrasonically dispersing it, and aging it at room temperature or a lower temperature (20-30°C) to form a precursor gel containing silicon-aluminum species.

[0034] Preferably, the ultrasonic dispersion time is 30–90 min, and the aging time is 6–12 h; 0.1–5 wt% of FAU structured seed crystals are added during the aging process. The addition of FAU structured seed crystals can induce directional growth of the crystal phase.

[0035] S4, In-situ hydrophobication-crystallization: A hydrophobic modifier is introduced during the formation of the precursor gel, the aging process and / or before hydrothermal crystallization, and the resulting system is subjected to hydrothermal crystallization so that the molecular sieve crystallization and the construction of the hydrophobic layer on the outer surface are carried out simultaneously.

[0036] In one specific embodiment, S4 includes: placing the precursor gel in a sealed reaction vessel, introducing a hydrophobic modifier after gel formation, during aging, and / or into the crystallization-forward system, and crystallizing at 80–110°C for 120–240 min under microwave heating conditions, so that the molecular sieve crystallization and hydrophobic layer construction occur simultaneously. Microwave-assisted hydrothermal crystallization is preferably used in this embodiment of the invention.

[0037] In one specific embodiment, the hydrophobic modifier is a silane, siloxane, fluorinated silane, and / or other hydrophobic precursor that can condense with the hydroxyl groups on the molecular sieve surface. Specifically, it can be one or more alkyl / fluoroalkyl silanes, including octadecyltrichlorosilane, hexadecyltrimethoxysilane, and dimethyldichlorosilane. The mass ratio of the hydrophobic modifier to the solid silicon-aluminum source in the system is 0.05–0.2:1. During crystallization, the hydrophobic modifier is in-situ loaded, grafted, and / or condensed on the outer surface of the molecular sieve, thereby forming an organosilicon hydrophobic layer.

[0038] In one specific embodiment, the hydrothermal crystallization temperature is 80–110°C, and the hydrothermal crystallization time is 120–240 min.

[0039] In this process, no organic structure-directing agents and / or template agents are added.

[0040] Optionally, after hydrothermal crystallization, the resulting product is subjected to a curing heat treatment at 200–350°C for 1–3 hours under an inert atmosphere or vacuum.

[0041] S5 is used for solid-liquid separation, washing, and drying to directly obtain a hydrophobic molecular sieve carrier.

[0042] The intermediate of the hydrophobic molecular sieve support has a FAU framework structure and is a NaX-type zeolite molecular sieve and / or a NaY-type zeolite molecular sieve. The intermediate can be an A-type, P-type, or other zeolite phase or a mixed phase.

[0043] The following is a specific embodiment, which includes the following steps: (1) Acid leaching and thermal activation of coal gangue: Coal gangue from a certain mining area was initially crushed and then ground in a ball mill to a mesh size of 200-400.

[0044] Coal gangue was leached in an acid solution (hydrochloric acid) with a concentration of 3–4 mol / L to remove impurities. The mass ratio of coal gangue to acid solution was 1:15–20. The leaching temperature was 50–80℃, and the leaching time was 6–12 h. After leaching, the mixture was filtered and washed with deionized water until nearly neutral. The leached coal gangue was then ground into powder and placed in a muffle furnace. The temperature was increased to 650–850℃ at a rate of 2–10℃ / min, and calcined for 1.5–3 h. After natural cooling, activated coal gangue was obtained.

[0045] XRF analysis showed that the SiO2 content in the activated coal gangue increased from 45.2% to 58.6%, the Al2O3 content increased from 35.8% to 42.3%, and the Fe2O3 content decreased from 4.4% to 0.7%.

[0046] (2) Alkali fusion treatment and preparation of precursor gel: Activated coal gangue is mixed and ground uniformly with an alkali source; the alkali source can be NaOH and / or Na2CO3; taking NaOH as an example, the activated coal gangue and NaOH are mixed at a mass ratio of 1:1.2-1.8 and then ball-milled uniformly. The uniformly ground mixture is then subjected to solid-phase alkali fusion at 600-750 °C for 1-3 h to obtain the alkali fusion product.

[0047] (3) Gel-ultrasonic dispersion-aging: The alkali-melted product is mixed with deionized water at a mass ratio of 1:5 to 10, ultrasonically dispersed for 30 to 90 minutes to form a uniform slurry, and aged at room temperature for 6 to 12 hours to obtain the precursor gel.

[0048] (4) In-situ hydrophobication and one-step crystallization The precursor gel was transferred to a microwave reactor, and a hydrophobic modifier was added to the system after gel formation, during aging, and / or before crystallization. The hydrophobic modifier was selected from one or more of octadecyltrichlorosilane, hexadecyltrimethoxysilane, dimethyldichlorosilane, methyltriethoxysilane, and hexamethyldisiloxane; the mass ratio of the hydrophobic modifier to the solid silica-alumina source in the system was 0.05–0.2:1. Hydrothermal crystallization was then performed at a temperature of 80–110 °C for 120–240 min. After crystallization, the mixture was filtered, washed with deionized water until the pH of the filtrate was approximately 8–10, and dried at 80–120 °C for 6–12 h to obtain zeolite molecular sieves.

[0049] Under one example condition: a crystallization temperature of 100 °C and a crystallization time of 180 min, without the addition of an organic template agent, a NaX-type zeolite molecular sieve with an FAU framework as the main component can be obtained.

[0050] (5) Post-curing treatment of one-step hydrophobic molecular sieves: In some embodiments, the hydrophobic molecular sieve obtained by the one-step method is pre-dried at 100-200°C to remove adsorbed water, and then subjected to curing heat treatment at 200-350°C for 1-3 hours under an inert atmosphere or vacuum to promote the stabilization of the hydrophobic layer.

[0051] In other embodiments, the hydrophobic molecular sieve obtained by the one-step method can be directly used as a carrier after washing and drying. Furthermore, heat treatment for curing can further enhance the stability of the hydrophobic layer.

[0052] (6) Material characterization and performance testing: The hydrophobic molecular sieve sample prepared through the above steps was subjected to XRD (X-ray diffraction), SEM (scanning electron microscopy), and waterproof performance testing. XRD was used to confirm the crystal phase; SEM was used to observe the crystal morphology. In the example sample, the XRD pattern diffraction peaks were sharp and symmetrical, completely matching the characteristic diffraction peaks of the 4A molecular sieve standard PDF card (011-0590), confirming the successful synthesis of the target 4A molecular sieve. Figure 1 As shown in the SEM images, the product exhibits a cubic structure with clear edges, smooth and complete crystal faces, and no obvious amorphous aggregates adhering to the surface. The grain size is mostly concentrated in the 1~5μm range, indicating that the crystallization reaction of the sample is complete and the crystal growth and development are good, which is consistent with the high crystallinity results characterized by XRD. Figure 2 As shown. Hydrophobic molecular sieves, used as metal and / or metal oxide supports for methane oxidation, exhibited a slight decrease in catalytic oxidation performance at low concentrations of methane after water resistance testing, but still maintained high catalytic conversion efficiency, demonstrating good overall water resistance. Figure 3 As shown.

[0053] This invention also provides a hydrophobic molecular sieve, which is prepared by the method for preparing a hydrophobic molecular sieve carrier based on coal gangue as described in the above embodiments. It includes a zeolite molecular sieve framework formed by the conversion of coal gangue, and a hydrophobic layer formed in situ on the outer surface of the zeolite molecular sieve framework. The hydrophobic layer is formed by the in-situ loading, condensation, grafting and / or coating of a hydrophobic modifier during the crystallization process of the hydrophobic molecular sieve.

[0054] In one specific embodiment, the zeolite molecular sieve framework is an FAU structure, preferably a NaX type zeolite molecular sieve and / or a NaY type zeolite molecular sieve; the hydrophobic layer is an organosilicon hydrophobic layer, and the water contact angle of the hydrophobic molecular sieve is ≥90°, preferably ≥120°.

[0055] In summary, this invention provides a hydrophobic FAU-structured molecular sieve support derived from coal gangue and its preparation method. Through a combined process of "controllable impurity removal, alkali fusion activation dissolution, ultrasonic-aging to form a precursor gel, and microwave rapid crystallization, with the introduction of hydrophobic modifiers during the gelation, aging, and / or crystallization stages to ensure simultaneous construction of the hydrophobic outer surface layer," a hydrophobic molecular sieve support is obtained without a separate post-treatment hydrophobic modification step and without the addition of organic structure-directing agents and / or template agents. This hydrophobic molecular sieve support can be further loaded with active components such as active metals and / or metal oxides for use as a catalytic material in the catalytic oxidation of low-concentration methane gas.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit 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 technical principles 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 preparing a hydrophobic molecular sieve support based on coal gangue, characterized in that, include: S1, Coal gangue activation and impurity removal: Coal gangue is crushed and ground and then activated to obtain activated coal gangue; S2, Alkali fusion treatment: Activated coal gangue is mixed with an alkali source and then subjected to alkali fusion treatment to obtain alkali fusion product; S3, Gel-Ultrasonic Dispersion-Aging: The alkali-melted product is mixed with water, ultrasonically dispersed, and aged to form a precursor gel; S4, In-situ hydrophobication-crystallization: A hydrophobic modifier is introduced during the formation of the precursor gel, the aging process and / or before hydrothermal crystallization, and the resulting system is subjected to hydrothermal crystallization so that the molecular sieve crystallization and the construction of the hydrophobic layer on the outer surface are carried out simultaneously. S5 is used for solid-liquid separation, washing, and drying to directly obtain a hydrophobic molecular sieve carrier.

2. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, S1 includes: The coal gangue is crushed and ground to 200-400 mesh, then acid-leached with acid solution to remove impurities, dried, and calcined at 650-850℃ for 1.5-3 hours to obtain activated coal gangue. The acid leaching process uses a 3-4 mol / L hydrochloric acid solution with a solid-liquid mass ratio of 1:15-20, an acid leaching temperature of 50-80℃, and a leaching time of 6-12 hours.

3. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, S2 includes: After the activated coal gangue and the alkali source are ball-milled and mixed evenly, they are subjected to alkali fusion treatment to convert the silica-aluminate phase into an easily soluble silicate / aluminate active phase, thus obtaining the alkali fusion product. The alkali source is sodium hydroxide and / or sodium carbonate; the mass ratio of sodium hydroxide to activated coal gangue is 1.2 to 1.8:1, the alkali fusion treatment temperature is 600 to 750°C, and the alkali fusion treatment time is 1 to 3 hours.

4. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, S3 includes: The alkali fusion product is mixed with water in a certain proportion, ultrasonically dispersed, and aged at room temperature or lower temperature to form a precursor gel containing silicon-aluminum species. The ultrasonic dispersion time is 30–90 min, and the aging time is 6–12 h; 0.1–5 wt% of FAU structure seed crystals are added during the aging process.

5. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, S4 includes: The precursor gel is placed in a closed reaction vessel, and a hydrophobic modifier is introduced after gel formation, during aging, and / or into the crystallization-forward system. The gel is then crystallized at 80–110 °C for 120–240 min under microwave heating conditions, so that the molecular sieve crystallization and hydrophobic layer construction are carried out simultaneously.

6. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, The hydrophobic modifier is one or more of alkyl / fluoroalkyl silanes, including octadecyltrichlorosilane, hexadecyltrimethoxysilane, and dimethyldichlorosilane; the mass ratio of the hydrophobic modifier to the solid silicon-aluminum source in the system is 0.05 to 0.2:

1.

7. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 1, characterized in that, The hydrothermal crystallization temperature is 80–110°C, and the hydrothermal crystallization time is 120–240 min.

8. The method for preparing a hydrophobic molecular sieve support based on coal gangue according to claim 7, characterized in that, After hydrothermal crystallization, the resulting product is subjected to a curing heat treatment at 200–350°C for 1–3 hours under an inert atmosphere or vacuum.

9. A hydrophobic molecular sieve, characterized in that, The hydrophobic molecular sieve carrier based on coal gangue, prepared by any one of claims 1 to 8, comprises a zeolite molecular sieve framework formed by the conversion of coal gangue, and a hydrophobic layer formed in situ on the outer surface of the zeolite molecular sieve framework; the hydrophobic layer is formed by in-situ loading, condensation, grafting and / or coating of a hydrophobic modifier during the crystallization process of the hydrophobic molecular sieve.

10. The hydrophobic molecular sieve according to claim 9, characterized in that, The zeolite molecular sieve framework is an FAU structure, the hydrophobic layer is an organosilicon hydrophobic layer, and the water contact angle of the hydrophobic molecular sieve is ≥90°.

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