Method for synthesizing mordenite by using coal gangue as raw material

Abstract

The invention relates to a method for synthesizing mordenite by using coal gangue as a raw material. The method comprises the following steps: firstly, carrying out acid treatment and activation on the coal gangue, extracting a silicon source and an aluminum source in the coal gangue as raw materials by accurately adjusting the use amount of sodium hydroxide, and finally preparing the pure-phase mordenite by accurately adjusting the content of acetic acid. The method for synthesizing the mordenite from the coal gangue is low in experiment cost, simple in process, good in repeatability and convenient for large-scale popularization to realize high value-added utilization of the coal gangue.

Description

Technical Field

[0001] The present invention utilizes coal gangue as raw material to prepare mordenite, which can be applied to the fields of gas adsorption and industrial catalysis. Background Art

[0002] As the main by-product of coal mining, coal gangue accounts for about 10% to 30% of the total solid waste. Affected by different regions and mining technologies, it sometimes accounts for about 30% to 40%, which cannot be ignored. The large-scale stacking of coal gangue will not only occupy land resources, but also the leaching water will penetrate into the ground, polluting the soil and groundwater; it will also release a large amount of harmful gases during spontaneous combustion, seriously polluting the environment and harming human health. Coal gangue mainly contains kaolinite and other clay minerals, so the silicon (Si) source and aluminum (Al) source can be extracted to synthesize other zeolite molecular sieves to achieve the conversion and utilization of waste. The main preparation process is to first treat the crushed coal gangue with acid to remove iron and other metal oxides to improve the performance of zeolite, and then add a certain proportion of alkali and other chemical structural agents for secondary treatment. For molecular sieves with a high silicon-aluminum ratio, additional silicon sources will be added to synthesize the target molecular sieve. The methods for synthesizing zeolite using coal gangue mainly include hydrothermal crystallization, alkali dissolution activation, microwave-assisted hydrothermal crystallization and solvent-free method. Among them, hydrothermal crystallization is widely used because the synthesized molecular sieve has high purity, good crystallinity, strong structural controllability and easy operation. At present, there are a large number of literature reports on the use of coal stone to prepare NaX zeolite, NaA zeolite and ZSM-5 molecular sieve. Mordenite has been widely studied and applied in industrial catalysis because of its good acidity, adsorption and thermal stability. Zhou Tongxiao (Microporous and Mesoporous Materials, 2021, 314: 110872.) synthesized mordenite using fly ash as raw material, but the synthesized zeolite contained other impurity phases such as mullite and quartz; Shen Xiang (CN201010149287.6) synthesized mordenite using mineral raw materials, but the need for additional silicon source increased the cost of raw materials. Therefore, in order to achieve efficient and inexpensive utilization of coal-based solid waste and to be able to stably synthesize mordenite, it is urgent to develop a preparation technology that has a simple preparation method, inexpensive raw materials and can stably obtain pure-phase mordenite molecular sieves. Summary of the invention

[0003] The purpose of the invention is to provide a method for synthesizing mordenite from coal gangue in view of the limitations of the current technology. The method first activates the coal gangue by acid treatment, extracts the silicon source and aluminum source in the coal gangue as raw materials by accurately adjusting the amount of sodium hydroxide used, and finally realizes the preparation of pure phase mordenite by accurately adjusting the acetic acid content. The invention has low experimental cost, simple method and process, good repeatability, and is convenient for large-scale promotion to realize high value-added utilization of coal gangue.

[0004] In order to achieve the above object, the present invention provides the following technical solutions: A method for synthesizing mordenite using coal gangue as raw material, the method comprising the following steps: (1) crushing the coal gangue into powder, transferring it to a muffle furnace and calcining it at 800-1000°C for 3-6 hours to obtain activated coal gangue; (2) The activated coal gangue is mixed with a hydrochloric acid solution, stirred at 70-90°C for 5-8 hours, filtered, washed to neutrality and dried to obtain acid-treated coal gangue powder; The activated gangue and hydrochloric acid solution are in a solid-liquid ratio of 1:5 to 10 by mass (g); The concentration of hydrochloric acid is 4~8 mol / L; (3) Mixing the acid-treated coal gangue powder with solid sodium hydroxide, then adding deionized water, stirring at 60-90°C for 4-8 hours to obtain a solution rich in silicon and aluminum; The mass ratio is coal gangue after acid treatment: sodium hydroxide = 1: 0.05~0.3; add 0.6g sodium hydroxide for every 30~50mL water; (4) first adding acetic acid to the solution obtained in step (3) to adjust the pH to 7-12, then adding tetraethylammonium hydroxide solution, and finally adding mordenite seed crystals, and aging for 1-24 h; The mass of the mordenite seed crystals is 0.5% to 10% of the mass of the coal gangue after acid treatment; the mass of the tetraethylammonium hydroxide is 0.5 to 1.5% of the mass of the coal gangue after acid treatment; (5) The sol-gel obtained in step (4) is hydroheated at 170-190° C. for 48 h-144 h, and the solid obtained after the treatment is filtered, washed, dried, and then calcined at high temperature to obtain mordenite.

[0005] Preferably, the coal gangue crushed in step (1) has a particle size between 100 and 200 meshes.

[0006] Preferably, the calcination in step (5) is: calcination at 550-600° C. for 4-6 hours in an air atmosphere.

[0007] The essential features of the present invention are: The existing method of synthesizing mordenite from coal-based solid waste has problems such as the presence of impure crystal phases in the product, low crystallinity of the synthetic product, and complex synthesis process. It is necessary to additionally add silicon source or aluminum source to adjust the solution pH, composition, etc. in order to obtain mordenite with high purity and good crystal structure.

[0008] The raw materials of the invention are all derived from coal gangue. The extraction of silicon-aluminum-rich solution is achieved by adjusting the addition ratio of sodium hydroxide solid in the coal gangue, and the gel solution is prepared by adjusting the content of acetic acid to obtain a mother solution with a relatively optimal concentration and alkalinity suitable for synthesizing mordenite. Mordenite without impurities is synthesized by a one-step hydrothermal method. The invention realizes the conversion of coal gangue into high value-added products, and the preparation conditions are simple and easy to achieve, and it is easy to mass-produce.

[0009] The present invention has the following beneficial effects: 1. Coal gangue is a coal-based solid waste. The present invention utilizes and transforms coal gangue waste into high value-added products, thus realizing the recycling of resources.

[0010] 2. The raw materials used in the synthesis of the present invention are cheap and readily available. The crystal phase of the generated product is adjusted by adjusting the content of acetic acid in detail, and the crystallinity of the synthesized product is controlled by adjusting the content of sodium hydroxide in detail. Therefore, the preparation process of the present invention is simple, the experimental cost is low, the conditions are easy to meet, and the repeatability is high, and batch and large-scale production can be achieved.

[0011] 3. The present invention uses a low amount of sodium hydroxide when extracting silicon source from coal gangue, which has little environmental pollution. The present invention only needs 0.6g of sodium hydroxide per 10g of coal gangue to extract silicon source from coal gangue and synthesize mordenite, which reduces environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The X-ray diffraction analysis spectrum (XRD) of the synthesized mordenite sample and the standard card of Example 2; Figure 2 This is a scanning electron microscope image (SEM) of the synthetic mordenite of Example 2; DETAILED DESCRIPTION

[0013] The present invention provides an experimental scheme for preparing mordenite from coal gangue, comprising the following steps: (1) Take 25 g of coal gangue that has passed through a 200-mesh sieve and place it in a muffle furnace. Heat the temperature at a rate of 10°C / min to 900°C in an air atmosphere and maintain the temperature for 6 h to obtain high-temperature activated coal gangue powder.

[0014] (2) Mix 25 g of high temperature activated coal gangue, 62.5 ml of hydrochloric acid (12 mol / L) and 62.5 ml of pure water, and stir at 80°C for 6 h. Take the acid-treated solid, wash it three times with pure water and then with ethanol three times, wash the acid-treated coal gangue to neutrality, and dry it in an oven at 100°C.

[0015] (3) Take 10 g of the acid-treated coal gangue dried in step (2), mix it with 0.6 g of sodium hydroxide solid, add 38-40 ml of pure water, stir at 80°C for 6 h, centrifuge and separate the clear liquid to obtain a silicon-rich alkali solution. Add 1 ml of acetic acid to the silicon-rich alkali solution to adjust the pH to 12 to obtain a gel solution, add 1.8-1.9 g of tetraethylammonium hydroxide solution to the gel solution, stir for about 3 min, then add 0.1 g of mordenite seed crystals, and age for 4-5 h.

[0016] (4) Preheat the oven to 170°C, pour the aged gel solution in step (3) into the reactor and transfer it to the oven for crystallization for 72 hours. After the hydrothermal treatment, separate the solid and liquid by filtration and wash with pure water three times. Dry the separated solid, place it in a muffle furnace and heat it to 550°C at a rate of 1°C / min in an air atmosphere, and calcine it for 4 hours to remove the template to obtain mordenite.

[0017] The technical solution provided by the present invention is described in detail below in conjunction with the embodiments and drawings, but they should not be understood as limiting the protection scope of the present invention.

[0018] In this embodiment, the XRD analysis of mordenite is performed using an X-ray diffractometer produced by Anton Paar, using Cu Kα radiation (λ= 1.5406 Å), with a scanning speed of 2θ= 10°C / min and a scanning range of 5° to 60°. The relative crystallinity of the product is calculated by the sum of the XRD peak areas of the (200), (300), (150), (202), and (350) crystal planes, with the crystallinity of Example 2 being 100%, and the relative crystallinity of the other samples to be tested being compared with it.

[0019] In this embodiment, the SEM morphology analysis of the mordenite is performed using a Phenom scanning electron microscope manufactured by Fu Na Scientific Instruments Co., Ltd.

[0020] The mordenite seed crystals are known materials purchased from Raodong (Liaoning) New Materials Co., Ltd., and tetraethylammonium hydroxide (content not less than 25%) was purchased from Tianjin Guangfu Technology Development Co., Ltd.; Example 1: 25 g of coal gangue was placed in a porcelain boat and transferred to a muffle furnace. The mixture was heated from room temperature to 900°C at a heating rate of 10°C / min in an air atmosphere for 6 h. After cooling, 25 g of coal gangue was weighed and mixed with 62.5 ml of hydrochloric acid (12 mol / L) and 62.5 ml of distilled water, and stirred at 80°C for 6 h to obtain acid-treated activated coal gangue. The acid-treated coal gangue can not only remove the metal oxide impurities therein, making silicon and aluminum more enriched, but also corrode the surface of the coal gangue to form more defects and pores, and activate the silicon and aluminum components, which is beneficial to the subsequent alkali treatment process to reduce the amount of sodium hydroxide added and extract the required silicon and aluminum elements, so that the utilization of coal gangue is more sufficient.

[0021] Example 2: Weigh 10 g of the acid-treated coal gangue treated in Example 1 and mix it with 0.6 g of sodium hydroxide solid, and then add 39 ml of pure water. Stir at 80°C for 6 h, centrifuge to separate the solid and liquid, take the liquid and place it in a polytetrafluoroethylene liner, add 2 ml of analytical pure acetic acid to adjust the pH to 12, and turn the solution into a gel state. Add 1.84 g of 25% tetraethylammonium hydroxide solution to the gel and stir at room temperature for 5 min, continue to add 1% of the mass of coal gangue to the gel, that is, 0.1 g of mordenite seeds, and stir at room temperature for 6 h (500 rpm). After the stirring is completed, lock the reactor and immediately put it into an oven preheated to 170°C for reaction for 72 h. After the oven is cooled to room temperature, filter, wash and dry overnight at 100°C to obtain a white powder. The white powder was transferred to a muffle furnace, and in an air atmosphere, the temperature was raised from room temperature to 550°C at a heating rate of 1°C / min and maintained for 2 h to remove tetraethylammonium hydroxide to obtain mordenite, which was then subjected to XRD and SEM tests.

[0022] Figure 1 The XRD test results of the mordenite zeolite have good correspondence with the crystal planes of the mordenite PDF standard card (PDF#04-011-3643), and the crystallinity is high. Figure 2 In the SEM image, it can be observed that the morphology is nanoparticles.

[0023] Example 3: The other steps are the same as Example 2, except that 4 ml of acetic acid is added dropwise during the adjustment to make the pH = 7, and the solution becomes a gel state. 1.84 g of tetraethylammonium hydroxide solution is added to the gel and stirred at room temperature for 5 min, and 0.1 g of mordenite seeds are added to the gel and stirred at room temperature for 6 h (500 rpm). After the stirring is completed, the reactor is locked and immediately placed in an oven preheated to 170°C for 72 h. After the oven is cooled to room temperature, a white powder is obtained by suction filtration, washing and drying at 100°C overnight. The white powder is transferred to a muffle furnace, and in an air atmosphere, the temperature is increased from room temperature to 550°C at a rate of 1°C / min and maintained for 2 h to remove the template to obtain mordenite.

[0024] Example 4: The other steps are the same as Example 2, except that acetic acid is not added to the solution, 1.84 g of tetraethylammonium hydroxide solution is directly added and stirred at room temperature for 5 min, and 0.1 g of mordenite seed is continuously added to the gel and stirred at room temperature for 6 h (500 rpm). After the stirring is completed, the reactor is locked and immediately placed in an oven preheated to 170°C for 72 h. After the oven is cooled to room temperature, a white powder is obtained by suction filtration, washing and drying at 100°C overnight. The white powder is transferred to a muffle furnace, and the template is removed by heating from room temperature to 550°C at a rate of 1°C / min in an air atmosphere and maintained for 2 h. After measurement, the obtained substance is shown to be analcime.

[0025] Example 5: The other steps are the same as Example 2, except that after stirring at room temperature for 6 h (500 rpm), the oven is preheated to 190°C and placed in a reactor for crystallization for 72 h. After the oven is cooled to room temperature, a white powder is obtained by suction filtration, washing and drying at 100°C overnight. The white powder is transferred to a muffle furnace, and the temperature is increased from room temperature to 550°C at a rate of 1°C / min under air atmosphere and maintained for 2 h to remove the template to obtain mordenite.

[0026] Example 6: Take 10 g of the gangue treated in Example 1 and mix it with 0.8 g of sodium hydroxide solid, and then add 39 ml of pure water. Stir at 80°C for 6 h, centrifuge to separate the solid and liquid, and take the liquid and place it in a polytetrafluoroethylene liner. After dissolution, add 1 ml of acetic acid to the solution to adjust the pH to 12, and the solution becomes a gel state. Then add 1.84 g of tetraethylammonium hydroxide to the gel and stir at room temperature for 5 min, continue to add 0.1 g of mordenite seeds to the gel, and stir at room temperature for 6 h (500 rpm). After the stirring is completed, lock the reactor and immediately put it into an oven preheated to 170°C for 72 h. After the oven is cooled to room temperature, filter, wash and dry at 100°C overnight to obtain a white powder. Transfer the white powder to a muffle furnace, and in an air atmosphere, heat it from room temperature to 550°C at a rate of 1°C / min and keep it for 2 h to remove the template to obtain mordenite.

[0027] Example 7: Take 10 g of the gangue treated in Example 1 and mix it with 1.2 g of sodium hydroxide solid, and then add 39 ml of pure water. Stir at 80°C for 6 h, centrifuge to separate the solid and liquid, and take the liquid and place it in a polytetrafluoroethylene liner. Then add 4 ml of acetic acid to the solution to adjust the pH to 12, and the solution becomes a gel state. Then add 1.84 g of tetraethylammonium hydroxide to the gel and stir at room temperature for 5 min, continue to add 0.1 g of mordenite seeds to the gel, and stir at room temperature for 6 h (500 rpm). After the stirring is completed, lock the reactor and immediately put it into an oven preheated to 170°C for 72 h. After the oven is cooled to room temperature, filter, wash and dry at 100°C overnight to obtain a white powder. The white powder is transferred to a muffle furnace, and in an air atmosphere, the temperature is increased from room temperature to 550°C at a rate of 1°C / min and maintained for 2 h to remove the template to obtain mordenite.

[0028] The concentration of sodium hydroxide and the pH value of the solution have an important influence on the crystallinity of mordenite. The synthesis of mordenite requires a specific pH value. Too high or too low a concentration will affect the crystallinity, and its crystal structure is very sensitive to the silicon-aluminum ratio during the synthesis process. An appropriate silicon-aluminum ratio is conducive to the formation of high-crystallinity mordenite. If the concentration of sodium hydroxide is too high, it may cause excessive dissolution of silicates, destroy the balance of silicon-aluminum ratio, and thus reduce crystallinity; if the concentration is too low, it may cause insufficient dissolution of aluminosilicate precursors, affecting crystal growth.

[0029]

[0030] The crystal phases and relative crystallinity of the samples synthesized in Examples 2-7 are summarized in Table 1. The relative crystallinity is calculated by selecting the sum of the XRD peak areas of the relative crystallinity (200), (300), (150), (202), and (350) crystal planes of the products, and taking the crystallinity of Example 2 as 100% and comparing it with the other samples to be tested.

[0031] Compared with Example 2, Example 3 has a lower alkalinity, and the crystallinity of mordenite will be significantly affected by different pH values, so the crystalline phase of mordenite synthesized in Example 3 is lower than that in Example 2. For Example 4, hydrothermal crystallization was performed using a silicon-rich solution without adjusting the pH, and the crystals obtained were analcime, because the strong alkaline environment is very conducive to the formation of analcime, so even if a structure directing agent is added, it will not induce it to grow into a mordenite crystal phase. Example 5 studied the effect of increasing temperature on the crystalline phase. From the calculated value of crystallinity, it can be seen that temperature will not affect the synthesized crystalline phase, but will slightly reduce its crystallinity. This is because the solubility of molecular sieve crystals will increase with increasing temperature, and the formed crystals will partially dissolve, and the released silicon-aluminum species may be re-disordered and stacked to form an amorphous phase or miscellaneous crystals, thereby reducing the crystallinity. Examples 6 and 7 investigated the effects of different sodium contents and pH values ​​on the synthetic products. From the crystallinity, it can be seen that when the sodium hydroxide content exceeds or is lower than a certain threshold, even if the pH value is adjusted to make its alkalinity consistent with the optimal synthesis pH, the crystallinity will be significantly reduced. Because aluminum in the mordenite framework needs to coordinate with four oxygens, the charge is balanced by sodium. When sodium is insufficient, the aluminum coordination environment is unstable, resulting in local charge imbalance in the framework and lattice defects. Excessive sodium will preferentially adsorb on the surface of the negatively charged precursor, hindering the directional assembly induced by the template, causing the pore structure to be distorted or collapsed, thus reducing the crystallinity.

[0032] Mordenite with high crystallinity is of great significance in the fields of catalysis, adsorption and ion exchange. Its stable crystal structure gives it high thermal stability and excellent performance in high-temperature catalytic reactions such as petroleum cracking; its complete crystal structure makes it excellent in chemical stability, able to maintain performance in strong acid and alkali environments, and has a longer service life; the regular and uniform pore structure not only provides a large specific surface area and high-efficiency adsorption capacity, but also can effectively improve the selectivity of gas separation and selective catalysis. At the same time, high crystallinity can bring more active sites and ion exchange sites, making its catalytic activity better and more efficient in ion exchange applications such as wastewater treatment.

[0033] As can be seen from the above embodiments, the present invention provides a method for synthesizing mordenite by a simple one-step hydrothermal method using coal gangue as a raw material. The high-temperature activated coal gangue is first mixed with hydrochloric acid and stirred at 80°C for 6 hours to obtain acid-treated coal gangue, and then the acid-treated coal gangue is mixed with a small amount of sodium hydroxide solid and dissolved in deionized water, stirred at 80°C for 6 hours to obtain a silicon-rich solution and added to a polytetrafluoroethylene liner, sodium aluminate is added to the solution and the pH is adjusted with acetic acid to obtain a gel solution, and then tetraethylammonium hydroxide solution and mordenite seeds are added to the solution, and finally the reactor is locked and immediately placed in an oven preheated to a certain temperature to react for a certain time. When the oven is cooled to room temperature, sodium-type mordenite is obtained by centrifugation, washing and drying, and finally the hydrothermally obtained mordenite is transferred to a muffle furnace and calcined in an air atmosphere to remove the template.

[0034] The above-described embodiments are cases explored and synthesized by the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made without departing from the core of the present invention should be included in the protection scope of the present invention.

[0035] Matters not covered by the present invention are known technologies.

Claims

1. A method for synthesizing mordenite using coal gangue as raw material, characterized in that the method comprises the following steps: (1) crushing the coal gangue into powder, transferring it to a muffle furnace and calcining it at 800-1000°C for 3-6 hours to obtain activated coal gangue; (2) The activated coal gangue is mixed with a hydrochloric acid solution, stirred at 70-90°C for 5-8 hours, filtered, washed to neutrality and dried to obtain acid-treated coal gangue powder; in, The mass ratio of activated coal gangue to hydrochloric acid solution is 1:5~10; (3) Mixing the acid-treated coal gangue powder with solid sodium hydroxide, then adding deionized water, stirring at 60-90°C for 4-8 hours to obtain a solution rich in silicon and aluminum; The mass ratio is coal gangue after acid treatment: sodium hydroxide = 1: 0.05~0.3; add 0.6 g of sodium hydroxide for every 30~50 mL of water; (4) first adding acetic acid to the solution obtained in step (3) to adjust the pH to 7-12, then adding tetraethylammonium hydroxide solution, and finally adding mordenite seed crystals, and aging for 1-24 h; The mass of the mordenite seed crystals is 0.5% to 10% of the mass of the coal gangue after acid treatment; the mass of the tetraethylammonium hydroxide is 0.5 to 1.5% of the mass of the coal gangue after acid treatment; (5) The sol-gel obtained in step (4) is hydroheated at 170-190° C. for 48 h-144 h, and the solid obtained after the treatment is filtered, washed, dried, and then calcined at high temperature to obtain mordenite.

2. The method for synthesizing mordenite using coal gangue as raw material according to claim 1, characterized in that: In step (1), the coal gangue is crushed to a particle size between 100 and 200 meshes.

3. The method for synthesizing mordenite using coal gangue as raw material as claimed in claim 1, characterized in that: The calcination in step (5) is as follows: calcination at 550-600° C. for 4-6 hours in an air atmosphere.

4. The method for synthesizing mordenite using coal gangue as raw material as claimed in claim 1, characterized in that: The concentration of hydrochloric acid in step (2) is 4-8 mol / L.

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