Method for preparing MCM-41 molecular sieve by using coal gasification fine slag

Abstract

The application provides a method for preparing MCM-41 molecular sieve by using coal gasification fine slag, and relates to the field of solid waste resource utilization. The method comprises the following steps: performing high-temperature calcination decarburization treatment on the coal gasification fine slag to obtain tail ash, mixing and grinding the tail ash and potassium hydroxide, and then performing high-temperature activation to obtain an alkali fusion product; performing acid pickling treatment on the alkali fusion product, and then performing deionized water filtration and drying to obtain an activated material; mixing the activated material with a sodium hydroxide solution, and then performing heating and dissolution to obtain a silicon source; dissolving CTAB in water to obtain a template agent solution; adding the silicon source drop by drop into the template agent solution, adjusting pH, stirring, and then aging to obtain an aging product; and performing hydrothermal reaction and calcination treatment on the aging product to obtain MCM-41 molecular sieve. The specific treatment method improves the solubility and silicon content of the activated material, reduces the required concentration of the sodium hydroxide solution, and also obtains a very high yield, thereby achieving an outstanding technical effect.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, specifically to a method for preparing MCM-41 molecular sieves using coal gasification fine slag. Background Technology

[0002] Compared to the direct combustion of coal, coal gasification technology can reduce environmental pollution and improve coal utilization, thus achieving the goal of clean and efficient utilization of coal resources. However, coal gasification production generates a large amount of fine coal gasification slag, which causes serious environmental pollution. Currently, most coal gasification slag from large-scale coal gasification projects is disposed of through landfill, failing to be effectively recycled. Achieving "zero emissions" in the coal gasification process requires the recycling of coal gasification slag; therefore, finding a method to convert coal gasification slag into products with higher added value is urgent. Coal gasification slag consists of minerals and unburned carbon particles, with minerals accounting for 50%–80%. The main components of these minerals are SiO2 and Al2O3. Therefore, efficiently utilizing the silicon and aluminum elements in the mineral composition is key to solving the resource utilization problem of coal gasification slag.

[0003] MCM-41 molecular sieves are currently the most widely used mesoporous materials due to their highly ordered structure, uniform mesoporous pore distribution, high specific surface area, and high pore volume. However, the current methods for preparing MCM-41 molecular sieves mostly use tetraethyl orthosilicate (TEOS) or sodium metasilicate as silicon sources. These silicon sources are extremely expensive, and some are toxic. Since coal gasification slag is rich in silicon components, using inexpensive solid waste as an alternative raw material to prepare MCM-41 molecular sieves has significant advantages and environmental benefits.

[0004] Existing technologies disclose numerous methods for preparing MCM-41 molecular sieves, but several problems remain. First, the yield of the prepared MCM-41 molecular sieves is low. M. Selvaraj successfully prepared MCM-41 molecular sieves using TEOS as the silicon source, with a yield of 30% (Microporous and Mesoporous Materials 2004, 70, 81-91); in Zhang's experiments, the highest yield of MCM-41 molecular sieves prepared by the hydrothermal method was only 12% (European Journal of Inorganic Chemistry, 2011, 59-67). Second, in the preparation of MCM-41 molecular sieves using silicon-containing solid waste as raw material, a high-concentration sodium hydroxide solution is used for silicon source extraction. Patent document CN106517222A discloses a method for synthesizing ordered mesoporous nano-silica from fly ash, including steps such as crushing fly ash, extracting the silicon source, separating and purifying with sodium silicate solution, and CO2-assisted precipitation of silicon dioxide. In the silicon source extraction process, the concentration of the sodium hydroxide solution used is 25 wt%. Patent document CN112441596A discloses a method for preparing MCM-41 molecular sieves using coal gasification fly ash as raw material, employing steps such as microwave-assisted alkali dissolution extraction of the silicon source and hydrothermal crystallization. In the alkali dissolution process, the concentration of the sodium hydroxide solution used is 20 wt%. Generally, the activity of the raw material affects the amount of alkali solution used, and excessive alkali addition not only affects production costs but also pollutes the environment. Finally, how to improve the purity of the silicon source is also a major problem that needs to be solved. Patent document CN110272058A discloses a method for preparing MCM-41 ordered mesoporous material using iron tailings as raw material. After optimization, the purity of silicon source extracted from iron tailings was increased from 65% to 95%, but there is still room for improvement.

[0005] Therefore, in the process of preparing MCM-41 molecular sieves from solid waste, how to improve the purity of silicon source, reduce the amount of alkali solution used, and improve the yield has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art in the preparation of MCM-41 molecular sieves using solid waste as raw material, such as low yield, large amount of alkali solution, and the need to improve the purity of silicon source, so as to provide a new method for preparing MCM-41 molecular sieves using coal gasification fine slag.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing MCM-41 molecular sieves using coal gasification fine slag, comprising the following steps:

[0009] (1) The fine slag from coal gasification is subjected to high-temperature calcination and decarbonization treatment to obtain tailings ash. The tailings ash is mixed and ground with potassium hydroxide at a mass ratio of 1:1.5-2 and then activated at 800-850℃ for 60-90 minutes to obtain alkali fusion product. The alkali fusion product is subjected to acid washing treatment, filtered with deionized water, and dried to obtain activated material.

[0010] (2) The activated material obtained in step (1) is mixed with 3-7 wt% sodium hydroxide solution at a mass-volume ratio of 0.5-1.0:8 g / mL, heated to dissolve, and a silicon source is obtained;

[0011] (3) Dissolve hexadecyltrimethylammonium bromide in water at a mass-to-volume ratio of 1.4–2.0:25 g / mL to obtain a template agent solution;

[0012] (4) The silicon source obtained in step (2) is added dropwise to the template agent solution obtained in step (3), wherein the activating material and hexadecyltrimethylammonium bromide are mixed at a mass ratio of 0.5-1.0:1.4-2.0, the pH value is adjusted to 8-9, stirred, and allowed to stand for aging to obtain the aging product;

[0013] (5) The aging product obtained in step (4) is subjected to hydrothermal reaction, filtered with deionized water and dried to obtain the dried product.

[0014] (6) The dried product obtained in step (5) is calcined to obtain MCM-41 molecular sieve.

[0015] Furthermore, in step (1),

[0016] The conditions for high-temperature calcination are: calcination at 750–850°C for 60–120 minutes;

[0017] The tailings ash and potassium hydroxide are mixed at a mass ratio of 1:2;

[0018] The high-temperature activation heating process involves heating to 400-450°C at a rate of 4-5°C / min, and then heating to 800-850°C at a rate of 1-2°C / min; the high-temperature activation cooling process involves cooling to room temperature in the furnace.

[0019] Acid washing is performed using a 25-37 wt% hydrochloric acid solution. Hydrochloric acid solution is added at a mass-to-volume ratio of 1:10-20 g / mL to tail ash. The mixture is stirred at 300-550 r / min for 7-8 hours at 50-60℃.

[0020] The drying conditions are as follows: drying at 90–110°C to constant weight.

[0021] Furthermore, in step (1),

[0022] The conditions for high-temperature calcination are: calcination at 815℃ for 60 minutes;

[0023] The conditions for high-temperature activation are as follows: heat up to 400°C at a rate of 5°C / min, then heat up to 800°C at a rate of 2°C / min, hold at that temperature for 60 min, and then cool to room temperature in the furnace.

[0024] Acid washing was performed using a 25wt% hydrochloric acid solution. Hydrochloric acid solution was added at a mass-to-volume ratio of 1:20 g / mL to tail ash. The mixture was stirred at 550 r / min for 7 h at 60 °C.

[0025] The drying conditions are as follows: drying at 105°C to constant weight.

[0026] Further, in step (2), the activated material is mixed with 3-7 wt% sodium hydroxide solution at a mass-to-volume ratio of 0.5:8 g / mL; the heating and dissolving conditions are: stirring at 350 r / min for 20 min at 60 °C.

[0027] Further, in step (3), hexadecyltrimethylammonium bromide is dissolved in water at a mass-to-volume ratio of 2.0:25 g / mL to obtain a template agent solution.

[0028] Furthermore, in step (4),

[0029] The silicon source is added at a rate of 1-2 mL / min and at a temperature of 25-35 °C.

[0030] The mass ratio of the activating material to cetyltrimethylammonium bromide is 0.5:2.0;

[0031] Adjust the pH value using a 1-5 mol / L sulfuric acid solution;

[0032] The stirring conditions are: stirring at 300-400 r / min for 2-3 hours at 25-35°C;

[0033] The conditions for static aging are: standing at room temperature for 3 to 4 hours.

[0034] Furthermore, in step (4),

[0035] The silicon source was added at a rate of 2 mL / min and at a temperature of 35 °C.

[0036] Adjust the pH to 8 using a 1–5 mol / L sulfuric acid solution;

[0037] The stirring conditions were: stirring at 35°C and 350 r / min for 2 hours;

[0038] The conditions for static aging are: static aging at room temperature for 3 hours.

[0039] Further, in step (5), the hydrothermal reaction conditions are: reacting at 100-110°C for 20-28 hours; the drying conditions are: drying at 90-110°C to constant weight.

[0040] In step (6), the calcination conditions are as follows: the temperature is increased to 500-550°C at a rate of 1-2°C / min, held for 5-6 hours, and then cooled to room temperature in the furnace.

[0041] Further, in step (5), the hydrothermal reaction conditions are: reacting at 100°C for 24 hours; the drying conditions are: drying at 105°C to constant weight;

[0042] In step (6), the calcination conditions are as follows: the temperature is increased to 550°C at a rate of 2°C / min, held for 5 hours, and then cooled to room temperature in the furnace.

[0043] Furthermore, the mineral content of the coal gasification slag is 68-72 wt%, and the unburned coal content is 28-32 wt%.

[0044] The technical solution of this invention has the following advantages:

[0045] 1. This invention first decarbonizes the fine slag from coal gasification by high-temperature calcination to obtain tailings ash. Then, the tailings ash is activated at high temperature using potassium hydroxide to obtain an alkali-fused product. Finally, the alkali-fused product is acid-washed to obtain activated material. XRF analysis shows that the SiO2 content in the activated material can reach 99%, exhibiting high solubility. A low-concentration sodium hydroxide solution is sufficient to completely dissolve the activated material, yielding a silicon source with extremely high purity. The alkali dissolution process uses a low-concentration sodium hydroxide solution of 3–7 wt%, which differs from the conventional use of 20–25 wt% sodium hydroxide solution in existing technologies. This not only reduces sodium hydroxide consumption and pollution but also results in a higher yield (up to 82%) when preparing MCM-41 using this high-purity silicon source.

[0046] However, existing technologies for preparing molecular sieves generally result in low yields, focusing primarily on the synthesis of molecular sieves rather than improving the solubility and silicon content of the activated materials, or even the yield. This invention employs a specific processing method that improves both the solubility and silicon content of the activated materials, reduces the required sodium hydroxide solution concentration, and achieves a very high yield, demonstrating outstanding technical effectiveness.

[0047] 2. The inventors discovered in their research that adjusting the pH of the solution after mixing the silicon source and template agent significantly affects the yield. The highest yield is achieved at pH 8, followed by pH 9, while the yield drops sharply at pH 11. Therefore, adjusting the pH to 8-9 is preferable. Furthermore, the inventors also accidentally discovered that using a higher concentration of sodium hydroxide solution is actually detrimental to improving the yield when employing the processing method provided by this invention. This may be due to the Na+ provided by NaOH. + The aggregation of these factors affects the formation of MCM-41. Therefore, the method for obtaining activated materials provided by this invention and the means of dissolving the silicon source with a low-concentration sodium hydroxide solution need to be used in combination to achieve a higher yield, breaking the prejudice in the field that high-concentration sodium hydroxide solution is used to improve yield.

[0048] 3. The MCM-41 molecular sieve product prepared by this invention exhibits excellent performance, an ordered structure, and a large specific surface area and pore volume, enabling effective adsorption of carbon dioxide. At 25℃, the adsorption capacity of the MCM-41 molecular sieve prepared by this invention for carbon dioxide can reach 2.169 mol / kg. Furthermore, compared to nitrogen, the surface of the MCM-41 molecular sieve prepared by this invention shows better affinity for carbon dioxide, making it effectively applicable in the field of carbon dioxide adsorption.

[0049] 4. This invention utilizes coal gasification fine slag to prepare MCM-41 molecular sieves, solving the current problem of recycling and utilizing coal gasification fine slag. Using coal gasification fine slag as a raw material significantly reduces costs while achieving resource utilization of solid waste, reducing the manpower and material resources required for landfilling coal gasification fine slag, and lowering soil pollution from solid waste, thus demonstrating good economic and social benefits. Attached Figure Description

[0050] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0051] Figure 1 This is a comparison image of the small-angle XRD pattern and PDF card of the MCM-41 molecular sieve powder prepared in Example 2 of the present invention. Detailed Implementation

[0052] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0053] Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental steps or conditions described in the literature in this field. All raw materials or instruments used are commercially available conventional products, including but not limited to those used in the embodiments of this application.

[0054] Example 1

[0055] This embodiment provides a method for preparing MCM-41 molecular sieves using coal gasification fine slag, the specific steps of which are as follows:

[0056] (1) The fine slag of coal gasification (mineral content 68wt%, unburned carbon content 32wt%) was calcined at 815℃ for 60min to obtain tailings ash. 6g of tailings ash and 12g of potassium hydroxide were weighed and mixed in a mortar and ground evenly. The mixture was placed in a muffle furnace and heated from room temperature to 400℃ at a rate of 5℃ / min, then from 400℃ to 800℃ at a rate of 2℃ / min. The temperature was then maintained at 800℃ for 60min and allowed to cool naturally to room temperature in the muffle furnace to obtain alkali fusion product. The alkali fusion product was added to a round-bottom flask and 120mL of 25wt% hydrochloric acid solution was added to the round-bottom flask. The mixture was stirred at 550r / min for 7h at 60℃. The mixture was filtered with deionized water and dried in a drying oven at 105℃ to constant weight to obtain activated material.

[0057] (2) Weigh 0.5g of activated material, add 8mL of 3wt% sodium hydroxide solution and mix. Heat to 60℃ using a magnetic stirrer and stir continuously at 350r / min for 20min until completely dissolved to obtain silicon source;

[0058] (3) Add 1.4g of cetyltrimethylammonium bromide (CTAB) powder to 25mL of distilled water and heat at 60℃ until completely dissolved to obtain a homogeneous transparent solution, which is used as the template solution. n(CTAB) / n(Si)=0.21;

[0059] (4) Place the template agent solution on a magnetic stirrer, set the temperature to 35℃, and add the silicon source dropwise to the template agent solution at a speed of 2mL / min. After all the silicon source is added, adjust the pH value to 9 with a sulfuric acid solution of 1mol / L. Continue stirring on the magnetic stirrer at a speed of 350r / min for 2h. After stopping the stirring, let it stand at room temperature for 3h to obtain the aging product (a layered gel-like substance, all of which is poured into a hydrothermal reactor).

[0060] (5) Transfer the aged product to a hydrothermal reactor with a polytetrafluoroethylene liner, place it in a drying oven for hydrothermal reaction at a temperature of 100°C for 24 hours. After the reaction is complete, filter the product with deionized water until there is less foam, place it in a drying oven and dry it at 105°C to constant weight to obtain the dried product.

[0061] (6) The dried product was placed in a muffle furnace for calcination treatment. The temperature was increased to 550°C at a rate of 2°C / min and kept at this temperature for 5 hours to ensure the removal of surfactant. The product was then allowed to cool naturally to room temperature in the muffle furnace to obtain MCM-41 molecular sieve powder.

[0062] The specific surface area, pore volume, and average pore diameter of MCM-41 molecular sieve powder were determined using a physical adsorption analyzer. The results are as follows: specific surface area was 1055 m² / g. 2 / g, pore volume is 1.004cm³ 3 / g, with an average pore diameter of 3.7972nm.

[0063] The activated material obtained in step (1) was subjected to XRF analysis using an X-ray fluorescence spectrometer, and the results are shown in Table 1. It can be seen that the activated material obtained using the method provided by this invention has a silicon content of over 99%.

[0064] Table 1. XRF detection results of the activated material obtained in Example 1.

[0065] content(%) 0.05 99.38 0.19 0.02 0.13 0.04 0.02 0.17

[0066] Example 2

[0067] This embodiment provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.5g of activated material is weighed and 8mL of 5wt% sodium hydroxide solution is added; in step (3), 2.0g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 9 using a 5mol / L sulfuric acid solution.

[0068] The specific surface area of ​​the MCM-41 molecular sieve powder prepared in this embodiment was measured to be 10¹⁵ m². 2 / g, pore volume is 0.956cm³ 3 / g, with an average pore diameter of 3.4092nm.

[0069] Example 3

[0070] This embodiment provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.5g of activated material is weighed and 8mL of 5wt% sodium hydroxide solution is added; in step (3), 2.0g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0071] The specific surface area of ​​the MCM-41 molecular sieve powder prepared in this embodiment was measured to be 985 m². 2 / g, pore volume is 0.956cm³ 3 / g, with an average pore diameter of 3.4092nm.

[0072] The CO2 adsorption of the sample obtained in Example 3 was tested using a multi-component adsorption breakthrough curve analyzer. The CO2 adsorption capacity at 25°C was 2.169 mol / kg.

[0073] Small-angle XRD patterns of the MCM-41 molecular sieve powder prepared in Example 2 were obtained by X-ray diffraction, comparing them with the PDF card. Figure 1 As shown, the prepared sample exhibited three peaks at 2.28°, 3.87°, and 4.45°, respectively, corresponding to (100), (110), and (200) characteristic diffraction peaks of MCM-41, indicating that the synthesized sample has the same crystal structure as MCM-41. Verification was also made that the samples obtained in Examples 1 and 3 also have the same crystal structure as MCM-41.

[0074] Comparative Example 1

[0075] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.05g of activated material is weighed and mixed with 8mL of 5wt% sodium hydroxide solution; in step (3), 0.2g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0076] Comparative Example 2

[0077] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.05g of activated material is weighed and mixed with 8mL of 20wt% sodium hydroxide solution; in step (3), 0.2g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0078] Comparative Example 3

[0079] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (3), 2.0 g of CTAB powder is dissolved in 25 mL of distilled water to make n(CTAB) / n(Si) = 0.31; in step (4), a 5 mol / L sulfuric acid solution is used to adjust the pH value to 11.

[0080] The specific surface area of ​​the MCM-41 molecular sieve powder prepared in this comparative example was measured to be 1656 m². 2 / g, pore volume is 0.872cm³ 3 / g, with an average pore diameter of 2.3764nm.

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.5g of activated material is weighed and 8mL of 10wt% sodium hydroxide solution is added; in step (3), 2.0g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0083] Comparative Example 5

[0084] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.5g of activated material is weighed and 8mL of 15wt% sodium hydroxide solution is added; in step (3), 2.0g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0085] Comparative Example 6

[0086] This comparative example provides a method for preparing MCM-41 molecular sieve using coal gasification fine slag. The specific steps are the same as in Example 1, except that: in step (2), 0.5g of activated material is weighed and 8mL of 25wt% sodium hydroxide solution is added; in step (3), 2.0g of CTAB powder is dissolved in 25mL of distilled water so that n(CTAB) / n(Si)=0.31; in step (4), the pH value is adjusted to 8 using a 3mol / L sulfuric acid solution.

[0087] Comparative Example 7

[0088] This comparative example provides a method for preparing MCM-41 molecular sieves using coal gasification fine slag. The specific steps are the same as in Example 1, with the only difference being:

[0089] Step (1) is replaced by: weighing 4g of coal gasification fine slag, adding it to a round-bottom flask, adding 80mL of 25wt% hydrochloric acid solution to the round-bottom flask, stirring at 550r / min for 7h at 60℃, filtering with deionized water, and drying in a drying oven at 105℃ to constant weight to obtain pickled material.

[0090] Step (2) is replaced by: weighing 0.5g of pickling material, adding 8mL of 10wt% sodium hydroxide solution and mixing, heating to 60℃ with a magnetic stirrer and stirring continuously for about 20min, then filtering, the filtrate is the silicon source, of which 0.3373g of solid remains after filtration, that is, 0.1627g of silicon is dissolved in the filtrate;

[0091] In step (3), 0.65g of CTAB powder is dissolved in 25mL of distilled water to make n(CTAB) / n(Si)=0.31;

[0092] In step (4), the pH value is adjusted to 8 using a sulfuric acid solution with a concentration of 3 mol / L.

[0093] The pickled material obtained in step (1) was subjected to XRF testing, and the results are shown in Table 2. It can be seen that directly pickling the coal gasification fine slag significantly reduces the silicon content in the resulting pickled material, thereby reducing its yield.

[0094] Table 2 shows the XRF detection results of the pickling materials prepared in Comparative Example 7.

[0095]

[0096] The yield of MCM-41 molecular sieves prepared in Examples 1-3 and Comparative Examples 1-7 was determined by weighing. The calculation formula was: yield (%) = product mass (g) / amount of activating material (g). The results are shown in Table 3.

[0097] Table 3 Yield determination results of MCM-41 molecular sieve

[0098]

[0099] As shown in Table 3, the yields of MCM-41 molecular sieves prepared in Examples 1-3 were relatively high, reaching 74%-82%, with Example 3 being the optimal example, achieving a yield as high as 82.20%. Compared to Example 3, Example 2 differed only in step (4) in adjusting the pH value; it is evident that adjusting the pH to 8 in this step resulted in a higher yield. Compared to Example 3, Comparative Example 1 showed a significantly lower yield due to a lower silicon source concentration, demonstrating that a suitable silicon source concentration is beneficial for improving the yield. Compared to Comparative Example 1, Comparative Example 2 had a higher sodium hydroxide solution concentration, but its yield was significantly lower, indicating that for activated materials, simply increasing the concentration of sodium hydroxide solution does not improve the yield but rather decreases it. Compared to Examples 2 and 3, Comparative Example 3 increased the pH value to 11, resulting in a larger decrease in yield. Compared to Comparative Examples 4, 5, and 6 and Example 3, the concentration of sodium hydroxide solution was increased from 5 wt% to 10 wt%, 15 wt%, and 20 wt%, respectively. However, the yield data shows that the yield did not increase with the increase of sodium hydroxide concentration; in fact, it decreased instead. This is different from conventional understanding in the art. It is evident that the activation treatment method provided by this invention, combined with a low-concentration sodium hydroxide solution, is actually beneficial for improving the yield. Compared to Example 3, Comparative Example 7 directly acid-washed the coal gasification fine slag. Using a 10 wt% sodium hydroxide solution, it was impossible to completely dissolve the acid-washed material, thus leading to a decrease in its yield.

[0100] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing MCM-41 molecular sieve using coal gasification fine slag, characterized in that, Includes the following steps: (1) The fine slag from coal gasification is subjected to high-temperature calcination and decarbonization treatment to obtain tailings ash. The tailings ash is mixed and ground with potassium hydroxide at a mass ratio of 1:1.5~2 and then activated at 800~850℃ for 60~90min to obtain alkali fusion product. The alkali fusion product is subjected to acid washing treatment, filtered with deionized water and dried to obtain activated material. The high-temperature calcination conditions are: calcination at 750~850℃ for 60~120min. (2) The activated material obtained in step (1) is mixed with 3-7 wt% sodium hydroxide solution at a mass-volume ratio of 0.5-1.0:8 g / mL, heated to dissolve, and a silicon source is obtained; (3) Dissolve hexadecyltrimethylammonium bromide in water at a mass-to-volume ratio of 1.4~2.0:25 g / mL to obtain a template agent solution; (4) The silicon source obtained in step (2) is added dropwise to the template agent solution obtained in step (3), wherein the activating material and hexadecyltrimethylammonium bromide are mixed at a mass ratio of 0.5~1.0:1.4~2.0, the pH value is adjusted to 8~9, stirred, and allowed to stand for aging to obtain the aging product; (5) The aging product obtained in step (4) is subjected to hydrothermal reaction, filtered with deionized water and dried to obtain the dried product; (6) The dried product obtained in step (5) is calcined to obtain MCM-41 molecular sieve.

2. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (1), The tailings ash and potassium hydroxide are mixed at a mass ratio of 1:2; The high-temperature activation heating process involves heating to 400-450°C at a rate of 4-5°C / min, and then heating to 800-850°C at a rate of 1-2°C / min; the high-temperature activation cooling process involves cooling to room temperature in the furnace. Acid washing is performed using a 25-37 wt% hydrochloric acid solution. Hydrochloric acid solution is added at a mass-to-volume ratio of 1:10-20 g / mL, and the mixture is stirred at 300-550 r / min for 7-8 hours at 50-60℃. The drying conditions are as follows: drying at 90~110℃ to constant weight.

3. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (1), The conditions for high-temperature calcination are: calcination at 815℃ for 60 minutes; The conditions for high-temperature activation are as follows: heat up to 400°C at a rate of 5°C / min, then heat up to 800°C at a rate of 2°C / min, hold at that temperature for 60 min, and then cool to room temperature in the furnace. Acid washing was performed using a 25wt% hydrochloric acid solution. Hydrochloric acid solution was added at a mass-to-volume ratio of 1:20 g / mL to tail ash. The mixture was stirred at 550 r / min for 7 h at 60 °C. The drying conditions are as follows: drying at 105°C to constant weight.

4. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (2), the activated material is mixed with 3-7 wt% sodium hydroxide solution at a mass-to-volume ratio of 0.5:8 g / mL; the heating and dissolving conditions are: stirring at 350 r / min for 20 min at 60℃.

5. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (3), hexadecyltrimethylammonium bromide is dissolved in water at a mass-to-volume ratio of 2.0:25 g / mL to obtain a template agent solution.

6. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (4), The silicon source is added at a rate of 1-2 mL / min and at a temperature of 25-35 °C. Adjust the pH value using a 1-5 mol / L sulfuric acid solution; The stirring conditions are: stirring at 300-400 r / min for 2-3 hours at 25-35℃; The conditions for static aging are: static aging at room temperature for 3-4 hours.

7. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 6, characterized in that, In step (4), The silicon source was added at a rate of 2 mL / min and at a temperature of 35 °C. The mass ratio of the activating material to cetyltrimethylammonium bromide is 0.5:2.0; Adjust the pH to 8 using a 1-5 mol / L sulfuric acid solution; The stirring conditions were: stirring at 35°C and 350 r / min for 2 hours; The conditions for static aging are: static aging at room temperature for 3 hours.

8. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (5), the hydrothermal reaction conditions are: reacting at 100~110℃ for 20~28h; the drying conditions are: drying at 90~110℃ to constant weight. In step (6), the calcination conditions are as follows: the temperature is increased to 500-550°C at a rate of 1-2°C / min, held for 5-6 hours, and then cooled to room temperature in the furnace.

9. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, In step (5), the hydrothermal reaction conditions are: reacting at 100°C for 24 hours; the drying conditions are: drying at 105°C to constant weight. In step (6), the calcination conditions are as follows: the temperature is increased to 550°C at a rate of 2°C / min, held for 5 hours, and then cooled to room temperature in the furnace.

10. The method for preparing MCM-41 molecular sieve using coal gasification fine slag according to claim 1, characterized in that, The mineral content of the coal gasification slag is 68-72 wt%, and the unburned coal content is 28-32 wt%.

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