Preparation method and application of modified MCM-22 molecular sieve catalyst

Abstract

The invention belongs to the technical field of chemical catalysis, and provides a preparation method and application of a modified MCM-22 molecular sieve catalyst. Unroasted MCM-22 (P) is used as a raw material, organic alkali (such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide or tetrabutylammonium hydroxide) is adopted for modification treatment, and then ion exchange and roasting are performed to obtain the hydrogen type modified molecular sieve. Organic alkali has the synergistic effect of alkali treatment and structure guiding, and the crystal phase purity and framework integrity are maintained while controllable desilicication is achieved. The catalyst is used for alkylation removal reaction of thiophenic sulfur in styrene, the selectivity of mono-substituted alkylation products is remarkably improved, and side reaction of styrene polymerization is effectively inhibited. The preparation method is simple, the catalytic performance is excellent, and the catalyst has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical catalysis technology, specifically to a method for preparing and applying a modified MCM-22 molecular sieve catalyst. Background Technology

[0002] Styrene obtained from the cracked gasoline extraction and distillation recovery method typically contains 30-100 ppm of sulfur, mainly thiophene-type heterocyclic sulfur compounds. These sulfur compounds severely affect the purity and quality of styrene products and negatively impact subsequent chemical utilization, becoming a bottleneck restricting enterprise profitability and product upgrading. Alkylation desulfurization technology is a non-hydrogenation catalytic desulfurization technology developed by BP for gasoline distillate fuels. This technology stands out among numerous desulfurization technologies due to its advantages of low octane number loss and high desulfurization efficiency.

[0003] Catalysts for alkylation desulfurization are mainly classified into two categories: solid acid catalysts and liquid acid catalysts. Chinese patent CN116023225A discloses a method for catalytic alkylation removal of thiophene sulfur from styrene, using concentrated phosphoric acid or dilute sulfuric acid as a catalyst. However, this liquid acid catalysis method has drawbacks in practical applications: it causes strong corrosion to equipment, resulting in high equipment investment and maintenance costs; the waste acid generated after the reaction is difficult to treat, posing a significant environmental burden; and trace amounts of acid remaining in the product during the separation process can affect the final purity of styrene. Solid acid catalysts, especially molecular sieve materials, have attracted widespread attention due to their unique advantages, exhibiting significant application prospects in this field due to their unique pore structure and selectivity, as well as excellent thermal and hydrothermal stability. For example, the MCM-22 molecular sieve, with its combination of twelve-membered and ten-membered ring structures, exhibits excellent potential in catalytic reactions. Chinese patent CN115772061A provides a method for the catalytic removal of thiophene-containing sulfur compounds from styrene. This method uses solid acid catalysts, namely MCM-22 and MCM-49 molecular sieves, to catalyze the alkylation reaction between styrene and thiophene-containing sulfur compounds, achieving good desulfurization results. Although the thiophene conversion rate is high, the styrene loss is also high.

[0004] To improve the catalytic performance of molecular sieves, researchers have employed appropriate modification methods to further enhance the catalytic performance of MCM-22, such as controlling the pore structure and surface acidity. Chinese patents CN1990104A and CN101543787A both employ inorganic alkali treatment to introduce mesopores into the calcined molecular sieve. However, for the specific reaction of styrene alkylation desulfurization, excessive pore expansion, while catalyzing thiophene alkylation, can easily induce styrene self-polymerization, leading to a decrease in the effective utilization rate of styrene. Single strong alkali treatment can easily destroy the unique tertiary pore structure of MCM-22 molecular sieves, readily deactivating them. Given the current shortcomings of alkali modification of MCM-22 molecular sieves, improvements are necessary. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing and applying a modified MCM-22 molecular sieve catalyst. The method involves using an organic base-modified molecular sieve to treat uncalcined MCM-22(P) with an alkali. The resulting catalyst can effectively inhibit the self-polymerization reaction of styrene, improve the selectivity of monosubstituted alkylation products, and enhance the effective utilization rate of styrene.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a modified MCM-22 molecular sieve catalyst, comprising the following steps: (1) Mix uncalcined MCM-22(P), organic base source, hexadecyltrimethylammonium bromide and water evenly to obtain a mixed solution; the organic base is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; (2) The mixed solution is subjected to alkali modification under stirring, and then subjected to ultrasonication, washing and drying to obtain sodium-type alkali-modified MCM-22 molecular sieve; (3) Add sodium-type alkali-modified MCM-22 molecular sieve to ammonium salt solution and stir to carry out ion exchange reaction. After the reaction is completed, filter, wash, dry and calcin to obtain hydrogen-type alkali-modified MCM-22 molecular sieve.

[0007] Furthermore, the organic base source is an aqueous solution of organic base with a mass percentage of 25-40 wt.%.

[0008] Furthermore, the mass ratio of the uncalcined MCM-22(P), hexadecyltrimethylammonium bromide, organic base source, and water is 1:5:3.94-7.1:18.52-20.34.

[0009] Furthermore, the alkali modification temperature is 80-90 ℃, more preferably 85 ℃, and the time is 10-14 h, more preferably 12 h.

[0010] Furthermore, the ultrasound duration is 0.5-1.5 h, and the temperature is 20-50 ℃.

[0011] Further, after sonication, 6 M HCl was added to adjust the pH to 2, followed by washing and drying.

[0012] Further, the drying temperature in step (2) is 90-120 ℃, more preferably 100 ℃; the drying time is 8 h-12 h; the drying temperature in step (3) is 90-120 ℃, and the drying time is 8 h-12 h.

[0013] Furthermore, the ion exchange reaction is carried out at a temperature of 80-90 °C for 4 hours, with 2-4 exchanges. The ammonium salt is ammonium chloride or ammonium nitrate.

[0014] Furthermore, the calcination is carried out in an air atmosphere at 530-560 °C for 4-6 h.

[0015] Furthermore, in step (3), the amount of sodium-type MCM-22 molecular sieve and ammonium chloride added is 1g:18-22mL according to the solid-liquid ratio (mass / volume).

[0016] Furthermore, the concentration of the ammonium salt solution is 1 mol / L.

[0017] Furthermore, the method for preparing the uncalcined MCM-22(P) includes the following steps: 1) Sodium hydroxide is dissolved in deionized water at room temperature, sodium aluminate is added, and the mixture is stirred until a clear solution is obtained; the mass ratio of sodium hydroxide to sodium aluminate is 1.23:1. 2) Add hexamethyleneimine dropwise to the clear solution obtained in step 1). After the addition is complete, stir for 0.2-0.7 h. Under vigorous stirring at 800-1200 r / min, slowly add 25-35 wt.% silica sol. Continue stirring and aging at room temperature for 20-24 h to obtain a milky white liquid. The mass ratio of hexamethyleneimine to sodium aluminate is 5.11:1. 3) Place the milky white liquid obtained in step 2) into a mechanically stirred tank or a magnetically stirred tank, rotate at 50-70 r / min, heat to 155-160 ℃, and crystallize for 70-74 h; (4) After dynamic crystallization in step (3), the obtained solid is washed and dried to obtain MCM-22 (P).

[0018] Furthermore, the silicon-aluminum molar ratio in the MCM-22(P) is 20-40:1, and more preferably 32.5:1.

[0019] A second aspect of the present invention provides a modified MCM-22 molecular sieve catalyst prepared by the above method.

[0020] A third aspect of the present invention provides the application of the modified MCM-22 molecular sieve catalyst in the catalytic alkylation desulfurization reaction of styrene.

[0021] Furthermore, the method of application is as follows: at 20 ℃-40 ℃, the modified MCM-22 molecular sieve catalyst is placed in a styrene solution containing thiophene to catalyze the alkylation reaction of styrene.

[0022] Furthermore, the molar ratio of styrene to thiophene is 95-105:1.

[0023] Furthermore, the reaction temperature is 35 °C.

[0024] The advantages and beneficial effects of this invention are: (1) In this invention, organic bases are used to modify uncalcined MCM-22(P). During the modification process, the organic bases exert a synergistic effect of alkali treatment and structure guidance. Unlike the "etching and pore-forming" mechanism of traditional inorganic bases, the role of organic bases in the modification of MCM-22 molecular sieves is mainly manifested in "surface cleaning" and "pore unblocking". They gently dissolve and remove amorphous silicon species remaining on the crystal surface and pores during the synthesis process. While achieving controllable desilication, they effectively maintain the purity of the crystal phase and the integrity of the framework. XRD characterization results show that the MCM-22 molecular sieve modified by organic bases still retains all the characteristic peaks of the MWW-type crystal structure and has good crystallinity. At the same time, the modified catalyst has reduced mesopores, increased micropore volume, and smaller average pore size, and the specific surface area is optimized, providing a more suitable pore environment for catalytic reactions.

[0025] (2) The modified MCM-22 molecular sieve catalyst prepared in this invention exhibits excellent catalytic activity in the alkylation removal reaction of thiophene sulfur in styrene. Thanks to the optimization of the pore structure and the improvement of mass transfer efficiency after modification, the catalyst significantly improves the selectivity of monosubstituted alkylation products, while effectively suppressing the polymerization side reaction of styrene. Taking the tetraethylammonium hydroxide (TEAOH) modified MCM-22 molecular sieve as an example, the thiophene conversion rate reached 77.95%, which is 15.9 percentage points higher than that of unmodified MCM-22 (62.1%), and the product selectivity is improved, which improves the effective utilization rate of styrene and reduces the difficulty of product separation, providing a green and mild technical solution for the efficient removal of thiophene sulfur from styrene. Attached Figure Description

[0026] Figure 1 These are the XRD patterns of the modified MCM-22 molecular sieve catalysts prepared in Examples 1-4 and Comparative Examples 2-3.

[0027] Figure 2 The graph shows the thiophene conversion rate of the modified MCM-22 molecular sieve catalysts prepared in Examples 1-4 and Comparative Examples 2-3 for catalytic alkylation reactions.

[0028] Figure 3 This is a product selectivity diagram of the alkylation reaction catalyzed by the modified MCM-22 molecular sieve catalyst prepared in Example 1.

[0029] Figure 4 This is a product selectivity diagram of the unmodified MCM-22 molecular sieve catalyzed alkylation reaction prepared in Comparative Example 1.

[0030] Figure 5 The graph shows the thiophene conversion rate after catalytic alkylation reaction using the MCM-22 molecular sieve catalyst prepared in Example 1 at different temperatures.

[0031] Figure 6 The graph shows the styrene conversion rate after alkylation reaction catalyzed by the MCM-22 molecular sieve catalyst prepared in Example 1 at different temperatures. Detailed Implementation

[0032] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) At room temperature, 0.63 g of sodium hydroxide was dissolved in 49 g of deionized water, and 0.51 g of sodium aluminate was added. After stirring evenly, a clear solution was obtained. 2.63 g of hexamethyleneimine was added dropwise to the clear solution. After the addition was complete, the mixture was stirred for 0.5 h. Under vigorous stirring at 800-1200 r / min, 20 g of 30 wt.% silica sol was slowly added. The mixture was stirred and aged at room temperature for 24 h to obtain a milky white liquid. The milky white liquid was placed in a mechanically stirred tank or a magnetically stirred tank, and the temperature was raised to 158 ℃ at 60 r / min for crystallization for 72 h. After dynamic crystallization, the obtained solid was washed with water and dried at 100 ℃ to obtain uncalcined MCM-22(P). The silicon-aluminum molar ratio in the uncalcined MCM-22(P) was 32.5:1.

[0034] (2) Mix 2 g of uncalcined MCM-22 (P), 12.745 g of 25 wt.% tetraethylammonium hydroxide aqueous solution, 10 g of hexadecyltrimethylammonium bromide and 37.042 g of water evenly to obtain a mixed solution; (3) The mixed solution was refluxed and stirred at 85 °C for 12 h for alkali modification, then sonicated at 40 °C for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was then washed with water until neutral and dried at 100 °C to obtain sodium-type alkali-modified MCM-22 molecular sieve.

[0035] (4) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85 °C for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100 °C for 12 h. Then it was calcined at 550 °C in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-TEAOH.

[0036] Comparative Example 1 A method for preparing an unmodified MCM-22 molecular sieve catalyst includes the following steps: Uncalcined MCM-22(P) (same as in Example 1) was placed in a muffle furnace and calcined to 550 °C at a programmed heating rate of 5 °C / min under air atmosphere for 6 h to completely remove the template agent, thus obtaining sodium-type MCM-22 molecular sieve. Subsequently, the sodium-type MCM-22 molecular sieve was added to a 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g:20 mL (mass / volume), and stirred at 80 °C for 4 h to carry out an ion exchange reaction. This operation was repeated 3 times. The mixture was then washed with deionized water, and the filter cake was dried in a 100 °C oven for 12 h, followed by calcination at 550 °C under air atmosphere for 5 h to obtain hydrogen-type MCM-22 molecular sieve catalyst.

[0037] Example 2 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) Mix 2 g of uncalcined MCM-22 (P) (same as in Example 1), 7.889 g of 25 wt.% tetramethylammonium hydroxide aqueous solution, 10 g of hexadecyltrimethylammonium bromide and 40.684 g of water evenly to obtain a mixed solution.

[0038] (2) The mixed solution was refluxed and stirred at 85 °C for 12 h, then sonicated at 40 °C for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was washed with water and dried at 100 °C to obtain sodium-type alkali-modified MCM-22 molecular sieve.

[0039] (3) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85 °C for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100 °C for 12 h. Then it was calcined at 550 °C in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-TMAOH.

[0040] Example 3 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) Mix 2 g of uncalcined MCM-22 (P) (same as in Example 1), 11 g of 40 wt.% tetrapropylammonium hydroxide aqueous solution, 10 g of hexadecyltrimethylammonium bromide and 40 g of water to obtain a mixed solution.

[0041] (2) The mixed solution was refluxed and stirred at 85 °C for 12 h, then sonicated at 40 °C for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was washed with water and dried at 100 °C to obtain sodium-type alkali-modified MCM-22 molecular sieve.

[0042] (3) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85 °C for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100 °C for 12 h. Then it was calcined at 550 °C in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-TPAOH.

[0043] Example 4 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) Mix 2 g of uncalcined MCM-22 (P) (same as in Example 1), 14.035 g of 25 wt.% tetrabutylammonium hydroxide aqueous solution, 10 g of hexadecyltrimethylammonium bromide and 38.179 g of water evenly to obtain a mixed solution.

[0044] (2) The mixed solution was refluxed and stirred at 85℃ for 12 h, then sonicated at 40℃ for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was then washed with water and 100 ml of HCl was added. o Sodium-type alkali-modified MCM-22 molecular sieve was obtained by drying at C.

[0045] (3) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85 °C for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100 °C for 12 h. Then it was calcined at 550 °C in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-TBAOH.

[0046] Comparative Example 2 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) Mix 2 g of uncalcined MCM-22 (P) (same as in Example 1), 0.865 g of sodium hydroxide, 10 g of cetyltrimethylammonium bromide and 46.6 g of water evenly to obtain a mixed solution.

[0047] (2) The mixed solution was refluxed and stirred at 85 °C for 12 h, then sonicated at 40 °C for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was then washed with water and 100 ml of HCl was added. o Sodium-type alkali-modified MCM-22 molecular sieve was obtained by drying at C.

[0048] (3) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85℃ for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100℃ for 12 h. Then it was calcined at 550℃ in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-NaOH.

[0049] Comparative Example 3 A method for preparing a modified MCM-22 molecular sieve catalyst includes the following steps: (1) Mix 2 g of uncalcined MCM-22 (P) (same as in Example 1), 1.215 g of potassium hydroxide, 10 g of cetyltrimethylammonium bromide and 46.6 g of water evenly to obtain a mixed solution.

[0050] (2) The mixed solution was refluxed and stirred at 85 °C for 12 h, then sonicated at 40 °C for 1 h. After sonication, 6 M HCl was added to adjust the pH to 2. The solution was washed with water and dried at 100 °C to obtain sodium-type alkali-modified MCM-22 molecular sieve.

[0051] (3) Sodium-type alkali-modified MCM-22 molecular sieve was added to 1 mol / L ammonium chloride solution at a solid-liquid ratio of 1 g: 20 mL (mass / volume) and ion exchanged at 85 °C for 4 h. The operation was repeated 3 times. The filter cake was washed with deionized water and dried in an oven at 100 °C for 12 h. Then it was calcined at 550 °C in air atmosphere for 5 h to obtain hydrogen-type alkali-modified MCM-22 molecular sieve catalyst, denoted as MCM-22-KOH.

[0052] Performance testing and analysis XRD spectra of the molecular sieve catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were analyzed, and the results are as follows: Figure 1 As shown, the self-made MCM-22 molecular sieve catalyst in Comparative Example 1 exhibits characteristic peaks of the MWW-type crystal structure. When tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide are used as alkali sources, the molecular sieves prepared after alkali modification still retain the characteristic peaks of the MWW-type crystal structure. When sodium hydroxide is used as the alkali source, the MCM-22-NaOH molecular sieve prepared after alkali modification retains the characteristic peaks of the MWW-type crystal structure, but the intensity of the characteristic peaks is significantly reduced, and the crystallinity decreases. When potassium hydroxide is used as the alkali source, the MCM-22-KOH molecular sieve prepared after alkali modification retains the characteristic peaks of the MWW-type crystal structure while also exhibiting diffraction peaks of mordenite, indicating that a mixture of mordenite is generated during the alkali treatment process, and the intensity of the characteristic peaks decreases, as does the crystallinity.

[0053] Catalytic performance test: Weigh 0.3 g of the molecular sieve catalysts prepared in Examples 1-4 and Comparative Examples 1-3 respectively, and then prepare 50 mL of 1 wt.% thiophene / styrene solution in a 100 mL three-necked flask. Fix the three-necked flask on a magnetic stirrer, and add the molecular sieve catalyst to the solution at room temperature and with vigorous stirring at 800 r / min. After the catalyst is added, adjust the water bath temperature to 35 ℃ and carry out the reaction at vigorous stirring at 800 r / min for 12 h. Take samples every 2 h to test the thiophene conversion rate of the catalytic alkylation reaction.

[0054] Thiophene conversion results are as follows Figure 2As shown, when tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide were used as alkali sources, the conversion rates of thiophene removed from styrene by the alkali-modified MCM-22 molecular sieve catalyst after 12 h of reaction were 77.95%, 66.28%, 73.22%, and 67.03%, respectively. In Comparative Example 1, the conversion rate of thiophene removed from styrene by the self-made MCM-22 molecular sieve catalyst was 62.1%. In Comparative Example 2, the conversion rate was 51.36% when sodium hydroxide was used as the alkali source, and in Comparative Example 3, the conversion rate was only 35.58% when potassium hydroxide was used as the alkali source.

[0055] Selectivity comparison of the products after catalytic reaction. Figure 3 This is a product selectivity diagram after alkylation catalyzed by the modified MCM-22 molecular sieve catalyst in Example 1. Figure 4 This is a product selectivity diagram of the alkylation reaction catalyzed by the unmodified MCM-22 molecular sieve in Comparative Example 1. It can be seen that the selectivity of the monosubstituted products is improved after modifying the uncalcined MCM-22 (P) with tetraethylammonium hydroxide, while the selectivity of the disubstituted and trisubstituted products decreases accordingly.

[0056] Weigh 0.3 g of the molecular sieve catalyst prepared in Example 1, and then prepare 50 mL of a 1 wt.% thiophene / styrene solution in a 100 mL three-necked flask. Fix the three-necked flask on a magnetic stirrer, and add the molecular sieve catalyst to the solution under strong stirring at 800 r / min at room temperature. After the catalyst is added, adjust the water bath temperature to 20 ℃, 25 ℃, 30 ℃, 35 ℃, and 40 ℃ to catalyze the alkylation reaction. The reaction is carried out under strong stirring at 800 r / min for 12 h. Samples are taken every 2 h to test the thiophene conversion rate of the catalytic alkylation reaction. The results are as follows. Figure 5 As shown. Figure 6 This is a graph showing the styrene conversion rate. It can be seen that the thiophene conversion rate increases with increasing temperature. At 40 °C, the thiophene conversion rate reaches as high as 92%. While the styrene conversion rate is slightly higher at this temperature compared to other temperatures, it is still below 20%. Overall, 35 °C is a suitable reaction temperature, capable of improving the thiophene conversion efficiency while ensuring styrene yield.

[0057] The pore structure of the molecular sieve catalysts prepared in the examples and comparative examples was tested using the N2 low-temperature adsorption-desorption method, and the results are shown in Table 1.

[0058] Table 1

[0059] Combined with Table 1 and Figure 3-6It can be seen that the selectivity of monosubstituted alkylation products of the catalyst treated with organic base is significantly improved, with a styrene conversion rate of 5-20%, effectively suppressing the polymerization side reactions of styrene. Regarding the pore structure, the catalyst modified with organic base exhibits reduced mesopores, increased micropore volume, and smaller average pore size. This phenomenon reveals the unique mechanism of organic base modification: unlike the "etching and pore-forming" effect of traditional inorganic bases (such as NaOH), the effect of organic base (TEAOH) on MCM-22 is mainly manifested as "surface cleaning" and "pore unblocking." Amorphous silicon species remaining on the surface and pores of MCM-22 crystals during synthesis are gently dissolved and removed by the organic base, thereby optimizing shape selectivity, improving mass transfer efficiency, and ultimately achieving a simultaneous improvement in conversion rate and selectivity.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a modified MCM-22 molecular sieve catalyst, characterized in that, Includes the following steps: (1) Mix uncalcined MCM-22(P), organic base source, hexadecyltrimethylammonium bromide and water evenly to obtain a mixed solution; the organic base is one or more of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; (2) The mixed solution was modified with alkali under stirring, and then subjected to ultrasonication, washing and drying to obtain sodium-type alkali-modified MCM-22 molecular sieve; (3) Add sodium-type alkali-modified MCM-22 molecular sieve to ammonium salt solution and stir to carry out ion exchange reaction. After the reaction is completed, filter, wash, dry and calcin to obtain hydrogen-type alkali-modified MCM-22 molecular sieve.

2. The preparation method according to claim 1, characterized in that, The organic base source is an aqueous solution of organic base with a mass percentage of 25-40 wt.%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the uncalcined MCM-22(P), hexadecyltrimethylammonium bromide, organic base source and water is 1:5:3.94-7.1:18.52-20.

34.

4. The preparation method according to claim 1, characterized in that, The alkali modification is performed at a temperature of 80-90 ℃ for 10-14 h, and the ultrasonication is performed at a temperature of 20-50 ℃ for 0.5-1.5 h. After ultrasonication, 6 M HCl is added to adjust the pH to 2, followed by washing and drying.

5. The preparation method according to claim 2, characterized in that, The drying temperature in step (2) is 90-120℃ and the drying time is 8-12 h; the drying temperature in step (3) is 90-120℃ and the drying time is 8-12 h.

6. The preparation method according to claim 2, characterized in that, The ion exchange reaction is carried out at a temperature of 80-90℃ for 10-12 h, and the ammonium salt is ammonium chloride or ammonium nitrate; the calcination is carried out at 530-560℃ in an air atmosphere for 4-6 h.

7. The preparation method according to claim 2, characterized in that, The method for preparing the uncalcined MCM-22(P) includes the following steps: 1) Sodium hydroxide is dissolved in deionized water at room temperature, sodium aluminate is added, and the mixture is stirred until a clear solution is obtained; the mass ratio of sodium hydroxide to sodium aluminate is 1.23:

1. 2) Add hexamethyleneimine dropwise to the clear solution obtained in step 1). After the addition is complete, stir for 0.2-0.7 h. Under vigorous stirring at 800-1200 r / min, slowly add 25-35 wt.% silica sol. Continue stirring and aging at room temperature for 20-24 h to obtain a milky white liquid. The mass ratio of hexamethyleneimine to sodium aluminate is 5.11:

1. 3) Place the milky white liquid obtained in step 2) into a mechanically stirred tank or a magnetically stirred tank, rotate at 50-70 r / min, heat to 155-160 ℃, and crystallize for 70-74 h; 4) After dynamic crystallization in step 3), the obtained solid is washed and dried to obtain MCM-22(P), wherein the silicon-aluminum molar ratio in MCM-22(P) is 20-40:

1.

8. The modified MCM-22 molecular sieve catalyst obtained by the preparation method according to any one of claims 1-7.

9. The application of the modified MCM-22 molecular sieve catalyst as described in claim 8 in the catalytic desulfurization reaction of styrene alkylation.

10. The application according to claim 9, characterized in that, The method of application is as follows: at 20 ℃-40 ℃, the modified MCM-22 molecular sieve catalyst is placed in a styrene solution containing thiophene to catalyze the alkylation reaction of styrene.

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