一种用于乙苯烷基化制对二乙苯反应的纳米级ZSM-5分子筛及其制备方法和应用

Abstract

This invention relates to a nanoscale ZSM-5 molecular sieve for the alkylation of ethylbenzene to p-diethylbenzene, its preparation method, and its applications. The ZSM-5 molecular sieve has an MFI-type framework structure. The nanoscale ZSM-5 molecular sieve comprises a bulk ZSM-5 phase and an outer surface. The silica-to-alumina ratio of the bulk ZSM-5 phase is between 90 and 300, and the silica-to-alumina ratio of the outer surface is between 350 and 600. The nanoscale ZSM-5 molecular sieve includes Lewis acid centers and Beta acid centers, with a Lewis acid center to Beta acid center ratio of 8 to 16. The nanoscale ZSM-5 molecular sieve prepared by this invention exhibits excellent catalytic activity for the alkylation of ethylbenzene and can significantly improve the selectivity of the target product to p-diethylbenzene (>98%). Furthermore, this molecular sieve catalyst possesses excellent catalytic stability.

Description

Technical Field

[0001] This invention relates to the field of catalysis, and more specifically to nanoscale ZSM-5 molecular sieves for the alkylation of ethylbenzene to p-diethylbenzene, their preparation methods, and applications. Background Technology

[0002] p-Diethylbenzene, also known as 1,4-diethylbenzene or p-ethylethylbenzene, is an important chemical raw material with a wide range of applications. It is mainly used as a desorbent in industrial separation processes and as a raw material for the preparation of benzodithiobenzene. Dehydrogenation of p-diethylbenzene yields p-divinylbenzene, which is an important resin crosslinking agent. In addition, p-diethylbenzene can also be used to produce many other chemical products such as terephthalamide and p-diacetylbenzene.

[0003] Wang Guiru et al. (Petrochemical Technology, 1987, V16(9): 616-621) studied the effects of the total surface acidity and the acid strength of the surface acid centers of ZSM-5 molecular sieve on the product selectivity (especially alkylation selectivity and para-selectivity) of the reaction of ethylbenzene alkylation to p-diethylbenzene.

[0004] CN101455978A discloses a method for preparing a shape-selective catalyst for the alkylation of ethylbenzene and ethylene to produce p-diethylbenzene. The method uses rare earth elements to modify the molecular sieve catalyst. The rare earth modification is completed in two steps: hot impregnation and cold impregnation. The catalyst prepared by this method is reported to have the advantages of high activity, long single-pass reaction cycle and good regeneration repeatability.

[0005] CN105381814A discloses a catalyst for the alkylation reaction of ethylbenzene and ethanol and its preparation method. It employs a modified hydrogen-form eutectic ZSM-5 / ZSM-11 molecular sieve and undergoes calcination under a steam atmosphere. Reportedly, this catalyst, when used in the alkylation reaction of ethylbenzene and ethanol to prepare diethylbenzene, achieves a high conversion rate of ethylbenzene (ethanol) while significantly suppressing side reactions such as alkyl transfer and improving the selectivity of the reaction product to diethylbenzene.

[0006] CN107913727A discloses a highly efficient catalyst for the alkylation of ethylbenzene to p-diethylbenzene and its preparation method. It employs nano-hydrogen-type ZSM-5 molecular sieves and modified components magnesium, silicon, and phosphorus, and has been reported to significantly improve the conversion rate of ethylbenzene and the selectivity for p-diethylbenzene.

[0007] CN101618335A discloses a method for preparing a catalyst for the synthesis of p-diethylbenzene by the alkylation reaction of ethylbenzene with ethylene or ethanol. This method uses HZSM-5 molecular sieve with SiO2 / Al2O3 = 16-200 as the matrix, first supporting silica, and then calcining and passivating it under conditions of simultaneous presence of air and water vapor.

[0008] The currently reported ethylbenzene alkylation reactions all aim to improve the selectivity of the product to diethylbenzene, primarily employing two methods: The first is impregnation, where HZSM-5 is modified with alkali metals, alkaline earth metal compounds, transition metal compounds, other inorganic acids, or organosilanes, mainly involving pore size and acid strength adjustment. This method involves multi-step impregnation, is cumbersome, difficult to control, and its effectiveness still needs improvement. The second method uses steam treatment to dealudealuminize the molecular sieve, which also suffers from complex control parameters and high energy consumption. Therefore, simplifying the catalyst preparation process, reducing costs, and improving the selectivity to diethylbenzene and catalyst stability remain problems that need to be addressed. Summary of the Invention

[0009] To address the shortcomings of existing technologies, one objective of this invention is to provide a nanoscale ZSM-5 molecular sieve for the alkylation of ethylbenzene to diethylbenzene. This nanoscale molecular sieve exhibits excellent catalytic activity for ethylbenzene alkylation and can significantly improve the selectivity of the target product to diethylbenzene (>98%). Furthermore, this molecular sieve catalyst possesses excellent catalytic stability.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A nanoscale ZSM-5 molecular sieve for the alkylation of ethylbenzene to p-diethylbenzene is disclosed. The nanoscale ZSM-5 molecular sieve has an MFI-type framework structure; the bulk silica-to-alumina ratio of the nanoscale ZSM-5 molecular sieve is between 90 and 300, and the surface silica-to-alumina ratio is between 350 and 600; the nanoscale ZSM-5 molecular sieve includes Lewis acid centers and Beta acid centers, with a molar ratio of Lewis acid centers to Beta acid centers of 8-16. Since the alkylation reaction of ethylbenzene belongs to a class of solid acid-catalyzed reactions, with a carbocation mechanism, based on previous reports and the research and analysis of this invention, the key factors affecting the selectivity of the reaction product to p-diethylbenzene are the pore size and acidity inside and outside the molecular sieve catalyst. Firstly, the acidity of the outer surface of the molecular sieve is crucial for the selectivity of p-diethylbenzene, because p-diethylbenzene readily undergoes isomerization reactions on the outer surface of the molecular sieve, leading to a significant decrease in selectivity. Secondly, since the alkylation of ethylbenzene involves side reactions such as disproportionation, dealkylation, and cracking, carbon deposition easily occurs on the molecular sieve, leading to deactivation. Therefore, it is necessary to minimize the pore size of the molecular sieve. Thus, through research, the inventors have proposed the aforementioned specific nanoscale ZSM-5 molecular sieve as a catalyst for the diethylbenzene isomerization reaction.

[0012] In the above technical solution, the particle size of the nano-sized ZSM-5 molecular sieve is between 100-250 nm, preferably 100-200 nm; the specific surface area of ​​the nano-sized ZSM-5 molecular sieve is 350-450 m². 2 / g, preferably 380-450m2 / g; wherein, the specific surface area of ​​the outer surface of the nano-sized ZSM-5 molecular sieve is 20%-30% of the total specific surface area of ​​the nano-sized ZSM-5 molecular sieve.

[0013] In the above technical solution, the nanoscale ZSM-5 molecular sieve has a composite pore structure of mesopores and micropores, with an average pore size of 3.5 nm-5.5 nm; wherein the proportion of mesopores is 50%-70%, the micropore volume is 0.10-0.20 cm³ / g, and the mesopore volume is 0.25-0.45 cm³ / g. Generally, pores with a diameter below 2 nm are considered micropores; pores with a diameter between 2 and 50 nm are considered mesopores; and pores with a diameter above 50 nm are considered macropores.

[0014] In the above technical solution, triisopropylbenzene pyrolysis is used as a probe reaction, and the conversion rate of triisopropylbenzene is measured to be ≤2%, and the acid content on the outer surface of the nano-sized ZSM-5 molecular sieve is ≤7.4 nmol / m 2 .

[0015] The surface acidity of molecular sieves is estimated using the following model:

[0016]

[0017] A second objective of this invention is to provide a method for preparing nanoscale ZSM-5 molecular sieves for the alkylation of ethylbenzene to produce diethylbenzene. The method includes: treating ZSM-5 seed crystals with an inorganic acid solution; mixing an aluminum source, a silicon source, a template agent, seed crystals, and water to form a mother liquor; crystallization; separation, drying, and hydrothermal treatment with an organic acid solution containing a surfactant; solid-liquid separation, drying, calcination, and exchange to obtain nanoscale ZSM-5 molecular sieves. This method can significantly improve the selectivity of the target product for diethylbenzene.

[0018] In the above technical solution, the pretreatment includes treating ZSM-5 seed crystals with an inorganic acid solution, wherein the inorganic acid solution is selected from at least one of hydrochloric acid, nitric acid and sulfuric acid, and the concentration of the inorganic acid solution is 10-40 wt%, preferably 15-30 wt%.

[0019] The liquid-to-solid ratio of the pretreatment is 4-10; preferably 4-8.

[0020] The pretreatment temperature is 30℃-90℃, preferably 40℃-80℃.

[0021] The pretreatment time is 1-10 hours, preferably 2-6 hours.

[0022] In the above technical solution, the molar ratios of aluminum source, silicon source, template agent, and water in the mother liquor are as follows, wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2:

[0023] SiO2 / Al2O3 = (150-450):1, preferably (200-400):1; and / or,

[0024] Template agent / SiO2 = (0.1-0.5):1, preferably (0.2-0.4):1; and / or,

[0025] H2O / SiO2 = (5-50):1, preferably (10-30):1; and / or,

[0026] The mass ratios of the seed crystals and silicon source in the mother liquor are as follows, wherein the silicon source is SiO2:

[0027] Seed / SiO2 = (0.01-0.1):1.

[0028] In the above technical solution, the aluminum source is selected from at least one of aluminum isopropoxide, sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0029] The silicon source is selected from at least one of tetraethyl orthosilicate, tetrapropyl orthosilicate, isopropyl orthosilicate, tetrabutyl orthosilicate, silica sol, water glass, and silica.

[0030] The template agent is selected from at least one of diethylamine, n-propylamine, n-butylamine, tetrapropylammonium hydroxide, and ethanolamine.

[0031] In the above technical solution, the crystallization includes first crystallizing at a high temperature of 120℃-160℃ for 6-12 hours; and then crystallizing at a low temperature of 50℃-100℃ for 24-48 hours.

[0032] In the above technical solution, the separation before hydrothermal treatment includes solid-liquid separation of the feed liquid and washing with water until the pH value of the supernatant is <8.

[0033] The surfactant is sodium dodecylbenzenesulfonate.

[0034] The concentration of the surfactant is 0.4 g / L to 2.0 g / L.

[0035] In the above technical solution, the organic acid solution is at least one of oxalic acid, citric acid and tartaric acid, and the concentration of the organic acid is 0.01-1.0 mol / L.

[0036] The liquid-to-solid weight ratio of the surfactant-containing organic acid solution to the molecular sieve is 1-10.

[0037] The hydrothermal treatment conditions are: hydrothermal temperature 60℃-150℃, and treatment time 1-12h.

[0038] The drying, calcination, and optional exchange following the hydrothermal treatment are all standard procedures in the prior art.

[0039] The calcination temperature after hydrothermal treatment is generally between 350 and 650°C, and the calcination time is between 8 and 48 hours. For example, calcination at 550°C for 12 hours.

[0040] The third objective of this invention is to provide an application for the aforementioned nano-sized ZSM-5 molecular sieve in the alkylation reaction of ethylbenzene and ethylene to produce p-diethylbenzene. The reaction conditions are: atmospheric pressure, reaction temperature of 300℃-450℃, molar ratio of ethylbenzene to ethylene of 1-10, and ethylbenzene mass hourly space velocity of 1-10 h⁻¹. -1 .

[0041] The beneficial effects of this invention are:

[0042] The nanoscale ZSM-5 molecular sieve prepared by this invention has excellent catalytic activity for ethylbenzene alkylation and can significantly improve the selectivity of the target product for diethylbenzene (>98%). Furthermore, the molecular sieve catalyst has good catalytic stability. Attached Figure Description

[0043] Figure 1 The XRD diffraction pattern obtained by characterizing the crystal phase structure of the nanoscale ZSM-5 molecular sieve obtained in Example 1 is shown.

[0044] Figure 1 The peaks at 2θ = 7.7°, 8.6°, 22.8°, 23.1°, and 23.8° of the nanoscale ZSM-5 molecules obtained in Example 1 are typical diffraction characteristic peaks of ZSM-5 molecular sieve.

[0045] Figure 2 The image shows a scanning electron microscope (SEM) image of the nanoscale ZSM-5 molecular sieve obtained in Example 1.

[0046] Figure 3 The image is a scanning electron microscope (SEM) image of the ZSM-5 molecular sieve obtained in Comparative Example 1.

[0047] Figure 2 The nanoscale ZSM-5 molecular sieve obtained in Example 1 is spherical with a particle size between 100-250 nm, distinct intergranular gaps, and high dispersion.

[0048] Figure 3 The results indicate that the ZSM-5 molecular sieve in the comparative example is elongated, with a particle size between 500-1000 nm, and the crystals are in an aggregated state with low dispersion. Detailed Implementation

[0049] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0050] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0051] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0052] Reagent source: All reagents are commercially available.

[0053] In the following examples, unless otherwise stated, all water used was deionized water, and all chemical reagents used were of analytical grade. The silica sol was a silica sol with a silica concentration of 40% by weight, an average particle size of 15 nanometers, and a pH of 8-9. The silica content in the solid particles of the silica was >99.9% by weight.

[0054] Example 1

[0055] First, weigh 30 grams of 25% nitric acid solution, then add 5 grams of ZSM-5 (SiO2 / Al2O3=150) seed crystals, stir at 60℃ for 6 hours, then filter, wash, dry and set aside for use.

[0056] Prepare the raw material slurry according to the following molar ratio: SiO2:Al2O3:template:H2O=1:0.005:0.40:30. Weigh 1.0 g of aluminum sulfate and dissolve it in 50 mL of deionized water to form a solution. Then add 98.0 g of tetrapropylammonium hydroxide solution (25%) as a template agent to the solution and mix thoroughly to prepare solution A. Then weigh 64.3 g of tetraethyl orthosilicate and add it to solution A and mix thoroughly to obtain mother liquor B. Stir and age the mother liquor B at room temperature for 1.5 hours. Then weigh 0.25 g of the seed crystals obtained in the first step and add them to mother liquor B. Continue stirring and aging for another 1.5 hours. Transfer the material to a stainless steel reactor, seal the reactor, and heat it to 150°C. Crystallize under this hydrothermal condition for 12 hours, and then continue crystallizing the reactor at 80°C for 48 hours. The product was centrifuged and washed with water until the pH of the supernatant was <8. The product was then transferred to an oven and dried at 120°C for 6 hours. The sample was then placed in a sodium dodecylbenzenesulfonate-citric acid solution (sodium dodecylbenzenesulfonate concentration: 0.8 g / L, citric acid concentration: 0.5 mol / L) with a liquid-to-solid ratio of 5:1. The solution was sealed in a reaction vessel and treated at 120°C for 4 hours. The nano-sized ZSM-5 molecular sieve sample was then separated, dried, and transferred to a muffle furnace and calcined at 550°C in air for 12 hours.

[0057] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was subjected to physical adsorption analysis (Table 1). The specific operating conditions were: Micromeritics TriStar 3000 physical adsorption analyzer, analytical medium: N2, sample weight: 0.25 g.

[0058] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was characterized for its crystal phase structure. Figure 1 Analysis was performed using a Rigaku Ultima IV X-ray powder diffractometer (Japan). A CuKα ray source was used. XRD diffraction patterns were obtained by scanning and recording under the following conditions: nickel filter, diffraction angle 2θ scanning range 5-50°, operating voltage 35KV, current 25mA, and scanning speed 10° / min.

[0059] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was analyzed by scanning electron microscopy. Figure 2 The analysis was performed using a ThermoFisher Nova NanoSEM 450 analyzer. High vacuum mode resolution: 1.0 nm@15 kV, 1.6 nm@1 kV.

[0060] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was subjected to pyridine infrared analysis (Table 2). A Thermo Fisher Scientific Nicolet 5700 Fourier transform infrared spectrometer was used. Wavenumber range: 4000-400 cm⁻¹ -1 Resolution: 0.125cm -1 Molecular sieve sample slices (13 mg, 13 mm in diameter) were placed in an infrared absorption cell with CaF2 as the window, pretreated at 400 °C under vacuum for 2 h, cooled to 200 °C to adsorb pyridine for 0.5 h, and after adsorption equilibrium, desorption was performed by heating, and the spectra were taken at 300 °C.

[0061] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was subjected to bulk and surface silicon-to-aluminum ratio analysis (Table 3). Bulk silicon-to-aluminum ratio measurements were performed on a Thermo IRIS XSP inductively coupled plasma atomic emission spectrometer. Surface silicon-to-aluminum ratio measurements were performed on a Kratos Axis DLD X-ray photoelectron spectrometer.

[0062] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was loaded into a laboratory pulsed reaction apparatus for the pyrolysis of triisopropylbenzene (Table 4). The specific reaction conditions were as follows: raw material: triisopropylbenzene, reaction temperature: 380℃, injection volume: 0.2 μL, catalyst loading: 0.05 g. Chromatography was performed using FFAP capillary column analysis and FID detection.

[0063] The nanoscale ZSM-5 molecular sieve obtained in Example 1 was loaded into a micro fixed-bed reactor for ethylbenzene alkylation reaction (Table 5). The specific reaction conditions were as follows: feedstock: ethylbenzene / ethylene, reaction temperature: 380℃, ethylbenzene to ethylene feed molar ratio: 4, ethylbenzene mass hourly space velocity: 6 h⁻¹. -1 Chromatography was performed using a PLOT / U column and FID detection.

[0064] Example 2

[0065] First, weigh 30 grams of 25% nitric acid solution, then add 5 grams of ZSM-5 (SiO2 / Al2O3=150) seed crystals, stir at 60℃ for 6 hours, then filter, wash, dry and set aside for use.

[0066] Prepare the raw material slurry according to the following molar ratio: SiO2:Al2O3:template:H2O=1:0.004:0.35:30. Weigh 0.4 g of sodium aluminate and dissolve it in 50 mL of deionized water to form a solution. Then add 114.0 g of tetrapropylammonium hydroxide solution (25%) as a template agent to the solution and mix thoroughly to prepare solution A. Then weigh 60 g of silica sol (40%) and add it to solution A and mix thoroughly to obtain mother liquor B. Stir and age the mother liquor at room temperature for 1.5 hours. Then weigh 0.5 g of the seed crystals obtained in the first step and add them to mother liquor B. Continue stirring and aging for another 1.5 hours. Transfer the material to a stainless steel reactor, seal the reactor, and heat it to 160°C. Crystallize under this hydrothermal condition for 10 hours, and then continue crystallizing the reactor at 90°C for 48 hours. The product was centrifuged and washed with water until the pH of the supernatant was <8. The product was then transferred to an oven and dried at 120°C for 6 hours. The sample was then placed in a sodium dodecylbenzenesulfonate-oxalic acid solution (sodium dodecylbenzenesulfonate concentration: 0.8 g / L, oxalic acid concentration: 0.3 mol / L) with a liquid-to-solid ratio of 5:1. The solution was sealed in a reactor and treated at 100°C for 4 hours. The molecular sieve sample was then subjected to solid-liquid separation, dried, and transferred to a muffle furnace for calcination in air at 550°C for 12 hours. The calcined molecular sieve was then mixed thoroughly with a 0.1 M ammonium nitrate solution at a solid-liquid ratio of 1:5. Ion exchange was performed at 60°C for 2 hours, and the process was repeated three times after solid-liquid separation. Finally, the mixture was dried and calcined to obtain the hydrogen-form molecular sieve catalyst sample.

[0067] The molecular sieve obtained in Example 2 was subjected to physical adsorption analysis (Table 1). The specific operating conditions were the same as in Example 1.

[0068] The molecular sieve obtained in Example 2 was subjected to pyridine infrared analysis (Table 2). The specific operating conditions were the same as in Example 1.

[0069] The molecular sieve obtained in Example 2 was subjected to bulk and surface silicon-to-aluminum ratio analysis (Table 3), with the specific operating conditions being the same as in Example 1.

[0070] The molecular sieve obtained in Example 2 was loaded into a laboratory pulse reaction apparatus for the cleavage reaction of triisopropylbenzene (Table 4), and the specific operating conditions were the same as in Example 1.

[0071] The molecular sieve obtained in Example 2 was loaded into a micro fixed-bed reactor for ethylbenzene alkylation reaction (Table 5), and the specific operating conditions were the same as in Example 1.

[0072] Example 3

[0073] First, weigh 40 grams of 30% hydrochloric acid solution, then add 4 grams of ZSM-5 (SiO2 / Al2O3=150) seed crystals, stir at 60℃ for 6 hours, then filter, wash, dry and set aside for use.

[0074] Prepare the raw material slurry according to the following molar ratio: SiO2:Al2O3:template:H2O=1:0.003:0.35:30. Weigh 0.3 g of sodium aluminate and dissolve it in 120 mL of deionized water to form a solution. Then add 114.0 g of tetrapropylammonium hydroxide solution (25%) as a template agent to the solution and mix thoroughly to prepare solution A. Then add 24 g of silica to solution A and mix thoroughly to obtain mother liquor B. Stir and age the mother liquor at room temperature for 1.5 hours. Then weigh 0.5 g of the seed crystals obtained in the first step and add them to mother liquor B. Continue stirring and aging for another 1.5 hours. Transfer the material to a stainless steel reactor, seal the reactor, and heat it to 160°C. Crystallize under this hydrothermal condition for 10 hours, and then continue crystallizing the reactor at 90°C for 48 hours. The product was centrifuged and washed with water until the pH of the supernatant was <8. The product was then transferred to an oven and dried at 120°C for 6 hours. The sample was then placed in a sodium dodecylbenzenesulfonate-oxalic acid solution (sodium dodecylbenzenesulfonate concentration: 0.8 g / L, oxalic acid concentration: 0.3 mol / L) with a liquid-to-solid ratio of 5:1. The solution was sealed in a reactor and treated at 100°C for 4 hours. The molecular sieve sample was then subjected to solid-liquid separation, dried, and transferred to a muffle furnace for calcination in air at 550°C for 12 hours. The calcined molecular sieve was then mixed thoroughly with a 0.1 M ammonium nitrate solution at a solid-liquid ratio of 1:5. Ion exchange was performed at 60°C for 2 hours, and the process was repeated three times after solid-liquid separation. Finally, the mixture was dried and calcined to obtain the hydrogen-form molecular sieve catalyst sample.

[0075] The molecular sieve obtained in Example 3 was subjected to physical adsorption analysis (Table 1). The specific operating conditions were the same as in Example 1.

[0076] The molecular sieve obtained in Example 3 was subjected to pyridine infrared analysis (Table 2). The specific operating conditions were the same as in Example 1.

[0077] The molecular sieve obtained in Example 3 was subjected to bulk and surface silicon-to-aluminum ratio analysis (Table 3), with the specific operating conditions being the same as in Example 1.

[0078] The molecular sieve obtained in Example 3 was loaded into a laboratory pulse reaction apparatus for the pyrolysis reaction of triisopropylbenzene (Table 4), and the specific operating conditions were the same as in Example 1.

[0079] The molecular sieve obtained in Example 3 was loaded into a micro fixed-bed reactor for ethylbenzene alkylation reaction (Table 5), and the specific operating conditions were the same as in Example 1.

[0080] Comparative Example 1

[0081] Prepare the raw material slurry according to the following molar ratio: SiO2:Al2O3:template agent:H2O=1:0.005:0.40:30. Weigh 1.0 g of aluminum sulfate and dissolve it in 50 mL of deionized water to form a solution. Then add 98.0 g of tetrapropylammonium hydroxide solution (25%) as a template agent to this solution and mix thoroughly to prepare solution A. Then weigh 64.3 g of tetraethyl orthosilicate and add it to solution A and mix thoroughly to obtain mother liquor B. Stir and age the solution at room temperature for 1.5 hours. Transfer the material to a stainless steel reactor, seal the reactor, and heat it to 160℃. Crystallize the solution under hydrothermal conditions for 72 hours. Centrifuge the product and wash it with water until the pH of the supernatant is <8. Transfer the product to an oven and dry it at 120℃ for 6 hours. Then transfer the sample to a muffle furnace and calcine it in air at 550℃ for 12 hours. The samples were subjected to conventional steam dealuminization and passivation treatment for 2 hours (100% steam, 550℃, mass hourly space velocity: 1.5h). -1 Then the sample was dried and calcined in air at 550°C for 12 hours.

[0082] The molecular sieve obtained in Comparative Example 1 was subjected to physical adsorption analysis (Table 1). The specific operating conditions were the same as in Example 1.

[0083] The molecular sieve obtained in Comparative Example 1 was analyzed by scanning electron microscopy. Figure 3 The specific operating conditions are the same as in Example 1.

[0084] The molecular sieve obtained in Comparative Example 1 was subjected to pyridine infrared analysis (Table 2). The specific operating conditions were the same as in Example 1.

[0085] The molecular sieve obtained in Comparative Example 1 was subjected to bulk and surface silicon-to-aluminum ratio analysis (Table 3), with the specific operating conditions being the same as in Example 1.

[0086] The molecular sieve obtained in Comparative Example 1 was loaded into a laboratory pulse reaction apparatus for the cleavage reaction of triisopropylbenzene (Table 4), and the specific operating conditions were the same as in Example 1.

[0087] The molecular sieve obtained in Comparative Example 1 was loaded into a micro fixed-bed reactor for ethylbenzene alkylation reaction (Table 5), with the specific operating conditions being the same as in Example 1.

[0088] Table 1

[0089]

[0090] Table 2

[0091]

[0092] Table 3

[0093]

[0094] Table 4

[0095]

[0096] Table 5

[0097]

[0098] As can be seen from the reaction data in Table 5, the nanoscale ZSM-5 molecular sieve sample prepared by the present invention not only has high selectivity for diethylbenzene (>98%), but also maintains a high ethylbenzene conversion rate after 72 hours, indicating that the molecular sieve of the present invention has good stability.

[0099] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A nanoscale ZSM-5 molecular sieve for the alkylation of ethylbenzene to produce p-diethylbenzene, wherein the nanoscale ZSM-5 molecular sieve has an MFI-type framework structure; the bulk silica-alumina ratio of the nanoscale ZSM-5 molecular sieve is between 90 and 300, and the surface silica-alumina ratio is between 350 and 600; the nanoscale ZSM-5 molecular sieve includes L-acid centers and Brønsted acid centers, wherein the molar ratio of L-acid centers to Brønsted acid centers is 8-16.

2. The nanoscale ZSM-5 molecular sieve according to claim 1, characterized in that, The nanoscale ZSM-5 molecular sieve has a particle size between 100-250 nm; and / or, The nanoscale ZSM-5 molecular sieve has a specific surface area of ​​350-450 m². 2 / g; and / or, The specific surface area of ​​the outer surface of the nanoscale ZSM-5 molecular sieve is 20%-30% of the total specific surface area of ​​the nanoscale ZSM-5 molecular sieve.

3. The nanoscale ZSM-5 molecular sieve according to claim 2, characterized in that, The nanoscale ZSM-5 molecular sieve has a particle size of 100-200 nm; and / or, The nanoscale ZSM-5 molecular sieve has a specific surface area of ​​380-450 m². 2 / g.

4. The nanoscale ZSM-5 molecular sieve according to any one of claims 1-3, characterized in that, The nanoscale ZSM-5 molecular sieve has a composite pore structure of mesopores and micropores, with an average pore size of 3.5 nm to 5.5 nm. The mesopores account for 50%-70%, and the micropores have a volume of 0.10-0.20 cm³. 3 / g, with a mesopore volume of 0.25-0.45cm³. 3 / g.

5. The nanoscale ZSM-5 molecular sieve according to any one of claims 1-3, characterized in that, Using triisopropylbenzene pyrolysis as a probe reaction, the conversion rate of triisopropylbenzene was measured to be ≤2%, and the acid content on the outer surface of the nano-sized ZSM-5 molecular sieve was ≤7.4 nmol / m 2 .

6. A method for preparing the nanoscale ZSM-5 molecular sieve according to any one of claims 1 to 5, comprising: ZSM-5 seed crystals were treated with an inorganic acid solution; an aluminum source, silicon source, template agent, seed crystals, and water were mixed to form a mother liquor; After crystallization, nano-sized ZSM-5 molecular sieves were obtained by hydrothermal treatment with an organic acid solution containing surfactants. The inorganic acid is selected from at least one of hydrochloric acid, nitric acid, and sulfuric acid; The organic acid solution is an aqueous solution of at least one of oxalic acid, citric acid, and tartaric acid.

7. The preparation method according to claim 6, characterized in that, The concentration of the inorganic acid solution is 10-40 wt%; and / or, The liquid-to-solid ratio of the inorganic acid solution treatment is 4-10; and / or, The inorganic acid solution treatment temperature is 30℃-90℃; and / or, The inorganic acid solution treatment time is 1-10 hours.

8. The preparation method according to claim 7, characterized in that, The concentration of the inorganic acid solution is 15-30 wt%; and / or, The liquid-to-solid ratio of the inorganic acid solution treatment is 4-8; and / or, The inorganic acid solution treatment temperature is 40℃-80℃; and / or, The inorganic acid solution treatment time is 2-6 hours.

9. The preparation method according to claim 6, characterized in that, The molar ratios of aluminum source, silicon source, template agent, and water in the mother liquor are as follows, wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2: SiO2 / Al2O3 = (150-450):1; and / or, Template agent / SiO2 = (0.1-0.5):1; and / or, H2O / SiO2 = (5-50):1; and / or, The mass ratios of the seed crystals and silicon source in the mother liquor are as follows, wherein the silicon source is SiO2: Seed crystal / SiO2 = (0.01-0.1):

1.

10. The preparation method according to claim 9, characterized in that, The molar ratios of aluminum source, silicon source, template agent, and water in the mother liquor are as follows, wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2: SiO2 / Al2O3 = (200-400):1; and / or, Template agent / SiO2 = (0.2-0.4):1; and / or, The mass ratios of the seed crystals and silicon source in the mother liquor are as follows, wherein the silicon source is SiO2: H2O / SiO2 = (10-30):

1.

11. The preparation method according to claim 6, characterized in that, The aluminum source is selected from at least one of aluminum isopropoxide, sodium aluminate, aluminum hydroxide, aluminum sulfate, aluminum nitrate, and aluminum chloride; and / or, The silicon source is selected from at least one of tetraethyl orthosilicate, n-propyl orthosilicate, isopropyl orthosilicate, n-butyl orthosilicate, silica sol, water glass, and silica; and / or, The template agent is selected from at least one of diethylamine, n-propylamine, n-butylamine, tetrapropylammonium hydroxide, and ethanolamine.

12. The preparation method according to claim 6, characterized in that, The crystallization process includes first crystallizing at a high temperature of 120℃-160℃ for 6-12 hours, and then crystallizing at a low temperature of 50℃-100℃ for 24-48 hours.

13. The preparation method according to claim 6, characterized in that, In the aforementioned hydrothermal treatment: The surfactant is sodium dodecylbenzenesulfonate; and / or, The surfactant concentration in the organic acid solution containing surfactant is 0.4-2.0 g / L; and / or, The concentration of the organic acid in the surfactant-containing organic acid solution is 0.01-1.0 mol / L; and / or, The liquid-to-solid weight ratio of the surfactant-containing organic acid solution to the molecular sieve is 1-10; and / or, The hydrothermal treatment conditions are: hydrothermal temperature 60℃-150℃; and / or, treatment time 1-12h.

14. The preparation method according to claim 13, characterized in that, In the aforementioned hydrothermal treatment: The surfactant concentration in the organic acid solution containing surfactant is 0.6-1.5 g / L; and / or, The concentration of the organic acid in the surfactant-containing organic acid solution is 0.05-0.5 mol / L; and / or, The liquid-to-solid weight ratio of the surfactant-containing organic acid solution to the molecular sieve is 1-6; and / or, The hydrothermal treatment conditions are: hydrothermal temperature of 60-110℃; and / or, treatment time of 5-10h.

15. The preparation method according to claim 6, characterized in that, The steps preceding the hydrothermal treatment include separation and drying. The separation includes solid-liquid separation of the feed liquid, washing with water until the pH of the supernatant is <8; and / or, The hydrothermal treatment is followed by post-processing steps including solid-liquid separation, drying, calcination, and optional exchange to obtain nanoscale ZSM-5 molecular sieves.

16. The application of a nano-sized ZSM-5 molecular sieve according to any one of claims 1 to 5 or a nano-sized ZSM-5 molecular sieve prepared by any one of claims 6 to 15, for the alkylation reaction of ethylbenzene with ethylene to produce p-diethylbenzene.

17. The application of the nanoscale ZSM-5 molecular sieve according to claim 16, characterized in that, The reaction conditions were: atmospheric pressure, reaction temperature 300℃-450℃, molar ratio of ethylbenzene to ethylene 1-10, and ethylbenzene mass hourly space velocity (HHSV) 1-10 h⁻¹. -1 .

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