A polymer template agent, a stepwise porous Silicalite-1 molecular sieve and its green preparation method

Abstract

This invention relates to the field of molecular sieve technology, and more specifically to a polymer template agent for preparing ladder-pore Silicalite-1 molecular sieves, the ladder-pore Silicalite-1 molecular sieve, and a green preparation method thereof. By employing a polymer template agent with a special chemical structure, the synthesized Silicalite-1 molecular sieve contains both micropores and mesopores, forming a ladder-pore structure, effectively solving the problems of low mass transfer efficiency and poor accessibility of active sites caused by the micropore structure of conventional Silicalite-1 molecular sieves. The polymer template agent can be completely removed by centrifugation, eliminating the need for high-temperature calcination of the synthesized Silicalite-1 molecular sieve, thus saving energy and avoiding environmental pollution caused by high-temperature calcination. The mesopore size of the ladder-pore Silicalite-1 molecular sieve is concentrated in the range of 10–30 nm, and it has a higher specific surface area of ​​600–700 m² compared to conventional Silicalite-1 molecular sieves. 2 / g and pore volume 1.00~1.60cm³ 3 / g, significantly improving the performance of Silicalite-1 molecular sieves. This invention also substantially reduces the production cost of stepwise porous Silicalite-1 molecular sieves, making it worthy of widespread industrial application.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, and more specifically to a polymer template agent for preparing a stepwise porous Silicalite-1 molecular sieve, a stepwise porous Silicalite-1 molecular sieve, and a green preparation method thereof. Background Technology

[0002] Silicalite-1 is an MFI-type molecular sieve with a special ten-membered ring channel (structure shown in the appendix). Figure 1 Silicalite-1 molecular sieves, containing no Al species in their structure, are pure silica molecular sieves. They are widely used in gas separation, catalysis, and fine chemical industries. However, in industrial applications, the presence of small micropores in the Silicalite-1 molecular sieve structure strongly affects mass transfer of reactants, hindering its widespread application. Cascade-pore Silicalite-1 molecular sieves with micro / mesopore, micro / macropore, and micro / meso / macropore combinations can effectively overcome the limitations of their small micropores.

[0003] The template method is a commonly used and effective approach for preparing stepwise porous Silicalite-1 molecular sieves. Cationic ammonium templates are typically used in this method, but they are expensive, usually require high-temperature calcination for removal, and their structure is easily destroyed during preparation, making them non-recyclable and causing environmental pollution. Therefore, developing low-cost, environmentally friendly, efficient, and recyclable templates for the synthesis of stepwise porous Silicalite-1 molecular sieves is urgently needed. Summary of the Invention

[0004] Therefore, there is a need to provide a template agent for Silicate-1 molecular sieves with stepped pores, Silicate-1 molecular sieves with stepped pores, and a green preparation method thereof, in order to solve the problems of high price, low efficiency, non-recyclability and easy environmental pollution of conventional template agents.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a polymeric template agent PPNOH with a number-average molecular weight of 60,000–80,000 g / mol, having the following chemical structural formula:

[0006]

[0007] Where n is an integer greater than 1.

[0008] In a second aspect, the present invention provides a method for preparing the polymer template agent PPNOH as described in the first aspect, comprising the following steps:

[0009] Isopropylacrylamide and azobisisobutyronitrile were added to a polymerization tube containing anhydrous tetrahydrofuran and reacted in an oil bath under nitrogen protection. After cooling, the solvent was evaporated, dissolved in acetone, and then added dropwise to n-hexane. The mixture was filtered and dried under vacuum to obtain poly-N-isopropylacrylamide.

[0010] The poly(N-isopropylacrylamide) was dissolved in diethyl ether, and bromoethane was added. The reaction was carried out to obtain a polyquaternary ammonium hydrohalate solution.

[0011] The polyquaternary ammonium hydrohalate was treated with a strongly basic anion exchange resin and filtered to obtain a polyquaternary ammonium alkaline solution.

[0012] The polyquaternary ammonium alkali solution was cooled in a water bath, neutralized with acid, distilled under reduced pressure, cooled again, extracted, separated, and the volatile components were removed under vacuum to obtain the polymer template agent PPNOH.

[0013] In a preferred embodiment of the present invention, the molar ratio of isopropylacrylamide, azobisisobutyronitrile and anhydrous tetrahydrofuran is (25-40): (0.02-0.06): (300-450).

[0014] In a preferred embodiment of the present invention, the oil bath reaction temperature is 70-85°C, the oil bath reaction time is 24-50 h, the vacuum drying temperature is 25-35°C, and the vacuum drying time is 24-48 h.

[0015] In a preferred embodiment of the present invention, the amount of bromoethane used is 300-600 mmol, the reaction temperature is 50-65°C, and the reaction time is 30-50 h.

[0016] Thirdly, the present invention provides a green preparation method for a stepwise porous Silicalite-1 molecular sieve, comprising the following steps:

[0017] Water and the polymer template agent described in the first aspect are mixed evenly, and a silicon source is added in batches to obtain a gel, such that the molar ratio of H2O, SiO2 and the polymer template agent in the gel is (20-30):1:(0.0005-0.0012);

[0018] The above gel was aged at 50°C for 2-4 hours and then placed in a reaction vessel for crystallization reaction. The crystallization reaction temperature was 160-180°C and the crystallization reaction time was 72-140 hours to obtain the crystallized product.

[0019] The crystallized product was centrifuged and dried to obtain the stepwise porous Silicalite-1 molecular sieve.

[0020] In a preferred embodiment of the present invention, the aluminum source is selected from one or more of sodium aluminate, aluminum sulfate, and aluminum isopropoxide.

[0021] In a preferred embodiment of the present invention, the silicon source is selected from one or more of tetraethyl orthosilicate, silica sol, industrial silica gel, and fumed silica.

[0022] In a preferred embodiment of the present invention, the crystallized product is centrifuged at a speed of 5000-8000 rpm, a processing temperature of 20-35°C, and a processing time of 30-60 min.

[0023] Fourthly, the present invention provides a stepwise porous Silicalite-1 molecular sieve prepared by the green preparation method described in the third aspect, wherein the mesopore size of the stepwise porous Silicalite-1 molecular sieve is concentrated in the range of 10–30 nm, and the specific surface area is 600–700 m². 2 / g, pore volume 1.00~1.60cm³ 3 / g.

[0024] Unlike existing technologies, the above-mentioned technical solution utilizes the polymer template agent PPNOH with a special chemical structure, enabling the synthesized Silicalite-1 molecular sieve to contain both micropores and mesopores, forming a ladder-pore structure. This effectively solves the problems of low mass transfer efficiency and poor accessibility of active sites caused by the micropore structure of conventional Silicalite-1 molecular sieves. Furthermore, since the polymer template agent PPNOH provided by this invention can be completely removed by centrifugation, there is no need for high-temperature calcination of the synthesized Silicalite-1 molecular sieve, saving energy and avoiding environmental pollution caused by high-temperature calcination, making it highly efficient, green, and environmentally friendly. Moreover, the mesopore size of the ladder-pore Silicalite-1 molecular sieve prepared using the polymer template agent provided by this invention is concentrated in the range of 10–30 nm, resulting in a higher specific surface area of ​​600–700 m² compared to conventional Silicalite-1 molecular sieves. 2 / g and pore volume 1.00~1.60cm³ 3 / g, significantly improving the performance of Silicalite-1 molecular sieves. Furthermore, since the polymer template agent provided by this invention can be removed by centrifugation and repeatedly recycled for the preparation of stepwise porous Silicalite-1 molecular sieves, the production cost of stepwise porous Silicalite-1 molecular sieves is greatly reduced, making it worthy of industrial promotion and application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of Silicalite-1 molecular sieve;

[0026] Figure 2 The XRD diffraction pattern of the cascade-pore Silicalite-1 molecular sieve prepared in Example 1 of this invention;

[0027] Figure 3 This is a SEM image of the cascade-pore Silicalite-1 molecular sieve prepared in Example 1 of this invention;

[0028] Figure 4 The XRD diffraction pattern of the sample prepared in Comparative Example 1 of this invention;

[0029] Figure 5 The XRD diffraction pattern of the sample prepared in Comparative Example 2 of this invention;

[0030] Figure 6 This is the XRD diffraction pattern of the sample prepared in Comparative Example 3 of this invention. Detailed Implementation

[0031] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0032] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0033] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0034] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0035] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0036] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0037] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0038] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0039] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0040] The preparation of stepwise porous Silicalite-1 molecular sieves typically begins with hydrothermal crystallization at high temperatures (140–180°C) using organic amines, inorganic amines, or alcohols as templates. After crystallization, the temperature is lowered to room temperature to obtain the molecular sieve, followed by calcination at high temperatures to remove the template. The templates used in these processes generally suffer from high costs, structural damage during high-temperature calcination leading to non-recyclability, and the emission of harmful substances. Through long-term theoretical research and practical exploration, the inventors discovered a polymeric template, PPNOH, which can guide the formation of the Silicalite-1 molecular sieve structure at the molecular sieve synthesis temperature. This template can be used as a template for the preparation of Silicalite-1 molecular sieves. Furthermore, this template can be removed at room temperature by centrifugation and can be recycled. Therefore, the template of this application can be removed from the molecular sieve channels simply by centrifugation, making the removal process simple. Moreover, the removed template can be recycled, effectively reducing the preparation cost and energy consumption of stepwise porous Silicalite-1 molecular sieves.

[0041] In this invention, unless otherwise specified, all reagents and raw materials used are commercially available.

[0042] In this invention, unless otherwise specified, the number-average molecular weight of the polymer template agent is determined using gel permeation chromatography. The specific test conditions and methods are as follows:

[0043] The tests were performed using a liquid chromatograph (Shimadzu, Japan) with a gel permeation column of model LC-10AD / SPD-10A and model Shodex KF-803. Before the test, 4 mg of polymer template agent was dissolved in 2 mL of tetrahydrofuran solution, filtered through a 2 μm filter membrane, and 20 μL of the above sample was taken for molecular weight distribution analysis of polymer template agent in the liquid chromatograph. The test temperature was 30 °C, chromatographically pure TCM was used as solvent, the solvent flow rate was 1 mL / min, and polystyrene was used as standard sample.

[0044] In this invention, unless otherwise specified, the mesopore size distribution of the step-pore Silicalite-1 molecular sieve is measured by physical adsorption. The specific test conditions and methods are as follows:

[0045] The physical adsorption analyzer (Micromeritics 2020, USA) was used for testing. Before testing, the samples were pretreated under vacuum at 150℃ for 12 hours, and then static adsorption was performed at -196℃ using Ar as the adsorbate. The adsorption-desorption curves of the samples were measured. The mesopore size distribution of the samples was obtained using the Barrett-Joyner-Halenda (BJH) model.

[0046] In this invention, unless otherwise specified, the specific surface area of ​​the Silicalite-1 molecular sieve with a stepped pore size is measured by physical adsorption. The specific test conditions and methods are as follows:

[0047] The physical adsorption analyzer (Micromeritics 2020, USA) was used for testing. Before testing, the samples were pretreated under vacuum at 150℃ for 12 hours, and then static adsorption was performed at -196℃ using Ar as the adsorbate. The adsorption-desorption curves of the samples were measured. Adsorption-desorption isotherms were plotted based on the Brunauer-Emmet-Teller (BET) equation, and the linearity of the adsorption isotherms (0.05) was used to determine the adsorption-desorption curves. <P / P 0 The total specific surface area (<0.30) was calculated using the BET equation; the specific surface areas of micropores and mesopores were calculated using the t-plot method.

[0048] In this invention, unless otherwise specified, the pore volume of the ladder-pore Silicalite-1 molecular sieve is measured by physical adsorption. The specific test conditions and methods are as follows:

[0049] The physical adsorption analyzer (Micromeritics 2020, USA) was used for testing. Before testing, the samples were pretreated under vacuum at 150℃ for 12 hours, and then static adsorption was performed at -196℃ using Ar as the adsorbate. The adsorption-desorption curves of the samples were measured. The pore volumes of micropores and mesopores were calculated using the t-plot method.

[0050] In this invention, unless otherwise specified, crystallinity is measured using X-ray diffraction (XRD), and the specific test conditions are as follows:

[0051] The phase structure of the synthesized molecular sieve samples was analyzed using a Rigaku D-Max 2550 X-ray diffractometer (Rigaku, Japan). The test conditions were: Cu target, Kα rays. The tube voltage was 40kV and the tube current was 40mA. The wide-angle scanning range was 2θ = 5–50°, and the scanning rate was 7° / min. The relative crystallinity described in the embodiments of this application was determined according to the ASTM D3906-03 (2013) standard. Spectra of the obtained product and the Silicalite-1 molecular sieve standard were acquired at a scanning rate of 0.7° / min, with 2θ = 22.5–25°. The peak areas of the synthesized sample and the reference sample were integrated to calculate the peak areas. The ratio of the peak areas of the former to the latter was the relative crystallinity of the synthesized molecular sieve. The standard sample was Silicalite-1 molecular sieve produced by the Catalyst Factory of Nankai University, and its crystallinity was defined as 100%.

[0052] In this invention, unless otherwise specified, the SiO2 / Al2O3 ratio is measured using the ICP method, and the specific test conditions are as follows:

[0053] An OPTIMA 8000 inductively coupled plasma atomic emission spectrometer manufactured by PerkinElmer, USA, was used. First, 10 mg of the sample was dissolved in aqua regia solution, transferred to a microwave digester, heated to 200 °C, and maintained for 2 hours to ensure complete dissolution. The solution was then cooled to room temperature and diluted to volume in a volumetric flask. Next, a standard liquid for the target metal element was prepared as a reference standard to plot a standard curve. Then, argon gas was used as the carrier gas to test the sample. Finally, the concentration of the target metal element was obtained and recorded.

[0054] In this invention, unless otherwise specified, SEM is used to characterize the morphology of the molecular sieves, and the specific test conditions are as follows:

[0055] SEM characterization was performed using a Helios G4CX focused ion beam (FIB) dual-beam field emission electron microscope (Thermo Scientific, USA). A small amount of dried sample was dispersed in an ethanol solution and sonicated for 10 min to ensure uniform dispersion. A drop of the supernatant was then placed on a clean silicon wafer and placed in a 60°C oven for 10 min. Subsequently, gold was sputtered onto the wafer, and electron micrographs were obtained and analyzed.

[0056] Example 1

[0057] 25 mmol of isopropylacrylamide and 0.02 mmol of azobisisobutyronitrile were added to a polymerization tube containing 300 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 70 °C for 24 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, and the mixture was dissolved in a small amount of acetone. Then, the solution was added dropwise to n-hexane, filtered, and dried under vacuum at 30 °C for 48 h to obtain a white solid of poly-N-isopropylacrylamide. The white solid was dissolved in the organic solvent diethyl ether, and 300 mmol of n-propane bromide was added. The mixture was reacted at 50 °C for 30 h to obtain a solution of polyquaternary ammonium hydrohalide. The above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halide ions were detected in the liquid phase. The solution was then filtered to obtain a polyquaternary ammonium base solution. The polyquaternary ammonium base solution was neutralized with acid under room temperature water bath cooling, and the organic solvent was then distilled off under reduced pressure. The above liquid was cooled, extracted with diethyl ether, and the diethyl ether phase was removed by separation. Volatile components were removed under vacuum to obtain polyquaternary ammonium salt PPNOH. The number average molecular weight was measured to be 60,000 g / mol by gel permeation chromatography.

[0058] Example 2

[0059] 30 mmol of isopropylacrylamide and 0.03 mmol of azobisisobutyronitrile were added to a polymerization tube containing 350 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 75 °C for 30 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, and the mixture was dissolved in a small amount of acetone. Then, the solution was added dropwise to n-hexane, filtered, and dried under vacuum at 30 °C for 48 h to obtain a white solid of poly-N-isopropylacrylamide. The white solid was dissolved in the organic solvent diethyl ether, and 400 mmol of n-bromopropane was added. The mixture was reacted at 55 °C for 36 h to obtain a solution of polyquaternary ammonium hydrohalide. The above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halide ions were detected in the liquid phase. The solution was then filtered to obtain a polyquaternary ammonium base solution. The polyquaternary ammonium base solution was neutralized with acid under room temperature water bath cooling, and the organic solvent was then distilled off under reduced pressure. The above liquid was cooled, extracted with diethyl ether, and the diethyl ether phase was removed by separation. Volatile components were removed under vacuum to obtain polyquaternary ammonium salt PPNOH. The number average molecular weight was measured to be 65000 g / mol by gel permeation chromatography.

[0060] Example 3

[0061] 35 mmol of isopropylacrylamide and 0.04 mmol of azobisisobutyronitrile were added to a polymerization tube containing 400 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 75 °C for 40 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, and the mixture was dissolved in a small amount of acetone. Then, the solution was added dropwise to n-hexane, filtered, and dried under vacuum at 30 °C for 48 h to obtain a white solid of poly-N-isopropylacrylamide. The white solid was dissolved in the organic solvent diethyl ether, and 500 mmol of n-propane bromide was added. The mixture was reacted at 60 °C for 36 h to obtain a solution of polyquaternary ammonium hydrohalide. The above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halide ions were detected in the liquid phase. The solution was then filtered to obtain a polyquaternary ammonium base solution. The polyquaternary ammonium base solution was neutralized with acid under room temperature water bath cooling, and the organic solvent was then distilled off under reduced pressure. The above liquid was cooled, extracted with diethyl ether, and the diethyl ether phase was removed by separation. Volatile components were removed under vacuum to obtain polyquaternary ammonium salt PPNOH. The number average molecular weight was measured to be 70,000 g / mol by gel permeation chromatography.

[0062] Example 4

[0063] 38 mmol of isopropylacrylamide and 0.05 mmol of azobisisobutyronitrile were added to a polymerization tube containing 420 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 80 °C for 36 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, and the mixture was dissolved in a small amount of acetone. Then, the solution was added dropwise to n-hexane, filtered, and dried under vacuum at 30 °C for 48 h to obtain a white solid of poly-N-isopropylacrylamide. The white solid was dissolved in the organic solvent diethyl ether, and 550 mmol of n-propane bromide was added. The mixture was reacted at 65 °C for 40 h to obtain a solution of polyquaternary ammonium hydrohalide. The above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halide ions were detected in the liquid phase. The solution was then filtered to obtain a polyquaternary ammonium base solution. The polyquaternary ammonium base solution was neutralized with acid under room temperature water bath cooling, and the organic solvent was then distilled off under reduced pressure. The above liquid was cooled, extracted with diethyl ether, and the diethyl ether phase was removed by separation. Volatile components were removed under vacuum to obtain polyquaternary ammonium salt PPNOH. The number average molecular weight was measured to be 75000 g / mol by gel permeation chromatography.

[0064] Example 5

[0065] 40 mmol of isopropylacrylamide and 0.06 mmol of azobisisobutyronitrile were added to a polymerization tube containing 450 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 85 °C for 50 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, and the mixture was dissolved in a small amount of acetone. Then, the solution was added dropwise to n-hexane, filtered, and dried under vacuum at 30 °C for 48 h to obtain a white solid of poly-N-isopropylacrylamide. The white solid was dissolved in the organic solvent diethyl ether, and 600 mmol of n-propane bromide was added. The mixture was reacted at 65 °C for 50 h to obtain a solution of polyquaternary ammonium hydrohalide. The above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halide ions were detected in the liquid phase. The solution was then filtered to obtain a polyquaternary ammonium base solution. The polyquaternary ammonium base solution was neutralized with acid under room temperature water bath cooling, and the organic solvent was then distilled off under reduced pressure. The above liquid was cooled, extracted with diethyl ether, and the diethyl ether phase was removed by separation. Volatile components were removed under vacuum to obtain polyquaternary ammonium salt PPNOH. The number average molecular weight was measured to be 80,000 g / mol by gel chromatography.

[0066] Example 6

[0067] A stepwise porous Silicalite-1 molecular sieve is prepared by the following steps:

[0068] The sample was prepared by hydrothermal method using PPNOH, the polymer template agent prepared in Example 1, as the template agent.

[0069] Molecular sieve preparation by hydrothermal method: First, 1.07 g of PPNOH was added to 23.4 mL of deionized water and stirred for 0.5 h; then 2.15 g of fumed silica was slowly added to obtain a synthetic gel with a molar composition of 1 SiO2 / 0.0005 polymer / 30 H2O; after stirring at 50 °C for 3 h, the obtained gel was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner (50 mL) and placed in a homogeneous reactor at 100 rpm for crystallization at 160 °C for 120 h; after crystallization, sample A containing the polymer template agent PPNOH was obtained.

[0070] The template agent was removed by centrifugation of the above sample A, and a stepwise porous Silicalite-1 molecular sieve was obtained.

[0071] The above samples were placed in centrifuge tubes and centrifuged at 7500 rpm and 25°C for 45 min. The upper layer consisted of an aqueous solution of the polymer template agent PPNOH, and the lower layer consisted of Silicalite-1 molecular sieve. The Silicalite-1 molecular sieve was washed with deionized water until pH ≈ 7, and then dried at 105°C for 12 h to obtain a solid powder. The XRD diffraction pattern of the obtained solid powder is shown below. Figure 2 As shown, the phase of the product obtained by XRD analysis belongs to Silicalite-1 molecular sieve.

[0072] like Figure 3 As shown, SEM characterization of the morphology and structure of the product shows that it is composed of nanocrystals with a particle size of approximately 60 nm.

[0073] As shown in Table 1, the Ar adsorption-desorption results indicate that the mesopore size is concentrated at 10 nm, and the specific surface area is 628 m². 2 / g, pore volume is 1.16cm³ 3 / g.

[0074] Table 1. Silicalite-1 molecular sieves prepared in Example 1

[0075]

[0076] Example 7

[0077] A stepwise porous Silicalite-1 molecular sieve is prepared by the following steps:

[0078] The polymer template agent PPNOH removed by centrifugation during the previous preparation of the Silicalite-1 molecular sieve with stepped pores was used as the template agent.

[0079] The molar ratio and order of raw material addition were the same as in Example 6, and the polymer PPNOH obtained by centrifugation in Example 6 was used as a template agent. XRD analysis showed that the phase of the product belonged to Silicalite-1 molecular sieve. The Ar adsorption-desorption results of the stepwise porous Silicalite-1 molecular sieve obtained in this example showed that its mesopore size was concentrated at 10 nm, and its specific surface area was 619 m². 2 / g, pore volume is 1.09cm³ 3 / g.

[0080] The morphological structure of the product obtained in this embodiment can be characterized by SEM, as described in the following reference. Figure 3 .

[0081] Example 8

[0082] A stepwise porous Silicalite-1 molecular sieve is prepared by the following steps:

[0083] The sample was prepared by hydrothermal method using PPNOH, the polymer template agent prepared in Example 3, as the template agent.

[0084] Hydrothermal preparation of molecular sieves: The template agent prepared in Example 1 was used, and tetraethyl orthosilicate was used as the silicon source. The order of raw material addition was the same as in Example 6. The amount of addition was adjusted so that the molar ratio of the feed materials met the following conditions: 1SiO2 / 0.0008 polymer template agent PPNOH / 30H2O. After stirring at 50°C for 3 hours, the resulting gel was transferred to a stainless steel autoclave (50 mL) with a polytetrafluoroethylene liner and placed in a homogeneous reactor with a rotation speed of 100 rpm. The gel was crystallized at 170°C for 96 hours to obtain sample A.

[0085] The sample A was centrifuged to remove the polymer template agent PPNOH, and a sieve with a scalar pore size, Silicalite-1, was obtained.

[0086] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm and 25°C for 50 min to obtain an upper layer of PPNOH and a lower layer of Silicalite-1 molecular sieve. The Silicalite-1 molecular sieve was washed with deionized water until pH≈7 and then dried at 105°C for 12 h to obtain a solid powder. The XRD diffraction pattern of the solid powder obtained in this example can be referred to [reference needed]. Figure 2 XRD analysis revealed that the product belongs to the Silicalite-1 molecular sieve. Ar adsorption-desorption results showed that its mesopore size is concentrated at 20 nm, with a specific surface area of ​​640 m². 2 / g, pore volume is 1.28cm³ 3 / g.

[0087] Example 9

[0088] A stepwise porous Silicalite-1 molecular sieve is prepared by the following steps:

[0089] Samples were prepared using a hydrothermal method with PPNOH as the polymer template agent.

[0090] Molecular sieve preparation by hydrothermal method: The polymer template agent PPNOH prepared in Example 5 was used, and industrial silica gel and silica sol were used as silicon sources. The order of adding raw materials was the same as in Example 6. The amount of addition was adjusted so that the molar ratio of the feed materials met the following condition: 1SiO2 / 0.0012 polymer template agent PPNOH / 30H2O. After stirring at 50°C for 3 hours, the resulting gel was transferred to a 50mL stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 180°C for 72 hours to obtain sample A.

[0091] The sample A was centrifuged to remove the polymer template agent PPNOH, and a stepwise porous Silicalite-1 molecular sieve was obtained.

[0092] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm and 25°C for 60 min to obtain an upper layer of polymer template agent PPNOH and a lower layer of Silicalite-1 molecular sieve. The Silicalite-1 molecular sieve was washed with deionized water until pH≈7 and then dried at 105°C for 12 h to obtain a solid powder. The XRD diffraction pattern of the solid powder obtained in this example can be referred to [reference needed]. Figure 2 XRD analysis revealed that the product's phase composition belongs to Silicalite-1 molecular sieve. Ar adsorption-desorption results showed that the mesopore size is concentrated at 30 nm, with a specific surface area of ​​682 m². 2 / g, pore volume 1.60cm³ 3 / g.

[0093] Compared with the prior art, the present invention has the following beneficial effects:

[0094] 1. The Silicalite-1 molecular sieve synthesized by this method contains both micropores and mesopores in its structure, forming a ladder-like pore structure, which effectively solves the mass transfer problem caused by microporous molecular sieves.

[0095] 2. The polymer template agent used in this method can be removed by centrifugation, and the synthesized Silicalite-1 molecular sieve does not require high-temperature calcination, which has the advantages of high efficiency and greenness.

[0096] 3. The polymer template agent of this application can be reused, which reduces costs and improves atom utilization;

[0097] 4. Compared with conventional molecular sieves, the Silicalite-1 molecular sieve synthesized using the method of this application has a higher specific surface area (600-700 m²). 2 / g) and pore volume (1.00~1.60cm³) 3 / g).

[0098] Comparative Example 1

[0099] Without adding PPNOH, other procedures are the same as in Example 6. The XRD diffraction pattern of the resulting solid powder can be found in [reference needed]. Figure 4 The phase of the product obtained by XRD analysis is amorphous silicon dioxide.

[0100] Comparative Example 2

[0101] Without adding PPNOH, other procedures are the same as in Example 8. The XRD diffraction pattern of the resulting solid powder can be found in [reference needed]. Figure 5 The phase of the product obtained by XRD analysis is amorphous silicon dioxide.

[0102] Comparative Example 3

[0103] Without adding PPNOH, other procedures are the same as in Example 9. The XRD diffraction pattern of the resulting solid powder can be found in [reference]. Figure 6 The phase of the product obtained by XRD analysis is amorphous silicon dioxide.

[0104] The comparison results between Examples 5-9 and Comparative Examples 1-3 show that the Silicalite-1 molecular sieve synthesized by the method of the present invention possesses both micropores and mesopores, forming a Silicalite-1 molecular sieve with a tiered pore structure, effectively solving the mass transfer problem existing in traditional Silicalite-1 molecular sieves. In contrast, the molecular sieves synthesized by the methods of Comparative Examples 1-3 all consist of amorphous silica, which does not belong to Silicalite-1 molecular sieves. Therefore, there is no basis for further exploring whether a Silicalite-1 molecular sieve with a micropore-mesopore tiered pore size is formed inside the molecular sieve. In other words, Comparative Examples 1-3, which do not use the polymer template agent provided by the present invention to prepare molecular sieves, cannot solve the technical problem to be solved by the present invention.

[0105] Furthermore, the mesopore size distribution of the Silicalite-1 molecular sieve with stepped pore size obtained through Examples 5-9 shows that the pore size increases with the increase of the amount of polymer template agent within an appropriate range.

[0106] Meanwhile, the polymer template agent used in the method of this invention can be removed by centrifugation and can be repeatedly recycled, reducing costs and improving atom utilization. Furthermore, the hierarchical porous Silicalite-1 molecular sieve synthesized from it does not require high-temperature calcination, avoiding severe dealumination of the molecular sieve framework, partial framework collapse, and decreased crystallinity, and possesses the advantages of high efficiency, greenness, and environmental friendliness.

[0107] Furthermore, compared with conventional molecular sieves, the hierarchical porous Silicalite-1 molecular sieve synthesized using the method of this invention has a higher specific surface area of ​​600–700 m². 2 / g and pore volume 1.00~1.60cm³ 3 / g, Silicalite-1 molecular sieve has better performance and thus expanded its application range.

[0108] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection for this invention. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of this invention, or equivalent structural or procedural transformations made using the description and drawings of this invention, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of patent protection for this invention.

Claims

1. A polymeric template agent PPNOH, characterized in that, With a number-average molecular weight of 60,000–80,000 g / mol, it has the following chemical structural formula: Where n is an integer greater than 1.

2. A method for preparing the polymer template agent PPNOH as described in claim 1, characterized in that, Includes the following steps: Isopropylacrylamide and azobisisobutyronitrile were added to a polymerization tube containing anhydrous tetrahydrofuran and reacted in an oil bath under nitrogen protection. After cooling, the solvent was evaporated, dissolved in acetone, and then added dropwise to n-hexane. The mixture was filtered and dried under vacuum to obtain poly-N-isopropylacrylamide. The poly(N-isopropylacrylamide) was dissolved in diethyl ether, and bromoethane was added. The reaction was carried out to obtain a polyquaternary ammonium hydrohalate solution. The polyquaternary ammonium hydrohalate was treated with a strongly basic anion exchange resin and filtered to obtain a polyquaternary ammonium alkaline solution. The polyquaternary ammonium alkali solution was cooled in a water bath, neutralized with acid, distilled under reduced pressure, cooled again, extracted, separated, and the volatile components were removed under vacuum to obtain the polymer template agent PPNOH.

3. The preparation method according to claim 2, characterized in that, The molar ratio of isopropylacrylamide, azobisisobutyronitrile, and anhydrous tetrahydrofuran is (25-40): (0.02-0.06): (300-450).

4. The preparation method according to claim 2, characterized in that, The oil bath reaction temperature is 70–85°C, the oil bath reaction time is 24–50 h, and the vacuum drying temperature is 25–35°C, the vacuum drying time is 24–48 h.

5. The preparation method according to claim 2, characterized in that, The amount of bromoethane used is 300–600 mmol, the reaction temperature is 50–65 °C, and the reaction time is 30–55 h.

6. A green preparation method for a stepwise porous Silicalite-1 molecular sieve, characterized in that, Includes the following steps: Water and the polymer template agent PPNOH according to claim 1 are mixed evenly, and a silicon source is added in batches to obtain a gel, such that the molar ratio of H2O, SiO2 and the polymer template agent PPNOH in the gel is (20-30):1:(0.0005-0.0012); The above gel was aged at 50°C for 2-4 hours and then placed in a reaction vessel for crystallization reaction. The crystallization reaction temperature was 160-180°C and the crystallization reaction time was 72-140 hours to obtain the crystallized product. The crystallized product was centrifuged and dried to obtain the stepwise porous Silicalite-1 molecular sieve.

7. The green preparation method according to claim 6, characterized in that, The aluminum source is selected from one or more of sodium aluminate, aluminum sulfate, and aluminum isopropoxide.

8. The green preparation method according to claim 6, characterized in that, The silicon source is selected from one or more of tetraethyl orthosilicate, silica sol, industrial silica gel, and fumed silica.

9. The green preparation method according to claim 6, characterized in that, The crystallized product was centrifuged at a speed of 5000-8000 rpm, a temperature of 20-35°C, and a processing time of 30-60 min.

10. A stepwise porous Silicalite-1 molecular sieve prepared by the green preparation method according to any one of claims 6-9, characterized in that, The mesopore size of the cascaded Silicalite-1 molecular sieve is concentrated in the range of 10–30 nm, and the specific surface area is 600–700 m². 2 / g, pore volume 1.00~1.60cm³ 3 / g.

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