Recyclable polymer template agent, hierarchical porous Beta molecular sieve and its preparation method

Abstract

This invention relates to the field of molecular sieve technology, and more specifically to a recyclable polymer template agent, a hierarchical gradient-pore Beta molecular sieve, and its green preparation method. By synthesizing a polymer template agent, and utilizing the unique temperature sensitivity of the hydrophilic quaternary ammonium salt structure and the hydrophobic isopropyl group in the recyclable polymer template agent provided by this invention, the molecular sieve precursor is locked inside the gel at the molecular sieve synthesis temperature, guiding the formation of the molecular sieve crystal structure. After crystallization, the reaction temperature is lowered to room temperature, the polymer shell opens, and the locked molecular sieve crystals are released through diffusion. Centrifugation is then used to separate the polymer from the molecular sieve. This invention's method for preparing hierarchical porous Beta molecular sieves eliminates the need for high-temperature calcination for removal, significantly reducing energy consumption. The polymer template agent can be repeatedly recycled for use in molecular sieve production, saving application costs and being environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, and more specifically to a recyclable polymer template agent, a multi-level gradient pore Beta molecular sieve, and a green preparation method thereof. Background Technology

[0002] The structure of Beta molecular sieves consists of type A, type B, and type C structures, respectively, following the... Figure 1 The structure shown in diagram a is a stacked fault structure along direction a, forming perpendicularly intersecting twelve-membered ring straight channels along directions b and c. These channels are open, cage-free structures with a pore size of approximately 0.66 × 0.76 nm. Along direction a, the channels are linearly curved with a pore size of approximately 0.56 × 0.65 nm. The cage-free three-dimensional channel system of Beta zeolites not only facilitates the diffusion of reactants and products but also exhibits stronger catalytic stability and product molecule shape selectivity. Therefore, Beta zeolites have been widely used in fine chemical synthesis and petrochemical industries. However, the presence of small micropores strongly affects the mass transfer of substances with sizes close to or larger than the micropore size, hindering their large-scale industrial application. Hierarchical porous Beta zeolites, due to their micro / mesoporous, micro / macroporous, and micro / meso / macroporous combinations, exhibit superior performance in catalytic reactions and adsorption compared to microporous Beta zeolites, effectively overcoming the limitations of traditional Beta zeolites that only have micropores.

[0003] Chinese patent document (CN112591765A) describes the preparation of a stepwise porous Beta molecular sieve using a neutral polymer in a green manner. The prepared molecular sieve is then acid-treated to remove the template agent, yielding the stepwise porous Beta molecular sieve. Chinese patent document (CN112939018A) describes the preparation of a high-silica Beta molecular sieve using non-toxic, inexpensive, and recyclable 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, or mixtures thereof as organic mineralizers, replacing highly toxic and corrosive inorganic mineralizers such as hydrofluoric acid or fluorine-containing salts. However, this preparation process requires the use of microporous template agents such as tetraethylammonium hydroxide, tetraethylammonium bromide, or tetraethylammonium chloride. Chinese patent document (CN111017954A) describes the preparation of an open macroporous Beta molecular sieve using tetraethylammonium hydroxide or tetraethylammonium bromide as a microporous template agent and alcohols, organic amines, or carbonates as fillers. The published patent (CN111333082A) uses tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, and tetraethylammonium fluoride as template agents, adding seed crystals and an appropriate amount of hydrofluoric acid to prepare all-silica H-Beta molecular sieves. The published patent (CN112607747B) discloses a green and efficient method for synthesizing high-silica Beta molecular sieves, using an aluminum source, inorganic alkali, tetraethylammonium hydroxide, and a fluorine-free mineralizing agent, with steam-assisted crystallization to prepare mesoporous high-silica Beta molecular sieves.

[0004] The above-mentioned technical solutions for achieving multi-level porous Beta molecular sieves are expensive to synthesize, the template agent structure is destroyed and cannot be recycled, and most of them require high-temperature calcination to remove the template agent, which can easily cause environmental pollution and damage to the molecular sieve structure. Summary of the Invention

[0005] Therefore, there is a need to provide an environmentally friendly template agent, a multi-level porous Beta molecular sieve, and its preparation method, in order to solve the problems of structural damage and non-recyclability caused by the need for high-temperature calcination to remove mesoporous or macroporous template agents in the prior art, and at the same time solve the problems of high production costs and environmental pollution in the production of multi-level porous Beta molecular sieves.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a recyclable polymer template agent having a number-average molecular weight of 28,000–35,000 g / mol and having the following chemical structural formula:

[0007]

[0008] Where n is a natural number greater than 1.

[0009] In a second aspect, the present invention provides a method for preparing a recyclable polymer template agent as described in the first aspect of the present invention, comprising the following steps:

[0010] 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.

[0011] 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.

[0012] The polyquaternary ammonium hydrohalate solution was treated with a strongly basic anion exchange resin and filtered to obtain a polyquaternary ammonium alkaline solution.

[0013] 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 recyclable polymer template agent.

[0014] In a preferred embodiment of the present invention, the molar amounts of isopropylacrylamide, azobisisobutyronitrile and anhydrous tetrahydrofuran are respectively: (8-12): (0.03-0.09): (90-210).

[0015] In a preferred embodiment of the present invention, the oil bath reaction temperature is 55-65°C, the oil bath reaction time is 18-36 h, the vacuum drying temperature is 25-30°C, and the vacuum drying time is 40-48 h.

[0016] In a preferred embodiment of the present invention, the amount of bromoethane used is 180–420 mmol, the reaction temperature is 40–45°C, and the reaction time is 20–30 h.

[0017] Thirdly, the present invention provides a method for preparing a hierarchical porous Beta molecular sieve, comprising the following steps:

[0018] Water, aluminum source, alkali source and the recyclable polymer template agent described in the first aspect of the present invention are mixed evenly, and a silicon source is added in batches to obtain a gel. The gel contains, by molar parts, 1500-6000 parts of H2O, 100-300 parts of SiO2, 1 part of Al2O3, 2.0-2.6 parts of Na2O and 0.012-0.026 parts of the recyclable polymer template agent.

[0019] The gel was aged and then crystallized in a reaction vessel to obtain sample A;

[0020] The sample A was centrifuged to remove the recyclable polymer template agent, and then dried to obtain the multi-level porous Beta molecular sieve.

[0021] In preparing hierarchical Beta molecular sieves, the amount of the recyclable polymer template agent described in the first aspect of this invention is not necessarily better the more it is used. Through extensive experimentation, it has been found that when its amount and the molar proportions of SiO2, Na2O, Al2O3, and H2O are within the aforementioned range, and at the molecular sieve synthesis temperature, the special groups in the recyclable polymer template agent structure can effectively play their role in guiding the formation of the molecular sieve crystal structure. After cooling following crystallization, the molecular sieve crystals are released. If the amount used is too small, the resulting mesopore size will be too small, making it difficult to form a hierarchical pore structure with the micropores; if the amount used is too large, the resulting mesopore size will be close to that of macropores, which is also not conducive to the formation of a hierarchical pore structure.

[0022] In a preferred embodiment of the present invention, the gel aging temperature is 23-25°C and the aging time is 2-4 hours, the crystallization temperature is 140-180°C and the crystallization time is 24-72 hours.

[0023] In a preferred embodiment of the present invention, the aluminum source includes sodium aluminate and / or aluminum sulfate, the silicon source includes one or more of silica sol, industrial silica gel and fumed silica, and the alkali source is sodium hydroxide.

[0024] In a preferred embodiment of the present invention, the centrifugation speed is 5000-8000 rpm, the centrifugation temperature is 20-35℃, and the centrifugation time is 10-30 min.

[0025] Fourthly, the present invention provides a hierarchical porous Beta molecular sieve prepared by the preparation method described in the third aspect of the present invention, wherein the mesopore size of the hierarchical porous Beta molecular sieve is concentrated in the range of 5-50 nm, and the specific surface area is 500-600 m². 2 / g, pore volume 0.36~0.72cm³ 3 / g.

[0026] Unlike existing technologies, the above-mentioned technical solution synthesizes a recyclable polymer template agent. Utilizing the unique temperature sensitivity of the hydrophilic quaternary ammonium salt structure and the hydrophobic isopropyl group in the recyclable polymer template agent provided by this invention, the molecular sieve precursor is locked inside the gel at the molecular sieve synthesis temperature, guiding the formation of the molecular sieve crystal structure. After crystallization, the reaction temperature is lowered to room temperature, the polymer shell opens, and the locked molecular sieve crystals are released through diffusion. Centrifugation then separates the polymer from the molecular sieve, removing the template agent. In the process of preparing hierarchical porous Beta molecular sieves using the recyclable polymer template agent of this invention, high-temperature calcination is unnecessary for removal, significantly reducing energy consumption. The removed recyclable polymer template agent can be repeatedly recycled in the molecular sieve production process, saving on template agent application costs and achieving zero-calcination pollutant emissions, making it environmentally friendly. Attached Figure Description

[0027] Figure 1 A schematic diagram of the stacking fault structure of Beta molecular sieve;

[0028] Figure 2 The XRD diffraction pattern of the hierarchical porous Beta molecular sieve prepared in Example 1 of this invention;

[0029] Figure 3 This is a SEM image of the hierarchical porous Beta molecular sieve prepared in Example 1 of this invention;

[0030] Figure 4 The XRD diffraction pattern of the sample prepared in Comparative Example 1 of this invention;

[0031] Figure 5 The XRD diffraction pattern of the sample prepared in Comparative Example 2 of this invention;

[0032] Figure 6 This is the XRD diffraction pattern of the sample prepared in Comparative Example 3 of this invention. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] To overcome the challenge of impaired mass transfer caused by the small micropores of Beta molecular sieves and expand their industrial applications, research on nanoscale hierarchical porous Beta molecular sieves is increasing, as listed in the background section. The synthesis of molecular sieves using polyquaternium salts (such as polyquaternium-6, polyquaternium-11, or polyquaternium-32) as templates has also been applied in the synthesis of nano-EMT molecular sieves, macroporous EMM-23 zeolite molecular sieves, and Beta-FER eutectic molecular sieves. However, if polyquaternium salts such as polyquaternium-6, polyquaternium-11, or polyquaternium-32 are directly used as templates to solve the technical problem of this invention, the inventors found that they cannot be removed by centrifugation and still require the traditional high-temperature calcination removal method. Besides releasing undesirable environmental pollutants, the high-temperature calcination removal method also causes severe dealuminization of the Beta molecular sieve framework and partial framework collapse, resulting in a significant decrease in crystallinity and affecting the practical industrial application of Beta molecular sieves. Therefore, the applicant took a different approach, preparing a polyquaternary ammonium salt polymer template agent with both hydrophilic quaternary ammonium groups and hydrophobic isopropyl groups in its structure through continuous experimental adjustments and theoretical analysis. Utilizing the temperature sensitivity inherent in its special structure, it can lock the molecular sieve precursor inside the gel at the molecular sieve synthesis temperature, guiding the formation of the molecular sieve crystal structure. After crystallization, the reaction temperature is lowered to room temperature, the polymer shell opens, and the locked molecular sieve crystals are released through a diffusion mechanism. Furthermore, the recyclable polymer template agent can be separated from the molecular sieve by centrifugation alone.

[0043] In this invention, unless otherwise specified, all reagents and raw materials used are commercially available.

[0044] In this invention, unless otherwise specified, the number-average molecular weight of the recyclable polymer template agent is determined using gel permeation chromatography. The specific test conditions and methods are as follows:

[0045] 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 the recyclable 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 the molecular weight distribution of the recyclable polymer template agent in the liquid chromatograph. The test temperature was 30 °C, chromatographically pure TCM was used as the solvent, the solvent flow rate was 1 mL / min, and polystyrene was used as the standard sample.

[0046] In this invention, unless otherwise specified, the mesopore size of hierarchical Beta molecular sieves is measured by physical adsorption. The specific test conditions and methods are as follows:

[0047] The test was carried out using a Micromeritics 2020 physical adsorption analyzer (Micromeritics, USA). Before the test, the sample was pretreated by vacuum pumping at 150 °C for 12 h, and then static adsorption was carried out at -196 °C with Ar as the adsorbate to measure the adsorption-desorption curve of the sample. The Barrett-Joyner-Halenda (BJH) model was used to obtain the mesopore size distribution of the sample.

[0048] In the present invention, unless otherwise specified, the specific surface area of the hierarchical pore Beta zeolite was measured by physical adsorption, and the specific test conditions and methods were as follows:

[0049] The test was carried out using a Micromeritics 2020 physical adsorption analyzer (Micromeritics, USA). Before the test, the sample was pretreated by vacuum pumping at 150 °C for 12 h, and then static adsorption was carried out at -196 °C with Ar as the adsorbate to measure the adsorption-desorption curve of the sample. The adsorption-desorption isotherm was plotted based on the Brunauer-Emmet-Teller (BET) equation, and the total specific surface area was calculated using the BET equation for the linear part (0.05 < P / P0 < 0.30) of the adsorption isotherm.

[0050] In the present invention, unless otherwise specified, the pore volume of the hierarchical pore Beta zeolite was measured by physical adsorption, and the specific test conditions and methods were as follows:

[0051] The test was carried out using a Micromeritics 2020 physical adsorption analyzer (Micromeritics, USA). Before the test, the sample was pretreated by vacuum pumping at 150 °C for 12 h, and then static adsorption was carried out at -196 °C with Ar as the adsorbate to measure the adsorption-desorption curve of the sample. The micropore and mesopore volumes were calculated by the t-plot method.

[0052] In the present invention, unless otherwise specified, the crystallinity was measured by X-ray diffraction (XRD) method, and the specific test conditions were as follows:

[0053] The phase structure of the synthesized zeolite sample was analyzed using a Rigaku D-Max 2550 X-ray diffractometer (Rigaku, Japan) under the test conditions of Cu target and Kα radiation. The tube voltage was 40 kV and the tube current was 40 mA. The wide-angle scanning range was 2θ = 5–40°, and the scanning rate was 7° / min. The relative crystallinity described in the embodiments of this application is based on the ASTM D3906-03 (2013) standard, using the ratio of the integral area of ​​2θ at 22.4° ± 0.2° in the XRD patterns of the obtained product and the Beta molecular sieve standard sample. The standard sample is a Beta molecular sieve with a SiO2 / Al2O3 molar ratio of 25 produced by the Catalyst Factory of Nankai University, and its crystallinity is defined as 100%.

[0054] In this invention, unless otherwise specified, the SiO2 / Al2O3 ratio is measured using the ICP method, and the specific test conditions are as follows:

[0055] 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.

[0056] 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:

[0057] 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 for morphological characterization. Finally, electron microscope images were obtained and analyzed.

[0058] Example 1

[0059] Recyclable polymer templates and their preparation methods

[0060] 12 mmol of isopropylacrylamide and 0.09 mmol of azobisisobutyronitrile were added to a polymerization tube containing 210 mmol of anhydrous tetrahydrofuran. The mixture was reacted in an oil bath at 65 °C for 36 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, dissolved in a small amount of acetone, and then added dropwise to n-hexane. After filtration, the mixture was dried under vacuum at 30 °C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid. The above solid was dissolved in the organic solvent diethyl ether, and 420 mmol of bromoethane was added. The mixture was reacted at 45°C for 30 h to obtain a solution of polyquaternary ammonium hydrogen halide. The 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 solution of polyquaternary ammonium base. 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 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 PENOH as shown in the following chemical structural formula I. The number average molecular weight of polyquaternary ammonium salt PENOH was measured to be 35000 g / mol by gel chromatography, which is the recyclable polymer template agent provided by this invention.

[0061]

[0062] Example 2

[0063] Recyclable polymer templates and their preparation methods

[0064] 11 mmol of isopropylacrylamide and 0.08 mmol of azobisisobutyronitrile were added to a polymerization tube containing 180 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 60 °C for 32 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, dissolved in a small amount of acetone, and then added dropwise to n-hexane. After filtration, the mixture was dried under vacuum at 30 °C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid. The above solid was dissolved in the organic solvent diethyl ether, and 360 mmol of bromoethane was added. The mixture was reacted at 45°C for 28 h to obtain a solution of polyquaternary ammonium hydrogen halide. The 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 solution of polyquaternary ammonium base. 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 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 PENOH as shown in chemical structural formula I. The number average molecular weight of polyquaternary ammonium salt PENOH was measured to be 33000 g / mol by gel permeation chromatography, which is the recyclable polymer template agent provided by this invention.

[0065] Example 3

[0066] Recyclable polymer templates and their preparation methods

[0067] 10 mmol of isopropylacrylamide and 0.07 mmol of azobisisobutyronitrile were added to a polymerization tube containing 150 mmol of anhydrous tetrahydrofuran. The mixture was reacted in an oil bath at 60 °C for 30 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, dissolved in a small amount of acetone, and then added dropwise to n-hexane. After filtration, the mixture was dried under vacuum at 30 °C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid. The above solid was dissolved in the organic solvent diethyl ether, and 300 mmol of bromoethane was added. The mixture was reacted at 43°C for 30 h to obtain a solution of polyquaternary ammonium hydrogen halide. The 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 solution of polyquaternary ammonium base. 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 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 PENOH as shown in chemical structural formula I. The number average molecular weight of polyquaternary ammonium salt PENOH was measured to be 31000 g / mol by gel chromatography, which is the recyclable polymer template agent provided by this invention.

[0068] Example 4

[0069] Recyclable polymer templates and their preparation methods

[0070] 9 mmol of isopropylacrylamide and 0.05 mmol of azobisisobutyronitrile were added to a polymerization tube containing 120 mmol of anhydrous tetrahydrofuran. The reaction was carried out in an oil bath at 58 °C for 36 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, dissolved in a small amount of acetone, and then added dropwise to n-hexane. After filtration, the mixture was dried under vacuum at 30 °C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid. The above solid was dissolved in the organic solvent diethyl ether, and 240 mmol of bromoethane was added. The mixture was reacted at 40°C for 28 h to obtain a solution of polyquaternary ammonium hydrogen halide. The 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 solution of polyquaternary ammonium base. 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 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 PENOH as shown in chemical structural formula I. The number average molecular weight of polyquaternary ammonium salt PENOH was measured to be 29000 g / mol by gel chromatography, which is the recyclable polymer template agent provided by this invention.

[0071] Example 5

[0072] Recyclable polymer templates and their preparation methods

[0073] 8 mmol of isopropylacrylamide and 0.03 mmol of azobisisobutyronitrile were added to a polymerization tube containing 90 mmol of anhydrous tetrahydrofuran. The mixture was reacted in an oil bath at 55 °C for 18 h under nitrogen protection. After cooling to room temperature, the solvent was evaporated, dissolved in a small amount of acetone, and then added dropwise to n-hexane. After filtration, the mixture was dried under vacuum at 25 °C for 48 h to obtain poly(N-isopropylacrylamide) as a white solid. The above solid was dissolved in the organic solvent diethyl ether, and 180 mmol of bromoethane was added. The mixture was reacted at 40°C for 20 h to obtain a solution of polyquaternary ammonium hydrogen halide. The 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 solution of polyquaternary ammonium base. 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 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 PENOH as shown in chemical structural formula I. The number average molecular weight of polyquaternary ammonium salt PENOH was measured to be 28000 g / mol by gel chromatography, which is the recyclable polymer template agent provided by this invention.

[0074] Example 6

[0075] A hierarchical porous Beta molecular sieve and its preparation method are disclosed. The sieve is prepared using the recyclable polymer template agent PENOH provided in Example 1 via a hydrothermal method. The specific operation steps are as follows:

[0076] Hydrothermal preparation of molecular sieves: First, 0.02 g NaAlO2 and 0.010 g NaOH were added to 13 mL of deionized water and stirred until the solution was clear. Then, 0.12 g of the recyclable polymer template agent PENOH provided in Example 1 was added and stirred for 0.5 h. Then, 2.17 g of fumed silica was slowly added to obtain a synthetic gel with a molar composition of 300SiO2 / 1Al2O3 / 2Na2O / 6000H2O / 0.026 polymer. After stirring at room temperature (25 °C) for 3 h, the obtained gel was transferred to a stainless steel autoclave (50 mL) with a polytetrafluoroethylene liner and placed in a homogeneous reactor at a rotation speed of 100 rpm for crystallization at 140 °C for 72 h. After crystallization, sample A containing the recyclable polymer template agent PENOH was obtained.

[0077] The template agent was removed by centrifugation of sample A, resulting in a hierarchical porous Beta molecular sieve. The specific procedure was as follows:

[0078] The sample A obtained above was placed in a centrifuge tube, centrifuged at 6500 rpm and 25°C for 15 min, yielding an upper layer of recyclable polymer template agent PENOH and a lower layer of Beta molecular sieve. The Beta molecular sieve was washed with deionized water until pH≈7, and then dried at 105°C for 12 h to obtain the attached powder. Figure 2The solid powder XRD diffraction pattern shown indicates that the phase of the product obtained by XRD determination belongs to Beta molecular sieve, and the SiO2 / Al2O3 ratio measured by ICP is 300.

[0079] Please see Figure 3 As can be seen from the SEM morphology and structure characterization image of the product, the hierarchical porous Beta molecular sieve provided in this embodiment is composed of nanocrystals with a particle size of approximately 30 nm.

[0080] Ar adsorption-desorption experiments were conducted using the hierarchical porous Beta molecular sieve provided in this embodiment, and the results are shown in Table 1. The Ar adsorption-desorption results show that the mesopore size of the hierarchical porous Beta molecular sieve provided in this embodiment is concentrated at 30 nm, and the specific surface area is 596 m². 2 / g, pore volume is 0.72cm³ 3 / g.

[0081] Table 1. Texture parameters of the hierarchical porous Beta molecular sieves prepared in Example 6.

[0082]

[0083] Example 7

[0084] A hierarchical porous Beta molecular sieve and its preparation method (using a centrifugally recovered polymer template as a template).

[0085] The method was followed in Example 6, except that PENOH obtained by centrifugation in Example 6 was used as the template agent. XRD analysis determined that the phase of the product obtained in this example belonged to Beta molecular sieves, and ICP analysis showed that the SiO2 / Al2O3 ratio was 300.

[0086] In this embodiment, the XRD diffraction pattern of the hierarchical porous Beta molecular sieve is compared with... Figure 2 Similarly, the SEM characterization images of hierarchical porous Beta molecular sieves are... Figure 3 similar.

[0087] Ar adsorption-desorption experiments were conducted using the hierarchical porous Beta molecular sieve provided in this embodiment, and the results are shown in Table 2. The Ar adsorption-desorption results show that the mesopore size of the hierarchical porous Beta molecular sieve provided in this embodiment is concentrated at 30 nm, and the specific surface area is 594 m². 2 / g, pore volume 0.70cm³ 3 / g.

[0088] Table 2. Texture parameters of the hierarchical porous Beta molecular sieves prepared in Example 7.

[0089]

[0090] Comparing the results in Tables 1 and 2, in Example 6, which used the newly prepared recyclable polymer template agent PENOH to prepare hierarchical porous Beta molecular sieves, and in Example 7, which used the recycled polymer template agent PENOH to prepare hierarchical porous Beta molecular sieves, the specific surface area and pore volume of the molecular sieves both decreased, but the decrease was not significant, at 0.34% and 2.78%, respectively. This demonstrates that the recyclable polymer template agent PENOH provided by this invention, after centrifugation and recovery for use as a template agent in the preparation of the next batch of hierarchical porous Beta molecular sieves, remains highly effective, while significantly reducing the cost of template agent raw materials.

[0091] Example 8

[0092] A hierarchical porous Beta molecular sieve and its preparation method are disclosed, comprising the following steps:

[0093] Molecular sieve preparation by hydrothermal method: The template agent prepared in Example 4 was used, with aluminum sulfate as the aluminum source and silica sol as the silicon source. The order of raw material addition was the same as in Example 1. The amount of addition was adjusted to ensure that the molar ratio of the feed met the following condition: the composition of the synthesized gel was 200SiO2 / 1Al2O3 / 2.4Na2O / 2800H2O / 0.022 recyclable polymer template agent PENOH. The gel was aged at 25°C for 4 hours and then transferred to a 50mL stainless steel autoclave with a polytetrafluoroethylene liner. It was crystallized at 160°C for 48 hours to obtain sample A.

[0094] The template agent was removed by centrifugation of sample A, resulting in a hierarchical porous Beta molecular sieve. The specific procedure was as follows:

[0095] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm for 25 min at 25 °C. The upper layer was a recyclable polymer template agent, PENOH, and the lower layer was a hierarchical porous Beta molecular sieve. The resulting hierarchical porous Beta molecular sieve was washed with deionized water until pH ≈ 7 and then dried at 105 °C for 12 h. XRD analysis showed that the product phase belonged to Beta molecular sieve, and ICP analysis showed that the SiO2 / Al2O3 ratio was 200.

[0096] Ar adsorption and desorption experiments were conducted using the hierarchical porous Beta molecular sieve provided in this embodiment. The results showed that the mesopore size was concentrated at 20 nm, and the specific surface area was 600 m². 2 / g, pore volume is 0.42cm³ 3 / g.

[0097] Example 9

[0098] A hierarchical porous Beta molecular sieve and its preparation method are disclosed, comprising the following steps:

[0099] Molecular sieve preparation by hydrothermal method: The recyclable polymer template agent prepared in Example 5 was used, sodium aluminate was used as the aluminum source and industrial silica gel was used as the silicon source. The order of raw material addition was the same as in Example 1. The amount of addition was adjusted to make the molar ratio of the feed materials meet the following condition: the composition of the synthesized gel is 100SiO2 / 1Al2O3 / 2.6Na2O / 1500H2O / 0.012 polymer. The gel was aged at 25℃ for 4h and then transferred to a 50mL stainless steel autoclave with a polytetrafluoroethylene liner. It was crystallized at 180℃ for 48h to obtain sample A.

[0100] The template agent was removed by centrifugation of sample A, resulting in a hierarchical porous Beta molecular sieve. The specific procedure was as follows:

[0101] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm for 30 min at 25°C. The upper layer was a recyclable polymer template agent, PENOH, and the lower layer was a hierarchical porous Beta molecular sieve. The hierarchical porous Beta molecular sieve obtained by centrifugation was washed with deionized water until pH≈7 and then dried at 105°C for 12 h. XRD analysis showed that the phase of the product belonged to Beta molecular sieve, and ICP analysis showed that the SiO2 / Al2O3 ratio was 100.

[0102] Ar adsorption and desorption experiments were conducted using the hierarchical porous Beta molecular sieve provided in this embodiment. The results showed that the mesopore size was concentrated at 8 nm, and the specific surface area was 500 m². 2 / g, pore volume is 0.36cm³ 3 / g.

[0103] Comparative Example 1

[0104] Without adding the recyclable polymer template agent PENOH, all other procedures were the same as in Example 6. The product obtained by XRD analysis was amorphous silica. For detailed XRD results of the product in Comparative Example 1, please refer to [link to Comparative Example 1]. Figure 4 .

[0105] Comparative Example 2

[0106] Without adding the recyclable polymer template agent PENOH, all other procedures were the same as in Example 8. The product obtained by XRD analysis was amorphous silica. For detailed XRD results of the product in Comparative Example 2, please refer to [link to Comparative Example 2]. Figure 5 .

[0107] Comparative Example 3

[0108] Without adding the recyclable polymer template agent PENOH, all other procedures were the same as in Example 9. XRD analysis revealed the product to be a mixture of ZSM-5 molecular sieve and amorphous silica. For detailed XRD results of the product in Comparative Example 3, please refer to [link to Comparative Example 3]. Figure 6 .

[0109] The comparison results between Examples 5-9 and Comparative Examples 1-3 show that the hierarchical porous Beta molecular sieve structure synthesized by the method of the present invention contains both micropores and mesopores, forming a hierarchical porous structure, which effectively solves the mass transfer problem existing in traditional Beta molecular sieves. In contrast, the molecular sieves synthesized by the methods of Comparative Examples 1-3 do not belong to the Beta molecular sieve category. Therefore, there is no basis for further exploring whether a micropore-mesopore hierarchical Beta molecular sieve is formed inside the molecular sieve. In other words, without using the recyclable polymer template agent provided by the present invention to prepare molecular sieves, the technical problem to be solved by the present invention cannot be solved.

[0110] Furthermore, the mesopore size distribution of the multi-level Beta molecular sieves obtained in Examples 5-9 shows that the pore size increases with the increase of the amount of recyclable polymer template agent within an appropriate range.

[0111] Meanwhile, the recyclable polymer template agent used in the method of this invention can be removed by centrifugation and reused repeatedly, reducing costs and improving atom utilization. Furthermore, the hierarchical porous Beta 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.

[0112] Furthermore, compared with conventional molecular sieves, the hierarchical porous Beta molecular sieve synthesized using the method of this invention has a higher specific surface area of ​​500-600 m². 2 / g and pore volume 0.36-0.72cm³ 3 / g, Beta molecular sieves have superior performance and thus expanded their application range.

[0113] 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 recyclable polymer templating agent, characterized in that, The number average molecular weight is 28000-35000 g / mol, and it has a chemical structure as shown below: Wherein, n is an integer greater than 1.

2. A method of preparing a recyclable polymeric stent according to claim 1, characterized in that, The method comprises the following steps: Isopropyl acrylamide and azobisisobutyronitrile are added into a polymerization tube containing anhydrous tetrahydrofuran, and oil bath reaction is carried out under nitrogen protection, and then the solvent is evaporated, dissolved in acetone, and then dropped into n-hexane drop by drop, and then filtered and vacuum dried to obtain poly-N-isopropyl acrylamide; The poly-N-isopropyl acrylamide is dissolved in diethyl ether, and bromoethane is added and reacted to obtain a polyquaternary ammonium hydrohalide salt; The polyquaternary ammonium hydrohalide salt is treated with a strong alkaline anion exchange resin, and filtered to obtain a polyquaternary ammonium base solution; The polyquaternary ammonium base solution is cooled in a water bath, neutralized with acid, distilled under reduced pressure, cooled again, extracted, separated, and then the volatile components are removed under vacuum to obtain the recyclable polymer template agent.

3. The production method according to claim 2, characterized by, The molar amount ratio of the isopropyl acrylamide, azobisisobutyronitrile and anhydrous tetrahydrofuran is (8-12):(0.03-0.09):(90-210).

4. The production method according to claim 2, characterized by, The oil bath reaction temperature is 55-65℃, the oil bath reaction time is 18-36h, the vacuum drying temperature is 25-30℃, and the vacuum drying time is 40-48h.

5. The preparation method according to claim 2, characterized in that, The amount of bromoethane is 180-420mmol, the reaction temperature is 40-45℃, and the reaction time is 20-30h.

6. A method for preparing a hierarchical-pore Beta molecular sieve, characterized in that, The method comprises the following steps: The water, an aluminum source, an alkali source and the recyclable polymer template agent of claim 1 are uniformly mixed, and a silicon source is added in batches to obtain a gel, wherein the gel comprises 1500-6000 parts of H2O, 100-300 parts of SiO2, 1 part of Al2O3, 2.0-2.6 parts of Na2O and 0.012-0.026 parts of the polymer template agent according to the mole fraction; The gel is aged and then placed in a reaction kettle for crystallization to obtain sample A; The sample A is centrifuged to remove the recyclable polymer template agent, and then dried to obtain the hierarchical pore Beta molecular sieve.

7. The preparation method according to claim 6, characterized in that, The gel aging temperature is 23-25℃, the aging time is 2-4h, the crystallization temperature is 140-180℃, and the crystallization time is 24-72h.

8. The preparation method according to claim 6, characterized in that, The aluminum source comprises sodium metaaluminate and / or aluminum sulfate, the silicon source comprises one or a combination of two or more of silica sol, industrial silica gel and fumed silica, and the alkali source is sodium hydroxide.

9. The preparation method according to claim 6, characterized in that, The centrifugation speed is 5000-8000rpm, the centrifugation temperature is 20-35℃, and the centrifugation time is 10-30min.

10. A hierarchical porous Beta molecular sieve prepared by the preparation method according to any one of claims 6-9, characterized in that, The mesopore size of the multi-level pore Beta molecular sieve is concentrated at 5-50 nm, the specific surface area is 500-600 m 2 / g, and the pore volume is 0.36-0.72 cm 3 / g.

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