Recyclable polymer template agent and preparation method therefor, and hierarchically porous beta molecular sieve and preparation method therefor

Abstract

A recyclable polymer template agent and a green preparation method therefor, and a hierarchically porous Beta molecular sieve and a green preparation method therefor. A polymer template agent is synthesized, and the temperature sensitivity specific to a special hydrophilic quaternary amide group and hydrophobic isopropyl group in a polyquaternium structure of the recyclable polymer template agent is utilized to lock a molecular sieve precursor inside a gel at the synthesis temperature of a molecular sieve, so as to guide the formation of a molecular sieve crystal structure; when crystallization is finished, the reaction temperature is reduced to room temperature, a polymer shell is opened, molecular sieve crystals locked in the polymer shell are released out by means of a diffusion mechanism, and then by means of the centrifugal effect, the polymer is separated from the molecular sieve and removed. According to the method for preparing the hierarchically porous Beta molecular sieve, high-temperature roasting is not required for removing the polymer template agent, greatly reducing energy consumption. The polymer template agent can be repeatedly recycled and utilized in production and preparation of the molecular sieve, reducing the application costs of the template agent, and the method is environmentally friendly.

Description

Recyclable polymer template, multi-level pore Beta molecular sieve and preparation method thereof Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and more particularly to a recyclable polymer template, a multi-stage gradient pore Beta molecular sieve and a green preparation method thereof. Background Art

[0002] The structure of Beta zeolite consists of A-type, B-type, and C-type structures stacked in a stacking fault structure along the a-direction as shown in Figure 1. In the b- and c-directions, these structures form perpendicularly intersecting twelve-membered ring straight channels. These channels are open and cage-free, with pore sizes of approximately 0.66 × 0.76 nm. In the a-direction, these channels form linear, curved channels with pore sizes of approximately 0.56 × 0.65 nm. The cage-free, three-dimensional pore system of Beta zeolite not only facilitates the diffusion of reactants and products but also exhibits enhanced catalytic stability and product shape selectivity. Therefore, Beta zeolite has been widely used in fine chemical synthesis and the petrochemical industry. However, the presence of small micropores significantly impedes mass transfer of materials with sizes close to or larger than the micropores, hindering its large-scale industrial application. Multi-level pore Beta zeolite, with its combination of micro / mesopores, micro / macropores, and micro / meso / macropores, exhibits superior performance in catalytic reactions and adsorption compared to microporous Beta zeolite, effectively overcoming the limitations of conventional Beta zeolite, which is limited to micropores.

[0003] Chinese patent document (CN112591765A) adopts a kind of neutral polymer green preparation step-pore Beta molecular sieve, and the prepared molecular sieve is acid-treated to remove the template agent to obtain step-pore Beta molecular sieve. Chinese patent document (CN112939018A) uses non-toxic, cheap, recyclable 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone or its mixture as organic mineralizer, instead of highly toxic, highly corrosive hydrofluoric acid or fluorine-containing salts and other inorganic mineralizers to prepare high silicon Beta molecular sieve, but microporous template agent tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride is required in the preparation process. Chinese patent document (CN111017954A) uses tetraethylammonium hydroxide or tetraethylammonium bromide as microporous template agent, alcohols, organic amines or carbonates as fillers to prepare open macroporous Beta molecular sieve. A patent publication (CN111333082A) describes the preparation of all-silica H-Beta molecular sieves using tetraethylammonium hydroxide, tetraethylammonium bromide, tetraethylammonium chloride, and tetraethylammonium fluoride as templates, with the addition of seed crystals and an appropriate amount of hydrofluoric acid. A patent publication (CN112607747B) discloses a green and efficient method for synthesizing high-silica Beta molecular sieves. The method involves combining an aluminum source, an inorganic base, tetraethylammonium hydroxide, and a fluorine-free mineralizer, and using steam-assisted crystallization to prepare a mesoporous, high-silica Beta molecular sieve.

[0004] The above-mentioned technical solutions for realizing multi-level pore Beta molecular sieves have high template synthesis costs, the template structure is destroyed and cannot be recovered, and most of them require high-temperature calcination to remove the template, which is very likely to cause environmental pollution and damage the molecular sieve structure.

[0005] Summary of the Invention

[0006] To this end, it is necessary to provide an environmentally friendly template, a multi-level pore Beta molecular sieve and a preparation method thereof, so as to solve the problem in the prior art that the mesoporous or macroporous templates need to be removed by high-temperature calcination, resulting in structural damage and inability to be recycled, and at the same time solve the problems of high production costs and environmental pollution in the production of multi-level pore Beta molecular sieves.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a recyclable polymer template having a number average molecular weight of 28,000 to 35,000 g / mol and a chemical structure as shown below:

[0008] Wherein, 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 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, reacted in an oil bath under nitrogen protection, cooled, the solvent evaporated, dissolved in acetone, and then dropwise added to n-hexane, filtered, and vacuum dried to obtain poly (N-isopropylacrylamide);

[0011] Dissolving the poly (N-isopropylacrylamide) in ether, adding ethyl bromide, and reacting to obtain a polyquaternary ammonium hydrohalide solution;

[0012] treating the polyquaternary ammonium hydrohalide solution with a strong basic anion exchange resin and filtering to obtain a polyquaternary ammonium base solution;

[0013] The polyquaternary ammonium base solution is cooled in a water bath, neutralized by adding acid, distilled under reduced pressure, cooled again, extracted, separated, and volatile components are removed in vacuo to obtain the recyclable polymer template.

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

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

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

[0017] In a third aspect, the present invention provides a method for preparing a multi-level pore Beta molecular sieve, comprising the following steps:

[0018] Mixing water, an aluminum source, an alkali source, and the recyclable polymer template according to the first aspect of the present invention uniformly, and adding a silicon source in batches to obtain a gel, wherein the gel comprises, by mole fraction, 1500 to 6000 parts of H2O, 100 to 300 parts of SiO2, 1 part of Al2O3, 2.0 to 2.6 parts of Na2O, and 0.012 to 0.026 parts of the recyclable polymer template;

[0019] After aging, the gel was placed in a reactor for crystallization to obtain sample A;

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

[0021] When preparing multi-level pore Beta molecular sieve, the amount of recyclable polymer template described in the first aspect of the present invention is not the more the better. Through a large number of experimental explorations, it was found that the amount and the molar fractions of SiO2, Na2O and Al2O3 and H2O are within the above range, and at the molecular sieve synthesis temperature, the special groups in the structure of the recyclable polymer template can be effectively brought into play, guiding the formation of the molecular sieve crystal structure, and releasing the molecular sieve crystals after the crystallization is completed and cooled. If the amount is too little, the mesopore diameter formed is too small, and it is difficult to form a multi-level aperture with small micropores; if the amount is too much, the mesopore diameter formed is close to the macropore, which is not conducive to the formation of a multi-level aperture.

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

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

[0024] As a preferred embodiment of the present invention, the centrifugal speed is 5000-8000 rpm, the centrifugal temperature is 20-35° C., and the centrifugal time is 10-30 min.

[0025] In a fourth aspect, the present invention provides a multi-level pore Beta molecular sieve prepared by the preparation method described in the third aspect of the present invention, wherein the mesopore diameter of the multi-level pore Beta molecular sieve is concentrated at 5 to 50 nm and the specific surface area is 500 to 600 m 2 / g, pore volume of 0.36~0.72cm 3 / g.

[0026] Different from the prior art, the above technical solution synthesizes a recyclable polymer template and utilizes the temperature sensitivity of the special hydrophilic quaternary amide group and the hydrophobic isopropyl group in the polyquaternary ammonium salt structure of the recyclable polymer template provided by the present invention, locks the molecular sieve precursor inside the gel at the molecular sieve synthesis temperature, and guides the formation of the molecular sieve crystal structure; after the crystallization is completed, the reaction temperature is lowered to room temperature, the polymer shell is opened, and the molecular sieve crystals locked inside are released by the diffusion mechanism, and then the polymer and the molecular sieve are separated and removed by centrifugation. In the process of preparing multi-level pore Beta molecular sieve using the recyclable polymer template of the present invention, it is not necessary to remove it by high-temperature calcination, which greatly reduces energy consumption. The recyclable polymer template after removal can be repeatedly recycled and reused in the production and preparation process of the molecular sieve, saving the application cost of the template, and achieving no calcination pollutant emissions and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] FIG2 is an XRD diffraction pattern of the multi-level pore Beta molecular sieve prepared in Example 1 of the present invention;

[0029] FIG3 is a SEM photograph of the multi-level pore Beta molecular sieve prepared in Example 1 of the present invention;

[0030] FIG4 is an XRD diffraction pattern of the sample prepared in Comparative Example 1 of the present invention;

[0031] FIG5 is an XRD diffraction pattern of the sample prepared in Comparative Example 2 of the present invention;

[0032] FIG6 is an XRD diffraction pattern of the sample prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0033] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0034] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0035] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0036] In the description of this application, the term "and / or" is used to describe a logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and both A and B exist. In addition, the character " / " in this document generally indicates that the objects before and after are in a logical "or" relationship.

[0037] In this application, terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, priority or sequence relationship between these entities or operations.

[0038] Without further limitations, in this application, the words "include", "comprise", "have" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those defined elements, but also other elements not explicitly listed, or elements inherent to such process, method or product.

[0039] Consistent with the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceed" are understood to exclude the number itself; expressions such as "above," "below," and "within" are understood to include the number itself. Furthermore, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this manner, such as "multiple groups," "multiple times," etc., unless otherwise specifically defined.

[0040] In the description of the embodiments of the present application, the space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating 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, it should not be understood as a limitation on the embodiments of the present application.

[0041] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms "installed", "connected", "connected", "fixed", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated 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 elements or the interaction relationship between two elements. For those skilled in the art of the present application, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0042] In order to improve the obstructed dilemma of the mass transfer brought by the small micropore of Beta molecular sieve, expand the industrial application range and field of Beta molecular sieve, as listed in background technology, the research for nano-scale multi-stage pore Beta molecular sieve increases day by day.With polyquaternium salt (such as polyquaternium salt-6, polyquaternium salt-11 or polyquaternium salt-32) as template agent synthetic molecular sieve also applies to some extent in the synthesis of nano EMT molecular sieve, macropore EMM-23 zeolite molecular sieve Beta-FER eutectic molecular sieve.But, if directly adopt polyquaternium salt such as polyquaternium salt-6, polyquaternium salt-11 or polyquaternium salt-32 as template to solve technical problem of the present invention, the inventor finds that it cannot be removed by centrifugation, still need adopt traditional high temperature roasting removal method.High temperature roasting removal method, except will discharge unexpected environmental pollutants, also causes Beta molecular sieve framework serious dealumination and part skeleton collapse, causes crystallinity to decline significantly, affects the application of Beta molecular sieve in actual industry. Therefore, the applicants took a different approach and, through continuous experimental adjustments and theoretical analysis, prepared a polyquaternary ammonium salt polymer template with both hydrophilic quaternary amido groups and hydrophobic isopropyl groups. Leveraging the temperature sensitivity of this unique structure, the polymer template can lock the molecular sieve precursor within 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 trapped molecular sieve crystals are released through diffusion. The recyclable polymer template can then be separated from the molecular sieve and removed simply by centrifugation.

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

[0044] In the present invention, unless otherwise specified, the number average molecular weight of the recyclable polymer template is measured by gel chromatography. The specific test conditions and methods are as follows:

[0045] The test was performed using a liquid chromatograph (Shimadzu, Japan) with a model LC-10AD / SPD-10A and a gel chromatography column with a model ShodexKF-803. Before the test, 4 mg of the recyclable polymer template was dissolved in 2 mL of tetrahydrofuran solution and filtered with a 2 μm filter membrane. 20 μL of the above sample was taken and the molecular weight distribution of the recyclable polymer template was tested 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 the present invention, unless otherwise specified, the mesopore diameter of the hierarchical pore Beta molecular sieve is measured by physical adsorption. The specific test conditions and methods are as follows:

[0047] The tests were carried out using a Micromeritics 2020 physical adsorption instrument (Micromeritics, USA). Before the tests, the samples were 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 curves of the samples. The Barrett-Joyner-Halenda (BJH) model was used to obtain the mesopore size distribution of the samples.

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

[0049] The tests were carried out using a Micromeritics 2020 physical adsorption instrument (Micromeritics, USA). Before the tests, the samples were 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 curves of the samples. 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. The specific test conditions and methods are as follows:

[0051] The tests were carried out using a Micromeritics 2020 physical adsorption instrument (Micromeritics, USA). Before the tests, the samples were pretreated by vacuum pumping at 150 °C for 12 h, and then static adsorption was carried out at -y196 °C with Ar as the adsorbate to measure the adsorption-desorption curves of the samples. 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). The specific test conditions are as follows:

[0053] The phase structure of the synthesized zeolite samples was analyzed using a Rigaku D-Max 2550 X-ray diffractometer (Rigaku, Japan). The test conditions were: Cu target, Kα radiation The tube voltage was 40 kV and the tube current was 40 mA. The wide-angle scanning range was 2θ = 5 to 40°, and the scanning rate was 7° / min. The relative crystallinity described in the examples of the present application is based on the ASTM D3906-03 (2013) standard, and is the ratio of the integrated area at 2θ at 22.4°±0.2° in the XRD spectrum of the obtained product to that of a 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 Plant of Nankai University, and its crystallinity is defined as 100%.

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

[0055] An OPTIMA 8000 inductively coupled plasma optical emission spectrometer (ICP-OES) manufactured by Perkin-Elmer (USA) was used. First, 10 mg of sample was dissolved in aqua regia solution, transferred to a microwave digester, and heated to 200°C for 2 hours to completely dissolve. The solution was then cooled to room temperature and brought to volume in a volumetric flask. A standard liquid of the metal element to be measured was then prepared as a reference standard to plot a calibration curve. The sample was then tested using argon as the carrier gas. Finally, the concentration of the metal element to be measured was obtained and recorded.

[0056] In the present invention, unless otherwise specified, the morphology of the molecular sieve was characterized by SEM, and the specific test conditions were as follows:

[0057] Scanning electron microscopy (SEM) was performed using a Helios G4CX focused ion beam (FIB) dual-beam field emission electron microscope (ThermoScientific, USA). A small amount of dried sample was dispersed in an ethanol solution and ultrasonicated for 10 minutes to achieve uniform dispersion. A drop of the supernatant was then placed on a clean silicon wafer and placed in a 60°C oven for 10 minutes. The wafer was then sprayed with gold for morphological characterization. Finally, electron micrographs were obtained and analyzed.

[0058] Example 1

[0059] Recyclable polymer template and preparation method thereof

[0060] Add 12 mmol of isopropylacrylamide and 0.09 mmol of azobisisobutyronitrile to a polymerization tube containing 210 mmol of anhydrous tetrahydrofuran, react in an oil bath at 65°C for 36 hours under nitrogen protection, cool to room temperature, evaporate the solvent, dissolve with a small amount of acetone, and then dropwise add to n-hexane. After filtration, vacuum dry at 30°C for 48 hours to obtain poly (N-isopropylacrylamide) as a white solid. The above solid is dissolved in an organic solvent of ether, 420 mmol of bromoethane is added, and the reaction is carried out at 45° C. for 30 hours to obtain a solution of a polyquaternary ammonium hydrohalide salt; the above solution is treated with a strong basic anion exchange resin (Type I, OH) until no halogen ions are detected in the liquid phase, and then filtered to obtain a solution of a polyquaternary ammonium base; the polyquaternary ammonium base solution is neutralized with an acid under room temperature water bath cooling, and the organic solvent is evaporated by reduced pressure distillation. The above liquid is cooled, extracted with ether, the ether phase is separated to remove, and the volatile components are removed in vacuo to obtain a polyquaternary ammonium salt PENOH shown in the following chemical formula I. The number average molecular weight of the polyquaternary ammonium salt PENOH measured by gel chromatography is 35,000 g / mol, which is the recyclable polymer template provided by the present invention.

[0061] Example 2

[0062] Recyclable polymer template and preparation method thereof

[0063] Add 11 mmol of isopropylacrylamide and 0.08 mmol of azobisisobutyronitrile to a polymerization tube containing 180 mmol of anhydrous tetrahydrofuran, react in an oil bath at 60°C for 32 hours under nitrogen protection, cool to room temperature, evaporate the solvent, dissolve with a small amount of acetone, and then dropwise add to n-hexane. After filtration, vacuum dry at 30°C for 48 hours to obtain poly (N-isopropylacrylamide) as a white solid. The above solid is dissolved in an organic solvent of ether, 360 mmol of ethyl bromide is added, and the mixture is reacted at 45° C. for 28 hours to obtain a solution of a polyquaternary ammonium hydrohalide salt; the above solution is treated with a strong basic anion exchange resin (Type I, OH) until no halogen ions are detected in the liquid phase, and then filtered to obtain a solution of a polyquaternary ammonium base; the polyquaternary ammonium base solution is neutralized with an acid under room temperature water bath cooling, and the organic solvent is evaporated by reduced pressure distillation. The above liquid is cooled, extracted with ether, the ether phase is separated to remove, and the volatile components are removed in vacuo to obtain a polyquaternary ammonium salt PENOH as shown in chemical formula I. The number average molecular weight of the polyquaternary ammonium salt PENOH measured by gel chromatography is 33,000 g / mol, which is the recyclable polymer template provided by the present invention.

[0064] Example 3

[0065] Recyclable polymer template and preparation method thereof

[0066] Add 10 mmol of isopropylacrylamide and 0.07 mmol of azobisisobutyronitrile to a polymerization tube containing 150 mmol of anhydrous tetrahydrofuran, react in an oil bath at 60°C for 30 h under nitrogen protection, cool to room temperature, evaporate the solvent, dissolve with a small amount of acetone, and then dropwise add to n-hexane. After filtration, vacuum dry at 30°C for 48 h to obtain poly (N-isopropylacrylamide) as a white solid. The above solid is dissolved in an organic solvent of ether, 300 mmol of ethyl bromide is added, and the reaction is carried out at 43° C. for 30 hours to obtain a solution of a polyquaternary ammonium hydrohalide salt; the above solution is treated with a strong basic anion exchange resin (Type I, OH) until no halogen ions are detected in the liquid phase, and then filtered to obtain a solution of a polyquaternary ammonium base; the polyquaternary ammonium base solution is neutralized with an acid under room temperature water bath cooling, and the organic solvent is evaporated by reduced pressure distillation. The above liquid is cooled, extracted with ether, the ether phase is separated to remove, and the volatile components are removed in vacuo to obtain a polyquaternary ammonium salt PENOH as shown in the chemical formula I. The number average molecular weight of the polyquaternary ammonium salt PENOH measured by gel chromatography is 31000 g / mol, which is the recyclable polymer template provided by the present invention.

[0067] Example 4

[0068] Recyclable polymer template and preparation method thereof

[0069] Add 9 mmol of isopropylacrylamide and 0.05 mmol of azobisisobutyronitrile to a polymerization tube containing 120 mmol of anhydrous tetrahydrofuran, react in an oil bath at 58°C for 36 hours under nitrogen protection, cool to room temperature, evaporate the solvent, dissolve with a small amount of acetone, and then dropwise add to n-hexane. After filtration, vacuum dry at 30°C for 48 hours to obtain poly (N-isopropylacrylamide) as a white solid. The above solid is dissolved in an organic solvent of ether, 240 mmol of ethyl bromide is added, and the mixture is reacted at 40° C. for 28 hours to obtain a solution of a polyquaternary ammonium hydrohalide salt; the above solution is treated with a strongly basic anion exchange resin (Type I, OH) until no halogen ions are detected in the liquid phase, and then filtered to obtain a solution of a polyquaternary ammonium base; the polyquaternary ammonium base solution is neutralized with an acid under room temperature water bath cooling, and the organic solvent is evaporated by reduced pressure distillation. The above liquid is cooled, extracted with ether, the ether phase is separated to remove, and the volatile components are removed in vacuo to obtain a polyquaternary ammonium salt PENOH as shown in the chemical formula I. The number average molecular weight of the polyquaternary ammonium salt PENOH measured by gel chromatography is 29000 g / mol, which is the recyclable polymer template provided by the present invention.

[0070] Example 5

[0071] Recyclable polymer template and preparation method thereof

[0072] Add 8 mmol of isopropylacrylamide and 0.03 mmol of azobisisobutyronitrile to a polymerization tube containing 90 mmol of anhydrous tetrahydrofuran, react in an oil bath at 55°C under nitrogen protection for 18 hours, cool to room temperature, evaporate the solvent, dissolve with a small amount of acetone, and then dropwise add to n-hexane. After filtration, vacuum dry at 25°C for 48 hours to obtain poly (N-isopropylacrylamide) as a white solid. The above solid was dissolved in an organic solvent of ether, 180 mmol of ethyl bromide was added, and the reaction was carried out at 40 ° C for 20 h to obtain a solution of a polyquaternary ammonium hydrohalide salt; the above solution was treated with a strong basic anion exchange resin (Type I, OH) until no halogen ions were detected in the liquid phase, and then filtered to obtain a solution of a polyquaternary ammonium base; under cooling in a water bath at room temperature, the polyquaternary ammonium base solution was neutralized with an acid, and the organic solvent was distilled off under reduced pressure. The above liquid was cooled, extracted with ether, the ether phase was separated and the volatile components were removed in vacuo to obtain the polyquaternary ammonium salt PENOH shown in the chemical formula I. The number average molecular weight of the polyquaternary ammonium salt PENOH was measured by gel chromatography to be 28000 g / mol, which is the recyclable polymer template provided by the present invention.

[0073] Example 6

[0074] A multi-level pore Beta molecular sieve and a preparation method thereof are prepared by a hydrothermal method using the recyclable polymer template PENOH provided in Example 1. The specific steps are as follows:

[0075] Molecular sieves were prepared by hydrothermal method: first, 0.02 g of NaAlO2 and 0.010 g of 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 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 300 SiO2 / 1 Al2O3 / 2 Na2O / 6000 H2O / 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) lined with polytetrafluoroethylene, placed in a homogeneous reactor at a rotation speed of 100 rpm, and crystallized at 140°C for 72 h; after the crystallization was completed, sample A containing the recyclable polymer template PENOH was obtained.

[0076] The above sample A is centrifuged to remove the template agent and obtain a multi-level pore Beta molecular sieve. The specific operation is:

[0077] Sample A obtained above was placed in a centrifuge tube and centrifuged at 6500 rpm and 25°C for 15 minutes. This yielded an upper layer consisting of the recyclable polymer template PENOH and a lower layer consisting of Beta molecular sieve. The Beta molecular sieve was washed with deionized water to a pH of ≈7 and then dried at 105°C for 12 hours to obtain the attached powder. The XRD diffraction pattern of the solid powder, shown in Figure 2, shows that the product phase was Beta molecular sieve as determined by XRD, and the SiO2 / Al2O3 ratio was 300 as determined by ICP.

[0078] Please refer to FIG3 . From the SEM morphology and structural characterization of the product, it can be seen that the multi-level pore Beta molecular sieve provided in this embodiment is composed of aggregated nanocrystals with a particle size of about 30 nm.

[0079] The multi-level pore Beta molecular sieve provided in this embodiment was used to conduct an Ar adsorption and desorption test, and the results are shown in Table 1. The Ar adsorption and desorption results show that the mesopore diameter of the multi-level pore Beta molecular sieve provided in this embodiment is concentrated at 30 nm, and the specific surface area is 596 m 2 / g, pore volume 0.72cm 3 / g.

[0080] Table 1 Texture parameters of the multi-level pore Beta molecular sieve prepared in Example 6

[0081] Example 7

[0082] A multi-level pore Beta molecular sieve and its preparation method (using a polymer template recovered by centrifugation as a template)

[0083] The method of Example 6 was followed, except that the PENOH obtained by centrifugation in Example 6 was used as the template. XRD analysis showed that the product obtained in this example was a Beta molecular sieve, and ICP analysis showed that the SiO2 / Al2O3 ratio was 300.

[0084] Among them, the XRD diffraction pattern of the multi-level pore Beta molecular sieve of this embodiment is similar to Figure 2, and the SEM characterization image of the multi-level pore Beta molecular sieve is similar to Figure 3.

[0085] The multi-level pore Beta molecular sieve provided in this embodiment was used to conduct an Ar adsorption and desorption test, and the results are shown in Table 2. The Ar adsorption and desorption results show that the mesopore diameter of the multi-level pore Beta molecular sieve provided in this embodiment is concentrated at 30 nm, and the specific surface area is 594 m 2 / g, pore volume 0.70cm 3 / g.

[0086] Table 2 Texture parameters of the multi-level pore Beta molecular sieve prepared in Example 7

[0087] Comparison of the results in Tables 1 and 2 reveals that the specific surface area and pore volume of the multi-level pore Beta molecular sieves prepared in Example 6 using the newly prepared recyclable polymer template PENOH and in Example 7 using the recycled polymer template PENOH were both reduced, but the decreases were small, at 0.34% and 2.78%, respectively. This demonstrates that the recyclable polymer template PENOH provided by the present invention, after centrifugal removal and subsequent recycling, is still highly effective as a template for preparing the next batch of multi-level pore Beta molecular sieves, while significantly reducing the cost of the template raw material.

[0088] Example 8

[0089] A multi-level pore Beta molecular sieve and a preparation method thereof are prepared by the following steps:

[0090] Preparation of molecular sieves by hydrothermal method: using the template prepared in Example 4, aluminum sulfate is used as the aluminum source, and silica sol is used as the silicon source. The order of adding the raw materials is the same as in Example 1, and the addition amount is adjusted so that the molar ratio of the feed is satisfied: the composition of the synthetic gel is 200SiO2 / 1Al2O3 / 2.4Na2O / 2800H2O / 0.022 recyclable polymer template PENOH. After aging at 25°C for 4h, the obtained gel is transferred to a 50mL stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 160°C for 48h to obtain sample A.

[0091] The above sample A is centrifuged to remove the template agent and obtain a multi-level pore Beta molecular sieve. The specific operation is:

[0092] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm and 25°C for 25 minutes. The resulting upper layer contained the recyclable polymer template PENOH, while the lower layer contained hierarchical Beta molecular sieves. The resulting hierarchical Beta molecular sieves were washed with deionized water to a pH of ≈7 and then dried at 105°C for 12 hours. XRD analysis confirmed the product to be a Beta molecular sieve phase, and ICP analysis revealed a SiO2 / Al2O3 ratio of 200.

[0093] The multi-level pore Beta molecular sieve provided in this embodiment was used to conduct an Ar adsorption and desorption test. The Ar adsorption and desorption results showed that the mesopore diameter was concentrated at 20 nm and the specific surface area was 600 m 2 / g, pore volume 0.42cm 3 / g.

[0094] Example 9

[0095] A multi-level pore Beta molecular sieve and a preparation method thereof are prepared by the following steps:

[0096] Preparation of molecular sieves by hydrothermal method: using the recyclable polymer template prepared in Example 5, sodium aluminate as the aluminum source and industrial silica gel as the silicon source, the order of adding the raw materials is the same as in Example 1, and the addition amount is adjusted to satisfy the molar ratio of the feed: the composition of the synthetic gel is 100SiO2 / 1Al2O3 / 2.6Na2O / 1500H2O / 0.012 polymer, and aged at 25°C for 4h. The obtained gel is transferred to a 50mL stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 180°C for 48h to obtain sample A.

[0097] The above sample A is centrifuged to remove the template agent and obtain a multi-level pore Beta molecular sieve. The specific operation is:

[0098] Sample A was placed in a centrifuge tube and centrifuged at 5000 rpm and 25°C for 30 minutes. The resulting upper layer contained the recyclable polymer template PENOH, while the lower layer contained hierarchical Beta molecular sieves. The resulting hierarchical Beta molecular sieves were washed with deionized water to a pH of ≈7 and then dried at 105°C for 12 hours. XRD analysis confirmed the product to be a Beta molecular sieve phase, while ICP analysis revealed a SiO2 / Al2O3 ratio of 100.

[0099] The multi-level pore Beta molecular sieve provided in this embodiment was used to conduct an Ar adsorption and desorption test. The Ar adsorption and desorption results showed that the mesopore diameter was concentrated at 8 nm and the specific surface area was 500 m 2 / g, pore volume 0.36cm 3 / g.

[0100] Comparative Example 1

[0101] No recyclable polymer template PENOH was added, and other operations were the same as in Example 6. XRD analysis showed that the obtained product was amorphous silicon dioxide. For detailed XRD results of the product of Comparative Example 1, please refer to FIG4 .

[0102] Comparative Example 2

[0103] No recyclable polymer template PENOH was added, and other operations were the same as in Example 8. XRD analysis showed that the obtained product was amorphous silicon dioxide. For detailed XRD results of the product of Comparative Example 2, please refer to FIG5 .

[0104] Comparative Example 3

[0105] No recyclable polymer template PENOH was added, and other operations were the same as in Example 9. XRD analysis showed that the obtained product was a mixture of ZSM-5 molecular sieve and amorphous silica. For detailed XRD results of the product of Comparative Example 3, please refer to FIG6 .

[0106] From the comparison results of Examples 5-9 and Comparative Examples 1-3, it can be seen that the multi-level pore Beta molecular sieve structure synthesized by the method of the present invention contains both micropores and mesopores, which is a multi-level pore structure, effectively solving the mass transfer problem existing in traditional Beta molecular sieves. However, the phases of the molecular sieves synthesized by the methods of Comparative Examples 1-3 do not belong to Beta molecular sieves. Therefore, there is no basis for further exploring whether the molecular sieves form a Beta molecular sieve with a microporous-mesoporous multi-level pore size. That is, Comparative Examples 1-3, which do not use the recyclable polymer template provided by the present invention to prepare the molecular sieve, cannot solve the technical problem to be solved by the present invention.

[0107] Furthermore, it can be seen from the mesopore size distribution of the Beta molecular sieves with multi-level pore sizes obtained in Examples 5-9 that the pore size increases with the increase in the amount of the recyclable polymer template within an appropriate range.

[0108] The recyclable polymer template employed in the present method can be removed simply by centrifugation and reused repeatedly, reducing costs and improving atomic utilization. Furthermore, the resulting hierarchical Beta molecular sieve does not require high-temperature calcination, avoiding severe dealumination of the molecular sieve framework, partial collapse of the framework, and decreased crystallinity. Furthermore, the method offers the advantages of high efficiency, greenness, and environmental friendliness.

[0109] In addition, compared with conventional molecular sieves, the multi-level pore Beta molecular sieve synthesized by the method of the present invention has a higher specific surface area of ​​500-600m 2 / g and pore volume 0.36-0.72cm 3 / g, Beta molecular sieve has better application performance and expands its application range.

[0110] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection of the present invention. Therefore, based on the innovative concept of the present invention, changes and modifications to the embodiments described herein, or equivalent structural or equivalent process transformations made using the contents of the present invention's specification and drawings, and direct or indirect application of the above technical solutions to other related technical fields, are all included in the scope of patent protection of the present invention.

Claims

1. A recyclable polymer template, characterized in that: The number average molecular weight is 28000-35000 g / mol, and it has the chemical structure shown below: Here, n is an integer greater than 1.

2. A method for preparing a recyclable polymer template as claimed in claim 1, characterized in that: The following steps are involved: Isopropyl acrylamide and azobisisobutyronitrile are added to a polymerization tube containing anhydrous tetrahydrofuran, reacted in an oil bath under a nitrogen atmosphere, cooled, the solvent evaporated, dissolved with acetone, then dripped into n-hexane dropwise, filtered, and dried in vacuum to obtain poly (N-isopropyl acrylamide); The poly(N-isopropylacrylamide) is dissolved in ether, ethyl bromide is added, and the mixture is reacted to obtain a poly(quaternary ammonium hydrohalide); Treating the polyquaternary ammonium hydrohalide with a strong alkaline anion exchange resin and filtering to obtain a polyquaternary ammonium base solution; The polyquaternary ammonium base solution is cooled in a water bath, neutralized by adding acid, distilled under reduced pressure, cooled again, extracted, separated, and volatile components are removed in vacuo to obtain the recyclable polymer template.

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

4. The preparation method according to claim 2, characterized in that: The temperature of the oil bath reaction is 55-65° C., the oil bath reaction time is 18-36 hours, the temperature of the vacuum drying is 25-30° C., and the vacuum drying time is 40-48 hours.

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

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

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

8. The preparation method according to claim 6, characterized in that: The aluminum source includes sodium metaaluminate and / or aluminum sulfate, the silicon source includes 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 centrifugal speed is 5000-8000 rpm, the centrifugal temperature is 20-35° C., and the centrifugal time is 10-30 min.

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

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