Modified l zeolite, preparation method thereof, modified l zeolite catalyst, preparation method and application thereof

Abstract

This invention relates to the field of molecular sieve preparation, and discloses a modified L-type molecular sieve and its preparation method, a modified L-type molecular sieve catalyst and its preparation method and application. The modified L-type molecular sieve contains silicon oxide, aluminum oxide, and element M, wherein element M is an alkali metal and / or alkaline earth metal; the microporous specific surface area is 280-330 m² / g. 2 / g, the proportion of pore volume with a pore size less than 0.7nm to the total pore volume is ≥50%, and the proportion of pore volume with a pore size greater than 0.9nm to the total pore volume is ≥10%. This modified L molecular sieve exhibits better selectivity, with a wider range of micropore sizes. The pore size distribution is concentrated at both ends, which is conducive to the entry of macromolecules into the molecular sieve channels. At the same time, the high proportion of micropore specific surface area helps to improve catalytic activity.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve preparation, specifically to a modified L molecular sieve and its preparation method, a modified L molecular sieve catalyst and its preparation method and application. Background Technology

[0002] L-type molecular sieves possess one-dimensional straight channels with twelve-membered rings and a channel diameter of 0.71 nm. They exhibit a unique one-dimensional channel structure. This special channel structure can be used for the separation and catalysis of alkane molecules.

[0003] By adjusting the pore size of molecular sieves, the diffusion resistance of diffusing substances, reactants, reaction intermediates, or products can be increased or decreased, thereby improving the shape selectivity of molecular sieves.

[0004] CN109529923B discloses a method for preparing oxide-modified microporous molecular sieve shape-selective catalysts. This method uses microporous molecular sieves ZSM-5 and MCM-22 (without removing the template agent) as supports and metal nitrates as precursors. The metal oxides are loaded onto the outer surface of the microporous molecular sieves via an impregnation method. At this stage, the pores of the microporous molecular sieves are still occupied by the template agent. Therefore, during the impregnation process, metal nitrate ions cannot diffuse into the inner pores of the molecular sieve, thus ensuring that the obtained shape-selective catalyst exhibits good catalytic activity during use.

[0005] CN114620742A discloses a method for preparing hierarchical porous molecular sieves. This method involves treating the molecular sieve with an alkali in the presence of a chelating agent to obtain a hierarchical porous molecular sieve precursor, followed by ion exchange to obtain the final hierarchical porous molecular sieve. This method improves the diffusion restriction of microporous molecular sieves, resulting in hierarchical porous molecular sieves with large pore volumes while maintaining their original microporous structure.

[0006] Therefore, there is a need for an L-type molecular sieve with better shape selectivity and better suitability for material diffusion. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of narrow micropore distribution range, difficulty for macromolecules to enter the molecular sieve channels, and low catalytic activity in existing L molecular sieves. This invention provides a modified L molecular sieve and its preparation method, a modified L molecular sieve catalyst and its preparation method and application. This modified L molecular sieve exhibits better selectivity, a wider micropore size range, and a pore size distribution that converges towards both ends, which facilitates the entry of macromolecules into the molecular sieve channels. Simultaneously, the high micropore specific surface area ratio helps improve catalytic activity.

[0008] To achieve the above objectives, a first aspect of the present invention provides a modified L-molecular sieve, wherein the modified L-molecular sieve contains silicon oxide, aluminum oxide, and an element M, wherein the element M is an alkali metal and / or an alkaline earth metal; and the micropore specific surface area is 280-330 m².2 / g, the proportion of pore volume with a pore size less than 0.7nm to the total pore volume is ≥50%, and the proportion of pore volume with a pore size greater than 0.9nm to the total pore volume is ≥10%.

[0009] Preferably, the modified L-molecular sieve has a microporous specific surface area of ​​310-330 m². 2 / g.

[0010] Preferably, the volume of pores with a diameter less than 0.7 nm accounts for 70-80% of the total pore volume, and the volume of pores with a diameter greater than 0.9 nm accounts for 14-18% of the total pore volume.

[0011] A second aspect of this invention provides a method for preparing modified L-molecular sieves, comprising the following steps:

[0012] (1) Provide a gelling mixture containing at least one inorganic alkali, an aluminum source, and a silicon source, and obtain L molecular sieve after crystallization;

[0013] (2) The L molecular sieve is post-treated in a solution containing alkali metal compounds and / or alkaline earth metal compounds, and then the resulting solid product is calcined to obtain modified L molecular sieve.

[0014] In step (2), the types of alkali metals and / or alkaline earth metals are different from the types of metal elements in the inorganic alkali described in step (1).

[0015] Preferably, the concentration of alkali metals and / or alkaline earth metals in the solution containing alkali metal compounds and / or alkaline earth metal compounds is 0.2-1 mol / L, more preferably 0.4-0.8 mol / L.

[0016] Preferably, the post-treatment conditions include: a temperature of 20-120℃, more preferably 25-100℃; a time of 6-24h, more preferably 8-14h; and preferably carried out under stirring and reflux conditions.

[0017] The third aspect of this invention provides a modified L-molecular sieve prepared by the preparation method described in the second aspect.

[0018] A fourth aspect of the present invention provides a modified L-molecular sieve catalyst, wherein the modified L-molecular sieve catalyst comprises the modified L-molecular sieve described in the first or third aspect, and Pt supported on the modified L-molecular sieve, wherein the content of Pt is 0.2-3 wt% based on a total mass of 100 wt% of the modified L-molecular sieve catalyst.

[0019] A fifth aspect of the present invention provides a method for preparing a modified L-zeolite catalyst, wherein the method comprises:

[0020] The modified L molecular sieve described in the first or third aspect is impregnated with a solution containing a Pt precursor, and then calcined to obtain a modified L molecular sieve catalyst.

[0021] Preferably, the concentration of Pt in the Pt precursor solution is 1.14 × 10⁻⁶. -2 -1.71×10 -1 mol / L.

[0022] Preferably, the calcination conditions include: a calcination temperature of 473-673K and a calcination time of 1-5h.

[0023] The sixth aspect of the present invention provides the application of the aforementioned modified L molecular sieve catalyst or the modified L molecular sieve catalyst prepared by the aforementioned preparation method in the alkane aromatization reaction.

[0024] The beneficial effects obtained by the present invention through the above technical solution are as follows:

[0025] (1) The modified L molecular sieve provided by the present invention has a wider micropore size distribution, with the pore size distribution clustered at both ends. The volume of pores with a pore size less than 0.7 nm accounts for ≥50% of the total pore volume, and the volume of pores with a pore size greater than 0.9 nm accounts for ≥10% of the total pore volume. The above pore structure is conducive to the entry of macromolecules into the L molecular sieve pores, and at the same time has a larger micropore specific surface area ratio, which helps to provide more active sites and improve the catalytic activity of L molecular sieve.

[0026] (2) In this invention, preferably, a special post-treatment solution is used to post-treat the L molecular sieve. The alkali metal and / or alkaline earth metal in the post-treatment solution replace some of the alkali metal in the L molecular sieve structure. By adjusting the pore size distribution of the modified L molecular sieve through different atomic sizes, the original L molecular sieve channel structure is not destroyed, thereby improving the catalytic activity of the L molecular sieve. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] The first aspect of this invention provides a modified L-molecule sieve, wherein the modified L-molecule sieve contains silicon oxide, aluminum oxide, and an element M, wherein the element M is an alkali metal and / or an alkaline earth metal; and the micropore specific surface area is 280-330 m². 2 / g, the proportion of pore volume with a pore size less than 0.7nm to the total pore volume is ≥50%, and the proportion of pore volume with a pore size greater than 0.9nm to the total pore volume is ≥10%.

[0029] In this invention, the modified L molecular sieve with the above structure has an increased proportion of pore volume with a pore size greater than 0.9 nm to the total pore volume, which is conducive to the entry of macromolecules into the L molecular sieve channels and is suitable for the diffusion of macromolecules.

[0030] In this invention, the specific surface area, micropore specific surface area, and pore size distribution of the modified L-molecule sieve were measured using a nitrogen isothermal adsorption-desorption curve method. The instrument used was a Micromeritics ASAP 2420 physical adsorption instrument. The test conditions were: sample at 300℃ and 1.33 × 10⁻⁶ ppm. -2 The sample was purified by maintaining a constant temperature and pressure for 4 hours. Then, the sample was brought into contact with the adsorbate at a liquid nitrogen temperature of 77K to reach adsorption equilibrium. The specific surface area, micropore specific surface area, and pore size distribution were calculated by the difference between the nitrogen gas inlet rate and the amount remaining in the gas phase after adsorption.

[0031] According to the present invention, preferably, the microporous specific surface area of ​​the modified L molecular sieve is 310-330 m². 2 / g. In this invention, the modified L molecular sieve has a large micropore specific surface area, which helps to provide more active sites and improve the catalytic activity of the modified L molecular sieve.

[0032] According to the present invention, preferably, the proportion of pore volume with a pore size less than 0.7 nm to the total pore volume is 70-80%, and the proportion of pore volume with a pore size greater than 0.9 nm to the total pore volume is 14-18%. In the present invention, the total pore volume is taken as 100%, and the remainder is the proportion of pore volume with a pore size of 0.7-0.9 nm to the total pore volume.

[0033] According to the present invention, preferably, the modified L molecular sieve has a specific surface area of ​​295-350 m². 2 / g, preferably 315-340m 2 / g.

[0034] According to the present invention, preferably, the micropore size of the modified L molecular sieve is 0.5-1.5 nm, more preferably 0.55-1.2 nm.

[0035] According to the present invention, preferably, the relative crystallinity of the modified L molecular sieve is >90%, more preferably >95%.

[0036] In this invention, the relative crystallinity of the modified L-type molecular sieve is based on the standard L-type molecular sieve, which is defined as 100%. The relative crystallinity is calculated as follows: the data obtained from the diffractometer are compiled into a text document format, and a phase spectrum is plotted using JADE 5.0 software. Peak areas of characteristic peaks with 2θ angles of approximately 14.7, 19.3, 22.6, 24.3, 25.5, 28.0, 29.0, and 30.6 are obtained by peak searching and integration. The peak areas of these eight characteristic peaks are summed, and the ratio of the sum of the peak areas of the eight characteristic peaks obtained under the same analytical conditions as the standard sample is calculated. This ratio represents the relative crystallinity. The XRD instrument used was a Rigaku D / MAX-Ⅲ AX-ray diffractometer (Japan). Experimental conditions: Cu target, Kα radiation, Ni filter, tube voltage 45kV, tube current 250mA, scanning range 5°-50°, step size 0.02°.

[0037] In this invention, the standard L molecular sieve is the PL-8 type L molecular sieve produced by Sinopec Catalyst Co., Ltd.

[0038] According to the present invention, preferably, the modified L molecular sieve further contains element A, which is different from element M, and element A is an alkali metal. In the present invention, element A is K and / or Na.

[0039] According to the present invention, preferably, the element M is selected from at least one of Li, Rb, Cs, Be, Mg, Ca, and Ba, and more preferably from at least one of Li, Mg, and Ba. In this invention, the atomic radius of the aforementioned element M differs from the atomic radius of the metal element A in the original L-type molecular sieve. Introducing the aforementioned element M into the L-type molecular sieve alters the pore size distribution of the L-type molecular sieve, which is beneficial for increasing the number of active sites on the L-type molecular sieve and improving its catalytic activity.

[0040] According to the present invention, preferably, element M is calculated as an oxide, element A is calculated as an oxide, and the molar ratio of each component in the modified L molecular sieve is n(M) / (A) = 1 / 2. x O):n(A2O):n(Al2O3):n(SiO2) = (0.05-0.25):(0.5-1.5):1:(3-8), preferably (0.07-0.23):(0.6-1.2):1:(5-6), where x is 1 or 2. In this invention, the modified L-type molecular sieve with the above molar ratio, combined with a special molecular sieve structure, improves the diffusion restriction of the original L-type molecular sieve and exhibits better catalytic activity.

[0041] In this invention, the content of each component in the modified L molecular sieve is determined by X-ray fluorescence spectrometry using an instrument of the Rigaku Electric Co., Ltd. 3013 X-ray fluorescence analyzer.

[0042] A second aspect of this invention provides a method for preparing modified L-molecular sieves, comprising the following steps:

[0043] (1) Provide a gelling mixture containing at least one inorganic alkali, an aluminum source, and a silicon source, and obtain L molecular sieve after crystallization;

[0044] (2) The L molecular sieve is post-treated in a solution containing alkali metal compounds and / or alkaline earth metal compounds, and then the resulting solid product is calcined to obtain modified L molecular sieve.

[0045] In step (2), the types of alkali metals and / or alkaline earth metals are different from the types of metal elements in the inorganic alkali described in step (1).

[0046] In this invention, the types of alkali metals and / or alkaline earth metals in step (2) are different from the types of metal elements in the inorganic alkali described in step (1). By replacing some of the alkali metal elements in the L-type molecular sieve obtained in step (1) with alkali metals and / or alkaline earth metals in step (2), the structure of the modified L-type molecular sieve changes because the atomic radii of the replaced metal elements are different from those of the original metal elements on the L-type molecular sieve. The proportion of pores with a pore size less than 0.7 nm increases, which is beneficial to increasing the number of active sites on the L-type molecular sieve and improving its catalytic activity.

[0047] According to the present invention, preferably, the alkali metal compound and / or alkaline earth metal compound are each independently selected from at least one of alkali metal and / or alkaline earth metal nitrates, chlorides, and hydroxides. In the present invention, there is no particular limitation on the alkali metal compound and / or alkaline earth metal compound, as long as it can dissolve in water to form a solution.

[0048] According to the present invention, preferably, the alkali metal and / or alkaline earth metal is selected from at least one of Li, Rb, Cs, Be, Mg, Ca, and Ba, and more preferably from at least one of Li, Mg, and Ba. In the present invention, the solution containing the alkali metal compound and / or alkaline earth metal compound is an alkaline solution. During the post-treatment of the L molecular sieve, it has a partial pore-expanding effect on the pores of the L molecular sieve, thereby increasing the proportion of pore volume with a pore size greater than 0.9 nm to the total pore volume.

[0049] According to the present invention, preferably, the concentration of alkali metal and / or alkaline earth metal in the solution containing alkali metal compound and / or alkaline earth metal compound is 0.2-1 mol / L, for example, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, or any range between any two values, preferably 0.4-0.8 mol / L. The solvent of the solution is water.

[0050] According to the present invention, preferably, in step (2), based on the mass of the L molecular sieve being 1g, the volume of the solution containing alkali metal compounds and / or alkaline earth metal compounds is 5-50mL, preferably 8-30mL.

[0051] According to the present invention, preferably, the post-processing conditions include: a temperature of 20-120°C, for example, 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, any range between any two values, preferably 25-100°C; and a time of 6-24h, for example, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, any range between any two values, preferably 8-14h.

[0052] In this invention, preferably, the post-processing is carried out under the above conditions, so that the alkali metal and / or alkaline earth metal elements in the solution containing alkali metal compounds and / or alkaline earth metal compounds can effectively replace part of the original metal elements in the L molecular sieve within a suitable temperature and time range, while not excessively corroding the pore structure of the L molecular sieve due to excessively high temperature or excessively long exchange time.

[0053] In this invention, the post-treatment is carried out under stirring and reflux conditions. The stirring rate is not particularly limited, and those skilled in the art can adapt the stirring and reflux conditions according to the post-treatment situation. The apparatus for the post-treatment is not particularly limited; according to a preferred embodiment of the invention, the post-treatment is carried out in a magnetic stirrer.

[0054] According to a preferred embodiment of the present invention, after preparing a solution containing an alkali metal compound and / or an alkaline earth metal compound, stirring and heating are initiated. L-molecular sieves are added to the solution, and the stirring rate and heating temperature are maintained at reflux. The above post-treatment method is an example of one post-treatment method of the present invention; the order in which the substances are added and the order in which stirring is initiated are not particularly limited during the post-treatment process.

[0055] According to the present invention, preferably, step (2) further includes washing and filtering the obtained solid product after post-processing until the pH of the washing solution is 7-9, drying the washed product, and then performing the calcination. The washing and filtering conditions are known to those skilled in the art and are not particularly limited.

[0056] In this invention, the drying process and equipment are not particularly limited, and those skilled in the art can make adaptive adjustments as needed. Preferably, the drying conditions include drying at 80-140°C for 10-16 hours.

[0057] According to the present invention, preferably, the calcination conditions include: a calcination temperature of 200-500℃, for example, 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, any range between any two values, preferably 300-450℃; and a calcination time of 1-12h, for example, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, any range between any two values, preferably 2-8h. In the present invention, calcination under the above conditions can yield modified L-molecular sieves with better structural stability and higher catalytic activity.

[0058] According to the present invention, preferably, the inorganic alkali added in step (1) is calculated as A2O, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2, so that the molar ratio of each component in the L molecular sieve is n(A2O):n(Al2O3):n(SiO2) is (0.8-1.8):1:(3-8), preferably (0.9-1.5):1:(5-6), and the A element is K and / or Na.

[0059] In this invention, preferably, the inorganic base in step (1) is KOH and / or NaOH.

[0060] In this invention, water is added in step (1) to prepare a gel mixture. The amount of water is not particularly limited, and those skilled in the art can make adaptive adjustments based on the preparation of the gel mixture. Preferably, in the gel mixture, the aluminum source is Al2O3, and the molar ratio of aluminum source to water, n(Al2O3):n(H2O), is 1:(20-200).

[0061] In this invention, the aluminum source is a conventional aluminum source for preparing molecular sieves, which can be adapted to the needs of those skilled in the art. Preferably, the aluminum source is hydrated alumina and / or aluminate, and more preferably aluminum hydroxide.

[0062] In this invention, the silicon source is a conventional silicon source for preparing molecular sieves, which can be adapted by those skilled in the art as needed. Preferably, the silicon source is selected from at least one of silica sol, silica, water glass, and diatomaceous earth.

[0063] According to the present invention, preferably, the crystallization conditions include: a crystallization temperature of 120-180℃, for example, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, or 180℃, any range between any two values, preferably 140-170℃; and a crystallization time of 30-100h, any range between any two values, preferably 50-80h. Using the above crystallization conditions for the crystallization reaction can produce L-type molecular sieves with a wider pore size distribution and a larger micropore specific surface area, which is beneficial for further post-processing to obtain modified L-type molecular sieve structures.

[0064] In this invention, the reaction equipment required for the preparation of L-molecular sieves is not particularly limited, and those skilled in the art can make adaptive adjustments as needed. Preferably, the preparation of the L-molecular sieves is carried out in a reaction vessel.

[0065] The third aspect of this invention provides a modified L-molecular sieve prepared by the preparation method described in the second aspect.

[0066] A fourth aspect of the present invention provides a modified L-molecular sieve catalyst, wherein the modified L-molecular sieve catalyst comprises the modified L-molecular sieve described in the first or third aspect, and Pt supported on the modified L-molecular sieve, wherein the content of Pt is 0.2-3 wt% based on a total mass of 100 wt% of the modified L-molecular sieve catalyst.

[0067] A fifth aspect of the present invention provides a method for preparing a modified L-zeolite catalyst, wherein the method comprises:

[0068] The modified L molecular sieve described in the first or third aspect is impregnated with a solution containing a Pt precursor, and then calcined to obtain a modified L molecular sieve catalyst.

[0069] According to the present invention, preferably, the concentration of Pt in the Pt precursor solution is 1.14 × 10⁻⁶. -2 -1.71×10 -1 mol / L.

[0070] In this invention, the amounts of the modified L-type molecular sieve and the Pt-containing precursor solution can be adjusted as needed by those skilled in the art, and the Pt content in the obtained modified L-type molecular sieve catalyst only needs to be 0.2-3 wt%. Preferably, the amount of the Pt-containing precursor solution relative to 10 g of the modified L-type molecular sieve is 5-15 mL, more preferably 8-12 mL.

[0071] In this invention, preferably, the Pt precursor solution is diluted with deionized water, and then the modified L molecular sieve is placed in the diluted solution. The volume of deionized water added is 1-20:1 for the Pt precursor solution, for example, 1:1, 2:1, 5:1, 10:1, 15:1, 20:1, and any range between any two values, preferably 2-10:1.

[0072] According to the present invention, preferably, the calcination conditions include: a calcination temperature of 473-673 K and a calcination time of 1-5 h.

[0073] In this invention, preferably, before calcination, the process further includes stirring and drying the impregnated modified L molecular sieve. There is no particular limitation on the stirring rate, which can be adjusted by those skilled in the art according to the preparation of the modified L molecular sieve catalyst.

[0074] In this invention, preferably, the drying conditions include: a drying temperature of 100-140℃ and a drying time of 8-16h.

[0075] The sixth aspect of the present invention provides the application of the aforementioned modified L molecular sieve catalyst or the modified L molecular sieve catalyst prepared by the aforementioned preparation method in the alkane aromatization reaction.

[0076] In this invention, preferably, the alkane is a C5 or higher alkane, and more preferably a C6-C8 alkane.

[0077] In this invention, the reaction conditions for the alkane aromatization reaction are not particularly limited, and those skilled in the art can make adaptive adjustments as needed.

[0078] According to a particularly preferred embodiment of the present invention, a method for preparing a modified L-molecular sieve includes the following steps:

[0079] (1) Provide a gelling mixture containing at least one inorganic alkali, an aluminum source, and a silicon source, and obtain L molecular sieve after crystallization;

[0080] (2) The L molecular sieve is post-treated in a solution containing alkali metal compounds and / or alkaline earth metal compounds, and then the resulting solid product is calcined to obtain modified L molecular sieve.

[0081] In step (2), the types of alkali metals and / or alkaline earth metals are different from the types of metal elements in the inorganic alkali described in step (1);

[0082] The alkali metal and / or alkaline earth metal is selected from at least one of Li, Mg and Ba;

[0083] The concentration of alkali metals and / or alkaline earth metals in the solution containing alkali metal compounds and / or alkaline earth metal compounds is 0.4-0.8 mol / L;

[0084] The post-processing conditions include: a temperature of 25-100℃ and a time of 8-14 hours;

[0085] The roasting conditions include: a roasting temperature of 300-450℃ and a roasting time of 2-8h.

[0086] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, the reagents and materials used in the following examples and comparative examples are commercially available, and the room temperature is 25°C.

[0087] The test methods and conditions for the specific surface area, micropore specific surface area, pore size distribution, relative crystallinity and chemical composition of the modified L molecular sieve are described in the aforementioned specification and will not be repeated here.

[0088] Example 1 of L-molecular sieve preparation

[0089] 19.62 g of KOH was dissolved in 68.72 g of deionized water. 10.44 g of Al(OH)3 was added to the solution and dissolved under magnetic stirring. 23.04 g of SiO2 was then added as a silica sol, and the mixture was stirred until homogeneous, yielding a gel-like mixture. This gel-like mixture was transferred to a stainless steel reactor and crystallized at 150 °C for 72 h. The product was centrifuged, and the resulting solid was washed with water and dried at 120 °C for 12 h to obtain L-1 molecular sieve.

[0090] Example 2 of L-molecular sieve preparation

[0091] 17.62 g of KOH was dissolved in 58.72 g of deionized water. 8.14 g of Al(OH)3 was added to the solution and dissolved under magnetic stirring. 31 g of SiO2 was then added as a silica sol, and the mixture was stirred until homogeneous, yielding a gel-like mixture. This mixture was transferred to a stainless steel reactor and crystallized at 150 °C for 72 h. The product was centrifuged, and the resulting solid was washed with water and dried at 120 °C for 12 h to obtain L-2 molecular sieve.

[0092] Example 3 of L-molecular sieve preparation

[0093] 12.89 g of NaOH was dissolved in 58.72 g of deionized water. 8.14 g of Al(OH)3 was added to the solution and dissolved under magnetic stirring. 31.00 g of SiO2 was then added as a silica sol, and the mixture was stirred until homogeneous, yielding a gel-like mixture. This gel-like mixture was transferred to a stainless steel reactor and crystallized at 170 °C for 58 h. The product was centrifuged, and the resulting solid was washed with water and dried at 120 °C for 12 h to obtain L-3 molecular sieve.

[0094] Example 1

[0095] 4.24 g of LiCl was dissolved in 200 mL of deionized water and heated to 50 °C with a magnetic stirrer. 20 g of L-1 molecular sieve was added to the solution and the mixture was post-treated under stirring and reflux for 8 h. The resulting solid product was washed and filtered until the pH of the washing solution was 9. The washing product was dried at 120 °C for 12 h and calcined at 400 °C for 4 h to obtain L-Li-1 molecular sieve.

[0096] Example 2

[0097] 9.52 g of MgCl2 was dissolved in 200 mL of deionized water and heated to 50 °C with a magnetic stirrer. 20 g of L-1 molecular sieve was added to the solution and the mixture was post-treated under stirring and reflux for 8 h. The resulting solid product was washed and filtered until the pH of the washing solution was 9. The washing product was dried at 120 °C for 12 h and calcined at 400 °C for 4 h to obtain L-Mg-1 molecular sieve.

[0098] Example 3

[0099] 4.24 g of LiCl was dissolved in 200 mL of deionized water and heated to 50 °C with a magnetic stirrer. 20 g of L-2 molecular sieve was added to the solution and the mixture was post-treated under stirring and reflux for 8 h. The resulting solid product was washed and filtered until the pH of the washing solution was 9. The washing product was dried at 120 °C for 12 h and calcined at 400 °C for 4 h to obtain L-Li-2 molecular sieve.

[0100] Example 4

[0101] Modified L-zeolite was prepared according to the method in Example 2, except that the post-treatment temperature was changed to 110℃ to obtain L-Mg-2 zeolite.

[0102] Example 5

[0103] Modified L-zeolite was prepared according to the method in Example 2, except that the post-treatment time was 16 h, resulting in L-Mg-3 zeolite.

[0104] Example 6

[0105] Modified L-zeolite was prepared according to the method in Example 2, except that 9.52 g of MgCl2 was replaced with 19.04 g of MgCl2 to obtain L-Mg-4 zeolite.

[0106] Example 7

[0107] Modified L-type molecular sieves were prepared according to the method in Example 2, except that 9.52 g of MgCl2 was replaced with 16.84 g of CsCl to obtain L-Cs-1 molecular sieves.

[0108] Example 8

[0109] Modified L-zeolite was prepared according to the method in Example 2, except that 20g of L-1 zeolite was replaced with 20g of L-3 zeolite to obtain NaL-Mg-5 zeolite.

[0110] Comparative Example 1

[0111] The L-zeolite of Example 1 was prepared using L-zeolite without post-treatment.

[0112] Test Example 1

[0113] The relative crystallinity test results of the modified L molecular sieve are shown in Table 1, and the specific surface area and pore size distribution test results are shown in Table 2.

[0114] Table 1

[0115]

[0116]

[0117] As can be seen from the results in Table 1, the modified L molecular sieve prepared by the method described in this invention can maintain a higher relative crystallinity.

[0118] Table 2

[0119]

[0120] Note: The proportion of pore volume with a diameter of 0.7-0.9 nm to the total pore volume = 100% minus the proportion of pore volume with a diameter less than 0.7 nm to the total pore volume, and then minus the proportion of pore volume with a diameter greater than 0.9 nm to the total pore volume.

[0121] As can be seen from the results in Table 2, the modified L molecular sieve prepared in the embodiments of the present invention has a larger microporous specific surface area, with pores smaller than 0.7 nm accounting for more than 50% and pores larger than 0.9 nm accounting for more than 10%.

[0122] Test Example 2: Evaluation of the Reaction Performance of Modified L-Molecular Sieves Catalyst

[0123] To prepare the modified L-molecular sieve catalyst, 9 mL of platinum ammonia solution (Pt molar concentration of 5.7 × 10⁻⁶) was taken. - 210 g of modified L molecular sieve (the L molecular sieves used in each catalyst preparation example are listed in Table 3) was added to each catalyst, stirred at 50 rpm for 6 h at room temperature, dried at 120 °C for 12 h, and calcined at 623 K for 3 h to obtain L molecular sieve catalyst with a Pt content of 1 wt%.

[0124] Using n-hexane as the reactant, the reaction temperature was 470℃, the reaction pressure was 0.3 MPa, and the volume hourly space velocity (VHSV) of the reactants was 4 h⁻¹. -1 The modified L-zeolite catalyst was evaluated for reaction, and its performance was characterized by benzene yield and reactant conversion after 10 hours of reaction.

[0125] The reaction performance evaluation results of the modified L molecular sieve catalyst are shown in Table 3.

[0126] Benzene yield = percentage of benzene by mass in the reaction product;

[0127] Reactant conversion rate = 1 - (mass of n-hexane in the product / amount of n-hexane raw material).

[0128] Table 3

[0129]

[0130] As shown in Table 3, the catalysts prepared using the L-Li-1 molecular sieve of Example 1 and the L-Mg-1 molecular sieve of Example 2, synthesized under the preferred modification conditions, exhibited higher reactant conversion rates and benzene yields after 10 hours of reaction compared to the catalysts prepared using unmodified L-zeolite as the support. When the modification conditions were too stringent and outside the preferred range, the catalysts prepared using L-Mg-2 of Example 4 and L-Mg-4 of Example 6 as supports showed slightly lower reactant conversion rates and benzene yields after 10 hours of reaction compared to the catalysts prepared in Catalyst Preparation Examples 1 and 2, but better than the catalyst prepared using the unmodified catalyst in Comparative Example 1. The molecular sieve modification method described in this invention demonstrates superior performance.

[0131] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified L-molecular sieve, characterized in that, The modified L-type molecular sieve contains silicon oxide, aluminum oxide, and element M, wherein element M is an alkali metal and / or alkaline earth metal; the microporous specific surface area is 280-330 m². 2 / g, the proportion of pore volume with a pore size less than 0.7 nm to the total pore volume is ≥50%, and the proportion of pore volume with a pore size greater than 0.9 nm to the total pore volume is ≥10%; the modified L molecular sieve also contains element A, which is different from element M, and element A is an alkali metal; element M is selected from at least one of Li, Rb, Cs, Be, Mg, Ca and Ba; element M is calculated as an oxide, element A is calculated as an oxide, and the molar ratio of each component in the modified L molecular sieve is n(M x O):n(A2O):n(Al2O3):n(SiO2)=(0.05-0.25):(0.5-1.5):1:(3-8), where x is 1 or 2.

2. The modified L-molecular sieve according to claim 1, wherein, The modified L-type molecular sieve has a microporous specific surface area of ​​310-330 m². 2 / g.

3. The modified L-molecular sieve according to claim 1, wherein, The volume of pores with a diameter less than 0.7 nm accounts for 70-80% of the total pore volume, while the volume of pores with a diameter greater than 0.9 nm accounts for 14-18% of the total pore volume.

4. The modified L-molecular sieve according to claim 1, wherein, The modified L-molecule sieve has a specific surface area of ​​295-350 m². 2 / g; And / or, the micropore size of the modified L molecular sieve is 0.5-1.5 nm.

5. The modified L-molecular sieve according to claim 4, wherein, The modified L-molecular sieve has a specific surface area of ​​315-340 m². 2 / g; And / or, the micropore size of the modified L molecular sieve is 0.55-1.2 nm.

6. The modified L-molecular sieve according to claim 1, wherein, The relative crystallinity of the modified L-zeolite is >90%.

7. The modified L-molecular sieve according to claim 6, wherein, The relative crystallinity of the modified L-zeolite is >95%.

8. The modified L-molecular sieve according to claim 1, wherein, The element M is selected from at least one of Li, Mg and Ba.

9. The modified L-molecular sieve according to claim 1, wherein, M is calculated as an oxide, A is calculated as an oxide, and the molar ratio of each component in the modified L molecular sieve is n(M) x O):n(A2O):n(Al2O3):n(SiO2)= (0.07-0.23):(0.6-1.2):1:(5-6), where x is 1 or 2.

10. A method for preparing the modified L-zeolite according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Provide a gelling mixture containing at least one inorganic alkali, an aluminum source, and a silicon source, and obtain L molecular sieve after crystallization; (2) The L molecular sieve is post-treated in a solution containing alkali metal compounds and / or alkaline earth metal compounds, and then the resulting solid product is calcined to obtain modified L molecular sieve. In step (2), the types of alkali metals and / or alkaline earth metals are different from the types of metal elements in the inorganic alkali described in step (1); the crystallization conditions include: a crystallization temperature of 120-180℃ and a crystallization time of 30-100 h; The concentration of alkali metals and / or alkaline earth metals in solutions containing alkali metal compounds and / or alkaline earth metal compounds is 0.2-1 mol / L; In step (2), with the mass of the L molecular sieve being 1g, the volume of the solution containing alkali metal compounds and / or alkaline earth metal compounds is 5-50mL. The inorganic alkali added in step (1) is calculated as A2O, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2, so that the molar ratio of each component in the L molecular sieve is n(A2O):n(Al2O3):n(SiO2) is (0.8-1.8):1:(3-8), and the A element is K and / or Na.

11. The preparation method according to claim 10, wherein, The alkali metal compound and / or alkaline earth metal compound are each independently selected from at least one of the nitrates, chlorides and hydroxides of alkali metals and / or alkaline earth metals.

12. The preparation method according to claim 11, wherein, The alkali metal and / or alkaline earth metal is selected from at least one of Li, Rb, Cs, Be, Mg, Ca and Ba.

13. The preparation method according to claim 12, wherein, The alkali metal and / or alkaline earth metal is selected from at least one of Li, Mg and Ba.

14. The preparation method according to claim 10, wherein, The concentration of alkali metals and / or alkaline earth metals in the solution containing alkali metal compounds and / or alkaline earth metal compounds is 0.4-0.8 mol / L; And / or, in step (2), based on the mass of the L molecular sieve being 1g, the volume of the solution containing alkali metal compounds and / or alkaline earth metal compounds is 8-30mL.

15. The preparation method according to claim 10, wherein, The post-treatment conditions include: a temperature of 20-120℃; a time of 6-24 hours; and the process being carried out under stirring and reflux conditions. And / or, the calcination conditions include: a calcination temperature of 200-500℃; and a calcination time of 1-12h.

16. The preparation method according to claim 15, wherein, The post-processing conditions include: a temperature of 25-100℃ and a time of 8-14 hours; And / or, the calcination conditions include: a calcination temperature of 300-450℃; and a calcination time of 2-8h.

17. The preparation method according to claim 10, wherein, The inorganic alkali added in step (1) is calculated as A2O, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2, so that the molar ratio of each component in the L molecular sieve is n(A2O):n(Al2O3):n(SiO2) is (0.9-1.5):1:(5-6), and the A element is K and / or Na.

18. The preparation method according to claim 10, wherein, The crystallization conditions include: a crystallization temperature of 140-170℃ and a crystallization time of 50-80h.

19. A modified L-molecular sieve catalyst, characterized in that, The modified L-zeolite catalyst comprises the modified L-zeolite according to any one of claims 1-9, and Pt supported on the modified L-zeolite, wherein the content of Pt is 0.2-3 wt% based on a total mass of 100 wt% of the modified L-zeolite catalyst.

20. A method for preparing a modified L-zeolite catalyst, characterized in that, The method includes: The modified L molecular sieve according to any one of claims 1-9 is impregnated with a solution containing a Pt precursor and then calcined to obtain a modified L molecular sieve catalyst.

21. The preparation method according to claim 20, wherein, The concentration of Pt in the Pt precursor solution is 1.14%. 10 -2 -1.71 10 -1 mol / L; And / or, the calcination conditions include: a calcination temperature of 473-673K and a calcination time of 1-5h.

22. The application of the modified L molecular sieve catalyst according to claim 19 or the modified L molecular sieve catalyst prepared by the preparation method according to claims 20-21 in the alkane aromatization reaction.

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