Modified L molecular sieve and preparation method thereof, modified L molecular sieve catalyst and preparation method and application thereof

Abstract

The invention relates to the field of molecular sieve preparation, and discloses a modified L molecular sieve and a preparation method thereof, a modified L molecular sieve catalyst and a preparation method and application thereof, the modified L molecular sieve contains silicon oxide, aluminum oxide and an M element, and the M element is alkali metal and / or alkaline earth metal; the micropore specific surface area is 280-330m < 2 > / g, the volume of pores with the pore diameter smaller than 0.7 nm accounts for more than or equal to 50% of the total pore volume, and the volume of pores with the pore diameter larger than 0.9 nm accounts for more than or equal to 10% of the total pore volume. The modified L molecular sieve is better in selectivity performance and has a wider micropore aperture range, the aperture distribution gathers towards two ends, macromolecules can enter the pore channels of the molecular sieve, the ratio of the micropore specific surface area is high, and the catalytic activity can be improved.

Description

Technical Field

[0001] The present invention relates to the field of molecular sieve preparation, and in particular to a modified L molecular sieve and a preparation method thereof, a modified L molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] L molecular sieve has a one-dimensional straight pore with twelve-membered rings and a pore diameter of 0.71nm. It has a unique one-dimensional pore structure. Its special pore structure can be used for the separation and catalysis of alkane molecules.

[0003] By adjusting the pore size of the molecular sieve, the diffusion resistance of the diffusing substance, reactant, reaction intermediate or product can be increased or decreased, thereby improving the shape selectivity of the molecular sieve.

[0004] CN109529923B discloses a method for preparing an oxide-modified microporous molecular sieve shape-selective catalyst. The method uses microporous molecular sieves ZSM-5 and MCM-22 from which the template agent has not been removed as carriers, and metal nitrates as precursors, and loads metal oxides on the outer surface of the microporous molecular sieve by an impregnation method. At this time, the pores of the microporous molecular sieve are still occupied by the template agent, so during the impregnation process, the ions of the metal nitrate cannot diffuse into the inner pores of the molecular sieve, thereby ensuring that the obtained shape-selective catalyst has good catalytic activity during use.

[0005] CN114620742A discloses a method for preparing a multi-level pore molecular sieve, which comprises treating the molecular sieve with alkali in the presence of a chelating agent to obtain a multi-level pore molecular sieve precursor, and then performing ion exchange to obtain a multi-level pore molecular sieve. The diffusion limitation of the microporous molecular sieve is improved, and a multi-level pore molecular sieve with a large pore volume and original microporous structure can be obtained.

[0006] Therefore, there is a need for an L molecular sieve with better shape selectivity and more suitable for material diffusion. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems of narrow micropore distribution range of L molecular sieve, difficulty for large molecules to enter the molecular sieve pores, and low catalytic activity in the prior art, and to provide a modified L molecular sieve and a preparation method thereof, a modified L molecular sieve catalyst and a preparation method and application thereof. The modified L molecular sieve has better selectivity and a wider micropore pore size range. The pore size distribution is concentrated at both ends, which is conducive to the entry of large molecules into the molecular sieve pores. At the same time, the micropore specific surface area accounts for a high proportion, which helps to improve the catalytic activity.

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

[0009] Preferably, the micropore specific surface area of ​​the modified L molecular sieve is 310-330m 2 / g.

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

[0011] The second aspect of the present invention provides a method for preparing a modified L molecular sieve, comprising the following steps:

[0012] (1) providing a colloid mixture containing at least one inorganic base, an aluminum source, and a silicon source, and obtaining an L molecular sieve after crystallization;

[0013] (2) post-treating the L molecular sieve in a solution containing an alkali metal compound and / or an alkaline earth metal compound, and then calcining the obtained solid product to obtain a modified L molecular sieve;

[0014] Wherein, the type of alkali metal and / or alkaline earth metal in step (2) is different from the type of metal element in the inorganic base in step (1).

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

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

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

[0018] The 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 aspect or the third aspect, and Pt loaded on the modified L molecular sieve, and the content of Pt is 0.2-3wt% based on the total mass of the modified L molecular sieve catalyst as 100wt%.

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

[0020] The modified L molecular sieve described in the first aspect or the third aspect is impregnated with a precursor solution containing Pt, 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 -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] A sixth aspect of the present invention provides the use of the aforementioned modified L molecular sieve catalyst or the modified L molecular sieve catalyst prepared by the aforementioned preparation method in an alkane aromatization reaction.

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

[0025] (1) The modified L molecular sieve provided by the present invention has a wider micropore pore size distribution, which is concentrated 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 pores of the L molecular sieve. At the same time, it has a larger micropore specific surface area, which helps to provide more active sites and improve the catalytic activity of the L molecular sieve.

[0026] (2) In the present invention, preferably, a special post-treatment solution is used to post-treat the L molecular sieve, and the alkali metal and / or alkaline earth metal in the post-treatment solution replaces part of the alkali metal in the L molecular sieve structure, and the pore size distribution of the modified L molecular sieve is adjusted by the difference in atomic size, while the original L molecular sieve pore structure is not destroyed, thereby improving the catalytic activity of the L molecular sieve. DETAILED DESCRIPTION

[0027] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

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

[0029] In the present invention, the modified L molecular sieve having the above structure has an increased proportion of pore volume with pore diameters greater than 0.9 nm in the total pore volume, which is beneficial for macromolecules to enter the L molecular sieve pores and is suitable for the diffusion of macromolecules.

[0030] In the present invention, the specific surface area, micropore specific surface area and pore size distribution of the modified L molecular sieve are tested by nitrogen isothermal adsorption-desorption curve method, and the instrument model is Micromeritics ASAP 2420 physical adsorption instrument. The test conditions are: the sample is heated at 300°C and 1.33×10 -2 Pa, constant temperature and pressure for 4 hours to purify the sample. Then, at liquid nitrogen temperature of 77K, the sample was brought into contact with the adsorbate to reach adsorption equilibrium, and the specific surface area, micropore specific surface area and pore size distribution were calculated from the difference between the nitrogen intake and the amount of nitrogen remaining in the gas phase after adsorption.

[0031] According to the present invention, preferably, the micropore specific surface area of ​​the modified L molecular sieve is 310-330m 2 In the present 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 volume of pores with a pore size less than 0.7 nm accounts for 70-80% of the total pore volume, and the volume of pores with a pore size greater than 0.9 nm accounts for 14-18% of the total pore volume. In the present invention, the total pore volume is 100%, and the rest is the volume of pores with a pore size of 0.7-0.9 nm.

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

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

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

[0036] In the present invention, the relative crystallinity of the modified L molecular sieve is based on the standard L molecular sieve, and the crystallinity of the standard L molecular sieve is defined as 100%. The relative crystallinity calculation method is: the data obtained by the diffractometer is summarized into a text document format, and the phase spectrum is drawn by JADE5.0 software, and the peak area of ​​the characteristic peaks near the 2θ angles of 14.7, 19.3, 22.6, 24.3, 25.5, 28.0, 29.0, and 30.6 is obtained by peak search and integral calculation, and the peak areas of the 8 characteristic peaks are summed to obtain the ratio of the sum of the peak areas of the 8 characteristic peaks obtained under the same analysis conditions with the standard sample, which is its relative crystallinity. XRD test instrument: Japanese Rigaku D / MAX-Ⅲ AX-ray diffractometer. Test conditions: Cu target, Kα radiation, Ni filter, tube voltage 45kV, tube current 250mA, scanning range 5°-50°, step width 0.02°.

[0037] In the present 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 an A element, which is different from the M element and is an alkali metal. In the present invention, the A element is K and / or Na.

[0039] According to the present invention, preferably, the M element is selected from at least one of Li, Rb, Cs, Be, Mg, Ca and Ba, preferably at least one of Li, Mg and Ba. In the present invention, the atomic radius of the M element is different from the atomic radius of the A metal element in the original L molecular sieve. The introduction of the M element into the L molecular sieve changes the pore size distribution of the L molecular sieve, which is beneficial to increase the number of active sites on the L molecular sieve and improve the catalytic activity of the molecular sieve.

[0040] According to the present invention, preferably, the M element is calculated as an oxide, the A element 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), preferably (0.07-0.23):(0.6-1.2):1:(5-6), x is 1 or 2. In the present invention, the modified L molecular sieve having the above molar ratio, combined with a special molecular sieve structure, improves the diffusion limitation of the original L molecular sieve and has better catalytic activity.

[0041] In the present invention, the content of each component in the modified L molecular sieve is determined by X-ray fluorescence spectrometry using an instrument model: 3013 X-ray fluorescence analyzer produced by Rigaku Corporation of Japan.

[0042] The second aspect of the present invention provides a method for preparing a modified L molecular sieve, comprising the following steps:

[0043] (1) providing a colloid mixture containing at least one inorganic base, an aluminum source, and a silicon source, and obtaining an L molecular sieve after crystallization;

[0044] (2) post-treating the L molecular sieve in a solution containing an alkali metal compound and / or an alkaline earth metal compound, and then calcining the obtained solid product to obtain a modified L molecular sieve;

[0045] Wherein, the type of alkali metal and / or alkaline earth metal in step (2) is different from the type of metal element in the inorganic base in step (1).

[0046] In the present invention, the type of alkali metal and / or alkaline earth metal in step (2) is different from the type of metal element in the inorganic base in step (1), and the alkali metal and / or alkaline earth metal element in step (2) replaces part of the alkali metal element in the L molecular sieve obtained in step (1). Since the atomic radius of the replaced metal element is different from that of the original metal element on the L molecular sieve, the structure of the modified L molecular sieve is changed. The proportion of pores with a pore size of less than 0.7 nm increases, which is beneficial to increase the number of active sites on the L molecular sieve and improve the catalytic activity of the molecular sieve.

[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 nitrates, chlorides and hydroxides of alkali metals and / or alkaline earth metals. In the present invention, the alkali metal compound and / or alkaline earth metal compound is not particularly limited, as long as it can be dissolved 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, preferably selected 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, and in the process of post-treatment of the L molecular sieve, the pores of the L molecular sieve are partially expanded, so that the proportion of the pore volume with a pore size greater than 0.9 nm in the total pore volume increases.

[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, such as 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, 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 1 g, the volume of the solution containing the alkali metal compound and / or alkaline earth metal compound is 5-50 mL, preferably 8-30 mL.

[0051] According to the present invention, preferably, the post-treatment conditions include: 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; 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 the present invention, preferably, post-treatment is carried out under the above conditions, and the alkali metal and / or alkaline earth metal elements in the solution containing the alkali metal compound and / or alkaline earth metal compound can effectively replace part of the original metal elements in the L molecular sieve within a suitable temperature and time range, and will not excessively corrode the pore structure of the L molecular sieve due to excessively high temperature or too long exchange time.

[0053] In the present invention, the post-treatment is carried out under stirring and reflux conditions, and the stirring rate of the stirring is not particularly limited. Those skilled in the art can adaptably adjust the stirring and reflux conditions according to the post-treatment conditions. The post-treatment device is not particularly limited. According to a preferred embodiment of the present 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 started, L molecular sieve is added to the solution, and the stirring rate and heating temperature of stirring and reflux are maintained. The above post-treatment method is an example of a post-treatment method of the present invention, and the order of feeding each substance and the order of starting stirring during the post-treatment process are not particularly limited.

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

[0056] In the present 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°C, such as 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, any range between any two values, preferably 300-450°C; a calcination time of 1-12h, such as 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 obtain a modified L molecular sieve with better structural stability and higher catalytic activity.

[0058] According to the present invention, preferably, the inorganic base 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 the components 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 the present invention, preferably, the inorganic base in step (1) is KOH and / or NaOH.

[0060] In the present invention, water is further added in step (1) to prepare a gelled mixture, and the amount of water used is not particularly limited, and those skilled in the art can make adaptive adjustments according to the preparation of the gelled mixture. Preferably, in the gelled mixture, the aluminum source is calculated as Al2O3, and the molar ratio of the aluminum source to water n(Al2O3):n(H2O) is 1:(20-200).

[0061] In the present invention, the aluminum source is a conventional aluminum source for preparing molecular sieves, and those skilled in the art can make adaptive adjustments as needed. Preferably, the aluminum source is hydrated aluminum oxide and / or metaaluminate, preferably aluminum hydroxide.

[0062] In the present invention, the silicon source is a conventional silicon source for preparing molecular sieves, and those skilled in the art can make adaptive adjustments as needed. Preferably, the silicon source is selected from at least one of silica sol, white carbon black, water glass and diatomaceous earth.

[0063] According to the present invention, preferably, the crystallization conditions include: a crystallization temperature of 120-180°C, such as 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, any range between any two values, preferably 140-170°C; a crystallization time of 30-100h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, any range between any two values, preferably 50-80h. The crystallization reaction is carried out under the above crystallization conditions to obtain an L molecular sieve with a wider pore size distribution and a larger micropore specific surface area, which is conducive to further post-processing to obtain a modified L molecular sieve structure.

[0064] In the present invention, there is no particular limitation on the reaction equipment required for the preparation of the L molecular sieve, and those skilled in the art can make adaptive adjustments as needed. Preferably, the preparation of the L molecular sieve is carried out in a reactor.

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

[0066] The 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 aspect or the third aspect, and Pt loaded on the modified L molecular sieve, and the content of Pt is 0.2-3wt% based on the total mass of the modified L molecular sieve catalyst as 100wt%.

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

[0068] The modified L molecular sieve described in the first aspect or the third aspect is impregnated with a precursor solution containing Pt, 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 -2 -1.71×10 -1 mol / L.

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

[0071] In the present invention, preferably, the Pt-containing precursor solution is diluted with deionized water, and then the modified L molecular sieve is placed in the diluted solution, and the volume of the added deionized water: the Pt-containing precursor solution is 1-20:1, 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 473-673K and a calcination time of 1-5h.

[0073] In the present invention, preferably, before the calcination, the impregnated modified L molecular sieve is further stirred and dried. There is no particular limitation on the stirring rate, and those skilled in the art can adjust it according to the preparation of the modified L molecular sieve catalyst.

[0074] In the present invention, preferably, the drying conditions include: a drying temperature of 100-140° C. and a drying time of 8-16 hours.

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

[0076] In the present invention, preferably, the alkane is an alkane of C5 or above, preferably a C6-C8 alkane.

[0077] In the present 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 comprises the following steps:

[0079] (1) providing a colloid mixture containing at least one inorganic base, an aluminum source, and a silicon source, and obtaining an L molecular sieve after crystallization;

[0080] (2) post-treating the L molecular sieve in a solution containing an alkali metal compound and / or an alkaline earth metal compound, and then calcining the obtained solid product to obtain a modified L molecular sieve;

[0081] Wherein, the type of alkali metal and / or alkaline earth metal in step (2) is different from the type of metal element in the inorganic base 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 metal and / or alkaline earth metal in the solution containing alkali metal compound and / or alkaline earth metal compound is 0.4-0.8 mol / L;

[0084] The post-treatment conditions include: temperature of 25-100°C and time of 8-14h;

[0085] The calcination conditions include: a calcination temperature of 300-450° C. and a calcination time of 2-8 hours.

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

[0087] The test methods and test 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] L molecular sieve preparation example 1

[0089] Take 19.62g of KOH and dissolve it in 68.72g of deionized water, add 10.44g of Al(OH)3 into the solution, dissolve it under magnetic stirring, add 23.04g of SiO2 in the form of silica sol, stir evenly, and obtain a gel mixture. Move the above gel mixture into a stainless steel reactor, crystallize it at 150℃ for 72h, separate the product by centrifugation, wash the solid with water, and dry it at 120℃ for 12h to obtain L molecular sieve L-1.

[0090] Preparation Example 2 of L Molecular Sieve

[0091] Take 17.62g of KOH and dissolve it in 58.72g of deionized water. Add 8.14g of Al(OH)3 into the solution and dissolve it under magnetic stirring. Add 31g of SiO2 in the form of silica sol and stir evenly to obtain a gel mixture. Move the gel mixture into a stainless steel reactor and crystallize it at 150℃ for 72h. The product is separated by centrifugation. The solid obtained is washed with water and dried at 120℃ for 12h to obtain L molecular sieve L-2.

[0092] Preparation Example 3 of L Molecular Sieve

[0093] Take 12.89g of NaOH and dissolve it in 58.72g of deionized water, add 8.14g of Al(OH)3 into the solution, dissolve it under magnetic stirring, add 31.00g of SiO2 in the form of silica sol, stir evenly, and obtain a gel mixture. Move the above gel mixture into a stainless steel reactor, crystallize it at 170℃ for 58h, separate the product by centrifugation, wash the solid with water, and dry it at 120℃ for 12h to obtain L molecular sieve L-3.

[0094] Example 1

[0095] 4.24 g of LiCl was dissolved in 200 mL of deionized water, heated to 50° C. with stirring on a magnetic stirrer, 20 g of L-1 molecular sieve was added to the solution, and post-treatment was performed under stirring and reflux for 8 h. The obtained solid product was washed and filtered until the pH of the washing liquid was 9. The washed 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, heated to 50°C with stirring on a magnetic stirrer, 20 g of L-1 molecular sieve was added to the solution, and post-treatment was carried out under stirring and reflux for 8 h. The obtained solid product was washed and filtered until the pH of the washing liquid was 9. The washed 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, heated to 50° C. with stirring on a magnetic stirrer, 20 g of L-2 molecular sieve was added to the solution, and post-treatment was performed under stirring and reflux for 8 h. The obtained solid product was washed and filtered until the pH of the washing liquid was 9. The washed 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] The modified L molecular sieve was prepared according to the method of Example 2, except that the post-treatment temperature was changed to 110° C. to obtain L-Mg-2 molecular sieve.

[0102] Example 5

[0103] The modified L molecular sieve was prepared according to the method of Example 2, except that the post-treatment time was 16 h, to obtain L-Mg-3 molecular sieve.

[0104] Example 6

[0105] The modified L molecular sieve was prepared according to the method of Example 2, except that 9.52 g of MgCl2 was replaced by 19.04 g of MgCl2 to obtain L-Mg-4 molecular sieve.

[0106] Example 7

[0107] The modified L molecular sieve was prepared according to the method of Example 2, except that 9.52 g of MgCl2 was replaced by 16.84 g of CsCl to obtain L-Cs-1 molecular sieve.

[0108] Example 8

[0109] The modified L molecular sieve was prepared according to the method of Example 2, except that 20 g of L-1 molecular sieve was replaced by 20 g of L-3 molecular sieve to obtain NaL-Mg-5 molecular sieve.

[0110] Comparative Example 1

[0111] The L molecular sieve prepared in Example 1 was used 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] It can be seen from the results in Table 1 that the modified L molecular sieve prepared by the preparation method of the present invention can maintain a higher relative crystallinity.

[0118] Table 2

[0119]

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

[0121] It can be seen from the results in Table 2 that the modified L molecular sieve prepared in the embodiment of the present invention has a larger micropore specific surface area, the pore size less than 0.7 nm accounts for more than 50%, and the pore size greater than 0.9 nm accounts for more than 10%.

[0122] Test Example 2 Evaluation of the reaction performance of modified L molecular sieve catalyst

[0123] To prepare the modified L molecular sieve catalyst, 9 mL of platinum-ammonia solution (Pt molar concentration is 5.7×10 - 2mol / L), 10 g of modified L molecular sieve (the L molecular sieves used in each catalyst preparation example are listed in Table 3) were added thereto respectively, stirred at room temperature at a speed of 50 rpm for 6 h, dried at 120 ° C for 12 h, and calcined at 623 K for 3 h to obtain L molecular sieve catalyst, wherein the Pt content was 1 wt%.

[0124] With n-hexane as the reaction material, the reaction temperature is 470°C, the reaction pressure is 0.3 MPa, and the volumetric space velocity of the reaction material is 4 h -1 The prepared modified L molecular sieve catalyst was evaluated for reaction, and the performance of the catalyst was characterized by the benzene yield and reactant conversion rate after 10 hours of reaction.

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

[0126] Benzene yield = mass percentage of benzene 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] It can be seen from the results of Table 3 that the catalyst prepared by using the L-Li-1 molecular sieve of Example 1 and the L-Mg-1 molecular sieve of Example 2 as carriers synthesized under the preferred modification conditions, the reactant conversion rate and the product benzene yield after 10 hours of reaction are higher than the catalyst prepared by using the unmodified L molecular sieve as the carrier. When the modification conditions are too harsh and not within the preferred range, the catalyst prepared by using the L-Mg-2 of Example 4 and the L-Mg-4 of Example 6 as carriers, the reactant conversion rate and the product benzene yield after 10 hours of reaction are slightly worse than the catalysts of Catalyst Preparation Examples 1 and Catalyst Preparation Examples 2, but better than the catalyst of the unmodified catalyst preparation comparative example 1. The molecular sieve modification method described in the present invention has better effects.

[0131] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A modified L molecular sieve, characterized in that: The modified L molecular sieve contains silicon oxide, aluminum oxide and M element, wherein the M element is an alkali metal and / or an alkaline earth metal; the micropore specific surface area is 280-330m 2 / g, the volume of pores with a pore diameter less than 0.7 nm accounts for ≥50% of the total pore volume, and the volume of pores with a pore diameter greater than 0.9 nm accounts for ≥10% of the total pore volume.

2. The modified L molecular sieve according to claim 1, wherein The micropore specific surface area of ​​the modified L molecular sieve is 310-330m 2 / g; Preferably, the volume of pores with a pore diameter less than 0.7 nm accounts for 70-80% of the total pore volume, and the volume of pores with a pore diameter greater than 0.9 nm accounts for 14-18% of the total pore volume; Preferably, the specific surface area of ​​the modified L molecular sieve is 295-350m 2 / g, preferably 315-340m 2 / g; Preferably, the micropore diameter of the modified L molecular sieve is 0.5-1.5 nm, preferably 0.55-1.2 nm; Preferably, the relative crystallinity of the modified L molecular sieve is >90%, preferably >95%.

3. The modified L molecular sieve according to claim 1 or 2, wherein The modified L molecular sieve further contains an A element, which is different from the M element and is an alkali metal; Preferably, the M element is selected from at least one of Li, Rb, Cs, Be, Mg, Ca and Ba, preferably at least one of Li, Mg and Ba; Preferably, the M element is calculated as an oxide, the A element 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), preferably (0.07-0.23):(0.6-1.2):1:(5-6), x is 1 or 2.

4. A method for preparing a modified L molecular sieve, characterized in that: The following steps are involved: (1) providing a colloid mixture containing at least one inorganic base, an aluminum source, and a silicon source, and obtaining an L molecular sieve after crystallization; (2) post-treating the L molecular sieve in a solution containing an alkali metal compound and / or an alkaline earth metal compound, and then calcining the obtained solid product to obtain a modified L molecular sieve; Wherein, the type of alkali metal and / or alkaline earth metal in step (2) is different from the type of metal element in the inorganic base in step (1).

5. The preparation method according to claim 4, wherein The alkali metal compound and / or alkaline earth metal compound are each independently selected from at least one of nitrates, chlorides and hydroxides of alkali metals and / or alkaline earth metals; Preferably, the alkali metal and / or alkaline earth metal is selected from at least one of Li, Rb, Cs, Be, Mg, Ca and Ba, preferably selected from at least one of Li, Mg and Ba; 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, preferably 0.4-0.8 mol / L; Preferably, in step (2), based on the mass of the L molecular sieve being 1 g, the volume of the solution containing the alkali metal compound and / or alkaline earth metal compound is 5-50 mL, preferably 8-30 mL.

6. The preparation method according to claim 4 or 5, wherein: The post-treatment conditions include: temperature of 20-120°C, preferably 25-100°C; time of 6-24h, preferably 8-14h; preferably carried out under stirring and reflux conditions; Preferably, the calcination conditions include: a calcination temperature of 200-500° C., preferably 300-450° C.; and a calcination time of 1-12 h, preferably 2-8 h.

7. The preparation method according to any one of claims 4 to 6, wherein: The inorganic base 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 the components 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; Preferably, the crystallization conditions include: a crystallization temperature of 120-180° C., preferably 140-170° C.; and a crystallization time of 30-100 h, preferably 50-80 h.

8. The modified L molecular sieve obtained according to the preparation method according to any one of claims 4 to 7.

9. A modified L molecular sieve catalyst, characterized in that: The modified L molecular sieve catalyst comprises the modified L molecular sieve according to any one of claims 1-3 and 8, and Pt loaded on the modified L molecular sieve, wherein the content of Pt is 0.2-3wt% based on the total mass of the modified L molecular sieve catalyst being 100wt%.

10. A method for preparing a modified L molecular sieve catalyst, characterized in that: The method comprises: The modified L molecular sieve according to any one of claims 1 to 3 and 8 is impregnated with a precursor solution containing Pt, and then calcined to obtain a modified L molecular sieve catalyst; Preferably, the concentration of Pt in the Pt precursor solution is 1.14×10 -2 -1.71×10 -1 mol / L; Preferably, the calcination conditions include: a calcination temperature of 473-673K and a calcination time of 1-5h.

11. Use of the modified L molecular sieve catalyst according to claim 9 or the modified L molecular sieve catalyst prepared by the preparation method according to claim 10 in an alkane aromatization reaction.

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