L molecular sieve, method for preparing same, l molecular sieve catalyst, method for preparing same and use thereof

Abstract

The application relates to the field of molecular sieves, and discloses an L molecular sieve, a preparation method of the L molecular sieve, an L molecular sieve catalyst, a preparation method of the L molecular sieve catalyst and application. 2 The L molecular sieve has a multistage pore structure of micropores and mesopores, a specific surface area of 310-330 m 2 / g, a total pore volume of 0.162-0.19 mL / g, a micropore volume of 0.137-0.145 mL / g, a crystal grain diameter of 100-800 nm, and a silicon-aluminum molar ratio of 3-10:1. The L molecular sieve has a multistage pore structure of micropores and mesopores and a small crystal grain size, the preparation method is simple, and the prepared L molecular sieve catalyst is suitable for alkane aromatization reaction, and can significantly improve the aromatic hydrocarbon yield of the catalyst and the conversion rate of reactants.

Description

TECHNICAL FIELD

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

[0002] L zeolite is an artificial zeolite first synthesized by Breck et al. in 1965, and its basic structural unit is cancrinite cage (CAN cage) and double six-membered ring (D6R). L molecular sieve has one-dimensional straight pore of twelve-membered ring, and the pore diameter is 0.71 nm. Due to its unique one-dimensional pore structure, Pt / LTL catalyst is considered to be the single-function catalyst with the most excellent performance in aromatic reaction.

[0003] For zeolite catalyst, the grain size and crystal morphology affect the length of zeolite pore, and further affect the diffusion and reaction performance of reactant molecules, intermediate products and product molecules in the zeolite crystal.

[0004] CN106395851A discloses a Ba-containing LTL molecular sieve, a preparation method and application thereof. A sol is obtained by mixing barium source, inorganic alkali, aluminum source, silicon source, water and alcohol according to the molar ratio, and then aging and crystallization are carried out in sequence. The obtained solid is separated, washed and dried, and then calcined to obtain the molecular sieve. The grain diameter of the L molecular sieve synthesized by the method is about 500 nm, the grain size of the molecular sieve is large, and the aromatic catalytic activity of the further prepared catalyst is poor.

[0005] CN112429749A discloses a small-grain high-pore-volume CHA zeolite molecular sieve, a synthesis method and catalyst application thereof. The molecular sieve is synthesized by using a complex organic template agent formed by a tetrahydro-naphthalene or decahydro-naphthalene group quaternary ammonium compound and a N,N,N-dimethyl ethyl cyclohexyl quaternary ammonium compound. The average grain diameter of the molecular sieve is ≤500 nm, and the grain diameter size in the (-210) direction is 50-160 nm. The molecular sieve needs to be additionally added with a template agent in the preparation process, the preparation scheme is complex, and the synthesis cost of the molecular sieve is high.

[0006] Therefore, there is a need for a L-type molecular sieve with appropriate grain size and crystal morphology and a simple preparation method. SUMMARY

[0007] The present application aims to overcome the problems of large grain size of L molecular sieve and the need to add a template agent in the synthesis of L molecular sieve in the prior art, and provides a L molecular sieve, a preparation method thereof, a L molecular sieve catalyst, a preparation method and application thereof. The L molecular sieve has a multi-level pore structure of micropore and mesopore and a small grain size, the preparation method is simple, the prepared L molecular sieve catalyst is suitable for alkane aromatization reaction, and the aromatic hydrocarbon yield and reactant conversion rate of the catalyst can be significantly improved.

[0008] To achieve the above object, the present application provides an L molecular sieve in a first aspect, wherein the L molecular sieve has a multi-level pore structure of micropores and mesopores, a specific surface area of 310-330 m 2 / g, a total pore volume of 0.162-0.19 mL / g, a micropore volume of 0.137-0.145 mL / g, a crystal grain diameter of 100-800 nm, and a silicon-aluminum molar ratio of 3-10:1.

[0009] The present application provides a preparation method of an L molecular sieve in a second aspect, comprising the following steps:

[0010] (1) providing a gelation mixture containing at least two inorganic bases, an aluminum source, L molecular sieve seeds, a silicon source, and water;

[0011] (2) performing crystallization on the gelation mixture;

[0012] The at least two inorganic bases include at least one alkali metal compound and at least one alkaline earth metal compound, and the molar ratio of the alkali metal compound to the alkaline earth metal compound is 20-600:1 in terms of oxides.

[0013] The present application provides an L molecular sieve catalyst in a third aspect, wherein the composition of the L molecular sieve catalyst includes the L molecular sieve in the first aspect or the L molecular sieve prepared by the preparation method in the second aspect, and Pt supported on the L molecular sieve, and the content of the Pt is 0.2-3 wt% based on 100 wt% of the total mass of the L molecular sieve catalyst.

[0014] The present application provides a preparation method of an L molecular sieve catalyst in a fourth aspect, which impregnates the L molecular sieve in the first aspect or the L molecular sieve prepared by the preparation method in the second aspect with a Pt precursor solution, and then performs calcination to obtain the L molecular sieve catalyst.

[0015] Preferably, the concentration of Pt in the Pt precursor solution is 1.14×10 -2 -1.71×10 -1 mol / L.

[0016] Preferably, the calcination conditions include a calcination temperature of 523-673 K and a calcination time of 1-5 h.

[0017] The present application provides an application of the L molecular sieve catalyst in the third aspect or the L molecular sieve catalyst prepared by the preparation method in the fourth aspect in the aromatization of alkanes in a fifth aspect.

[0018] Preferably, the alkanes are C5+ alkanes, preferably C6-C8 alkanes.

[0019] The above technical solution can achieve the following beneficial technical effects:

[0020] (1) In this invention, the preparation method provided does not require the addition of a template agent, the preparation process is simple, and L molecular sieves can be obtained quickly and economically.

[0021] (2) The L molecular sieve provided by the present invention has a suitable grain diameter and a larger total pore volume and mesopore volume. The L molecular sieve provided by the present invention has both micropores and mesopores. The catalyst prepared by the L molecular sieve can effectively improve the diffusion path of reactants, reaction intermediates and products, and can improve the reaction activity and aromatization selectivity of the catalyst. Attached Figure Description

[0022] Figure 1 These are the XRD patterns of the L molecular sieves prepared in Examples 1-3 and Comparative Example 1 of this invention and the standard L molecular sieve.

[0023] Figure 2 Here is a scanning electron microscope image of the L-type molecular sieve prepared in Example 1 of this invention;

[0024] Figure 3 Here is a scanning electron microscope image of the L-type molecular sieve prepared in Example 2 of this invention;

[0025] Figure 4 Here is a scanning electron microscope image of the L-type molecular sieve prepared in Example 3 of this invention;

[0026] Figure 5 This is a scanning electron microscope image of the L molecular sieve prepared in Comparative Example 1 of this invention.

[0027] Figure 6 This is a comparison of the aromatization performance of the catalysts prepared in Examples 1, 3, and 5 of this invention and Comparative Example 1. Detailed Implementation

[0028] 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.

[0029] The first aspect of this invention provides an L-type molecular sieve, wherein the L-type molecular sieve has a hierarchical pore structure of micropores and mesopores, and a specific surface area of ​​310-330 m². 2The specific surface area of the L molecular sieve is 315-330 m2 / g, the total pore volume is 0.162-0.19 mL / g, the micropore volume is 0.137-0.145 mL / g, the grain diameter is 100-800 nm, and the molar ratio of silicon to aluminum is 3-10:1.

[0030] According to the present application, preferably, the specific surface area of the L molecular sieve is 315-330 m 2 / g.

[0031] The L molecular sieve provided by the present application has a multi-level pore structure of micropores and mesopores, a suitable grain diameter, a larger total pore volume, and a larger mesopore and / or bulk pore volume. The bulk pore has a conventional interpretation in the art, which refers to the pores generated by the stacking between particles, and the mesopore and / or bulk pore volume = total pore volume-micropore volume.

[0032] In the present application, the specific surface area, total pore volume, and micropore volume of the L molecular sieve are tested by a nitrogen isothermal adsorption-desorption curve method, and the instrument model is Micromeritics ASAP 2420 physical adsorption instrument. The test conditions are as follows: the sample is at 300℃, 1.33×10 -2 Pa, and the sample is purified for 4 hours under constant temperature and pressure. Then, the sample is contacted with the adsorbate at a liquid nitrogen temperature of 77K to reach adsorption equilibrium, and the specific surface area and pore volume are calculated from the difference between the nitrogen inlet amount and the residual amount in the gas phase after adsorption.

[0033] In the present application, the L molecular sieve grain is a cylindrical structure, and the grain diameter of the L molecular sieve is observed by a scanning electron microscope. During the measurement process, the size of at least five molecular sieve grains is randomly measured. The grain diameter in the present application refers to the maximum straight line distance between two relatively flat edges on the particle in the scanning electron microscope image. The minimum value of the measured grain diameter is taken as the lower limit value of the grain size of the L molecular sieve, and the maximum value of the grain diameter is taken as the upper limit value of the grain size of the L molecular sieve, and the grain diameter is used to represent the difference in grain size.

[0034] In the present application, the grain diameter of the L molecular sieve is 100-800 nm. When the L molecular sieve contains a large amount of grains with a grain size greater than 800 nm, the size of the grains is too large, which can increase the length of the pore channel of the L molecular sieve and increase the difficulty of material diffusion in the pore channel.

[0035] In the present application, the structure of the L molecular sieve can be characterized by an XRD spectrum. The XRD spectrum of the standard sample of the L molecular sieve is shown in FIG. 1, and no impurity crystal peak is observed by comparing the XRD spectrum of the prepared L molecular sieve with the standard sample. Figure 1

[0036] ​In the present application, the XRD testing instrument is D / MAX-III AX ray diffractometer of Japan Rikagaku, the testing conditions are Cu target, K alpha radiation, Ni filter, tube voltage 45 kV, tube current 250 mA, scanning range 5-50°, and step width 0.02°.

[0037] According to the present application, preferably, the L molecular sieve further comprises M elements, and the M elements are alkali metals and / or alkaline earth metals.

[0038] According to the present application, preferably, the molar ratio of n(M x O) : n(Al2O3) is (1-3) : 1, preferably (1-2) : 1, and x is 1 or 2.

[0039] According to the present application, preferably, the molar ratio of the alkali metals and the alkaline earth metals is 100-350:1, preferably 120-310:1, in terms of oxides.

[0040] In the present application, the L molecular sieve with the above chemical composition and structure can effectively improve the diffusion path of reactants, reaction intermediates and products, and improve the reaction activity and aromatization selectivity of the catalyst.

[0041] The second aspect of the present application provides a preparation method of the L molecular sieve, comprising the following steps:

[0042] (1) providing a gelation mixture containing at least two inorganic bases, an aluminum source, L molecular sieve seeds, a silicon source and water;

[0043] (2) crystallizing the gelation mixture;

[0044] The at least two inorganic bases comprise at least one alkali metal compound and at least one alkaline earth metal compound, and the molar ratio of the alkali metal compound and the alkaline earth metal compound in the gelation mixture is 20-600:1, in terms of oxides.

[0045] In the present application, the provided preparation method of the L molecular sieve does not need to add a template agent, the preparation process is simple, raw materials are easy to obtain, and the L molecular sieve can be economically obtained.

[0046] According to the present application, preferably, the molar ratio of n(M x O) : n(Al2O3) : n(SiO2) : n(H2O) is (2-6) : 1 : (6-15) : (80-200), preferably (2-4) : 1 : (8-12) : (120-180), the M elements are alkali metals and / or alkaline earth metals, and x is 1 or 2.

[0047] The gelling mixture is prepared under stirring in the present application, and the stirring condition can be adjusted by those skilled in the art, and the gelling mixture can be obtained.

[0048] According to the present application, preferably, the crystallization condition comprises: the crystallization temperature is 130-180℃, such as 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, any range between any two values, preferably 150-170℃; the crystallization time is 30-100h, such as 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, any range between any two values, preferably 50-80h. The L molecular sieve with smaller grain size and multi-level pore structure can be prepared by using the above-mentioned crystallization condition for crystallization reaction.

[0049] According to the present application, preferably, the molar ratio of the alkali metal compound and the alkaline earth metal compound in the gelling mixture is 80-600:1 in terms of oxides.

[0050] According to the present application, preferably, the alkali metal compound is selected from compounds of K and / or Na, preferably at least one selected from KOH, NaOH, K2SiO3 and Na2SiO3.

[0051] According to the present application, preferably, the alkaline earth metal compound is at least one selected from compounds of Mg, Ba and Ca, preferably at least one selected from Ba(NO3)2, Mg(NO3)2, Ca(NO3)2 and Ba(OH)2.

[0052] In the present application, the alkali metal compound and the alkaline earth metal compound with the above-mentioned molar ratio can be used to prepare the molecular sieve with smaller grain size. When the molar ratio of the alkali metal and the alkaline earth metal is greater than 600:1, the effect of reducing the grain size of the molecular sieve is not obvious, and the grain size of the prepared molecular sieve is too large. When the molar ratio of the alkali metal and the alkaline earth metal is less than 80:1, the content of the alkaline earth metal is too high, and the grain size of the prepared molecular sieve is too small. The above-mentioned L molecular sieve is used to prepare the L molecular sieve catalyst, and the catalytic performance of the catalyst is reduced.

[0053] According to the present application, preferably, the L molecular sieve seed is obtained by mixing inorganic base, aluminum source, silicon source and water, stirring into sol, and hydrothermal treatment.

[0054] According to the present application, preferably, the L molecular sieve seed has a smaller grain size, and the grain size is ≤100nm. The L molecular sieve seed with smaller grain size can be used to prepare the L molecular sieve with smaller grain size.

[0055] According to the present application, preferably, the molar ratio of the components in the sol is n(R yO):n(Al2O3):n(SiO2):n(H2O) is (2-6):1:(6-15):(80-200), preferably (2-4):1:(8-12):(120-180), R element is alkali metal and / or alkaline earth metal, and y is 1 or 2.

[0056] According to the present application, preferably, the hydrothermal treatment conditions include: a hydrothermal treatment temperature of 120-180℃, such as 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, any range formed between any two values, preferably 140-160℃, and a hydrothermal treatment time of 8-20h, such as 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, any range formed between any two values, preferably 9-15h.

[0057] According to the present application, preferably, the molar ratio of Al2O3 in the L molecular sieve seed crystal to Al2O3 in the gelation mixture is 1-10%, such as 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, any range formed between any two values, preferably 2-5%.

[0058] According to the present application, preferably, the components are sequentially added in the order of alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed crystal and silicon source in step (1). More preferably, the alkali metal compound is dissolved in water, the aluminum source is added and stirred, the alkaline earth metal compound is added after the solution is clear and stirred uniformly, the L molecular sieve seed crystal is added, the silicon source is added after stirring uniformly, and the gelation mixture is obtained by stirring. Sequentially adding the components in the above order can prepare the L molecular sieve with high crystallinity.

[0059] In the present application, the components are not sequentially added in the order of alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed crystal and silicon source, and the basic structural unit of the molecular sieve cannot be generated by chemical reaction before hydrothermal crystallization, so that the L molecular sieve with high crystallinity cannot be obtained.

[0060] According to the present application, preferably, the silicon source is selected from at least one of silica sol, white carbon black, water glass and diatomite.

[0061] According to the present application, preferably, the aluminum source is hydrated aluminum oxide and / or aluminate.

[0062] In the present application, the L molecular sieve seed crystal prepared by the above method is used to prepare the L molecular sieve, which can accelerate the crystallization rate of the molecular sieve, does not need to add additional template agent in the preparation process of the molecular sieve, and the prepared molecular sieve has smaller crystal grain diameter.

[0063] Preferably, the preparation of the L molecular sieve seed crystal further comprises a process of separation, washing and drying of the product after the hydrothermal treatment.

[0064] In the present application, the process of separation and washing is not particularly limited and can be adjusted by those skilled in the art as needed to obtain the L molecular sieve seed crystal. Preferably, the washing is performed using deionized water and the separation is performed by centrifugal separation.

[0065] In the present application, the process of drying is not particularly limited and can be adjusted by those skilled in the art as needed. Preferably, the drying conditions include drying at 80-140℃ for 10-16h.

[0066] In the present application, the reaction equipment required for the preparation of the L molecular sieve seed crystal and the L molecular sieve is not particularly limited and can be adjusted by those skilled in the art as needed. Preferably, the preparation of the L molecular sieve seed crystal and the L molecular sieve is performed in a reaction kettle.

[0067] In the present application, the preparation method of the L molecular sieve is simple, and the preparation process does not require additional addition of a template agent, and the L molecular sieve can be quickly and economically obtained.

[0068] The third aspect of the present application provides an L molecular sieve catalyst, wherein the composition of the L molecular sieve catalyst comprises the L molecular sieve of the first aspect or the L molecular sieve prepared by the preparation method of the second aspect, and Pt supported on the L molecular sieve, and the content of the Pt is 0.2-3wt% based on the total mass of the L molecular sieve catalyst.

[0069] The fourth aspect of the present application provides a preparation method of an L molecular sieve catalyst, which impregnates the L molecular sieve of the first aspect or the L molecular sieve prepared by the preparation method of the second aspect with a Pt precursor solution, and then calcines to obtain the L molecular sieve catalyst.

[0070] According to the present application, preferably, the concentration of Pt in the Pt precursor solution is 1.14×10 -2 -1.71×10 -1 mol / L.

[0071] In the present application, the amount of the L molecular sieve and the Pt precursor solution can be adjusted by those skilled in the art as needed, and the content of Pt in the prepared L molecular sieve catalyst satisfies 0.2-3wt%. Preferably, the amount of the Pt precursor solution is 5-15mL, preferably 8-12mL, relative to 10g of the L molecular sieve.

[0072] Preferably, in the present application, the Pt precursor-containing solution is diluted with deionized water, and then the L molecular sieve is placed in the diluted solution, and the volume ratio of deionized water to the Pt precursor-containing solution is 1-20:1, for example, 1:1, 2:1, 5:1, 10:1, 15:1, 20:1, and any range formed by any two values, preferably 2-10:1.

[0073] According to the present application, preferably, the calcination conditions include: the calcination temperature is 523-673K, and the calcination time is 1-5h.

[0074] Preferably, in the present application, before calcination, the impregnated L molecular sieve is subjected to stirring and drying processes, and the stirring rate is not particularly limited and can be adjusted by those skilled in the art according to the preparation of the L molecular sieve catalyst.

[0075] Preferably, in the present application, the drying conditions include: the drying temperature is 100-140℃, and the drying time is 8-16h.

[0076] In the present application, the L molecular sieve catalyst contains a molecular sieve with micropores and mesopores, and the multi-level pore channels can effectively improve the diffusion path of reactants, reaction intermediates and products, improve the reaction activity and aromatization selectivity of the catalyst, and significantly improve the aromatic hydrocarbon yield and reactant conversion rate of the catalyst.

[0077] The fifth aspect of the present application provides an application of the L molecular sieve catalyst of the third aspect or the L molecular sieve catalyst prepared by the preparation method of the fourth aspect in alkanes aromatization.

[0078] Preferably, the alkanes are C5+ alkanes, preferably C6-C8 alkanes.

[0079] In the present application, the reaction conditions for the alkanes aromatization are not particularly limited and can be adjusted as needed by those skilled in the art.

[0080] According to a particularly preferred embodiment of the present application, a preparation method of an L molecular sieve includes the following steps:

[0081] (1) The components are added in the order of alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed and silicon source, and stirring is performed to obtain a gelation mixture; the inorganic base is calculated as an oxide, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2, and the molar ratio of the components in the gelation mixture is n(M x O):n(Al2O3):n(SiO2):n(H2O) is (2-4):1:(8-12):(120-180);

[0082] (2) crystallizing the gelation mixture; the crystallization temperature is 150-170°C, and the crystallization time is 50-80h;

[0083] The at least two inorganic bases include at least one alkali metal compound and at least one alkaline earth metal compound, and the molar ratio of the alkali metal compound to the alkaline earth metal compound is 80-600:1 in terms of oxides.

[0084] The application will be described in detail below through examples and comparative examples. In the following examples and comparative examples, the reagents and materials used are commercially available unless otherwise specified, and room temperature is 25°C.

[0085] Preparation Example 1 of L molecular sieve seed

[0086] 20g of KOH was dissolved in 50g of deionized water, 7.86g of Al(OH)3 was added to the solution, and after the solution was clarified, 37.5g of SiO2 was added to the mixture in the form of silica sol, and after stirring, a mixture was obtained. The above reaction mixture was moved into a stainless steel reaction kettle and treated at 150°C for 12h, and the product was separated by centrifugation, and the obtained solid was washed with water and dried at 120°C for 12h to obtain L molecular sieve seed, which is denoted as S1. The molar ratio of the chemical composition in the seed was 1.0K2O·Al2O3·3.0SiO2 in terms of oxides, and the crystal grain diameter of the L molecular sieve seed was <100nm.

[0087] Example 1

[0088] 17.5g of KOH was dissolved in 83g of deionized water, 7.86g of Al(OH)3 was added to the solution, and after the solution was clarified, 3.6mL of a Ba(NO3)2 solution with a concentration of 0.15mol / L was added, and after stirring, the solution was clarified, and the seed S1 was added, and after stirring, 25g of SiO2 was added to the mixture in the form of silica sol, and after stirring, a gelation mixture was obtained. The molar ratio of Al2O3 in the seed to Al2O3 in the gelation mixture was 2.5%.

[0089] The above reaction mixture was moved into a stainless steel reaction kettle and crystallized at 150°C for 60h, and the product was separated by centrifugation, and the obtained solid was washed with water and dried at 120°C for 12h to obtain L-1-B. The molar ratio of the chemical composition of the L molecular sieve was 1.8K2O·0.006BaO·Al2O3·6.5SiO2.

[0090] Figure 1 The XRD pattern of the molecular sieve prepared in Example 1 is marked as L-1-B, and the XRD pattern of the comparative example is shown in Figure 1. Figure 1It can be seen from the figure that the product obtained by the synthesis method is L molecular sieve, and no impurity crystal peak is observed, indicating that the method can obtain L molecular sieve with high crystallinity.

[0091] Example 2

[0092] Take 17.5g KOH dissolved in 83g deionized water, 7.86g Al(OH)3 is put into the solution, after the solution is clear, 3.6mL of 0.15mol / L Mg(NO3)2 solution is added, and the solution is stirred until it is clear. Then, seed S1 is added, and the mixture is stirred until it is uniform. Then, 25g of SiO2 is added to the mixture in the form of silica sol, and the mixture is stirred until it is uniform. The molar ratio of Al2O3 in the seed to Al2O3 in the gel mixture is 2.5%.

[0093] The above reaction mixture is moved into a stainless steel reactor and crystallized at 150°C for 60h. The product is centrifuged, and the obtained solid is washed with water and dried at 120°C for 12h to obtain L-1-M. The molar ratio of each component in the chemical composition of the L molecular sieve is: 1.6K2O·0.006MgO·Al2O3·5.5SiO2.

[0094] Figure 1 The XRD pattern of the molecular sieve prepared in Example 2 is marked as L-1-M in the figure, and the XRD pattern of the molecular sieve prepared in Example 3 is marked as L-2-B in the figure. Figure 1 It can be seen from the figure that the product obtained by the synthesis method is L molecular sieve, and no impurity crystal peak is observed, indicating that the method can obtain L molecular sieve with high crystallinity.

[0095] Example 3

[0096] Take 17.5g KOH dissolved in 83g deionized water, 7.86g Al(OH)3 is put into the solution, after the solution is clear, 3.6mL of 0.15mol / L Mg(NO3)2 solution is added, and the solution is stirred until it is clear. Then, seed S1 is added, and the mixture is stirred until it is uniform. Then, 25g of SiO2 is added to the mixture in the form of silica sol, and the mixture is stirred until it is uniform. The molar ratio of Al2O3 in the seed to Al2O3 in the gel mixture is 2.5%.

[0097] The above reaction mixture is moved into a stainless steel reactor and crystallized at 150°C for 60h. The product is centrifuged, and the obtained solid is washed with water and dried at 120°C for 12h to obtain L-1-M. The molar ratio of each component in the chemical composition of the L molecular sieve is: 1.6K2O·0.006MgO·Al2O3·5.5SiO2.

[0098] Figure 1 The XRD pattern of the molecular sieve prepared in Example 2 is marked as L-1-M in the figure, and the XRD pattern of the molecular sieve prepared in Example 3 is marked as L-2-B in the figure. Figure 1It can be seen from the figure that the product obtained by the synthesis method is L molecular sieve, and no impurity crystal peak is observed, indicating that the method can obtain L molecular sieve with high crystallinity.

[0099] Example 4

[0100] The L molecular sieve was prepared according to the method of Example 3, except that the addition amount of the alkaline earth metal compound was changed, so that the molar ratio of the added alkali metal compound and alkaline earth metal compound was 96.3:1 in terms of oxides, to obtain L molecular sieve L-3-B with a chemical composition of 1.23K2O·0.009BaO·Al2O3·5.5SiO2.

[0101] Example 5

[0102] The L molecular sieve was prepared according to the method of Example 3, except that the addition amount of the alkaline earth metal compound was changed, so that the molar ratio of the added alkali metal compound and alkaline earth metal compound was 72:1 in terms of oxides, to obtain L molecular sieve L-4-B with a chemical composition of 1.20K2O·0.02BaO·Al2O3·5.5SiO2.

[0103] Catalyst preparation examples 1-5

[0104] 9 mL of platinum ammonia solution (with a molar concentration of 5.7 x 10 -2 mol / L) was taken, 10 g of L molecular sieve was added to each, and stirred at a speed of 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 catalysts with a Pt content of 1 wt%.

[0105] Comparative Example 1

[0106] This comparative example provides a conventional L molecular sieve, which is prepared by the following steps:

[0107] 17.5 g of KOH was dissolved in 83 g of deionized water, 7.86 g of Al(OH)3 was added to the solution, and stirred until the solution was clear, then seed S1 was added, and the mixture was stirred until uniform, then 25 g of SiO2 was added to the mixture in the form of silica sol, and the mixture was stirred until uniform to obtain a gel mixture, and the molar ratio of Al2O3 in the seed to Al2O3 in the gel mixture was 2.5%.

[0108] The above reaction mixture was moved into a stainless steel reaction kettle and crystallized at 150°C for 60 h, the product was separated by centrifugation, the obtained solid was washed with water, and dried at 120°C for 12 h to obtain L-0, and the chemical composition of the L molecular sieve was: 1.8K2O·Al2O3·5.5SiO2.

[0109] Figure 1The XRD pattern of the molecular sieve prepared for Comparative Example 1 is shown in Figure 1 From the XRD pattern, it can be seen that the product obtained by the synthesis method is L molecular sieve, and no impurity crystal peak is observed.

[0110] Comparative Example 2

[0111] The L molecular sieve was prepared according to the method of Example 3, except that no L molecular sieve seed was added, and the prepared molecular sieve was denoted as L-N.

[0112] Comparative Example 3

[0113] The L molecular sieve was prepared according to the method of Example 3, except that equal amounts of Al(OH)3 and Ba(OH)2 were added, and after appropriate stirring, equal amounts of L molecular sieve seed and silica sol of Example 3 were added, and no L molecular sieve with high crystallinity was obtained.

[0114] Catalyst preparation comparative example 1-2

[0115] The L molecular sieve catalyst was prepared according to the method of catalyst preparation examples 1-5, except that the molecular sieve was the L molecular sieve prepared in Comparative Example 1-2.

[0116] Test Example 1

[0117] The scanning electron microscope photograph of the L molecular sieve of Example 1 is shown in Figure 2 , the scanning electron microscope photograph of the L molecular sieve of Example 2 is shown in Figure 3 , and the scanning electron microscope photograph of the L molecular sieve of Example 3 is shown in Figure 4 From Figure 2 , Figure 3 and Figure 4 , the crystal grain structure of the prepared L molecular sieve can be observed, and the L molecular sieve has a smaller crystal grain diameter. The scanning electron microscope photograph of the L molecular sieve of Comparative Example 1 is shown in Figure 5 From Figure 5 , it can be seen that the crystal grain size of the L molecular sieve of Comparative Example 1 is larger than that of the examples, and the structures of the L molecular sieves of the examples and the comparative example are shown in Table 1.

[0118] Table 1

[0119]

[0120] From Table 1, it can be seen that the L molecular sieves prepared in Examples 1-5 have larger total pore volume and smaller micropore volume than the comparative example, and have a hierarchical pore structure. And the crystal grain diameter of the L molecular sieves prepared in Examples 1-5 is smaller than that of the comparative example.

[0121] Test Example 2

[0122] Evaluation of the reaction performance of the molecular sieve catalyst

[0123] Using n-hexane, 2-methylpentane, and 3-methylpentane as mixed feedstocks in a volume ratio of 1:1:1, the reaction was carried out at a temperature of 460℃, a pressure of 0.32 MPa, and a volume hourly space velocity (VHSV) of 4 h⁻¹. -1 The prepared L molecular sieve catalyst was evaluated for reaction performance, and the benzene yield was used to characterize the catalyst's performance.

[0124] The reaction performance evaluation test results of L molecular sieve catalyst are shown in Table 2.

[0125] Table 2

[0126]

[0127] The catalytic performance stability of catalyst preparation examples 1-5 and comparative examples 1-2 is as follows: Figure 6 As shown, from Figure 6 As can be seen, compared with catalyst Pt / L-0, catalysts Pt / L-1-B and Pt / L-2-B exhibit superior catalytic performance in the C6 alkane aromatization reaction. After 14 hours of reaction, catalyst Pt / L-1-B has a benzene yield that is about 1 percentage point higher than that of catalyst Pt / L-0, and catalyst Pt / L-2-B has a benzene yield that is about 1.5 percentage points higher than that of catalyst Pt / L-0.

[0128] 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. An L-type molecular sieve, characterized in that, The L-type molecular sieve has a hierarchical pore structure of micropores and mesopores, with a specific surface area of ​​310-330 m². 2 / g, total pore volume is 0.162-0.19mL / g, micropore volume is 0.137-0.145mL / g, grain diameter is 100-800nm, and silicon-aluminum molar ratio is 3-10:1; The L molecular sieve also includes an M element, which is an alkali metal or an alkaline earth metal.

2. The L-molecular sieve according to claim 1, wherein, The specific surface area of ​​the L-type molecular sieve is 315-330 m². 2 / g.

3. The L-molecular sieve according to claim 1, wherein, In terms of oxides, n(M) x The molar ratio of O:n(Al2O3) is (1-3):1, where x is 1 or 2.

4. The L-molecular sieve according to claim 3, wherein, In terms of oxides, n(M) x The molar ratio of O:n(Al2O3) is (1-2):1, where x is 1 or 2.

5. The L-molecular sieve according to claim 1, wherein, The molar ratio of the alkali metal to the alkaline earth metal, calculated as oxides, is 100-350:

1.

6. The L-molecular sieve according to claim 5, wherein, The molar ratio of the alkali metal to the alkaline earth metal, calculated as oxides, is 120-310:

1.

7. A method for preparing L-type molecular sieves, characterized in that, Includes the following steps: (1) Provide a gelling mixture containing at least two inorganic bases, an aluminum source, L molecular sieve seed crystals, a silicon source and water; (2) Crystallize the gel-forming mixture; Wherein, the at least two inorganic bases include at least one alkali metal compound and at least one alkaline earth metal compound, and the molar ratio of alkali metal compound to alkaline earth metal compound in the gelling mixture is 20-600:1, calculated as oxides; In step (1), the components are added in the following order: alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed crystal and silicon source.

8. The preparation method according to claim 7, wherein, The inorganic alkali is calculated as an oxide, the aluminum source as Al2O3, and the silicon source as SiO2. The molar ratio of each component in the gelling mixture is n(M) x The formula O:n(Al2O3):n(SiO2):n(H2O) is (2-6):1:(6-15):(80-200), where M is an alkali metal and an alkaline earth metal, and x is 1 or 2.

9. The preparation method according to claim 8, wherein, The inorganic alkali is calculated as an oxide, the aluminum source as Al2O3, and the silicon source as SiO2. The molar ratio of each component in the gelling mixture is n(M) x O):n(Al2O3):n(SiO2):n(H2O) is (2-4):1: (8-12):(120-180), M is an alkali metal and an alkaline earth metal, and x is 1 or 2.

10. The preparation method according to claim 7, wherein, The crystallization conditions include: a crystallization temperature of 130-180℃ and a crystallization time of 30-100 h.

11. The preparation method according to claim 10, wherein, The crystallization conditions include: a crystallization temperature of 150-170℃ and a crystallization time of 50-80h.

12. The preparation method according to claim 7, wherein, The molar ratio of alkali metal compounds to alkaline earth metal compounds in the gelling mixture is 80-600:1, calculated by oxides.

13. The preparation method according to claim 7, wherein, The alkali metal compound is selected from compounds of K and / or Na; And / or, the alkaline earth metal compound is selected from at least one compound of Mg, Ba and Ca.

14. The preparation method according to claim 7, wherein, The L-type molecular sieve seed crystals are obtained by mixing inorganic alkali, aluminum source, silicon source and water, stirring to form a sol, and then hydrothermally treating it.

15. The preparation method according to claim 7, wherein, The L molecular sieve seed crystals have a grain diameter ≤100 nm.

16. The preparation method according to claim 14, wherein, The molar ratio of each component in the sol n(R) y O):n(Al2O3):n(SiO2):n(H2O) is (2-6):1: (6-15):(80-200), R is an alkali metal and / or alkaline earth metal, and y is 1 or 2.

17. The preparation method according to claim 16, wherein, The molar ratio of each component in the sol n(R) y O):n(Al2O3):n(SiO2):n(H2O) is (2-4):1: (8-12):(120-180), R is an alkali metal and / or alkaline earth metal, and y is 1 or 2.

18. The preparation method according to claim 14, wherein, The hydrothermal treatment conditions include: a hydrothermal treatment temperature of 120-180℃ and a hydrothermal treatment time of 8-20h.

19. The preparation method according to claim 18, wherein, The hydrothermal treatment conditions include: a hydrothermal treatment temperature of 140-160℃ and a hydrothermal treatment time of 9-15h.

20. The preparation method according to claim 7, wherein, The molar proportion of Al2O3 in the L molecular sieve seed crystals to the total Al2O3 in the gelling mixture is 1-10%.

21. The preparation method according to claim 20, wherein, The molar proportion of Al2O3 in the L molecular sieve seed crystals to the total Al2O3 in the gelling mixture is 2-5%.

22. The preparation method according to claim 7, wherein, The silicon source is selected from at least one of silica sol, silica, water glass and diatomaceous earth; And / or, the aluminum source is hydrated alumina and / or aluminate.

23. An L-type molecular sieve catalyst, characterized in that, The composition of the L molecular sieve catalyst includes the L molecular sieve as described in any one of claims 1-6 or the L molecular sieve prepared by the preparation method described in any one of claims 7-22, and Pt supported on the L molecular sieve. The content of Pt is 0.2-3 wt% based on the total mass of the L molecular sieve catalyst being 100 wt%.

24. A method for preparing an L-type molecular sieve catalyst, characterized in that, The method includes: An L-molecular sieve prepared by any one of claims 1-6 or any one of claims 7-22 is impregnated with a solution containing a Pt precursor and then calcined to obtain an L-molecular sieve catalyst.

25. The preparation method according to claim 24, wherein, The concentration of Pt in the Pt precursor solution is 1.14 × 10⁻⁶. -2 -1.71×10 -1 mol / L; And / or, the calcination conditions include: a calcination temperature of 523-673K and a calcination time of 1-5h.

26. The application of the L molecular sieve catalyst according to claim 23 or the L molecular sieve catalyst prepared by the preparation method according to claim 24 or 25 in alkane aromatization.

27. The application according to claim 26, wherein, The alkane is an alkane with 5 or more carbon atoms.

28. The application according to claim 27, wherein, The alkane is a C6-C8 alkane.

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