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

Abstract

The invention relates to the field of molecular sieves, and discloses an L molecular sieve and a preparation method thereof, and an L molecular sieve catalyst and a preparation method and application thereof. The L molecular sieve has a hierarchical porous structure of micropores and mesopores, the specific surface area is 310-330 m < 2 > / 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. The L molecular sieve has a hierarchical porous structure of micropores and mesopores and is relatively small in grain size, the preparation method is simple and convenient, 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 remarkably improved.

Description

Technical Field

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

[0002] L zeolite is an artificial zeolite first synthesized by Breck et al. in 1965. Its basic structural units are cancrinite cages (CAN cages) and double six-membered rings (D6R). L molecular sieves have one-dimensional straight channels with twelve-membered rings and a channel diameter of 0.71nm. Due to its unique one-dimensional channel structure, Pt / LTL catalyst is considered to be the most excellent monofunctional catalyst in aromatization reaction.

[0003] For zeolite catalysts, the crystal size and crystal morphology affect the zeolite pore length, which in turn affects the diffusion and reaction performance of reactant molecules, intermediates and product molecules within the zeolite crystals.

[0004] CN106395851A discloses a Ba-containing heteroatom LTL molecular sieve and its preparation method and application, wherein a barium source, an inorganic base, an aluminum source, a silicon source, water and an alcohol are mixed in molar ratio to obtain a sol, and then aged and crystallized in sequence, and the obtained solid is separated, washed, dried and then roasted to obtain the molecular sieve. The L molecular sieve synthesized by the method has a grain diameter of about 500nm, and the molecular sieve grain size is relatively large, and the aromatization catalytic activity of the catalyst further prepared is relatively poor.

[0005] CN112429749A discloses a small-grain high-pore volume CHA zeolite molecular sieve and its synthesis method and catalyst application, which is synthesized by a composite organic template formed by a quaternary ammonium compound containing a tetralin or decalin group and an N,N,N-dimethylethylcyclohexyl quaternary ammonium compound. The average crystal diameter of the molecular sieve is ≤500nm, and the crystal diameter size in the crystal plane (-210) direction is 50-160nm. The molecular sieve needs to add an additional template during the preparation process, the preparation scheme is relatively complicated, and the cost of synthesizing the molecular sieve is relatively high.

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

[0007] The purpose of the present invention is to overcome the problems in the prior art that the L molecular sieve has a large grain size and that a template agent needs to be added to synthesize the L molecular sieve, and to provide an L molecular sieve and a preparation method thereof, an L molecular sieve catalyst and a preparation method and application thereof. The L molecular sieve has a multi-level pore structure of micropores and mesopores and a small grain size, and the preparation method is simple. The prepared L molecular sieve catalyst is suitable for alkane aromatization reaction and can significantly improve the catalyst aromatics yield and reactant conversion rate.

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

[0009] The second aspect of the present invention provides a method for preparing L molecular sieve, comprising the following steps:

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

[0011] (2) crystallizing the colloid-forming 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 calculated as oxides.

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

[0014] The fourth aspect of the present invention provides a method for preparing an L molecular sieve catalyst, comprising impregnating the L molecular sieve described in the first aspect or the L molecular sieve prepared by the preparation method described in the second aspect with a Pt precursor solution, and then calcining the solution 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 523-673K and a calcination time of 1-5h.

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

[0018] Preferably, the alkane is an alkane of C5 or above, preferably a C6-C8 alkane.

[0019] Through the above technical solution, the following beneficial technical effects can be obtained:

[0020] (1) In the present invention, the preparation method provided does not require the addition of a template, the preparation process is simple, and the L molecular sieve is obtained quickly and economically;

[0021] (2) The L molecular sieve provided by the present invention has a suitable grain diameter, a larger total pore volume and a larger mesopore volume; the L molecular sieve provided by the present invention has both micropores and mesopores. The catalyst prepared by using the L molecular sieve has multi-level pores that can effectively improve the diffusion paths of reactants, reaction intermediates and products, and can improve the reaction activity and aromatization selectivity of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The XRD spectra of the L molecular sieves prepared in Examples 1-3 and Comparative Example 1 of the present invention and the standard L molecular sieve;

[0023] Figure 2 is a scanning electron microscope photograph of the L molecular sieve prepared in Example 1 of the present invention;

[0024] Figure 3 is a scanning electron microscope photograph of the L molecular sieve prepared in Example 2 of the present invention;

[0025] Figure 4 is a scanning electron microscope photograph of the L molecular sieve prepared in Example 3 of the present invention;

[0026] Figure 5 is a scanning electron microscope photograph of the L molecular sieve prepared in Comparative Example 1 of the present invention;

[0027] Figure 6 It is a comparison of the aromatization performance of the catalysts of Catalyst Preparation Examples 1, 3, 5 of the present invention and Catalyst Preparation Comparative Example 1. DETAILED DESCRIPTION

[0028] 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.

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

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

[0031] The L molecular sieve provided by the present invention has a multi-level pore structure of micropores and mesopores, a suitable crystal diameter, a larger total pore volume, and a larger mesopore and / or stacked pore volume. The stacked pores have a conventional definition in the art, referring to the pores generated by the accumulation of particles, and the mesopore and / or stacked pore volume = total pore volume - micropore volume.

[0032] In the present invention, the specific surface area, total pore volume and micropore volume of the 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 and pore volume were calculated from the difference between the nitrogen intake and the amount remaining in the gas phase after adsorption.

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

[0034] In the present invention, the L molecular sieve has a grain diameter of 100-800 nm. When the L molecular sieve contains a large number of grains with a grain size greater than 800 nm, the grain size is too large, which will increase the pore length of the L molecular sieve and increase the difficulty of diffusion of substances in the pores.

[0035] In the present invention, the structure of the L molecular sieve can be characterized by an XRD spectrum. The XRD spectrum of the L molecular sieve standard sample is as follows: Figure 1 As shown, no impurity crystal peak was observed in the XRD spectra of the prepared L molecular sieve and the standard sample.

[0036] In the present invention, the XRD test instrument is a Japanese Rigaku D / MAX-Ⅲ AX-ray diffractometer. Test conditions are: Cu target, Kα radiation, Ni filter, tube voltage 45 kV, tube current 250 mA, scanning range 5°-50°, step width 0.02°.

[0037] According to the present invention, preferably, the L molecular sieve further comprises an M element, and the M element is an alkali metal and / or an alkaline earth metal.

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

[0039] According to the present invention, preferably, the molar ratio of the alkali metal to the alkaline earth metal is 100-350:1, preferably 120-310:1, calculated as oxide.

[0040] In the present invention, the L molecular sieve having the above chemical composition and structure has multi-level pores which can effectively improve the diffusion paths of reactants, reaction intermediates and products, and enhance the reaction activity and aromatization selectivity of the catalyst.

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

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

[0043] (2) crystallizing the colloid-forming mixture;

[0044] The at least two inorganic bases include at least one alkali metal compound and at least one alkaline earth metal compound. The molar ratio of the alkali metal compound to the alkaline earth metal compound in the colloid-forming mixture is 20-600:1, calculated as oxides.

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

[0046] According to the present invention, preferably, the inorganic base is calculated as oxide, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, and the molar ratio of each component in the colloid-forming mixture is 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 element is an alkali metal and / or an alkaline earth metal, and x is 1 or 2.

[0047] In the present invention, the above-mentioned gelling mixture is prepared under stirring conditions, and those skilled in the art can adaptively adjust the stirring conditions as long as the gelling mixture can be obtained.

[0048] According to the present invention, preferably, the crystallization conditions include: a crystallization temperature of 130-180°C, such as 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, any range between any two values, preferably 150-170°C; a crystallization time of 30-100h, such as 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 multi-level pore structure with a smaller grain diameter.

[0049] According to the present invention, preferably, the molar ratio of the alkali metal compound to the alkaline earth metal compound in the colloid-forming mixture is 80-600:1, calculated as oxides.

[0050] According to the present invention, 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 invention, preferably, the alkaline earth metal compound is selected from at least one of compounds of Mg, Ba and Ca, preferably selected from at least one of Ba(NO3)2, Mg(NO3)2, Ca(NO3)2 and Ba(OH)2.

[0052] In the present invention, by using the above molar ratio of alkali metal compounds and alkaline earth metal compounds, a molecular sieve with a smaller crystal diameter can be prepared. When the molar ratio of alkali metal to alkaline earth metal is greater than 600:1, the effect of reducing the crystal diameter of the molecular sieve is not obvious, and the crystal diameter of the prepared molecular sieve is too large. When the molar ratio of alkali metal to alkaline earth metal is less than 80:1, the alkaline earth metal content is too high, the crystal diameter of the prepared molecular sieve is too small, and the above L molecular sieve is used to prepare L molecular sieve catalyst, and the catalytic performance of the catalyst is reduced.

[0053] According to the present invention, preferably, the L molecular sieve seed crystals are obtained by mixing an inorganic base, an aluminum source, a silicon source and water, stirring the mixture into a sol, and subjecting the mixture to a hydrothermal treatment.

[0054] According to the present invention, preferably, the L molecular sieve seed crystal has a smaller crystal size, with a crystal diameter of ≤100 nm. By using L molecular sieve seed crystals with a smaller crystal size, an L molecular sieve with a smaller crystal diameter can be produced.

[0055] According to the present invention, preferably, the molar ratio of each component 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), the R element is an alkali metal and / or an alkaline earth metal, and y is 1 or 2.

[0056] According to the present invention, preferably, the hydrothermal treatment conditions include: the hydrothermal treatment temperature is 120-180°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, any range formed between any two values, preferably 140-160°C, and the hydrothermal treatment time is 8-20h, for example, 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 invention, preferably, the molar ratio of Al2O3 in the L molecular sieve seed to Al2O3 in the colloid mixture is 1-10%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, any range between any two values, preferably 2-5%.

[0058] According to the present invention, preferably, in step (1), each component is added in the order of alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed crystal and silicon source. More preferably, the alkali metal compound is dissolved in water, the aluminum source is added and stirred, and after the solution is clarified, the alkaline earth metal compound is added and stirred evenly, the L molecular sieve seed crystal is added, and the silicon source is added after stirring evenly, and stirred to obtain a gel-forming mixture. By adding each component in the above order, a high-crystallinity L molecular sieve can be prepared.

[0059] In the present invention, the alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed and silicon source are not added in the order in which they are added. Before hydrothermal crystallization, the basic structural unit of the molecular sieve cannot be generated by chemical reaction, and thus a high-crystallinity L molecular sieve cannot be obtained.

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

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

[0062] In the present invention, the L molecular sieve seed crystals prepared by the above method are used to prepare L molecular sieve, which can accelerate the crystallization rate of the molecular sieve. No additional template agent is required during the preparation of the molecular sieve, and the prepared molecular sieve has a smaller particle diameter.

[0063] In the present invention, preferably, the preparation of the L molecular sieve seed crystals also includes the process of separating, washing and drying the product after the hydrothermal treatment.

[0064] In the present invention, the separation and washing process is not particularly limited, and those skilled in the art can make adaptive adjustments as needed to obtain L molecular sieve seed crystals. Preferably, the washing is performed using deionized water, and the separation is performed using centrifugal separation.

[0065] In the present invention, the drying process is 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.

[0066] In the present invention, there is no particular limitation on the reaction equipment required for the preparation of L molecular sieve seeds and L molecular sieve, and those skilled in the art can make adaptive adjustments as needed. Preferably, the preparation of L molecular sieve seeds and L molecular sieve is carried out in a reactor.

[0067] In the present invention, the preparation method of the L molecular sieve is simple and convenient, and no additional template agent needs to be added during the preparation process, so the L molecular sieve can be obtained quickly and economically.

[0068] The third aspect of the present invention provides an L molecular sieve catalyst, wherein the L molecular sieve catalyst comprises the L molecular sieve described in the first aspect or the L molecular sieve prepared by the preparation method described in the second aspect, and Pt loaded on the L molecular sieve, and the content of Pt is 0.2-3wt% based on the total mass of the L molecular sieve catalyst as 100wt%.

[0069] The fourth aspect of the present invention provides a method for preparing an L molecular sieve catalyst, comprising impregnating the L molecular sieve described in the first aspect or the L molecular sieve prepared by the preparation method described in the second aspect with a Pt precursor solution, and then calcining the solution to obtain the L molecular sieve catalyst.

[0070] 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.

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

[0072] In the present invention, preferably, the Pt precursor solution is diluted with deionized water, and then the L molecular sieve is placed in the diluted solution, and the volume of the added deionized water: the Pt 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.

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

[0074] In the present invention, preferably, before the calcination, the impregnated 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 L molecular sieve catalyst.

[0075] In the present invention, preferably, the drying conditions include: a drying temperature of 100-140° C. and a drying time of 8-16 hours.

[0076] In the present invention, the molecular sieve contained in the L molecular sieve catalyst has micropores and mesopores, and the multi-level pores can effectively improve the diffusion paths of reactants, reaction intermediates and products, improve the reaction activity and aromatization selectivity of the catalyst, and can significantly improve the catalyst aromatics yield and reactant conversion rate.

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

[0078] Preferably, the alkane is an alkane of C5 or above, preferably a C6-C8 alkane.

[0079] In the present invention, the reaction conditions for the alkane aromatization are not particularly limited, and those skilled in the art can make adaptive adjustments as needed.

[0080] According to a particularly preferred embodiment of the present invention, a method for preparing L molecular sieve comprises the following steps:

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

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

[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 calculated as oxides.

[0084] 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 from commercial sources, and the room temperature is 25°C.

[0085] Preparation Example 1 of L Molecular Sieve Seed

[0086] Take 20g KOH and dissolve it in 50g deionized water, add 7.86g Al(OH)3 into the solution, stir evenly, and after the solution is clarified, add 37.5g SiO2 into the mixture in the nature of silica sol, stir evenly, and obtain a mixture. The above reaction mixture is transferred into a stainless steel reactor and treated at 150℃ for 12h. The product is separated by centrifugation, and the obtained solid is washed with water and dried at 120℃ for 12h to obtain L molecular sieve seed crystals, which are recorded as S1. The molar ratio of the chemical composition in the seed crystals is: 1.0K2O·Al2O3·3.0SiO2, and the grain diameter of the L molecular sieve seed crystals is less than 100nm.

[0087] Example 1

[0088] Take 17.5g KOH and dissolve it in 83g deionized water. Add 7.86g Al(OH)3 into the solution. After the solution is clarified, add 3.6mL Ba(NO3)2 solution with a molar concentration of 0.15mol / L. Stir evenly. After the solution is clarified, add seed crystal S1. Continue to stir evenly. Add 25g SiO2 to the mixture in the form of silica sol. After stirring evenly, a gelled mixture is obtained. The molar ratio of Al2O3 in the seed crystal to Al2O3 in the gelled mixture is 2.5%.

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

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

[0091] Example 2

[0092] Take 17.5g KOH and dissolve it in 83g deionized water. Add 7.86g Al(OH)3 into the solution. After the solution is clarified, add 3.6mL Mg(NO3)2 solution with a molar concentration of 0.15mol / L. Stir evenly. After the solution is clarified, add seed crystal S1. Continue to stir evenly. Add 25g SiO2 to the mixture in the form of silica sol. After stirring evenly, a gelled mixture is obtained. The molar ratio of Al2O3 in the seed crystal to Al2O3 in the gelled mixture is 2.5%.

[0093] The reaction mixture was transferred into a stainless steel reactor and crystallized at 150°C for 60 hours. The product was separated by centrifugation, and the solid was washed with water and dried at 120°C for 12 hours to obtain L-1-M. The molar ratio of 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 marked L-1-M in Example 2 is as follows. Figure 1 It can be concluded that the product obtained by this synthesis method is L molecular sieve, and no impurity crystal peak is observed, indicating that this method can obtain L molecular sieve with high crystallinity.

[0095] Example 3

[0096] Take 17.5g KOH and dissolve it in 83g deionized water. Add 7.86g Al(OH)3 into the solution. After the solution is clarified, add 7.2mL Ba(OH)2 solution with a molar concentration of 0.15mol / L. After the solution is clarified, add seed crystal S1. Continue to stir evenly. Add 25g SiO2 to the mixture in the form of silica sol. After stirring evenly, a gelled mixture is obtained. The molar ratio of Al2O3 in the seed crystal to Al2O3 in the gelled mixture is 2.5%.

[0097] The reaction mixture was transferred into a stainless steel reactor and crystallized at 150°C for 60 hours. The product was separated by centrifugation, and the solid was washed with water and dried at 120°C for 12 hours to obtain L-2-B. The molar ratio of the chemical composition of the L molecular sieve is 1.35K2O·0.007BaO·Al2O3·5.5SiO2.

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

[0099] Example 4

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

[0101] Example 5

[0102] L molecular sieve was prepared according to the method of Example 3, except that the amount of alkaline earth metal compound added was changed so that the molar ratio of the added alkali metal compound to the alkaline earth metal compound was 72:1, calculated as oxide, 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] Take 9 mL of platinum-ammonia solution (its molar concentration is 5.7×10 -2 mol / L), 10 g of L molecular sieve were added thereto respectively, the mixture was 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 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] Take 17.5g KOH and dissolve it in 83g deionized water. Add 7.86g Al(OH)3 into the solution and stir it evenly. After the solution becomes clear, add seed crystal S1 and continue to stir evenly. Then, add 25g SiO2 into the mixture in the form of silica sol and stir evenly to obtain a gelled mixture. The molar ratio of Al2O3 in the seed crystal to Al2O3 in the gelled mixture is 2.5%.

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

[0109] Figure 1The XRD pattern of the molecular sieve prepared in Comparative Example 1 is shown in FIG. Figure 1 It can be seen that the product obtained by this 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. The prepared molecular sieve was denoted as LN.

[0112] Comparative Example 3

[0113] L molecular sieve was prepared according to the method of Example 3, except that after adding Al(OH)3 and Ba(OH)2 in the same amount as in Example 3 and stirring appropriately, adding L molecular sieve seeds and silica sol in the same amount as in Example 3, L molecular sieve with high crystallinity could not be obtained.

[0114] Catalyst Preparation Comparative Example 1-2

[0115] An 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 photo of the L molecular sieve of Example 1 is shown in Figure 2 The scanning electron microscope photo of the L molecular sieve of Example 2 is shown in Figure 3 The scanning electron microscope photo of the L molecular sieve of Example 3 is shown in Figure 4 ,from Figure 2 , Figure 3 and Figure 4 The crystal structure of the prepared L molecular sieve can be observed, and the L molecular sieve has a smaller crystal diameter. The scanning electron microscope photo of the L molecular sieve of comparative example 1 is shown in Figure 5 ,from Figure 5 It can be seen that the grain size of the L molecular sieve in Comparative Example 1 is larger than that in the embodiment. The structures of the L molecular sieves in the embodiment and the comparative example are shown in Table 1.

[0118] Table 1

[0119]

[0120] As can be seen from Table 1, the L molecular sieves prepared in Examples 1-5 have a larger total pore volume and a smaller micropore volume than the comparative example, and have a multi-level pore structure. In addition, the L molecular sieves prepared in Examples 1-5 have a smaller crystal diameter than the comparative example.

[0121] Test Example 2

[0122] Evaluation of the Reaction Performance of Molecular Sieve Catalysts

[0123] n-Hexane, 2-methylpentane and 3-methylpentane were used as mixed raw materials, the volume ratio of each raw material was 1:1:1, the reaction temperature was 460°C, the reaction pressure was 0.32MPa, and the volume space velocity of the mixed raw materials was 4h -1 The prepared L molecular sieve catalyst was evaluated for reaction, and the performance of the catalyst was characterized by the reaction benzene yield.

[0124] The reaction performance evaluation test results of the 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 catalyst preparation comparative examples 1-2 is as follows: Figure 6 As shown, from Figure 6 It can be seen that compared with catalyst Pt / L-0, catalysts Pt / L-1-B and Pt / L-2-B show better catalytic performance in the aromatization reaction of C6 alkane. After 14 hours of reaction, the benzene yield of catalyst Pt / L-1-B is about 1 percentage point higher than that of catalyst Pt / L-0, and the benzene yield of catalyst Pt / L-2-B is about 1.5 percentage points higher than that of catalyst Pt / L-0.

[0128] 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. An L molecular sieve, characterized in that The L molecular sieve has a multi-level pore structure of micropores and mesopores, and a specific surface area of ​​310-330m 2 / g, the total pore volume is 0.162-0.19mL / g, the micropore volume is 0.137-0.145mL / g, the grain diameter is 100-800nm, and the silicon-aluminum molar ratio is 3-10:

1.

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

3. The L molecular sieve according to claim 1 or 2, wherein The L molecular sieve further includes an M element, and the M element is an alkali metal and / or an alkaline earth metal; Calculated in terms of oxide, n(M x The molar ratio of (O):n(Al2O3) is (1-3):1, preferably (1-2):1, and x is 1 or 2; Preferably, the molar ratio of the alkali metal to the alkaline earth metal is 100-350:1, preferably 120-310:1, calculated as oxide.

4. A method for preparing L molecular sieve, characterized in that: The following steps are involved: (1) providing a colloid-forming mixture containing at least two inorganic bases, an aluminum source, L molecular sieve seeds, a silicon source and water; (2) crystallizing the colloid-forming mixture; The at least two inorganic bases include at least one alkali metal compound and at least one alkaline earth metal compound. The molar ratio of the alkali metal compound to the alkaline earth metal compound in the colloid-forming mixture is 20-600:1, calculated as oxides.

5. The preparation method according to claim 4, wherein The inorganic base is calculated as oxide, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2. The molar ratio of each component in the colloid-forming mixture is 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 element is an alkali metal and / or an alkaline earth metal, and x is 1 or 2; Preferably, the crystallization conditions include: a crystallization temperature of 130-180° C., preferably 150-170° C.; and a crystallization time of 30-100 h, preferably 50-80 h.

6. The preparation method according to claim 4 or 5, wherein: The molar ratio of the alkali metal compound to the alkaline earth metal compound in the colloid-forming mixture is 80-600:1, calculated as oxide; Preferably, the alkali metal compound is selected from compounds of K and / or Na; Preferably, the alkaline earth metal compound is at least one selected from compounds of Mg, Ba and Ca.

7. The preparation method according to any one of claims 4 to 6, wherein: The L molecular sieve seed crystals are obtained by mixing an inorganic base, an aluminum source, a silicon source and water, stirring the mixture into a sol, and subjecting the mixture to a hydrothermal treatment; Preferably, the L molecular sieve seed crystal has a grain diameter of ≤100 nm; Preferably, the molar ratio of each component in the sol is n(R y O):n(Al2O3):n(SiO2):n(H2O) is (2-6):1:(6-15):(80-200), preferably (2-4):1:(8-12):(120-180), the R element is an alkali metal and / or an alkaline earth metal, and y is 1 or 2; Preferably, the hydrothermal treatment conditions include: a hydrothermal treatment temperature of 120-180° C., preferably 140-160° C., and a hydrothermal treatment time of 8-20 h, preferably 9-15 h.

8. The preparation method according to any one of claims 4 to 7, wherein: The molar ratio of Al2O3 in the L molecular sieve seed crystals to Al2O3 in the colloid-forming mixture is 1-10%, preferably 2-5%.

9. The preparation method according to any one of claims 4 to 8, wherein: In step (1), the components are added in the order of alkali metal compound, aluminum source, alkaline earth metal compound, L molecular sieve seed crystal and silicon source; Preferably, the silicon source is selected from at least one of silica sol, white carbon black, water glass and diatomaceous earth; Preferably, the aluminum source is hydrated aluminum oxide and / or metaaluminate.

10. An L molecular sieve catalyst, characterized in that The L molecular sieve catalyst comprises the L molecular sieve described in any one of claims 1 to 3 or the L molecular sieve prepared by the preparation method described in any one of claims 4 to 9, and Pt supported on the L molecular sieve, wherein the content of Pt is 0.2-3wt% based on the total mass of the L molecular sieve catalyst being 100wt%.

11. A method for preparing an L molecular sieve catalyst, characterized in that: The method comprises: The L molecular sieve described in any one of claims 1 to 3 or the L molecular sieve prepared by the preparation method described in any one of claims 4 to 9 is impregnated with a Pt precursor solution, and then calcined to obtain an 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 523-673 K and a calcination time of 1-5 h.

12. Use of the L molecular sieve catalyst according to claim 10 or the L molecular sieve catalyst prepared by the preparation method according to claim 11 in alkane aromatization; Preferably, the alkane is an alkane of C5 or above, preferably a C6-C8 alkane.

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