ZSM-5 molecular sieve microsphere as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molecular sieves, and discloses ZSM-5 molecular sieve microspheres as well as a preparation method and application thereof. The ZSM-5 molecular sieve microsphere has a spherical structure formed by stacking molecular sieve crystal grains; the spherical structure comprises macropores formed by stacking molecular sieve crystal grains and micropores in the molecular sieve crystal grains, and the volume ratio of the macropores to the micropores is (1-2.5): 1; the average diameter of macropores is greater than or equal to 50nm, and the average diameter of micropores is less than or equal to 2nm. The ZSM-5 molecular sieve microsphere provided by the invention has the advantages of high macropore ratio, large macropore diameter and more contactable active sites, and is beneficial to improving the catalytic reaction efficiency and the selectivity to a target product. The method for preparing the ZSM-5 molecular sieve microspheres provided by the invention is simple and convenient for large-scale production. The ZSM-5 molecular sieve microspheres provided by the invention have good application prospects in catalysis of alcohol benzylation reaction, catalytic cracking of petroleum, waste gas treatment and wastewater treatment.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieves, and in particular to ZSM-5 molecular sieve microspheres and a preparation method and application thereof. Background Art

[0002] ZSM-5 molecular sieve is a type of crystalline material with an ordered microporous structure. Due to its unique selectivity, special acidity and high hydrothermal stability, it is widely used in petrochemical and fine chemical industries.

[0003] However, most ZSM-5 zeolites have only microporous channels, which severely limits the high flow diffusion performance required in the catalytic reaction. The catalytic reaction only occurs at the surface active sites of the zeolite, and most of the active sites inside the zeolite cannot be effectively utilized, resulting in great waste.

[0004] Studies have shown that ZSM-5 molecular sieves with large pores can effectively overcome the diffusion limitations of microporous molecular sieves. However, the existing large-pore ZSM-5 molecular sieves have the following problems: the large pores produced only exist on the outer surface, the proportion of large pores is low, and it is difficult for reactant molecules to contact the active sites inside the molecular sieve; at the same time, the preparation of large-pore ZSM-5 molecular sieve microspheres often requires the use of a large number of expensive and complex templates, and some of them will cause certain pollution to the environment. Summary of the invention

[0005] To solve the above problems, the present invention provides a ZSM-5 molecular sieve microsphere and a preparation method and application thereof. The ZSM-5 molecular sieve of the present invention has a high proportion of macropores, a large pore size, and many accessible active sites, which is beneficial to improving the catalytic reaction efficiency and the selectivity for the target product, and can overcome the problem of low utilization of active sites inside the ZSM-5 molecular sieve in the prior art.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a ZSM-5 molecular sieve microsphere, wherein the ZSM-5 molecular sieve microsphere has a spherical structure formed by the accumulation of molecular sieve crystals;

[0007] The spherical structure includes macropores formed by the accumulation of the molecular sieve crystals and micropores in the molecular sieve crystals, and the volume ratio of the macropores to the micropores is (1-2.5):1;

[0008] The average diameter of the macropores is ≥50 nm, and the average diameter of the micropores is ≤2 nm.

[0009] The second aspect of the present invention provides a method for preparing the ZSM-5 molecular sieve microspheres described in the first aspect, the method comprising:

[0010] (1) stirring and mixing a precursor solution containing a silicon source, an aluminum source and a template and silicone oil to obtain a mixed solution;

[0011] (2) subjecting the mixed solution to an aging treatment to obtain a powder;

[0012] (3) The powder is subjected to crystallization treatment and calcination treatment in sequence to obtain the molecular sieve microspheres.

[0013] The third aspect of the present invention provides the use of the ZSM-5 molecular sieve microspheres described in the first aspect or the ZSM-5 molecular sieve microspheres obtained according to the method described in the second aspect in catalytic alcohol benzylation reaction, catalytic cracking of petroleum, waste gas treatment and wastewater treatment.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The ZSM-5 molecular sieve microspheres provided by the present invention are spherical structures formed by the accumulation of molecular sieve crystals. The surface area that can be contacted in heterogeneous reactions is larger, which can increase the probability of contacting reaction active sites in heterogeneous reactions and improve reaction efficiency. At the same time, the ZSM-5 molecular sieve microspheres of the present invention introduce a macroporous structure with a volume of 1 to 2.5 times the micropore volume without destroying the original microporous structure of the molecular sieve crystals, so that the macropores can not only exist on the outer surface of the microspheres but also be uniformly dispersed inside the microspheres. Therefore, when the molecular sieve is used for catalytic reactions, the reactant molecules can contact the active sites inside and outside the molecular sieve, which is beneficial to improving the catalytic reaction efficiency and the selectivity for the target product.

[0016] The present invention synthesizes a spherical ZSM-5 molecular sieve with a high proportion of internal macropores by a method of dispersing a molecular sieve precursor liquid using the high-speed shear force of silicone oil. The synthesis process is simple and efficient, the preparation method is universal, and is convenient for large-scale production. It can also be applied to the preparation of other molecular sieves to improve the catalytic performance of a series of macromolecular reactions.

[0017] The ZSM-5 molecular sieve microspheres of the present invention have a wide range of application fields, and have good application prospects in catalytic alcohol benzylation reactions, catalytic cracking of petroleum, waste gas treatment, and wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a SEM image of the ZSM-5 molecular sieve microspheres obtained in Example 1 of the present invention;

[0019] Figure 2 TEM image (left) and energy spectrum (right) of ZSM-5 molecular sieve microspheres obtained in Example 1 of the present invention;

[0020] Figure 3 is the XRD pattern of the ZSM-5 molecular sieve microspheres obtained in Example 1 of the present invention;

[0021] Figure 4It is a nitrogen adsorption and desorption curve diagram and a micropore size distribution diagram of the ZSM-5 molecular sieve microspheres obtained in Example 1 of the present invention;

[0022] Figure 5 The mercury intrusion curve and macropore size distribution diagram of the ZSM-5 molecular sieve microspheres obtained in Example 1 of the present invention are shown;

[0023] Figure 6 is a SEM image of the ZSM-5 molecular sieve microspheres obtained in Example 2 of the present invention;

[0024] Figure 7 is the XRD pattern of the ZSM-5 molecular sieve microspheres obtained in Example 2 of the present invention;

[0025] Figure 8 is a SEM image of the ZSM-5 molecular sieve microspheres obtained in Example 3 of the present invention;

[0026] Fig. 9 is the XRD pattern of the ZSM-5 molecular sieve microspheres obtained in Example 3 of the present invention;

[0027] Fig.10 is a SEM image of the ZSM-5 molecular sieve microspheres obtained in Comparative Example 1 of the present invention;

[0028] Fig.11 is the XRD diagram of the ZSM-5 molecular sieve microspheres obtained in Comparative Example 1 of the present invention;

[0029] Fig.12 is a SEM image of the ZSM-5 molecular sieve microspheres obtained in Comparative Example 2 of the present invention;

[0030] Fig.13 is the XRD diagram of the ZSM-5 molecular sieve microspheres obtained in Comparative Example 2 of the present invention;

[0031] Fig.14 The catalytic performance results of the ZSM-5 molecular sieve microspheres obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention for the benzylation reaction of benzyl alcohol and 1,3,5-trimethylbenzene are shown. DETAILED DESCRIPTION

[0032] 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.

[0033] As mentioned above, the first aspect of the present invention provides a ZSM-5 molecular sieve microsphere, which has a spherical structure formed by the accumulation of molecular sieve grains;

[0034] The spherical structure includes macropores formed by the accumulation of the molecular sieve crystals and micropores in the molecular sieve crystals, and the volume ratio of the macropores to the micropores is (1-2.5):1;

[0035] The average diameter of the macropores is ≥50 nm, and the average diameter of the micropores is ≤2 nm.

[0036] Compared with the ZSM-5 molecular sieve of the prior art formed by the assembly of crystal grains, the ZSM-5 molecular sieve microspheres provided by the present invention are spherical structures formed by the accumulation of molecular sieve crystal grains, and the surface area that can be contacted in the heterogeneous reaction is larger, thereby increasing the probability of contacting the active sites of the reaction in the heterogeneous reaction and improving the reaction efficiency. At the same time, the volume ratio of the ZSM-5 molecular sieve microspheres of the present invention controls the macropores (average diameter of the macropores ≥ 50nm) formed by the accumulation of molecular sieve crystal grains and the micropores (average diameter of the micropores ≤ 2nm) in the molecular sieve crystal grains to be (1-2.5): 1, so that under the premise of not destroying the original micropore structure of the molecular sieve crystal grains, a macropore structure of 1-2.5 times the volume of the micropores is introduced, so that the macropores can not only exist on the outer surface of the microspheres but also be uniformly dispersed inside the microspheres, and then the molecular sieve can be used for catalytic reaction. Reactant molecules can contact the active sites inside and outside the molecular sieve, thereby improving the catalytic reaction efficiency and the selectivity of the target product.

[0037] Preferably, the average particle size of the molecular sieve crystals is 300-600nm. In the present invention, the average particle size of the molecular sieve crystals is controlled at 300-600nm, which can effectively retain the micropores in the crystals, and can also increase the proportion of crystals stacked with macropores, so that more active sites can be contacted, further improving the efficiency of the catalytic reaction. The inventors of the present invention have found that in this preferred case, the ZSM-5 molecular sieve microspheres are used to catalyze the benzylation reaction of benzyl alcohol and 1,3,5-trimethylbenzene, showing more excellent catalytic performance.

[0038] Preferably, the pore volume of the macropores is 0.18-0.23 m 3 / g, the pore volume of the micropores is 0.1-0.15m 3 / g, the inventors of the present invention found that in this preferred case, the ZSM-5 molecular sieve microspheres exhibit better mass transfer performance, that is, the ZSM-5 molecular sieve microspheres have stronger adsorption and desorption capabilities for gases and liquids in catalytic reactions, and the diffusion rate of reactant molecules in the pores of the ZSM-5 molecular sieve microspheres is faster, thereby further improving the catalytic reaction rate.

[0039] Preferably, the average diameter of the macropores is 0.8-1.2 μm, and the average diameter of the micropores is 0.4-0.6 nm. The inventors of the present invention have found that in this preferred case, the ZSM-5 molecular sieve microspheres have better selectivity for the target product, because in the catalytic reaction, some reactants or product molecules are too large to enter and exit the pores of the molecular sieve catalyst, and only those molecules with a diameter smaller than the pore size of the molecular sieve can enter the pores, so more and larger pores need to be introduced to allow the reactants to enter the interior of the molecular sieve and the products to come out of the interior of the molecular sieve to obtain a higher selectivity for the target product. The ZSM-5 molecular sieve microspheres are used to catalyze the benzylation reaction of benzyl alcohol and 1,3,5-trimethylbenzene, and can have a higher selectivity for 2-benzyl-1,3,5-trimethylbenzene.

[0040] Preferably, the volume ratio of the macropores to the micropores is (1.5-2): 1. The inventors of the present invention have found that in this preferred case, the macropore volume ratio in the ZSM-5 molecular sieve microspheres is high, which is conducive to the circulation of reactant molecules and target products in the pores, and can further improve the catalytic reaction efficiency and the selectivity of the target product.

[0041] Preferably, the specific surface area of ​​the ZSM-5 molecular sieve microspheres is 426-447 m 2 The inventors of the present invention have found that, in this preferred case, the ZSM-5 molecular sieve microspheres can further increase the contact probability between the reactant molecules and the active sites when used in the catalytic reaction, thereby further improving the catalytic reaction efficiency.

[0042] Preferably, the average diameter of the ZSM-5 molecular sieve microspheres is 1-6 μm. The inventors of the present invention have found that in this preferred case, the ZSM-5 molecular sieve microspheres are more stable, and the reaction active sites and pore flow distances in the ZSM-5 molecular sieve microspheres are in a more suitable state. If the diameter of the ZSM-5 molecular sieve microspheres is too large, the transmission distance will be increased, which is not conducive to the diffusion of reactants and product molecules, and the microspheres will be fragile. If the diameter of the ZSM-5 molecular sieve microspheres is too small, the reaction active sites in the ZSM-5 molecular sieve microspheres are reduced, which affects the efficiency of the catalytic reaction.

[0043] Preferably, the molar ratio of silicon to aluminum in the molecular sieve crystals is 50-200: 1. In the present invention, Si:Al is controlled to be (50-200): 1, mainly to regulate the number of acid sites in the molecular sieve, thereby further regulating the active sites in the molecular sieve and further improving the catalytic reaction efficiency of the molecular sieve.

[0044] As mentioned above, the second aspect of the present invention provides a method for preparing the ZSM-5 molecular sieve microspheres described in the first aspect, the method comprising:

[0045] (1) stirring and mixing a precursor solution containing a silicon source, an aluminum source and a template and silicone oil to obtain a mixed solution;

[0046] (2) subjecting the mixed solution to an aging treatment to obtain a powder;

[0047] (3) The powder is subjected to crystallization treatment and calcination treatment in sequence to obtain the molecular sieve microspheres.

[0048] The present invention synthesizes a spherical ZSM-5 molecular sieve with a high proportion of internal macropores by a method of dispersing a molecular sieve precursor liquid using the high-speed shear force of silicone oil. The synthesis process is simple and efficient, the preparation method is universal, and is convenient for large-scale production. It can also be applied to the preparation of other molecular sieves to improve the catalytic performance of a series of macromolecular reactions.

[0049] Preferably, in step (1), the molar ratio of the silicon source, the aluminum source and the template in the precursor solution is 1:0.005-0.02:0.05-0.2.

[0050] Preferably, in step (1), the volume ratio of the precursor solution to the silicone oil is 1:20-80.

[0051] Preferably, in step (1), the silicon source is selected from at least one of tetraethyl silicate, silica sol, sodium silicate and white carbon black.

[0052] Preferably, in step (1), the aluminum source is selected from at least one of aluminum isopropoxide, pseudo-boehmite, sodium aluminate, aluminum nitrate, and aluminum sulfate.

[0053] Preferably, in step (1), the template agent may be at least one of tetramethylammonium hydroxide, tetramethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide and tetraethylammonium bromide.

[0054] The raw materials used above are all conventional and readily available materials, which can further reduce the cost of obtaining ZSM-5 molecular sieve microspheres and will not cause pollution to the environment.

[0055] According to a preferred embodiment, the precursor solution is prepared by the following steps:

[0056] (i) first stirring water, a template and an aluminum source to obtain a solution I;

[0057] (ii) stirring the silicon source and the solution I for a second time to obtain a precursor solution.

[0058] Preferably, the first stirring conditions include: a rotation speed of 200-600 rpm and a time of 0.5-1.5 h.

[0059] Preferably, the second stirring conditions include: a rotation speed of 200-600 rpm and a time of 5-8 hours.

[0060] According to a preferred specific embodiment, in step (1), the silicone oil is at least one of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, methylchlorophenyl silicone oil, methylethoxy silicone oil, methylvinyl silicone oil, methylhydroxy silicone oil, and hydroxy hydrogen silicone oil.

[0061] More preferably, the silicone oil is dimethyl silicone oil.

[0062] Preferably, in step (1), the stirring and mixing conditions include: a rotation speed of 4000-8000 rpm and a time of 1-3 hours. The inventors found that in this preferred case, the yield of the obtained ZSM-5 molecular sieve microspheres is higher.

[0063] Preferably, in step (2), the aging treatment conditions include: temperature of 40-80°C and time of 48-72h.

[0064] Preferably, the method further comprises subjecting the material after the aging treatment in step (2) to layering treatment, washing and drying treatment I in sequence to obtain the powder.

[0065] Preferably, the stratification treatment is to pour out the upper layer of silicone oil in the material after the aging treatment to obtain the lower layer of material.

[0066] Preferably, a non-polar organic solvent is used to wash the lower layer material.

[0067] Preferably, the non-polar organic solvent is at least one of n-hexane, toluene, xylene, petroleum ether, chloroform and the like.

[0068] The present invention has no special requirements on the number of washing times, and it is only necessary to remove the silicone oil in the lower layer material. Exemplarily, the lower layer material is washed 15-25 times with a non-polar organic solvent.

[0069] Preferably, the conditions of the drying treatment I include: a temperature of 50-70° C. and a time of 20-40 min.

[0070] Preferably, in step (3), the conditions of the crystallization treatment include: a temperature of 100-140° C. and a time of 60-80 h.

[0071] Preferably, the crystallization treatment is performed in a reactor with the aid of water vapor. Exemplarily, the powder is placed in the middle and upper part of a polytetrafluoroethylene liner, the substrate of the liner is filled with water, and then the polytetrafluoroethylene liner is placed in a stainless steel hydrothermal reactor for the crystallization treatment.

[0072] Preferably, the method further comprises filtering and drying the material after the crystallization treatment in step (3) in sequence, and then calcining the material obtained by the drying treatment II.

[0073] The present invention has no special requirements on the conditions of the filtration. Exemplarily, water and anhydrous ethanol are used for filtration 3-5 times each.

[0074] Preferably, the conditions of the drying treatment II include: a temperature of 50-70° C. and a time of 6-12 h.

[0075] Preferably, in step (3), the calcination treatment conditions include: temperature of 500-640° C. and time of 5-10 h.

[0076] Preferably, the calcination treatment is performed in an air atmosphere.

[0077] The present invention has no special requirements for the selection of the water, and those skilled in the art can select it as needed. Exemplarily, the water is deionized water.

[0078] As described above, the third aspect of the present invention provides the use of the ZSM-5 molecular sieve microspheres described in the first aspect or the ZSM-5 molecular sieve microspheres obtained according to the method described in the second aspect in catalytic alcohol benzylation reaction, catalytic cracking of petroleum, waste gas treatment and wastewater treatment.

[0079] The ZSM-5 molecular sieve microspheres of the present invention have a wide range of application fields, and have good application prospects in catalytic alcohol benzylation reactions, catalytic cracking of petroleum, waste gas treatment, and wastewater treatment.

[0080] According to a preferred specific embodiment, the present invention provides the use of the SM-5 molecular sieve microspheres in catalyzing the benzylation reaction of 1,3,5-trimethylbenzene and benzyl alcohol.

[0081] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the instruments, reagents, materials, etc. involved are all conventional instruments, reagents, materials, etc., which can be obtained through regular commercial channels. Among them, unless otherwise specified, the reagents used are all commercially available analytically pure products.

[0082] Template:

[0083] Template agent I: tetrapropylammonium hydroxide (TPAOH), with a mass fraction of 25 wt%.

[0084] Template II: tetramethylammonium hydroxide, mass fraction is 25 wt%.

[0085] Template III: tetraethylammonium bromide, mass fraction is 10 wt%.

[0086] Aluminum source:

[0087] Aluminum source I: aluminum isopropoxide.

[0088] Aluminum source II: sodium aluminate.

[0089] Silicon source:

[0090] Silicon source I: tetraethyl orthosilicate.

[0091] Silicon source II: sodium silicate.

[0092] Silicone oil: dimethyl silicone oil, CAS number is 9006-65-9.

[0093] Molecular sieve I-D2: Commercially available ZSM-5 molecular sieve, with a measured specific surface area of ​​325 m 2 / g, purchased from Tianjin Nanhua Catalyst Co., Ltd.

[0094] Preparation Example 1

[0095] This preparation example is used to illustrate the preparation of a precursor solution according to the following steps with reference to the formula in Table 1: (i) first stirring water, a template and an aluminum source to obtain a solution I;

[0096] (ii) stirring the silicon source and the solution I for a second time to obtain a precursor solution, named Y1;

[0097] The first stirring speed is 400 rpm and the time is 1 h;

[0098] The second stirring speed was 400 rpm and the time was 5 h.

[0099] Preparation Examples 2-3 were carried out using a method similar to Preparation Example 1, except that the formulas were different, as shown in Table 1 below, and the unlisted parts were the same as those in Preparation Example 1.

[0100] Table 1

[0101] Preparation Example 1 Preparation Example 2 Preparation Example 3 Deionized water / g 5.4 5.4 5.4 Template type Template I Template II Template III Dosage / g 1.8 1.46 2.1 Aluminum source type Aluminum Source I Aluminum Source II Same as Preparation Example 1 Dosage / g 0.04 0.033 0.02 Silicon source type Silicon Source I Same as Preparation Example 1 Silicon Source II Dosage / g 4.2 4.2 2.44 Naming of precursor solution Y1 Y2 Y3

[0102] Example 1

[0103] In this example, ZSM-5 molecular sieve microspheres were prepared according to the following steps with reference to the formula and process parameters in Table 2:

[0104] (1) stirring and mixing the precursor solution (obtained in the above-mentioned Preparation Example 1) and silicone oil to obtain a mixed solution;

[0105] (2) subjecting the mixed solution to an aging treatment, and then pouring out the upper layer of silicone oil in the aged material to obtain a lower layer of material; washing the lower layer of material with n-hexane for 20 times, and then subjecting the lower layer of material to a drying treatment I (at 60° C. for 30 min) to obtain a powder;

[0106] (3) placing the powder in the middle and upper part of a polytetrafluoroethylene liner, filling the substrate of the liner with water, and then placing the polytetrafluoroethylene liner in a stainless steel hydrothermal reactor for crystallization treatment, and then filtering the crystallized material with water and anhydrous ethanol for 5 times respectively, and then performing drying treatment II (temperature of 60°C, time of 10 hours); finally, calcining the material obtained by the drying treatment II in an air atmosphere to obtain ZSM-5 molecular sieve microspheres, named molecular sieve I-1.

[0107] Examples 2 and 3 are all carried out using a method similar to that of Example 1, except that the formula and process parameters are different, as shown in Table 2. The unlisted parts are the same as those of Example 1.

[0108] Comparative Example 1

[0109] The precursor liquid Y1 was poured into a tetrafluoroethylene liner and loaded into a stainless steel hydrothermal reactor for crystallization treatment (180°C, 24h), and then the crystallized material was filtered 5 times with water and anhydrous ethanol respectively, and then dried II (temperature was 60°C, time was 10h); finally, the material obtained by the drying treatment II was calcined in an air atmosphere (550°C, 7h) to obtain a ZSM-5 molecular sieve, named molecular sieve I-D1.

[0110] The specific surface area of ​​molecular sieve I-D1 was measured by the method specified in GB / T19587-2004, and the specific surface area of ​​molecular sieve I-D1 was 416m 2 / g.

[0111] Comparative Example 2

[0112] This comparative example directly uses commercially available ZSM-5 molecular sieve as a comparison, and is named molecular sieve I-D2.

[0113] Table 2

[0114]

[0115]

[0116] Test Case

[0117] 1. The morphology of each ZSM-5 molecular sieve obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 was tested using a scanning electron microscope (SEM). The results are as follows: Figure 1 , Figure 6 , Figure 8 , Fig.10 , Fig.12 as shown in .

[0118] pass Figure 1 It can be seen that the diameter of the ZSM-5 molecular sieve microspheres prepared in Example 1 is about 6 μm, and the ZSM-5 molecular sieve microspheres have a large number of macropores, and the macropores (pores) are formed by stacking of grains with an average particle size of about 300 nm;

[0119] pass Figure 6 It can be seen that the diameter of the ZSM-5 molecular sieve microspheres prepared in Example 2 is about 5 μm, and the ZSM-5 molecular sieve microspheres have a large number of macropores. The macropores (pores) are formed by stacking of grains with an average particle size of about 300 nm, and the grains are stacked relatively loosely.

[0120] pass Figure 8 It can be seen that the diameter of the ZSM-5 molecular sieve microspheres prepared in Example 3 is about 4 μm, and the ZSM-5 molecular sieve microspheres have a large number of macropores. The macropores (pores) are formed by stacking of grains with an average particle size of about 600 nm, and the grains are stacked relatively tightly.

[0121] pass Fig.10 It can be seen that the ZSM-5 molecular sieve microspheres prepared in Comparative Example 1 are of a lamellar crystal structure, and the length of the crystals is about 400 nm.

[0122] pass Fig.12 It can be seen that the ZSM-5 molecular sieve obtained in Comparative Example 2 has a flaky crystal structure, and the crystal length is about 4 μm and the crystal width is about 2 μm.

[0123] 2. The morphology of the ZSM-5 molecular sieve microspheres obtained in Example 1 and the distribution of each element in the ZSM-5 molecular sieve microspheres were tested using a transmission electron microscope (TEM). The results are as follows: Figure 2 as shown in .

[0124] pass Figure 2 (Left) It can be seen that the ZSM-5 molecular sieve microspheres are formed by stacking of crystals with an average particle size of about 300 nm, and there are also obvious macropores inside them; Figure 2 (Right) The energy spectrum shows that the silicon, aluminum and oxygen elements of the ZSM-5 molecular sieve microspheres are evenly distributed without obvious agglomeration.

[0125] 3. XRD was used to test the diffraction peaks of the ZSM-5 molecular sieve microspheres obtained in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2. The results are as follows: Figure 3 , Figure 7 , Fig. 9 , Fig.11 , Fig.13 as shown in .

[0126] pass Figure 3 , Figure 7 and Fig. 9 It can be seen that within the scanning range of 5-50°, five characteristic diffraction peaks of the MFI topological structure with high intensity appear: 2Theta=7.9°, 8.8°, 23.1°, 23.9°, 24.4°, which correspond to the diffraction peak positions of the ZSM-5 molecular sieve standard PDF card (PDF No.44-0003), and no other amorphous peaks or impurity peaks are found, indicating that the ZSM-5 molecular sieve microspheres prepared by the present invention have high purity;

[0127] pass Fig.11 , Fig.13 It can be seen that the ZSM-5 molecular sieves obtained in Comparative Examples 1 and 2 have high purity.

[0128] 4. The pore structure of the ZSM-5 molecular sieve microspheres obtained in Example 1 was tested using the methods specified in GB / T19587-2004 and GB / T 21650.1-2008. The results are as follows: Figure 4 and Figure 5 as shown in .

[0129] Figure 4 The nitrogen adsorption-desorption curve and micropore size distribution diagram of the ZSM-5 molecular sieve microspheres prepared in Example 1 show that the isotherm is a typical type IV adsorption curve. There is an obvious adsorption transition in the P / Po<0.01 range, indicating that there are a large number of microporous structures inside the ZSM-5 molecular sieve microspheres. An obvious hysteresis loop can be seen in the P / Po range of 0.4 to 1.0, indicating that the ZSM-5 molecular sieve microspheres contain a large number of macropores. From the micropore size distribution of the ZSM-5 molecular sieve microspheres, it can be seen that there is a micropore size distribution centered at 0.5 nm, which is the basic feature of the ten-membered ring channel of the ZSM-5 molecular sieve; according to Figure 4 Calculation shows that the specific surface area of ​​the ZSM-5 molecular sieve microspheres reaches 447m 2 / g.

[0130] Figure 5The mercury injection curve and macropore pore size distribution of the ZSM-5 molecular sieve microspheres prepared in Example 1 show that there is an obvious hysteresis in the mercury injection curve and the mercury withdrawal curve in the figure, indicating that there are a large number of macropores in the ZSM-5 molecular sieve microspheres. From the macropore pore size distribution, it can also be seen that the ZSM-5 molecular sieve microspheres have a macropore pore size distribution centered at 1 μm. A large number of macroporous structures are conducive to the guest macromolecules entering and exiting the molecular sieve, contacting more active sites, and effectively improving the catalytic performance.

[0131] Application Examples

[0132] The catalytic performance of the three ZSM-5 molecular sieves of Example 1, Comparative Example 1 and Comparative Example 2 was evaluated by the benzylation reaction of benzyl alcohol and 1,3,5-trimethylbenzene (the kinetic diameter of the reactant molecule is 0.8 nm> the micropore diameter of the ZSM-5 molecular sieve is 0.5 nm). The specific process is as follows:

[0133] 15 mL of 1,3,5-trimethylbenzene and 0.25 mL of benzyl alcohol were poured into a two-necked flask (with a condenser and a stirrer) and stirred for 30 min. After heating to 110°C, 0.2 g of the above molecular sieve was added as a catalyst. Samples were taken every 15 min and analyzed using a gas chromatograph Agilent 7890B. The conversion rate of benzyl alcohol and the selectivity for the target product 2-benzyl-1,3,5-trimethylbenzene at different reaction times were calculated. For specific results, see Fig.14 .

[0134] Conversion rate of benzyl alcohol = (peak area of ​​2-benzyl-1,3,5-trimethylbenzene + peak area of ​​dibenzyl ether) / (peak area of ​​2-benzyl-1,3,5-trimethylbenzene + peak area of ​​dibenzyl ether + peak area of ​​benzyl alcohol) × 100%;

[0135] Selectivity for 2-benzyl-1,3,5-trimethylbenzene=peak area of ​​2-benzyl-1,3,5-trimethylbenzene / (peak area of ​​2-benzyl-1,3,5-trimethylbenzene+peak area of ​​dibenzyl ether)×100%.

[0136] pass Fig.14 (Left) It can be seen that at 135 min of reaction, the conversion rate of benzyl alcohol by the ZSM-5 molecular sieve microspheres of Example 1 reached 99.35%, which is much higher than the conversion rate of benzyl alcohol by the ZSM-5 molecular sieves of Comparative Examples 1 and 2;

[0137] pass Fig.14 (Right) It can be seen that the selectivity of Example 1 to the product 2-benzyl-1,3,5-trimethylbenzene reaches 89.76%, while the selectivity of Comparative Examples 1 and 2 to the product 2-benzyl-1,3,5-trimethylbenzene is only 65.2% and 48.74%.

[0138] The above results show that the introduction of more macropores into the ZSM-5 molecular sieve microspheres provided by the present invention can effectively improve the diffusion performance of macromolecular reactants and products, making it easier for the reactants to contact the active centers inside the molecular sieve, thereby obtaining better catalytic performance.

[0139] 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 ZSM-5 molecular sieve microsphere, characterized in that: The ZSM-5 molecular sieve microspheres have a spherical structure formed by the accumulation of molecular sieve crystals; The spherical structure includes macropores formed by the accumulation of the molecular sieve crystals and micropores in the molecular sieve crystals, and the volume ratio of the macropores to the micropores is (1-2.5):1; The average diameter of the macropores is ≥50 nm, and the average diameter of the micropores is ≤2 nm.

2. The ZSM-5 molecular sieve microspheres according to claim 1, characterized in that: The average particle size of the molecular sieve crystals is 300-600 nm.

3. The ZSM-5 molecular sieve microspheres according to claim 1, characterized in that: The pore volume of the macropores is 0.18-0.23m 3 / g; And / or, the pore volume of the micropores is 0.1-0.15m 3 / g.

4. The ZSM-5 molecular sieve microspheres according to claim 3, characterized in that: The average diameter of the macropores is 0.8-1.2 μm; And / or, the average diameter of the micropores is 0.4-0.6 nm.

5. The ZSM-5 molecular sieve microspheres according to claim 4, characterized in that: The volume ratio of the macropores to the micropores is (1.5-2):1; And / or, the specific surface area of ​​the ZSM-5 molecular sieve microspheres is 426-447m 2 / g.

6. The ZSM-5 molecular sieve microspheres according to claim 1, characterized in that: The average diameter of the ZSM-5 molecular sieve microspheres is 1-6 μm.

7. The ZSM-5 molecular sieve microspheres according to claim 1, characterized in that: The molar ratio of silicon element to aluminum element in the molecular sieve crystal particles is 50-200:

1.

8. A method for preparing the ZSM-5 molecular sieve microspheres according to any one of claims 1 to 7, characterized in that: The method includes: (1) stirring and mixing a precursor solution containing a silicon source, an aluminum source and a template and silicone oil to obtain a mixed solution; (2) subjecting the mixed solution to an aging treatment to obtain a powder; (3) The powder is subjected to crystallization treatment and calcination treatment in sequence to obtain the molecular sieve microspheres.

9. The method according to claim 8, characterized in that In step (1), the molar ratio of the silicon source, the aluminum source and the template in the precursor solution is 1:0.005-0.02:0.05-0.2; And / or, in step (1), the silicon source is selected from at least one of tetraethyl silicate, silica sol, sodium silicate and white carbon black; And / or, in step (1), the aluminum source is selected from at least one of aluminum isopropoxide, pseudo-boehmite, sodium aluminate, aluminum nitrate, and aluminum sulfate; And / or, in step (1), the template may be at least one of tetramethylammonium hydroxide, tetramethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide and tetraethylammonium bromide.

10. Use of the ZSM-5 molecular sieve microspheres according to any one of claims 1 to 7 or the ZSM-5 molecular sieve microspheres obtained according to the method according to any one of claims 8 to 9 in catalytic alcohol benzylation reaction, catalytic cracking of petroleum, waste gas treatment and wastewater treatment.

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