High-crystallinity aluminous zsm-5 molecular sieve, preparation method and application thereof

Abstract

The present application relates to the technical field of ZSM-5 molecular sieve preparation, and provides a high-crystallinity aluminum-rich ZSM-5 molecular sieve, a preparation method and application thereof.The preparation method of the high-crystallinity aluminum-rich ZSM-5 molecular sieve provided by the present application realizes the skeleton composition control of the ZSM-5 molecular sieve by adding a second aluminum source and then performing secondary crystallization, solves the technical bottleneck that it is difficult to directly synthesize the high-crystallinity aluminum-rich ZSM-5, breaks through the lower limit of the Si / Al ratio phase region of the artificial in-situ synthesis of the molecular sieve, effectively controls the crystal parameter and improves the production efficiency, realizes the precise construction of the high-crystallinity aluminum-rich ZSM-5 molecular sieve, and thus enhances the micropore crystallinity of the molecular sieve, optimizes the acid distribution, greatly enriches the metastable surface active acid center distribution of the molecular sieve, and has good aromatic hydrocarbon conversion performance.

Description

Technical Field

[0001] This invention relates to the field of ZSM-5 molecular sieve preparation technology, and more specifically, to a highly crystalline aluminum-rich ZSM-5 molecular sieve, its preparation method, and its applications. Background Technology

[0002] ZSM-5 molecular sieve is a high-silica zeolite molecular sieve with a unique pore structure, developed by researchers at Mobil in the 1970s. It was quickly adopted as a catalytic material in industrial applications due to its high thermal stability, high specific surface area, and excellent adsorption capacity for molecules such as aromatics. The artificial synthesis of ZSM-5 molecular sieve was epoch-making, revolutionizing the petrochemical and catalysis fields. Due to its unique pore structure and acid properties, ZSM-5 molecular sieve is a highly valuable catalytic material. ZSM-5 molecular sieves typically possess more active centers for moderately strong acids and contain higher... The / Lewis acid center ratio facilitates the electrophilic activation of the benzene ring and the formation of carbocations, and has demonstrated high catalytic activity and stability in hydrocarbon reactions. Currently, ZSM-5 molecular sieves have achieved industrial applications in aromatic hydrocarbon conversion reactions such as toluene disproportionation. They have also been extensively studied in petrochemical fields such as methanol-to-hydrocarbons, methane aromatization (MDA), alkyl transfer, and alkyl isomerization, and can be used in catalytic reactions such as heavy oil lightening, polycyclic aromatic hydrocarbon lightening, and xylene isomerization.

[0003] The catalytic active centers of molecular sieves are influenced by various factors. It is generally believed that the framework composition of ZSM-5 molecular sieves is closely related to its structure and surface properties. The number of active centers is generally proportional to the aluminum atom content of the framework. In particular, the quantitative information of the framework crystallographic T sites and the coordination chemical environment largely determine the type and properties of the catalytically active solid acid centers. Therefore, for catalytic reactions requiring high-density acid centers, a higher number of Al species in the framework is more conducive to the catalytic reaction. Developing aluminum-rich (low-silicon) ZSM-5 materials and improving their crystallinity are key technical challenges that urgently need to be addressed to advance efficient catalytic applications.

[0004] The tetrapropylammonium ion (quaternary ammonium base or quaternary ammonium salt) system is crucial for the ideal OSDA (organic structure directing agent) chemical environment for the efficient artificial synthesis of highly crystalline ZSM-5. However, in OSDA-containing systems with low charge density, the atomic bonding activation ability is strongly affected by factors such as pH value, and the high-aluminum raw material composition cannot be uniformly and effectively activated. Synthetic systems containing organic template agents typically only yield ZSM-5 molecular sieves with Si / Al > 10. Adjusting the gel chemistry of mixtures has limited effect on broadening the Si / Al ratio range of the aforementioned molecular sieve products, and the yield and crystallinity are easily and significantly affected by the aluminum-rich composition. Simultaneously, the controllability of additives and other regulatory methods is poor, making it difficult to achieve stable industrial production. On the other hand, based on Pauling's electrostatic valence rule and Loewenstein's rule, the synthesis of aluminum-rich frameworks requires stronger basicity and more balanced framework cations. In the publicly reported literature to date, even in inorganic cation systems with high charge density, it is still difficult to directly synthesize aluminum-rich molecular sieves with Si / Al < 10. Furthermore, this synthetic system is limited by a high nucleation activation energy, which is extremely unfavorable for molecular sieve crystallization. The crystallinity of the molecular sieve product is much lower than that synthesized in the organic structure-directing agent (OSDA) system. This not only results in low yield but also, due to the lack of an OSDA agent, it easily leads to the formation of small-pore alumina-rich zeolite impurities such as SOD, GIS, and ANA, which is very detrimental to the synthesis of ZSM-5 molecular sieves. Meanwhile, seed crystal methods or OSDA methods cannot fundamentally improve these problems.

[0005] In summary, the effective activation of aluminum atoms in an aluminum-rich environment and the stability factors such as bond angles and bond energies of the aluminum-containing framework make the in-situ direct synthesis of aluminum-rich molecular sieves with Si / Al < 10 a recognized challenge in both research and industry. It is also a key technological challenge that urgently needs to be addressed for the application of efficient solid acid catalysis. If the problems of high yield and high crystallinity can be solved simultaneously, the aluminum content in the framework can be significantly increased, providing more abundant active acid catalytic centers, which will have great potential for industrial applications. Summary of the Invention

[0006] The purpose of this invention is to provide a highly crystalline alumina-rich ZSM-5 molecular sieve and its preparation method, so as to solve the technical problem that it is difficult to prepare alumina-rich ZSM-5 molecular sieves with high yield and high crystallinity in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a ZSM-5 molecular sieve, wherein the Si / Al ratio of the ZSM-5 molecular sieve is <10 and the relative crystallinity is >80%.

[0009] It should be noted that the Si / Al used in this invention refers to the molar ratio of Si and Al elements.

[0010] According to some embodiments of the present invention, the acid strength of the ZSM-5 molecular sieve is shown to be 360-500°C as the peak temperature of the desorption peak of temperature-programmed ammonia desorption (NH3-TPD).

[0011] To understand the acidity of solid acid catalysis, temperature-programmed desorption (NH3-TPD) of ammonia is commonly used for characterization. For example, it can be measured on an Altamira AMI-3300 chemisorption analyzer manufactured by Micrometrics Instruments, Inc. The obtained temperature-programmed ammonia desorption curves show characteristic peaks at different desorption temperatures, corresponding to different acid strengths; the higher the desorption temperature corresponding to the characteristic peak, the greater the acid strength.

[0012] According to some embodiments of the present invention, the content of skeletal aluminum in the ZSM-5 molecular sieve accounts for more than 80 wt% of the total aluminum content.

[0013] According to some embodiments of the present invention, the content of skeletal aluminum in the ZSM-5 molecular sieve accounts for more than 85 wt% of the total aluminum content.

[0014] According to some embodiments of the present invention, the specific surface area S of the ZSM-5 molecular sieve BET ≥350m 2 / g, micropore volume V micro >0.15cm 3 / g.

[0015] According to some embodiments of the present invention, the specific surface area S of the ZSM-5 molecular sieve BET 390-500m 2 / g, micropore volume V micro The value is 0.17–0.25 cm. 3 / g.

[0016] According to some embodiments of the present invention, the specific surface area S of the ZSM-5 molecular sieve BET 425-467m 2 / g, micropore volume V micro The value is 0.19–0.23 cm. 3 / g.

[0017] The ZSM-5 molecular sieve provided by this invention, through the regulation of the distribution of silicon and aluminum atoms in the framework, breaks through the existing silicon-aluminum ratio, and has the characteristics of high acid strength and good crystallinity. It also improves the microporous diffusion, mass transfer and reaction performance of the ZSM-5 molecular sieve.

[0018] Secondly, the present invention provides a method for preparing ZSM-5 molecular sieve, comprising:

[0019] S1. Obtain a colloid comprising a silicon source, a first aluminum source, an alkali source, a template agent R, and a solvent I; wherein the molar ratio of silicon in the silicon source to aluminum in the first aluminum source is greater than 10, preferably greater than 15;

[0020] S2. The colloid obtained in step S1 is crystallized once to obtain a slurry;

[0021] S3. Add a second aluminum source to the slurry obtained in step S2 so that the molar ratio of silicon to aluminum in the entire reaction system is less than 10;

[0022] S4. Perform secondary crystallization to obtain the ZSM-5 molecular sieve;

[0023] Optionally, it also includes S5. Calcining the ZSM-5 molecular sieve once, then performing ion exchange, and then performing a second calcination.

[0024] The present invention provides a method for preparing ZSM-5 molecular sieves. First, a first aluminum source, an alkali source, a silicon source, a template agent, and solvent I are mixed and crystallized once according to a conventional Si / Al ratio > 10 to obtain a highly crystalline ZSM-5 molecular sieve. Then, a second aluminum source is added to enhance atomic coordination and bonding capabilities, followed by a second crystallization to obtain the ZSM-5 molecular sieve. The selection of raw material composition and conditions during the first crystallization, as well as the addition of the second aluminum source, significantly affect the crystallization degree of the aluminum-rich ZSM-5 molecular sieve. By optimizing the synthesis ratio and process, and enhancing the activity of the aluminum source, the crystallization degree of the molecular sieve can be improved.

[0025] According to some embodiments of the present invention, in step S3, while adding the second aluminum source to the slurry obtained in step S2, it can be determined whether an appropriate amount of solvent I needs to be added based on the state of the slurry. Whether solvent I needs to be added and the specific amount of solvent I to be added are readily available to those skilled in the art.

[0026] According to some embodiments of the present invention, the first aluminum source and the second aluminum source may be the same or different, and each is independently selected from at least one of aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide.

[0027] According to some embodiments of the present invention, the second aluminum source is selected from at least one of aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0028] According to some embodiments of the present invention, the alkali source includes alkali metal hydroxide and / or ammonia; preferably, the alkali metal includes at least one of Li, Na, K, Rb, and Cs.

[0029] According to some embodiments of the present invention, the silicon source includes at least one of silicon powder, silicon balls, silica gel, silica sol, sodium silicate (sodium silicate / water glass), aluminosilicate, silicate esters (such as methyl silicate, ethyl silicate, propyl silicate, etc.), silicon tetrachloride, silane, silica, and diatomaceous earth.

[0030] According to some embodiments of the present invention, the silicon source is selected from at least one of tetramethylsilane (Si(CH3)4), methyltrimethoxysilane (MTMS), isobutylenetriethoxysilane, trichlorosilane (SiHCl3), and tetraethoxysilane (Si(OC2H5)4).

[0031] According to some embodiments of the present invention, the template agent R comprises at least one selected from ammonia, piperidine, N,N,N-trimethyl-1-adamantylammonium bromide, pyridine, cyclopropylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, n-butylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium iodide, tetrapropylammonium bromide, tetraethylammonium bromide, tetraethylammonium chloride, or tetramethylammonium chloride.

[0032] According to some embodiments of the present invention, solvent I includes at least one of deionized water, alcohol solvents, and imidazole ionic liquids.

[0033] According to some embodiments of the present invention, solvent I includes at least one selected from deionized water, methanol, ethanol, isopropanol, ethylene glycol, glycerol, acetone, and n-butanol.

[0034] According to some embodiments of the present invention, the molar ratio of the alkaline source to the silicon element in the silicon source is: OH - / Si = 0.01 to 0.45, for example, it can be 0.01, 0.02, 0.03, 0.05, 0.07, 0.08, 0.10, 0.11, 0.12, 0.15, 0.18, 0.20, 0.23, 0.25, 0.30, 0.31, 0.34, 0.35, 0.36, 0.40, 0.41, 0.45, etc.

[0035] According to some embodiments of the present invention, the molar ratio of the solvent I to the silicon element in the silicon source is: I / Si = 5 to 50, for example, it can be 5, 6, 8, 10, 13, 15, 16, 19, 20, 23, 25, 26, 28, 30, 35, 38, 40, 44, 46, 50, etc.

[0036] According to some embodiments of the present invention, the molar ratio of the template agent R to the silicon element in the silicon source is: R / Si = 0.001 to 0.55, for example, it can be 0.001, 0.002, 0.005, 0.007, 0.01, 0.02, 0.04, 0.05, 0.07, 0.08, 0.10, 0.11, 0.13, 0.15, 0.20, 0.25, 0.28, 0.30, 0.35, 0.37, 0.40, 0.42, 0.43, 0.48, 0.50, 0.52, 0.55, etc.

[0037] According to some embodiments of the present invention, the ion exchange includes ammonium exchange.

[0038] According to some embodiments of the present invention, the ammonium exchange reagent includes at least one of ammonium nitrate, ammonium chloride, ammonium oxalate, and ammonium sulfate.

[0039] According to some embodiments of the present invention, the ammonium exchange is carried out at a temperature of 10 to 120°C for 0.1 to 1000 hours, preferably at a temperature of 50 to 80°C for 0.5 to 5 hours.

[0040] According to some embodiments of the present invention, the concentration of the ammonium exchange reagent aqueous solution is 0.01 to 5 mol / L.

[0041] According to some embodiments of the present invention, the volume-to-mass ratio of the ammonium exchange reagent aqueous solution to the ZSM-5 molecular sieve is 4-10 mL: 1 g.

[0042] According to some embodiments of the present invention, the number of ion exchanges is 1 to 20 times, preferably 2 to 6 times.

[0043] According to some embodiments of the present invention, after ion exchange, the material is first filtered, washed and dried, and then calcined a second time; preferably, the drying temperature is 30-200°C, more preferably 80-120°C, and the drying time is 0.1-1000h, more preferably 0.5-10h.

[0044] According to some embodiments of the present invention, the stirring speed of the first crystallization is 0 to 6000 rpm, preferably 10 to 100 rpm, the crystallization temperature is 80 to 200°C, preferably 120 to 180°C, and the crystallization time is 2 to 2000 hours, preferably 100 to 300 hours.

[0045] According to some embodiments of the present invention, a pre-crystallization is performed before the primary crystallization, and the pre-crystallization temperature is 70-140°C and the time is 2-10 hours.

[0046] According to some embodiments of the present invention, the stirring speed of the secondary crystallization is 0 to 6000 rpm, preferably 10 to 100 rpm, the crystallization temperature is 80 to 200°C, preferably 120 to 180°C, and the crystallization time is 2 to 2000 hours, preferably 100 to 300 hours.

[0047] According to some embodiments of the present invention, a pre-crystallization is performed before the secondary crystallization, and the pre-crystallization temperature is 70-140°C and the time is 2-10 hours.

[0048] According to some embodiments of the present invention, after the secondary crystallization, the process further includes filtration, washing, and drying steps; preferably, the drying temperature is 30-200°C, more preferably 80-120°C, and the time is 0.1-1000h, more preferably 0.5-10h.

[0049] According to some embodiments of the present invention, the temperature of the first roasting is 200-980°C, preferably 400-650°C, more preferably 500-550°C; the time of the first roasting is 0.1-250h, preferably 1-10h.

[0050] According to some embodiments of the present invention, the temperature of the secondary roasting is 400-650°C, preferably 500-550°C; the time of the secondary roasting is 1-10 hours.

[0051] According to some embodiments of the present invention, the secondary calcination adopts a segmented calcination method, including: calcination at a temperature of 150-200°C for 0.5-3 hours, calcination at a temperature of 250-350°C for 0.5-3 hours, calcination at a temperature of 400-500°C for 0.5-3 hours, and finally calcination at a temperature of 200-900°C for 0.1-100 hours.

[0052] Thirdly, the present invention provides a ZSM-5 molecular sieve, which is prepared by the preparation method described in the second aspect.

[0053] Fourthly, the present invention provides the application of the ZSM-5 molecular sieve described in the first aspect or the ZSM-5 molecular sieve described in the third aspect in aromatic hydrocarbon conversion.

[0054] According to some embodiments of the present invention, the aromatic weight space velocity in the aromatic conversion is 0.01 to 50 h⁻¹. -1 The hydrogen-to-oil molar ratio is 0–300.

[0055] The ZSM-5 molecular sieve provided by this invention is a solid acid catalytic material with a unique structure. It has high crystallinity and is rich in aluminum. It has a large specific surface area and high acid density of external surface active centers. It exhibits excellent adsorption and catalytic performance for aromatic molecules. It can provide more acidic sites for aromatic conversion and has the characteristics of high selectivity, high activity and high stability when used to catalyze aromatic conversion.

[0056] According to some embodiments of the invention, the application includes applications in aromatic dealkylation reactions, such as in the selective dealkylation reaction of tricresyl.

[0057] According to some embodiments of the present invention, the selective dealkylation reaction of tricresyl is carried out at a temperature of 250–650°C and a pressure of 0–20 MPa.

[0058] Fifthly, the present invention provides an aromatic hydrocarbon conversion catalyst, the catalyst comprising the ZSM-5 molecular sieve described in the first aspect or the ZSM-5 molecular sieve described in the third aspect.

[0059] According to some embodiments of the present invention, the catalyst further includes an active component.

[0060] According to some embodiments of the present invention, the active component includes at least one of Group IIIA bauxite metals, Group IVA metals, Group VA metals, and transition metals (including Group IB to VIIB metals and Group VIII metals).

[0061] According to some embodiments of the present invention, the active component is selected from at least one of Y, La, Ce, Pr, Nd, Fe, Co, and Ni.

[0062] According to some embodiments of the present invention, the catalyst includes a reduction step prior to the reaction.

[0063] According to some embodiments of the present invention, the reduction is carried out using hydrogen reduction, wherein the hydrogen flow rate is 8-800 mL / min; during the reduction, the temperature is first increased to 100-280°C at a rate of 0.1-20°C / min and held at that temperature for 0-48 h, and then increased to 300-750°C at a rate of 0.1-50°C / min and held at that temperature for 0-48 h.

[0064] The beneficial effects of this invention are at least as follows:

[0065] The ZSM-5 molecular sieve preparation method provided by this invention achieves control over the framework composition of ZSM-5 molecular sieves by adding a second aluminum source and then performing secondary crystallization. This solves the technical bottleneck of directly synthesizing high-crystallinity, high-yield aluminum-rich ZSM-5, expands the range of bond lengths and bond angles that can be constructed in the aluminum-rich framework, optimizes the framework bending force constant, enhances framework flexibility, reduces structural stress and achieves coordination stabilization, solves the problems of low crystallization activity and poor uniformity in desilication and aluminum supplementation under high alkalinity conditions, breaks through the lower limit of the Si / Al ratio phase region of artificial in-situ synthesis of molecular sieves, effectively controls crystal parameters and improves product yield, and achieves precise construction of high-crystallinity aluminum-rich ZSM-5 molecular sieves. This enhances the microporous crystallinity of the molecular sieve, optimizes its acidity distribution, greatly enriches the distribution of metastable surface active acid centers of the molecular sieve, and has excellent aromatic hydrocarbon conversion performance. Attached Figure Description

[0066] Figure 1 The XRD pattern of the highly crystalline aluminum-rich ZSM-5 molecular sieve prepared in Example 1 of this invention;

[0067] Figure 2 SEM image of the highly crystalline alumina-rich ZSM-5 molecular sieve prepared in Example 1 of this invention;

[0068] Figure 3 HR-TEM image of the highly crystalline aluminum-rich ZSM-5 molecular sieve prepared in Example 1 of this invention. Detailed Implementation

[0069] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.

[0070] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.

[0071] In the various embodiments and comparative examples of the present invention, the performance data were tested according to the following test methods:

[0072] (1) Phase analysis (XRD pattern): The phase analysis was performed using a Bruker D8 Focus diffractometer with a graphite monochromator, a Cu target Kα light source, a wavelength λ of 0.154 nm, a tube voltage of 40 kV, a tube current of 40 mA, and the diffraction signal was recorded in the 2θ range of 3-90° (scanning speed of 2° / min).

[0073] (2) Scanning electron imaging (SEM) images: taken using a FEI Nova Nano SEM 450 microscope.

[0074] (3) Spherical aberration transmission imaging (TEM) images: taken using a FEI Tecnai 20S-Twin microscope.

[0075] (4) The signal information of the ammonia temperature-programmed desorption (NH3-TPD) curve was collected using an Altamira AMI-3300 chemisorption analyzer manufactured by Micrometrics.

[0076] (5) The molecular sieve samples were characterized by low-temperature N2 adsorption-desorption using a Micrometrics 3Flex-Physisorption analyzer at a test temperature of 77K. The specific surface area and pore structure parameters were calculated by analyzing the isotherms using the BET method and the BJH method, respectively.

[0077] (6) Silicon-to-aluminum ratio of the test sample: The test sample was dissolved in HF aqueous solution at room temperature and then quantitatively analyzed on a PerkinElmer Optima 3300DV inductively coupled plasma emission spectrometer (ICP).

[0078] (7) 27 Al MAS NMR testing: performed on a VARIAN VNMRS-400WB NMR spectrometer, with a measurement frequency of 104.18MHz, a rotation speed of 10000r / s, and a relaxation time of 4s. KAl(SO4)2·12H2O was used as the standard. The chemical shift signal peak of ~60ppm corresponds to four-coordinate framework aluminum, and the chemical shift signal peak of ~0ppm corresponds to six-coordinate non-framework aluminum.

[0079] In the various embodiments and comparative examples of the present invention, the polytetrafluoroethylene-lined pressure steel autoclave used was purchased from Shandong Yantai Muping Shuguang Precision Instrument Factory, with a specification of 100mL; the rotary oven was purchased from Beijing Keruishi Company as a 200L space rotary oven.

[0080] Example 1

[0081] A highly crystalline, alumina-rich ZSM-5 molecular sieve is synthesized as follows:

[0082] First, dissolve NaOH and sodium aluminate in deionized water. Then, add the silicon source tetraethoxysilane. Finally, add a 25 wt% aqueous solution of tetrapropylammonium hydroxide (template agent R). The silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content) are all present in the solution. - The molar ratio of PTFE (polytetrafluoroethylene) and deionized water is 40:5:2:1.2:2000. After stirring evenly, a milky white gelling solution is obtained. The gelling solution is then placed in a pressure steel autoclave lined with polytetrafluoroethylene and pre-crystallized at 90℃ for 6 hours. After that, it is placed in a rotary oven at 150℃ and 20 rpm for 160 hours of hydrothermal crystallization. Then, it is cooled to room temperature with tap water to obtain a slurry.

[0083] Add appropriate amounts of sodium aluminate and deionized water to the slurry to make the reaction system contain silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content). - The molar ratio of α-hydroxyl group (α) to deionized water is 40:5:4.5:1.2:2460; the above crystallization procedure is repeated for secondary crystallization, and the product is cooled to room temperature with tap water. The obtained product is filtered, washed, and dried in an oven at 100℃ for 2 hours to obtain molecular sieve powder.

[0084] The molecular sieve raw powder was tested, and the XRD test results are shown below. Figure 1 It can be seen that this is a pure-phase MFI configuration with a relative crystallinity of 90%. SEM and TEM images are shown below. Figure 2 and Figure 3 The obtained ZSM-5 molecular sieve sample with aluminum-rich MFI topology exhibits a nano-agglomeration morphology, with individual crystals being relatively distinct. Transmission electron microscopy reveals clear lattice fringes in the highly dispersed sample, indicating good microporous crystallinity of the sample. 27 Al MAS NMR results showed that 86 wt% of aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 8.9, and the specific surface area was S0. BET 448m 2 / g, micropore volume V micro It is 0.21cm 3 / g.

[0085] Molecular sieve powder was calcined at 550℃ for 2 hours and then cooled. The powder was then subjected to ion exchange and a second calcination treatment. Specifically, the calcined molecular sieve powder and a 1 mol / L ammonium chloride aqueous solution were mixed evenly at a solid-to-liquid ratio of 1:6, and heated in a water bath to 65℃ for 1 hour for ion exchange. The mixture was then filtered and washed with deionized water. This process was repeated four times to obtain a filter cake, which was dried in an oven at 100℃ for 2 hours to obtain NH4. +The molecular sieve was calcined at 520℃ for 3 hours to obtain the hydrogen-type molecular sieve, which was designated as AZ1. The temperature-programmed ammonia desorption (NH3-TPD) curve showed that the peak temperature of the desorption peak of the sample was 393℃.

[0086] Example 2

[0087] A highly crystalline, alumina-rich ZSM-5 molecular sieve is synthesized as follows:

[0088] First, add KOH and ammonia (K + :NH4 + Molar ratio 2) and aluminum isopropoxide are dissolved in deionized water, followed by the addition of silicon source trichlorosilane, and finally a 25 wt% aqueous solution of tetrapropylammonium bromide (template agent R) is added. The silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content) are then added. - The molar ratio of PTFE (polytetrafluoroethylene) and deionized water is 46:5:2:5:1250. After stirring evenly, a milky white gelling solution is obtained. The gelling solution is then placed in a pressure steel autoclave lined with polytetrafluoroethylene and pre-crystallized at 90℃ for 6 hours. After that, it is placed in a rotary oven at 150℃ and 20 rpm for 160 hours of hydrothermal crystallization. Then, it is cooled to room temperature with tap water to obtain a slurry.

[0089] Add appropriate amounts of aluminum nitrate and deionized water to the slurry to make the reaction system contain silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content). - The molar ratio of α-hydroxyl group (α) to deionized water is 46:5:5.5:5:1480; the above crystallization procedure is repeated for secondary crystallization, and the product is cooled to room temperature with tap water. The obtained product is filtered, washed, and dried in an oven at 100°C for 2 hours to obtain molecular sieve powder.

[0090] The molecular sieve powder was tested, and the XRD results showed that the obtained sample was a pure-phase MFI configuration with a relative crystallinity of 87%. SEM and TEM images showed that the sample exhibited good microporous crystallinity. 27 Al MAS NMR results showed that 92 wt% of the aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 8.5, and the specific surface area was S0. BET 438m 2 / g, micropore volume V micro 0.20cm 3 / g.

[0091] Molecular sieve powder was calcined at 520℃ for 4 hours and then cooled. The powder was then subjected to ion exchange and a second calcination treatment. Specifically, the calcined molecular sieve powder and a 1 mol / L ammonium chloride aqueous solution were mixed evenly at a solid (mass, g) to liquid (volume, mL) ratio of 1:6. The mixture was heated in a water bath to 65℃ and held at that temperature for 1 hour for ion exchange. The mixture was then filtered and washed with deionized water. This process was repeated four times to obtain a filter cake, which was then dried in a 100℃ oven for 2 hours to obtain NH4. + The molecular sieve was calcined at 520℃ for 3 hours to obtain the hydrogen-type molecular sieve, which was designated as AZ2. The temperature-programmed ammonia desorption (NH3-TPD) curve showed that the peak temperature of the desorption peak of the sample was 405℃.

[0092] Example 3

[0093] A highly crystalline, alumina-rich ZSM-5 molecular sieve is synthesized as follows:

[0094] First, CsOH and aluminum isopropoxide are dissolved in deionized water. Then, the silicon source methyltrimethoxysilane is added. Finally, a 25 wt% aqueous solution of tetrapropylammonium bromide (template agent R) is added. The silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content) are then added. - The molar ratio of PTFE (polytetrafluoroethylene) and deionized water is 40:5:2:2.4:1300. After stirring evenly, a milky white gelling solution is obtained. The gelling solution is then placed in a pressure steel autoclave lined with polytetrafluoroethylene and pre-crystallized at 90℃ for 6 hours. After that, it is placed in a rotary oven at 150℃ and 20 rpm for 160 hours of hydrothermal crystallization. Then, it is cooled to room temperature with tap water to obtain a slurry.

[0095] Add appropriate amounts of aluminum chloride and deionized water to the slurry to make the reaction system contain silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content). - The molar ratio of α-methyl ether (MME) and deionized water is 40:5:4.4:2.4:1400; the above crystallization procedure is repeated for secondary crystallization, and the product is cooled to room temperature with tap water. The obtained product is filtered, washed, and dried in an oven at 100°C for 2 hours to obtain molecular sieve powder.

[0096] The molecular sieve powder was tested, and the XRD results showed that the obtained sample had a pure-phase MFI configuration with a relative crystallinity of 85%. SEM and TEM images showed that the aluminous ZSM-5 molecular sieve sample exhibited good microporous crystallinity. 27 Al MAS NMR results showed that 91 wt% of the aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 9.8, and the specific surface area was S0. BET 467m 2 / g, micropore volume V microIt is 0.23cm 3 / g.

[0097] Molecular sieve powder was calcined at 550℃ for 2 hours and then cooled. The powder was then subjected to ion exchange and a second calcination treatment. Specifically, the calcined molecular sieve powder and a 1 mol / L ammonium chloride aqueous solution were mixed evenly at a solid-to-liquid ratio of 1:6, and heated in a water bath to 65℃ for 1 hour for ion exchange. The mixture was then filtered and washed with deionized water. This process was repeated four times to obtain a filter cake, which was dried in an oven at 100℃ for 2 hours to obtain NH4. + The molecular sieve was calcined at 520℃ for 3 hours to obtain the hydrogen-type molecular sieve, which was designated as AZ3. The temperature-programmed ammonia desorption (NH3-TPD) curve showed that the desorption peak temperature of the sample was 365℃.

[0098] Example 4

[0099] A highly crystalline, alumina-rich ZSM-5 molecular sieve is synthesized as follows:

[0100] First, add RbOH and ammonia water (Rb + :NH4 + Molar ratio 1) and aluminum sec-butoxide are dissolved in deionized water, followed by the addition of silicon source isobutylene triethoxysilane, and finally n-butammonium (template agent R). The silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content) are all present in the solution. - The molar ratio of PTFE (polytetrafluoroethylene) and deionized water is 40:4:2.5:1.4:1200. After stirring evenly, a milky white gelling solution is obtained. The gelling solution is then placed in a pressure steel autoclave lined with polytetrafluoroethylene and pre-crystallized at 90℃ for 6 hours. After that, it is placed in a rotary oven at 150℃ and 20 rpm for 160 hours of hydrothermal crystallization. Then, it is cooled to room temperature with tap water to obtain a slurry.

[0101] Add appropriate amounts of sodium aluminate and deionized water to the slurry to make the reaction system contain silicon source (based on Si content), template agent R, aluminum source (based on Al content), and alkali source (based on OH content). - The molar ratio of α-(x) and deionized water is 40:4:6:1.4:1450; the above crystallization procedure is repeated for secondary crystallization, and the product is cooled to room temperature with tap water. The obtained product is filtered, washed, and dried in an oven at 100°C for 2 hours to obtain molecular sieve powder.

[0102] The molecular sieve powder was tested, and the XRD results showed that the obtained sample had a pure-phase MFI configuration with a relative crystallinity of 82%. SEM and TEM images showed that the aluminous ZSM-5 molecular sieve sample exhibited good microporous crystallinity. 27Al MAS NMR results showed that 87 wt% of aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 7.3, and the specific surface area was S0. BET 425m 2 / g, micropore volume V micro It is 0.19cm 3 / g.

[0103] Molecular sieve powder was calcined at 500℃ for 5.5 h and then cooled. The powder was then subjected to ion exchange and a second calcination treatment. Specifically, the calcined molecular sieve powder and a 1 mol / L ammonium chloride aqueous solution were mixed evenly at a solid (mass, g) to liquid (volume, mL) ratio of 1:6. The mixture was heated in a water bath to 65℃ and held at that temperature for 1 h for ion exchange. The mixture was then filtered and washed with deionized water. This process was repeated four times to obtain a filter cake, which was then dried in a 100℃ oven for 2 h to obtain NH4. + The molecular sieve was calcined at 520℃ for 3 hours to obtain the hydrogen-type molecular sieve, which was designated as AZ4. The temperature-programmed ammonia desorption (NH3-TPD) curve showed that the desorption peak temperature of the sample was 495℃.

[0104] Example 5

[0105] A highly crystalline aluminum-rich ZSM-5 molecular sieve was synthesized using the same method as in Example 1, except that the sodium aluminate added to the slurry was replaced with an equimolar amount (calculated in terms of Al element) of aluminum hydroxide.

[0106] The obtained molecular sieve powder was tested. XRD results showed that the sample was a pure-phase MFI configuration with a relative crystallinity of 83%. SEM and TEM images showed that the aluminous ZSM-5 molecular sieve sample exhibited good microporous crystallinity. 27 Al MAS NMR results showed that 83 wt% of aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 9.9, and the specific surface area was S0. BET 397m 2 / g, micropore volume V micro It is 0.18cm 3 / g.

[0107] The prepared molecular sieve is designated AZ5. The temperature-programmed ammonia desorption (NH3-TPD) curve shows that the desorption peak temperature of the sample is 425℃.

[0108] Example 6

[0109] A highly crystalline aluminum-rich ZSM-5 molecular sieve, the synthesis method of which is the same as in Example 2, except that the aluminum nitrate added to the slurry is replaced with an equimolar amount (calculated in terms of Al element) of alumina.

[0110] The obtained molecular sieve powder was tested. XRD results showed that the sample was a pure-phase MFI configuration with a relative crystallinity of 80%. SEM and TEM images showed that the alumina-rich ZSM-5 molecular sieve sample exhibited good microporous crystallinity. 27 Al MAS NMR results showed that 93 wt% of the aluminum species were in a four-coordinate state. The Si / Al ratio of this sample was 9.3, and the specific surface area was S0. BET 385m 2 / g, micropore volume V micro It is 0.17cm 3 / g.

[0111] The prepared molecular sieve is designated AZ6. The temperature-programmed ammonia desorption (NH3-TPD) curve shows that the peak temperature of the desorption peak of the sample is 380℃.

[0112] Comparative Example 1

[0113] A ZSM-5 molecular sieve was synthesized using the same method as in Example 1, except that only one feeding was used to achieve a molar ratio of silicon source (based on Si content), template agent R, sodium aluminate (based on Al content), NaOH, and deionized water in the reaction system of 40:5:8:1.2:2460, and only one crystallization was used. The resulting molecular sieve is denoted as DZ1.

[0114] Testing of DZ1 revealed that it exhibits a pure-phase MFI configuration; its Si / Al ratio is 22, indicating low crystallinity and a high specific surface area S0. BET 298m 2 / g, micropore volume V micro It is 0.15cm 3 / g, with low specific surface area and micropore volume, and irregular morphology. 27 Al MAS NMR results showed that 89 wt% of aluminum species were in a four-coordinate state. Temperature-programmed ammonia desorption (NH3-TPD) curves showed a desorption peak temperature of 330 °C for the sample.

[0115] Comparative Example 2

[0116] A method for synthesizing a molecular sieve, referring to Example 1, differs only in that only one feeding is used to achieve a molar ratio of silicon source (based on Si content), template agent R, sodium aluminate (based on Al content), NaOH, and deionized water in the reaction system of 40:5:8:1.2:2460. Only one crystallization is performed. The resulting molecular sieve is treated with a 5% (w / w) NaOH aqueous solution in a water bath at 80°C for 30 minutes to perform in-situ aluminum addition and desiliconization of the sample. After filtration and washing, it is dried in an oven at 100°C for 2 hours. The resulting sample is designated as DZ2.

[0117] Testing of DZ2 revealed that it exhibits a pure-phase MFI configuration; its Si / Al ratio is 12, its relative crystallinity is 65%, and its specific surface area S0 is [missing information]. BET 276m 2 / g, micropore volume V micro It is 0.08cm 3 / g, with low specific surface area and micropore volume, and irregular morphology. 27 Al MAS NMR results showed that 91 wt% of aluminum species were in a four-coordinate state. Temperature-programmed ammonia desorption (NH3-TPD) curves showed that the desorption peak temperature of the sample was 507 °C.

[0118] Catalytic performance evaluation

[0119] The ZSM-5 molecular sieves prepared in each example and comparative example were used as catalysts, and their catalytic performance was tested.

[0120] The ZSM-5 molecular sieves prepared in each embodiment and comparative example were shaped into φ1mm×1mm particles; 800g were weighed and stirred evenly with 8g of active component solution with a mass concentration of 5%, and then allowed to stand and impregnate at room temperature for 12h; then the impregnated molecular sieves were transferred to an oven and dried at a temperature of 110℃ for 3h; then the dried molecular sieves were calcined in air at a temperature of 500℃ for 3h to obtain the catalyst.

[0121] Each of the above catalysts (5g) was loaded into a stainless steel fixed-bed tubular reactor and reduced with pure hydrogen. The reduction conditions were: hydrogen flow rate 80 mL / min, temperature increased at 2℃ / min to 180℃ and held for 2 h, then increased at 2.5℃ / min to 375℃ and held for 2 h. Trimethylbenzene was then added for selective dealkylation. The products were analyzed by an HP6890 gas chromatograph. Reaction conditions: reaction temperature 375℃, reaction pressure 0.6 MPa, feed weight hourly space velocity (WHSV) 3.35 h⁻¹. -1 The hydrogen-to-oil molar ratio was 3. The statistical results of the online 100-hour reaction are shown in Table 1.

[0122] Activity (conversion rate C) and BTX selectivity (yield of high-quality low-carbon aromatics) were used as performance evaluation indicators for catalysts.

[0123]

[0124] (TMB stands for trimethylbenzene, including 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and mixtures thereof)

[0125] S BTX = (BTX in the product / Σ product) × 100%

[0126] (B represents benzene, T represents toluene, and X represents xylene)

[0127] Table 1

[0128]

[0129]

[0130] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing ZSM-5 molecular sieve, characterized in that, include: S1. Obtain a colloid comprising a silicon source, a first aluminum source, an alkali source, a template agent R, and a solvent I; wherein the molar ratio of silicon in the silicon source to aluminum in the first aluminum source is greater than 10; S2. The colloid obtained in step S1 is crystallized once to obtain a slurry; S3. Add a second aluminum source to the slurry obtained in step S2 so that the molar ratio of silicon to aluminum in the entire reaction system is less than 10; S4. Perform secondary crystallization to obtain the ZSM-5 molecular sieve; Optionally, it also includes S5. Calcining the ZSM-5 molecular sieve once, then performing ion exchange, and then performing a second calcination; The crystallization temperature for the first crystallization is 80–200°C, and the crystallization time is 100–2000 hours. The secondary crystallization temperature is 80–200°C, and the crystallization time is 160–2000 hours.

2. The preparation method according to claim 1, characterized in that, The first aluminum source and the second aluminum source may be the same or different, and each is independently selected from at least one of aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum oxide; And / or, the molar ratio of silicon in the silicon source to aluminum in the first aluminum source in step S1 is greater than 15.

3. The preparation method according to claim 2, characterized in that, The second aluminum source is selected from at least one of aluminum isopropoxide, aluminum sec-butoxide, sodium aluminate, aluminum sulfate, aluminum nitrate, and aluminum chloride.

4. The preparation method according to any one of claims 1-3, characterized in that, The alkaline source includes alkali metal hydroxides and / or ammonia; And / or, the silicon source includes at least one of silicon powder, silicon balls, silica gel, silica sol, sodium silicate, aluminosilicate, silicate ester, silicon tetrachloride, silane, silica, and diatomaceous earth; And / or, the template agent R comprises at least one of ammonia, piperidine, N,N,N-trimethyl-1-adamantylammonium bromide, pyridine, cyclopropylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, tripropylamine, n-butylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium iodide, tetrapropylammonium bromide, tetraethylammonium bromide, tetraethylammonium chloride, or tetramethylammonium chloride; And / or, the solvent I includes at least one of deionized water, alcohol solvents, and imidazole ionic liquids.

5. The preparation method according to claim 4, characterized in that, The alkali metal includes at least one of Li, Na, K, Rb, and Cs; And / or, the silane is selected from at least one of tetramethylsilane, methyltrimethoxysilane, isobutylenetriethoxysilane, trichlorosilane and tetraethoxysilane; And / or, the solvent I includes at least one of deionized water, methanol, ethanol, isopropanol, ethylene glycol, glycerol, acetone, and n-butanol.

6. The preparation method according to any one of claims 1-3, characterized in that, The molar ratio of the alkaline source to the silicon element in the silicon source is: OH - / Si=0.01~0.45; And / or, the molar ratio of the solvent I to the silicon element in the silicon source is: I / Si = 5 to 50; And / or, the molar ratio of the template agent R to the silicon element in the silicon source is: R / Si = 0.001 to 0.

55.

7. The preparation method according to any one of claims 1-3, characterized in that, The ion exchange includes ammonium exchange.

8. The preparation method according to claim 7, characterized in that, Ammonium exchange reagents include at least one of ammonium nitrate, ammonium chloride, ammonium oxalate, and ammonium sulfate; And / or, the ammonium exchange is performed at a temperature of 10–120°C for 0.1–1000 h; And / or, the concentration of the ammonium exchange reagent aqueous solution is 0.01–5 mol / L; And / or, the volume-to-mass ratio of the ammonium exchange reagent aqueous solution to the ZSM-5 molecular sieve is 4-10 mL: 1 g.

9. The preparation method according to any one of claims 1-3, characterized in that, The number of ion exchanges is 1 to 20. And / or, after ion exchange, the process involves filtration, washing, and drying, followed by a second calcination. And / or, the stirring speed for the primary crystallization is 0 to 6000 rpm; And / or, the stirring speed for the secondary crystallization is 0 to 6000 rpm; And / or, after the secondary crystallization, the process further includes filtration, washing, and drying steps; And / or, the temperature of the first calcination is 200–980°C, and the calcination time is 0.1–250 h; And / or, the temperature of the secondary calcination is 400-650℃, and the time of the secondary calcination is 1-10h.

10. The preparation method according to claim 9, characterized in that, The drying temperature after ion exchange is 30–200°C; And / or, the temperature of the drying step after the secondary crystallization is 30 to 200°C.

11. A ZSM-5 molecular sieve, prepared by the preparation method described in any one of claims 1-10.

12. The ZSM-5 molecular sieve according to claim 11, characterized in that, The ZSM-5 molecular sieve has a Si / Al ratio of <10 and a relative crystallinity of >80%.

13. The ZSM-5 molecular sieve according to claim 11 or 12, characterized in that, The acid strength of the ZSM-5 molecular sieve is shown to be 360-500℃, which is the peak temperature of the desorption peak during temperature-programmed ammonia desorption. And / or, in the ZSM-5 molecular sieve, the content of skeletal aluminum accounts for more than 80 wt% of the total aluminum content; And / or, the specific surface area S of the ZSM-5 molecular sieve BET ≥350m 2 / g, micropore volume V micro >0.15cm 3 / g; And / or, the molar ratio of silicon in the silicon source to aluminum in the first aluminum source in step S1 is greater than 15.

14. The application of the ZSM-5 molecular sieve according to any one of claims 11-13 in aromatic hydrocarbon conversion.

15. An aromatic hydrocarbon conversion catalyst, characterized in that, The catalyst comprises the ZSM-5 molecular sieve according to any one of claims 11-13.

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