Preparation method and application of a two-dimensional lamellar molecular sieve with external surface passivation

Abstract

The present invention discloses a kind of outer surface passivation type two-dimensional lamellar molecular sieve and its preparation method and application, and is specifically related to the field of catalyst preparation technology.A kind of preparation method of outer surface passivation type two-dimensional lamellar molecular sieve, comprising the steps of: first preparing ZSM‑5 molecular sieve, then performing outer surface passivation on ZSM‑5 molecular sieve, obtaining outer surface passivation type ZSM‑5@Silicalite‑1 molecular sieve, wherein ZSM‑5 molecular sieve is two-dimensional lamellar ZSM‑5 molecular sieve.The present invention can improve the utilization rate of molecular sieve active sites under the harsh conditions of high mass space velocity, and the molecular sieve is used as a solid acid catalyst to catalyze the alkylation reaction of toluene and methanol to prepare p-xylene under harsh conditions, with 30~35% p-xylene selectivity and 30~50h service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and in particular relates to an outer surface passivated two-dimensional lamellar molecular sieve and a preparation method and application thereof. Background Art

[0002] Para-xylene is an important aromatic hydrocarbon compound. Oxidation can produce terephthalic acid (PTA), which reacts with ethylene glycol to form polyethylene terephthalate (PET), which can then be processed into PET bottles, plastic alloys, and other industrial components. With the rapid economic and social growth and rapid development of the polyester industry, para-xylene is in short supply. Industrial para-xylene production primarily involves petroleum-based and non-petroleum-based production processes. The petroleum-based production process is constrained by high costs, high energy consumption, and the increasing depletion of petroleum resources. Due to its low economic efficiency, the non-petroleum-based production process has not been commercialized on a large scale. To address these challenges, para-xylene production using inexpensive methanol and toluene as raw materials not only maximizes the value of raw materials but also meets my country's coal-rich, oil-scarce national conditions. The alkylation of toluene and methanol to produce p-xylene mainly uses molecular sieve catalysts, among which ZSM-5 molecular sieve has a ten-ring cross-channel structure with pore diameters of 0.56nm×0.55nm and 0.53nm×0.51nm, which matches the kinetic diameter of p-xylene and has a special advantage of shape-selective catalysis in the alkylation of toluene and methanol to produce p-xylene. However, the single microporous structure of traditional ZSM-5 molecular sieve increases the mass transfer resistance of the reactants, which, on the one hand, makes the active sites inside the molecular sieve unable to be effectively utilized, and on the other hand, the exposed pores on the outer surface of the molecular sieve The acid sites lack selectivity for the reaction, leading to further isomerization of para-xylene, forming a thermodynamically balanced xylene mixture and severely reducing para-xylene selectivity. Therefore, developing a ZSM-5 catalyst with improved mass transfer performance while simultaneously suppressing para-xylene isomerization is a pressing challenge for its application in the efficient alkylation of toluene with methanol to produce para-xylene.

[0003] The prior art discloses a catalyst, preparation method, and application for producing p-xylene from toluene and methanol. The catalyst in the prior art is a silanized ZSM@Silicalite-1 core-shell molecular sieve, wherein the core phase of the core-shell molecular sieve is a ZSM-5 molecular sieve and the shell layer is a silanized Silicalite-1 molecular sieve. The molecular sieve is used to produce p-xylene from toluene and methanol. However, the molecular sieve provided by the prior art can only be used at a mass space velocity of 3h / min. -1 When used under the conditions of high mass space velocity, the catalyst is easily deactivated when the mass space velocity is further increased, resulting in the inability to maintain high paraxylene selectivity and molecular sieve activity under the harsh conditions of high mass space velocity of existing industrial production. Summary of the Invention

[0004] In order to solve the problems in the prior art of low utilization of molecular sieve active sites and poor toluene conversion in the preparation of p-xylene from toluene and methanol under harsh conditions of high mass space velocity, the present invention provides a method for preparing an outer surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve. By independently synthesizing two-dimensional lamellae ZSM-5 molecular sieves, the utilization of the molecular sieve active sites is improved. At the same time, the prepared ZSM-5@Silicalite-1 molecular sieve is used in the preparation of p-xylene from toluene and methanol under harsh conditions of high mass space velocity, and has good toluene conversion, p-xylene selectivity and a long molecular sieve service life.

[0005] Another object of the present invention is to provide a two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve with passivated outer surface.

[0006] Another object of the present invention is to provide an application of an outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing an outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve comprises the following steps:

[0009] S1. Mix deionized water and an aluminum source and adjust the pH to 7 to 14 to obtain solution A;

[0010] S2. An organic template is added to the solution A obtained in step S1, and the mixture is mixed to obtain a solution B;

[0011] S3. A silicon source is added dropwise to the solution B obtained in step S2 to obtain a two-dimensional sheet ZSM-5 molecular sieve after crystallization;

[0012] S4. Mixing the silicon source, the template, and deionized water to obtain a solution C;

[0013] S5. The two-dimensional sheet ZSM-5 molecular sieve obtained in S3 is added to the solution C obtained in step S4, and the mixture is heated and mixed to obtain a precursor D;

[0014] S6. The silicon source, template, and deionized water were stirred and mixed, and the precursor D in S5 was added. After crystallization, the outer surface passivated ZSM-5@Silicalite-1 molecular sieve was obtained;

[0015] The ZSM-5 molecular sieve in step S3 is a two-dimensional lamellar ZSM-5 molecular sieve.

[0016] Compared with traditional three-dimensional block ZSM-5 molecular sieves, two-dimensional lamellar ZSM-5 molecular sieves have a larger specific surface area, can expose more active sites, and have an open pore structure, which can enhance diffusion, improve the utilization rate of the active center of the ZSM-5 molecular sieve and the toluene conversion rate in the production of p-xylene from toluene and methanol. However, the active sites on the surface of the two-dimensional lamellar ZSM-5 molecular sieve will cause p-xylene to isomerize into o-xylene or m-xylene at the active sites on the surface of the molecular sieve. Both all-silicon Silicalite-1 and ZSM-5 molecular sieves have MFI topological structures. Silicalite-1 and ZSM-5 molecular sieves have mutually interconnected pores. The difference is that Silicalite-1 has no acidity because it does not contain aluminum in its skeleton, and has no catalytic activity for the alkylation reaction of toluene and methanol. Silicalite-1 is epitaxially grown on the surface of the two-dimensional lamellar ZSM-5 molecular sieve particles to modify the surface of the particles, shielding the exposed pores on the surface of the two-dimensional lamellar ZSM-5 molecular sieve particles. Acid sites, thereby inhibiting the occurrence of isomerization side reactions of p-xylene. The acid concentration is 0.059mmol / g, and the outer surface The acid concentration is 0.034mmol / g, and the outer surface of the molecular sieve Acid concentration accounts for the total The acid concentration ratio is 58%. The total amount of the modified outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve is The acid concentration is 0.025mmol / g, the outer surface An acid concentration of 0 can enhance the diffusion capacity of p-xylene (dynamic diameters of xylene: p-xylene, ∼0.58 nm; m-xylene, ∼0.70 nm; o-xylene, ∼0.74 nm), thereby improving the p-xylene selectivity.

[0017] Preferably, the b-axis thickness of the ZSM-5 molecular sieve in step S3 is less than 15 nm.

[0018] The b-axis thickness of the two-dimensional ZSM-5 zeolite is less than 15 nm, which enables faster diffusion of guest molecules within the zeolite, improving the utilization of the zeolite's active sites. This can increase toluene conversion and para-xylene selectivity in applications involving the catalytic alkylation of toluene and methanol to produce para-xylene. Furthermore, it is less likely to form carbon deposits that clog the pores, thereby extending the life of the zeolite. When the b-axis thickness is too large, guest molecules diffuse slowly within the zeolite, which can easily lead to carbon deposits that clog the pores, reducing the utilization of the zeolite's active sites and shortening its life. Furthermore, in applications involving the catalytic alkylation of toluene and methanol to produce para-xylene, this can reduce toluene conversion and para-xylene selectivity.

[0019] More preferably, the b-axis thickness of the ZSM-5 molecular sieve in step S3 is 10 to 15 nm.

[0020] At this b-axis thickness, the active sites of the molecular sieve can be fully exposed, while reducing the diffusion path of the guest molecules, thereby improving the catalytic activity of the molecular sieve and, in applications, increasing the toluene conversion rate and the catalytic selectivity for paraxylene.

[0021] Preferably, the molar ratio of silicon to aluminum in the ZSM-5 molecular sieve in step S3 is (30-80):1.

[0022] ZSM-5 molecular sieve The acid sites mainly come from Si-OH + -Al bridged hydroxyl structure, in the process of synthesizing gel, appropriately increasing the Al content can improve the ZSM-5 molecular sieve The smaller the acid concentration, the smaller the molar ratio of silicon to aluminum, The higher the acid concentration, the more active sites there are and the better the catalytic activity of the catalyst. However, if the molar ratio of silicon to aluminum is lower than the limit, it will result in poor crystallization during the hydrothermal synthesis of molecular sieves.

[0023] More preferably, the molar ratio of silicon to aluminum in the ZSM-5 molecular sieve is (45-55):1. Further, the molar ratio of silicon to aluminum in the ZSM-5 molecular sieve is 50:1.

[0024] At this silicon:aluminum molar ratio, the ZSM-5 molecular sieve has the largest number of active sites and can exhibit the best catalytic performance.

[0025] Preferably, an alkaline substance is used to adjust the pH in step S1; and in steps S1 to S3, the molar ratio of the organic template, silicon source, aluminum source, alkaline substance and deionized water is 1:20:(0.25-0.67):2.5:800.

[0026] The present invention adjusts the molar ratio of silicon source to aluminum source to control the molar ratio of silicon to aluminum of the molecular sieve within the range of (30-80):1, so that the prepared two-dimensional lamellar molecular sieve can better exert catalytic activity. When the molar ratio of silicon to aluminum exceeds 80:1, the active sites will be reduced and the catalytic activity of the molecular sieve will be reduced. At the same time, if the ratio of alkaline substance to deionized water is too large or too small, the crystalline product will be in an amorphous state, which is not conducive to the synthesis of two-dimensional lamellar molecular sieves.

[0027] Preferably, in step S4, the molar ratio of the silicon source, the template and the deionized water is (15-20):14:9500.

[0028] More preferably, in step S4, the molar ratio of the silicon source, the template and the deionized water is 17:14:9500.

[0029] The degree of passivation on the outer surface of the two-dimensional lamellar ZSM-5 molecular sieve can be adjusted by adjusting the amount of silicon source added. At this silicon source addition amount, the prepared two-dimensional lamellar ZSM-5 molecular sieve can have good catalytic activity.

[0030] Preferably, in step S6, the molar ratio of the silicon source, the template and the deionized water may be (20-30):14:9500.

[0031] Too little silicon source (less than the range defined in the present invention) will result in poor surface passivation of the two-dimensional lamellar molecular sieve, while too much silicon source (exceeding the range defined in the present invention) will easily lead to blockage of the external pores of the two-dimensional lamellar molecular sieve and deactivation of the molecular sieve.

[0032] Preferably, the organic template in step S2 is a long-chain diquaternary ammonium surfactant; and the template in steps S4 and S6 is one or more of tetrapropylammonium hydroxide, tetrapropylammonium chloride, and tetrapropylammonium bromide.

[0033] More preferably, the organic template in step S2 is C6H5-C6H4-OC 10 H 20 -N + (CH3)2-C6H 12 -N + (CH3)2-C6H 13 , hereinafter referred to as C ph-10-6-6 .

[0034] Surfactant two N + As the head group, it is an effective structure-directing agent for ZSM-5 zeolite, while the hydrophobic interaction between the long-chain tails induces the formation of a mesoporous micelle structure. Using surfactants, an ultra-thin zeolite framework is formed in the hydrophilic part of the micelle. The hydrophobic tails limit the excessive growth of the molecular sieve and can control the prepared molecular sieve to have a two-dimensional lamellar structure, thereby improving the catalytic activity and service life of the surface-passivated ZSM-5@Silicalite-1 molecular sieve.

[0035] The invention uses a two-dimensional lamella ZSM-5 molecular sieve with a silicon to aluminum molar ratio of (30 to 80):1 as a matrix, and modifies the outer surface of the two-dimensional lamella ZSM-5 molecular sieve with a layer of all-silicon Silicalite-1 by a hydrothermal synthesis method to obtain an outer surface passivated ZSM-5@Silicalite-1 molecular sieve.

[0036] In a specific embodiment of the present invention, mixing can be performed by stirring;

[0037] The pH can be adjusted by using one or more of the alkaline substances sodium hydroxide and potassium hydroxide;

[0038] The aluminum source can be one or more of sodium metaaluminate, aluminum isopropoxide, aluminum oxide, and aluminum sulfate;

[0039] The silicon source can be one or more of ethyl orthosilicate, silica sol, and sodium silicate;

[0040] The crystallization temperature in step S3 may be 140-160° C., and the crystallization time may be 5-7 days;

[0041] In step S5, the amount of the two-dimensional sheet ZSM-5 molecular sieve added may be 1 wt%; the heating and mixing may be performed in a rotary oven at a heating temperature of 80 to 120° C.; and the crystallization time may be 24 to 48 hours.

[0042] The crystallization time in step S6 may be 7 to 12 days.

[0043] Preferably, sodium hydroxide can be used to adjust the pH in step S1.

[0044] The sodium ions in sodium hydroxide have a structural guiding effect, which can allow more aluminum sources to enter the molecular sieve framework to form Si-OH + —Al bridged hydroxyl structure, increasing The acid concentration is increased, thereby increasing the active sites of the ZSM-5 molecular sieve, so that the prepared ZSM-5@Silicalite-1 molecular sieve has better catalytic activity.

[0045] The invention comprises protecting an outer surface passivated ZSM-5@Silicalite-1 molecular sieve prepared by the above preparation method.

[0046] The present invention also protects the use of the above-mentioned outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in catalyzing the alkylation reaction of toluene and methanol to prepare p-xylene.

[0047] The two-dimensional sheet ZSM-5 molecular sieve has an open pore structure, which can enhance diffusion and improve the utilization rate of the active center of the ZSM-5 molecular sieve. The all-silicon Silicalite-1 and ZSM-5 molecular sieve both have MFI topology structures. Silicalite-1 and ZSM-5 molecular sieves have mutually interpenetrating pores. The outer surface of the two-dimensional sheet ZSM-5 molecular sieve particles is exposed to the full-silicon Silicalite-1. The acid sites are shielded, and the prepared outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve is used as a solid acid catalyst to catalyze the alkylation reaction of toluene and methanol. The non-selective catalytic process of the xylene isomerization side reaction of the outer surface acid center can be suppressed, and the selectivity of the target product to xylene is improved. In addition, the smaller b-axis thickness of the molecular sieve can make the guest molecules diffuse faster in the molecular sieve, improve the utilization rate of the molecular sieve active sites, the toluene conversion rate and the catalytic selectivity to xylene, and it is not easy to form carbon deposits to block the pores, thereby extending the service life of the molecular sieve.

[0048] Preferably, when the outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve is used as a solid acid catalyst to catalyze the alkylation reaction of toluene and methanol to produce p-xylene, the molar ratio of toluene to methanol is (0.5-5):1.

[0049] More preferably, the molar ratio of toluene to methanol is 1:1.

[0050] The molar ratio of toluene to methanol is low, and the reaction is not thorough. The molar ratio of toluene to methanol is high, which is not conducive to energy conservation.

[0051] Preferably, the catalytic reaction temperature is 400-500°C, and the mass space velocity is 8-12.5h -1 .

[0052] More preferably, the mass space velocity is 10h -1 .

[0053] At this mass space velocity, it is more in line with industrial production needs, and the surface-passivated ZSM-5@Silicalite-1 molecular sieve of the present invention can achieve catalytic selectivity for paraxylene and a molecular sieve service life that is higher than that of traditional molecular sieves while maintaining good catalytic activity.

[0054] In a specific embodiment of the present invention, the alkylation reaction can be carried out in a fixed bed reactor, the catalytic temperature is the bed temperature, and the reaction pressure is normal pressure.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] The outer surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared by the preparation method provided by the present invention can improve the utilization rate of the molecular sieve active sites, the toluene conversion rate and the catalytic selectivity for p-xylene under the harsh conditions of high-quality space velocity that are more in line with industrial production. When the molecular sieve is used as a solid acid catalyst to catalyze the alkylation reaction of toluene and methanol to prepare p-xylene, it has a p-xylene selectivity of 30 to 35% and a service life of 30 to 50 hours. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 This is the X-ray diffraction pattern of the commercial HZSM-5 molecular sieve of Comparative Example 1 of the present invention.

[0058] Figure 2 These are the X-ray diffraction patterns of the two-dimensional lamellae ZSM-5 molecular sieve prepared in Comparative Example 2 and the outer surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared in Examples 1 and 2.

[0059] Figure 3 These are pyridine-infrared spectra of the commercial HZSM-5 molecular sieve of Comparative Example 1 of the present invention, the two-dimensional lamellae ZSM-5 molecular sieve prepared in Comparative Example 2, and the external surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared in Examples 1 and 2.

[0060] Figure 4 2,6-di-tert-butylpyridine-infrared spectra of the commercial HZSM-5 molecular sieve of Comparative Example 1 of the present invention, the two-dimensional lamellae ZSM-5 molecular sieve prepared in Comparative Example 2, and the outer surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared in Examples 1 and 2.

[0061] Figure 5 This is a graph showing the toluene conversion rate in the alkylation reaction of toluene and methanol catalyzed by the commercial HZSM-5 molecular sieve of Comparative Example 1, the two-dimensional lamellae ZSM-5 molecular sieve prepared in Comparative Example 2, the external surface passivated HZSM-5@Silicalite-1 molecular sieve prepared in Comparative Example 3, and the external surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared in Examples 1 to 2 of the present invention.

[0062] Figure 6 This is a graph showing the selectivity for xylene in the alkylation reaction of toluene and methanol catalyzed by the commercial HZSM-5 molecular sieve of Comparative Example 1, the two-dimensional lamellar ZSM-5 molecular sieve prepared in Comparative Example 2, the external surface passivated HZSM-5@Silicalite-1 molecular sieve prepared in Comparative Example 3, and the external surface passivated two-dimensional lamellar ZSM-5@Silicalite-1 molecular sieve prepared in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0063] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0064] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0065] Example 1

[0066] A method for preparing an outer surface passivated two-dimensional lamellar molecular sieve comprises the following steps:

[0067] S1. Sodium hydroxide, deionized water and sodium aluminate were stirred and mixed for 30 min, and the pH was adjusted to 11 to obtain solution A;

[0068] S2. Add organic template C to solution A obtained in step S1 ph-10-6-6 , after stirring, solution B was obtained;

[0069] S3. To the solution B obtained in step S2 was added dropwise ethyl orthosilicate, the crystallization temperature was 150 ° C, the crystallization time was 5 days, and a ZSM-5 molecular sieve was obtained;

[0070] S4. TEOS, tetrapropylammonium hydroxide and deionized water were mixed to obtain a solution C;

[0071] S5. The ZSM-5 molecular sieve obtained in S3 was added to the solution C obtained in step S4, and the precursor D was obtained after crystallization in a rotary oven at 100 ° C for 24 h;

[0072] S6. Ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water were stirred and mixed, and the precursor D in S5 was added. The mixture was crystallized at 170°C for 7 days to obtain an external surface passivated ZSM-5@Silicalite-1 molecular sieve.

[0073] The ZSM-5 molecular sieve in step S3 is a two-dimensional layered ZSM-5 molecular sieve with a b-axis thickness of 12 nm and a molar ratio of silicon to aluminum of 50:1.

[0074] Among them, the organic template C in steps S1 to S3 ph-10-6-6 , the molar ratio of ethyl orthosilicate, sodium metaaluminate, sodium hydroxide and deionized water is 1:20:0.4:2.5:800;

[0075] In step S4, the molar ratio of ethyl orthosilicate, tetrapropylammonium hydroxide and deionized water is 17:14:9500;

[0076] In step S5, the amount of two-dimensional sheet ZSM-5 molecular sieve added is 1 wt%;

[0077] In step S6, the molar ratio of ethyl orthosilicate, tetrapropylammonium hydroxide and deionized water is 20:14:9500.

[0078] Example 2

[0079] A method for preparing an outer surface passivated two-dimensional lamellar molecular sieve, which differs from Example 1 in that:

[0080] In step S6, the molar ratio of ethyl orthosilicate, tetrapropylammonium hydroxide and deionized water is 30:14:9500.

[0081] Example 3

[0082] Use of an external surface passivated ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene, wherein the external surface passivated ZSM-5@Silicalite-1 molecular sieve is prepared by the preparation method of Example 1;

[0083] The surface-passivated ZSM-5@Silicalite-1 molecular sieve prepared in Example 1 was granulated and passed through a 20-40 mesh sieve. A sample of about 0.2 g was placed in an oven and activated at 450°C for 2 h in an air atmosphere. Toluene and methanol were added in a molar ratio of 1:1 to prepare a reaction solution. The flow rate of the reaction solution was adjusted to a weight hourly space velocity of 10 h. -1 , reaction at normal pressure, N2 flow rate is 50mL / min.

[0084] Example 4

[0085] The invention relates to the use of an external surface passivated ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene, which differs from Example 3 in that the external surface passivated ZSM-5@Silicalite-1 molecular sieve is prepared by the preparation method of Example 2.

[0086] Comparative Example 1

[0087] A commercial HZSM-5 molecular sieve, wherein the molar ratio of silicon to aluminum in the HZSM-5 molecular sieve is 54:1.

[0088] Comparative Example 2

[0089] A method for preparing an unmodified two-dimensional lamellar ZSM-5 molecular sieve is different from that of Example 1 in that only steps S1 to S3 are performed.

[0090] Comparative Example 3

[0091] A method for preparing ZSM-5@Silicalite-1 molecular sieve, which differs from Example 1 in that commercial HZSM-5 molecular sieve is surface passivated using all-silicon Silicalite-1. The method comprises the following steps:

[0092] S1. TEOS, tetrapropylammonium hydroxide, and deionized water were mixed for 30 min and the pH was adjusted to 11 to obtain a solution A.

[0093] S2. ZSM-5 molecular sieve was added to the solution A obtained in step S1, and the precursor B was obtained after crystallization in a rotary oven at 100 ° C for 24 hours;

[0094] S3. Ethyl orthosilicate, tetrapropylammonium hydroxide, and deionized water were stirred and mixed, and the precursor B in S2 was added. The mixture was crystallized at 170°C for 7 days to obtain an external surface passivated HZSM-5@Silicalite-1 molecular sieve.

[0095] The ZSM-5 molecular sieve in step S2 is a commercial HZSM-5 molecular sieve with a b-axis thickness of 2 μm and a molar ratio of silicon to aluminum of 54:1;

[0096] In step S1, the molar ratio of ethyl orthosilicate, tetrapropylammonium hydroxide and deionized water is 17:14:9500;

[0097] In step S2, the amount of two-dimensional sheet ZSM-5 molecular sieve added is 1 wt%;

[0098] In step S3, the molar ratio of ethyl orthosilicate, tetrapropylammonium hydroxide and deionized water is 30:14:9500.

[0099] Comparative Example 4

[0100] A commercial HZSM-5 molecular sieve is used as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene. The difference from Example 3 is that the outer surface passivated ZSM-5@Silicalite-1 molecular sieve is replaced by the commercial HZSM-5 molecular sieve in Comparative Example 1.

[0101] An unmodified two-dimensional lamellar ZSM-5 molecular sieve is used as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene. The difference from Example 3 is that the outer surface passivated ZSM-5@Silicalite-1 molecular sieve is replaced by the unmodified two-dimensional lamellar ZSM-5 molecular sieve in Comparative Example 2.

[0102] Comparative Example 6

[0103] The invention relates to an application of a ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene. The application of the ZSM-5@Silicalite-1 molecular sieve as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene is different from that in Example 3 in that the outer surface passivated ZSM-5@Silicalite-1 molecular sieve is replaced by the ZSM-5@Silicalite-1 molecular sieve in Comparative Example 3.

[0104] Test example performance measurement

[0105] (1) In the present invention, the b-axis thickness of the two-dimensional sheet ZSM-5 molecular sieve can be directly measured by transmission electron microscopy (TEM).

[0106] (2) In the present invention, the outer surface passivation configuration of the outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve can be determined by high-resolution transmission electron microscopy (HRTEM) combined with EDS line scanning (HRTEM-EDS).

[0107] (3) In the present invention, the outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve is Acid concentration and external surface The acid concentration was obtained by pyridine and 2,6-di-tert-butylpyridine adsorption infrared characterization test.

[0108] (4) The calculation formulas for toluene conversion and para-xylene selectivity in the comparative examples and embodiments of the present invention are as follows:

[0109]

[0110]

[0111]

[0112]

[0113] (5) The D8 Advance X-ray diffractometer of Bruker Company of Germany was used to characterize the small-angle and wide-angle diffraction of Comparative Examples 1-2 and Examples 1-2. The test results are as follows: Figure 1 shown.

[0114] from Figure 1 (b) and Figure 2 (b) It can be seen that Comparative Example 1, Comparative Example 2 and Examples 1-2 all exhibit MFI zeolite characteristics. From the low-angle XRD patterns ( Figure 1 (a) and Figure 2 (a) As can be seen, Comparative Example 2 exhibits primary and secondary diffraction peaks, indicating that the two-dimensional lamellar ZSM-5 molecular sieve has an ordered interlayer structure. As the surface of the two-dimensional lamellar ZSM-5 molecular sieve particles is modified by all-silicon Silicalite-1, the low-angle diffraction peaks of Example 1 begin to broaden, while the low-angle diffraction peaks of Example 2 disappear, indicating that Silicalite-1 fills the mesopores of the lamellar ZSM-5 molecular sieve.

[0115] (6) Using pyridine and 2,6-di-tert-butylpyridine as probe molecules, data were collected on a German Bruker Vertex 70 Fourier transform infrared spectrometer for the external surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve catalysts prepared in Comparative Examples 1-2 and Examples 1-2, and Beer's law was used to calculate the Acid and Lewis acid concentration. The results are as follows Figure 3 、 Figure 4 As shown in Table 1.

[0116] Depend on Figure 3 It can be found that both Comparative Examples 1-2 and Examples 1-2 show The characteristic absorption peaks of acid sites and Lewis acid sites are at 1545 cm -1 The characteristic absorption peak is attributed to the pyridine molecule in Adsorption of acid sites at ∼1455 cm -1 The characteristic absorption peak is attributed to the adsorption of pyridine molecules on the Lewis acid sites.

[0117] from Figure 4 It can be found that the comparative example 2 has a peak at 1616 cm -1 There is a broad absorption peak at the molecular sieve, which is attributed to the presence of 2,6-di-tert-butylpyridine on the outside of the molecular sieve. Adsorption on the acid site, Examples 1-2 at 1616 cm -1 There is no absorption peak at the outer surface of Examples 1 and 2. The acid sites are effectively shielded. The acid concentration is 0.059mmol / g, and the outer surface The acid concentration is 0.034mmol / g, and the outer surface of the molecular sieve Acid concentration accounts for the total The acid concentration ratio is 58%. The total amount of the modified outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve is The acid concentration is 0.031~0.041mmol / g, the outer surface Acid concentration 0.

[0118] Table 1 Acid concentration of molecular sieves in Comparative Example 1-2 and Example 1-2

[0119]

[0120] (3) The catalysts prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Examples 1-2 were granulated and passed through a 20-40 mesh sieve. A sample of about 0.2 g was placed in an oven and activated at 450°C for 2 h in an air atmosphere. Toluene and methanol were prepared in a molar ratio of 1:1 to prepare the reaction solution, and the flow rate of the reaction solution was adjusted to a weight hourly space velocity of 10 h.-1 , reaction at normal pressure, N2 flow rate of 50ml / min, the catalyst conversion rate is less than 3% when it is considered deactivated. The test results of toluene conversion rate and para-xylene selectivity in Comparative Example 2 and Examples 3-4 are as follows Figure 5 、 Figure 6 Specific values are shown in Table 2 and Table 3.

[0121] Table 2 Toluene conversion of molecular sieves of Comparative Examples 1-2 and Examples 3-4

[0122]

[0123] Table 3 p-Xylene selectivity of molecular sieves of Comparative Examples 1-2 and Examples 3-4

[0124]

[0125]

[0126] Note: “-” in Table 2 and Table 3 indicates that the molecular sieve has been deactivated and has no toluene conversion rate and para-xylene selectivity.

[0127] As can be seen from Tables 2 and 3, the novel surface-passivated two-dimensional ZSM-5@Silicalite-1 molecular sieve of the present invention, Example 4, exhibited a maximum toluene conversion of 39.97% and a maximum para-xylene selectivity of 35.69%, while Comparative Example 4 (commercial HZSM-5 molecular sieve) and Comparative Example 6 (surface passivation of commercial HZSM-5 molecular sieve using all-silicon Silicalite-1) both deactivated after 3 hours of reaction, and Example 3 and Example 4 were inactivated at WHSV=10h. -1 Under the harsh conditions of , the selectivity for p-xylene and the service life of the molecular sieve are higher than those of Comparative Examples 4 and 6. This is mainly due to the fact that the embodiment of the present invention uses a two-dimensional sheet ZSM-5 molecular sieve and uses all-silicon Silicalite-1 to clean the outer surface of the two-dimensional sheet ZSM-5 molecular sieve. The shielding of acid sites makes the prepared outer surface passivated two-dimensional sheet ZSM-5@Silicalite-1 molecular sieve have better para-xylene selectivity and molecular sieve service life.

[0128] Comparative Example 5 uses the unmodified two-dimensional lamellae ZSM-5 molecular sieve in Comparative Example 2. Under the reaction time of 48h, it has a higher toluene conversion rate than the example, but its para-xylene selectivity is only 25.27%, which is significantly lower than 31.69% and 34.21% of Examples 1 and 2 of the present invention. This shows that the outer surface passivated two-dimensional lamellae ZSM-5@Silicalite-1 molecular sieve prepared by the present invention has broad prospects in the industrial application of alkylation of toluene and methanol to prepare para-xylene.

[0129] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other modifications or variations can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an outer surface passivated two-dimensional lamellar molecular sieve, characterized in that: The steps include: S1. Mix deionized water and an aluminum source and adjust the pH to 7 to 14 to obtain solution A; S2. An organic template is added to the solution A obtained in step S1, and the mixture is mixed to obtain a solution B; S3. A silicon source is added dropwise to the solution B obtained in step S2 to obtain a ZSM-5 molecular sieve after crystallization; S4. Mixing the silicon source, the template, and deionized water to obtain a solution C; S5. The ZSM-5 molecular sieve obtained in S3 was added to the solution C obtained in step S4, and the mixture was heated and mixed to obtain a precursor D; S6. The silicon source, template, and deionized water were stirred and mixed, and the precursor D in S5 was added. After crystallization, the outer surface passivated ZSM-5@Silicalite-1 molecular sieve was obtained; The organic template in step S2 is a long-chain diquaternary ammonium surfactant; The ZSM-5 molecular sieve in step S3 is a two-dimensional layered ZSM-5 molecular sieve; the molar ratio of silicon to aluminum in the ZSM-5 molecular sieve is (30-80):1; In step S4, the molar ratio of the silicon source to the template is (15-20):14; In step S6, the molar ratio of the silicon source to the template is (20-30):

14.

2. The method for preparing the outer surface passivated two-dimensional lamellar molecular sieve according to claim 1, characterized in that: The b-axis thickness of the ZSM-5 molecular sieve in step S3 is less than 15 nm.

3. The method for preparing the outer surface passivated two-dimensional lamellar molecular sieve according to claim 1, characterized in that: In the step S1, an alkaline substance is used to adjust the pH; in the steps S1 to S3, the molar ratio of the organic template, the silicon source, the aluminum source, the alkaline substance and the deionized water is 1:20:(0.25-0.67):2.5:

800.

4. The method for preparing the outer surface passivated two-dimensional lamellar molecular sieve according to claim 1, characterized in that: The molar ratio of the silicon source to the deionized water in step S6 is (20-30):9500.

5. The method for preparing the outer surface passivated two-dimensional lamellar molecular sieve according to claim 1, characterized in that: The template agent in step S4 and step S6 is one or more of tetrapropylammonium hydroxide, tetrapropylammonium chloride, and tetrapropylammonium bromide.

6. An external surface passivated ZSM-5@Silicalite-1 molecular sieve prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the external surface passivated ZSM-5@Silicalite-1 molecular sieve according to claim 6 as a solid acid catalyst in the catalytic alkylation reaction of toluene and methanol to produce p-xylene.

8. The use according to claim 7, characterized in that The molar ratio of toluene to methanol is (0.5-5):

1.

9. The use according to claim 7, characterized in that The catalytic reaction temperature is 400-500°C, and the mass space velocity is 8-12.5h -1 .

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