ZSM-5 molecular sieve, preparation method thereof and catalyst

Abstract

The invention provides a ZSM-5 molecular sieve, a preparation method thereof and a catalyst. The preparation method of the ZSM-5 molecular sieve comprises the following steps: mixing a seed crystal with a seed crystal assembling agent to obtain a seed crystal mixture; mixing the seed crystal mixture with an alkali source, a first aluminum source and a first silicon source to obtain crystallized gel; and carrying out first crystallization on the crystallized gel, and roasting to obtain the ZSM-5 molecular sieve. The invention also provides the ZSM-5 molecular sieve obtained by the preparation method, and a catalyst comprising the ZSM-5 molecular sieve or prepared from the ZSM-5 molecular sieve. The preparation method is green, simple and low in cost, and the flaky ZSM-5 molecular sieve can be prepared.

Description

Technical Field

[0001] The present invention relates to the field of chemical engineering technology, and in particular to a ZSM-5 molecular sieve and a preparation method and a catalyst thereof. Background Art

[0002] As a porous material, ZSM-5 molecular sieve has always received much attention in the fields of catalysis and adsorption due to its flexible and adjustable acidity, excellent thermal stability and other characteristics. ZSM-5 molecular sieve has two intersecting pore structures, one is a straight 10-membered ring pore along the b-axis, and the other is a sinusoidal 10-membered ring pore along the a-axis: the pore structure is 0.51 nm × 0.55 nm (

[100] direction) and 0.53 nm × 0.56 nm (

[010] direction). Straight pores are more conducive to the diffusion of reactant molecules. The synthesis of thin-sheet ZSM-5 molecular sieves with shorter straight pores can effectively enhance the diffusion of macromolecules between and within crystals.

[0003] The existing technology mainly realizes the preparation of thin-flaked ZSM-5 molecular sieves by designing a diquaternary ammonium salt template with a special structure or using a long-chain monoammonium or long-chain diammonium surfactant. The templates reported so far for synthesizing thin-flaked ZSM-5 molecular sieves include: a long-chain alkane structure {C 22 H 45 -(CH4)4C6H 12 N2-C6H 13 The diquaternary ammonium salt template of}Br2 has a complex preparation process and a high synthesis cost.

[0004] The long-chain monoammonium or long-chain diammonium surfactants that can synthesize thin-layer ZSM-5 molecular sieves reported so far can be used as templates to obtain thin-layer ZSM-5 molecular sieves with a thickness of 2-100 nm. In the process of induced crystallization, the long-chain monoammonium or long-chain diammonium surfactant templates mainly rely on the double long chain or single long chain to generate steric hindrance outside the crystal to organize the crystal to continue to grow along a fixed axis, and use the amino group to induce the formation of MFI crystal structure. However, this type of surfactant as a template also has the following disadvantages: 1. The commonly used reaction solvent is water. After the surfactant is dissolved in water, it is easy to produce a large amount of foam under dynamic conditions, affecting the uniformity of the product; 2. Using diammonium or monoamine surfactants as templates will make the crystallization process of the molecular sieve difficult to control; 3. The cost of diammonium or monoammonium surfactant templates is high, difficult to recycle, and often needs to be prepared by themselves, which seriously affects the practicality of the method and reduces the practical value of the product.

[0005] Therefore, it is very important to develop a green, simple and low-cost method for preparing flaky molecular sieves. Summary of the invention

[0006] In order to solve the above problems, the present invention aims to provide a ZSM-5 molecular sieve and a preparation method and catalyst thereof. The preparation method is green, simple, and low-cost, and can prepare a sheet-shaped ZSM-5 molecular sieve.

[0007] In order to achieve the above object, the present invention provides a method for preparing a ZSM-5 molecular sieve, the preparation method comprising:

[0008] S1, mixing the seed crystals with the seed crystal assembly agent to obtain a seed crystal mixture;

[0009] S2, mixing the seed mixture with an alkali source, a first aluminum source, and a first silicon source to obtain a crystallized gel;

[0010] S3, crystallizing and calcining the crystallized gel to obtain a ZSM-5 molecular sieve.

[0011] The present invention has found that by first mixing the seed with the diamine seed assembly agent, the nitrogen atom of the amine group and the interaction of the silanol group on the seed surface can make the seed orderly pre-assembled to obtain the secondary seed. The secondary seed is mixed with a silicon source, an aluminum source, and an alkali source to carry out a hydrothermal crystallization reaction. Since the secondary seed is orderly assembled, the molecular sieve can be promoted to be orderly reunited during the crystallization process, and then the fin-shaped ZSM-5 molecular sieve is obtained. The reaction raw materials used in the method are all cheap industrial products, and the diamine seed assembly agent has a stable structure, can be recycled after the crystallization reaction ends, and reduces the pollutant discharge in the product post-processing process. Compared with the existing synthetic method using an ammonium surfactant template or a diquaternary ammonium salt template with a special structure, the above-mentioned ZSM-5 preparation method adopted by the present invention can effectively reduce product production costs and environmental protection costs, and has a strong practical application significance.

[0012] In the above preparation method, in S1, the process of mixing the seed crystal with the seed crystal assembly agent is the process of pre-assembling the seed crystal under the action of the seed crystal assembly agent to form a secondary seed crystal. The mixing temperature can be 20°C-80°C, for example, 60-80°C; the mixing temperature can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0013] In the above preparation method, in S1, the mixing time can be 0.5h-24h, for example 2-12h. In some specific embodiments, the mixing time can be specific values ​​such as 0.5h, 1h, 2h, 6h, 12h, 24h, and a range with any two of the above specific values ​​as endpoints.

[0014] In the above preparation method, the seed crystal includes a molecular sieve having an MFI crystal structure.

[0015] In the above preparation method, the silicon-to-aluminum ratio (molar ratio of silicon dioxide to aluminum oxide) of the seed crystal is greater than or equal to 30, for example, it can be 30-400, 30-150, and the silicon-to-aluminum ratio of the seed crystal can reach pure silicon at the highest.

[0016] In the above preparation method, the grain size of the seed crystal is 10nm-200nm. The grain size of the seed crystal can be specific values ​​such as 10nm, 50nm, 100nm, 150nm, 200nm, and a range with any two of the above specific values ​​as endpoints.

[0017] According to a specific embodiment of the present invention, the seed crystal can be a commercially available molecular sieve with an MFI structure, or a seed crystal obtained by the following preparation method of the present invention. Compared with the commercially available molecular sieve, the seed crystal prepared by the present invention has a smaller crystal size and a better preparation effect of the ZSM-5 molecular sieve. Specifically, the preparation method of the seed crystal may include: mixing a second silicon source, an organic template and water to obtain a seed crystal precursor, subjecting the seed crystal precursor to a second crystallization to obtain the seed crystal; wherein the second silicon source is calculated as SiO2, and the organic template is calculated as an organic cation R + The chemical composition of the seed precursor satisfies the following molar ratio range: R + / SiO2=0.15-0.4, H2O / SiO2=15-50.

[0018] In some specific embodiments, R + The molar ratio of H2O / SiO2 can be 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, etc., and ranges with any two of the above specific values ​​as endpoints. The molar ratio of H2O / SiO2 can be 15, 20, 25, 30, 35, 40, 45, 50, etc., and ranges with any two of the above specific values ​​as endpoints.

[0019] In the above seed crystal preparation method, the seed crystal precursor may further include a second aluminum source, the second silicon source is calculated as SiO2, and the second aluminum source is calculated as Al2O3, and the chemical composition of the seed crystal precursor further satisfies the following molar ratio range: SiO2 / Al2O3≥25. The molar ratio of SiO2 / Al2O3 may be specific values ​​such as 25, 30, 35, 40, 45, 50, 60, 70, 80, and a range with any two of the above specific values ​​as endpoints.

[0020] In the above-mentioned method for preparing seed crystals, the temperature of the second crystallization can be controlled to be 80℃-110℃, specifically 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃ and other specific values, as well as a range with any two of the above-mentioned specific values ​​as endpoints. The time of the second crystallization can be controlled to be 16h-24h, specifically 16h, 18h, 20h, 22h, 24h and other specific values, as well as a range with any two of the above-mentioned specific values ​​as endpoints.

[0021] In the above-mentioned method for preparing seed crystals, the second silicon source may include tetraethyl orthosilicate and / or fumed silica.

[0022] In the above-mentioned method for preparing seed crystals, the organic template may include tetrapropylammonium hydroxide and / or n-butylamine.

[0023] In the above-mentioned method for preparing seed crystals, the second aluminum source may include aluminum isopropoxide and / or sodium metaaluminate, etc.

[0024] In the above preparation method, the seed assembly agent can be an organic substance having two amino groups (i.e., a diamine seed assembly agent). For example, the seed assembly agent can include one or a combination of two or more of p-phenylenediamine, m-phenylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, piperazine, homopiperazine, 1,4-diazabicyclo[2.2.2]octane, 1,5-naphthalenediamine, and 2,6-naphthalenediamine.

[0025] In the above preparation method, the first silicon source is calculated as SiO2, the first aluminum source is calculated as Al2O3, and the seed crystal is calculated as the contained SiO2, and the chemical composition of the crystallized gel satisfies the following molar ratio range:

[0026] SiO2 (from the first silicon source) / Al2O3=25-400, seed / SiO2 (from the first silicon source)=0.002-0.25, MO / SiO2 (from the first silicon source)=0.05-0.50, H2O / SiO2 (from the first silicon source)=15-120, seed assembly agent / SiO2 (from the first silicon source)=0.03-0.20; wherein M is an alkali metal and / or alkaline earth metal.

[0027] The above-mentioned M includes at least metal cations in the alkali source, and may further include alkali metals, alkaline earth metals, etc. in other sources (such as aluminum sources) in the raw materials. It is understood that MO represents the oxide of the metal cation in the alkali source, which is not limited to the case where the molar ratio of M to O is 1:1, and also includes the case where M:O is less than 1, for example, MO can be Na2O, K2O, etc.

[0028] In the above preparation method, the first silicon source is calculated as SiO2, the seed crystal is calculated as contained SiO2, and the chemical composition of the crystallized gel can further meet the following molar ratio range: seed crystal / SiO2=0.005-0.15. That is, SiO2 / Al2O3=25-400, seed crystal / SiO2=0.005-0.15, M2O / SiO2=0.05-0.50, H2O / SiO2=15-120, seed crystal assembly agent / SiO2=0.03-0.20; wherein M is an alkali metal. In some specific embodiments, the molar ratio of seed crystal / SiO2 (from the first silicon source) can be 0.002, 0.005, 0.010, 0.015, 0.020, 0.050, 0.070, 0.080, 0.10, 0.15, 0.20, 0.25 and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0029] In the above preparation method, in the crystallized gel, the molar ratio of SiO2 (from the first silicon source) / Al2O3 can be 25-400, specifically 25, 30, 50, 100, 150, 200, 250, 300, 350, 400 and the like, as well as a range with any two of the above specific values ​​as endpoints.

[0030] In the above preparation method, in the crystallized gel, the molar ratio of MO / SiO2 (from the first silicon source) can be 0.05-0.50, specifically 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50 and the like, as well as a range with any two of the above specific values ​​as endpoints.

[0031] In the above preparation method, in the crystallized gel, the molar ratio of H2O / SiO2 (from the first silicon source) can be 15-120, specifically 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120 and the like, as well as a range with any two of the above specific values ​​as endpoints.

[0032] In the above preparation method, in the crystallized gel, the molar ratio of the seed assembly agent / SiO2 (from the first silicon source) is 0.03-0.20, and specifically can be 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.13, 0.15, 0.17, 0.19, 0.20 and the like, as well as a range with any two of the above specific values ​​as endpoints.

[0033] In the above preparation method, the temperature of the first crystallization is 120° C.-190° C., for example, 140° C.-180° C., 140° C.-175° C. The temperature of the first crystallization can be specifically 120° C., 125° C., 130° C., 135° C., 140° C., 145° C., 150° C., 155° C., 160° C., 165° C., 170° C., 175° C., 180° C., 185° C., 190° C., and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0034] In the above preparation method, the first crystallization time is 12h-120h, for example, 12h-96h. The first crystallization time can be 12h, 24h, 36h, 48h, 60h, 72h, 84h, 96h, 108h, 120h and other specific values, and a range with any two of the above specific values ​​as endpoints.

[0035] In the above preparation method, the first crystallization may be a dynamic crystallization process.

[0036] The preparation method may further include the operation of post-treating the first crystallized product and then calcining the product. The post-treating includes filtering, washing, drying and the like.

[0037] In the above preparation method, the first silicon source may include one or a combination of two or more of silica gel, silica sol, white carbon black, and tetraethyl orthosilicate. In some specific embodiments, the silica gel may be macroporous silica gel.

[0038] In the above preparation method, the first aluminum source may include one or a combination of two or more of pseudo-boehmite, aluminum isopropoxide, sodium aluminate and aluminum sulfate.

[0039] In the above preparation method, the alkali source may include sodium hydroxide and / or potassium hydroxide.

[0040] The present invention also provides a ZSM-5 molecular sieve obtained by the above preparation method.

[0041] According to a specific embodiment of the present invention, compared with conventional ZSM-5 molecular sieves, the ZSM-5 molecular sieve prepared by the present invention has an orientation change trend of shortening the a-axis and extending the b-axis. Specifically, the ratio of the diffraction peak intensity of the (051) crystal plane to the diffraction peak intensity of the (501) crystal plane, and the ratio of the diffraction peak intensity of the (151) crystal plane to the diffraction peak intensity of the (303) crystal plane of the ZSM-5 molecular sieve of the present invention are both higher than those of conventional ZSM-5 molecular sieves.

[0042] Furthermore, in the above ZSM-5 molecular sieve, the diffraction peak intensity of the (051) crystal plane is higher than the diffraction peak intensity of the (501) crystal plane, and the diffraction peak intensity of the (151) crystal plane is higher than the diffraction peak intensity of the (303) crystal plane. In the X-ray diffraction spectrum of the ZSM-5 molecular sieve, the crystal plane corresponding to 2θ=23.18±0.5° is the (501) crystal plane, and the diffraction peak intensity of the 2θ angle is a;

[0043] The crystal plane corresponding to 2θ=23.32±0.5° is the (051) crystal plane, and the diffraction peak intensity of this 2θ angle is b;

[0044] The crystal plane corresponding to 2θ=23.74±0.5° is the (151) crystal plane, and the diffraction peak intensity of this 2θ angle is c;

[0045] The crystal plane corresponding to 2θ=23.99±0.5° is the (303) crystal plane, and the diffraction peak intensity of this 2θ angle is d;

[0046] b≥a, c≥d.

[0047] The above-mentioned diffraction peak characteristics indicate that the ZSM-5 molecular sieve of the present invention has a long b-axis and a short a-axis, and has both a long straight channel and a short tortuous channel structure. The crystallites with a long b-axis and a short a-axis are arranged in parallel in the molecular sieve, and the exposed crystal faces and acid sites are different from those of conventional ZSM-5 molecular sieves, so that the morphology and catalytic activity (for example, the catalytic activity for producing more ethylene in the catalytic cracking process) of the ZSM-5 molecular sieve of the present invention are different from those of the existing ZSM-5 molecular sieves.

[0048] The ZSM-5 molecular sieve synthesized by the present invention has a flaky morphology. Further, the morphology of the molecular sieve can be a "fin-like" structure formed by orderly agglomeration of a number of lamellar grains. The advantages of the flaky and fin-like structures are that the outer surface is rich and the diffusion distance of the sinusoidal zigzag channels is short. The "fin-like" structure refers to a loose structure (rather than a dense combination) formed by flaky grains in a parallel (mainly) or vertically crossed (a small amount). Conventional nanocrystals are usually spherical particles formed by disordered accumulation, and the stacking gaps between nanocrystals are small, and the particles are relatively dense. In contrast, the fin-like morphology of the ZSM-5 molecular sieve provided by the present invention is an ordered agglomeration structure, and the molecular sieve has better stability. In some specific embodiments, the above-mentioned ordered agglomeration structure can be achieved by orderly pre-assembly of seed crystals during the preparation process.

[0049] According to a specific embodiment of the present invention, for a ZSM-5 molecular sieve having a fin-like morphology, the ZSM-5 molecular sieve is formed by stacking a single sheet with a thickness of 20nm-200nm. The thickness of a single sheet of the ZSM-5 molecular sieve is 20nm-200nm. In some specific embodiments, the thickness of a single sheet of the ZSM-5 molecular sieve can be specifically 20nm, 50nm, 100nm, 150nm, 200nm and other specific values ​​and a range with any two of the above specific values ​​as endpoints.

[0050] According to a specific embodiment of the present invention, the particle size of the ZSM-5 molecular sieve is 300nm-3μm, and the particle size of the ZSM-5 molecular sieve is the overall particle size of the ZSM-5 molecular sieve. For a ZSM-5 molecular sieve having a fin-like morphology, the particle size of the ZSM-5 molecular sieve is the overall particle size of the ZSM-5 molecular sieve formed after the layers are stacked in an orderly manner. In some specific embodiments, the particle size of the ZSM-5 molecular sieve can be specifically 300nm, 400nm, 500nm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm and other specific values ​​and a range with any two of the above specific values ​​as endpoints.

[0051] According to a specific embodiment of the present invention, the ZSM-5 molecular sieve has a developed total specific surface area and external specific surface area, which is beneficial to improving the selectivity of the catalyst. The total specific surface area of ​​the ZSM-5 molecular sieve can be 300m 2 / g-500m 2 / g, for example 360m 2 / g-440m 2 / g.

[0052] According to a specific embodiment of the present invention, the external specific surface area of ​​the ZSM-5 molecular sieve can be 80m 2 / g-220m 2 / g, for example 120m 2 / g-210m 2 / g.

[0053] The present invention also provides a catalyst, which comprises the above ZSM-5 molecular sieve or is made of the ZSM-5 molecular sieve. The ZSM-5 molecular sieve is used in catalytic cracking reactions and exhibits high catalytic activity and good catalytic effect.

[0054] The beneficial effects of the present invention include:

[0055] The fin-shaped ZSM-5 molecular sieve obtained by the preparation method of the present invention has both long straight pores and short tortuous pore structures, showing a morphology and catalytic properties different from those of conventional ZSM-5 molecular sieves, and at the same time has a very developed external specific surface area. When used in catalytic cracking reactions, it can improve the selectivity of light olefins and has very broad application prospects in the fields of catalytic cracking and catalytic cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is the XRD spectrum of seed crystal 1.

[0057] Figure 2 This is the SEM image of seed crystal 1.

[0058] Figure 3 This is the XRD spectrum of seed crystal 2.

[0059] Figure 4 This is the SEM image of seed crystal 2.

[0060] Figure 5 The XRD spectrum of the molecular sieve prepared in Example 1 is shown in FIG.

[0061] Figure 6 This is the SEM image of the molecular sieve prepared in Example 1.

[0062] Figure 7 The XRD spectrum of the molecular sieve prepared in Example 2 is shown in FIG.

[0063] Figure 8 This is the SEM image of the molecular sieve prepared in Example 2.

[0064] Fig. 9 This is the XRD spectrum of the molecular sieve prepared in Example 3.

[0065] Fig.10 This is the SEM image of the molecular sieve prepared in Example 3.

[0066] Fig.11 This is the XRD spectrum of the molecular sieve prepared in Example 4.

[0067] Fig.12 This is the SEM image of the molecular sieve prepared in Example 4.

[0068] Fig.13 This is the XRD spectrum of the molecular sieve prepared in Example 7.

[0069] Fig.14 This is the SEM image of the molecular sieve prepared in Example 7.

[0070] Fig.15 This is the XRD spectrum of the molecular sieve prepared in Example 8.

[0071] Fig.16 This is the SEM image of the molecular sieve prepared in Example 8.

[0072] Fig.17 This is the XRD spectrum of the molecular sieve prepared in Comparative Example 1.

[0073] Fig.18 This is the SEM image of the molecular sieve prepared in Comparative Example 1.

[0074] Fig.19 , Fig. 20 The XRD spectra of the molecular sieves prepared in Example 1 and Comparative Example 1 are compared. DETAILED DESCRIPTION

[0075] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional conditions.

[0076] The raw materials used in the examples are:

[0077] Silicon source: macroporous silica gel (purity 99%), silica sol (aqueous solution with SiO2 mass concentration of 30%), white carbon black (purity 99%)

[0078] Aluminum source: pseudo-boehmite (alumina content 65%), aluminum isopropoxide (purity 99%), sodium aluminate (alumina content 41wt%, Na2O content 25wt%), aluminum sulfate (purity 99%).

[0079] Seed assembly agent: p-phenylenediamine (purity 99%), m-phenylenediamine (purity 99%), 1,3-propylenediamine (purity 99%), 1,4-butylenediamine (purity 99%), 1,5-pentanediamine (purity 99%), 1,6-hexanediamine (purity 99%), piperazine (purity 99%), homopiperazine (purity 99%), 1,4-diazabicyclo[2.2.2]octane (CAS: 280-57-9, molecular weight 112, purity 99%), 1,5-naphthalenediamine (purity 99%), 2,6-naphthalenediamine (purity 99%).

[0080] Alkali source: sodium hydroxide (purity 99%), potassium hydroxide (purity 99%).

[0081] Others: Deionized water.

[0082] Preparation Example

[0083] This experiment provides two methods for preparing seed solutions, including:

[0084] The seed solution 1 is a molecular sieve with an MFI crystal structure, which can be prepared by the following method: tetraethyl orthosilicate, tetrapropylammonium hydroxide and deionized water are fully mixed, and the molar ratio of the mixed materials (the silicon source is calculated by the effective component of SiO2 contained, and the template agent is calculated by the organic cation R + R + / SiO2=0.25,H2O / SiO2=30,carry out crystallization reaction under hydrothermal conditions,the conditions of crystallization reaction are:temperature 90℃,time 24h,add 2 times the mass of deionized water to the above reaction product and mix evenly,that is, dilute the effective seed solubility in the reaction product to one third of the original solubility,marked as seed solution 1,the average grain size is 200nm。The SiO2 content in seed solution 1 is 2.48wt% 。The XRD results of the seed solution are shown in Figure 1 , SEM image reference Figure 2 .

[0085] The seed solution 2 is a molecular sieve with an MFI crystal structure, which can be prepared by the following method: tetraethyl orthosilicate, aluminum isopropoxide, tetrapropylammonium hydroxide and deionized water are fully mixed, and the molar ratio of the mixed materials (the silicon source is calculated by the effective component of SiO2 contained, and the template agent is calculated by the organic cation R + =SiO2 / Al2O3=30, R + / SiO2=0.25,H2O / SiO2=30,carry out crystallization reaction under hydrothermal conditions,the crystallization reaction conditions are: 90℃,time 16h,add 2 times the mass of deionized water to the above reaction product and mix evenly,that is, dilute the effective seed solubility in the reaction product to one third of the original solubility,marked as seed solution 2,the average grain size is 100nm. The SiO2 content in seed solution 2 is 2.43wt%. The XRD results of the seed solution are shown in Figure 3 , SEM image reference Figure 4 .from Figure 1 , Figure 2 It can be seen that the seeds in both seed solution 1 and seed solution 2 have MFI crystal structure. The silicon-aluminum ratio of seed solution 2 is 30.

[0086] It should be noted that the raw materials, ratios, reaction conditions, dilution ratios, etc. used in the preparation of the seed solution of the present invention are not limited to the above process; alternatively, the seed solution can also be prepared using purchased molecular sieve products.

[0087] Example 1

[0088] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0089] In a 60°C water bath, 1.83g of seed solution 1 was dispersed in 20g of deionized water, and 1.0g of p-phenylenediamine was slowly added under continuous stirring, and stirred for 3h until the liquid had no obvious stratification to obtain a seed mixture. 0.28g of sodium hydroxide and 0.82g of sodium aluminate were dissolved in 25g of deionized water, and 20.0g of silica sol was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 150°C for 72h. The product was washed, filtered, dried, and calcined to obtain a molecular sieve product.

[0090] The XRD spectrum of the molecular sieve product is shown in Figure 5 The product has typical MFI structural characteristic peaks; SEM picture see Figure 6 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 413.5m 2 / g, of which the external specific surface area is 201.1m 2 / g.

[0091] Example 2

[0092] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0093] In a 60°C water bath, 1.83g of seed solution 1 was dispersed in 20g of deionized water, and 0.69g of 1,3-propylenediamine was slowly added under continuous stirring, and stirred for 3h until the liquid had no obvious stratification to obtain a seed mixture. 0.28g of sodium hydroxide and 0.82g of sodium aluminate were dissolved in 25g of deionized water, and 20.0g of silica sol was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 150°C for 72h. The product was washed, filtered, dried, and calcined to obtain a molecular sieve product.

[0094] The XRD spectrum of the molecular sieve product is shown in Figure 7 The product has typical MFI structural characteristic peaks, SEM images are shown in Figure 8 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 436.3m 2 / g, of which the external specific surface area is 197.2m 2 / g.

[0095] Example 3

[0096] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0097] Under 70℃ water bath condition, 3.66g of seed solution 1 was dispersed in 40g of deionized water, and 2.0g of 1,6-hexanediamine was slowly added under continuous stirring, and stirred for 2h until the liquid had no obvious stratification to obtain a seed mixture. 0.35g of sodium hydroxide and 0.45g of pseudo-boehmite were dissolved in 50g of deionized water, and 20.0g of silica sol was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 160℃ for 96h. After washing, filtering, drying and calcining the product, a molecular sieve product was obtained.

[0098] The XRD spectrum of the molecular sieve product is shown in Fig. 9 The product has typical MFI structural characteristic peaks, SEM images are shown in Fig.10 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 383.5m 2 / g, of which the external specific surface area is 125.7m 2 / g.

[0099] Example 4

[0100] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0101] Under 80℃ water bath condition, 3.66g of seed solution 2 was dispersed in 25g of deionized water, and 2.0g of 1,4-diazabicyclo[2.2.2]octane was slowly added under continuous stirring, and stirred for 3h until the liquid had no obvious stratification to obtain a seed mixture. 0.38g of potassium hydroxide and 0.27g of sodium aluminate were dissolved in 25g of deionized water, and 20.0g of silica sol was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 170℃ for 48h. The product was washed, filtered, dried, and calcined to obtain a molecular sieve product.

[0102] The XRD spectrum of the molecular sieve product is shown in Fig.11 The product has typical MFI structural characteristic peaks, SEM images are shown in Fig.12 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 375.9m 2 / g, of which the external specific surface area is 164.8m 2 / g.

[0103] Example 5

[0104] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0105] In a water bath at 80°C, 1.83g of seed solution 2 was dispersed in 60g of deionized water, and 2.8g of 2,6-naphthalenediamine was slowly added under continuous stirring, and stirred for 12h until the liquid had no obvious stratification to obtain a seed mixture. 0.45g of sodium hydroxide and 0.15g of sodium aluminate were dissolved in 60g of deionized water, and 6.0g of coarse-porous silica gel was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 170°C for 72h. The product was washed, filtered, dried, and calcined to obtain a molecular sieve product.

[0106] The product is a fin-shaped ZSM-5 molecular sieve. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 365.5m 2 / g, of which the external specific surface area is 121.3m 2 / g.

[0107] Example 6

[0108] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0109] In a water bath at 80°C, 1.83g of seed solution 2 was dispersed in 30g of deionized water, and 2.2g of piperazine was slowly added under continuous stirring, and stirred for 12h until the liquid had no obvious stratification to obtain a seed mixture. 0.33g of sodium hydroxide and 0.55g of aluminum isopropoxide were dissolved in 120g of deionized water, and 6.0g of white carbon black was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 160°C for 96h. After washing, filtering, drying and calcining the product, a molecular sieve product was obtained.

[0110] The product is a fin-shaped ZSM-5 molecular sieve. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 425.5m 2 / g, of which the external specific surface area is 197.6m 2 / g.

[0111] Example 7

[0112] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0113] In a 40°C water bath, 1.83g of seed solution 1 was dispersed in 20g of deionized water, and 1.0g of p-phenylenediamine was slowly added under continuous stirring, and stirred for 18h until the liquid had no obvious stratification to obtain a seed mixture. 0.28g of sodium hydroxide and 0.82g of sodium aluminate were dissolved in 25g of deionized water, and 20.0g of silica sol was slowly added under continuous stirring, and the seed mixture was slowly added. After mixing, stirring was continued for 3h to obtain a crystallized gel. The crystallized gel was transferred to a high-pressure reactor and crystallized at 120°C for 120h. After washing, filtering, drying and calcining the product, a molecular sieve product was obtained.

[0114] The XRD spectrum of the molecular sieve product is shown in Fig.13 The product has typical MFI structural characteristic peaks, SEM images are shown in Fig.14 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 363.1m 2 / g, with an external specific surface area of ​​131.8m 2 / g.

[0115] Example 8

[0116] This embodiment provides a ZSM-5 molecular sieve, the preparation method of which includes:

[0117] In a 20°C water bath, slowly add 2.0g of 1,4-diazabicyclo[2.2.2]octane to 3.66g of seed solution 2 under continuous stirring, and stir for 24h until the liquid has no obvious stratification to obtain a seed mixture. Dissolve 0.38g of potassium hydroxide and 0.27g of sodium aluminate in 25g of deionized water, slowly add 20.0g of silica sol under continuous stirring, slowly add the seed mixture, and continue stirring for 3h after mixing to obtain a crystallized gel. Transfer the crystallized gel to a high-pressure reactor and crystallize at 180°C for 12h. After washing, filtering, drying and calcining the product, a molecular sieve product is obtained.

[0118] The XRD spectrum of the molecular sieve product is shown in Fig.15 The product has typical MFI structural characteristic peaks, SEM images are shown in Fig.16 The product is a fin-shaped product formed by orderly stacking of molecular sieve sheets. The molecular sieve was analyzed for its total specific surface area and porosity, and its total specific surface area is 368.2m 2 / g, of which the external specific surface area is 141.3m 2 / g.

[0119] Comparative Example 1

[0120] This comparative example provides a ZSM-5 molecular sieve, the preparation method of which comprises:

[0121] Dissolve 0.28g of sodium hydroxide, 0.82g of sodium aluminate and 1.0g of p-phenylenediamine in 45g of deionized water, slowly add 20.0g of silica sol under continuous stirring, slowly add 1.83g of seed solution 1, and continue stirring for 3h after mixing to obtain a crystallized gel. Transfer the crystallized gel to a high-pressure reactor and crystallize at 150°C for 72h. After washing, filtering, drying and calcining the product, a molecular sieve product is obtained.

[0122] The XRD spectrum of the molecular sieve product is shown in Fig.17 The product has typical MFI structural characteristic peaks, SEM images are shown in Fig.18 The product is a microcrystalline stacking morphology. Compared with the lamellar molecular sieves in the above examples, which are structural units with fin-like morphology, the microcrystalline molecular sieves in the stacking morphology of the comparative example are larger in size and stacked in disorder. The molecular sieve was subjected to full pore specific surface area and porosity analysis, and its total specific surface area was 365.7 m 2 / g, of which the external specific surface area is 103.2m 2 / g.

[0123] By comparison with Example 1, it can be seen that the addition of a seed assembly agent during the preparation of a crystallized gel does not play a role in pre-assembling seeds, and the process of pre-assembling seeds with a seed assembly agent is helpful in preparing fin-shaped ZSM-5 molecular sieves.

[0124] Fig.19 and Fig. 20 It is a comparison of the XRD spectra of the molecular sieves prepared in Example 1 and Comparative Example 1. It can be seen that in the molecular sieve of Comparative Example 1, the peak intensity of the characteristic peak of the (303) crystal plane is higher than the peak intensity of the characteristic peak of the (151) crystal plane. In the molecular sieve of Example 1, the peak intensity of the characteristic peak of the (303) crystal plane is weaker than the peak intensity of the characteristic peak of the (151) crystal plane. The above comparison shows that the dominant crystal plane exposed by the ZSM-5 molecular sieve prepared by the present invention is different from the dominant crystal plane of the conventional ZSM-5 molecular sieve; and, compared with the molecular sieve of Comparative Example 1, Example 1 has long straight channels and short tortuous channels, that is, it has a structural feature of a long b axis and a short a axis. Therefore, the performance of the ZSM-5 molecular sieve prepared by the present invention is also different from that of conventional molecular sieves and has better catalytic performance.

[0125] The molecular sieve products obtained in Example 1, Example 2, Example 7, Example 8 and Comparative Example 1 were subjected to calcination, ammonium exchange and other treatment processes to obtain hydrogen-type molecular sieve products, which were applied to the catalytic cracking reaction of n-heptane for performance evaluation. The reaction conditions were: 550° C., mass space velocity 2.0 h -1 , nitrogen carrier gas flow rate 200mL / h, the evaluation results are shown in Table 1. The raw material ratios and product morphologies of the embodiments and comparative examples are shown in Table 2.

[0126] Table 1

[0127] project n-Heptane conversion rate (%) Propylene selectivity (%) Ethylene selectivity (%) Example 1 98.7 31.2 23.5 Example 2 98.2 30.8 25.8 Example 7 99.2 31.0 22.3 Example 8 98.1 32.1 22.9 Comparative Example 1 97.8 30.1 12.6

[0128] Table 2

[0129]

[0130]

[0131] From the comparison results, it can be seen that the fin-shaped molecular sieve obtained by the preparation method of the present invention can improve the conversion rate of n-heptane and the selectivity of low-carbon olefins such as ethylene and propylene during catalytic cracking, especially can improve the selectivity of ethylene. The catalytic cracking performance of the fin-shaped ZSM-5 molecular sieves with similar silicon-aluminum ratios synthesized by different seed assembly agents of the present invention is similar, which also shows that the stability of the ZSM-5 molecular sieve preparation method provided by the present invention is relatively high.

[0132] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a ZSM-5 molecular sieve, the method comprising: S1, mixing the seed crystals with the seed crystal assembly agent to obtain a seed crystal mixture; S2, mixing the seed mixture with an alkali source, a first aluminum source, and a first silicon source to obtain a crystallized gel; S3, subjecting the crystallized gel to a first crystallization and calcination to obtain a ZSM-5 molecular sieve.

2. The preparation method according to claim 1, wherein In S1, the mixing temperature is 20°C-80°C, and the mixing time is 0.5h-24h.

3. The preparation method according to claim 1, wherein The seed crystals include a molecular sieve having an MFI crystal structure; Preferably, the seed crystal has a grain size of 10-200 nm.

4. The preparation method according to claim 1, wherein The method for preparing the seed crystal comprises: Mixing a second silicon source, an organic template and water to obtain a seed crystal precursor, and subjecting the seed crystal precursor to a second crystallization to obtain the seed crystal; The second silicon source is calculated as SiO2, the organic template is calculated as organic cation R + The chemical composition of the seed precursor satisfies the following molar ratio range: R + / SiO2=0.15-0.4, H2O / SiO2=15-50; Preferably, the temperature of the second crystallization is 80° C.-110° C., and the time of the second crystallization is 16 h-24 h.

5. The preparation method according to claim 4, wherein The seed crystal precursor also includes a second aluminum source, the second silicon source is calculated as SiO2, and the second aluminum source is calculated as Al2O3. The chemical composition of the seed crystal precursor further satisfies the following molar ratio range: SiO2 / Al2O3≥25.

6. The preparation method according to claim 1, wherein The seed assembly agent is an organic substance having two amine groups; Preferably, the seed assembly agent includes one or a combination of two or more of p-phenylenediamine, m-phenylenediamine, 1,3-propylenediamine, 1,4-butylenediamine, 1,5-pentanediamine, 1,6-hexanediamine, piperazine, homopiperazine, 1,4-diazabicyclo[2.2.2]octane, 1,5-naphthalenediamine, and 2,6-naphthalenediamine.

7. The preparation method according to claim 1, wherein The first silicon source is calculated as SiO2, the first aluminum source is calculated as Al2O3, and the seed crystal is calculated as the contained SiO2. The chemical composition of the crystallized gel satisfies the following molar ratio range: SiO2 / Al2O3=25-400, seed / SiO2=0.002-0.25, MO / SiO2=0.05-0.50, H2O / SiO2=15-120, Seed assembly agent / SiO2=0.03-0.20; wherein M is an alkali metal and / or an alkaline earth metal; Preferably, seed crystal / SiO2=0.005-0.

15.

8. The preparation method according to claim 1, wherein The temperature of the first crystallization is 120° C.-190° C., and the time of the first crystallization is 12 h-120 h; Preferably, the temperature of the first crystallization is 140-180° C., and the time of the first crystallization is 12 h-96 h.

9. A ZSM-5 molecular sieve obtained by the preparation method according to any one of claims 1 to 8.

10. The ZSM-5 molecular sieve according to claim 9, wherein In the X-ray diffraction spectrum of the ZSM-5 molecular sieve, the crystal plane corresponding to 2θ=23.18±0.5° is the (501) crystal plane, and the diffraction peak intensity of the 2θ angle is a; The crystal plane corresponding to 2θ=23.32±0.5° is the (051) crystal plane, and the diffraction peak intensity of this 2θ angle is b; The crystal plane corresponding to 2θ=23.74±0.5° is the (151) crystal plane, and the diffraction peak intensity of this 2θ angle is c; The crystal plane corresponding to 2θ=23.99±0.5° is the (303) crystal plane, and the diffraction peak intensity of this 2θ angle is d; b≥a, c≥d.

11. The ZSM-5 molecular sieve according to claim 9, wherein: The particle size of the ZSM-5 molecular sieve is 300nm-3μm, and the thickness of a single layer of the ZSM-5 molecular sieve is 20nm-200nm; The total specific surface area of ​​the ZSM-5 molecular sieve is 300 m 2 / g-500m 2 / g; The external specific surface area of ​​the ZSM-5 molecular sieve is 80 m 2 / g-220m 2 / g.

12. A catalyst comprising the ZSM-5 molecular sieve according to any one of claims 9 to 11 or made from the ZSM-5 molecular sieve.

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