Short b-axis ZSM-5 zeolite as well as preparation method and application thereof

Abstract

The invention provides short b-axis ZSM-5 zeolite as well as a preparation method and application thereof, and the preparation method comprises the following steps: uniformly mixing seed crystal, guar gum, sodium hydroxide and water; adding and dissolving an aluminum source; adding a silicon source and uniformly mixing to obtain gel; carrying out crystallization treatment on the gel, cooling a crystallization product, separating, washing with water until the crystallization product is neutral, and then drying and roasting to obtain Na-ZSM-5 zeolite; carrying out ion exchange and roasting on the Na-ZSM-5 zeolite to obtain H-ZSM-5 zeolite, namely short b-axis ZSM-5 zeolite; the dosage of the seed crystal and the dosage of the guar gum are respectively 1-5% and 1-20% of the mass of SiO2. The ZSM-5 zeolite disclosed by the invention is short in b-axis thickness, high in crystallinity, high in product yield and excellent in molecular diffusion performance, and has relatively high catalytic activity and relatively high catalytic activity stability when being used as a catalyst for preparing olefin through catalytic cracking of low-carbon hydrocarbon.

Description

Technical Field

[0001] This invention relates to a short b-axis ZSM-5 zeolite, its preparation method, and its application, belonging to the field of catalytic materials technology. Background Technology

[0002] Ethylene, propylene, and other low-carbon olefins are important basic chemical raw materials. Currently, the main methods for producing low-carbon olefins are steam cracking and catalytic cracking. Compared with steam cracking, catalytic cracking not only reduces reaction temperature and energy consumption but also allows for flexible adjustment of product distribution, making it a current research hotspot.

[0003] In catalytic cracking processes, one of the core research focuses on selecting suitable molecular sieve catalysts. The pore structure and acid properties of molecular sieves affect the cracking and hydrogen transfer reactions during catalytic cracking, thus influencing product distribution. Therefore, developing ZSM-5 zeolite with excellent diffusion properties is crucial for significantly improving the yield of low-carbon olefins in catalytic cracking. Currently, a large body of literature reports on the synthesis of ZSM-5 zeolite, and significant progress has been made in improving its diffusion performance. Many studies have focused on reducing crystal size, obtaining nanoscale ZSM-5 zeolite materials by optimizing synthesis conditions. Although these novel nanomaterials exhibit higher catalytic activity than industrial-grade ZSM-5 zeolite, from a practical application perspective, the crystal size of ZSM-5 zeolite should not be too small. Excessively small crystal sizes make zeolite recovery difficult, posing challenges to actual production operations. Furthermore, nanoscale zeolites are prone to agglomeration and even symbiosis; the interfaces formed by agglomeration and symbiosis contain numerous defective hydroxyl groups, easily inducing coke formation.

[0004] Currently, many researchers have focused on synthesizing lamellar ZSM-5 zeolites, aiming to alter their morphology by adjusting the orientation of the pore structure relative to the dominant crystal face, thereby affecting diffusion resistance. Selectively reducing particle size and shape with a controllable a / b or a / c aspect ratio to adjust morphology is considered an effective way to reduce diffusion paths, increase the accessibility of active sites, and ultimately improve catalytic activity. Ryoo et al. [Nature 461, 246-249 (2009)] used bifunctional surfactants as templates to induce the formation of molecular sieve structures at both mesoporous and microporous scales, thus synthesizing MFI zeolite nanosheets only 2 nm thick. The numerous acidic sites exposed on their outer surface gave them high activity for the catalytic transformation of organic macromolecules, and the reduced crystal thickness promoted molecular diffusion, decreased coke formation rate, and significantly inhibited catalyst deactivation. However, bifunctional surfactants are expensive and have complex preparation processes, which are not conducive to industrial applications. Dai et al. (J.Am.Chem.Soc.2021,143,1993-2004) developed a method for synthesizing plate-like MFI zeolites by combining preliminary aging and fluoride-assisted low-temperature crystallization with a common structure-directing agent (TPAOH) and a modifier. They chose ammonium fluoride (NH4F) as an additive in the zeolite synthesis to change the aspect ratio between crystal surfaces. The synthesized MFI crystals were in the micrometer range along the a-axis and c-axis, while the thickness along the b-axis could be effectively adjusted to tens of nanometers, thus shortening the diffusion path. However, the amount of ammonium fluoride used was large, which was extremely environmentally unfriendly and did not conform to the concept of green chemistry. Liu et al. (Liu et al.,Sci.Adv.2020;6:eaay5993) developed a progressive b-axis thinning method to prepare MFI molecular sieve nanosheets with high uniformity and high aspect ratio with a thickness of 12 unit cells by adding MFI nanosheet seeds. These nanosheets exhibited excellent catalytic performance, but the process was complex and difficult to operate.

[0005] Therefore, researching and exploring a low-cost one-step method for synthesizing short b-axis ZSM-5 zeolite is of great significance, as it can provide an important theoretical basis and supporting evidence for its industrial application. Summary of the Invention

[0006] To address the aforementioned shortcomings and deficiencies, the present invention aims to provide a short b-axis ZSM-5 zeolite, its preparation method, and its applications. The ZSM-5 zeolite of this invention exhibits a short b-axis thickness, high crystallinity, high product yield, and excellent molecular diffusion properties. When used as a catalyst for the catalytic cracking of low-carbon hydrocarbons to olefins, it demonstrates high catalytic activity and high catalytic activity stability.

[0007] To achieve the above objectives, on the one hand, the present invention provides a method for preparing short b-axis ZSM-5 zeolite, wherein the preparation method includes:

[0008] Step (1): Mix the seed crystals, guar gum, sodium hydroxide and water evenly;

[0009] Step (2): Add aluminum source and dissolve it;

[0010] Step (3): Add the silicon source and mix it evenly to obtain a gel;

[0011] Step (4): The gel is crystallized, the crystallized product is cooled and separated and washed with water until neutral, and then dried and calcined to obtain Na-ZSM-5 zeolite;

[0012] Step (5): Ion exchange and calcination of Na-ZSM-5 zeolite to obtain H-ZSM-5 zeolite, namely short b-axis ZSM-5 zeolite;

[0013] The molar ratio of sodium hydroxide, aluminum source, silicon source and water, calculated as Na2O, Al2O3, SiO2 and H2O, is (5-15):(0.5-5):(50-100):(500-2200); the amounts of seed crystals and guar gum are 1-5% and 1-20% of the mass of SiO2, respectively. That is, based on the total weight of silicon source calculated as SiO2 as 100%, the amounts of seed crystals and guar gum are 1-5% and 1-20%, respectively.

[0014] As a specific embodiment of the preparation method described above in this invention, the method for preparing the seed crystal includes:

[0015] The template agent and water are mixed and stirred evenly; the silicon source is added and stirring is continued until dissolved to obtain a gel; the gel is crystallized, the crystallized product is cooled and separated and washed with water until neutral, and then dried and calcined to remove the template agent to obtain seed crystals.

[0016] This invention does not specify the exact substances and amounts of the template agent, silicon source, etc., used in the seed crystal preparation process, nor the process parameters used. These can be reasonably selected and adjusted as needed, as long as the purpose of obtaining the seed crystal is achieved. For example, in some embodiments of this invention, the template agent can be tetrapropylammonium hydroxide, etc., and the separation can be centrifugation or filtration.

[0017] As a specific embodiment of the preparation method described above in this invention, in step (2), the aluminum source includes one or a combination of aluminum hydroxide, aluminum sulfate and sodium aluminate; and / or the silicon source includes one or a combination of silica sol, silica gel and solid silica gel.

[0018] In steps (1) to (3) of the preparation method described above, the mixing or dissolution can be achieved by stirring. This invention does not specify a particular stirring time, which can be adjusted as needed, as long as the goal of uniform mixing and dissolution is achieved. For example, in some embodiments of this invention, in step (3), after adding the silicon source, the stirring time can be controlled to be 6-18 hours.

[0019] As a specific embodiment of the preparation method described above in this invention, in step (4), the temperature of the crystallization treatment is 140-180℃ and the time is 2-5 days.

[0020] As a specific embodiment of the preparation method described above in this invention, in step (4), the crystallization treatment is static crystallization or dynamic crystallization, preferably dynamic crystallization.

[0021] As a specific embodiment of the preparation method described above in this invention, in step (4), the separation can be centrifugation or vacuum filtration.

[0022] As a specific embodiment of the preparation method described above in this invention, in step (4), the drying is carried out at 80-120°C overnight.

[0023] As a specific embodiment of the preparation method described above in this invention, in step (4), the calcination temperature is 500-600℃ and the time is 6-10h; preferably, the calcination is carried out at a heating rate of 2℃ / min to 550-580℃ and held at that temperature for 6-10h.

[0024] In one specific embodiment of the preparation method described above, in step (5), the ion exchange is performed using an NH4Cl solution. This invention does not specify a particular concentration of the NH4Cl solution used for ion exchange, and it can be adjusted as needed. For example, in some embodiments of this invention, the concentration of the NH4Cl solution is 1M.

[0025] As a specific embodiment of the preparation method described above in this invention, in step (5), the amount of Na-ZSM-5 zeolite and NH4Cl solution used is: 1-2g of Na-ZSM-5 zeolite for every 100mL of NH4Cl solution, preferably 1g of Na-ZSM-5 zeolite for every 50mL of NH4Cl solution.

[0026] As a specific embodiment of the preparation method described above in this invention, in step (5), the temperature of the ion exchange is 60-80℃, preferably 70℃.

[0027] As a specific embodiment of the preparation method described above in this invention, in step (5), the ion exchange is repeated three times, each time for 1-3 hours, preferably for 2 hours each time.

[0028] The present invention does not make specific requirements on the calcination conditions, such as temperature and time, in step (5) of the preparation method described above. These conditions can be reasonably adjusted as needed, as long as the purpose of obtaining H-ZSM-5 zeolite can be achieved after calcination.

[0029] On the other hand, the present invention also provides a short b-axis ZSM-5 zeolite, which is prepared by the above-described method for preparing short b-axis ZSM-5 zeolite, wherein the short b-axis ZSM-5 zeolite has a silicon-to-aluminum ratio (atomic ratio of Si to Al) of 10-100 and a micropore volume of 0.05-0.20 cm³. 3 / g, preferably 0.11cm 3 / g, specific surface area of ​​200-500m² 2 / g, preferably 273m 2 / g, with an average thickness of 50-100nm along the b-axis.

[0030] Furthermore, this invention also provides the application of the aforementioned short b-axis ZSM-5 zeolite as a catalyst for the catalytic cracking of low-carbon hydrocarbons to olefins. In some embodiments of this invention, the low-carbon hydrocarbons include, but are not limited to, n-hexane.

[0031] The technical solution of the present invention has at least the following beneficial effects:

[0032] The core of the preparation method provided by this invention is the use of guar gum as an additive, which is mainly used for thickening and restricting mass transfer of materials, thereby limiting the growth of zeolite, i.e., restricting crystal growth. In the synthesis of ZSM-5 zeolite, this method replaces the traditional expensive template agent with guar gum and controls the addition ratio of guar gum through a seed-induction method to obtain short b-axis ZSM-5 zeolite with high yield, high crystallinity, and low cost.

[0033] Compared with existing conventional ZSM-5 zeolite preparation methods, the ZSM-5 zeolite prepared by the method of this invention has a shorter b-axis thickness, higher crystallinity, higher product yield, and excellent molecular diffusion properties. When the ZSM-5 zeolite obtained by this invention is used as a catalyst for the catalytic cracking of low-carbon hydrocarbons to olefins, it exhibits high catalytic activity and high catalytic activity stability. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 The XRD patterns are those of conventional H-Ref zeolite of Comparative Example 1, ZSM-5 zeolite of Comparative Example 2, and short b-axis ZSM-5 zeolite provided in Example 1 of this invention.

[0036] Figures 2a-2f The images are scanning electron microscope (SEM) images of conventional H-Ref zeolite (Comparative Example 1), short b-axis ZSM-5 zeolite (Example 1 of this invention), and ZSM-5 zeolite (Comparative Example 2), respectively.

[0037] Figure 3 Nitrogen adsorption-desorption isotherms for conventional H-Ref zeolite of Comparative Example 1, ZSM-5 zeolite of Comparative Example 2, and short b-axis ZSM-5 zeolite provided in Example 1 of this invention.

[0038] Figures 4a-4f The figures show the b-axis statistics of conventional H-Ref zeolite in Comparative Example 1, short b-axis ZSM-5 zeolite provided in Example 1 of this invention, and ZSM-5 zeolite in Comparative Example 2, respectively.

[0039] Figure 5 The yield curves of the ZSM-5 zeolite products obtained in Example 1 and Comparative Example 2 of this invention are shown.

[0040] Figure 6 The curve showing the change in hexane conversion rate with reaction temperature in Test Example 2, where ZSM-5 zeolite is used as a catalyst for the catalytic cracking of hexane to olefins.

[0041] Figure 7 The curve showing the yield of diolefins as a function of reaction temperature when ZSM-5 zeolite is used as a catalyst for the catalytic cracking of hexane to olefins in Test Example 2.

[0042] Figure 8 The curve showing the change in hexane conversion rate with reaction time when ZSM-5 zeolite is used as a catalyst for the catalytic cracking of hexane to olefins in Test Example 2.

[0043] Figure 9 The curve showing the change in diolefin yield with reaction time when ZSM-5 zeolite is used as a catalyst for the catalytic cracking of hexane to olefins in Test Example 2. Detailed Implementation

[0044] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0045] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0046] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0047] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0048] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0049] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying tables, drawings, and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0051] According to a specific embodiment of the present invention, the preparation method of the short b-axis ZSM-5 zeolite of the present invention includes the following specific steps:

[0052] S1: Weigh out the template agent tetrapropylammonium hydroxide and water, mix and stir evenly; add the silicon source, continue stirring until dissolved to obtain a gel; crystallize the gel, cool the crystallized product, centrifuge or filter and wash with water until neutral, then dry; calcine the dried product to remove the template agent to obtain seed crystals;

[0053] S2: Weigh out the seed crystals, guar gum and sodium hydroxide, add a certain amount of water, stir vigorously and mix evenly;

[0054] S3: Add aluminum source to the solution obtained in S2 and continue stirring until the aluminum source dissolves;

[0055] S4: Add a silicon source to the solution obtained in S3 and continue stirring for 6-18 hours to obtain a gel;

[0056] S5: Transfer the gel obtained in S4 to a stainless steel crystallization vessel for crystallization at a temperature of 140-180℃ for 2-5 days. After crystallization, remove the vessel, cool it, centrifuge or filter the sample to neutralize the pH, and dry it overnight at 80-120℃.

[0057] S6: The zeolite product obtained by calcining S5 at a temperature of 500-600℃ for 6-10 hours yields Na-ZSM-5 zeolite.

[0058] S7: The Na-ZSM-5 zeolite obtained in S6 was subjected to ion exchange in a 1M NH4Cl solution at a temperature of 60-80℃. After calcination, H-ZSM-5 zeolite, i.e., short b-axis ZSM-5 zeolite, was obtained.

[0059] The technical solution of the present invention will be described in detail below with reference to embodiments and comparative examples.

[0060] Example 1

[0061] This embodiment provides a method for preparing short b-axis ZSM-5 zeolite, which includes the following steps:

[0062] A certain amount of TPAOH was added to deionized water and stirred at room temperature for 10 minutes to mix it evenly. Then, tetraethyl orthosilicate was added dropwise using a dropper, and the mixture was stirred vigorously at room temperature for 12 hours until the solution became clear and transparent, resulting in a gel. The molar composition of the gel was 100SiO2:30TPAOH:3000H2O. The gel was transferred to a crystallization vessel and dynamically crystallized at 120℃ for 48 hours. After crystallization, the crystallization vessel was removed and rapidly cooled. The sample was centrifuged and thoroughly washed. The washed sample was placed in an oven and dried overnight at 120℃. The dried sample was then placed in a muffle furnace and calcined at 550℃ for 10 hours to remove the TPAOH template agent, resulting in a release seed crystal.

[0063] Weigh out a certain amount of guar gum, 2.0g of seed crystals, and 6.7g of sodium hydroxide (96wt.%), add 183.3g of deionized water, and stir to mix evenly to obtain a mixed solution;

[0064] Add 3.1g of aluminum hydroxide to the above mixed solution and stir vigorously for 10 minutes;

[0065] Add 200g of silica sol (30wt.%) at once and continue stirring vigorously for 12h to obtain a gel;

[0066] The obtained gel was transferred to a stainless steel crystallization vessel for dynamic crystallization at a temperature of 160℃ for 2 days. After crystallization, the vessel was removed and cooled to room temperature with cold water. The gel was centrifuged and washed with water until neutral. The resulting sample was dried in a 120℃ oven. The resulting sample was denoted as ZSM-5-R(X), where R represents guar gum and X represents the percentage of guar gum, i.e., the percentage of guar gum used in the mass of SiO2 (X = 2.0%, 4.0%, 8.0%, or 17.0%).

[0067] The above sample was calcined at high temperature in a muffle furnace, wherein the calcination was carried out by raising the temperature to 550°C at a rate of 2°C / min and holding the temperature for 10 hours.

[0068] The calcined sample underwent three ion exchanges in a 1M NH4Cl solution at 70℃ for 2 hours each time. After collecting and drying the sample, it was then calcined at high temperature to obtain the hydrogen-form zeolite, namely the short b-axis ZSM-5 zeolite, denoted as H-ZSM-5-R(X), where X = 2.0%, 4.0%, 8.0%, or 17.0%. The amount of NH4Cl solution used was 1 g of zeolite for every 50 mL of NH4Cl solution.

[0069] Example 2

[0070] This embodiment provides a method for preparing short b-axis ZSM-5 zeolite, which includes the following steps:

[0071] A certain amount of TPAOH was added to deionized water and stirred at room temperature for 10 minutes to mix it evenly. Then, tetraethyl orthosilicate was added dropwise using a dropper, and the mixture was stirred vigorously at room temperature for 12 hours until the solution became clear and transparent, resulting in a gel with the following composition: 100SiO2:30TPAOH:3000H2O. The gel was transferred to a crystallization vessel and dynamically crystallized at 120℃ for 48 hours. After crystallization, the crystallization vessel was removed and rapidly cooled. The sample was centrifuged and thoroughly washed. The washed sample was placed in an oven and dried overnight at 120℃. The dried sample was then placed in a muffle furnace and calcined at 550℃ for 10 hours to remove the TPAOH template agent, resulting in a release seed crystal.

[0072] Weigh out 10g of guar gum (corresponding to X = 17.0%), 2.0g of seed crystals, and 6.7g of sodium hydroxide (96wt.%), add 183.3g of deionized water, and stir to mix evenly to obtain a mixed solution;

[0073] Add 3.1g of aluminum hydroxide to the above mixed solution and stir vigorously for 10 minutes;

[0074] Add 200g of silica sol (30wt.%) at once and continue stirring vigorously for 12h to obtain a gel;

[0075] The obtained gel was transferred to a stainless steel crystallization vessel for dynamic crystallization. The crystallization temperature was set to Y, and the crystallization time was 2 days. After crystallization, the vessel was removed and cooled to room temperature with water. The gel was centrifuged and washed with water until neutral. The resulting sample was dried in an oven at 120℃. The resulting sample was denoted as ZSM-5T(Y), where Y represents the crystallization temperature, Y = 140, 150, 160, 170℃.

[0076] The above-mentioned sample was calcined in a muffle furnace at high temperature, wherein the calcination was carried out by raising the temperature to 550°C at a rate of 2°C / min and holding it at that temperature for 10 hours.

[0077] The calcined sample underwent three ion exchanges in a 1M NH4Cl solution at 70℃ for 2 hours each time. After collecting and drying the sample, it was then calcined at high temperature to obtain hydrogen-form zeolite. The amount of NH4Cl solution used was 1g of zeolite for every 50mL of NH4Cl solution.

[0078] Example 3

[0079] This embodiment provides a method for preparing short b-axis ZSM-5 zeolite, which includes the following steps:

[0080] A certain amount of TPAOH was added to deionized water and stirred at room temperature for 10 minutes to mix it evenly. Then, tetraethyl orthosilicate was added dropwise using a dropper, and the mixture was stirred vigorously at room temperature for 12 hours until the solution became clear and transparent, resulting in a gel with the following composition: 100SiO2:30TPAOH:3000H2O. The gel was transferred to a crystallization vessel and dynamically crystallized at 120℃ for 48 hours. After crystallization, the crystallization vessel was removed and rapidly cooled. The sample was centrifuged and thoroughly washed. The washed sample was placed in an oven and dried overnight at 120℃. The dried sample was then placed in a muffle furnace and calcined at 550℃ for 10 hours to remove the TPAOH template agent, resulting in a release seed crystal.

[0081] Weigh out 10g of guar gum, 2.0g of seed crystals, and a certain amount of sodium hydroxide (96wt.%), add 183.3g of deionized water, and stir to mix evenly to obtain a mixed solution;

[0082] Add 3.1g of aluminum hydroxide to the above mixed solution and stir vigorously for 10 minutes;

[0083] Add 200g of silica sol (30wt.%) at once and continue stirring vigorously for 12h to obtain a gel;

[0084] The obtained gel was transferred to a stainless steel crystallization vessel for dynamic crystallization at a temperature of 160℃ for 2 days. After crystallization, the vessel was removed and cooled to room temperature with water. The gel was centrifuged and washed with water until neutral. The resulting sample was dried in an oven at 120℃. The resulting sample was denoted as ZSM-5JD(Z), where Z represents alkalinity, i.e., the molar ratio of sodium hydroxide (calculated as Na2O) to silicon source (calculated as SiO2), Z = 7, 8, 9, 10.

[0085] The above-mentioned sample was calcined in a muffle furnace at high temperature, wherein the calcination was carried out by raising the temperature to 550°C at a rate of 2°C / min and holding it at that temperature for 10 hours.

[0086] The calcined sample underwent three ion exchanges in a 1M NH4Cl solution at 70℃ for 2 hours each time. After collecting and drying the sample, it was then calcined at high temperature to obtain hydrogen-form zeolite. The amount of NH4Cl solution used was 1g of zeolite for every 50mL of NH4Cl solution.

[0087] Comparative Example 1

[0088] This comparative example uses commercial hydrogen-type ZSM-5 zeolite purchased from the Catalyst Plant of Nankai University as a standard (named H-Ref).

[0089] Comparative Example 2

[0090] This comparative example provides a method for preparing ZSM-5 zeolite, which differs from Example 1 only in that:

[0091] In H-ZSM-5-R(X), X is 33.0%.

[0092] Comparative Example 3

[0093] This comparative example provides a method for preparing ZSM-5 zeolite, which differs from Example 1 only in that:

[0094] In H-ZSM-5-R(X), X is 0.5%.

[0095] Test Example 1

[0096] This test example evaluates the physicochemical properties and yield of H-Ref from Comparative Example 1, ZSM-5 zeolite from Comparative Examples 2 and 3, and short b-axis ZSM-5 zeolite provided in Example 1 of this invention.

[0097] The XRD patterns of the conventional H-Ref zeolite of Comparative Example 1, the ZSM-5 zeolite of Comparative Example 2, and the short b-axis ZSM-5 zeolite provided in Example 1 of this invention are shown below. Figure 1 As shown, from Figure 1 It can be seen that all samples have the MFI topology and no impurities are present.

[0098] Scanning electron microscope (SEM) images of conventional H-Ref zeolite of Comparative Example 1, short b-axis ZSM-5 zeolite provided in Example 1 of this invention, and ZSM-5 zeolite of Comparative Example 2 are shown below. Figures 2a-2f As shown in the figure. Based on the characterization results above, the guar gum added during the preparation process is not present in the obtained short b-axis ZSM-5 zeolite crystals.

[0099] The pore structure properties of conventional H-Ref zeolite in Comparative Example 1, ZSM-5 zeolite in Comparative Examples 2 and 3, and short b-axis ZSM-5 zeolite provided in Example 1 of this invention are as follows: Figure 3 As shown in Table 1.

[0100] Table 1. Pore structure properties of zeolites and their silica-alumina ratio

[0101]

[0102] a The silicon-to-aluminum ratio was measured by XRF.

[0103] Depend on Figure 3As shown in Table 1 above, the conventional H-Ref of Comparative Example 1, the ZSM-5 zeolite of Comparative Examples 2 and 3, and the H-ZSM-5-R(X) zeolite synthesized from the short b-axis system provided in Example 1 of this invention all have similar micropore volumes, indicating that both have high crystallinity. Figures 2a-2f It can also be seen that, apart from the inconsistent morphology of the purchased commercial ZSM-5 zeolite samples, the other five samples synthesized by adding guar gum provided in Comparative Example 2 and Example 1 of the present invention all have the morphology of flake ZSM-5 zeolite, and no obvious large-particle impurity crystal morphology was observed. This indicates that the addition of guar gum is beneficial to synthesizing samples with regular morphology.

[0104] This test example also provides a detailed statistical analysis of the b-axis thickness of the conventional H-Ref zeolite in Comparative Example 1, the short b-axis ZSM-5 zeolite provided in Example 1 of this invention, and the ZSM-5 zeolites in Comparative Examples 2 and 3, such as... Figures 4a-4f As shown in Table 2.

[0105] Table 2. Statistical table of b-axis dimensions for samples with different amounts of guar gum.

[0106]

[0107]

[0108] from Figures 4a-4f As shown in Table 2, with the increase of guar gum addition, the b-axis dimension of the sample first decreases and then increases, with a minimum point. Furthermore, the average b-axis thickness of the short b-axis ZSM-5 zeolite provided in Example 1 of this invention is significantly shorter than that of the conventional H-Ref of Comparative Example 1 and the ZSM-5 zeolites of Comparative Examples 2 and 3, indicating that the examples of this invention successfully prepared short b-axis ZSM-5 zeolite.

[0109] In addition, the yield variation curves of the ZSM-5 zeolite products obtained in Example 1 and Comparative Example 2 are as follows: Figure 5 As shown. The product yield is defined as the mass of the ZSM-5 zeolite product obtained in Example 1 and Comparative Example 2 divided by the sum of the masses of the added silica and alumina. Figure 5 As can be seen from the above, the yields of the short b-axis ZSM-5 zeolite obtained in Example 1 and the ZSM-5 zeolite products obtained in Comparative Example 2 are both above 90%.

[0110] Test Example 2

[0111] This test example evaluates the catalytic cracking performance of H-Ref from Comparative Example 1, ZSM-5 zeolite from Comparative Example 2, and the short b-axis ZSM-5 zeolite provided in Example 1 of this invention.

[0112] During the evaluation process, nitrogen gas and the feedstock n-hexane were mixed and passed from top to bottom through the catalyst fixed bed. The process conditions used for evaluating each catalyst example were: atmospheric pressure, mass hourly space velocity (HHSV) of 4.2 h⁻¹. -1 The reaction temperatures were 400℃, 450℃, 500℃, 550℃, and 600℃. The evaluation results at these temperatures are shown below. Figure 6 and Figure 7 As shown, from Figure 6 and Figure 7 As can be seen, with the increase of temperature, both the conversion rate of n-hexane and the yield of diene are improved. The conversion rate of n-hexane and the yield of diene of H-ZSM-5-R (8.0%) zeolite catalyst are slightly higher than those of conventional H-Ref zeolite.

[0113] At atmospheric pressure, the mass hourly space velocity is 4.2 h⁻¹. -1 The evaluation results at different reaction times when the reaction temperature is 550℃ are shown in the figure. Figure 8 and Figure 9 As shown, from Figure 8 and Figure 9 It can be seen that the hexane conversion rates of H-ZSM-5-R (8.0%) zeolite catalyst and conventional H-Ref zeolite are similar, but the diene yield of H-ZSM-5-R (8.0%) zeolite catalyst is higher than that of conventional H-Ref zeolite.

[0114] In summary, as demonstrated by Test Examples 1 and 2, the core of the preparation method provided in this invention is the use of guar gum as an additive, primarily for thickening and limiting mass transfer of materials, thereby restricting zeolite growth, i.e., limiting crystal growth. This preparation method replaces traditional expensive template agents in the synthesis of ZSM-5 zeolite and controls the addition ratio of guar gum through a seed-induced crystal method to obtain short b-axis ZSM-5 zeolite with high yield, high crystallinity, and low cost.

[0115] Compared with existing conventional ZSM-5 zeolite preparation methods, the ZSM-5 zeolite prepared by the method of this invention has a shorter b-axis thickness, higher crystallinity, higher product yield, and excellent molecular diffusion properties. When the ZSM-5 zeolite obtained by this invention is used as a catalyst for the catalytic cracking of low-carbon hydrocarbons to olefins, it exhibits high catalytic activity and high catalytic activity stability.

[0116] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A method for preparing short b-axis ZSM-5 zeolite, characterized in that, The preparation method includes: Step (1): Mix the seed crystals, guar gum, sodium hydroxide and water evenly; Step (2): Add aluminum source and dissolve it; Step (3): Add the silicon source and mix it evenly to obtain a gel; Step (4): The gel is crystallized, the crystallized product is cooled and separated and washed with water until neutral, and then dried and calcined to obtain Na-ZSM-5 zeolite; Step (5): Ion exchange and calcination of Na-ZSM-5 zeolite to obtain H-ZSM-5 zeolite, namely short b-axis ZSM-5 zeolite; The molar ratio of sodium hydroxide, aluminum source, silicon source and water, calculated as Na2O, Al2O3, SiO2 and H2O, is (5-15):(0.5-5):(50-100):(500-2200); the amounts of seed crystals and guar gum are 1-5% and 1-20% of the mass of SiO2, respectively.

2. The preparation method according to claim 1, characterized in that, The method for preparing the seed crystals includes: The template agent and water are mixed and stirred evenly; the silicon source is added and stirring is continued until dissolved to obtain a gel; the gel is crystallized, the crystallized product is cooled and separated and washed with water until neutral, and then dried and calcined to obtain seed crystals.

3. The preparation method according to claim 1, characterized in that, In step (2), the aluminum source includes one or a combination of aluminum hydroxide, aluminum sulfate and sodium aluminate; and / or the silicon source includes one or a combination of silica sol, silica fume and solid silica gel.

4. The preparation method according to claim 1, characterized in that, In step (4), the crystallization treatment is carried out at a temperature of 140-180℃ for 2-5 days.

5. The preparation method according to claim 1 or 4, characterized in that, In step (4), the crystallization process is either static crystallization or dynamic crystallization.

6. The preparation method according to claim 1 or 4, characterized in that, In step (4), the drying process involves drying at 80-120°C overnight.

7. The preparation method according to claim 1 or 4, characterized in that, In step (4), the roasting temperature is 500-600℃ and the time is 6-10h.

8. The preparation method according to claim 1, characterized in that, In step (5), the ion exchange is carried out using NH4Cl solution.

9. The preparation method according to claim 8, characterized in that, In step (5), the amount of Na-ZSM-5 zeolite and NH4Cl solution used is: 1-2g of Na-ZSM-5 zeolite for every 100mL of NH4Cl solution.

10. The preparation method according to any one of claims 1, 8-9, characterized in that, In step (5), the temperature of the ion exchange is 60-80℃.

11. A short-b-axis ZSM-5 zeolite prepared by the method for preparing a short-b-axis ZSM-5 zeolite according to any one of claims 1 to 10, having a silica-alumina ratio of 10 to 100, a micropore volume of 0.05 to 0.20 cm3 / g, a specific surface area of 200 to 500 m2 / g, and an average b-axis thickness of 50 to 100 nm. 3 2 / g, a specific surface area of 200 to 500 m2 / g, and an average b-axis thickness of 50 to 100 nm.​ 12. The application of the short b-axis ZSM-5 zeolite as described in claim 11 as a catalyst for the catalytic cracking of low-carbon hydrocarbons to olefins.

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