A method for preparing hierarchical porous molecular sieves by dynamic regulation

Abstract

This invention discloses a kinetically controlled method for preparing hierarchical porous molecular sieves, belonging to the field of catalyst preparation technology. It employs a two-step crystallization method: first, nucleation occurs at low and ultra-low H2O / SiO2 molar ratios; then, after the low-temperature phase, water is added, followed by rapid growth at high temperature and high H2O / SiO2 molar ratios. The solid-phase and liquid-phase crystallization mechanisms in the synthesis system work in succession to prepare hierarchical molecular sieves. This invention, without adding any mesoporous pore-forming agents, only modulates the crystallization temperature and the H2O / SiO2 molar ratio of the synthesis system to kinetically control the crystallization mechanism, resulting in molecular sieves with higher catalytic performance than those obtained using traditional methods. Furthermore, it overcomes the drawbacks of traditional hierarchical porous molecular sieve preparation processes, such as high cost, high calcination energy consumption, poor mesopore connectivity, and severe contamination from pore-forming agents.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology and relates to a method for preparing hierarchical porous molecular sieves by kinetic regulation; specifically, it is a method for preparing hierarchical porous molecular sieves under conditions without mesoporous pore-forming agents. Background Technology

[0002] Molecular sieves, due to their unique pore structure, good shape selectivity, thermal and hydrothermal stability, and tunable acid properties, are widely used as acid catalysts in various petrochemical and fine chemical processes, such as catalytic cracking, hydrocracking, isomerization, alkylation, catalytic oxidation, and methanol conversion to olefins or gasoline. However, the inherent micropores (generally less than 2 nm) of molecular sieves severely restrict diffusion, leading to a significant reduction in the catalytic performance of traditional molecular sieves. Studies have shown that in most catalytic reactions (especially those involving macromolecules), the external active sites of molecular sieves are fully utilized due to the internal diffusion control of reactants, while the utilization rate of internal active sites is low (Chemical Society Reviews, 2015, 44(24): 8877-8903). To address this problem, one of the most common solutions researchers have developed is to introduce mesopores into microporous molecular sieves to prepare hierarchical porous molecular sieves, thereby compensating for the diffusion difficulties of reactants and products within the molecular sieve.

[0003] Over the past two decades, methods for preparing hierarchical porous molecular sieves have mainly included soft template methods, hard template methods, and post-treatment methods. Soft template methods involve adding surfactants to the synthesis system; however, surfactants are expensive and may be toxic. Hard template methods mainly involve adding materials such as carbon black and carbon nanotubes to the synthesis system. These hard template materials, besides having low water solubility and low utilization during synthesis, also lead to poor mesopore connectivity in the prepared hierarchical porous molecular sieves. Furthermore, post-treatment methods use acid or alkaline solutions to destroy the silica and alumina species in the molecular sieve framework, with the detached silica and alumina species sites forming intracrystalline mesopores. However, these methods are cumbersome and generate large amounts of wastewater, reducing molecular sieve yield. Therefore, how to synthesize hierarchical porous molecular sieves in a green, one-step process remains a significant challenge.

[0004] Growth kinetics control is a common strategy for the green synthesis of hierarchical porous molecular sieves. Zhang Qiang (dissertation from Jilin University, "Synthesis and Catalytic Performance Study of Single-Crystal Nano / Hierarchical Porous ZSM-5 and Beta Molecular Sieves") points out that molecular sieve growth kinetics refers to effectively controlling the diffusion rate and aggregation mode of atoms, clusters, and nanoparticles by changing parameters such as the type of raw materials, the properties and amount of template agent, the amount of water and alkalinity in the synthesis system, the crystallization temperature and time, and whether seed crystals are added, ultimately achieving the goal of controlling the crystal nucleation and growth process. One approach is to use segmented crystallization to reduce the particle size of the molecular sieve product, preparing a hierarchical molecular sieve. For example, patent CN107055568 A proposes a method for synthesizing ZSM-5 molecular sieves at varying temperatures. The prepared synthetic gel is first crystallized at 80-110 ℃ for 10-20 hours; then the temperature is raised to 115-130 ℃ for crystallization for 10-40 hours. The synthesized molecular sieve powder has a narrow crystal size distribution (0.9-1.1 μm). Patent CN104495869 B provides a method for preparing small-grained ZSM-35 molecular sieves. This method includes the following steps: mixing silicon source, aluminum source, alkali source, template agent, and water evenly to obtain a colloidal solution, wherein the molar ratio of each component is: SiO2 / Al2O3 = 18.5-28.6, template agent / SiO2 = 0.81-1.25, OH... - The ratio of SiO2 / SiO2 is 0.03-0.18, and the ratio of H2O / SiO2 is 10-26. The colloidal solution is first crystallized at 15-80℃ for 5-30 hours, and then crystallized again at 150-200℃ for 10-30 hours. After filtration, washing, and drying, the small-crystal ZSM-35 molecular sieve is obtained. This preparation method uses inexpensive ethylenediamine as a template agent, and controls the crystallization process by adding seed crystals and two-stage crystallization to synthesize small-crystal ZSM-35 molecular sieves with a minimum crystal size of about 0.5μm. Patent CN104495869B proposes to pre-crystallize the synthesized gel at 60-90℃ for 1-24 hours, then pre-crystallize at 100-120℃ for 1-48 hours, and finally crystallize at 150℃-200℃ for 24-192 hours. In addition to the micropores of the zeolite structure, the synthesized sample also has intercrystalline and intracrystalline mesoporous structures, with the primary nanocrystal particles having a size of 40-500 nm and the secondary stacked particles having a size of 500 nm-5 μm.

[0005] On the other hand, reducing the water-to-silica ratio in the synthesis system can also reduce the particle size of the product and form a large number of mesopores (Chemical Engineering Journal 291 (2016) 82–93). However, in industrial production, low water-to-silica ratio synthesis systems are difficult to stir, which can easily lead to uneven heat and mass transfer, thus affecting the crystallinity of the product and forming a large number of defect sites. In catalysts supported by molecular sieves, a large number of defect sites can have some adverse effects, such as the formation of carbon deposits, leading to a decrease in catalyst lifetime (Chem. Soc. Rev., 2021, 50, 11156–11179). To this end, this invention adopts a strategy of explosive nucleation under low temperature and low water-to-silica ratio conditions and crystallization growth under high temperature and high water-to-silica ratio conditions to prepare hierarchical porous molecular sieves. Summary of the Invention

[0006] This invention overcomes the shortcomings of existing technologies and proposes a method for preparing hierarchical porous molecular sieves through kinetic regulation. This addresses the problem of using mesoporous pore-forming agents in traditional synthesis systems for preparing hierarchical porous molecular sieves.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] A method for preparing hierarchical porous molecular sieves by kinetic control involves mixing raw materials for preparing molecular sieves, and then performing low-temperature crystallization at a low temperature range of 60 ℃-120 ℃ with an H2O / SiO2 molar ratio of 1-3 to promote explosive nucleation. Then, water is added, and high-temperature crystallization is performed at a high temperature range of 140 ℃-220 ℃ with an H2O / SiO2 molar ratio of 15-50 to rapidly grow the multi-hierarchical porous molecular sieve.

[0009] Preferably, the low temperature range is 80 ℃-100 ℃.

[0010] Preferably, the high temperature range is 140 ℃-180 ℃.

[0011] Even better, the corresponding H2O / SiO2 molar ratio at high temperatures is 20-30.

[0012] The molecular sieves are silica-alumina molecular sieves, phosphorus-alumina molecular sieves, or heteroatom zeolites. Common silica-alumina molecular sieves include ZSM-5, ZSM-11, ZSM-12, mordenite, Y-type molecular sieves, type A molecular sieves, Beta molecular sieves, SSZ-13, ZSM-48, SSZ-39, EU-1, and MCM-22 molecular sieves; phosphorus-alumina molecular sieves include SAPO-31, SAPO-18, and SAPO-34; and heteroatom zeolites include TS-1, TS-2, Ti-Beta, B-ZSM-5, Fe-ZSM-5, and Ga-ZSM-5 molecular sieves. ZSM-5, Beta, EU-1, MCM-22, and Silicalite-1 molecular sieves are preferred.

[0013] Preferably, the raw materials for the molecular sieve include silicon source, aluminum source, NaOH, and organic template agent.

[0014] The silicon source is one of silica gel, silica sol, water glass, fumed silica, tetraethyl orthosilicate, and methyl orthosilicate. Silica gel, fumed silica, and tetraethyl orthosilicate are preferred.

[0015] The aluminum sources for molecular sieve synthesis include sodium aluminate, boehmite, amorphous aluminum hydroxide, and aluminum isopropoxide. Among these, sodium aluminate and boehmite are preferred.

[0016] Organic templates for molecular sieves are the most reported organic compounds. The organic templates used in the synthesis of ZSM-5 molecular sieve are tetrapropylammonium bromide, those for Beta molecular sieve are tetraethylammonium bromide, those for EU-1 molecular sieve are hexamethyldiammonium bromide, those for MCM-22 molecular sieve are hexamethyleneimine, those for TS-1 molecular sieve are tetrapropylammonium bromide, and those for Silicalite-1 molecular sieve are tetrapropylammonium bromide.

[0017] More preferably, the NaOH / SiO2 molar ratio is in the range of 0.05-0.5, with a preferred range of 0.1-0.3; the R / SiO2 molar ratio is in the range of 0.01-0.2, where R represents an organic template agent; and the SiO2 / Al2O3 molar ratio is ≥30, preferably 30-100.

[0018] More preferably, it also includes seed crystals, wherein the amount of seed crystals added is 0-10% of the mass fraction of the silicon source, wherein 0-5% is preferred.

[0019] The seed crystal can be in the form of a solid seed crystal or a seed crystal solution. The solid seed crystal can be a seed crystal that has not undergone high-temperature calcination to remove the template agent, or a seed crystal that has undergone high-temperature calcination to remove the template agent. Among these, solid seed crystals that have undergone high-temperature calcination to remove the template agent are preferred.

[0020] The preferred seed crystal is a homogeneous seed crystal that has the same crystal form as the product.

[0021] The catalysts prepared from the aforementioned molecular sieves can be used in methanol-to-olefins, methanol-to-propylene, xylene isomerization, ethylbenzene ethylation to p-diethylbenzene, trimethylbenzene isomerization, naphthalene methylation, catalytic cracking, catalytic diesel hydrocracking to BTX, benzene-ethylene alkylation to ethylbenzene, toluene-methanol alkylation, toluene disproportionation, cyclohexanone oximeation, propane dehydrogenation to propylene, and the Beckmann rearrangement. Among these, xylene isomerization, catalytic diesel hydrocracking to BTX and benzene, cyclohexanone oximeation and ethylene alkylation to ethylbenzene, propane dehydrogenation to propylene, and the Beckmann rearrangement are preferred.

[0022] The beneficial effects of this invention compared to the prior art are as follows:

[0023] (1) This invention successfully prepared several hierarchical porous molecular sieve structures by adjusting the crystallization temperature and the H2O / SiO2 molar ratio of the gel without adding mesoporous pore-forming agents. This method does not require the addition of mesoporous pore-forming agents in the synthesis system, thereby reducing the preparation cost of hierarchical porous molecular sieves and making it more environmentally friendly; at the same time, it does not require high-temperature removal of the mesoporous template agent in the later stage, which greatly reduces energy consumption. This method adopts a two-step crystallization method. First, nucleation occurs under low temperature and ultra-low H2O / SiO2 molar ratio conditions. Then, after the low temperature is completed, water is added, and rapid growth is carried out under high temperature and high H2O / SiO2 molar ratio conditions to prepare hierarchical molecular sieves.

[0024] (2) Because the hierarchical porous molecular sieve prepared by this method has good interconnectivity, it improves the diffusion performance of reactants and products. Therefore, the hierarchical porous molecular sieve catalyst prepared by this method exhibits high activity and low side reactions in the corresponding catalytic reactions.

[0025] (3) Because this method combines the solid-phase transformation and liquid-phase transformation crystallization mechanisms in the molecular sieve preparation process, it overcomes the shortcomings of a single mechanism. The prepared hierarchical porous molecular sieve product has relatively perfect crystallization and few defect sites. However, in the catalytic reaction process, the molecular sieve defect sites are prone to carbon deposition and other problems during long-term operation, which reduces its stability. Therefore, the molecular sieve catalyst prepared by this method has good stability. Attached Figure Description

[0026] Figure 1The XRD patterns of the hierarchical porous ZSM-5 molecular sieves prepared in Comparative Example 1 and Examples 1-2 are shown. As can be seen from the figures, the ZSM-5 molecular sieve samples prepared by this method exhibit a pure-phase MFI topology and good crystallinity.

[0027] Figure 2 SEM images of the hierarchical porous ZSM-5 molecular sieves prepared in Comparative Example 1 and Examples 1-2 are shown. As can be seen from the figures, the ZSM-5 molecular sieve samples prepared by this method have smaller particle sizes compared to samples prepared by the conventional method.

[0028] Figure 3 The figures show the external specific surface area data of the hierarchical porous ZSM-5 molecular sieves prepared in Comparative Example 1 and Examples 1-2. As can be seen from the figures, the ZSM-5 molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0029] Figure 4 The XRD patterns of the hierarchical porous EU-1 molecular sieves prepared in Comparative Example 2 and Examples 3-4 are shown. As can be seen from the figures, the EU-1 molecular sieve samples prepared by this method exhibit a pure-phase EUO topology and good crystallinity.

[0030] Figure 5 SEM images of the hierarchical porous EU-1 molecular sieves prepared in Comparative Example 2 and Examples 3-4 are shown. As can be seen from the figures, the EU-1 molecular sieve samples prepared by this method have smaller particle sizes compared to samples prepared by conventional methods.

[0031] Figure 6 The figures show the external specific surface area data of the hierarchical porous EU-1 molecular sieves prepared in Comparative Example 2 and Examples 3-4. As can be seen from the figures, the EU-1 molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0032] Figure 7 The XRD patterns of the hierarchical porous Beta molecular sieves prepared in Comparative Example 3 and Examples 5-6 are shown. As can be seen from the figures, the Beta molecular sieve samples prepared by this method exhibit a pure-phase BEA topology and good crystallinity.

[0033] Figure 8 SEM images of the hierarchical porous Beta molecular sieves prepared in Comparative Example 3 and Examples 5-6 are shown. As can be seen from the figures, the Beta molecular sieve samples prepared by this method have smaller particle sizes compared to those prepared by conventional methods.

[0034] Figure 9 The figures show the external specific surface area data of the hierarchical porous Beta molecular sieves prepared in Comparative Example 3 and Examples 5-6. As can be seen from the figures, the Beta molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0035] Figure 10The XRD patterns of the hierarchical porous MCM-22 molecular sieves prepared in Comparative Example 4 and Examples 7-8 are shown in the figures. As can be seen from the figures, the MCM-22 molecular sieve samples prepared by this method exhibit a pure-phase MWW topology and good crystallinity.

[0036] Figure 11 SEM images of the hierarchical porous MCM-22 molecular sieves prepared in Comparative Example 4 and Examples 7-8 are shown. As can be seen from the figures, the MCM-22 molecular sieve samples prepared by this method have smaller particle sizes compared to samples prepared by conventional methods.

[0037] Figure 12 The figure shows the external specific surface area data of the hierarchical porous MCM-22 molecular sieves prepared in Comparative Example 4 and Examples 7-8. As can be seen from the figure, the MCM-22 molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0038] Figure 13 The XRD patterns of the hierarchical porous TS-1 molecular sieves prepared in Comparative Example 5 and Examples 9-10 are shown. As can be seen from the figures, the TS-1 molecular sieve samples prepared by this method exhibit a pure-phase MFI topology and good crystallinity.

[0039] Figure 14 SEM images of the hierarchical porous TS-1 molecular sieves prepared in Comparative Example 5 and Examples 9-10 are shown. As can be seen from the figures, the TS-1 molecular sieve samples prepared by this method have smaller particle sizes compared to samples prepared by conventional methods.

[0040] Figure 15 The figures show the external specific surface area data of the hierarchical porous TS-1 molecular sieves prepared in Comparative Example 5 and Examples 9-10. As can be seen from the figures, the TS-1 molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0041] Figure 16 The conversion data of the hierarchical porous TS-1 molecular sieves prepared in Comparative Example 5 and Examples 9-10 are shown in the figure.

[0042] Figure 17 Selectivity data for the hierarchical porous TS-1 molecular sieves prepared in Comparative Example 5 and Examples 9-10.

[0043] Figure 18 The XRD patterns are shown for the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12. As can be seen from the figures, the Silicalite-1 molecular sieve samples prepared by this method exhibit a pure-phase MFI topology and good crystallinity.

[0044] Figure 19SEM images of the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12 are shown. As can be seen from the figures, the Silicalite-1 molecular sieve samples prepared by this method have smaller particle sizes compared to samples prepared by conventional methods.

[0045] Figure 20 The figure shows the external specific surface area data of the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12. As can be seen from the figure, the Silicalite-1 molecular sieve samples prepared by this method have a larger external surface area compared to samples prepared by the conventional method.

[0046] Figure 21 Beckmann rearrangement conversion performance data for the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12.

[0047] Figure 22 Beckmann rearrangement selection performance data for the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12.

[0048] Figure 23 Propane dehydrogenation conversion data for the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12.

[0049] Figure 24 Propane dehydrogenation selectivity data for the hierarchical porous Silicalite-1 molecular sieves prepared in Comparative Example 6 and Examples 11-12. Detailed Implementation

[0050] To make the technical problems to be solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail with reference to the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The technical solutions of this invention are described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection is not limited thereto.

[0051] Example 1

[0052] A kinetically controlled method for preparing hierarchical porous ZSM-5 molecular sieves: Sodium hydroxide is added to water, followed by tetrapropylammonium bromide (TPABr) and sodium aluminate. The mixture is stirred for 5 minutes, then silica gel is added. The initial molar ratio of the gel is SiO2:0.033 Al2O3:0.1 NaOH:0.15 TPABr:1H2O. Crystallization is carried out at 100℃ for 1 day. After low-temperature crystallization, deionized water is added to the reactor to achieve a molar ratio of SiO2:0.033 Al2O3:0.1 NaOH:0.15 TPABr:30H2O. Crystallization is then carried out at 180℃ for 1 day. After crystallization, the mixture is rapidly cooled, dried, and calcined to obtain ZSM-5 molecular sieve, denoted as Z-1.

[0053] Example 2

[0054] A kinetically controlled method for preparing hierarchical porous ZSM-5 molecular sieves: Sodium hydroxide is added to water, followed by tetrapropylammonium bromide (TPABr) and boehmite. The mixture is stirred for 5 minutes, then silica gel is added. The initial molar ratio of the gel is SiO2: 0.01Al2O3: 0.1NaOH: 0.15TPABr: 2H2O. Crystallization is carried out at 100℃ for 1 day. After low-temperature crystallization, deionized water is added to the reactor to achieve a molar ratio of SiO2: 0.01Al2O3: 0.1NaOH: 0.15TPABr: 20H2O. Crystallization is then carried out at 180℃ for 1 day. After crystallization, the mixture is rapidly cooled, dried, and calcined to obtain ZSM-5 molecular sieve, denoted as Z-2.

[0055] Example 3

[0056] A kinetically controlled preparation method for hierarchical porous EU-1 molecular sieves: Sodium hydroxide was added to water, followed by hexamethyl diammonium bromide (HMBr) and sodium aluminate. The mixture was stirred for 5 min, then silica gel and 5% seed crystals (relative to the mass fraction of the silicon source) were added. The initial molar ratio of the gel was SiO2: 0.033Al2O3: 0.3NaOH: 0.05HMBr: 2H2O. Crystallization was carried out at 100℃ for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve the desired molar ratio of SiO2: 0.033Al2O3: 0.3NaOH: 0.05HMBr: 25H2O. Crystallization was then carried out at 170℃ for 2 days. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the EU-1 molecular sieve, denoted as E-1.

[0057] Example 4

[0058] A kinetically controlled preparation method for hierarchical porous EU-1 molecular sieves: Sodium hydroxide was added to water, followed by hexamethyl diammonium bromide (HMBr) and sodium aluminate. The mixture was stirred for 5 min, then silica gel and 1% seed crystals (relative to the mass fraction of the silicon source) were added. The initial molar ratio of the gel was SiO2: 0.033Al2O3: 0.3NaOH: 0.05HMBr: 3H2O. Crystallization was carried out at 100℃ for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve a molar ratio of SiO2: 0.033Al2O3: 0.3NaOH: 0.05HMBr: 20H2O. Crystallization was then carried out at 180℃ for 2 days. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the EU-1 molecular sieve, denoted as E-2.

[0059] Example 5

[0060] A kinetically controlled preparation method for hierarchical porous Beta molecular sieves: Sodium hydroxide was added to water, followed by tetraethylammonium bromide (TEABr) and boehmite. The mixture was stirred for 5 min, then silica gel and 1% seed crystals (relative to the mass fraction of the silicon source) were added. The initial molar ratio of the gel was SiO2: 0.033 Al2O3: 0.2 NaOH: 0.1 TEABr: 1 H2O. Crystallization was carried out at 100℃ for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve the desired molar ratio of SiO2: 0.033 Al2O3: 0.2 NaOH: 0.1 TEABr: 30 H2O. Crystallization was carried out at 180℃ for 1 day. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the Beta molecular sieve, denoted as B-1.

[0061] Example 6

[0062] A kinetically controlled preparation method for hierarchical porous Beta molecular sieves: Sodium hydroxide was added to water, followed by tetraethylammonium bromide (TEABr) and boehmite. The mixture was stirred for 5 min, then silica gel and 2% seed crystals (relative to the mass fraction of the silicon source) were added. The initial molar ratio of the gel was SiO2: 0.01 Al2O3: 0.2 NaOH: 0.15 TEABr: 2H2O. Crystallization was carried out at 100 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve a molar ratio of SiO2: 0.01 Al2O3: 0.2 NaOH: 0.15 TEABr: 25H2O. Crystallization was carried out at 180 °C for 1 day. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the Beta molecular sieve, denoted as B-2.

[0063] Example 7

[0064] A kinetically controlled preparation method for hierarchical porous MCM-22 molecular sieves: Sodium hydroxide was added to water, followed by hexamethyleneimine (HMI) and boehmite. The mixture was stirred for 5 minutes, then silica gel was added. The initial molar ratio of the gel was SiO2: 0.033 Al2O3: 0.25 NaOH: 0.15 HMI: 1 H2O. Crystallization was carried out at 90 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve a molar ratio of SiO2: 0.033 Al2O3: 0.25 NaOH: 0.15 HMI: 20H2O. Crystallization was carried out at 180 °C for 1 day. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the MCM-22 molecular sieve, denoted as M-1.

[0065] Example 8

[0066] A kinetically controlled preparation method for hierarchical porous MCM-22 molecular sieves: Sodium hydroxide was added to water, followed by hexamethyleneimine (HMI) and boehmite. The mixture was stirred for 5 minutes, then silica gel was added. The initial molar ratio of the gel was SiO2: 0.033Al2O3: 0.25NaOH: 0.15HMI: 2H2O. Crystallization was carried out at 100 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve the desired molar ratio of SiO2: 0.033Al2O3: 0.25NaOH: 0.15HMI: 25H2O. Crystallization was then carried out at 180 °C for 1 day. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the MCM-22 molecular sieve, denoted as M-2.

[0067] Example 9

[0068] A kinetically controlled preparation method for hierarchical porous TS-1 molecular sieve: Tetraethyl orthosilicate was added to tetrapropylammonium bromide, followed by tetraethyl titanate. After stirring for 30 min, ethanol was removed by distillation at 60 °C for 3 h. After ethanol removal, water was added to make the molar ratio of the entire gel system SiO2: 0.02TiO2: 0.2TPABr: 3H2O, and the system was crystallized at 100 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to make the molar ratio of the system SiO2: 0.02TiO2: 0.2TPABr: 10H2O, and the system was crystallized at 170 °C for 3 days. After crystallization, the system was rapidly cooled, dried, and calcined to obtain TS-1 molecular sieve, denoted as T-1.

[0069] Example 10

[0070] A kinetically controlled preparation method for hierarchical porous TS-1 molecular sieve: Tetraethyl orthosilicate was added to tetrapropylammonium bromide, followed by tetraethyl titanate. After stirring for 30 min, ethanol was removed by distillation at 60 °C for 3 h. After ethanol removal, water was added to make the molar ratio of the entire gel system SiO2: 0.02 TiO2: 0.2 TPABr: 2H2O, and the system was crystallized at 100 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to make the molar ratio of the system SiO2: 0.02 TiO2: 0.2 TPABr: 30H2O, and the system was crystallized at 170 °C for 3 days. After crystallization, the system was rapidly cooled, dried, and calcined to obtain TS-1 molecular sieve, denoted as T-2.

[0071] Example 11

[0072] A kinetically controlled preparation method for hierarchical porous Silicalite-1 molecular sieves: Sodium hydroxide was added to water, followed by silica gel, sodium aluminate, and tetrapropylammonium bromide, which were then mixed. The initial molar ratio of the gel was SiO2:0.033Al2O3:0.25NaOH:0.15TPABr:1H2O. Crystallization was carried out at 90 °C for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve the desired molar ratio of SiO2:0.033Al2O3:0.25NaOH:0.15TPABr:25H2O. Crystallization was then carried out at 170 °C for 3 days. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the Silicalite-1 molecular sieve, denoted as S-1.

[0073] Example 12

[0074] A kinetically controlled preparation method for hierarchical porous Silicalite-1 molecular sieves: Sodium hydroxide was added to water, followed by silica gel, sodium aluminate, and tetrapropylammonium bromide, which were then mixed. The initial molar ratio of the gel was SiO2: 0.033Al2O3: 0.25NaOH: 0.15TPABr: 2H2O. Crystallization was carried out at 90℃ for 1 day. After low-temperature crystallization, deionized water was added to the reactor to achieve a molar ratio of SiO2: 0.033Al2O3: 0.25NaOH: 0.15TPABr: 40H2O. Crystallization was then carried out at 170℃ for 3 days. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain the Silicalite-1 molecular sieve, denoted as S-2.

[0075] Comparative Example 1

[0076] Preparation of traditional ZSM-5 molecular sieve: Sodium hydroxide was added to water, followed by tetrapropylammonium bromide (TPABr) and sodium aluminate. The mixture was stirred for 5 minutes, and then silica gel was added. The initial molar ratio of the gel was SiO2:0.033 Al2O3:0.1 NaOH:0.2 TPABr:30 H2O. The mixture was crystallized at 180℃ for 1 day. After crystallization, it was rapidly cooled, dried, and calcined to obtain ZSM-5 molecular sieve, denoted as Z-0.

[0077] Comparative Example 2

[0078] Preparation of traditional EU-1 molecular sieve: Sodium hydroxide is added to water, followed by hexamethyl diammonium bromide (HMBr) and sodium aluminate. The mixture is stirred for 5 minutes, then silica gel and 5% seed crystals (relative to the mass fraction of the silicon source) are added. The initial molar ratio of the gel is SiO2: 0.033Al2O3: 0.3NaOH: 0.05HMBr: 30H2O. The mixture is crystallized at 170 ℃ for 2 days. After crystallization, it is rapidly cooled, dried, and calcined to obtain the EU-1 molecular sieve, denoted as E-0.

[0079] Comparative Example 3

[0080] Preparation of traditional Beta molecular sieves: Sodium hydroxide is added to water, followed by tetraethylammonium bromide (TEABr) and boehmite. The mixture is stirred for 5 minutes, then silica gel and 1% seed crystals (relative to the mass fraction of the silicon source) are added. The initial molar ratio of the gel is SiO2: 0.033Al2O3: 0.2NaOH: 0.1TEABr: 30H2O. The mixture is crystallized at 140 ℃ for 2 days. After crystallization, it is rapidly cooled, dried, and calcined to obtain the Beta molecular sieve, denoted as B-0.

[0081] Comparative Example 4

[0082] Preparation of traditional MCM-22 molecular sieve: Sodium hydroxide was added to water, followed by hexamethyleneimine (HMI) and boehmite. The mixture was stirred for 5 minutes, and then silica gel was added. The initial molar ratio of the gel was SiO2:0.033Al2O3:0.25NaOH:0.30HMI:30H2O. The mixture was crystallized at 180 ℃ for 1 day. After crystallization, it was rapidly cooled, dried, and calcined to obtain the MCM-22 molecular sieve, denoted as M-0.

[0083] Comparative Example 5

[0084] Preparation of traditional TS-1 molecular sieve: Tetraethyl orthosilicate was added to tetrapropylammonium bromide, followed by tetraethyl titanate. After stirring for 30 minutes, ethanol was removed by distillation at 60 °C for 3 hours. After alcohol removal, water was added to make the molar ratio of the entire gel system SiO2: 0.02TiO2: 0.2TPABr: 10 H2O. The mixture was crystallized at 170 °C for 3 days. After crystallization, the mixture was rapidly cooled, dried, and calcined to obtain TS-1 molecular sieve, denoted as T-0.

[0085] Comparative Example 6

[0086] Preparation of traditional Silicalite-1 molecular sieve: Sodium hydroxide is added to water, followed by silica gel, sodium aluminate, and tetrapropylammonium bromide, and then mixed. The initial molar ratio of the gel is SiO2: 0.033 Al2O3: 0.25 NaOH: 0.15 TPABr: 25 H2O. Crystallization is carried out at 170 ℃ for 3 days. After crystallization, the gel is rapidly cooled, dried, and calcined to obtain Silicalite-1 molecular sieve, denoted as S-0.

[0087] To verify the catalytic performance of the molecular sieves prepared in this invention, various characteristic reactions were selected as specific application examples, as follows:

[0088] Catalyst performance test example 1

[0089] The catalytic performance of the ZSM-5 molecular sieve-based catalyst for the deethylation isomerization of ethylbenzene was tested. The reactants consisted of 7.0% ethylbenzene and 93.0% m-xylene by mass. Before the catalytic performance test, the molecular sieve sample was loaded with 0.05% Pt, preparing a catalyst containing both acidic and metal centers for the deethylation isomerization of ethylbenzene. The catalytic performance of Comparative Example 1 and Examples 1-2 was tested, and the specific results are shown in Table 1.

[0090] The conditions for testing the catalyst's catalytic performance were as follows: reaction temperature, 370 ℃; reaction pressure, 0.8 MPa; space velocity, 8.0 h⁻¹. -1 The hydrogen-to-hydrogen molar ratio was 2.0. After 24 hours of reaction, the liquid reaction product was analyzed by gas chromatography. Catalytic performance parameters included ethylbenzene conversion rate X. EB and isomerization activity S PX Its definition is as follows: X EB =(1-w EB / w EB,0 )×100%, S PX =w PX / w ΣX ×100% Where, w EB w PX and w ΣXw represents the mass fraction of ethylbenzene, p-xylene, and total xylene in the liquid product, respectively. EB,0 This indicates the mass fraction of ethylbenzene in the feedstock oil.

[0091] As can be seen from Table 1, the ethylbenzene conversion rate of the synthesized samples in Example 1 is higher than that of Comparative Example 1.

[0092]

[0093] Catalyst performance test example 2

[0094] The catalyst prepared using EU-1 molecular sieve was used for catalytic performance testing of xylene isomerization. To verify the catalytic performance of the xylene isomerization prepared in Examples 3-4 (the evaluation method of the catalyst was based on XF Li et al. Chinese Journal of Chemical Engineering 24 (2016) 1577–1583), 15.0% ethylbenzene and 85.0% m-xylene were used as reactants, and the catalytic performance of the samples was tested. The results are shown in Table 2.

[0095] The conditions for testing the catalytic performance of the catalyst were: reaction temperature, 360 ℃; reaction pressure, 0.5 MPa; space velocity, 4.5 h⁻¹. -1 The hydrogen-to-hydrocarbon molar ratio was 2.0. After 3 hours of reaction, the liquid reaction product was analyzed by gas chromatography. The catalytic performance parameter showed isomerization activity. PX =w PX / w ΣX ×100%, w PX and w ΣX These represent the mass fractions of p-xylene and total xylene in the liquid product, respectively.

[0096]

[0097] Catalyst performance test example 3

[0098] The catalyst prepared from Beta molecular sieves was used for catalytic performance testing in the liquid-phase alkylation of benzene and ethylene. To verify the catalytic performance of the hierarchical porous Beta molecular sieve synthesized in this invention, the alkylation reaction of benzene and ethylene was used as a probe reaction. The catalytic data for samples from Comparative Example 3, Example 5, and Example 6 are shown in Table 3. (Reaction conditions: reaction temperature, 250 °C; reaction pressure, 3 MPa; space velocity, 13.3 h⁻¹) -1 The benzene-to-benzene ratio was 4.16. After 6 hours of reaction, samples were taken and analyzed by gas chromatography. The ethylbenzene selectivity was calculated as: (ethylbenzene content in the hydrocarbonation solution / (100 - benzene content in the hydrocarbonation solution)) × 100%.

[0099]

[0100] Catalyst performance test example 4

[0101] The catalyst prepared using MCM-22 molecular sieve was tested for its catalytic performance in the liquid-phase alkylation of benzene and ethylene. To verify the catalytic performance of the hierarchical porous MCM-22 molecular sieve synthesized in this invention, the alkylation reaction of benzene and ethylene was used as a probe reaction. The catalytic data for samples from Comparative Example 4, Example 7, and Example 8 are shown in Table 4. (Reaction conditions: reaction temperature, 250℃; reaction pressure, 3 MPa; space velocity, 13.3 h⁻¹) -1 The benzene-to-benzene ratio was 4.16. After 6 hours of reaction, samples were taken and analyzed by gas chromatography. The ethylbenzene selectivity was calculated as: (ethylbenzene content in the hydrocarbonation solution / (100 - benzene content in the hydrocarbonation solution)) × 100%.

[0102]

[0103] Catalyst performance test example 5

[0104] The catalytic performance of the TS-1 molecular sieve in this invention was tested by cyclohexanone ammoniation oxime. The reaction temperature was 76 °C, tert-butanol was used as the solvent, the volume ratio of tert-butanol to cyclohexanone was 3.4:1, the molar ratio of cyclohexanone:ammonia:hydrogen peroxide was 1:2.3:1.05, and the amount of catalyst used was 1.8% (mass fraction). The catalytic performance mainly included the conversion rate of cyclohexanone and the selectivity of cyclohexanone oxime. The specific calculations and evaluations were based on the literature: Industrial Catalysis, 2018, 26(5):83-88. The catalytic data of Comparative Example 5, Example 9, and Example 10 are attached. Figure 16 and 17 .

[0105] Catalyst performance test example 6

[0106] The catalytic performance of the Silicalite-1 molecular sieve in this invention was tested using a gas-phase Beckmann rearrangement reaction. First, activation was performed at 350 °C for 1 hour, followed by a temperature reduction to 300 °C. A 5 wt% toluene solution of cyclohexanone oxime was used as the reactant, with a space velocity of 5 h⁻¹. -1 Catalytic performance mainly includes conversion and selectivity. The gas-phase Beckmann rearrangement catalytic data for Comparative Example 6, Example 11, and Example 12 are shown in the appendix. Figure 21 and 22 .

[0107] Catalyst performance test example 7

[0108] Alternatively, the catalytic performance of the Silicalite-1 molecular sieve in this invention can be tested using a propane dehydrogenation reaction. Before evaluating the catalytic performance, the Silicalite-1 molecular sieve is impregnated with an equal volume of Pt (0.5%) and Sn (1.0%). After the catalyst is loaded, the temperature is raised to 600 °C, and the reaction is initiated after a 3-hour purging. The conditions for catalytic evaluation are: atmospheric pressure, reaction temperature of 600 °C, and propane space velocity of 3 h⁻¹. -1 Catalytic data for propane dehydrogenation of Comparative Examples 6, 11, and 12 are shown in the appendix. Figure 23 and 24 .

[0109] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the present invention, and all of these should be considered to fall within the scope of patent protection determined by the submitted claims.

Claims

1. A method for preparing hierarchical porous molecular sieves by kinetic control, characterized in that, The raw materials for preparing molecular sieves are mixed and subjected to low-temperature crystallization at a low temperature range of 60 ℃-120 ℃ with an H2O / SiO2 molar ratio of 1-3 to promote nucleation. Then, water is added and high-temperature crystallization is carried out at a high temperature range of 140 ℃-220 ℃ with an H2O / SiO2 molar ratio of 20-30 to rapidly grow multi-level porous molecular sieves. The molecular sieves are silicon-aluminum molecular sieves, phosphorus-aluminum molecular sieves, or heteroatom zeolites.

2. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 1, characterized in that, The low temperature range is 80 ℃-100 ℃.

3. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 2, characterized in that, The high temperature range is 140 ℃-180 ℃.

4. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 1, characterized in that, The raw materials for the molecular sieve include silicon source, aluminum source, NaOH, and organic template agent.

5. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 4, characterized in that, The silicon source is one of silica gel, silica sol, water glass, silica fume, tetraethyl orthosilicate, and methyl orthosilicate.

6. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 4, characterized in that, The organic template for synthesizing ZSM-5 molecular sieve is tetrapropylammonium bromide; the organic template for synthesizing Beta molecular sieve is tetraethylammonium bromide; the organic template for synthesizing EU-1 molecular sieve is hexamethyldiammonium bromide; the organic template for synthesizing MCM-22 molecular sieve is hexamethyleneimine; the organic template for synthesizing TS-1 molecular sieve is tetrapropylammonium bromide; and the organic template for synthesizing Silicalite-1 molecular sieve is tetrapropylammonium bromide.

7. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 4, characterized in that, The NaOH / SiO2 molar ratio ranges from 0.05 to 0.5; the R / SiO2 molar ratio ranges from 0.01 to 0.2, where R represents an organic template agent; and the SiO2 / Al2O3 molar ratio is ≥30.

8. The method for preparing hierarchical porous molecular sieves by kinetic control according to claim 4, characterized in that, It also includes seed crystals, the amount of which is 0-10% of the mass fraction of the silicon source.

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