Iron-containing zsm-5 molecular sieve, method for preparing same, and use thereof

Abstract

The present disclosure relates to a kind of iron-containing ZSM-5 molecular sieve and its preparation method and application, the method comprises: S1, silicon source, aluminum source, alkali source, seed crystal and water are mixed to obtain first mixture;S2, after iron source, peroxide, water and the first mixture are mixed, hydrothermal reaction is carried out;Wherein, the peroxide is selected from one or several of sodium persulfate, hydrogen peroxide and Fenton reagent.The method of the present disclosure does not use amine nitrogen organic matter and amine nitrogen ligand, and iron component is encapsulated by peroxide, which avoids amine nitrogen wastewater discharge, so as to realize the clean production of encapsulated iron ZSM-5 molecular sieve.

Description

Technical Field

[0001] This application relates to an iron-containing ZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] Catalytic cracking refers to the process of converting hydrocarbons into low-carbon olefins such as ethylene, propylene, and butene under the action of a catalyst, while simultaneously producing light aromatics. The heavy oil catalytic cracking process for producing low-carbon olefins has long held a significant market share due to its advantages of strong feedstock adaptability and lower production costs. Since the mid-1980s, the Research Institute of Petroleum Processing (RIPP) of China Petroleum & Chemical Corporation (Sinopec) has been continuously researching this technology. In 1994, RIPP developed a catalytic cracking (DCC) process for producing low-carbon olefins from heavy oil (vacuum distillate, coking wax oil, and residue oil, etc.). After the successful industrialization of DCC technology, RIPP further developed a catalytic thermal cracking (CPP) process for directly producing ethylene and propylene from heavy oil, offering multiple production options including maximum ethylene production, maximum propylene production, and the simultaneous production of ethylene and propylene. Compared to steam cracking, the CPP process broadens the sources of ethylene feedstock, reduces ethylene feedstock costs, and, due to its lower reaction temperature compared to steam cracking, significantly reduces energy consumption. Light oil catalytic cracking mainly refers to the process of producing ethylene and propylene from light gasoline or naphtha in the presence of a catalyst. This process enables the conversion of petroleum resources into basic chemical feedstocks and will play an important role in future chemical refineries.

[0003] Catalyst development is considered a core aspect of catalytic cracking technology research and development. Early research on catalytic cracking catalysts focused primarily on metal oxides; however, catalysts used in industrially applied catalytic cracking technologies are now predominantly based on zeolite molecular sieves as the active component. ZSM-5 molecular sieve is a silica-alumina type MFI molecular sieve. Due to its unique three-dimensional ten-membered ring channel structure and suitable acid properties, it exhibits excellent propylene selectivity. Furthermore, its good hydrothermal stability and effective inhibition of coke precursors make it one of the most promising active components for catalytic cracking catalysts. The acid properties of molecular sieves include acid type, acid quantity, acid strength, and acid center distribution. Elemental modification is a simple and effective method for modulating the acidity of molecular sieves. Studies have shown that modifying ZSM-5 molecular sieves with alkaline earth metals such as Mg, Ca, Ba, and Sr promotes the conversion of some strong acid sites into weak acid sites. When n-butane is used as a reactant, the introduction of Ba yielded the highest ethylene and propylene yields, while the aromatic yield decreased significantly, possibly due to the inhibition of hydrogen transfer reactions.

[0004] Encapsulation is an important method for introducing metal components into molecular sieves. Encapsulation not only ensures uniform dispersion of the metal component within the molecular sieve but also leverages the shape-selective properties of the sieve to activate terminal C-H bonds in alkanes, selectively dehydrogenating them and thus reducing methane content while increasing selectivity for low-carbon olefins. Studies have reported the direct synthesis of encapsulated Pd-containing molecular sieves using ethylenediamine as a ligand, achieving the direct synthesis of high-silica molecular sieves with encapsulated metals. However, while there has been considerable research on encapsulating metals into all-silica or high-silica MFI molecular sieves, research on encapsulating metals into aluminosilicate MFI molecular sieves is limited. This is because directly introducing metals into the synthesis system can lead to the formation of hydroxide precipitates in alkaline environments, and the metals readily interact with phosphorus, resulting in difficult synthesis or low activity. The ligand-assisted method is one approach for synthesizing encapsulated metal aluminosilicate MFI molecular sieves. The criterion for selecting ligands is that the ion product constant of the complex is less than the solubility product constant of the metal oxide to achieve a complexed state of the metal. Therefore, an alcoholic amine complex that can complex with ferric nitrate is chosen as the ligand to form a metal complex, thereby protecting the metal and not affecting the molecular sieve synthesis system. However, the ligand-assisted method generally uses organic reagents as ligands, such as alcoholic amine complexes and hexamethylenediamine, which still presents problems such as the discharge of organic wastewater.

[0005] In 2016, Professor Yu Jihong's research group at Jilin University discovered the presence of hydroxyl radicals in the hydrothermal synthesis system of molecular sieves. They also found that introducing hydroxyl radicals into the molecular sieve synthesis system can significantly accelerate the crystallization process of molecular sieves. Summary of the Invention

[0006] The purpose of this disclosure is to provide an iron-containing ZSM-5 molecular sieve, its preparation method, and its application. The method of this disclosure uses peroxides to synthesize and encapsulate the molecular sieve, encapsulating the metal into the ZSM-5 molecular sieve. It does not use amine nitrogen organic compounds or amine nitrogen ligands, thus avoiding the discharge of amine nitrogen wastewater and achieving clean production of encapsulated iron ZSM-5 molecular sieve throughout the entire process.

[0007] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing iron-containing ZSM-5 molecular sieves, the method comprising:

[0008] S1. Mix the silicon source, aluminum source, alkali source, seed crystal and water to obtain the first mixture;

[0009] S2. After mixing the iron source, peroxide, water and the first mixture, a hydrothermal reaction is carried out.

[0010] The peroxide is selected from one or more of sodium persulfate, hydrogen peroxide, and Fenton's reagent.

[0011] Optionally, step S2 includes:

[0012] SS1. The iron source, peroxide and water are mixed to obtain a second mixture; the molar ratio of the iron source, peroxide and water, calculated as Fe2O3, is 1:(0.2-2.5):(200-1400); preferably 1:(0.3-2.0):(200-800);

[0013] SS2. The first mixture and the second mixture are mixed and then subjected to the hydrothermal reaction; the molar ratio of the first mixture (calculated as Al2O3) to the second mixture (calculated as Fe2O3) is 1:(0.01-3.0); preferably 1:(0.4-2.3).

[0014] Optionally, in step S1, the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the alkali source (calculated as alkali metal oxide), and the water is (20-300):1:(2-30):(300-2500), preferably (35-60):1:(4-20):(500-1000);

[0015] Based on SiO2, the amount of the seed crystal is 5-15% by weight, preferably 7-12% by weight, relative to the total weight of the silicon source.

[0016] Optionally, in step S2, the conditions for the hydrothermal reaction include: a temperature of 150-220℃ and a time of 8-32h.

[0017] Optionally, the method further includes: subjecting the product obtained by hydrothermal treatment to ammonium exchange and calcination; the calcination conditions include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

[0018] Optionally, in step S1, the silicon source includes one or more of silica gel, silicon dioxide, silica fume, and silicates;

[0019] The aluminum source includes one or more of sodium aluminate, SB powder, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate;

[0020] The alkaline source includes sodium hydroxide and / or potassium hydroxide;

[0021] The seed crystals include one or more ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 20-50, and the average particle size of the ZSM-5 molecular sieve is 0.5-2 μm.

[0022] The iron source is selected from one or more of ferric nitrate, ferric oxalate, ferric sulfate, and ferric hydroxide.

[0023] The second aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve prepared by the method provided in the first aspect of this disclosure.

[0024] Optionally, the iron-containing ZSM-5 molecular sieve has a structure in which the iron active component is internally encapsulated within the ZSM-5 molecular sieve; the iron active component is distributed on the framework of the ZSM-5 molecular sieve.

[0025] Optionally, the specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 200-450 m². 2 / g, total pore volume is 0.130-0.24cm³. 3 ·g -1 The micropore volume is 0.100-0.20 cm³. 3 ·g -1 The mesopore volume is 0.010-0.10 cm³. 3 ·g -1 The relative crystallinity is 80-100%;

[0026] In the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 20-300;

[0027] The content of the iron-active component, calculated as Fe2O3, is 1-3% by weight relative to the total weight of the iron-containing ZSM-5 molecular sieve.

[0028] The third aspect of this disclosure provides an application of the iron-containing ZSM-5 molecular sieve provided in the first aspect of this disclosure in the catalytic cracking reaction of n-tetradecane.

[0029] Optionally, the conditions for the catalytic cracking reaction include: a temperature of 500-680℃, a reaction mass hourly space velocity of 20-40 h⁻¹, a reaction pressure of 0.8-1.2 MPa, and a catalyst-to-oil weight ratio of 1-1.8. Through the above technical solution, the method disclosed herein uses peroxides to synthesize encapsulated molecular sieves, encapsulating metals into ZSM-5 molecular sieves without using amine nitrogen-based organic compounds or amine nitrogen-based ligands, thus avoiding the discharge of amine nitrogen wastewater and achieving a completely clean production process for encapsulated iron ZSM-5 molecular sieves.

[0030] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0032] Figure 1 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve prepared in Example 1 of this disclosure;

[0033] Figure 2This is a transmission electron microscope (TEM) image of the iron-containing ZSM-5 molecular sieve prepared in Example 1 of this disclosure;

[0034] Figure 3 This is a STEM-Mapping image of the iron-containing ZSM-5 molecular sieve prepared in Example 1 of this disclosure;

[0035] Figure 4 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve prepared in Example 2 of this disclosure;

[0036] Figure 5 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve prepared in Example 3 of this disclosure;

[0037] Figure 6 These are the H2-TPR images of iron-containing ZSM-5 molecular sieve sample C and control sample D1 prepared in Example 3 and Comparative Example 1 of this disclosure. Detailed Implementation

[0038] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0039] The first aspect of this disclosure provides a method for preparing iron-containing ZSM-5 molecular sieves, the method comprising: S1, mixing a silicon source, an aluminum source, an alkali source, a seed crystal and water to obtain a first mixture; S2, mixing an iron source, a peroxide, water and the first mixture and then carrying out a hydrothermal reaction; wherein the peroxide is selected from one or more of sodium persulfate, hydrogen peroxide and Fenton's reagent.

[0040] The method disclosed herein uses peroxides to synthesize molecular sieves without using template agents containing amine nitrogen, thus avoiding the discharge of amine nitrogen wastewater and achieving clean production of iron-containing ZSM-5 molecular sieves.

[0041] In a preferred embodiment of this disclosure, the peroxide is sodium persulfate or hydrogen peroxide, more preferably sodium persulfate. The aforementioned peroxide can simultaneously interact with both the metal and the molecular sieve precursor, promoting molecular sieve nucleation around the metal and encapsulating the metal within the molecular sieve.

[0042] In one specific embodiment of this disclosure, step S2 includes: SS1, mixing the iron source, peroxide, and water to obtain a second mixture; the molar ratio of the iron source, peroxide, and water, calculated as Fe2O3, is 1:(0.2-2.5):(500-1400); preferably 1:(0.3-2.0):(800-1200); more preferably 1:(0.5-1.8):(800-1000); SS2, mixing the first mixture and the second mixture and then performing the hydrothermal reaction; the molar ratio of the first mixture, calculated as Al2O3, to the second mixture, calculated as Fe2O3, is 1:(0.01-3.0); preferably 1:(0.4-2.3). Within the above range of proportions, the second mixture can be free of free iron ions or ferrous ions, avoiding the presence of aggregated iron active components in the prepared molecular sieve, thereby further improving its catalytic performance.

[0043] In one specific embodiment of this disclosure, in step S1, the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the alkali source (calculated as alkali metal oxide), and the water is (20-300):1:(2-30):(300-2500), preferably (35-60):1:(4-20):(500-1000); the amount of the seed crystal (calculated as SiO2) relative to the total weight of the silicon source is 5-15% by weight, preferably 7-12% by weight.

[0044] According to this disclosure, hydrothermal treatment is well known to those skilled in the art and can be carried out in equipment familiar to those skilled in the art, such as a closed, heat-resistant, and pressure-resistant reactor. In one specific embodiment of this disclosure, in step S2, the conditions for the hydrothermal reaction include: a temperature of 150-220°C and a time of 8-32 hours; preferably, a temperature of 150-180°C and a time of 8-20 hours. This disclosure does not impose specific limitations on the pressure of the hydrothermal reaction; for example, it can be carried out under the autogenous pressure of the reaction system or under an applied pressure, preferably under the autogenous pressure of the reaction system.

[0045] In one specific embodiment of this disclosure, the method further includes: subjecting the solid product obtained from the hydrothermal treatment to ammonium exchange and calcination; the calcination conditions include: a temperature of 400-800°C, a time of 0.5-8 hours, and an atmosphere of air or water vapor; preferably, the temperature is 500-600°C, and the time is 2-4 hours. Calcination is well known to those skilled in the art and can be performed, for example, in a muffle furnace, a tube furnace, etc. In a preferred embodiment, the solid product is washed until neutral before ammonium exchange; the washing liquid can be any type of liquid that does not react with the solid product, such as deionized water. In another preferred embodiment, the solid obtained from ammonium exchange is dried before calcination; the drying conditions may include: a temperature of 100-150°C, and a time of 5-20 hours.

[0046] In one specific embodiment of this disclosure, the solid product obtained from hydrothermal treatment can be removed by methods such as centrifugation and precipitation.

[0047] According to this disclosure, the silicon source, aluminum source, and alkali source are well known to those skilled in the art. In one specific embodiment of this disclosure, the silicon source includes one or more of silica gel, silicon dioxide, silica fume, and silicates; the aluminum source includes one or more of sodium aluminate, SB powder, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate; and the alkali source includes sodium hydroxide and / or potassium hydroxide.

[0048] According to this disclosure, the iron source can be a water-soluble ferric salt and / or ferrous salt. In one specific embodiment of this disclosure, the iron source is selected from one or more of ferric nitrate, ferric oxalate, ferric sulfate, and ferric hydroxide.

[0049] In one specific embodiment of this disclosure, the seed crystals include one or more ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 20-50, such as, but not limited to, ZPR molecular sieves and ZSP molecular sieves; the average particle size of the ZSM-5 molecular sieve is 0.5-2 μm, preferably 1-2 μm. In this disclosure, the average particle size of the ZSM-5 molecular sieve refers to the average particle size estimated by performing SEM analysis on the molecular sieve and measuring the particle size of 50 randomly selected particles from its SEM image, using a HITACHI S-4800 SEM instrument.

[0050] The second aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve prepared by the method provided in the first aspect of this disclosure.

[0051] In one specific embodiment of this disclosure, the iron-containing ZSM-5 molecular sieve has a structure in which an iron-active component is internally encapsulated within the ZSM-5 molecular sieve; the iron-active component is distributed on the framework of the ZSM-5 molecular sieve.

[0052] In this disclosure, "the iron-containing active component is distributed on the framework of the ZSM-5 molecular sieve" means that at least a portion of the Si and Al on the ZSM-5 molecular sieve framework is replaced by Fe. The introduction of iron can modulate the acidity of the ZSM-5 molecular sieve, improve its catalytic function in cracking and dehydrogenation, and introduce the iron-containing active component into the interior of the molecular sieve through encapsulation, further reducing the severity of the catalytic cracking reaction of light hydrocarbons and improving the conversion rate of saturated hydrocarbons and the selectivity of low-carbon olefins. In one specific embodiment of this disclosure, the specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 200-450 m². 2 / g, preferably 300-400m 2 / g, total pore volume is 0.130-0.24cm³. 3 ·g -1 The preferred size is 0.18-0.22cm. 3 ·g -1 The micropore volume is 0.100-0.200 cm³. 3 ·g -1 The preferred size is 0.120-0.180cm. 3 ·g -1 The mesopore volume is 0.010-0.10 cm³. 3 ·g -1 The preferred value is 0.030-0.080cm. 3 ·g -1 The relative crystallinity is 80-100%, preferably 85-100%; in the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 20-300, preferably 27-50; relative to the total weight of the iron-containing ZSM-5 molecular sieve, the content of the iron active component, calculated as Fe2O3, is 0.5-3% by weight, preferably 1-3% by weight, more preferably 1-1.5% by weight. The molar ratio of SiO2 to Al2O3 can be obtained by X-ray fluorescence spectroscopy. The relative crystallinity is determined using a Siemens D5005 X-ray diffractometer, with the ZSM-5 molecular sieve standard sample from the Research Institute of Petroleum Processing (i.e., the relative crystallinity of the ZSM-5 molecular sieve standard sample from the Research Institute of Petroleum Processing, China Petroleum & Chemical Corporation, is 100%) as a benchmark. Specific surface area and pore volume parameters can be determined using a specific surface area analyzer based on the N2 adsorption principle and according to the BET calculation method (see Petrochemical Analytical Methods (RIPP Test Methods), RIPP 151-90, Science Press, 1990). The content of iron active components, calculated as Fe2O3, is obtained by X-ray fluorescence spectroscopy.

[0053] This disclosure provides a third aspect of the application of the iron-containing ZSM-5 molecular sieve provided in the second aspect of this disclosure in the catalytic cracking reaction of n-tetradecane. In one specific embodiment of this disclosure, the conditions for the catalytic cracking reaction include: a temperature of 500-680°C and a reaction mass hourly space velocity (USHSV) of 20-40 h⁻¹. -1 The reaction pressure is 0.8-1.2 MPa, and the agent-to-oil weight ratio is 1-2; preferably, the temperature is 540-600℃, and the reaction mass hourly space velocity is 20-40 h⁻¹. -1 The reaction pressure is 1-1.2 MPa, and the agent-to-oil weight ratio is 1.28-1.92.

[0054] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereto.

[0055] The silicon-aluminum molar ratio is the molar ratio of SiO2 to Al2O3, which is detected by X-ray fluorescence spectroscopy. The instrument is a Rigaku Electric Co., Ltd. 3013 X-ray fluorescence spectrometer. The test conditions are: tungsten target, excitation voltage 40kV, and excitation current 50mA.

[0056] Relative crystallinity: Based on the ZSM-5 molecular sieve standard sample from the Research Institute of Petroleum Processing (i.e., the relative crystallinity of the ZSM-5 molecular sieve standard sample from the Research Institute of Petroleum Processing of China Petroleum & Chemical Corporation is 100%), the crystallinity was measured using a Siemens D5005 X-ray diffractometer.

[0057] Specific surface area: determined using a specific surface area analyzer based on the N2 adsorption principle and the BET calculation method (see Petrochemical Analysis Methods (RIPP Test Methods), RIPP151-90, Science Press, 1990).

[0058] Method for testing pore volume: The sample is evacuated to a vacuum of 1.33 × 10⁻⁶ at 350°C. -2 The pressure was maintained at a constant temperature and pressure for 15 hours. Tests were conducted at liquid nitrogen temperature -196℃ to measure the adsorption and desorption of N2 by the sample under different relative pressures (p / p0). Desorption branching data were calculated using the BJH (Barrett-Joyner-Halenda) method to obtain the pore size distribution data of the sample.

[0059] The transmission electron microscope was a JEM-2100 (200kV) transmission electron microscope manufactured by Nippon Electron Ltd.; the test conditions were: accelerating voltage of 200kV, sample preparation, and observation of the crystal morphology and size of the molecular sieve samples at magnifications of 5000-30000.

[0060] STEM-Mapping test method and instrument: JEM-2100 (200kV) transmission electron microscope, NEC Corporation. The accelerating voltage of the electron microscope was 200kV. The sample was dispersed in anhydrous ethanol and then dropped onto a sample grid with a diameter of 3mm for observation and testing.

[0061] H2-TPR testing method and instrumentation: Micromeritic AutochemⅡ2920 temperature-programmed desorption system. 0.2 g (20-40 mesh) of molecular sieve catalyst was weighed and placed in a sample tube, then placed in a thermal conductivity cell furnace. He gas was used as the carrier gas (25 mL / min), and the temperature was increased to 550 °C at a rate of 20 °C / min. The sample was then purged for 60 min to remove impurities adsorbed on the catalyst surface. The temperature was then reduced to 150 °C and held for 60 min. An H2-He mixture (10.02% H2 + 89.98% He) was then used for adsorption for 60 min, followed by purging with He gas for 120 min until the baseline stabilized. The temperature was then programmed to increase to 550 °C at a rate of 10 °C / min for desorption. The temperature was held for 30 min to complete desorption, and the gas composition change was detected using a TCD detector.

[0062] Test method for the content of iron active components, calculated as Fe2O3: Semi-quantitative analysis of iron element is performed by measuring the intensity of characteristic spectral lines of each element by XRF.

[0063] Example 1

[0064] This embodiment uses the following steps to prepare iron-containing ZSM-5 molecular sieve A:

[0065] (1) Add 0.99g sodium hydroxide, 40.8g deionized water, 20g silica gel, 6.78g low-alkali sodium aluminate (Na2O: 153.5g / L, Al2O3: 102.5g / L) and 1.97g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0066] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 55:1:4.68:589; the amount of ZSM-5 seed crystals is 10% by weight relative to the total weight of silicon source (SiO2); the silicon-aluminum ratio of ZSM-5 seed crystals is 27, and the average particle size is 1-2 μm.

[0067] (2) Dissolve 1.13g of ferric nitrate nonahydrate in 10g of deionized water, add 0.14g of sodium persulfate, and stir thoroughly until clear and transparent to obtain the second mixture;

[0068] The molar ratio of iron source (calculated as Fe2O3), sodium persulfate, and water is 1:0.2:200, and the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.40.

[0069] (3) Add the second mixture to the first mixture, mix thoroughly and evenly, then transfer to a stainless steel autoclave and perform hydrothermal treatment at 170°C for 12 hours;

[0070] (4) The product obtained from the hydrothermal treatment in step (3) was filtered, washed until pH = 7-8, and then subjected to ammonium exchange. It was dried at 120℃ for 12h and then calcined at 550℃ for 2h in air to obtain iron-containing ZSM-5 molecular sieve, denoted as A. Its structural parameters are listed in Table 1, its X-ray diffraction pattern is shown in Figure 1, and its transmission electron microscope image is shown in Figure 2. Figure 2 STEM-Mapping photos can be found Figure 3 .

[0071] Example 2

[0072] Iron-containing ZSM-5 molecular sieve B was prepared using the same method as in Example 1, except that in step (2), 1.13 g of ferric nitrate nonahydrate was dissolved in 10 g of deionized water, and 0.576 g of sodium persulfate was added. The mixture was stirred thoroughly until it became clear and transparent, resulting in a second mixture. The molar ratio of iron source (calculated as Fe2O3), sodium persulfate, and water was 1:0.8:200. Encapsulated iron ZSM-5 molecular sieve B was obtained, and its structural parameters are listed in Table 1. Its X-ray diffraction pattern is shown in Table 4.

[0073] Example 3

[0074] Iron-containing ZSM-5 molecular sieve C was prepared using the same method as in Example 1, except that in step (2), 1.13 g of ferric nitrate nonahydrate was dissolved in 10 g of deionized water, and 1.15 g of sodium persulfate was added. The mixture was stirred thoroughly until it became clear and transparent, resulting in a second mixture. The molar ratio of iron source (calculated as Fe2O3), sodium persulfate, and water was 1:1.6:200. Encapsulated iron ZSM-5 molecular sieve C was obtained, and its structural parameters are listed in Table 1. Its X-ray diffraction pattern is shown in Table 5, and its H2-TPR pattern is shown in Table 6. Figure 6 .

[0075] Example 4

[0076] Iron-containing ZSM-5 molecular sieve D was prepared using the same method as in Example 1, except that in step (2), 1.13 g of ferric nitrate nonahydrate was dissolved in 10 g of deionized water, and 0.095 g of hydrogen peroxide was added. The mixture was stirred thoroughly until it became clear and transparent, resulting in a second mixture. The molar ratio of iron source (calculated as Fe2O3), hydrogen peroxide, and water was 1:1:200, resulting in encapsulated iron ZSM-5 molecular sieve D. The structural parameters are listed in Table 1.

[0077] Example 5

[0078] Iron-containing ZSM-5 molecular sieve E was prepared using the same method as in Example 3, except that in step (2), 1.13 g of ferric nitrate nonahydrate was dissolved in 10 g of deionized water, and 1.80 g of sodium persulfate was added. The second mixture contained free iron ions. The molar ratio of iron source (calculated as Fe2O3), sodium persulfate and water was 1:2.5:200. The structural parameters are listed in Table 1.

[0079] Example 6

[0080] Iron-containing ZSM-5 molecular sieve G was prepared using the same method as in Example 3, except that in step (1), 0.79g sodium hydroxide, 56.63g deionized water, 13g silica gel, 3.45g low-alkali sodium aluminate (Na2O: 153.5g / L, Al2O3: 102.5g / L), and 1.38g ZSM-5 seed crystals were added sequentially under stirring and stirred thoroughly to obtain the first mixture;

[0081] In step (2), 1.13g of ferric nitrate nonahydrate is dissolved in 10g of deionized water, and 0.14g of sodium persulfate is added. The mixture is stirred thoroughly until it is clear and transparent to obtain the second mixture.

[0082] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 70:1:5.95:1400; the amount of ZSM-5 seed crystals is 7% by weight relative to the total weight of silicon source (SiO2); the silicon-aluminum ratio of ZSM-5 seed crystals is 27, and the average particle size is 1-2 μm.

[0083] Comparative Example 1

[0084] This comparative example illustrates the differences between iron-free parent ZSM-5 molecular sieves.

[0085] (1) Add 0.99g sodium hydroxide, 50.8g deionized water, 20g silica gel, 6.78g low-alkali sodium aluminate (Na2O: 153.5g / L, Al2O3: 102.5g / L) and 1.97g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture; after thorough mixing, transfer to a stainless steel kettle and hydrothermally treat at 170℃ for 12h;

[0086] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 55:1:4.68:589; the amount of ZSM-5 seed crystals is 10% by weight relative to the total weight of silicon source (SiO2); the silicon-aluminum ratio of ZSM-5 seed crystals is 27, and the average particle size is 1-2 μm.

[0087] (2) The product obtained from the hydrothermal treatment in step (1) was filtered, washed until pH = 7-8, and then subjected to ammonium exchange. After drying at 120℃ for 12h, it was calcined at 550℃ for 2h in air to obtain the parent ZSM-5 molecular sieve, denoted as D1. Its structural parameters are listed in Table 1, and its H2-TPR diagram is shown in Table 1. Figure 6 .

[0088] Comparative Example 2

[0089] Iron-containing ZSM-5 molecular sieve D2 was prepared using the same method as in Example 1, except that sodium persulfate was not added. Its structural parameters are listed in Table 1.

[0090] Comparative Example 3

[0091] This comparative example illustrates the differences in the synthesis of iron-containing ZSM-5 molecular sieves using the ligand-assisted method for triethanolamine.

[0092] Iron-containing ZSM-5 molecular sieve D3 was prepared using the same method as in Example 1, except that sodium persulfate was replaced with triethanolamine, wherein the amount of triethanolamine used was 0.42 g, and the molar ratio of iron source (calculated as Fe2O3), triethanolamine and water was 1:1:200. The structural parameters are listed in Table 1.

[0093] Test Example 1

[0094] The iron-containing ZSM-5 molecular sieves prepared in the examples and comparative examples were subjected to aging treatment. The specific aging treatment method is as follows: the aging furnace was a self-made hydrothermal aging device from the Institute of Petroleum Research, and the state after aging at 800℃ for 17 hours was used to simulate the balancing agent during industrial operation.

[0095] The ZSM-5 molecular sieves prepared in the examples and comparative examples were used as catalysts in the catalytic cracking reaction of n-tetradecane. The specific method is as follows: the reaction was carried out in a fixed-bed reactor, the feedstock was n-tetradecane, the carrier gas was nitrogen at a flow rate of 30 mL / min, the reaction temperature was 550 °C, the regeneration temperature was 600 °C, the reaction pressure was 0.1 MPa, and the weight hourly space velocity was 20 hr. -1 The molecular sieve tablets were sieved into 20-40 mesh particles, with a loading of 2.0 g and an oil-to-catalyst ratio of 1.28. Samples were taken for analysis after 900 s of reaction, and material balance calculations were performed. The product distribution is shown in Table 1.

[0096] The micro-reaction conversion rate X of the raw material and the yield S of the product are calculated using the following formulas. i :

[0097]

[0098]

[0099]

[0100]

[0101] Table 1

[0102]

[0103] According to the data in Table 1, the iron-containing ZSM-5 molecular sieve prepared by the method of introducing peroxides in this disclosure has a relatively high crystallinity of approximately 80-87%. Transmission electron microscopy (TEM) images of the iron-containing ZSM-5 molecular sieve prepared in Example 1 show that the grain size of the iron-containing ZSM-5 molecular sieve prepared by the method of this disclosure is 1-2 μm. STEM-Mapping images of the iron-containing ZSM-5 molecular sieve prepared in Example 1 show that the iron active component is uniformly distributed in the iron-containing ZSM-5 molecular sieve prepared by the method of this disclosure. H2-TPR diagrams of the iron-containing ZSM-5 molecular sieve prepared in Example 3 show that the molecular sieve of Example 3 does not exhibit obvious peaks within the temperature range of 100-700℃, indicating that the iron active component in the iron-containing ZSM-5 molecular sieve prepared by the method of this disclosure is entirely present on the molecular sieve framework and not distributed on the outer surface of the molecular sieve. The H2-TPR spectrum of the parent ZSM-5 molecular sieve prepared in Comparative Example D1 did not show obvious peaks in the range of 100-700℃ because it does not contain iron species and therefore does not contain reducing species.

[0104] Furthermore, according to the data in Tables 1 and 2, when the iron-containing ZSM-5 molecular sieve prepared using the method of this disclosure is used in the catalytic cracking reaction of n-tetradecane and the catalytic cracking reaction of light hydrocarbons, a high micro-reaction conversion rate and a better yield of low-carbon olefins can be obtained. A comparison of Examples 1-3 and 5 shows that when the molar ratio of iron source (calculated as Fe2O3), sodium persulfate, and water is preferably 1:(0.3-2.0):(200-800), the prepared catalyst can achieve a higher micro-reaction conversion rate and propylene yield in the catalytic cracking of n-tetradecane. A comparison of Examples 1-3 and 5 shows that… When the sodium persulfate content increases within a certain range, the crystallinity of the molecular sieve increases, and the catalyst prepared can achieve higher micro-reaction conversion and lower carbon olefin yield when used for the catalytic cracking of n-tetradecane. According to Examples 3 and 6, when the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the alkali source (calculated as alkali metal oxide), and the water is preferably (35-90):1:(4-20):(500-1000), the prepared molecular sieve has better catalytic cracking performance, and its use for the catalytic cracking of n-tetradecane can achieve higher micro-reaction conversion and lower carbon olefin yield.

[0105] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0106] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0107] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing iron-containing ZSM-5 molecular sieves, the method comprising: S1. A silicon source, an aluminum source, an alkali source, seed crystals, and water are mixed to obtain a first mixture; wherein the molar ratio of the silicon source (based on SiO2), the aluminum source (based on Al2O3), the alkali source (based on alkali metal oxides), and the water is (20-300):1:(2-30):(300-2500); and the amount of seed crystals is 5-15% by weight relative to the total weight of the silicon source (based on SiO2). S2. Mix the iron source, peroxide, and water to obtain a second mixture; the molar ratio of the iron source, peroxide, and water, calculated as Fe2O3, is 1:(0.2-2.5):(200-1400). The first mixture and the second mixture are mixed and then subjected to a hydrothermal reaction; the molar ratio of the first mixture (calculated as Al2O3) to the second mixture (calculated as Fe2O3) is 1:(0.01-3.0). The peroxide is selected from one or more of sodium persulfate, hydrogen peroxide, and Fenton's reagent; the iron-containing ZSM-5 molecular sieve has a structure in which iron active components are encapsulated internally by the ZSM-5 molecular sieve; the iron active components are distributed on the framework of the ZSM-5 molecular sieve.

2. The method according to claim 1, wherein, Step S2 includes: SS1. The iron source, peroxide, and water are mixed to obtain a second mixture; the molar ratio of the iron source, peroxide, and water, calculated as Fe2O3, is 1:(0.3-2.0):(200-800). SS2. The first mixture and the second mixture are mixed and then subjected to the hydrothermal reaction; the molar ratio of the first mixture (calculated as Al2O3) to the second mixture (calculated as Fe2O3) is 1:(0.4-2.3).

3. The method according to claim 1, wherein, In step S1, the molar ratio of the silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the alkali source (calculated as alkali metal oxide), and the water is (35-60):1:(4-20):(500-1000). Based on SiO2, the amount of seed crystals used is 7-12 by weight relative to the total weight of the silicon source.

4. The method according to claim 1, wherein, In step S2, the conditions for the hydrothermal reaction include: a temperature of 150-220℃ and a time of 8-32h.

5. The method according to claim 1, wherein, The method further includes: subjecting the solid product obtained by the hydrothermal reaction treatment to ammonium exchange and calcination treatment; the calcination treatment conditions include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

6. The method according to claim 1, wherein, The silicon source includes one or more of silica gel, silicon dioxide, silica fume, and silicates; The aluminum source includes one or more of sodium aluminate, SB powder, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate; The alkaline source includes sodium hydroxide and / or potassium hydroxide; The seed crystals include one or more ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 20-50, and the average particle size of the ZSM-5 molecular sieve is 0.5-2 μm. The iron source is selected from one or more of ferric nitrate, ferric oxalate, ferric sulfate, and ferric hydroxide.

7. The iron-containing ZSM-5 molecular sieve prepared by the method according to any one of claims 1-6.

8. The iron-containing ZSM-5 molecular sieve according to claim 7, wherein, The iron-containing ZSM-5 molecular sieve has a structure in which iron active components are internally encapsulated within the ZSM-5 molecular sieve; the iron active components are distributed on the framework of the ZSM-5 molecular sieve.

9. The iron-containing ZSM-5 molecular sieve according to claim 7, wherein, The specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 200-450 m². 2 / g, total pore volume is 0.130-0.24cm³. 3 ·g -1 The micropore volume is 0.100-0.20 cm³. 3 ·g -1 The mesopore volume is 0.010-0.10 cm³. 3 ·g -1 The relative crystallinity is 80-100%; In the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 20-300; The content of the iron active component, calculated as Fe2O3, is 1-3% by weight relative to the total weight of the iron-containing ZSM-5 molecular sieve.

10. The application of the iron-containing ZSM-5 molecular sieve according to any one of claims 7-9 in the catalytic cracking reaction of n-tetradecane.

11. The application according to claim 10, wherein, The conditions for the catalytic cracking reaction include: a temperature of 500-680℃ and a reaction mass hourly space velocity of 20-40 h⁻¹. -1 The reaction pressure is 0.8-1.2 MPa, and the agent-to-oil weight ratio is 1-2.

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