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, the iron-containing ZSM-5 molecular sieve has the structure of internal encapsulation iron active component of ZSM-5 molecular sieve, the outer surface of the particle of the iron-containing ZSM-5 molecular sieve does not contain iron active component.The present disclosure uses amine-free method, and by using ligand, iron active component is encapsulated in the interior of ZSM-5 molecular sieve, and the encapsulated iron ZSM-5 molecular sieve prepared has the characteristics of high relative crystallinity, high silica-alumina ratio, uniform iron distribution and not distributed on the surface of molecular sieve;It is used for light hydrocarbon catalytic cracking reaction and naphtha catalytic cracking reaction, and has the yield of relatively optimal low carbon olefin, while reducing the generation of coke and other non-ideal components.

Description

Technical Field

[0001] This disclosure relates to the field of molecular sieve preparation, specifically 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, while simultaneously producing light aromatics, under the action of a catalyst. Catalytic cracking technology integrates the advantages of both traditional steam cracking and fluidized bed catalytic cracking (FCC) processes, utilizing heavy oil, naphtha, olefins, or alkanes as feedstocks. Catalytic cracking using heavy oil as feedstock can produce the largest quantities of low-carbon olefins such as ethylene and propylene, enabling the conversion of petroleum resources into basic chemical feedstocks and playing a crucial role in future chemical refineries. Hydrogenating heavy oil before using it as feedstock removes non-hydrocarbon components and heavy metals, expanding the feedstock sources and further increasing the yield of low-carbon olefins such as ethylene and propylene in the catalytic cracking products. However, hydrogenation increases the saturated alkane content in the feedstock, further complicating the catalytic cracking reaction. Therefore, both catalytic cracking technologies using different feedstocks face the trend of increasing saturated alkane content in the feedstock. Dealing with this portion of alkanes that are more difficult to crack is an important problem facing catalytic cracking technologies.

[0003] ZSM-5 molecular sieve is a silica-alumina type MFI molecular sieve. Due to its unique three-dimensional ten-membered ring pore structure and suitable acid properties, it exhibits good propylene selectivity. Furthermore, its excellent hydrothermal stability and good inhibition of coke precursors make it considered one of the most promising active components for catalytic cracking catalysts. Factors affecting the catalytic performance of molecular sieves in catalytic cracking reactions include the silica-alumina ratio, pore structure, and crystal size. Methods and techniques for improving the catalytic cracking performance of ZSM-5 molecular sieves mainly focus on three aspects: modifying its acid properties and pore structure, and enhancing its hydrothermal stability. 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. However, directly introducing metals into the synthesis system results in low activity due to the interactions between the metal and aluminum / phosphorus. Summary of the Invention

[0004] The purpose of this disclosure is to provide an iron-containing ZSM-5 molecular sieve, its preparation method, and its application. This molecular sieve has the characteristics of high relative crystallinity, high silicon-to-aluminum ratio, and uniform iron distribution that is not distributed on the surface of the molecular sieve. When used in the catalytic cracking reaction of light hydrocarbons and naphtha, it has a better yield of low-carbon olefins, while reducing the formation of non-ideal components such as coke.

[0005] To achieve the above objectives, the first aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve, 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, and the outer surface of the particles of the iron-containing ZSM-5 molecular sieve does not contain iron active components.

[0006] Optionally, the iron-active component is distributed on the framework or within the pores of the ZSM-5 molecular sieve.

[0007] Optionally, the specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 240-400 m². 2 / g, total pore volume is 0.13-0.25cm³. 3 ·g -1 The micropore volume is 0.12-0.22 cm³. 3 ·g -1 The mesopore volume is 0.01-0.1 cm³. 3 ·g -1 The average particle size is 0.5-2 μm, and the relative crystallinity is 75-100%.

[0008] In the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-50;

[0009] 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.

[0010] A second aspect of this disclosure provides a method for preparing iron-containing ZSM-5 molecular sieves, the method comprising the following steps:

[0011] S1 mixes silicon source, aluminum source, alkali source, seed crystal and water to obtain the first mixture;

[0012] S2 brings the iron complex into contact with the first mixture to carry out a hydrothermal reaction.

[0013] Optionally, the method further includes: mixing an iron source, a ligand, and water to obtain the iron complex; wherein the molar ratio of the iron source, the ligand, and the water, calculated as Fe2O3, is 1:(0.5-3):(100-1500).

[0014] Optionally, the ligand is a nitrogen-containing ligand, preferably triethanolamine or ethylenediaminetetraacetic acid;

[0015] The iron source includes one or more of ferric nitrate, ferrous nitrate, ferric sulfate, and ferrous sulfate.

[0016] Optionally, in step S1, the silicon source includes one or more of silica gel, silicon dioxide, silica fume, and silicates;

[0017] The aluminum source includes one or more of sodium aluminate, SB powder, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate;

[0018] The alkaline source includes one or more of sodium hydroxide, water glass, and potassium hydroxide;

[0019] 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.

[0020] 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 (20-75):1:(1-7):(140-800), preferably (40-60):1:(3-5):(300-600), and more preferably (35-50):1:(3-4):(360-600).

[0021] Based on SiO2, the amount of the seed crystal is 1-10% by weight, preferably 8-10% by weight, relative to the total weight of the silicon source.

[0022] Optionally, the molar ratio of the aluminum source (calculated as Al2O3) to the iron source (calculated as Fe2O3) is 1:(0.01-2.5).

[0023] Optionally, in step S2, the conditions for the hydrothermal reaction include: a time of 8-24 hours and a temperature of 150-220°C.

[0024] Optionally, the method further includes: subjecting the product obtained from the hydrothermal treatment to ammonium exchange and calcination;

[0025] Optionally, the calcination conditions include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

[0026] The third aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve prepared using the method described in the second aspect of this disclosure.

[0027] This fourth aspect of the disclosure provides the application of the ZSM-5 molecular sieve described in the first or third aspect of the disclosure in the catalytic cracking of light hydrocarbons and naphtha.

[0028] Through the above technical solution, this disclosure adopts an amine-free method and encapsulates the iron active component with dehydrogenation activity into the interior of the ten-membered ring silica-alumina type MFI molecular sieve—ZSM-5 molecular sieve by using ligands. This method is simple to operate, and the prepared encapsulated iron ZSM-5 molecular sieve has the characteristics of high relative crystallinity, high silica-alumina ratio, uniform iron distribution and non-distribution on the surface of the molecular sieve. When used in the catalytic cracking reaction of light hydrocarbons and naphtha, it has a better yield of low-carbon olefins, while reducing the formation of non-ideal components such as coke.

[0029] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0030] 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:

[0031] Figure 1 This is a hydrogen-TPR diagram of iron-containing ZSM-5 molecular sieves A and D2 prepared in Example 1 and Comparative Example 2 of this disclosure.

[0032] Figure 2 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

[0033] Figure 3 This is a scanning electron microscope image of the iron-containing ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

[0034] Figure 4 This is a STEM-Mapping image of the iron-containing ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

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

[0036] Figure 6 This is a scanning electron microscope image of the iron-containing ZSM-5 molecular sieve B prepared in Example 2 of this disclosure.

[0037] Figure 7 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve C prepared in Example 3 of this disclosure.

[0038] Figure 8 This is a scanning electron microscope image of the iron-containing ZSM-5 molecular sieve C prepared in Example 3 of this disclosure.

[0039] Figure 9 This is the X-ray diffraction pattern of the iron-containing ZSM-5 molecular sieve D1 prepared in Comparative Example 1 of this disclosure.

[0040] Figure 10 This is a scanning electron microscope image of the iron-containing ZSM-5 molecular sieve D1 prepared in Comparative Example 1 of this disclosure.

[0041] Figure 11 This is the X-ray diffraction pattern of iron-containing ZSM-5 molecular sieve D2 prepared in Comparative Example 2 of this disclosure.

[0042] Figure 12 This is a STEM-Mapping image of the iron-containing ZSM-5 molecular sieve D2 prepared in Comparative Example 2 of this publication. Detailed Implementation

[0043] 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.

[0044] The first aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve, 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, and the outer surface of the particles of the iron-containing ZSM-5 molecular sieve does not contain iron active components.

[0045] In this disclosure, "the iron-containing ZSM-5 molecular sieve having a structure in which iron active components are internally encapsulated within the ZSM-5 molecular sieve" refers to the iron active components being distributed within the crystals, channels, or framework of the ZSM-5 molecular sieve; preferably, the iron active components are at least partially distributed within the framework or channels of the ZSM-5 molecular sieve; more preferably, all the iron active components are distributed within the framework of the ZSM-5 molecular sieve; wherein, "the iron active components are distributed within the framework of the ZSM-5 molecular sieve" means that at least a portion of the Si and Al in the ZSM-5 molecular sieve framework are replaced by Fe. The introduction of iron can modulate the acid properties of the ZSM-5 molecular sieve, improve its catalytic function for cracking and dehydrogenation, and introduce the iron active components into the interior of the molecular sieve in an encapsulated manner, further reducing the severity of light hydrocarbon catalytic cracking reactions and naphtha catalytic cracking reactions, improving the conversion rate of saturated hydrocarbons and the selectivity of low-carbon olefins, and reducing the formation of non-ideal components such as coke.

[0046] In this disclosure, "the outer surface of the iron-containing ZSM-5 molecular sieve particles does not contain iron-active components" means that the iron-active components are not distributed on the outer surface of the molecular sieve, and the outer surface of the iron-active components is not connected to the outer surface of the ZSM-5 molecular sieve. Compared to the presence of iron-active components on the outer surface of the molecular sieve, the iron-active components of the molecular sieve in this disclosure are more evenly distributed inside the molecular sieve, which is more conducive to the selective dehydrogenation of alkanes into alkenes in the molecular sieve channels, rather than dehydrogenation on the outer surface of the molecular sieve.

[0047] In this disclosure, the iron-active component may include skeletal iron and / or Fe2O3.

[0048] In one specific embodiment of this disclosure, the specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 240-400 m². 2 / g, preferably 320-360m 2 / g; total pore volume is 0.13-0.25cm³. 3 ·g -1 The preferred size is 0.13-0.22cm. 3 ·g -1 The micropore volume is 0.12-0.22 cm³. 3 ·g -1 The preferred size is 0.12-0.18cm. 3 ·g -1 The mesopore volume is 0.01-0.1 cm³. 3 ·g -1 The preferred size is 0.02-0.03cm. 3 ·g -1 The average particle size is 0.5-2 μm, preferably 1-2 μm; the relative crystallinity is 75-100%, preferably 85-95%; in the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-50, preferably 35-45; relative to the total weight of the iron-containing ZSM-5 molecular sieve, the content of the iron active component, calculated as Fe2O3, is 1-3% by weight, preferably 1-2% 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) as a benchmark. Specific surface area can be determined using a specific surface area analyzer based on the N2 adsorption principle and the BET calculation method (see Petrochemical Analytical Methods (RIPP Test Methods), RIPP 151-90, Science Press, 1990). Particle size can be estimated by performing SEM analysis on the molecular sieve and measuring the particle size of 50 randomly selected particles from the SEM image, then calculating the average value. The content of the iron active component, calculated as Fe2O3, is obtained by X-ray fluorescence spectroscopy.

[0049] A second aspect of this disclosure provides a method for preparing iron-containing ZSM-5 molecular sieves, the method comprising the following steps:

[0050] S1 mixes silicon source, aluminum source, alkali source, seed crystal and water to obtain the first mixture;

[0051] S2 brings the iron complex into contact with the first mixture to carry out a hydrothermal reaction.

[0052] The method disclosed herein encapsulates the iron-containing active component into the interior of a molecular sieve by adding ligands. The iron-containing ZSM-5 molecular sieve prepared can achieve good catalytic effects when used in the catalytic cracking reaction of light hydrocarbons and naphtha, improve the conversion rate of saturated hydrocarbons and the selectivity of low-carbon olefins, and reduce the generation of non-ideal components such as coke.

[0053] In this disclosure, the iron in the "iron complex" can be ferrous iron or ferric iron, and the iron complex can be a complex formed by ferric ions or ferrous ions and triethanolamine, or a complex formed by ferric ions or ferrous ions and ethylenediaminetetraacetic acid.

[0054] In this disclosure, the iron complex is contacted with the first mixture to form a second mixture, neither of which contains free iron ions or ferrous ions. This operation avoids the presence of aggregated iron active components in the prepared molecular sieve, which could affect its catalytic performance.

[0055] In one specific embodiment of this disclosure, the method further includes: mixing an iron source, a ligand, and water to obtain an iron complex; preferably, the molar ratio of the iron source, the ligand, and water, calculated as Fe2O3, is 1:(0.5-3):(100-1500), more preferably 1:(0.5-1.5):(500-1300), and even more preferably 1:(0.5-1.5):(1000-1300). By using the above ratio range, it can be ensured that the second mixture does not contain free iron ions or ferrous ions.

[0056] In one specific embodiment of this disclosure, the ligand is a nitrogen-containing ligand, preferably triethanolamine or ethylenediaminetetraacetic acid (EDTA), more preferably triethanolamine. The aforementioned ligand 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.

[0057] In one specific embodiment of this disclosure, the iron source includes water-soluble iron salts and / or ferrous salts, preferably one or more of ferric nitrate, ferrous nitrate, ferric sulfate, and ferrous sulfate.

[0058] In one specific embodiment of this disclosure, the silicon source, aluminum source, and alkali source are well known to those skilled in the art; preferably, 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 alkali source includes one or more of sodium hydroxide, water glass, and potassium hydroxide; wherein, water glass can be used as both an alkali source and a silicon source.

[0059] In one specific embodiment of this disclosure, the seed crystals include one or more of ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 20-50, and an average particle size of 0.5-2 μm, preferably 1-2 μm.

[0060] In one specific embodiment of this disclosure, in step S1, the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), alkali source (calculated as alkali metal oxide), and water is (20-75):1:(1-7):(140-800), preferably (40-60):1:(3-5):(300-600), and more preferably (35-50):1:(3-4):(360-600).

[0061] In one specific embodiment of this disclosure, the amount of seed crystals relative to the total weight of the silicon source, based on SiO2, is 1-10% by weight, preferably 5-10% by weight, and more preferably 8-10% by weight.

[0062] In one specific embodiment of this disclosure, the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:(0.01-2.5), preferably 1:(0.4-2.5).

[0063] In one specific embodiment of this disclosure, the hydrothermal reaction conditions in step S2 include: a time of 8-24 hours, preferably 8-16 hours; and a temperature of 150-220°C, preferably 160-180°C. According to this disclosure, hydrothermal reactions are well known to those skilled in the art and can be carried out in apparatus conventionally used by those skilled in the art, such as in a heat-resistant, sealed container, preferably a high-pressure reactor. This disclosure does not specifically limit the reaction pressure of the hydrothermal reaction; for example, it can be the autogenous pressure of the reaction system or under external pressure, preferably under the autogenous pressure of the reaction system.

[0064] In one specific embodiment of this disclosure, the method further includes: subjecting the product obtained from hydrothermal treatment to ammonium exchange and calcination; preferably, the solid product is washed until neutral before ammonium exchange, and the washing liquid can be any type of liquid that does not react with the solid product, such as deionized water. This disclosure does not impose specific limitations on the method for collecting the solid product; methods such as filtration and centrifugation can be used. The calcination treatment is well known to those skilled in the art, and can be carried out, for example, in a tube furnace, muffle furnace, etc. Before calcination, the solid obtained from ammonium exchange is dried under conventional conditions; more preferably, the calcination conditions may include: a temperature of 400-800°C and a time of 0.5-8 hours, and calcination can be carried out in an air atmosphere or a steam atmosphere.

[0065] The third aspect of this disclosure provides an iron-containing ZSM-5 molecular sieve prepared using the method described in the second aspect of this disclosure.

[0066] The aforementioned iron-containing ZSM-5 molecular sieve has the same characteristics as the iron-containing ZSM-5 molecular sieve described in the first aspect of this disclosure, and will not be repeated here.

[0067] This fourth aspect of the disclosure provides the application of the iron-containing ZSM-5 molecular sieve described in the first or third aspect of the disclosure in the catalytic cracking of light hydrocarbons and naphtha.

[0068] According to a specific embodiment of this disclosure, the catalytic cracking reaction of light hydrocarbons can be carried out in a fixed-bed reactor. The reaction conditions for the catalytic cracking reaction of light hydrocarbons may include: a temperature of 500-550°C and a mass hourly space velocity of 20-40 h⁻¹. -1 The reaction pressure is 0.1-1.2 MPa.

[0069] According to a specific embodiment of this disclosure, the naphtha catalytic cracking reaction can be carried out in a fixed-bed reactor. The reaction conditions for the naphtha catalytic cracking reaction may include: a temperature of 600-650°C and a reaction mass hourly space velocity of 20-40 h⁻¹. -1 The reaction pressure is 0.1-1.2 MPa.

[0070] According to one specific embodiment of this disclosure, light hydrocarbons may include alkanes having 2-16 carbon atoms, such as ethane, propane, n-tetradecane, etc.

[0071] The present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereto. Unless otherwise specified, all raw materials used in the following examples and comparative examples were commercially available.

[0072] 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.

[0073] 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.

[0074] 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).

[0075] Average particle size: The average particle size was estimated by performing SEM analysis on the molecular sieve and measuring the particle size of 50 randomly selected particles in the SEM image. The SEM instrument model was HITACHI S-4800.

[0076] 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). Isothermal adsorption data from the linear portion of the N2 adsorption-desorption curve (p / p0 = 0-0.25) were selected, and the specific surface area of ​​the sample was calculated using the BET method. The desorption branch data were calculated using the BJH (Barrett-Joyner-Halenda) method to obtain the pore size distribution data of the sample.

[0077] The scanning electron microscope (SEM) used was a HITACHI S-4800. The testing conditions were: accelerating voltage of 20.0 kV, sample preparation, and observation of the crystal morphology and size of the molecular sieve samples at magnifications of 5000-30000.

[0078] Hydrogen-TPR testing method and instrumentation: Micromeritic AutochemⅡ2920 temperature-programmed desorption apparatus. Weigh 0.2 g (20-40 mesh) of molecular sieve catalyst and load it into a sample tube. Place the tube in a thermal conductivity cell furnace with He gas as the carrier gas (25 mL / min). Heat to 550 °C at a rate of 20 °C / min, and purge for 60 min to remove impurities adsorbed on the catalyst surface. Then cool to 150 °C, hold at that temperature for min, switch to an H2-He mixture (10.02% H2 + 89.98% He) for adsorption for 60 min, and continue purging with He gas for 120 min until the baseline stabilizes. Desorption is then performed by programming the temperature to 550 °C at a rate of 10 °C / min. Hold for 30 min to complete desorption, and use a TCD detector to detect changes in gas composition.

[0079] STEM-Mapping test method and instrument: JEM-2100 (200kV) transmission electron microscope, manufactured by Nippon Electron Ltd. 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.

[0080] 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.

[0081] Example 1

[0082] (1) Add 0.81g sodium hydroxide, 49.35g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0083] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 54:1:4.05:578; 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.

[0084] (2) Dissolve 1.1g of ferric nitrate nonahydrate in 10g of deionized water, add 0.4g of triethanolamine ligand, and stir thoroughly until clear and transparent;

[0085] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:204, and the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.46.

[0086] (3) Add the mixture obtained in step (2) to the first mixture, mix thoroughly to obtain the second mixture, and then transfer it to a stainless steel autoclave for hydrothermal treatment at 170°C for 12 hours; wherein the second mixture does not contain free iron ions;

[0087] (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 the ZSM-5 molecular sieve encapsulated with iron, denoted as A. Its structural parameters are listed in Table 1, and its hydrogen-TPR diagram is shown in Table 1. Figure 1 X-ray diffraction pattern is shown in Figure 2, and scanning electron microscope image is shown in Figure 3. Figure 3 See STEM-Mapping photos Figure 4 .

[0088] Example 2

[0089] (1) Add 1.14g sodium hydroxide, 49.35g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0090] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 54:1:5.4:578; 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.

[0091] (2) Dissolve 1.1g of ferric nitrate nonahydrate in 10g of deionized water, add 0.4g of triethanolamine ligand, and stir thoroughly until clear and transparent;

[0092] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:204; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.46.

[0093] (3) Add the mixture obtained in step (2) to the first mixture, mix thoroughly to obtain the second mixture, and then transfer it to a stainless steel autoclave for hydrothermal treatment at 170°C for 10 hours; wherein the second mixture does not contain free iron ions;

[0094] (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 the ZSM-5 molecular sieve encapsulated with iron, denoted as B. Its structural parameters are listed in Table 1, its X-ray diffraction pattern is shown in Table 5, and its scanning electron microscope image is shown in Table 6. Figure 6 .

[0095] Example 3

[0096] (1) Add 2g sodium hydroxide, 49.32g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0097] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 54:1:6.75:578; 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.

[0098] (2) Dissolve 1.1g of ferric nitrate nonahydrate in 10g of deionized water, add 0.4g of triethanolamine ligand, and stir thoroughly until clear and transparent;

[0099] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:204; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.46.

[0100] (3) Add the mixture obtained in step (2) to the first mixture, mix thoroughly to obtain the second mixture, and then transfer it to a stainless steel autoclave for hydrothermal treatment at 170°C for 12 hours; wherein the second mixture does not contain free iron ions;

[0101] (4) The product obtained from the hydrothermal treatment in step (3) 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 ZSM-5 molecular sieve encapsulated with iron, denoted as C. The structural parameters are listed in Table 1, and its X-ray diffraction pattern is shown in Table 1. Figure 7 Scanning electron microscope images can be found Figure 8 .

[0102] Example 4

[0103] (1) Add 0.81g sodium hydroxide, 49.35g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0104] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 54:1:4.05:578; 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.

[0105] (2) Dissolve 1.1g of ferric nitrate nonahydrate in 10g of deionized water, add 0.8g of triethanolamine ligand, and stir thoroughly until clear and transparent;

[0106] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:2:204; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.46.

[0107] (3) Add the mixture obtained in step (2) to the first mixture, mix thoroughly to obtain the second mixture, and then transfer it to a stainless steel autoclave for hydrothermal treatment at 170°C for 12 hours; wherein the second mixture does not contain free iron ions;

[0108] (4) The product obtained by hydrothermal treatment in step (3) is filtered, washed until pH=7-8, and then ammonium exchanged. It is dried at 120℃ for 12h and then calcined at 550℃ for 2h in air atmosphere to obtain ZSM-5 molecular sieve encapsulated iron, denoted as D. The structural parameters are listed in Table 1.

[0109] Example 5

[0110] Iron-containing ZSM-5 molecular sieve E was prepared using the method of Example 1, except that silica gel was replaced with fumed silica, low-alkali sodium aluminate was replaced with solid aluminum hydroxide, ferric nitrate was replaced with ferrous nitrate hexahydrate, and triethanolamine was replaced with EDTA.

[0111] The molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), alkali source (calculated as alkali metal oxide), and water is 40:1:4.8:600; the second mixture does not contain free ferrous ions;

[0112] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:150; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.56. Their structural parameters are listed in Table 1.

[0113] Comparative Example 1

[0114] Molecular sieve D1 was prepared using the method described in Example 1, except that triethanolamine ligand was not added. Its structural parameters are listed in Table 1, X-ray diffraction pattern is shown in Figure 9, and scanning electron microscope image is shown in Figure 1. Figure 10 .

[0115] Comparative Example 2

[0116] (1) Add 0.81g sodium hydroxide, 49.35g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring. After stirring thoroughly, transfer to a stainless steel kettle and hydrothermally treat at 170℃ for 12h. Then filter, wash until pH=7-8, perform ammonium exchange, and dry at 120℃ for 12h.

[0117] (2) Dissolve 1.7g diammonium hydrogen phosphate and 1.1g ferric nitrate in 10g deionized water and stir thoroughly until clear and transparent. Modify the sodium molecular sieve with phosphorus and iron by impregnation, and then calcine at 550℃ for 2h after ammonium exchange.

[0118] The product sample is designated D2, and its structural parameters are listed in Table 1. Its hydrogen-TPR diagram is shown below. Figure 1 X-ray diffraction pattern can be found in [the image]. Figure 11 See STEM-Mapping photos Figure 12 .

[0119] Comparative Example 3

[0120] (1) Add 0.81g sodium hydroxide, 49.35g deionized water, 20g silica gel, 5.99g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L) and 2.01g ZSM-5 seed crystals in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0121] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), and water is 54:1:4.05:578; 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.

[0122] (2) Add 1.1g ferric nitrate, 10g deionized water and 0.4g triethanolamine ligand to the first mixture obtained in step (1), mix thoroughly to obtain the second mixture, and then transfer it to a stainless steel autoclave for hydrothermal treatment at 170℃ for 12h.

[0123] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:204; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.46.

[0124] (3) The product obtained by hydrothermal treatment in step (2) is filtered, washed until pH=7-8, and then ammonium exchanged. It is dried at 120℃ for 12h and then calcined at 550℃ for 2h in air atmosphere to obtain ZSM-5 molecular sieve encapsulated iron, denoted as D3. The structural parameters are listed in Table 1.

[0125] Comparative Example 4

[0126] ZSM-5 molecular sieve D4 was prepared using the method of Example 1, with the only difference being that the amount of triethanolamine ligand used was 0.08 g, the second mixture contained free iron ions, and the molar ratio of iron source, ligand and water (calculated as Fe2O3) was 1:0.2:204. The structural parameters are listed in Table 1.

[0127] The molecular sieve D4 prepared in Comparative Example 4 was subjected to hydrogen-TPR testing, and peaks were observed at 100-700℃, indicating that iron-active components are distributed on its outer surface.

[0128] Test Examples 1-9

[0129] 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.

[0130] Aged molecular sieves were used as catalysts in the catalytic cracking of light hydrocarbons, specifically for the cracking of n-tetradecane. The specific method is as follows: the reaction was carried out in a fixed-bed reactor, with n-tetradecane as the feedstock, nitrogen as the carrier gas at a flow rate of 30 mL / min, a reaction temperature of 550 °C, a regeneration temperature of 600 °C, and a weight hourly space velocity (WHSV) of 20 h⁻¹. -1 The molecular sieve tablets were sieved into 20-40 mesh particles, with a loading of 2.0 g and an oil-to-solvent ratio of 1.28. Samples were taken for analysis after 900 s of reaction under normal pressure, and material balance calculations were performed. The product distribution is shown in Table 1.

[0131] The micro-reaction conversion rate X of the raw material and the yield Y of the product are calculated using the following formulas. i :

[0132] X = 100% - (yield of liquid products × content of n-tetradecane in liquid products) × 100%, where liquid products refer to gasoline and diesel;

[0133] Y i = Mass of component i in the product / Mass of converted n-tetradecane × 100%, where i represents ethylene, propylene, and butene.

[0134] Table 1

[0135]

[0136]

[0137] Test Example 10-18

[0138] The iron-containing ZSM-5 molecular sieves prepared in the examples and comparative examples were aged (the aging treatment method was the same as in Test Example 1) and used as catalysts in the catalytic cracking reaction of naphtha. The specific method is as follows: the reaction was carried out in a fixed-bed reactor, the feedstock was naphtha (Yanshan Petrochemical's Changding oil), the carrier gas was nitrogen at a flow rate of 30 mL / min, the reaction temperature was 650 °C, the regeneration temperature was 600 °C, and the weight hourly space velocity was 20 h⁻¹. -1 The molecular sieve tablets were sieved into 20-40 mesh particles, with a loading of 2.0 g and an oil-to-solvent ratio of 1.28. Samples were taken for analysis after 900 s of reaction under normal pressure, and material balance calculations were performed. The product distribution is shown in Table 2.

[0139] The micro-reaction conversion rate X of the raw material and the yield Y of the product are calculated using the following formulas. i :

[0140] X = 100% - (yield of liquid products × naphtha content in liquid products) × 100%, where liquid products refer to gasoline and diesel;

[0141] Yi = Mass of component i in the product / Mass of converted naphtha × 100%, where i represents ethylene, propylene, and butene.

[0142] Table 2

[0143]

[0144] According to the data in Table 1, the iron-containing ZSM-5 molecular sieve prepared by the method disclosed herein has a relatively high crystallinity of 78.1-85.1%. Meanwhile, comparing the scanning electron microscope (SEM) images of the iron-containing ZSM-5 molecular sieves prepared in Examples 1-3 with those of the iron-containing ZSM-5 molecular sieve prepared in Comparative Example 1, it can be seen that the iron active component in the iron-containing ZSM-5 molecular sieve prepared by the method disclosed herein has a low degree of aggregation. According to the STEM-Mapping images of the iron-containing ZSM-5 molecular sieve prepared in Example 1 and the iron-containing molecular sieve prepared in Comparative Example 2, it can be seen that the iron active component in the iron-containing ZSM-5 molecular sieve prepared by the method disclosed herein is uniformly distributed. According to the hydrogen-TPR diagrams of the iron-containing ZSM-5 molecular sieve prepared in Example 1 and the iron-containing ZSM-5 molecular sieve prepared in Comparative Example 2, it can be seen that the molecular sieve of Example 1 does not show any 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 disclosed herein exists entirely on the molecular sieve framework and is not distributed on the outer surface of the molecular sieve.

[0145] In summary, and based on the data in Tables 1 and 2, the iron-containing ZSM-5 molecular sieve prepared by the method of this disclosure has its iron active components uniformly distributed inside the molecular sieve and not distributed on the outer surface of the molecular sieve particles. When used for catalytic cracking of light hydrocarbons and naphtha, it can achieve better yields of low-carbon olefins, and can also increase the yield of propylene and reduce the yield of coke.

[0146] Data from Example 1 and Comparative Example 4 show that when the second mixture contains free iron ions or ferrous ions, aggregated iron active components are distributed on the surface of the molecular sieve, resulting in poor catalytic activity.

[0147] 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.

[0148] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0149] 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 for catalytic cracking of light hydrocarbons and naphtha, characterized in that, The method includes the following steps: S1 mixes silicon source, aluminum source, alkali source, seed crystal and water to obtain the first mixture; S2 brings the iron complex into contact with the first mixture to carry out a hydrothermal reaction; 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 (40-60):1:(3-5):(300-600). The method further includes: mixing an iron source, a ligand, and water to obtain the iron complex; The ligand is triethanolamine; The molar ratio of the iron source, the ligand, and the water, calculated as Fe2O3, is 1:(0.5-3):(100-1500).

2. The method according to claim 1, wherein, The iron source includes one or more of ferric nitrate, ferrous nitrate, ferric sulfate, and ferrous sulfate.

3. The method according to claim 1, wherein, In step S1, 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, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate; The alkaline source includes one or more of sodium hydroxide, water glass, and potassium hydroxide; The seed crystals include one or more ZSM-5 molecular sieves with a silicon-to-aluminum ratio of 20-50, wherein the average particle size of the seed ZSM-5 molecular sieve is 0.5-2 μm.

4. The method according to claim 1, wherein, In step S1, the amount of seed crystals used is 1-10 by weight relative to the total weight of the silicon source, based on SiO2.

5. 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 (35-50):1:(3-4):(360-600).

6. The method according to claim 1, wherein, Based on SiO2, the amount of seed crystals used is 8-10% by weight relative to the total weight of the silicon source.

7. The method according to claim 1, wherein, The molar ratio of the aluminum source (calculated as Al2O3) to the iron source (calculated as Fe2O3) is 1:(0.01-2.5).

8. The method according to claim 1, wherein, In step S2, the conditions for the hydrothermal reaction include: a time of 8-24 hours and a temperature of 150-220°C.

9. The method according to claim 1, wherein, The method further includes: subjecting the product obtained from the hydrothermal treatment to ammonium exchange and calcination.

10. The method according to claim 9, wherein, The conditions for the roasting treatment include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

11. Iron-containing ZSM-5 molecular sieve prepared by the method according to any one of claims 1-10.

12. The iron-containing ZSM-5 molecular sieve according to claim 11, wherein, The iron-containing ZSM-5 molecular sieve has a structure in which iron-active components are encapsulated internally by the ZSM-5 molecular sieve, and the outer surface of the particles of the iron-containing ZSM-5 molecular sieve does not contain iron-active components.

13. The iron-containing ZSM-5 molecular sieve according to claim 12, wherein, The iron-active component is distributed on the framework or within the pores of the ZSM-5 molecular sieve.

14. The iron-containing ZSM-5 molecular sieve according to claim 12, wherein, The specific surface area of ​​the iron-containing ZSM-5 molecular sieve is 240-400 m². 2 / g, total pore volume is 0.13-0.25cm³. 3 ·g -1 The micropore volume is 0.12-0.22 cm³. 3 ·g -1 The mesopore volume is 0.01-0.1 cm³. 3 ·g -1 The average particle size is 0.5-2 μm, and the relative crystallinity is 75-100%. In the iron-containing ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-50; The content of iron active component, calculated as Fe2O3, is 1-3% by weight relative to the total weight of the iron-containing ZSM-5 molecular sieve.

15. The application of the iron-containing ZSM-5 molecular sieve according to any one of claims 11-14 in the catalytic cracking reaction of light hydrocarbons and the catalytic cracking reaction of naphtha.

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