Iron-containing small crystal zsm-5 molecular sieve, preparation method and application thereof

Abstract

The present disclosure relates to a kind of iron-containing small crystal ZSM-5 molecular sieve and its preparation method and application, the iron-containing small crystal 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 small crystal ZSM-5 molecular sieve does not contain iron active component;The grain size of the iron-containing small crystal ZSM-5 molecular sieve is 0.5-1 μm.The present disclosure uses template agent method, and by using ligand, iron active component is encapsulated in the inside of ZSM-5 molecular sieve, and the ZSM-5 molecular sieve of encapsulated iron prepared has the characteristics of small grain size, high relative crystallinity, high silica-alumina ratio, iron active component is uniformly distributed and not distributed on the surface of molecular sieve;It is used for light hydrocarbon catalytic cracking reaction and naphtha catalytic cracking reaction, has higher conversion rate and the yield of relatively optimal low carbon olefin.

Description

Technical Field

[0001] This disclosure relates to the field of molecular sieve preparation, specifically to a ZSM-5 molecular sieve containing iron small crystals, 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. Characterization results showed that the Pd particles after hydrogen reduction were approximately 1.5 nm in size and distributed at the intersection of the two sets of ten-membered ring channels in the MFI molecular sieve. However, while there has been considerable research on encapsulating metals into all-silica or high-silica MFI molecular sieves, research on encapsulating metals into silica-alumina type MFI molecular sieves is limited. This is because directly introducing metals into the synthesis system can lead to difficulties in synthesis or low activity due to the tendency of metals to form hydroxide precipitates in alkaline environments and their susceptibility to phosphorus interactions. Summary of the Invention

[0005] The purpose of this disclosure is to provide an iron-containing small-crystal ZSM-5 molecular sieve, its preparation method and application. This molecular sieve has the characteristics of small crystal size, 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.

[0006] To achieve the above objectives, the first aspect of this disclosure provides an iron-containing small-crystal ZSM-5 molecular sieve, wherein the iron-containing small-crystal 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 small-crystal ZSM-5 molecular sieve does not contain iron active components.

[0007] The iron-containing small-crystal ZSM-5 molecular sieve has a crystal size of 0.5-1 μm.

[0008] Optionally, the iron-active component is distributed on the framework or within the pores of the ZSM-5 molecular sieve.

[0009] Optionally, the specific surface area of ​​the iron-containing small-crystal ZSM-5 molecular sieve is 240-450 m². 2 / g, total pore volume is 0.160-0.22cm³ 3 ·g -1 The micropore volume is 0.140-0.180 cm³. 3 ·g -1 The mesopore volume is 0.010-0.080 cm³. 3 ·g -1 The relative crystallinity is 80-100%;

[0010] In the iron-containing small-crystal ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-300;

[0011] The content of the iron active component, calculated as Fe2O3, is 1-3% by weight relative to the total weight of the iron-containing small-crystal ZSM-5 molecular sieve.

[0012] A second aspect of this disclosure provides a method for preparing iron-containing small-crystal ZSM-5 molecular sieves, the method comprising the following steps:

[0013] S1 mixes silicon source, aluminum source, alkali source, seed crystal, template agent and water to obtain the first mixture;

[0014] S2 brings the iron complex into contact with the first mixture to carry out a hydrothermal reaction.

[0015] 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).

[0016] Optionally, the ligand is a nitrogen-containing ligand, preferably triethanolamine or ethylenediaminetetraacetic acid;

[0017] The iron source includes one or more of ferric nitrate, ferrous nitrate, ferric sulfate, and ferrous sulfate.

[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 template agent includes an organic nitrogen-containing template agent, preferably one or more of n-butylamine, tetrapropylammonium hydroxide and tetrapropylammonium bromide;

[0022] 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.

[0023] 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), the template agent, and the water is (50-300):1:(4-30):(4.5-30):(500-2500), preferably (50-90):1:(4-20):(4.5-15):(500-1200);

[0024] 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.

[0025] Optionally, the molar ratio of the aluminum source (calculated as Al2O3) to the iron source (calculated as Fe2O3) is 1:(0.01-2.5).

[0026] Optionally, in step S2, the conditions for the hydrothermal reaction include: a time of 8-32 hours and a temperature of 150-220°C.

[0027] Optionally, the method further includes: subjecting the product obtained from the hydrothermal treatment to ammonium exchange and calcination;

[0028] Optionally, the calcination conditions include: a temperature of 400-800℃, a time of 0.5-8h, and an atmosphere of air or water vapor.

[0029] The third aspect of this disclosure provides an iron-containing small-crystal ZSM-5 molecular sieve prepared using the method described in the second aspect of this disclosure.

[0030] This fourth aspect of the disclosure provides the application of the iron-containing small-crystal ZSM-5 molecular sieve described in the first or third aspect of the disclosure in the catalytic cracking reaction of light hydrocarbons and the catalytic cracking reaction of naphtha.

[0031] Through the above technical solution, this disclosure adopts the template agent 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 small grain size, fast mass transfer rate, high relative crystallinity, high silica-alumina ratio, uniform iron distribution and not distributed on the surface of the molecular sieve. When used in the catalytic cracking reaction of light hydrocarbons and the catalytic cracking reaction of naphtha, it has high conversion rate and better yield of low carbon olefins, and can obtain a high propylene yield.

[0032] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0033] 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:

[0034] Figure 1 This is the X-ray diffraction pattern of the iron-containing small-crystal ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

[0035] Figure 2This is a scanning electron microscope image of the iron-containing small-crystal ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

[0036] Figure 3 This is a STEM-Mapping image of the iron-containing small-crystal ZSM-5 molecular sieve A prepared in Example 1 of this disclosure.

[0037] Figure 4 This is the X-ray diffraction pattern of the iron-containing small-crystal ZSM-5 molecular sieve B prepared in Example 2 of this disclosure.

[0038] Figure 5 This is a scanning electron microscope image of the iron-containing small-crystal ZSM-5 molecular sieve B prepared in Example 2 of this disclosure.

[0039] Figure 6 This is a STEM-Mapping image of the iron-containing small-crystal ZSM-5 molecular sieve B prepared in Example 2 of this disclosure.

[0040] Figure 7 This is the X-ray diffraction pattern of the iron-containing small-crystal ZSM-5 molecular sieve C prepared in Example 3 of this disclosure.

[0041] Figure 8 This is a scanning electron microscope image of the iron-containing small-crystal ZSM-5 molecular sieve C prepared in Example 3 of this disclosure.

[0042] Figure 9 This is a STEM-Mapping image of the iron-containing small-crystal ZSM-5 molecular sieve C prepared in Example 3 of this disclosure.

[0043] Figure 10 These are hydrogen-TPR diagrams of iron-containing small-crystal ZSM-5 molecular sieve samples A, B, and C prepared in Examples 1, 2, and 3 of this disclosure. Detailed Implementation

[0044] 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.

[0045] The first aspect of this disclosure provides an iron-containing small-crystal ZSM-5 molecular sieve, wherein the iron-containing small-crystal 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 small-crystal ZSM-5 molecular sieve does not contain iron-active components.

[0046] The iron-containing small-crystal ZSM-5 molecular sieve has a crystal size of 0.5-1 μm.

[0047] In this disclosure, "the iron-containing small-crystal 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 is replaced by Fe. The introduction of iron can modulate the acidity 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, and improving the conversion rate of saturated hydrocarbons and the selectivity of low-carbon olefins.

[0048] 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.

[0049] In this disclosure, the iron-active component may include skeletal iron and / or Fe2O3.

[0050] In one specific embodiment of this disclosure, the grain size of the iron-containing ZSM-5 molecular sieve is 0.5-0.8 μm. The grain size can be estimated by performing SEM analysis on the molecular sieve and taking the average value of the particle size of any 50 particles selected from its SEM image.

[0051] In one specific embodiment of this disclosure, the specific surface area of ​​the iron-containing small-crystal ZSM-5 molecular sieve is 240-450 m². 2 / g, preferably 350-400m 2 / g; total pore volume is 0.160-0.22cm³. 3 ·g -1 The preferred size is 0.180-0.195cm. 3 ·g -1 The micropore volume is 0.140-0.180 cm³. 3 ·g -1 The preferred value is 0.155-0.175cm. 3 ·g -1 The mesopore volume is 0.010-0.080 cm³. 3 ·g-1 The preferred value is 0.020-0.040cm. 3 ·g -1 The relative crystallinity is 80-100%, preferably 88-97%; in the iron-containing small-crystal ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-300, preferably 30-100; relative to the total weight of the iron-containing small-crystal ZSM-5 molecular sieve, the content of the iron active component, calculated as Fe2O3, is 1-3% by weight, preferably 1.3-2% 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, 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, China Petroleum & Chemical Corporation is 100%). The specific surface area can be determined using a specific surface area analyzer according to the N2 adsorption principle and 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, was determined by X-ray fluorescence spectroscopy.

[0052] A second aspect of this disclosure provides a method for preparing iron-containing small-crystal ZSM-5 molecular sieves, the method comprising the following steps:

[0053] S1 mixes silicon source, aluminum source, alkali source, seed crystal, template agent and water to obtain the first mixture;

[0054] S2 brings the iron complex into contact with the first mixture to carry out a hydrothermal reaction.

[0055] The method disclosed herein encapsulates the iron-containing active component into the interior of a molecular sieve by adding ligands. The resulting iron-containing small-crystal ZSM-5 molecular sieve exhibits good catalytic performance in light hydrocarbon catalytic cracking and naphtha catalytic cracking reactions, improving the conversion rate of saturated hydrocarbons and the selectivity of low-carbon olefins.

[0056] 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.

[0057] 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.

[0058] 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):(800-1300). By using the above ratio range, it can be ensured that the second mixture does not contain free iron ions or ferrous ions.

[0059] 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.

[0060] 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.

[0061] 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; and the alkali source includes sodium hydroxide and / or potassium hydroxide.

[0062] In one specific embodiment of this disclosure, the template agent includes an organic nitrogen-containing template agent, preferably one or more of aminoalkane, nitrogen-containing organic hydroxide and organic ammonium bromide; more preferably one or more of n-butylamine, tetrapropylammonium hydroxide and tetrapropylammonium bromide.

[0063] 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.

[0064] 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), template agent and water is (50-300):1:(4-30):(4.5-30):(500-2500), preferably (50-90):1:(4-20):(4.5-15):(500-1200).

[0065] 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.

[0066] 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).

[0067] In one specific embodiment of this disclosure, the hydrothermal reaction conditions in step S2 include: a time of 8-32 hours, preferably 8-20 hours; and a temperature of 150-220°C, preferably 150-180°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.

[0068] 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.

[0069] The third aspect of this disclosure provides an iron-containing small-crystal ZSM-5 molecular sieve prepared using the method described in the second aspect of this disclosure.

[0070] The aforementioned iron-containing small-crystal ZSM-5 molecular sieve has the same characteristics as the iron-containing small-crystal ZSM-5 molecular sieve described in the first aspect of this disclosure, and will not be repeated here.

[0071] This fourth aspect of the disclosure provides the application of the iron-containing small-crystal ZSM-5 molecular sieve described in the first or third aspect of the disclosure in the catalytic cracking reaction of light hydrocarbons and the catalytic cracking reaction of naphtha.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Grain size: The size of the molecular sieve was estimated by SEM analysis and by taking the average value of 50 randomly selected particles from the SEM image. The SEM instrument used was a HITACHI S-4800.

[0078] 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.

[0079] 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).

[0080] Method for testing pore volume: The sample is evacuated to a vacuum of 1.33 × 10⁻⁶ at 350°C. -2The 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.

[0081] 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.

[0082] 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.

[0083] 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 60 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.

[0084] 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.

[0085] Example 1

[0086] This embodiment uses the following steps to prepare iron-containing small-crystal ZSM-5 molecular sieve A:

[0087] (1) Add 0.87g sodium hydroxide, 40.35g deionized water, 20g silica gel, 7.35g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals and 1.98g n-butylamine in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0088] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), n-butylamine, and water is 50:1:4.25:4.5:535; 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.

[0089] (2) Dissolve 1.07g of ferric nitrate nonahydrate in 10g of deionized water, add 0.40g of triethanolamine ligand, and stir thoroughly until clear and transparent to obtain the second mixture;

[0090] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:210, and the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.40.

[0091] (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;

[0092] (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 small-crystal ZSM-5 molecular sieve encapsulated with iron, denoted as A. Its structural parameters are listed in Table 1. Its X-ray diffraction pattern is shown in Figure 1, and its scanning electron microscope image is shown in Figure 2. Figure 2 See STEM-Mapping photos Figure 3 .

[0093] Example 2

[0094] This embodiment uses the following steps to prepare iron-containing small-crystal ZSM-5 molecular sieve B:

[0095] (1) Add 1.15g sodium hydroxide, 41.69g deionized water, 20g silica gel, 5.66g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals and 1.98g n-butylamine in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0096] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), template agent, and water is 65:1:5.52:5.85:696; 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.

[0097] (2) Dissolve 1.02g of ferric nitrate nonahydrate in 10g of deionized water, add 0.38g of triethanolamine ligand, and stir thoroughly until clear and transparent to obtain the second mixture;

[0098] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:223; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.51.

[0099] (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;

[0100] (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 small-crystal 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 4, and its scanning electron microscope image is shown in Table 5. Figure 5 See STEM-Mapping photos Figure 6 .

[0101] Example 3

[0102] This embodiment uses the following steps to prepare iron-containing small-crystal ZSM-5 molecular sieve C:

[0103] (1) Add 1.48g sodium hydroxide, 43.24g deionized water, 20g silica gel, 3.68g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals and 1.98g n-butylamine 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), template agent, and water is 100:1:9:8.5:1070; 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 0.96g of ferric nitrate nonahydrate in 10g of deionized water, add 0.36g of triethanolamine ligand, and stir thoroughly until clear and transparent to obtain the second mixture;

[0106] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:236; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.79.

[0107] (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;

[0108] (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 small-crystal ZSM-5 molecular sieve encapsulated with iron, denoted as C. Its structural parameters are listed in Table 1, its X-ray diffraction pattern is shown in Figure 7, and its scanning electron microscope image is shown in Figure 8. Figure 8 See STEM-Mapping photos Figure 9 .

[0109] The molecular sieves A, B, and C prepared in Examples 1-3 were subjected to hydrogen-TPR testing, and the results are shown in the figure. Figure 10 .

[0110] Example 4

[0111] This embodiment uses the following steps to prepare iron-containing small-crystal ZSM-5 molecular sieve D:

[0112] (1) Add 1.15g sodium hydroxide, 41.69g deionized water, 20g silica gel, 5.66g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals, and 5.5g tetrapropylammonium hydroxide in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0113] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), template agent, and water is 65:1:5.52:5.85:696; 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.

[0114] (2) Dissolve 1.02g of ferric nitrate nonahydrate in 10g of deionized water, add 1.58g of EDTA ligand, and stir thoroughly until clear and transparent to obtain the second mixture;

[0115] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:223; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.51.

[0116] (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;

[0117] (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 small-crystal ZSM-5 molecular sieve of encapsulated iron, denoted as D. The structural parameters are listed in Table 1.

[0118] Example 5

[0119] This embodiment uses the following steps to prepare iron-containing small-crystal ZSM-5 molecular sieve E:

[0120] (1) Add 1.15g sodium hydroxide, 41.69g deionized water, 20g silica gel, 5.66g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals and 1.98g n-butylamine 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), template agent, and water is 65:1:5.52:5.85:696; 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) Dissolve 1.02g of ferric nitrate nonahydrate in 10g of deionized water, add 0.76g of triethanolamine ligand, and stir thoroughly until clear and transparent to obtain the second mixture;

[0123] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:2:223; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.51.

[0124] (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;

[0125] (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 small-crystal ZSM-5 molecular sieve of encapsulated iron, denoted as E. The structural parameters are listed in Table 1.

[0126] Comparative Example 1

[0127] Iron-containing ZSM-5 molecular sieve D1 was prepared using the method of Example 2, the only difference being that triethanolamine ligand was not added. Its structural parameters are listed in Table 1.

[0128] Comparative Example 2

[0129] This comparative example illustrates the effect of the feeding sequence on iron-containing ZSM-5 molecular sieves.

[0130] (1) Add 1.15g sodium hydroxide, 1.69g deionized water, 20g silica gel, 5.66g low-alkali sodium aluminate (Na2O: 156.3g / L, Al2O3: 103.8g / L), 1.97g ZSM-5 seed crystals and 1.98g triethylamine in sequence under stirring, and stir thoroughly to obtain the first mixture;

[0131] The molar ratio of silicon source (SiO2), aluminum source (Al2O3), alkali source (alkali metal oxide), template agent, and water is 65:1:5.52:5.85:696; 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.

[0132] (2) Add 1.02g of ferric nitrate, 10g of deionized water and 0.38g of triethanolamine ligand to the first mixture obtained in step (1) in sequence, mix thoroughly and evenly, then transfer to a stainless steel autoclave and hydrothermally treat at 170℃ for 12h.

[0133] The molar ratio of iron source, ligand and water (calculated as Fe2O3) is 1:1:223; the molar ratio of aluminum source (calculated as Al2O3) to iron source (calculated as Fe2O3) is 1:0.51.

[0134] (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 a hydrogen atmosphere to obtain ZSM-5 molecular sieve encapsulated iron, denoted as D2. The structural parameters are listed in Table 1.

[0135] Comparative Example 3

[0136] Iron-containing ZSM-5 molecular sieve D3 was prepared using the method of Example 2, the only difference being that the amount of triethanolamine ligand used was 0.13 g, the second mixture contained free iron ions, and the molar ratio of iron source, ligand and water (calculated as Fe2O3) was 1:0.3:223. The structural parameters are listed in Table 1.

[0137] Test Examples 1-8

[0138] 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.

[0139] The iron-containing ZSM-5 molecular sieves prepared in the examples and comparative examples were used as catalysts in the catalytic cracking reaction of light hydrocarbons to carry out 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-dosage 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.

[0140] The micro-reaction conversion rate X of the raw material and the yield S of the product are calculated using the following formulas. i :

[0141]

[0142]

[0143]

[0144]

[0145] Table 1

[0146]

[0147] Test Example 9-16

[0148] 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℃, the regeneration temperature was 600℃, 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 2.

[0149] The micro-reaction conversion rate X of the raw material and the yield Y of the product are calculated using the following formulas. i :

[0150] X = 100% - (yield of liquid products × naphtha content in liquid products) × 100%, where liquid products refer to gasoline and diesel;

[0151] Y i= Mass of component i in the product / Mass of converted naphtha × 100%, where i represents ethylene, propylene, and butene.

[0152] Table 2

[0153]

[0154] As shown in Table 1, the iron-containing small-crystal ZSM-5 molecular sieve prepared by the template agent method and ligands in this disclosure has a relatively high crystallinity of 88.9-96.8% and a small crystal size of 0.5-0.7 μm. Scanning electron micrographs of the iron-containing ZSM-5 molecular sieves prepared in Examples 1-3 show that the crystal size of the iron-containing ZSM-5 molecular sieve prepared by the method of this disclosure is 0.5-1 μm, which belongs to the category of small-crystal molecular sieves. STEM-Mapping images of the iron-containing ZSM-5 molecular sieves prepared in Examples 1-3 show that the iron active component in the iron-containing ZSM-5 molecular sieves prepared by the method of this disclosure is uniformly distributed. According to the hydrogen-TPR chromatograms of the iron-containing small-crystal ZSM-5 molecular sieves prepared in Examples 1-3, the molecular sieves of Examples 1-3 did not have obvious peaks in the range of 100-700℃, indicating that the iron active components in the iron-containing small-crystal ZSM-5 molecular sieves prepared by the method disclosed herein are all present on the framework of the molecular sieve and are not distributed on the outer surface of the molecular sieve.

[0155] Furthermore, according to the data in Tables 1 and 2, when the iron-containing small-crystal ZSM-5 molecular sieve prepared using the method of this disclosure is used in the catalytic cracking reaction of light hydrocarbons and naphtha, a higher micro-reaction conversion rate and a better yield of low-carbon olefins can be obtained, and the yield of propylene can be improved. According to the comparison between Examples 1-2 and Example 3, when the molar ratio of silicon source (based on SiO2), aluminum source (based on Al2O3), alkali source (based on alkali metal oxide), template agent and water is (50-90):1:(4-20):(4.5-15):(500-1200), a higher micro-reaction conversion rate and propylene yield can be obtained. According to the comparison between Examples 1 and 2, when the silicon-aluminum ratio is lower, the molecular sieve is more acidic and a higher micro-reaction conversion rate can be obtained.

[0156] 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.

[0157] 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.

[0158] 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. The application of iron-containing small-crystal ZSM-5 molecular sieve in the catalytic cracking reaction of light hydrocarbons or naphtha, characterized in that, The method for preparing the iron-containing small-crystal ZSM-5 molecular sieve includes the following steps: S1 mixes silicon source, aluminum source, alkali source, seed crystal, template agent 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), the template agent, and the water is (50-90):1:(4-20):(4.5-15):(500-1200). The method further includes: mixing an iron source, a ligand, and water to obtain the iron complex; the molar ratio of the iron source, the ligand, and the water, calculated as Fe2O3, is 1:(0.5). 3): (100) 1500); The ligand is triethanolamine.

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

3. The application 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, SB powder, aluminum alkoxide, aluminum oxide, aluminum hydroxide, and aluminum sulfate; The alkaline source includes sodium hydroxide and / or potassium hydroxide; The template agent includes an organic nitrogen-containing template agent; 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 seed crystals is 0.5-2 μm.

4. The application according to claim 3, wherein, The template agent includes one or more of n-butylamine, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

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

6. The application 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 application 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 application according to claim 1, wherein, In step S2, the conditions for the hydrothermal reaction include: a time of 8-32 hours and a temperature of 150-220°C.

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

10. The application 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. The application according to claim 1, wherein, The iron-containing small-crystal ZSM-5 molecular sieve has a structure in which iron-active components are encapsulated inside the ZSM-5 molecular sieve, and the outer surface of the iron-containing small-crystal ZSM-5 molecular sieve particles does not contain iron-active components. The iron-containing small-crystal ZSM-5 molecular sieve has a crystal size of 0.5-1 μm.

12. The application according to claim 11, wherein, The iron-active component is distributed on the framework or within the pores of the ZSM-5 molecular sieve.

13. The application according to claim 11, wherein, The specific surface area of ​​the iron-containing small-crystal ZSM-5 molecular sieve is 240-450 m². 2 / g, total pore volume is 0.160-0.22 cm³. 3 ·g -1 The micropore volume is 0.140-0.180 cm³. 3 ·g -1 The mesopore volume is 0.010-0.080 cm³. 3 ·g -1 The relative crystallinity is 80-100%; In the iron-containing small-crystal ZSM-5 molecular sieve, the molar ratio of SiO2 to Al2O3 is 30-300; The content of iron active component, calculated as Fe2O3, is 1-3% by weight relative to the total weight of the iron-containing small-crystal ZSM-5 molecular sieve.

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