An MFI molecular sieve catalyst, its preparation method and application

Abstract

This invention discloses an MFI molecular sieve catalyst, its preparation method, and its application. In the catalyst, the molar ratio of monoclinic molecular sieve to orthorhombic molecular sieve is 5:1 to ∞, and the hydroxyl infrared spectrum of the catalyst shows a range of 3400–3500 cm⁻¹. ‑1 Hydroxyl characteristic peak. The novel MFI molecular sieve catalyst provided by this invention is used for the catalytic cracking of olefins to produce propylene and ethylene, and features good stability and high diene selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalytic cracking, specifically to a novel MFI molecular sieve catalyst and its preparation method, as well as its application in increasing the production of propylene and ethylene through catalytic cracking of olefins. Background Technology

[0002] Low-carbon olefins (mainly propylene and ethylene) are important basic organic chemical raw materials. Driven by the increasing demand for polyolefins and alkyl aromatics, the demand for ethylene and propylene has grown strongly in recent years. Currently, most of the world's propylene production comes from byproducts of steam cracking and catalytic cracking units. In steam cracking units, the propylene-to-ethylene ratio is around 0.6, while increasing propylene yield in refinery FCC units is costly. To increase propylene production, various countries have developed other methods, such as the butene disproportionation (OMT) process, which uses the reaction of ethylene and butene to increase propylene production; propane dehydrogenation (PDH), which directly utilizes propane in chemical processes; and methanol-to-olefins (MTP / MTO) technology, which uses coal-based methanol to produce propylene and ethylene. Utilizing the large quantities of C4 and C5 olefins generated by ethylene plants, FCC units, and MTO units, and then using catalytic cracking of olefins to increase propylene and ethylene production, is also an important research and development direction for petrochemical companies worldwide. Catalysts are the core technology of catalytic processes; their reaction rate, selectivity, and stability are closely related to the catalyst's pore structure and crystal structure. Post-processing, elemental modification, and the synthesis of hydrothermal resistant molecular sieves with novel structures all directly affect catalytic performance and product distribution.

[0003] Olefin cracking catalysts are mainly MFI molecular sieves with regular channels. Conventional molecular sieve synthesis methods require aging times of 4-48 hours and crystallization times of 6-120 hours, resulting in long processing times and low efficiency. Furthermore, the resulting catalysts exhibit low catalytic activity, diene selectivity, and poor stability due to the coexistence of side reactions such as polymerization, dehydrogenation, and cyclization with the cracking process, and the easy formation of coke species on the surface of the aluminosilicate molecular sieve. EP0109059A1 discloses a method for... 12 A method for producing propylene from olefins via cracking, wherein conventionally synthesized ZSM-5 or ZSM-11 molecular sieves are used as catalysts. US6307117 discloses a C4-C... 12Methods for producing propylene and ethylene by olefin cracking, wherein the active component of the catalyst used is ZSM-5 molecular sieve obtained by traditional synthesis methods without protic acids and containing Group IB metals. CN200910072747.7 describes a method for preparing MFI molecular sieve, in which pre-crystallized seed crystals are added to a gel system for synthesizing nano-molecular sieves without template agents, and then crystallized at 160-180℃ for 24 hours. After cooling to room temperature, the product is centrifuged, filtered, washed, dried, and calcined to obtain a molecular sieve without impurity crystalline phase. The above patents all use traditional molecular sieve synthesis methods, and the olefin cracking catalysts obtained all have drawbacks to varying degrees, such as poor product selectivity, poor catalyst stability, and easy coking and deactivation. Summary of the Invention

[0004] The technical problem this invention aims to solve is the poor stability, low diene selectivity, and low efficiency of existing catalysts for the catalytic cracking of olefins to produce propylene and ethylene. This invention provides an MFI molecular sieve catalyst and its preparation method, as well as its application in increasing propylene and ethylene production through olefin catalytic cracking. The novel MFI molecular sieve catalyst provided by this invention, used for the catalytic cracking of olefins to produce propylene and ethylene, exhibits good stability and high diene selectivity.

[0005] The first aspect of this invention provides an MFI molecular sieve catalyst, wherein the molar ratio of monoclinic molecular sieve to orthorhombic molecular sieve is 5:1 to ∞, and the hydroxyl infrared spectrum of the catalyst shows a range of 3400 to 3500 cm⁻¹. -1 Hydroxyl characteristic peak.

[0006] Furthermore, in the MFI molecular sieve catalyst, the molar ratio of monoclinic to orthorhombic crystal system is preferably 6:1 to 50:1, more preferably 8:1 to 20:1, and even more preferably 8:1 to 15:1.

[0007] Furthermore, the molar ratio of the monoclinic to orthorhombic crystal content of the MFI molecular sieve catalyst can be, without limitation, 8.1:1, 8.2:1, 8.3:1, 8.4:1, 8.5:1, 8.6:1, 8.7:1, 8.8:1, 8.9:1, 9:1, 9.1:1, 9.2:1, 9.3:1, 9.4:1, 9.5:1, 9.6:1, 9.7:1, 9.8:1, 9.9:1, 10:1, etc.

[0008] Furthermore, the total specific surface area of ​​the MFI molecular sieve catalyst is 200–1000 m². 2 / g, preferably 300-800m 2 / g, more preferably 400-600m 2 / g.

[0009] Furthermore, in the MFI molecular sieve catalyst, the molecular sieve is a hydrogen-type molecular sieve.

[0010] Furthermore, the MFI molecular sieve catalyst, by mass fraction, comprises the following components:

[0011] a) MFI molecular sieve 90-100%, preferably 92-99%;

[0012] b) Boron group elements R1 0-5%, preferably 0.5-3.0%;

[0013] c) Nitrogen group element R2 0-5%, preferably 0.5-5.0%.

[0014] Furthermore, in the MFI molecular sieve catalyst, the SiO2 / Al2O3 molar ratio of the molecular sieve is 80-1500, preferably 80-1000.

[0015] Furthermore, in the MFI molecular sieve catalyst, the boron group element R1 is selected from at least one of B and Ga; and / or, the nitrogen group element R2 is selected from at least one of N, P, As, Sb, and Bi.

[0016] Furthermore, the MFI molecular sieve catalyst also contains a binder, and the mass content of the binder is less than 5% based on the mass of the catalyst, preferably less than 2%, and more preferably less than 0.5%.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned MFI molecular sieve catalyst, comprising:

[0018] Step 1: Preparation of MFI molecular sieve raw powder;

[0019] Step 2: Mix the molecular sieve powder obtained in Step 1 with a binder, knead it into shape, and then dry it to obtain catalyst particles;

[0020] Step 3: The catalyst particles obtained in Step 2 are subjected to hydrothermal crystallization and ammonium exchange in the presence of template agent T3 atmosphere to obtain MFI molecular sieve catalyst.

[0021] Furthermore, the method for preparing MFI molecular sieve raw powder in the first step includes:

[0022] Prepare the initial gel, including silicon source, aluminum source, template agent T1, template agent T2, water, and non-essential boron group R1 and / or non-essential nitrogen group R2 elements;

[0023] Crystallization, washing, and drying.

[0024] Further, in the method for preparing MFI molecular sieve raw powder, the template agent T1 is at least one selected from tetrapropylammonium bromide, tetrapropylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide; the template agent T2 is at least one selected from phthalimide, taurine, and naphthyldiamine. The catalyst is obtained by introducing T2 and by adjusting the ratio of template agents T1 and T2 to control the ratio of orthorhombic and monoclinic crystal systems.

[0025] Furthermore, in the method for preparing the MFI molecular sieve raw powder, the silicon source is at least one of silica sol, tetraethyl orthosilicate, and silicate; and / or the aluminum source is at least one of aluminum sulfate, aluminum isopropoxide, and aluminate.

[0026] Furthermore, in the preparation method of the MFI molecular sieve raw powder, the molar ratio of the silicon source, aluminum source, template agent, boron group elements, nitrogen group elements and water is H2O / SiO2 = 10-500; Si / Al = 20-∞; T1 / SiO2 = 0.01-20; T2 / T1 = 0.01-30, preferably 0.1-20; R1 / SiO2 = 0-50, preferably 0.1-30; R2 / SiO2 = 0-50, preferably 0.1-30.

[0027] Furthermore, the preparation of MFI molecular sieve raw powder is carried out in a hypergravity reactor. For example, an initial gel is prepared, including a silicon source, an aluminum source, template agent T1, template agent T2, water, and non-essential boron group R1 and / or non-essential nitrogen group R2 elements, and fed into a hypergravity aging and crystallization integrated device for premixing and circulation, followed by direct crystallization. After exiting the device, it is dried to obtain MFI molecular sieve raw powder; the crystallization is carried out directly without circulation after premixing and circulation in the hypergravity aging and crystallization integrated device. The rotation speed of the hypergravity reactor used is 0-3000 rpm, preferably 1000-2000 rpm. The flow rate of the hypergravity reactor used is 10 mL / min-5000 mL / min, preferably 20 mL / min-1000 mL / min, and the time is 0.5-15 h. The crystallization temperature is 80-180℃, and the time is 5 min-24 h. The molecular sieve raw powder synthesized in the hypergravity reactor gives the catalyst a higher specific surface area.

[0028] Furthermore, in the preparation method of the MFI molecular sieve raw powder, after crystallization, it is washed and dried. The washing can be done with deionized water. The drying conditions are as follows: drying temperature is 80–100℃, and drying time is 10–20 h.

[0029] Furthermore, in the preparation method of the MFI molecular sieve raw powder, the boron group R1 and nitrogen group R2 elements are directly added to the molecular sieve synthesis mother liquor without impregnation and post-treatment, and a novel MFI molecular sieve is obtained in one step.

[0030] Further, in the second step, the binder is a silicon compound, or a mixture of a silicon compound and an aluminum compound. The aluminum compound is selected from at least one of alumina and alumina sol, and the silicon compound is selected from at least one of silica and silicon sol. The amount of binder added, based on the sum of the masses of alumina and silica, accounts for 3% to 50% of the total mass of the molecular sieve powder and the binder, preferably 5% to 40%.

[0031] Furthermore, in the second step, the molding process can employ conventional molding methods, such as extrusion molding. Depending on the molding requirements, an appropriate amount of water can be added. The drying conditions are as follows: drying temperature 80–120℃, drying time 5–10 hours.

[0032] Furthermore, the third step is to place the catalyst particles obtained in the second step in the template agent T3 atmosphere and hydrothermally crystallize them at 100-200°C for 12-180 hours.

[0033] Further, in the third step, the template agent T3 is at least one selected from ammonia, ethylamine, ethylenediamine, triethylamine, n-butylamine, hexamethylenediamine, tetrapropylammonium bromide, or tetrapropylammonium hydroxide; the template agent atmosphere is generated by the volatilization of an aqueous solution containing template agent T3 in a closed system under autogenous pressure. The mass concentration of the aqueous solution of template agent T3 is 0.5-40%, and the mass ratio of it to the catalyst particles is 1-5:1.

[0034] Furthermore, in the third step, after hydrothermal crystallization, the obtained product is washed, dried, and calcined. The washing can be done with deionized water. The drying conditions are as follows: drying temperature 80–100℃, drying time 10–20 h. The calcination conditions are as follows: calcination temperature 500–650℃, calcination time 8–15 h.

[0035] Further, in the third step, the ammonium exchange needs to be carried out in an aqueous solution of ammonium salt, wherein the ammonium salt is selected from one or more of ammonium chloride, ammonium nitrate, and ammonium sulfate. The mass content of the ammonium salt in the aqueous solution is 5% to 10%. The temperature of the ammonium exchange is 80 to 90°C; the number of ammonium exchange cycles can be 3 to 6. The product obtained after the ammonium exchange is calcined; the calcination conditions are as follows: calcination temperature is 500 to 600°C, and calcination time is 4 to 8 hours.

[0036] A third aspect of the present invention provides the application of the above-mentioned MFI molecular sieve catalyst in the catalytic cracking of olefins to produce propylene and ethylene.

[0037] Furthermore, the process of producing propylene and ethylene by catalytic cracking of olefins is as follows: the olefin feedstock reacts with the above-mentioned MFI molecular sieve catalyst to obtain propylene and ethylene products.

[0038] Furthermore, using at least one of C4 to C6 olefins as raw materials, the reaction conditions are as follows: reaction temperature of 400–600°C, preferably 420–580°C; reaction pressure of 0–0.3 MPa, preferably 0.01–0.2 MPa; and weight hourly space velocity of 1–50 h⁻¹. -1 Preferably 2–40 hours -1 .

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] The MFI molecular sieve catalyst provided by this invention has the aforementioned ratio of monoclinic to orthorhombic crystal content, and the hydroxyl infrared spectrum of the catalyst shows a range of 3400–3500 cm⁻¹. -1 The characteristic hydroxyl peaks of this invention enable the catalyst to exhibit high stability, high olefin conversion rate, and high overall selectivity for the addition of propylene and ethylene when used in the catalytic cracking reaction to produce propylene and ethylene. Furthermore, the catalyst of this invention has a higher specific surface area than existing catalysts in the art, further enhancing the olefin conversion rate. Attached Figure Description

[0041] Figure 1 The XRD pattern of the catalyst obtained in Example 1 is shown below.

[0042] Figure 2 The infrared spectrum of the hydroxyl group of the catalyst obtained in Example 1;

[0043] Figure 3 The XRD pattern of the catalyst obtained in Example 3

[0044] Figure 4 The XRD pattern of the catalyst obtained in Comparative Example 1 is shown below.

[0045] Figure 5 The image shows the infrared spectrum of the hydroxyl group of the catalyst obtained in Comparative Example 2.

[0046] The present invention will be further illustrated below through examples.

[0047] In this invention, the specific surface area was determined using a TriStar 3000 physical adsorption analyzer. After vacuum treatment at 300°C for 3 hours, the sample was placed in the analyzer and liquid nitrogen was added for testing. The Barret-Joyner-Halenda (BJH) model was used to calculate the sample's specific surface area.

[0048] In this invention, XRD analysis was performed on a Rigaku D / MAX-1400X polycrystalline X-ray diffractometer with a graphite monochromator, Cu Kα rays, a tube voltage of 40 kV, a tube current of 40 mA, and a scanning range of 2θ from 2 to 70°. By refining the XRD spectrum data using software and calculating the lattice constant, the proportions of orthorhombic and monoclinic crystal systems in the catalyst can be obtained.

[0049] In this invention, the SiO2 / Al2O3 molar ratio was calculated by analyzing the elemental composition of the solid sample using a Magix X-type fluorescence spectrometer from Philips GmbH, Netherlands, with an operating voltage of 40 kV and an operating current of 40 mA.

[0050] In the embodiments and comparative examples of this invention, at least one of C4 to C6 olefins is used as a raw material for catalytic cracking to produce ethylene and propylene, wherein,

[0051] Olefin conversion rate (%) = (1 - mass of olefins in product / mass of olefins in feedstock) × 100%;

[0052] Diene selectivity (%) = Mass of propylene and ethylene produced in the product / (Mass of olefins in the feedstock - Mass of olefins remaining after the reaction) × 100%.

[0053] Example 1

[0054] Step 1: Preparation of molecular sieve raw powder

[0055] The silicon source, aluminum source, template agents T1 and T2 and water were mixed to obtain the initial gel. The initial gel was fed through the feeding system of the integrated supergravity device at a feeding rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, and the template agent T1 was TPABr. Additionally, Ga (group R1) and P (group R2) were added, with Ga source being GaCl3 and P source being H3PO4. T2 was phthalimide. The molar ratio of silicon source, aluminum source, template agent, and water was H2O / SiO2 = 20; Si / Al = 300; T1 / SiO2 = 0.05; R1 / SiO2 = 0.03; R2 / SiO2 = 0.02. The ratio of T1 to T2 was adjusted to T2 / T1 = 1.2. The initial gel circulated within the reaction system of the integrated hypergravity aging and crystallization device. The hypergravity rotation speed was 1500 rpm, the flow rate of the hypergravity reactor was 100 mL / min, and the time was 5 h. This process ensured uniform mixing of the gel. The pre-mixed and circulated raw material was directly crystallized. After 12 h of hypergravity non-circulating crystallization at 170℃, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, ZSM-5 molecular sieve raw powder is obtained.

[0056] The second step is catalyst particle preparation.

[0057] 100g of the above ZSM-5 molecular sieve raw powder, 20g of silica sol containing 40wt% SiO2 and 0.06g of alumina were mixed, extruded into strips, and dried at 80℃ for 10h to obtain catalyst particles.

[0058] The third step is to prepare ammonium-exchanged ZSM-5 molecular sieves.

[0059] The obtained catalyst particles were placed in a template atmosphere (T3), where the template agent T3 was ethylenediamine with a mass concentration of 10%. Gas-solid phase hydrothermal crystallization was performed at 130°C for 112 h. The template agent atmosphere T3 was generated by the volatilization of an aqueous solution containing the template agent T3 (ethylenediamine) under autogenous pressure in a closed system. The mass ratio of the aqueous solution containing the template agent T3 to the catalyst particles was 1.5. After hydrothermal crystallization, the product was removed, washed with distilled water, dried at 90°C for 15 h, and then calcined in air at 550°C for 10 h.

[0060] The ammonium exchange was performed three times in a 5wt% ammonium nitrate solution at 90℃, and after drying, it was calcined in a muffle furnace at 500℃ for 4 hours to obtain the ammonium-exchanged ZSM-5 molecular sieve catalyst.

[0061] The obtained ZSM-5 molecular sieve catalyst was characterized by XRD, see below. Figure 1 By refining the XRD pattern data using software and calculating the lattice constant, the ratio of monoclinic to orthorhombic crystal systems in the catalyst was found to be 8:1, with a binder content of less than 0.2%. Characterization of nitrogen adsorption-desorption on the catalyst revealed a total specific surface area of ​​420 cm². 2 / g. X-ray fluorescence spectrometry analysis showed that the SiO2 / Al2O3 molar ratio of the catalyst was 300. In the obtained catalyst, ZSM-5 molecular sieve accounted for 98.9% of the catalyst by mass, Ga accounted for 0.5% of the catalyst by mass, P accounted for 0.5% of the catalyst by mass, and the remainder was a binder.

[0062] Figure 2 The image shows the infrared spectrum of the hydroxyl group in the catalyst. The infrared spectrum of the hydroxyl group in the catalyst is shown in the 3400–3500 cm⁻¹ range. -1 Hydroxyl characteristic peak.

[0063] A fixed-bed catalytic cracking reactor was used as feedstock, consisting of a mixed C4 mixture (40% butane and 60% butene by mass) from an ethylene plant. The activity of the prepared catalyst in the catalytic cracking of olefins to propylene and ethylene was evaluated. The process conditions used were: 3 g catalyst, reaction temperature of 530 °C, reaction pressure of 0.03 MPa, and weight hourly space velocity of 20 h⁻¹. -1The reaction results showed a 79% conversion rate of C4 olefins and a selectivity of 81% for propylene and ethylene. After 80 hours of reaction, the catalyst activity and selectivity did not change significantly, demonstrating good stability.

[0064] Example 2

[0065] Step 1: Preparation of molecular sieve raw powder

[0066] A silicon source, an aluminum source, template agents T1 and T2, and water were mixed to obtain an initial gel. This initial gel was fed through the feeding system of a centrifugal integrated device at a feed rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, template agent T1 was TPABr, and T2 was phthalimide. The molar ratio of silicon source, aluminum source, template agent, and water was H2O / SiO2 = 20; Si / Al = 300; T1 / SiO2 = 0.05. The ratio of T1 to T2 was adjusted to T2 / T1 = 1.2. The initial gel was circulated within the reaction system of the centrifugal aging and crystallization integrated device at a centrifugal rotation speed of 1500 rpm and a centrifugal reactor flow rate of 100 mL / min for 5 hours. This process ensured uniform mixing of the gel. The pre-mixed and circulated raw material was directly crystallized. After 12 hours of non-circulating centrifugal crystallization at 170°C, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, ZSM-5 molecular sieve raw powder is obtained.

[0067] The second step is catalyst particle preparation.

[0068] 100g of the above ZSM-5 molecular sieve raw powder, 20g of silica sol containing 40wt% SiO2 and 0.06g of alumina were mixed, extruded into strips, and dried at 80℃ for 10h to obtain catalyst particles.

[0069] The third step is to prepare ammonium-exchanged ZSM-5 molecular sieves.

[0070] The obtained catalyst particles were placed in a template atmosphere (T3, ethylenediamine, 30% by mass) and subjected to gas-solid phase hydrothermal crystallization at 130°C for 112 h. The template atmosphere (T3) was generated by the volatilization of an aqueous solution containing template agent T3 (ethylenediamine) under autogenous pressure in a closed system. The mass ratio of the aqueous solution containing template agent T3 (ethylenediamine) to the catalyst particles was 1.5. After hydrothermal crystallization, the product was removed, washed with distilled water, dried at 90°C for 15 h, and then calcined in air at 550°C for 10 h.

[0071] The ammonium exchange was performed three times in a 5wt% ammonium nitrate solution at 90℃, and after drying, it was calcined in a muffle furnace at 500℃ for 4 hours to obtain the ammonium-exchanged ZSM-5 molecular sieve catalyst.

[0072] The obtained ZSM-5 molecular sieve catalyst was characterized by XRD. The XRD data were refined using software, and the lattice constant was calculated. The ratio of monoclinic to orthorhombic crystal systems was found to be 8:1, and the binder content was less than 0.2%. Nitrogen adsorption-desorption characterization of the catalyst showed a total specific surface area of ​​410 cm². 2 / g. X-ray fluorescence spectrometry analysis showed that the SiO2 / Al2O3 molar ratio of the catalyst was 300. In the obtained catalyst, ZSM-5 molecular sieve accounted for 99.9% of the mass fraction of the catalyst, with the remainder being a binder.

[0073] The infrared spectrum of the catalyst's hydroxyl group shows 3400–3500 cm⁻¹ -1 Hydroxyl characteristic peak.

[0074] A fixed-bed catalytic cracking reactor was used as feedstock, consisting of a mixed C4 mixture (40% butane and 60% butene by mass) from an ethylene plant. The activity of the prepared catalyst in the catalytic cracking of olefins to propylene and ethylene was evaluated. The process conditions used were: 3 g catalyst, reaction temperature of 530 °C, reaction pressure of 0.03 MPa, and weight hourly space velocity of 20 h⁻¹. -1 The reaction results showed a 78% conversion rate of C4 olefins and an 80% selectivity for propylene and ethylene. After 80 hours of reaction, the catalyst activity and selectivity did not change significantly, demonstrating good stability.

[0075] Example 3

[0076] Step 1: Preparation of molecular sieve raw powder

[0077] The silicon source, aluminum source, template agents T1 and T2 and water were mixed to obtain the initial gel. The initial gel was fed through the feeding system of the integrated supergravity device at a feeding rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, and the template agent T1 was TPABr. Additionally, Ga (group R1) and P (group R2) were added, with Ga source being GaCl3, P source being H3PO4, and T2 being naphthalenediamine. The molar ratios of silicon source, aluminum source, template agent, and water were H2O / SiO2 = 20; Si / Al = 300; T1 / SiO2 = 0.05; R1 / SiO2 = 0.03; and R2 / SiO2 = 0.02. The ratio of T1 to T2 was adjusted to T2 / T1 = 3. The initial gel circulated within the reaction system of the integrated hypergravity aging and crystallization device. The hypergravity rotation speed was 1500 rpm, the flow rate of the hypergravity reactor was 100 mL / min, and the reaction time was 5 h. This process ensured uniform mixing of the gel. The pre-mixed and circulated raw material was directly crystallized. After 12 h of non-circulating hypergravity crystallization at 170°C, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, ZSM-5 molecular sieve raw powder is obtained.

[0078] The second step is catalyst particle preparation.

[0079] 100g of the above ZSM-5 molecular sieve raw powder, 20g of silica sol containing 40wt% SiO2 and 0.06g of alumina were mixed, extruded into strips, and dried at 80℃ for 10h to obtain catalyst particles.

[0080] The third step is to prepare ammonium-exchanged ZSM-5 molecular sieves.

[0081] The obtained catalyst particles were placed in a template atmosphere (T3), where the template agent T3 was ethylenediamine with a mass concentration of 20%, and subjected to gas-solid phase hydrothermal crystallization at 130°C for 112 h. The template agent atmosphere T3 was generated by the volatilization of an aqueous solution containing the template agent T3 (ethylenediamine) under autogenous pressure in a closed system. The mass ratio of the aqueous solution containing the template agent T3 (ethylenediamine) to the catalyst particles was 1.5. After hydrothermal crystallization, the product was removed, washed with distilled water, dried at 90°C for 15 h, and then calcined in air at 550°C for 10 h.

[0082] The ammonium exchange was performed three times in a 5wt% ammonium nitrate solution at 90℃, and after drying, it was calcined in a muffle furnace at 500℃ for 4 hours to obtain the ammonium-exchanged ZSM-5 molecular sieve catalyst.

[0083] The obtained ZSM-5 molecular sieve catalyst was characterized by XRD, see below. Figure 3By refining the XRD pattern data using software and calculating the lattice constant, the ratio of monoclinic to orthorhombic crystal systems in the catalyst was found to be 10:1, with a binder content of less than 0.2%. Characterization of nitrogen adsorption-desorption on the catalyst revealed a total specific surface area of ​​400 cm². 2 / g. X-ray fluorescence spectrometry analysis showed that the SiO2 / Al2O3 molar ratio of this catalyst was 300. The hydroxyl group infrared spectrum of the catalyst showed a range of 3400–3500 cm⁻¹. -1 Hydroxyl characteristic peak. In the obtained catalyst, ZSM-5 molecular sieve accounts for 98.8% of the catalyst by mass, Ga element accounts for 0.6% of the catalyst by mass, P element accounts for 0.5% of the catalyst by mass, and the remainder is binder.

[0084] A fixed-bed catalytic cracking reactor was used as feedstock, consisting of a mixed C4 mixture (40% butane and 60% butene by mass) from an ethylene plant. The activity of the prepared catalyst in the catalytic cracking of olefins to propylene and ethylene was evaluated. The process conditions used were: 3 g catalyst, reaction temperature of 530 °C, reaction pressure of 0.03 MPa, and weight hourly space velocity of 20 h⁻¹. -1 The reaction results were: 77% conversion of C4 olefins and 79% selectivity for propylene and ethylene. After 80 hours of catalytic reaction, there was no significant decrease in catalyst activity or selectivity.

[0085] Comparative Example 1

[0086] Step 1: Preparation of molecular sieve raw powder

[0087] The silicon source, aluminum source, template agent T1 and water were mixed to obtain the initial gel. The initial gel was fed through the feeding system of the integrated supergravity device at a feeding rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, and the template agent T1 was TPABr. Additionally, Ga (group R1) and P (group R2) were added, with GaCl3 as the Ga source and H3PO4 as the P source. The molar ratios of silicon source, aluminum source, template agent, and water were H2O / SiO2 = 20; Si / Al = 300; T1 / SiO2 = 0.11; R1 / SiO2 = 0.03; and R2 / SiO2 = 0.02. The initial gel circulated within the reaction system of the integrated hypergravity aging and crystallization device. The hypergravity rotation speed was 1500 rpm, the flow rate of the hypergravity reactor was 100 mL / min, and the reaction time was 5 h. This process ensured uniform mixing of the gel. The pre-mixed and circulated raw material was directly crystallized. After 12 h of non-circulating hypergravity crystallization at 170°C, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, ZSM-5 molecular sieve raw powder is obtained.

[0088] The second step is catalyst particle preparation.

[0089] 100g of the above ZSM-5 molecular sieve raw powder, 20g of silica sol containing 40wt% SiO2 and 0.06g of alumina were mixed, extruded into strips, and dried at 80℃ for 10h to obtain catalyst particles.

[0090] The third step is to prepare ammonium-exchanged ZSM-5 molecular sieves.

[0091] The obtained catalyst particles were placed in a template atmosphere (T3, ethylenediamine, 10% by mass) and subjected to gas-solid phase hydrothermal crystallization at 130°C for 112 h. The template atmosphere (T3) was generated by the volatilization of an aqueous solution containing template agent T3 (ethylenediamine) under autogenous pressure in a closed system. The mass ratio of the aqueous solution containing template agent T3 (ethylenediamine) to the catalyst particles was 1.5. After hydrothermal crystallization, the product was removed, washed with distilled water, dried at 90°C for 15 h, and then calcined in air at 550°C for 10 h.

[0092] The ammonium exchange was performed three times in a 5wt% ammonium nitrate solution at 90℃, and after drying, it was calcined in a muffle furnace at 500℃ for 4 hours to obtain the ammonium-exchanged ZSM-5 molecular sieve catalyst.

[0093] The obtained ZSM-5 molecular sieve catalyst was characterized by XRD, see below. Figure 4 The XRD pattern data was refined using software, and the lattice constant was calculated. The orthorhombic crystal system content was 100%, and the binder content was less than 0.2%. Nitrogen adsorption-desorption characterization of the catalyst showed a total specific surface area of ​​200 cm². 2 / g. X-ray fluorescence spectrometry analysis showed that the SiO2 / Al2O3 molar ratio of the catalyst was 300. In the obtained catalyst, ZSM-5 molecular sieve accounted for 98.9% of the catalyst by mass, Ga accounted for 0.5% of the catalyst by mass, and P accounted for 0.5% of the catalyst by mass.

[0094] The infrared spectrum of the catalyst's hydroxyl group showed no 3400–3500 cm⁻¹. -1 Hydroxyl characteristic peak.

[0095] A fixed-bed catalytic cracking reactor was used as feedstock, consisting of a mixed C4 mixture (40% butane and 60% butene by mass) from an ethylene plant. The activity of the prepared catalyst in the catalytic cracking of olefins to propylene and ethylene was evaluated. The process conditions used were: 3 g catalyst, reaction temperature of 530 °C, reaction pressure of 0.03 MPa, and weight hourly space velocity of 20 h⁻¹. -1 The reaction results were: 59% conversion of C4 olefins and 60% selectivity for propylene and ethylene. After 80 hours of reaction, the catalyst activity and selectivity decreased significantly.

[0096] Comparative Example 2

[0097] Step 1: Preparation of molecular sieve raw powder

[0098] The silicon source, aluminum source, template agent T2 and water were mixed to obtain the initial gel. The initial gel was fed through the feeding system of the integrated supergravity device at a feeding rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, and additionally, Ga (group R1) and P (group R2) were added. The Ga source was GaCl3, the P source was H3PO4, and T2 was phthalimide. The molar ratios of silicon source, aluminum source, template agent, and water were H2O / SiO2 = 20, Si / Al = 300, T2 / SiO2 = 0.11, R1 / SiO2 = 0.03, and R2 / SiO2 = 0.02. The initial gel was circulated in the reaction system of the integrated hypergravity aging and crystallization device. The hypergravity rotation speed was 1500 rpm, the flow rate of the hypergravity reactor was 100 mL / min, and the time was 5 h. This process ensured that the gel was uniformly mixed. The premixed and circulated raw material was directly crystallized. After 12 h of hypergravity non-circulating crystallization at 170℃, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, no molecular sieve catalyst is obtained; it is an amorphous powder.

[0099] Comparative Example 3

[0100] Step 1: Preparation of molecular sieve raw powder

[0101] The silicon source, aluminum source, template agent T1 and water were mixed to obtain the initial gel. The initial gel was fed through the feeding system of the integrated supergravity device at a feeding rate of 50 mL / min. The silicon source was silica sol, the aluminum source was aluminum sulfate, and the template agent T1 was TPABr. Additionally, Ga (group R1) and P (group R2) were added, with GaCl3 as the Ga source and H3PO4 as the P source. The molar ratios of silicon source, aluminum source, template agent, and water were H2O / SiO2 = 20; Si / Al = 300; T1 / SiO2 = 0.11; R1 / SiO2 = 0.03; and R2 / SiO2 = 0.02. The initial gel circulated within the reaction system of the integrated hypergravity aging and crystallization device. The hypergravity rotation speed was 1500 rpm, the flow rate of the hypergravity reactor was 100 mL / min, and the reaction time was 5 h. This process ensured uniform mixing of the gel. The pre-mixed and circulated raw material was directly crystallized. After 12 h of non-circulating hypergravity crystallization at 170°C, the reaction was stopped. After cooling to room temperature, the product is removed from the integrated device through the discharge system, washed and centrifuged three times, and dried at 80°C for 12 hours. After drying, ZSM-5 molecular sieve raw powder is obtained.

[0102] The second step is catalyst particle preparation.

[0103] 100g of the above ZSM-5 molecular sieve raw powder, 20g of silica sol containing 40wt% SiO2 and 0.06g of alumina were mixed, extruded into strips, and dried at 80℃ for 10h to obtain catalyst particles.

[0104] The third step is to prepare ammonium-exchanged ZSM-5 molecular sieves.

[0105] The resulting catalyst particles were treated with conventional steam and then hydrothermally roasted at 550 degrees Celsius for 4 hours.

[0106] The ammonium exchange was performed three times in a 5wt% ammonium nitrate solution at 90℃, and after drying, it was calcined in a muffle furnace at 500℃ for 4 hours to obtain the ammonium-exchanged ZSM-5 molecular sieve catalyst.

[0107] The obtained ZSM-5 molecular sieve catalyst was characterized by XRD. The XRD data were refined using software, and the lattice constant was calculated, revealing a monoclinic to orthorhombic crystal ratio of 50:1. Nitrogen adsorption-desorption characterization showed a total specific surface area of ​​200 cm² / g. X-ray fluorescence spectroscopy analysis indicated a SiO₂ / Al₂O₃ molar ratio of 300. In the obtained catalyst, ZSM-5 molecular sieve accounted for 90% of the mass fraction, Ga for 0.5%, and P for 0.5%.

[0108] The obtained catalyst hydroxyl infrared spectroscopy is shown in Figure 1. Figure 5 The infrared spectrum of the catalyst's hydroxyl group showed no value in the 3400–3500 cm⁻¹ range. -1 Hydroxyl characteristic peak.

[0109] A fixed-bed catalytic cracking reactor was used as feedstock, consisting of a mixed C4 mixture (40% butane and 60% butene by mass) from an ethylene plant. The activity of the prepared catalyst in the catalytic cracking of olefins to propylene and ethylene was evaluated. The process conditions used were: 3 g catalyst, reaction temperature of 530 °C, reaction pressure of 0.03 MPa, and weight hourly space velocity of 20 h⁻¹. -1 The reaction results were: 62% conversion of C4 olefins and 59% selectivity for propylene and ethylene. After 80 hours of reaction, the catalyst activity and selectivity decreased significantly.

[0110] For ease of comparison, the main process conditions and results are listed in Table 1.

[0111] Table 1

[0112]

[0113] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An MFI molecular sieve catalyst, wherein the catalyst has a molar ratio of monoclinic molecular sieve to orthorhombic molecular sieve of from 5: 1 to 20: 1, and the catalyst has a hydroxyl infrared spectrum showing a hydroxyl characteristic peak at 3400 to 3500 cm -1 .

2. The catalyst according to claim 1, characterized in that, The MFI molecular sieve catalyst has a molar ratio of 6:1-20:1 between the monoclinic molecular sieve and the orthorhombic molecular sieve.

3. The catalyst of claim 1, wherein The total specific surface area of the MFI molecular sieve catalyst is 200-1000 m 2 / g.

4. The catalyst of claim 1, wherein The MFI molecular sieve catalyst has a hydrogen-type molecular sieve.

5. The catalyst of claim 1, wherein The MFI molecular sieve catalyst comprises the following components in mass fraction: a) MFI molecular sieve 90-100%; b) boron element R1 0-5%; c) nitrogen element R2 0-5%.

6. The catalyst of claim 1, wherein The MFI molecular sieve catalyst has a SiO2 / Al2O3 molar ratio of 80-1500.

7. The catalyst of claim 5, wherein The MFI molecular sieve catalyst has at least one selected from B and Ga as the boron element R1; and / or at least one selected from N, P, As, Sb, and Bi as the nitrogen element R2.

8. The catalyst of claim 1, wherein The MFI molecular sieve catalyst further comprises a binder, and the mass content of the binder is less than 5% based on the mass of the catalyst.

9. A preparation method of the MFI molecular sieve catalyst according to any one of claims 1-8, comprising: Step 1: preparing MFI molecular sieve raw powder; Step 2: mixing and kneading the MFI molecular sieve raw powder obtained in Step 1 with a binder to form a catalyst particle, and drying the catalyst particle to obtain a catalyst granule; Step 3: hydrothermally crystallizing the catalyst granule obtained in Step 2 in the presence of a template T3, and ammonium exchanging to obtain the MFI molecular sieve catalyst.

10. The method of claim 9, wherein, The method for preparing the MFI molecular sieve raw powder in Step 1 comprises: preparing an initial gel, which comprises a silicon source, an aluminum source, a template T1, a template T2, water, and optionally a boron element R1 and / or an optional nitrogen element R2; crystallizing, washing, and drying.

11. The method of claim 10, wherein, In the method for preparing the MFI molecular sieve raw powder, the molar ratio of the silicon source, the aluminum source, the templates, the boron element, the nitrogen element, and water is H2O / SiO2=10-500; Si / Al=20-∞, T1 / SiO2=0.01-20; T2 / T1=0.01-30; R1 / SiO2=0-50; and R2 / SiO2=0-50.

12. The method of claim 9, wherein, In Step 2, the binder is a silicon compound or a mixture of a silicon compound and an aluminum compound; the aluminum compound is at least one selected from alumina and aluminum sol, and the silicon compound is at least one selected from white carbon black and silicon sol; and the addition amount of the binder, calculated based on the sum of the mass of alumina and the mass of silicon oxide, is 3%-50% of the total mass of the MFI molecular sieve raw powder and the binder.

13. The preparation method according to claim 9, characterized in that, In Step 3, the template T3 is at least one selected from ammonia, ethylamine, ethylenediamine, triethylamine, n-butylamine, hexanediamine, tetrapropylammonium bromide, and tetrapropylammonium hydroxide; the template atmosphere is generated by volatilization of an aqueous solution of the template T3 under autogenous pressure in a closed system; and the mass concentration of the aqueous solution of the template T3 is 0.5-40%, and the mass ratio of the aqueous solution of the template T3 to the catalyst granule is 1-5:

1.

14. Use of the MFI molecular sieve catalyst according to any one of claims 1-8 in the production of propylene and ethylene through catalytic cracking of olefins.

15. Use according to claim 14, characterized in that, The process for producing propylene and ethylene through catalytic cracking of olefins is as follows: an olefin raw material is contacted with the MFI molecular sieve catalyst to obtain a propylene and ethylene product. The reaction conditions are as follows: the reaction temperature is 400-600 DEG C, the reaction pressure is 0-0.3 MPa, the weight space velocity is 1-50 h -1 .

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