Preparation method of MCM-22 catalyst for alkylation of liquid-phase benzene and dilute ethylene

Abstract

The invention discloses a preparation method of an MCM-22 catalyst for alkylation of liquid-phase benzene and dilute ethylene, belongs to the technical field of catalyst production, and aims to solve the three technical bottlenecks of discrete acid strength distribution, insufficient pore connectivity and lack of metal synergistic effect of the existing MCM-22 catalyst in alkylation reaction of liquid-phase benzene and dilute ethylene. The ethylene conversion rate, the ethylbenzene selectivity and the carbon deposition resistance of the catalyst under the condition of low ethylene concentration (5%-20%) are remarkably improved through the synergistic technical means of step-by-step acid modification, steam-assisted chambering and bimetallic synergistic loading. The industrial problems of AlCl3 corrosivity, ZSM-5 low efficiency and MCM-22 pore-acid-metal coordination deficiency in the prior art are thoroughly solved, and an innovative solution is provided for high-value utilization of dilute ethylene resources.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst production, and particularly relates to a method for preparing an MCM-22 catalyst for alkylation of liquid-phase benzene and dilute ethylene. Background Art

[0002] As an important petrochemical intermediate, the industrial production of ethylbenzene has long relied on the gas-phase alkylation process using an AlCl3 catalytic system. However, this process has the following significant drawbacks: (1) AlCl3 is highly corrosive, requiring frequent replacement of the lining material of the reaction equipment, resulting in extremely high equipment maintenance costs; (2) The effective utilization rate of ethylene is insufficient. Due to the limitations of gas-solid phase reaction kinetics, ethylene raw materials with a purity of >90% must be used to ensure sufficient mass transfer efficiency. However, high ethylene concentrations can easily cause local overheating, leading to the formation of by-products such as xylene, and increasing the energy consumption of the unreacted ethylene cycle compression; (3) The catalyst is non-regenerative, and the deactivation of AlCl3 forms chlorine-containing waste residues, which pose environmental challenges.

[0003] To overcome these issues, ZSM-5 zeolite catalysts were developed for vapor-phase alkylation. While its shape-selective pores (0.51-0.56 nm) can suppress some macromolecular side reactions, the ethylene conversion of ZSM-5 drops sharply from 92% to 68% at low ethylene concentrations (<20%). This is primarily attributed to the inability of the micropore-dominated diffusion pathway to effectively capture dilute ethylene molecules. Furthermore, strong Brønsted acid sites (acid content >0.8 mmol / g) induce ethylene oligomerization to form C4 hydrocarbons, leading to pore blockage.

[0004] In recent years, the liquid-phase alkylation process has attracted much attention due to its mild reaction conditions (temperature < 250°C) and higher ethylene dissolution efficiency. MCM-22 molecular sieve, with its unique two-dimensional sinusoidal channels (0.40 × 0.54 nm) and supercage structure (0.71 nm), can theoretically achieve both rapid diffusion of benzene molecules and shape-selective adsorption of ethylene. However, the practical application of industrial-grade MCM-22 (SiO2 / Al2O3 = 25-35) still faces three major bottlenecks: (1) The acid strength distribution is discretized. The strong acid sites generated by non-framework aluminum (NH3-TPD shows that the desorption peak at >400°C accounts for >40%) easily induce the deep dehydrogenation of ethylene to form coke precursors; (2) The pore connectivity is insufficient. The stacking defects generated during the hydrothermal synthesis cause about 30% of the supercages to become "dead-end" cavities, significantly reducing the accessibility of active sites; (3) The lack of metal synergy. The single metal component (such as Mo or La) loaded by conventional impregnation method is difficult to achieve both ethylene π-complexation activation and carbon deposition inhibition.

[0005] Existing techniques use phosphoric acid to treat MCM-22 to adjust acid strength, but this method can lead to pore blockage by framework aluminophosphates. Other existing approaches propose pore expansion through steam treatment, but simple hydrothermal treatment accelerates framework dealumination, causing the acid center density to drop by over 40%. None of these solutions systematically address the challenge of synergistic regulation of the acid-pore-metal ternary system, making it difficult for the catalyst to achieve both high conversion and long-term stability in dilute ethylene (5%-20%) alkylation. Summary of the Invention

[0006] The present invention aims to provide a method for preparing an MCM-22 catalyst for the alkylation of liquid-phase benzene with dilute ethylene. The present invention optimizes the surface acidity and pore accessibility of MCM-22 through graded acid modification and metal co-loading technology, thereby improving the dilute ethylene adsorption capacity and carbon deposition resistance. Furthermore, the present invention achieves efficient alkylation of low-concentration ethylene (5% to 20%) with benzene through a dynamic liquid-phase reaction process, thereby reducing raw material costs and energy consumption.

[0007] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene comprises the following steps: S1, subjecting MCM-22 raw powder to acid modification to obtain acid-modified MCM-22 molecular sieve, and subjecting the acid-modified MCM-22 molecular sieve to steam-assisted pore expansion to obtain expanded pore MCM-22 molecular sieve; S2. Place the expanded pore MCM-22 molecular sieve in a rotary evaporator, add the impregnation liquid dropwise at 60° C., the amount of the impregnation liquid is 1.1-1.2 times the mass of the expanded pore MCM-22 molecular sieve, and after the addition is completed, let it stand and age for 12 hours to obtain the impregnated MCM-22 molecular sieve; S3. Under nitrogen atmosphere, the impregnated MCM-22 molecular sieve was placed in a muffle furnace and heated to 350°C at 3°C / min for 4 hours, then switched to air atmosphere and treated at 400°C for 2 hours to obtain the loaded MCM-22 molecular sieve; S4. The loaded MCM-22 molecular sieve and pseudo-boehmite were mixed in a mass ratio of 8:2 to obtain a mixture, and then 2 wt% of a pore-forming agent and 3 wt% of a peptizing agent were added to the mixture. The mixture was ball-milled for 30 minutes, and then formed by a twin-screw extruder with an extrusion pressure of 8-12 MPa. The obtained wet strips were aged at room temperature for 24 hours, then dried at 120°C for 6 hours, and calcined at 500°C for 3 hours to obtain the finished catalyst.

[0008] Furthermore, the acid modification treatment in S1 includes the following steps: The MCM-22 raw powder was mixed with 0.1-0.5 mol / L oxalic acid solution at a solid-liquid ratio of 1:10, stirred and refluxed at 60-80°C for 2-4 hours, centrifuged and washed until neutral, and dried at 110°C for 6 hours. The MCM-22 molecular sieve treated with oxalic acid was mixed with 0.05-0.20 mol / L citric acid solution at a solid-liquid ratio of 1:8, ultrasonically treated at 80-90°C for 1-2 hours, filtered, and dried at 120°C for 12 hours to obtain an acid-modified MCM-22 molecular sieve.

[0009] Furthermore, the molar ratio of SiO2 / Al2O3 in the MCM-22 raw powder is 25-35.

[0010] Furthermore, the steam-assisted pore expansion process in S1 includes the following steps: The acid-modified MCM-22 molecular sieve was placed in a tube furnace, a mixture of nitrogen and water vapor was introduced, and the temperature was increased to 430-470°C at a rate of 2°C / min. After maintaining the temperature for 2-3 hours, the temperature was cooled with the furnace to obtain the expanded pore MCM-22 molecular sieve.

[0011] Furthermore, the partial pressure of water vapor in the mixed gas is 10-30 kPa.

[0012] Furthermore, the impregnation solution in S2 is prepared by the following steps: weighing molybdenum nitrate and lanthanum nitrate, dissolving them in deionized water respectively, preparing molybdenum nitrate mother liquor and lanthanum nitrate mother liquor with Mo concentration of 0.05-0.1 g / mL and La concentration of 0.02-0.05 g / mL, and mixing the molybdenum nitrate mother liquor and the lanthanum nitrate mother liquor in a volume ratio of 1:1 to obtain an impregnation solution.

[0013] Furthermore, the content of MoO3 in the molybdenum nitrate is ≥99%; the content of La2O3 in the lanthanum nitrate is ≥99%.

[0014] Furthermore, the Al2O3 content in the pseudo-boehmite in S4 is ≥70%.

[0015] Furthermore, the pore-forming agent in S4 is sesbania powder; and the peptizing agent is dilute nitric acid.

[0016] Furthermore, the mass fraction of the dilute nitric acid is 5%.

[0017] Beneficial effects of the present invention: This invention addresses the three major technical bottlenecks of existing MCM-22 catalysts in the alkylation of liquid benzene with dilute ethylene: discrete acid strength distribution, insufficient pore connectivity, and lack of metal synergy. By employing a synergistic approach combining step-by-step acid modification, steam-assisted pore expansion, and bimetallic synergistic loading, the catalyst significantly improves ethylene conversion, ethylbenzene selectivity, and carbon deposition resistance at low ethylene concentrations (5%-20%). The following, combined with test data from examples and comparative examples, details the innovative features of this invention: First, the present invention utilizes a step-by-step oxalic acid-citric acid treatment process. Oxalic acid preferentially removes non-framework aluminum (the primary source of strong acid sites), while citric acid further modulates the distribution of framework aluminum, achieving a gradient distribution of acid strength. Data validation: In Example 2, after synergistic treatment with oxalic acid (0.5 mol / L) and citric acid (0.20 mol / L), the catalyst exhibited a carbon deposition rate of only 2.7±0.1% (after 1200 hours of operation) at a 20% ethylene concentration. This is significantly lower than that observed in Comparative Example 1 (oxalic acid treatment alone, carbon deposition rate of 4.2±0.3%) and Comparative Example 4 (phosphoric acid treatment, carbon deposition rate of 6.8±0.2%). Omitting citric acid treatment in Comparative Example 1 resulted in a decrease in ethylene conversion to 92.5±0.7% (compared to 97.5±0.2% in Example 2), demonstrating that citric acid optimizes the density and strength of acid sites by modulating the distribution of framework aluminum, thereby suppressing the side reaction of deep ethylene dehydrogenation.

[0018] The present invention then employs a gradient temperature expansion technique under a nitrogen-water vapor mixed atmosphere. Water molecules selectively etch defective regions in the laminate stack, opening up "dead-end" supercages and forming a network of through-hole channels. Data validation: After water vapor expansion (partial pressure 20 kPa, 450°C) in Example 2, the ethylbenzene selectivity reached 98.8±0.3%, while in Comparative Example 2 (no expansion), the selectivity dropped to 95.1±0.3%, and the carbon deposition rate increased to 5.1±0.5% (600 hours). In Comparative Example 5, increasing the expansion temperature to 500°C (water vapor partial pressure 50 kPa) resulted in a sharp drop in ethylene conversion to 80.4±0.5%, confirming the need for precise control of expansion parameters to avoid excessive skeleton damage.

[0019] Next, the present invention co-impregnates MoO₃ (for ethylene π-complexation activation) and La₂O₃ (for electron transfer inhibition of carbon deposition) to form bimetallic synergistic active sites. Data confirms that the bimetallic-supported catalyst in Example 2 achieves an ethylene conversion of 97.5±0.2%, significantly higher than that of Comparative Example 3 (MoO₃ loaded alone, 88.5±0.5%) and Comparative Example 6 (stepwise loading, 96.5±0.5%). Stepwise loading in Comparative Example 6 increases the carbon deposition rate to 3.9±0.3% (compared to 2.7±0.1% in Example 2), demonstrating that bimetallic co-impregnation promotes electronic coupling at the Mo-La interface and enhances carbon deposition resistance.

[0020] Finally, the catalyst's optimized pore-acid-metal ternary design, combined with a dynamic liquid-phase reaction process (temperature 220°C, pressure 3.0 MPa), enhances dilute ethylene dissolution and mass transfer efficiency. Data confirms that Example 2 achieves a conversion of 97.5±0.2% at 20% ethylene concentration, nearly 30 percentage points higher than the prior art ZSM-5 (low-concentration ethylene conversion of 68%). Furthermore, the ethylbenzene selectivity reaches 98.8±0.3%, surpassing existing technologies. Comparative Example 2 (without pore expansion) exhibits an increased carbon deposition rate of 5.1±0.5% (600 hours) at the same ethylene concentration, demonstrating that pore expansion and the liquid-phase process synergistically reduce mass transfer resistance and inhibit localized coking.

[0021] At the same time, the present invention achieves the following unexpected technical effects through the synergistic effects of step-by-step acid modification, water vapor pore expansion and bimetallic loading: Acid-pore synergy: After acid modification optimized the acid distribution, the pore expansion treatment did not lead to skeleton dealumination (high-temperature pore expansion in comparative example 5 caused skeleton collapse). Instead, by retaining the synergistic effect of medium-strong acid sites and through-pores, the ethylene conversion rate remained at >97% at low concentrations; Metal-pore synergy: After the bimetal was loaded on the pores, MoO3 enhanced ethylene adsorption and La2O3 inhibited the diffusion of large molecules. The two synergized to make the ethylbenzene selectivity exceed 98%; Process-material synergy: The dynamic liquid phase reaction pressure (3.0 MPa) enabled benzene molecules to quickly fill the pores to form a "liquid phase molecular sieve" effect, further inhibiting the ethylene polymerization side reaction.

[0022] In summary, the present invention, through multi-scale coordinated regulation, simultaneously achieves high conversion rate (>95%), high selectivity (>98%) and long-term stability (carbon deposition rate <3% after 1200 hours) in the alkylation of dilute ethylene for the first time, completely solving the industry problems of AlCl3 corrosiveness, ZSM-5 inefficiency and lack of pore-acid-metal synergy in MCM-22 in the background technology, and provides an innovative solution for the high-value utilization of dilute ethylene resources. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] Example 1 A method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene comprises the following steps: S1, MCM-22 molecular sieve pretreatment: Acid modification treatment: MCM-22 raw powder (SiO2 / Al2O3=25 (molar ratio)) was mixed with 0.1 mol / L oxalic acid solution at a solid-liquid ratio of 1:10, stirred and refluxed at 60°C for 2 hours, centrifuged and washed until neutral, and dried at 110°C for 6 hours. The MCM-22 molecular sieve treated with oxalic acid was mixed with 0.05 mol / L citric acid solution at a solid-liquid ratio of 1:8, ultrasonically treated at 80°C (40 kHz) for 1 hour, filtered, and dried at 120°C for 12 hours to obtain acid-modified MCM-22 molecular sieve. During the above acid modification treatment, oxalic acid preferentially removed non-framework aluminum, and citric acid further adjusted the distribution of framework aluminum.

[0025] Steam-assisted pore expansion: The acid-modified MCM-22 molecular sieve was placed in a tubular furnace, and a mixture of nitrogen and water vapor (water vapor partial pressure 10 kPa) was introduced. The temperature was raised to 430°C at a rate of 2°C / min. After maintaining the temperature for 2 hours, the mixture was cooled in the furnace to obtain the expanded pore MCM-22 molecular sieve.

[0026] S2, bimetallic load: Preparation of impregnation solution: Molybdenum nitrate (MoO3 content ≥ 99%) and lanthanum nitrate (La2O3 content ≥ 99%) were weighed and dissolved in deionized water respectively to prepare molybdenum nitrate mother liquor and lanthanum nitrate mother liquor with Mo concentration of 0.05 g / mL and La concentration of 0.02 g / mL, respectively. The molybdenum nitrate mother liquor and lanthanum nitrate mother liquor were mixed in a volume ratio of 1:1 to obtain the impregnation solution.

[0027] Impregnation treatment: Place the expanded pore MCM-22 molecular sieve in a rotary evaporator, add the impregnation liquid dropwise at 60°C, and the amount of the impregnation liquid is 1.1 times the mass of the expanded pore MCM-22 molecular sieve. After the addition is completed, let it stand and age for 12 hours to obtain the impregnated MCM-22 molecular sieve.

[0028] Calcination activation: Under nitrogen atmosphere, the impregnated MCM-22 molecular sieve was placed in a muffle furnace and heated to 350°C at 3°C / min for 4 hours. Then it was switched to air atmosphere and treated at 400°C for 2 hours to decompose the metal precursor into MoO3-La2O3 composite oxide to obtain the loaded MCM-22 molecular sieve.

[0029] S3. Catalyst molding: The loaded MCM-22 molecular sieve and pseudo-boehmite (Al2O3 content ≥70%) were mixed in a mass ratio of 8:2 to obtain a mixture. 2 wt% sesbania powder was added as a pore-forming agent and 3 wt% dilute nitric acid (mass fraction 5%) was added as a peptizer. The mixture was ball-milled for 30 minutes and then formed using a twin-screw extruder (die head aperture 1.5 mm) with an extrusion pressure of 8 MPa. The obtained wet strips were aged at room temperature for 24 hours, then dried at 120°C for 6 hours, and calcined at 500°C for 3 hours to obtain the finished catalyst.

[0030] The alkylation reaction test was carried out on the finished catalyst prepared above: (1) Test equipment and condition control: A high-pressure fixed-bed continuous flow reactor (material: Hastelloy C276) was used, with a reaction tube measuring 25 mm x 600 mm. Catalyst loading was performed by laying two layers of 80-mesh stainless steel wire mesh at the bottom of the reaction tube, followed by 20 g of ground, 40-mesh finished catalyst particles. The top layer was then filled with 3 mm quartz sand to a bed height of 450 mm to ensure uniform airflow distribution.

[0031] (2) Raw material pretreatment: Benzene purification: Industrial-grade benzene (purity ≥99.5%) is dehydrated through an adsorption tower filled with 4A molecular sieves to a moisture content of <10 ppm, and then passed through a silica gel column to remove thiophene sulfides to a sulfur content of <0.1 ppm; Preparation of ethylene mixed gas: A mass flow controller (MFC, accuracy ±0.5% FS) was used to control the flow rates of ethylene (purity ≥99.9%) and nitrogen (purity ≥99.999%), respectively, to prepare an ethylene-nitrogen mixed gas with a volume concentration of 5%. The mixed gas was fully homogenized in a static mixer and then entered the reaction system.

[0032] (3) Reaction operation process: Catalyst activation: Under nitrogen atmosphere (flow rate 50 mL / min), the temperature was increased to 400°C at 3°C / min and maintained for 2 hours to remove physically adsorbed water on the catalyst surface; System pressure balance: switch to hydrogen (purity ≥ 99.999%), at 2.0 MPa pressure with LHSV = 2.0 h -1 The product was reduced at a hydrogen flow rate of 1000 nm for 4 hours (reduction temperature 350°C), and then the pressure was released to room temperature; Liquid phase feed start: Benzene is fed into the liquid phase feed pump at a LHSV of 1.2 h -1 The gaseous ethylene mixture is injected into the preheater (preheating temperature 150°C) at a flow rate of 10000 ℃. After being adjusted to the reaction pressure by a pressure reducing valve, it is fully contacted with liquid benzene in the gas-liquid mixer (mixing temperature 120°C) to form a homogeneous feed. Reaction stage: Maintaining the set temperature (180°C) and pressure (2.0 MPa), the product was collected every 24 hours, and data recording began after 48 hours of stable operation; Product separation: The reaction effluent is separated by three stages of condensation (the first stage is water-cooled to 80°C, the second stage is ethanol-cooled to -10°C, and the third stage is deep-cooled to -30°C). The liquid product is collected in a pressurized storage tank, and the uncondensed gas is discharged through a back-pressure valve.

[0033] (4) Alkylation reaction test results: Gas chromatography and thermogravimetric analysis showed that the ethylene conversion rate was 95.8±0.4%, the ethylbenzene selectivity was 98.2±0.7%, and the carbon deposition rate was 2.5±0.1% after the catalyst was operated for 1200 hours.

[0034] Example 2 A method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene comprises the following steps: S1, MCM-22 molecular sieve pretreatment: Acid modification treatment: MCM-22 raw powder (SiO2 / Al2O3=30 (molar ratio)) was mixed with 0.5 mol / L oxalic acid solution at a solid-liquid ratio of 1:10, stirred and refluxed at 70℃ for 4 hours, centrifuged and washed until neutral, and dried at 110℃ for 6 hours. The MCM-22 molecular sieve treated with oxalic acid was mixed with 0.20 mol / L citric acid solution at a solid-liquid ratio of 1:8, ultrasonically treated at 90℃ (40 kHz) for 2 hours, filtered, and dried at 120℃ for 12 hours to obtain acid-modified MCM-22 molecular sieve. During the above acid modification treatment, oxalic acid preferentially removed non-framework aluminum, and citric acid further adjusted the distribution of framework aluminum.

[0035] Steam-assisted pore expansion: The acid-modified MCM-22 molecular sieve was placed in a tubular furnace, and a mixture of nitrogen and water vapor (water vapor partial pressure 20 kPa) was introduced. The temperature was raised to 450°C at a rate of 2°C / min. After maintaining the temperature for 3 hours, the mixture was cooled in the furnace to obtain the expanded pore MCM-22 molecular sieve.

[0036] S2, bimetallic load: Preparation of impregnation solution: Molybdenum nitrate (MoO3 content ≥ 99%) and lanthanum nitrate (La2O3 content ≥ 99%) were weighed and dissolved in deionized water respectively to prepare molybdenum nitrate mother liquor and lanthanum nitrate mother liquor with Mo concentration of 0.1 g / mL and La concentration of 0.05 g / mL, respectively. The molybdenum nitrate mother liquor and lanthanum nitrate mother liquor were mixed in a volume ratio of 1:1 to obtain the impregnation solution.

[0037] Impregnation treatment: Place the expanded pore MCM-22 molecular sieve in a rotary evaporator, add the impregnation liquid dropwise at 60°C, and the amount of the impregnation liquid is 1.2 times the mass of the expanded pore MCM-22 molecular sieve. After the addition is completed, let it stand and age for 12 hours to obtain the impregnated MCM-22 molecular sieve.

[0038] Calcination activation: Under nitrogen atmosphere, the impregnated MCM-22 molecular sieve was placed in a muffle furnace and heated to 350°C at 3°C / min for 4 hours. Then it was switched to air atmosphere and treated at 400°C for 2 hours to decompose the metal precursor into MoO3-La2O3 composite oxide to obtain the loaded MCM-22 molecular sieve.

[0039] S3. Catalyst molding: The loaded MCM-22 molecular sieve and pseudo-boehmite (Al2O3 content ≥70%) were mixed in a mass ratio of 8:2 to obtain a mixture. 2 wt% sesbania powder was added as a pore-forming agent and 3 wt% dilute nitric acid (mass fraction 5%) was added as a peptizer. The mixture was ball-milled for 30 minutes and then formed using a twin-screw extruder (die head aperture 1.5 mm) with an extrusion pressure of 12 MPa. The obtained wet strips were aged at room temperature for 24 hours, then dried at 120°C for 6 hours, and calcined at 500°C for 3 hours to obtain the finished catalyst.

[0040] The alkylation reaction test was carried out on the finished catalyst prepared above: (1) Test equipment and condition control: A high-pressure fixed-bed continuous flow reactor (material: Hastelloy C276) was used, with a reaction tube measuring 25 mm x 600 mm. Catalyst loading was performed by laying two layers of 80-mesh stainless steel wire mesh at the bottom of the reaction tube, followed by 20 g of ground, 20-mesh finished catalyst particles. The top layer was then filled with 3 mm quartz sand to a bed height of 450 mm to ensure uniform airflow distribution.

[0041] (2) Raw material pretreatment: Benzene purification: Industrial-grade benzene (purity ≥99.5%) is dehydrated through an adsorption tower filled with 4A molecular sieves to a moisture content of <10 ppm, and then passed through a silica gel column to remove thiophene sulfides to a sulfur content of <0.1 ppm; Preparation of ethylene mixed gas: A mass flow controller (MFC, accuracy ±0.5% FS) was used to control the flow rates of ethylene (purity ≥99.9%) and nitrogen (purity ≥99.999%), respectively, to prepare an ethylene-nitrogen mixed gas with a volume concentration of 20%. The mixed gas was fully homogenized in a static mixer and then entered the reaction system.

[0042] (3) Reaction operation process: Catalyst activation: Under nitrogen atmosphere (flow rate 50 mL / min), the temperature was increased to 400°C at 3°C / min and maintained for 2 hours to remove physically adsorbed water on the catalyst surface; System pressure balance: switch to hydrogen (purity ≥ 99.999%), at 2.0 MPa pressure with LHSV = 2.0 h -1 The product was reduced at a hydrogen flow rate of 1000 nm for 4 hours (reduction temperature 350°C), and then the pressure was released to room temperature; Liquid phase feed start: Benzene is fed into the liquid phase feed pump at a LHSV of 1.2 h -1 The gaseous ethylene mixture is injected into the preheater (preheating temperature 150°C) at a flow rate of 10000 ℃. After being adjusted to the reaction pressure by a pressure reducing valve, it is fully contacted with liquid benzene in the gas-liquid mixer (mixing temperature 120°C) to form a homogeneous feed. Reaction stage: Maintain the set temperature (220°C) and pressure (3.0 MPa), collect products every 24 hours, and start data recording after 48 hours of stable operation; Product separation: The reaction effluent is separated by three stages of condensation (the first stage is water-cooled to 80°C, the second stage is ethanol-cooled to -10°C, and the third stage is deep-cooled to -30°C). The liquid product is collected in a pressurized storage tank, and the uncondensed gas is discharged through a back-pressure valve.

[0043] (4) Alkylation reaction test results: Gas chromatography and thermogravimetric analysis showed that the ethylene conversion rate was 97.5±0.2%, the ethylbenzene selectivity was 98.8±0.3%, and the carbon deposition rate was 2.7±0.1% after the catalyst was operated for 1200 hours.

[0044] Example 3 A method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene comprises the following steps: S1, MCM-22 molecular sieve pretreatment: Acid modification treatment: MCM-22 raw powder (SiO2 / Al2O3=35 (molar ratio)) was mixed with 0.5 mol / L oxalic acid solution at a solid-liquid ratio of 1:10, stirred and refluxed at 60-80℃ for 4 hours, centrifuged and washed until neutral, and dried at 110℃ for 6 hours. The MCM-22 molecular sieve treated with oxalic acid was mixed with 0.20 mol / L citric acid solution at a solid-liquid ratio of 1:8, ultrasonically treated at 90℃ (40 kHz) for 2 hours, filtered, and dried at 120℃ for 12 hours to obtain acid-modified MCM-22 molecular sieve. During the above acid modification treatment, oxalic acid preferentially removed non-framework aluminum, and citric acid further adjusted the distribution of framework aluminum.

[0045] Steam-assisted pore expansion: The acid-modified MCM-22 molecular sieve was placed in a tubular furnace, and a mixture of nitrogen and water vapor (water vapor partial pressure 30 kPa) was introduced. The temperature was raised to 470°C at a rate of 2°C / min. After maintaining the temperature for 3 hours, the furnace was cooled to obtain the expanded pore MCM-22 molecular sieve.

[0046] S2, bimetallic load: Preparation of impregnation solution: Molybdenum nitrate (MoO3 content ≥ 99%) and lanthanum nitrate (La2O3 content ≥ 99%) were weighed and dissolved in deionized water respectively to prepare molybdenum nitrate mother liquor and lanthanum nitrate mother liquor with Mo concentration of 0.1 g / mL and La concentration of 0.05 g / mL, respectively. The molybdenum nitrate mother liquor and lanthanum nitrate mother liquor were mixed in a volume ratio of 1:1 to obtain the impregnation solution.

[0047] Impregnation treatment: Place the expanded pore MCM-22 molecular sieve in a rotary evaporator, add the impregnation liquid dropwise at 60°C, and the amount of the impregnation liquid is 1.2 times the mass of the expanded pore MCM-22 molecular sieve. After the addition is completed, let it stand and age for 12 hours to obtain the impregnated MCM-22 molecular sieve.

[0048] Calcination activation: Under nitrogen atmosphere, the impregnated MCM-22 molecular sieve was placed in a muffle furnace and heated to 350°C at 3°C / min for 4 hours. Then it was switched to air atmosphere and treated at 400°C for 2 hours to decompose the metal precursor into MoO3-La2O3 composite oxide to obtain the loaded MCM-22 molecular sieve.

[0049] S3. Catalyst molding: The loaded MCM-22 molecular sieve and pseudo-boehmite (Al2O3 content ≥70%) were mixed in a mass ratio of 8:2 to obtain a mixture. 2 wt% sesbania powder was added as a pore-forming agent and 3 wt% dilute nitric acid (mass fraction 5%) was added as a peptizer. The mixture was ball-milled for 30 minutes and then formed using a twin-screw extruder (die head aperture 1.5 mm) with an extrusion pressure of 12 MPa. The obtained wet strips were aged at room temperature for 24 hours, then dried at 120°C for 6 hours, and calcined at 500°C for 3 hours to obtain the finished catalyst.

[0050] The alkylation reaction test was carried out on the finished catalyst prepared above: (1) Test equipment and condition control: A high-pressure fixed-bed continuous flow reactor (material: Hastelloy C276) was used, with a reaction tube measuring 25 mm x 600 mm. Catalyst loading was performed by laying two layers of 80-mesh stainless steel wire mesh at the bottom of the reaction tube, followed by 20 g of ground, 30-mesh finished catalyst particles. The top layer was then filled with 3 mm quartz sand to a bed height of 450 mm to ensure uniform airflow distribution.

[0051] (2) Raw material pretreatment: Benzene purification: Industrial-grade benzene (purity ≥99.5%) is dehydrated through an adsorption tower filled with 4A molecular sieves to a moisture content of <10 ppm, and then passed through a silica gel column to remove thiophene sulfides to a sulfur content of <0.1 ppm; Preparation of ethylene mixed gas: A mass flow controller (MFC, accuracy ±0.5% FS) was used to control the flow rates of ethylene (purity ≥99.9%) and nitrogen (purity ≥99.999%), respectively, to prepare an ethylene-nitrogen mixed gas with a volume concentration of 15%. The mixed gas was fully homogenized in a static mixer and then entered the reaction system.

[0052] (3) Reaction operation process: Catalyst activation: Under nitrogen atmosphere (flow rate 50 mL / min), the temperature was increased to 400°C at 3°C / min and maintained for 2 hours to remove physically adsorbed water on the catalyst surface; System pressure balance: switch to hydrogen (purity ≥ 99.999%), at 2.0 MPa pressure with LHSV = 2.0 h -1 The product was reduced at a hydrogen flow rate of 1000 nm for 4 hours (reduction temperature 350°C), and then the pressure was released to room temperature; Liquid phase feed start: Benzene is fed into the liquid phase feed pump at a LHSV of 1.2 h -1 The gaseous ethylene mixture is injected into the preheater (preheating temperature 150°C) at a flow rate of 10000 ℃. After being adjusted to the reaction pressure by a pressure reducing valve, it is fully contacted with liquid benzene in the gas-liquid mixer (mixing temperature 120°C) to form a homogeneous feed. Reaction stage: Maintain the set temperature (240°C) and pressure (4.0 MPa), collect products every 24 hours, and start data recording after 48 hours of stable operation; Product separation: The reaction effluent is separated by three stages of condensation (the first stage is water-cooled to 80°C, the second stage is ethanol-cooled to -10°C, and the third stage is deep-cooled to -30°C). The liquid product is collected in a pressurized storage tank, and the uncondensed gas is discharged through a back-pressure valve.

[0053] (4) Alkylation reaction test results: Gas chromatography and thermogravimetric analysis showed that the ethylene conversion rate was 97.1±0.2%, the ethylbenzene selectivity was 98.7±0.4%, and the carbon deposition rate was 2.7±0.1% after the catalyst was operated for 1200 hours.

[0054] Comparative Example 1 Comparative Example 1 is the control group of Example 2, and Comparative Example 1 is the single acid treatment control group.

[0055] Variable adjustment: only oxalic acid treatment was used, citric acid treatment was omitted, and the remaining steps were consistent with Example 2.

[0056] Alkylation reaction test results: ethylene conversion rate dropped to 92.5±0.7%, and carbon deposition rate increased to 4.2±0.3% after 1200 hours of operation of the catalyst.

[0057] Result analysis: Comparative Example 1 confirms the necessity of citric acid to regulate the distribution of framework aluminum.

[0058] Comparative Example 2 Comparative Example 2 is the control group of Example 2, and Comparative Example 2 is a control group without hole expansion treatment.

[0059] Variable adjustment: Skip the steam-assisted pore expansion step and directly load the acid-modified MCM-22 with metal. The remaining steps remain the same as in Example 2.

[0060] Alkylation reaction test results: ethylbenzene selectivity dropped to 95.1±0.3%, and the carbon deposition rate increased to 5.1±0.5% after the catalyst ran for 600 hours.

[0061] Result analysis: Comparative Example 2 confirms the optimization effect of pore expansion treatment on pore structure.

[0062] Comparative Example 3 Comparative Example 3 is the control group of Example 2, and Comparative Example 3 is a single metal loading control group.

[0063] Variable adjustment: only MoO3 is loaded (without adding La2O3), and the rest of the steps are consistent with Example 2.

[0064] Alkylation reaction test results: ethylene conversion rate dropped to 88.5±0.5%.

[0065] Result analysis: Comparative Example 3 confirms the synergistic effect of La2O3 on ethylene activation.

[0066] Comparative Example 4 Comparative Example 4 is the control group of Example 2, and Comparative Example 4 is a phosphoric acid-modified control group.

[0067] Variable adjustment: 0.1 mol / L phosphoric acid solution was used instead of oxalic acid-citric acid treatment, and the remaining steps were consistent with Example 2.

[0068] Alkylation reaction test results: After the catalyst ran for 600 hours, the carbon deposition rate increased to 6.8±0.2%.

[0069] Result analysis: Comparative Example 4 confirms the defects of phosphoric acid treatment in the prior art.

[0070] Comparative Example 5 Comparative Example 5 is the control group of Example 2, and Comparative Example 5 is the high-temperature hole expansion control group.

[0071] Variable adjustment: the water vapor partial pressure was increased to 50 kPa, and then the temperature was increased to 500°C at a rate of 2°C / min. The remaining steps were the same as those in Example 2.

[0072] Alkylation reaction test results: ethylene conversion rate dropped sharply to 80.4±0.5%.

[0073] Result analysis: Comparative Example 5 confirms the critical control significance of pore expansion temperature / partial pressure.

[0074] Comparative Example 6 Comparative Example 6 is the control group of Example 2, and Comparative Example 6 is a step-by-step metal loading control group.

[0075] Variable adjustment: MoO3 is loaded first and then La2O3 is loaded (step-by-step impregnation, not blending). The other steps are consistent with Example 2.

[0076] Alkylation reaction test results: The synergistic effect failed, the ethylbenzene selectivity dropped to 96.5±0.5%, and the carbon deposition rate increased to 3.9±0.3%.

[0077] Result analysis: Comparative Example 5 confirms the necessity of bimetallic co-impregnation for synergistic structure.

[0078] It should be noted that, in this document, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0079] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene, characterized in that: The following steps are involved: S1, subjecting MCM-22 raw powder to acid modification to obtain acid-modified MCM-22 molecular sieve, and subjecting the acid-modified MCM-22 molecular sieve to steam-assisted pore expansion to obtain expanded pore MCM-22 molecular sieve; S2. Place the expanded pore MCM-22 molecular sieve in a rotary evaporator, add the impregnation liquid dropwise at 60° C., the amount of the impregnation liquid is 1.1-1.2 times the mass of the expanded pore MCM-22 molecular sieve, and after the addition is completed, let it stand and age for 12 hours to obtain the impregnated MCM-22 molecular sieve; S3. Under nitrogen atmosphere, the impregnated MCM-22 molecular sieve was placed in a muffle furnace and heated to 350°C at 3°C / min for 4 hours, then switched to air atmosphere and treated at 400°C for 2 hours to obtain the loaded MCM-22 molecular sieve; S4. The loaded MCM-22 molecular sieve and pseudo-boehmite were mixed in a mass ratio of 8:2 to obtain a mixture, and then 2 wt% of a pore-forming agent and 3 wt% of a peptizing agent were added to the mixture. The mixture was ball-milled for 30 minutes, and then formed by a twin-screw extruder with an extrusion pressure of 8-12 MPa. The obtained wet strips were aged at room temperature for 24 hours, then dried at 120°C for 6 hours, and calcined at 500°C for 3 hours to obtain the finished catalyst.

2. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 1, characterized in that: The acid modification treatment in S1 comprises the following steps: The MCM-22 raw powder was mixed with 0.1-0.5 mol / L oxalic acid solution at a solid-liquid ratio of 1:10, stirred and refluxed at 60-80°C for 2-4 hours, centrifuged and washed until neutral, and dried at 110°C for 6 hours. The MCM-22 molecular sieve treated with oxalic acid was mixed with 0.05-0.20 mol / L citric acid solution at a solid-liquid ratio of 1:8, ultrasonically treated at 80-90°C for 1-2 hours, filtered, and dried at 120°C for 12 hours to obtain the acid-modified MCM-22 molecular sieve.

3. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 2, characterized in that: The molar ratio of SiO2 / Al2O3 in the MCM-22 raw powder is 25-35.

4. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 1, characterized in that: The water vapor assisted pore expansion treatment in S1 comprises the following steps: placing the acid-modified MCM-22 molecular sieve in a tube furnace, introducing a mixture of nitrogen and water vapor, heating the mixture to 430-470° C. at a rate of 2° C. / min, maintaining the temperature for 2-3 hours, and then cooling the mixture with the furnace to obtain the expanded pore MCM-22 molecular sieve.

5. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 4, characterized in that: The partial pressure of water vapor in the mixed gas is 10-30 kPa.

6. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 1, characterized in that: The impregnation solution in S2 is prepared by the following steps: weighing molybdenum nitrate and lanthanum nitrate, dissolving them in deionized water respectively, preparing molybdenum nitrate mother liquor and lanthanum nitrate mother liquor with Mo concentration of 0.05-0.1 g / mL and La concentration of 0.02-0.05 g / mL, and mixing the molybdenum nitrate mother liquor and the lanthanum nitrate mother liquor in a volume ratio of 1:1 to obtain an impregnation solution.

7. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 6, characterized in that: The content of MoO3 in the molybdenum nitrate is ≥99%; the content of La2O3 in the lanthanum nitrate is ≥99%.

8. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 1, characterized in that: The Al2O3 content in the pseudo-boehmite described in S4 is ≥70%.

9. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 1, characterized in that: The pore-forming agent in S4 is sesbania powder; and the peptizing agent is dilute nitric acid.

10. The method for preparing an MCM-22 catalyst for the alkylation of liquid benzene with dilute ethylene according to claim 9, characterized in that: The mass fraction of the dilute nitric acid is 5%.