ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization, modification method and application

Abstract

The invention discloses a ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization, a modification method and application, the ZSM-5 molecular sieve modified catalyst is Zn / ZSM-5, and Zn with the mass fraction of 1-10% is loaded on a ZSM-5 molecular sieve through a strong electrostatic adsorption method. The modification method of Zn / ZSM-5 comprises the following steps: preparing a zinc solution, pretreating a catalyst, and carrying out isovolumetric strong electrostatic adsorption; through the modification method, the dispersion uniformity and bonding firmness of Zn on the surface of the catalyst carrier can be enhanced, the microscopic distribution state and chemical bonding effect of Zn are optimized, the catalytic efficiency of the Zn / HZSM-5 catalyst in propane aromatization reaction is remarkably improved, and collaborative optimization of propane conversion rate, aromatic hydrocarbon selectivity and catalytic stability is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization, a modification method and application thereof. BACKGROUND

[0002] BTX (benzene, toluene, xylene) is an essential basic raw material in organic chemical industry, and its application involves important fields such as medicine, fabric, rubber and dye. At present, it is mainly produced in petroleum chemical processes such as naphtha reforming and steam cracking, and the shortage of petroleum resources and high production cost make it difficult to meet the growing market demand. Catalytic conversion of abundant low-value low-carbon alkanes into high-value BTX has been an important research topic in recent decades. Especially with the rapid development of shale gas exploitation technology, the catalytic conversion of cheap propane, as the main component, to BTX has attracted more and more attention.

[0003] ZSM-5 molecular sieve is a kind of zeolite material developed by the United States Mobile Company in 1970, which has MFI crystal structure. Its unique cross-ten-membered ring pore structure endows it with excellent shape-selective catalytic performance. ZSM-5 molecular sieve structure is composed of silicon and aluminum oxide tetrahedron, which has good acidity and thermal stability, and the pore size is about 5.5 Å, which has unique performance in catalytic conversion of small molecule reactions. It is widely used in petroleum refining, methanol to olefins (MTO), olefin aromatization and other processes.

[0004] Propane aromatization (PDA) process is usually carried out at 500-600 ℃. Zn / HZSM-5 has been proved to be an efficient catalyst for activating and catalyzing the conversion of low-carbon alkanes to aromatic hydrocarbons, and has been applied in related commercial processes. The commonly used preparation methods include impregnation method, ion exchange method, atomic layer deposition method, chemical vapor deposition method, etc. Zn-modified HZSM-5 has a significant promoting effect on improving catalytic efficiency and product selectivity, but the aggregation of metal ions and the formation of carbon deposition accelerate the recombination of surface H atoms on the active site, reducing the activity and service life. The regeneration process will significantly increase energy consumption and cost. Therefore, high dispersion of Zn sites has important significance for improving the catalytic activity and stability of Zn / HZSM-5.

[0005] Strong electrostatic adsorption method (SEA) is an advanced method for catalyst preparation, which focuses on the precise control of active component (such as Zn) deposition on the surface of the carrier (such as HZSM-5) through electrostatic interaction. It usually includes the following steps: a) solution pH adjustment: by controlling the acidity or alkalinity of the solution, the metal center / carrier surface is charged with a specific charge (such as positive or negative); b) electrostatic adsorption: make two metal precursors with opposite charges contact with the carrier, and use electrostatic attraction to make the metal component selectively adsorb to the surface of the carrier; c) subsequent treatment: through the steps of separation, drying, calcination and other steps to fix the metal component and form the target catalyst structure. This method has the following advantages: a) high dispersion and small particle size: this method can significantly improve the dispersion of active metal, form smaller nanoparticles (generally 3~4 nm, while the traditional impregnation method is usually 8~9 nm), thereby improving the catalytic activity and utilization rate of active metal component; b) enhanced metal-carrier interaction: through electrostatic adsorption, the active component can be anchored at the specific modified area of the carrier, optimizing the electronic structure and geometric effect, and improving the catalytic performance; c) controllability and uniformity: the metal loading and distribution can be precisely controlled, the agglomeration phenomenon is inhibited, and the problems of active site utilization caused by uneven deposition in traditional methods are avoided; d) environmentally friendly: the preparation process is mild and the energy consumption is low.

[0006] The existing propane aromatization zinc modified catalyst has the problems of incomplete dispersion of Zn after modification and existence of a large number of ZnO clusters. A ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization, a modification method and application are provided. SUMMARY

[0007] The present application aims to innovatively provide a Zn / HZSM-5 catalyst preparation method based on strong electrostatic adsorption technology. This method focuses on enhancing the dispersion uniformity and binding firmness of Zn species on the surface of the carrier, and by optimizing the micro-distribution state and chemical bonding effect of Zn species, the catalytic efficiency of Zn / HZSM-5 catalyst in propane aromatization reaction is significantly improved. Finally, the synergistic optimization of propane conversion rate, aromatic hydrocarbon selectivity and catalytic stability is realized, providing an efficient and stable catalyst solution for the industrial application of propane aromatization.

[0008] The object of the present application is achieved by the following technical solutions.

[0009] According to one aspect of the present application, a ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization is provided, which is Zn / ZSM-5, wherein a Zn salt with a mass fraction of 1~10% is loaded on the ZSM-5 molecular sieve by a strong electrostatic adsorption method, and the pore size of the ZSM-5 molecular sieve is 0.52~0.58mm; The Zn / ZSM-5 has a coffin-shaped, sheet-shaped or bundled material-shaped morphology.

[0010] According to the technical scheme, the ZSM-5 molecular sieve is a hydrogen type ZSM-5 molecular sieve with a silicon-aluminum ratio of 15-300.

[0011] According to the technical scheme, the Zn source is at least one of zinc nitrate, zinc acetate and zinc sulfate.

[0012] According to a second aspect of the present application, a modification method of a ZSM-5 molecular sieve modified catalyst is provided, and the modification method comprises the following steps: Step 1, zinc solution preparation: weighing a Zn salt and dissolving it in water, adding an alkaline substance to adjust the pH of the solution, and ultrasonic oscillation to obtain a uniformly oscillated zinc solution; Step 2, catalyst pretreatment: taking a ZSM-5 molecular sieve catalyst and performing pretreatment in an oven to obtain a pretreated ZSM-5 molecular sieve catalyst; Step 3, strong electrostatic adsorption: using an equal volume method to mix the pretreated ZSM-5 molecular sieve catalyst of step 2 and the uniformly oscillated zinc solution of step 1 uniformly, and performing strong electrostatic adsorption reaction, drying, calcination and natural cooling to room temperature to obtain a ZSM-5 molecular sieve modified catalyst, i.e. Zn / ZSM-5.

[0013] According to the technical scheme, the Zn salt in step 1 is at least one of zinc nitrate, zinc acetate and zinc sulfate. The mass fraction of zinc in the uniformly oscillated zinc solution in step 1 is 1-10%.

[0014] According to the technical scheme, the alkaline substance in step 1 is selected from concentrated ammonia, methylamine solution and ethylamine solution. The concentration of the alkaline substance is 0.1-2 mol / L. The pH of the solution adjusted by adding the alkaline substance in step 1 is 9-13. The ultrasonic oscillation conditions in step 1 are as follows: The ultrasonic oscillation temperature is 25-50℃. The ultrasonic oscillation time is 5-30 min.

[0015] According to the technical scheme, the pretreatment conditions in step 2 are as follows: The pretreatment temperature is 8-120℃. The pretreatment time is 2-24 h.

[0016] According to the technical scheme, the strong electrostatic adsorption reaction conditions in step 3 are as follows: The strong electrostatic adsorption reaction temperature is 20-30℃. The strong electrostatic adsorption reaction time is 4-12 h; The drying conditions in step 3 are as follows: The drying temperature is 60-80 DEG C; The drying time is 2-6 h; The calcination conditions in step 3 are as follows: The calcination temperature is 350-550 DEG C; The calcination time is 2-6 h.

[0017] Based on the above technical solution, the configuration of the zinc solution in step 1 further comprises: dissolving the weighed Zn salt in water, stirring at 300-3000 rpm for 0.2-0.5 h to obtain the stirred zinc solution, and the ZSM-5 molecular sieve catalyst in step 2 is selected from one of a commercial ZSM-5 molecular sieve, a ZSM-5 molecular sieve modified catalyst, and a modified ZSM-5 molecular sieve modified catalyst obtained by a modification method. According to a third aspect of the present application, a ZSM-5 molecular sieve modified catalyst for catalyzing propane aromatization and its application in catalyzing propane aromatization to produce aromatic hydrocarbons, including benzene, toluene and xylene, are provided.

[0018] Compared with the prior art, the present application has the following beneficial effects: (1) The technical solution disclosed in the present application, in terms of technical mechanism, precisely regulates the pH value of the solution and innovatively uses the strong electrostatic adsorption strategy to promote the atomic-level uniform dispersion of zinc ions on the surface of the carrier, so that the zinc loading is more uniform and presents a highly dispersed nano-scale particle morphology; this uniform morphology not only significantly improves the active site density and intrinsic activity of the catalyst, but also significantly enhances the structural stability of the catalyst through the strengthening of zinc-carrier interaction, thereby effectively improving the selectivity of aromatic hydrocarbon products in the propane aromatization reaction.

[0019] (2) The technical solution disclosed in the present application, in terms of process characteristics, realizes precise adjustment of the metal loading amount and is completed under mild conditions of normal pressure and low temperature throughout the process, with a simple and efficient operation process, significantly shortened single-batch preparation period, and complete conformity with the needs of industrial continuous production; the technical solution loads Zn ions with high dispersion on the surface of ZSM-5 based on the strong electrostatic adsorption method to improve the activity and stability of ZSM-5 in the catalytic propane aromatization process. Zn with a mass fraction of 1-10% is loaded on the ZSM-5 molecular sieve to prepare a Zn / ZSM-5 catalyst; when the Zn loading amount is less than 1%, the active site density is insufficient, the propane conversion rate significantly decreases, and the aromatic hydrocarbon selectivity is also difficult to improve; when the Zn loading amount exceeds 5%, ZnO clusters are easily formed on the surface, which leads to the decrease of active sites Zn(OH) +The relative quantity is reduced and the channel is partially blocked, the aromatization activity is reduced and the side reactions such as hydrogenolysis are intensified. The zinc source comes from different zinc salts (zinc nitrate, zinc acetate, zinc sulfate), and the modification process also involves the participation of alkaline substances such as concentrated ammonia, methylamine solution and ethylamine solution, aiming at the high dispersion of Zn on ZSM-5 and the strong interaction between them, so as to realize the efficient activation of C-H bond of low carbon alkane and inhibit the occurrence of side reactions such as hydrogenolysis.

[0020] (3) The technical scheme disclosed by the application has excellent catalytic performance in the propane dehydrogenation aromatization reaction system, excellent thermal stability, and can greatly prolong the service life of the catalyst: compared with the commercial catalyst, the service life of the catalyst is only 4h when the conventional modification method is used, but the service life of the catalyst can reach 8h when the method is used. This method can be adapted to various carriers and reaction systems of HZSM-5, and has broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The SEM characterization spectrum of the Zn / HZSM-5-11 catalyst prepared in Example 11 of the application is shown in the figure; Figure 2 The XRD characterization spectrum of the Zn / HZSM-5-11 catalyst prepared in Example 11 of the application is shown in the figure. DETAILED DESCRIPTION

[0022] The application will be further described below in combination with specific examples, but the application is not limited in any way by the examples.

[0023] Unless otherwise specified, the raw materials and catalysts in the examples are purchased through commercial channels.

[0024] The commercial HZSM-5 molecular sieve (pore size 0.52mm) used in the examples of the application is purchased from the catalyst factory of Nankai University, and the nanosheet HZSM-5 is self-made.

[0025] The analysis method in the examples and the calculation of conversion rate and selectivity are as follows: Quantitative analysis is carried out by using Tianmei GC7900 gas chromatograph with PONA chromatographic column.

[0026] In the examples of the application, the propane conversion rate is shown as formula 1, and the selectivity is shown as formula 2, and the specific calculation formula is as follows (taking propane conversion rate as evaluation index):

[0027] Formula 1;

[0028] Formula 2.

[0029] Example 1 Step 1, Zinc solution preparation: A 1% mass fraction of zinc nitrate solution was prepared by weighing 0.455 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 9, and the solution was continuously ultrasonically oscillated at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0030] Step 2, Catalyst pretreatment: 10 g of commercial HZSM-5 molecular sieve was pretreated in an oven at 120 °C for 2 h to obtain pretreated commercial HZSM-5 molecular sieve.

[0031] Step 3, Strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 molecular sieve described in step 2 using the equal volume method, and the molecular sieve dosage was 10 g. The reaction was carried out at room temperature under strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and then calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-1.

[0032] Example 2 Step 1, Zinc solution preparation: A 3% mass fraction of zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 9, and the solution was continuously ultrasonically oscillated at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0033] Step 2, Catalyst pretreatment: 10 g of commercial HZSM-5 molecular sieve was pretreated in an oven at 120 °C for 2 h to obtain pretreated commercial HZSM-5 molecular sieve.

[0034] Step 3, Strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 molecular sieve described in step 2 using the equal volume method, and the molecular sieve dosage was 10 g. The reaction was carried out at room temperature under strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and then calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-2.

[0035] Example 3 Step 1, Zinc solution preparation: A 5% mass fraction of zinc nitrate solution was prepared by weighing 2.275 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 9, and the solution was continuously ultrasonically oscillated at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0036] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was weighed and pretreated in an oven at 120 °C for 2 h to obtain pretreated commercial HZSM-5 zeolite.

[0037] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 using the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-3.

[0038] Example 4 Step 1, zinc solution preparation: a 3% zinc acetate solution was prepared by weighing 0.756 g of zinc acetate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After stirring uniformly, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 9, and the oscillation was continued at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0039] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was weighed and pretreated in an oven at 120 °C for 2 h to obtain pretreated commercial HZSM-5 zeolite.

[0040] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 using the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-4.

[0041] Example 5 Step 1, zinc solution preparation: a 3% zinc sulfate solution was prepared by weighing 0.888 g of zinc sulfate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After stirring uniformly, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 9, and the oscillation was continued at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0042] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was weighed and pretreated in an oven at 120 °C for 2 h to obtain pretreated commercial HZSM-5 zeolite.

[0043] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 by the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 ℃ oven for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-5.

[0044] Example 6 Step 1, zinc solution preparation: A 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1.2 mol / L was added dropwise, the pH was adjusted to 10, and the oscillation was continued at 25 ℃ for 30 min to obtain a uniformly oscillated solution.

[0045] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was pretreated in an oven at 120 ℃ for 2 h to obtain pretreated commercial HZSM-5 zeolite.

[0046] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 by the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 ℃ oven for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-6.

[0047] Example 7 Step 1, zinc solution preparation: A 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1.2 mol / L was added dropwise, the pH was adjusted to 10, and the oscillation was continued at 25 ℃ for 30 min to obtain a uniformly oscillated solution.

[0048] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was pretreated in an oven at 120 ℃ for 2 h to obtain pretreated commercial HZSM-5 zeolite.

[0049] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 by the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 ℃ oven for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-6.

[0050] Example 8 Step 1, zinc solution configuration: A 3% mass fraction of zinc nitrate solution was configured, 1.36 g of zinc nitrate and 10 g of deionized water were weighed and mixed at room temperature, and then fully stirred. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1.8 mol / L was added dropwise, the pH was adjusted to 12, and then ultrasonic oscillation was continued at 25°C for 30 min to obtain a uniformly oscillated solution.

[0051] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 molecular sieve was weighed and pretreated in an oven at 120°C for 2 h to obtain pretreated commercial HZSM-5 molecular sieve.

[0052] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 molecular sieve described in step 2 by equal volume method, and the molecular sieve was used in an amount of 10 g. Reaction under strong electrostatic adsorption at room temperature for 12 h, drying in an 80°C oven for 6 h, and calcination in a muffle furnace at 550°C for 5 h to obtain Zn / HZSM-5-8.

[0053] Example 9 Step 1, zinc solution configuration: A 3% mass fraction of zinc nitrate solution was configured, 1.36 g of zinc nitrate and 10 g of deionized water were weighed and mixed at room temperature, and then fully stirred. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1.8 mol / L was added dropwise, the pH was adjusted to 12, and then ultrasonic oscillation was continued at 25°C for 30 min to obtain a uniformly oscillated solution.

[0054] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 molecular sieve was weighed and pretreated in an oven at 120°C for 2 h to obtain pretreated commercial HZSM-5 molecular sieve.

[0055] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 molecular sieve described in step 2 by equal volume method, and the molecular sieve was used in an amount of 10 g. Reaction under strong electrostatic adsorption at room temperature for 12 h, drying in an 80°C oven for 6 h, and calcination in a muffle furnace at 550°C for 5 h to obtain Zn / HZSM-5-8.

[0056] Example 10 Step 1, zinc solution configuration: A 3% mass fraction of zinc nitrate solution was configured, 1.36 g of zinc nitrate and 10 g of deionized water were weighed and mixed at room temperature, and then fully stirred. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1.8 mol / L was added dropwise, the pH was adjusted to 12, and then ultrasonic oscillation was continued at 25°C for 30 min to obtain a uniformly oscillated solution.

[0057] Step 2, catalyst pretreatment: 10 g of the commercial HZSM-5 zeolite was weighed into an oven and pretreated at 120 °C for 2 h to obtain the pretreated commercial HZSM-5 zeolite.

[0058] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 by the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-10.

[0059] Example 11 Step 1, zinc solution preparation: a 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 10, and the oscillation was continued at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0060] Step 2, catalyst pretreatment: 10 g of the nanosheet type HZSM-5 zeolite (P-HZSM-5 obtained in Example 15) was weighed into an oven and pretreated at 120 °C for 2 h to obtain the pretreated nanosheet type HZSM-5 zeolite.

[0061] Step 3, strong electrostatic adsorption: 15 ml of the uniformly oscillated solution described in step 1 was added dropwise to 10 g of the pretreated nanosheet type HZSM-5 zeolite described in step 2 by the equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature under the action of strong electrostatic adsorption for 12 h, dried in an 80 °C oven for 6 h, and calcined in a muffle furnace at 550 °C for 5 h to obtain Zn / HZSM-5-11, the SEM characterization spectrum of the Zn / HZSM-5-11 catalyst is shown in Figure 1 , and the XRD characterization spectrum is shown in Figure 2 . Example 12 Step 1, zinc solution preparation: a 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and then stirring thoroughly. After complete dissolution, 5 ml of concentrated ammonia water with a concentration of 1 mol / L was added dropwise, the pH was adjusted to 10, and the oscillation was continued at 25 °C for 30 min to obtain a uniformly oscillated solution.

[0062] Step 2, catalyst pretreatment: 10 g of the nanorod type HZSM-5 zeolite (B-HZSM-5 obtained in Example 16) was weighed into an oven and pretreated at 120 °C for 2 h to obtain the pretreated nanosheet type HZSM-5 zeolite.

[0063] Step 3, strong electrostatic adsorption: 15 ml of the solution described in step 1 was added dropwise to 10 g of the pretreated nanorod type HZSM-5 zeolite described in step 2 by equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature for 12 h under the action of strong electrostatic adsorption, dried in an oven at 80 ℃ for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-12. Example 13 Step 1, zinc solution preparation: a 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and fully stirring at 500 rpm for 0.25 h to obtain the stirred solution.

[0064] Step 2, catalyst pretreatment: 10 g of commercial HZSM-5 zeolite was pretreated in an oven at 120 ℃ for 2 h to obtain the pretreated commercial HZSM-5 zeolite.

[0065] Step 3, strong electrostatic adsorption: 15 ml of the stirred solution described in step 1 was added dropwise to 10 g of the pretreated commercial HZSM-5 zeolite described in step 2 by equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature for 12 h under the action of strong electrostatic adsorption, dried in an oven at 80 ℃ for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-13.

[0066] Example 14 Step 1, zinc solution preparation: a 3% zinc nitrate solution was prepared by weighing 1.36 g of zinc nitrate and 10 g of deionized water, mixing at room temperature, and fully stirring at 500 rpm for 0.25 h to obtain the stirred solution.

[0067] Step 2, catalyst pretreatment: 10 g of nanosheet type HZSM-5 zeolite (B-HZSM-5 obtained in Example 16) was pretreated in an oven at 120 ℃ for 2 h to obtain the pretreated nanosheet type HZSM-5 zeolite.

[0068] Step 3, strong electrostatic adsorption: 15 ml of the stirred solution described in step 1 was added dropwise to 10 g of the pretreated nanosheet type HZSM-5 zeolite described in step 2 by equal volume method, and the zeolite dosage was 10 g. The reaction was carried out at room temperature for 12 h under the action of strong electrostatic adsorption, dried in an oven at 80 ℃ for 6 h, and calcined in a muffle furnace at 550 ℃ for 5 h to obtain Zn / HZSM-5-14.

[0069] Example 15 Step 1, precursor solution preparation: 2.4 g of urea, 8 g of TPAOH (tetrapropylammonium hydroxide), 40 ml of water, and 2.3 g of NaOH were mixed and stirred for 0.5 h to obtain a precursor solution.

[0070] Step 2, addition of silicon source: 16 ml of 30 wt% silicon sol was added to the precursor solution of step 1 to obtain a mixed solution.

[0071] Step 3, addition of aluminum source: 0.47 g of aluminum nitrate nonahydrate was added to the mixed solution of step 2 to obtain a mother solution.

[0072] Step 4, aging: the mother solution of step 3 was stirred at room temperature for 4 h.

[0073] Step 5, crystallization: the stirred solution of step 4 was transferred to a hydrothermal reactor, which was placed in a 170 ℃ oven and allowed to stand for 24 h.

[0074] Step 6, catalyst calcination: after the reactor was taken out, the supernatant was poured out, and the lower layer solid was centrifuged to neutral, then dried to constant weight in a 110 ℃ oven. The dried solid was transferred to a muffle furnace, and the temperature was raised to 550 ℃ at a rate of 5 ℃ / min, and calcined for 6 h. After the temperature naturally decreased to room temperature, P-HZSM-5 was obtained.

[0075] Example 16 The difference from example 15 is that 5 g of 10% mass fraction CTAB solution (cetyltrimethylammonium bromide solution) is added in the preparation of the precursor solution to obtain B-HZSM-5.

[0076] Application Example 1 A series of catalysts prepared by examples 1-14 were used to carry out performance test of propane aromatization reaction. The reaction conditions were set as follows: the reaction temperature was constant at 550 ℃, nitrogen (N2) was used as the balance gas, the flow rate was accurately controlled at 20 mL / min, the propane (C3H8) feed flow rate was set at 10 mL / min. The catalyst loading was 1.0 g (±0.005 g), and the total gas hourly space velocity (GHSV) was calculated to be 7200 mL·gcat. -1 ·min -1 After the reaction system reached steady state after the induction period, online gas chromatography (GC) was used to analyze the raw material gas and the reaction products simultaneously, and the specific reaction results are shown in Table 1. The Zn / HZSM catalyst prepared in example 11 showed higher raw material conversion rate and product selectivity in the catalytic propane aromatization reaction, C 9+ C9+ is the compound with carbon number greater than or equal to 9 (byproduct, usually refers to coke).

[0077] Table 1 is the performance test results of a series of catalysts prepared in Examples 1-14

[0078] Application Example 2 The series of catalysts prepared in Examples 1-10 were used to carry out life test, and the specific test conditions were as follows: the reaction temperature was constant at 550 ℃, nitrogen (N2) was used as the balance gas, the flow rate was accurately controlled at 20 mL / min, the propane (C3H8) feed flow rate was set at 10 mL / min. The catalyst loading was 1.0 g (±0.005 g), and the total gas hourly space velocity (GHSV) was calculated to be 7200 mL·gcat. -1 ·min -1 After the reaction system reached steady state after the induction period, online gas chromatography (GC) was used to analyze the raw material gas and the reaction products simultaneously, and the life test results of the catalysts prepared in Examples 6, 11, 13, and 14 are shown in Tables 2-5. Among them, the Zn / HZSM catalyst prepared in Example 11 exhibited higher catalyst life in the catalytic propane aromatization reaction.

[0079] Table 2 is the life test results of the catalyst prepared in Example 6

[0080] Table 3 is the life test results of the catalyst prepared in Example 11

[0081] Table 4 is the life test results of the catalyst prepared in Example 13

[0082] Table 5 is the life test results of the catalyst prepared in Example 14

[0083] Through the above technical scheme, the strong electrostatic adsorption strategy is used to accurately control the pH value of the solution, which promotes the atomic-level uniform dispersion of zinc ions on the surface of the carrier. The modified catalyst maintains the morphology of the catalyst before modification, such as typical coffin-shaped, flaky, and rod-shaped. Not only does it significantly improve the activity site density and intrinsic activity of the catalyst, but also greatly enhances the structural stability by strengthening the zinc-carrier interaction. The specific reaction principle is as follows: in the weak alkaline environment, the strong electrostatic adsorption method described in the application causes the coordination between zinc ions (Zn 2+ ) and ammonium ions (NH4⁺) in the system to form stable tetraammine zinc (II) complex cations ([Zn(NH3)4] 2+ ). The complex cation has a positive charge characteristic, which can interact with the The acid site (B acid site, =Si-O(H)-Al=) generates strong electrostatic interaction, thereby realizing atomic-level uniform anchoring of the Zn species on the support surface. Compared with the Zn 2+ The direct deposition is prone to form ZnO clusters. The method induces the formation of [Zn(NH3)4] 2+ The intermediate effectively avoids migration and aggregation of the Zn species during calcination, significantly inhibits the generation of ZnO clusters, and improves the dispersion and utilization of active sites. In addition, the combination of [Zn(NH3)4] 2+ With the B acid site can induce Zn 2+ In the molecular sieve framework, more stable Zn(OH) + Or [Zn-O-Al] 2+ structure, strengthen the Zn-support interaction, and further improve the intrinsic activity and structural stability of the catalyst in the propane aromatization reaction. This mechanism not only optimizes the electronic environment of the Zn species, promotes efficient activation of the C-H bond of low-carbon alkanes, but also inhibits side reactions such as hydrogenolysis and carbon deposition, ultimately achieving a synergistic improvement in the propane conversion rate, BTX selectivity, and catalyst life. The catalyst obtained by the method has a BTX selectivity of 59.1238% in the propane dehydrogenation aromatization reaction, a propane conversion rate of 65.0428%, and a catalyst life of 15h.

[0084] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which are equivalent to equivalent embodiments and belong to the scope of the technical solution.

Claims

1. A ZSM-5 molecular sieve modified catalyst for catalyzing the aromatization of propane, characterized in that, The ZSM-5 molecular sieve modified catalyst is Zn / ZSM-5, and a Zn salt with a mass fraction of 1-10% is loaded on the ZSM-5 molecular sieve by strong electrostatic adsorption.

2. The ZSM-5 molecular sieve modified catalyst of claim 1, wherein, The ZSM-5 molecular sieve is a hydrogen type ZSM-5 molecular sieve with a silicon-aluminum ratio of 15-300.

3. The ZSM-5 molecular sieve modified catalyst of claim 1, wherein, The Zn salt is at least one selected from zinc nitrate, zinc acetate and zinc sulfate.

4. The modification method of the ZSM-5 molecular sieve modified catalyst according to any one of claims 1 to 3, characterized by, The modification method comprises the following steps: Step 1, zinc solution preparation: weighing the Zn salt and dissolving it in water, adding an alkaline substance to adjust the pH of the solution, and ultrasonic oscillation to obtain a uniformly oscillated zinc solution; Step 2, catalyst pretreatment: taking the ZSM-5 molecular sieve catalyst to an oven for pretreatment to obtain a pretreated ZSM-5 molecular sieve catalyst; Step 3, strong electrostatic adsorption: using the equal volume method to mix the pretreated ZSM-5 molecular sieve catalyst in step 2 and the uniformly oscillated zinc solution in step 1 uniformly, strong electrostatic adsorption reaction, drying, calcination, and natural cooling to room temperature to obtain the ZSM-5 molecular sieve modified catalyst, namely Zn / ZSM-5.

5. The modification method according to claim 4, wherein The Zn salt in step 1 is at least one selected from zinc nitrate, zinc acetate and zinc sulfate; The mass fraction of zinc in the uniformly oscillated zinc solution in step 1 is 1-10%.

6. The modification method of claim 4, wherein, The alkaline substance in step 1 is selected from concentrated ammonia, methylamine solution and ethylamine solution; The concentration of the alkaline substance is 0.1-2 mol / L; The pH of the solution adjusted by adding the alkaline substance in step 1 is 9-13; The ultrasonic oscillation conditions in step 1 are as follows: The ultrasonic oscillation temperature is 25-50℃; The ultrasonic oscillation time is 5-30 min.

7. The modification method of claim 4, wherein, The pretreatment conditions in step 2 are as follows: The pretreatment temperature is 80-120℃; The pretreatment time is 2-24 h.

8. The modification method of claim 4, wherein, The strong electrostatic adsorption reaction conditions in step 3 are as follows: The strong electrostatic adsorption reaction temperature is 20-30℃; The strong electrostatic adsorption reaction time is 4-12 h; The drying conditions in step 3 are as follows: The drying temperature is 60-80℃; The drying time is 2-6 h; The calcination conditions in step 3 are as follows: The calcination temperature is 350-550℃; The calcination time is 2-6 h.

9. The modification method of claim 4, wherein The preparation of the zinc solution in step 1 further comprises: weighing the Zn salt and dissolving it in water, stirring at 300-3000 rpm for 0.2-0.5 h to obtain a stirred zinc solution, the ZSM-5 molecular sieve catalyst in step 2 is selected from one of a commercial ZSM-5 molecular sieve, the ZSM-5 molecular sieve modified catalyst in claims 1-3, and the ZSM-5 molecular sieve modified catalyst obtained by the modification method in claims 4-8, and the remaining steps are consistent with claim 4.

10. Application of the ZSM-5 molecular sieve modified catalyst in claims 1-3 and / or the ZSM-5 molecular sieve modified catalyst obtained by the modification method in any one of claims 4-8 in catalyzing propane aromatization to produce aromatic hydrocarbons, wherein the aromatic hydrocarbons include benzene, toluene and xylene.

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