Desulfurizer, and preparation method therefor and use thereof

Abstract

The present invention provides a desulfurizer, and a preparation method therefor and a use thereof. The preparation method for the desulfurizer comprises: subjecting a first structure directing agent, a second structure directing agent, a first silicon source, a first aluminum source, and a ZSM-5 molecular sieve seed crystal to hydrothermal crystallization and calcination to obtain a ZSM-5 molecular sieve nanocrystal; and then performing extrusion forming and calcination to obtain a desulfurizer, wherein the cationic charge density of the first structure directing agent is higher than that of the second structure directing agent. In the present invention, two structure directing agents are used together with a seed crystal to synergistically induce and regulate a crystallization process, thereby greatly improving the desulfurization activity of the desulfurizer.

Description

A desulfurizing agent, its preparation method and application

[0001] Cross-reference information

[0002] This application claims priority to Chinese Patent Application No. 202411954462.7, filed on December 17, 2024, entitled "A desulfurizing agent and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of flue gas desulfurization technology, specifically to a desulfurizing agent, its preparation method, and its application. Background Technology

[0004] Flue gas desulfurization technology is an effective means of controlling SO2 emissions. Its principle is to utilize alkaline substances to react with acidic SO2. x The reaction produces sulfates or sulfites, and flue gas desulfurization can be classified into wet, dry, and semi-dry processes based on its characteristics. Compared with the other two processes, dry flue gas desulfurization has advantages such as simple equipment, low investment cost, small footprint, and no wastewater treatment system. Among them, regenerative dry flue gas desulfurization technology utilizes reducing gases to regenerate sulfur elements adsorbed on solid desulfurizing agents, further improving resource utilization.

[0005] The well-ordered pore structure of ZSM-5 molecular sieves gives them good mechanical stability and a large specific surface area, making them suitable for removing SO2 from flue gas. However, ordinary ZSM-5 molecular sieves have large crystal sizes, and their isolated microporous structures exhibit significant diffusion resistance during catalytic reactions, thus affecting the desulfurization effect.

[0006] CN106824064B proposes a method for adsorbing and removing sulfur dioxide from flue gas using a double-shell ZSM-5 molecular sieve. First, ZSM-5 molecular sieves are prepared using tetrapropylammonium hydroxide, citric acid, tetraethyl orthosilicate, and sodium hydroxide as raw materials. Then, the prepared molecular sieve is reacted with an alkaline aqueous solution to obtain a double-shell ZSM-5 molecular sieve. Its large specific surface area gives it a large sulfur capacity. However, during the alkaline aqueous solution treatment, the pore distribution inside the ZSM-5 molecular sieve crystals is uneven, the crystal framework is prone to collapse, and the preparation process is complex.

[0007] CN105883849A discloses a method for synthesizing ZSM-5 molecular sieves with controllable morphology, mainly using a tetrapropylammonium hydroxide and an organic amine composite template agent. In the preparation process, potassium hydroxide or sodium hydroxide and an aluminum source are first dissolved in water and stirred until homogeneous. Then, tetrapropylammonium hydroxide and the second template agent are added separately, stirred at room temperature, and a silicon source is added to form a sol. The sol is then crystallized at 100-200℃ for 0.5-5 days. After crystallization, the product is obtained by filtration, washing, and drying. Under certain synthesis ratios, by changing only the type and amount of the template agent, ZSM-5 molecular sieves with different crystal sizes and shapes can be synthesized in a controlled manner. This method is simple to operate and produces products with regular shapes, but the reduction in crystal size is limited (at the micrometer level). Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a desulfurizing agent, its preparation method, and its application, so as to obtain a desulfurizing agent with a large specific surface area and good desulfurization performance.

[0009] To achieve the above objectives, the present invention provides a method for preparing a desulfurizing agent, comprising:

[0010] S1: Mix the first structure directing agent, the second structure directing agent, the first silicon source, and the first aluminum source in water, then add ZSM-5 molecular sieve seed crystals and disperse them evenly, perform hydrothermal crystallization, and calcine the crystallized product to obtain ZSM-5 molecular sieve nanocrystals.

[0011] S2: Mix the ZSM-5 molecular sieve nanocrystals, binder, pore expander and active metal salt solution, extrude and calcine to obtain the desulfurizing agent;

[0012] Wherein, the first structure directing agent is selected from quaternary ammonium bases and / or quaternary ammonium salts, and the second structure directing agent is selected from quaternary ammonium bases; the cationic charge density of the first structure directing agent is higher than that of the second structure directing agent; the molar ratio of the first structure directing agent to the second structure directing agent is 1-8:20-40.

[0013] In the preparation process of the solid desulfurizer described in this invention, a dual-structure directing agent is used for induction, including a first structure directing agent and a second structure directing agent. The charge density of the first structure directing agent is higher than that of the second structure directing agent, thereby effectively regulating the nucleation and formation process of ZSM-5 molecular sieve crystals to prepare nano-molecular sieves. The crystallization process of ZSM-5 molecular sieves can be divided into two stages: induction crystal nucleation and ripening growth. The amount of the second structure directing agent is much greater than that of the first structure directing agent, so the nucleation process of ZSM-5 molecular sieves is mainly driven by the second structure directing agent, inducing crystal nucleation and entering the MFI lattice to balance the negative charge of the framework. However, compared with the second structure directing agent, the first structure directing agent has a higher charge density and a stronger interaction force with the ZSM-5 molecular sieve framework. As the crystallization process proceeds, it gradually enters the MFI lattice and replaces the second structure directing agent, thereby inducing the dissolution of crystal nuclei and recrystallization. However, the amount of the first structure directing agent is insufficient to occupy all the cross sites in the MFI lattice, so the second structure directing agent acts as a co-structure directing agent in the subsequent recrystallization process. As the crystal recrystallization and ripening growth process proceeds, the first structure-directing agent completely enters the crystal lattice. However, the amount of the second structure-directing agent added is far greater than the amount needed to balance the negative charge of the crystal framework. The excess second structure-directing agent cations adsorb onto the surface of the ZSM-5 crystal, stabilizing the ac crystal plane and inhibiting the growth of the ZSM-5 crystal along the b-axis, ultimately ripening and growing into ZSM-5 molecular sieve nanocrystals. Then, the ZSM-5 molecular sieve loaded with active metal oxides was used for flue gas desulfurization, exhibiting high desulfurization efficiency and cycle stability.

[0014] ZSM-5 molecular sieve is a type of desulfurizer with promising future development and application prospects. Reducing the crystal size can significantly increase the specific surface area, thereby fully leveraging the catalytic effect of the active metal.

[0015] In the above-mentioned method for preparing the desulfurizing agent, preferably, the ZSM-5 molecular sieve seed crystals do not contain cations except for aluminum. More preferably, the ZSM-5 molecular sieve seed crystals do not contain any metal elements except for aluminum.

[0016] In this invention, the ZSM-5 molecular sieve seed crystals do not contain metal cations, such as Na+ ions. + or K + This is mainly because, compared with the second structure directing agent cation, the two metal cations mentioned above have relatively smaller kinetic radii and significantly higher charge densities, thus exhibiting stronger competitive adsorption capabilities during the nucleation and growth of ZSM-5 molecular sieve nanocrystals. This weakens the modification ability of the second structure directing agent cation on the crystals and affects the morphology of the final crystals.

[0017] In the above-mentioned method for preparing desulfurizing agent, preferably, the first structure directing agent is selected from a compound with the general formula (R1)4NX, and the second structure directing agent is selected from a compound with the general formula (R2)4NOH;

[0018] Wherein, R1 is selected from C1-C5 alkyl, R2 is selected from C2-C6 alkyl, and the number of carbons in R2 is greater than that in R1;

[0019] X is selected from OH - ,Br - or Cl - .

[0020] In the above-mentioned method for preparing desulfurizing agent, preferably, R1 is selected from C1-C3 alkyl groups and R2 is selected from C4-C6 alkyl groups.

[0021] In the above-mentioned method for preparing the desulfurizing agent, preferably, the first structure directing agent is selected from one or more of tetramethylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium hydroxide, tetrapentylammonium bromide, and tetrapentylammonium hydroxide, more preferably, it is selected from one or more of tetramethylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

[0022] In the above-mentioned method for preparing desulfurizing agent, preferably, the second structure directing agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide, and more preferably from one or more of tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide.

[0023] In the above-mentioned method for preparing desulfurizing agent, preferably, the molar ratio of the first structure directing agent, the second structure directing agent, the first silicon source, and the first aluminum source is 1-8:20-40:100:0.3-2, wherein the first silicon source is calculated as SiO2 and the first aluminum source is calculated as Al2O3.

[0024] In the above-mentioned method for preparing desulfurizing agent, preferably, the molar ratio of the first silicon source to water, based on SiO2, is 1:10-20.

[0025] In the above-mentioned method for preparing desulfurizing agent, preferably, the amount of ZSM-5 molecular sieve seed crystals added is 2-8 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals.

[0026] In the above-mentioned method for preparing desulfurizing agent, preferably, the first silicon source is an organosilicon source.

[0027] In the above-mentioned method for preparing desulfurizing agent, preferably, the first silicon source includes one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

[0028] In the above-mentioned method for preparing desulfurizing agent, preferably, the first aluminum source includes one or more of boehmite, aluminum nitrate, aluminum sulfate, aluminum trichloride, aluminum hydroxide, and aluminum isopropoxide.

[0029] In the above-mentioned method for preparing desulfurizing agent, preferably, in S1, the hydrothermal crystallization temperature is 110-180℃ and the time is 24-96h.

[0030] In the above-mentioned method for preparing desulfurizing agent, preferably, in S1, the calcination temperature is 450-600℃ and the calcination time is 5-12h.

[0031] In the above-mentioned method for preparing the desulfurizing agent, preferably, the method further includes: after adding ZSM-5 molecular sieve seed crystals and before hydrothermal crystallization, ultrasonically dispersing the hydrothermal system for 0.5-1 h.

[0032] In the above-mentioned method for preparing desulfurizing agent, preferably, the ZSM-5 molecular sieve seed crystals do not contain sodium or potassium.

[0033] In the above-mentioned method for preparing desulfurizing agent, preferably, the ZSM-5 molecular sieve seed crystal is prepared by the following method: a third structure directing agent, an alkali source (based on its own molar amount), a second silicon source, and a second aluminum source are mixed in water in a molar ratio of 15-25:0-30:100:0.1-1, hydrothermally crystallized, and the crystallized product is calcined to obtain the ZSM-5 molecular sieve; wherein the second silicon source is calculated as SiO2 and the second aluminum source is calculated as Al2O3.

[0034] In the above-mentioned method for preparing desulfurizing agents, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the molar ratio of the third structure directing agent, the alkali source, the second silicon source, and the second aluminum source is 15-25:1-30:100:0.1-1. The alkali source can be added or not added depending on the situation. When the third structure directing agent is a quaternary ammonium base (such as tetrapropylammonium hydroxide), the alkali source does not need to be added. If it is not a quaternary ammonium salt, the alkali source needs to be added.

[0035] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the molar ratio of silicon source to water, calculated as SiO2, is 1:10-20.

[0036] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the third structure directing agent includes tetrapropylammonium hydroxide and / or tetrapropylammonium bromide.

[0037] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the alkali source includes ammonia and / or urea.

[0038] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the second silicon source includes one or more of silica gel, fumed silica, white carbon black, water glass, tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

[0039] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the second aluminum source includes one or more of boehmite, aluminum nitrate, aluminum sulfate, aluminum trichloride, aluminum hydroxide, and aluminum isopropoxide.

[0040] In the above-mentioned method for preparing desulfurizing agent, preferably, in the preparation of ZSM-5 molecular sieve seed crystals, the hydrothermal crystallization temperature is 110-180℃ and the time is 24-96h.

[0041] In the above-mentioned method for preparing desulfurizing agent, preferably, in S2, the mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander and active metal salt is 30-70:10-50:1-10:5-20.

[0042] In the above-mentioned method for preparing desulfurizing agent, preferably, the active metal provided by the active metal salt includes one or more combinations of Zn, Ni, Cu, Mn, Fe, Ce, La, and V.

[0043] In the above-mentioned method for preparing desulfurizing agent, preferably, the binder includes one or more of cement, water glass, boehmite, and alumina sol.

[0044] In the above-mentioned method for preparing desulfurizing agent, preferably, the pore-expanding agent includes one or more of the following: guar gum powder, hydroxymethyl cellulose, and hexadecyltrimethylammonium bromide.

[0045] In the above-mentioned method for preparing desulfurizing agent, preferably, in step S2, the calcination temperature is 350-500℃ and the time is 5-12h.

[0046] According to a specific embodiment of the present invention, preferably, the preparation method of the above-mentioned desulfurizing agent includes the following steps:

[0047] (1) Mix the third structure directing agent with deionized water, then add the second aluminum source. After the aluminum source is completely dissolved, add the second silicon source dropwise. After the addition is complete, stir at room temperature for 1-10 hours to form a mixed system A.

[0048] (2) After the mixture A is crystallized at high temperature for a period of time, it is separated by centrifugation and washed with deionized water until neutral, then dried and calcined to obtain ZSM-5 molecular sieve seed crystals.

[0049] (3) Mix the first structure directing agent and the second structure directing agent with deionized water and stir evenly. Then add the first aluminum source. After the first aluminum source dissolves, add the first silicon source drop by drop. After the addition is complete, stir at room temperature for 1-10 hours to form a mixed system B.

[0050] (4) Add the ZSM-5 molecular sieve seed crystals prepared above to the mixed system B, mix evenly, crystallize at high temperature for a period of time, separate by centrifugation and wash with deionized water until neutral, dry and calcine to obtain ZSM-5 molecular sieve nanocrystals.

[0051] (5) Add binder, pore expander and active metal salt precursor solution to the ZSM-5 molecular sieve nanocrystals prepared above and mix to form mixed system C, and extrude and calcine to obtain the desulfurizer.

[0052] The present invention also provides a desulfurizing agent, which is prepared by the above-described method for preparing the desulfurizing agent.

[0053] According to a specific embodiment of the present invention, preferably, the desulfurizing agent is cylindrical in shape and has a specification of φ2-4mm.

[0054] The present invention also provides an application of the above-mentioned desulfurizing agent in treating low-temperature flue gas at 250-400℃.

[0055] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0056] The desulfurizer preparation method provided by this invention uses a dual-structure directing agent and seed crystals to synergistically induce and regulate the crystallization process, thereby effectively controlling the mesoscopic structure of the desulfurizer, significantly improving the desulfurization activity, and the preparation process is simple. Detailed Implementation

[0057] Example 1

[0058] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0059] (1) Preparation of ZSM-5 molecular sieve seeds:

[0060] Tetraethoxysilane was selected as the silicon source, boehmite as the aluminum source, and tetrapropylammonium hydroxide (TPAOH) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), third structure directing agent, and water was 100:0.1:15:1000. The specific steps are as follows:

[0061] Weigh 5.0840 g of TPAOH (40% aqueous solution) and 8.9497 g of deionized water, mix them evenly, add 0.0097 g of boehmite, and after it is completely dissolved, weigh 13.8887 g of tetraethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0062] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 110°C for 96 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0063] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0064] Tetraethoxysilane was selected as the silicon source, aluminum sulfate as the aluminum source, tetrapropylammonium hydroxide (TPAOH) as the first structure directing agent, and tetrabutylammonium hydroxide (TBAOH) as the second structure directing agent. These were mixed with water to prepare a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:2.0:1:20:1000 (abbreviated as 100 SiO2:0.3 Al2O3:1 TPAOH:20 TBAOH:1000H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 8 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0065] First, weigh 0.3389 g of TPAOH (40% aqueous solution), 8.6490 g of TBAOH (40% aqueous solution), and 6.6073 g of deionized water, mix them evenly, and then add 0.0684 g of aluminum sulfate. After the aluminum sulfate is completely dissolved, weigh 10.1481 g of tetramethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system B. Weigh 0.3221 g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 1 h to disperse the seed crystals evenly.

[0066] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 110°C for 96 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0067] (4) Preparation of desulfurizing agent

[0068] Aluminum sol was selected as the binder, guar gum powder as the pore expander, and nickel nitrate as the active metal salt. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to prepare a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, and active metal salt solution (calculated as metal oxide) in mixed system C was 70:50:10:20.

[0069] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S1.

[0070] Example 2

[0071] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0072] (1) Preparation of ZSM-5 molecular sieve seeds:

[0073] Tetramethoxysilane was selected as the silicon source, aluminum nitrate as the aluminum source, and tetrapropylammonium bromide (TPABr) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (SiO2), aluminum source (Al2O3), third structure directing agent, alkali source, and water was 100:1.0:25:30:2000. The specific steps are as follows:

[0074] Weigh out 4.4377 g of tetrapropylammonium bromide, 1.3625 g of ammonia (25%) and 22.9781 g of deionized water, mix them evenly, add 0.2840 g of aluminum nitrate, and after it is completely dissolved, weigh out 10.1481 g of tetramethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0075] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 180°C for 48 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0076] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0077] Tetraethoxysilane was selected as the silicon source, boehmite as the aluminum source, tetrapropylammonium bromide (TPABr) as the first structure directing agent, and tetrapentylammonium hydroxide (TPeAOH) as the second structure directing agent. These were mixed with water to form a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:2.0:4:30:1200 (abbreviated as 100 SiO2:1.0 Al2O3:4 TPABr:30 TPeAOH:1200H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 4 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0078] First, weigh 0.7100g of TPABr, 15.7789g of TBAOH (40% aqueous solution), and 4.9327g of deionized water, mix them thoroughly, and then add 0.0970g of boehmite. After the boehmite is completely dissolved, weigh 13.8887g of tetraethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 hours to form mixed system B. Weigh 0.1583g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 0.5 hours to disperse the seed crystals evenly.

[0079] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 180°C for 24 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0080] (3) Preparation of desulfurizing agent

[0081] Aluminum sol was selected as the binder, guar gum powder as the pore expander, and ferric nitrate and copper nitrate as active metal salts. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to form a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, ferric nitrate solution (calculated as metal oxides), and copper nitrate solution (calculated as metal oxides) in mixed system C was 30:10:1:2:3.

[0082] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S2.

[0083] Example 3

[0084] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0085] (1) Preparation of ZSM-5 molecular sieve seeds:

[0086] Tetrapropoxysilane was selected as the silicon source, aluminum hydroxide as the aluminum source, and tetrapropylammonium hydroxide (TPAOH) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), third structure directing agent, and water was 100:1.0:20:1500. The specific steps are as follows:

[0087] Weigh 6.7787 g of TPAOH (40% aqueous solution) and 13.9328 g of deionized water, mix them evenly, add 0.1041 g of aluminum hydroxide, and after it is completely dissolved, weigh 17.6289 g of tetrapropoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0088] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 160°C for 48 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0089] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0090] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, tetraethylammonium hydroxide (TEAOH) as the first structure directing agent, and tetrabutylammonium hydroxide (TBAOH) as the second structure directing agent. These were mixed with water to form a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:2.0:8:40:2000 (abbreviated as 100 SiO2:2.0 Al2O3:8 TEAOH:40 TBAOH:2000H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 8 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0091] First, weigh 1.9634 g of TEAOH (40% aqueous solution), 17.2981 g of TBAOH (40% aqueous solution), and 12.4431 g of deionized water, mix them evenly, and then add 0.2080 g of aluminum hydroxide. After the aluminum hydroxide is completely dissolved, weigh 17.6289 g of tetrapropoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system B. Weigh 0.3314 g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 1 h to disperse the seed crystals evenly.

[0092] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 150°C for 72 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0093] (3) Preparation of desulfurizing agent

[0094] Aluminum sol was selected as the binder, guar gum powder as the pore expander, and cerium nitrate and ferric nitrate as active metal salts. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to form a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, cerium nitrate solution (based on metal oxides), and ferric nitrate solution (based on metal oxides) in mixed system C was 50:20:7:4:5.

[0095] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S3.

[0096] Example 4

[0097] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0098] (1) Preparation of ZSM-5 molecular sieve seeds:

[0099] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, and tetrapropylammonium hydroxide (TPAOH) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), third structure directing agent, and water was 100:0.5:20:1500. The specific steps are as follows:

[0100] Weigh 6.7787 g of TPAOH (40% aqueous solution) and 13.9328 g of deionized water, mix them evenly, add 0.1362 g of aluminum isopropoxide, and after it is completely dissolved, weigh 13.8887 g of tetraethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0101] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 180°C for 48 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0102] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0103] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, tetraethylammonium bromide (TEABr) as the first structure directing agent, and tetrapentylammonium hydroxide (TPeAOH) as the second structure directing agent. These were mixed with water to form a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:1.0:3:35:1800 (abbreviated as 100 SiO2:1.0 Al2O3:3 TEABr:35 TPeAOH:1800H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 3wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0104] First, weigh 0.4211g of TEABr, 18.4086g of TPeAOH (40% aqueous solution), and 10.5548g of deionized water, mix them thoroughly, and then add 0.2724g of aluminum isopropoxide. After the aluminum isopropoxide is completely dissolved, weigh 14.5058g of tetraethyl orthosilicate and add it dropwise. After the addition is complete, stir at room temperature for 5 hours to form mixed system B. Weigh 0.1239g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 0.5 hours to disperse the seed crystals evenly.

[0105] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 160°C for 48 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0106] (3) Preparation of desulfurizing agent

[0107] Aluminum sol was selected as the binder, guar gum powder as the pore-expanding agent, and manganese nitrate and vanadium nitrate as active metal salts. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to prepare a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore-expanding agent, manganese nitrate solution (calculated as metal oxides), and vanadium nitrate solution (calculated as metal oxides) in mixed system C was 40:20:3:5:10.

[0108] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S4.

[0109] Example 5

[0110] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0111] (1) Preparation of ZSM-5 molecular sieve seeds:

[0112] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, and tetrapropylammonium hydroxide (TPAOH) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), third structure directing agent, and water was 100:0.2:20:1500. The specific steps are as follows:

[0113] Weigh 6.7787 g of TPAOH (40% aqueous solution) and 13.9328 g of deionized water, mix them evenly, add 0.0545 g of aluminum isopropoxide, and after it is completely dissolved, weigh 13.8887 g of tetraethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0114] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 180°C for 24 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0115] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0116] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, tetramethylammonium hydroxide (TMAOH) as the first structure directing agent, and tetrabutylammonium hydroxide (TBAOH) as the second structure directing agent. These were mixed with water to form a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:0.5:4:30:1500 (abbreviated as 100 SiO2:0.5 Al2O3:4 TMAOH:30 TBAOH:1500H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 5 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0117] First, weigh 0.6077 g of TMAOH (40% aqueous solution), 12.9736 g of TBAOH (40% aqueous solution), and 9.8512 g of deionized water, mix them thoroughly, and then add 0.1420 g of aluminum nitrate. After the aluminum nitrate is completely dissolved, weigh 10.1481 g of tetramethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system B. Weigh 0.2020 g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 0.5 h to disperse the seed crystals evenly.

[0118] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 150°C for 72 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0119] (3) Preparation of desulfurizing agent

[0120] Aluminum sol was selected as the binder, guar gum powder as the pore expander, and zinc nitrate and lanthanum nitrate as active metal salts. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to prepare a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, zinc nitrate solution (based on metal oxides), and lanthanum nitrate solution (based on metal oxides) in mixed system C was 60:25:5:10:8.

[0121] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S5.

[0122] Example 6

[0123] The desulfurizing agent provided in this embodiment is prepared by the following method:

[0124] (1) Preparation of ZSM-5 molecular sieve seeds:

[0125] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, and tetrapropylammonium hydroxide (TPAOH) as the third structure directing agent. A mixed system A was prepared with water, wherein the molar ratio of silicon source (calculated as SiO2), aluminum source (calculated as Al2O3), third structure directing agent, and water was 100:0.3:20:1100. The specific steps are as follows:

[0126] Weigh 6.7787 g of TPAOH (40% aqueous solution) and 9.1328 g of deionized water, mix them evenly, add 0.0817 g of aluminum isopropoxide, and after it is completely dissolved, weigh 13.8887 g of tetraethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system A.

[0127] The mixed system A was transferred to a polytetrafluoroethylene reactor and crystallized at 180°C for 24 hours. After that, it was taken out and naturally cooled to room temperature. The solid product was then separated by centrifugation and washed with deionized water until neutral. The product was dried at 80°C for 8 hours and calcined at 500°C for 6 hours to obtain ZSM-5 molecular sieve seed crystals.

[0128] (2) Preparation of ZSM-5 molecular sieve nanocrystals

[0129] Tetraethoxysilane was selected as the silicon source, aluminum isopropoxide as the aluminum source, tetramethylammonium hydroxide (TMAOH) as the first structure directing agent, and tetrahexylammonium hydroxide (THeAOH) as the second structure directing agent. These were mixed with water to form a mixture B, and ZSM-5 molecular sieve seed crystals were added. The molar ratio of silicon source (SiO2), aluminum source (Al2O3), first structure directing agent, second structure directing agent, and water in mixture B was 100:0.5:4:25:1200 (abbreviated as 100 SiO2:0.5 Al2O3:4 TMAOH:25 THeAOH:1200H2O). The amount of ZSM-5 molecular sieve seed crystals added to mixture B was 6 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals. The specific steps are as follows:

[0130] First, weigh 0.6077 g of TMAOH (40% aqueous solution), 15.4867 g of THAOH (40% aqueous solution), and 4.7434 g of deionized water, mix them evenly, and then add 0.1361 g of aluminum isopropoxide. After the aluminum nitrate is completely dissolved, weigh 10.1481 g of tetramethoxysilane and add it dropwise. After the addition is complete, stir at room temperature for 5 h to form mixed system B. Weigh 0.2424 g of the ZSM-5 molecular sieve seed crystals prepared above and add them to mixed system B. Stir and use ultrasonic-assisted treatment for 1 h to disperse the seed crystals evenly.

[0131] The above mixture was transferred to a polytetrafluoroethylene reactor and crystallized at 160°C for 72 hours. After that, it was taken out and naturally cooled to room temperature. Then, the solid product was separated by centrifugation and washed with deionized water until neutral. It was dried at 80°C for 8 hours and calcined at 500°C for 10 hours to obtain ZSM-5 molecular sieve nanocrystals.

[0132] (3) Preparation of desulfurizing agent

[0133] Aluminum sol was selected as the binder, guar gum powder as the pore expander, and ferric nitrate and cerium nitrate as active metal salts. These were mixed with the above-mentioned ZSM-5 molecular sieve nanocrystals to form a mixed system C. The mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, ferric nitrate solution (based on metal oxides), and cerium nitrate solution (based on metal oxides) in mixed system C was 50:20:4:10:4.

[0134] A binder, a pore expander and an active metal salt solution were added sequentially to the ZSM-5 molecular sieve nanocrystals obtained in step (1) and mixed evenly to form a mixed system C. The mixture was then extruded and calcined at 400°C for 6 hours to obtain desulfurizer S6.

[0135] Comparative Example 1

[0136] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that the hydrothermal crystallization temperature of ZSM-5 molecular sieve nanocrystals is 200℃ and the hydrothermal crystallization time is 20h.

[0137] Comparative Example 2

[0138] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that the two structure directing agents in step (2) are both tetrabutylammonium hydroxide (TBAOH), and the total molar amount of structure directing agents remains unchanged.

[0139] Comparative Example 3

[0140] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that the two structure directing agents in step (2) are both tetraethylammonium hydroxide (TEAOH), and the total molar amount of structure directing agents remains unchanged.

[0141] Comparative Example 4

[0142] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that the molar ratio of the first structure directing agent (tetraethylammonium hydroxide) to the second structure directing agent (tetrabutylammonium hydroxide) in step (2) is 40:8.

[0143] Comparative Example 5

[0144] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that ZSM-5 molecular sieve seed crystals are not added.

[0145] Comparative Example 6

[0146] This comparative example provides a desulfurizing agent, which is prepared in the same way as in Example 3, except that tetrapropoxysilane is replaced with an equimolar amount of fumed silica.

[0147] Experimental Example

[0148] This experimental example is used to evaluate the desulfurization performance of the desulfurization adsorbents in the above embodiments and comparative examples.

[0149] Specific surface area measurement:

[0150] The specific surface area of ​​the desulfurizing agents in the above examples and comparative examples was analyzed and detected using a fully automated nitrogen adsorption specific surface area analyzer. The results are shown in Table 1.

[0151] Strength analysis:

[0152] The crushing resistance of the desulfurizers in the above examples and comparative examples was tested using a catalyst compressive strength tester according to the HG / T2782-2011 method for determining the crushing resistance of fertilizer catalyst particles. The results are shown in Table 1.

[0153] Desulfurization performance evaluation method:

[0154] The composition of the imported feed gas in this experiment is shown in Table 2, and the desulfurization reaction space velocity is 500 h⁻¹. -1 The desulfurization activity was evaluated at a reaction temperature of 350℃.

[0155] First, the prepared desulfurizing agent is crushed and sieved to obtain desulfurizing agent particles with a particle size of 20-40 mesh. Then, 2.3g of the above desulfurizing agent particles with a particle size of 20-40 mesh are weighed and loaded into a fixed-bed microreactor, with the upper and lower layers fixed with quartz wool respectively.

[0156] During the evaluation process, the inlet air flow rate and SO2 content were controlled using a mass flow meter. The inlet SO2 concentration was controlled at 2000 ppm, and the SO2 content in the outlet gas was detected using a Hiden QGA quantitative gas mass spectrometer. When the SO2 content at the reactor outlet exceeded 150 ppm, it was assumed that the desulfurizer had been deactivated. The sulfur capacity of the desulfurizer at this point was calculated, and the results are shown in Table 1.

[0157] Table 1. Specific surface area and sulfur capacity of desulfurizing agents

[0158] Table 2 Composition of Raw Gas

[0159] The results show that the sulfur capacity of the desulfurizing agents in the embodiments of the present invention can reach 0.16 gSO2 / gcat. and above, indicating that the desulfurizing agents prepared by the present invention have excellent desulfurization activity.

[0160] Furthermore, comparing Example 3 and Comparative Example 1, it can be seen that during the crystallization process of ZSM-5 molecular sieve nanocrystals, as the crystallization temperature increases, the crystal growth rate accelerates and the crystal size increases, which leads to a decrease in the specific surface area of ​​the desulfurizer. Therefore, the specific surface area of ​​Comparative Example 1 is significantly smaller, and the sulfur capacity is significantly reduced.

[0161] Comparing Example 3 with Comparative Examples 2 and 3, it can be seen that the presence of dual-structure directing agents with different charge densities can induce crystal nucleus dissolution and recrystallization. Simultaneously, the surface modification effect of the high-content, low-charge-density second-structure directing agent, the quaternary ammonium salt cation, ultimately leads to the crystallization and formation of ZSM-5 molecular sieve nanocrystals. When only one structure directing agent is present, only the surface modification of the quaternary ammonium salt cation results in a relatively large ZSM-5 molecular sieve, thus significantly reducing the specific surface area and sulfur capacity of Comparative Example 2.

[0162] Comparing Example 3 and Comparative Example 4, it can be seen that because the amount of the first structure directing agent cation with high charge density is significantly higher than that of the second structure directing agent, the first structure directing agent can completely occupy all the cross sites in the MFI lattice during the crystallization process of ZSM-5 molecular sieve. Therefore, it will not induce crystal nucleus dissolution and recrystallization. Furthermore, since the crystal surface is mainly modified by an excess of the first structure directing agent, the crystal size of the ZSM-5 molecular sieve produced by crystallization is relatively large. Therefore, the specific surface area and sulfur capacity of Comparative Example 3 are significantly reduced.

[0163] Comparing Example 3 and Comparative Example 5, it is evident that seed crystals play a crucial role in crystal growth. Adding pre-prepared ZSM-5 molecular sieve seed crystals facilitates the crystallization process, resulting in uniform ZSM-5 molecular sieve nanocrystals and effectively improving crystal yield and quality. Therefore, Comparative Example 3 exhibits a significantly reduced specific surface area and decreased sulfur capacity.

[0164] Comparing Example 3 and Comparative Example 6, it can be seen that, compared with tetrapropoxysilane, silicon atoms in fumed silica exist in a polymerized state, which is not conducive to the homogeneous nucleation process. As a result, the ZSM-5 crystals generated in the final crystallization are larger in size, have a significantly reduced specific surface area, and have a lower sulfur capacity.

Claims

1. A method for preparing a desulfurizing agent, comprising: S1: Mix the first structure directing agent, the second structure directing agent, the first silicon source, and the first aluminum source in water, then add ZSM-5 molecular sieve seed crystals and disperse them evenly, perform hydrothermal crystallization, and calcine the crystallized product to obtain ZSM-5 molecular sieve nanocrystals. S2: Mix the ZSM-5 molecular sieve nanocrystals, binder, pore expander and active metal salt solution, extrude and calcine to obtain the desulfurizing agent; Wherein, the first structure-directing agent is selected from quaternary ammonium bases and / or quaternary ammonium salts, and the second structure-directing agent is selected from quaternary ammonium bases; the cationic charge density of the first structure-directing agent is higher than that of the second structure-directing agent; The molar ratio of the first structural directing agent to the second structural directing agent is 1-8:20-40.

2. The method for preparing the desulfurizing agent according to claim 1, wherein, Apart from aluminum, the ZSM-5 molecular sieve seed crystals do not contain cations.

3. The method for preparing the desulfurizing agent according to claim 1, wherein, Apart from aluminum, the ZSM-5 molecular sieve seed crystals do not contain any metal elements.

4. The method for preparing the desulfurizing agent according to claim 1, wherein, The first structure directing agent is selected from compounds with the general formula (R1)4NX, and the second structure directing agent is selected from compounds with the general formula (R2)4NOH; Wherein, R1 is selected from C1-C5 alkyl, R2 is selected from C2-C6 alkyl, and the number of carbons in R2 is greater than that in R1; X is selected from OH - ,Br - or Cl - .

5. The method for preparing the desulfurizing agent according to claim 4, wherein, R1 is selected from C1-C3 alkyl groups, and R2 is selected from C4-C6 alkyl groups.

6. The method for preparing the desulfurizing agent according to claim 1, wherein, The first structure directing agent is selected from one or more of tetramethylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium hydroxide, tetrapentylammonium bromide, and tetrapentylammonium hydroxide.

7. The method for preparing the desulfurizing agent according to claim 1, wherein, The first structure directing agent is selected from one or more of tetramethylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide.

8. The method for preparing the desulfurizing agent according to claim 1, wherein, The second structure directing agent is selected from one or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide.

9. The method for preparing the desulfurizing agent according to claim 1, wherein, The second structure directing agent is selected from one or more of tetrabutylammonium hydroxide, tetrapentylammonium hydroxide, and tetrahexylammonium hydroxide.

10. The method for preparing the desulfurizing agent according to claim 1, wherein, The molar ratio of the first structural directing agent, the second structural directing agent, the first silicon source, and the first aluminum source is 1-8:20-40:100:0.3-2, wherein the first silicon source is calculated as SiO2 and the first aluminum source is calculated as Al2O3.

11. The method for preparing the desulfurizing agent according to claim 10, wherein, Based on SiO2, the molar ratio of the first silicon source to water is 1:10-20.

12. The method for preparing the desulfurizing agent according to claim 1, wherein, The amount of ZSM-5 molecular sieve seed crystals added is 2-8 wt% of the theoretical yield of ZSM-5 molecular sieve nanocrystals.

13. The method for preparing the desulfurizing agent according to claim 1, wherein, The first silicon source is an organosilicon source.

14. The method for preparing the desulfurizing agent according to claim 13, wherein, The first silicon source includes one or more of tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

15. The method for preparing the desulfurizing agent according to claim 1, wherein, The first aluminum source includes one or more of boehmite, aluminum nitrate, aluminum sulfate, aluminum trichloride, aluminum hydroxide, and aluminum isopropoxide.

16. The method for preparing the desulfurizing agent according to claim 1, wherein, In S1, the hydrothermal crystallization temperature is 110-180℃ and the time is 24-96h.

17. The method for preparing the desulfurizing agent according to claim 1, wherein, In S1, the calcination temperature is 450-600℃ and the calcination time is 5-12h.

18. The method for preparing the desulfurizing agent according to claim 1, wherein, The preparation method of the desulfurizing agent further includes: after adding ZSM-5 molecular sieve seed crystals, ultrasonically dispersing the hydrothermal system for 0.5-1 h.

19. The method for preparing the desulfurizing agent according to claim 1 or 2, wherein, The ZSM-5 molecular sieve seed crystals do not contain sodium or potassium.

20. The method for preparing the desulfurizing agent according to claim 19, wherein, The ZSM-5 molecular sieve seed crystals are prepared by the following method: a third structure directing agent, an alkali source, a second silicon source, and a second aluminum source are mixed in water in a molar ratio of 15-25:0-30:100:0.1-1, hydrothermally crystallized, and the crystallized product is calcined to obtain the ZSM-5 molecular sieve; wherein the second silicon source is calculated as SiO2 and the second aluminum source is calculated as Al2O3.

21. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the molar ratio of the third structure directing agent, the alkali source, the second silicon source, and the second aluminum source is 15-25:1-30:100:0.1-1.

22. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the molar ratio of silicon source to water, calculated as SiO2, is 1:10-20.

23. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the third structure directing agent includes tetrapropylammonium hydroxide and / or tetrapropylammonium bromide.

24. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the alkali source includes ammonia and / or urea.

25. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the second silicon source includes one or more of silica gel, fumed silica, silica fume, water glass, tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

26. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the second aluminum source includes one or more of boehmite, aluminum nitrate, aluminum sulfate, aluminum trichloride, aluminum hydroxide, and aluminum isopropoxide.

27. The method for preparing the desulfurizing agent according to claim 20, wherein, In the preparation of ZSM-5 molecular sieve seed crystals, the hydrothermal crystallization temperature is 110-180℃ and the time is 24-96h.

28. The method for preparing the desulfurizing agent according to claim 1, wherein, In S2, the mass ratio of ZSM-5 molecular sieve nanocrystals, binder, pore expander, and active metal salt is 30-70:10-50:1-10:5-20.

29. The method for preparing the desulfurizing agent according to claim 1, wherein, The active metal salt provides an active metal including one or more of Zn, Ni, Cu, Mn, Fe, Ce, La, and V.

30. The method for preparing the desulfurizing agent according to claim 1, wherein, The binder includes one or more of cement, water glass, boehmite, and aluminosilicate.

31. The method for preparing the desulfurizing agent according to claim 1, wherein, The pore-expanding agent includes one or more of the following: guar gum powder, hydroxymethyl cellulose, and hexadecyltrimethylammonium bromide.

32. In the method for preparing the desulfurizing agent according to claim 1, in step S2, the calcination temperature is 350-500℃ and the time is 5-12h.

33. A desulfurizing agent, which is prepared by the method for preparing the desulfurizing agent according to any one of claims 1-32.

34. The application of the desulfurizing agent according to claim 33 in treating low-temperature flue gas at 250-400°C.

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