Method for synthesizing ZSM-5 molecular sieve with low silica-alumina ratio by green single template agent one-step method

Abstract

The invention discloses a green single-template one-step method for synthesizing a ZSM-5 molecular sieve with a low silica-alumina ratio, which comprises the following steps: by taking a triblock copolymer P123 or F127 as a template, uniformly mixing a silicon source, an aluminum source, an alkali source NaOH, the template and water to obtain a synthetic sol, then carrying out hydrothermal crystallization at 90-190 DEG C for 24-192 hours, cooling, filtering, washing and drying to obtain the ZSM-5 molecular sieve with the low silica-alumina ratio. According to the invention, a triblock copolymer P123 or F127 is used as a single template agent, and the ZSM-5 molecular sieve with low silica-alumina ratio is prepared without adding seed crystal or other organic or inorganic template agents. The method avoids the high toxicity and complex post-treatment process of the traditional template agent, and can be used in the fields of catalytic cracking, aromatization, alkylation, disproportionation, gasoline preparation through methanol conversion, low-carbon olefin preparation through methanol conversion and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of inorganic porous materials, and particularly relates to a method for directly synthesizing low-silica-alumina ratio ZSM-5 molecular sieve by a green single-template agent one-step method. Background Art

[0002] ZSM-5 molecular sieve was first publicly reported by Mobil Company in the United States in 1972. It belongs to the orthorhombic crystal system, and its unit cell parameters are a = 2.017 nm, b = 1.996 nm, and c = 1.343 nm, respectively. The pore structure of ZSM-5 molecular sieve is composed of the intersection of elliptical straight channels (pore size: 0.54 nm×0.56 nm) and Z-shaped channels (pore size: 0.52 nm×0.58 nm), and the size at the intersection of the two channels is 0.9 nm. It has a unique pore structure, adjustable acid sites, excellent thermal stability and hydrothermal stability.

[0003] The type of template agent significantly affects the morphology, acidity and textural characteristics of ZSM-5 molecular sieve, and thus modulates its catalytic performance. Template agents are organic substances (amines, alcohols, alkanolamines, etc.), quaternary ammonium bases and quaternary ammonium salts added during the synthesis of molecular sieves. Their functions are usually divided into four aspects, namely: real template agent, structure directing agent, filler and charge balance. Template agent molecules affect the gelation and nucleation processes, reduce the chemical potential for the formation of the molecular sieve lattice, and thus are thermodynamically and kinetically beneficial to promoting the formation of the molecular sieve lattice. The structure of the template agent (charge distribution, size and spatial shape of the template agent molecule) has an important influence on the morphology of the molecular sieve and is also the reason for its guiding performance.

[0004] Sun Shuhong, Sang, etc. studied the influence of the type and dosage of template agent on the morphology of ZSM-5 molecular sieve, highlighting the importance of the use of template agent in the synthesis of molecular sieve. (Sun Shuhong, Wang Ningsheng, Yan Weijian, Progress in the synthesis and modification technology of ZSM-5 zeolite, Industrial Catalysis, 2007, 15(6): 6-10; Shiyun Sang, Fuxiang Chang, Zhongmin Liu, Changqing He, Yanli He, Lei Xu, Difference of ZSM-5 zeolites synthesized with various templates, Catalysis Today 93–95 (2004) 729–734) Wu et al. (Leilei Wu, Pieter C.M.M. Magusin, Volkan Degirmenci, Meiqin Li, Sami M.T. Almutairi, Xiaochun Zhu, Brahim Mezari, Emiel J.M. Hensen, Acidic properties of nanolayered ZSM-5 zeolites, Microporous and Mesoporous Materials 189 (2014) 144–157) used C 22-6-6 Br2, C 22-6-6 Br3, C 22-6-6 Br4, C 22-6-6 (OH)2, C 22-6-6 (OH)3 and C 22-6-6 (OH)4 as the template agent, tetraethyl orthosilicate as the silicon source, aluminum sulfate as the aluminum source, sodium hydroxide as the base source, and 30% sulfuric acid to adjust the pH value of the solution. Monolayer or multilayer nanosheet ZSM-5 molecular sieves with a silica-alumina ratio of 30 - 50 were synthesized by adjusting the amounts of the template agent, sodium hydroxide, and water. Fereydoon et al. (Fereydoon Yaripour, Zahra Shariatinia, Saeed Sahebdelfar, Akbar Irandoukht, Conventional hydrothermal synthesis of nanostructured H-ZSM-5 catalysts using various templates for light olefin production from methanol, Journal of Natural Gas Science and Engineering 22 (2015) 260 - 269) used silica sol (Ludox, 40 wt.%), sodium aluminate, sodium hydroxide, and sulfuric acid as raw materials, and used morpholine, n-butylamine, tetrapropylammonium hydroxide, and tetrapropylammonium bromide as the template agent respectively to synthesize ZSM-5 molecular sieves with a silica-alumina ratio of 200 and different crystal sizes and shapes.

[0005] The inventors of the present application once synthesized ZSM-5 / MCM-41 composite zeolite by a one-step method using a single template agent (cetyltrimethylammonium bromide). (Yang Zhiwen, Zhang Hairong, Tao Xun, Fu Liqing, Miao Yuqing, A method for synthesizing ZSM-5 / MCM-41 composite zeolite, Chinese invention patent, patent number: ZL201310697837.1). In this method, the product synthesized using a cationic surfactant has a high silica-alumina ratio. Although ZSM-5 zeolite with a high silica-alumina ratio has good acid resistance and hydrothermal stability, the aluminum content in its framework is relatively low, resulting in a reduction in the number of acid sites and relatively low catalytic activity and selectivity. In addition, the surface activity of the high silica-alumina zeolite is weak and the adsorption capacity is limited. In some catalytic reactions, due to insufficient acid sites, the high silica-alumina ZSM-5 zeolite may lead to a decrease in reaction activity and product selectivity.

[0006] Generally speaking, the synthesis methods in the prior art have the characteristics of long synthesis time, large amount of template agent used, toxicity, cumbersome operation process, and being not conducive to large-scale production. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for synthesizing low silica-alumina ratio ZSM-5 zeolite by a green single-template agent one-step method, using P 123 or F 127 as the template agent, and no seed crystal or other organic template agent needs to be added to the synthesis sol.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: A method for synthesizing low silica-alumina ratio ZSM-5 zeolite by a green single-template agent one-step method, using triblock copolymer P 123 or F 127 as the template agent, mixing a silicon source, an aluminum source, a base source NaOH, the template agent and water evenly to obtain a synthesis sol, then carrying out hydrothermal crystallization at 90 - 190 °C for 24 - 192 hours, and after cooling, filtering, washing and drying, low silica-alumina ratio ZSM-5 zeolite is obtained.

[0009] P 123 (English name: Pluronic P-123) is a triblock copolymer, and its full name is polyethylene oxide - polypropylene oxide - polyethylene oxide triblock copolymer. Its molecular formula is generally expressed as HO(C2H4O) 10-15 (C3H6O) 18-23 (C2H4O) 10-15 H. The average molecular weight is about 5800.

[0010] F 127(English name: Pluronic F-127) is a triblock copolymer, and its Chinese name is polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer. Its molecular formula is usually expressed as H(C2H4O)x(C3H6O)y(C2H4O)zOH, and the average molecular weight is about 12,600 - 14,600. When calculating the amount of substance in the present invention, the average molecular weight of 13,000 is adopted.

[0011] P 123 or F 127 As a single template agent, it can synthesize ZSM-5 zeolite with a low silica-alumina ratio by a one-step method. In addition, P 123 or F 127 As a template agent, it can inhibit the formation of quartz phase or MOR zeolite phase. In some expressions of this application document, R represents the above template agent.

[0012] As a preferred embodiment, in the synthetic sol, the molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R)=1:(0.006~0.0093):0.39:(0.012~0.12), and R is P 123 or F 127 .

[0013] As a preferred embodiment, the molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R)=1:(0.007~0.008):0.39:(0.012~0.12).

[0014] As a preferred embodiment, the molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R)=1:(0.007~0.008):0.39:(0.05~0.08).

[0015] As a preferred embodiment, the molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R)=1:0.0068:0.39:0.012.

[0016] As a preferred embodiment, the aluminum source is selected from aluminum sulfate, aluminum hydroxide, alumina, sodium aluminate or aluminum isopropoxide.

[0017] As a preferred embodiment, the silicon source is selected from tetraethyl orthosilicate, silicic acid, silica sol or fumed silica.

[0018] As a preferred embodiment, it is crystallized at 170 °C for 36 hours.

[0019] The present invention uses the triblock copolymer P 123 or F127 Using a single template agent without the need to add seeds or other organic or inorganic template agents, a ZSM-5 molecular sieve with a low silica-alumina ratio is prepared. This method avoids the strong toxicity of traditional template agents and the complex post-treatment process, and can be used in fields such as catalytic cracking, aromatization, alkylation, disproportionation, methanol conversion to gasoline, and methanol conversion to light olefins.

[0020] In addition, the method of the present invention also has the advantages of less template agent consumption, short synthesis time, simple process, easy operation, and good repeatability. Brief Description of the Drawings

[0021] Figure 1 It is the X-ray diffraction (XRD) pattern of the ZSM-5 molecular sieve sample synthesized in Example 1.

[0022] Figure 2 It is the X-ray diffraction (XRD) pattern of the ZSM-5 molecular sieve sample synthesized in Example 2.

[0023] Figure 3 It is the X-ray diffraction (XRD) pattern of the ZSM-5 molecular sieve sample synthesized in Example 3.

[0024] Figure 4 It is the X-ray diffraction (XRD) pattern of the ZSM-5 molecular sieve sample synthesized in Example 4. Detailed Description of the Embodiments

[0025] The following further illustrates the technical solutions claimed in the present invention through some embodiments. However, the embodiments are used to explain the implementation solutions of the present invention and do not exceed the scope of the subject matter of the present invention. The protection scope of the present invention is not limited by the described embodiments. Unless otherwise specified, the materials and reagents used in the present invention can be obtained from commercial products in the art. Example 1

[0026] First, 1.0 g of template agent P 123 is dissolved in distilled water, then 0.4415 g of sodium hydroxide and 0.0557 g of aluminum sulfate octadecahydrate are added in sequence. After stirring evenly, 2.8 ml of silica sol is added. After adding, continue to stir to make it mix evenly to obtain a synthesis sol. The molar composition of the synthesis sol is: SiO2:Al2O3::Na2O:R:H2O = 1.0:0.0060:0.39:0.012:121 (R is P 123, SAR = 167). The above synthetic sol was sealed in a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 170 °C for 36 hours. After the autoclave was taken out, it was quickly cooled to room temperature. The solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. The X-ray diffraction (XRD) test showed that it was the crystal phase structure of pure ZSM-5 molecular sieve. The X-ray diffraction (XRD) pattern of the sample is shown in the appendix Figure 1 . Example 2

[0027] First, 1.0 g of template P 123 was dissolved in distilled water, then 0.4415 g of sodium hydroxide and 0.0634 g of aluminum sulfate octadecahydrate were added in sequence. After stirring evenly, 2.8 ml of silica sol was added. After adding, stirring was continued to make it mix evenly to obtain a synthetic sol. The molar composition of the synthetic sol was: SiO2:Al2O3::Na2O:R:H2O = 1.0:0.0068:0.39:0.012:121 (R is P 123 , SAR = 147). The above synthetic sol was sealed in a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 170 °C for 36 hours. After the autoclave was taken out, it was quickly cooled to room temperature. The solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. The X-ray diffraction (XRD) test showed that it was the crystal phase structure of pure ZSM-5 molecular sieve. The X-ray diffraction (XRD) pattern of the sample is shown in the appendix Figure 2 . Example 3

[0028] First, 1.0 g of template P 123 was dissolved in distilled water, then 0.4415 g of sodium hydroxide and 0.0871 g of aluminum sulfate octadecahydrate were added in sequence. After stirring evenly, 2.8 ml of silica sol was added. After adding, stirring was continued to make it mix evenly to obtain a synthetic sol. The molar composition of the synthetic sol was: SiO2:Al2O3::Na2O:R:H2O = 1.0:0.0093:0.39:0.012:121 (R is P 123 , SAR = 107). The above synthetic sol was sealed in a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner and crystallized at 170 °C for 36 hours. After the autoclave was taken out, it was quickly cooled to room temperature. The solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. The X-ray diffraction (XRD) test showed that it was the crystal phase structure of pure ZSM-5 molecular sieve. The X-ray diffraction (XRD) pattern of the sample is shown in the appendix Figure 3 . Example 4

[0029] First, 2.2 g of template F127 Dissolve it in distilled water, then successively add 0.4415 g of sodium hydroxide and 0.0557 g of aluminum sulfate octadecahydrate. After stirring evenly, add 2.8 ml of silica sol. After adding, continue to stir to make it evenly mixed to obtain a synthetic sol. The molar composition of the synthetic sol is: SiO₂:Al₂O₃:Na₂O:R:H₂O = 1.0:0.0060:0.39:0.012:121 (R is F 127 , SAR = 167). Seal the above synthetic sol in a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner, crystallize at 170 °C for 36 hours. After taking out the autoclave, quickly cool it to room temperature, filter and separate the solid product, wash it with deionized water until neutral, and dry it overnight at 100 °C to obtain the product. The product is examined by X-ray diffraction (XRD) to be the crystal phase structure of pure phase ZSM-5 molecular sieve. Example 5

[0030] First, dissolve 2.27 g of template agent F 127 in distilled water, then successively add 0.11 g of sodium hydroxide and 0.002 g of aluminum hydroxide. After stirring evenly, add 2.8 ml of tetraethyl orthosilicate. After adding, continue to stir to make it evenly mixed to obtain a synthetic sol. The molar composition of the synthetic sol is: SiO₂:Al₂O₃:Na₂O:R:H₂O = 1.0:0.0070:0.39:0.05:121 (R is F 127 , SAR = 167). Seal the above synthetic sol in a 100 ml stainless steel autoclave with a polytetrafluoroethylene liner, crystallize at 90 °C for 192 hours. After taking out the autoclave, quickly cool it to room temperature, filter and separate the solid product, wash it with deionized water until neutral, and dry it overnight at 100 °C to obtain the product. The product is examined by X-ray diffraction (XRD) to be the crystal phase structure of pure phase ZSM-5 molecular sieve. Example 6

[0031] First, dissolve 6.66 g of template agent F 127 in distilled water, then successively add 0.2 g of sodium hydroxide and 0.005 g of alumina. After stirring evenly, add 0.5 g of silicic acid. After adding, continue to stir to make it evenly mixed to obtain a synthetic sol. The molar composition of the synthetic sol is: SiO₂:Al₂O₃:Na₂O:R:H₂O = 1.0:0.0080:0.39:0.08:121 (R is F 127, SAR = 167). The above-mentioned synthetic sol was sealed in a 100 ml stainless steel autoclave with a Teflon liner, crystallized at 190 °C for 24 hours, quickly cooled to room temperature after taking out the autoclave, the solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. After being tested by X-ray diffraction (XRD), it was the crystal phase structure of pure-phase ZSM-5 molecular sieve. Example 7

[0032] First, 6.5 g of template F 127 was dissolved in distilled water, then 0.13 g of sodium hydroxide and 0.005 g of aluminum isopropoxide were added in sequence. After stirring evenly, 0.25 g of silica white was added. After adding, continue to stir to make it evenly mixed to obtain a synthetic sol. The molar composition of the synthetic sol was: SiO2:Al2O3::Na2O:R:H2O = 1.0:0.0060:0.39:0.12:121 (R was F 127 , SAR = 167). The above-mentioned synthetic sol was sealed in a 100 ml stainless steel autoclave with a Teflon liner, crystallized at 170 °C for 36 hours, quickly cooled to room temperature after taking out the autoclave, the solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. After being tested by X-ray diffraction (XRD), it was the crystal phase structure of pure-phase ZSM-5 molecular sieve. Example 8

[0033] First, 2.2 g of template F 127 was dissolved in distilled water, then 0.43 g of sodium hydroxide and 0.014 g of sodium aluminate were added in sequence. After stirring evenly, 2.8 ml of silica sol was added. After adding, continue to stir to make it evenly mixed to obtain a synthetic sol. The molar composition of the synthetic sol was: SiO2:Al2O3::Na2O:R:H2O = 1.0:0.0060:0.39:0.012:121 (R was F 127 , SAR = 167). The above-mentioned synthetic sol was sealed in a 100 ml stainless steel autoclave with a Teflon liner, crystallized at 170 °C for 36 hours, quickly cooled to room temperature after taking out the autoclave, the solid product was separated by filtration, washed with deionized water until neutral, and dried overnight at 100 °C to obtain the product. After being tested by X-ray diffraction (XRD), it was the crystal phase structure of pure-phase ZSM-5 molecular sieve.

[0034] The scope of protection required by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention can have various deformations and changes. Any modification, improvement, and equivalent replacement made within the concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for synthesizing low-silica-alumina ratio ZSM-5 molecular sieve by a one-step method with a green single template agent, characterized in that: With triblock copolymer P 123 or F 127 As a template, a silicon source, an aluminum source, an alkali source NaOH, a template and water are uniformly mixed to obtain a synthetic sol, which is then hydrothermally crystallized at 90-190°C for 24-192 hours. After cooling, the sol is filtered, washed and dried to obtain a low silicon-aluminum ratio ZSM-5 molecular sieve.

2. The method according to claim 1, wherein: In the synthetic sol, the molar ratio of raw materials is n(SiO₂):n(Al₂O₃):n(Na₂O):n(R) = 1:(0.006~0.0093):0.39:(0.012~0.12), where R is P 123 or F 127 .

3. The method according to claim 2, wherein: The molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R) = 1:(0.007 - 0.008):0.39:(0.012 - 0.12).

4. The method according to claim 2, wherein: The molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R) = 1:(0.007 - 0.008):0.39:(0.05 - 0.08).

5. The method according to claim 2, characterized in that: The molar ratio of raw materials is n(SiO2):n(Al2O3):n(Na2O):n(R) = 1:0.0068:0.39:0.

012.

6. The method according to claim 1, 2, 3, 4 or 5, characterized in that: The aluminum source is selected from aluminum sulfate, aluminum hydroxide, aluminum oxide, sodium aluminate or aluminum isopropoxide.

7. The method according to claim 6, characterized in that: The silicon source is selected from tetraethyl orthosilicate, silicic acid, silica sol or white carbon black.

8. The method according to claim 1 or 7, characterized in that: Crystallize at 170 °C for 36 hours.

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