Preparation method of zinc isomorphous replacement modified nano [Zn / Al] ZSM-12 molecular sieve

Abstract

The invention relates to a preparation method of a zinc isomorphous replacement modified nano [Zn / Al] ZSM-12 molecular sieve, and aims to solve the problems that the acidity of the existing ZSM-12 molecular sieve is too strong, so that side reactions such as cracking in an acid catalytic reaction process are aggravated, and coking and carbon deposition are easy to occur. The preparation method comprises the following steps: 1, mixing silica sol serving as a silicon source, sodium metaaluminate serving as an aluminum source, sodium hydroxide serving as an alkali source and tetraethylammonium bromide serving as a template agent with water to form initial gel, and performing crystallization reaction at the temperature of 150-158 DEG C to synthesize a ZSM-12 molecular sieve; and 2, mixing the ZSM-12 molecular sieve with an ammonium fluorozincate aqueous solution, carrying out heating treatment at 60-90 DEG C, and carrying out roasting treatment on the collected solid-phase substance to obtain the zinc isomorphous replacement modified nano [Zn / Al] ZSM-12 molecular sieve. The preparation method provided by the invention is simple and easy to implement, realizes fine modulation of acidity and pore characteristics of the molecular sieve at the same time, and has universality for other molecular sieves.

Description

Technical Field

[0001] This invention belongs to the field of zeolite molecular sieve catalyst preparation, specifically relating to a method for zinc-partially isomorphous substitution modification of [Zn / Al]ZSM-12 zeolite molecular sieve. Background Technology

[0002] Zeolite molecular sieves are widely used as catalysts or supports in petrochemical and other fields due to their excellent properties, such as regular pore structure, good thermal and hydrothermal stability, and shape-selective catalysis. However, the strong acidity of molecular sieves can exacerbate side reactions in the catalytic process, reducing the selectivity of the target product. Furthermore, the strong acidity can lead to carbon deposition during the process, covering surface active sites or blocking pores and channels, resulting in deactivation of the molecular sieve. Therefore, to improve the selectivity of the target product and extend the service life of molecular sieve catalysts, developing new preparation methods or modifying existing molecular sieves to regulate their acidity and pore characteristics are effective ways to improve their catalytic performance.

[0003] Heteroatom isomorphic substitution modification refers to the introduction of atoms such as gallium, zinc, iron, or boron into the molecular sieve framework, partially or completely replacing the framework aluminum atoms, thereby effectively modulating the acidity and other properties of the molecular sieve. Compared with modification methods such as liquid phase deposition modification, ion exchange modification, acid dealumination, and alkali desilication, heteroatom isomorphic substitution modification can finely modulate the acidity of the molecular sieve and avoid the adverse effects of liquid phase deposition modification, such as pore blockage, and pore collapse caused by acid dealumination and alkali desilication. Compared with in-situ synthesis of isomorphic substitution modified molecular sieves, the secondary synthesis method is simpler and easier to implement, avoiding the problems of increased non-framework species and excessive framework defect sites caused by competition between aluminum atoms and heteroatoms for entry into the molecular sieve framework in in-situ synthesis methods.

[0004] ZSM-12 molecular sieve is a microporous zeolite molecular sieve with a one-dimensional channel structure and twelve-membered ring pores, with a pore size of 0.56 nm × 0.60 nm, belonging to the MTW type topology. Compared with zeolite molecular sieves such as ZSM-22 and ZSM-48, which have one-dimensional channel structures, ZSM-12 molecular sieve has a larger opening size, which is more conducive to the diffusion of reactants and products within the molecular sieve channels. Summary of the Invention

[0005] The present application solves the problems of existing ZSM-12 molecular sieve, such as too strong acid leading to intensified cracking and other side reactions of acid catalysis, easy coking and carbon deposition, poor mass transfer characteristics of single micropore channel, intensified cracking side reactions when used as an acidic catalyst or an acidic carrier of a catalyst, low selectivity of target products, and easy carbon deposition and deactivation, and provides a simple and easy effective method of adjusting the acidity of ZSM-12 molecular sieve by partially replacing framework aluminum atoms of ZSM-12 molecular sieve with zinc isomorphism.

[0006] The preparation method of the zinc isomorphism modified nano [Zn / Al] ZSM-12 molecular sieve according to the present application is realized according to the following steps:

[0007] I. Using silica sol as a silicon source, sodium aluminate as an aluminum source, sodium hydroxide as an alkali source, and tetraethylammonium bromide as a template agent, the silicon source accounts for SiO2, the aluminum source accounts for Al2O3, the template agent accounts for TEA + , the alkali source accounts for OH - , and the molar ratio of SiO2:Al2O3:TEA + :OH - :H2O is (70-90):1:(8.75-11.25):(2.28-2.93):(910-1170), the silicon source, the aluminum source, the alkali source, the template agent and water are mixed to form an initial gel, and the ZSM-12 molecular sieve is synthesized by crystallization reaction at a temperature of 150-158°C;

[0008] II. The ZSM-12 molecular sieve is mixed with an aqueous ammonium zinc fluoride solution according to a solid-liquid ratio (weight ratio) of 1:(10-40), heated at 60-90°C, cooled to room temperature, and then the collected solid phase is calcined at 500-700°C to obtain the zinc isomorphism modified nano [Zn / Al] ZSM-12 molecular sieve.

[0009] The present application uses the secondary synthesis method to modify the ZSM-12 molecular sieve by zinc isomorphism, so that the zinc atoms partially replace the framework aluminum atoms, which can effectively reduce the acid strength of the molecular sieve and appropriately reduce the acidic sites, and due to the fact that the number of inserted zinc atoms in the framework of the isomorphism modified molecular sieve is less than the number of removed framework aluminum atoms, intracrystalline mesopores are formed, thereby improving the transport performance of the molecular sieve channel and the reaction performance of the molecular sieve based catalyst.

[0010] The preparation method of the zinc isomorphism modified nano [Zn / Al] ZSM-12 molecular sieve provided by the present application has the following beneficial effects:

[0011] 1. The method provided by the application, which adopts a simple and easy-to-operate secondary synthesis method to prepare zinc isomorphously substituted [Zn / Al]ZSM-12 nanomolecular sieves with zinc partially replacing aluminum atoms in the molecular sieve framework, so as to weaken the acid strength of the molecular sieve, and by adjusting the molar ratio of zinc content in the ammonium zinc fluoride aqueous solution to aluminum in the ZSM-12 molecular sieve, the acid amount of the [Zn / Al]ZSM-12 molecular sieve can be adjusted in a wide range, the acid strength is weakened, and the [Zn / Al]ZSM-12 molecular sieve is applied to a normal alkane hydroisomerization reaction as a bifunctional catalyst with metal loading, so that the cracking side reaction can be effectively inhibited, and the isomerization selectivity and the yield of isomerization products are improved.

[0012] 2. The prepared Zn isomorphously substituted modified nanometer [Zn / Al]ZSM-12 molecular sieve has a smaller particle size and a larger mesopore volume, can form intracrystalline mesopores, and effectively improves the mass transfer characteristics of the molecular sieve channel. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is an XRD spectrum of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0014] Figure 2 is a scanning electron microscope (SEM) photo of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0015] Figure 3 is an N2 adsorption-desorption isotherm of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0016] Figure 4 is a pore size distribution curve of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0017] Figure 5 is an FT-IR spectrum of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0018] Figure 6 is a temperature programmed desorption (NH3-TPD) curve of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0019] Figure 7 is an infrared spectrum of pyridine adsorption (Py-IR) of the modified parent ZSM-12 molecular sieve prepared in Example 1;

[0020] Figure 8 is a scanning electron microscope (SEM) photo of the Zn isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example 1;

[0021] Figure 9N2adsorption-desorption isotherm of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example One;

[0022] Figure 10 Pore size distribution curve of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example One;

[0023] Figure 11 FT-IR spectrum of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example One;

[0024] Figure 12 NH3-TPD curve of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example One;

[0025] Figure 13 Pyridine adsorption infrared spectrum (Py-IR) of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-1 prepared in Example One;

[0026] Figure 14 N2adsorption-desorption isotherm of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-2 prepared in Example Two;

[0027] Figure 15 Pore size distribution curve of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-2 prepared in Example Two;

[0028] Figure 16 FT-IR spectrum of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-2 prepared in Example Two;

[0029] Figure 17 NH3-TPD curve of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-2 prepared in Example Two;

[0030] Figure 18 Pyridine adsorption infrared spectrum (Py-IR) of the zinc isomorphously substituted modified ZSM-12 molecular sieve sample [Zn / Al]ZSM-12-2 prepared in Example Two. DETAILED DESCRIPTION

[0031] DETAILED DESCRIPTION ONE: The method for preparing the zinc isomorphously substituted modified nano-ZSM-12 molecular sieve [Zn / Al]ZSM-12 of this embodiment is carried out according to the following steps:

[0032] I. Using silica sol as silicon source, sodium aluminate as aluminum source, sodium hydroxide as alkali source, and tetraethylammonium bromide as template, the silicon source is calculated according to the amount of SiO2, the silicon source is calculated according to the amount of Al2O3, the template is calculated according to the amount of TEA + , the alkali source is calculated according to the amount of OH - , and the molar ratio of SiO2:Al2O3:TEA + :OH - :H2O is (70-90):1:(8.75-11.25):(2.28-2.93):(910-1170). The silicon source, aluminum source, alkali source, template, and water are mixed to form an initial gel, and a crystallization reaction is carried out at a temperature of 150-158°C to synthesize ZSM-12 molecular sieve.

[0033] II. The ZSM-12 molecular sieve is mixed with an aqueous ammonium zinc fluoride solution at a solid-liquid ratio (weight ratio) of 1:(10-40) and heated at 60-90°C. After cooling to room temperature, the collected solid phase is calcined at 500-700°C to obtain a zinc isomorphously substituted nano [Zn / Al]ZSM-12 molecular sieve.

[0034] The present embodiment provides a new method for preparing a zinc partially isomorphously substituted [Zn / Al]ZSM-12 molecular sieve by a secondary synthesis method. Since zinc partially enters the molecular sieve framework, the acid strength of the molecular sieve can be effectively reduced, and secondary mesopores are generated in the molecular sieve crystal, effectively improving the mass transfer performance of the channel.

[0035] The method for preparing a [Zn / Al]ZSM-12 molecular sieve provided by the present embodiment is simple and easy to implement, can simultaneously achieve fine adjustment of the acidity and channel characteristics of the molecular sieve, has universality for other molecular sieves, and has important industrial application value.

[0036] Specific embodiment II: The difference between the present embodiment and specific embodiment I is that the SiO2 content in the silica sol in step I is 30wt.%-35wt.%.

[0037] Specific embodiment III: The difference between the present embodiment and specific embodiment I or II is that in step I, the molar ratio of SiO2:Al2O3:TEA + :OH - :H2O is 80:1:(8.75-11.25):(2.28-2.93):(910-1170). The silicon source, aluminum source, alkali source, template, and water are mixed to form an initial gel.

[0038] Specific embodiment IV: The difference between the present embodiment and any one of specific embodiments I to III is that in step I, the crystallization is carried out at a temperature of 150-158°C for 3 days.

[0039] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the ammonium fluozincate aqueous solution in step two is prepared by mixing zinc nitrate hexahydrate and ammonium fluoride in a molar ratio of 1:6 in deionized water.

[0040] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the molar ratio of ammonium fluozincate to aluminum in the ZSM-12 molecular sieve in step two is (0.5-3):1.

[0041] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the heating treatment in step two is carried out at 70-80°C for 1-3h.

[0042] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that after centrifugal separation in step two, the solid phase is collected, and then washed and dried.

[0043] Specific embodiment nine: the difference between this embodiment and specific embodiment seven is that the centrifugal separation in step two is carried out at a speed of 3000-5000r / min for 5-10min, washed with deionized water for 3-5 times, and dried at 110°C.

[0044] Specific embodiment ten: the difference between this embodiment and one of the specific embodiments one to nine is that the calcination in step two is carried out at 550-650°C for 3-6h.

[0045] Example one: the preparation method of the zinc isomorphously substituted modified nano [Zn / Al] ZSM-12 molecular sieve is carried out according to the following steps:

[0046] I. Using silica sol (SiO2 content of 32.13wt.%) as a silicon source, sodium metaaluminate as an aluminum source, sodium hydroxide as an alkali source, and tetraethylammonium bromide as a template agent, the silicon source is calculated according to the amount of SiO2, the silicon source is calculated according to the amount of Al2O3, the template agent is calculated according to the amount of TEA + , the alkali source is calculated according to the amount of OH - , and the molar ratio of SiO2:Al2O3:TEA + :OH - :H2O is 80:1:10:2.6:1040, the silicon source, aluminum source, alkali source, template agent and water are mixed to form an initial gel, and the ZSM-12 molecular sieve is synthesized by crystallization at a temperature of 158°C for 3 days;

[0047] II. 4 g of ZSM-12 molecular sieve was mixed with an aqueous solution of ammonium zinc fluoride, which was prepared by dissolving 0.124 g of zinc nitrate hexahydrate and 0.095 g of ammonium fluoride in 80 g of deionized water, and the mixture was heated at 80°C for 1 h. After cooling to room temperature, the sample was washed for 3 times, and after each washing, the sample was centrifuged at a speed of 4000 r / min for 5 min using a high-speed centrifuge. After the supernatant was separated, the sample was dried at 110°C for 12 h, and then calcined at 550°C for 3 h to obtain a zinc isomorphously substituted modified nano [Zn / Al]ZSM-12 molecular sieve, which was denoted as [Zn / Al]ZSM-12-1.

[0048] Figures 1 to 7 The XRD pattern, SEM image, N2 adsorption-desorption isotherm, pore size distribution curve (based on the DFT model), FT-IR spectrum, NH3-TPD curve, and Py-IR spectrum of the modified parent ZSM-12 molecular sieve synthesized according to step one in Example One are shown in sequence.

[0049] The XRD pattern of the ZSM-12 molecular sieve (the initial gel had a silicon-aluminum ratio SiO2 / Al2O3 = 80) synthesized according to step one in this example is shown in Figure 1 As can be seen from Figure 1 , characteristic diffraction peaks of the MTW topology structure appeared at 2θ = 7.6°, 8.8°, 20.9°, 22.9°, and 23.3°, and there were no diffraction peaks of other impurity crystals.

[0050] The SEM image of the ZSM-12 molecular sieve synthesized according to step one in this example is shown in Figure 2 As can be seen from Figure 2 , the synthesized molecular sieve was an aggregate formed by highly ordered arrangement of small crystal grains with uniform size and regular morphology. The size of the single crystal grain was about 40-50 nm, and the diameter of the aggregate was about 1 μm.

[0051] The pore size distribution curve of the ZSM-12 molecular sieve synthesized according to step one in this example is shown in Figure 4 As can be seen from Figure 4 , the molecular sieve only formed a mesopore distribution in a relatively narrow range (3-4 nm).

[0052] Figures 8 to 13 The SEM image, N2 adsorption-desorption isotherm, pore size distribution curve, FT-IR spectrum, NH3-TPD curve, and Py-IR spectrum of the zinc isomorphously substituted modified sample [Zn / Al]ZSM-12-1 prepared in Example One are shown in sequence.

[0053] The [Zn / Al]ZSM-12-1 sample prepared in this example still maintains the aggregate morphology of ZSM-12 molecular sieve, and the regularity of the aggregate slightly decreases. Figure 8 As can be seen from the pore size distribution curve (based on the DFT model), the sample forms a mesopore distribution in a wide range of 2.5-10 nm, Figure 10 which can be attributed to the formation of abundant secondary mesopores in the Zn isomorphous substitution modification process.

[0054] The texture property data and the acidity data of the modified parent ZSM-12 molecular sieve and the sample [Zn / Al]ZSM-12-1 modified by zinc isomorphous substitution are respectively listed in Tables 1, 2 and 3. As can be seen from the texture property data in Table 1, the sample [Zn / Al]ZSM-12-1 modified by zinc isomorphous substitution has a larger mesopore volume. As can be seen from the acidity data in Tables 2 and 3, the acid strength of the strong acid sites of the sample [Zn / Al]ZSM-12-1 modified by zinc isomorphous substitution is weakened, and the amount of the strong acid sites is reduced. As can be seen from the FT-IR spectra of the sample before and after modification Figure 5 and Figure 11 ), compared with the modified parent ZSM-12 molecular sieve (the adsorption peak appears at 1099 cm -1 ), the adsorption peak corresponding to the T-O-T bond vibration in the FT-IR spectrum of the sample [Zn / Al]ZSM-12-1 modified by zinc isomorphous substitution is red-shifted to 1095 cm -1 , indicating that zinc is introduced into the framework of the sample [Zn / Al]ZSM-12-1 after the ZSM-12 molecular sieve is modified by zinc isomorphous substitution.

[0055] Example 2: The difference between this example and Example 1 is that in step 2, after the mixed solution is transferred into the three-necked flask, it is treated at 80°C for 2 h.

[0056] Figures 14 to 18 is the N2adsorption-desorption isotherm, the pore size distribution curve, the FT-IR spectrum, the NH3-TPD curve and the Py-IR spectrum of the sample [Zn / Al]ZSM-12-2 modified by zinc isomorphous substitution prepared in Example 2.

[0057] As can be seen from the pore size distribution curve (based on the DFT model) of the sample [Zn / Al]ZSM-12-2 prepared in this example, the sample forms a mesopore distribution in a wide range of 2.5-10 nm, Figure 15 which can be attributed to the formation of abundant secondary mesopores in the Zn isomorphous substitution modification process. As can be seen from the FT-IR spectra of the ZSM-12 molecular sieve before and after zinc modification Figure 5 and Figure 11 ), compared with the modified parent ZSM-12 molecular sieve (the adsorption peak appears at 1099 cm -1), the adsorption peak corresponding to T-O-T bond vibration in the FT-IR spectrum of the isomorphously modified sample Zn / Al]ZSM-12-2 was red-shifted to 1095 cm -1 , indicating that zinc was introduced into the framework of the ZSM-12 molecular sieve after isomorphous modification of the ZSM-12 molecular sieve.

[0058] The texture property data and acidity data of the isomorphously modified sample [Zn / Al]ZSM-12-2 are also listed in Tables 1, 2 and 3, respectively. From the texture property data in Table 1, it can be seen that when the isomorphous modification time of zinc was extended from 1 h to 2 h, the micropore volume and micropore surface area of the modified sample [Zn / Al]ZSM-12-2 decreased, the mesopore volume slightly increased, the acid strength of the strong acid sites weakened, and the total acid amount slightly decreased. the acid strength weakened, and the total acid amount slightly decreased.

[0059] Table 1 Texture properties of ZSM-12 and [Zn / Al]ZSM-12-t molecular sieves

[0060]

[0061] Table 2 Acidity of ZSM-12 and [Zn / Al]ZSM-12-t molecular sieves (determined by NH3-TPD method)

[0062]

[0063] Table 3 Acid site density of ZSM-12 and [Zn / Al]ZSM-12-t molecular sieves (determined by Py-IR method)

[0064]

Claims

1. A process for the preparation of a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve, characterized in that The preparation method is realized according to the following steps: I. With silica sol as silicon source, sodium metaaluminate as aluminum source, sodium hydroxide as alkali source, and tetraethylammonium bromide as template agent, the silicon source is calculated according to the amount of SiO2, the silicon source is calculated according to the amount of Al2O3, the template agent is calculated according to the amount of TEA + , the alkali source is calculated according to the amount of OH - , and the molar ratio of SiO2:Al2O3:TEA + :OH - :H2O is (70-90):1:(8.75-11.25):(2.28-2.93):(910-1170). The silicon source, aluminum source, alkali source, template agent, and water are mixed to form an initial gel, and a ZSM-12 molecular sieve is synthesized by crystallization reaction at a temperature of 150-158°C. II. The ZSM-12 molecular sieve is mixed with an aqueous solution of ammonium zinc fluoride according to a solid-liquid ratio of 1:(10-40), heated and treated at 60-90 ℃, and after cooling to room temperature, the collected solid phase is calcined and treated at 500-700 ℃ to obtain a zinc isomorphously substituted modified nano [Zn / Al] ZSM-12 molecular sieve.

2. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, characterized in that The SiO2 content in the silica sol in step I is 30-35 wt.%.

3. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein Step one: SiO2:Al2O3:TEA + :OH - :H2O = 80:1:(8.75-11.25):(2.28-2.93):(910-1170) 4. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step I, the crystallization is carried out at a temperature of 150-158 ℃ for 3 days.

5. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step II, the aqueous solution of ammonium zinc fluoride is prepared by mixing zinc nitrate hexahydrate and ammonium fluoride in deionized water according to a molar ratio of 1:

6.

6. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step II, the molar ratio of ammonium zinc fluoride to aluminum in the ZSM-12 molecular sieve is (0.5-3):

1.

7. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step II, the heating and treatment is carried out at 70-80 ℃ for 1-3 h.

8. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step II, the solid phase is collected after centrifugal separation, and then washed, dried and treated.

9. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 8, wherein In step II, the centrifugal separation is carried out at a speed of 3000-5000 r / min for 5-10 min, washed with deionized water for 3-5 times, and dried at 110 ℃.

10. The method of making a zinc isomorphously substituted modified nano- [Zn / Al]ZSM-12 molecular sieve of claim 1, wherein In step II, the calcination is carried out at 550-650 ℃ for 3-6 h.

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