Aluminum-rich ZSM-5 molecular sieve and synthesis method thereof
阅读说明：本技术 富铝zsm-5分子筛及其合成方法 (Aluminum-rich ZSM-5 molecular sieve and synthesis method thereof ) 是由 闫文付 张启明 王振东 于 2019-09-19 设计创作，主要内容包括：本发明公开了一种富铝ZSM-5分子筛及其合成方法。该富铝ZSM-5分子筛中,SiO-2/Al-2O-3摩尔比为6-9,其中骨架铝的含量占铝总量的95％以上。该分子筛的合成方法,包括：在晶化条件下使得碱源、水、铝源、硅源、特定的ZSM-5晶种及有机模板剂X接触,以获得分子筛的步骤。该分子筛不但硅铝比小,而且富含骨架铝,适用于正己烷、异丙苯的催化裂化及甲醇转化反应中。(The invention discloses an aluminum-rich ZSM-5 molecular sieve and a synthesis method thereof. In the aluminum-rich ZSM-5 molecular sieve, SiO 2 /Al 2 O 3 The molar ratio is 6-9, wherein the content of framework aluminum accounts for more than 95 percent of the total amount of aluminum. The synthesis method of the molecular sieve comprises the following steps: contacting an alkali source, water, an aluminum source, a silicon source, a specific ZSM-5 seed crystal and an organic template agent X under crystallization conditions to obtain the molecular sieve. The molecular sieve has small silica-alumina ratio and is rich in framework aluminum, and is suitable for catalytic cracking of normal hexane and cumene and methanol conversion reaction.)
1. An aluminum-rich ZSM-5 molecular sieve, wherein SiO2/Al2O3The molar ratio is 6-9, wherein the content of framework aluminum accounts for more than 95 percent of the total amount of aluminum.
2. A method of synthesizing the aluminum rich ZSM-5 molecular sieve of claim 1, comprising: contacting an alkali source, water, an aluminum source, a silicon source, a ZSM-5 seed crystal and an organic template agent X under a crystallization condition to obtain a molecular sieve; SiO in the ZSM-5 seed crystal2/Al2O3The molar ratio is from 25 to 80, preferably from 25 to 50.
3. The method of synthesis according to claim 2, characterized in that: the synthesis method of the aluminum-rich ZSM-5 molecular sieve comprises the following steps: firstly, uniformly mixing an alkali source, an aluminum source and water, then adding an organic template agent X, uniformly mixing, then adding a silicon source and a ZSM-5 seed crystal, uniformly mixing, and then carrying out hydrothermal crystallization to obtain the aluminum-rich ZSM-5 molecular sieve.
4. A synthesis method according to claim 2 or 3, characterized in that: the alkali source is represented by M2Calculated by O, M is an alkali metal element, and the aluminum source is Al2O3The silicon source is calculated by SiO2The molar ratio of the organic template agent X to the water is M2O：Al2O3：SiO2：X：H2O ═ 0.03 to 0.16: (0.015-0.070): 1: (0.1-4.0): (5-50); preferably M2O：Al2O3：SiO2：X：H2O ═ 0.04-0.15: (0.015-0.070): 1(0.1-3.0): (5-40); the addition amount of the ZSM-5 seed crystal accounts for SiO which is the silicon source21 to 10 wt%, preferably 2 to 8 wt%, and more preferably 2 to 6 wt% of the mass.
5. A synthesis method according to claim 2 or 3, characterized in that: the silicon source comprises one or more selected from sodium silicate, ethyl orthosilicate, white carbon black and silica sol; the aluminum source comprises one or more selected from aluminum hydroxide, aluminum nitrate, boehmite, aluminum sulfate and sodium aluminate; the alkali source comprises one or more selected from sodium hydroxide and potassium hydroxide.
6. A synthesis method according to claim 2 or 3, characterized in that: the organic template agent comprises one or more of tetraethylenepentamine, triethylene tetramine, ethylamine and ethylenediamine.
7. A synthesis method according to claim 2 or 3, characterized in that: the crystallization conditions comprise crystallization at the temperature of 140 ℃ and 190 ℃ for 6-72 h.
8. A synthesis method according to claim 2 or 3, characterized in that: the crystallization condition comprises crystallization at 170-190 ℃ for 12-48 h.
9. A synthesis method according to claim 2 or 3, characterized in that: the method also comprises the steps of filtering, washing and drying after the crystallization step, wherein the drying conditions are as follows: the drying temperature is 60-100 deg.C, and the drying time is 6-12 h.
10. The method of synthesis according to claim 2, characterized in that: in the synthesis method of the molecular sieve, roasting the molecular sieve obtained by crystallization to obtain a roasted molecular sieve; the roasting conditions were as follows: the roasting temperature is 300-800 ℃, and the roasting time is 1-10 hours.
Technical Field
The invention relates to a ZSM-5 molecular sieve and a synthetic method thereof, in particular to an aluminum-rich ZSM-5 molecular sieve and a synthetic method thereof.
Background
The ZSM-5 molecular sieve is a high-silicon molecular sieve synthesized by Mobil company in 1972 by tetrapropylammonium hydroxide as a template. ZSM-5 belongs to MFI framework structure, and the basic structural unit is five-membered ring composed of silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron, which are connected with each other through bridge oxygen and have two-dimensional cross pore canal. The size of the straight channel of the ten-membered ring parallel to the [010] direction is 0.53 × 0.56nm, and the size of the channel of the Z-shaped ten-membered ring parallel to the [100] direction is 0.51 × 0.53 nm. Due to the proper pore diameter, the ZSM-5 molecular sieve is widely used in the research fields of petrochemical industry, fine chemical industry, environmental protection and the like, is widely used as a catalyst for acid catalytic reaction due to good ion exchange performance and carbon deposition resistance, has higher activity and selectivity on low-carbon olefin and aromatic hydrocarbon, and shows excellent catalytic performance in catalytic cracking, isomerization, aromatization, amidation, alkylation and other reactions. Therefore, the synthesis of ZSM-5 molecular sieves is of great interest.
The framework aluminum in the ZSM-5 molecular sieve is a main factor generated by the acid site B, the acid site is an active center of reactions such as catalytic cracking and the like, and the acid site generated by the framework aluminum can be increased by reducing the framework silica-alumina ratio of the ZSM-5, so that the catalytic activity of the ZSM-5 is improved, and therefore people hope to synthesize the aluminum-rich ZSM-5 molecular sieve.
The literature Synthesis and Characterization of Aluminum-Rich Zeolite ZSM-5(chem. Eng. Technol,23(2000)322-324.) reports a method for synthesizing an Aluminum-Rich ZSM-5 molecular sieve, which uses tetrapropylammonium hydroxide as a template agent to reduce the silica-alumina ratio in the initial gel to 10, the Si/Al of the molecular sieve framework of the product ZSM-5 to 9.1, and when the silica-alumina ratio in the initial gel is further reduced to below 10, a analcite heterogeneous phase appears in the product.
The Laws-observed in the synthesis of zeolite having the structure of ZSM-5and varying chemical composition (Zeolite, 3(1983)311-320.) reported a method for synthesizing a ZSM-5 molecular sieve of Si/Al-12, but the hydrogen form of the sample27The nuclear magnetic resonance spectrum of the Al solid shows that a part of aluminum is not in the molecular sieve framework, and the Al solid is not suitable for industrial production. If the silica to alumina ratio of the initial gel is reduced, a analcime heterophase appears in the product.
CN200810224857.6 discloses a method for synthesizing ZSM-5 molecular sieve from natural rectorite mineral, the product of which has minimum Si/Al of 10.
The currently reported method for synthesizing the aluminum-rich ZSM-5 molecular sieve can only prepare ZSM-5 molecular sieves with Si/Al more than 9, and the synthesis of ZSM-5 molecular sieves with lower Si/Al still has challenges, so that the application of the ZSM-5 molecular sieves in the field of petrochemical industry is limited.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides an aluminum-rich ZSM-5 molecular sieve and a synthesis method thereof. The aluminum-rich ZSM-5 molecular sieve has a small silica-alumina ratio and is rich in framework aluminum.
In a first aspect, the invention provides an aluminum-rich ZSM-5 molecular sieve in which SiO is2/Al2O3The molar ratio is 6 to 9, wherein the content of framework aluminum accounts for more than 95 percent of the total aluminum, preferably more than 98 percent, and more preferably 100 percent.
The invention provides a synthesis method of an aluminum-rich ZSM-5 molecular sieve, which comprises the following steps: contacting an alkali source, water, an aluminum source, a silicon source, a ZSM-5 seed crystal and an organic template agent X under a crystallization condition to obtain a molecular sieve; SiO in the ZSM-5 seed crystal2/Al2O3The molar ratio is from 25 to 80, preferably from 25 to 50.
In the above technical scheme, the method for synthesizing the aluminum-rich ZSM-5 molecular sieve specifically comprises the following steps: firstly, uniformly mixing an alkali source, an aluminum source and water (preferably deionized water), then adding an organic template agent X, uniformly mixing, then adding a silicon source and ZSM-5 seed crystals, uniformly mixing, and then carrying out hydrothermal crystallization to obtain the aluminum-rich ZSM-5 molecular sieve.
In the above technical scheme, the alkali source (as M)2Calculated as O, M is an alkali metal element), the aluminum source (calculated as Al)2O3Calculated), the silicon source (in SiO)2Calculated), the molar ratio of the organic template agent X to the water is M2O：Al2O3：SiO2：X：H2O ═ 0.03 to 0.16: (0.015-0.070): 1: (0.1-4.0): (5-50), preferably M2O：Al2O3：SiO2：X：H2O＝(0.04-0.15)：(0.015-0.070)：1(0.1-3.0)：(5-40)。
In the technical scheme, the addition amount of the ZSM-5 seed crystal accounts for the silicon source in terms of SiO21 to 10 wt%, preferably 2 to 8 wt%, and more preferably 2 to 6 wt% of the mass.
In the above technical scheme, the silicon source comprises one or more selected from sodium silicate, ethyl orthosilicate, white carbon black and silica sol.
In the above technical solution, the aluminum source comprises one or more selected from aluminum hydroxide, aluminum nitrate, boehmite, aluminum sulfate and sodium aluminate.
In the above technical solution, the alkali source includes one or more selected from sodium hydroxide and potassium hydroxide.
In the above technical scheme, the organic template comprises one or more selected from tetraethylenepentamine, triethylene tetramine, ethylamine and ethylenediamine.
In the above technical solution, the crystallization condition comprises crystallization at 190 ℃ of 140-.
In the above technical scheme, the crystallization step further comprises conventional post-treatment steps such as filtration, washing, drying and the like. The drying conditions were as follows: the drying temperature can be 60-100 ℃, and the drying time can be 6-12 h.
In the above technical solution, in the synthesis method of the molecular sieve, the molecular sieve obtained by crystallization may be calcined according to needs to remove the organic template agent and possibly present moisture, and the like, thereby obtaining the calcined molecular sieve. The firing step is performed after drying. The calcination may be carried out in any manner conventionally known in the art, such as at a calcination temperature of typically 300-800 deg.C, preferably 400-650 deg.C, and a calcination time of typically 1-10 hours, preferably 3-6 hours. In addition, the calcination is generally carried out in an oxygen-containing atmosphere, such as air or oxygen.
The aluminum-rich ZSM-5 molecular sieve has small silica-alumina ratio and is rich in framework aluminum, and is suitable for catalytic cracking of normal hexane and cumene and methanol conversion reaction.
By adopting the method, the ZSM-5 molecular sieve rich in framework aluminum can be synthesized under the condition of low silicon-aluminum ratio. The method is simple, short in synthesis time, suitable for large-scale industrial production and good in technical effect.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.
FIG. 1 is an X-ray diffraction pattern of the aluminum-rich ZSM-5 molecular sieve of example 1;
FIG. 2 is an X-ray diffraction pattern of the aluminum-rich ZSM-5 molecular sieve of example 2;
FIG. 3 is an X-ray diffraction pattern of the aluminum-rich ZSM-5 molecular sieve of example 3;
FIG. 4 is an X-ray diffraction pattern of the aluminum-rich ZSM-5 molecular sieve of example 4;
FIG. 5 is a depiction of the aluminum-rich ZSM-5 molecular sieve of example 227An Al solid nuclear magnetic resonance spectrogram;
FIG. 6 is a graphical representation of the ZSM-5 molecular sieve synthesized in comparative example 327Al solid nuclear magnetic resonance spectrum.
Detailed Description
In the context of the present specification, including in the following examples and comparative examples, the molecular sieve product XRD measurement method is: analyzing the phase of the sample by using a Nippon Rigaku Ultima type IV X-ray powder diffractometer, a CuK alpha ray sourceThe 2 theta scanning range of the nickel filter is 2-50 degrees, the operating voltage is 35KV, the current is 25mA, and the scanning speed is 10 degrees/min.
In the context of this specification, including the following examples and comparative examples, the method of measuring the silica to alumina ratio in a molecular sieve product is: the Si/Al ratio of the sample was analyzed by means of a Model S-35 inductively coupled plasma atomic emission spectrometer (ICP-AES) instrument from Kontron. The solid molecular sieve sample was dissolved with HF to make a solution before testing.
In the context of the present specification, the following are includedIn the examples and comparative examples, the determination of the aluminum content on the framework in the molecular sieve product was carried out by: the test was carried out using an VARIAN VNMRS-400WB NMR spectrometer.27Al spectroscopy at 104.18MHz, rotation speed 10000rps, relaxation time 4s, in KAl (SO)4)2·12H2O is a standard substance. The signal peak near 50ppm corresponds to the integrated peak area S1 for four coordinated framework aluminum, while the signal peak near 0ppm corresponds to the integrated peak area S2 for six coordinated non-framework aluminum. The aluminum content on the skeleton was S1/(S1+ S2) × 100%.
In examples and comparative examples of the present invention, SiO in silica sol was used2The mass content is 40%.
[ example 1 ]
(1) Adding 0.12g of sodium hydroxide and 0.056g of boehmite into 1.8g of deionized water, and uniformly stirring;
(2) adding 1.514g of tetraethylenepentamine under stirring, and continuing stirring for 30 min;
(3) 0.60g of white carbon black and 0.03g of ZSM-5 seed crystal (SiO) were added under stirring2/Al2O3The molar ratio is 25), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 12 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 60 ℃ for 10h to give sample Z1. The XRD pattern of Z1 is shown in FIG. 1, and Z1 is ZSM-5 molecular sieve as can be seen from FIG. 1. The Si/Al ratio of Z1 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance represents the aluminum state, the aluminum in Z1 is basically located on the framework, and the content of the framework aluminum accounts for 96% of the total amount of the aluminum.
[ example 2 ]
(1) Adding 0.158g of potassium hydroxide and 0.290g of aluminum sulfate octadecahydrate into 0.9g of deionized water, and uniformly stirring;
(2) adding 0.585g of triethylene tetramine under stirring, and continuing stirring for 30 min;
(3) 2.14g of tetraethylorthosilicate and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 50), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 170 ℃ for 48 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 80 ℃ for 8h to give sample Z2. The XRD pattern of Z2 is shown in FIG. 2, and Z2 is ZSM-5 molecular sieve as can be seen from FIG. 2. The Si/Al ratio of Z2 was measured by ICP-AES, and the results are shown in Table 1. Of Z227The NMR spectrum of the Al solid is shown in FIG. 5, in which a signal peak corresponding to aluminum on the four-coordinate skeleton appears only at 50ppm, and a signal peak corresponding to six-coordinate non-skeleton aluminum does not appear in the vicinity of 0 ppm. The result shows that the aluminum in the ZSM-5 molecular sieve exists in the molecular sieve in the form of framework aluminum, no non-framework aluminum exists, and the framework aluminum content is 100%.
[ example 3 ]
(1) Adding 0.04g of sodium hydroxide and 0.067g of sodium aluminate into 6.3g of deionized water, and uniformly stirring;
(2) adding 0.9g of ethylamine while stirring, and continuing stirring for 2 hours;
(3) 2.14g of tetraethylorthosilicate and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 38), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 12 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 90 ℃ for 10h to give sample Z3. The XRD pattern of Z3 is shown in FIG. 3, and Z3 is ZSM-5 molecular sieve as can be seen from FIG. 3. The Si/Al ratio of Z3 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance represents the aluminum state, the aluminum in Z3 is basically located on the framework, and the content of the framework aluminum accounts for 98 percent of the total amount of the aluminum.
[ example 4 ]
(1) Adding 0.096g of sodium hydroxide and 0.108g of aluminum hydroxide into 6.3g of deionized water, and uniformly stirring;
(2) adding 0.092g of ethylenediamine under stirring, and continuing stirring for 30 min;
(3) 1.5g of silica sol and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3Molar ratio of30), stirring for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 24 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 100 ℃ for 6h to give sample Z4. The XRD pattern of Z4 is shown in FIG. 4, and Z4 is ZSM-5 molecular sieve as shown in FIG. 4. The Si/Al ratio of Z4 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance represents the aluminum state, the aluminum in Z4 is basically located on the framework, and the content of the framework aluminum accounts for 97 percent of the total amount of the aluminum.
[ example 5 ]
(1) Adding 0.171g of potassium hydroxide and 0.289g of aluminum nitrate nonahydrate into 9g of deionized water, and uniformly stirring;
(2) 1.893g of tetraethylenepentamine are added under stirring, and the stirring is continued for 30 min;
(3) 6g of sodium silicate nonahydrate and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 45), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 48 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 100 ℃ for 6h to give sample Z5. The XRD pattern of Z5 shows that Z5 is ZSM-5 molecular sieve. The Si/Al ratio of Z5 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance spectrum represents the state of aluminum, the aluminum in Z5 is basically positioned on the framework, and the content of the framework aluminum accounts for 95 percent of the total amount of the aluminum.
[ example 6 ]
(1) Adding 0.088g of sodium hydroxide and 0.303g of aluminum sulfate octadecahydrate into 2.7g of deionized water, and uniformly stirring;
(2) adding 1.61g of ethylenediamine under stirring, and continuing stirring for 30 min;
(3) 1.5g of silica sol and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 35), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 190 ℃ for 24 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 70 ℃ for 9h to give sample Z6. The XRD pattern of Z6 shows that Z6 is ZSM-5 molecular sieve. The Si/Al ratio of Z6 was measured by ICP-AES, and the results are shown in Table 1. Of Z627The nuclear magnetic resonance spectrum of the Al solid is similar to that of FIG. 5, and the aluminum in Z6 exists in the molecular sieve in the form of framework aluminum, and non-framework aluminum is not existed, namely the framework aluminum content is 100%.
[ example 7 ]
(1) Adding 0.104g of sodium hydroxide and 0.341g of aluminum nitrate nonahydrate into 6.3g of deionized water, and uniformly stirring;
(2) adding 0.27g of ethylamine while stirring, and continuing stirring for 30 min;
(3) 2.14g of tetraethyl orthosilicate and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 30), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 48 hours;
(5) the product was centrifuged, washed three times with deionized water and ethanol, and dried at 90 ℃ for 6h to give sample Z7. The XRD pattern of Z7 shows that Z7 is ZSM-5 molecular sieve. The Si/Al ratio of Z7 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance represents the aluminum state, the aluminum in Z7 is basically located on the framework, and the content of the framework aluminum accounts for 98 percent of the total amount of the aluminum.
[ example 8 ]
(1) Adding 0.072g of sodium hydroxide and 0.303g of aluminum sulfate octadecahydrate into 4.5g of deionized water, and uniformly stirring;
(2) 1.46g of triethylene tetramine is added under stirring, and the stirring is continued for 30 min;
(3) 1.5g of silica sol and 0.03g of ZSM-5 seed crystals (SiO) were added with stirring2/Al2O3The molar ratio is 40), and stirring is continued for 2 hours;
(4) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 170 ℃ for 48 hours;
(5) the product was centrifuged and washed three times with deionized water and ethanol at 70Drying at deg.C for 10h gave sample Z8. The XRD pattern of Z8 shows that Z8 is ZSM-5 molecular sieve. The Si/Al ratio of Z8 was measured by ICP-AES, and the results are shown in Table 1. By using27The Al solid nuclear magnetic resonance spectrum represents the state of aluminum, the aluminum in Z8 is basically positioned on the framework, and the content of the framework aluminum accounts for 95 percent of the total amount of the aluminum.
Comparative example 1
According to the synthesis method of the aluminum-rich ZSM-5 molecular sieve of patent CN200810224857.6, 8.8g of water glass (26 wt% SiO)2，8wt％Na2O), 1.83g of TPABr, 57g of deionized water, 2g of a 3M concentrated sulfuric acid aqueous solution, and the calcined montmorillonite were added to a beaker, and stirred to obtain a mixture gel. The mol ratio of each component in the gel is SiO calculated by oxide2/Al2O3The molar ratio is 16, (Na)2O+K2O)/SiO2＝0.2，H2O/SiO2＝92，TPABr/SiO20.18. And transferring the mixture gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, statically crystallizing for 72 hours at 155 ℃, cooling, filtering to remove mother liquor, washing, drying and roasting at 550 ℃ to obtain a crystallized product, which is marked as A1. The XRD pattern of A1 shows that A1 is ZSM-5 molecular sieve. The Si/Al ratio of A1 was measured by ICP-AES, and the results are shown in Table 1.
Comparative example 2
Dissolving 0.096g of sodium hydroxide in 3.6g of deionized water, sequentially adding 0.09g of aluminum hydroxide after the sodium hydroxide is dissolved, uniformly stirring, adding 0.48g of ethylenediamine, and stirring for 30 min. 0.6g of white carbon black and 0.03g of ZSM-5 seed crystal (SiO)2/Al2O3Molar ratio of 100), stirring for 2 h. And transferring the obtained silicon-aluminum gel into a reaction kettle, and crystallizing at 170 ℃ for 48 hours. The product was centrifuged, washed three times with deionized water and ethanol, and dried at 80 ℃ for 12h to give sample a 2. The XRD pattern of A2 shows that A2 is ZSM-5 molecular sieve. Determination of SiO in A2 by ICP-AES2/Al2O3The molar ratio was 11.5.
Comparative example 3
According to the synthesis method of the ZSM-5 molecular sieve with the extremely low silica-alumina ratio of the patent CN107857281A, 0.334g of sodium bromide, 0.387g of potassium bromide, 2.74g of sodium bromide and 35 percent of mass fractionTetraethylammonium hydroxide aqueous solution was added to 7g of deionized water and stirred until completely dissolved. 0.091g boehmite was added under stirring and stirring was continued for 30 min. 0.78g of white carbon black is added under stirring, and stirring is continued for 2 h. And (3) putting the obtained silicon-aluminum gel into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and crystallizing at 180 ℃ for 96 hours. The product was centrifuged, washed with deionized water and ethanol, and dried at 60 ℃ for 10h to give sample A3. A327The Al NMR spectrum is shown in FIG. 6, in which a peak corresponding to aluminum on the four-coordinate skeleton appears at 50ppm, while a peak corresponding to six-coordinate non-skeleton aluminum appears near 0 ppm. The obtained ZSM-5 molecular sieve has framework aluminum and non-framework aluminum simultaneously, most of the aluminum is non-framework aluminum, and the framework aluminum content is 31%.
Comparative example 4
0.072g of sodium hydroxide is dissolved in 4.5g of deionized water, 0.064g of pseudo-boehmite is sequentially added after the sodium hydroxide is dissolved, 0.3g of ethylenediamine is added after the mixture is uniformly stirred, and the mixture is stirred for 30 min. 1.5g of silica sol and 0.03g of the aluminum-rich ZSM-5 seed crystal (SiO) synthesized in example 3 were added2/Al2O3Molar ratio of 8.9), stirring for 2 h. And transferring the obtained silicon-aluminum gel into a reaction kettle, and crystallizing at 180 ℃ for 24 h. The product was centrifuged, washed three times with deionized water and ethanol, and dried at 100 ℃ for 6h to give sample a 4. The XRD pattern of A4 revealed that Z6 was substantially amorphous.
TABLE 1
SiO2/Al2O3Molar ratio of
Example 1
7.8
Example 2
7.0
Example 3
8.9
Example 4
6.1
Example 5
8.5
Example 6
6.5
Example 7
8.2
Example 8
8.8
Comparative example 1
9.7
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