CN113620307A

CN113620307A - Synthesis method of ZSM-48 molecular sieve with low silica-alumina ratio

Info

Publication number: CN113620307A
Application number: CN202010371926.7A
Authority: CN
Inventors: 邢恩会; 王萍; 方文秀; 毕云飞; 罗一斌
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2020-05-06
Filing date: 2020-05-06
Publication date: 2021-11-09
Anticipated expiration: 2040-05-06
Also published as: CN113620307B

Abstract

The invention discloses a synthesis method of a ZSM-48 molecular sieve with a low silica-alumina ratio, which is characterized in that a first mixture of a silicon source, inorganic alkali and a first organic template agent is subjected to hydrothermal crystallization to obtain a pure silica ZSM-48 molecular sieve with the relative crystallinity of more than or equal to 90 as an intermediate product, an aluminum source, an alkali source and an optionally added second organic template agent are added, the mixture is uniformly mixed to obtain a second mixture for aluminum supplement, and a product is recovered. The method takes cheap diamine as an organic template agent, and can efficiently and stably synthesize the ZSM-48 molecular sieve with the low silica-alumina ratio.

Description

Synthesis method of ZSM-48 molecular sieve with low silica-alumina ratio

Technical Field

The invention relates to a method for synthesizing a ZSM-48 molecular sieve, in particular to a SiO molecular sieve₂/Al₂O₃A method for synthesizing a silicon-aluminum ZSM-48 molecular sieve with the molecular weight less than or equal to 200.

Background

The ZSM-48 molecular sieve with MRE topological structure is a kind of high-silicon zeolite, belonging to orthorhombic system, its pore channel structure is ten-membered ring opened one-dimensional linear pore channels which are not mutually communicated, and the pore channels are mutually connected by five-membered ring, and the diameter of pore channel is 0.56nm x 0.56 nm. The ten-membered ring channels of the ZSM-48 molecular sieve can be regarded as six-membered ring belts formed by 20T atoms, the channels can form two connections among the channels by moving 1/2 units in the channel direction, one connection is a curved chain connection, the other connection is a four-membered ring connection, each tubular channel is adjacent to 4 tubular channels, and various polymorphs can be formed among the channels. Thus, the ZSM-48 molecular sieve is not a code for one material but represents a series of similar tubular channel materials.

Schlenker et al (Nature,1981,294, 340-.

In 1983, US4397827 for the first time discloses the synthesis of a ZSM-48 molecular sieve, the template agent is C2-C12 alkylamine, preferably the mixture of C3-C5 alkylamine and tetramethylammonium hydroxide, and the silicon-aluminum ratio (SiO) of the synthesized ZSM-48 molecular sieve is₂/Al₂O₃Hereinafter, the same) range of 25 to infinity. The synthesized ZSM-48 molecular sieve has a needle-shaped or rod-shaped appearance, and a trace amount of octahedral metastable ZSM-48 precursor exists in a product. Subsequent research results show that when tetramethyl ammonium ions are used as a template agent, NaOH is used as an alkali source, and crystal seeds or other template agents are not added, the synthesized main product is the ZSM-39 molecular sieve, and the pure-phase ZSM-48 molecular sieve cannot be synthesized.

US4423021 discloses a method for synthesizing ZSM-48 molecular sieve with high Si/Al ratio by using diamine of C4-C12 as template agent, wherein the product contains no or little aluminum because of the use of organic template agent different from that of US4397827, and the Si/Al ratio is in the range of 50 to infinity, preferably in the range of 100 to infinity.

Currently, ZSM-48 molecular sieves can be synthesized using a variety of organic templates. For example, N-methylpyridine (US4585747), ethylenediamine (US5961951), alkylamines and tetramethylammonium (CN101330975A), N-diethylhexamethyleneimine quaternary ammonium (CN102040231A), hexamethylenediamine chloride (US7482300/US7625478), 1, 6-hexanediamine or 1, 8-octanediamine (US6923949A) and the like.

In addition to the simple and relatively simple templates described above, a number of structurally complex templates are disclosed. EP-A-142317 discloses specific linear diquaternary amines of the general formulｃAZSM-48 molecular sieve synthesis in the presence of the compound: [ (R)₃N⁺(Z)_m[(R)₃N⁺](X^-)²Wherein each R is an alkyl or heteroalkyl group having 1 to 20 carbon atoms, a cycloalkyl or cycloheteroalkyl group having 3 to 6 carbon atoms, or an aryl or heteroaryl group, Z is an alkylene or heteroalkylene group having 1 to 20 carbon atoms, an alkenylene or heteroalkylene group having 2 to 20 carbon atoms, or an arylenemetal or heteroarylene group, m is 5, 6, 8, 9, or 10, and X-is an anion. CN102910642A discloses a method for synthesizing a ZSM-48 molecular sieve by using dibromohexane, trimethylamine and ethanol as template agents, and the method has the characteristic of low synthesis cost, and the silica-alumina ratio is 150-500.

Generally, the silica to alumina ratio of the molecular sieve product is closely related to the templating agent. The research focus of the existing ZSM-48 molecular sieve is still the synthesis process, and the synthesis process has the following characteristics: 1) the synthesized molecular sieve has high silicon-aluminum ratio, so the application in the aspect of acid catalytic reaction faces certain limitation, even if a template agent with a complex structure and high price is adopted, the silicon-aluminum ratio of the generally synthesized ZSM-48 molecular sieve is more than 100; 2) if a template agent with lower cost is adopted, not only the synthesized ZSM-48 molecular sieve has higher silica-alumina ratio, but also long crystallization time is needed.

The method disclosed in US4585747 synthesizes ZSM-48 molecular sieve by using monomolecular or bimolecular N-methylpyridine as template agent, the feeding silica-alumina ratio is more than 250, and the synthesis time is more than 5 days. The method for synthesizing ZSM-48 disclosed in US5961951 takes cheap ethylenediamine as a template agent, the feeding silica-alumina ratio can be reduced to 200, and the synthesis time is greatly shortened to 65 h. US7482300 and US7625478 disclose a synthesis method of a ZSM-48 molecular sieve with a low silica alumina ratio, which uses expensive hexamethonium chloride as a template agent, and can obtain the ZSM-48 molecular sieve with the silica alumina ratio of about 100 after crystallization for 48 hours with the charge silica alumina ratio of about 100.

The synthesis of the ZSM-48 molecular sieve with low silica-alumina ratio by using different templates is also researched. CN104003413A discloses a method for synthesizing a ZSM-48 molecular sieve by using 1, N-bis (N-methylpyrrolidine) hexane bromide (N is 1-10), wherein the ZSM-48 molecular sieve obtained by the method is a regular rice grain block-shaped molecular sieve consisting of nano rods and has a particle size range500 to 2000nm, and the size of the cubic small crystal grains is about 20 to 50 nm. Reported in microporus and mesoporus materials, 2004, 68(1-3), 97-104 as (CH3)₃N⁺(CH₂)_nN⁺(CH₃)₃Is taken as a template agent, and the raw material composition is SiO₂/Al₂O₃＝60、R/SiO₂A method for synthesizing a ZSM-48 molecular sieve under the condition of 0.1. CN106608635A discloses a method for preparing ZSM-48 molecular sieve, the template agent used is dinitrogen oxacycloalkane dibromide salt or organic matter with similar structure, synthesized SiO₂/Al₂O₃The range is 10 to 50.

In conclusion, although the synthesis of the ZSM-48 molecular sieve with the silicon-aluminum ratio lower than 200 is advanced to a certain extent, the ZSM-48 molecular sieve usually adopts a template agent with a complex structure and high cost, and is not beneficial to the large-scale use of the ZSM-48 molecular sieve; if the organic amine with low cost is used, the ZSM-48 molecular sieve can be synthesized, but the application of the ZSM-48 molecular sieve as an acid catalyst is limited due to the high silica-alumina ratio (generally more than 200).

Disclosure of Invention

The invention aims to provide a method for synthesizing ZSM-48 with a low silica-alumina ratio at low cost without adopting a template agent with a complex structure and high cost.

Therefore, the synthesis method of the ZSM-48 molecular sieve with the low silica-alumina ratio is characterized in that a first mixture of a silicon source, inorganic alkali and a first organic template agent is subjected to hydrothermal crystallization to obtain a pure silica ZSM-48 molecular sieve with the relative crystallinity of more than or equal to 90% as an intermediate product, an aluminum source, an alkali source and a second organic template agent are added, and a second mixture which is uniformly mixed is subjected to hydrothermal aluminum supplement and product recovery; wherein the molar ratio of the first mixture is as follows: m⁺/SiO₂＝0.01～0.30、R1/SiO₂＝0.01～0.50、H₂O/SiO₂5-100, M is an alkali metal, and R1 is a first organic template; the molar ratio of the second mixture is as follows: SiO 2₂/Al₂O₃＝5～500、M⁺/SiO₂＝0.01～0.30、R2/SiO₂＝0.01～0.50、H₂O/SiO₂And R2 is a second organic template agent, wherein R is 5-30.

In the invention, the silicon source is a silicon source which can be stably dispersed in a water phase and form a uniform colloidal solution, and is preferably silica sol, white carbon black, ethyl orthosilicate or water glass. The inorganic base is NaOH or KOH. The first organic template is selected from one or a mixture of ethylenediamine, 1, 3-propanediamine, 1, 4-butanediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine, 1, 8-octanediamine, 1, 9-nonanediamine and the diamine with substituent groups; preferably one or a mixture of ethylenediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine or the diamines with substituent groups; more preferably 1, 6-hexanediamine.

In the invention, the preferable molar ratio of the first mixture is as follows: m⁺/SiO₂＝0.01～0.20、R1/SiO₂＝0.03～0.30、H₂O/SiO₂20-50. The hydrothermal crystallization is to heat the first mixture uniformly mixed in a crystallization kettle to 100-180 ℃, preferably 140-180 ℃, for 4-240 hours, preferably 12-96 hours, so as to achieve the crystallinity of more than or equal to 90%, preferably 95%. The hydrothermal crystallization process can be static crystallization or dynamic crystallization, and dynamic crystallization is preferred. The first mixture is also suitable for promoting the crystallization of the pure silicon molecular sieve by adding a small amount of pure silicon ZSM-48 seed crystals.

In the invention, the pure silicon ZSM-48 molecular sieve refers to a molecular sieve with a silicon-aluminum molar ratio of more than 500 determined by an XRF method, wherein a small amount of aluminum is possibly carried in by a silicon source. Characterization by XRD indicated that the molecular sieve had pure phase ZSM-48 characteristics.

In the invention, the pure silicon ZSM-48 molecular sieve obtained from the first mixture after hydrothermal crystallization is used as an intermediate product, and the intermediate product can be in one of the following forms: (a) a molecular sieve slurry; (b) filtering and washing the molecular sieve filter cake; (c) filtering, washing and drying the molecular sieve raw powder; (d) and filtering, washing, drying and roasting the molecular sieve to remove the first organic template agent.

In the invention, the aluminum source in the second mixture is a clear and transparent aluminum source in an alkaline system, and can promote aluminum to enter a molecular sieve framework under a crystallization condition, so that acidity is generated, and no obvious non-framework aluminum exists. For example, the synthesis of aluminum sources for common molecular sieves: aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium metaaluminate or aluminum sol, preferably sodium metaaluminate and/or aluminum sol.

In the present invention, the second mixture preferably has a molar composition of: SiO 2₂/Al₂O₃＝20～200、M⁺/SiO₂＝0.01～0.20、R2/SiO₂＝0～0.20、H₂O/SiO₂5-20. R2 is a second organic template agent, which can be one or a mixture of ethylenediamine, 1, 3-propanediamine, 1, 4-butanediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine, 1, 8-octanediamine, 1, 9-nonanediamine and the diamine with substituent groups. In the second mixture, the silicon brought by the all-silicon ZSM-48 molecular sieve is completely adopted without adding a new silicon source; when the intermediate product is in the form of (d), a template-free ZSM-48 molecular sieve after filtration, washing, drying and calcination, the second organic template (i.e., R2/SiO) may not be used in the second mixture₂0), aluminum is only supplemented in the presence of an inorganic base such as NaOH and/or KOH, and aluminum is similarly inserted into the framework of a pure silicon ZSM-48 molecular sieve to form framework aluminum and no non-framework aluminum is generated, thereby obtaining a ZSM-48 molecular sieve with a low silica-alumina ratio.

In the invention, the aluminum supplementing process is to treat the second mixture for 1 to 48 hours, preferably 2 to 24 hours at a wide temperature range of 0 to 180 ℃, preferably 20 to 160 ℃. The hydrothermal aluminum supplementing process can be static crystallization or dynamic crystallization, and dynamic crystallization is preferred. The procedure for recovering the product generally comprises washing, filtering, drying and the like, which are well known to those skilled in the art and will not be described in detail herein. The molecular sieve after drying or drying and roasting can be subjected to conventional ammonium exchange and roasting processes to obtain the hydrogen type molecular sieve.

The synthesis method of the ZSM-48 molecular sieve with the low silica-alumina ratio adopts a synthesis route of supplementing aluminum by using the pure silica molecular sieve, and the synthesis route fully utilizes the characteristic that the pure silica ZSM-48 molecular sieve is very easy to synthesize when the low-price diamine is used as an organic template agentFirstly, synthesizing pure silicon ZSM-48 molecular sieve, once the crystal growth of ZSM-48 molecular sieve is complete, its crystal seed guiding action is reinforced, at this time an aluminium source is added, the aluminium can be completely inserted into skeleton to produce skeleton aluminium, and has no obvious non-skeleton aluminium: (²⁷Al MAS NMR spectrum) to produce a low silica to alumina ratio ZSM-48 molecular sieve. The synthesis method has low cost, and can efficiently and stably synthesize the silicon-aluminum ZSM-48 molecular sieve.

Drawings

Figure 1 XRD spectrum of example 1 sample.

FIG. 2 example 1 preparation of samples²⁷Al MAS NMR spectrum.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.

In the examples, the chemical composition of the molecular sieve was determined by X-ray fluorescence.

The relative crystallinity is expressed by percentage according to the ratio of the sum of the peak heights of two characteristic diffraction peaks of 20-24 degrees of 2 theta of an X-ray diffraction (XRD) spectrum of the obtained product and a ZSM-48 molecular sieve standard sample. The ZSM-48 molecular sieve synthesized using the method of example 5 in US4423021 was used as a standard and its crystallinity was determined to be 100%. XRD was measured on a SIMENS D5005X-ray diffractometer at CuK α radiation, 44 kV, 40 mA, scan rate of 2^°In terms of a/minute.

²⁷The Al MAS NMR spectrum is obtained by a Bruker AVANCE III 600 WB type nuclear magnetic resonance spectrometer test, and the test conditions are as follows: the resonance frequency is 78.155MHz, the magic angle rotating speed is 5kHz, the pulse width is 1.6 mus, the cycle delay time is 1s, and the scanning times are 8000 times.

Example 1

400g of silica sol (Shandong Yiming Industrial Co., Ltd., 30% SiO)₂) 7g of NaOH, 48g of 1, 6-hexanediamine (analytical grade, chemical reagents of the national pharmaceutical group Co., Ltd.) and 260g of water were mixed thoroughly and homogeneously, the reaction mixture had the following molar composition: m⁺/SiO₂＝0.1；R/SiO₂＝0.2；H₂O/SiO₂15. The mixture is put into a crystallization kettle and heated to 160 ℃, hydrothermal dynamic crystallization is carried out for 48 hours, and the mixture is filtered, washed and driedAnd drying to obtain pure silicon ZSM-48 molecular sieve raw powder with the crystallinity of 90 percent, and performing hydrothermal aluminum supplement in the next step as an intermediate product.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product, and uniformly mixing 20g of the pure silicon molecular sieve, 2.26g of sodium metaaluminate, 0.8g of NaOH and 53g of water, wherein the mixture has the following molar composition: SiO 2₂/Al₂O₃＝110、M⁺/SiO₂＝0.1、H₂O/SiO₂9. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 150 ℃, and supplementing aluminum for crystallization for 23 hours. After crystallization, a molecular sieve sample with the code B1 is obtained after filtration, washing and drying.

XRD showed that sample B1 was ZSM-48 with 99% relative crystallinity and a silica to alumina ratio of 100 (FIG. 1). From²⁷As can be seen in the Al MAS NMR spectrum (FIG. 2), the complete insertion of aluminum into the framework produced skeletal aluminum, with no significant non-skeletal aluminum.

Comparative example 1

400g of silica sol, 13.56g of sodium metaaluminate, 48g of 1, 6-hexamethylenediamine, 4.8g of NaOH and 315g of water are mixed homogeneously, the mixture having the following molar composition: SiO 2₂/Al₂O₃＝110、M⁺/SiO₂＝0.1、R/SiO₂＝0.2,H₂O/SiO₂And (9) uniformly mixing the mixture, putting the mixture into a crystallization kettle, and heating the mixture to 160 ℃ for hydrothermal crystallization for 50 hours. After crystallization, a molecular sieve comparison sample is obtained through filtering, washing and drying, and the comparison sample is a ZSM-22 molecular sieve with a silica-alumina ratio of 98 through XRD test.

Comparative example 2

The difference from example 1 is that the hydrothermal dynamic crystallization is changed to 12, 24 and 36 hours, and the corresponding ZSM-48 molecular sieve intermediate product crystallinity is 0%, 26% and 78%, respectively. And (3) carrying out hydrothermal aluminum supplement on the three ZSM-48 molecular sieves which are not completely crystallized to respectively obtain three molecular sieve comparison samples. XRD tests show that the three comparative samples are ZSM-5 molecular sieves with the silica-alumina ratio of 98.

Example 2

281g of tetraethoxysilane (containing 28% SiO)₂Beijing chemical reagent company), 10.5g NaOH, 16.5g 1, 6-hexanediamine and 378g water are fully and evenly mixed and reactedThe mixture had the following molar composition: m⁺/SiO₂＝0.2、R/SiO₂＝0.1、H₂O/SiO₂16. The mixture is put into a crystallization kettle, the temperature is raised to 160 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. And directly using molecular sieve slurry (the molecular sieve slurry is subjected to filtration, washing and drying treatment, and the crystallinity of the obtained pure silicon molecular sieve is determined to be 91%) as an intermediate product for the next aluminum supplement after crystallization.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product: the above pure silica molecular sieve slurry containing 20g dry basis was mixed well with 4.9g sodium metaaluminate, 1g naoh, 0.5g 1, 6-hexanediamine and appropriate amount of water, the mixture having the following molar composition: SiO 2₂/Al₂O₃＝51、M⁺/SiO₂＝0.17、R/SiO₂＝0.01、H₂O/SiO ₂20. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 140 ℃, and supplementing aluminum for 24 hours. After crystallization, a molecular sieve sample with the code B2 is obtained after filtration, washing and drying.

XRD showed that sample B2 was ZSM-48 with 98% relative crystallinity and 50% Si/Al ratio.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 3

200g of silica sol, 6.7g of NaOH,18g of 1, 6-hexamethylenediamine and 220g of water are mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.167；R/SiO₂＝0.15；H₂O/SiO ₂20. The mixture is put into a crystallization kettle, the temperature is raised to 140 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. After crystallization, filtering, washing and drying to obtain pure silicon ZSM-48 molecular sieve raw powder with the crystallinity of 93 percent, and taking the pure silicon ZSM-48 molecular sieve raw powder as an intermediate product for the next aluminum supplement.

31g of pure silicon ZSM-48 molecular sieve raw powder was mixed uniformly with 4.8g of sodium metaaluminate, 2g of NaOH, 14g of 1, 6-hexanediamine and 137g of water, the mixture having the following molar composition: SiO 2₂/Al₂O₃＝80，M⁺/SiO₂＝0.15，R/SiO₂＝0.23，H₂O/SiO₂15. Mixing the mixture evenly, putting the mixture into a crystallization kettle to be heatedSupplementing aluminum for 20h at 160 ℃. After crystallization, a molecular sieve sample with the code B3 is obtained after filtration, washing and drying.

XRD showed that sample B3 was ZSM-48 with a relative crystallinity of 105% and a silica to alumina ratio of 78.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 4

200g of silica sol, 10g of NaOH, 12g of 1, 6-hexanediamine and 400g of water are mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.25、R/SiO₂＝0.1、H₂O/SiO ₂30. The mixture is put into a crystallization kettle, the temperature is raised to 160 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. After crystallization, filtering, washing and drying are carried out, and roasting is carried out for 3h at 580 ℃ to obtain the pure silicon ZSM-48 molecular sieve (with the crystallinity degree of 95%) without the template agent, which is used as an intermediate product for carrying out the next hydrothermal aluminum supplement.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product, and uniformly mixing 20g of the pure silicon molecular sieve, 5g of sodium metaaluminate, 1.4g of NaOH and 120g of water, wherein the mixture has the following molar composition: SiO 2₂/Al₂O₃＝50、M⁺/SiO₂＝0.2、H₂O/SiO ₂20. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 160 ℃, and supplementing aluminum for 23 hours. After crystallization, a molecular sieve sample with the code B4 is obtained after filtration, washing and drying.

XRD showed that sample B4 was ZSM-48 with 102% relative crystallinity and 48 Si/Al ratio.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 5

140g of ethyl orthosilicate, 2.2g of NaOH, 16g of 1, 6-hexanediamine and 360g of water are mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.08、R/SiO₂＝0.2、H₂O/SiO ₂30. The mixture is put into a crystallization kettle, the temperature is raised to 160 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. Directly using molecular sieve slurry (filtering, washing and drying the molecular sieve slurry to determine the structure of the obtained pure silicon molecular sieve after crystallizationThe crystallinity is 96 percent) is used as an intermediate product for the next aluminum supplement.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product: the above molecular sieve slurry, containing 40g dry basis, was mixed well with 4.9g sodium metaaluminate, 0.08g NaOH, 8g1, 6-hexanediamine and an appropriate amount of water, the mixture having the following molar composition: SiO 2₂/Al₂O₃＝102、M⁺/SiO₂＝0.05、R/SiO₂＝0.1、H₂O/SiO ₂20. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 80 ℃, and supplementing aluminum for 24 hours. After crystallization, a molecular sieve sample with the code B5 is obtained after filtration, washing and drying.

XRD showed that sample B5 was ZSM-48 with a relative crystallinity of 105% and a silica to alumina ratio of 99.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 6

200g of silica sol, 4g of NaOH, 30g of 1, 6-hexamethylenediamine and 220g of water are mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.1、R/SiO₂＝0.25、H₂O/SiO ₂20. The mixture is put into a crystallization kettle, the temperature is raised to 140 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. After crystallization is finished, the ZSM-48 molecular sieve filter cake is used as an intermediate product to be subjected to aluminum supplement in the next step, and the crystallinity of the molecular sieve is measured to be 95%.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product, and uniformly mixing 58g of pure silicon molecular sieve, 4.8g of sodium metaaluminate, 4.5g of NaOH, 23g of 1, 6-hexamethylene diamine and 310g of water, wherein the mixture has the following molar composition: SiO 2₂/Al₂O₃＝151、M⁺/SiO₂＝0.15、R/SiO₂＝0.2、H₂O/SiO₂18. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 50 ℃, and supplementing aluminum for 36 hours. After crystallization, a molecular sieve sample with the code B6 is obtained after filtration, washing and drying.

XRD showed that sample B6 was ZSM-48 with a relative crystallinity of 105% and a silica to alumina ratio of 140.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 7

200g of silica sol, 4g of NaOH, 16g of 1, 5-pentanediamine and 185g of water are mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.1、R/SiO₂＝0.15、H₂O/SiO₂18. The mixture is put into a crystallization kettle, the temperature is raised to 150 ℃, and hydrothermal dynamic crystallization is carried out for 50 hours. After crystallization is finished, the molecular sieve raw powder obtained after filtration, washing and drying is used as an intermediate product for the next aluminum supplement, and the crystallinity is 95%.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product, and uniformly mixing 40g of pure silicon molecular sieve, 4.8g of sodium metaaluminate, 4.5g of NaOH, 6g of 1, 5-pentanediamine and 250g of water, wherein the mixture has the following molar composition: SiO 2₂/Al₂O₃＝104、M⁺/SiO₂＝0.21、R/SiO₂＝0.08、H₂O/SiO₂21. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 100 ℃, and supplementing aluminum for 24 hours. After crystallization, a molecular sieve sample with the code B7 is obtained after filtration, washing and drying.

XRD showed that sample B7 was ZSM-48 with a relative crystallinity of 101% and a silica to alumina ratio of 98.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

Example 8

195g of silica sol, 4g of NaOH, 20g of 1, 7-heptanediamine and 145g of water were mixed thoroughly and homogeneously, the reaction mixture having the following molar composition: m⁺/SiO₂＝0.1、R/SiO₂＝0.15、H₂O/SiO₂16. The mixture is put into a crystallization kettle, the temperature is raised to 140 ℃, and hydrothermal dynamic crystallization is carried out for 48 hours. After crystallization is finished, the molecular sieve raw powder obtained after filtration, washing and drying is used as an intermediate product for the next aluminum supplement, and the crystallinity is 92%.

And (3) carrying out hydrothermal aluminum supplement on the intermediate product, and uniformly mixing 42g of pure silicon molecular sieve, 4.8g of sodium metaaluminate, 4.5g of NaOH, 7g of 1, 7-heptadiamine and 230g of water, wherein the mixture has the following molar composition: SiO 2₂/Al₂O₃＝109、M⁺/SiO₂＝0.20、R/SiO₂＝0.07、H₂O/SiO₂18. And uniformly mixing the mixture, putting the mixture into a crystallization kettle, heating the mixture to 100 ℃, and supplementing aluminum for 24 hours. After crystallization, a molecular sieve sample with the code B8 is obtained after filtration, washing and drying.

XRD showed that sample B8 was ZSM-48 with 96% relative crystallinity and 101 Si/Al ratio.²⁷The Al MAS NMR spectrum showed that the complete insertion of aluminum into the framework produced framework aluminum, with no significant non-framework aluminum.

The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications can be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.

It should be noted that the various technical features described in the above embodiments can be combined in any suitable manner without contradiction, and the invention is not described in any way for the possible combinations in order to avoid unnecessary repetition.

In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present disclosure.

Claims

1. A synthetic method of ZSM-48 molecular sieve with low silica-alumina ratio is characterized in that a first mixture of a silica source, an inorganic alkali and a first organic template agent is subjected to hydrothermal crystallization to obtain a pure silica ZSM-48 molecular sieve with the relative crystallinity of more than or equal to 90% as an intermediate product, an aluminum source, an alkali source and an optionally added second organic template agent are added, the mixture is uniformly mixed to obtain a second mixture for aluminum supplement, and a product is recovered; wherein the molar ratio of the first mixture is as follows: m⁺/SiO₂＝0.01～0.30、R1/SiO₂＝0.01～0.50、H₂O/SiO₂5-100, M is an alkali metal, and R1 is a first organic template; the molar ratio of the second mixture is as follows: SiO 2₂/Al₂O₃＝5～500、M⁺/SiO₂＝0.01～0.30、R2/SiO₂＝0～0.50、H₂O/SiO₂And R2 is a second organic template agent, wherein R is 5-30.

2. The synthesis method according to claim 1, wherein said first organic template is selected from one or a mixture of ethylenediamine, 1, 3-propanediamine, 1, 4-butanediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine, 1, 8-octanediamine, 1, 9-nonanediamine and said substituted diamines; preferably one or a mixture of ethylenediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine or the diamines with substituent groups; more preferably 1, 6-hexanediamine.

3. The method of synthesis according to claim 1, wherein said intermediate product is in one of the following forms: (a) a molecular sieve slurry; (b) filtering and washing the molecular sieve filter cake; (c) filtering, washing and drying the molecular sieve raw powder; (d) and filtering, washing, drying and roasting to remove the molecular sieve of the first organic template agent.

4. The synthesis method according to claim 1, wherein the molar ratio of the first mixture is: m⁺/SiO₂＝0.01～0.20、R1/SiO₂＝0.03～0.30、H₂O/SiO₂＝20～50。

5. The synthesis process according to claim 1, wherein the inorganic base is NaOH or KOH.

6. The synthesis process according to claim 1, wherein the silicon source is a silicon source which is stably dispersed in an aqueous phase and forms a homogeneous colloidal solution.

7. A synthesis method according to claim 6, wherein the silicon source is selected from silica sol, silica white, ethyl orthosilicate or water glass.

8. The synthesis method according to claim 1, wherein the molar ratio of the second mixture is: SiO 2₂/Al₂O₃＝20～200、M⁺/SiO₂＝0.01～0.20、R2/SiO₂＝0～0.20、H₂O/SiO₂＝5～20。

9. The synthesis method according to claim 1, wherein said second organic template is selected from one or a mixture of ethylenediamine, 1, 3-propanediamine, 1, 4-butanediamine, 1, 5-pentanediamine, 1, 6-hexanediamine, 1, 7-heptanediamine, 1, 8-octanediamine, 1, 9-nonanediamine and said substituted diamines.

10. The method of synthesis according to claim 1, wherein the first organic templating agent is the same as the second organic templating agent.

11. The method of synthesis according to claim 10, wherein the first organic template and the second organic template are both 1, 6-hexanediamine.

12. The synthesis method according to claim 1, wherein the aluminum source is clear and transparent in an alkaline system and can promote aluminum to enter a molecular sieve framework under crystallization conditions.

13. The process of claim 11 wherein said aluminum source is aluminum chloride, aluminum sulfate, aluminum hydroxide, sodium metaaluminate or alumina sol.

14. The process of claim 12 wherein said aluminum source is sodium metaaluminate and/or alumina sol.

15. A synthesis process according to claim 1 wherein a small amount of pure silicon ZSM-48 seed crystals are added to said first mixture.