阅读说明：本技术 一种快速合成无铝Sn-Beta分子筛的方法 (Method for rapidly synthesizing aluminum-free Sn-Beta molecular sieve ) 是由 杨晓梅 周利鹏 吕斌 陈旭 于 2021-03-30 设计创作，主要内容包括：本发明属于分子筛合成技术领域,涉及一种快速合成无铝Sn-Beta分子筛的方法。该方法通过向Sn-Beta分子筛合成体系中加入少量碱金属盐或碱土金属盐加快其晶化,可显著缩短水热晶化时间。(The invention belongs to the technical field of molecular sieve synthesis, and relates to a method for quickly synthesizing an aluminum-free Sn-Beta molecular sieve. The method accelerates the crystallization by adding a small amount of alkali metal salt or alkaline earth metal salt into the Sn-Beta molecular sieve synthesis system, and can obviously shorten the hydrothermal crystallization time.)

1. A method for rapidly synthesizing an aluminum-free Sn-Beta molecular sieve is characterized in that a silicon source is mixed with tetraethylammonium hydroxide serving as an organic template, alkali metal or alkaline earth metal salt and a Sn source are added into the mixture, hydrofluoric acid or ammonium fluoride is added as a mineralizer after stirring and reacting for a certain time, dealuminized Beta or pure Si-Beta is added as a seed crystal, the mixture is uniformly mixed and then is put into a molecular sieve crystallization kettle, and the molecular sieve crystallization kettle is placed in an oven with the temperature of 140-; taking out, cooling to room temperature, washing with distilled water, drying, and roasting to remove the template agent to obtain the Sn-Beta molecular sieve.

2. The method for rapid synthesis of aluminum-free Sn-Beta molecular sieves according to claim 1, wherein the alkali metal or alkaline earth metal salt used comprises Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ba²⁺Chlorides, sulfates, nitrates, acetates.

3. The method for rapidly synthesizing the aluminum-free Sn-Beta molecular sieve according to claim 1, wherein the alkali metal or alkaline earth metal salt is added in a molar ratio of the alkali metal or alkaline earth metal ions Me to Sn, i.e., Me/Sn is 0.25-5.

4. The method for rapid synthesis of an aluminum-free Sn-Beta molecular sieve of claim 1, wherein the alkali or alkaline earth metal salt and the Sn source are dissolved in water and added together; or adding the components separately and one by one.

Technical Field

The invention relates to a method for quickly synthesizing an Sn-Beta molecular sieve, belonging to the technical field of molecular sieve synthesis.

Background

Zeolite molecular sieves are a class of microporous silicate crystal materials with high specific surface area and regular pore structure, and have wide application in the fields of adsorption, separation and catalysis. The Beta molecular sieve belongs to BEA configuration and has a twelve-membered ring three-dimensional channel system. The Si/Al ratio of the silicon-aluminum Beta molecular sieve can be changed in a larger range, so that the acidity of the silicon-aluminum Beta molecular sieve is wide in modulation range and plays an important role in the field of petrochemical industry. When Al in the framework is replaced by other metals such as Sn, Ti, Zr and the like, the aluminum-free metal silicate Beta molecular sieve is obtained, and because the metal silicate Beta molecular sieve has unique oxidation-reduction property and strong Lewis acidity, the metal silicate Beta molecular sieve has excellent catalytic performance in important oxidation reaction, reduction reaction and Lewis acid catalytic reaction. For example, the Sn-Beta molecular sieve shows excellent catalytic activity and selectivity in Baeyer-Villiger oxidation, olefin epoxidation, Meerwein-ponndorf-Verley reduction and other oxidation-reduction reactions; in addition, with the increasing attention of people to the utilization of biomass renewable resources, the Sn-Beta molecular sieve has unique catalytic performance in the reaction of catalyzing biomass sugar to be converted into important platform compounds and high-value-added chemicals, and can efficiently catalyze glucose to be isomerized into fructose and six-carbon sugars such as glucose and sucrose to be converted into lactic acid or lactate and the like.

Currently, there are two methods for synthesizing Sn-Beta molecular sieves: the post-synthesis method adopts a silicon-aluminum Beta molecular sieve as a matrix, generates T-vacancy through post-treatment dealumination, and then implants Sn into the T-vacancy to obtain the Sn-Beta molecular sieve. The direct synthesis method generally obtains the Sn-Beta molecular sieve by direct hydrothermal synthesis in a fluorine-containing system. Compared with the Sn-Beta molecular sieve prepared by a post-synthesis method, the Sn-Beta molecular sieve synthesized in a fluorine-containing system has less defects, so that the Sn-Beta molecular sieve is more water-resistant and has more advantages in a water reaction system. However, when the existing hydrothermal synthesis method is adopted to synthesize the Sn-Beta molecular sieve, the Sn atom diameter is far larger than the Si atom diameter, the crystallization time is long, and the crystallization time is often 20 to 40 days, which severely limits the application of the Sn-Beta molecular sieve, so that the needs of accelerating the crystallization of the Sn-Beta molecular sieve and shortening the synthesis time are urgently needed.

The conventional hydrothermal synthesis of the Sn-Beta molecular sieve is generally that a silicon source is mixed with tetraethylammonium hydroxide serving as an organic template, then the Sn source is added into the mixture, after a period of reaction, a mineralizer hydrofluoric acid or ammonium fluoride is added, and then the dealuminated Beta molecular sieve or the pure silicon Beta molecular sieve is added to be used as a seed crystal. And after uniform mixing, putting the gel into a molecular sieve crystallization kettle, crystallizing for a certain time in an oven at the temperature of 140-. However, the crystallization time is long during synthesis, and particularly, crystallization is often required for ten days when the Sn content in the gel is high.

Disclosure of Invention

The invention aims to provide a method for quickly synthesizing an aluminum-free Sn-Beta molecular sieve, which can remarkably shorten the hydrothermal crystallization time by adding a small amount of alkali metal salt or alkaline earth metal salt into a Sn-Beta molecular sieve synthesis system to accelerate the crystallization of the Sn-Beta molecular sieve.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for rapidly synthesizing an aluminum-free Sn-Beta molecular sieve is characterized in that alkali metal salt or alkaline earth metal salt is added into gel of a conventional hydrothermal synthesis Sn-Beta molecular sieve to accelerate the crystallization process of the Sn-Beta molecular sieve and shorten the time required by crystallization, and the specific synthesis steps are as follows: mixing a silicon source and an organic template tetraethylammonium hydroxide, adding an alkali metal or alkaline earth metal salt and a Sn source into the mixture, stirring and reacting for a certain time, then adding hydrofluoric acid or ammonium fluoride as a mineralizer, then adding dealuminized Beta or pure Si-Beta as a seed crystal, uniformly mixing, putting into a molecular sieve crystallization kettle, and placing in an oven at 140 ℃ and 150 ℃ for crystallization; taking out, cooling to room temperature, washing with distilled water, drying, and roasting to remove the template agent to obtain the Sn-Beta molecular sieve.

Compared with the conventional Sn-Beta molecular sieve synthesized without adding alkali metal or alkaline earth metal salt, the molecular sieve synthesized by the method has the advantages that the complete crystallization time is obviously shortened, and the molecular sieve is used for catalyzing the reaction of preparing lactate by converting hexose and shows higher selectivity.

Further, the alkali metal or alkaline earth metal salt used includes Li⁺、Na⁺、K⁺、Mg²⁺、Ca²⁺、Ba²⁺Chlorides, sulfates, nitrates, acetates.

Furthermore, the addition amount of the alkali metal or alkaline earth metal salt is the molar ratio of the alkali metal or alkaline earth metal ions Me to Sn, namely Me/Sn is 0.25-5.

Further, the alkali metal or alkaline earth metal salt and the Sn source may be dissolved in a solvent such as water, and added together; or adding the components separately and one by one.

Compared with the prior art, the invention has the beneficial effects that:

the addition of a small amount of alkali metal salt or alkaline earth metal salt can obviously change the property of colloid in the colloid forming process and promote the polymerization of silicate and other species, thereby accelerating the nucleation and growth of the Sn-Beta molecular sieve and shortening the time required by crystallization.

Drawings

FIG. 1 is an XRD pattern of a Sn-Beta molecular sieve, wherein curve (a) is an XRD pattern of a Sn-Beta molecular sieve synthesized in example 4, and curve (b) is an XRD pattern of a Sn-Beta molecular sieve synthesized in a comparative example;

FIG. 2 is a scanning electron micrograph of the Sn-Beta molecular sieve synthesized in example 4;

FIG. 3 is a scanning electron micrograph of a Sn-Beta molecular sieve synthesized in the comparative example.

Detailed Description

The technical solutions and effects of the present invention will be further described with reference to the drawings and specific embodiments, but the scope of the present invention is not limited thereto.

Comparative example

And synthesizing the Sn-Beta molecular sieve by adopting a conventional hydrothermal method. The method specifically comprises the following steps: adding ethyl silicate into tetraethyl ammonium hydroxide (TEAOH) aqueous solution under stirring at room temperature, stirring for 1.5 h, and adding SnCl₄·5H₂Continuously stirring the O water solution to evaporate the generated ethanol and excessive water, then adding hydrofluoric acid, and finally adding Beta seed crystal (accounting for SiO)₂4% of mass) and mixed uniformly. The obtained gel has a ratio of 0.01SnO₂/1.0SiO₂/0.54TEAOH/0.54HF:7.5H₂And O. And crystallizing the gel at 140 ℃ for 20 days, washing and separating to obtain Sn-Beta molecular sieve raw powder, roasting at 550 ℃ for 24 hours in air atmosphere, and removing the template agent to obtain the prepared molecular sieve sample. The crystallinity of this sample (XRD pattern shown in FIG. 1, and scanning electron micrograph shown in FIG. 3) was defined as 100%, and the crystallinity of the other samples was the relative value to which it was compared.

Example 1

Adding ethyl silicate into tetraethyl ammonium hydroxide (TEAOH) aqueous solution under stirring at room temperature, stirring for 1.5 h, and adding SnC₄·5H₂Continuously stirring the water solution of O and sodium chloride to evaporate the generated ethanol and excessive water, then adding hydrofluoric acid, and finally adding Beta seed crystal (SiO in the content of the Beta seed crystal)₂4% of mass) and mixed uniformly. The proportion of the obtained gel is 0.01NaCl/0.01SnO₂/1.0SiO₂/0.54TEAOH/0.54HF:7.5H₂O。The gel was crystallized at 140 ℃ for 5 days, and the other steps were the same as in comparative example 1, and the prepared sample was pure Beta structure by XRD characterization. The relative crystallinity of this sample was 97%.

Example 2

This example is different from example 1 in that potassium chloride is used instead of sodium chloride, and the rest is the same as example 1. The relative crystallinity of the obtained Sn-Beta molecular sieve is 102 percent.

Example 3

This example is different from example 1 in that lithium chloride is used instead of sodium chloride, and the rest is the same as example 1. The relative crystallinity of the obtained Sn-Beta molecular sieve is 92 percent.

Example 4

This example is different from example 1 in that magnesium chloride is used instead of sodium chloride, and the rest is the same as example 1. The relative crystallinity of the obtained Sn-Beta molecular sieve is 121%, and XRD patterns and scanning electron microscope pictures of a sample are shown in figures 1 and 2.

Example 5

This example is different from example 1 in that calcium chloride is used instead of sodium chloride, and the rest is the same as example 1. The relative crystallinity of the obtained Sn-Beta molecular sieve is 103 percent.

Example 6

This example is different from example 1 in that barium chloride is used instead of sodium chloride, and the rest is the same as example 1. The relative crystallinity of the obtained Sn-Beta molecular sieve is 110%.

Example 7

This example is different from example 4 in that the Mg/Sn ratio in the gel is 0.25, and the rest is the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 103 percent.

Example 8

This example is different from example 4 in that the Mg/Sn ratio in the gel is 0.5, and the rest is the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 110%.

Example 9

This example is different from example 4 in that the Mg/Sn ratio in the gel is 2.5, and the rest is the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 108 percent.

Example 10

This example is different from example 4 in that the Mg/Sn ratio in the gel is 5, and the rest is the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 96 percent.

Example 11

This example is different from example 4 in that magnesium sulfate is used instead of magnesium chloride, and the rest is the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 101 percent.

Example 12

This example is different from example 4 in that magnesium chloride was replaced with magnesium nitrate, and the rest was the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 104 percent.

Example 13

This example is different from example 4 in that magnesium acetate was used instead of magnesium chloride, and the rest was the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 98 percent.

Example 14

This example is different from example 4 in that the crystallization time was 1 day, and the rest was the same as example 4. The relative crystallinity of the obtained Sn-Beta molecular sieve is 76%.

Example 15

When the sample prepared in the comparative example is used as a catalyst to catalyze the reaction of converting glucose into methyl lactate, the reaction is carried out for 15 h at 120 ℃, and the yield of methyl lactate is 20%; under the same reaction conditions, when the sample prepared in example 4 was used as a catalyst, the yield of methyl lactate was increased to 44%.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.