阅读说明：本技术 一种绿色合成纳米晶粒Beta分子筛的方法 (Method for green synthesis of nanocrystalline Beta molecular sieve ) 是由 孙先勇 张伟 柴志波 于 2021-01-13 设计创作，主要内容包括：本发明公开了一种绿色合成纳米晶粒Beta分子筛的方法,属于分子筛的合成方法领域。目前常见的合成Beta分子筛采用模板法合成,不但价格昂贵,而且在焙烧去除模板剂过程中消耗资源,处理废水废气环境污染,同时市场上常规Beta分子筛晶粒尺寸在200nm-300nm之间,本方法通过选择合适的硅源、铝源、碱源、晶种等原料,优化配方和工艺,在不使用模板剂的情况下合成出晶粒尺寸在100nm左右的纳米Beta分子筛,在降低产品成本的同时,也减轻了环保方面的压力,进一步提高产品的竞争力。(The invention discloses a method for green synthesis of a nanocrystalline Beta molecular sieve, and belongs to the field of synthesis methods of molecular sieves. The conventional Beta molecular sieve is synthesized by a template method, so that the price is high, resources are consumed in the process of removing a template agent by roasting, the environmental pollution of waste water and waste gas is treated, and the grain size of the conventional Beta molecular sieve in the market is between 200nm and 300 nm.)

1. A method for green synthesis of a nanocrystalline Beta molecular sieve is characterized by comprising the following steps: selecting proper silicon source, aluminum source, alkali source and seed crystal, and then sequentially carrying out the following steps:

weighing a certain mass of water in a conical flask, adding an alkali source, and starting stirring;

after the alkali source is dissolved, adding an aluminum source, and continuously stirring for 15 minutes;

adding a silicon source to prepare a gel mixture for synthesizing the nano Beta molecular sieve;

fourthly, adding a seed crystal and stirring for 30 minutes;

fifthly, filling the nanometer Beta molecular sieve gel mixture obtained in the step four into a reaction kettle with a polytetrafluoroethylene lining, and crystallizing for a period of time by adopting a programmed heating method to obtain corresponding Beta molecular sieve crystallized slurry;

sixthly, separating the Beta molecular sieve slurry obtained in the step of the fifthly to obtain Beta molecular sieve solid and mother liquor, and drying and roasting the Beta molecular sieve solid to obtain nano Beta molecular sieve raw powder.

2. The method of claim 1, wherein: the alkali source is selected from any one or more of sodium hydroxide and potassium hydroxide.

3. The method of claim 1, wherein: the aluminum source is selected from any one or more of sodium aluminate, aluminum sulfate, aluminum hydroxide or aluminum oxide.

4. The method of claim 1, wherein: the silicon source is selected from any one or more of silica sol, water glass, tetraethyl orthosilicate or silica gel.

5. The method of claim 1, wherein: the molar ratio of the components in the gel mixture obtained in the step four is as follows: SiO 2₂：Al₂O₃Seed crystal of Na₂O/K₂O：H₂O＝1：10～30:0.05～0.1：0.01～0.3：10～150。

6. The method of claim 1, wherein: the programmed heating method is to heat the mixture from normal temperature to 120-180 ℃ at a speed of 2-20 ℃/hour, and the crystallization time is 24-120 hours.

Technical Field

The invention relates to the technical field of molecular sieve synthesis methods, in particular to a synthesis method for green synthesis of a nanocrystalline Beta molecular sieve.

Background

In 1967, mobil corporation disclosed the first synthesis of Beta molecular sieves in sodium-containing silica-alumina gels using tetraethylammonium hydroxide as a template in USP3308069, which have a unique three-dimensional staggered macroporous structure. Compared with the Y-type molecular sieve, the energy ratio of silicon-aluminum substances of the Beta molecular sieve can be adjusted within a range of dozens to hundreds, and the Beta molecular sieve has good structural selectivity, acid catalysis property, hydrothermal stability and excellent performances in the aspects of adsorption, catalysis and the like, and is widely applied to various petrochemical processes such as VOCs adsorption, hydrocracking, burnt base transfer reaction, acetification, isomerization, olefin hydration and the like.

Volatile organic pollutants, namely VOCs, are a general term for volatile organic compounds with melting points lower than room temperature and boiling points between 50 ℃ and 260 ℃, and mainly comprise hydrocarbons, halogenated hydrocarbons, nitrogen hydrocarbons, polycyclic aromatic hydrocarbons with low boiling points and the like. VOCs are widely present in air, soil, water and the like, are various and serious in harm, damage the respiratory system and the immune system of a human body, cause respiratory tract infection of the human body, decline of the immune system and the like, and can cause three-cause effects (carcinogenesis, teratogenesis, mutagenesis) in addition. Moreover, most VOCs can cause photochemical smog to generate, and secondary pollution is formed to cause greater threat and harm to human bodies and the environment. VOCs are treated by various methods, including absorption, catalytic combustion, photocatalytic degradation, adsorption, etc. Compared with other methods for treating VOCs, the adsorption method has unique advantages and can effectively remove VOCs, and the adsorption method is simple to operate; secondly, it is low cost and can be effectively removed for low concentrations of contaminants. Therefore, the adsorption method for treating VOCs is a better choice and is also a method which is widely applied at present. The key of the adsorption method treatment lies in the selection of the adsorbent, and the selection of the adsorbent which is environment-friendly and has good performance is particularly important. And the Beta molecular sieve has the characteristics of high thermal stability and good hydrophobicity, and is an ideal adsorbent for adsorbing VOCs.

For the application of Beta molecular sieves, the most critical issue is the preparation of Beta molecular sieves. The hydrothermal synthesis method is a classical synthesis method of a Beta molecular sieve, and an expensive organic template agent is required to participate in the process to play a role in structure guiding; generally, the yield of the synthesized molecular sieve by the hydrothermal method is 50-80%, so that the crystallization mother liquor after the synthesis of the molecular sieve contains a large amount of unreacted raw material components and molecular sieve microcrystals. Except that a part of the template is adsorbed by the molecular sieve and is slightly decomposed, a part of the template still exists in the mother liquor and is not efficiently utilized, and the template accounts for 50-70% of the raw material cost in the synthesis cost of the molecular sieve. At present, the template mainly comprises tetrapropylammonium hydroxide, n-butylamine, ethylenediamine, tetraethylammonium hydroxide and the like, but the use of the template causes the wastewater of a molecular sieve synthesis mother liquor to become high ammonia nitrogen wastewater which is strong in alkalinity and easy to form colloid, and becomes one of main pollution sources of the molecular sieve synthesis industry. Under the alkaline condition, a part of silicon is remained in the mother liquor and is not fully utilized, and the utilization rate of the silicon is reduced. The silicon content in the mother liquor is large, and free silicon dioxide is not easy to settle, so that the suspended matters of the discharged sewage are easy to exceed the standard, and the sewage treatment difficulty is increased; and the Na2O in the crystallization mother liquor is high, which increases the cost for treating filter residue.

Under the environment of energy conservation and emission reduction and large sustainable development, the template-free method is adopted to synthesize the nano Beta molecular sieve, so that the raw material cost of the molecular sieve can be greatly reduced, the resource waste caused by roasting the template can be avoided, the emission of high ammonia nitrogen wastewater is reduced, the generated nitrogen oxide waste is reduced, the resource is saved, the environmental pressure is reduced, and the method is a green synthesis method.

Disclosure of Invention

The invention aims to make up the defects of the prior art, provides a green synthesis method, and synthesizes the nanocrystalline Beta molecular sieve.

In order to achieve the purpose of the invention, the technical scheme is as follows:

a method for green synthesis of a nanocrystalline Beta molecular sieve is characterized by comprising the following steps: selecting proper silicon source, aluminum source, alkali source and seed crystal, and then sequentially carrying out the following steps:

weighing a certain mass of water in a conical flask, adding an alkali source, and starting stirring;

after the alkali source is dissolved, adding an aluminum source, and continuously stirring for 15 minutes;

adding a silicon source to prepare a gel mixture for synthesizing the nano Beta molecular sieve;

fourthly, adding a seed crystal and stirring for 30 minutes;

fifthly, filling the nanometer Beta molecular sieve gel mixture obtained in the step four into a reaction kettle with a polytetrafluoroethylene lining, and crystallizing for a period of time by adopting a programmed heating method to obtain corresponding Beta molecular sieve crystallized slurry;

sixthly, separating the Beta molecular sieve slurry obtained in the step of the fifthly to obtain Beta molecular sieve solid and mother liquor, and drying and roasting the Beta molecular sieve solid to obtain nano Beta molecular sieve raw powder;

further, the alkali source is selected from any one or more of sodium hydroxide and potassium hydroxide.

Further, the aluminum source is selected from any one or more of sodium aluminate, aluminum sulfate, aluminum hydroxide or aluminum oxide.

Further, the silicon source is selected from any one or more of silica sol, water glass, tetraethyl orthosilicate or silica gel.

Further, the molar ratio of each component in the gel mixture obtained in the fourth step is as follows: SiO 2₂：Al₂O₃Seed crystal of Na₂O/K₂O：H₂O＝1：10～30:0.05～0.1：0.01～0.3：10～150。

Furthermore, the temperature is raised from the normal temperature to 120-180 ℃ at a rate of 2-20 ℃/h, and the crystallization time is 24-120 h.

The invention has the following beneficial effects:

the method adopts a template-free method to synthesize the Beta molecular sieve, synthesizes the molecular sieve with the particle size of about 100nm, has small crystal grains, can greatly reduce the raw material cost of the molecular sieve, simultaneously can avoid resource waste caused by roasting the template agent, reduce the discharge amount of high ammonia nitrogen wastewater and generate the molecular sieve

The nitrogen oxide waste gas can save resources and reduce environmental pressure, and is a green synthesis method.

Drawings

FIG. 1 is an XRD spectrum and an electron micrograph of comparative example 1;

FIG. 2 is an XRD spectrum and an electron micrograph of example 1;

FIG. 3 is an XRD spectrum and an electron micrograph of comparative example 2;

FIG. 4 is an XRD pattern and an electron micrograph of example 2;

FIG. 5 is an XRD spectrum and an electron micrograph of comparative example 3;

FIG. 6 is an XRD pattern and an electron micrograph of example 3.

Detailed Description

The invention will be further described with reference to the following examples, but the scope of the invention is not limited to these examples.

Comparative example 1

4.3g NaOH and 6.7g sodium aluminate are added to 180.2g distilled water and stirred to a clear solution. Slowly dripping 200g of silica sol into the mixed solution under magnetic stirring to form silicate gel A; weighing a certain amount of tetraethylammonium bromide, wherein the added tetraethylammonium bromide is mixed with SiO in the silicate gel₂Dissolving the tetraethylammonium bromide into 30.8g of deionized water, stirring until the tetraethylammonium bromide is completely dissolved to obtain a mixed solution B, slowly adding the solution B into the gel A under the stirring condition to uniformly mix, finally transferring the mixture into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, heating to 130 ℃ from normal temperature at a speed of 5 ℃/h, and then crystallizing for 120 hours at 130 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

example 1

5.6g NaOH was added to 230.8g distilled water, stirred to a clear solution, and 4.3g alumina was added and stirring continued. Slowly dripping 260g of silica sol into the mixed solution under magnetic stirring to form silicate gel; weighing a certain amount of seed crystal, wherein the added seed crystal is mixed with SiO in the silicate gel₂Is 0.03, adding the crystal seeds into silicate gel, stirring, transferring the mixture into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, and collecting the mixture at 10 deg.CRaising the temperature to 140 ℃ in hours, and then crystallizing for 72 hours at the temperature of 140 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

comparative example 2

4.8g NaOH was added to 160.2g distilled water and stirred to a clear solution. Slowly dripping 200g of silica sol into the mixed solution under magnetic stirring to form silicate gel A; weighing a certain amount of tetraethylammonium bromide, wherein the added tetraethylammonium bromide is mixed with SiO in the silicate gel₂Dissolving the tetraethylammonium bromide into 30.8g of deionized water, stirring until the tetraethylammonium bromide is completely dissolved to obtain a mixed solution B, slowly adding the solution B into the gel A under the stirring condition to uniformly mix, finally transferring the mixture into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, heating to 130 ℃ from normal temperature at a speed of 5 ℃/h, and then crystallizing for 96 hours at 130 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

example 2

6.3g KOH was added to 230.8g distilled water and stirred until clear solution, and stirring was continued after adding 4.3g alumina. Slowly dripping 260g of silica sol into the mixed solution under magnetic stirring to form silicate gel; weighing a certain amount of seed crystal, wherein the added seed crystal is mixed with SiO in the silicate gel₂The mass ratio of the crystal seeds is 0.1, the crystal seeds are added into silicate gel and stirred, and finally the mixture is transferred into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, the temperature is raised to 140 ℃ from normal temperature at a rate of 10 ℃/hour, and then the mixture is crystallized for 72 hours at a temperature of 140 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

comparative example 3

4.3g NaOH and 8g sodium aluminate were added to 175.g distilled water and stirred to a clear solution. Slowly dripping 200g of silica sol into the mixed solution under magnetic stirring to form silicateGel A; weighing a certain amount of tetraethylammonium bromide, wherein the added tetraethylammonium bromide is mixed with SiO in the silicate gel₂Dissolving the tetraethylammonium bromide into 30.8g of deionized water, stirring until the tetraethylammonium bromide is completely dissolved to obtain a mixed solution B, slowly adding the solution B into the gel A under the stirring condition to uniformly mix, finally transferring the mixture into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, heating to 130 ℃ from normal temperature at a speed of 5 ℃/h, and then crystallizing for 120 hours at 130 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

example 3

5.3g NaOH was added to 230.8g distilled water, stirred to a clear solution, and 8.7g sodium aluminate was added and stirring was continued. Slowly dripping 260g of silica sol into the mixed solution under magnetic stirring to form silicate gel; weighing a certain amount of seed crystal, wherein the added seed crystal is mixed with SiO in the silicate gel₂The mass ratio of the crystal seeds is 0.05, the crystal seeds are added into silicate gel and stirred, and finally the mixture is transferred into a stainless steel crystallization kettle with a polytetrafluoroethylene lining, the temperature is raised to 160 ℃ from normal temperature at a rate of 10 ℃/hour, and then the mixture is crystallized for 72 hours at a temperature of 160 ℃; separating the product to obtain Beta molecular sieve solid and mother liquor, washing the Beta molecular sieve solid, drying at 85 deg.C for 14h, and roasting at 550 deg.C for 10h to obtain Beta molecular sieve raw powder;

from the XRD patterns of the comparative example and the example, the synthesized Beta molecular sieve in the comparative example and the example are in BEA pure phase and are consistent with the standard spectrum of the Beta molecular sieve, which shows that the Beta molecular sieve with similar physical property can be synthesized even if a template agent is not used, and the method is a green synthesis method. Meanwhile, as can be seen from an electron microscope image, the full-silicon Beta molecular sieve synthesized in the comparative example has the morphology and the size of 200-300nm, while the Beta synthesized in the example is a nanocrystal with the most of the size of 50-100 nm.

Finally, it should be noted that: therefore, although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may be modified or substituted with equivalents without departing from the spirit and scope of the present invention, and all such modifications and improvements are intended to be covered by the following claims.