阅读说明：本技术 一种以稻壳为硅源制备sapo-34分子筛的方法 (Method for preparing SAPO-34 molecular sieve by using rice hulls as silicon source ) 是由 王利军 刘晨 于 2020-08-14 设计创作，主要内容包括：本发明公开了一种以稻壳为硅源制备SAPO-34分子筛的方法。本发明以稻壳为硅源和硬模板剂,通过水热法合成SAPO-34分子筛；具体步骤如下：将稻壳置于马弗炉中在一定温度下热解3-4h得到稻壳灰,以拟薄水铝石为铝源,磷酸为磷源,二乙胺为模板剂,按铝源、磷源、去离子水、稻壳灰、模板剂、SAPO-34分子筛原粉的质量比为10:16:60:(5~8):10:(0.1~0.3)制成晶化液,将晶化液转移至反应釜中再水热晶化,然后将水热之后的料液进行多次离心、洗涤、抽滤、烘干,得到SAPO-34分子筛产品,本发明充分采用了价格低廉的稻壳灰为硅源,实现了硅源的平价替代,既可以降低合成成本,又可实现固体废弃物的高附加值利用。(The invention discloses a method for preparing an SAPO-34 molecular sieve by using rice husks as silicon sources. The method takes rice hulls as a silicon source and a hard template agent, and synthesizes the SAPO-34 molecular sieve by a hydrothermal method; the method comprises the following specific steps: the method comprises the steps of putting rice hulls in a muffle furnace, pyrolyzing the rice hulls for 3-4 hours at a certain temperature to obtain rice hull ash, preparing a crystallization liquid by using pseudo-boehmite as an aluminum source, phosphoric acid as a phosphorus source and diethylamine as a template agent according to the mass ratio of the aluminum source to the phosphorus source to deionized water to the rice hull ash to the SAPO-34 molecular sieve raw powder of 10:16:60 (5-8) to 10 (0.1-0.3), transferring the crystallization liquid to a reaction kettle, carrying out hydrothermal crystallization, centrifuging, washing, suction filtering and drying the hydrothermal liquid for multiple times to obtain the SAPO-34 molecular sieve product.)

1. A method for preparing an SAPO-34 molecular sieve by using rice husks as a silicon source is characterized by comprising the following specific steps:

(1) pretreatment: cleaning and drying the rice hulls, and putting the rice hulls in a muffle furnace for pyrolysis to obtain rice hull ash;

(2) mixing and pre-crystallizing: mixing an aluminum source, a phosphorus source, rice hull ash, a template agent, deionized water and SAPO-34 molecular sieve raw powder in proportion by taking the rice hull ash as a silicon source and a hard template agent and deionized water as a solvent, and stirring for a certain time;

(3) and (3) crystallization: placing the mixture obtained in the step (2) in a polytetrafluoroethylene reaction kettle for hydrothermal reaction, taking out a product after the reaction is finished, centrifuging, washing, performing suction filtration, and drying a filter cake to obtain SAPO-34 molecular sieve coarse powder;

(4) and (3) post-treatment: and (3) roasting the coarse powder of the SAPO-34 molecular sieve in a muffle furnace at high temperature, and removing a template agent to obtain pure SAPO-34 molecular sieve powder.

2. The method as claimed in claim 1, wherein in the step (1), the drying temperature is 60-80 ℃, the pyrolysis temperature is 400-800 ℃, and the pyrolysis time is 2-5 h.

3. The method according to claim 1, wherein in the step (1), the total mass of the rice hull ash is 100%: 80-86wt% of Si, 9-10wt% of Ca, 2-3wt% of K and 0.8-1wt% of Fe.

4. The method of claim 1, wherein in step (2), the aluminum source is pseudoboehmite, the phosphorus source is phosphoric acid, and the templating agent is diethylamine.

5. The method according to claim 4, wherein in the step (2), the mass ratio of the aluminum source, the phosphorus source, the deionized water, the rice hull ash, the template and the SAPO-34 molecular sieve raw powder is 10:16:60 (5-8: 10) (0.1-0.3).

6. The method of claim 1, wherein in step (2), the pre-crystallization stirring time is 2-3 hours.

7. The method of claim 1, wherein in the step (3), the hydrothermal reaction temperature is 195-205 ℃ and the hydrothermal time is 48-72 h.

8. The method as claimed in claim 1, wherein in the step (3), the calcination temperature is 540-.

Technical Field

The invention belongs to the technical field of inorganic non-metallic material synthesis, and particularly relates to a method for preparing an SAPO-34 molecular sieve by using rice husks as silicon sources.

Background

The zeolite is a crystalline aluminosilicate mineral, sharing SiO by corners₄ ^-And AlO₄ ^-A tetrahedron. Many zeolites have a three-dimensional framework core and cage composed of nanostructures, resulting in a higher specific surface area. Small reactant molecules can diffuse into the microporous system of Zeo and react at internal acid sites. These acids are located in the zeolite boneThe shelves may be size and shape selective catalytic. Thus, zeolites are widely used as heterogeneous catalysts and have played an important role in the chemical industry. The SAPO-34 molecular sieve has an acid center with medium strength and an eight-membered ring microporous structure, and shows excellent catalytic performance in the reaction of preparing low-carbon olefin from methanol.

Rice is a typical silicon-loving plant, and rice hulls contain a large amount of silicon sources. Rice hulls are the largest number of by-products of rice processing and comprise approximately 20% of rice by weight. Worldwide rice production is about 6 million tons per year and produces over 1 million tons of rice hulls. Most agricultural wastes are burned in farmlands or open air, which not only occupies land resources, but also releases a large amount of harmful substances, resulting in environmental pollution. If the rice hulls are reasonably developed and utilized, the problem of environmental pollution can be solved, and a considerable amount of silicon sources can be provided for the development of high and new technology industries. The silicon element in the rice hulls is generally present as amorphous silica, while the silica is in the form of a hydrate (SiO)₂·mh₂O) is present in the tissues of the rice hulls as one of the components of the cells and cell walls, accounting for 90% -95% of the total silicon content of the rice hulls, while the silicic acid content accounts for 0.5% -0.8% of the total silicon content, and the colloidal silicic acid accounts for 0.00% -0.33%, wherein the silicon of the xylem is present in the form of monosilicic acid. At present, the main focus of development and utilization of rice hull silicon is still how to extract silicon dioxide from rice hulls, and the synthesis of molecular sieves such as A-type molecular sieves and P-type molecular sieves by taking the rice hull silicon as a raw material has been reported.

Chinese patent CN107640775B discloses a method for preparing ZSM-5 molecular sieve by using solid waste, which also takes rice hull ash as a silicon source, but synthesizes high-silicon ZSM-5 molecular sieve.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a method for preparing an SAPO-34 molecular sieve by using rice husks as a silicon source; the invention fully adopts the cheap rice hull ash as the silicon source, realizes the flat substitution of the silicon source, can reduce the synthesis cost, and can realize the high added value utilization of the solid waste. The method has the advantages of low raw material price, low requirement on technical equipment, simple operation, uniform product particles, high yield and easy realization of industrialization, and provides reference value for resource utilization of agricultural solid wastes. The CHA-type SAPO-34 molecular sieve synthesized by the method has smaller pore diameter and stronger adaptability to MTO reaction compared with ZSM-5 molecular sieve.

The technical scheme of the invention is specifically introduced as follows.

A method for preparing an SAPO-34 molecular sieve by using rice husks as a silicon source comprises the following specific steps:

(1) pretreatment: cleaning and drying the rice hulls, and putting the rice hulls in a muffle furnace for pyrolysis to obtain rice hull ash;

(2) mixing and pre-crystallizing: mixing an aluminum source, a phosphorus source, rice hull ash, a template agent, deionized water and SAPO-34 molecular sieve raw powder in proportion by taking the rice hull ash as a silicon source and a hard template agent and deionized water as a solvent, and stirring for a certain time;

(3) and (3) crystallization: placing the mixture obtained in the step (2) in a polytetrafluoroethylene reaction kettle for hydrothermal reaction, taking out a product after the reaction is finished, centrifuging, washing, performing suction filtration, and drying a filter cake to obtain SAPO-34 molecular sieve coarse powder;

(4) and (3) post-treatment: and (3) roasting the coarse powder of the SAPO-34 molecular sieve in a muffle furnace at high temperature, and removing a template agent to obtain pure SAPO-34 molecular sieve powder.

In the invention, in the step (1), the drying temperature is 60-80 ℃, the pyrolysis temperature is 400-800 ℃, and the pyrolysis time is 2-5 h. Preferably, the pyrolysis temperature is 500-.

In the present invention, in the step (1), the total mass of the rice hull ash is 100%: si accounts for 80-86wt%, Ca accounts for

9-10wt%, K2-3 wt%, Fe 0.8-1 wt%.

In the invention, in the step (2), an aluminum source is pseudo-boehmite, a phosphorus source is phosphoric acid, and a template agent is diethylamine.

In the invention, in the step (2), the mass ratio of the aluminum source, the phosphorus source, the deionized water, the rice hull ash, the template agent and the SAPO-34 molecular sieve raw powder is 10:16:60 (5-8) to 10 (0.1-0.3).

In the invention, in the step (2), the pre-crystallization stirring time is 2-3 h.

In the invention, in the step (3), the hydrothermal reaction temperature is 195-205 ℃, and the hydrothermal time is 48-72 h.

In the invention, in the step (3), the roasting temperature is 540-.

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

according to the invention, rice hull ash obtained by pyrolyzing rice hulls which are agricultural solid wastes is used as a silicon source and a hard template agent, and the SAPO-34 molecular sieve is prepared by a simple and feasible hydrothermal method, so that resource utilization of the solid wastes can be realized, and certain environmental benefits are achieved;

the experimental operation is simple, the requirement on technical equipment is low, and the prepared SAPO-34 molecular sieve has regular appearance and uniform particle size and is easy to realize industrialization.

Drawings

FIG. 1 is an XRD pattern of rice hull ash obtained by pyrolysis at different temperatures in examples 1 to 5 of the present invention.

FIG. 2 is SEM pictures of parts of rice hull ash obtained by pyrolysis at different temperatures in examples 1 to 5 of the present invention.

FIG. 3 is an SEM photograph of a sample obtained in example 1 of the present invention.

FIG. 4 is an SEM photograph of a portion of a sample obtained in example 1 of the present invention.

Detailed Description

The invention will be further explained in more detail below with reference to the figures and examples, without limiting the scope of the invention thereto.