阅读说明：本技术 一种超声辅助合成多级孔sapo-34分子筛的方法 (Method for synthesizing hierarchical pore SAPO-34 molecular sieve with assistance of ultrasound ) 是由 杨刚 邵川 孙朋飞 于 2020-05-14 设计创作，主要内容包括：本发明提供了一种超声辅助合成多级孔SAPO-34分子筛的方法,包括如下步骤：将一定量的去离子水、铝源、磷源、硅源、模板剂、酸性溶液按照一定的比例、顺序混合并搅拌,老化一定时间后,将老化液进行超声处理一定时间。将上述制得的老化液进行晶化处理,之后洗涤、干燥、焙烧,制得多级孔SAPO-34分子筛催化剂。本发明制备的多级孔SAPO-34分子筛粒径分布均匀、晶化时间短,具有多级孔结构复合的优点,其分子筛表面呈现类沙漏形状；分子筛粒径分布在2-5μm,比表面积≥535m2/g。多级孔状结构有助于为反应物分子提供更多的活性位点,且反应产物扩散出分子筛速度较快；同时分子筛表面的B酸与L酸性中心及酸量较原始分子筛有所改变。(The invention provides a method for synthesizing a hierarchical pore SAPO-34 molecular sieve by ultrasonic assistance, which comprises the following steps: mixing and stirring a certain amount of deionized water, an aluminum source, a phosphorus source, a silicon source, a template agent and an acidic solution in sequence according to a certain proportion, aging for a certain time, and carrying out ultrasonic treatment on the aging solution for a certain time. And crystallizing the prepared aging liquid, and then washing, drying and roasting to prepare the hierarchical pore SAPO-34 molecular sieve catalyst. The hierarchical pore SAPO-34 molecular sieve prepared by the method has the advantages of uniform particle size distribution, short crystallization time and composite hierarchical pore structure, and the surface of the molecular sieve is in a shape similar to an hourglass; the particle size of the molecular sieve is distributed between 2 and 5 mu m, and the specific surface area is more than or equal to 535m 2/g. The multilevel porous structure is beneficial to providing more active sites for reactant molecules, and the diffusion speed of reaction products out of the molecular sieve is higher; meanwhile, the acid centers and the acid amounts of the B acid and the L acid on the surface of the molecular sieve are changed compared with those of the original molecular sieve.)

1. A method for synthesizing a hierarchical pore SAPO-34 molecular sieve by ultrasonic assistance is characterized by comprising the following steps:

(1) respectively weighing required deionized water, an aluminum source, a phosphorus source, a silicon source, a template agent and acid, and uniformly mixing to obtain a sol-gel precursor solution;

(2) and (3) sequentially carrying out constant-temperature water bath aging treatment, ultrasonic treatment and crystallization treatment on the sol-gel precursor solution, and carrying out centrifugal separation, washing, drying, grinding and roasting on the obtained product to obtain the hierarchical porous SAPO-34 molecular sieve catalyst.

2. The method for ultrasonically assisted synthesizing the hierarchical pore SAPO-34 molecular sieve according to claim 1, wherein in the step (S1), the molar ratio of the weighed materials is as follows: (40-120) H₂O：(0.8-1.5)Al₂O₃：(0.4-1.0)P₂O₅：(0.2-0.8)SiO₂: (1.5-5) template agent: (0.1-2.5) acid.

3. The method for ultrasonically assisted synthesizing the hierarchical pore SAPO-34 molecular sieve according to claim 1, wherein the required aluminum source is one or more of aluminum isopropoxide, pseudo-boehmite, aluminum nitrate; the required phosphorus source is one or two of phosphoric acid and ammonium phosphate; the silicon source is one or more of silica sol, gas-phase silica, sodium silicate and water glass; the template agent is one or more of tetraethylammonium hydroxide (TEAOH), Triethylamine (TEA) and morpholine Mor; the required acid is one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, citric acid and oxalic acid.

4. The method for ultrasonically assisted synthesizing the hierarchical pore SAPO-34 molecular sieve according to claim 1, wherein in the step (1), the required deionized water, the aluminum source, the phosphorus source, the silicon source, the template agent and the acid are respectively weighed and uniformly mixed, and specifically comprises the following steps:

(11) taking part of weighed deionized water, and uniformly mixing the deionized water with the weighed phosphorus source to form a first mixed solution;

(12) uniformly mixing the rest part of deionized water with the weighed aluminum source, adding a silicon source, uniformly mixing, adding a template, and uniformly mixing to form a second mixed solution;

(13) and (3) uniformly mixing the first mixed solution and the second mixed solution, adding the weighed acid, and uniformly mixing.

5. The method for ultrasonically assisted synthesizing the hierarchical pore SAPO-34 molecular sieve according to claim 1, wherein in the step (1), the required deionized water, the aluminum source, the phosphorus source, the silicon source, the template agent and the acid are respectively weighed and uniformly mixed, and specifically comprises the following steps:

(11) uniformly mixing the weighed deionized water and a phosphorus source to form a first mixed solution;

(12) uniformly mixing the weighed aluminum source and the template agent, adding a silicon source, and uniformly mixing to form a second mixed solution;

(13) uniformly mixing the first mixed solution and the second mixed solution, adding the weighed acid, and uniformly mixing;

or specifically comprises the following steps:

(11) uniformly mixing the weighed deionized water and the phosphorus source, adding the weighed acid, and uniformly mixing to form a first mixed solution;

(12) uniformly mixing the weighed aluminum source and the template agent, adding a silicon source, and uniformly mixing to form a second mixed solution;

(13) and uniformly mixing the first mixed solution and the second mixed solution.

6. The method for synthesizing the hierarchical pore SAPO-34 molecular sieve by the aid of the ultrasonic waves as claimed in claim 1, wherein the ultrasonic waves are applied for 10-60min in the step (2).

7. The method for synthesizing the hierarchical pore SAPO-34 molecular sieve with the assistance of the ultrasonic waves as claimed in claim 1, wherein the aging time of the constant temperature water bath aging treatment in the step (2) is 120-360 min.

8. The method for synthesizing the hierarchical pore SAPO-34 molecular sieve with the assistance of ultrasound as claimed in claim 1, wherein in the step (2), the crystallization temperature of the crystallization treatment is between 150 ℃ and 300 ℃, and the crystallization time is between 20h and 50 h.

9. The method for synthesizing the hierarchical pore SAPO-34 molecular sieve with the assistance of ultrasound as claimed in claim 1, wherein in the step (2), the drying temperature is between 100 ℃ and 150 ℃ and the drying time is between 8h and 12 h.

10. The method for synthesizing the hierarchical pore SAPO-34 molecular sieve with the assistance of the ultrasonic waves as claimed in claim 1, wherein in the step (2), the calcination temperature is between 500 ℃ and 650 ℃ and the calcination time is between 260 ℃ and 400 min.

Technical Field

The invention relates to the field of synthesis of molecular sieve catalysts, in particular to a method for synthesizing a hierarchical pore SAPO-34 molecular sieve by ultrasonic assistance.

Background

The low-carbon olefins such as ethylene are taken as a mark for measuring the development of the national chemical industry, are mainly prepared by the traditional petroleum route, and people are more and more expected to develop a new route for preparing the low-carbon olefins along with the increasing exhaustion of petroleum resources and the increasing improvement of the environmental protection requirement of the chemical industry. The methanol-to-olefin (MTO) reaction, as the name suggests, is to prepare low-carbon olefins (ethylene and propylene) from methanol. The raw material methanol of the process route can be prepared from coal synthesis gas or other biomass by catalytic pyrolysis, and the source is wide. Therefore, the process for preparing the low-carbon olefin from the methanol has great hope of replacing a petroleum route to prepare the low-carbon olefin.

Because the SAPO-34 molecular sieve has proper acidity and a smaller pore structure, the selectivity of the SAPO-34 molecular sieve on low-carbon olefins (ethylene and propylene) can reach more than 80 percent, and the SAPO-34 molecular sieve is widely applied to the reaction of preparing the low-carbon olefins from methanol. However, due to the tiny pore structure, it is difficult for reactant molecules to enter active sites of the catalyst, and large carbon deposition substances in the product are difficult to diffuse out of catalyst molecules, so that the traditional SAPO-34 molecular sieve is easy to deactivate due to carbon deposition, and has a certain inhibiting effect on the selectivity of low-carbon olefins. Therefore, some mesoporous or macroporous structures are formed on SAPO-34 molecules selectively to form a microporous-mesoporous or microporous-mesoporous-macroporous structure called a hierarchical pore SAPO-34 molecular sieve, so that the service life of the catalyst is prolonged, and the selectivity of the low-carbon olefin is improved.

In patent CN 107697925a, a method for preparing a hierarchical pore SAPO-34 molecular sieve is specifically disclosed, although this method does not require acid or alkali treatment in the synthesis process, the crystallization time of this method is 60h, which consumes a long time and requires a lot of energy. Patent CN 107285342A also relates to a method for preparing a hierarchical pore SAPO-34 molecular sieve by adopting solid acid post-treatment, but the method needs post-treatment, has long synthesis time, more complex synthesis process and lower recovery rate of the hierarchical pore molecular sieve product. Other prior art also has some problems, for example, the mother liquor for synthesizing the molecular sieve has strong alkalinity, needs a large amount of water for cleaning and neutralization, is easy to cause environmental pollution, and wastes water resources.

Disclosure of Invention

The purpose of the invention is as follows: in order to overcome the defects of the prior art, the invention aims to provide a method for synthesizing a hierarchical pore SAPO-34 molecular sieve by ultrasonic assistance, so as to solve the problems of long crystallization time, large particle size, strong alkalinity of a mother liquor for synthesizing the molecular sieve and the like in the conventional process for synthesizing the molecular sieve.

The technical scheme is as follows: the method for synthesizing the hierarchical pore SAPO-34 molecular sieve by the aid of the ultrasonic comprises the following steps:

(1) respectively weighing required deionized water, an aluminum source, a phosphorus source, a silicon source, a template agent and acid, and uniformly mixing to obtain a sol-gel precursor solution;

(2) and (3) sequentially carrying out constant-temperature water bath aging treatment, ultrasonic treatment and crystallization treatment on the sol-gel precursor solution, and carrying out centrifugal separation, washing, drying, grinding and roasting on the obtained product to obtain the hierarchical porous SAPO-34 molecular sieve catalyst.

Preferably, in the step (S1), the molar ratio of each material weighed is: (40-120) H₂O：(0.8-1.5)Al₂O₃：(0.4-1.0)P₂O₅：(0.2-0.8)SiO₂: (1.5-5) template agent: (0.1-2.5) acid.

Further, in the step (S1), the required aluminum source is one or more of aluminum isopropoxide, pseudo-boehmite, and aluminum nitrate; the required phosphorus source is one or two of phosphoric acid and ammonium phosphate; the silicon source is one or more of silica sol, gas-phase silica, sodium silicate and water glass; the template agent is one or more of tetraethylammonium hydroxide (TEAOH), Triethylamine (TEA) and morpholine Mor; the required acid is one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, citric acid and oxalic acid.

Preferably, in the step (1), the required deionized water, aluminum source, phosphorus source, silicon source, template agent and acid are respectively weighed and uniformly mixed, and the method specifically comprises the following steps:

(11) taking part of weighed deionized water, and uniformly mixing the deionized water with the weighed phosphorus source to form a first mixed solution;

(12) uniformly mixing the rest part of deionized water with the weighed aluminum source, adding a silicon source, uniformly mixing, adding a template, and uniformly mixing to form a second mixed solution;

(13) and (3) uniformly mixing the first mixed solution and the second mixed solution, adding the weighed acid, and uniformly mixing.

Preferably, in the step (1), the required deionized water, aluminum source, phosphorus source, silicon source, template agent and acid are respectively weighed and uniformly mixed, and the method specifically comprises the following steps:

(11) uniformly mixing the weighed deionized water and a phosphorus source to form a first mixed solution;

(12) uniformly mixing the weighed aluminum source and the template agent, adding a silicon source, and uniformly mixing to form a second mixed solution;

(13) uniformly mixing the first mixed solution and the second mixed solution, adding the weighed acid, and uniformly mixing; or specifically comprises the following steps:

(11) uniformly mixing the weighed deionized water and the phosphorus source, adding the weighed acid, and uniformly mixing to form a first mixed solution;

(12) uniformly mixing the weighed aluminum source and the template agent, adding a silicon source, and uniformly mixing to form a second mixed solution;

(13) and uniformly mixing the first mixed solution and the second mixed solution.

Preferably, in the step (2), the ultrasonic time is 10-60 min; the aging time of the constant-temperature water bath aging treatment is 120-360 min; the crystallization temperature of the crystallization treatment is between 150 and 300 ℃, and the crystallization time is between 20 and 50 hours; the drying temperature is between 100 ℃ and 150 ℃, and the drying time is between 8h and 12 h; the roasting temperature is between 500 ℃ and 650 ℃, and the roasting time is between 260 ℃ and 400 min.

Has the advantages that: compared with the prior art, the invention has the following advantages:

(1) the synthesized SAPO-34 molecular sieve has a multi-stage pore channel structure, and the surface of the molecular sieve is in an hourglass-like shape; the multilevel porous structure is beneficial to providing more active sites for reactant molecules, and the diffusion speed of reaction products out of the molecular sieve is higher; meanwhile, the acid centers and the acid amounts of the acid B and the acid L on the surface of the molecular sieve are changed compared with those of the original molecular sieve;

(2) ultrasonic-assisted crystallization is adopted in the stage of aging crystallization liquid, the required crystallization time is shorter, the crystallization effect is more excellent, a large amount of energy can be saved, and the crystallinity of the SAPO-34 molecular sieve can be obviously improved; the crystallization product obtained after the ultrasonic treatment has better appearance, higher crystallinity, smaller particle size (distributed in 2-5 mu m), more uniform particle size distribution and larger increase of specific surface area (not less than 535m 2/g);

(3) by elaborately designing the adding sequence of various materials, different raw materials can be mixed more uniformly; meanwhile, the phosphorus source is not mixed with other raw materials in the early stage, so that the nucleation and growth of molecular sieve crystals in the early stage can be inhibited, and the acid is added after the phosphorus source is uniformly mixed, so that the effect of acid pore-forming can be exerted to a greater extent.

(4) By adopting an in-situ synthesis-one-step method, acid is directly added into mother liquor for synthesizing the molecular sieve to prepare the hierarchical pore SAPO-34 molecular sieve, and compared with a post-treatment method (namely obtaining the non-porous SAPO-34 molecular sieve firstly and then carrying out acid-base etching), the method saves the processes of repeated stirring, water washing, drying and roasting, and saves a large amount of energy; the experimental procedure is also much simplified.

Therefore, the synthesis method has great significance and industrial application value.

Drawings

FIG. 1 is an X-ray diffraction pattern of a multi-stage pore SAPO-34 molecular sieve of example 1 of the invention.

FIG. 2 is a scanning electron micrograph of the multi-stage pore SAPO-34 molecular sieve of example 2 of the invention.

FIG. 3 is a scanning electron micrograph of the multi-stage pore SAPO-34 molecular sieve of example 3 of the invention.

FIG. 4 is an X-ray diffraction pattern of the multi-stage pore SAPO-34 molecular sieve of example 3 of the invention.

FIG. 5 is a scanning electron micrograph of the multi-stage pore SAPO-34 molecular sieve of example 4 of the invention.

FIG. 6 is an X-ray diffraction pattern of the multi-stage pore SAPO-34 molecular sieve of example 5 of the invention.

FIG. 7 is a scanning electron micrograph of a multi-stage pore SAPO-34 molecular sieve in example 5 of the invention.

FIG. 8 is an X-ray diffraction pattern of the multi-stage pore SAPO-34 molecular sieve of example 6 of the invention.

FIG. 9 is a scanning electron micrograph of a multi-stage pore SAPO-34 molecular sieve of example 7 of the invention.

FIG. 10 is an X-ray diffraction pattern of a multi-stage pore SAPO-34 molecular sieve of example 8 of the invention.

Detailed Description

Embodiments of the present invention will be described below with reference to specific embodiments and drawings. The following examples are only for clearly illustrating the technical solutions of the present invention, and should not be taken as limiting the scope of the present invention. The following experimental procedures are carried out under specific conditions not shown in the examples, and are generally carried out under conventional conditions or under conditions suggested by other standards.

The embodiment of the invention adopts a characterization instrument which is as follows: the X-ray diffraction adopts a Japanese MiniFlex 600X-ray diffractometer, a Cu target, a tube voltage of 40KV, a tube current of 15mA, a scanning speed of 10 DEG/min and a scanning angle of 5-50 deg. Scanning Electron Microscopy (SEM) used a Japanese Hitachi model S4800. And in the sample preparation process, a small amount of dried molecular sieve sample is coated on the conductive adhesive, the unfixed sample is blown off by an ear washing ball, and then the gold spraying treatment is carried out for 40s, so that the sample preparation is completed.