CN115784252A - Preparation method of mesoporous ZSM-5 molecular sieve - Google Patents
Preparation method of mesoporous ZSM-5 molecular sieve Download PDFInfo
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- CN115784252A CN115784252A CN202310053044.XA CN202310053044A CN115784252A CN 115784252 A CN115784252 A CN 115784252A CN 202310053044 A CN202310053044 A CN 202310053044A CN 115784252 A CN115784252 A CN 115784252A
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Abstract
The invention relates to a preparation method of a mesoporous molecular sieve, in particular to a preparation method of a mesoporous ZSM-5 molecular sieve, which comprises the following steps: (1) Preparing an alkaline system solution mixed by inorganic alkali and weak acid salt; (2) Adding a ZSM-5 molecular sieve into the alkaline system solution prepared in the step (1), and stirring at the temperature of 25-95 ℃; (3) Filtering, washing and drying the sample prepared in the step (2); (4) Preparing an acidic system solution mixed by weak acid and weak acid salt, and keeping the pH value of the acidic system solution within the range of 2.0-6.0; (5) And (4) adding the sample obtained in the step (3) into the acidic system solution prepared in the step (4) according to the solid-to-liquid ratio of 1-100, stirring at 25-95 ℃, and filtering, washing and drying the obtained product to obtain the product. The invention is a molecular sieve post-treatment modification method with economy, high efficiency, high specific surface area and complete microporous structure.
Description
Technical Field
The invention relates to a modification method of a mesoporous molecular sieve, belongs to the field of molecular sieve modification, and particularly relates to a preparation method of a mesoporous ZSM-5 molecular sieve.
Background
The mesoporous ZSM-5 molecular sieve is a hierarchical pore molecular sieve material which has a secondary mesoporous system besides inherent microporous pore channels of the molecular sieve. The introduction of mesopores into the molecular sieve crystals improves the mass transfer rate of reactant or product molecules within the molecular sieve channels and increases the number of accessible pores. For molecules which react in the microporous pore channel, the diffusion path length of the guest molecules in the pore channel of the molecular sieve is shortened, and the mass transfer rate is improved. For the reaction related to macromolecules, the microporous molecular sieve can only react on an orifice due to the problem of the limitation of the size of a pore passage, and mesopores are introduced into the microporous molecular sieve to expose a large number of active centers on the outer surface of the molecular sieve, so that the accessibility of acid sites on the surface of the molecular sieve is increased, and the effective utilization rate of the active sites is improved. The mesopores in the molecular sieve crystal can make up the defect of the microporous molecular sieve in the diffusion limitation, and provide a proper space structure for macromolecular reaction.
Appl Catal (2001, 219, 33-43) forms a relatively regular mesoporous structure in the molecular sieve crystal by alkali selective removal of silicon element in the molecular sieve framework, and the specific surface area of the modified mesopores is from 7m 2 The/g is increased to 115m 2 A specific surface area of the micropores is from 296m 2 The/g is reduced to 205m 2 (iv) g. Although the specific surface area of the micropores remains more, the mesopore content is still lower.
The sample obtained in patent CN104229824A has a mesoporous specific surface area of only 170m 2 About/g, the total specific surface area is only 410m 2 And about/g.
The ZSM-5 molecular sieve prepared by the patent CN101428817A has the maximum mesoporous specific surface area of 217m 2 About/g, but the specific surface area of micropores is seriously damaged, and is only 141m 2 In terms of a/g ratio, this greatly reduces the reactivity of the molecular sieve.
Patent CN104628011A gave the highest 225m 2 The mesoporous specific surface area per gram is only 474m but the highest total specific surface area 2 /g。
The mesoporous specific surface area of patent CN102464336A can be up to 300m 2 Per g, the specific surface area of micropores can be reserved at least 220m 2 However, the pore diameter is only about 3.5 nm.
At present, the reported literature and patent about ZSM-5 molecular sieve post-treatment mainly use alkali to destroy the skeleton structure of the ZSM-5 molecular sieve to manufacture mesopores, increase the specific surface area of the mesopores and enlarge the aperture of the ZSM-5 molecular sieve, thereby improving the diffusion of substances in the molecular sieve crystal and achieving the purpose of improving the catalytic performance. However, the crystal structure of the prior art is seriously damaged in the alkali treatment process, and the result of the damage is that a great deal of micropores are lost, and the reactive centers of the zeolite are reduced. And a large amount of extra-framework aluminum species are enriched on the surface of the molecular sieve, the molecular sieve is easy to generate carbon deposition in catalytic cracking, the application of the molecular sieve in a catalytic cracking process is limited, the specific surface area is too low, and the catalytic activity of the molecular sieve is seriously reduced. At present, ZSM-5 molecular sieve materials with high mesoporous specific surface area and complete microporous structures are yet to be developed.
Disclosure of Invention
The invention aims to provide a preparation method of a mesoporous ZSM-5 molecular sieve. Aiming at the problems of serious damage of a crystal structure, low specific surface area of micropores and low catalytic activity in the prior art, the method for post-treating and modifying the molecular sieve is economic, efficient, high in specific surface area and complete in micropore structure.
The preparation method of the mesoporous ZSM-5 molecular sieve provided by the invention comprises the following steps:
(1) Preparing an alkaline system solution mixed by inorganic alkali and weak acid salt, and keeping the pH value of the alkaline system solution within the range of 7.0-10.0;
(2) Adding a ZSM-5 molecular sieve into the alkaline system solution prepared in the step (1) according to the solid-to-liquid ratio of 1-15, and stirring at 25-95 ℃ for 60-360 min;
(3) Filtering, washing and drying the sample prepared in the step (2);
(4) Preparing an acidic system solution mixed by weak acid and weak acid salt, and keeping the pH value of the acidic system solution within the range of 2.0-6.0;
(5) And (3) adding the sample obtained in the step (3) into the acidic system solution prepared in the step (4) according to the solid-to-liquid ratio of 1-100, stirring at 25-95 ℃ for 60-600 min, and filtering, washing and drying the obtained product to obtain the modified mesoporous ZSM-5 molecular sieve.
The ZSM-5 molecular sieve used in the invention is a ZSM-5 molecular sieve without mesopores as a raw material, and the product is a ZSM-5 molecular sieve rich in mesopores.
The inorganic alkali in the alkaline system solution in the step (1) is one or two of sodium hydroxide or potassium hydroxide; the weak acid salt is one or more of sodium acetate, potassium acetate or potassium citrate.
The molar ratio of the weak acid salt to the inorganic base in the alkaline system solution in the step (1) is 1-10.
The molar ratio of the weak acid salt to the inorganic base in the alkaline system solution in the step (1) is 3-6.
The pH of the alkaline system solution is preferably 8.0 to 9.0.
In the step (2), the ZSM-5 molecular sieve is added into the alkaline system solution prepared in the step (1), and the solid-to-liquid ratio is 1-15, preferably 8-10.
Adding the ZSM-5 molecular sieve into the alkaline system solution in the step (2), and then stirring at the temperature of 25-95 ℃, preferably 55-85 ℃; the stirring time is 60min-360min, preferably 90min-240min.
The weak acid in the acidic system solution in the step (4) is one or two of acetic acid or citric acid; the weak acid salt is one or more of sodium acetate, sodium citrate, potassium acetate or potassium citrate.
The pH of the acidic system solution is in the range of 2.0-6.0, preferably 3.0-4.0.
And (5) in the step (4), the molar ratio of the weak acid salt to the weak acid in the acidic system solution is 1-5.
The molar ratio of the weak acid salt to the weak acid in the acidic system solution in the step (4) is preferably 2-3.
In the step (5), the sample obtained in the step (3) is added into the acidic system solution prepared in the step (4), and the solid-to-liquid ratio is 1-100, preferably 40-80.
In the step (5), the sample obtained in the step (3) is added into the acidic system solution prepared in the step (4) to be stirred, and the stirring temperature is 25-95 ℃, and preferably 55-85 ℃; the stirring time is 60min-600min, preferably 240min-480min.
Compared with the prior art, the invention has the following beneficial effects:
the mesoporous is generated by destroying the microporous structure of the molecular sieve only depending on the inorganic alkali solution environment, so that a great amount of loss of micropores is inevitably caused, and the reaction active center of the molecular sieve is reduced. However, the treatment method provided by the invention is carried out in an alkaline system solution prepared from inorganic base and weak acid salt. In the alkali treatment process of the molecular sieve, the free weak acidic radical can promote the generation of a mesoporous structure and can play a certain role in stabilizing and protecting a microporous structure; the subsequent acid treatment is carried out in an acid system solution prepared from weak acid and weak acid salt, and amorphous aluminum in the molecular sieve crystal is eluted, so that the aims of loosening the pore channel and increasing the total specific surface area are fulfilled. Therefore, the mesoporous ZSM-5 molecular sieve prepared by the invention has outstanding specific surface area and unique structure.
The mesoporous size of the product obtained by the method is more than 25% larger than that of the product obtained by the method in the patent CN102874840A, and the mesoporous volume is more than 28% larger than that of the product obtained by the method in the patent CN 104628011A. The product of the invention has a pore diameter more than 42% larger than that of CN 102464336A. The mesoporous material has more complete micropores while providing a higher-quality mesoporous product, and the preparation raw materials are cheap and easy to obtain, so that the mesoporous material is suitable for large-scale industrial production.
Drawings
FIG. 1 is an XRD spectrum of the mesoporous ZSM-5 molecular sieve obtained in example 1.
FIG. 2 is a pore size distribution diagram of the mesoporous ZSM-5 molecular sieve obtained in example 1.
FIG. 3 is the adsorption and desorption diagram of the mesoporous ZSM-5 molecular sieve obtained in example 1.
Detailed Description
The present invention will be further illustrated by the following examples, but the present invention is not limited to these examples.
The following examples used a ZSM-5 molecular sieve as the starting material having a silica to alumina ratio of 27.5 and a specific surface area of 354m 2 Per g, specific micropore surface area 349m 2 G, mesoporous specific surface area 5m 2 (iv) g. The acid, alkali and solvent used are all analytical pure chemical reagents.
Example 1
Adding 10mL of 0.1mol/L NaOH solution, 600mL of deionized water and 2.46g of anhydrous sodium acetate into a 2000mL beaker, heating in a water bath to 60 ℃ to obtain an alkaline system solution with the pH value of 10, then adding 60.0g of ZSM-5 molecular sieve raw material, treating in the water bath for 2h, quickly cooling to room temperature, filtering, washing to neutrality, and drying in an oven at 120 ℃ for 12h. Adding 1500mL of 0.1mol/L acetic acid solution and 12.3g of anhydrous sodium acetate into a 2000mL beaker, heating in a water bath to 70 ℃ to obtain an acid system solution with the pH value of 6.0, then putting 20.0g of dried sample into the beaker, keeping the temperature of 70 ℃ for 6h, quickly cooling, filtering, washing, and putting the sample in an oven to dry for 12h at 120 ℃ to obtain the sample with the sample number A1.
Example 2
Adding 5mL of 0.1mol/L NaOH solution, 600mL of deionized water and 1.41g of anhydrous sodium acetate into a 2000mL beaker, heating in a water bath to 60 ℃ to obtain an alkaline system solution with the pH value of 9, adding 60.0g of ZSM-5 molecular sieve raw material, treating in the water bath for 2h, quickly cooling to room temperature, filtering, washing to neutrality, and drying in an oven at 120 ℃ for 12h; adding 1500mL of 0.05mol/L acetic acid solution and 6.75g of anhydrous sodium acetate into a 2000mL beaker, heating in a water bath to 70 ℃ to obtain an acid system solution with the pH value of 5.0, then taking 20g of dried sample, placing the sample into the beaker, keeping the temperature of 70 ℃ for 4h, quickly cooling, filtering, washing, placing the sample in an oven for drying at 120 ℃ for 12h to obtain a sample with the sample number A2.
Example 3
Adding 10mL of 0.1mol/L NaOH solution, 600mL of deionized water and 5.16g of sodium citrate into a 2000mL beaker, heating in a water bath to 60 ℃ to obtain an alkaline system solution with the pH value of 8, adding 60.0g of ZSM-5 molecular sieve raw material, treating in the water bath for 3 hours, quickly cooling to room temperature, filtering, washing to neutrality, and drying in an oven at 120 ℃ for 12 hours; adding 1500mL of 0.1mol/L citric acid solution and 13.44g of sodium citrate into a 2000mL beaker, heating in a water bath to 70 ℃ to obtain an acid system solution with the pH value of 5.0, then putting 20.0g of dried sample into the beaker, keeping the temperature of 70 ℃ for 8h, quickly cooling, filtering, washing, and drying in an oven at 120 ℃ for 12h to obtain a sample with the sample number of A3.
Example 4
Adding 10mL of 0.1mol/L KOH solution, 600mL of deionized water and 5.16g of potassium citrate into a 2000mL beaker, heating in a water bath to 60 ℃ to obtain an alkaline system solution with the pH value of 9, adding 60.0g of ZSM-5 molecular sieve raw material, treating in the water bath for 3 hours, quickly cooling to room temperature, filtering, washing to neutrality, and drying in an oven at 120 ℃ for 12 hours. Adding 1500mL of 0.05mol/L citric acid solution and 7.13g of potassium citrate into a 2000mL beaker, heating in a water bath to 70 ℃ to obtain an acid system solution with the pH value of 4.0, then putting 20.0g of dried sample into the beaker, keeping the temperature of 70 ℃ for 6h, quickly cooling, filtering, washing, and putting the sample in an oven to dry for 12h at 120 ℃ to obtain a sample with the sample number A4.
Example 5
Adding 10mL of 0.1mol/L KOH solution, 600mL of deionized water and 2.94g of anhydrous potassium acetate into a 2000mL beaker, heating in a water bath to 60 ℃ to obtain an alkaline system solution with the pH value of 8, adding 60.0g of ZSM-5 molecular sieve raw material, treating in the water bath for 3h, quickly cooling to room temperature, filtering, washing to neutrality, and drying in an oven at 120 ℃ for 12h. Adding 1500mL of 0.1mol/L acetic acid solution and 13.03g of anhydrous potassium acetate into a 2000mL beaker, heating in a water bath to 70 ℃ to obtain an acid system solution with the pH value of 5.0, then taking 20.0g of dried sample, putting the sample into the beaker, keeping the temperature at 70 ℃ for 6h, quickly cooling, filtering, washing, and putting the sample in an oven to dry for 12h at 120 ℃ to obtain a sample with the sample number of A5.
The pore structure properties of the ZSM-5 modified zeolite samples prepared in examples 1-5 are listed in table 1.
TABLE 1 pore Structure Properties of samples referred to in examples 1-5
The mesoporous size of the products obtained in the examples 1-5 is more than 25% larger than that of the product obtained in the patent CN102874840A, and the mesoporous volume is more than 28% larger than that of the product obtained in the patent CN 104628011A.
The products obtained in examples 1-5 have a pore size more than 42% larger than that of CN 102464336A.
Claims (7)
1. A preparation method of a mesoporous ZSM-5 molecular sieve is characterized by comprising the following steps: the method is realized by the following steps:
(1) Preparing an alkaline system solution mixed by inorganic alkali and weak acid salt, and keeping the pH value of the alkaline system solution within the range of 7.0-10.0;
(2) Adding a ZSM-5 molecular sieve into the alkaline system solution prepared in the step (1) according to the solid-to-liquid ratio of 1-15, and stirring at 25-95 ℃ for 60-360 min;
(3) Filtering, washing and drying the sample prepared in the step (2);
(4) Preparing an acidic system solution mixed by weak acid and weak acid salt, and keeping the pH value of the acidic system solution within the range of 2.0-6.0;
(5) And (3) adding the sample obtained in the step (3) into the acidic system solution prepared in the step (4) according to the solid-to-liquid ratio of 1-100, stirring at 25-95 ℃ for 60-600 min, and filtering, washing and drying the obtained product to obtain the modified mesoporous ZSM-5 molecular sieve.
2. The method for preparing the mesoporous ZSM-5 molecular sieve of claim 1, wherein: the inorganic alkali in the alkaline system solution in the step (1) is one or two of sodium hydroxide or potassium hydroxide; the weak acid salt is one or more of sodium acetate, potassium acetate or potassium citrate.
3. The preparation method of the mesoporous ZSM-5 molecular sieve of claim 1, wherein: the molar ratio of the weak acid salt to the inorganic base in the alkaline system solution in the step (1) is 1-10.
4. The preparation method of the mesoporous ZSM-5 molecular sieve of claim 3, wherein: the molar ratio of the weak acid salt to the inorganic base in the alkaline system solution in the step (1) is 3-6.
5. The preparation method of the mesoporous ZSM-5 molecular sieve of claim 1, wherein: the weak acid in the acidic system solution in the step (4) is one or two of acetic acid or citric acid; the weak acid salt is one or more of sodium acetate, sodium citrate, potassium acetate or potassium citrate.
6. The method for preparing the mesoporous ZSM-5 molecular sieve of claim 1 or 5, wherein: the molar ratio of the weak acid salt to the weak acid in the acidic system solution in the step (4) is 1-5.
7. The method for preparing the mesoporous ZSM-5 molecular sieve of claim 1 or 5, wherein: the molar ratio of the weak acid salt to the weak acid in the acidic system solution in the step (4) is 2-3.
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| CN108654678A (en) * | 2018-05-31 | 2018-10-16 | 上海绿强新材料有限公司 | One type Fenton oxidation catalyst and its application |
| CN108927213A (en) * | 2018-06-26 | 2018-12-04 | 上海绿强新材料有限公司 | A kind of catalyst and preparation method thereof for preparing propylene by dehydrogenating propane |
| CN111375444A (en) * | 2018-12-27 | 2020-07-07 | 中国科学院广州能源研究所 | Core-shell iron-based catalyst for directly producing aromatic hydrocarbon from synthesis gas and preparation method and application thereof |
| CN112892582A (en) * | 2019-12-03 | 2021-06-04 | 中国石油化工股份有限公司 | Light gasoline cracking catalyst containing all-silicon three-hole spherical mesoporous composite material and preparation method and application thereof |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108654678A (en) * | 2018-05-31 | 2018-10-16 | 上海绿强新材料有限公司 | One type Fenton oxidation catalyst and its application |
| CN108927213A (en) * | 2018-06-26 | 2018-12-04 | 上海绿强新材料有限公司 | A kind of catalyst and preparation method thereof for preparing propylene by dehydrogenating propane |
| CN111375444A (en) * | 2018-12-27 | 2020-07-07 | 中国科学院广州能源研究所 | Core-shell iron-based catalyst for directly producing aromatic hydrocarbon from synthesis gas and preparation method and application thereof |
| CN112892582A (en) * | 2019-12-03 | 2021-06-04 | 中国石油化工股份有限公司 | Light gasoline cracking catalyst containing all-silicon three-hole spherical mesoporous composite material and preparation method and application thereof |
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