CN112279268A

CN112279268A - Preparation method and application of hierarchical pore ZSM-5 nano lamellar zeolite

Info

Publication number: CN112279268A
Application number: CN202011282816.XA
Authority: CN
Inventors: 陈艳红; 韩东敏; 刘焕荣; 崔红霞; 刘香芝
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2020-08-06
Filing date: 2020-11-17
Publication date: 2021-01-29

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method and application of hierarchical pore ZSM-5 nano lamellar zeolite. The preparation method comprises the following steps: dissolving an aluminum source, a silicon source, an alkali source and seed crystals in deionized water, fully stirring, and uniformly mixing to form gel; aging the gel, adding a surfactant into the aged gel, uniformly stirring, transferring to a crystallization kettle with a polytetrafluoroethylene lining for crystallization, washing, drying and roasting a crystallized product after crystallization is finished, thereby obtaining the boiling and boiling multi-level pore ZSM-5 nano-layer sheetAnd (4) stone. The product has rich mesoporous structure and BET specific surface area as high as 1320m²A regular mesoporous distribution of 4-6nm and 0.52cm³The mesoporous volume structure per gram has excellent macromolecular diffusion performance, and shows excellent propylene selectivity and anti-carbon deposition capability in the reaction of preparing propylene from methanol.

Description

Preparation method and application of hierarchical pore ZSM-5 nano lamellar zeolite

Technical Field

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method and application of hierarchical pore ZSM-5 nano lamellar zeolite.

Background

Propylene is used as an important chemical raw material, is mainly used for synthetic resin, synthetic rubber, various fine chemicals and the like, and has important application value in the aspects of chemical industry, medicine, military industry and the like. With the increasing shortage of crude oil resources, the traditional process route for producing propylene by using petroleum as a raw material cannot meet the requirement of the chemical industry of China on propylene. The Methanol To Propylene (MTP) process is currently considered to be the most successful method for producing lower olefins using non-petroleum routes. After long-term research on MTP catalytic reaction catalysts, people find that an aluminosilicate molecular sieve ZSM-5 catalyst with an MFI topological structure has the highest MTP catalytic performance, and particularly when the conversion rate of methanol is 100%, the yield of ethylene and propylene diene can exceed 80%. However, the average pore diameter of the conventional ZSM-5 zeolite with a ten-membered ring structure is about 0.56nm, the diffusion efficiency of macromolecules is low due to the pore diameter of micropores, and the service life of the catalyst is influenced due to easy coking of the catalyst.

The hierarchical pore ZSM-5 zeolite molecular sieve not only retains the advantages of adjustable acidity, good hydrothermal stability and the like of the microporous molecular sieve; meanwhile, the limitation of mass transfer and diffusion is overcome by introducing part of mesopores, so that the hierarchical pore ZSM-5 zeolite has stronger macromolecular diffusion performance on the premise of ensuring high conversion rate, and the stability and high catalytic reaction performance of the catalyst are ensured, thereby having good application prospect and economic benefit. The preparation of the hierarchical pore ZSM-5 zeolite mainly has two ways: one method is to carry out post-treatment such as acid-base treatment and the like on conventional ZSM-5 zeolite to generate a part of mesopores, however, the post-treatment method has strict requirements on acid-base conditions of a solution, zeolite framework collapse is easy to occur in the dealumination or desilication process, the micropore volume is reduced, the yield is low, the mesopore connectivity is poor, a large amount of waste liquid is generated, the environment is polluted, medicines are wasted, and the influence is particularly prominent in large-scale industrial production. The other method is to introduce a mesoporous template in the synthesis of zeolite, and the most representative work in this respect is that Ryoo and the like prepare the hierarchical pore ZSM-5 nano-layer zeolite by designing a double-head quaternary ammonium salt surfactant as the mesoporous template. The nano lamellar structure has large external surface area, and active sites are mainly distributed on the external specific surface, so that the structure is more favorable for the diffusion of reactant and product molecules, the adsorption and catalysis processes almost completely occur on the external surface, the utilization rate of the active sites is high, the coking and inactivation of a catalyst are effectively avoided, and the catalytic activity and stability of the molecular sieve are greatly improved. The main disadvantages of the method are that the mesoporous template agent has complicated synthesis steps and high synthesis cost, thereby greatly limiting the industrial application of the method.

Therefore, an economic, simple and efficient preparation method of the hierarchical pore ZSM-5 nano layer zeolite is found, and the method has important application value.

Disclosure of Invention

The invention aims to provide a preparation method and application of hierarchical pore ZSM-5 nano lamellar zeolite aiming at the defects of the prior art. The method adopts a low-cost and low-toxicity commercialized long-chain alkyl surfactant as a mesoporous template agent, and replaces microporous template agent quaternary ammonium salt with conventional microporous ZSM-5 zeolite to prepare the hierarchical pore ZSM-5 nano lamellar zeolite structure with a two-dimensional nano lamellar structure, wherein the product has a rich mesoporous structure, and the BET specific surface area is up to 1320m²A regular mesoporous distribution of 4-6nm and 0.52cm³In terms of/gThe mesoporous structure has excellent macromolecular diffusion performance, and shows excellent propylene selectivity and carbon deposition resistance in the reaction of preparing propylene from methanol.

According to a first aspect of the present invention, there is provided a process for preparing a hierarchical pore ZSM-5 nano-layer sheet zeolite, the process comprising:

(1) dissolving an aluminum source, a silicon source, an alkali source and seed crystals in deionized water, fully stirring, and uniformly mixing to form gel;

(2) and (3) aging the gel, adding a surfactant into the aged gel, uniformly stirring, transferring to a crystallization kettle with a polytetrafluoroethylene lining for crystallization, washing, drying and roasting a crystallized product after crystallization is finished, and thus obtaining the hierarchical pore ZSM-5 nano layer sheet zeolite.

According to a specific embodiment of the present invention, preferably, the above method further comprises: and carrying out ion exchange, drying and roasting on the hierarchical pore ZSM-5 nano layer zeolite to obtain the hydrogen type hierarchical pore ZSM-5 nano layer zeolite.

According to the specific embodiment of the present invention, preferably, the aluminum source is one or a combination of two or more of aluminum isopropoxide, pseudo-boehmite, sodium aluminate and aluminum sulfate.

According to the specific embodiment of the present invention, preferably, the silicon source is one or a combination of two or more of silica sol, water glass, white carbon black and tetraethoxysilane.

According to a specific embodiment of the present invention, preferably, the alkali source is one or two of sodium hydroxide, sodium oxide and potassium hydroxide.

According to a particular embodiment of the invention, preferably, the seeds are conventional microporous ZSM-5 zeolite.

According to the specific embodiment of the present invention, preferably, the surfactant is one of tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide, and is preferably hexadecyltrimethylammonium bromide. The surfactant adopted by the invention is a low-cost and low-toxicity surfactant.

According to a particular embodiment of the invention, preferably, the silicon source is SiO₂Calculated by Al as the aluminum source₂O₃Calculated by Na as alkali source₂And calculated by O, the molar ratio of the silicon source to the aluminum source to the alkali source to the surfactant to the deionized water is as follows: 100SiO 2₂:（1.4~3.3）Al₂O₃: （12~20）Na₂O (5-15) surfactant: (1800-4000) deionized water.

According to a specific embodiment of the present invention, preferably, the seed crystal is used in an amount of a silicon Source (SiO)₂) 5-10w% of the mass.

According to a particular embodiment of the present invention, preferably, the gel has an aging temperature of 60 to 80 ℃ and an aging time of 12 to 24 hours.

According to the specific embodiment of the present invention, preferably, the temperature of the crystallization treatment is 120-180 ℃, and the time of the crystallization treatment is 1-3 d.

According to a specific embodiment of the present invention, preferably, the temperature of the ion exchange is 80 ℃ water bath, and the solution of the ion exchange is NH with the concentration of 1M₄Cl solution, and the ion exchange was repeated 2 times for 4h each time.

According to a particular embodiment of the present invention, preferably, the preparation method comprises the following particular steps:

(1) mixing and stirring an aluminum source, an alkali source and deionized water uniformly at room temperature;

(2) adding a silicon source into the product obtained in the step (1), and continuously stirring uniformly until a gel is formed;

(3) adding seed crystals into the gel, and continuously stirring for 1-2 h;

(4) aging the gel obtained in the step (3) for 12-24h at the aging temperature of 60-80 ℃;

(5) adding a mesoporous template surfactant into the aged gel obtained in the step (4), stirring for 1-2h, transferring to a crystallization kettle with a polytetrafluoroethylene lining for crystallization reaction at the crystallization temperature of 150-180 ℃ for 1-3d, and washing and drying a solid product after crystallization;

(6) placing the dried solid in a muffle furnace, and roasting at 500-600 ℃ for 6-8h to obtain a multi-stage pore ZSM-5 nano-layer sheet; more preferably, the hierarchical pore ZSM-5 nano-layer zeolite is subjected to ion exchange, drying and roasting to obtain the hydrogen type hierarchical pore ZSM-5 nano-layer zeolite.

According to a second aspect of the invention, the invention also provides the hierarchical pore ZSM-5 nano lamellar zeolite prepared by the method, wherein the hierarchical pore ZSM-5 nano lamellar zeolite has the silica-alumina ratio of 30-80 and the BET specific surface area of 1320m²More than g, the average pore diameter of micropores is 0.56nm, the average pore diameter of mesopores is 4-6nm, and the pore volume of mesopores is 0.46-0.52cm³The/g, abundant mesoporous structure and great specific surface area effectively improve the macromolecule diffusion performance.

According to a third aspect of the invention, the invention also provides an application of the hierarchical pore ZSM-5 nano-layer zeolite as a catalyst in a reaction of preparing propylene from methanol.

Compared with the conventional microporous ZSM-5 zeolite, the hierarchical pore ZSM-5 nano lamellar zeolite prepared by the method has a two-dimensional nano lamellar structure, and the specific surface area is up to 1320m²More than g, rich mesoporous structure. Meanwhile, the preparation method adopts the seed crystal to replace organic amine as a guiding agent of a microporous structure, adopts the surface active agent with low price and general commercialization to replace the double-end quaternary ammonium salt surface active agent with complicated preparation process and high cost as a mesoporous template agent, has the advantages of simple synthesis step, low cost and the like, the molecular sieve prepared by the method shows excellent propylene selectivity and anti-carbon deposition capability in the reaction of preparing propylene from methanol, compared with the conventional microporous ZSM-5 zeolite, the propylene selectivity of the multi-stage pore ZSM-5 nano lamellar zeolite prepared by the method is improved by more than 10 percent, and the catalyst stability is 3 times or more of that of the microporous ZSM-5 zeolite.

Drawings

FIG. 1 is an XRD spectrum of conventional microporous ZSM-5 and hierarchical porous ZSM-5 nano-layer zeolite.

FIG. 2 is a scanning electron microscope and a transmission electron microscope picture of hierarchical porous ZSM-5 nano layer zeolite.

FIG. 3 is the nitrogen adsorption and desorption isotherm and BJH pore size distribution curves of conventional microporous ZSM-5 and hierarchical ZSM-5 nano-layer zeolite.

FIG. 4 shows the performance results of catalytic reactions for conventional microporous ZSM-5 and hierarchical ZSM-5 nano-layer zeolites.

Detailed Description

The present invention will now be further described by way of examples for better understanding of the technical features, objects and advantages of the present invention, but the present invention is not limited thereto.

Comparative example 1

The comparative example provides a preparation method of large-grain conventional microporous ZSM-5 zeolite, which mainly comprises the following steps:

dissolving 0.28g of sodium aluminate, 0.4g of sodium hydroxide and 0.74g of n-butylamine template agent in 20g of deionized water at room temperature, uniformly stirring, adding 15g of silica sol (40%), continuously stirring for 1h to obtain uniform gel, transferring the gel to a reaction kettle with a polytetrafluoroethylene lining for hydrothermal treatment, wherein the crystallization temperature is 160 ℃, the crystallization time is 3d, and after crystallization is finished, carrying out suction filtration, washing and drying on the obtained solid product;

roasting the dried solid product in a muffle furnace at 550 ℃ for 6h, and removing the organic template to obtain the sodium type large-grain conventional microporous ZSM-5 zeolite

In 80 deg.C water bath, the above sodium type ZSM-5 zeolite is ion exchanged, NH₄The Cl solution concentration was 1M, and the number of exchanges was 2 times for 4h each time. Drying and roasting the product to obtain the hydrogen type conventional microporous ZSM-5 zeolite.

The XRD spectrogram, crystal morphology and nitrogen adsorption and desorption isotherm of the sample are respectively shown in figure 1, figure 2 and figure 3.

Example 1

The invention provides a preparation method of a hierarchical pore ZSM-5 nano layer sheet, which comprises the following steps:

firstly, 1.2g of aluminum sulfate octadecahydrate and 30g of deionized water are mixed and stirred until the aluminum sulfate octadecahydrate and the deionized water are completely dissolved, and 25g of water glass (SiO in the water glass) is added₂ 30%，Na₂O9%) is stirred uniformly to form a gel, and finally 0.75g of seed crystal (the seed crystal is added in SiO)₂5% of mass) continuingVigorous stirring formed a homogeneous gel. Aging the gel at 60 ℃ for 12h, adding 5g of hexadecyl trimethyl ammonium bromide into the aged gel, stirring for 1h, transferring the stirred gel into a reaction kettle with a polytetrafluoroethylene lining for crystallization treatment, wherein the crystallization temperature is 150 ℃, the crystallization time is 3d, washing and drying the obtained solid product after crystallization is finished, and roasting the dried solid product in a muffle furnace at 550 ℃ for 6h to remove a mesoporous template agent to obtain the sodium-type hierarchical pore ZSM-5 nano lamellar zeolite.

Performing ion exchange on the hierarchical porous ZSM-5 nano layer zeolite, and adopting NH with the concentration of 1M₄And the Cl solution is exchanged for 2 times, each time is 4 hours, and the hydrogen type hierarchical pore ZSM-5 nano layer zeolite is obtained after drying and roasting.

The XRD spectrum, crystal morphology and nitrogen adsorption and desorption isotherm of the sample are shown in figures 1, 2 and 3.

Example 2

firstly, 0.28g of sodium aluminate and 1.12g of potassium hydroxide are added into 30g of deionized water to be mixed and stirred until the sodium aluminate and the potassium hydroxide are completely dissolved, 6g of white carbon black is added and stirred uniformly to form gel, and finally 0.9g of seed crystal (the seed crystal addition is SiO)₂10% of mass), stirring vigorously to form a homogeneous gel. Aging the gel at 80 ℃ for 24h, adding 4g of octadecyl trimethyl ammonium bromide into the aged gel, stirring for 1h, transferring the stirred gel into a reaction kettle with a polytetrafluoroethylene lining for crystallization treatment at 160 ℃ for 2d, washing and drying the obtained solid product after crystallization, and roasting the dried solid product in a muffle furnace at 500 ℃ for 7h to remove the mesoporous template agent to obtain the sodium-type hierarchical pore ZSM-5 nano-layer sheet.

Performing ion exchange on the hierarchical porous ZSM-5 nano layer zeolite, and adopting NH with the concentration of 1M₄And (3) Cl solution, wherein the exchange times are 2 times and 4 hours each time, and the hydrogen type hierarchical pore ZSM-5 nano layer sheet zeolite is obtained by drying and roasting.

Example 3

firstly, 0.52g of sodium aluminate and 0.9g of sodium hydroxide are added into 20g of deionized water to be mixed and stirred until the sodium aluminate and the sodium hydroxide are completely dissolved, 22g of silica sol (40%) is added and stirred uniformly to form gel, and finally 0.8g of seed crystal (the seed crystal adding amount is SiO)₂8% of mass) and vigorous stirring was continued to form a homogeneous gel. Aging the gel at 70 ℃ for 20h, adding 5g of hexadecyl trimethyl ammonium bromide into the aged gel, stirring for 1h, transferring the stirred gel into a reaction kettle with a polytetrafluoroethylene lining for crystallization treatment, wherein the crystallization temperature is 180 ℃, the crystallization time is 1d, washing and drying the obtained solid product after crystallization is finished, and roasting the dried solid product in a muffle furnace at 600 ℃ for 8h to remove a mesoporous template agent to obtain the sodium-type hierarchical pore ZSM-5 nano-layer sheet.

Test example 1

The large-grain conventional microporous ZSM-5 of comparative example 1 and the multistage-pore ZSM-5 nano-layer zeolite of example 1 were subjected to evaluation of the reaction for producing propylene from methanol using a fixed bed reactor in the following specific manner:

the hydrogen type conventional microporous ZSM-5 zeolite and the hierarchical pore ZSM-5 nano-layer sheet zeolite are tabletted, the particle size is between 20 and 60 meshes, the loading amount of the catalyst is 0.5g, and the reaction product is detected by a gas chromatograph (TCD + FID detector).

The reaction test conditions were: the mass space velocity is 5h^-1The reaction temperature was 400 ℃ and the operation was carried out under normal pressure, and the results of the evaluation are shown in FIG. 4.

Test example 2

The phase and MTP catalytic performance of the samples from example 1 and comparative example 1 were evaluated. The XRD spectrum of the sample is shown in fig. 1, and the crystallinity of the multi-pore ZSM-5 nano lamellar zeolite of example 1 is slightly low and the diffraction peak is broad due to the formation of the nano lamellar structure.

The scanning electron microscope and the transmission electron microscope of the sample are shown in fig. 2, the comparative example 1 is shown in fig. 2a, the typical MFI morphology is about 2 microns, and the transmission electron microscope is shown in fig. 2c, and no obvious mesoporous structure exists. The multi-stage pore ZSM-5 nano-layer zeolite synthesized in example 1 has a nano-layer structure as shown in FIG. 2b by scanning electron microscopy, and a nano-layer stacking structure as shown in FIG. 2d by transmission electron microscopy.

The pore structure properties are shown in figure 3 and table 1. As can be seen from fig. 3, comparative example 1 is a typical type i adsorption and desorption isotherm, and has a typical microporous structure. The sample of example 1 is an isotherm of type i at low pressure and type iv at high pressure, an obvious hysteresis loop exists, indicating that the product generates mesopores, and the BJH pore size distribution diagram indicates that the mesopore pore size is mainly distributed in the range of 4-6 nm. The data in table 1 illustrate that the sample of example 1 has a larger external specific surface area and mesoporous pore volume.

FIG. 4 shows MTP performance evaluation of comparative example 1 and example 1 under a condition of a mass space velocity of 5h^-1The reaction temperature was 400 ℃ and the operation was carried out at normal pressure. The catalyst life is defined as the reaction time when the methanol conversion rate is reduced to 95%, and it can be seen from fig. 4 that the life of the conventional ZSM-5 zeolite is 14 hours, the life of the multi-stage pore ZSM-5 nano-layer sheet in example 1 is 42 hours, the catalyst stability is 3 times that of the original microporous ZSM-5, and the average propylene selectivity is improved by 10.2%.

TABLE 1 Zeolite sample pore Structure

Claims

1. a preparation method of hierarchical pore ZSM-5 nano-layer sheet zeolite, is characterized in that, this preparation method comprises the following steps:

(1) Dissolve aluminum source, silicon source, alkali source and crystal seed in deionized water, stir well, and mix well to form gel;

(2) The above-mentioned gel is subjected to aging treatment, and a surfactant is added to the gel after the aging treatment. After stirring evenly, it is transferred to a crystallization kettle lined with polytetrafluoroethylene for crystallization treatment. After the crystallization, the crystallization product is washed, dried and calcined to obtain the hierarchically porous ZSM-5 nano-layer flake zeolite;

Ion exchange, drying and calcination are performed on the hierarchically porous ZSM-5 nanosheet zeolite to obtain a hydrogen-type hierarchically porous ZSM-5 nanosheet zeolite.

2. preparation method according to claim 1 is characterized in that, described aluminium source is one or more combinations in aluminium isopropoxide, pseudoboehmite, sodium aluminate and aluminium sulfate; The silicon source is one or a combination of two or more selected from silica sol, water glass, white carbon black and ethyl orthosilicate.

3. preparation method according to claim 1 is characterized in that, described alkali source is one or both in sodium hydroxide, sodium oxide and potassium hydroxide; Described crystal seed is conventional microporous ZSM -5 Zeolite.

4. preparation method according to claim 1 is characterized in that, described surfactant is tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl bromide One of methyl ammonium bromide.

5 . The preparation method according to claim 1 , wherein the silicon source is calculated as SiO ₂ , the aluminum source is calculated as Al ₂ O ₃ , the alkali source is calculated as Na ₂ O , and the silicon source, aluminum source, alkali The molar ratio of source, surfactant and deionized water is: 100SiO ₂ : (1.4~3.3) Al ₂ O ₃ : (12~20) Na ₂ O: (5-15) Surfactant: (1800~4000) Deionized water.

6 . The preparation method according to claim 1 , wherein the dosage of the seed crystal is 5-10 w% of the mass of the silicon source (SiO ₂ ). 7 .

7. The preparation method according to claim 1, wherein the aging temperature of the gel is 60-80°C, and the aging time is 12-24h; the temperature of the crystallization treatment is 120-180°C , the crystallization treatment time is 1-3d; the temperature of the ion exchange is a water bath of 80°C, the solution of the ion exchange is a NH ₄ Cl solution with a concentration of 1M, and the ion exchange is repeated 2 times, 4h each time .

8. preparation method according to claim 1, is characterized in that, this method specifically comprises the following steps:

(1) Mix and stir the aluminum source, alkali source and deionized water evenly at room temperature;

(2) adding a silicon source to the product of step (1), and continuing to stir until a gel is formed;

(3) Add seed crystals to the gel and continue stirring for 1-2 hours;

(4) aging the gel obtained in step (3) for 12-24 hours, and the aging temperature is 60-80°C;

(5) Add mesoporous template surfactant to the aged gel in step (4), and after stirring for 1-2 hours, transfer to a polytetrafluoroethylene-lined crystallization kettle for crystallization reaction, and crystallization The temperature is 150-180°C, the crystallization time is 1-3d, and the solid product is washed and dried after crystallization;

(6) The above-mentioned dried solid is calcined in a muffle furnace at 500-600° C. for 6-8 hours to obtain a multi-level porous ZSM-5 nanosheet;

9. The hierarchically porous ZSM-5 nanosheet zeolite prepared by the method according to any one of claims 1-8, wherein the silica-alumina ratio of the hierarchically porous ZSM-5 nanosheet zeolite is 30-80, The BET specific surface area is 1200-1500 m ² /g, the average pore diameter of micropores is 0.56 nm, the average pore diameter of mesopores is 4-6 nm, and the mesopore volume is 0.46-0.52 cm ³ /g.

10. The application of the hierarchically porous ZSM-5 nanosheet zeolite according to claim 9 as a catalyst in the reaction of methanol to propylene.