阅读说明：本技术 金属改性mfi@mfi核壳型分子筛催化剂及其制备 (Metal modified MFI @ MFI core-shell type molecular sieve catalyst and preparation thereof ) 是由 孙玉坤 刘亚圣 翟岩亮 于 2019-12-05 设计创作，主要内容包括：本发明提供了一种金属改性MFI@MFI核壳型分子筛催化剂及其制备。所述方法包括如下步骤：(1)采用纳米金属氧化物通过溶剂热法对ZSM-5分子筛进行金属氧化物改性得到改性ZSM-5分子筛；所述金属选自Mn、Ce、Fe、Co、Ni、La、Ga和W的一种或多种的任意混合；(2)将步骤(1)得到的改性ZSM-5分子筛在Silicalite-1分子筛或B-ZSM-5分子筛的晶化液中二次水热合成得到所述的金属改性MFI@MFI核壳型分子筛催化剂。本发明的金属改性MFI@MFI核壳型分子筛催化剂可以大幅降低甲醇制丙烯反应的积炭速率,提高丙烯选择性和催化寿命,改性效果比传统方式提高的更多。(The invention provides a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof. The method comprises the following steps: (1) carrying out metal oxide modification on the ZSM-5 molecular sieve by adopting a nano metal oxide through a solvothermal method to obtain a modified ZSM-5 molecular sieve; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W; (2) and (2) carrying out secondary hydrothermal synthesis on the modified ZSM-5 molecular sieve obtained in the step (1) in a crystalline liquid of the Silicalite-1 molecular sieve or the B-ZSM-5 molecular sieve to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst. The metal modified MFI @ MFI core-shell type molecular sieve catalyst can greatly reduce the carbon deposition rate of the reaction for preparing propylene from methanol, improve the selectivity of propylene and prolong the catalytic life, and the modification effect is improved more than that of the traditional mode.)

1. A preparation method of a metal modified MFI @ MFI core-shell type molecular sieve catalyst comprises the following steps:

(1) carrying out metal oxide modification on the ZSM-5 molecular sieve by adopting a nano metal oxide (preferably, the particle diameter of the nano metal oxide is 10-500nm, preferably 10-150nm) through a solvothermal method to obtain a modified ZSM-5 molecular sieve; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W;

(2) preparing the modified ZSM-5 molecular sieve obtained in the step (1) into a crystallization liquid of a Silicalite-1 molecular sieve or a B-ZSM-5 molecular sieve (preferably, the mass of the modified ZSM-5 molecular sieve accounts for SiO in the crystallization liquid₂10-100% of the mass) to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst.

2. The preparation method according to claim 1, wherein the step (1) comprises adding nano metal oxide, organosilane (preferably aminoorganosilane (preferably selected from one or more of N-aminoethyl-3-aminopropylmethyldimethoxysilane and N- (2-aminoethyl) -3-aminopropyltrimethoxysilane)), ZSM-5 molecular sieve into solvent (preferably selected from one or a mixture of any two of methanol, ethanol, N-hexane, cyclohexane, N-heptane and toluene) to modify metal oxide to obtain modified ZSM-5 molecular sieve; wherein the mass of the metal oxide for modification is 0.01-20% of that of the ZSM-5 molecular sieve, the mass of the solvent is 1-10 times of that of the ZSM-5 molecular sieve, and the mass of the organosilane is 0-30% of that of the ZSM-5 molecular sieve, wherein the mass of the ZSM-5 molecular sieve is 100%.

3. The preparation method according to claim 2, wherein the step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into the solvent, fully stirring for 1-12h (preferably for 2-6h), then reacting at 100-300 ℃ for 6-48h (preferably for 10-24h), and drying (preferably at a drying temperature in the range of 50-150 ℃, preferably for 2-20 h) to obtain the modified ZSM-5 molecular sieve.

4. The preparation method of claim 1, wherein the step (2) comprises mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source (preferably a combination of one or more selected from water glass, silica sol, silicic acid, ethyl orthosilicate, coarse silica gel and white carbon black), a boron source (preferably a combination of one or more selected from boric acid, sodium metaborate and sodium tetraborate), a template (preferably any combination of one or more selected from tetrapropylammonium bromide and tetrapropylammonium hydroxide) and deionized water (preferably the molar ratio of the silicon source, the boron source, the template and the deionized water is 1 (0-0.05): 0.05-0.5): 5-75) to form a secondary crystallized gel, and then crystallizing (preferably at 100-200 ℃ for 2-96 h; more preferably at 140-180 ℃ for 24-72h), and (3) carrying out post-treatment (preferably comprising carrying out suction filtration, washing, drying and ion exchange on a product after continuous crystallization) to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst.

5. The preparation method according to claim 4, wherein the step (2) comprises mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and then stirring for 60-300min (preferably 120-180min) (preferably at a stirring rate of 60-500r/min (more preferably 120-300r/min)) to form the secondary crystallized gel.

6. The preparation method according to claim 4, wherein the washing in the step (2) comprises washing with one or two of deionized water, methanol and ethanol as a solvent; the drying temperature range is 50-150 ℃, and the drying time is 2-24 h.

7. The preparation method according to claim 4, wherein the ion exchange in the step (2) comprises preparing a mixed solution of a molecular sieve and 0.5-2 mol/L ammonium chloride solution in a mass ratio of 1: 5-1: 20, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and calcining at 500-600 ℃ for 4-24 h (preferably, the ion exchange process is repeated for 2 times).

8. The metal modified MFI @ MFI core-shell type molecular sieve catalyst prepared by the preparation method of any one of claims 1 to 7.

9. A method for preparing propylene by methanol conversion, wherein the method comprises the step of carrying out catalytic reaction on a mixture of methanol and water as a raw material by using the metal modified MFI @ MFI core-shell type molecular sieve catalyst as defined in claim 8 to obtain the propylene.

10. The method of claim 9, wherein the conditions of the reaction comprise: the reaction temperature is 450-500 ℃; the space velocity is 0.5-15h^-1(ii) a Preferably, the pressure is atmospheric.

Technical Field

The invention relates to the field of chemical industry, in particular to the field of catalysts for preparing propylene from methanol, and more particularly relates to a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof.

Background

Propylene is an important basic raw material in the field of petrochemical industry, has very wide application, such as production of polypropylene, acrylonitrile, butanol, octanol, propylene oxide and other products, and the world demand of the propylene is rapidly increased. The traditional propylene production route is excessively dependent on petroleum resources and cannot meet the global propylene demand, so that countries in the world are beginning to focus on the development of non-petroleum route propylene preparation technology, wherein Methanol To Propylene (MTP) technology is receiving more and more extensive attention. The source of the raw material methanol is very wide, and the methanol can be prepared from coal, natural gas or biomass through synthesis gas, so that the pressure of using petroleum resources is relieved. In order to improve the propylene yield of the MTP process, researchers are devoted to research and development of core catalysts of the MTP process. For fixed bed reaction processes, ZSM-5 molecular sieves are the most widely accepted catalyst for MTP reactions. A fixed bed MTP process successfully developed by German Lurgi company in 1996 adopts a ZSM-5 molecular sieve developed by German south chemical company as a catalyst, propylene as a target product and byproducts such as liquefied gas, gasoline, fuel gas and the like with high added values. At present, a lot of catalysts are reported for preparing propylene from methanol, for example, U.S. Pat. No. 9738570B1 and chinese patent CN102059137B, the selectivity of low-carbon olefin of these molecular sieve catalysts is improved to a certain extent, but the catalytic performance of the molecular sieve catalysts still has a large promotion space, and the poor carbon deposition resistance of the catalysts is also a major problem of the existing catalysts, so a more suitable catalyst for preparing propylene from methanol needs to be found out to improve the selectivity of propylene and reduce the carbon deposition speed of the catalyst.

At present, the research on the process for preparing propylene from methanol at home and abroad is in a primary stage, and the key point of the process is still the design and preparation of a catalyst. In order to improve the yield of the low-carbon olefin, from 2008, people begin to use a metal modified ZSM-5 molecular sieve catalyst, and find that the selectivity of the target product propylene of the ZSM-5 molecular sieve catalyst modified by metals such as Ce, W, Mn, Fe and the like is improved to a certain extent. The modification method usually employed is an impregnation method or an ion exchange method. The propylene selectivity of the metal modified ZSM-5 catalyst is usually 35-45% under different reaction raw materials and reaction temperatures.

Although the molecular sieve catalyst has many advantages, the defects of short service life and fast carbon deposition for high-temperature hydrothermal reaction make the industrial production of the molecular sieve catalyst to be further perfected. On one hand, during the reaction, the reactant, the intermediate and the product molecules (such as olefin and aromatic hydrocarbon products) are not easy to diffuse, so that carbon deposition is caused by secondary reaction, in addition, the pore blocking or acid site covering of the molecular sieve caused by the carbon deposition during the reaction, and the framework dealumination caused by high-temperature hydrothermal during the reaction are all the reasons for molecular sieve inactivation. Generally, the acid property of the molecular sieve is regulated and controlled, the grain size of the molecular sieve is reduced in a combined manner, and the ZSM-5 molecular sieve with a mesoporous structure is synthesized, so that the reaction and diffusion performance of the molecular sieve is improved, and the comprehensive reaction performance of the catalyst is improved. However, the ZSM-5 molecular sieve with the hierarchical pore structure, such as nanocrystal stacking ZSM-5, nano thin layer ZSM-5, small crystal ZSM-5 and the like, has very high external surface area, shorter diffusion pore channels and excellent diffusion performance, is beneficial to the smooth progress of the reaction of preparing propylene from methanol, but the strong acid density on the external surface of the hierarchical pore molecular sieve is high, and carbon deposition preferentially occurs near the external surface, so that the inactivation is fast. In view of the reasons, the invention provides a novel preparation method of a metal oxide modified MFI @ MFI core-shell type molecular sieve catalyst, wherein the internal acidity and the inert shell layer coverage are regulated and controlled through metal oxide modification, the microstructure of the molecular sieve can be regulated and controlled by combining the internal acidity and the inert shell layer coverage, the strong acid density on the outer surface of the catalyst is greatly reduced, and the acid properties on the inner surface and the outer surface of the catalyst are reasonably regulated and controlled, so that the carbon deposition rate of the reaction for preparing propylene from methanol is reduced, and the selectivity of the target product.

Disclosure of Invention

One object of the present invention is to provide a metal-modified MFI @ MFI core-shell molecular sieve catalyst; the molecular sieve has a core-shell structure with a metal oxide modified Al-ZSM-5 molecular sieve as a core phase and a Silicalite-1 or B-ZSM-5 molecular sieve as a shell phase, has gradient acid distribution with more and less cores and strong and weak cores, and reasonably modulates the acid properties of the inner surface and the outer surface; the core-shell molecular sieve simultaneously has a multi-stage pore channel structure with a core phase rich in mesopores and a shell phase rich in micropores;

the invention also aims to provide a preparation method of the metal modified MFI @ MFI core-shell type molecular sieve catalyst; compared with the traditional impregnation method and the like, the metal modification method can reduce the addition amount of modified metal species, improve the utilization rate of the metal species and modulate the surface acid property of the molecular sieve; in addition, the metal oxide clusters can be encapsulated inside the molecular sieve by adopting the microporous MFI molecular sieve shell layer grown by epitaxy, so that the loss of the metal oxide is slowed down, the preparation process is simple and controllable, and the catalytic performance is obviously improved after modification;

the invention also aims to provide application of the metal modified MFI @ MFI core-shell type molecular sieve catalyst.

In order to achieve the above object, in one aspect, the present invention provides a preparation method of a metal modified MFI @ MFI core-shell type molecular sieve catalyst, wherein the method comprises the following steps:

(1) carrying out metal oxide modification on the ZSM-5 molecular sieve by adopting a nano metal oxide through a solvothermal method to obtain a modified ZSM-5 molecular sieve; the metal is selected from one or more of Mn, Ce, Fe, Co, Ni, La, Ga and W;

(2) and (2) carrying out secondary hydrothermal synthesis on the modified ZSM-5 molecular sieve obtained in the step (1) in a crystalline liquid of the Silicalite-1 molecular sieve or the B-ZSM-5 molecular sieve to obtain the metal modified MFI @ MFI core-shell type molecular sieve catalyst.

According to some embodiments of the present invention, the ZSM-5 molecular sieve is a small-grained ZSM-5 molecular sieve, a nanocrystal-packed ZSM-5 molecular sieve, a nano-thin layer ZSM-5 molecular sieve, or the like.

Wherein, the preparation method of the small crystal grain ZSM-5 molecular sieve is disclosed in patent CN104787777A, and the silicon-aluminum ratio of the small crystal grain ZSM-5 molecular sieve is 100-600 in some embodiments of the invention;

the preparation method of the nanocrystalline stacking ZSM-5 molecular sieve is disclosed in patent CN104525245A, and the silica-alumina ratio of the nanocrystalline stacking ZSM-5 molecular sieve is 100-600 in some specific embodiments of the invention;

the preparation method of the nano thin layer ZSM-5 molecular sieve is disclosed in patent CN106673007A, and the silica-alumina ratio of the nano thin layer ZSM-5 molecular sieve is 100-600 in some embodiments of the invention.

According to some embodiments of the present invention, in the step (1), the diameter of the nano metal oxide particles is 10 to 500 nm.

According to some embodiments of the present invention, in the step (1), the diameter of the nano metal oxide particles is 10 to 150 nm.

According to some embodiments of the invention, wherein the nano metal oxide has a particle diameter distribution within a range of ± 30 nm.

According to some embodiments of the invention, wherein the nano metal oxide has a particle diameter distribution within a range of ± 10 nm.

According to some embodiments of the invention, wherein the nanometal oxide is selected from MnO₂、Mn₂O₃、Mn₃O₄、CeO₂、Ce₂O₃、FeO、Fe₂O₃、Fe₃O₄、CoO、Co₂O₃、Co₃O₄、NiO、Ni₂O₃、La₂O₃、Ga₂O₃、WO₂And WO₃Any combination of one or more of the above.

According to some specific embodiments of the present invention, step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into a solvent to perform metal oxide modification to obtain a modified ZSM-5 molecular sieve; wherein the mass of the metal oxide for modification is 0.01-20% of that of the ZSM-5 molecular sieve, the mass of the solvent is 1-10 times of that of the ZSM-5 molecular sieve, and the mass of the organosilane is 0-30% of that of the ZSM-5 molecular sieve, wherein the mass of the ZSM-5 molecular sieve is 100%.

According to some embodiments of the invention, the organosilane is an amino-containing organosiloxane.

According to some embodiments of the invention, the organosilane is selected from the group consisting of aminopropyltriethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, and combinations of one or more thereof.

According to some embodiments of the present invention, the solvent is selected from one or a mixture of any two of methanol, ethanol, n-hexane, cyclohexane, n-heptane and toluene.

According to some specific embodiments of the invention, the step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into the solvent, fully stirring for 1-12h, then treating at 100-300 ℃ (transferring into a high-temperature reaction kettle) for 6-48h, and drying to obtain the modified ZSM-5 molecular sieve.

According to some embodiments of the present invention, step (1) comprises adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into the solvent, fully stirring for 2-6h, and then treating at 100-300 ℃.

According to some embodiments of the present invention, the step (1) of adding the nano metal oxide, the organosilane and the ZSM-5 molecular sieve into the solvent, and then fully stirring, is performed at 180 ℃ and 270 ℃.

According to some embodiments of the present invention, step (1) is performed at 100-300 ℃ for 10-24 h.

According to some embodiments of the invention, wherein the drying temperature in step (1) is in the range of 50-150 ℃.

According to some embodiments of the invention, the drying time in step (1) is 2h to 20 h.

According to some embodiments of the invention, step (1) is drying the treated product without filtration.

According to some embodiments of the present invention, the modified ZSM-5 molecular sieve in step (2) accounts for SiO in the crystallization liquid₂10-100% of the mass.

According to some specific embodiments of the present invention, the step (2) includes mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent, and deionized water to form a secondary crystallized gel, then crystallizing, and performing post-treatment to obtain the metal-modified MFI @ MFI core-shell molecular sieve catalyst.

According to some specific embodiments of the present invention, wherein the silicon source in step (2) is selected from one or more of water glass, silica sol, silicic acid, ethyl orthosilicate, coarse silica gel and silica white.

According to some embodiments of the invention, wherein the boron source of step (2) is selected from the group consisting of boric acid, sodium metaborate and sodium tetraborate.

According to some specific embodiments of the present invention, the template agent in step (2) is selected from one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide in any combination.

According to some embodiments of the present invention, in the step (2), the molar ratio of the silicon source, the boron source, the template agent and the deionized water gel is 1: (0-0.05): (0.05-0.5): (5-75).

According to some embodiments of the present invention, the crystallizing in step (2) comprises crystallizing at 100 ℃ to 200 ℃ for 2 to 96 hours.

According to some embodiments of the present invention, the crystallizing in step (2) comprises crystallizing at 140 ℃ to 180 ℃ for 24 to 72 hours.

According to some specific embodiments of the present invention, the post-treatment in step (2) comprises subjecting the product after further crystallization to suction filtration, washing, drying and ion exchange.

According to some specific embodiments of the present invention, the step (2) includes mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and stirring for 60-300min to form a secondary crystallized gel.

According to some specific embodiments of the present invention, the step (2) includes mixing the modified ZSM-5 molecular sieve obtained in the step (1) with a silicon source, a boron source, a template agent and deionized water, and stirring for 180min to form a secondary crystallized gel.

According to some embodiments of the invention, the stirring speed in step (2) is 60 to 500 r/min.

According to some embodiments of the present invention, the stirring speed in step (2) is 120-300 r/min.

According to some embodiments of the present invention, the washing in step (2) comprises washing with one or two of deionized water, methanol and ethanol as a solvent; the drying temperature range is 50-150 ℃, and the drying time is 2-24 h.

According to some specific embodiments of the invention, the ion exchange in the step (2) comprises preparing a mixed solution of a molecular sieve and 0.5-2 mol/L ammonium chloride solution in a mass ratio of 1: 5-1: 20, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and roasting at 500-600 ℃ for 4-24 hours.

According to some specific embodiments of the present invention, the ion exchange in step (2) includes preparing a mixed solution of a molecular sieve and 1mol/L ammonium chloride solution in a mass ratio of 1:10, performing ion exchange at 90 ℃, performing suction filtration, washing, drying, and calcining at 550 ℃ for 6 hours.

According to some embodiments of the invention, the ion exchange process of step (2) is repeated 2 times.

It is understood that the "ion exchange process is repeated 2 times" in the present invention means that the step of repeating the ion exchange with ammonium chloride is repeated 2 times.

On the other hand, the invention also provides the metal modified MFI @ MFI core-shell type molecular sieve catalyst prepared by the preparation method.

In another aspect, the invention further provides a method for preparing propylene by methanol conversion, wherein the method comprises the step of carrying out catalytic reaction on a mixture of methanol and water serving as a raw material by using the metal modified MFI @ MFI core-shell type molecular sieve catalyst to obtain the propylene.

The method of the invention can obtain propylene and higher butene, and the catalyst can make the sum of trienes of ethylene, propylene and butene higher, and typically the selectivity of the trienes reaches more than 83%.

According to some embodiments of the invention, wherein the reaction conditions comprise: the reaction temperature is 450-500 ℃; the space velocity is 0.5-15h^-1。

According to some embodiments of the invention, the reaction conditions further comprise: the pressure is normal pressure.

In conclusion, the invention provides a metal modified MFI @ MFI core-shell type molecular sieve catalyst and a preparation method thereof. The catalyst of the invention has the following advantages:

through the thermal modification of a metal oxide solvent, under the high-temperature and high-pressure thermal condition of the solvent and the synergistic effect of organosilane, the metal oxide can enter the inside of a molecular sieve pore channel, is bonded with a molecular sieve and hydroxyl of the organosilane, is stable in the molecular sieve, and can properly reduce the density of a strong acid in the molecular sieve; meanwhile, the optimized sample has a multi-stage pore channel structure with a core phase rich in mesopores and a shell phase rich in micropores, and the oxidation-reduction property of the metal oxide can oxidize carbon deposition into CO or CO₂And (4) removing and further delaying the carbon deposition rate. Due to the advantages, the metal oxide modified MFI @ MFI type core-shell molecular sieve catalyst can greatly reduce the carbon deposition rate of the reaction of preparing propylene from methanol, improve the selectivity of propylene and prolong the catalytic life, and the modification effect is improved more than that of the traditional mode.

Drawings

FIG. 1 is an X-ray diffraction (XRD) pattern of each of the examples of the present invention and the comparative example.

FIG. 2 is a Scanning Electron Microscope (SEM) image of a catalyst prepared according to example 1. It can be seen from the figure that the core-shell molecular sieve particles have uniform size and are distributed in the range of 300-500nm, and the scanning electron microscope images of the core-shell molecular sieves prepared in other examples also have the morphology similar to that of FIG. 2.

FIG. 3 shows MnO in example 2₂The SEM images of the nanoparticles show that the metal oxide particles are uniform in size and distributed in the range of 20-60nm, and the electron microscope images of the metal oxide particles of other examples also have similar particle sizes and distributions to those of FIG. 3.

Fig. 4 is a Transmission Electron Microscope (TEM) image of the catalyst prepared in example 1. The figure shows that the core-shell molecular sieve has a hierarchical pore channel structure with a core phase rich in mesopores and a shell phase rich in micropores. Transmission electron micrographs of the core-shell molecular sieves prepared in the other examples also have morphologies and channel structures similar to those of fig. 4.

FIG. 5 is a hydroxyl radical infrared (OH-IR) plot for comparative example 3 and example 1. The difference between comparative example 3 and example 1 is that example 1 was solvothermally modified with a metal oxide, whereas comparative example 3 was not solvothermally modified with a metal oxide, as can be seen in the figure, example 1 is 3740cm relative to comparative example 3^-1、3725cm^-1And 3610cm^-1The peak intensity is obviously reduced, which shows that the metal oxide can enter the inside of the molecular sieve pore channel through the solvent thermal modification of the metal oxide, and is stably bonded with the molecular sieve and the hydroxyl of organosilane, so that the content of the silicon hydroxyl and the bridged hydroxyl on the inner and outer surfaces is reduced.

FIG. 6 shows temperature programmed desorption (NH) of ammonia gas in comparative example 3 and example 1₃-TPD) map. As can be seen from the figure, the amount of strong acid in example 1 is significantly reduced relative to comparative example 3, indicating that solvothermal modification of the metal oxide can reduce the strong acid density of the molecular sieve.

Fig. 7 is a bar graph showing the conversion of triisopropylbenzene cracking reaction in comparative example 1 and example 1. As can be seen from the figure, the TIPB conversion rate of example 1 is greatly reduced relative to comparative example 1, indicating that the density of the strong acid on the outer surface of the molecular sieve is greatly reduced relative to comparative example 1, and the inert MFI molecular sieve shell coating can greatly reduce the density of the strong acid on the outer surface of the molecular sieve.

Detailed Description

The following detailed description is provided for the purpose of illustrating the embodiments and the advantageous effects thereof, and is not intended to limit the scope of the present disclosure.