Hierarchical pore zeolite molecular sieve as well as preparation method and application thereof

Abstract

The invention provides a hierarchical pore zeolite molecular sieve as well as a preparation method and application thereof. The preparation method comprises the following steps: 1) pretreating a hydrogen-type zeolite molecular sieve at 500-600 DEG C to obtain a pretreated hydrogen-type zeolite molecular sieve; 2) in an inert gas environment, cooling the pretreated hydrogen type zeolite molecular sieve to 300-500 DEG C, introducing an inert gas containing a carbon source into the system, and carrying out carbon pre-deposition treatment to obtain a carbon pre-deposited zeolite molecular sieve; and (3) sequentially carrying out alkali treatment, roasting treatment, acid pickling treatment and drying treatment on the pre-carbon-deposited zeolite molecular sieve to obtain the hierarchical pore zeolite molecular sieve. Through carbon pre-deposition treatment, carbon deposition layers are formed on the surface and in the zeolite, disordered etching of alkali is resisted, and the hierarchical pore zeolite molecular sieve with rich mesopores and micropore structures is obtained. The prepared hierarchical pore zeolite has good molecular diffusivity as a methanol-to-olefin catalyst, and the conversion rate of methanol and the service life of the catalyst are both improved.

Description

Technical Field

[0001] The invention relates to a multi-level pore zeolite molecular sieve, in particular to a multi-level pore zeolite molecular sieve and a preparation method and application thereof, belonging to the technical field of molecular sieve catalysts. Background Art

[0002] Controllable preparation of multi-level pore zeolite molecular sieves is an important topic of concern to the petrochemical industry and academia. Catalysts are the core of the development of oil refining and chemical technology, and zeolite molecular sieves are one of the important solid acid catalysts. The mass transfer defects of their micropores seriously affect the utilization of active sites and the rate of catalytic reactions. Introducing mesopores or macropores into the microporous system of zeolite molecular sieves has a positive effect on improving molecular mass transfer capacity and slowing down catalyst deactivation.

[0003] Studies have shown that etching zeolite molecular sieves with alkaline media can artificially create a mesoporous structure inside the zeolite molecular sieve crystals, forming multi-level pores to obtain multi-level pore zeolite molecular sieves, thereby reducing the diffusion resistance of reactant molecules in the molecular sieve and improving mass transfer efficiency. However, during the pore expansion treatment, the disordered etching of the alkali will cause the zeolite molecular sieve framework to collapse rapidly, resulting in a significant decrease in the crystallinity, micropore volume and specific surface area of ​​the final zeolite molecular sieve. The above problems are particularly prominent when alkali is used to treat zeolite molecular sieves with a high silicon-aluminum ratio or unstable skeleton aluminum.

[0004] At present, there have been studies on the introduction of small molecule organic compounds as pore directing agents of the zeolite molecular sieve framework before alkali treatment, thereby forming a "protective layer" on the surface or inside the pores of the zeolite molecular sieve crystal. During the alkaline etching process, the collapse of the zeolite molecular sieve framework can be alleviated, and the original microporous structure of the molecular sieve can be retained as much as possible while obtaining a mesoporous structure. However, the yield of the multi-level porous zeolite obtained by this method is too low, and the protective ability of the pore directing agent is weak. When the multi-level porous zeolite molecular sieve is used to catalyze the methanol to olefin reaction, its catalytic life is still unsatisfactory. Summary of the invention

[0005] The present invention provides a method for preparing a multi-level pore zeolite molecular sieve. Through pre-carbon deposition treatment, a carbon deposition layer is formed on the surface of the zeolite and inside the pores as a pore protective agent to resist the rapid diffusion and disordered etching in the micropores of the zeolite during subsequent alkali treatment, thereby improving the crystallinity, micropore volume, mesopore volume, specific surface area and yield of the multi-level pore zeolite molecular sieve. The method is applied to catalyze the methanol to olefin reaction, which can accelerate the mass transfer efficiency of the catalyst and reduce the carbon deposition rate.

[0006] The present invention also provides a multi-level pore zeolite molecular sieve prepared by the above method, which has high crystallinity, high specific surface area and abundant micropores and mesopores uniformly distributed, and the multi-level pore zeolite molecular sieve prepared by the method has a high product yield. Due to its high active site utilization rate and high mass transfer efficiency, it is applied to catalyze the methanol to olefin reaction, which is conducive to improving the catalytic effect of the catalyst.

[0007] The present invention also provides a hydrogen-type multi-level pore zeolite molecular sieve, which is obtained by ion exchange and calcination of the multi-level pore zeolite molecular sieve, and can significantly improve the catalytic efficiency and life of the catalytic reaction.

[0008] The present invention also provides a methanol to olefin catalyst obtained by tableting, crushing and sieving the above hydrogen-type multi-level pore zeolite molecular sieve. The catalyst has excellent performance and can significantly improve the conversion rate of methanol and the life of the catalyst.

[0009] The present invention also provides a method for preparing olefins by cracking alcohols, which adopts the multi-level pore zeolite molecular sieve or hydrogen-type multi-level pore zeolite molecular sieve or methanol to olefin catalyst and has excellent catalytic performance.

[0010] In a first aspect, the present invention provides a method for preparing a multi-level pore zeolite molecular sieve, comprising the following steps:

[0011] 1) pre-treating the hydrogen-type zeolite molecular sieve at 500-600° C. to obtain the pre-treated hydrogen-type zeolite molecular sieve;

[0012] 2) In an inert gas environment, the pretreated hydrogen-type zeolite molecular sieve is cooled to 300-500° C., and an inert gas including a carbon source is introduced into the system to perform a pre-carbon deposition treatment to obtain a pre-carbon deposition zeolite molecular sieve;

[0013] 3) The pre-carbonized zeolite molecular sieve is sequentially subjected to alkali treatment, calcination treatment, acid washing treatment and drying treatment to obtain a multi-level pore zeolite molecular sieve.

[0014] In the preparation method as described above, in step 2), the mass space velocity of the inert gas including the carbon source is 0.1-10h -1 .

[0015] In the preparation method as described above, in step 2), the carbon source includes at least one of methanol, ethanol, C1-C4 alkanes, and C1-C4 alkenes.

[0016] In the preparation method as described above, the mesh size of the hydrogen-type zeolite molecular sieve raw material in step 1) is 10-100 meshes.

[0017] In the preparation method as described above, in step 1), the pretreatment step is carried out in a tube furnace.

[0018] In the preparation method as described above, in the step 1), the pretreatment is performed in an air or oxygen atmosphere.

[0019] A second aspect of the present invention provides a multi-level pore zeolite molecular sieve, wherein the multi-level pore zeolite molecular sieve is prepared according to the method described in any one of claims 1-6.

[0020] The third aspect of the present invention provides a hydrogen-type hierarchical pore zeolite molecular sieve, wherein the hydrogen-type hierarchical pore zeolite molecular sieve is obtained by subjecting the hierarchical pore zeolite molecular sieve according to claim 7 to ammonium ion exchange and calcination.

[0021] A fourth aspect of the present invention provides a methanol to olefins catalyst, which is obtained by tableting, crushing and sieving the hydrogen-type multi-level pore zeolite molecular sieve according to claim 8.

[0022] The method for preparing a multi-level pore zeolite molecular sieve of the present invention pre-carbonizes the hydrogen-type zeolite molecular sieve, forms carbon deposits on the surface of the zeolite and inside the pores as a pore protector to resist the rapid diffusion and disordered etching of alkali in the zeolite micropores, and realizes that the hydrogen-type zeolite molecular sieve constructs multi-level pores through alkali treatment while protecting the integrity of its zeolite skeleton as much as possible, thereby obtaining a multi-level pore zeolite molecular sieve with high crystallinity and abundant micropores and mesopores uniformly distributed after alkali treatment and acid washing. It is applied to the catalytic methanol to olefin reaction, which can accelerate the mass transfer efficiency of the catalyst, reduce the carbon deposition efficiency, and thus improve the conversion rate of methanol and the life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The fluorescence images of carbon deposit distribution in the central cross section of the hydrogen-type zeolite molecular sieve crystals prepared in Examples 5, 1, 6 and 7 of the present invention are as follows;

[0024] Figure 2 The carbon deposition amount variation curves of the hydrogen-type zeolite molecular sieves prepared in Example 5, Example 1, Example 6, Example 7, Example 8 and Example 9 of the present invention at different pre-carbon deposition reaction times are shown;

[0025] Figure 3 It is a comparison chart of XRD spectra of the hierarchical pore zeolite molecular sieves prepared in Example 1, Examples 5-7 and Comparative Example 1 of the present invention and the original SSZ-13 zeolite powder;

[0026] Figure 4 The scanning electron microscope comparison diagram of the hierarchical pore zeolite molecular sieve prepared in Example 1, Example 7 and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder;

[0027] Figure 5AA comparison diagram of nitrogen adsorption-desorption isotherms of the hierarchical pore zeolite molecular sieves prepared in Example 1, Examples 5-7, and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder;

[0028] Figure 5B A comparison chart of pore distribution curves of the multi-level pore zeolite molecular sieves prepared in Example 1, Examples 5-7, and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder;

[0029] Figure 6 This is a comparison chart of NH3-TPD acidity characterization of the hierarchical pore zeolite molecular sieve prepared in Example 1, Example 7 and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder;

[0030] Figure 7 It is a comparison chart of the evaluation results of the methanol to olefins reaction of the methanol to olefins catalysts prepared in Example 1, Examples 5-7 and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In a first aspect, the present invention provides a method for preparing a multi-level pore zeolite molecular sieve, comprising the following steps:

[0033] 1) pre-treating the hydrogen-type zeolite molecular sieve at 500-600° C. to obtain the pre-treated hydrogen-type zeolite molecular sieve;

[0034] 2) In an inert gas environment, the pretreated hydrogen-type zeolite molecular sieve is cooled to 300-500° C., and an inert gas including a carbon source is introduced into the system to perform a pre-carbon deposition treatment to obtain a pre-carbon deposition zeolite molecular sieve;

[0035] 3) The pre-carbonized zeolite molecular sieve is sequentially subjected to alkali treatment, calcination treatment, acid washing treatment and drying treatment to obtain a multi-level pore zeolite molecular sieve.

[0036] The hydrogen-type zeolite molecular sieve in the present invention can be any acidic zeolite molecular sieve, for example, at least one of SSZ-13 zeolite and SAPO-34 zeolite of CHA configuration, ZSM-5 zeolite of MFI configuration, and the like.

[0037] The present invention does not strictly limit the acquisition of the above hydrogen-type zeolite molecular sieve, which can be obtained from the market or prepared. For example, the hydrogen-type SSZ-13 zeolite molecular sieve can be prepared by the following steps.

[0038] 1A) SSZ-13 zeolite molecular sieve is calcined at high temperature to obtain Na-SSZ-13 zeolite molecular sieve;

[0039] 2A) exchanging Na-SSZ-13 zeolite molecular sieve with ammonium ions to obtain H-SSZ-13 zeolite molecular sieve;

[0040] In the above step 1A), the SSZ-13 zeolite molecular sieve is conventionally commercially available, and the product after high-temperature calcination is a Na-type zeolite molecular sieve, namely, Na-SSZ-13 zeolite molecular sieve.

[0041] It should be noted that the present invention is not limited to the treatment of SSZ-13 zeolite when using the above method to obtain hydrogen-type zeolite molecular sieves, but can also treat other zeolite molecular sieves with different topological structures of more than eight-membered rings, as long as hydrogen-type zeolite molecular sieves can be generated.

[0042] In one embodiment, the silicon-to-aluminum ratio of the SSZ-13 zeolite molecular sieve raw material is 10-50.

[0043] In another embodiment, the SSZ-13 zeolite molecular sieve is calcined at a temperature of 500-600° C., a calcination time of 4-10 h, and a heating rate of 1-10° C. / min.

[0044] Furthermore, the high temperature calcination temperature of the SSZ-13 zeolite molecular sieve is 550° C., the calcination time is 10 h, and the heating rate during the calcination process is 1° C. / min.

[0045] In the above step 2A), the hydrogen-type SSZ-13 zeolite molecular sieve, namely, the H-SSZ-13 zeolite molecular sieve, is obtained by exchanging the Na-SSZ-13 zeolite molecular sieve with ammonium ions.

[0046] In one embodiment, the ammonium ion exchange uses an ammonium chloride aqueous solution with a concentration of 1-3 mol / L, the temperature of the ammonium ion exchange is 60-80°C, the exchange time is 1-3 hours, and the number of exchanges is 2-4 times. The usage ratio of the zeolite molecular sieve to the ammonium chloride aqueous solution is 1 g: (50-100) mL, that is, the solid-liquid ratio is 1: (50-100).

[0047] Furthermore, the ammonium ion exchange uses an ammonium chloride aqueous solution with a concentration of 1 mol / L, the temperature of the ammonium ion exchange is 70°C, the time of the ammonium ion exchange is 2 hours, and the number of exchanges is 3. The solid-liquid ratio of the zeolite molecular sieve to the ammonium chloride aqueous solution is 1:50.

[0048] The hydrogen-type SSZ-13 zeolite molecular sieve is calcined in step 1A) to remove the organic template in the micropores. Step 2A) The Na ions of the SSZ-13 zeolite are replaced by ammonium ion exchange to obtain an H-SSZ-13 zeolite molecular sieve with acidic activity, which is beneficial to the subsequent pre-carbon deposition reaction.

[0049] The pre-carbon deposition of the present invention refers to the process of forming a carbonaceous material inside the zeolite pores at high temperature. Alkali treatment is a process of "destructively" dissolving or etching the framework of the zeolite molecular sieve through an alkaline medium, thereby artificially creating a multi-level pore inside the zeolite molecular sieve crystal. Before the alkali treatment, the present invention first performs a pre-carbon deposition treatment on the hydrogen-type zeolite molecular sieve to obtain a multi-level pore zeolite molecular sieve with rich mesopore volume, high specific surface area and crystallinity and high yield. It should be noted that the inventors have found that when the pretreatment process in step 1) is performed before the pre-carbon deposition treatment, the uniform distribution of carbon deposits on the surface of the hydrogen-type molecular sieve can be achieved during the subsequent pre-carbon deposition process, thereby promoting the protection of the molecular sieve framework by the carbon deposition layer in the subsequent alkali treatment step, thereby improving the crystallinity and pore volume of the obtained molecular sieve, and improving the catalytic efficiency of the molecular sieve. In addition, due to the above-mentioned protective effect, the multi-level pore zeolite molecular sieve obtained by the present invention also has a higher yield.

[0050] After the pre-carbon deposition treatment, the pre-carbon deposition zeolite molecular sieve is subjected to an alkali treatment, and the framework of the zeolite molecular sieve is "destructively" dissolved or etched by the alkaline medium, thereby artificially creating multi-level channels inside the hydrogen-type zeolite molecular sieve crystals to improve its mass transfer efficiency.

[0051] The present invention does not strictly limit the alkaline medium used, including at least one of sodium hydroxide, sodium carbonate, ammonia water and the like commonly used in the art.

[0052] In a specific embodiment, the concentration of the sodium hydroxide aqueous solution used in the alkali treatment is (0.05-0.5) mol / L. The dosage ratio of the sodium hydroxide aqueous solution to the pre-carbonized zeolite molecular sieve is 100 mL: (1-4) g, that is, the solid-liquid ratio is (1-4): 100. The temperature of the alkali treatment is 50-80°C, and the time of the alkali treatment is 1-2 hours.

[0053] The centrifuged solid sample collected after the alkali treatment is washed with water until neutral and subjected to a calcination treatment. Specifically, the calcination treatment temperature is 80-140° C. and the drying time is 4-12 hours.

[0054] Then, the calcined sample is pickled with an acid solution to remove the remaining amorphous substances in the product and fully expose the pores in the molecular sieve.

[0055] Specifically, the conditions for pickling the sample after calcination are: the acid solution includes hydrochloric acid aqueous solution, and the concentration is 0.1~0.5mol / L. The amount ratio of hydrochloric acid aqueous solution to the sample after calcination is 100mL: (1~3)g, that is, the solid-liquid ratio is (1~3): 100. The temperature of the pickling treatment is 50~100℃, and the time of the pickling treatment is 1~3h.

[0056] Furthermore, the concentration of the hydrochloric acid aqueous solution in the pickling treatment is 0.2 mol / L, the temperature of the pickling treatment is 80° C., and the time of the pickling treatment is 2 hours.

[0057] Finally, the centrifuged solid sample collected after the acid washing treatment is washed with water to neutrality and subjected to a second drying to obtain a hierarchical pore zeolite molecular sieve.

[0058] As an optional implementation, the temperature of the pickling and drying treatments is 80-140° C., and the drying time is 4-12 hours.

[0059] In the present invention, by pre-carbon deposition treatment of the hydrogen-type zeolite molecular sieve, multi-directional protection of the molecular sieve framework is achieved, the damage to the framework caused by alkali etching is reduced, the collapse of the zeolite molecular sieve framework can be alleviated, and the original microporous structure of the molecular sieve can be retained as much as possible while obtaining the mesoporous structure. In the end, not only a multi-level pore zeolite molecular sieve with high crystallinity and high specific surface area can be obtained, but also the yield of the molecular sieve can be improved. Thanks to the high specific surface area and complete crystal structure of the multi-level pore zeolite molecular sieve, the prepared methanol to olefin catalyst has abundant catalytic active sites, fast mass transfer efficiency, and exhibits a lower carbon deposition rate, achieving a dual increase in the conversion rate of methanol and the life of the catalyst.

[0060] In one embodiment, the mass space velocity of the inert gas including the carbon source can be controlled to be between 0.1 and 10 h −1 , to adjust the ratio of zeolite molecular sieve and carbon source, so as to obtain a zeolite molecular sieve with appropriate carbon deposition amount, which can fully protect the skeleton structure of the molecular sieve and prevent excessive carbon deposition, making it difficult to form pores in the subsequent alkali treatment, thus affecting the conversion efficiency of the prepared methanol to olefins catalyst.

[0061] In addition, the amount of carbon deposits on the hydrogen-type zeolite molecular sieve can be controlled by controlling the pre-carbon deposition reaction time. Therefore, according to actual needs, the distribution state of carbon deposits on the molecular sieve surface can be controlled through the carbon deposition distribution fluorescence map to obtain the corresponding high-performance catalyst.

[0062] The present invention does not impose any particular limitation on the cooling rate in step 2), as long as the hydrogen-type zeolite molecular sieve can be cooled to 300-500° C. For example, the hydrogen-type zeolite molecular sieve can be cooled naturally, or an external cooling device can be used to cool the hydrogen-type zeolite molecular sieve to 300-500° C.

[0063] The carbon source of the present invention includes at least one of low-carbon organic compounds such as methanol, ethanol, C1-C4 alkanes, C1-C4 olefins, etc., which is beneficial to the diffusion of the carbon source into the zeolite molecular sieve, improves the uniformity of the pore distribution of the subsequent multi-level pore molecular sieve, and further improves the yield and crystallinity of the multi-level pore zeolite molecular sieve.

[0064] In addition, in order to promote the diffusion of carbon source on the surface and inside of the hydrogen-type zeolite molecular sieve after pretreatment, obtain a uniformly distributed carbon deposition layer, and then obtain a high-crystallinity multi-level pore zeolite molecular sieve, before the pre-carbon deposition treatment, the above-mentioned carbon source should be gasified first, and then carried into the system by an inert gas for pre-carbon deposition treatment.

[0065] Specifically, the gasification step includes: first, injecting the liquid carbon source into the tubular furnace using an injection pump, heating the carbon source using a heating device, and converting it into a gas when the temperature reaches above the boiling point of the liquid carbon source, and then using an inert gas to carry out the gaseous carbon source for pre-carbon deposition treatment.

[0066] As an optional implementation, in order to improve the yield of the multi-level pore zeolite molecular sieve and the uniformity of the carbon deposition layer, the hydrogen-type zeolite molecular sieve raw material with a mesh size of 10 to 100 can also be screened out for subsequent treatment.

[0067] In a specific embodiment, the pretreatment process of step 1) can be carried out in a tube furnace, which is not only conducive to the operability of the subsequent pre-carbon deposition treatment, but also can quickly remove the volatile impurities.

[0068] In addition, the pretreatment in the above step 1) can be performed in an air or oxygen atmosphere.

[0069] In step 2) of the present invention, the temperature can be lowered by natural cooling in a tube furnace under the purge of inert gas.

[0070] In a second aspect, the present invention provides a multi-level pore zeolite molecular sieve prepared by the above method, which is treated with pre-carbon deposition to protect the surface and interior of the hydrogen-type zeolite molecular sieve. The multi-level pore zeolite molecular sieve has good crystal retention, high mesopore volume, micropore volume and high specific surface area. The mesopore volume, micropore volume and specific surface area can reach 0.11 m 3 g -1 , 0.27 m 3 g -1 、678 m 2 g -1 Applying it to catalysts is beneficial to improving the utilization rate of active sites and mass transfer efficiency of catalysts.

[0071] In the third aspect, the present invention also provides a hydrogen-type multi-level porous zeolite molecular sieve, which is obtained by exchanging the above-mentioned multi-level porous zeolite molecular sieve with ammonium ions and calcining. Thanks to the excellent mesopore volume, micropore volume and high specific surface area of ​​the above-mentioned multi-level porous zeolite molecular sieve, the active vacancies of the obtained hydrogen-type multi-level porous zeolite molecular sieve are fully exposed, which is beneficial to the adsorption, reaction, desorption and diffusion of each reactant in the active sites in the zeolite micropores during the reaction, thereby improving its catalytic efficiency.

[0072] The above-mentioned ammonium ion exchange reaction is to replace the cations of the hierarchical pore zeolite molecular sieve of the second aspect, so as to obtain a hydrogen-type hierarchical pore zeolite molecular sieve rich in acidic active sites.

[0073] Specifically, the multi-level pore zeolite molecular sieve can be subjected to ammonium ion exchange to obtain the hydrogen-type multi-level pore zeolite molecular sieve through the following steps.

[0074] The multi-level pore zeolite molecular sieve is weighed, and an ammonium ion exchange reaction is carried out using a 1-3 mol / L ammonium chloride aqueous solution. The amount ratio of the multi-level pore zeolite molecular sieve to the ammonium chloride aqueous solution is 1 g: (50-100) mL, that is, the solid-liquid ratio is 1: (50-100), the reaction temperature is 60-80°C, the reaction time is 1-3 h, and the number of ion exchanges is 2-4 times.

[0075] Furthermore, the ammonium ion exchange uses an ammonium chloride aqueous solution with a concentration of 1 mol / L, the temperature of the ammonium ion exchange is 70°C, the time of the ammonium ion exchange is 2 hours, and the number of exchanges is 3. The solid-liquid ratio of the multi-level pore zeolite molecular sieve to the ammonium chloride aqueous solution is 1:50.

[0076] After the ammonium ion exchange reaction is completed, the hydrogen-type multi-level pore zeolite molecular sieve is calcined to remove the carbon deposit layer used as a "pore protecting agent".

[0077] Specifically, the calcination can be performed under the following conditions: the calcination temperature is 500-600° C., the calcination time is 4-10 hours, and the heating rate during the calcination process is 1-10° C. / min.

[0078] In one embodiment, active metal elements, including at least one of metal ions such as calcium and magnesium, can be loaded on the hydrogen-type multi-level pore zeolite molecular sieve as a catalyst for the MTP reaction, which has a catalytic effect of catalyzing the production of propylene from methanol.

[0079] In a fourth aspect, the present invention also provides a methanol to olefins catalyst, which has a complete morphology and a hollow cubic crystal. It has high crystallinity, good skeleton preservation, high acid site retention, high mesopore volume, and stronger mass transfer capacity. It exhibits better catalytic performance and a lower carbon deposition rate in the methanol to olefins reaction.

[0080] Furthermore, the particle size of the methanol to olefin catalyst of the present invention is 250-450 μm, the crystal morphology is a hollow cube, the silicon-aluminum ratio is 10-50, and the micropore volume is 0.20-0.35 cm 3 / g, mesopore volume is 0.03~0.30cm 3 / g, BET specific surface area is 540~700m 2 / g. In addition, the present invention significantly improves the yield of methanol to olefins catalyst and has greater industrial economic efficiency.

[0081] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] The present invention is further described below by specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, conventional materials and conventional instruments, which can be commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0083] Example 1

[0084] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve of this embodiment comprises the following steps:

[0085] (1) The SSZ-13 zeolite raw powder (Si / Al=23) was calcined at 550°C for 10 h with a heating rate of 1°C / min to obtain Na-SSZ-13 zeolite raw powder.

[0086] (2) Weigh 3 g of the Na-SSZ-13 zeolite raw powder in the above step (1), and use 1 mol / L ammonium chloride aqueous solution to carry out ammonium ion exchange reaction, with a solid-liquid ratio of 1:50, a reaction temperature of 70°C, a reaction time of 2 h, and the number of ion exchanges being 3 times; after the ammonium ion exchange is completed, calcination is carried out, the calcination temperature is 550°C, the calcination time is 4 h, and the calcination heating rate is 1°C / min, and H-SSZ-13 zeolite molecular sieve is obtained after calcination.

[0087] (3) The H-SSZ-13 zeolite molecular sieve in step (2) is subjected to a pre-carbon deposition treatment, specifically comprising the following steps:

[0088] 1) The H-SSZ-13 zeolite molecular sieve in step (2) is placed in a tablet press and sieved out 40-60 mesh particles. 2.5 g of the particles are weighed and placed in a tubular furnace, spread evenly, and air is introduced to heat the mixture to 550°C at a rate of 5°C / min for pretreatment. After 2 hours, a pretreated hydrogen-type zeolite molecular sieve is obtained.

[0089] 2) After the pretreatment is completed, switch the gas to nitrogen, cool naturally to 350°C, and then use nitrogen to carry the vaporized methanol at a mass space velocity of 1h −1 The pre-carbon deposition reaction was carried out for 1 h to obtain a pre-carbon deposition SSZ-13 zeolite sample.

[0090] (4) The pre-carbonized SSZ-13 zeolite obtained in step (3) is poured into a 0.2 mol / L sodium hydroxide aqueous solution, wherein the solid-to-liquid ratio of the pre-carbonized SSZ-13 zeolite to the sodium hydroxide aqueous solution is 1:30, and the mixture is placed in a 70° C. water bath and stirred for 1 h. After the alkali treatment, the solid sample is collected by centrifugation, washed with water until neutral, and dried in an oven at 100° C. for 12 h to obtain an intermediate product.

[0091] (5) Take 1 g of the intermediate product in the above step (4) and pour it into 100 mL of a 0.2 mol / L hydrochloric acid aqueous solution, place it in an 80°C water bath and stir it for 2 h; after the acid washing treatment, collect the solid sample by centrifugation, wash it with water until it is neutral, and dry it in an oven at 100°C for 12 h to obtain a multi-level pore SSZ-13 zeolite molecular sieve.

[0092] (6) The multi-level pore SSZ-13 zeolite molecular sieve obtained by acid washing in step (5) was subjected to ammonium ion exchange reaction using a 1 mol / L aqueous ammonium chloride solution at a solid-to-liquid ratio of 1:50, a reaction temperature of 70°C, a reaction time of 2 h, and ion exchange times of 3 times; after the ammonium ion exchange, the multi-level pore H-SSZ-13 zeolite molecular sieve was calcined at a temperature of 550°C, a calcination time of 4 h, and a calcination heating rate of 1°C / min to obtain a multi-level pore H-SSZ-13 zeolite molecular sieve, which was named SZ-1h-AT.

[0093] Example 2

[0094] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve of this embodiment is basically the same as that of Embodiment 1, except that step (3) includes the following steps:

[0095] 1) The H-SSZ-13 zeolite molecular sieve in step (2) is placed in a tablet press to screen out 80-100 mesh particles, 2.5 g of the particles are weighed and placed in a tubular furnace, spread evenly, and air is introduced to heat the mixture to 500°C at a rate of 5°C / min for pretreatment. After 1 hour, a pretreated hydrogen-type zeolite molecular sieve is obtained.

[0096] 2) After the pretreatment is completed, switch the gas to nitrogen and naturally cool to 300°C. Then, nitrogen carries the vaporized methanol at a mass space velocity of 10h −1 The pre-carbon deposition reaction was carried out for 1 hour to obtain a pre-carbon deposition SSZ-13 zeolite sample.

[0097] Example 3

[0098] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve of this embodiment is basically the same as that of Embodiment 1, except that step (3) includes the following steps:

[0099] 1) The H-SSZ-13 zeolite molecular sieve in step (2) is placed in a tablet press to screen out 10-40 mesh particles, 2.5 g of the particles are weighed and placed in a tubular furnace, spread evenly, and air is introduced at a rate of 10°C / min, and the temperature is raised to 600°C for pretreatment. After 1 hour, the pretreated hydrogen-type zeolite molecular sieve is obtained.

[0100] 2) After the pretreatment, switch the gas to nitrogen and cool naturally to 500°C. Then, nitrogen is used to carry the vaporized ethanol at a mass space velocity of 5 h −1 The pre-carbon deposition reaction was carried out for 12 hours to obtain a pre-carbon deposition SSZ-13 zeolite sample.

[0101] Example 4

[0102] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve of this embodiment is basically the same as that of Example 1, except that the raw material of this embodiment is SAPO-34 zeolite powder.

[0103] Example 5

[0104] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve in this embodiment is basically the same as that in Example 1, except that the pre-carbon deposition reaction time in step (3) is 0.5 h.

[0105] Example 6

[0106] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve in this embodiment is basically the same as that in Example 1, except that the pre-carbon deposition reaction time in step (3) is 2 hours.

[0107] Example 7

[0108] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve in this embodiment is basically the same as that in Example 1, except that the pre-carbon deposition reaction time in step (3) is 3 hours.

[0109] Example 8

[0110] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve in this embodiment is basically the same as that in Example 1, except that the pre-carbon deposition reaction time in step (3) is 6 hours.

[0111] Example 9

[0112] The preparation method of the hydrogen-type multi-level pore zeolite molecular sieve in this embodiment is basically the same as that in Example 1, except that the pre-carbon deposition reaction time in step (3) is 12 hours.

[0113] Example 10

[0114] The preparation method of the hydrogen-type hierarchical pore zeolite molecular sieve of this embodiment is basically the same as that of Embodiment 1, except that in step (3), nitrogen is used to carry out the pre-carbon deposition reaction of the vaporized ethanol.

[0115] Comparative Example 1:

[0116] This comparative example provides a method for preparing a hydrogen-type multi-level pore H-SSZ-13 zeolite molecular sieve by a conventional alkali treatment method, wherein the preparation method comprises the following steps:

[0117] (1) The SSZ-13 zeolite raw powder (Si / Al=23) was calcined at 550°C for 10 h with a heating rate of 1°C / min to obtain Na-SSZ-13 zeolite raw powder, which was then placed in a vacuum drying oven at 160°C for 4 h to complete dehydration.

[0118] (2) Weigh 3 g of the Na-SSZ-13 zeolite powder dehydrated in step (1) above, pour it into a 0.2 mol / L sodium hydroxide aqueous solution (solid-liquid ratio 1:30), place it in a 70°C water bath and stir for 1 h; after the alkali treatment, collect the solid sample by centrifugation, wash it with water until it is neutral, and dry it in an oven at 100°C for 12 h.

[0119] (3) Take 1 g of the solid sample collected by the alkali treatment in the above step (2), introduce it into 100 mL of a 0.2 mol / L hydrochloric acid aqueous solution, place it in an 80°C water bath and stir it for 2 h; after the acid washing treatment, collect the solid sample by centrifugation, wash it with water until it is neutral, and dry it in an oven at 100°C for 12 h to obtain a multi-level pore SSZ-13 zeolite molecular sieve.

[0120] (4) The multi-level pore SSZ-13 zeolite molecular sieve obtained by acid washing in step (3) was subjected to ammonium ion exchange reaction using a 1 mol / L ammonium chloride aqueous solution, with a solid-liquid ratio of 1:50, a reaction temperature of 70°C, a reaction time of 2 h, and the number of ion exchanges being 3 times; after the ammonium ion exchange was completed, it was calcined at a calcination temperature of 550°C, a calcination time of 4 h, and a calcination heating rate of 1°C / min. After calcination, a hydrogen-type multi-level pore H-SSZ-13 zeolite molecular sieve was obtained, which was named AT.

[0121] Comparative Example 2

[0122] The present embodiment provides a method for preparing a hydrogen-type multi-level pore H-SSZ-13 zeolite molecular sieve, which comprises the following steps:

[0123] (1) The SSZ-13 zeolite raw powder (Si / Al=23) was calcined at 550°C for 10 h with a heating rate of 1°C / min to obtain Na-SSZ-13 zeolite raw powder, which was then placed in a vacuum drying oven at 160°C for 4 h to complete dehydration.

[0124] (2) Weigh 3 g of the Na-SSZ-13 zeolite powder prepared in step (1) above and place it in a sealed container. Then add a sufficient amount of diethylamine and stir for 1 h to allow the Na-SSZ-13 zeolite powder to fully adsorb the diethylamine. Then, filter and separate the zeolite powder. Place the obtained solid sample in a fume hood for a period of time to allow the diethylamine on the surface of the zeolite to evaporate.

[0125] (3) The Na-SSZ-13 zeolite raw powder obtained in step (2) was poured into a 0.2 mol / L sodium hydroxide aqueous solution with a solid-liquid ratio of 1:30, and placed in a 70°C water bath and stirred for 1 h. After the alkali treatment, the solid sample was collected by centrifugation, washed with water until neutral, and dried in an oven at 100°C for 12 h.

[0126] (4) Take 1 g of the solid sample collected by the alkali treatment in the above step (3), add it to 100 mL of a 0.2 mol / L hydrochloric acid aqueous solution, place it in an 80°C water bath and stir it for 2 h; after the acid washing treatment, collect the solid sample by centrifugation, wash it with water until it is neutral, and dry it in an oven at 100°C for 12 h to obtain a multi-level pore SSZ-13 zeolite molecular sieve.

[0127] (5) The multi-level pore SSZ-13 zeolite molecular sieve obtained by acid washing in step (4) was subjected to ammonium ion exchange reaction using 1 mol / L ammonium chloride aqueous solution, with a solid-liquid ratio of 1:50, a reaction temperature of 70°C, a reaction time of 2 h, and ion exchange times of 3 times. After the ammonium ion exchange, it was calcined at a temperature of 550°C, a calcination time of 4 h, and a heating rate of 1°C / min. After calcination, a multi-level pore H-SSZ-13 zeolite molecular sieve was obtained, which was named DEA-0.2AT.

[0128] Test Example 1

[0129] Fluorescence measurement of carbon deposit distribution was performed on the hydrogen-type hierarchical pore zeolite molecular sieves prepared in Example 5, Example 1, Example 6, and Example 7. The carbon deposits showed red fluorescence under laser excitation, as shown in FIG. Figure 1As shown, it can be seen that when the pre-carbon deposition time in Example 5 is 0.5h, the red fluorescence exhibited by the carbon deposition under the excitation of the laser is only distributed on the outer surface of the hydrogen-type multi-level pore zeolite crystal, and no carbon deposition occurs inside the crystal. As the pre-carbon deposition reaction time increases, the carbon deposition in Example 1 gradually penetrates into the interior of the zeolite crystal. When the pre-carbon deposition time in Example 6 is 2h, the carbon deposition has spread throughout the entire crystal. Therefore, the effect of carbon deposition can be regulated according to the carbon deposition distribution fluorescence diagram to obtain the desired zeolite molecular sieve catalyst.

[0130] Test Example 2

[0131] Figure 2 The graph is a graph showing the change in the amount of carbon deposits in the hydrogen-type multi-level pore zeolite molecular sieves obtained in Example 5, Example 1, Example 6, Example 7, Example 8, and Example 9 of the present invention as a function of the pre-carbon deposition time. As can be seen from the figure, as the pre-carbon deposition time increases, the amount of carbon deposits increases accordingly. In Example 8, when the pre-carbon deposition treatment time is 6 hours, the pre-carbon deposition amount basically reaches the maximum value. After 6 hours, as the pre-carbon deposition time increases, the pre-carbon deposition amount no longer changes significantly. It is worth noting that the catalytic effect of the obtained hydrogen-type multi-level pore zeolite molecular sieve does not increase with the increase in the amount of carbon deposition. Therefore, the pre-carbon deposition time can be regulated according to actual needs.

[0132] Test Example 3

[0133] Figure 3 The XRD spectra of the multi-level pore zeolite molecular sieve prepared in Example 1, Examples 5-7 and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder are compared. Figure 1 As shown, in Example 1 and Examples 5-7, all samples after alkali treatment still retain the basic characteristic peaks of the CHA topological structure. In Comparative Example 1, the XRD diffraction peak intensity of the conventional alkali-treated sample SZ-AT dropped sharply, indicating that the SSZ-13 zeolite framework collapsed rapidly without protection and the crystallinity dropped significantly. Compared with the SZ-AT sample, the peak intensity of the SZ-1h-AT sample of Example 1 and the SZ-3h-AT sample of Example 7 decreased less, proving that the zeolite was protected by reaction pre-carbon deposition, and the SSZ-13 zeolite framework did not collapse on a large scale in the alkali solution, and the crystallinity retention was high.

[0134] Test Example 4

[0135] Figure 4 The following is a scanning electron microscope comparison of the hierarchical pore zeolite molecular sieves prepared in Example 1, Example 7, and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder. Figure 4As shown, the crystal morphology of the REF sample is relatively regular, a typical CHA zeolite cubic morphology, with a smooth surface, high crystallinity, and a particle size of about 1.5 μm. The SZ-AT sample in Comparative Example 1 is relatively broken, which is due to the low crystallinity and poor mechanical stability of the hollow structure sample. The degree of fragmentation of the SZ-1h-AT sample of Example 1 and the SZ-3h-AT sample of Example 7 is greatly reduced, the morphology is relatively complete, and a relatively complete zeolite can be observed. The above analysis shows that the purpose of occupying micropores and protecting the skeleton is achieved through reaction pre-carbon deposition. This strategy can effectively alleviate the disordered etching of alkali treatment.

[0136] Test Example 5

[0137] Figure 5A It is a comparison diagram of nitrogen adsorption-desorption isotherms of the hierarchical pore zeolite molecular sieves prepared in Example 1, Examples 5-7, and Comparative Example 1 of the present invention and SSZ-13 zeolite raw powder. Figure 5B The pore distribution curves of the multi-level pore zeolite molecular sieves prepared in Example 1, Examples 5-7, and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder are compared. The specific pore volume data are shown in Table 1. Figure 5A It can be seen that the nitrogen adsorption amount of the SZ-AT sample in Comparative Example 1 is significantly lower than that of other embodiments and comparative examples, indicating that without pre-carbon deposition treatment, its skeleton collapsed severely during the alkali treatment process and a large number of pore structures were destroyed. It can be inferred that its pore volume was also greatly reduced and the crystal structure was destroyed. Figure 5B The above speculation is also verified. Due to the loss of pore structure, the pore size distribution of the SZ-AT sample of Comparative Example 1 is completely different from that of the zeolite raw stone and Example 1 after pre-carbon deposition treatment.

[0138] according to Figure 5A , 5B The BET data and corresponding pore volume data of the corresponding embodiments and comparative examples were calculated using the BET equation, as shown in Table 1.

[0139] Table 1: Zeolite molecular sieve pore structure properties and silicon-aluminum ratio

[0140]

[0141] Here, “-” means that no measurement was performed.

[0142] According to Table 1, the specific surface area and micropore volume of the SZ-AT sample of Comparative Example 1 increased from 650 m2 before alkali treatment to 1.5 m2 after alkali treatment. 2 g −1 and 0.32cm 3 g −1 Sharp drop to 476m 2 g −1 and 0.12cm3 g −1 , indicating that the zeolite framework has collapsed, which is consistent with the above analysis. After alkali treatment and acid washing, the specific surface area and micropore volume of the SZ-1h-AT sample of Example 1 have approached the level before treatment, and the mesopore volume has reached 0.11cm 3 g −1 , indicating that after the reaction pre-carbon deposition, the zeolite framework has withstood the etching of the alkali, and while obtaining the mesoporous structure, its microporous structure has been well preserved. In addition, the pore structure data of the remaining embodiments show that after the pre-carbon deposition treatment step of the present invention, the skeleton of the zeolite raw powder is well protected, the specific surface area and micropore volume retention are high, and the yield is greatly increased compared to the conventional alkali treatment, proving that the reaction pre-carbon deposition can well protect the zeolite framework. It is worth noting that, relative to Comparative Examples 1-2, Examples 1-10 significantly improve the yield of hydrogen-type zeolite molecular sieves, which shows that the present invention uses pre-carbon deposition to better protect the zeolite framework, so that the hydrogen-type zeolite molecular sieve will not have a large mass loss during the alkali treatment process, thereby improving the yield of the hydrogen-type zeolite molecular sieve.

[0143] Test Example 6

[0144] The hierarchical pore zeolite molecular sieves prepared in Example 1, Example 7 and Comparative Example 1 of the present invention and the SSZ-13 zeolite raw powder were subjected to NH3-TPD acidity characterization. The results are as follows: Figure 6 As shown. Compared with the REF sample, the amount of strong acid in the SZ-AT sample of comparative example 1 is greatly reduced, indicating that a large amount of aluminum is removed from the framework during the alkali treatment. Different from this, the amount of strong acid in the SZ-1h-AT sample of Example 1 and the SZ-3h-AT sample of Example 7 increases. Combined with the silicon-aluminum ratio data in Table 1, it is inferred that a large amount of framework aluminum is not lost while desiliconizing during the alkali treatment, so the silicon-aluminum ratio of the finally obtained hierarchical pore zeolite sample decreases.

[0145] Test Example 7

[0146] The MTO catalytic performance of the methanol to olefins catalyst prepared by the hydrogen-type multi-level porous H-SSZ-13 zeolite prepared in Example 1 and Comparative Example 1 was investigated by using a fixed bed microreactor-gas chromatography apparatus. The evaluation method was as follows:

[0147] The hydrogen-type multi-level pore H-SSZ-13 zeolite prepared in Example 1, Examples 5-7 and Comparative Example 1 was tableted and crushed using a mold, and catalyst particles of 40-60 mesh were screened out. 100 mg of methanol to olefin catalyst with a particle size of 250-450 μm was weighed and loaded into a quartz reaction tube. Nitrogen was used as a carrier gas, and methanol saturated vapor was brought into the quartz reaction tube by bubbling. The reaction product was detected online by a gas chromatograph (TCD+dual FID detector). Before the MTO reaction, the catalyst sample was pretreated (550°C, 0.5-2h), and then the reaction temperature was reduced to 350°C. After the temperature stabilized, methanol saturated vapor was introduced for reaction, and the mass space velocity WHSV was maintained at 1h. −1 Data were recorded every 20 minutes from the start of the reaction until the catalyst was deactivated. The catalytic life of the catalyst was defined as the reaction time when the methanol conversion rate dropped to 98%, and the final products included olefins mainly composed of ethylene and propylene.

[0148] like Figure 7 As shown, the catalytic life of the SZ-AT sample of comparative example 1 is not extended due to the generation of mesopores, but is deactivated faster than the original powder of SSZ-13 zeolite, which is attributed to the collapse of the skeleton and the loss of skeleton aluminum during the pore formation by alkali treatment, and the strong acid sites are greatly reduced. It is worth noting that the catalytic life of the SZ-1h-AT sample of Example 1 and the SZ-3h-AT sample of Example 7 is significantly increased, and the reason why the life of the SZ-1h-AT sample is longer than that of the SZ-3h-AT sample may be that by pre-carbon deposition treatment of the hydrogen-type zeolite molecular sieve, the multi-directional protection of the molecular sieve skeleton is achieved, and the damage to the skeleton by alkali etching is reduced, which can alleviate the occurrence of the collapse of the zeolite molecular sieve skeleton, and retain the original microporous structure of the molecular sieve as much as possible while obtaining the mesoporous structure. Thanks to the high specific surface area and complete crystal structure of the multi-level pore zeolite molecular sieve, the prepared methanol to olefin catalyst has abundant catalytic active sites, showing a lower carbon deposition rate, and realizing the double improvement of the conversion rate of methanol and the life of the catalyst. If the reaction time when the methanol conversion rate drops to 98% is taken as the catalytic life, the life of the SZ-1h-AT sample in Example 1 is more than three times that of the Ref sample, which also proves that the reaction pre-carbon deposition strategy is feasible for protecting the zeolite framework during alkali treatment.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a multi-level pore zeolite molecular sieve, characterized in that: The following steps are involved: Step 1) pre-treating the hydrogen-type zeolite molecular sieve at 500-600° C. to obtain the pre-treated hydrogen-type zeolite molecular sieve; Step 2) in an inert gas environment, the pretreated hydrogen-type zeolite molecular sieve is cooled to 300-500° C., and an inert gas including a carbon source is introduced into the system to perform a pre-carbon deposition treatment to obtain a pre-carbon deposition zeolite molecular sieve; Step 3) The pre-carbonized zeolite molecular sieve is sequentially subjected to alkali treatment, calcination treatment, acid washing treatment, and drying treatment to obtain a multi-level pore zeolite molecular sieve.

2. The method for preparing a multi-level pore zeolite molecular sieve according to claim 1, characterized in that: In step 2), the mass space velocity of the inert gas including the carbon source is 0.1-10h -1 .

3. The method for preparing a multi-level pore zeolite molecular sieve according to claim 1 or 2, characterized in that: In the step 2), the carbon source includes at least one of methanol, ethanol, C1-C4 alkanes, and C1-C4 alkenes.

4. The method for preparing a multi-level pore zeolite molecular sieve according to any one of claims 1 to 3, characterized in that: The mesh size of the hydrogen-type zeolite molecular sieve raw material in step 1) is 10-100 meshes.

5. The method for preparing a multi-level pore zeolite molecular sieve according to any one of claims 1 to 4, characterized in that: In the step 1), the pretreatment step is carried out in a tube furnace.

6. The method for preparing a multi-level pore zeolite molecular sieve according to any one of claims 1 to 5, characterized in that: In the step 1), the pretreatment is performed in an air or oxygen atmosphere.

7. A multi-level pore zeolite molecular sieve, characterized in that: The multi-level pore zeolite molecular sieve is prepared according to the method for preparing a multi-level pore zeolite molecular sieve according to any one of claims 1 to 6.

8. A hydrogen-type hierarchical pore zeolite molecular sieve, characterized in that: The hydrogen-type hierarchical pore zeolite molecular sieve is obtained by exchanging the hierarchical pore zeolite molecular sieve according to claim 7 with ammonium ions and calcining.

9. A methanol to olefins catalyst, characterized in that: The catalyst is obtained by tableting, crushing and sieving the hydrogen-type multi-level pore zeolite molecular sieve described in claim 8.

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