Zsm-5 / y composite structure molecular sieve and preparation method thereof

Abstract

The present application relates to a preparation method of ZSM-5 and Y type composite structure molecular sieve, and belongs to the field of synthesis of new catalytic materials. The preparation method of ZSM-5 / Y composite molecular sieve comprises the following steps: mixing ZSM-5 molecular sieve, water and sodium hydroxide for a certain time, then adding an aluminum source and Y type molecular sieve seed crystal, and then performing crystallization treatment at a certain temperature; and finally, the obtained mixture is washed and dried to obtain ZSM-5 / Y composite structure molecular sieve with a multi-level pore structure and an acid gradient distribution. In the preparation process, an expensive organic structure directing agent does not need to be used, the water usage amount can be reduced, even without using water, the product yield is high, the preparation time is short, and the method is suitable for industrial production. When a catalytic cracking catalyst prepared by using the molecular sieve as an active component is applied to a catalytic cracking reaction of vacuum gas oil or crude oil, the catalytic ability of complex parallel sequential reactions can be realized, the low carbon olefin yield reaches more than 27%, and the characteristics of high activity and high ethylene propylene yield are shown.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalyst preparation, and relates to a ZSM-5 / Y composite structure molecular sieve and a preparation method thereof, in particular to a composite structure molecular sieve containing ZSM-5 molecular sieve and Y-type molecular sieve crystal phase and a preparation method thereof. BACKGROUND

[0002] The "double carbon" target drives the acceleration of energy transformation, and the contradiction between the rapid growth of low-carbon energy and biofuels and the sustained growth of demand for chemical products such as ethylene and propylene intensifies. In addition, China's low-end refining capacity is overcapacity, and the high-end refining capacity for preparing fine chemicals and new chemical materials from low-carbon olefins is insufficient, which determines that the future of refining enterprises is to shift to "oil conversion and oil production" on the basis of meeting domestic clean oil demand. Among them, the direct catalytic cracking of crude oil / heavy oil to produce low-carbon olefins is an important route to promote "oil conversion". The key to promoting the industrialization of this technology is the development of high-efficiency catalysts. Due to the complexity of the composition of crude oil and the chemical properties of the required products, the existing industrial catalysts have many problems such as low conversion rate, low yield of low-carbon olefins, and high coke yield, and the diffusion limitation of macromolecular reactants and hydrogen transfer reactions make it difficult to flexibly control the product distribution. Therefore, it is crucial to design a catalyst for direct catalytic cracking of crude oil / heavy oil.

[0003] Adjusting the total acid amount and acid strength of the catalyst and shortening the accessible distance of the reactant molecules and acid centers is an important way to improve the efficiency of the catalyst for direct catalytic cracking of crude oil. Adjusting the total acid amount and acid strength, introducing multi-level pores to shorten the accessible distance of the acid centers can strengthen the occurrence of carbonium ion mechanism, and the multi-level pore structure can reduce the diffusion energy barrier, realize "one-step cracking" to "multi-step cracking" of crude oil, and thus improve the conversion rate of crude oil and the selectivity of low-carbon olefins. However, the direct catalytic cracking of crude oil to produce low-carbon olefins is a complex parallel-sequential reaction, and the required catalyst should have both high acid amount to facilitate efficient conversion of crude oil and high acid strength to achieve high-efficiency selection of low-carbon olefins. However, a single molecular sieve catalyst material has the bottleneck of matching acid strength and acid amount.

[0004] Y zeolite and ZSM-5 zeolite are commonly used as active components of catalytic cracking catalysts. The large micropore channels and high acid density of Y zeolite can ensure the pre-cracking of large oil molecules into small molecules. The special cross-pore channels and strong acid strength of ZSM-5 zeolite promote the shape-selective catalysis of small molecule hydrocarbons into low-carbon olefins. However, the existing industrial catalysts are simply mechanically mixed with Y and ZSM-5. On the one hand, Y zeolite and ZSM-5 zeolite are mechanically mixed and then prepared into catalysts according to the conventional molding method of catalytic cracking catalysts. On the other hand, Y zeolite and ZSM-5 zeolite are prepared into catalysts respectively and then ZSM-5 is mixed as an additive. The acid synergy is not obvious, and the uncertainty of the diffusion path and direction of the reactant molecules between the two active centers limits the efficient conversion of crude oil into low-carbon olefins.

[0005] Studies have shown that by special synthesis technology, two or more kinds of molecular sieves with different topological structures are combined together to prepare composite molecular sieve materials. Due to their different acid distribution (acid type, acid strength, acid density) and pore structure, they exhibit superior catalytic reaction performance in heterogeneous catalytic reactions than single molecular sieves or mechanically mixed molecular sieves. Therefore, it is necessary to synthesize ZSM-5 / Y composite structure zeolite, combine the large pore channel, high acid density of Y zeolite and the special pore channel, strong acid strength of ZSM-5 zeolite, and improve the conversion rate of crude oil / heavy oil while improving the yield and selectivity of low-carbon olefins.

[0006] Some scholars have synthesized composite molecular sieves by two-step crystallization method, molecular sieve silicon aluminum source method and other methods, but the synthesis methods of molecular sieves are all traditional hydrothermal synthesis, which involves the use of a large amount of water in the synthesis process, causing wastewater discharge problems. The synthesis process is complicated and lengthy, involving multiple crystallization processes, the use of expensive templates, or the pre-synthesis of single molecular sieve precursors, which reduces production efficiency and causes low yield problems. CN105293519A, CN115055205A, CN115814848A and CN101767034A all disclose methods for preparing ZSM-5 / Y composite molecular sieves by two-step crystallization method, which are all synthesized in the same reaction system after preparing single molecular sieves. CN108745410A, CN112657547A and CN105621441A all involve molecular sieve silicon aluminum source method, that is, ZSM-5 or Y is synthesized first, and then ZSM-5 or Y is used as a silicon source and an aluminum source respectively to prepare ZSM-5 / Y composite molecular sieves in a new hydrothermal synthesis system. In the above methods, whether Y is used as an aluminum source or ZSM-5 is used as a silicon source to synthesize ZSM-5 / Y composite molecular sieves, the synthesis process is hydrothermal synthesis, which involves the addition of a large amount of water, increasing wastewater discharge. The synthesis process involves the addition of expensive templates, increasing the preparation cost, and the templates involve environmental pollution problems in the removal process. The preparation process is complicated, time-consuming, and not suitable for industrialization. The hydrothermal method for preparing composite molecular sieves has the problem of low yield due to the presence of a large amount of water in the reaction kettle. SUMMARY

[0007] The purpose of the present application is to provide a ZSM-5 / Y composite structure molecular sieve and a preparation method thereof. When the ZSM-5 / Y composite structure molecular sieve is used as an active component to prepare a catalyst for catalytic cracking of vacuum gas oil or crude oil, it has the characteristics of high activity and high ethylene propylene yield, can provide mutually cooperative acid centers and pore structures, can reduce the amount of water used in the preparation process, greatly improve the product yield, does not need to use an organic structure directing agent, has a short preparation time, and is suitable for industrial production.

[0008] To achieve the above purpose, the technical scheme provided by the present application is as follows: a preparation method of a ZSM-5 / Y composite structure molecular sieve, comprising the following steps:

[0009] (1) mixing ZSM-5 molecular sieve, water and sodium hydroxide for a certain time to prepare a mixture A;

[0010] (2) mixing an aluminum source and Y-type molecular sieve seeds with the mixture A obtained in step (1) for a certain time to obtain a mixture B;

[0011] (3) crystallizing the mixture B obtained in step (2) at a certain temperature for a certain time;

[0012] (4) washing and drying the mixture obtained in step (3) to obtain ZSM-5 / Y composite molecular sieve.

[0013] In step (1) of the present application, the Si / Al molar ratio of the ZSM-5 molecular sieve is not less than 9; and the ZSM-5 molecular sieve: water: sodium hydroxide = (4-10) : (0-40) : (0.7-2.56) by mass ratio.

[0014] In step (1) of the present application, the mixing time is 10-90 min; and the mixing mode is stirring or grinding. In particular, when no water is added, the mixture A is obtained by grinding the ZSM-5 molecular sieve and sodium hydroxide.

[0015] In step (2) of the present application, the aluminum source is one or more of aluminum sulfate, sodium metaaluminate, aluminum hydroxide, pseudo-boehmite, and aluminum isopropoxide.

[0016] In step (2) of the present application, for the convenience of calculation of the amount, the aluminum source is calculated as equivalent aluminum oxide Al2O3, and the Al2O3: ZSM-5 molecular sieve = 1: (4-10) by mass ratio; and the Y-type molecular sieve seed: ZSM-5 molecular sieve = (0.05-0.20) : 1.

[0017] In step (2) of the present application, the mixing time is 10-90 min; and the mixing mode is stirring or grinding.

[0018] In step (3) of the present application, the crystallization temperature is 80-120℃, and the time is 3-24 h.

[0019] In step (4) of the present application, the solvent used for washing is deionized water, and the pH of the filtrate after washing is 6.5-7.5.

[0020] In step (4) of the present application, the drying temperature is 80-120℃, and the drying time is 8-24 h.

[0021] The present application also provides a ZSM-5 / Y composite structure molecular sieve prepared by the above method, which has a multi-level pore structure, mainly containing mesopores and micropores, a mesopore specific surface area of 50-110 m 2 ·g -1 , a mesopore pore volume of 0.20-0.38 cm 3 ·g -1 , a micropore specific surface area of 191-330 m 2 ·g -1 , a micropore pore volume of 0.08-0.14 cm 3 ·g -1 ; and a specific surface area of the ZSM-5 / Y composite structure molecular sieve of 300 m2 ·g -1 ~450m 2 ·g -1 The pore size is mainly distributed in the ranges of 3-5 nm, 20-40 nm and greater than 60 nm; the acid strength of the ZSM-5 / Y composite structure molecular sieve is distributed in a gradient, according to the NH3-TPD data, the weak acid amount is distributed in the range of 30-50 μmol / g, the medium strong acid amount is distributed in the range of 70-90 μmol / g, the strong acid amount is distributed in the range of 70-100 μmol / g, and the total acid amount is distributed in the range of 180-230 μmol / g.

[0022] The yield of the ZSM-5 / Y composite structure molecular sieve in the application is 90-95%. The yield is calculated according to the ratio of the mass of the harvested ZSM-5 / Y composite structure molecular sieve to the mass of the solid raw material (commercial ZSM-5, aluminum source, NaOH and Y crystal seed). The yield of the molecular sieve synthesized by the conventional hydrothermal method is only 70-80%. The solid phase method in the application can greatly improve the yield of the molecular sieve synthesis and improve the production efficiency.

[0023] The application also provides the application of the ZSM-5 / Y composite structure molecular sieve catalyst obtained by the above method in catalytic cracking of vacuum gas oil and catalytic cracking of crude oil. In the application of catalytic cracking of vacuum gas oil, the yield of low-carbon olefins is 27.79%, in which the yield of ethylene is 2.81% and the yield of propylene is 14.10%. In the application of catalytic cracking of Daqing crude oil, the yield of low-carbon olefins is 27.89%, in which the yield of ethylene is 3.65% and the yield of propylene is 14.12%.

[0024] In step (1), the ZSM-5 molecular sieve, water and sodium hydroxide are mixed for a certain time to obtain a mixture A, so that the NaOH only reacts with the ZSM-5 molecular sieve and the framework silicon atoms on the ZSM-5 molecular sieve are removed better, and the removed silicon atoms are used as raw materials for the growth of the Y molecular sieve. In step (2), the aluminum source and the Y molecular sieve crystal seed are mixed with the mixture A obtained in step (1) for a certain time to obtain a mixture B; the aluminum source is added to provide raw materials for the growth of the Y molecular sieve, and the crystal seed is added to guide the growth of the Y molecular sieve, so that the crystallization time of the composite molecular sieve can be shortened.

[0025] The present application is prepared by a solid phase synthesis method, and the amount of water added in the synthesis process is greatly reduced, and the ZSM-5 / Y composite molecular sieve with a multi-level pore structure and an acid strength gradient distribution can be prepared with a small amount of water or without adding water, the introduction of the multi-level pore structure solves the problem of the accessibility of the acid sites of the microporous molecular sieve to the reactant molecules and the diffusion limitation, and the acid synergy of the ZSM-5 and Y molecular sieves is fully exerted. Due to the reduction of the amount of water added, the yield of the composite molecular sieve is greatly improved. And the reduction of the amount of water added reduces the requirements for the production equipment and reduces the production risk. The preparation process of the present application is simple, time-consuming and low in cost. The ZSM-5 / Y composite molecular sieve prepared as a catalytic cracking catalyst is applied to the catalytic cracking reaction of crude oil / vacuum gas oil, and has excellent heavy oil conversion rate and low carbon olefin yield.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The ZSM-5 / Y composite structure molecular sieve preparation method provided by the present application can reduce the amount of water used, does not need to use an organic structure directing agent, has a short preparation time, and is suitable for industrial production.

[0028] (2) The present application obtains a ZSM-5 / Y composite molecular sieve with a multi-level pore structure and an acid strength gradient distribution, solves the problem of the accessibility of the acid sites of the microporous molecular sieve to the reactant molecules and the diffusion limitation through the introduction of the multi-level pore structure, and fully exerts the acid synergy of the ZSM-5 and Y molecular sieves. The ethylene, propylene and butene yield in the vacuum gas oil catalytic cracking and crude oil catalytic cracking reactions is higher than that of the commercial catalytic cracking catalyst, which shows great commercial potential. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The X-ray diffraction pattern of the hydrogen type ZSM-5 / Y composite structure molecular sieve obtained in Example 1.

[0030] Figure 2 The X-ray diffraction pattern of the hydrogen type ZSM-5 / Y composite structure molecular sieve obtained in Example 2.

[0031] Figure 3 The X-ray diffraction pattern of the hydrogen type ZSM-5 / Y composite structure molecular sieve obtained in Example 3.

[0032] Figure 4 The X-ray diffraction pattern of the hydrogen type ZSM-5 / Y composite structure molecular sieve obtained in Example 4.

[0033] Figure 5 The NH3-TPD pattern of the hydrogen type ZSM-5 / Y composite structure molecular sieve obtained in Example 1.

[0034] Figure 6NH3-TPD pattern of the ZSM-5 / Y composite structure molecular sieve in hydrogen form obtained in Example 2.

[0035] Figure 7 NH3-TPD pattern of the ZSM-5 / Y composite structure molecular sieve in hydrogen form obtained in Example 3.

[0036] Figure 8 NH3-TPD pattern of the ZSM-5 / Y composite structure molecular sieve in hydrogen form obtained in Example 4. DETAILED DESCRIPTION

[0037] The present application is further described in conjunction with the following specific examples, it should be noted that the scope of the present application is not limited by these specific examples.

[0038] Description of the molecular sieve physicochemical properties and reaction performance evaluation

[0039] X-ray diffraction characterization: The powder X-ray diffraction (XRD) pattern of the ZSM-5 / Y composite structure molecular sieve was recorded on a Bruker D8 Advance, with a diffractometer using Ni-filtered Cu Ka radiation (λ = 0.15418 nm). The working voltage and current were 40 kV and 40 mA, respectively. The step size was 0.01°, and the scanning speed was 1.2 seconds per step. The scanning range was 3° to 50° in 2θ.

[0040] NH3-TPD characterization: Measured on an AutoChem II 2920 chemisorption analyzer (Micromeritics Corporation) with a thermal conductivity detector (TCD), about 0.2 grams of sample (20-40 mesh) were loaded in the middle of a U-shaped quartz tube. Before analysis, the sample was treated at 550°C for 2 hours in a high-purity He (99.999%) gas stream. After cooling to 110°C, the sample was saturated with a NH3 (10%) / He mixed gas, and then purged with high-purity He at 110°C for one hour. Then, the temperature was raised at a rate of 10°C / min in a high-purity He gas stream (30 mL / min), and the desorption of NH3 was monitored. The temperature was raised from 110°C to 600°C to obtain the TPD curve.

[0041] Nitrogen physisorption-desorption characterization: N2 adsorption-desorption isotherms obtained by a Quadrasorb evo physisorption analyzer (Anton Paar). Before testing, the sample was degassed in a vacuum environment at 300°C for 6 hours. The specific surface area and micropore specific surface area of the sample were calculated by the BET method and t-plot method. The mesopore size distribution and mesopore specific surface were analyzed by the BJH method for the adsorption branch of the isotherm. The total pore volume was determined at P / P0 = 0.989.

[0042] The catalytic cracking experiments in the examples and comparative examples were evaluated in a micro fixed-bed reactor to simulate the industrial catalytic cracking process. The catalyst reaction conditions were: reaction temperature 590°C, regeneration temperature 650°C, 1.667 g of reactant fed over 70 s, catalyst loading 5 g, and mass hourly space velocity (WHSV) 17 h⁻¹. -1 Gas phase products were analyzed using an Agilent 8890 gas chromatograph, and liquid phase products were analyzed using an Agilent 8890 gas chromatograph.

[0043] Example 1

[0044] 5g of ZSM-5 molecular sieve, 0.7g of sodium hydroxide, and 2.8g of deionized water were mixed and ground for 10 minutes until clear. 0.625g of sodium aluminate and 0.5g of Y-type molecular sieve seed crystals were added, and grinding continued for 30 minutes. The mixture was then transferred to a 100ml polytetrafluoroethylene-lined synthesis vessel, sealed, and placed in a 100℃ oven for 18 hours. The mixture was then filtered and washed with deionized water until neutral, and dried in a 100℃ oven for 12 hours to obtain the ZSM-5 / Y composite molecular sieve. The yield of the composite molecular sieve was 91.6%.

[0045] According to the mass ratio, the composite molecular sieve and 1 mol / L ammonium sulfate solution are 1:10. Ion exchange is carried out at 80℃ for 1 h, followed by washing and drying. The above operation is repeated once. Finally, the sieve is calcined at 550℃ for 4 h. The resulting ammonium-exchanged hydrogen-form ZSM-5 / Y composite molecular sieve is denoted as S1.

[0046] The obtained hydrogen-form ZSM-5 / Y composite molecular sieve was mixed with kaolin, silica sol, and deionized water in a mass ratio of 40%:50%:10%:200%, slurried, molded, and aged at 800℃ and 100wt% steam for 4 hours to obtain a catalytic cracking catalyst, denoted as CS1. The catalytic cracking results of vacuum wax oil and Daqing crude oil are shown in Table 2.

[0047] Depend on Figure 1 Characteristic peaks of Y and ZSM-5 zeolite were observed in the composite material. The diffraction peaks observed at 2θ = 7.9°, 8.9°, 23.0°, 23.3°, and 23.9° correspond to orthogonal ZSM-5 (PDF number: 00-044-0003), while the peaks observed at 2θ = 15.64°, 18.66°, 20.36°, 23.63°, 27.04°, 30.73°, 31.79°, and 34.05° correspond to NaY (PDF number: 00-043-0168). The simultaneous appearance of characteristic diffraction peaks of Y and ZSM-5 confirms that the material is a composite material, indicating that the ZSM-5 / Y composite molecular sieve was successfully prepared via a solid-state-like method.

[0048] Depend on Figure 5It can be seen from Table 3 that three NH3 desorption peaks appeared in the composite material. The desorption peak at 175℃-185℃ was attributed to weak acid, the desorption peak at 220℃-240℃ was attributed to medium acid, and the desorption peak at 320℃-350℃ was attributed to strong acid. The amount of weak acid was 48 mol / g, the amount of medium acid was 88 mol / g, the amount of strong acid was 95 mol / g, and the total acid amount was 230 mol / g.

[0049] Example 2

[0050] 5 g of ZSM-5 molecular sieve, 0.7 g of sodium hydroxide and 5.6 g of deionized water were mixed and ground for 10 minutes until clear; 0.625 g of sodium metaaluminate and 0.5 g of Y-type molecular sieve seed crystals were added and ground for another 30 min, and then transferred to a 100 ml synthesis kettle lined with polytetrafluoroethylene, sealed and transferred to a 100℃ oven for constant temperature for 18 h; then washed with deionized water until neutral, and dried in a 100℃ oven for 12 h to obtain a ZSM-5 / Y composite structure molecular sieve. The yield of the composite molecular sieve was 92.3%.

[0051] According to the mass ratio of composite molecular sieve: 1 mol / L ammonium sulfate solution = 1:10, ion exchange was carried out at 80℃ for 1 h, and then washed and dried; the above operation was repeated once; finally, ammonium exchanged hydrogen type ZSM-5 / Y composite structure molecular sieve was obtained by calcining at 550℃ for 4 h, and was recorded as S2.

[0052] The obtained hydrogen type ZSM-5 / Y composite structure molecular sieve was mixed with kaolin, silica sol and deionized water according to the mass ratio of 40%:50%:10%:200%, and then paled and shaped to obtain a catalytic cracking catalyst after aging at 800℃ for 4 h with 100 wt% steam, and was recorded as CS2. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0053] It can be seen from Table 3 that three NH3 desorption peaks appeared in the composite material. The desorption peak at 175℃-185℃ was attributed to weak acid, the desorption peak at 220℃-240℃ was attributed to medium acid, and the desorption peak at 320℃-350℃ was attributed to strong acid. The amount of weak acid was 48 mol / g, the amount of medium acid was 88 mol / g, the amount of strong acid was 95 mol / g, and the total acid amount was 230 mol / g. Figure 2 It can be seen from Table 3 that three NH3 desorption peaks appeared in the composite material. The desorption peak at 175℃-185℃ was attributed to weak acid, the desorption peak at 220℃-240℃ was attributed to medium acid, and the desorption peak at 320℃-350℃ was attributed to strong acid. The amount of weak acid was 48 mol / g, the amount of medium acid was 88 mol / g, the amount of strong acid was 95 mol / g, and the total acid amount was 230 mol / g.

[0054] It can be seen from Table 3 that three NH3 desorption peaks appeared in the composite material. The desorption peak at 175℃-185℃ was attributed to weak acid, the desorption peak at 220℃-240℃ was attributed to medium acid, and the desorption peak at 320℃-350℃ was attributed to strong acid. The amount of weak acid was 48 mol / g, the amount of medium acid was 88 mol / g, the amount of strong acid was 95 mol / g, and the total acid amount was 230 mol / g. Figure 6It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 36 mol / g, the amount of medium acid is 78 mol / g, the amount of strong acid is 87 mol / g, and the total acid amount is 201 mol / g.

[0055] Example 3

[0056] 5 g of ZSM-5 molecular sieve, 0.5 g of sodium hydroxide and 2.8 g of deionized water were mixed and ground for 10 minutes until clear; 0.625 g of sodium metaaluminate and 0.5 g of Y-type molecular sieve seed were added and ground for another 30 min, and then transferred to a 100 ml synthesis kettle lined with polytetrafluoroethylene, sealed and transferred to a 100℃ oven for constant temperature for 18 h; then washed with deionized water until neutral, and dried in a 100℃ oven for 12 h to obtain a ZSM-5 / Y composite structure molecular sieve. The yield of the composite molecular sieve is 94.2%.

[0057] According to the mass ratio of composite molecular sieve: 1 mol / L ammonium sulfate solution = 1:10, ion exchange was carried out at 80℃ for 1 h, and then washed and dried; the above operation was repeated once; finally, ammonium exchanged hydrogen type ZSM-5 / Y composite structure molecular sieve was obtained by calcining at 550℃ for 4 h, and was recorded as S3.

[0058] The obtained hydrogen type ZSM-5 / Y composite structure molecular sieve was mixed with kaolin, silica sol and deionized water according to the mass ratio of 40%:50%:10%:200%, and then paled and shaped to obtain a catalytic cracking catalyst after aging at 800℃ for 4 h with 100 wt% steam, and was recorded as CS3. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0059] It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 36 mol / g, the amount of medium acid is 78 mol / g, the amount of strong acid is 87 mol / g, and the total acid amount is 201 mol / g. Figure 3 It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 36 mol / g, the amount of medium acid is 78 mol / g, the amount of strong acid is 87 mol / g, and the total acid amount is 201 mol / g.

[0060] It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 36 mol / g, the amount of medium acid is 78 mol / g, the amount of strong acid is 87 mol / g, and the total acid amount is 201 mol / g. Figure 7It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 46mol / g, the amount of medium acid is 70mol / g, the amount of strong acid is 72mol / g, and the total amount of acid is 188mol / g.

[0061] Example 4

[0062] 5g of ZSM-5 molecular sieve, 0.5g of sodium hydroxide were mixed and ground for 10 minutes; 0.625g of sodium metaaluminate and 0.5g of Y-type molecular sieve seed were added and ground for another 30 minutes, and then transferred into a 100ml synthesis kettle lined with polytetrafluoroethylene, sealed and transferred into a 100℃ oven for constant temperature for 18h; then washed with deionized water until neutral, and dried in a 100℃ oven for 12h to obtain a ZSM-5 / Y composite structure molecular sieve. The yield of the composite molecular sieve is 93.9%.

[0063] According to the mass ratio, the composite molecular sieve: 1mol / L ammonium sulfate solution = 1:10, ion exchange was carried out at 80℃ for 1h, and then washed and dried; the above operation was repeated once; finally, ammonium exchanged hydrogen type ZSM-5 / Y composite structure molecular sieve was obtained by calcining at 550℃ for 4h, and was recorded as S4.

[0064] The obtained hydrogen type ZSM-5 / Y composite structure molecular sieve was mixed with kaolin, silica sol and deionized water according to the mass ratio of 40%:50%:10%:200%, and then panned and shaped, and then aged at 800℃ for 4h under 100wt% steam to obtain a catalytic cracking catalyst, which was recorded as CS4. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0065] It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 46mol / g, the amount of medium acid is 70mol / g, the amount of strong acid is 72mol / g, and the total amount of acid is 188mol / g. Figure 4 It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 46mol / g, the amount of medium acid is 70mol / g, the amount of strong acid is 72mol / g, and the total amount of acid is 188mol / g.

[0066] Figure 8 ​It can be seen from Table 3 that three NH3 desorption peaks appear in the composite material. The desorption peak at 175℃-185℃ is attributed to weak acid, the desorption peak at 220℃-240℃ is attributed to medium acid, and the desorption peak at 320℃-350℃ is attributed to strong acid. The amount of weak acid is 51 mol / g, the amount of medium acid is 76 mol / g, the amount of strong acid is 99 mol / g, and the total acid amount is 226 mol / g.

[0067] Comparative Example 1

[0068] An industrial catalytic cracking catalyst comprising a catalytic cracking main agent USY molecular sieve as an active component, which is denoted as CD1. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0069] Comparative Example 2

[0070] A hydrogen type ZSM-5 molecular sieve, a hydrogen type Y molecular sieve, kaolin, silica sol and deionized water are mixed at a mass ratio of 33.4%:6.6%:50%:10%:200% to form a slurry, which is shaped to obtain a catalytic cracking catalyst after aging at 800℃ for 4h with 100wt% steam, which is denoted as CD2. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0071] Comparative Example 3

[0072] A hydrogen type ZSM-5 molecular sieve, kaolin, silica sol and deionized water are mixed at a mass ratio of 40%:50%:10%:200% to form a slurry, which is shaped to obtain a catalytic cracking catalyst after aging at 800℃ for 4h with 100wt% steam, which is denoted as CD3. The catalytic cracking results of vacuum gas oil and Daqing crude oil are shown in Table 2.

[0073] Table 1 Pore structure data of hydrogen type ZSM-5 / Y composite structure molecular sieves of Examples 1-4

[0074] Item S1 S2 S3 S4 S BET (m 2 ·g -1 )]]> 425 344 434 306 S micro (m 2 ·g -1 )]]> 250 258 330 191 S meso (m 2 ·g -1 )]]> 108 58 74 78 V micro (cm 3 ·g -1 )]]> 0.12 0.11 0.14 0.08 V meso (cm 3 ·g -1 )]]> 0.34 0.20 0.38 0.29 V total (cm 3 ·g -1 )]]> 0.50 0.32 0.53 0.39

[0075] Description:

[0076] S BET : Total specific surface area of ZSM-5 / Y composite molecular sieve calculated by BET method;

[0077] S micro : Micropore specific surface area of ZSM-5 / Y composite molecular sieve calculated by t-plot method;

[0078] S meso : Mesopore specific surface area of ZSM-5 / Y composite molecular sieve calculated by BJH method;

[0079] V micro : Micropore volume of ZSM-5 / Y composite molecular sieve calculated by t-plot method;

[0080] V meso Mesopore volume of ZSM-5 / Y composite molecular sieve calculated by BJH method;

[0081] V total Total pore volume of ZSM-5 / Y composite molecular sieve.

[0082] From the pore structure data table of the hydrogen type ZSM-5 / Y composite structure molecular sieve of examples 1-4, it can be seen that the ZSM-5 / Y composite molecular sieve prepared by the method has a hierarchical pore structure, mainly containing mesopores and micropores, and the ZSM-5 / Y composite molecular sieve has a larger specific surface area S BET The specific surface area of the ZSM-5 / Y composite molecular sieve is between 300m 2 ·g -1 ~ 450m 2 ·g -1 , and the S BET of example S3 can even reach 434m 2 ·g -1 . The large specific surface area of the ZSM-5 / Y composite molecular sieve can provide more active sites for the conversion of reactant molecules. The composite molecular sieve ZSM-5 / Y has a large mesopore specific surface area, and the mesopore specific surface area of example S1 reaches 108m 2 ·g -1 , and example S3 has a large mesopore volume, and the mesopore volume of example S3 reaches 0.38cm 3 ·g -1 . The pore size of the ZSM-5 / Y composite structure molecular sieve material is mainly distributed in three ranges of 3-5nm, 20-40nm and greater than 60nm. The large mesopore specific surface area and mesopore volume of the composite molecular sieve reduce the diffusion limitation of large reactant molecules, which can reduce the occurrence of side reactions. In summary, the ZSM-5 / Y composite molecular sieve prepared by the method has a hierarchical pore structure and is a typical mesoporous material.

[0083] Table 2 Evaluation results of catalytic cracking of vacuum gas oil and Daqing crude oil of examples and comparative examples

[0084]

[0085]

[0086] Table 3 Acid amount data table of examples

[0087]

[0088] The content of acid in the molecular sieve affects the catalytic reaction activity. The weak acid, the medium strong acid and the strong acid of the composite molecular sieve are changed by adjusting the synthesis conditions of the composite molecular sieve, so that the composite molecular sieve with gradient distribution of weak acid, medium strong acid and strong acid can be obtained.

[0089] In the catalytic cracking reaction of vacuum gas oil, the performance of the comparative example 1CD1 is the most outstanding in heavy oil conversion, light oil yield (gasoline yield and diesel yield) and liquid product yield (gasoline yield, diesel yield and liquefied gas yield), which are 95.85%, 65.90% and 86.84% respectively. However, the comparative example 1CD1 performs the worst in the total yield of light olefins (ethylene propylene butylene), which is only 16.26%. The examples CS1, CS2, CS3 and CS4 still maintain high heavy oil conversion, light oil yield and liquid product yield, while performing particularly well in the total yield of light olefins (ethylene propylene butylene), and the example 1CS1 reaches 26.64%. The total yield of light olefins of the comparative examples CD2 and CD3 is very close, both of which are between 21% and 22%. Considering the heavy oil conversion and the low-carbon olefin yield, the composite molecular sieve catalyst (such as the example 1CS1) of the present application has obvious advantages, the heavy oil conversion is more than 7 percentage points than the comparative example 2CD2, the liquid product yield is more than 6 percentage points than CD2, and the total yield of light olefins is more than 4.5 percentage points than CD2. Therefore, it can be concluded that the composite molecular sieve catalyst prepared by the method of the present application has superior performance in terms of heavy oil conversion and low-carbon olefin yield.

[0090] In the catalytic cracking reaction of Daqing crude oil, the total yield of ethylene, propylene and butylene of the example 2CS2 is 27.89%, while the total yield of ethylene, propylene and butylene of the comparative example 1CD1 is 19.32%, and the CS2 is about 8.5 percentage points higher than the CD1. From the background of producing low-carbon olefins from catalytic cracking of crude oil, the composite molecular sieve catalyst prepared by the method of the present application has more advantages in producing low-carbon olefins from catalytic cracking of crude oil.

Claims

1. A method for preparing a ZSM-5 / Y composite structure molecular sieve, characterized in that, The method comprises the following specific steps: (1) mixing ZSM-5 molecular sieve, water and sodium hydroxide for a certain time to prepare mixture A; the mass ratio of ZSM-5 molecular sieve, water and sodium hydroxide is (4-10):0:(0.7-2.56); or the mass of ZSM-5 molecular sieve, water and sodium hydroxide is 5 g, 2.8 g and 0.7 g, respectively, or 5 g, 5.6 g and 0.7 g, respectively, or 5 g, 2.8 g and 0.5 g, respectively; (2) mixing an aluminum source and Y-type molecular sieve seeds with the mixture A obtained in step (1) for a certain time to obtain mixture B; (3) subjecting the mixture B obtained in step (2) to crystallization treatment at a certain temperature for a certain time; (4) washing and drying the mixture obtained in step (3) to obtain ZSM-5 / Y composite structure molecular sieve, and the yield of the ZSM-5 / Y composite structure molecular sieve reaches 90-95%.

2. The method for preparing ZSM-5 / Y composite structure molecular sieve according to claim 1, characterized in that, In step (1), the Si / Al molar ratio of the ZSM-5 molecular sieve is not less than 9; and the mixing time is 10-90 min.

3. The method for preparing ZSM-5 / Y composite structure molecular sieve according to claim 1, characterized in that, In step (2), the aluminum source is one or more of aluminum sulfate, sodium metaaluminate, aluminum hydroxide, pseudo-boehmite and aluminum isopropoxide; for the convenience of calculating the amount, the aluminum source is calculated as equivalent aluminum oxide Al2O3, and the mass ratio of Al2O3:ZSM-5 molecular sieve is 1:(4-10); the mass ratio of Y-type molecular sieve seeds:ZSM-5 molecular sieve is (0.05-0.20):1; and the mixing time is 10-90 min.

4. The method for preparing ZSM-5 / Y composite structure molecular sieve according to claim 1, characterized in that, In step (3), the crystallization temperature is 80-120 DEG C, and the time is 3-24 h.

5. The method for preparing ZSM-5 / Y composite structure molecular sieve according to claim 1, characterized in that, In step (4), the solvent used for washing is deionized water, the pH of the filtrate after washing is 6.5-7.5; the drying temperature is 80-120 DEG C, and the drying time is 8-24 h.

6. The ZSM-5 / Y composite structure molecular sieve prepared by the method of any one of claims 1-5, characterized in that, The ZSM-5 / Y composite structure molecular sieve has a multi-level pore structure, mainly containing mesopores and micropores, and the specific surface area of the ZSM-5 / Y composite structure molecular sieve is 300 m 2 ·g -1 ~450 m 2 ·g -1 ; the pore size is mainly distributed in three ranges of 3-5 nm, 20-40 nm and greater than 60 nm; the ZSM-5 / Y composite structure molecular sieve has a gradient distribution of acid strength, and the total acid amount ranges from 180 to 230 μmol / g.

7. The ZSM-5 / Y composite structure molecular sieve of claim 6, wherein, mesopore specific surface area of 50 to 110 m 2 ·g -1 mesopore volume of 0.20 to 0.38 cm 3 ·g -1 micropore specific surface area of 191 to 330 m 2 ·g -1 micropore volume of 0.08 to 0.14 cm 3 ·g -1 .

8. The ZSM-5 / Y composite structure molecular sieve of claim 6, wherein, The weak acid amount in the ZSM-5 / Y composite structure molecular sieve is distributed in the range of 30-50 mu mol / g, the medium strong acid amount is distributed in the range of 70-90 mu mol / g, and the strong acid amount is distributed in the range of 70-100 mu mol / g.

9. The ZSM-5 / Y composite structure molecular sieve of claim 6, wherein, In the application of the ZSM-5 / Y composite structure molecular sieve catalyst in catalytic cracking of vacuum gas oil, the low-carbon olefin yield reaches 27.79%, in which the ethylene yield is 2.81%, and the propylene yield is 14.10%; in the application of the ZSM-5 / Y composite structure molecular sieve catalyst in catalytic cracking of Daqing crude oil, the low-carbon olefin yield reaches 27.89%, in which the ethylene yield is 3.65%, and the propylene yield is 14.12%.

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