Composite aperture molecular sieve catalytic cracking catalyst and preparation method thereof

Abstract

The invention discloses a composite aperture molecular sieve catalytic cracking catalyst and a preparation method thereof, and belongs to the technical field of catalytic cracking, the composite aperture molecular sieve catalytic cracking catalyst comprises 20-30% of a macroporous material, 40-60% of a mesoporous-microporous molecular sieve and 20-30% of a binder; the macroporous material is a macroporous alumina / kaolin compound, and the macroporous alumina / kaolin compound takes macroporous alumina as a core and macroporous kaolin as a shell; the mesoporous-microporous molecular sieve is a ZMQ-1 molecular sieve. According to the mode, the macroporous material is prepared from the macroporous aluminum oxide / kaolin compound, the ZMQ-1 molecular sieve and the binder, and the macroporous material takes macroporous aluminum oxide as a core and macroporous kaolin as a shell in the macroporous aluminum oxide / kaolin compound. The catalyst for catalytic cracking of heavy oil has the advantages of high yields of dry gas, liquefied gas, gasoline and diesel oil, low yields of coke and heavy oil and the like. The secondary cracking reaction of gasoline or diesel oil can be effectively prevented, so that the yield of gasoline and diesel oil is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic cracking, and particularly relates to a composite pore size molecular sieve catalytic cracking catalyst and a preparation method thereof. Background Art

[0002] At present, catalytic cracking catalysts are generally prepared by using microporous molecular sieves as active components, kaolin as a matrix, and pseudoboehmite as a binder. Hierarchical pore molecular sieves and micro-mesoporous composite supports have strong acidic microporous structures and mesoporous channels with small mass transfer resistance, and are widely used in the field of heavy oil catalytic cracking catalysts.

[0003] However, traditional catalytic cracking catalysts are difficult to control the reaction process, easily leading to further cracking of gasoline and diesel, thereby affecting the yields of gasoline and diesel. Therefore, it is necessary to develop a composite pore size molecular sieve catalytic cracking catalyst for improving the yields of gasoline and diesel.

[0004] Based on this, the present invention designs a composite pore size molecular sieve catalytic cracking catalyst and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] In view of the above-mentioned drawbacks of the prior art, the present invention provides a composite pore size molecular sieve catalytic cracking catalyst and a preparation method thereof.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A composite pore size molecular sieve catalytic cracking catalyst, comprising 20-30% of a macroporous material, 40-60% of a meso-microporous molecular sieve, and 20-30% of a binder; the macroporous material is a macroporous alumina / kaolin composite, and the macroporous alumina / kaolin composite has a macroporous alumina core and a macroporous kaolin shell; the meso-microporous molecular sieve is a ZMQ-1 molecular sieve.

[0008] Furthermore, the preparation method of the macroporous alumina / kaolin composite is as follows:

[0009] (1) Preparation of macroporous alumina: Add aluminum isopropoxide to a hydrochloric acid solution, first carry out a cyclic aging reaction at 55-65 °C for 2-5 h, and then carry out a cyclic aging reaction at 85-95 °C for 6-8 h to form an aluminum sol. Add a pore-forming agent to the aluminum sol, and the pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; after freezing, freeze-drying is carried out under vacuum conditions, and then calcination is carried out to obtain macroporous alumina particles;

[0010] (2) Preparation of macroporous kaolin: Disperse kaolin powder in water, add starch, adjust the pH to 7 - 8 to form a kaolin gel; then add a mixture of ammonium bicarbonate and sucrose for a foaming reaction to obtain a foamed kaolin gel.

[0011] (3) Immerse the macroporous alumina particles in the foamed kaolin gel until submerged, take them out, dry and calcine to obtain a macroporous alumina / kaolin composite.

[0012] Furthermore, in the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2 - 3:1.

[0013] Furthermore, the binder used is silica sol.

[0014] Furthermore, the preparation method of the pore former is as follows: Disperse 25 - 30 parts of sesbania powder and 40 - 60 parts of polyvinyl alcohol in water respectively to form a mixed solution, add 0.3 - 1% of borax by its mass to the mixed solution, adjust the pH value to 5.5 - 6.3, and carry out a cross-linking reaction at 55 - 65°C for 1.5 - 2 h.

[0015] To better achieve the object of the present invention, the present invention also provides a preparation method of a composite pore size molecular sieve catalytic cracking catalyst, comprising the following steps:

[0016] Put the macroporous alumina / kaolin composite, ZMQ-1 molecular sieve and binder into a high-speed mixer for mixing for 10 - 20 min, set the rotation speed at 1000 - 2000 r / min, and control the temperature at 40 - 55°C; after mixing, extrude into pellets and calcine at 450 - 500°C for 1 - 3 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0017] Furthermore, the preparation method of the macroporous alumina / kaolin composite is as follows:

[0018] (1) Preparation of macroporous alumina: Add 50 - 80 parts of aluminum isopropoxide to 200 - 250 parts of a hydrochloric acid solution with a mass concentration of 15 - 18%, first carry out a cyclic aging reaction at 55 - 65°C for 2 - 5 h, and then carry out a cyclic aging reaction at 85 - 95°C for 6 - 8 h to form an aluminum sol. Add 3 - 5% of a pore former by its mass to the aluminum sol, and the pore former is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; then place them at -10 - -5°C for freezing, the solvent in the aluminum sol will form ice crystals, and then carry out freeze-drying under vacuum conditions to sublime the solvent, and the space left by the ice crystals forms pores. Then calcine at 500 - 550°C, and the pore former completely decomposes to further obtain macroporous alumina particles.

[0019] (2) Preparation of macroporous kaolin: Disperse kaolin powder with a mesh size of 200 - 300 in water, add starch, adjust the pH to 7 - 8 to form a kaolin gel; then add a mixture of ammonium bicarbonate and sucrose accounting for 12 - 18% of its mass, and carry out a foaming reaction at 22 - 25°C for 0.5 - 1 h to obtain a foamed kaolin gel.

[0020] (3) Immerse the macroporous alumina particles in the foamed kaolin gel for 1 - 2 h, take them out and dry at 100 - 105°C for 1 - 2 h, and then calcine at 400 - 500°C for 2 - 3 h to obtain a macroporous alumina / kaolin composite.

[0021] Furthermore, the preparation method of the pore-forming agent is as follows: Disperse 25 - 30 parts of sesbania powder and 40 - 60 parts of polyvinyl alcohol in water respectively to form a mixed solution, add borax accounting for 0.3 - 1% of its mass to the mixed solution, adjust the pH value to 5.5 - 6.3, and carry out a cross-linking reaction at 55 - 65°C for 1.5 - 2 h.

[0022] To better achieve the purpose of the present invention, the present invention also provides a composite pore size molecular sieve catalytic cracking catalyst prepared according to the above preparation method.

[0023] To better achieve the purpose of the present invention, the present invention also provides an application of the composite pore size molecular sieve catalytic cracking catalyst in the preparation of a catalytic cracking catalyst for enhancing the yields of gasoline and diesel.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention is prepared from a macroporous alumina / kaolin composite, ZMQ-1 molecular sieve and a binder. The macroporous material is the macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell. Using the catalyst of the present invention for catalytic cracking of heavy oil has the advantages of high yields of dry gas, liquefied gas, gasoline and diesel, and low yields of coke and heavy oil. It can effectively prevent the occurrence of secondary cracking reactions of gasoline or diesel, thereby increasing the yields of gasoline and diesel. Detailed Embodiments

[0025] To make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0026] Example 1: In some embodiments, a preparation method of a composite pore size molecular sieve catalytic cracking catalyst includes the following steps:

[0027] I. Preparation of macroporous alumina / kaolin composite

[0028] (1) Preparation of macroporous alumina: Add 50 parts of aluminum isopropoxide to 200 parts of hydrochloric acid solution with a mass concentration of 15%. First, carry out a cyclic aging reaction at 55°C for 2 h, and then carry out a cyclic aging reaction at 85°C for 6 h to form an aluminum sol. Add a pore-forming agent accounting for 3% of its mass to the aluminum sol. The pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; then freeze at -10°C. The solvent in the aluminum sol will form ice crystals, and then carry out freeze-drying under vacuum conditions to sublime the solvent, and the space left by the ice crystals forms pores. Then calcine at 500°C, and the pore-forming agent completely decomposes to further obtain macroporous alumina particles.

[0029] The preparation method of the pore-forming agent is as follows: Disperse 25 parts of sesbania powder and 40 parts of polyvinyl alcohol in water respectively to form a mixed solution. Add borax accounting for 0.3% of its mass to the mixed solution, adjust the pH value to 5.5, and carry out a cross-linking reaction at 55°C for 1.5 h;

[0030] (2) Preparation of macroporous kaolin: Disperse 200-mesh kaolin powder in water, add starch, and adjust the pH to 7 to form a kaolin gel; then add a mixture of ammonium bicarbonate and sucrose accounting for 12% of its mass, and carry out a foaming reaction at 22°C for 0.5 h to obtain a foamed kaolin gel;

[0031] In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2:1;

[0032] (3) Immerse the macroporous alumina particles in the foamed kaolin gel for 1 h, take them out and dry at 100°C for 1 h, and then calcine at 400°C for 2 h to obtain a macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell.

[0033] II. Put 20% macroporous alumina / kaolin composite, 60% ZMQ-1 molecular sieve (prepared by the method disclosed in CN 118515294 A) and 20% silica sol into a high-speed mixer and mix for 10 min. Set the rotation speed at 1000 r / min and control the temperature at 40°C; after mixing, extrude and form, and calcine at 450°C for 1 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0034] Example 2: In some embodiments, a preparation method of a composite pore size molecular sieve catalytic cracking catalyst includes the following steps:

[0035] I. Preparation of macroporous alumina / kaolin composite

[0036] (1) Preparation of macroporous alumina: Add 55 parts of aluminum isopropoxide to 240 parts of hydrochloric acid solution with a mass concentration of 15.5%, first carry out cyclic aging reaction at 62 °C for 2.5 h, and then carry out cyclic aging reaction at 92 °C for 6.5 h to form aluminum sol. Add a pore-forming agent accounting for 4% of its mass to the aluminum sol. The pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; then freeze at -6 °C. The solvent in the aluminum sol will form ice crystals, and then carry out freeze-drying under vacuum conditions to sublimate the solvent, and the space left by the ice crystals forms pores. Then calcine at 535 °C, and the pore-forming agent completely decomposes to further obtain macroporous alumina particles.

[0037] The preparation method of the pore-forming agent is as follows: Disperse 26 parts of sesbania powder and 45 parts of polyvinyl alcohol in water respectively to form a mixed solution. Add borax accounting for 0.7% of its mass to the mixed solution, adjust the pH value to 6, and carry out cross-linking reaction at 60 °C for 1.7 h;

[0038] (2) Preparation of macroporous kaolin: Disperse 220-mesh kaolin powder in water, add starch, and adjust the pH to 7.2 to form kaolin gel; then add a mixture of ammonium bicarbonate and sucrose accounting for 14% of its mass, and carry out foaming reaction at 23 °C for 0.7 h to obtain foamed kaolin gel;

[0039] In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2.2:1;

[0040] (3) Immerse the macroporous alumina particles in the foamed kaolin gel for 1.5 h, take them out and dry at 104 °C for 1.8 h, and then calcine at 485 °C for 2.4 h to obtain a macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell.

[0041] Second, put 25% of the macroporous alumina / kaolin composite, 45% of ZMQ-1 molecular sieve (prepared by the method disclosed in CN 118515294 A) and 30% of silica sol into a high-speed mixer for mixing for 12 min, set the rotation speed at 1500 r / min, and control the temperature at 51 °C; after mixing, extrude and form, and calcine at 465 °C for 2.4 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0042] Example 3: In some embodiments, a preparation method of a composite pore size molecular sieve catalytic cracking catalyst includes the following steps:

[0043] I. Preparation of macroporous alumina / kaolin composite

[0044] (1) Preparation of macroporous alumina: Add 62 parts of aluminum isopropoxide to 230 parts of hydrochloric acid solution with a mass concentration of 16%, first carry out a cyclic aging reaction at 60°C for 3 h, and then carry out a cyclic aging reaction at 90°C for 7 h to form an aluminum sol. Add a pore-forming agent accounting for 4.5% of its mass to the aluminum sol. The pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; then freeze at -8°C. The solvent in the aluminum sol will form ice crystals, and then carry out freeze-drying under vacuum conditions to sublime the solvent, and the space left by the ice crystals forms pores. Then calcine at 530°C, and the pore-forming agent completely decomposes to further obtain macroporous alumina particles.

[0045] The preparation method of the pore-forming agent is as follows: Disperse 27 parts of sesbania powder and 50 parts of polyvinyl alcohol in water respectively to form a mixed solution. Add borax accounting for 0.9% of its mass to the mixed solution, adjust the pH value to 6.2, and carry out a cross-linking reaction at 63°C for 1.8 h;

[0046] (2) Preparation of macroporous kaolin: Disperse kaolin powder with a mesh size of 240 in water, add starch, and adjust the pH to 7.5 to form a kaolin gel; then add a mixture of ammonium bicarbonate and sucrose accounting for 16% of its mass, and carry out a foaming reaction at 24°C for 0.9 h to obtain a foamed kaolin gel;

[0047] In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2.4:1;

[0048] (3) Immerse the macroporous alumina particles in the foamed kaolin gel for 1.4 h, take them out and dry at 103°C for 1.5 h, and then calcine at 460°C for 2.7 h to obtain a macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell.

[0049] Second, put 25% of the macroporous alumina / kaolin composite, 50% of ZMQ-1 molecular sieve (prepared by the method disclosed in CN 118515294 A) and 25% of silica sol into a high-speed mixer for mixing for 17 min, set the rotation speed at 1800 r / min, and control the temperature at 50°C; after mixing, extrude into strips and calcine at 495°C for 1.7 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0050] Example 4: In some embodiments, a preparation method of a composite pore size molecular sieve catalytic cracking catalyst includes the following steps:

[0051] I. Preparation of macroporous alumina / kaolin composite

[0052] (1) Preparation of macroporous alumina: 73 parts of aluminum isopropoxide were added to 220 parts of hydrochloric acid solution with a mass concentration of 17%. First, it was subjected to cyclic aging reaction at 58 °C for 4 h, and then at 88 °C for 7.5 h to form an aluminum sol. A pore-forming agent accounting for 3.5% of its mass was added to the aluminum sol. The pore-forming agent was prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles were obtained; then it was placed at -5 °C for freezing. The solvent in the aluminum sol would form ice crystals, and then freeze-drying was carried out under vacuum conditions to sublime the solvent, and the space left by the ice crystals formed pores. Then it was calcined at 520 °C, and the pore-forming agent was completely decomposed to further obtain macroporous alumina particles.

[0053] The preparation method of the pore-forming agent is as follows: 28 parts of sesbania powder and 55 parts of polyvinyl alcohol were respectively dispersed in water to form a mixed solution. 0.5% of borax based on its mass was added to the mixed solution, and the pH value was adjusted to 5.8, and a cross-linking reaction was carried out at 58 °C for 1.6 h;

[0054] (2) Preparation of macroporous kaolin: Kaolin powder with a mesh size of 280 was dispersed in water, starch was added, and the pH was adjusted to 7.8 to form a kaolin gel; then a mixture of ammonium bicarbonate and sucrose accounting for 17% of its mass was added, and a foaming reaction was carried out at 23 °C for 0.7 h to obtain a foamed kaolin gel;

[0055] In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2.8:1;

[0056] (3) The macroporous alumina particles were immersed in the foamed kaolin gel for 1.2 h, taken out and dried at 102 °C for 1.2 h, and then calcined at 430 °C for 2.2 h to obtain a macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell.

[0057] Second, 20% of the macroporous alumina / kaolin composite, 55% of ZMQ-1 molecular sieve (prepared by the method disclosed in CN 118515294 A), and 25% of silica sol were put into a high-speed mixer for mixing for 12 min. The rotation speed was set at 1300 r / min, and the temperature was controlled at 45 °C; after mixing, it was extruded into strips and calcined at 480 °C for 1.5 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0058] Example 5: In some embodiments, a preparation method of a composite pore size molecular sieve catalytic cracking catalyst includes the following steps:

[0059] I. Preparation of macroporous alumina / kaolin composite

[0060] (1) Preparation of macroporous alumina: 80 parts of aluminum isopropoxide are added to 250 parts of hydrochloric acid solution with a mass concentration of 18%. First, a cyclic aging reaction is carried out at 65 °C for 5 h, and then a cyclic aging reaction is carried out at 95 °C for 8 h to form an aluminum sol. A pore-forming agent accounting for 5% of its mass is added to the aluminum sol. The pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; after spray granulation, alumina particles are obtained; then it is placed at -5 °C for freezing. The solvent in the aluminum sol will form ice crystals, and then freeze-drying is carried out under vacuum conditions to sublimate the solvent, and the space left by the ice crystals forms pores. Then it is calcined at 550 °C, and the pore-forming agent is completely decomposed to further obtain macroporous alumina particles.

[0061] The preparation method of the pore-forming agent is as follows: 30 parts of sesbania powder and 60 parts of polyvinyl alcohol are respectively dispersed in water to form a mixed solution. 1% of borax by mass is added to the mixed solution, and the pH value is adjusted to 6.3, and a cross-linking reaction is carried out at 65 °C for 2 h;

[0062] (2) Preparation of macroporous kaolin: Kaolin powder with 300 meshes is dispersed in water, starch is added, and the pH is adjusted to 8 to form a kaolin gel; then a mixture of ammonium bicarbonate and sucrose accounting for 18% of its mass is added, and a foaming reaction is carried out at 25 °C for 1 h to obtain a foamed kaolin gel;

[0063] In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 3:1;

[0064] (3) The macroporous alumina particles are immersed in the foamed kaolin gel for 2 h, taken out and dried at 105 °C for 2 h, and then calcined at 500 °C for 3 h to obtain a macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell.

[0065] Second, 30% of the macroporous alumina / kaolin composite, 40% of ZMQ-1 molecular sieve (prepared by the method disclosed in CN 118515294 A) and 30% of silica sol are put into a high-speed mixer for mixing for 20 min, the rotation speed is set at 2000 r / min, and the temperature is controlled at 55 °C; after mixing, it is extruded into strips and calcined at 500 °C for 3 h to obtain a composite pore size molecular sieve catalytic cracking catalyst.

[0066] Comparative Example 1: The difference from Example 5 is that the ZMQ-1 molecular sieve is replaced with a commercially available ZSM 5 molecular sieve.

[0067] Experimental Example

[0068] Test conditions: FFB small fixed fluidized bed, catalytic cracking reaction temperature 625 °C, catalyst-oil weight ratio 15. The basic properties of the feedstock oil are shown in Table 1.

[0069] Table 1 Basic properties of the feedstock oil

[0070] Project Value <![CDATA[Density (20 °C) kg / m 3 > 921.6 Residual carbon, m% 8.7 Hydrogen, m% 14.39 Sulfur, m% 0.15 Fe ppm 7.5 Ni ppm 5.8 V ppm 0.3 Na ppm 1.6

[0071] The test results are shown in Table 2.

[0072] Table 2 Test Results

[0073] Product distribution, wt% Example 1 Example 3 Example 5 Comparative Example 1 Dry gas 21.65 20.48 20.11 22.36 Liquefied gas 35.94 34.95 37.09 34.17 Coke 7.21 8.17 7.16 10.36 Gasoline 22.3 23.23 23.04 19.48 Diesel 8.64 9.05 8.52 7.38 Heavy oil 4.26 4.12 4.08 6.25

[0074] The present invention is prepared by using a macroporous alumina / kaolin composite, a ZMQ-1 molecular sieve and a binder. The macroporous material is the macroporous alumina / kaolin composite with macroporous alumina as the core and macroporous kaolin as the shell. Using the catalyst of the present invention for catalytic cracking of heavy oil has the advantages of high yields of dry gas, liquefied gas, gasoline and diesel, and low yields of coke and heavy oil. It can effectively prevent the occurrence of secondary cracking reactions of gasoline or diesel, thereby increasing the yields of gasoline and diesel.

[0075] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A composite pore size molecular sieve catalytic cracking catalyst, characterized in that: It comprises 20-30% of macroporous material, 40-60% of meso-microporous molecular sieve and 20-30% of binder; the macroporous material is a macroporous alumina / kaolin composite, the macroporous alumina / kaolin composite has macroporous alumina as the core and macroporous kaolin as the shell; the meso-microporous molecular sieve is a ZMQ-1 molecular sieve.

2. The composite pore size molecular sieve catalytic cracking catalyst according to claim 1, characterized in that: The preparation method of the macroporous alumina / kaolin composite is as follows: (1) Preparing macroporous alumina: adding aluminum isopropoxide to a hydrochloric acid solution, firstly subjecting the solution to a cyclic aging reaction at 55-65° C. for 2-5 hours, and then subjecting the solution to a cyclic aging reaction at 85-95° C. for 6-8 hours to form an aluminum sol, adding a pore-forming agent to the aluminum sol, wherein the pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; spray granulation is performed to obtain alumina particles; after freezing, freeze-drying is performed under vacuum conditions, and then calcination is performed to obtain macroporous alumina particles; (2) Preparing macroporous kaolin: dispersing kaolin powder in water, adding starch, and adjusting the pH to 7-8 to form kaolin gel; then adding a mixture of ammonium bicarbonate and sucrose to perform a foaming reaction to obtain a foamed kaolin gel; (3) The macroporous alumina particles are immersed in the foamed kaolin gel, taken out, dried, and calcined to obtain a macroporous alumina / kaolin composite.

3. The composite pore size molecular sieve catalytic cracking catalyst according to claim 2, characterized in that: In the mixture of ammonium bicarbonate and sucrose, the mass ratio of ammonium bicarbonate to sucrose is 2-3:

1.

4. The composite pore size molecular sieve catalytic cracking catalyst according to claim 3, characterized in that: The binder is silica sol.

5. The composite pore size molecular sieve catalytic cracking catalyst according to claim 4, characterized in that: The preparation method of the pore-forming agent is as follows: 25-30 parts of sesbania powder and 40-60 parts of polyvinyl alcohol are dispersed in water to form a mixed solution, 0.3-1% of borax by weight is added to the mixed solution, the pH value is adjusted to 5.5-6.3, and a cross-linking reaction is carried out at 55-65° C. for 1.5-2 hours.

6. A method for preparing the composite pore size molecular sieve catalytic cracking catalyst according to claim 1, characterized in that: The following steps are involved: The macroporous alumina / kaolin composite, ZMQ-1 molecular sieve and binder are placed in a high-speed mixer and mixed for 10 to 20 minutes, the speed is set at 1000 to 2000 r / min, and the temperature is controlled at 40 to 55° C. After mixing, the mixture is extruded into strips, and calcined at 450 to 500° C. for 1 to 3 hours to obtain a composite pore size molecular sieve catalytic cracking catalyst.

7. The method for preparing the composite pore size molecular sieve catalytic cracking catalyst according to claim 6, characterized in that: The preparation method of the macroporous alumina / kaolin composite is as follows: (1) Preparation of macroporous alumina: 50-80 parts of aluminum isopropoxide are added to 200-250 parts of hydrochloric acid solution with a mass concentration of 15-18%, and then subjected to a cyclic aging reaction at 55-65°C for 2-5 hours, and then subjected to a cyclic aging reaction at 85-95°C for 6-8 hours to form an aluminum sol, and a pore-forming agent of 3-5% by mass is added to the aluminum sol, wherein the pore-forming agent is prepared from sesbania powder and polyvinyl alcohol; alumina particles are obtained after spray granulation; the aluminum sol is then frozen at -10--5°C, and the solvent in the aluminum sol forms ice crystals; the aluminum sol is then freeze-dried under vacuum conditions to sublime the solvent, and the space left by the ice crystals forms pores; the aluminum sol is then calcined at 500-550°C, and the pore-forming agent is completely decomposed, and macroporous alumina particles are further obtained; (2) Preparation of macroporous kaolin: 200-300 mesh kaolin powder is dispersed in water, starch is added, and the pH is adjusted to 7-8 to form a kaolin gel; then 12-18% by weight of a mixture of ammonium bicarbonate and sucrose is added, and a foaming reaction is carried out at 22-25° C. for 0.5-1 h to obtain a foamed kaolin gel; (3) The macroporous alumina particles are immersed in the foamed kaolin gel for 1 to 2 hours, taken out and dried at 100 to 105° C. for 1 to 2 hours, and then calcined at 400 to 500° C. for 2 to 3 hours to obtain a macroporous alumina / kaolin composite.

8. The method for preparing the composite pore size molecular sieve catalytic cracking catalyst according to claim 7, characterized in that: The preparation method of the pore-forming agent is as follows: 25-30 parts of sesbania powder and 40-60 parts of polyvinyl alcohol are dispersed in water to form a mixed solution, 0.3-1% of borax by weight is added to the mixed solution, the pH value is adjusted to 5.5-6.3, and a cross-linking reaction is carried out at 55-65° C. for 1.5-2 hours.

9. A composite pore size molecular sieve catalytic cracking catalyst prepared according to the preparation method according to any one of claims 6 to 8.

10. Use of the composite pore size molecular sieve catalytic cracking catalyst according to claim 9 in the preparation of a catalytic cracking catalyst for improving the yield of gasoline and diesel.