A method and system for producing light olefins and aromatics in a downflow catalytic cracking

Abstract

The application provides a method for producing low-carbon olefins and aromatic hydrocarbons by catalytic cracking, which comprises: feeding a catalyst and a first fluidizing medium into a top end of a down-flow bed reactor and moving downward, feeding a raw oil into a lower part of the down-flow bed reactor, feeding a second fluidizing medium into the down-flow bed reactor through a cyclone distribution device and rotating upward, the second fluidizing medium rotating upward carrying the raw oil to rotate upward and contact with the catalyst in a countercurrent manner to carry the catalyst to form a rotating fluidized state and perform a catalytic cracking reaction to obtain a reacted material. The application also provides a system for producing low-carbon olefins and aromatic hydrocarbons by catalytic cracking. Through the above technical scheme, the application strengthens the gas-solid contact between the raw oil and the catalyst, and further effectively improves the conversion rate and selectivity of the catalytic cracking for producing low-carbon olefins and aromatic hydrocarbons.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of petroleum chemical industry, in particular, to a method for producing low-carbon olefins and aromatic hydrocarbons by down-flow bed catalytic cracking and a system for producing low-carbon olefins and aromatic hydrocarbons by down-flow bed catalytic cracking. BACKGROUND

[0002] LCO (light cycle oil) is rich in aromatic hydrocarbons and is an ideal raw material for producing aromatic hydrocarbons. Monocyclic aromatic hydrocarbons can be directly catalytically cracked to produce aromatic hydrocarbons, and polycyclic aromatic hydrocarbons can be easily saturated into monocyclic aromatic hydrocarbons after hydrotreating. Therefore, it is expected to improve the production capacity of aromatic hydrocarbons by hydrotreating LCO and combining catalytic cracking process.

[0003] US6656346B2 discloses a catalytic cracking process which uses a down-flow bed reactor to carry out catalytic cracking reaction at high severity to produce propylene.

[0004] However, the conversion rate and selectivity of the existing catalytic cracking method still need to be further improved. SUMMARY

[0005] The purpose of the present application is to further improve the conversion rate and selectivity of catalytic cracking for producing low-carbon olefins and aromatic hydrocarbons.

[0006] In order to achieve the above purpose, the present application provides a method for producing low-carbon olefins and aromatic hydrocarbons by down-flow bed catalytic cracking, which comprises: introducing a catalyst and a first fluidizing medium into the top end of a down-flow bed reactor and moving downward, introducing a raw oil into the lower part of the down-flow bed reactor, and introducing a second fluidizing medium into the down-flow bed reactor through a cyclone distribution device and rotating upward; the second fluidizing medium rotating upward carries the raw oil also rotating upward and counter-currently contacts with the catalyst to form a rotating fluidized state and carries out catalytic cracking reaction, to obtain a reacted material, and the reacted material is subjected to gas-solid separation and stripping to obtain spent catalyst and reaction product oil gas, and the spent catalyst is regenerated and returned to the catalytic cracking reaction.

[0007] The present application also provides a system for producing low-carbon olefins and aromatic hydrocarbons by catalytic cracking, which comprises a down-flow bed reactor, a gas-solid separation device, a stripper and a regenerator connected in sequence, and the discharge port of the regenerator is connected with the catalyst inlet of the fluidized bed reactor; wherein the top of the down-flow bed reactor is provided with a catalyst inlet and a first fluidizing medium inlet; the bottom of the down-flow bed reactor is provided with a second fluidizing medium inlet and a cyclone distribution device communicating with the second fluidizing medium inlet.

[0008] Through the technical scheme, the gas-solid contact of the raw oil and the catalyst is strengthened by the cyclone, and then the conversion rate and the selectivity of the catalytic cracking for producing low-carbon olefins and aromatic hydrocarbons are effectively improved.

[0009] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0010] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate the present application and explain the principles of the present application together with the specific embodiments described in the following detailed description.

[0011] Figure 1 The system structure schematic diagram in a preferred embodiment of the present application.

[0012] Figure 2 The structure schematic diagram of the cyclone inlet pipe in a preferred embodiment of the present application.

[0013] Figure 3 The structure schematic diagram of the tangential cyclone discharge port on the sidewall of the upper end of the down-flow bed reactor in a preferred embodiment of the present application.

[0014] BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 In the figure, 1 is the first fluidizing medium; 2 is the catalyst inlet distributor; 3 is the spent slide valve; 4 is the product oil gas discharge pipeline; 5 is the cyclone separator; 6 is the cyclone discharge port; 7 is the down-flow bed reactor; 8 is the oil inlet nozzle; 9 is the multi-tube cyclone inlet distributor; 10 is the second fluidizing medium; 11 is the stripper; 12 is the stripping steam; 13 is the regeneration slide valve; 14 is the regeneration medium; 15 is the riser regenerator; 16 is the riser outlet cyclone separator; 17 is the settler; 18 is the settler cyclone separator; and 19 is the flue gas outlet pipeline. DETAILED DESCRIPTION

[0016] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0017] The present application provides a method for producing low carbon olefins and aromatics by downer catalytic cracking, which comprises: feeding catalyst and first fluidization medium into the top end of a downer reactor and moving downward, feeding raw oil into the lower part of the downer reactor, feeding second fluidization medium into the downer reactor through a cyclone distribution device and moving upward in a cyclone state; the second fluidization medium moving upward in a cyclone state carries the raw oil to move upward in a cyclone state and contacts with the catalyst in a countercurrent manner to carry the catalyst to form a rotating fluidization state and carry out catalytic cracking reaction to obtain reacted material, and the reacted material is subjected to gas-solid separation and stripping to obtain spent catalyst and reaction product oil gas, and the spent catalyst is regenerated and returned to the catalytic cracking reaction.

[0018] The inventors of the present application find that harsh reaction conditions and high gas-solid contact efficiency are beneficial to improve the conversion rate and selectivity of producing low carbon olefins and aromatics by catalytic cracking reaction. However, the existing downer reactor has low bed particle concentration and weak backmixing degree, resulting in low gas-solid contact efficiency, which affects the conversion rate and selectivity of the catalytic cracking reaction. The inventors of the present application further find that if the catalytic cracking reaction is carried out in a cyclone state in the downer reactor, the gas-solid contact efficiency can be effectively enhanced, so that more harsh reaction conditions (higher temperature and larger catalyst / oil ratio) can be used and the gas-solid residence time can be prolonged, thereby improving the reaction conversion rate and selectivity and increasing the yield of olefin and aromatic products.

[0019] Optionally, the cyclone distribution device is a multi-tube cyclone inlet distributor, which comprises a gas inlet pipe, a horizontal pipe and a gas outlet pipe connected in sequence, the gas outlet pipe extends obliquely upward from the upper side wall of the horizontal pipe into the downer reactor, and the inclination angle of the gas outlet pipe is 5°-85°, preferably 20°-70°.

[0020] Optionally, the reacted material is led out of the downer reactor through a cyclone discharge port tangentially arranged on the side wall of the upper end of the downer reactor.

[0021] The gas inlet pipe is 2-6, and the gas inlet pipe is horizontally directed to the center of the cross section of the downer reactor; the horizontal pipe comprises 2-6 concentric annular horizontal pipes, and 2-6 straight horizontal pipes for communication are arranged between adjacent two annular horizontal pipes; 2-6 gas outlet pipes are arranged on each annular horizontal pipe, and the projection of the gas outlet pipe on the plane of the annular horizontal pipe is the tangent direction of the annular horizontal pipe.

[0022] Typically, the gas linear velocity of the cyclone can be 0.1-10 m / s, preferably 1-5 m / s, and the gas angular velocity of the cyclone can be 0.01-10 s -1, preferably 0.1-5s -1 The angular velocity of the swirling gas can be adjusted by adjusting the weight flow ratio and linear velocity ratio of the first fluidizing medium to the second fluidizing medium.

[0023] Optionally, the downer reactor has a length-to-diameter ratio of 2-50:1, preferably 5-20:1.

[0024] Optionally, the catalytic cracking conditions include: reaction temperature of 500-800°C, preferably 560-690°C; reaction pressure of 0.1-2.0 MPa, preferably 0.3-1 MPa; catalyst-oil weight ratio of 10-150, preferably 15-50; residence time of 0.2-10 seconds, preferably 0.5-5 seconds.

[0025] Optionally, the catalyst regeneration conditions may include: a regeneration temperature of 550-850° C., and air as the regeneration medium.

[0026] Optionally, the fluidizing medium is at least one of water vapor and dry gas.

[0027] Optionally, the catalyst contains 10-60wt% of a molecular sieve, 1-40wt% of a binder and 1-90wt% of a carrier; the molecular sieve is a modified Y-type molecular sieve and / or an unmodified Y-type molecular sieve; the binder is a silica binder and / or an alumina binder; and the carrier can be selected from one or more of silica, kaolin, montmorillonite, diatomaceous earth, halloysite, saponite, rectorite, sepiolite, attapulgite, hydrotalcite and bentonite.

[0028] The method of the present invention is highly adaptable to feedstocks and is applicable not only to light catalytic cracking feedstocks such as hydrogenated LCO, but also to deep catalytic cracking of low-quality heavy feedstocks with high density and low hydrogen content. Optionally, the feedstock oil is at least one of unhydrogenated LCO, hydrogenated LCO, straight-run diesel, coker diesel, and hydrorefined straight-run diesel.

[0029] Optionally, in the modified Y-type molecular sieve, calculated as oxide, the rare earth element content is 3-15wt%, the sodium element content is 0.01-0.8wt%, and the zinc element content is 0.2-4.5wt%; the rare earth element may be but is not limited to one or more of La, Ce, Pr and Nd.

[0030] On the other hand, reference Figure 1The present invention also provides a system for producing light olefins and aromatics by downer catalytic cracking, the system comprising a downer reactor, a gas-solid separation device, a stripper and a regenerator connected in sequence, the discharge port of the regenerator being connected to the catalyst inlet of the fluidized bed reactor; wherein a catalyst inlet and a first fluidizing medium inlet are provided at the top of the downer reactor; and a second fluidizing medium inlet and a swirl distribution device connected to the second fluidizing medium inlet are provided at the bottom of the downer reactor.

[0031] Among them, optionally, the swirl distribution device is a multi-tube swirl inlet distributor, and the multi-tube swirl inlet distributor includes an air inlet pipe, a cross pipe and an air outlet pipe connected in sequence, and the air outlet pipe extends upward from the upper side wall of the cross pipe to the down-flow bed reactor, and the inclination angle of the air outlet pipe is 5°-85°, preferably 20°-70°.

[0032] Optionally, 2-6 swirl discharge ports are tangentially arranged on the side wall of the upper end of the downer reactor.

[0033] Optionally, a catalyst fluidizing hopper is further provided on the top of the down-flow bed reactor, the catalyst inlet and the first fluidizing medium inlet are connected to the top of the catalyst fluidizing hopper, and the bottom outlet of the catalyst hopper extends downward to below the swirl discharge port.

[0034] Optionally, the downer reactor has an aspect ratio of 2-50:1, preferably 5-20:1.

[0035] Among them, optionally, there are 2-6 air inlet pipes, and the air inlet pipes point horizontally to the center of the cross-section of the down-flow bed reactor; the cross pipes include 2-6 concentrically arranged annular cross pipes, and 2-6 straight cross pipes for communication are arranged between two adjacent annular cross pipes; each of the annular cross pipes is provided with 2-6 air outlet pipes, and the projection of the air outlet pipe on the plane where the annular cross pipe is located is the tangent direction of the annular cross pipe.

[0036] According to a particularly preferred embodiment of the present invention, Figure 1-3The catalyst enters the catalyst inlet distributor 2 through the spent catalyst slide valve 3, is fluidized by the first fluidizing medium 1, enters the top end of the downflow bed reactor 7, the feed oil, after being preheated, enters the bottom of the downflow bed reactor through the oil inlet nozzle 8, the second fluidizing medium 10 generates a rotating gas stream through the multi-tube cyclone inlet distributor 9, and then is mixed and contacted with the feed oil, drives the upflowing feed oil to rotate, and the feed oil gas and the catalyst rotate and flow countercurrently in the downflow bed reactor 7 to perform catalytic cracking reaction. The reaction product oil gas is discharged through the cyclone outlet 6 at the top of the downflow bed, enters the cyclone separator 5, and then the separated product oil gas enters the fractionation unit through the discharge pipeline 4. The catalyst separated by the cyclone separator 5 enters the stripper 11 and is stripped by the stripping steam 12. After being stripped, the catalyst enters the riser regenerator 15 through the regenerated catalyst slide valve 13, is coke-burning regenerated by the regeneration medium 14, is separated by the cyclone separator 16 at the outlet of the riser, and is deposited in the settler 17. The flue gas generated by the regeneration is separated by the settler cyclone separator 18, is discharged from the flue gas outlet pipeline 19, and then the regenerated catalyst enters the reactor through the spent catalyst slide valve to perform the next cycle.

[0037] The present application is further illustrated in detail by the following examples. In the absence of special instructions, the raw materials used in the examples can be obtained by commercial channels.

[0038] The properties of the raw material hydrogenated LCO used in the examples and comparative examples are shown in Table 1.

[0039] Table 1

[0040] Raw oil name Hydrogenated LCO Density (20°C), kg / m3 3 ]] 888.7 Carbon content, weight % 88.37 Hydrogen content, weight % 11.63 Hydrocarbon mass composition Paraffins, weight % 13.0 Total cycloalkanes 34.4 Total aromatics 52.6 Gum, weight % 0 Total weight, weight % 100

[0041] The catalyst SLA-10 used in the examples and comparative examples is the same, and the catalyst properties are listed in Table 2. The preparation method is as follows: (1) NaY molecular sieve is ion exchanged with a rare earth salt solution (cerium nitrate) at a temperature of 40°C for 100 minutes. The mass ratio of the NaY molecular sieve, rare earth salt, and solvent water is 1:0.1:10; the masses of the NaY molecular sieve and rare earth salt are calculated on a dry basis and rare earth oxide basis, respectively. (2) The molecular sieve after ion exchange is calcined at a temperature of 400°C in an atmosphere with a water vapor content of 40% by volume for 6 hours. (3) The calcined molecular sieve is reacted with silicon tetrachloride at a temperature of 500°C for 3 hours. The mass ratio of the silicon tetrachloride to the calcined molecular sieve is 0.5:1. The mass of the calcined molecular sieve is calculated on a dry basis. (4) The molecular sieve was impregnated with a zinc salt solution (zinc nitrate), and the impregnated molecular sieve was calcined at an impregnation temperature of 40° C., a calcination temperature of 500° C., and a calcination time of 3 hours to obtain a modified Y molecular sieve having a rare earth element (Ce) content of 9 wt%, a sodium content of 0.5 wt%, and a zinc content of 2 wt%. (5) 15 wt% of the modified Y molecular sieve, 10 wt% of a binder (silicon oxide binder), 70 wt% of a carrier (kaolin), and water were formed into a slurry (solid content of 40 wt%), and the slurry was spray-dried to obtain the catalyst.

[0042] Table 2

[0043] Catalyst No. SLA-10 Micro-anti-activity 75 <![CDATA[比表面积,米 2 / g]]> 124 Pore ​​volume, ml / g 0.26 Sieve composition, weight % 0~40 microns 11.8 40-80 microns 53.2 >80 microns 35

[0044] Example 1

[0045] This embodiment follows Figure 1 The device and process were tested in a small down-flow reactor, using a countercurrent operation mode, using the hydrogenated LCO in Table 1 as the feed oil, and the test was carried out on the down-flow reactor. The SLA-10 catalyst was used, the catalyst activity was 75, and the catalyst properties are listed in Table 2. The multi-tube swirl inlet distributor adopts a similar Figure 2 structure, and Figure 2 The difference is that there are only 4 outlet pipes on the outer ring, and no outlet pipe on the inner ring. The process conditions for reaction and regeneration are: hydrogenation LCO preheating temperature is 200℃, reaction outlet temperature is 650℃, reaction pressure is 0.2MPa, catalyst-oil ratio is 20, residence time is 1.0 second, swirl gas linear velocity is 4m / s, gas angular velocity is 2s -1 , the regenerator outlet temperature is 700℃, the regenerator pressure is 0.6MPa, the regenerator medium is air, and the weight ratio of water vapor to total raw materials is 0.15.

[0046] The catalyst enters the inlet distributor through a slide valve, where it is fluidized by the first fluidizing medium and enters the top of the downer reactor. After preheating, the feedstock oil enters the bottom of the downer reactor section through an oil inlet nozzle. The second fluidizing medium generates a swirling airflow through a multi-tubular swirl inlet distributor, mixing with the feedstock oil and driving the ascending feedstock oil into a swirling flow. The feedstock oil and catalyst swirl countercurrently in the downer reactor section, undergoing catalytic cracking. The reaction product oil and gas are discharged from the top of the downer through a swirl outlet into a cyclone separator. The separated product oil and gas enter the fractionation unit through a discharge pipeline. The catalyst separated by the cyclone separator enters a stripper where it is stripped with stripping steam. After the catalyst is stripped, the stripped oil and gas enter the cyclone separator through a stripping oil and gas pipeline. The stripped catalyst enters the riser regenerator through the regeneration slide valve, where it is charred and regenerated by the regeneration medium. A cyclone separator separates the catalyst at the riser outlet and settles it in a settler. The regenerated flue gas is separated by a cyclone separator in the settler and discharged through the flue gas outlet pipeline. The regenerated catalyst enters the reactor through the waiting slide valve for the next cycle. The operating conditions and products are listed in Table 3.

[0047] Example 2

[0048] Catalytic cracking was carried out according to the method of Example 1, except that the multi-tube cyclone inlet distributor was Figure 2 The outer and inner rings each have four outlet pipes. The oil and gas residence time is 1.5 seconds. The operating conditions and products are listed in Table 3.

[0049] Comparative Example 1

[0050] This comparative example employed a conventional riser catalytic cracking process, conducted in a small riser reactor, operating in a non-hydrogenation mode. The catalyst and feedstock were the same as in Example 1. The reaction and regeneration conditions were as follows: hydrogenated LCO preheat temperature of 200°C, reactor outlet temperature of 550°C, reaction pressure of 0.2 MPa, catalyst-to-oil ratio of 10, residence time of 3.5 seconds, fluidizing gas linear velocity of 4 m / s, regenerator outlet temperature of 700°C, regenerator pressure of 0.6 MPa, air as the regeneration medium, and a steam-to-total feedstock weight ratio of 0.15. The operating conditions and product distribution are listed in Table 3.

[0051] Comparative Example 2

[0052] This comparative example employed a conventional downer catalytic cracking process in a small downer reactor, operating in a non-hydrogenation mode. The catalyst and feedstock were identical to those in Example 1, and catalytic cracking was carried out according to the method of Example 1. The only difference was that no multi-tubular swirl inlet distributor or swirl fluidizing medium was used, and the oil and gas residence time was 0.7 s. The operating conditions and products are listed in Table 3.

[0053] Table 3

[0054] Comparative Example 1 Comparative Example 2 Example 1 Example 2 crude oil Hydrogenated LCO Hydrogenated LCO Hydrogenated LCO Hydrogenated LCO Reaction method Riser Down bed Down bed Down bed Multi-tube swirl inlet distributor none none 4 outlet pipe 8 outlet pipe Catalyst name SLA-10 SLA-10 SLA-10 SLA-10 Catalyst activity (MAT) 75 75 75 75 Reaction operating conditions Reaction pressure, MPa 0.2 0.4 0.4 0.4 Reaction zone outlet temperature, ℃ 550 650 650 650 Catalyst / feedstock oil weight ratio 10 20 20 20 Oil and gas residence time, s 3.5 0.7 1.0 1.5 Product yield, weight % dry gas 5.09 5.5 5.52 5.93 Liquefied gas 14.27 15.61 16.52 17.37 gasoline 41.18 43.25 44.12 45.39 diesel fuel 28.92 26.62 25.03 23.49 Slurry 2.06 1.98 1.97 1.93 coke 8.48 7.04 6.84 5.89 total 100 100 100 100.00 Ethylene + propylene + butene 7.14 10.76 11.52 12.84 BTX 15.32 17.24 18.25 20.10

[0055] As can be seen in Table 3, Examples 1 and 2 exhibit higher triene and BTX yields than Comparative Examples 1 and 2. These results demonstrate that the use of a high-temperature, high-dose-to-oil ratio, cyclonic down-flow reactor achieves higher yields of light olefins and aromatics. By enhancing gas-solid contact efficiency and fully utilizing the advantages of high severity, product selectivity is increased.

[0056] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0057] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0058] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for producing light olefins and aromatics by downer catalytic cracking, characterized in that: The method comprises: allowing a catalyst and a first fluidizing medium to enter the top of a downer reactor and move downward, allowing crude oil to enter the lower part of the downer reactor, and allowing a second fluidizing medium to enter the downer reactor through a swirl distribution device and move upward in rotation; the second fluidizing medium moving upward in rotation also carries the crude oil and moves upward in rotation, and contacts the catalyst in countercurrent flow to carry the catalyst to form a swirl fluidized state and perform a catalytic cracking reaction to obtain a reacted material; performing gas-solid separation and stripping on the reacted material to obtain a catalyst to be regenerated and reaction product oil and gas; and regenerating the catalyst to be regenerated and then returning it to perform the catalytic cracking reaction. The swirl distribution device is a multi-tube swirl inlet distributor, which includes an inlet pipe, a transverse pipe, and an outlet pipe connected in sequence. The outlet pipe extends obliquely upward from the upper side wall of the transverse pipe into the downer reactor. There are 2 to 6 inlet pipes, and each inlet pipe is horizontally directed toward the center of the cross section of the downer reactor. The raw oil is at least one of unhydrogenated LCO, hydrogenated LCO, straight-run diesel, coker diesel and hydrorefined diesel.

2. The method according to claim 1, wherein The inclination angle of the air outlet pipe is 5°-85°; The reacted material is led out of the downer reactor through a swirl discharge port tangentially arranged on the side wall of the upper end of the downer reactor.

3. The method according to claim 2, wherein: The inclination angle of the air outlet pipe is 20°-70°.

4. The method according to claim 2, wherein: The cross tube includes 2-6 concentrically arranged annular cross tubes, and 2-6 straight cross tubes are arranged between two adjacent annular cross tubes for communication; each of the annular cross tubes is provided with 2-6 air outlet pipes, and the projection of the air outlet pipe on the plane where the annular cross tube is located is the tangent direction of the annular cross tube.

5. The method according to any one of claims 1 to 4, wherein: The linear velocity of the gas in the swirling fluidization state is 0.1-10 m / s; the angular velocity of the gas in the swirling fluidization state is 0.01-10 s -1 .

6. The method according to claim 5, wherein: The linear velocity of the gas in the swirling fluidization state is 1-5 m / s; the angular velocity of the gas in the swirling fluidization state is 0.1-5 s -1 .

7. The method according to any one of claims 1 to 4, wherein: The downer reactor has an aspect ratio of 2-50:1; The catalytic cracking conditions include: reaction temperature of 500-800° C.; reaction pressure of 0.1-2.0 MPa; catalyst-oil weight ratio of 10-150; and residence time of 0.2-10 seconds.

8. The method according to claim 7, wherein: The downer reactor has an aspect ratio of 5-20:1; The catalytic cracking conditions include: reaction temperature of 560-690° C.; reaction pressure of 0.3-1 MPa; catalyst-to-oil weight ratio of 15-50; and residence time of 0.5-5 seconds.

9. The method according to any one of claims 1 to 4, wherein: The fluidizing medium is water vapor and / or dry gas; The catalyst contains 10-60wt% of a molecular sieve, 1-40wt% of a binder and 1-90wt% of a carrier, and the sum of the components of the catalyst is 100%; the molecular sieve is a modified Y-type molecular sieve and / or an unmodified Y-type molecular sieve; the binder is selected from a silica binder and / or an alumina binder; and the carrier is selected from at least one of silica, kaolin, montmorillonite, diatomaceous earth, halloysite, saponite, rectorite, sepiolite, attapulgite, hydrotalcite and bentonite.

10. The method according to claim 9, wherein: In the modified Y-type molecular sieve, the rare earth element content, calculated as oxide, is 3-15wt%, the sodium element content is 0.01-0.8wt%, and the zinc element content is 0.2-4.5wt%; the rare earth element is one or more of La, Ce, Pr and Nd.

11. A system for the method for producing light olefins and aromatics by downer catalytic cracking according to any one of claims 1 to 10, characterized in that: The system comprises a downer reactor, a gas-solid separation device, a stripper, and a regenerator connected in sequence, wherein the discharge port of the regenerator is connected to the catalyst inlet of the downer reactor; wherein the top of the downer reactor is provided with a catalyst inlet and a first fluidizing medium inlet; and the bottom of the downer reactor is provided with a second fluidizing medium inlet and a swirl distribution device connected to the second fluidizing medium inlet; The swirl distribution device is a multi-tube swirl inlet distributor, which includes an air inlet pipe, a cross pipe and an air outlet pipe connected in sequence. The air outlet pipe extends obliquely upward from the upper side wall of the cross pipe to the down-flow bed reactor; 2-6 swirl discharge ports are tangentially arranged on the side wall of the upper end of the down-flow bed reactor.

12. The system according to claim 11, wherein The inclination angle of the air outlet pipe is 5°-85°; A catalyst fluidizing hopper is further provided on the top of the downcomer reactor, the catalyst inlet and the first fluidizing medium inlet are connected to the top of the catalyst fluidizing hopper, and the bottom outlet of the catalyst hopper extends downward to below the swirl discharge port; The downer reactor has a length-to-diameter ratio of 2-50:

1.

13. The system according to claim 12, wherein: The inclination angle of the air outlet pipe is 20°-70°; The downer reactor has a length-to-diameter ratio of 5-20:

1.

14. The system according to claim 12, wherein: There are 2-6 air inlet pipes, and the air inlet pipes are horizontally pointed to the center of the cross section of the down-flow bed reactor; the cross pipes include 2-6 concentrically arranged annular cross pipes, and 2-6 straight cross pipes for communication are arranged between two adjacent annular cross pipes; each of the annular cross pipes is provided with 2-6 air outlet pipes, and the projection of the air outlet pipe on the plane where the annular cross pipe is located is the tangent direction of the annular cross pipe.

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