A catalytic conversion method and system for producing ethylene and propylene from light hydrocarbons

Abstract

The present invention provides a catalytic conversion method for producing ethylene and propylene from light hydrocarbons, comprising: S1, contacting a light hydrocarbon raw material with a mixed catalyst containing a first catalyst and a second catalyst in a riser reactor to obtain a first oil-catalyst mixture; S2, introducing the first oil-catalyst mixture into a catalyst separation device for separation to obtain a first spent catalyst and a second oil-catalyst mixture; S3, performing gas-solid separation on the second oil-catalyst mixture to obtain reaction oil gas and a second spent catalyst; S4, performing first stripping and first regeneration on the first spent catalyst to obtain a first regenerated catalyst; performing second stripping and second regeneration on the second spent catalyst to obtain a second regenerated catalyst; and mixing the first regenerated catalyst with the second regenerated catalyst and then returning to step S1. The present invention also provides a catalytic conversion system. Through the above technical solution, the present invention improves the yield of ethylene and propylene produced by catalytic conversion of light hydrocarbons.

Description

Technical Field

[0001] The present invention relates to the field of petrochemical industry, and particularly to a catalytic conversion method and system for producing ethylene and propylene from light hydrocarbons. Background Art

[0002] Light hydrocarbons are important intermediate products in the process of petrochemical production, mainly distributed in products such as associated gas, refinery dry gas, refinery liquefied gas, and naphtha. Among them, the fractions with 4 to 12 carbon atoms are mainly used for civil or industrial fuels, as well as for producing gasoline blending components, and a small part is used for producing chemical raw materials such as ethylene, propylene, and light aromatics. Catalytic cracking technology, as an important secondary processing method in refineries, is applied to the conversion of light hydrocarbons to produce ethylene and propylene.

[0003] For example, CN104152174A discloses a catalytic cracking method for naphtha. The method includes reacting a naphtha raw material with a catalytic cracking catalyst under catalytic cracking conditions in the presence of a promoter component, so as to improve the conversion rate of naphtha catalytic cracking and the yield of light olefins.

[0004] For another example, CN103509595A discloses a catalytic conversion method for light fuel oil. The light fuel oil raw material enters the riser reactor of the catalytic cracking unit to contact and react with the catalyst. After the reaction is completed, the reaction oil gas and the spent catalyst are separated, and further separated to obtain ethylene, propylene, C2-C3 alkanes, C4 hydrocarbon fractions and other products; the spent catalyst is regenerated by burning and then recycled; the catalytic cracking unit includes a regenerator (2), a riser reactor (1), a closed hood (3) outside the outlet of the riser reactor (1), and a cyclone separator (5); the outlet of the riser reactor is communicated with the inlet of the cyclone separator (5) through the outlet at the top of the closed hood (3), and the lower leg of the cyclone separator (5) is communicated with the closed hood (3); the lower part of the closed hood (3) is communicated with the regenerator (2) through a spent catalyst inclined pipe (9). A fuel inlet, such as a fuel oil and gas nozzle, is arranged in the pipeline of the spent catalyst inclined pipe (9) to spray fuel oil and / or fuel gas into the spent catalyst inclined pipe 9, and after being fully mixed with the spent catalyst, it enters the regenerator 2.

[0005] However, the yields of ethylene and propylene produced by the existing catalytic conversion methods for light fuel oil still need to be further improved. Summary of the Invention

[0006] The purpose of the present invention is to further improve the yields of ethylene and propylene produced by the catalytic conversion of light hydrocarbons.

[0007] To achieve the above object, the present invention provides a catalytic conversion method for producing ethylene and propylene from light hydrocarbons. The catalytic conversion method comprises the following steps: S1. Contacting a light hydrocarbon raw material with a mixed catalyst containing a first catalyst and a second catalyst in a riser reactor to carry out a catalytic conversion reaction to obtain a first oil-agent mixture; the molecular sieve content of the first catalyst is less than that of the second catalyst; S2. Introducing the first oil-agent mixture into a catalyst separation device for separation to obtain a first spent catalyst and a second oil-agent mixture; S3. Separating the second oil-agent mixture into reaction oil gas and a second spent catalyst by gas-solid separation; S4. Subjecting the first spent catalyst to a first stripping and a first regeneration to obtain a first regenerated catalyst; subjecting the second spent catalyst to a second stripping and a second regeneration to obtain a second regenerated catalyst; the temperature of the first regenerated catalyst is higher than that of the second regenerated catalyst; mixing the first regenerated catalyst and the second regenerated catalyst and returning the obtained mixed regenerated catalyst to step S1 as a mixed catalyst to participate in the catalytic conversion reaction.

[0008] The present invention also provides a catalytic conversion system for producing ethylene and propylene from light hydrocarbons. The catalytic conversion system comprises a riser reactor, a settler and a regeneration unit; a settler partition and a catalyst separator are arranged in the settler, and the settler partition divides the settler into a first settling zone and a second settling zone; a material inlet of the catalyst separator is communicated with the upper end of the riser reactor, and the catalyst separator further has a first material outlet opened in the first settling zone and a second material outlet opened in the second settling zone; a first stripper is further connected to the lower part of the first settling zone, and a second stripper is further connected to the outside of the second settling zone; the regeneration unit comprises a catalyst mixer and a first regeneration zone and a second regeneration zone arranged in parallel; a first spent catalyst conveying connection is provided between the first stripper and the first regeneration zone; a second spent catalyst conveying connection is provided between the second stripper and the second regeneration zone; a first regenerated catalyst conveying connection is provided between the first regeneration zone and the catalyst mixer; a second regenerated catalyst conveying connection is provided between the second regeneration zone and the catalyst mixer; a mixed regenerated catalyst conveying connection is provided between the catalyst mixer and the riser reactor.

[0009] By the above technical solution, the present invention uses the first regenerated catalyst with a lower molecular sieve content and a higher temperature to transfer heat to the second regenerated catalyst with a higher molecular sieve content and a lower temperature, reducing the damage to the molecular sieve caused by local high temperature during regeneration, and at the same time increasing the temperature and catalytic activity of the mixed regenerated catalyst, thereby further increasing the yield of ethylene and propylene produced by the catalytic conversion of light hydrocarbons and also improving the service life of the catalyst.

[0010] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation part. Description of the Drawings

[0011] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation to the present invention. In the accompanying drawings:

[0012] Figure 1 It is a schematic structural diagram of a catalytic conversion system according to an embodiment of the present invention.

[0013] Explanation of the reference numerals in the drawings

[0014] Figure 1 In the [drawing], the reference numerals are explained as follows:

[0015] 1 - riser reactor; 2 - catalyst separator; 3 - first settling zone

[0016] 4 - first stripping vessel; 5 - second settling zone; 6 - second stripping vessel

[0017] 7 - first regeneration zone; 8 - second regeneration zone; 9 - catalyst mixer

[0018] 11 - light hydrocarbon feedstock; 12 - pre - lift gas; 13 - oil - catalyst mixture transfer pipe

[0019] 14 - settler partition; 15, 20 - stripping gas; 16, 21 - stripping baffle

[0020] 17 - first spent catalyst transfer pipe; 18, 23 - oil - gas pipeline; 19, 22 - second spent catalyst transfer pipe

[0021] 24 - cyclone separator; 25 - gas collection chamber; 26 - reaction oil - gas

[0022] 27, 33 - main air; 28 - fuel; 29 - first regenerated catalyst transfer pipe

[0023] 30, 35 - cyclone separator; 31, 36 - gas collection chamber; 32 - incomplete regeneration flue gas

[0024] 34 - second regenerated catalyst transfer pipe; 37 - regeneration flue gas; 38 - mixed regenerated catalyst transfer pipe Specific embodiments

[0025] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and do not limit the present invention.

[0026] Refer to Figure 1, the present invention provides a catalytic conversion method for producing ethylene and propylene from light hydrocarbons. The catalytic conversion method comprises the following steps: S1. contacting a light hydrocarbon raw material with a mixed catalyst containing a first catalyst and a second catalyst in a riser reactor to carry out a catalytic conversion reaction to obtain a first oil-catalyst mixture; the molecular sieve content of the first catalyst is less than that of the second catalyst; S2. introducing the first oil-catalyst mixture into a catalyst separation device for separation to obtain a first spent catalyst and a second oil-catalyst mixture; S3. carrying out gas-solid separation on the second oil-catalyst mixture to obtain reaction oil gas and a second spent catalyst; S4. carrying out first stripping and first regeneration on the first spent catalyst to obtain a first regenerated catalyst; carrying out second stripping and second regeneration on the second spent catalyst to obtain a second regenerated catalyst; the temperature of the first regenerated catalyst is higher than that of the second regenerated catalyst; mixing the first regenerated catalyst and the second regenerated catalyst, and returning the obtained mixed regenerated catalyst to step S1 as the mixed catalyst to participate in the catalytic conversion reaction.

[0027] One of the technical difficulties in improving the yield of ethylene and propylene produced by catalytic conversion of light hydrocarbons is that: the temperature of catalytic conversion of light hydrocarbons is relatively high, so a relatively high temperature of the regenerated catalyst is required, which requires an increase in the regeneration temperature; however, an increase in the regeneration temperature will lead to an excessively high local regeneration temperature, which will cause irreversible deactivation of the molecular sieve. The present invention uses a mixed catalyst obtained by mixing a first catalyst with a lower molecular sieve content and a second catalyst with a higher molecular sieve content to participate in the reaction. After the reaction, the first catalyst and the second catalyst are separated, and then the first catalyst is regenerated at a higher temperature and the second catalyst is regenerated at a lower temperature. Subsequently, heat is transferred from the first regenerated catalyst with a lower molecular sieve content and a higher temperature to the second regenerated catalyst with a higher molecular sieve content and a lower temperature, reducing the damage to the molecular sieve caused by local high temperature during regeneration, and at the same time increasing the temperature and catalytic activity of the mixed regenerated catalyst, thereby further increasing the yield of ethylene and propylene produced by catalytic conversion of light hydrocarbons.

[0028] Optionally, in order to facilitate the separation of the first spent catalyst and the second spent catalyst, the particle size and density of the first catalyst are both greater than those of the second catalyst.

[0029] Optionally, the first catalyst contains 80-100% by mass of a heat carrier and 0-20% by mass of a cracking catalyst; the second catalyst contains 0-20% by mass of a heat carrier and 80-100% by mass of a cracking catalyst.

[0030] Preferably, the first catalyst contains 90-100% by mass of a heat carrier and 0-10% by mass of a cracking catalyst; the second catalyst contains 0-10% by mass of a heat carrier and 90-100% by mass of a cracking catalyst.

[0031] Optionally, the cracking catalyst comprises unmodified ZSM-5 molecular sieve or modified ZSM-5 molecular sieve, clay and binder.

[0032] Optionally, based on the total weight of the cracking catalyst, the content of unmodified ZSM-5 molecular sieve or modified ZSM-5 molecular sieve is 10-80%, preferably 30-60%, the content of clay is 10-80%, preferably 15-60%, and the content of binder is 10-30%, preferably 10-20%.

[0033] Optionally, the particle size range of the cracking catalyst is 10-100 μm, preferably 30-80 μm, and the particle density is 800-1200 kg / m 3 , preferably 900-1100 kg / m 3 .

[0034] The modified ZSM-5 molecular sieve is selected from one or more of ZRP zeolite, phosphorus-containing ZRP zeolite, rare earth-containing ZRP zeolite, phosphorus- and rare earth-containing ZRP zeolite, phosphorus- and alkaline earth metal-containing ZRP zeolite, and phosphorus- and transition metal-containing ZRP zeolite, preferably phosphorus- and rare earth-containing ZRP zeolite.

[0035] The clay is selected from various clays that can be used as catalyst components, such as kaolin, montmorillonite, bentonite, etc. The binder is selected from one or a mixture of two or three of silica sol, aluminum sol and pseudo-boehmite, and the preferred binder is the double-aluminum binder of aluminum sol and pseudo-boehmite.

[0036] Optionally, the heat carrier is selected from a mixture of one or more of SiO2, MgO, CaO, BaO and MnO2.

[0037] Optionally, the particle size range of the heat carrier is 60-250 μm, preferably 80-200 μm, and the particle density is 1500-2200 kg / m 3 , preferably 1800-2000 kg / m 3 .

[0038] Optionally, the first regeneration and the second regeneration are carried out in a first regeneration zone and a second regeneration zone respectively; the first regeneration zone and the second regeneration zone are arranged side by side, and can be arranged in the same regenerator or in a first regenerator and a second regenerator respectively; incomplete regeneration is carried out in the first regeneration zone; complete regeneration is carried out in the second regeneration zone and the incomplete regeneration flue gas from the first regeneration zone is introduced.

[0039] Among them, fuel can be introduced into the regeneration unit; preferably, the amount of fuel introduced into the second regeneration zone is 0-30% of the amount of fuel introduced into the first regeneration zone, and preferably fuel is only introduced into the first regeneration zone and no fuel is introduced into the second regeneration zone.

[0040] Among them, optionally, the regeneration temperature of the first regeneration zone is 700-770°C, preferably 720-750°C, the catalyst density is 50-400 kg / m 3 , preferably 100-300 kg / m 3 , and the main air residence time is 0.5-20 s, preferably 2-10 s.

[0041] Among them, optionally, the regeneration temperature of the second regeneration zone is 670-730°C, preferably 680-700°C, the catalyst density is 30-350 kg / m 3 , preferably 80-250 kg / m 3 , and the main air residence time is 0.5-15 s, preferably 2-10 s.

[0042] Among them, optionally, the temperature of the first regenerant is 720-750°C, the temperature of the second regenerant is 680-700°C, the temperature difference between the first regenerant and the second regenerant is 20-70°C, and the temperature of the mixed regenerant is 680-720°C.

[0043] Among them, optionally, the reaction temperature of the riser reactor is 640-720°C, preferably 660-700°C, the catalyst-to-oil ratio is 5-30, preferably 10-20, and the reaction time is 0.1-5 seconds, preferably 0.5-3 seconds.

[0044] Among them, optionally, the method further includes introducing a pre-lift gas to the bottom of the riser reactor, and the pre-lift gas can be selected from one or more of steam, nitrogen, and dry gas, preferably steam.

[0045] The present invention also provides a catalytic conversion system for producing ethylene and propylene from light hydrocarbons. The catalytic conversion system includes a riser reactor, a settler, and a regeneration unit. A settler partition and a catalyst separator are provided in the settler. The settler partition divides the settler into a first settling zone and a second settling zone. The material inlet of the catalyst separator is communicated with the upper end of the riser reactor. The catalyst separator also has a first material outlet opened in the first settling zone and a second material outlet opened in the second settling zone. A first stripping vessel is further connected to the lower part of the first settling zone, and a second stripping vessel is further connected to the lower part of the second settling zone. The regeneration unit includes a catalyst mixer and a first regeneration zone and a second regeneration zone arranged in parallel. There is a first spent catalyst conveying connection between the first stripping vessel and the first regeneration zone. There is a second spent catalyst conveying connection between the second stripping vessel and the second regeneration zone. There is a first regenerated catalyst conveying connection between the first regeneration zone and the catalyst mixer. There is a second regenerated catalyst conveying connection between the second regeneration zone and the catalyst mixer. There is a mixed regenerated catalyst conveying connection between the catalyst mixer and the riser reactor.

[0046] Optionally, the riser reactor is selected from one or more of an equal-diameter riser reactor and a variable-diameter riser reactor.

[0047] Optionally, the catalyst separation device separates the first catalyst from the second catalyst based on the particle size and density difference between the first catalyst and the second catalyst.

[0048] As an implementation manner where there is a mixed regenerated catalyst conveying connection between the catalyst mixer and the riser reactor, a mixed catalyst inlet is further provided at the lower part of the riser reactor. The mixed catalyst inlet can be used to introduce fresh mixed catalyst or regenerated mixed catalyst.

[0049] Optionally, the catalyst separator is a combination form of one or more of a cyclone type fast separator, a three-blade type fast separator, an ejection type fast separator, a U-shaped tube type separator, an attached-wall cutting type fast separator, etc., preferably a cyclone type fast separator. The number of the catalyst separators provided in each settler is one or more. A series and / or parallel relationship exists between the multiple catalyst separators.

[0050] As a particularly preferred implementation manner of the present invention, refer to Figure 1After the light hydrocarbon feedstock 11 is preheated to 150 - 250°C, it is sprayed into the bottom of the riser reactor 1 through a nozzle. Under the conditions that the reaction temperature is 640 - 720°C, preferably 660 - 700°C, the catalyst-oil ratio is 5 - 30, preferably 10 - 20, and the reaction time is 0.1 - 5 seconds, preferably 0.5 - 3 seconds, it contacts and reacts with the mixed catalyst introduced into the bottom of the riser reactor 1 through the mixed regenerated catalyst transfer pipe 38. The obtained first catalyst-oil mixture is introduced into the catalyst separator 2 through the catalyst-oil mixture transfer pipe 13, and is separated into the first spent catalyst and the second catalyst-oil mixture. The first spent catalyst is introduced into the first stripper 4 through the first settling zone 3 for stripping. After stripping, the first spent catalyst is introduced into the first regeneration zone 7 through the first spent catalyst transfer pipe 17 for regeneration. The regenerated first regenerated catalyst is introduced into the catalyst mixer 9 through the first regenerated catalyst transfer pipe 29. The second catalyst-oil mixture is subjected to gas-solid separation by the cyclone separator 24 in the second settling zone 5 to obtain the reaction oil gas and the second spent catalyst. The second spent catalyst is introduced into the second stripper 6 through the second settling zone 5 for stripping. After stripping, the second spent catalyst is introduced into the second regeneration zone 8 through the second spent catalyst transfer pipe 22 for regeneration. The regenerated second catalyst is introduced into the catalyst mixer 9 through the second catalyst transfer pipe 34. The main air 27 and the fuel 28 are introduced into the first regeneration zone 7 and undergo an incomplete regeneration reaction with the first spent catalyst. The obtained incomplete regeneration flue gas is separated from the carried catalyst by the cyclone separator 30 and then introduced into the second regeneration zone 8, where it undergoes a complete regeneration reaction with the supplementary main air 33 and the second spent catalyst. The obtained regeneration flue gas is separated from the carried catalyst by the cyclone separator 35 and then led out of the device. The first regenerated catalyst and the second regenerated catalyst obtained in the first regeneration zone 7 and the second regeneration zone 8 are respectively introduced into the catalyst mixer 9 through the first regenerated catalyst transfer pipe 29 and the second regenerated catalyst transfer pipe 34 for mixing. The obtained mixed regenerated catalyst is introduced into the riser reactor 1 through the mixed regenerated catalyst transfer pipe 38 for recycling. The reaction oil gas 26 enters the subsequent product separation system (not shown in the figure). In the product separation system, the catalytic cracking products are separated into fuel gas, ethylene, ethane, propylene, propane, C4 hydrocarbons, light gasoline, heavy gasoline, diesel, and slurry. The C4 hydrocarbons and / or light gasoline are introduced into the bottom of the riser reactor as feedstock, and the fuel gas, ethane, and propane are introduced into the first regeneration zone as fuel.

[0051] The present invention will be further described in detail below through examples.

[0052] The catalyst used in the examples and comparative examples is the RAG-6 catalyst containing ZSM-5 molecular sieve, which is a commercial catalyst. The heat carrier used is quartz sand with a density of 2000 kg / m 3, with an average particle size of 180 μm and a main component of 99.5% SiO₂. Before the experiment, the catalyst was aged for 17 hours under the conditions of 800 °C and 100% water vapor. The chemical composition and properties of the RAG-6 catalyst are shown in Table 1. The light hydrocarbons used in the examples and comparative examples are gasoline fraction 1 and gasoline fraction 2, and the specific properties are shown in Table 2.

[0053] Table 1 Composition and Properties of RAG-6 Catalyst

[0054] Catalyst RAG-6 Chemical components, %(w) <![CDATA[Al2O3]]> 51.2 <![CDATA[SiO2]]> 43.1 BET total analysis <![CDATA[BET total surface area / (m 2 ·g -1 )]]> 197.000 <![CDATA[Micropore area / (m 2 ·g -1 )]]> 98.000 <![CDATA[Total pore volume / (cm 3 ·g -1 )]]> 0.1500 <![CDATA[Micropore volume / (cm 3 ·g -1 )]]> 0.0450 <![CDATA[Particle density / (kg / m 3 )]]> 965 Particle size distribution, %(w) 0 - 20μm 0.5 0 - 40μm 32.6 0 - 80μm 87.3 0 - 105μm 98.5 > 105μm 1.5

[0055] Table 2 Composition and Properties of Gasoline Fraction 1 and Gasoline Fraction 2

[0056]

[0057]

[0058] Example 1

[0059] The experiment was carried out on the Figure 1 shown device. The inner diameter of the riser reactor is 16 mm and the length is 3200 mm. The preheated gasoline fraction 1 was introduced into the bottom of the riser reactor and contacted and reacted with the mixed catalyst obtained by mixing quartz sand and RAG-6 catalyst in a certain mass ratio. The resulting oil-catalyst mixture was introduced into the catalyst separator for separation to obtain the first spent catalyst rich in heat carrier catalyst and the second spent catalyst rich in RAG-6 catalyst. The two catalysts were introduced into the stripper through the settling zone for stripping. The stripped spent catalysts were respectively introduced into different regeneration zones for regeneration. The regenerated catalysts were introduced into the catalyst mixer to obtain the mixed catalyst, and the mixed catalyst was introduced into the reactor for recycling. The reaction conditions and results are shown in Table 3.

[0060] Example 2

[0061] According to the method of Example 1, the difference is that the raw material used is gasoline fraction 2, and the light gasoline fraction obtained in the product is used as part of the raw material. The reaction conditions and results are shown in Table 3.

[0062] Comparative Example 1

[0063] According to the method of Example 1, the difference is that the catalyst used is the RAG-6 catalyst. The reaction conditions and results are shown in Table 3.

[0064] Comparative Example 2

[0065] According to the method of Example 1, the difference is that a catalyst separator is not provided. The oil-agent mixture generated in the riser reactor is introduced into the stripper through the settling zone for stripping. The stripped mixed spent catalyst is introduced into the regeneration zone for regeneration, and the regenerated mixed regenerated catalyst is introduced into the reactor for recycling. The reaction conditions and results are shown in Table 3.

[0066] As can be seen from Table 3, higher ethylene and propylene yields can be obtained by using the method and device provided by the present invention.

[0067] Table 3 Reaction conditions and results of Examples 1-2 and Comparative Examples 1-2

[0068]

[0069] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of 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 belong to the protection scope of the present invention.

[0070] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0071] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A catalytic conversion method for producing ethylene and propylene from light hydrocarbons, characterized in that, The catalytic conversion method comprises the following steps: S1. Contacting a light hydrocarbon feedstock with a mixed catalyst containing a first catalyst and a second catalyst in a riser reactor to carry out a catalytic conversion reaction to obtain a first oil-catalyst mixture; the molecular sieve content of the first catalyst is less than that of the second catalyst; S2. Introducing the first oil-catalyst mixture into a catalyst separation device for separation to obtain a first spent catalyst and a second oil-catalyst mixture; S3. Carrying out gas-solid separation on the second oil-catalyst mixture to obtain reaction oil gas and a second spent catalyst; S4. Carrying out first stripping and first regeneration on the first spent catalyst to obtain a first regenerated catalyst; carrying out second stripping and second regeneration on the second spent catalyst to obtain a second regenerated catalyst; the temperature of the first regenerated catalyst is higher than that of the second regenerated catalyst; mixing the first regenerated catalyst and the second regenerated catalyst and returning the obtained mixed regenerated catalyst to step S1 as the mixed catalyst to participate in the catalytic conversion reaction; Wherein, the first catalyst contains 80-100% by mass of a heat carrier and 0-20% by mass of a cracking catalyst; the second catalyst contains 0-20% by mass of a heat carrier and 80-100% by mass of a cracking catalyst; the cracking catalyst comprises unmodified ZSM-5 molecular sieve or modified ZSM-5 molecular sieve, clay and a binder; based on the total weight of the cracking catalyst, the content of unmodified ZSM-5 molecular sieve or modified ZSM-5 molecular sieve is 10-80%, the content of clay is 10-80%, and the content of the binder is 10-30%; the heat carrier is selected from one or a mixture of more of SiO2, MgO, CaO, BaO and MnO2.

2. The catalytic conversion method according to claim 1, wherein The particle size and density of the first catalyst are both greater than those of the second catalyst.

3. The catalytic conversion method according to claim 1 or 2, wherein The first catalyst contains 90-100% by mass of a heat carrier and 0-10% by mass of a cracking catalyst; the second catalyst contains 0-10% by mass of a heat carrier and 90-100% by mass of a cracking catalyst.

4. The catalytic conversion method according to claim 1, wherein, Based on the total weight of the cracking catalyst, the content of unmodified ZSM-5 molecular sieve or modified ZSM-5 molecular sieve is 30-60%, the content of clay is 15-60%, and the content of the binder is 10-20%; The particle size range of the cracking catalyst is 10 to 100 μm, and the particle density is 800 to 1200 kg / m 3 .

5. The catalytic conversion method according to claim 4, wherein, The particle size range of the cracking catalyst is 30 - 80 μm, and the particle density is 900 - 1100 kg / m 3 .

6. The catalytic conversion method according to claim 1, wherein The particle size range of the heat carrier is 60 to 250 μm, and the particle density is 1500 to 2200 kg / m 3 .

7. The catalytic conversion method according to claim 6, wherein The particle size range of the heat carrier is 80 to 200 μm, and the particle density is 1800 to 2000 kg / m 3 .

8. The catalytic conversion method according to claim 1, wherein The first regeneration and the second regeneration are respectively carried out in a first regeneration zone and a second regeneration zone of a regenerator; the first regeneration zone and the second regeneration zone are respectively arranged in a first regenerator and a second regenerator; incomplete regeneration is carried out in the first regeneration zone; complete regeneration is carried out in the second regeneration zone and incomplete regeneration flue gas from the first regeneration zone is introduced; the amount of fuel introduced into the second regeneration zone is 0-30% of the amount of fuel introduced into the first regeneration zone.

9. The catalytic conversion method according to claim 8, wherein, Fuel is only introduced into the first regeneration zone and no fuel is introduced into the second regeneration zone.

10. The catalytic conversion method according to claim 8 or 9, wherein The regeneration temperature of the first regeneration zone is 700 to 770 °C, the catalyst density is 50 to 400 kg / m 3 , and the main air residence time is 0.5 to 20 s; The regeneration temperature of the second regeneration zone is 670 to 730 °C, the catalyst density is 30 to 350 kg / m 3 , and the main air residence time is 0.5 to 15 s; The temperature of the first regenerated catalyst is 720-750 °C, the temperature of the second regenerated catalyst is 680-700 °C, the temperature difference between the first regenerated catalyst and the second regenerated catalyst is 20-70 °C, and the temperature of the mixed regenerated catalyst is 680-720 °C.

11. The catalytic conversion method according to claim 10, wherein The regeneration temperature of the first regeneration zone is 720 to 750 °C, the catalyst density is 100 to 300 kg / m 3 , and the main air residence time is 2 to 10 s; The regeneration temperature of the second regeneration zone is 680 to 700 °C, the catalyst density is 80 to 250 kg / m 3 , and the main air residence time is 2 to 10 s.

12. The catalytic conversion method according to claim 1, wherein, The reaction temperature of the riser reactor is 640 to 720 °C, the catalyst-oil ratio is 5 to 30, and the reaction time is 0.1 to 5 seconds.

13. The catalytic conversion method according to claim 12, wherein The reaction temperature of the riser reactor is 660 to 700 °C, the catalyst-oil ratio is 10 to 20, and the reaction time is 0.5 to 3 seconds.

14. The catalytic conversion method according to claim 1, wherein The light hydrocarbon feedstock contains a mixed hydrocarbon of C4 to C12.

15. The catalytic conversion method according to claim 14, wherein, The light hydrocarbon feedstock is a mixture of one or more of C4 fraction, light gasoline fraction, straight-run naphtha, pyrolysis naphtha, coker naphtha, and hydrocracked naphtha.

16. A catalytic conversion system for producing ethylene and propylene from light hydrocarbons, characterized in that, For the catalytic conversion method according to any one of claims 1-15, the catalytic conversion system includes a riser reactor, a settler, and a regeneration unit; A settler partition and a catalyst separator are provided in the settler. The settler partition divides the settler into a first settling zone and a second settling zone; the material inlet of the catalyst separator is communicated with the upper end of the riser reactor, and the catalyst separator further has a first material outlet opened in the first settling zone and a second material outlet opened in the second settling zone; A first stripper is further connected to the lower part of the first settling zone, and a second stripper is further connected to the outside of the second settling zone; The regeneration unit includes a catalyst mixer and a first regeneration zone and a second regeneration zone arranged in parallel; there is a first spent catalyst conveying connection between the first stripper and the first regeneration zone; there is a second spent catalyst conveying connection between the second stripper and the second regeneration zone; there is a first regenerated catalyst conveying connection between the first regeneration zone and the catalyst mixer; there is a second regenerated catalyst conveying connection between the second regeneration zone and the catalyst mixer; there is a mixed regenerated catalyst conveying connection between the catalyst mixer and the riser reactor.

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