CN112322324A

CN112322324A - Multi-zone coupling control multistage catalytic cracking method and device based on raw material types

Info

Publication number: CN112322324A
Application number: CN202011129522.3A
Authority: CN
Inventors: 赵亮; 张宇豪; 高金森; 白宇恩; 郝天臻; 孟庆飞; 徐春明; 李德忠
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2020-10-21
Filing date: 2020-10-21
Publication date: 2021-02-05

Abstract

The invention provides a multi-region coupling control multistage catalytic cracking method and a device based on raw material types, wherein the catalytic cracking method adopts a reaction device comprising three descending tubes and a zoned regenerator, and comprises the following steps: enabling the C4 hydrocarbon-rich raw material to undergo a first cracking reaction in a first descending pipe, and enabling the C5-C6 hydrocarbon-rich raw material to undergo a second cracking reaction in a second descending pipe; converging a product of the first cracking reaction and a product of the second cracking reaction, then carrying out gas-solid separation, regenerating the separated first catalyst to be regenerated, and enabling the partially regenerated first catalyst to enter a first descending pipe and a second descending pipe respectively to form circulation; and (3) carrying out a third cracking reaction on the raw material rich in C7-C8 hydrocarbon in a third descending pipe, carrying out gas-solid separation on the product of the third cracking reaction, regenerating the separated second spent catalyst, and allowing part of the obtained second regenerated catalyst to enter the third descending pipe to form circulation. The method can obviously improve the yield of the low-carbon olefins such as propylene and the like.

Description

Multi-zone coupling control multistage catalytic cracking method and device based on raw material types

Technical Field

The invention relates to the field of catalytic cracking of hydrocarbon raw materials, in particular to a multi-zone coupling control multi-stage catalytic cracking method and device based on raw material types.

Background

In recent years, with the improvement of technology and capacity, the surplus trend of oil refining and supply capacity has been shown, taking our country as an example, the oil refining capacity reaches 8.4 hundred million tons in 2018, 6.1 hundred million tons of crude oil are processed, 3.64 hundred million tons of produced gasoline and diesel oil are total, the average operating load is 72.4%, 1.1 hundred million tons are expected to be surplus in 2020, and with the further strictness of environmental requirements, the rapid development of new energy represented by electric power, hydrogen energy, biological fuel and the like and the improvement of the fuel efficiency of automobiles and other motor vehicles, the demand acceleration of gasoline will gradually decrease. Meanwhile, the demand of global chemicals is increased by 4% every year and is higher than the GDP acceleration of 3% in the world, so that the transformation of the traditional fuel type refineries into chemical type refineries is urgent, and particularly, how to transform the fuel type products such as gasoline and the like into the comprehensive production of high value-added chemicals is realized, and the social benefit and the economic benefit are improved.

Still taking our country as an example, in order to promote scientific development and continuous progress of petrochemical industry, the ministry of industry and informatization made and published "2016-2020 developments planning", which pointed out: in 2015-2020, the ethylene consumption in China is increased from 4030 ten thousand tons to 4800 ten thousand tons, the annual average growth rate of demand is 3.6%, the propylene consumption is increased from 3180 ten thousand tons to 4000 ten thousand tons, the annual average growth rate is 4.7%, the ethylene yield in 2018 in China is 1841 ten thousand tons, the import is 258 ten thousand tons, the import dependence is 12.3%, the propylene yield is 3035 ten thousand tons, the import is 28.4 ten thousand tons, and the import dependence is 8.6%. Therefore, the domestic demand gap for several low-carbon olefins such as ethylene, propylene and the like is huge, the constraint of olefin import is eliminated, the overall development of the industry is promoted, and the method has important significance for the national overall strategic requirements. The gasoline or other light oil products are reasonably converted into low-carbon olefin products, and the urgent problems of excess oil refining and olefin product shortage in China can be solved at the same time.

At present, on the technical level, light olefins mainly come from a heavy oil fraction cracking process, and the overall yield of propylene is significantly lower than that of ethylene. In the future global low-carbon olefin market, the growth rate of propylene demand is greater than that of ethylene, so that process exploration on how to produce propylene at high yield is more and more concerned, and the catalytic cracking process is also a main direction of research.

The research and development of a deep catalytic cracking process (DCC process) is a technology for preparing gas olefin by taking heavy oil as a raw material and utilizing shape-selective catalytic reaction, is considered to realize the extension of an oil refining process to petrochemical industry, and creates a new way for directly preparing low-carbon olefin by taking heavy oil as a raw material. Aiming at the characteristics of heavy oil, in order to produce propylene in maximum quantity, the process adopts a riser plus bed reactor type, combines harsh operating conditions and catalyst selection, and has the advantages that the content of propylene in the cracking product can reach 21 percent, but the yield of byproduct dry gas and coke is also higher.

Chinese patent application CN101045667A discloses a combined catalytic conversion method for high yield of low carbon olefins, in which a heavy oil raw material is contacted with a regenerated catalyst and a selected carbon deposition catalyst in a down tube reactor for pre-cracking, a cracked product generated by the down tube is rapidly separated from a catalyst to be generated, then low carbon olefins in the cracked product are separated, the rest products (insufficient cracked product) are further subjected to deep cracking reaction in a riser under a harsher condition, then oil gas is separated from the carbon deposition catalyst, the carbon deposition catalyst enters one or more devices of a pre-lifting section of the down tube reactor, a stripper connected with the down tube reactor and a regenerator after being stripped, and the catalyst to be generated and an optional carbon deposition catalyst generated by the down tube are returned to the down tube reactor and the riser reactor after being coked and regenerated. The method adopts heavy oil raw materials to produce low-carbon olefins, designs a catalytic cracking process aiming at the heavy oil raw materials, and achieves the purpose of improving the yield of low-carbon hydrocarbons such as propylene and the like by quickly separating low-carbon hydrocarbon products and carrying out secondary deep cracking on insufficiently cracked products.

Chinese patent application CN101074392A discloses a method for producing propylene and high-quality gasoline and diesel oil by two-stage catalytic cracking, which aims at heavy hydrocarbons or various animal and vegetable oil raw materials rich in hydrocarbon and achieves the purpose of producing both propylene and high-quality light oil products by two-stage riser catalytic process. According to the method, heavy raw oil is in contact reaction with a regenerated catalyst in a first section riser, and diesel oil, gasoline with high olefin content, gaseous products and circulating oil with good properties are obtained after products are separated; then, the circulating oil obtained by the reaction of the first section of riser and the gasoline fraction with high olefin content enter the second section of riser to contact and react with the regenerated catalyst from the regenerator, so that more propylene is obtained and the quality of gasoline is greatly improved, thereby achieving the purpose of producing light oil products such as propylene and high-quality gasoline and diesel oil. The method still aims at the cracking of heavy oil raw materials, and also aims at the production of light oil products such as diesel oil and the like and improving the quality of the light oil products, the conversion rate of the raw materials to propane is reduced, and the yield of dry gas and coke is higher.

Chinese patent application CN102690682A discloses a catalytic cracking method and a device for producing propylene, in the method, heavy raw materials (including heavy hydrocarbons or various animal and vegetable oil raw materials rich in hydrocarbons) and a first catalytic cracking catalyst which takes Y-type zeolite as a main active component are subjected to contact reaction in a first lifting pipe, oil gas after the reaction is separated from the catalyst, and the oil gas is introduced into a product separation system; the light hydrocarbon (comprising gasoline and/or C4 hydrocarbon generated in the first riser or gasoline fraction produced by other devices such as one or more of catalytic cracking crude gasoline, catalytic cracking stable gasoline, coking gasoline and visbreaking gasoline) and a second catalytic cracking catalyst which takes shape selective zeolite with the pore diameter less than 0.7nm as a main active component are in contact reaction in a second riser reactor, oil gas and catalyst after reaction are introduced into a fluidized bed reactor connected with the second riser reactor in series for reaction, and the oil gas is introduced into a product separation system; the oil gas products in the first riser and the fluidized bed reactor are collected and fractionated by a common pipeline leading-out device. The method enables the heavy raw material and the light raw material to be separately reacted, and can achieve the aim of producing propylene, but the yield of the propylene is not ideal, and the yield of coke and dry gas is high.

At present, most of the catalytic cracking researches focus on the catalytic cracking of heavy raw materials or light hydrocarbon raw materials such as gasoline and the like, but the cracking products are complex, the propylene selectivity is low, and the yield of byproducts such as dry gas and coke is high in the process of pursuing relatively high propylene selectivity, which is still a common problem which is difficult to span. On the other hand, the design of these catalytic cracking processes and systems is around the property of heavy oil raw materials, and there are few studies and reports on the processes and systems mainly feeding light hydrocarbon processing products or byproducts (light hydrocarbon oil products such as C4+, etc.) from various processes or production lines and realizing high-efficiency catalytic cracking; in addition, as the heavy oil feedstock processing and oil refining technology and the capacity are improved, there may be many cases in which the byproduct fraction output downstream may be, for example, a certain hydrocarbon as a main raw material or an incoming material with a large number of hydrocarbons with a specific carbon number, and how to design a more feasible process according to the composition and properties of the incoming material, and at the same time, the yield of the target olefins can be improved, which is also one direction for realizing the improvement of the capacity of the low carbon olefins.

Disclosure of Invention

The invention aims to solve the technical problem of providing a multi-zone coupling control multistage catalytic cracking method based on raw material types, which can crack different light hydrocarbon raw materials in a zone in the same system according to the carbon number of the hydrocarbon rich in the raw materials, can effectively improve the yield of low-carbon olefins such as propylene and the like, and simultaneously reduces the generation of coke and dry gas.

The invention also provides a multi-region coupling control multistage catalytic cracking device, which can realize catalytic cracking of the light hydrocarbon raw material, has the advantages of simple structure, small occupied area and the like, and is beneficial to practical industrial application.

In one aspect of the present invention, there is provided a multi-zone coupling control multistage catalytic cracking method based on feedstock types, using a light hydrocarbon feedstock as a cracking feedstock, the light hydrocarbon feedstock including a first feedstock rich in C4 hydrocarbons, a second feedstock rich in C5-C6 hydrocarbons, and a third feedstock rich in C7-C8 hydrocarbons, using a reaction apparatus including a first downcomer, a second downcomer, and a third downcomer, and a regenerator having a first regeneration zone and a second regeneration zone inside, which are independent of each other, the method comprising:

enabling the first raw material to enter a first descending pipe to contact with a first catalyst to generate a first cracking reaction, and enabling the second raw material to enter a second descending pipe to contact with a second catalyst to generate a second cracking reaction; converging the product of the first cracking reaction and the product of the second cracking reaction, and then carrying out gas-solid separation to respectively obtain a first oil-gas product and a first catalyst to be generated; allowing the first catalyst to be regenerated to enter a first regeneration area for regeneration after steam stripping to obtain a first regenerated catalyst; allowing part of the first regenerated catalyst to enter a first descending pipe to form a first cycle, and allowing part of the first regenerated catalyst to enter a second descending pipe to form a second cycle;

enabling a third raw material to enter a third descending pipe to contact with a third catalyst to generate a third cracking reaction, and performing gas-solid separation on a product of the third cracking reaction to respectively obtain a second oil gas product and a second spent catalyst; allowing the second spent catalyst to enter a second regeneration zone for regeneration after steam stripping to obtain a second regenerated catalyst; passing at least a portion of the second regenerated catalyst into a third downcomer to form a third cycle;

and collecting the separated first oil gas product and the second oil gas product to obtain a cracking product.

According to the catalytic cracking method provided by the invention, hydrocarbon raw materials (namely the first raw material, the second raw material and the third raw material) rich in different carbon numbers are subjected to zone reaction according to the process flow, and the catalytic cracking reaction of different raw materials can be strengthened according to the reaction conditions of the targeted regulation and control of the properties of the raw materials, so that the conversion rate of the raw materials and the yield of low-carbon olefins such as propylene are improved, the generation of byproducts such as dry gas and coke is reduced, and the energy consumption can be reduced; meanwhile, the descending tube is adopted to carry out catalytic cracking on the light hydrocarbon raw material, and materials such as the catalyst and the like in the descending tube move along the direction of gravity, so that the method has the advantages of reducing density unevenness, residence time and the like, further improving the yield of low-carbon olefins such as propylene and the like and reducing energy consumption; in addition, the regeneration and utilization of the catalyst to be regenerated can not only reduce the preparation cost of low-carbon olefins such as propylene, but also realize the adjustment of reaction parameters inside the riser by flexibly controlling the amount of the regenerated catalyst returned to the riser, such as reaction temperature, solvent-oil ratio and the like, thereby being beneficial to the light-weight process.

In the invention, the obtained cracking product can be further subjected to treatments such as fractionation and the like to obtain products such as dry gas, liquefied gas, gasoline, diesel oil, oil slurry and the like, and can also be further refined to obtain low-carbon olefin products such as propylene and the like.

By regulating and controlling the cracking reaction conditions, the hydrocarbon raw materials rich in different carbon numbers can be cracked under respective proper conditions, so that the retention time of intermediate products is reduced, and the aims of improving the yield of target products, reducing the generation of by-products, reducing energy consumption and the like are favorably fulfilled. Specifically, according to the study of the inventors, the reaction conditions (conditions of the first cleavage reaction) of the above-described first downflow can be: the reaction temperature is 500-700 ℃, for example 600-700 ℃, the reaction pressure is 0.1-0.35MPa, for example 0.1-0.3MPa or 0.1-0.2MPa, the catalyst-oil ratio is 5-40, for example 20-30, and the residence time is 0.2-4s, for example 1-3 s; the reaction conditions of the second downcomer (conditions of the second cleavage reaction) may be: the reaction temperature is 480-650 ℃, for example 500-600 ℃, the reaction pressure is 0.1-0.4MPa, for example 0.1-0.3MPa or 0.1-0.2MPa, the agent-oil ratio is 3-30, for example 15-25, and the retention time is 0.3-6s, for example 1-3 s; the reaction conditions of the third downcomer (conditions of the third cleavage reaction) were: the reaction temperature is 480-630 ℃, the reaction pressure is 0.1-0.4MPa, such as 0.1-0.3MPa or 0.1-0.2MPa, the catalyst-oil ratio is 3-25, such as 10-20, and the retention time is 0.3-6s, such as 1-3 s. In specific implementation, the reaction temperature of the first cracking reaction is generally higher than that of the second cracking reaction, and the reaction temperature of the second cracking reaction is higher than that of the third cracking reaction; the agent-oil ratio of the first cracking reaction is greater than that of the second cracking reaction, and the agent-oil ratio of the second cracking reaction is greater than that of the third cracking reaction; the residence time of the first cleavage reaction is greater than the residence time of the second cleavage reaction and the residence time of the third cleavage reaction.

In the specific implementation process of the invention, the first raw material and/or the second raw material and/or the third raw material can enter the descending pipe for cracking reaction after being preheated, which is more beneficial to the generation and the implementation of the reaction, wherein the preheating temperature of the first raw material can be generally 100-250 ℃, the preheating temperature of the second raw material can be 100-300 ℃, and the preheating temperature of the third raw material can be generally 100-250 ℃; and/or, the first raw material, the second raw material and the third raw material can be mixed with the atomized steam respectively and then enter the corresponding descending pipe, the atomized steam not only can be used as lifting gas to lift the raw materials, but also can play a role in partial pressure to maintain a more appropriate cracking atmosphere in the first descending pipe, the second descending pipe and the third descending pipe, and specifically, the mass ratio of the first raw material to the atomized steam can be generally 1: (0.1-3), and further may be 1: (0.1-1), further 1 (0.1-0.8) or 1: (0.2-0.6) or 1: (0.2-0.4), and/or the mass ratio of the second feedstock to atomizing vapor may be 1: (0.1-3), and further may be 1: (0.1-1), and further may be 1: (0.1-0.8) or 1: (0.2-0.6) or 1: (0.2-0.4), and/or the mass ratio of the third feedstock to atomizing vapor may be 1: (0.1-3), and further may be 1: (0.1-1), and further may be 1: (0.1-0.8) or 1: (0.2-0.7) or 1: (0.3-0.5); the atomizing steam may be water steam or the like commonly used in the art, and the present invention is not particularly limited thereto.

Specifically, in one embodiment of the present invention, the catalytic cracking method may be carried out using a reaction apparatus including a first downflow pipe, a second downflow pipe, and a third downflow pipe, a stripping apparatus having a first zone and a second zone provided therein independently of each other, a settler provided at an upper portion of the stripping apparatus and communicating with the first zone and the second zone, and a regenerator having a first regeneration zone and a second regeneration zone provided therein independently of each other. Specifically, in the catalytic cracking process, a first cracking reaction product and a second cracking reaction product enter a first partition, in the first partition, a first oil-gas product (namely, an oil-gas phase in the first partition) in the products ascends to enter a settler, is output from the settler after gas-solid separation, and a first catalyst to be generated (namely, a solid phase in the first partition) descends and enters a first regeneration area after being subjected to steam stripping treatment (in countercurrent contact with a stripping gas to strip out the oil-gas product adsorbed on the surface of the first catalyst); and the product of the third cracking reaction enters a second subarea, in the second subarea, a second oil gas product (namely, an oil gas phase in the second subarea) in the product ascends to enter a settler, is output from the settler after gas-solid separation, and a second spent catalyst (namely, a solid phase in the second subarea) descends and enters a second regeneration area after steam stripping treatment. In specific implementation, for example, the stripping device may be divided into a first partition and a second partition by using a structure such as a partition (the structure such as the partition is disposed at the middle position of the stripping device along the axial direction of the stripping device), and the partitioned stripping device may be connected to the settler by using a conventional assembly method in the art, so that both the first partition and the second partition are communicated with the settler, thereby separating oil and gas products in the first partition and the second partition. The stripping device may be a conventional stripper in the art or a reactor with a stripping function, and may be selected according to the requirement, and the lower portion thereof may be provided with a stripping gas inlet communicated with the first partition and the second partition, for example, for introducing a stripping gas to strip the spent catalyst in the first partition and the second partition.

In an embodiment of the present invention, the reaction apparatus may further include a fluidized bed reactor having a first reaction zone and a second reaction zone provided therein, the first reaction zone and the second reaction zone being independent of each other, and the method further includes: enabling the product of the first cracking reaction and the product of the second cracking reaction to enter a first reaction zone to carry out a fourth cracking reaction, and carrying out gas-solid separation on the product of the fourth cracking reaction to respectively obtain a first oil-gas product and a first catalyst to be generated; and enabling the product of the third cracking reaction to enter a second reaction zone to carry out a fifth cracking reaction, and carrying out gas-solid separation on the product of the fifth cracking reaction to respectively obtain a second oil gas product and a second spent catalyst.

Specifically, the stripping device may be a fluidized bed reactor (the lower portion of which is provided with a stripping gas inlet communicated with the first reaction zone and the second reaction zone for introducing stripping gas to strip the spent catalyst in the first reaction zone and the second reaction zone) in which a first reaction zone (i.e., the first zone) and a second reaction zone (i.e., the second zone) are independent of each other, specifically, in the first reaction zone, a first oil-gas product in a fourth cracking reaction product ascends to enter a settler, is output from the settler after gas-solid separation, and a first catalyst to be regenerated descends and enters a first regeneration zone after stripping treatment; in the second reaction zone, a second oil gas product in the fifth cracking reaction product ascends to enter a settler, is output from the settler after gas-solid separation, and a second spent catalyst descends and enters a second regeneration zone after steam stripping treatment.

The catalytic cracking process adopts a matching cracking mode of parallel connection of two descending pipes and partition reaction of the fluidized bed, can further enhance the cracking depth of the light hydrocarbon raw material, is particularly suitable for cracking the light hydrocarbon raw material which is difficult to crack, and effectively improves the yield of the low-carbon olefins such as propylene.

In the practice of the present invention, the reaction conditions of the fluidized bed reactor can be generally controlled as follows: the mass space velocity is 5-25h^-1For example, it can be 15-25h^-1The bed linear velocity is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃. In the specific operation, the reaction conditions of the fluidized bed reactor can be properly adjusted according to the composition of the first raw material, the second raw material, the third raw material or the cracked product of each descending tube. The condition is favorable for further coordinating the matching of the material flow and the energy flow of the whole cracking system, improves the stability of the system, improves the overall energy efficiency and realizes the industryFeasibility.

Further, a portion of the first regenerated catalyst may also be passed to the first reaction zone to form a fourth cycle; and/or, passing a portion of the second regenerated catalyst to the second reaction zone to form a fifth cycle. In practice, for example, a regenerated catalyst delivery pipe from the first regeneration zone to the first reaction zone may be added, and/or a regenerated catalyst delivery pipe from the second regeneration zone to the second reaction zone may be added. Through the fourth cycle and the fifth cycle, the first regenerated catalyst and the second regenerated catalyst can be respectively provided for the first reaction zone and the second reaction zone, which is beneficial to further improving the cracking reaction efficiency.

The stripping gas used in the above process may be, for example, high-temperature steam or the like which is commonly used in the art, and the present invention is not particularly limited thereto, and the linear velocity of the stripping gas may be generally 0.1 to 0.8m/s, and may further be 0.2 to 0.7m/s, or 0.2 to 0.6m/s, or 0.3 to 0.5 m/s.

In the invention, less spent catalyst is mixed in the oil gas product and goes into the settler, so that the first spent catalyst and the second spent catalyst are basically not mixed in the settler, namely, the independent cracking reaction of each raw material is not influenced.

In the above process, the oil gas product enters the settler and then stays in the settler for a certain time, and the oil gas product has a higher temperature during the time, so that secondary reaction (mainly thermal cracking reaction) of a considerable degree is easy to occur, and the yield of by-products such as dry gas and coke is increased. Specifically, by using the gas-solid rapid separation device, the dilute phase space volume of the settler is properly reduced, the oil-gas product and the spent catalyst can be rapidly separated, and the side reaction is inhibited. The gas-solid rapid separation component can be a common semicircular cap-shaped component, a T-shaped component or a primary cyclone separator and the like in the field, for example, in a specific embodiment, the gas-solid rapid separation component can be the primary cyclone separator, the distance between the outlet of a riser of the primary cyclone separator and the inlet of the cyclone separator at the top of the settler is shortened, the secondary reaction can be obviously reduced, the yield of oil and gas products is favorably improved, and the generation rate of coke and dry gas is reduced.

The spent catalyst enters a regeneration zone of a regenerator and is in countercurrent contact with regenerated gas, and a scorching exothermic reaction is carried out at high temperature to burn off carbon deposition on the spent catalyst, so that regeneration is realized. In the present invention, the regeneration conditions in the regenerator can generally be controlled as follows: the temperature is 600-850 deg.C, such as 650-750 deg.C, and the linear velocity of the regeneration gas is 0.5-20m/s, such as 0.5-15m/s, 0.5-10m/s, 0.5-5m/s, 0.5-1m/s, 0.7-1m/s, or 0.7-0.8 m/s. Wherein the regeneration gas may be an oxygen-containing gas having an oxygen content of 10 to 35 wt%, and further may be an oxygen-containing gas having an oxygen content of 15 to 25 wt%, and may be, for example, air or the like.

Specifically, for example, the dense-phase zone of the regenerator may be divided into a first regeneration zone and a second regeneration zone which are independent of each other by a partition or other structure, and the dilute-phase zone may not be partitioned (the first regeneration zone and the second regeneration zone are controlled to be communicated with the dilute-phase zone during partitioning, and specifically, the partition or other structure may be disposed at the middle position of the dense-phase zone along the axial direction of the dense-phase zone), so as to implement the partitioned regeneration.

If the coking amount on the surface of the spent catalyst is large, the carbon deposit on the surface of the spent catalyst can be combusted to generate enough heat to meet the regeneration of the spent catalyst, because the invention aims at light hydrocarbon raw materials, less coke is generated on the surface of the spent catalyst during cracking, and the heat generated by the combustion of the coke is not enough to provide the heat required by the regeneration of the spent catalyst, in order to ensure the high-efficiency regeneration of the spent catalyst, the heat can be supplemented to the regeneration process of the spent catalyst in a mode of increasing the coke amount on the surface of the spent catalyst or other combustion promoters, for example, the spent catalyst can be contacted with fuel capable of forming coke and can be subjected to pre-combustion treatment to achieve the purpose of increasing the coke amount. Specifically, in one embodiment of the present invention, at least a portion of the first catalyst to be regenerated may be contacted with fuel and subjected to a pre-combustion process before entering the first regeneration zone; and/or, enabling at least part of the second spent catalyst to contact with fuel, pre-burning the second spent catalyst, and then entering a second regeneration zone; the pre-combustion treatment can be carried out by adopting an outer heat compensator arranged outside the regenerator, and the pre-combustion conditions in the outer heat compensator are as follows: the temperature is 400-800 deg.C, such as 500-600 deg.C, absolute pressure is 0.05-0.4MPa, such as 0.06-0.3MPa or 0.07-0.2MPa or 0.08-0.15MPa, and oxygen content is 0.005-7 wt%, such as 0.1-1 wt%. In the process, the spent catalyst (first spent catalyst/second spent catalyst) is contacted with the fuel and is subjected to pre-combustion (insufficient combustion/incomplete combustion) in a low-oxygen environment, so that combustion improver (such as coke and the like) formed by pre-combustion of the fuel is attached to the spent catalyst, and after the combustion improver attached to the spent catalyst enters a regeneration zone, the combustion improver is contacted with regeneration gas (such as air and the like) to be completely combusted (heat release), heat required by a regeneration reaction is supplied in a supplementing manner (namely heat is supplemented to the regeneration process), and the regeneration efficiency is improved; meanwhile, the processing can also make the combustion improver such as coke on the surface of the spent catalyst more uniform, and avoid the problems of catalyst structure damage, inactivation and the like caused by overhigh local temperature due to the aggregation of local combustion improver such as coke, thereby improving the heat balance and the production capacity of the whole device (system). The external heat compensator is matched with the regenerator, pre-combustion and regeneration treatment are carried out on the catalyst to be regenerated, the operation is continuous, the catalyst to be regenerated is subjected to mild and stable combustion and regeneration, the structure and the physicochemical property of the catalyst can be well maintained, high-efficiency regeneration is realized, and the catalytic cracking reaction of the first raw material, the second raw material and the third raw material is favorably carried out.

Specifically, the spent catalyst (first spent catalyst/second spent catalyst) enters an external heat compensator through a pipeline to be subjected to the pre-combustion treatment and then enters a regeneration zone to be regenerated; the fuel can be CO combustion improver commonly used in the field (for example, Al is adopted)₂O₃Or SiO₂-Al₂O₃A CO combustion improver which is a carrier on which a noble metal such as platinum or palladium is supported as an active component); the oxygen can be maintained by introducing low oxygen-containing gas into the external heat compensatorA low oxygen environment in an amount of 0.005 to 7 wt% while providing a pre-combustion medium, and specifically, the linear velocity of the low oxygen-containing gas may be generally 0.3 to 0.5 m/s; the two external heat compensators may be adopted, wherein one external heat compensator performs pre-combustion treatment on the first catalyst to be generated, and the other external heat compensator performs pre-combustion treatment on the second catalyst to be generated, or one external heat compensator may be divided into two independent pre-combustion areas by a partition plate or other structures, wherein one pre-combustion area is used for performing pre-combustion treatment on the first catalyst to be generated, and the other pre-combustion area performs pre-combustion treatment on the second catalyst to be generated.

Furthermore, fuel can enter the external heat compensator through a fuel distributor arranged at the upper part of a spent catalyst inlet (a first spent catalyst inlet/a second spent catalyst inlet) of the external heat compensator, so that the fuel is favorably and uniformly distributed on the surface of the spent catalyst, and after pre-combustion treatment, the surface of the spent catalyst is more uniformly attached with a combustion improver, so that the subsequent regeneration reaction is favorably realized. In addition, a fluidizing medium can be introduced from the lower part or the bottom of the external heat compensator to fluidize materials such as a combustion improver and a spent catalyst in the external heat compensator, so that the flowability of the materials is improved, and the uniform adhesion of the combustion improver to the surface of the spent catalyst is facilitated; the fluidizing medium may be conventional steam, and the like, and the present invention is not particularly limited thereto.

During specific operation, control valves can be arranged on the conveying pipelines of the spent catalyst and the regenerated catalyst, so that the catalyst amount and the operation temperature in the regenerator and the external heat compensator are kept stable, and independent operation can be performed when necessary; the amount of the regenerated catalyst to be fed to each reactor (the first downcomer, the second downcomer, the third downcomer, and the fluidized bed reactor) may be adjusted as necessary, so that the reaction parameters (for example, the reaction temperature, the oil-to-oil ratio, and the like) of the reactors such as the first riser and the second riser can be adjusted.

In the present invention, the first catalyst and the second catalyst may be the same or different. In a specific embodiment, the first catalyst and the second catalyst are the same, and the raw material composition comprises 20-50 wt% of modified molecular sieve, 1-50 wt% of matrix, 3-35 wt% of binder and 3-15 wt% of composite auxiliary agent; the modified molecular sieve is obtained by alkali treatment of a molecular sieve, then non-metal element modification and metal element modification, and hydrothermal treatment can be carried out between the two modifications; the non-metallic elements are selected from at least two non-metallic elements in IIIA group, VA group, VIA group and VIIA group of the periodic table; the metal elements are at least three elements selected from IIA group, IVB group, VB group, VIB group, VIIB group, VIII group and lanthanide series of the periodic table, and at least comprise one transition metal element except lanthanide series; the composite auxiliary agent comprises inorganic acid and cellulose.

Further, the nonmetal can be at least two selected from B, P, S, Cl and Br, optionally, the nonmetal elements at least include S, such as P and S; and/or the metal element is selected from at least three of Mn, V, Fe, Nb, Cr, Mo, W, Mg, Ca and La, optionally the metal element comprises at least one group IIA metal (such as Mg) and one lanthanide metal, such as Nb, Mn, Mg and La.

Further, the molecular sieve may include at least one of ZSM-5, SAPO34, Y molecular sieve, beta molecular sieve. The particle size and the silica-alumina ratio of the molecular sieve are in proper ranges, which is more favorable for providing proper acid centers and alkali centers as a carrier, thereby being more favorable for loading metal and nonmetal elements. In one possible embodiment, it may be advantageous to select nanoscale molecular sieve particles, for example, having a particle size of about 500 to 3000nm, such as 1500 to 2000nm, and a silica to alumina ratio of 90 to 110, such as about 100. The molecular sieve raw material can be purchased commercially according to design requirements, or entrusted to production, and can also be synthesized by self.

In the molecular sieve modification process, the molecular sieve is subjected to alkali treatment to realize desilication and pore expansion, so that coking of catalyst orifices is avoided, and ammonium exchange treatment can be carried out after pore expansion to recover the acidity of the molecular sieve, but ammonium exchange is not necessary. The alkali solution used for carrying out the alkali treatment may be an alkali solution conventionally used in the art for this purpose, and is selected from, for example, one or two of sodium hydroxide solution, potassium hydroxide solution, aqueous ammonia and the like; the ammonium ion exchange reagent used may be one or two conventionally used in the art for this purpose, and is selected from, for example, ammonium nitrate, ammonium chloride and the like.

Specifically, the following operations may be employed: mixing a molecular sieve and 0.2-1.0mol/L alkaline solution according to a mass ratio of 1:4-8, exchanging at 70-90 ℃ for 1-5h, washing the molecular sieve to be neutral, drying at 60-150 ℃ for 3-12h, and roasting at 400-600 ℃ for 2-6 h; mixing the molecular sieve treated by the alkaline solution with 0.5-1.2mol/L ammonium ion-containing solution (such as 1mol/L ammonium nitrate solution) according to the mass ratio of 1:4-10, exchanging at the temperature of 70-90 ℃ for 1-5h, washing to be neutral, then drying at the temperature of 60-150 ℃ for 3-12h, and roasting at the temperature of 400-600 ℃ for 2-6h to obtain the molecular sieve treated by the alkaline solution.

Subsequently, the molecular sieve treated by the alkali can be modified by adopting an impregnation mode through various non-metal elements and metal elements. In specific implementation, although the loading sites of the nonmetal elements and the metal elements are different, and there is no adsorption competition relationship between the nonmetal elements and the metal elements, due to solubility and other reasons, separate impregnation is generally selected, for example, the nonmetal elements may be impregnated first and then the metal elements may be impregnated, and synchronous impregnation or stepwise impregnation may be generally selected among a plurality of metal elements and among a plurality of nonmetal elements according to solubility.

The metal modification can be generally achieved by impregnating the molecular sieve with a salt solution of a metal element, and in the metal element impregnation modification, for some metal salts which are difficult to dissolve, the corresponding salt of the metal can be dissolved in a dispersing agent to increase the solubility of the metal salt, for example, the corresponding salt of the metal can be dissolved by using a dispersing agent (such as a citric acid and/or oxalic acid solution) with a total concentration of about 0.1 to 4mol/L to prepare an impregnation solution, and then the molecular sieve is subjected to the metal element impregnation modification. The selection of the dispersant with the concentration is beneficial to both the dispersing effect and the impregnating effect (the dispersing effect can not be achieved when the concentration of the dispersant is too low, and the impregnating effect can be influenced when the concentration of the dispersant is too high), and the performance of the catalyst is beneficial. Wherein, the mass ratio of the impregnating solution to the molecular sieve can be set according to the expected metal element loading.

In one embodiment of the present invention, the first catalyst may have a loading of non-metallic elements and metallic elements in excess or in excess of the loading of non-metallic elements and metallic elements in the range of about 0.05 to about 5 wt%, such as 0.1 to about 1 wt%, and/or the first catalyst may have a loading of metallic elements in the range of about 0.1 to about 10 wt%, such as 0.2 to about 2 wt%, based on the mass of the first catalyst.

When the nonmetal modification and the metal modification are carried out, the hydrothermal treatment is needed between the two types of modification regardless of the sequence so as to dredge the molecular sieve channel and facilitate the loading of the next type of modification element. The conditions of the hydrothermal treatment are not particularly limited, and the treatment is generally carried out in an environment at a temperature of less than 550 ℃.

In general, each impregnation is followed by aging, drying and calcination. The aging temperature after each impregnation is 0-50 deg.C, such as 20-40 deg.C, and the aging time is 2-20h, such as 4-12 h; drying at 50-160 deg.C, such as 70-120 deg.C for 2-20h, such as 3-12 h; the calcination temperature is 300-800 deg.C, such as 400-600 deg.C, and the calcination time is 1-10h, such as 2-6 h.

Under the composition system of the first catalyst/the second catalyst, a proper amount of matrix material can provide a dispersion environment for a carrier and an active ingredient, increase the mechanical strength and the carbon capacity of the catalyst, and is also beneficial to preventing the catalyst from coking and deactivating and prolonging the service life of the catalyst; meanwhile, the required catalyst is finally obtained by utilizing the bonding effect of the binder. Specifically, the binder includes at least one of alumina sol, silica sol, sesbania powder, and the like; the matrix may comprise at least one of pseudoboehmite, kaolin, a group IVB metal oxide, such as titania and/or zirconia, which may increase the pore structure of the matrix, thereby extending the reaction path of the alkane-rich feedstock in the catalyst and allowing the catalyst to perform better.

According to the research of the invention, if the content of the composite additive is too low, the loss amount of the catalyst can be increased, but if the content of the composite additive is too high, the viscosity of the raw material is too high, and the raw material is not easy to form. Therefore, the present invention limits the content of the composite assistant, and the mass content of the composite assistant is 3 to 30 wt% (if the composite assistant comprises a plurality of components, the sum of the mass contents of all the components is 3 to 30 wt%), for example, 3 to 12 wt%, or 5 to 12 wt%, or 8 to 12 wt%, or 10 to 12 wt%.

In order to further ensure that the acid property of the first catalyst is not easily changed and to be beneficial to ensuring the pore structure and the mechanical property of the first catalyst, the types and the contents of the inorganic acid and the cellulose in the composite auxiliary agent can be properly adjusted and selected within the set range, the mass fraction of the inorganic acid is preferably not more than 2 wt% based on the mass of the catalyst, and the inorganic acid can comprise common inorganic acids such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and the like, and can be selected from one of the nitric acid and the hydrochloric acid under comprehensive consideration; the cellulose may be selected from one of methyl cellulose and ethyl cellulose, but is not limited thereto.

After the selection and modification of the raw material components are completed, the preparation of the first catalyst can be completed according to the conventional operation, the modified molecular sieve, the matrix, the binder and the composite auxiliary agent can be mixed and pulped to obtain slurry with the solid content of about 20-50 wt%, generally, the catalyst microspheres with the particle size of about 20-200nm can be obtained by drying (such as spray drying) and molding, and then, the operations of drying and roasting can be carried out in multiple steps, for example, the first catalyst can be obtained by sequentially drying at about 20-50 ℃ for 12-50h, drying at 100-200 ℃ for 12-50h and roasting at 500-700 ℃ for 1-12 h; in addition, hydrothermal aging treatment can be further carried out, for example, hydrothermal aging treatment is carried out at the temperature of 500-800 ℃, and the final first catalyst product is obtained.

According to the research of the invention, the yield of propylene can be further improved by selecting the first catalyst, and the molecular sieve is modified by utilizing a plurality of metal elements and nonmetal elements, so that the acid strength and the acid density of the molecular sieve carrier are controlled in a targeted manner, the first catalyst has acid centers of different types such as super acid, strong acid, weak acid and the like, the adsorption capacity of olefin and alkane can be simultaneously improved, the cracking efficiency of hydrocarbon which is difficult to crack such as alkane and the like can be particularly improved, and the cracking method can achieve better yield of propylene while improving the conversion rate of raw materials. In addition, the synergistic effect of the specific composite auxiliary agent is introduced, so that the wear resistance of the catalyst is improved while the catalytic performance is ensured, and the service life of the catalyst is prolonged.

In the invention, the raw material composition of the third catalyst comprises 20-50 wt% of modified composite molecular sieve, 1-50 wt% of matrix and 3-35 wt% of binder, wherein the modified composite molecular sieve is obtained by silanizing a composite molecular sieve formed by at least two molecular sieves, and then modifying the composite molecular sieve by using non-metallic elements and metallic elements; the at least two molecular sieves can be selected from at least two of HZSM-5, USY molecular sieve, SAPO34 and beta molecular sieve, the matrix comprises at least one of pseudo-boehmite, kaolin, titanium dioxide and zirconia, and the binder comprises at least one of alumina sol, silica sol, sesbania powder and the like.

Specifically, the modified composite molecular sieve can be prepared according to the following processes: mixing the pretreated SAPO-34 molecular sieve, ZSM-5 molecular sieve, beta molecular sieve and USY molecular sieve according to the mass ratio of 0-30:50-80:0-30:0-50 to prepare the composite molecular sieve at least comprising two molecular sieves, wherein the pretreatment is used for expanding pores of the molecular sieves so as to be beneficial to subsequent nonmetal and metal modification and improve the performance of the catalyst, and specifically comprises the following steps: respectively treating a ZSM-5 molecular sieve, a beta molecular sieve and a USY molecular sieve by using alkali, and treating an SAPO-34 molecular sieve by using acid; wherein, the operation of alkali treatment can adopt the conventional mode in the field, for example, alkali liquor with higher concentration (for example, common alkali liquor with 0.4mol/L-0.8 mol/L) with concentration of more than 0.4mol/L is used to desiliconize and expand pores of the molecular sieve, and then ammonium ion exchange is carried out to recover the acidity of the molecular sieve, and the specific process can refer to the alkali treatment process of the first catalyst part, and is not described herein again; the acid treatment is generally carried out by using an acid solution having a concentration of 0.02mol/L to 0.1mol/L, and the acid used may be an inorganic acid such as nitric acid.

And then, drying and dehydrating the composite molecular sieve in an inert gas atmosphere, and then performing silanization treatment, wherein the dosage of a silanization reagent is 0.1-1.0mL/g of the composite molecular sieve. The silylating agent may be selected from compounds of the general formula:

wherein R1 is selected from alkyl of C1-C3 or phenyl; r2 is selected from hydrogen, hydroxy, C1-C3 alkyl, C1-C3 alkoxy, or phenyl;

when the method is concretely implemented, the silanization reagent is dissolved in an anhydrous nonpolar solvent in advance, and the composite molecular sieve is subjected to silanization treatment after high-temperature dehydration, wherein the silanization treatment temperature is 120-250 ℃ and the silanization treatment time is 0.5-5 hours.

The modified composite molecular sieve can be obtained by sequentially modifying the composite molecular sieve subjected to silanization treatment by adopting a conventional method in the field such as an impregnation method and the like through a non-metal element and a metal element, and the specific modification process can be similar or identical to the non-metal modification and metal modification treatment process of the first catalyst part, so that redundant description is omitted. Specifically, the non-metallic element may be selected from at least one of group va, group VIA and group IIA of the periodic table, and further may be selected from one or more of P, S, F and Cl, with an element loading of 0.01 to 3 wt% (based on the mass of the catalyst); the metal element can be selected from at least one of IA group, IIA group, IB group, VIB group, VIIB group, VIII group and lanthanide series of the periodic table, and further can be selected from one or more of Na, K, Mg, Ca, La, Ce, Cu, Ag, Ni, Co, Fe, Mn and Cr, and the element loading is 0.01-3 wt% (based on the mass of the catalyst).

After the selection and modification of the raw material components are completed, the preparation of the third catalyst can be completed according to conventional operations, for example, the modified composite molecular sieve, the matrix and the binder can be mixed and pulped, and then aged and roasted to obtain the third catalyst, and the conditions of drying, roasting, hydrothermal aging and the like related to the preparation process can also refer to the preparation process of the first catalyst, which is not described in detail herein.

In the present invention, "wt%" represents a mass content unless otherwise specified.

In the invention, the first raw material rich in C4 hydrocarbon refers to light hydrocarbon raw material with the main component of C4 hydrocarbon, the second raw material rich in C5-C6 hydrocarbon refers to light hydrocarbon raw material with the main component of C5-C6 hydrocarbon, and the third raw material rich in C7-C8 hydrocarbon refers to light hydrocarbon raw material with the main component of C7-C8 hydrocarbon. In order to facilitate the yield of the lower olefins such as propylene, in one embodiment of the present invention, the content of the C4 hydrocarbon in the first raw material is generally not less than 40 wt%, and further not less than 50 wt%; the C5-C6 hydrocarbon content of the second feedstock is generally not less than 40 wt%, further not less than 50 wt%; the C7-C8 hydrocarbon content of the third feedstock is generally not less than 40 wt.%. Of course, the present invention is not limited to the above-mentioned limited range (for example, some light hydrocarbon raw materials with a hydrocarbon content of less than 40 wt% of C4 may be used as the first raw material), but according to the research of the present invention, the yield of the lower olefins such as propylene is more favorably increased within the above-mentioned limited range of the hydrocarbon content of the first raw material, the second raw material and the third raw material.

The light hydrocarbon raw material of the present invention may be fractions or oil products from different processes, and specifically may be C4+ light hydrocarbon raw material (such as C4+ gasoline fraction, etc.), in some embodiments of the present invention, the light hydrocarbon raw material may be naphtha, catalytically cracked gasoline, pressurized gas oil, C4 component or light cracked gasoline by steam cracking, C4 component of FCC unit or cracking unit, C4+ olefin component by methanol to olefins unit (MTO unit), etc., during specific operation, it may be catalytically cracked as a first raw material or a second raw material or a third raw material according to the C4 hydrocarbon, C5-C6 hydrocarbon, C7-C8 hydrocarbon content therein; of course, C4 hydrocarbons, C5-C6 hydrocarbons, and C7-C8 hydrocarbons may be selected as the first feedstock, the second feedstock, and the third feedstock, respectively, in the present invention.

The downer (the first downer/the second downer/the third downer) may be a constant linear speed downer, a variable diameter downer, a constant diameter downer, etc., and generally a nozzle may be disposed at a material inlet (such as a raw material inlet, a fresh catalyst inlet, a regenerated catalyst inlet, etc.) of the downer, so that the corresponding raw material, catalyst, etc. are sprayed into the downer through the nozzle, thereby facilitating a material mixing reaction; the nozzle may be a hollow cone nozzle, a solid cone nozzle, a square nozzle, a rectangular nozzle, an elliptical nozzle, a fan nozzle, a cylindrical flow (direct flow) nozzle, a two-fluid nozzle, a multi-fluid nozzle, etc., which are commonly used in the art. In addition, the acute included angle between the material inlet of each descending tube and the axis of each descending tube is 30-60 degrees, and the acute included angle can ensure that the materials entering the descending tube reactor are mixed more fully, thereby being more beneficial to the cracking reaction.

In still another aspect of the present invention, there is provided a multi-zone coupling control multi-stage catalytic cracking apparatus, comprising: the device comprises a first descending pipe, a second descending pipe, a third descending pipe, a steam stripping device, a settler and a regenerator, wherein the steam stripping device is internally provided with a first subarea and a second subarea which are mutually independent; the lower part of the stripping device is provided with a stripping gas inlet communicated with the first partition and the second partition, a material outlet of the first descending pipe and a material outlet of the second descending pipe are communicated with the material inlet of the first partition, a spent catalyst outlet of the first partition is communicated with a spent catalyst inlet of the first regeneration partition, a regenerated catalyst outlet of the first regeneration partition is communicated with a regenerated catalyst inlet of the first descending pipe and a regenerated catalyst inlet of the second descending pipe, a material outlet of the third descending pipe is communicated with the material inlet of the second partition, a spent catalyst outlet of the second partition is communicated with a spent catalyst inlet of the second regeneration partition, and a regenerated catalyst outlet of the second regeneration partition is communicated with a regenerated catalyst inlet of the third descending pipe.

Specifically, the stripping device may be a conventional stripper in the art or a reactor having a stripping function, and may be selected as needed. In specific implementation, for example, the stripping device may be divided into a first partition and a second partition by using a structure such as a partition (the structure such as the partition is disposed at the middle position of the stripping device along the axial direction of the stripping device), and the partitioned stripping device may be connected to the settler by using a conventional assembly method in the art, so that both the first partition and the second partition are communicated with the settler; the dense-phase zone of the regenerator can be divided into a first regeneration zone and a second regeneration zone by a partition plate, and the partition plate is arranged at the middle position of the dense-phase zone along the axial direction of the dense-phase zone so as to ensure that the first regeneration zone and the second regeneration zone are both communicated with the dilute-phase zone of the regenerator.

Furthermore, an outer heat compensator is arranged outside the regenerator, a first pre-combustion area and a second pre-combustion area which are independent of each other are arranged inside the outer heat compensator, a spent catalyst outlet of the first sub-area is communicated with a spent catalyst inlet of the first regeneration area through the first pre-combustion area, and a spent catalyst outlet of the second sub-area is communicated with a spent catalyst inlet of the second regeneration area through the second pre-combustion area.

In the present invention, the above-mentioned apparatus can be assembled/modified by the conventional method in the art, and if not specifically mentioned, the structures/components/apparatuses, etc. can be communicated with each other by the structures such as pipes/tubes, etc. commonly used in the art.

The implementation of the invention has at least the following advantages:

the multi-zone coupling control multistage catalytic cracking method based on the raw material type provided by the invention has the advantages that the cracking is carried out on light hydrocarbon raw materials, the light hydrocarbon raw materials rich in different carbon numbers are subjected to zone cracking through the descending tube reactor and the catalyst regeneration system which are matched and cooperated with each other based on the characteristics and cracking principles of different types of hydrocarbons, the yield of low-carbon olefins such as propylene can be higher, and the yield of byproducts such as dry gas and coke is lower, and researches show that by adopting the catalytic cracking method provided by the invention, the yield of propylene can reach more than 32%, the yield of ethylene can reach more than 21% (the total yield of two types of olefins reaches more than 53%), the yield of coke is basically not higher than 0.1%, and the yield of dry gas is basically not higher than 0.2%; meanwhile, the method can adjust and control the respective reaction conditions of the raw materials according to the hydrocarbon type, so that the raw materials are cracked under the respective proper conditions, thereby ensuring high target product yield and low byproduct yield and having lower energy consumption; in addition, the light hydrocarbon raw material can be from a byproduct of cracking processing of the heavy raw material, so that the catalytic cracking method can be used as a downstream treatment process of a cracking treatment product of the existing heavy raw material, high yield of low-carbon olefins such as propylene and the like is realized, and the utilization rate of the heavy raw material can be further improved.

The multi-region coupling control multistage catalytic cracking device provided by the invention can realize independent reaction of three light hydrocarbon raw materials (such as the first raw material, the second raw material and the third raw material), realizes the purpose-specific regulation and control of reaction conditions according to the properties of hydrocarbon raw materials, and has the advantages of simple structure, small occupied area, easiness in operation and contribution to practical industrial application.

Drawings

FIG. 1 is a schematic view of a multi-zone coupled multi-stage catalytic cracking apparatus according to an embodiment of the present invention;

FIG. 2 is a schematic view of a multi-zone coupled multi-stage catalytic cracking unit according to another embodiment of the present invention;

FIG. 3 is a schematic view of a multi-zone coupled multi-stage catalytic cracking apparatus according to still another embodiment of the present invention;

description of reference numerals:

1. a first down tube; 2. a second down tube; 3. a fluidized bed reactor; 31. a first reaction zone; 32. a second reaction zone; 3', a stripper; 31', a first stripping zone; 32', a second stripping zone; 4. a settler; 5. a regenerator; 51. a first regeneration zone; 52. a second regeneration zone; 6. an external heat compensator; 7. a third down pipe; a1, a first raw material; a2, a second raw material; a3, third raw material; b1, product of the first cleavage reaction; b2, product of the second cleavage reaction; b3, product of the third cleavage reaction; c1, a first oil and gas product; c2, a second oil and gas product; d1, a first catalyst to be regenerated; d2, a second spent catalyst; e1, first regenerated catalyst; e2, second regenerated catalyst; f. stripping gas; g. a cleavage product; h. regenerating gas; i. flue gas.

Detailed Description

The present invention will be described in more detail with reference to examples. It is to be understood that the practice of the invention is not limited to the following examples, and that any variations and/or modifications may be made thereto without departing from the scope of the invention.

Example 1

FIG. 1 is a schematic diagram of a multi-zone coupled multi-stage catalytic cracking apparatus according to an embodiment of the present invention, the apparatus comprising: a first downflow pipe 1, a second downflow pipe 2, a third downflow pipe 7, a stripper 3 'provided with a first stripping zone (i.e., a first partition) 31' and a second stripping zone (i.e., a second partition) 32 'inside thereof which are independent of each other, a settler 4 provided at the upper part of the stripper 3' and communicating with the first stripping zone 31 'and the second stripping zone 32', and a regenerator 5 provided with a first regeneration zone 51 and a second regeneration zone 52 inside thereof which are independent of each other; the material outlet of the first downer 1 and the material outlet of the second downer 2 are both communicated with the material inlet of the first stripping area 31 ', the spent catalyst outlet of the first stripping area 31' is communicated with the spent catalyst inlet of the first regeneration area 51, and the regenerated catalyst outlet of the first regeneration area 51 is communicated with the regenerated catalyst inlet of the first downer 1 and the regenerated catalyst inlet of the second downer 2; the material outlet of the third descending pipe 7 is communicated with the material inlet of the second stripping zone 32 ', the spent catalyst outlet of the second stripping zone 32' is communicated with the spent catalyst inlet of the second regeneration zone 52, and the regenerated catalyst outlet of the second regeneration zone 52 is communicated with the regenerated catalyst inlet of the third descending pipe 7.

Specifically, the bottom of the stripper is provided with a stripping gas inlet communicated with the first stripping zone 31 'and the second stripping zone 32' for introducing a stripping gas f to strip the spent catalyst in the first stripping zone 31 'and the second stripping zone 32'.

The dense phase zone of the regenerator 5 is divided into the first regeneration zone 51 and the second regeneration zone 52 by a partition, and the partition is arranged at the middle position of the dense phase zone along the axial direction of the dense phase zone, so that the first regeneration zone 51 and the second regeneration zone 52 are both communicated with the dilute phase zone at the upper part of the regenerator 5; the bottom of the dense phase zone of the regenerator is provided with a regeneration gas inlet communicated with the first regeneration zone 51 and the second regeneration zone 52 and used for introducing regeneration gas h into the first regeneration zone 51 and the second regeneration zone 52, and the top of the dilute phase zone of the regenerator is provided with a flue gas outlet used for discharging flue gas i generated in the regenerator.

An outer heat compensator 6 is arranged outside the regenerator 5, a first pre-combustion area and a second pre-combustion area which are independent from each other are arranged inside the outer heat compensator 6, a spent catalyst outlet of the first stripping area 31 'is communicated with a spent catalyst inlet of the first regeneration area 51 through the first pre-combustion area, and a spent catalyst outlet of the second stripping area 32' is communicated with a spent catalyst inlet of the second regeneration area 52 through the second pre-combustion area; and fuel distributors are arranged above the spent catalyst inlet of the first pre-combustion zone and above the spent catalyst inlet of the second pre-combustion zone.

The multi-zone coupling control multi-stage catalytic cracking method based on the raw material type by using the catalytic cracking device of the embodiment is briefly as follows:

mixing the preheated (or not preheated) first raw material a1 with first atomized steam (water vapor) according to a certain mass ratio, then enabling the mixture and a first catalyst to enter a first descending tube 1 to perform a first cracking reaction, and mixing the preheated (or not preheated) second raw material a2 with second atomized steam (water vapor) according to a certain mass ratio, then enabling the mixture and a second catalyst to enter a second descending tube 2 to perform a second cracking reaction; a product b1 of the first cracking reaction and a product b2 of the second cracking reaction enter a first stripping zone 31 ', in the first stripping zone 31', a first oil-gas product c1 in the products goes upward to enter a settler 4, is output from the settler 4 after gas-solid separation, and a first catalyst d1 goes downward and enters a first regeneration zone 51 for regeneration after being stripped, so that a first regenerated catalyst e1 is obtained; a part of the first regenerated catalyst e1 enters the first descending pipe 1 to participate in the first cracking reaction to form a first cycle, and a part of the first regenerated catalyst e1 enters the second descending pipe 2 to participate in the second cracking reaction to form a second cycle;

mixing a preheated (or not preheated) third raw material a3 with third atomized steam (steam) according to a certain proportion, then enabling the mixture and a third catalyst to enter a third descending pipe 7 to carry out a third cracking reaction, enabling a product b3 of the third cracking reaction to enter a second stripping area 32 ', enabling a second oil gas product c2 in the product to ascend into a settler 4 in the second stripping area 32', outputting the product from the settler 4 after gas-solid separation, enabling a second spent catalyst d2 to descend, carrying out steam stripping treatment, and then enabling the product to enter a second regeneration area 52 for regeneration to obtain a second regenerated catalyst e 2; and enabling the second regenerated catalyst e2 to enter a third descending pipe 7 to participate in a third cracking reaction, so as to form a third cycle.

The method can realize the zone cracking of the first raw material rich in C4 hydrocarbon, the second raw material rich in C5-C6 hydrocarbon, the third raw material rich in C7-C8 hydrocarbon and the zone regeneration treatment of the first spent catalyst and the second spent catalyst, and the regeneration of the catalyst can not be satisfied by directly burning the catalyst in consideration of the small coking content on the surface of the catalyst in the cracking process, and the recycled spent catalysts (namely the first spent catalyst and the second spent catalyst) can be completely or partially respectively sent into the first pre-combustion zone and the second pre-combustion zone of the outer heat compensator 6 to be contacted with the fuel introduced through the fuel distributor and enter the corresponding regeneration zones for regeneration after the pre-combustion treatment (the combustion improver such as coke is attached to the surface of the spent catalyst).

The first oil gas product and the second oil gas product obtained by gas-solid separation are converged and output from the top of the settler 4 to become a cracking product g.

The obtained cracked product can be introduced into a product separation device (not shown) for further treatment such as fractionation and the like to obtain products such as dry gas, liquefied gas, gasoline, diesel oil, oil slurry and the like, and can also be further refined to obtain low-carbon olefin products such as propylene and the like.

Example 2

FIG. 2 is a schematic diagram of a multi-zone coupling control multi-stage catalytic cracking unit according to an embodiment of the present invention, which is different from the catalytic cracking unit shown in FIG. 1 in that: in this embodiment, the stripper 3' is replaced by a fluidized bed reactor 3 having a first reaction zone (i.e., a first partition) 31 and a second reaction zone (i.e., a second partition) 32, which are independent of each other, and a stripping gas inlet communicated with the first reaction zone 31 and the second reaction zone 32 is disposed at a lower portion of the fluidized bed reactor 3 for introducing a stripping gas f to strip the spent catalyst in the first reaction zone 31 and the second reaction zone 32.

The multi-zone coupling control multi-stage catalytic cracking method based on the types of raw materials using the catalytic cracking unit of this embodiment is different from that of example 1 in that:

a product b1 of the first cracking reaction and a product b2 of the second cracking reaction enter the first reaction zone 31 to carry out a fourth cracking reaction, a first oil-gas product c1 in the product of the fourth cracking reaction goes upward to enter the settler 4, is output from the settler 4 after gas-solid separation, and a first catalyst d1 to be regenerated goes downward and enters the first regeneration zone 51 for regeneration after being subjected to steam stripping treatment;

the product b2 of the third cracking reaction enters the second reaction zone 32 to carry out a fifth cracking reaction, a second oil gas product c2 in the fifth cracking reaction product ascends to enter the settler 4, is output from the settler 4 after gas-solid separation, and a second spent catalyst d2 descends and enters the second regeneration zone 52 for regeneration after steam stripping treatment.

Example 3

FIG. 3 is a schematic diagram of a multi-zone coupling control multi-stage catalytic cracking unit according to an embodiment of the present invention, which is different from the catalytic cracking unit shown in FIG. 2 in that: in this embodiment, the regenerated catalyst outlet of the first regeneration zone 51 is also in communication with the first reaction zone 31, and the regenerated catalyst outlet of the second regeneration zone 52 is also in communication with the second reaction zone 32.

The multi-zone coupling control multi-stage catalytic cracking method based on the types of raw materials using the catalytic cracking unit of this embodiment is different from that of example 2 in that:

allowing a part of the first regenerated catalyst e1 to enter the first downer 1 to participate in the first cracking reaction, so as to form a first cycle; a part of the first regenerated catalyst e1 enters the second descending pipe 2 to participate in the second cracking reaction, and a second cycle is formed; allowing a portion of the first regenerated catalyst e1 to enter the first reaction zone 31 to participate in the fourth cracking reaction, forming a fourth cycle;

a part of the second regenerated catalyst e2 enters a third descending pipe 7 to participate in a third cracking reaction, so that a third cycle is formed; a portion of the second regenerated catalyst e2 is passed to the second reaction zone 32 to participate in the fifth cracking reaction, forming a fifth cycle.

In the relevant experiments/comparative experiments in the following application examples, the first catalyst and the second catalyst were identical, and, if not specified otherwise, the composition of the first catalyst/the second catalyst used and the preparation process were as follows:

1. preparation of ZSM-5

Firstly, ethyl orthosilicate, sodium aluminate, tetrapropylammonium hydroxide, ammonia water and water are mixed according to 100SiO₂:1Al₂O₃:20TPABr:120NH₃·H₂O:2000H₂Mixing the components in the molar ratio of O, crystallizing at 80 deg.c for 12 hr, and crystallizing at 180 deg.cAnd crystallizing for 48 hours to obtain ZSM-5 with the grain size of 500-3000nm and the silica-alumina molar ratio of 100, then washing, filtering, drying at 120 ℃ for 12 hours, and roasting at 600 ℃ for 10 hours to obtain the molecular sieve ZSM-5.

2. Alkali treatment of catalyst supports

Mixing the molecular sieve ZSM-5 with 0.4mol/L NaOH solution according to the mass ratio of 1:6, then exchanging for 2h at the temperature of 90 ℃, then washing the mixture to be neutral, then drying for 12h at the temperature of 120 ℃ and roasting for 2h at the temperature of 540 ℃.

Mixing a ZSM-5 molecular sieve with 1mol/L ammonium nitrate solution according to the mass ratio of 1:10, then carrying out ammonium exchange for 4h at the temperature of 90 ℃, then washing the mixture to be neutral, then drying the mixture for 12h at the temperature of 120 ℃ and roasting the mixture for 2h at the temperature of 540 ℃ in sequence to obtain the catalyst carrier HZSM-5.

3. Modification of non-metallic elements

According to alkali-treated HZSM-5 with NH₄H₂PO₄And (NH)₄)₂SO₄The mixed solution is dipped with P and S on HZSM-5 with the mass ratio of 0.5:1 to obtain the load of P of 0.8 wt% and the load of S of 0.5 wt%, and then the mixture is aged for 6h at room temperature, dried for 12h at the temperature of 120 ℃ and roasted for 4h at the temperature of 540 ℃.

4. Hydrothermal treatment

Carrying out hydrothermal treatment on the nonmetal element impregnated and modified HZSM-5 for 4h at the temperature of 550 ℃ in a steam atmosphere.

5. Modification of metallic elements

5.1 impregnation of Nb

Firstly (NH)₄)₃[NbO(C₂O₄)]Heating the aqueous solution to 60 ℃ to dissolve the aqueous solution, then soaking the HZSM-5 subjected to the hydrothermal treatment according to the mass ratio of 1:0.4 to obtain the Nb loading of 0.2 wt%, aging at room temperature for 6h, drying at 120 ℃ for 12h, and roasting at 540 ℃ for 4 h.

5.2 impregnation of Mn, Mg and La

Mixing MnCl₂、MgCl₂And La (NO)₃)₃Adding the mixture into 4mol/L citric acid solution, wherein the mass ratio of citric acid to HZSM-5 is 0.3:1,mn, Mg and La are impregnated on Nb-loaded HZSM-5 to obtain the load of Mn of 1.8 wt%, the load of Mg of 1.5 wt% and the load of La of 0.5 wt%, and then the modified HZSM-5 is obtained by aging for 6h at room temperature, drying for 12h at the temperature of 120 ℃ and roasting for 4h at the temperature of 540 ℃.

6. Preparation of the first catalyst

Mixing modified HZSM-5, a matrix (comprising kaolin, pseudo-boehmite and ZrO in a mass ratio of 7:3: 1), silica sol, sesbania powder, methyl cellulose and nitric acid according to the mass fractions of 40%, 30%, 15%, 4%, 10% and 1%, adding water to prepare slurry with the solid content of 35 wt%, spray-drying and forming to obtain catalyst microspheres with the particle size of 20-200nm, roasting at 600 ℃ for 4 hours, and performing hydrothermal aging treatment at 650 ℃ in a steam atmosphere for 8 hours to obtain a first catalyst.

In the relevant tests/comparative tests of the following application examples, the third catalyst composition used and the method for its preparation were, unless otherwise specified, as follows:

1. pretreatment of

(1) Alkali treatment of HZSM-5 molecular sieve and USY molecular sieve

Mixing HZSM-5 molecular sieve (with the particle size of 0.5-2 mu m and the silica-alumina ratio of 25) and 0.5mol/L NaOH solution according to the mass ratio of 1:6, then exchanging for 2h at the temperature of 80 ℃, then washing the mixture to be neutral, then drying for 12h at the temperature of 110 ℃ and roasting for 2h at the temperature of 550 ℃.

Mixing the roasted ZSM-5 molecular sieve with 0.1M ammonium nitrate solution according to the mass ratio of 1:6, then carrying out ammonium exchange at the temperature of 80 ℃ for 2h, and then washing the mixture to be neutral; and performing ammonium exchange again in the same operation, and drying at 120 ℃ for 12h (without roasting) after the ammonium exchange twice to obtain the alkali-treated HZSM-5 molecular sieve.

And (3) carrying out alkali treatment on the USY molecular sieve according to the method to obtain the alkali-treated USY molecular sieve (the granularity is micron and the silica-alumina ratio is 5).

(2) Acid-treated SAPO-34 molecular sieves

SAPO-34 molecular sieve (with micron-sized particle size) and 0.05mol/L HNO₃The solution is prepared by mixing the following components in a mass ratio of 1:6 mixing, then heating at 80 deg.CAnd maintaining the temperature for about 2 hours, washing the mixture to be neutral, drying the mixture for 2 hours at 110 ℃, and roasting the mixture for 4 hours at 550 ℃ in sequence to obtain the SAPO-34 molecular sieve subjected to acid treatment.

2. Preparation of composite molecular sieves

Mixing the HZSM-5 molecular sieve subjected to alkali treatment, the USY molecular sieve subjected to alkali treatment and the SAPO-34 molecular sieve subjected to acid treatment in a ratio of 5:2:1 to obtain the HZSM-5/USY/SAPO-34 composite molecular sieve.

3. Composite molecular sieve for silanization treatment

And (3) filling the composite molecular sieve obtained in the step (2) into a reaction tube for olefin cracking, introducing nitrogen at 350 ℃ at a volume flow of 1L/min, purging for 1 hour, and performing high-temperature dehydration and drying on the composite molecular sieve.

And (3) cooling the dehydrated composite molecular sieve to 200 ℃, and pumping methyldiethoxysilane into a composite molecular sieve bed layer under the nitrogen flow of 300 mL/min: cyclohexane volume ratio 1: 50 of silanization reagent, wherein the pump flow rate is 0.1mL/min, and the adding amount of silanization reagent is 0.5mL of methyldiethoxysilane/g of composite molecular sieve.

After the feeding is finished, the silanization reaction is kept for 2 hours, then the temperature of the system is continuously increased to 400 ℃, nitrogen is continuously introduced, the flow rate of the nitrogen is 1L/min, and the high-temperature purging is carried out for 1 hour.

Filtering the system subjected to the silanization treatment to recover a cyclohexane solvent, placing the composite molecular sieve in a muffle furnace, roasting at 540 ℃ for 4 hours, and setting a programmed temperature rise of 4 ℃/min; adding 0.05mol/L HNO into the roasted composite molecular sieve₃The solution was acid-washed and maintained at 80 ℃ for 2 hours (in order to wash away silicon oxide and prevent pore blocking), to obtain a silanized composite molecular sieve.

4. Modified composite molecular sieve

(4.1) nonmetallic element modified composite molecular sieve

And (3) carrying out equal-volume impregnation on the silanized composite molecular sieve obtained in the step (3) by using a diammonium hydrogen phosphate solution at room temperature for about 1 hour, wherein the load of P is 1%, aging at room temperature for 12 hours after the impregnation is finished, then placing the composite molecular sieve in a drying oven for drying at 120 ℃ for 12 hours, then placing the composite molecular sieve in a muffle furnace for roasting at 540 ℃ for 4 hours, and cooling to obtain the non-metal element modified composite molecular sieve.

(4.2) Metal element modified composite molecular sieve

And (4) adding the nonmetal element modified composite molecular sieve obtained in the step (4.1) into a lanthanum nitrate solution, and soaking for about 1 hour at room temperature in an equal volume mode, wherein the loading amount of La is 1%, so as to obtain a soaking mixture. After the impregnation is finished, the aging is continued for 12 hours at room temperature, then the mixture is placed in an oven to be dried for 12 hours at 120 ℃, and then the mixture is placed in a muffle furnace to be roasted for 4 hours at 540 ℃, and the mixture is cooled to obtain the metal element modified composite molecular sieve (namely the modified composite molecular sieve).

5. Preparation of the third catalyst

And (3) mixing and pulping the modified composite molecular sieve obtained in the step (4) with kaolin, pseudo-boehmite, titanium dioxide, alumina sol and sesbania powder according to the dry basis mass ratio of 40:30:10:5:14:1, and stirring for 4 hours by adopting an electric mechanical stirrer to obtain a uniform mixture containing the modified composite molecular sieve, the matrix and the binder.

The uniform mixture is aged for 12 hours at room temperature, and then dried for 12 hours at 120 ℃ and roasted for 4 hours at 540 ℃. And then carrying out hydrothermal aging on the calcined catalyst for 6h at the temperature of 600 ℃ in the atmosphere of 100% of water vapor to obtain a third catalyst.

Application examples

Run 1 was carried out using the catalytic cracking method of example 1; run 2, comparative runs 1-3 were performed using the catalytic cracking method of example 2; run 3, comparative runs 4-5 were performed using the catalytic cracking method of example 3. In tests 1 to 3 and comparative tests 1 to 5, the compositions of the first raw material a1, the second raw material a2 and the third raw material a3 are shown in table 1; the conditions/parameters of the catalytic cracking process for each test are shown in Table 2, and the test results (dry gas (CH)₄) Ethylene (C)₂H₄) Propylene (C)₂H₆) Coke yield) is shown in table 3.

Wherein:

in comparative experiment 1, a1, a2, a3 were measured at a ratio of 1:1, so that the mixed raw materials are evenly divided into three parts, one part is fed from a first descending pipe, the other part is fed from a second descending pipe, the other part is fed from a third descending pipe, and the rest conditions are the same as those of the experiment 2;

in comparative experiment 2, the temperature of the first cracking reaction was 730 ℃, the temperature of the second cracking reaction was 700 ℃, the temperature of the third cracking reaction was 680 ℃, and the rest conditions were the same as those in experiment 2;

in comparative experiment 3, the temperature of the first cracking reaction was 480 ℃, the temperature of the second cracking reaction was 450 ℃, the temperature of the third cracking reaction was 430 ℃, and the other conditions were the same as those in experiment 2;

in comparative experiment 4, the temperature of the first cracking reaction was 730 ℃, the temperature of the second cracking reaction was 700 ℃, the temperature of the third cracking reaction was 680 ℃, and the rest conditions were the same as those in experiment 3;

in comparative experiment 5, the temperature of the first cleavage reaction was 480 ℃, the temperature of the second cleavage reaction was 450 ℃, the temperature of the third cleavage reaction was 430 ℃, and the rest of the conditions were the same as those in experiment 3.

TABLE 1 composition of the raw materials

TABLE 2 EXPERIMENTAL 1-3 CATALYTIC CRACKING CONDITIONS

TABLE 3 test results of tests 1-3 and comparative tests 1-5

Claims

1. A multi-zone coupling control multistage catalytic cracking method based on raw material types is characterized in that light hydrocarbon raw materials are adopted as cracking raw materials, the light hydrocarbon raw materials comprise a first raw material rich in C4 hydrocarbon, a second raw material rich in C5-C6 hydrocarbon and a third raw material rich in C7-C8 hydrocarbon, a reaction device comprising a first descending pipe, a second descending pipe and a third descending pipe is adopted, and a regenerator is arranged in the reaction device, wherein the regenerator is provided with a first regeneration zone and a second regeneration zone which are independent of each other, and the method comprises the following steps:

enabling the first raw material to enter a first descending pipe to contact with a first catalyst to generate a first cracking reaction, and enabling the second raw material to enter a second descending pipe to contact with a second catalyst to generate a second cracking reaction; converging the product of the first cracking reaction and the product of the second cracking reaction, and then carrying out gas-solid separation to respectively obtain a first oil-gas product and a first catalyst to be generated; allowing the first catalyst to be regenerated to enter a first regeneration area for regeneration after steam stripping to obtain a first regenerated catalyst; enabling part of the first regenerated catalyst to enter a first descending pipe to form a first cycle, and enabling part of the first regenerated catalyst to enter a second descending pipe to form a second cycle;

2. The catalytic cracking process of claim 1, wherein the reaction conditions of the first downflow reactor are: the reaction temperature is 500-700 ℃, the reaction pressure is 0.1-0.35MPa, the agent-oil ratio is 5-40, and the retention time is 0.2-4 s; the reaction conditions of the second descending tube are as follows: the reaction temperature is 480-650 ℃, the reaction pressure is 0.1-0.4MPa, the agent-oil ratio is 3-30, and the retention time is 0.3-6 s; the reaction conditions of the third descending tube are as follows: the reaction temperature is 480-630 ℃, the reaction pressure is 0.1-0.4MPa, the agent-oil ratio is 3-25, and the retention time is 0.3-6 s.

3. The catalytic cracking method according to claim 1 or 2, wherein the reaction apparatus further comprises a fluidized-bed reactor in which a first reaction zone and a second reaction zone are provided independently of each other, the method further comprising:

enabling the product of the first cracking reaction and the product of the second cracking reaction to enter the first reaction zone to carry out a fourth cracking reaction, and carrying out gas-solid separation on the product of the fourth cracking reaction to respectively obtain the first oil-gas product and the first catalyst to be generated;

and enabling the product of the third cracking reaction to enter the second reaction zone to carry out a fifth cracking reaction, and carrying out gas-solid separation on the product of the fifth cracking reaction to respectively obtain the second oil gas product and the second spent catalyst.

4. The catalytic cracking process of claim 3, wherein the reaction conditions of the fluidized bed reactor are: the mass space velocity is 5-25h^-1The bed linear velocity is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃.

5. A catalytic cracking process according to claim 3 or 4, characterized in that part of the first regenerated catalyst is passed to the first reaction zone to form a fourth cycle; and/or, passing a portion of the second regenerated catalyst to the second reaction zone to form a fifth cycle.

6. A catalytic cracking process according to claim 1, characterized in that the regeneration conditions in the regenerator are: the temperature is 600-850 ℃, and the linear velocity of the regeneration gas is 0.5-30 m/s. Preferably, the regeneration gas is an oxygen-containing gas having an oxygen content of from 10 to 35 wt.%.

7. The catalytic cracking process of claim 1 or 6, wherein at least a part of the first catalyst to be regenerated is brought into contact with the fuel and subjected to a pre-combustion treatment before entering the first regeneration zone; and/or, enabling at least part of the second spent catalyst to contact with fuel, pre-burning the second spent catalyst, and then entering a second regeneration zone; wherein, the pre-combustion treatment is carried out by an outer heat compensator arranged outside the regenerator, and the pre-combustion conditions in the outer heat compensator are as follows: the temperature is 400-800 ℃, the absolute pressure is 0.05-0.4MPa, and the oxygen content is 0.005-7 wt%.

8. The catalytic cracking process of claim 1 or 2, wherein the first catalyst and the second catalyst are the same, and the raw material composition comprises 20-50 wt% of modified molecular sieve, 1-50 wt% of matrix, 3-35 wt% of binder and 3-15 wt% of composite auxiliary agent; wherein,

the modified molecular sieve is obtained by carrying out alkali treatment on the molecular sieve and then carrying out non-metal element modification and metal element modification treatment on the molecular sieve;

the non-metallic elements are selected from at least two non-metallic elements in IIIA group, VA group, VIA group and VIIA group of the periodic table;

the metal elements are at least three elements selected from IIA group, IVB group, VB group, VIB group, VIIB group, VIII group and lanthanide series of the periodic table, and at least comprise one transition metal element except lanthanide series;

the composite auxiliary agent comprises inorganic acid and cellulose.

9. The catalytic cracking process of claim 1 or 8, wherein the feed composition of the third catalyst comprises 20-50 wt% of the modified composite molecular sieve, 1-50 wt% of the matrix, and 3-35 wt% of the binder; the modified composite molecular sieve is obtained by silanizing a composite molecular sieve formed by at least two molecular sieves, and then modifying by using non-metallic elements and metallic elements; the at least two molecular sieves are selected from at least two of HZSM-5, USY molecular sieve, SAPO34 and beta molecular sieve.

10. A multi-zone coupled control multi-stage catalytic cracking unit, comprising: the device comprises a first descending pipe, a second descending pipe, a third descending pipe, a steam stripping device, a settler and a regenerator, wherein the steam stripping device is internally provided with a first subarea and a second subarea which are mutually independent; the lower part of the stripping device is provided with a stripping gas inlet communicated with the first partition and the second partition, the material outlet of the first descending pipe and the material outlet of the second descending pipe are communicated with the material inlet of the first partition, the spent catalyst outlet of the first partition is communicated with the spent catalyst inlet of the first regeneration partition, the regenerated catalyst outlet of the first regeneration partition is communicated with the regenerated catalyst inlet of the first descending pipe and the regenerated catalyst inlet of the second descending pipe, the material outlet of the third descending pipe is communicated with the material inlet of the second partition, the spent catalyst outlet of the second partition is communicated with the spent catalyst inlet of the second regeneration partition, and the regenerated catalyst outlet of the second regeneration partition is communicated with the regenerated catalyst inlet of the third descending pipe.