CN112322335A

CN112322335A - Method for controlling multistage catalytic cracking by double-zone parallel coupling bed layers according to properties of raw materials

Info

Publication number: CN112322335A
Application number: CN202011130967.3A
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 method for controlling multistage catalytic cracking by using a double-zone parallel coupling bed layer according to the properties of raw materials, wherein the raw materials comprise a first raw material rich in alkane and a second raw material rich in olefin, a reaction device comprising a first descending tube and a second descending tube is adopted, and the method comprises the following steps: enabling the first raw material to enter a first down pipe to perform a first catalytic cracking reaction to obtain a first catalytic cracking product and a first catalyst to be generated; enabling the second raw material to enter a second descending pipe to perform a second catalytic cracking reaction to obtain a second catalytic cracking product and a second spent catalyst; carrying out gas-solid separation on the first catalytic cracking product and the first spent catalyst, and the second catalytic cracking product and the second spent catalyst to obtain an oil gas product and a spent catalyst; the spent catalyst is stripped and regenerated and then returned to participate in each catalytic cracking reaction. The invention adjusts the cracking process according to the cracking characteristics of various hydrocarbon raw materials, so that different light hydrocarbon raw materials are cracked by using one system, and the production of high-yield light olefins is realized.

Description

Method for controlling multistage catalytic cracking by double-zone parallel coupling bed layers according to properties of raw materials

Technical Field

The invention relates to a catalytic cracking method of light hydrocarbons, in particular to a method for controlling multistage catalytic cracking by using double-zone parallel coupling bed layers according to the properties of raw materials, belonging to the technical field of petroleum processing.

Background

The gasoline or light hydrocarbon oil product is reasonably converted into the olefin product, 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 as a cracking product is significantly lower than that of ethylene.

In the global low-carbon olefin market in the future, the growth rate of the demand of propylene is greater than that of ethylene,

therefore, the process exploration about how to produce propylene at high yield is receiving more and more attention, and the catalytic cracking process is also the 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 document CN101045667A discloses a combined catalytic conversion method for producing a large amount of light olefins. In the method, a heavy oil raw material is contacted with a regenerated catalyst and a selected carbon-deposited catalyst in a descending tube reactor, a cracked product is separated from a spent catalyst, the cracked product is separated to obtain low-carbon olefin, one part of the rest of the products (the rest of the products are used as a product leading-out device) is introduced into a riser reactor to be contacted with the regenerated catalyst, oil gas and the catalyst are separated, and the oil gas is separated to obtain the low-carbon olefin. The spent catalyst enters one or more of a pre-lifting section of the downer reactor, a stripper connected with the downer reactor and a regenerator after being stripped, and the spent catalyst and the selected carbon-deposited catalyst return to the downer reactor and the riser reactor after being burnt and regenerated. The key point of the method is that propylene generated in the descending tube reactor is separated from the catalyst in time to achieve the purpose of inhibiting the secondary reaction of the propylene, and simultaneously, the components which are not fully cracked are introduced into the riser reactor again to be contacted with the regenerated catalyst, so that the deep cracking reaction is performed under the harsher condition, and the purpose of further improving the yield of the low-carbon olefin is achieved. However, the catalyst after the riser reaction is introduced into the catalyst pre-lifting section of the downer reactor and contacts with the heavy oil raw material, although the contact between the heavy oil raw material and the catalyst can be increased, the carbon-deposited catalyst has low activity and insufficient capacity of catalytically cracking heavy oil, so that the catalyst is simply introduced into the downer to improve the yield of propylene by improving the conversion rate of heavy oil cracking, and the effect is very limited.

Chinese patent document CN101074392A discloses a method for producing propylene and high quality gasoline and diesel oil by two-stage catalytic cracking. The method aims at heavy hydrocarbons or various animal and plant raw materials rich in hydrocarbons, and achieves the purposes of improving the yield of propylene, simultaneously considering the yield and quality of light oil and inhibiting the generation rate of coke and coke by utilizing a two-section riser catalysis process. According to the method, the feeding of the first section of riser is fresh heavy raw oil, the feeding of the second section of riser is gasoline and circulating oil with high olefin content obtained by the reaction of the first section of riser, the yield of low-carbon olefin (especially propylene) is improved by deeper cracking, and diesel oil with low olefin content and higher cetane number is obtained at the same time. The method still aims at the cracking of the heavy oil hydrocarbon raw material, and also aims at the production of diesel oil, so that the conversion rate of the raw material to propylene is reduced, and the yield of dry gas and coke is higher.

Chinese patent document CN102690682A discloses a catalytic cracking method and apparatus for producing propylene. The method comprises the steps of enabling heavy raw materials (including heavy hydrocarbons or various animal and vegetable oil raw materials rich in hydrocarbon) to contact and react with a first catalytic cracking catalyst taking Y-type zeolite as a main active component in a first riser reactor to generate oil gas; the light hydrocarbon (including gasoline and/or C4 hydrocarbon produced in the first riser or gasoline fraction produced in other equipment, such as one or more of catalytically cracked naphtha, catalytically cracked stabilized gasoline, coker gasoline and visbreaker gasoline) is made to contact with the second catalytic cracking catalyst with shape selective zeolite with pore size less than 0.7nm as main active component in the second riser reactor, and the reacted oil gas and catalyst are introduced into the serial fluidized bed reactor connected to the second riser reactor for reaction. The oil gas products in the first riser and the fluidized bed reactor are collected and fractionated by a common pipeline leading-out device. Although the method can improve the yield of propylene, the improvement of the selectivity of the propylene is limited because the yield of the butylene is also improved. In addition, the yield of coke and dry gas is high when heavy hydrocarbons or various animal and vegetable oils rich in hydrocarbons are used as raw materials. More importantly, the method needs to adopt different catalysts to participate in the cracking reaction in the first riser reactor and the second riser reactor respectively, so that different regeneration paths need to be arranged when the catalyst to be regenerated after the reaction is regenerated, the device is complicated, and the industrial application is not facilitated.

Most of the current catalytic cracking researches focus on the catalytic cracking of heavy oil raw materials or light hydrocarbon (gasoline) raw materials, but the complex cracking products and low propylene selectivity can also result in high yield of dry gas and coke in the process of pursuing relatively high propylene selectivity, and the problems are still common problems which are difficult to span. On the other hand, the design of these catalytic cracking processes and systems is around the property of heavy oil feedstock, and cannot be applied to cracking treatment of light fraction feedstock (such as light hydrocarbon oil product) simply, and as heavy oil processing and oil refining technology and capacity increase, there may be many cases in which by-product fraction is output downstream, for example, there may be some hydrocarbon as main material or many hydrocarbons with specific carbon number as incoming material, how to design more feasible process according to the composition and properties of these incoming material, and at the same time, can increase the yield of target olefin, so to speak, it is a direction to achieve the increase of olefin capacity.

Disclosure of Invention

The invention provides a method for controlling multistage catalytic cracking by double-zone parallel coupling bed layers according to the properties of raw materials, which adjusts the cracking process according to the cracking characteristics of various hydrocarbon raw materials, so that different types of light hydrocarbon raw materials are cracked by using one system, and the production of high-yield light olefins is realized.

The invention provides a method for controlling multistage catalytic cracking by using a double-zone parallel coupling bed layer according to the properties of raw materials, wherein the raw materials comprise a first raw material rich in alkane and a second raw material rich in olefin, a reaction device comprising a first descending tube and a second descending tube is adopted, and the method comprises the following steps:

enabling a first raw material to enter the first descending pipe to contact with a catalyst to generate a first catalytic cracking reaction, and obtaining a first catalytic cracking product and a first catalyst to be generated; enabling a second raw material to enter the second descending pipe to contact with the catalyst to generate a second catalytic cracking reaction, and obtaining a second catalytic cracking product and a second spent catalyst; carrying out gas-solid separation on the first catalytic cracking product and the first spent catalyst from the first descending pipe, and the second catalytic cracking product and the second spent catalyst from the second descending pipe to respectively obtain an oil gas product and a spent catalyst; the spent catalyst is subjected to steam stripping treatment, enters a regenerator for regeneration treatment, and then returns to participate in each catalytic cracking reaction;

the conditions of the first catalytic cracking reaction are as follows: the reaction temperature is 500 ℃ and 700 ℃, the catalyst-oil ratio is 5-40, the reaction pressure is 0.1-0.35MPa, and the retention time is 0.2-4 s;

the conditions of the second catalytic cracking reaction are as follows: the reaction temperature is 480 ℃ and 650 ℃, the catalyst-oil ratio is 3-30, the reaction pressure is 0.1-0.4MPa, and the retention time is 0.3-6 s.

The method as described above, wherein the reaction apparatus further comprises a fluidized bed reactor connected in series with the first and second downers, respectively, the method further comprising:

the first catalytic cracking product and the first catalyst to be generated from the first descending pipe, and the second catalytic cracking product and the second catalyst to be generated from the second descending pipe enter the fluidized bed reactor to generate a third catalytic cracking reaction, and the oil gas product and the catalyst to be generated are respectively obtained after the gas-solid separation of the products of the third catalytic cracking reaction;

the conditions of the third catalytic cracking reaction are as follows: space velocity of 5-25h^-1The linear speed is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃.

The method as described above, wherein the alkane content in the first feedstock is greater than 40%;

the second feedstock has an olefin content greater than 30%.

The method as described above, wherein the reaction temperature of the first catalytic cracking reaction is higher than the reaction temperature of the second catalytic cracking reaction; the catalyst-oil ratio of the first catalytic cracking reaction is larger than that of the second catalytic cracking reaction; the residence time of the first catalytic cracking reaction is greater than the residence time of the second catalytic cracking reaction.

The method as described above, wherein the temperature of the first catalytic cracking reaction is at least 50 ℃ higher than the reaction temperature of the second catalytic cracking reaction;

the catalyst-oil ratio of the first catalytic cracking reaction is at least 3 greater than that of the second catalytic cracking reaction;

the residence time of the first catalytic cracking reaction is at least 0.2s greater than the residence time of the second catalytic cracking reaction.

The method as described above, wherein the conditions of the first catalytic cracking reaction are: the reaction temperature is 630-700 ℃, the catalyst-oil ratio is 20-40, and the retention time is 2-4 s;

the conditions of the second catalytic cracking reaction are as follows: the reaction temperature is 530 ℃ to 550 ℃, the catalyst-oil ratio is 5-20, and the retention time is 1-2 s.

The method as described above, wherein, before the first raw material enters the first descending tube, the method further comprises preheating the first raw material to 100-250 ℃;

before the second raw material enters the second descending pipe, preheating the second raw material to 100-300 ℃.

The method as described above, wherein the regeneration process comprises:

inputting the catalyst to be regenerated into a heat compensator outside the regenerator through the regenerator, carrying out fluidization and pre-combustion treatment, then entering the regenerator, and carrying out regeneration treatment under the action of regenerated gas to obtain the regenerated catalyst.

The method as described above, wherein the temperature of the regeneration treatment is 600 ℃ to 850 ℃, the oxygen concentration in the regeneration gas is 10 wt% to 35 wt% and the linear velocity of the regeneration gas is 0.5m/s to 30 m/s.

The method as described above, wherein the temperature in the heat compensator is 400 ℃ to 800 ℃, and the oxygen content is 0.005 wt% to 7 wt%.

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

1. reaction conditions and processes with pertinence are designed based on the cracking performance of light hydrocarbon types contained in the raw materials, catalytic cracking reactions of different types of hydrocarbons can be pertinently enhanced, the depth of the cracking reactions and the conversion rate of the raw materials are improved, and the selectivity and the yield of propylene are particularly improved;

2. aiming at the cracking principle and the characteristics of different types of light hydrocarbons, by designing a descending tube reactor and a catalyst regeneration system which are matched and cooperated with each other, the raw material realizes the combination of zone cracking and deep cracking, is more suitable for the catalytic cracking of light hydrocarbon raw materials or light oil raw materials, not only meets the requirements of reaction time and atmosphere of different hydrocarbon cracking, but also reduces the retention time of intermediate products, and achieves the effect of reducing the yield of dry gas and coke;

3. the different reaction conditions of the alkane raw material and the olefin raw material are beneficial to realizing the deep cracking of each raw material, and can further realize the matching of material flow and energy flow in the whole cracking system, ensure the stability of the whole light hydrocarbon catalytic cracking process, improve the overall energy efficiency and realize the industrial feasibility;

4. the catalytic cracking light hydrocarbon raw material can come from a byproduct of cracking processing of the heavy raw material, so the catalytic cracking method can be used as a downstream processing technology of the cracking processing product of the existing heavy raw material, the high yield of propylene is realized, and the utilization rate of the heavy raw material can be further improved.

Drawings

FIG. 1 is a schematic diagram of a system for controlling multi-stage catalytic cracking with dual-zone parallel coupled beds for feedstock properties according to one embodiment of the present invention;

FIG. 2 is a schematic diagram of a system for controlling multi-stage catalytic cracking with dual-zone parallel coupled beds for feedstock properties according to yet another embodiment of the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the embodiments of the present invention more comprehensible, embodiments of the present invention are described in detail below with reference to the accompanying drawings. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

the conditions of the second catalytic cracking reaction are as follows: the reaction temperature is 480 ℃ and 650 ℃, the catalyst-oil ratio is 3-30, the reaction pressure is 0.1-0.4MPa, and the retention time is 0.3-6 s. The agent-oil ratio of the invention refers to the agent-oil volume ratio.

The method of the invention is a method for producing propylene with high yield by catalytic cracking light hydrocarbon (the number of carbon atoms is 4-8 more) as a raw material. Specifically, the first raw material refers to light hydrocarbons with alkanes as main components, and can be pure alkanes or raw materials rich in alkanes; the second feedstock is a light hydrocarbon comprising olefins as the main constituent, and may be pure olefins or an olefin-rich feedstock. The alkane or alkene feedstock referred to herein may be a pure alkane or alkene feed, but is more commonly understood in the art to include feedstocks or distillates based on alkane or alkene components, and thus, for example, "alkane feedstock" and "alkane-rich feedstock" are intended to have the same meaning in the present invention.

The reaction device of the invention comprises a first descending tube and a second descending tube. In the invention, the descending tube is adopted for catalytic cracking reaction, so that the retention time of the raw materials and the catalyst can be reduced under the action of gravity, and the generation of intermediate products is favorably inhibited; and the density distribution of the catalyst is more uniform, and the yield of the propylene is improved.

In the method, a first raw material rich in alkane enters a first descending pipe through an inlet of the first descending pipe, and undergoes a first catalytic cracking reaction with a catalyst in the descending process inside the first descending pipe to obtain a first catalytic cracking product (a catalytic cracking product of the first raw material) and a first catalyst to be generated; meanwhile, a second raw material rich in olefin enters the second descending tube through the inlet of the second descending tube, and undergoes a second catalytic cracking reaction with the catalyst in the process of descending in the second descending tube to obtain a second catalytic cracking product (catalytic cracking product of the second raw material) and a second spent catalyst.

The first catalytic cracking product and the first catalyst to be generated output from the first descending pipe, and the second catalytic cracking product and the second catalyst to be generated output from the second descending pipe respectively enter a gas-solid separation device for gas-solid separation, the gas phase obtained by separation is collected as an oil-gas product, and then products such as propylene, ethylene and the like are obtained by treatment such as fractionation and refining; the solid phase obtained by separation can be used as spent catalyst to be stripped and regenerated catalyst obtained by regeneration treatment can be recycled. The recycling comprises the steps that the regenerated catalyst after the catalyst to be regenerated is conveyed back to the first descending pipe and the second descending pipe respectively to participate in the first catalytic cracking reaction and the second catalytic cracking reaction, the preparation cost of propylene can be reduced by the regeneration and the utilization of the catalyst to be regenerated, and the adjustment of reaction parameters, such as reaction temperature and oil-to-oil ratio, in the descending pipe can be realized by controlling the amount of the regenerated catalyst returned to the descending pipe. It is emphasized that before the spent catalyst obtained by gas-solid separation is regenerated, the descending spent catalyst is stripped by ascending stripping gas (such as steam) to adsorb the oil gas product on the surface, and the steam adsorbed with the oil gas product can ascend under the action of the stripping gas to enter a gas-solid separation device to be collected as the oil gas product for fractional distillation and refining.

The method can utilize a designed system to realize catalytic cracking of alkane and olefin raw materials, and light hydrocarbons are divided into different hydrocarbon raw materials according to hydrocarbon types to carry out catalytic cracking reaction in different zones by controlling the technological process and conditions, so that the yield and selectivity of propylene are further improved, and the generation of coke and dry gas in the reaction is reduced.

In the specific implementation process, the first raw material rich in alkane and the water vapor are jointly fed into the first downer according to a certain ratio (for example, the mass ratio of the first raw material to the water vapor is 1: 0.1-3), and the water vapor can play a role in partial pressure to maintain a more proper cracking atmosphere of the downer. After the first raw material enters the first descending tube, the first raw material is contacted with the catalyst to generate a first catalytic cracking reaction by controlling the reaction temperature to be 500-.

In the specific implementation process, the second raw material rich in olefin and steam (for example, the mass ratio of the second raw material to the steam is 1: 0.1-3) enter the second descending tube together, and a second catalytic cracking reaction occurs under the conditions of a reaction temperature of 480-.

And then carrying out gas-solid separation on the first catalytic cracking product, the first catalyst to be generated, the second catalytic cracking product and the second catalyst to be generated to respectively obtain an oil gas product and a catalyst to be generated. The first catalytic cracking product, the first to-be-generated catalyst, the second catalytic cracking product and the second to-be-generated catalyst can be subjected to gas-solid separation respectively, or the first catalytic cracking product, the first to-be-generated catalyst, the second to-be-generated catalyst and the second to-be-generated catalyst can be mixed together to perform gas-solid separation.

Because the adsorption capacity of the alkane and the olefin on the catalyst is different, the alkane raw material is not easy to crack compared with the olefin raw material, so that the alkane raw material and the olefin raw material are cracked in a partition mode, the phenomenon that the catalytic cracking of the alkane is influenced due to adsorption competition of alkane and olefin on the catalyst is avoided, the yield of the low-carbon olefin, particularly the propylene, is further increased, and meanwhile, the output of dry gas and coke is further inhibited.

The first raw material and the second raw material can be preheated before entering the first descending pipe and the second descending pipe respectively, then the preheated first raw material enters the first descending pipe to participate in the first catalytic cracking reaction, and the preheated second raw material enters the second descending pipe to participate in the second catalytic cracking reaction. Specifically, the first raw material can be preheated to 100-.

The invention takes light hydrocarbon as raw material, can come from fractions or oil products of different processes, introduces alkane-rich raw material (also called alkane feed) and alkene-rich raw material (also called alkene feed) as first raw material and second raw material into two down tubes respectively, and controls process conditions respectively to realize the zone reaction of the first raw material and the second raw material under more proper conditions. If necessary, the product systems (i.e. the first catalytic cracking product, the first catalyst to be generated, the second catalytic cracking product and the second catalyst to be generated) from the first descending pipe and the second descending pipe can be continuously fed into the fluidized bed reactors which are subsequently and respectively connected with the first descending pipe and the second descending pipe in series for further deep cracking, and on the basis of alkane and olefin cracking, the operating conditions of the fluidized bed reactors can be more flexibly regulated, controlled and matched, so that the reaction depth and the conversion rate of the raw materials can be improved, and the propylene yield is finally improved. Therefore, the method of the invention not only can set more suitable cracking conditions aiming at the difference of raw materials to improve the selectivity of propylene, but also can improve the yield of propylene and the conversion rate of the raw materials. The zone reaction of the raw materials can also reduce the retention time of the raw materials and reduce the generation of dry gas and coke.

In addition, the light hydrocarbon raw material can be derived from various light hydrocarbon byproducts obtained after cracking heavy oil, and the light hydrocarbon raw material is introduced into the cracking system according to the composition condition of the light hydrocarbon byproducts, so that the conversion rate of the heavy oil can be effectively improved, and the conversion of the high value-added chemical comprehensive production is realized.

Further, the reaction apparatus of the present invention may further comprise a fluidized bed reactor connected in series with the first down tube and the second down tube, respectively, that is, the outlet of the first down tube and the outlet of the second down tube are respectively communicated with the inlet of the fluidized bed reactor.

In order to avoid incomplete cracking degree of the first catalytic cracking reaction and the second catalytic cracking reaction, the method can also enable a product system of the first catalytic cracking reaction and a product system of the second catalytic cracking reaction to be output from the outlets of the first descending pipe and the second descending pipe respectively and then enter the fluidized bed reactor for a third catalytic cracking reaction on the basis of the method. Specifically, the conditions of the third catalytic cracking reaction are: space velocity of 5-25h^-1The linear speed is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃.

In the third catalytic cracking reaction, the first catalytic cracking product and the second catalytic cracking product are further catalytically cracked in the bed of the fluidized bed reactor. Under the action of the fluidized gas, in the process that the product of the third catalytic cracking reaction goes upward through a settler (section), the spent catalyst particles are separated and fall back to a stripping section, and the cracked oil gas product is output from the top of the settler and is used as a cracking product, or the product is subjected to subsequent refining and separation procedures to respectively collect ethylene, propylene and other products; the spent catalyst falling back to the stripping section is stripped under the action of lifting gas to remove oil gas products adsorbed on the surface, then the spent catalyst is discharged out of the reaction device and sent into a regenerator to be regenerated, and the regenerated catalyst (regenerated catalyst) returns to each descending pipe for recycling. The recycling comprises that the regenerated catalyst after the catalyst to be regenerated is respectively conveyed back to the first descending pipe and the second descending pipe to participate in the first catalytic cracking reaction and the second catalytic cracking reaction, or respectively conveyed back to the first descending pipe, the second descending pipe and the fluidized bed reactor to participate in the first catalytic cracking reaction, the second catalytic cracking reaction and the third catalytic cracking reaction.

The method comprises the steps that by adopting a reaction device comprising a first descending pipe, a second descending pipe and a fluidized bed reactor, a first raw material rich in alkane and a catalyst undergo a first catalytic cracking reaction in the first descending pipe to generate a first catalytic cracking product and a first catalyst to be generated; and carrying out a second catalytic cracking reaction on the second raw material rich in the olefin and the catalyst in a second descending pipe to generate a second catalytic cracking product and a second spent catalyst. Then, the first catalytic cracking product and the first catalyst to be generated from the first descending pipe, and the second catalytic cracking product and the second catalyst to be generated from the second descending pipe enter the fluidized bed reactor to carry out a third catalytic cracking reaction so that the first catalytic cracking product and the second catalytic cracking product continue to be deeply cracked. And products of the third catalytic cracking reaction in the fluidized bed reactor are respectively collected after gas-solid separation in a settling section of the fluidized bed reactor, the collected gas phase is an oil gas product, and the collected spent catalyst can be recycled as a regenerated catalyst after regeneration treatment.

After the outlets of the first descending pipe and the second descending pipe are connected in series with the fluidized bed reactor, the deep cracking of the first raw material and the second raw material can be further ensured under the reaction condition of the fluidized bed reactor defined by the invention, so that the yield of the low-carbon olefin, especially propylene, is further increased, and the output of dry gas and coke is further inhibited.

In the process of the third catalytic cracking reaction, the product of the third catalytic cracking reaction has a certain residence time in a settling section and a transfer pipeline in the fluidized bed reactor, the temperature is high, secondary reactions can occur to a certain degree, mainly thermal cracking reactions, and the yield of dry gas and coke is increased. Specifically, the gas-solid phase in the product of the third catalytic cracking reaction is rapidly separated by using the gas-solid rapid separation device, so that the progress of side reaction is inhibited, and the dilute phase space volume of the settling section is properly reduced. The form of the gas-solid rapid separation component is various, and a semi-circular cap-shaped separation component, a T-shaped component or a primary cyclone separator is commonly used. In a specific embodiment, the gas-solid rapid separation component can be a primary cyclone separator, and the distance between the outlet of the riser of the primary cyclone separator and the inlet of the cyclone separator at the top of the settling section is shortened, so that the occurrence of secondary reaction can be obviously reduced, the yield of light oil is improved, and the generation rate of coke and dry gas is reduced. Meanwhile, a settling section is arranged in a dilute phase zone at the upper part of the fluidized bed reactor, so that the gas and solid phases in the product of the third catalytic cracking reaction can be quickly separated.

Further, a nozzle may be provided at the inlets of the first and second down pipes and the fluidized-bed reactor, through which the materials introduced into the down pipes and the fluidized-bed reactor are mixed and contacted, and the raw material is catalytically cracked while moving upward with a predetermined residence time. The form of the nozzle may be many and may be selected according to the actual needs, for example, the form of the nozzle is a hollow cone nozzle, a solid cone nozzle, a square nozzle, a rectangular nozzle, an oval nozzle, a fan nozzle, a cylindrical flow (straight flow) nozzle, a two-fluid nozzle, a multi-fluid nozzle, etc.

In addition, the acute included angle between the inlets of the first descending pipe and the second descending pipe and the axis of each descending pipe is 30-60 degrees, and the acute included angle can ensure that the materials entering the reactor are mixed more fully, so that the cracking is more complete.

The first feedstock rich in alkanes and the second feedstock rich in olefins are not limited to a large amount, and may be, for example, naphtha, catalytically cracked gasoline, pressurized gas oil, a steam cracking by-product or light cracked gasoline, a by-product of a fluid catalytic cracking apparatus or cracking apparatus, a by-product of a methanol-to-olefins apparatus, and the like. The catalytic cracking process of the present invention is determined to be carried out as the first feedstock or the second feedstock depending on the alkane and alkene content therein. It is of course also possible to select an alkane and an alkene as the first alkane-rich feedstock and the second alkene-rich feedstock, respectively.

The alkane-rich first raw material has the alkane mass content of not less than 40%, and the alkene mass content of not less than 30% in the alkene-rich second raw material.

Further, in order to ensure the deep cracking of the alkane and the alkene and ensure the yield and the selectivity of the propylene, the reaction conditions of each reaction can be further defined on the basis of the first catalytic cracking reaction condition and the second catalytic cracking reaction condition. Specifically, the reaction temperature of the first catalytic cracking reaction is higher than that of the second catalytic cracking reaction, the catalyst-to-oil ratio of the first catalytic cracking reaction is greater than that of the second catalytic cracking reaction, and the residence time of the first catalytic cracking reaction is greater than that of the second catalytic cracking reaction.

Specifically, the temperature of the first catalytic cracking reaction is at least 50 ℃ higher than the reaction temperature of the second catalytic cracking reaction; the catalyst-oil ratio of the first catalytic cracking reaction is at least 3 (which means the difference between the catalyst-oil ratio of the first catalytic cracking reaction and the catalyst-oil ratio of the second catalytic cracking reaction) larger than that of the second catalytic cracking reaction; the residence time of the first catalytic cracking reaction is at least 0.2s greater than the residence time of the second catalytic cracking reaction.

As a preferred embodiment, the reaction conditions of the first catalytic cracking reaction are: the reaction temperature is 630-700 ℃, the catalyst-oil ratio is 20-40, and the retention time is 2-4 s; the conditions of the second catalytic cracking reaction are as follows: the reaction temperature is 530 ℃ and 550 ℃, the catalyst-oil ratio is 5-20, and the retention time is 1-2s, so that the matching of material flow and energy flow in the whole cracking system is further realized, the stability of the whole catalytic cracking process of the light hydrocarbons is ensured, the overall energy efficiency is improved, and the industrial feasibility is realized.

In practical applications, the determination of the specific operating conditions of the fluidized bed reactor may also be adjusted to achieve deep cracking of the feedstock in response to changes in the first catalytic cracking product and the second catalytic cracking product.

The invention can further improve the yield of the propylene by selecting a specific catalyst. The catalyst can ensure the catalytic performance, improve the wear resistance of the catalyst and prolong the service life of the catalyst.

Specifically, the raw material composition of the catalyst 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, and the catalyst is obtained by hydrothermal aging treatment at the temperature of 500-; the modified molecular sieve is obtained by alkali treatment of a molecular sieve raw material with the mass content of at least 80% of a ZSM-5 molecular sieve, non-metal element modification and metal element impregnation modification, and hydrothermal treatment is carried out between the two modification treatments; the non-metal elements are impregnated by at least two non-metal elements selected from 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 at least comprises inorganic acid and cellulose.

Wherein, the molecular sieve raw material is mainly ZSM-5 molecular sieve, and HZSM-5 molecular sieve obtained by conventionally hydrogenating and converting the ZSM-5 molecular sieve is also covered in the range of the molecular sieve raw material. The pore channel structure of the ZSM-5 molecular sieve has good shape selectivity, and is more suitable for impregnating various metals and non-metals. Therefore, the content of the ZSM-5 molecular sieve in the molecular sieve raw material selected by the catalyst is at least 80 percent in consideration of the quality and the cost of the catalyst.

The particle size and the silica-alumina ratio of the molecular sieve raw material are in proper ranges, so that the molecular sieve raw material is more favorable for serving as a carrier to provide proper acid centers and alkali centers, and is further favorable for loading metal and nonmetal elements. In one possible embodiment, it may be advantageous to select nanoscale molecular sieve particles, for example, ZSM-5 having a particle size of about 500-3000nm, such as 1500-2000nm, and a silica to alumina ratio of 90-110, 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 process of modifying the molecular sieve raw material, the molecular sieve raw material is firstly subjected to alkali treatment to realize desilication and pore expansion, so that coking of the catalyst orifice 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: firstly, mixing a molecular sieve raw material and 0.2-1.0mol/L alkaline solution according to the mass ratio of 1:4-8, exchanging for 1-5h at the temperature of 70-90 ℃, then washing the molecular sieve to be neutral, and then drying for 3-12h at the temperature of 60-150 ℃ and roasting for 2-6h at the temperature of 400-600 ℃. 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 2-6 h.

Subsequently, the alkali-treated molecular sieve raw material is impregnated with a plurality of non-metallic elements and metallic elements.

The non-metal elements are selected from at least two elements in IIIA group, VA group, VIA and VIIA group of the periodic table, for example, the non-metal elements can be selected from two elements of P, B, S, Cl and Br, for example, P or B is loaded on the molecular sieve, the hydrothermal stability of the molecular sieve can be improved, and deacidification is avoided; the loading of S on the molecular sieve is favorable for improving the acidity.

The selection of all three or more metal elements includes acidic metals and basic metals, advantageously at least three metal elements, and includes one group IIA metal and one lanthanide metal. Briefly, the metal elements are selected from three or more of the above groups of the periodic table, including alkaline earth metals, lanthanide metals and transition metals of the listed sub-groups, and may be specifically selected from three or more of Mn, V, Fe, Nb, Cr, Mo, W, Mg, Ca and La, for example, in accordance with the principles set forth above. As the conversion rate of the alkane and alkene blending material is mainly limited by the conversion rate of alkane, the adsorption capacity of alkane on the catalyst is improved by the synergistic effect of a plurality of metal elements selected according to the principle, and the simultaneous catalytic cracking of alkane and alkene is possible, so that the conversion rate of alkane and alkene and the yield of propylene are improved.

When the molecular sieve is modified, although the loading sites of the non-metal element and the metal element are different, and no adsorption competition relationship exists between the non-metal element and the metal element, the non-metal element and the metal element are generally selected to be separately impregnated due to the solubility and the like. For example, the non-metal elements may be impregnated first and then the metal elements may be impregnated, and simultaneous impregnation or stepwise impregnation may be generally selected among a plurality of metal elements and a plurality of non-metal elements depending on the solubility.

When the metal element is modified by impregnation, for some metal salts which are difficult to dissolve, the corresponding salts of the metal can be dissolved in the dispersing agent to increase the solubility. For example, a dispersing agent (such as citric acid and/or oxalic acid solution) with a total concentration of about 0.1-4mol/L is used to dissolve the corresponding salt of the metal element to prepare an impregnation solution, and then the molecular sieve is subjected to metal element impregnation modification. If the concentration of the dispersant is too low, the dispersing effect may not be obtained, and if the concentration is too high, the impregnation effect may be impaired. The mass ratio of the impregnation liquid to the molecular sieve can be set according to the expected loading amount, and can be 0.2-0.8:1, for example.

In the preparation of the catalyst, the catalytic effect of the catalyst can be influenced by too much or too little loading of the non-metallic elements and the metallic elements. For example, if the amount of the supported metal element/nonmetal element is too large, the dispersibility is poor, and the catalyst tends to aggregate at the catalyst pore and coke. If the amount of the supported metallic element/non-metallic element is too small, the desired catalytic effect cannot be achieved even if the catalytic reaction time is prolonged. Thus, the loading of each non-metallic element in the catalyst is about 0.05 to 5 wt%, and the loading of each metallic element is about 0.1 to 10 wt%, based on the mass of the 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 2-20 hr, such as 4-12 hr; drying at 50-160 deg.C, such as 70-120 deg.C, for 2-20 hr, such as 3-12 hr; the calcination temperature is 300-800 deg.C, such as 400-600 deg.C, and the calcination time is 1-10 hours, such as 2-6 hours.

As with the conventional preparation process of the catalyst, a proper amount of matrix material can provide a dispersion environment for the carrier and the active ingredients, increase the mechanical strength and the carbon capacity of the catalyst, and is also beneficial to preventing the catalyst from coking and inactivation and prolonging the service life of the catalyst. Meanwhile, the required catalyst is finally obtained by utilizing the bonding effect of the binder. In addition, the composite auxiliary agent adopts inorganic acid and cellulose to perform synergistic action, so that the wear resistance of the auxiliary agent can be improved.

If the content of the composite assistant is too low, the loss of the catalyst is increased, but if the content of the composite assistant is too high, the viscosity of the raw material is too high, and the raw material is not easy to form. Thus, the present invention defines the amount of compounding aid, and the sum of the mass fractions of all compounding aids is about 3 to 15 wt%, for example 3 to 12 wt%.

In order to further ensure that the acid properties of the catalyst are not easily changed and to facilitate the ensuring of the pore structure and mechanical properties of the catalyst, the types and contents of the inorganic acid and cellulose in the composite assistant may be properly adjusted and selected within the above-mentioned set ranges, and the mass fraction of the inorganic acid is preferably not more than 2 wt% based on the mass of the catalyst, and may include the commonly used inorganic acids: sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, etc., and the inorganic acid may be one selected from nitric acid and hydrochloric acid; the cellulose may be selected from one of methyl cellulose and ethyl cellulose, but is not limited thereto.

Further, the selection of the components of the binder and the matrix is not particularly limited. The binder includes sesbania powder, which has strong binding property and can better perform the function of the binder, and may further include silica sol and/or alumina sol, but is not limited thereto.

The matrix may be kaolin, pseudo-boehmite, or a group IVB metal oxide. The IVB group metal oxide can increase the pore structure of the matrix, thereby prolonging the reaction path of the alkane-alkene blending material in the catalyst and leading the catalyst to exert the effect better. For example, it may be an oxide of Ti and/or Zr.

After the selection and modification treatment of the raw material components are finished, the preparation of the catalyst can be finished 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, catalyst microspheres with the particle size of about 20-200nm can be obtained by drying (such as spray drying) and molding, then, the operations of drying and roasting can be carried out in multiple steps, for example, the catalyst can be obtained by drying at about 20-50 ℃ for 12-50h, drying at 100-200 ℃ for 12-50h and roasting at 500-800 ℃ for 1-12h in sequence, and further hydrothermal aging treatment, for example, hydrothermal aging treatment at 500-800 ℃.

Because the invention aims at light hydrocarbon raw materials, the coke attached to the surface of the spent catalyst after each stage of catalytic cracking reaction is less, and the heat generated by burning the coke may not be enough to provide the heat for regenerating the spent catalyst. In order to ensure the high-efficiency regeneration of the spent catalyst, the invention adopts the regenerator provided with the heat compensator to regenerate the spent catalyst, specifically, the heat compensator is arranged outside the regenerator (also called as an external heat compensator), the spent catalyst inlet of the regenerator is communicated with the spent catalyst outlet of the stripping section, used for receiving the spent catalyst after steam stripping, the spent catalyst outlet of the regenerator is communicated with the spent catalyst inlet of the heat compensator through a spent catalyst conveying pipeline, the pre-combustion catalyst outlet of the heat compensator is communicated with the pre-combustion catalyst inlet of the regenerator through a pre-combustion catalyst conveying pipeline, the regenerated catalyst outlet of the regenerator is respectively communicated with the inlets of the first downpipe and the second downpipe, or the regenerated catalyst outlet of the regenerator is respectively communicated with the first descending pipe, the second descending pipe and the fluidized bed reactor, so that the regenerated catalyst is returned to each stage of reactor for recycling. The device comprises a heat compensator, a fuel distributor, a combustion improver distributor and a fluidizing and pre-burning medium distributor, wherein the fuel distributor is used for releasing and spraying fuel to a spent catalyst in the heat compensator, the combustion improver distributor is used for releasing and spraying combustion improver to the spent catalyst in the heat compensator, and the fluidizing and pre-burning medium distributor is used for enabling the spent catalyst in the heat compensator to be in a fluidizing state and enabling the spent catalyst to be pre-burned.

Hereinafter, the regeneration treatment of the present invention will be described by taking the spent catalyst after the third catalytic cracking reaction as an example.

In the fluidized bed reactor, the product of the third catalytic cracking reaction is subjected to gas-solid separation in a settling section of the fluidized bed reactor, the gas-phase cracking product is collected as an oil-gas product, the solid spent catalyst is subjected to steam stripping treatment by ascending steam in the descending process, then is output to the fluidized bed reactor through a spent catalyst outlet of the fluidized bed reactor, and enters the regenerator through a spent catalyst inlet of the regenerator. The steam stripping treatment of the spent catalyst is to collect the gas-phase cracking products attached to the surface of the spent catalyst by using steam, and the gas-phase cracking products collected by the steam stripping treatment can enter a gas-solid separation device to be collected as oil-gas products.

The spent catalyst in the regenerator firstly enters the heat compensator through a spent catalyst conveying pipeline, then the fuel distributor and the combustion improver distributor enable the fuel and the combustion improver to be uniformly distributed on the surface of the spent catalyst, and the fluidization and pre-combustion medium distributor enables the spent catalyst with the fuel distributed on the surface to be in a fluidization state and pre-combust at low temperature and under low temperature and oxygen deficiency, so that the spent catalyst is converted into the pre-combustion catalyst with coke on the surface. It can be understood that the coke concentration attached to the spent catalyst is maximally homogenized during the process of fluidizing the spent catalyst by the fluidizing medium.

And then, the pre-combustion catalyst enters a regenerator through a pre-combustion catalyst conveying pipeline, bed layers in the regenerator are uniformly distributed, regenerated gas is introduced to carry out a coking and heat release reaction, heat required by the regeneration of the catalytic cracking catalyst is supplied to obtain a regenerated catalyst, the regenerated catalyst is output from the regenerator, and the regenerated catalyst returns to the reactor through each conveying pipeline communicated with the reactor to be recycled. In the process, because the coke is uniformly distributed on the surface of the pre-combustion catalyst, the pre-combustion catalyst can not be deactivated due to local overheating when being combusted in the regenerator, the control of the homogenization and the scorching process is realized to the greatest extent, the regeneration performance and the physicochemical property of the catalyst can be better maintained, and the high-efficiency regeneration of the catalyst to be regenerated is facilitated.

According to the invention, the spent catalyst is subjected to pre-burning (namely afterburning) and heat supplement, so that on one hand, heat is supplemented to the spent catalyst, and on the other hand, the problem that the structure of the catalyst is damaged and catalyst particles are crushed to cause catalyst inactivation due to overhigh local temperature caused by violent combustion of the spent catalyst under the action of main air (namely regenerated gas) can be solved, and the heat balance and the production capacity of the whole device are improved. In the process of matching the heat compensator and the regenerator, the preheating and the afterburning are simultaneously carried out, the operation is continuous, the uniformly mixed catalyst is moderated and stably burnt, and the structural property and the physicochemical property of the catalyst are protected.

In the heat compensator, the operation temperature is 400-800 ℃, for example, 500-600 ℃ and the absolute pressure is 0.05-0.4 MPa. In addition, the heat compensator is in a low oxygen state, the linear velocity of the low oxygen-containing gas is 0.3-0.5m/s, and the oxygen content in the low oxygen-containing gas is 0.005 wt% -7 wt%, further 0.1 wt% -1 wt%. The pre-combustion degree can be well controlled by controlling the oxygen content in the heat compensator within a certain range, thereby ensuring the catalytic performance of the regenerated catalyst. In practice, the oxygen content in the outer regenerator can be maintained by controlling the linear velocity of the pre-combustion medium (e.g., air). In addition, the fuel can be a CO combustion improver (using Al)₂O₃Or SiO₂-Al₂O₃A CO combustion improver which is a carrier on which noble metals such as platinum and palladium are supported as main active components); the fluidizing medium may be steam and the pre-combustion medium may be air.

In the regenerator, the regeneration temperature is 600-850 ℃, preferably 650-750 ℃, and the linear velocity of the regeneration gas is 0.5-30 m/s; the regeneration gas is an oxygen-containing gas having an oxygen concentration of 10 wt% to 35 wt%, preferably 15 wt% to 25 wt%.

Furthermore, valves can be arranged on the spent catalyst conveying pipeline and the pre-burning catalyst conveying pipeline, so that the amount and the operating temperature of the catalyst in the regenerator and the heat compensator are kept stable, and independent operation can be performed when necessary.

The method for controlling multi-stage catalytic cracking by two parallel coupled beds according to the nature of the raw material of the present invention will be described in detail by specific examples.

Example 1

FIG. 1 is a schematic diagram of a system for controlling multi-stage catalytic cracking with dual-zone parallel coupled beds by feedstock properties according to one embodiment of the present invention. As shown in fig. 1, the system includes a first down pipe 1, a second down pipe 2, a fluidized-bed reactor 3, a regenerator 4, and an economizer 5 outside the regenerator 4. The outlet of the first downer 1 and the outlet of the second downer 2 are respectively communicated with the inlet of the fluidized bed reactor 3 through pipelines, the outlet of a spent catalyst of the fluidized bed reactor 3 is communicated with the inlet of a spent catalyst of the regenerator 4 through a pipeline, the outlet of the spent catalyst of the regenerator 4 is communicated with the inlet of a spent catalyst of the heat compensator 5 through a spent catalyst conveying pipeline, and the outlet of a pre-combustion catalyst of the heat compensator 5 is communicated with the inlet of a pre-combustion catalyst of the regenerator 4 through a pre-combustion catalyst conveying pipeline. The regenerated catalyst outlet of the regenerator 4 is communicated with the inlets of the first and second down pipes 1 and 2, respectively, and is used for inputting and returning the regenerated catalyst a to the first and second down pipes 1 and 2 for recycling.

In the fluidized bed reactor 3, a gas-solid separation device 6 (used for carrying out gas-solid separation on the product of the third catalytic cracking reaction) is arranged at the settling section at the upper part of the fluidized bed layer, and a steam stripping device 7 (used for carrying out steam stripping treatment on the catalyst b1 going downwards in the fluidized bed reactor 3) is arranged at the lower part of the fluidized bed layer; an oil gas product outlet is arranged at the top of the fluidized bed reactor 3 and is used for collecting an oil gas product c separated by the gas-solid separation device 6 for further fractionation and refining; a lift gas inlet is provided at the bottom of the fluidized bed reactor 3 for inputting a lift gas d to the steam stripping device 7 to strip the descending spent catalyst b 1.

A fuel distributor is arranged in the regenerator 4, particularly above the inlet of the spent catalyst; the top of the regenerator 4 is provided with a flue gas outlet for discharging flue gas e generated by burning in the regeneration treatment; and a regeneration gas inlet is arranged at the bottom of the regenerator 4 and used for introducing regeneration gas f into the regenerator 4 to assist the combustion regeneration of the pre-combustion catalyst.

The heat compensator 5 is internally provided with a fuel distributor (not shown), an oxidant distributor (not shown) and a fluidizing and pre-burning medium distributor (not shown), wherein the fuel distributor is used for releasing and spraying fuel to the spent catalyst in the heat compensator 5, the oxidant distributor is used for releasing and spraying oxidant to the spent catalyst in the heat compensator 5, and the fluidizing and pre-burning medium distributor is used for enabling the spent catalyst in the heat compensator 5 to be in a fluidizing state and enabling the spent catalyst to be pre-burned.

The system shown in fig. 1 is used for catalytic cracking of light hydrocarbons, and the method is briefly described as follows:

the preheated first raw material a, the first catalyst and the steam enter the first descending tube 1 through the inlet of the first descending tube 1, and the first raw material a and the first catalyst undergo a first catalytic cracking reaction in the process of descending in the first descending tube 1 to generate a product a1 (a first catalytic cracking product and a first catalyst to be generated) of the first catalytic cracking reaction.

The preheated second raw material B, the first catalyst and the steam enter the second descending pipe 2 through the inlet of the second descending pipe 2, and the second raw material B and the first catalyst undergo a second catalytic cracking reaction in the process of descending inside the second descending pipe 2 to generate a product B1 (a second catalytic cracking product and a second spent catalyst) of the second catalytic cracking reaction.

The first catalytic cracking product and the first catalyst to be generated are output through an outlet of the first descending pipe 1, the second catalytic cracking product and the second catalyst to be generated are output through an outlet of the second descending pipe 2, and the two materials enter the fluidized bed reactor 3 through an inlet of the fluidized bed reactor 3 to carry out the third catalytic cracking reaction.

In the fluidized bed reactor 3, a product b2 of a third catalytic cracking reaction obtained by fluidized bed layer reaction ascends to a gas-solid separation device 6 of a settling section under the action of fluidized gas and lifting gas d for gas-solid separation, the separated gas phase is collected as an oil gas product c at an oil gas product outlet, and then the oil gas product c is fractionated and refined to respectively obtain propylene, ethylene and the like; the separated solid phase b1 (spent catalyst) and the residual spent catalyst b1 (spent catalyst which does not enter the gas-solid separation device) can descend to the steam stripping device 7, the gas-phase cracking product on the surface of the spent catalyst b1 is stripped by steam adsorption under the action of the lifting gas d, and then the stripped spent catalyst b3 is output to the fluidized bed reactor 3 through a spent catalyst outlet and enters the regenerator 4 through a spent catalyst inlet; and the steam of the gas-phase cracking product carried with the spent catalyst surface can go up to the settling section to be collected as an oil gas product c.

The stripped spent catalyst b3 enters the heat compensator 5 through a spent catalyst conveying pipeline in the regenerator 4, and pre-burning treatment is carried out under the action of fuel, combustion-supporting medium, fluidizing medium and pre-burning medium to generate pre-burning catalyst with coke uniformly distributed on the surface. The pre-combustion catalyst enters the regenerator 4 through a pre-combustion catalyst conveying pipeline, and is combusted and regenerated under the action of regenerated gas f and fuel to obtain a regenerated catalyst a. The regenerated catalyst a is respectively returned and input to the interiors of the first descending pipe 1 and the second descending pipe 2 through the regenerated catalyst conveying pipeline for recycling, and in the recycling process of the regenerated catalyst, the adjustment of reaction parameters (such as reaction temperature and oil ratio) of the first descending pipe 1 and the second descending pipe 2 can be realized by respectively controlling the amount of the regenerated catalyst returned to the first descending pipe 1 and the second descending pipe 2.

The specific reaction conditions for catalytic cracking in this example are given in the table below.

Example 2

FIG. 2 is a schematic diagram of a system for controlling multi-stage catalytic cracking with dual-zone parallel coupled beds for feedstock properties according to yet another embodiment of the present invention. As shown in fig. 2, the system of the present embodiment differs from the system shown in fig. 1 in that:

the regenerated catalyst outlet of the regenerator 4 communicates with the inlets of the first and second down pipes 1 and 2 and the inlet of the fluidized bed reactor 3, and is used for feeding the regenerated catalyst a back to the first and second down pipes 1 and 2 and the fluidized bed reactor 3 for recycling.

The method for catalytic cracking of light hydrocarbons by using the system shown in fig. 2 is different from that of example 1 in that:

the regenerated catalyst a in the regenerator 4 is respectively returned to the first downer 1, the second downer 2 and the fluidized bed reactor 3 through the regenerated catalyst conveying pipeline for recycling, and in the recycling process of the regenerated catalyst, the adjustment of reaction parameters (such as reaction temperature and oil ratio) of the first downer 1, the second downer 2 and the fluidized bed reactor 3 can be realized by respectively controlling the amounts of the regenerated catalyst returned to the first downer 1, the second downer 2 and the fluidized bed reactor 3.

The specific reaction conditions for this example are seen in the table below.

Example 3

The catalytic cracking process for the light hydrocarbon feedstock of this example is essentially the same as that of example 1, except for the specific reaction conditions of the catalytic cracking.

The specific reaction conditions for catalytic cracking for this example are seen in the table below.

Example 4

The system of the present embodiment differs from the system shown in fig. 1 in that:

the system in the embodiment does not contain a fluidized bed layer, and a first catalytic cracking product and a first catalyst to be generated from the first descending pipe 1, and a second catalytic cracking product and a second catalyst to be generated from the second descending pipe 2 directly enter the gas-solid separation device 6 for gas-solid separation.

The method for catalytically cracking light hydrocarbons by using the system of the present embodiment is different from that of embodiment 1 in that:

the first catalytic cracking product and the first catalyst to be generated are output through an outlet of the first descending pipe 1, the second catalytic cracking product and the second catalyst to be generated are output through an outlet of the second descending pipe 2, the two materials can go up to a gas-solid separation device 6 of a settling section under the action of lifting gas d for gas-solid separation, the separated gas phase is collected as an oil gas product c at an oil gas product outlet, and then the oil gas product c is fractionated and refined to respectively obtain propylene, ethylene and the like; the separated solid phase b1 (spent catalyst) and the residual spent catalyst b1 (spent catalyst which does not enter the gas-solid separation device) can descend to the steam stripping device 7, a gas-phase cracking product on the surface of the spent catalyst b1 is adsorbed and stripped by steam under the action of the lifting gas d, and then the stripped spent catalyst b3 enters the regenerator 4 through a spent catalyst inlet; and the steam of the gas-phase cracking product carried with the spent catalyst surface can go up to the settling section to be collected as an oil gas product c.

Example 5

The catalytic cracking process for the light hydrocarbon feedstock of this example was substantially the same as the catalytic cracking process of example 2, except that the first catalyst was replaced with a second catalyst.

Example 6

The catalytic cracking process for the light hydrocarbon feedstock of this example was substantially the same as the catalytic cracking process of example 2, except that the first catalyst was replaced with a third catalyst.

Comparative example 1

This comparative example 1 uses the system of example 1 for catalytic cracking of light hydrocarbons, which differs from the process of example 1 in that: and replacing the first raw material and the second raw material with the first raw material and the second raw material respectively, and mixing to obtain a mixed raw material.

See table below for specific reaction conditions for this comparative example.

Comparative example 2

This comparative example 2 uses the system of example 1 for catalytic cracking of light hydrocarbons, which differs from the process of example 1 in that: the specific reaction conditions for catalytic cracking of this comparative example were different from those of example 1.

See table below for specific reaction conditions for this comparative example.

Comparative example 3

This comparative example 3 uses the system of example 1 for the catalytic cracking of light hydrocarbons, which differs from the process of example 1 in that: the specific reaction conditions for catalytic cracking of this comparative example were different from those of example 1.

See table below for specific reaction conditions for this comparative example.

Comparative example 4

This comparative example 4 uses the system of example 2 for catalytic cracking of light hydrocarbons, which differs from the process of example 2 in that: the specific reaction conditions for catalytic cracking of this comparative example were different from those of example 2.

See table below for specific reaction conditions for this comparative example.

Comparative example 5

This comparative example 5 uses the system of example 2 for catalytic cracking of light hydrocarbons, which differs from the process of example 2 in that: the specific reaction conditions for catalytic cracking of this comparative example were different from those of example 2.

See table below for specific reaction conditions for this comparative example.

The composition and preparation method of the first catalyst in the above examples and comparative examples include:

(1) preparation of ZSM-5

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

(2) Alkali treatment of catalyst supports

Mixing the molecular sieve raw material 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 a 4mol/L citric acid solution, soaking Mn, Mg and La on Nb-loaded HZSM-5 according to the mass ratio of citric acid to HZSM-5 of 0.3:1 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 sequentially aging at room temperature for 6h, drying at 120 ℃ for 12h and roasting at 540 ℃ for 4h to obtain the modified HZSM-5.

(6) Preparation of alkane-alkene co-cracking 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.

The composition and preparation method of the second catalyst in the above examples include:

a second catalyst was prepared in the same procedure as the first catalyst except that the second catalyst was prepared in a different composition ratio, and the modified HZSM-5, the matrix (including kaolin, pseudoboehmite, and ZrO in a mass ratio of 7:3: 1), the silica sol, sesbania powder, methyl cellulose, and nitric acid were mixed in mass fractions of 36%, 40%, 15%, 0.4%, 8%, and 0.6%, respectively, and the rest was the same as in example 1.

The composition and preparation method of the third catalyst in the above example includes:

1) carrying out alkali treatment on a ZSM-5 molecular sieve, namely mixing a molecular sieve raw material 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 molecular sieve raw material ZSM-5 to be neutral, then drying for 12h at the temperature of 120 ℃ and roasting for 2h at the temperature of 540 ℃;

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

3) HZSM-5 and NH obtained according to step 3)₄H₂PO₄And (NH)₄)₂SO₄The mixed solution is dipped with P on HZSM-5 with the mass ratio of 0.5:1 to obtain the load of P of 0.8 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) The modified ZSM-5 molecular sieve obtained in the step 3), the Y molecular sieve, the matrix (the mass percentage of kaolin to pseudo-boehmite is 1:1), the binder (the mass percentage of alumina sol to sesbania powder is 1:1) and the metal oxide (MnO and Fe)₂O₃The mass percent is 1:1), respectively mixing 30%, 10%, 20% and 20% according to the mass fraction, mechanically stirring for 4h at 500r/min, aging for 12h at room temperature, drying for 8h at 120 ℃, roasting for 4h at 600 ℃, and performing hydrothermal aging treatment for 8h in a water vapor atmosphere at 650 ℃ to obtain the third catalyst.

In the foregoing examples and comparative examples, the composition of the first feedstock is shown in table 1, the composition of the second feedstock is shown in table 2, the specific reaction conditions for catalytic cracking are shown in tables 3 to 4, and the specific reaction results for catalytic cracking are shown in table 5.

TABLE 1 composition of the first raw materials

TABLE 2 composition of the second raw material

TABLE 3 specific reaction conditions for the examples

TABLE 4 specific reaction conditions for comparative examples

TABLE 5 reaction results of examples and comparative examples

As can be seen from Table 5: 1. the minimum content and the maximum content of propylene in the oil gas products obtained in the embodiment of the invention are respectively example 6 (31.03%) and example 2 (34.38%), which are higher than the propylene content of the comparative example;

in addition, the ethylene content in the oil gas product obtained by the embodiment of the invention is also higher than that in the comparative example;

2. in the oil gas product obtained by the embodiment of the invention, the content of dry gas and coke is obviously lower than that of a comparative example, so that the method can reduce cracking and coke formation of the raw material, and is favorable for improving the yield of propylene.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling multi-stage catalytic cracking by using dual-zone parallel coupled beds of a feedstock property, wherein the feedstock comprises a first feedstock rich in alkane and a second feedstock rich in alkene, and a reaction device comprising a first descending tube and a second descending tube is adopted, and the method comprises the following steps:

2. The method of claim 1, wherein the reaction apparatus further comprises a fluidized bed reactor in series with the first and second downcomers, respectively, the method further comprising:

3. The process of any one of claims 1-2, wherein the first feedstock has an alkane content of greater than 40%;

the second feedstock has an olefin content greater than 30%.

4. The method of any one of claims 1-2, wherein the reaction temperature of the first catalytic cracking reaction is higher than the reaction temperature of the second catalytic cracking reaction; the catalyst-oil ratio of the first catalytic cracking reaction is larger than that of the second catalytic cracking reaction; the residence time of the first catalytic cracking reaction is greater than the residence time of the second catalytic cracking reaction.

5. The method of claim 4, wherein the temperature of the first catalytic cracking reaction is at least 50 ℃ higher than the reaction temperature of the second catalytic cracking reaction;

6. The method of claim 1, wherein the conditions of the first catalytic cracking reaction are: the reaction temperature is 630-700 ℃, the catalyst-oil ratio is 20-40, and the retention time is 2-4 s;

7. The method as claimed in claim 1, further comprising preheating the first raw material to 100-250 ℃ before the first raw material enters the first descending tube; and/or the presence of a gas in the gas,

8. The method of claim 1, wherein the regeneration process comprises:

9. The method of claim 8, wherein the temperature of the regeneration process is 600 ℃ to 850 ℃, the oxygen concentration in the regeneration gas is 10 wt% to 35 wt% and the linear velocity of the regeneration gas is 0.5m/s to 30 m/s.

10. The method of claim 8 or 9, wherein the temperature in the heat compensator is 400 ℃ to 800 ℃ and the oxygen content is 0.005 wt% to 7 wt%.