CN112457874A

CN112457874A - Method for controlling multi-stage catalytic cracking by multi-zone coupling bed layer according to raw material type

Info

Publication number: CN112457874A
Application number: CN202011129515.3A
Authority: CN
Inventors: 赵亮; 高金森; 张宇豪; 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: 2021-03-09
Anticipated expiration: 2040-10-21
Also published as: CN112457874B

Abstract

The invention provides a method for controlling multistage catalytic cracking according to a multi-zone coupling bed of a raw material type, wherein the raw material comprises a first raw material containing C4 hydrocarbon, a second raw material containing C5-C6 hydrocarbon and a third raw material containing C7-C8 hydrocarbon, a reaction device comprising a first descending pipe, a second descending pipe and a lifting pipe is adopted, and the method comprises the following steps: the first raw material enters a first down pipe to generate a first catalytic cracking reaction; the second raw material enters a second descending pipe to carry out a second catalytic cracking reaction; the product of the first catalytic cracking reaction, the product of the second catalytic cracking reaction and a third raw material enter a riser to carry out a third catalytic cracking reaction; gas-solid separation is carried out on the product of the third catalytic cracking reaction to obtain an oil gas product and a spent catalyst; the spent catalyst is stripped and regenerated and then returns to each catalytic cracking reaction. The invention can crack different light hydrocarbon materials under different conditions by using one system according to the cracking characteristics of various hydrocarbon materials, thereby realizing high yield of light olefin.

Description

Method for controlling multi-stage catalytic cracking by multi-zone coupling bed layer according to raw material type

Technical Field

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

Background

With the improvement of technology and capacity, the surplus trend of oil refining and supply capacity is shown, for example, in China, the oil refining capacity of 2018 reaches 8.4 hundred million tons, the processed crude oil is 6.1 hundred million tons, the total produced gasoline, diesel and kerosene is 3.64 hundred million tons, the average operating load is 72.4 percent, and 1.1 hundred million tons are expected to be surplus in 2020. Meanwhile, with the further stricter environmental requirements, the development of new energy resources represented by electric power, hydrogen energy, biological fuel and the like and the improvement of the fuel efficiency of automobiles, the demand acceleration of gasoline will be further reduced, and the global demand of chemicals is increased by 4% every year and is higher than the global GDP acceleration by 3%. Therefore, the transformation of the traditional fuel type refinery into chemical type refiners becomes one of development trend and outlet, and particularly, how to transform gasoline into fuel type products to fuel-high value-added chemicals comprehensive production improves social benefit and economic benefit.

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 "development plans of petrochemical and chemical industries (2016-: 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 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 future global low-carbon olefin market, the growth rate of propylene demand is greater than that of ethylene, so that the 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 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 according to a multi-zone coupling bed layer of a raw material type, which adjusts a 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 a multi-zone coupled bed of raw material types, wherein the 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 tube, a second descending tube and a riser 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 perform a second catalytic cracking reaction to obtain a second catalytic cracking product and a second spent catalyst; the first catalytic cracking product and the first catalyst to be generated from the first descending pipe, the second catalytic cracking product and the second catalyst to be generated from the second descending pipe and a third raw material enter the riser pipe to generate a third catalytic cracking reaction; carrying out gas-solid separation on the product of the third catalytic cracking reaction to obtain an oil gas product and a spent catalyst respectively; 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 0.1-0.4MPa, and the retention time is 0.3-6 s;

the conditions of the second catalytic cracking reaction are as follows: the reaction temperature is 480-;

the conditions of the third catalytic cracking reaction are as follows: the reaction temperature is 450 ℃ and 650 ℃, the catalyst-oil ratio is 3-30, the reaction pressure is 0.1-0.35MPa, and the retention time is 0.2-4 s.

The process as described above, wherein the reactor apparatus further comprises a fluidized bed reactor in series with the riser, the process further comprising:

the product of the third catalytic cracking reaction enters the fluidized bed reactor to carry out a fourth catalytic cracking reaction, and the product of the fourth catalytic cracking reaction is subjected to gas-solid separation to obtain the oil gas product and the spent catalyst respectively;

the conditions of the fourth catalytic cracking reaction are as follows: space velocity of 2-25h^-1The linear speed of the bed layer is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃.

The method as described above, wherein the content of C4 hydrocarbons in the first feedstock is greater than 40%;

the content of C5-C6 hydrocarbons in the second raw material is more than 40%;

the third feedstock has a content of C7-C8 hydrocarbons greater than 40%.

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 reaction temperature of the second catalytic cracking reaction is higher than that of the third catalytic cracking reaction;

the catalyst-oil ratio of the first catalytic cracking reaction is larger than that of the second catalytic cracking reaction; the catalyst-oil ratio of the second catalytic cracking reaction is larger than that of the third 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 residence time of the second catalytic cracking reaction is greater than the residence time of the third 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 temperature of the second catalytic cracking reaction is at least 40 ℃ higher than the reaction temperature of the third 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 catalyst-oil ratio of the second catalytic cracking reaction is at least 3 greater than that of the third 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 residence time of the second catalytic cracking reaction is at least 0.2s greater than the residence time of the third catalytic cracking reaction.

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 100-300 ℃; and/or the presence of a gas in the gas,

before the second raw material enters the second descending pipe, preheating the second raw material to 100-250 ℃; and/or the presence of a gas in the gas,

before the third raw material enters the riser, preheating the third raw material to 100-250 ℃.

The method comprises the following steps of preparing the catalyst by using a raw material composition comprising 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 catalyst is obtained by performing hydrothermal aging treatment at the temperature of 500-800 ℃; wherein,

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, modification by non-metal elements and impregnation modification by metal elements, and hydrothermal treatment is carried out between the two modification treatments; the non-metallic elements are impregnated by at least two non-metallic 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.

The method as described above, wherein the non-metallic element is at least two selected from B, P, S, Cl and Br; optionally, the non-metallic element comprises at least S;

the metal elements comprise at least one group IIA metal and one lanthanide metal; optionally, the metal element is selected from three or more of Mn, V, Fe, Nb, Cr, Mo, W, Mg, Ca, and La.

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 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 light hydrocarbons with different carbon numbers, by designing a descending tube reactor, a riser reactor and a catalyst regeneration system which are matched and cooperated with each other, the raw materials realize the combination of zone cracking and deep cracking, and are more suitable for the catalytic cracking of light hydrocarbon raw materials or light oil raw materials, thereby not only meeting the requirements of reaction time and atmosphere of the cracking of different hydrocarbons, but also reducing the retention time of intermediate products and achieving the effect of reducing the yield of dry gas and coke;

3. reaction conditions of the C4 hydrocarbon raw material, the C5-C6 hydrocarbon raw material and the C7-C8 hydrocarbon raw material are refined and distinguished, so that deep cracking of all raw materials is facilitated, matching of material flow and energy flow in the whole cracking system can be further achieved, stability of the whole light hydrocarbon catalytic cracking process is guaranteed, overall energy efficiency is improved, and industrial feasibility is achieved;

4. the catalytic cracking light hydrocarbon raw material can be from the by-products of the cracking processing of the heavy raw material, even products with different distillation ranges, so the catalytic cracking method can be used as a downstream processing technology of the cracking processing products 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-zone catalytic cracking with multi-zone coupled beds of feedstock type according to one embodiment of the present invention;

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

FIG. 3 is a schematic diagram of a system for controlling multi-zone catalytic cracking with multi-zone coupled beds of feedstock type 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 invention provides a method for controlling multistage catalytic cracking according to a multi-zone coupling bed of a raw material type, wherein the raw material comprises 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 first descending pipe, a second descending pipe and a lifting pipe which are sequentially connected in series are adopted as a reaction device, and the method comprises the following steps:

the conditions of the third catalytic cracking reaction are as follows: the reaction temperature is 450 ℃ and 650 ℃, the catalyst-oil ratio is 3-30, the reaction pressure is 0.1-0.35MPa, and the retention time is 0.2-4 s. The agent-oil ratio of the present 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 with light hydrocarbon as raw material. Specifically, the first feedstock refers to light hydrocarbons with a C4 hydrocarbon as the main component, the second feedstock refers to light hydrocarbons with a C5-C6 hydrocarbon as the main component, and the third feedstock refers to light hydrocarbons with a C7-C8 hydrocarbon as the main component.

The reaction device comprises a first descending pipe, a second descending pipe and a lifting pipe, wherein specifically, an outlet of the first descending pipe and an outlet of the second descending pipe are respectively communicated with an outlet of the lifting pipe. 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 addition, the specific structural form of the riser of the present invention can be selected according to actual needs, for example, one selected from the group consisting of an equal linear velocity riser reactor, a variable diameter riser reactor and an equal diameter riser reactor.

In the method, a first raw material rich in C4 hydrocarbon enters a first downer reactor through an inlet of the first downer reactor, and undergoes a first catalytic cracking reaction with a catalyst in the process of descending in the first downer reactor to obtain a first catalytic cracking product (catalytic cracking product of the first raw material) and a first catalyst to be generated;

a second raw material rich in C5-C6 hydrocarbon enters a second descending pipe through an inlet of the second descending pipe and undergoes a second catalytic cracking reaction in the descending process inside the second descending pipe to obtain a second catalytic cracking product (a catalytic cracking product of the second raw material) and a second spent catalyst;

the first catalytic cracking product and the first spent catalyst at the lower part of the first downer are output from the outlet of the first downer, the second catalytic cracking product and the second spent catalyst at the lower part of the second downer are output from the outlet of the second downer, and the two materials and a third raw material rich in C7-C8 hydrocarbon enter the riser together through the inlet of the riser, and a third catalytic cracking reaction occurs in the process of ascending in the riser reactor. The product of the third catalytic cracking reaction is output through an outlet of the lifting pipe and then enters 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 through 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 of conveying the regenerated catalyst after the catalyst to be regenerated back to the first descending pipe, the second descending pipe and the lifting pipe to participate in the first catalytic cracking reaction, the second catalytic cracking reaction and the third catalytic cracking reaction respectively, so that the regeneration and utilization of the catalyst to be regenerated can reduce the preparation cost of propylene, and can adjust reaction parameters, such as reaction temperature and oil-to-oil ratio, in the descending pipe and the lifting pipe by controlling the amount of the regenerated catalyst returned back to the descending pipe and the lifting pipe. It is emphasized that before the spent catalyst obtained by gas-solid separation is regenerated, the descending spent catalyst is stripped by using ascending stripping gas (such as water vapor) to adsorb the oil gas product on the surface, and the vapor adsorbed with the oil gas product can ascend into the gas-solid separation device under the action of the stripping gas and be collected as the oil gas product to be fractionated and refined.

The method can utilize a designed system to divide light hydrocarbons into different hydrocarbon raw materials according to the number of carbon atoms for carrying out the catalytic cracking reaction in a subarea manner by controlling the technological process and conditions, thereby further improving the yield and the selectivity of propylene and simultaneously reducing the generation of coke and dry gas in the reaction.

In the specific implementation, the first raw material rich in C4 hydrocarbon and steam are jointly fed into the first downer according to a certain ratio (for example, the mass ratio of the first raw material to the steam is 1: 0.1-3), and the steam can play a role in partial pressure to maintain a more suitable cracking atmosphere in the downer. After the first raw material enters the first descending tube, a first catalytic cracking reaction is carried out by controlling the reaction temperature to be 500-.

The second raw material rich in C5-C6 and steam (for example, the mass ratio of the second raw material to the steam is 1: 0.1-3) enter a second descending tube together, and a second catalytic cracking reaction is carried out under the conditions of the reaction temperature of 480-. Specifically, the second raw material is subjected to a second catalytic cracking reaction under the action of the catalyst, so as to obtain a product of the second catalytic cracking reaction (a second catalytic cracking product and a second spent catalyst).

Then, the first catalytic cracking product, the first spent catalyst, the second catalytic cracking product, the second spent catalyst, a third raw material rich in C7-C8 and steam (for example, the mass ratio of the third raw material to the steam is 1: 0.1-3) enter a riser together, and a third catalytic cracking reaction is carried out under the conditions of the reaction temperature of 450-. And (3) carrying out gas-solid separation on the product of the third catalytic cracking reaction to respectively obtain light oil gas and the spent catalyst.

Because the low carbon number hydrocarbon is not easy to crack, the invention firstly cracks C4 hydrocarbon and C5-C6 hydrocarbon, introduces the generated catalytic cracking product into the C7-C8 hydrocarbon to crack together with the C7-C8 hydrocarbon, is beneficial to increasing the cracking time of the C4 hydrocarbon and the C5-C6 hydrocarbon and promoting the deep cracking of the respective catalytic cracking products of the C4 hydrocarbon and the C5-C6 hydrocarbon, thereby further increasing the yield of the low carbon olefin, especially propylene, and further inhibiting the yield of dry gas and coke.

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

The invention takes light hydrocarbon as raw material, can be from fractions or oil products of different processes, the raw material rich in C4 hydrocarbon, the raw material rich in C5-C6 hydrocarbon and the raw material rich in C7-C8 hydrocarbon are respectively led into a first descending pipe, a second descending pipe and a riser as a first raw material, a second raw material and a third raw material, the process conditions are respectively controlled to realize the zone reaction of the raw materials, the first catalytic cracking reaction and the second catalytic cracking reaction are respectively realized in the first descending pipe and the second descending pipe aiming at the C4 hydrocarbon and the C5-C6 hydrocarbon which are more difficult to crack, the cracked material is then respectively sent into the riser respectively connected with the first descending pipe and the second descending pipe in series, the third catalytic cracking reaction is carried out together with the C7-C8 hydrocarbon, if necessary, the cracked material can be continuously sent into a subsequent fluidized bed reactor in series to further deeply crack, and the C4 hydrocarbon, On the basis of cracking of C5-C6 hydrocarbon, the operation conditions of the riser and the fluidized bed reactor can be more flexibly regulated and matched, which is favorable for improving the reaction depth and the conversion rate of raw materials and finally improving the yield of propylene. 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 is introduced into the cracking system according to the composition condition of the light hydrocarbon raw material.

Further, the reactor apparatus of the present invention may further comprise a fluidized bed reactor in series with the riser, i.e. the outlet of the riser communicates with the inlet of the fluidized bed reactor.

In order to avoid incomplete cracking degree of the third catalytic cracking reaction, the method can also enable the product of the third catalytic cracking reaction to enter the fluidized bed reactor for the fourth catalytic cracking reaction after being output from the outlet of the riser on the basis of the method. Specifically, the conditions of the fourth catalytic cracking reaction are: space velocity of 2-25h^-1The linear speed is 0.1-0.5m/s, and the reaction temperature is 600-650 ℃.

In the fourth catalytic cracking reaction, the product of the third catalytic cracking reaction is further catalytically cracked in the bed layer of the fluidized bed reactor to obtain the product of the fourth catalytic cracking reaction. Under the action of the fluidized gas, in the process that the product of the fourth 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, the second descending pipe and the lifting pipe to participate in the first catalytic cracking reaction, the second catalytic cracking reaction and the third catalytic cracking reaction, or is respectively conveyed back to the first descending pipe, the second descending pipe, the lifting pipe and the fluidized bed to participate in the first catalytic cracking reaction, the second catalytic cracking reaction, the third catalytic cracking reaction and the fourth catalytic cracking reaction.

The method comprises the steps that a first descending pipe, a second descending pipe, a riser and a fluidized bed reactor are used as reaction devices, and a first raw material rich in C4 hydrocarbon and a catalyst generate 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 the second raw material rich in C5-C6 hydrocarbon enters a second descending tube, and in the second descending tube, the second raw material is subjected to a second catalytic cracking reaction under the action of the catalyst to obtain a second catalytic cracking product and a second spent catalyst. And then, the first catalytic cracking product, the first spent catalyst, the second catalytic cracking product, the second spent catalyst and a third raw material rich in C7-C8 hydrocarbon enter a riser together to perform a third catalytic cracking reaction, so that products of the third catalytic cracking reaction (the third catalytic cracking product and the third spent catalyst) are obtained. And finally, the product of the third catalytic cracking reaction from the riser enters the fluidized bed reactor for a fourth catalytic cracking reaction, so that the catalytic cracking product of the first raw material, the catalytic cracking product of the second raw material and the catalytic cracking product of the third raw material are continuously and deeply cracked. And products of the fourth 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 obtained by cracking the raw material, the collected solid phase is a spent catalyst, and the spent catalyst can be recycled as a regenerated catalyst after being regenerated.

After the outlet of the riser is connected with the fluidized bed reactor in series, the deep cracking of the first raw material, the second raw material and the third raw material can be further ensured under the reaction condition of the fluidized bed reactor limited 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 fourth catalytic cracking reaction, the product of the fourth 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 of the product of the fourth catalytic cracking reaction is rapidly separated by the gas-solid rapid separation device, so that the 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 oil-gas products 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 fourth catalytic cracking reaction can be quickly separated.

Further, a nozzle may be provided at the inlet of the first downer, the second downer, the riser and the fluidized-bed reactor, through which the materials introduced into the downer, the riser or the fluidized-bed reactor are mixed and contacted, and the raw materials are 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 sharp included angle between the inlets of the first descending pipe, the second descending pipe and the riser and the inner axes of the first descending pipe, the second descending pipe and the riser is 30-60 degrees, the acute included angle can enable materials entering the reactor to be mixed more fully, and further the cracking can be more full.

The first feedstock rich in C4 hydrocarbons, the second feedstock rich in C5 to C6 hydrocarbons, and the third feedstock rich in C7 to C8 hydrocarbons are not limited to a large amount, and may be, for example, naphtha, catalytically cracked gasoline, pressurized gas oil, steam cracked by-product or light cracked gasoline, by-products of a fluid catalytic cracking apparatus or cracking apparatus, by-products of an apparatus for producing olefins from methanol, and the like. According to the content of C4 hydrocarbon, C5-C6 hydrocarbon and C7-C8 hydrocarbon, the method for catalytic cracking which is used as the first raw material or the second raw material or the third raw material is determined. Of course, C4 hydrocarbons, C5-C6 hydrocarbons, and C7-C8 hydrocarbons may also be selected as the first feedstock, the second feedstock, or the third feedstock, respectively.

The mass content of C4 hydrocarbon in the first raw material is not less than 40%, the mass content of C5-C6 hydrocarbon in the second raw material is not less than 40%, and the mass content of C7-C8 hydrocarbon in the third raw material is not less than 40%.

Further, in order to ensure the deep cracking of the raw material and the yield and selectivity of propylene, the reaction conditions of each reaction may be further defined on the basis of the first catalytic cracking reaction condition, the second catalytic cracking reaction condition and the third catalytic cracking reaction condition. Specifically, the reaction temperature of the first catalytic cracking reaction is made higher than the reaction temperature of the second catalytic cracking reaction, and the reaction temperature of the second catalytic cracking reaction is made higher than the reaction temperature of the third catalytic cracking reaction; the catalyst-oil ratio of the first catalytic cracking reaction is larger than that of the second catalytic cracking reaction, and the catalyst-oil ratio of the second catalytic cracking reaction is larger than that of the third catalytic cracking reaction; the residence time of the first catalytic cracking reaction is made longer than that of the second catalytic cracking reaction, and the residence time of the second catalytic cracking reaction is made longer than that of the third 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 temperature of the second catalytic cracking reaction is at least 40 ℃ higher than the reaction temperature of the third 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 catalyst-oil ratio of the second catalytic cracking reaction is at least 3 greater than that of the third 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 residence time of the second catalytic cracking reaction is at least 0.2s greater than the residence time of the third catalytic cracking reaction.

As a preferred embodiment, the conditions of the first catalytic cracking reaction are as follows: the reaction temperature is 600-680 ℃, 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 600 ℃, the catalyst-oil ratio is 15-25, and the retention time is 2-3 s; the conditions of the third catalytic cracking reaction are as follows: the reaction temperature is 480 ℃ and 530 ℃, the catalyst-oil ratio is 15-25, and the retention time is 2-4 s. Thereby further realizing the matching of material flow and energy flow in the whole cracking system, ensuring the stability of the whole light olefin catalytic cracking process, improving the overall energy efficiency and realizing industrial feasibility.

In practical applications, the determination of the specific operating conditions of the second downcomer, the riser and the fluidized bed reactor can be further adjusted according to the changes of the first catalytic cracking product and the second catalytic cracking product to realize the deep cracking of the raw material.

The present invention also allows the propylene yield to be further enhanced by selecting a specific catalyst that is capable of simultaneously catalytically cracking a first feedstock rich in C4 hydrocarbons, a second feedstock rich in C5-C6 hydrocarbons and a third feedstock rich in C7-C8 hydrocarbons.

The catalyst is capable of simultaneously catalytically cracking alkane and alkene, and utilizes a plurality of metal elements and nonmetal element groups to modify a molecular sieve, so that the acid strength and the acid density of a molecular sieve carrier are controlled in a targeted manner, the catalyst has acid centers of different types such as super acid, strong acid, weak acid and the like, the adsorption capacity of the alkene and the alkane can be simultaneously improved, the simultaneous catalytic cracking of the alkane and the alkene becomes possible, and the better propylene yield is provided while the higher total conversion rate of the alkane and the alkene is provided. By means of the synergistic effect of the specific composite auxiliary agent, the wear resistance of the catalyst is improved while the catalytic performance is ensured, and the service life of the catalyst is prolonged.

The catalyst comprises the raw materials of 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 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 with 0.2-1.0mol/L alkaline solution according to the mass ratio of 1:4-8, exchanging for 1-5h at 70-90 ℃, then washing the molecular sieve to be neutral, drying for 3-12h at 60-150 ℃, and roasting for 2-6h at 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 60-150 ℃ for 3-12h, and roasting at 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 catalytic cracking reaction at each stage is less, and the heat generated by burning the coke is not 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 a regenerator comprising a heat compensator for regeneration treatment of the spent catalyst, specifically, the heat compensator is arranged outside the regenerator, a spent catalyst inlet of the regenerator is communicated with a spent catalyst outlet of a stripping section and used for receiving the stripped spent catalyst, a spent catalyst outlet of the regenerator is communicated with a spent catalyst inlet of the heat compensator through a spent catalyst conveying pipeline, a pre-combustion catalyst outlet of the heat compensator is communicated with a pre-combustion catalyst inlet of the regenerator through a pre-combustion catalyst conveying pipeline, a regenerated catalyst outlet of the regenerator is respectively communicated with inlets of a first descending pipe, a second descending pipe and a lifting pipe, or a regenerated catalyst outlet of the regenerator is respectively communicated with inlets of the first descending pipe, the second descending pipe, the lifting pipe and the fluidized bed reactor. In addition, a fuel distributor, a combustion improver distributor and a fluidization and pre-combustion medium distributor are arranged in the heat compensator, wherein the fuel distributor is used for releasing and spraying fuel to the catalyst to be generated in the heat compensator, the combustion improver distributor is used for releasing and spraying combustion improver to the catalyst to be generated in the heat compensator, and the fluidization and pre-combustion medium distributor is used for enabling the catalyst to be generated in the heat compensator to be in a fluidization state and enabling the catalyst to be generated to be pre-combusted.

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

In the fluidized bed reactor, the product of the fourth 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 (whole spent catalyst or part of 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 under low-temperature oxygen-poor condition, 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 gas is 0.3-0.5m/s, and the oxygen content in the low-oxygen gas is 0.005-7 wt%, and further 0.1-1 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 multi-zone coupled beds according to the type of 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-zone catalytic cracking with multi-zone coupled beds of feedstock types 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 riser 3, a fluidized bed reactor 4, a regenerator 5, and an afterheater 6 outside the regenerator 5. The outlet of the first downer 1 and the outlet of the second downer 2 are respectively communicated with the inlet of a riser 3 through pipelines, the outlet of the riser 3 is communicated with the inlet of a fluidized bed reactor 4 through a pipeline, the outlet of a spent catalyst of the fluidized bed reactor 4 is communicated with the inlet of a spent catalyst of a regenerator 5 through a pipeline, the outlet of the spent catalyst of the regenerator 5 is communicated with the inlet of a spent catalyst of a heat compensator 6 through a spent catalyst conveying pipeline, and the outlet of a pre-combustion catalyst of the heat compensator 6 is communicated with the inlet of a pre-combustion catalyst of the regenerator 5 through a pre-combustion catalyst conveying pipeline. The outlet of the regenerator 5 is connected to the inlets of the first downward pipe 1, the second downward pipe 2 and the riser 3, for inputting and returning the regenerated catalyst a to the first downward pipe 1, the second downward pipe 2 and the third downward pipe 3 for recycling.

In the fluidized bed reactor 4, a gas-solid separation device 7 (used for performing gas-solid separation on the product of the fourth catalytic cracking reaction) is arranged at the settling section at the upper part of the fluidized bed layer, and a steam stripping device 8 (used for performing steam stripping treatment on the spent catalyst b1 descending in the fluidized bed reactor) 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 4 and is used for collecting an oil-gas product c separated by a gas-solid separation device for further fractionation and refining; a lift gas inlet is provided at the bottom of the fluidized bed reactor 4 for inputting a lift gas d to the steam stripping device 8 to strip the descending spent catalyst b 1.

A fuel distributor is arranged in the regenerator 5, particularly above the inlet of the spent catalyst; the top of the regenerator 5 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 5 and used for introducing regeneration gas f into the regenerator 5 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 together, and the second raw material B generates a second catalytic cracking reaction under the action of the first catalyst in the descending process 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 spent catalyst are output through an outlet of the first descending pipe 1, the second catalytic cracking product and the second spent catalyst are output through an outlet of the second descending pipe 2, the two materials flow through an inlet of the lifting pipe 3 and enter the lifting pipe 3 together with the preheated third raw material C and the steam, and the first catalytic cracking product, the second catalytic cracking product and the third raw material C generate a third catalytic cracking reaction in the ascending process inside the lifting pipe 3 to obtain a product C1 (the third catalytic cracking product and the third spent catalyst) of the third catalytic cracking reaction.

The product C1 of the third catalytic cracking reaction is output through the outlet of the riser 3 and enters the fluidized bed reactor 4 through the inlet of the fluidized bed reactor 4 to carry out a fourth catalytic cracking reaction.

In the fluidized bed reactor 4, the product b2 of the fourth catalytic cracking reaction ascends to a gas-solid separation device 7 of a settling section under the action of the fluidized gas and the lifting gas d for gas-solid separation, the separated oil-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 spent catalyst b1 and the residual spent catalyst b1 (the spent catalyst which does not enter the gas-solid separation device) can descend to a steam stripping device 8, under the action of a lifting gas d, the oil gas phase on the surface b1 of the spent catalyst is stripped by steam adsorption, and then the stripped spent catalyst b3 is output to the fluidized bed reactor 4 through a spent catalyst outlet and enters a regenerator 5 through a spent catalyst inlet; and the steam of the oil gas phase carrying 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 6 through a spent catalyst conveying pipeline in the regenerator 5, 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 5 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 first descending pipe 1, the second descending pipe 2 and the riser 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 descending pipe 1, the second descending pipe 2 and the riser 3 can be realized by respectively controlling the amounts of the regenerated catalyst returned to the first descending pipe 1, the second descending pipe 2 and the riser 3.

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-zone catalytic cracking with multi-zone coupled beds of feedstock type 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 5 is connected to the inlets of the first downflow pipe 1, the second downflow pipe 2, and the riser 3, and to the inlet of the fluidized bed reactor 4, and is used for feeding the regenerated catalyst a back to the first downflow pipe 1, the second downflow pipe 2, the riser 3, and the fluidized bed reactor 4, and recycling the regenerated catalyst a.

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

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

Example 3

FIG. 3 is a schematic diagram of a system for controlling multi-zone catalytic cracking with multi-zone coupled beds of feedstock type according to yet another embodiment of the present invention. As shown in fig. 3, the system of the present embodiment differs from the system shown in fig. 1 in that:

the system in this embodiment does not contain a fluidized bed, and the product C1 of the third catalytic cracking reaction from the riser 3 directly enters the gas-solid separation device 7 for gas-solid separation.

The method for catalytic cracking of light hydrocarbons by using the system shown in fig. 3 is different from that of example 1 in that:

the product C1 of the third catalytic cracking reaction from the riser 3 directly enters a gas-solid separation device 7 for gas-solid separation under the action of a lifting gas d (stripping steam), the separated oil-gas phase is taken as an oil-gas product C to be collected 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 spent catalyst b1 and the residual spent catalyst b1 (the spent catalyst which is not mixed in the oil gas phase) can descend to a steam stripping device 8, the oil gas phase on the surface of the spent catalyst b1 is adsorbed and stripped by steam under the action of a lifting gas d, and then the stripped spent catalyst b3 enters a regenerator 5 through a spent catalyst inlet after passing through an output steam stripping section; and the steam of the oil gas phase carrying the spent catalyst surface can go up to the settling section to be collected as an oil gas product c.

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

Example 4

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 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 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: replacing the first raw material, the second raw material and the third raw material with mixed raw materials obtained by mixing the first raw material, the second raw material and the third raw material respectively.

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 100SiO₂:1Al₂O₃:20TPABr: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 compositions of the first, second and third feedstocks are shown in table 1, the specific reaction conditions for catalytic cracking are shown in tables 2 to 3, and the specific reaction results for catalytic cracking are shown in table 4.

TABLE 1 composition of the raw materials

TABLE 2 specific reaction conditions of the examples

TABLE 3 specific reaction conditions for comparative examples

TABLE 4 reaction results of examples and comparative examples

As can be seen from Table 4: 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 5 (31.16%) and example 2 (34.54%), 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 process for controlling multi-stage catalytic cracking in a multi-zone coupled bed of feedstock type, wherein the feedstock comprises 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 comprising a first downcomer, a second downcomer, a riser, the process comprising the steps of:

2. The process of claim 1, wherein the reaction apparatus further comprises a fluidized bed reactor in series with the riser, the process further comprising:

3. The process of any one of claims 1-2, wherein the first feedstock has a C4 hydrocarbon content of greater than 40%;

the content of C5-C6 hydrocarbons in the second raw material is more than 40%;

the third feedstock has a content of C7-C8 hydrocarbons greater than 40%.

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 reaction temperature of the second catalytic cracking reaction is higher than that of the third 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; the temperature of the second catalytic cracking reaction is at least 40 ℃ higher than the reaction temperature of the third catalytic cracking reaction;

6. The method as claimed in claim 1, further comprising preheating the first raw material to 100-300 ℃ before the first raw material enters the first descending tube; and/or the presence of a gas in the gas,

7. The method as claimed in claim 1, wherein 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 assistant, and the catalyst is obtained by hydrothermal aging treatment at 800 ℃ and 500 ℃; wherein,

the composite auxiliary agent at least comprises inorganic acid and cellulose.

8. The method of claim 7, wherein the non-metallic element is at least two selected from B, P, S, Cl and Br; optionally, the non-metallic element comprises at least S; and/or the presence of a gas in the gas,

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

10. The method of claim 9, 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.