Process and apparatus for the catalytic cracking of olefins to produce propylene

Abstract

The application discloses a method and device for preparing propylene by catalytic cracking of olefins. The method comprises the following steps: (1) feeding the raw material rich in olefins into a reactor from the bottom, and then into a catalyst bed layer through a gas distributor, and then flowing upwards into a separator at the upper part of the reactor after a catalytic cracking reaction occurs in the catalyst bed layer; (2) separating the product into a C3 and below fraction, a C4 fraction and a C5 and above fraction in the separator; and the ratio of the diameter to the height of the catalyst bed layer is 2:1-10:1, preferably 3:1-6:1. The application combines the thin-layer catalyst bed layer with the gas distributor and the design of directly connecting the separator to the upper part of the reactor, so that the reaction product is rapidly taken away from the olefin cracking reactor for separation, the reaction depth can be effectively controlled, the occurrence of a side reaction is avoided, the reaction efficiency is improved, and the load of a subsequent separation process is reduced.

Description

Technical Field

[0001] The present invention relates to a method and a device for preparing propylene, in particular to a method and a device for preparing propylene by catalytic cracking of olefins. Background Art

[0002] Propylene is a key chemical raw material second only to ethylene. Driven by the rapid growth in demand for polypropylene and its derivatives, propylene demand is currently growing faster than ethylene, resulting in a shortage of propylene. Furthermore, ethylene plants, catalytic cracking plants, methanol-to-propylene (MTP), and gasoline plants all produce significant by-products containing olefins (C4-C8). These by-products are generally used only as low-value-added products such as liquefied petroleum gas (LPG). Utilizing these inexpensive olefin feedstocks through catalytic cracking to produce ethylene, propylene, and other low-carbon olefins not only addresses the issue of excess by-product olefins and increases their chemical utilization, but also mitigates the imbalance between propylene supply and demand, reduces refining companies' dependence on crude oil, and improves their economic efficiency. This is of significant practical significance.

[0003] The essence of olefin catalytic cracking technology is to convert higher olefins into lower carbon olefins such as ethylene and propylene. Its representative processes include Lurgi's Propylur technology, Atofina and UOP's OCP technology, Asahi Kasei's Omega technology, Arco Chemical's Superflex technology, Mobil's MOI technology, Shanghai Petrochemical Research Institute's OCC technology, and Beijing Research Institute of Chemical Industry's BOC process. The olefin catalytic cracking reaction to produce propylene is a process of olefin dimerization and intermediate species cracking as the main reaction process, accompanied by side reactions such as isomerization, hydrogen transfer, cyclization, dehydrogenation, aromatization, and coking. The problems of these olefin cracking processes reported in the literature are: (1) low olefin selectivity and yield at high ethylene and propylene selectivity, and low raw material single-pass utilization rate; (2) rapid catalyst coking and deactivation at high conversion rate, poor stability, and short regeneration cycle.

[0004] Olefin cracking technology comprises olefin catalytic cracking reaction technology and product separation technology. The core of the reaction technology lies in the development of catalysts and reactors. Research institutes around the world have achieved some success in catalyst development, but there are relatively few reports on reactor development and separation processes.

[0005] The aspect ratio (ratio of the reactor bed's total height to its diameter) of a conventional fixed-bed hydrogenation reaction is generally chosen to be between 2 and 10 to ensure sufficient contact between the reactants and the solid catalyst, achieving the desired reaction depth and efficiency. Dong Fangliang et al., in "Determination of the Main Structural Parameters of Hydrogenation Reactors," published in "First Heavy Industries Technology," 1998.1 (Total 75), note that to avoid "uneven fluid distribution and poor catalyst contact efficiency due to a small aspect ratio," conventional fixed-bed reactors typically have aspect ratios of 4 to 9. Patent CN109679689 A also states that the aspect ratio of a hydrogenation reactor is generally between 2.5 and 12. This aspect ratio design for hydrogenation reactors has become a well-established concept among those skilled in the art. Numerous industrial applications have confirmed its rationality and widespread adaptability. This widespread industrial success may have also prevented researchers from conducting more comprehensive and in-depth research into whether other optimal options exist for different reaction types. For a long time, no relevant research reports have been published, or only reports have been published demonstrating that the current aspect ratio is a suitable design.

[0006] CN1915930A employs a gas-solid radial or axial-radial adiabatic fixed-bed reactor, both of which offer large flow areas and low bed pressure drops. These reactors are suitable for the industrial production of propylene from catalytic cracking of C4 and higher olefins, improving selectivity and yield of the target product, propylene. However, even with these reactors, the problems of rapid catalyst deactivation due to carbon deposition, poor stability, and short regeneration cycles in fixed-bed reactors for catalytic cracking of olefins remain unresolved, making it difficult to achieve the desired propylene yield.

[0007] CN1927784A discloses a method for separating olefin catalytic cracking products. The gaseous catalytic cracking products are compressed to 1.0-4.0 MPa and fed into a first separation tower. Ethylene and ethane are obtained at the top of the tower, and the bottoms of the tower are fed into a second separation tower. The second separation tower produces a C3 fraction at the top, and C4 and above fractions at the bottom. The C3 fraction feeds a third separation tower, where a side draw is taken to produce propylene with a mass fraction of 90%-99%, and propane is obtained at the bottom. A fourth separation tower produces C4 and C5 fractions at the top, and C6 and above fractions at the bottom. CN101205162A discloses a combined process for producing olefins using refinery C4. After pretreatment, the refinery's C4 gas is sent to the catalytic olefin cracking system. The resulting cracked gas mixture enters a cooling system for cooling before entering the compression section. The compressed catalytic cracked gas enters an absorption tower, where C5 and heavier components serve as absorbent. Light components such as methane and C2 are extracted from the tower overhead. The bottoms of the tower are separated through a debutanizer, a depropanizer, and a propylene tower, yielding C3, C4, and C5 and heavier components, respectively. As can be seen, the existing separation process for catalytic olefin cracking products is complex, requiring specialized compression equipment at the front end of the separation tower to increase the separation pressure. This heavy separation load, high cost, and high energy consumption are associated with this equipment. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention aims to provide a method and apparatus for preparing propylene by catalytic cracking of olefins, so as to effectively control the reaction depth, thereby improving the selectivity of the target product propylene and the stability of the catalyst, while reducing the load of subsequent separation processes.

[0009] The first aspect of the present invention is to provide a method for preparing propylene by catalytic cracking of olefins, comprising the following steps:

[0010] (1) Olefin-rich feedstock enters the bottom of the reactor, passes through the gas distributor and enters the catalyst bed. After catalytic cracking reaction occurs in the catalyst bed, the catalytic cracking products continue to flow upward and enter the separator above the reactor;

[0011] (2) The catalytic cracking products are separated into C3 and below fractions, C4 fractions, and C5 and above fractions in the separator;

[0012] The diameter-to-height ratio of the catalyst bed (calculated based on the maximum equivalent diameter of the rectangle, where the height is the total height of the catalyst bed) is 2:1 to 10:1, preferably 3:1 to 6:1.

[0013] Furthermore, in the above technical solution, the catalyst bed height is 100 to 5000 mm, preferably 200 to 1000 mm.

[0014] Furthermore, in the above technical solution, the olefin-rich raw material in step (1) comes from the by-product C4 fraction, C4 and C5 fractions of ethylene steam cracking unit, catalytic cracking unit, methanol to olefins and methanol to propylene unit, as well as hydrocarbon materials rich in C4~C8 olefins.

[0015] Furthermore, in the above technical solution, the olefin-rich feedstock in step (1) is heated to 410°C to 610°C before entering the reactor. Preferably, the feedstock is heat exchanged with the catalytic cracking product at the bottom of the separator before being heated.

[0016] Furthermore, in the above technical solution, in step (2), the C3 and lower fractions flow out from the top of the separator in the upper part of the reactor in the gas phase, and the C4 fraction and the C5 and higher fractions are extracted from the side line of the separator.

[0017] Furthermore, in the above technical solution, the C4 fraction and the C5 and above fractions are withdrawn from the separator sideline outlet at different locations of the separator according to actual conditions. Furthermore, the sideline withdrawal temperature of the C4 fraction is 20°C to 60°C, and the sideline withdrawal temperature of the C5 and above fraction is 80°C to 150°C.

[0018] Furthermore, in the above technical solution, the C4 fraction drawn from the side line passes through a cooler and enters a gas-liquid separator, where the C3 and lower fractions are discharged at the top of the gas-liquid separator, and the C4 fraction is separated at the bottom. Furthermore, the pressure of the gas-liquid separator is 0.1 MPa to 0.7 MPa, and the temperature is -20°C to 30°C.

[0019] Furthermore, in the above technical solution, 20% to 95% of the separated C4 fraction is recycled into the reactor.

[0020] Furthermore, in the above technical solution, the method is applicable to various catalytic cracking catalysts, including any one or more of supported metal oxide catalysts, alkaline oxide catalysts, and modified or unmodified molecular sieve catalysts. Preferably, the catalytic cracking catalyst is ZSM-5, ZSM-11, SAPO-34, or MCM-22 molecular sieve. Preferably, the catalyst is a ZSM-5 molecular sieve catalyst having a silicon-to-aluminum molar ratio greater than 50, and more preferably, a ZSM-5 molecular sieve catalyst modified with a precursor compound of an alkaline earth metal and / or a rare earth metal oxide. The alkaline earth metal is selected from at least one of beryllium, magnesium, calcium, strontium, barium, and radium. The rare earth metal element is selected from at least one of lanthanum, cerium, praseodymium, and neodymium.

[0021] Furthermore, in the above technical solution, the operating conditions of the catalytic cracking reaction are as follows: reaction temperature is 400°C to 600°C, reaction pressure is 0.1MPa to 0.8MPa, and weight space velocity is 5h -1 ~50h -1 .

[0022] Furthermore, in the above technical solution, the operating conditions of the separator above the reactor are the same as the operating conditions of the catalytic cracking reaction.

[0023] A second aspect of the present invention provides a catalytic cracking device comprising an olefin cracking reactor and a separator disposed on top of the olefin cracking reactor. The olefin cracking reactor comprises, from top to bottom, an olefin cracking reaction zone and a gas distribution chamber. The olefin cracking reactor is rectangular or circular, and has a diameter-to-height ratio of 2:1 to 10:1, preferably 3:1 to 6:1. The diameter in the diameter-to-height ratio is calculated based on the maximum equivalent diameter, and the height is the total height of the olefin cracking reactor.

[0024] Furthermore, in the above technical solution, the olefin cracking reactor is preferably isodiametric, i.e., the cross-sectional area is the same at different locations within the entire olefin cracking reactor. The cross-sectional area of ​​the olefin cracking reactor refers to the top view cross-section, i.e., the cross-sectional area perpendicular to the vertical line within the olefin cracking reactor. If the cross-sectional area of ​​the reactor varies within the catalyst bed height range, the cross-sectional area here refers to the average value of the cross-sectional area of ​​the olefin cracking reactor at each location within the catalyst bed. At a higher diameter-to-height ratio, the material flux through the bed can be greatly increased while reducing the residence time of the material in the catalyst bed.

[0025] Furthermore, in the above technical solution, the height of the olefin cracking reactor is 100 to 5000 mm, preferably 200 to 1000 mm.

[0026] Furthermore, in the above technical solution, the olefin cracking reactor is a horizontal storage tank with its axis arranged in the transverse direction and with heads provided at both ends of the horizontal storage tank. Alternatively, the olefin cracking reactor is a flat cylindrical tank with its axis arranged in the longitudinal direction.

[0027] Furthermore, in the above technical solution, a plurality of partitions are provided in parallel along the vertical direction in the middle of the gas distribution chamber, the plurality of partitions dividing the gas distribution chamber into a plurality of gas inlet units, and at least one feed port is provided at the bottom of each gas inlet unit. Preferably, the plurality of partitions are coaxial annular partitions.

[0028] Furthermore, in the above technical solution, a plurality of circular holes are distributed on each partition.

[0029] Furthermore, in the above technical solution, multiple partitions extend upward to the olefin cracking reaction zone, the opening rate of the partitions below the olefin cracking reaction zone is less than 70%, and the opening rate of the partitions in the olefin cracking reaction zone is greater than 50%.

[0030] Furthermore, in the above technical solution, the separator is provided with trays, which may be one or more of the following trays with downcomers, such as bubble cap trays, sieve trays, float valve trays, mesh trays, tongue-shaped trays, guide sieve trays, and multi-downcomer trays. Trays without downcomers, such as flow-through sieve trays and flow-through corrugated trays, may also be used. High-efficiency trays, such as guide valve trays and sieve trays, are preferred.

[0031] Furthermore, in the above technical solution, the ratio of the cross-sectional area of ​​the separator to that of the olefin cracking reactor is 1:1.2 to 1:10, preferably 1:2 to 1:10. In the present invention, the diameter of the separator above the catalytic cracking reactor is reduced, so that the product fraction load is fully matched with the tray, the tray separation efficiency is high, and it has the ability to completely replace the distillation tower.

[0032] Further, in the above technical solution, the catalytic cracking reactor, the lower olefin cracking reactor and the upper separator are integrated equipment and are completely communicated with each other. The lower reaction section is in the form of a horizontal storage tank with heads on both sides, facilitating the loading and unloading of catalyst. The middle part of the reactor is filled with a plurality of catalyst units to form a catalyst bed, and the plurality of reactor units are separated by a mesh partition, but the present application is not limited to whether there is a partition.

[0033] Further, in the above technical solution, a feed heat exchanger is arranged in the separator, and the cracking products and the raw materials are heat exchanged in the feed heat exchanger.

[0034] The technical principle of the present application is that: olefins have a strong tendency to polymerize, dehydrocyclize and aromatize to form aromatic hydrocarbons in thermodynamics, and the isomerization, cracking and polymerization reactions between olefins are all reversible reactions, so the selectivity and yield of the target products ethylene and propylene are low, and the catalyst is deactivated quickly by carbon deposition and has poor stability. The reactor of the present application adopts a horizontal or flat disc structure, and the catalyst bed is relatively thin. After the olefin raw material enters the reactor, the primary reaction products such as ethylene, propylene, butane, isobutane, C5, C8, etc. are rapidly taken away from the olefin cracking reactor and enter the upper separator for preliminary separation, effectively avoiding the secondary reactions such as olefin cyclization, dehydrogenation and hydrogen transfer of unstable primary products, that is, effectively avoiding the saturation of low-carbon olefins in the system to alkanes, and the generation of benzene series compounds, which are attached to the surface of the catalyst by condensation reaction, resulting in the deactivation of the active sites of the catalyst. In addition, since the product partial pressure is always kept low, the reaction rate is accelerated and the reaction efficiency is improved, which is conducive to moving the reaction equilibrium to the desired cracking direction, and inhibiting side reactions such as hydrogen transfer reactions that require two molecules. The purpose of controlling the degree of reaction is achieved.

[0035] Compared with the prior art, the present application has the following advantages:

[0036] (1) The present application can form uniform gas distribution of the raw material in the reactor by reasonably arranging the gas distribution chamber and controlling the structure of the catalyst bed, and the primary products after the catalytic cracking of olefins can be rapidly separated from the reaction system, effectively avoiding the occurrence of secondary reactions, prolonging the service life of the catalyst, and increasing the selectivity and yield of the target product propylene.

[0037] (2) The present application can realize the timely production of light products through flash evaporation and stripping by the arrangement of the separator, so as to effectively control the degree of reaction and maximize the propylene yield. At the same time, since the product partial pressure is always kept low, the reaction rate is accelerated, which is conducive to improving the reaction efficiency and removing the easily coking hydrogen sulfide and ammonia and other undesirable components.

[0038] (3) A feed heat exchanger is set in the separator placed on the upper part of the reactor, and the cracking products and the raw materials are directly heat-exchanged without the need for heat loss through pipes, which improves the heat utilization rate, simplifies the process, and saves energy.

[0039] (4) Compared with conventional olefin catalytic cracking units, there is no need to install a compression device at the front end of the separator to increase the separation pressure, which reduces the separation load of the unit, simplifies the process, and reduces costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a schematic diagram of the process flow of preparing propylene by catalytic cracking of olefins according to the present invention.

[0041] Among them: 1-olefin raw material; 2-heating furnace; 3-olefin cracking reactor; 4-olefin cracking reaction zone; 5-separator; 6-crude C3 and below fractions; 7-crude C4 fraction; 8-C5 and above fractions; 9-cooler; 10-gas-liquid separator; 11-C3 fraction; 12-C4 fraction; 13-circulating C4 fraction; 14-feed heat exchanger.

[0042] Figure 2 1 is a side structural schematic diagram of a circular segment partition according to one embodiment of the present invention.

[0043] Figure 3 It is a side view structural diagram of a notch partition according to another embodiment of the present invention. The partition is only located in the hydrogen distribution chamber, and there is no notch partition inside the catalyst bed.

[0044] Figure 4 3 is a schematic top view of the annular partition according to one embodiment of the present invention.

[0045] Figure 5-1 and Figure 5-2 is a schematic side view of the annular partition according to two embodiments of the present invention, wherein Figure 5-2 The partition is only in the hydrogen distribution chamber, and there is no annular partition inside the catalyst bed.

[0046] Figure 6 3 is a schematic top view of the structure of a liquid distribution assembly according to one embodiment of the present invention. DETAILED DESCRIPTION

[0047] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0048] Unless expressly stated otherwise, throughout the specification and claims, the term “comprise” or variations such as “include” or “comprising” will be understood to include the stated elements or components but not to exclude other elements or components.

[0049] In this document, for ease of description, spatially relative terms such as "below," "beneath," "below," "above," "above," etc. may be used to describe the relationship of one element or feature to another element or feature in the accompanying drawings. It should be understood that the spatially relative terms are intended to encompass different orientations of the object in use or operation in addition to the orientation depicted in the drawings. For example, if the object in the drawings is turned over, the element described as being "below" or "beneath" other elements or features will be oriented "above" the elements or features. Therefore, the exemplary term "below" can include both below and above. Objects may also have other orientations (rotated 90 degrees or other orientations) and the spatially relative terms used herein should be interpreted accordingly.

[0050] In this document, the terms "first", "second", etc. are used to distinguish two different elements or parts, and are not used to limit specific positions or relative relationships. In other words, in some embodiments, the terms "first", "second", etc. can also be interchangeable with each other.

[0051] like Figure 1 The figure shows a schematic flow diagram of the olefin catalytic cracking process for producing propylene according to the present invention. The olefin feedstock 1 exchanges heat with the feed heat exchanger 14 at the bottom of the separator 5, is heated in the heating furnace 2, and then mixed with hydrogen before entering the olefin cracking reactor 3. The olefin cracking reactor is topped with the separator 5. The olefin cracking reactor comprises a catalyst bed and a gas distribution chamber. The catalyst bed has a diameter-to-height ratio (calculated based on the maximum equivalent diameter of the rectangle, where the height is the total height of the catalyst bed) of 2:1 to 10:1, preferably 3:1 to 6:1. The catalyst bed height is 100 to 5000 mm, preferably 200 to 1000 mm. The catalyst bed forms the olefin cracking reaction zone 4. The feedstock and hydrogen enter the olefin cracking reaction zone 4 through the gas distributor, where a cracking reaction occurs. The cracking products continue to flow upward into the separator 5 above the reactor.

[0052] After exchanging heat with the feedstock at the bottom of the separator, the catalytic cracking product is separated into a C3 and below fraction 6, a crude C4 fraction 7, and a C5 and above fraction 8. The crude C3 and below fraction 6 flows out of the top of the separator in the vapor phase, while the crude C4 fraction 7 and the C5 and above fraction 8 are withdrawn from the separator sideline. The sideline withdrawal temperature for the C4 fraction is 20°C to 60°C, while the sideline withdrawal temperature for the C5 and above fraction is 80°C to 150°C. The C4 fraction 7 withdrawn from the sideline passes through a cooler 9 and enters a gas-liquid separator 10. A C3 and below fraction 11 is discharged from the top of the gas-liquid separator 10, and a C4 fraction 12 is separated at the bottom. 20% to 95% of the separated C4 fraction is recycled into the reactor as the recycle C4 fraction 13.

[0053] Further, in one or more exemplary embodiments of the present invention, the olefin cracking reactor may be a horizontal storage tank, such as Figure 1 As shown, the axial direction is arranged in the horizontal direction, and the ends of the horizontal storage tank are provided with heads. Further, in one or more exemplary embodiments of the present invention, the olefin cracking reactor can also be a flat cylindrical tank, the axial direction of which is arranged in the longitudinal direction.

[0054] Furthermore, in one or more exemplary embodiments of the present invention, the shape of the partition matches the bottom of the olefin cracking reactor. When the olefin cracking reactor is a horizontal storage tank, the partition is a circular partition, such as Figure 2 and Figure 3 As shown; when the olefin cracking reactor is a flat cylindrical tank, the multiple partitions are coaxial annular partitions, such as Figures 4 to 6 As shown. Furthermore, in one or more exemplary embodiments of the present invention, multiple circular holes are distributed on each partition. Furthermore, in one or more exemplary embodiments of the present invention, multiple partitions can extend upward to the catalyst bed, and the partitions at the bottom that do not contact the catalyst bed have an open porosity of less than 70%. A lower open porosity helps increase resistance, allowing hydrogen to enter the catalyst bed as much as possible, further serving as a gas distributor. The open porosity of the partitions within the catalyst bed is greater than 50%, which helps to more fully utilize the catalyst.

[0055] Further, in one or more exemplary embodiments of the present invention, the ratio of the cross-sectional area of ​​the separator to that of the olefin cracking reactor is 1:1.2 to 1:10, preferably 1:2 to 1:10.

[0056] The following examples further illustrate the method for preparing propylene by catalytic cracking of olefins and the effects of the invention. Detailed implementation methods and specific operating procedures are given in the examples based on the technical solutions of the present invention, but the scope of protection of the present invention is not limited to the following specific examples.

[0057] Unless otherwise specified, the experimental methods in the following examples are conventional methods in the art. Example 1

[0058] Using the present invention Figure 1The flow chart shown uses the C4 fraction from vinyl etherification as the feedstock, with properties shown in Table 1. The feedstock undergoes heat exchange with the catalytic cracking product at the bottom of the separator, then undergoes heating in a furnace before entering the olefin cracking reactor. The separator is located above the reactor. The olefin cracking reactor contains an olefin cracking reaction zone consisting of a catalyst bed. The reactor is loaded with ZSM-5 molecular sieve catalyst (2 mm diameter, 8-12 mm length, acid content 0.27 mmol / g). Specific catalyst properties are shown in Table 2. The catalyst bed has an equivalent diameter-to-height ratio of 4:1. The olefin cracking reactor contains a circular catalyst bed with a height of 800 mm. Four annular baffles are installed within the catalyst bed. These baffles have multiple holes and extend upward to the catalyst bed. The baffles below the catalyst bed have an open porosity of 40% and those within the catalyst bed have an open porosity of 70%. The cross-sectional area ratio of the separator to the olefin cracking reactor is 1:7.

[0059] The crude oil undergoes cracking reaction in the olefin cracking reactor, and the cracking products continue to flow upward into the separator above the reactor.

[0060] The catalytic cracking products are separated in the separator into a C3 and below fraction, a crude C4 fraction, and a C5 and above fraction. The crude C3 and below fraction flows out of the top of the separator as a vapor, while the crude C4 fraction and the C5 and above fraction are withdrawn from the separator sideline. The sideline withdrawal temperature for the C4 fraction is 20°C to 60°C, while the sideline withdrawal temperature for the C5 and above fraction is 80°C to 150°C. The C4 fraction withdrawn from the sideline passes through a cooler and is cooled to -20°C to -10°C before entering the gas-liquid separator. The C3 and below fraction is discharged from the top of the gas-liquid separator, while the C4 fraction is separated at the bottom. 50% of the separated C4 fraction is recycled back to the reactor as the recycle C4 fraction.

[0061] The specific operating conditions are shown in Table 3. The reaction results are shown in Table 4. Example 2

[0062] This example differs from Example 1 in that the feedstock used is a C4 fraction from a catalytic cracking unit, the properties of which are shown in Table 1. The catalyst bed in the olefin cracking reactor has an equivalent diameter-to-height ratio of 5:1, and the catalyst bed contains six baffles. The baffles are provided with multiple holes; the baffles extend upward into the catalyst layer. The baffles below the catalyst layer have an open porosity of 30%, while the baffles within the catalyst layer have an open porosity of 80%. The ratio of the cross-sectional area of ​​the separator to that of the olefin cracking reactor is 1:8. The reaction conditions are shown in Table 3; all other conditions are the same as in Example 1. Example 3

[0063] This example differs from Example 1 in that the raw materials used are C4 and C5 byproducts from a methanol-to-olefins (MTO) unit, with properties shown in Table 1. The catalyst bed equivalent diameter-to-height ratio is 6:1. The cross-sectional area ratio of the separator to the olefin cracking reactor is 1:2. The reaction conditions are shown in Table 3; all other conditions are the same as in Example 1. Example 4

[0064] This embodiment differs from embodiment 1 in that the catalyst bed of the olefin cracking reactor has an equivalent diameter-to-height ratio of 6:1. The remaining conditions are the same as those of embodiment 1. Example 5

[0065] This embodiment differs from Example 1 in that the catalyst bed of the olefin cracking reactor has an equivalent diameter-to-height ratio of 8:1. The remaining conditions are the same as those of Example 1. Example 6

[0066] The same as Example 1, except that the diameter-to-height ratio of the catalyst bed in the olefin cracking reactor is 1:3.

[0067] Comparative Example 1

[0068] The same method as in Example 1 was used, except that a separate separation device was installed above the olefin cracking reactor instead of a separator. The olefin cracking reactor was loaded with the same ZSM-5 molecular sieve catalyst as in Example 1, with a catalyst bed equivalent diameter-to-height ratio of 4:1. The product from the reactor was compressed to 2.0 MPa by a compressor before entering the separation device for product separation. The cross-sectional area ratio of the separate separation device to the olefin cracking reactor was the same as in Example 1. The operating conditions of the separate separation device were the same as those for the separator in Example 1.

[0069] Comparative Example 2

[0070] A conventional olefin catalytic cracking process for producing propylene was employed. The feedstock flowed from top to bottom into a conventional olefin cracking reactor. The catalyst bed had an equivalent diameter-to-height ratio of 1:5 and a catalyst bed height of 5000 mm. The cracking product was compressed to 2.0 MPa by a compressor and then separated in a series of separation towers before being delivered as the product. The cross-sectional area ratio of the separation tower to the reactor was 1:2. The operating conditions of the separation tower were identical to those of the separator in Example 1. All other process conditions were the same as in Example 1.

[0071] The properties of the raw materials of the above embodiments and comparative examples are shown in Table 1, the properties of the ZSM-5 molecular sieve catalyst are shown in Table 2, the process conditions are shown in Table 3, and the product distribution of the embodiments and comparative examples is shown in Table 4.

[0072] Table 1 Properties of raw materials

[0073]

[0074] Table 2 ZSM-5 molecular sieve catalyst properties

[0075]

[0076] Table 3 Example and Comparative Example operating process conditions

[0077]

[0078] Table 4 Example and Comparative Example reaction results

[0079]

[0080] From the results in Table 4, using the present application, the butene conversion is high, and the propylene and ethylene yields are significantly higher than the comparative examples.

Claims

1. A method for preparing propylene by catalytic cracking of olefins, characterized in that: An olefin cracking reactor is used, and a separator is set on the top of the olefin cracking reactor, comprising the following steps: (1) Olefin-rich feedstock enters the bottom of the reactor, passes through the gas distributor and enters the catalyst bed. After catalytic cracking reaction occurs in the catalyst bed, the catalytic cracking products continue to flow upward and enter the separator above the reactor; (2) The catalytic cracking products are separated into C3 and below fractions, C4 fractions, and C5 and above fractions in the separator; The diameter-to-height ratio of the catalyst bed is 2:1 to 10:1; the height of the catalyst bed is 100 to 5000 mm; The operating conditions of the catalytic cracking reaction are as follows: reaction temperature is 400℃~600℃, reaction pressure is 0.1MPa~0.8MPa, weight space velocity is 5h -1 ~50h -1 .

2. The method according to claim 1, characterized in that The diameter-to-height ratio of the catalyst bed is 3:1 to 6:

1.

3. The method according to claim 1, characterized in that The catalyst bed height is 200-1000 mm.

4. The method according to claim 1, wherein The olefin-rich raw material in step (1) is heated to 410° C. to 610° C. and then enters the reactor. Before being heated, the raw material is first heat-exchanged with the catalytic cracking product at the bottom of the separator.

5. The method according to claim 1, characterized in that The operating conditions of the separator above the reactor are the same as those of the catalytic cracking reaction.

6. A catalytic cracking device, characterized in that: The device comprises an olefin cracking reactor and a separator arranged on the top of the olefin cracking reactor; the olefin cracking reactor comprises, from top to bottom, an olefin cracking reaction zone and a gas distributor; the olefin cracking reactor is rectangular or circular, and the diameter-to-height ratio of the catalyst bed in the olefin cracking reactor is 2:1 to 10:1; the height of the catalyst bed in the olefin cracking reactor is 100 to 5000 mm.

7. The device according to claim 6, characterized in that The diameter-to-height ratio of the catalyst bed in the olefin cracking reactor is 3:1 to 6:

1.

8. The device according to claim 6, characterized in that The height of the catalyst bed in the olefin cracking reactor is 200 to 1000 mm.

9. The device according to claim 6, characterized in that The olefin cracking reactor is a horizontal storage tank with its axial direction arranged in the transverse direction and heads provided at both ends of the horizontal storage tank, or the olefin cracking reactor is a flat cylindrical tank with its axial direction arranged in the longitudinal direction.

10. The device according to claim 6, characterized in that A plurality of partitions are arranged in parallel in the vertical direction in the middle of the gas distributor, and the plurality of partitions divide the gas distributor into a plurality of air inlet units. At least one feed port is arranged at the bottom of each air inlet unit.

11. The device according to claim 10, characterized in that The plurality of partitions are coaxial annular partitions.

12. The device according to claim 10, characterized in that A plurality of partitions extend upward to the olefin cracking reaction zone, the opening rate of the partitions below the olefin cracking reaction zone is less than 70%, and the opening rate of the partitions in the olefin cracking reaction zone is greater than 50%.

13. The device according to claim 6, characterized in that The ratio of the cross-sectional area of ​​the separator to that of the olefin cracking reactor is 1:1.2 to 1:

10.

14. The device according to claim 13, characterized in that The ratio of the cross-sectional area of ​​the separator to that of the olefin cracking reactor is 1:2 to 1:

10.

15. The device according to claim 6, characterized in that A feed heat exchanger is provided in the separator, in which the cracking product and the raw material exchange heat.

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