A method for olefin cracking to increase propylene production, a system for increasing propylene production and application

Abstract

The application provides a method and system for increasing propylene yield, comprising the step of passing an olefin raw material through a multi-stage bed olefin cracking reactor to obtain a light stream rich in propylene, a C4-C6 medium stream, and a heavy stream of C7 and above. The first stage, the second stage and the third stage of the multi-stage bed are filled with different silicon-aluminum molecular sieve catalysts. According to the reaction characteristics of different beds in the multi-stage bed olefin cracking reactor, the method of filling each bed with olefin cracking catalysts with different catalytic properties can improve the utilization efficiency of the olefin raw material in different beds. Compared with the traditional multi-stage bed reactor which only improves the service life of the catalyst, the application can significantly improve the yield of propylene.

Description

Technical Field

[0001] This invention belongs to the field of propylene preparation technology, specifically relating to a method, system and application of propylene production enhancement through olefin cracking. Background Technology

[0002] Propylene is one of the important basic organic chemical raw materials, mainly used in the production of polypropylene, cumene, acrylonitrile, acrylic acid, and many other products. In recent years, driven by strong demand for propylene derivatives, the market demand for propylene has grown faster than that for ethylene, with polypropylene and alkyl aromatic compounds being the fastest-growing propylene derivatives in terms of demand.

[0003] Currently, propylene production mainly relies on ethylene plant co-products and refinery byproducts. Approximately 70% of the world's propylene comes from steam cracking units as co-products and conventional catalytic cracking units in refineries. However, there is limited room for further increasing propylene production through these two processes. New technologies for increasing propylene production include propane dehydrogenation, olefin disproportionation, olefin cracking, methanol-to-olefins (MTO), and methanol-to-propylene (MTO). Propane dehydrogenation technology limits propylene production due to raw material availability and cost, while olefin disproportionation technology has a long process route, requires significant investment, and results in high production costs.

[0004] In the processes of steam cracking, catalytic cracking, and methanol-to-olefins production, in addition to producing the main products of ethylene and propylene, a certain amount of C4 and above fractions are also produced as byproducts. These C4 and above fractions are rich in olefin components, and their efficient utilization has become a major issue for petrochemical enterprises.

[0005] Traditional utilization of C4 hydrocarbons includes both fuel and chemical applications. Fuel utilization primarily involves liquefied petroleum gas (LPG), MTBE, and alkylated oils, while chemical utilization mainly utilizes the separable components in C4 fractions to produce various related derivatives. In addition, to increase the added value of C4 and higher fractions, new technologies have emerged, such as olefin cracking to enhance propylene production. These technologies not only increase the added value of C4 fractions but also meet the growing market demand for propylene.

[0006] Olefin catalytic cracking technology is a process technology that uses C4 and above olefins as feedstock and utilizes catalysts with unique shape selectivity and acidity to achieve catalytic cracking and increase propylene production. Its advantages include a flexible feedstock range, allowing the use of C4 and above olefins as byproducts from FCC units, steam cracking units, or MTO units. Olefin cracking technology has become an important bridge connecting petroleum and coal resources with propylene products in the petrochemical and coal chemical industries.

[0007] Chinese patent CN1274342A reports a method for producing ethylene and propylene from olefin feedstocks via catalytic conversion. The catalyst used is a mesoporous zeolite with a SiO2 / Al2O3 molar ratio of 200 to 5000. However, it is a molecular sieve that is essentially proton-free. At least one metal selected from Group IB elements is also required to modify the catalyst.

[0008] Chinese patent CN103030501A discloses a method for producing propylene, using C4 and above olefins as raw materials to generate propylene over a catalyst. The catalyst, by weight fraction, comprises 48-89 parts of HZSM-5 molecular sieve with a SiO2 / Al2O3 molar ratio of 200-800, 0.1-2 parts of at least one element from Group VIII of the periodic table, and 10-50 parts of a binder selected from at least one of silica or alumina. This patent details the preparation conditions and catalytic performance of the molecular sieve catalyst, but does not mention the catalyst loading method in the reactor, and the propylene yield cannot meet the growing demand for propylene products.

[0009] Chinese patent CN1915929A discloses a method for producing propylene from C4 and higher olefins through cracking. The method involves passing olefin feedstock through a fixed-bed reactor comprising at least two catalyst beds to generate an effluent containing propylene. The reactor consists of a feed pipe, a gas distributor, a first catalyst bed, an intermediate heat exchanger, a second catalyst bed, and an outlet pipe. Both the first and second catalyst beds in this patented reactor use ZSM-5 molecular sieve catalysts, and an intermediate heat exchanger is arranged within the reactor to maximize propylene yield and extend the catalyst stabilization period. However, the reactor design in this patent is relatively complex, and the propylene yield is low, only in the range of 21.0% to 23.0%.

[0010] Currently, olefin catalytic cracking technology typically uses a single-bed fixed-bed reactor. The reaction process mainly involves the feed olefins being heated into high-temperature gaseous olefins via feed and discharge heat exchangers before entering the fixed-bed reactor and reacting with the catalyst. The gaseous products are cooled by the feed and discharge heat exchangers and then enter the compressor, where they are compressed and then sent to the product separation system. Summary of the Invention

[0011] The technical problem to be solved by the present invention is the low yield of propylene as the target product in the catalytic cracking of C4 and above olefins to produce propylene in the prior art. The present invention provides a method for increasing propylene production by cracking olefins, which has the characteristic of high propylene selectivity.

[0012] One objective of this invention is to provide a method for increasing propylene production, comprising passing olefin feedstock through a multi-stage bed olefin cracking reactor to obtain a light stream containing propylene, a C4-C6 medium stream, and a heavy stream containing C7 and above, wherein the first, second, and third stages of the multi-stage bed olefin cracking reactor are filled with different silica-alumina molecular sieve catalysts.

[0013] In this invention, the multi-bed olefin cracking reactor is sequentially loaded with olefin cracking catalysts of different catalytic properties in the first, second, and third bed sections from the feed direction. In a preferred embodiment, the SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 20–800, preferably 50–500; the silica-alumina molecular sieve catalysts in the first, second, and third bed sections are selected from ZSM-5 molecular sieve, ZSM-11 molecular sieve, or ZSM-5 / ZSM-11 eutectic molecular sieve, respectively; in a more preferred embodiment, the silica-alumina molecular sieve catalysts in the first and third bed sections are selected from ZSM-5 molecular sieve or ZSM-11 molecular sieve; and the silica-alumina molecular sieve catalyst in the second bed section is a ZSM-5 / ZSM-11 eutectic molecular sieve.

[0014] In a preferred embodiment, the method for increasing propylene production specifically includes the following steps: heating the olefin feedstock and then feeding it into a multi-bed olefin cracking reactor, where it reacts under the action of a catalyst. During the reaction, the products from each bed and the olefin feedstock from the feed side inlet of the next bed are fed into the next bed to continue the reaction until the last bed. The products obtained from the reaction in the last bed are separated to obtain a light stream containing propylene, a medium stream of C4 to C6, and a heavy stream of C7 and above. The medium stream of C4 to C6 is returned to the olefin feedstock inlet of the first bed and incorporated into the olefin feedstock for further reaction.

[0015] According to a specific embodiment of the present invention, the method for increasing propylene production includes: employing a multi-stage bed olefin cracking reactor, the multi-stage bed reactor including a first-stage bed inlet for olefin feedstock, a second-stage bed inlet for olefin feedstock, and a third-stage bed inlet for olefin feedstock; a first stream of olefin feedstock entering from the first-stage bed inlet reacts in the first-stage bed; the material obtained from the first-stage bed reaction merges with a second stream of olefin feedstock entering from the second-stage bed inlet and enters the second-stage bed reaction; the material obtained from the second-stage bed reaction merges with a third stream of olefin feedstock entering from the third-stage bed inlet and enters the third-stage bed reaction; the material obtained from the third-stage bed reaction flows out of the olefin cracking reactor; the first-stage bed, the second-stage bed, and the third-stage bed are filled with olefin cracking catalysts with different catalytic properties; the reaction streams are separated to obtain a light stream rich in propylene, a medium stream of C4-C6, and a heavy stream of C7 and above, wherein the medium stream of C4-C6 is returned to the first-stage bed inlet of the reactor.

[0016] In a further preferred embodiment:

[0017] The aforementioned silicon-aluminum molecular sieve catalyst can be selected from silicon-aluminum molecular sieve catalysts with a commonly used silicon-aluminum ratio range in the art. Preferably, the SiO2 / Al2O3 molar ratio of the silicon-aluminum molecular sieve catalyst is 20 to 800, more preferably 50 to 500.

[0018] The olefin feedstock is selected from at least one of the following: C4 and above fractions produced by an FCC unit, C4 and above fractions produced by an MTO unit, and C4 and above fractions produced by an ethylene unit.

[0019] The heating of the olefin feedstock includes heating the olefin feedstock sequentially through a heat exchanger and a heating furnace. Preferably, the temperature of the olefin feedstock is 50-60°C; the temperature of the olefin feedstock after heating is 450-650°C, preferably 500-600°C.

[0020] The multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor.

[0021] The multi-stage bed olefin cracking reactor includes at least 3 bed stages, preferably 3 to 5 stages; the catalyst in the 4th to 5th stages of the reactor (excluding stages 1 to 3) is not particularly limited and can be any silica-alumina molecular sieve catalyst.

[0022] In the multi-stage bed olefin cracking reactor, the reaction process conditions for each bed are: reaction temperature 500–600°C and reaction gas weight hourly space velocity 2–40 h⁻¹. -1 The catalyst bed pressure drop is 0–0.2 MPa.

[0023] The product obtained from the final bed reaction needs to be cooled, compressed, and then separated into its components.

[0024] A second objective of this invention is to provide a system for increasing propylene production, for implementing the above-described method for increasing propylene production.

[0025] Specifically, the system includes a raw material storage tank, a heat exchanger, a heating furnace, a multi-bed olefin cracking reactor, and a separation system, which are connected in sequence by material pipelines. The separation system is equipped with a light stream pipeline rich in propylene, a medium stream pipeline for C4 to C6, and a heavy stream pipeline for C7 and above. The medium stream pipeline for C4 to C6 is connected to the raw material input pipeline of the heat exchanger.

[0026] Furthermore, the multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor;

[0027] The multi-stage bed olefin cracking reactor comprises at least three vertically arranged reaction beds, preferably three to five; from the feed direction, the beds are sequentially arranged as a first bed, a second bed, a third bed, and so on. The first, second, and third beds are filled with different silica-alumina molecular sieve catalysts. Preferably, the silica-alumina molecular sieve catalysts in the first, second, and third beds are independently selected from ZSM-5 molecular sieve, ZSM-11 molecular sieve, or ZSM-5 / ZSM-11 eutectic molecular sieve. More preferably, the silica-alumina molecular sieve catalysts in the first and third beds are selected from ZSM-5 or ZSM-11 molecular sieves, and the silica-alumina molecular sieve catalyst in the second bed is a ZSM-5 / ZSM-11 eutectic molecular sieve. The SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 20 to 800, preferably 50 to 500.

[0028] In the multi-stage bed olefin cracking reactor, each bed except the first bed is provided with a feed side inlet, which is connected to the raw material output pipeline of the heating furnace; a heat exchanger and a compressor are provided between the multi-stage bed olefin cracking reactor and the separation system.

[0029] A third objective of this invention is to apply the above-described method or system for increasing propylene production to olefin cracking for increasing propylene production.

[0030] This invention addresses the reaction characteristics of different beds in a multi-bed olefin cracking reactor. The extent of various reactions in each bed varies depending on the composition of the reactants, requiring optimized catalysts. In this invention, olefin cracking catalysts with different catalytic properties are loaded into each bed, thereby improving the utilization efficiency of olefin-rich feedstocks in different beds. After the olefin feedstock enters the first bed reactor, it contacts the bed packed with ZSM-5 catalyst, undergoing olefin cracking to produce hydrocarbons with different carbon numbers as reaction products, which then enter the second bed. Since the reaction is endothermic, the temperature of the products decreases, and they mix and react with the second olefin feedstock in the second bed. Part of the second olefin feedstock undergoes its own cracking reaction, while another part undergoes polymerization with the products from the previous bed. Due to the lower reaction temperature and the increased variety of reactions, the use of a ZSM-5 / ZSM-11 eutectic molecular sieve with both structures in the second bed can exert a synergistic effect, promoting the propylene production pathway. The resulting products enter the third bed, contacting the third olefin feedstock. Using ZSM-11 as the main catalyst, it reacts with the products from the previous bed in polymerization and cracking reactions, further reducing the content of hydrocarbons with different carbon numbers, thereby promoting propylene production and extending the catalyst's lifespan. Using different catalysts and a eutectic molecular sieve as an intermediate bed, a gradual structural change plays a synergistic and transitional role, reducing the occurrence of uncontrollable reactions caused by structural abrupt changes.

[0031] Compared to traditional multi-bed reactors, this invention employs a uniquely designed multi-bed olefin cracking reactor, which not only extends catalyst lifespan but also significantly improves propylene yield. By utilizing a multi-bed olefin cracking reactor and loading each bed with olefin cracking catalysts of different catalytic properties, this invention effectively increases propylene production while also improving feedstock throughput, providing inspiration for large-scale plant development. The propylene production enhancement system provided by this invention is simple in design, safe, and reliable, effectively addressing the demand for higher propylene yields in actual production. Attached Figure Description

[0032] Figure 1 This invention provides a method for increasing propylene production through olefin cracking. In the figure: A. Feed / Discharge heat exchanger; B. Heating furnace; C. Multi-stage bed olefin cracking reactor; D. Compressor; E. Separation system; F. Feed tank; 1. Main olefin feed pipeline; 2. Main feed pipeline; 3. Hot end outlet pipeline of heat exchanger; 4. First stage bed inlet pipeline of olefin feed; 5. Second stage bed inlet pipeline of olefin feed; 6. Third stage bed inlet pipeline of olefin feed; 7. Reactor outlet pipeline; 8. Cold end outlet pipeline of heat exchanger; 9. Compressor outlet pipeline; 10. C4-C6 intermediate stream pipeline; 11. Propylene product pipeline; 12. Other product pipelines. Detailed Implementation

[0033] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0034] In one specific embodiment of the present invention, the following is adopted: Figure 1 The specific process of using the system shown to increase propylene production is as follows:

[0035] Olefin-rich feedstock at 50-60℃ enters the boundary area via the olefin feedstock main pipeline 1, where it mixes with the circulating stream (C4-C6 intermediate stream) 10 from the E separation system and flows into the 2 feedstock main pipeline. It then enters the A feed-in / outfeed heat exchanger, passes through the B heater, and is heated to the reaction temperature. Subsequently, under flow control, the feedstock enters the C multi-stage bed olefin cracking reactor via pipelines 4, 5, and 6. Feedstock flowing in via pipeline 4 enters the reactor from the upper part of the first stage bed, which is packed with one type of molecular sieve catalyst. Feedstock flowing in via pipeline 5 enters the reactor from the upper part of the second stage bed, which is packed with another type of eutectic molecular sieve catalyst. Feedstock flowing in via pipeline 6 enters the reactor from the upper part of the third stage bed, which is packed with yet another type of molecular sieve catalyst. Feedstock from pipeline 5 contacts the reaction products from the first stage bed, reacting in the second stage bed. The resulting product then contacts the olefin-rich feedstock from pipeline 6 before passing through the third stage bed. The total product is cooled by the A feed heat exchanger after exiting the reactor 7 outlet pipeline and then pressurized by the D compressor before entering the E separation system. The medium stream of C4 to C6 is returned to the 2 feed main pipeline as a circulating stream, the light stream rich in propylene is discharged from the 11 propylene product pipeline, and the heavy stream of C7 and above is discharged from the 12 other product pipeline.

[0036] Example 1:

[0037] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown. Olefin-rich feedstock at 50℃ enters the boundary area via olefin feedstock main line 1, where it mixes with C4-C6 intermediate stream 10 from separation system E and flows into feedstock main line 2. It then enters inlet / outlet heat exchanger A, and passes through heater B, where it is heated to 560℃. The feedstock then enters multi-bed olefin cracking reactor C via lines 4, 5, and 6, with the weight hourly space velocity (WHSV) of each bed controlled at 25 h⁻¹. -1The pressure drop is 0.15 MPa. Raw materials flowing in through pipeline 4 enter the reactor from the top of the first bed, which is packed with ZSM-5 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 5 enter the reactor from the top of the second bed, which is packed with ZSM-5 / ZSM-11 eutectic molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 6 enter the reactor from the top of the third bed, which is packed with ZSM-11 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). The raw materials from pipeline 5 contact the reaction products from the first bed, and the reaction occurs in the second bed at 545°C. The resulting products then contact the olefin-rich raw materials from pipeline 6 before passing through the third bed, where the reaction occurs at 530°C. The total product, after being cooled by the feed heat exchanger (A) via the reactor outlet pipeline (7), enters the compressor (D) for pressurization and then enters the separation system (E). The C4-C6 medium stream is returned to the feed main pipeline (2) as circulating stream (10). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy streams are discharged through the other products pipeline (12). The propylene yield is 56%.

[0038] Example 2:

[0039] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown. Olefin-rich feedstock at 50℃ enters the boundary area via olefin feedstock main line 1, where it mixes with C4-C6 intermediate stream 10 from separation system E and flows into feedstock main line 2. It then enters inlet / outlet heat exchanger A, and passes through heater B, where it is heated to 560℃. The feedstock then enters multi-bed olefin cracking reactor C via lines 4, 5, and 6, with the weight hourly space velocity (WHSV) of each bed controlled at 25 h⁻¹. -1The pressure drop is 0.15 MPa. Raw materials flowing in through pipeline 4 enter the reactor from the top of the first bed, which is filled with ZSM-11 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 5 enter the reactor from the top of the second bed, which is filled with ZSM-5 / ZSM-11 eutectic molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 6 enter the reactor from the top of the third bed, which is filled with ZSM-5 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). The raw materials from pipeline 5 contact the reaction products from the first bed, and the reaction occurs in the second bed at 545°C. The resulting products then contact the olefin-rich raw materials from pipeline 6 before passing through the third bed, where the reaction occurs at 530°C. The total product, after being cooled by the feed heat exchanger (A) via the reactor outlet pipeline (7), enters the compressor (D) for pressurization and then enters the separation system (E). The C4-C6 medium stream is returned to the feed main pipeline (2) as circulating stream (10). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy streams are discharged through the other products pipeline (12). The propylene yield is 53%.

[0040] Example 3:

[0041] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown. Olefin-rich feedstock at 50℃ enters the boundary area via olefin feedstock main line 1, where it mixes with C4-C6 intermediate stream 10 from separation system E and flows into feedstock main line 2. It then enters inlet / outlet heat exchanger A, and passes through heater B, where it is heated to 560℃. The feedstock then enters multi-bed olefin cracking reactor C via lines 4, 5, and 6, with the weight hourly space velocity (WHSV) of each bed controlled at 25 h⁻¹. -1The pressure drop is 0.15 MPa. Raw materials flowing in through pipeline 4 enter the reactor from the top of the first bed, which is packed with ZSM-5 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 360). Raw materials flowing in through pipeline 5 enter the reactor from the top of the second bed, which is packed with ZSM-5 / ZSM-11 eutectic molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 6 enter the reactor from the top of the third bed, which is packed with ZSM-11 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). The raw materials from pipeline 5 contact the reaction products from the first bed, and the reaction occurs in the second bed at 545°C. The resulting products then contact the olefin-rich raw materials from pipeline 6 before passing through the third bed, where the reaction occurs at 530°C. The total product, after being cooled by the feed heat exchanger (A) via the reactor outlet pipeline (7), enters the compressor (D) for pressurization and then enters the separation system (E). The C4-C6 medium stream is returned to the feed main pipeline (2) as circulating stream (10). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy streams are discharged through the other products pipeline (12). The propylene yield is 54%.

[0042] Example 4:

[0043] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown. Olefin-rich feedstock at 50℃ enters the boundary area via olefin feedstock main line 1, where it mixes with C4-C6 intermediate stream 10 from separation system E and flows into feedstock main line 2. It then enters inlet / outlet heat exchanger A, and passes through heater B, where it is heated to 560℃. The feedstock then enters multi-bed olefin cracking reactor C via lines 4, 5, and 6, with the weight hourly space velocity (WHSV) of each bed controlled at 25 h⁻¹. -1The pressure drop is 0.15 MPa. Raw materials flowing in through pipeline 4 enter the reactor from the top of the first bed, which is packed with ZSM-5 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). Raw materials flowing in through pipeline 5 enter the reactor from the top of the second bed, which is packed with ZSM-5 / ZSM-11 eutectic molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 100). Raw materials flowing in through pipeline 6 enter the reactor from the top of the third bed, which is packed with ZSM-11 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). The raw materials from pipeline 5 contact the reaction products from the first bed, and the reaction occurs in the second bed at 545°C. The resulting products then contact the olefin-rich raw materials from pipeline 6 before passing through the third bed, where the reaction occurs at 530°C. The total product, after being cooled by the feed heat exchanger (A) via the reactor outlet pipeline (7), enters the compressor (D) for pressurization and then enters the separation system (E). The C4-C6 medium stream is returned to the feed main pipeline (2) as circulating stream (10). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy streams are discharged through the other products pipeline (12). The propylene yield is 54%.

[0044] Comparative Example 1:

[0045] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve catalyst used in each bed section is 200. The olefin-rich feedstock at 50℃ enters the boundary area via the olefin-rich feedstock main feed line 1, mixes with the circulating stream 10, and then enters the feed heat exchanger A via the olefin-rich feedstock main feed line 2. After passing through the heater B, the feedstock reaches 560℃ after two heating cycles. It then enters the reactor from the top of each bed section of the multi-bed olefin reactor C via lines 4, 5, and 6, respectively. The weight hourly space velocity (WHSV) of each bed section is controlled at 25 h⁻¹. -1 The pressure drop is 0.15 MPa. The temperatures of the second and third beds are 545℃ and 530℃, respectively. Olefin cracking occurs in contact with beds packed with the same ZSM-5 molecular sieve catalyst in each section. The total product is cooled by the A feed heat exchanger after exiting the reactor (reactor 7) and then pressurized by the D compressor before entering the E separation system. The C4-C6 medium stream is returned as a recycle stream to the 2 feed main line, the propylene-rich light stream is discharged through the 11 propylene product line, and the C7 and higher heavy streams are discharged through the 12 other products line. The propylene yield is 47%.

[0046] Comparative Example 2:

[0047] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1As shown, the SiO2 / Al2O3 molar ratio of the ZSM-11 molecular sieve catalyst used in each bed section is 200. The olefin-rich feedstock at 50℃ enters the boundary area via the olefin-rich feedstock main feed line 1, mixes with the circulating stream 10, and then enters the feed-discharge heat exchanger A via the olefin-rich feedstock main feed line 2. After passing through the heater B, the feedstock reaches 560℃ after two heating cycles. It then enters the reactor from the top of each bed section of the multi-bed olefin reactor C via lines 4, 5, and 6, respectively. The weight hourly space velocity (WHSV) of each bed section is controlled at 25 h⁻¹. -1 The pressure drop is 0.15 MPa. The temperatures of the second and third beds are 545℃ and 530℃, respectively. These beds, each packed with the same ZSM-11 molecular sieve catalyst, react with the olefins to undergo cracking. The total product exits from reactor 7 via the outlet pipeline, is cooled by the A feed heat exchanger, then enters compressor D for pressurization before entering separation system E. The C4-C6 medium stream is returned as a recycle stream to the 2 feed main pipeline, the propylene-rich light stream is discharged from the 11 propylene product pipeline, and the C7 and higher heavy streams are discharged from the 12 other products pipeline. The propylene yield is 37%.

[0048] Comparative Example 3:

[0049] A schematic diagram of the process flow using a three-stage bed feeding method is shown below. Figure 1 As shown, the SiO2 / Al2O3 molar ratio of the ZSM-5 / ZSM-11 eutectic molecular sieve catalyst used in each bed section is 200. Olefin-rich feedstock at 50℃ enters the boundary area via the 1 olefin-rich feedstock main feed line, mixes with the 10 circulating stream, and then enters the A feed-in / outlet heat exchanger via the 2 olefin-rich feedstock main feed line. After passing through the B heating furnace, the feedstock reaches 560℃ after two heating cycles. It then enters the reactor from the top of each bed section of the C multi-bed olefin reactor via pipelines 4, 5, and 6, respectively, with the weight hourly space velocity (WHSV) of each bed section controlled at 25 h⁻¹. -1 The pressure drop is 0.15 MPa. The temperatures of the second and third beds are 545℃ and 530℃, respectively. Olefin cracking occurs in contact with beds packed with the same ZSM-5 / ZSM-11 eutectic molecular sieve catalyst in each section. The total product is cooled by the A feed heat exchanger after exiting the reactor (reactor 7) and then pressurized by the D compressor before entering the E separation system. The C4-C6 medium stream is returned as a recycle stream to the 2 feed main line, the propylene-rich light stream is discharged through the 11 propylene product line, and the C7 and higher heavy streams are discharged through the 12 other products line. The propylene yield is 40%.

[0050] Comparative Example 4:

[0051] The process flow adopting a three-stage bed feeding method and Figure 1Similar to the diagram, but without pipelines 5 and 6. Olefin-rich feedstock at 50°C enters the boundary area via olefin feedstock 1, mixing with C4-C6 middle stream 10 from separation system E before flowing into feedstock 2. It then enters inlet / outlet heat exchanger A, passes through heater B, and is heated to 560°C. The feedstock then enters multi-bed olefin cracking reactor C via pipeline 4, with the weight hourly space velocity (WHSV) of each bed controlled at 25 h⁻¹. -1 With a pressure drop of 0.15 MPa, the raw material flowing in through pipeline 4 enters the reactor from the top of the first bed, reacting with the first bed packed with ZSM-5 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). It then passes through a second bed packed with ZSM-5 / ZSM-11 eutectic molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200) and a third bed packed with ZSM-11 molecular sieve catalyst (SiO2 / Al2O3 molar ratio = 200). The reaction products from the first bed react in the second bed at 545°C, and the resulting products then pass through the third bed, where they react again at 530°C. The total product, after being cooled by the feed heat exchanger (A) via the reactor outlet pipeline (7), enters the compressor (D) for pressurization and then enters the separation system (E). The C4-C6 medium stream is returned to the feed main pipeline (2) as circulating stream (10). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy streams are discharged through the other products pipeline (12). The propylene yield is 25%.

[0052] Table 1. Catalyst types and propylene yields used in Examples 1-4 and Comparative Examples 1-9

[0053]

[0054] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for increasing propylene production, comprising the following steps: After heating, the olefin feedstock enters a multi-bed olefin cracking reactor and reacts under the action of a silica-alumina molecular sieve catalyst. During the reaction, the products from each bed stage and the olefin feedstock from the feed side inlet of the next bed stage are fed into the next bed stage to continue the reaction until the last bed stage. The products from the reaction in the last bed stage are separated to obtain a light stream containing propylene, a C4-C6 medium stream, and a C7 and above heavy stream. The C4-C6 medium stream is returned to the olefin feedstock inlet of the first bed stage and incorporated into the olefin feedstock for further reaction. The olefin feedstock is selected from at least one of the following: C4 and above fractions produced by FCC unit, C4 and above fractions produced by MTO unit, and C4 and above fractions produced by ethylene unit; the first, second, and third beds of the multi-bed olefin cracking reactor are filled with different silica-alumina molecular sieve catalysts, the silica-alumina molecular sieve catalysts of the first and third beds are selected from ZSM-5 molecular sieve or ZSM-11 molecular sieve, and the silica-alumina molecular sieve catalyst of the second bed is ZSM-5 / ZSM-11 eutectic molecular sieve.

2. The method according to claim 1, characterized in that, The SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 20~800.

3. The method according to claim 2, characterized in that, The SiO2 / Al2O3 molar ratio of the silicon-aluminum molecular sieve catalyst is 50–500.

4. The method according to claim 1, characterized in that, The heating of the olefin feedstock includes heating the olefin feedstock sequentially through a heat exchanger and then through a heating furnace.

5. The method according to claim 4, characterized in that, The temperature of the olefin feedstock is 50~60℃, and the temperature of the olefin feedstock after heating is 450~650℃.

6. The method according to claim 5, characterized in that, The temperature of the heated olefin feedstock is 500~600℃.

7. The method according to claim 1, characterized in that, The multi-stage bed olefin cracking reactor comprises at least three bed stages; and / or, In the multi-stage bed olefin cracking reactor, the reaction process conditions for each bed are as follows: reaction temperature 500–600℃, reaction gas weight hourly space velocity 2–40 h⁻¹. -1 Catalyst bed pressure drop 0–0.2 MPa; and / or, The product obtained from the final bed reaction needs to be cooled, compressed, and then separated into its components.

8. The method according to claim 7, characterized in that, The multi-stage bed olefin cracking reactor comprises 3 to 5 stages.

9. The method for increasing propylene production according to any one of claims 1 to 8, applied in olefin cracking for increasing propylene production.

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