A method for increasing propylene production from an olefin-rich feedstock, a propylene production system and applications

Abstract

The present application provides a method for increasing propylene production from olefin-rich feedstock and a propylene production system, which adopts a multi-bed olefin cracking reactor, different catalysts are loaded in different beds, and during the reaction, the product from the first bed continues to react in the second bed, the product from the second bed continues to react in the next bed, part of the product from the second bed returns to the inlet of the first bed, the third bed is supplemented with the olefin-rich feedstock and the product from the previous bed, and the product from the last bed is separated to obtain a light stream rich in propylene, a C4-C6 medium stream, and a heavy stream of C7 and above, and the C4-C6 medium stream returns to the reactor. The present application adopts a distributed cross-feeding method, which improves the utilization efficiency of the olefin-rich feedstock in different beds and significantly improves the yield of propylene.

Description

Technical Field

[0001] This invention belongs to the field of propylene production technology, specifically relating to a method for increasing propylene production from olefin-rich feedstocks, a propylene production system, and its applications. Background Technology

[0002] As a fundamental raw material for national economic development, propylene occupies a crucial position in the petrochemical industry. Propylene possesses a series of important derivative chemicals, such as polypropylene produced through polymerization, alcohols through hydration, and epoxides through oxidation. In recent years, although domestic propylene production capacity has grown at a rate of around 10% and maintained a steady upward trend, it still cannot meet the continuously growing demand for propylene feedstock from various industries.

[0003] Currently, diversified development is one of the important trends in domestic propylene production. Plants using naphtha as feedstock still constitute the majority, while various production processes using coal, methanol, propane, and small-molecule hydrocarbons such as butene and pentene as feedstocks are gradually increasing. Therefore, developing new propylene-boosting processes, such as olefin cracking and olefin disproportionation technologies, is key to resolving future supply and demand imbalances.

[0004] With the rapid development of coal-to-olefins and methanol-to-olefins processes, a large amount of C4+ fractions are produced as byproducts. Furthermore, traditional steam cracking and catalytic cracking processes also produce C4+ fractions with similar compositions. These C4+ fractions are typically rich in olefin components, making them a suitable feedstock for olefin cracking. Olefin cracking technology converts C4+ fractions into high-value-added propylene, achieving both efficient utilization of carbon resources and increased propylene production. Therefore, further development of olefin cracking technology has a significant impact on improving enterprise economic efficiency and promoting national social development.

[0005] The basic principle of olefin catalytic cracking to propylene technology is to use molecular sieve catalysts with unique shape selectivity and acidity to selectively convert low-carbon olefins into propylene and ethylene. Its advantage is that the feedstock range is very flexible, and by-product C4 and above olefins from FCC units, steam cracking units or MTO units can be used.

[0006] Chinese patent CN1490287A discloses a method for preparing ethylene and propylene. In a fixed-bed reactor, a mixture of hydrocarbons containing C4 or C5 monoolefins is subjected to a temperature of 350–500°C, a pressure of 0.6–1.0 MPa, and a time of 1–10 h⁻¹. -1 Under conditions of specific weight-space velocity, a reaction mixture containing ethylene and propylene is produced. However, this patent uses a single-structure reactor, which cannot meet the higher propylene yield requirements of actual production.

[0007] Chinese patent CN106608779A discloses a method for catalytic cracking of C4 and higher hydrocarbons to produce propylene. By designing a thin-bed reactor with a diameter-to-height ratio between 5 and 50, the pressure drop of the catalyst bed is significantly reduced. This allows C4 and higher hydrocarbon feedstocks to contact an aluminosilicate catalyst with a SiO2 / Al2O3 molar ratio of 30 to 800 to produce products containing propylene and other byproducts. This method effectively solves the problems of low propylene selectivity and poor catalyst stability. While this patent uses a fixed-bed reactor with a thin-panel bed, achieving a propylene selectivity greater than 40%, it does not mention a multi-stage catalyst bed structure, meaning the yield of the target product and the stability of the catalyst still fall short of ideal conditions. Summary of the Invention

[0008] To address the problem of low propylene yield in existing technologies, this invention provides a method for increasing propylene production from olefin-rich feedstocks, as well as a propylene production system employing this method. This invention utilizes a multi-bed olefin cracking reactor, with different catalysts used in different beds. Furthermore, during the reaction, olefin-rich feedstocks are added to the first and third beds of the cracking reactor, and a portion of the stream from the second bed is returned to the inlet of that bed. This method can effectively improve propylene yield.

[0009] One objective of this invention is to provide a method for increasing propylene production from olefin-rich feedstock, comprising the steps of reacting the olefin-rich feedstock in a multi-bed olefin cracking reactor to obtain a light stream rich in propylene, a C4-C6 medium stream, and a C7 and above heavy stream. The multi-bed olefin cracking reactor comprises at least three beds. During the reaction, the olefin-rich feedstock is fed into the first and third beds of the cracking reactor, and a portion of the stream obtained from the second bed is returned to the stream inlet of the second bed.

[0010] According to an embodiment of the present invention, the method specifically includes the following steps: An olefin-rich feedstock is heated and then fed into a multi-bed olefin cracking reactor via a first bed. The reactor reacts under the action of a catalyst. The product obtained from the reaction in the first bed enters the second bed for further reaction. A portion of the product from the reaction in the second bed enters the next bed for further reaction, while a portion returns to the inlet of this bed. An olefin-rich feedstock and the product from the previous bed are added to the third bed for further reaction. The product from the reaction enters the next bed. The even-numbered beds following the third bed repeat the second bed operation, and the odd-numbered beds following the third bed repeat the third bed operation until the last bed. The product obtained from the reaction in the last bed is separated to obtain a light stream rich in propylene, a medium stream of C4-C6, and a heavy stream of C7 and above. The medium stream of C4-C6 is returned to the inlet of the first bed and incorporated into the olefin-rich feedstock for further reaction.

[0011] According to a preferred embodiment of the present invention, the olefin-rich feedstock can be derived from any olefin-rich feedstock containing C4 or higher fractions, for example, at least one selected from C4 or higher fractions from FCC units, C4 or higher fractions as by-products of MTO units, and C4 or higher fractions produced by ethylene units. The olefin-rich feedstock, by mass percentage, contains 60-75% butene, 15-25% pentene, and 0-25% other hydrocarbon components.

[0012] According to a preferred embodiment of the present invention, the olefin-rich feedstock is heated before entering the bed olefin cracking reactor. Preferably, the heating includes heat exchanger heating and furnace heating. The temperature of the olefin-rich feedstock after heating is 500-600°C. The heated olefin-rich feedstock enters the reactor and reacts under the action of a catalyst. Finally, the product obtained from the bed reaction needs to be cooled, compressed, and then separated into components to obtain a light stream rich in propylene, a medium stream of C4-C6, and a heavy stream of C7 and above.

[0013] According to a preferred embodiment of the present invention:

[0014] The multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor. The temperature of the reactants in the first bed is 500-600℃, and the temperature of the reactants in the remaining beds is 500-580℃. The heated olefin feedstock achieves olefin cracking reaction in the reactor through its own temperature, reducing heat dissipation and achieving energy saving. In addition, the adiabatic fixed-bed reactor has a simple structure, small size, and low construction cost.

[0015] In the multi-bed olefin cracking reactor, the weight hourly space velocity (WHSV) of the olefin-rich feedstock in the first bed is 2–40 h⁻¹. -1 The ratio of the side feed rate in the remaining beds to the weight space velocity of the olefin-rich feed in the first bed is 1:(1-20).

[0016] The multi-bed olefin cracking reactor comprises 3 to 5 layers, with different beds filled with different silica-alumina molecular sieve catalysts. The SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 10 to 700, preferably 20 to 500. Starting from the first bed at the material inlet, the catalyst for the odd-numbered beds is ZSM-5 molecular sieve, and the catalyst for the even-numbered beds is a ZSM-5 / ZSM-35 composite molecular sieve. Preferably, the ratio of ZSM-5 to ZSM-35 in the ZSM-5 / ZSM-35 composite molecular sieve is 1:(1 to 49), more preferably 1:(3 to 19). In the multi-bed olefin cracking reactor, starting from the first bed at the material inlet, the loading weight of the catalyst in each bed decreases sequentially. Preferably, with the first bed having a catalyst loading weight of 100 parts, the other beds have a catalyst loading weight of 10 to 90 parts, more preferably 30 to 80 parts.

[0017] The second objective of this invention is to provide a propylene production system for implementing the above-mentioned method of increasing propylene production from olefin-rich feedstocks.

[0018] 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. A heat exchanger and a compressor are provided between the multi-bed olefin cracking reactor and the separation system. The separation system is provided 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. Preferably, the medium stream pipeline for C4 to C6 is connected to the raw material input pipeline of the heat exchanger.

[0019] According to an embodiment of the present invention, the multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor; the reactor comprises at least three vertically arranged bed layers, preferably three to five bed layers; wherein different bed layers are filled with different silica-alumina molecular sieve catalysts, and the SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalysts used is 10 to 700, preferably 20 to 500; starting from the first bed layer at the material inlet, the catalyst of the odd-numbered bed layers is ZSM-5 molecular sieve, and the catalyst of the even-numbered bed layers is ZSM-5 / ZSM-35 composite molecular sieve; preferably, the ratio of ZSM-5 to ZSM-35 in the ZSM-5 / ZSM-35 composite molecular sieve is 1:(1 to 49), preferably 1:(3 to 19); in the multi-bed olefin cracking reactor, starting from the first bed layer at the material inlet, the loading weight of the catalyst in each bed layer decreases sequentially; preferably, with the first bed layer catalyst loading weight being 100 parts, the other bed layer catalyst loading weights are 10 to 90 parts. Preferably 30 to 80 parts;

[0020] In the multi-stage bed olefin cracking reactor, the second bed and subsequent even-numbered beds are equipped with side streamers at the flow outlet to return part of the flow to the inlet of the bed segment, while the third bed and subsequent odd-numbered beds are equipped with olefin feedstock side streamers at the flow inlet of the bed segment.

[0021] A third objective of this invention is to provide a method for increasing propylene production from the aforementioned olefin-rich feedstock, or a propylene production system thereof, for increasing propylene production from olefin-rich feedstock.

[0022] In this invention, a distributed cross-feed method is used, with different weights and types of catalysts loaded according to the reaction characteristics of different beds. Furthermore, in the third and subsequent odd-numbered beds, a cold olefin-rich feedstock is added via a side stream. After contacting the products from the previous high-temperature reaction, the reaction temperature is lowered, and the reaction occurs in the corresponding bed under the action of the catalyst. The olefin-rich feedstock and the product components from the previous bed undergo a complex olefin cracking reaction to produce propylene. In the second and subsequent even-numbered beds, a portion of the product from this bed reaction enters the next bed for further reaction, while another portion returns via pipeline to the inlet of this bed section to further crack the long-chain olefins in the previous bed product into smaller molecule olefins such as propylene and ethylene. After separation of the products from the cracking reactor, the C4-C6 midstream stream is returned to the inlet of the first bed section and incorporated into the first olefin-rich feedstock. This method improves the utilization efficiency of the olefin-rich feedstock in different beds. Compared to traditional multi-bed reactors that only improve catalyst lifespan, this invention can significantly increase the propylene yield.

[0023] This invention utilizes a multi-bed olefin cracking reactor and a distributed cross-feed feedstock, with different catalysts loaded in different beds, effectively increasing propylene production and feedstock throughput, providing inspiration for large-scale plant development. The design is simple, safe, and reliable, effectively addressing the demand for higher propylene yields in actual production. Attached Figure Description

[0024] Figure 1 This invention provides a propylene production system. In the figure: A. Feed / Discharge heat exchanger; B. Heating furnace; C. Multi-stage bed olefin cracking reactor; D. Compressor; E. Separation system; 1. Main feed line for olefin-rich feedstock; 2. Main feed line for feedstock; 3. Hot end outlet line of heat exchanger; 4. Outlet line of heating furnace; 5. Outlet line of reactor; 6. Cold end outlet line of heat exchanger; 7. Outlet line of compressor; 8. C4~C6 intermediate stream pipeline; 9. Side feed line for olefin-rich feedstock; 10. Side stream return pipeline; 11. Bed inlet pipeline for side feed line for olefin-rich feedstock; 12. Propylene product pipeline; 13. Other product pipelines. Figure 2The diagram shows the propylene production system used in Comparative Example 1. In the diagram: A. Feed / Discharge Heat Exchanger, B. Heating Furnace, C. Multi-bed Olefin Cracking Reactor, D. Compressor, E. Separation System, 1. Main Feed Line for Olefin-Rich Feed, 2. Main Feed Line for Feed, 3. Hot End Outlet Line for Heat Exchanger, 4. Outlet Line for Heating Furnace, 5. Feed Side Line 1 for Reactor, 6. Feed Side Line 2 for Reactor, 7. Outlet Line for Reactor, 8. Cold End Outlet Line for Heat Exchanger, 9. Outlet Line for Compressor, 10. C4~C6 Intermediate Flow Lines, 11. Propylene Product Line, 12. Other Product Lines. Detailed Implementation

[0025] 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.

[0026] In one specific embodiment of the present invention, the following is adopted: Figure 1 The specific process for producing propylene using the system shown is as follows:

[0027] Olefin-rich feedstock at 50-60℃ enters the boundary area through main olefin-rich feedstock pipeline 1. The first stream of olefin-rich feedstock enters main feedstock pipeline 2, and the remaining feedstock enters side feedstock pipeline 9. The C4-C6 medium stream from pipeline 8 is combined with the first stream of olefin-rich feedstock, heated, and then enters the inlet of the first bed of the reactor. The first olefin-rich feedstock enters heat exchanger A from feedstock main line 2, then passes through heater B. After two heating cycles, this portion of feedstock reaches the design temperature and enters the reactor from the top of the multi-bed olefin cracking reactor C, contacting the catalyst in the first bed. Here, the olefin-rich feedstock and the circulating material undergo olefin cracking reaction to produce propylene and a series of other products. The reaction products then react in the second bed. Part of the products from the second reaction enter the next bed for further reaction, while the other part returns to the inlet of the current bed via pipeline 10 to further crack the long-chain olefins in the previous bed into smaller molecule olefins such as propylene and ethylene. On the other hand, the remaining olefin-rich feedstock is transported to the reactor via feedstock side line 9. Depending on the number of beds, it enters the reactor from the inlet of the third bed and the odd-numbered beds below. The cold olefin-rich feedstock comes into contact with the products from the high-temperature reaction in the previous bed, lowering the reaction temperature. Under the action of the catalyst in the third bed, the olefin-rich feedstock entering the reactor and the product components from the previous bed react to produce propylene. The total product is cooled by the A feed heat exchanger after exiting the reactor 5, then pressurized by the D compressor and enters the E separation system. The medium streams of C4 to C6 are returned to the 2 feed main line via the 8 circulation line. The light streams rich in propylene are discharged from the 12 propylene product line, and the heavy streams of C7 and above are discharged from the 13 other product line.

[0028] The olefin-rich feedstock in this embodiment of the invention is derived from the C4 and above fractions produced by the MTO unit, containing 70% butene, 20% pentene, and 10% other hydrocarbon components.

[0029] Example 1:

[0030] A schematic diagram of the process flow for a three-stage bed olefin cracking reactor is shown below. Figure 1As shown. Olefin-rich feedstock at 50℃ enters the boundary area via the 1st olefin-rich feedstock main feed line. The first stream of olefin-rich feedstock enters the 2nd feedstock main feed line, and the remaining feedstock enters the 9th olefin-rich feedstock side feed line. The C4-C6 intermediate stream from pipeline 8 merges with the first stream of olefin-rich feedstock and returns to the inlet of the first bed of the reactor. The first stream of feedstock enters the A feed-in / outlet heat exchanger from the 2nd feedstock main feed line, then passes through the B heater. After two heating cycles, the material temperature is 580℃. It enters the first bed of the olefin feedstock inlet of the C multi-bed olefin cracking reactor, contacting the first bed of the catalyst. The reaction products react in the second bed. Part of the product from the second reaction enters the next bed for further reaction, while the other part returns via pipeline 10 to the side feedstock inlet of this bed section, mixes with the product from the previous bed, and re-enters the second bed for reaction. The remaining olefin-rich feedstock is transported from the 9th olefin-rich feedstock side feed line to the reactor side line, enters the 11th olefin-rich feedstock side feed line bed inlet pipeline, and enters the reactor from the third bed of the olefin feedstock. The olefin-rich feedstock from pipeline 11 comes into contact with the reaction products from the second bed and reacts in the third bed.

[0031] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1 The first bed is filled with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is filled with 80 parts by weight of ZSM-5 / ZSM-35 composite molecular sieve catalyst (ZSM-5 to ZSM-35 ratio of 1:19) under the reaction conditions of 560℃ and a side-stream return stream weight hourly space velocity ratio of 4:1; the third bed is filled with 70 parts by weight of ZSM-5 molecular sieve catalyst under the reaction conditions of 540℃ and a side-stream return stream weight hourly space velocity ratio of 1:1.

[0032] The total product, after being cooled by the feed heat exchanger A via the reactor outlet pipeline (5), enters the compressor (D) for pressurization and then enters the separation system (E). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the feed main pipeline (2) and merged into the first olefin-rich feed stream. The propylene-rich light stream is discharged through the propylene product pipeline (12), and the C7 and higher heavy stream is discharged through the other products pipeline (13). The propylene yield is 59%.

[0033] Example 2

[0034] A schematic diagram of the process flow for a three-stage bed olefin cracking reactor is shown below. Figure 1As shown. Olefin-rich feedstock at 50℃ enters the boundary area via the 1st olefin-rich feedstock main feed line. The first stream of olefin-rich feedstock enters the 2nd feedstock main feed line, and the remaining feedstock enters the 9th olefin-rich feedstock side feed line. The C4-C6 medium stream from pipeline 8 merges with the first stream of olefin-rich feedstock and returns to the inlet of the first bed of the reactor. The first stream of feedstock enters the A feed-in / outlet heat exchanger from the 2nd feedstock main feed line, then passes through the B heater. After two heating cycles, the material temperature is 580℃. It enters the first bed of the olefin feedstock inlet of the C multi-bed olefin cracking reactor, contacting the first bed of catalyst. The reaction products react in the second bed. Part of the product from the second reaction enters the next bed for further reaction, while the other part returns via pipeline 10 to the inlet of this bed, mixes with the product from the previous bed, and re-enters the second bed for reaction. The remaining olefin-rich feedstock is transported from the 9th olefin-rich feedstock side feed line to the reactor side line, enters the 11th olefin-rich feedstock side feed line bed inlet pipeline, and enters the reactor from the third bed of olefin feedstock inlet. The olefin-rich feedstock from pipeline 11 comes into contact with the reaction products from the second bed and reacts in the third bed.

[0035] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1 The first bed is filled with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is filled with 80 parts by weight of ZSM-5 / ZSM-35 composite molecular sieve catalyst (ZSM-5 to ZSM-35 ratio of 1:15) under the reaction conditions of 560℃ and a side-stream return stream weight hourly space velocity ratio of 4:1; the third bed is filled with 60 parts by weight of ZSM-5 molecular sieve catalyst under the reaction conditions of 540℃ and a side-stream return stream weight hourly space velocity ratio of 1:1.

[0036] The total product, after being cooled by the feed heat exchanger A via the reactor outlet pipeline (5), enters the compressor (D) for pressurization and then enters the separation system (E). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the feed main pipeline (2) and incorporated into the first olefin-rich feed stream. The propylene-rich light stream is discharged through the propylene product pipeline (12), and the C7 and higher heavy stream is discharged through the other products pipeline (13). The propylene yield is 58%.

[0037] Example 3

[0038] A schematic diagram of the process flow for a three-stage bed olefin cracking reactor is shown below. Figure 1As shown. Olefin-rich feedstock at 50℃ enters the boundary area via the 1st olefin-rich feedstock main feed line. The first stream of olefin-rich feedstock enters the 2nd feedstock main feed line, and the remaining feedstock enters the 9th olefin-rich feedstock side feed line. The C4-C6 medium stream from pipeline 8 merges with the first stream of olefin-rich feedstock and returns to the inlet of the first bed of the reactor. The first stream of feedstock enters the A feed-in / outlet heat exchanger from the 2nd feedstock main feed line, then passes through the B heater. After two heating cycles, the material temperature is 580℃. It enters the first bed of the olefin feedstock inlet of the C multi-bed olefin cracking reactor, contacting the first bed of catalyst. The reaction products react in the second bed. Part of the product from the second reaction enters the next bed for further reaction, while the other part returns via pipeline 10 to the inlet of this bed, mixes with the product from the previous bed, and re-enters the second bed for reaction. The remaining olefin-rich feedstock is transported from the 9th olefin-rich feedstock side feed line to the reactor side line, enters the 11th olefin-rich feedstock side feed line bed inlet pipeline, and enters the reactor from the third bed of olefin feedstock inlet. The olefin-rich feedstock from pipeline 11 comes into contact with the reaction products from the second bed and reacts in the third bed.

[0039] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1 The first bed is filled with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is filled with 80 parts by weight of ZSM-5 / ZSM-35 composite molecular sieve catalyst (ZSM-5 to ZSM-35 ratio of 1:7) under the reaction conditions of 560℃ and a side-stream return stream weight hourly space velocity ratio of 2:1; the third bed is filled with 70 parts by weight of ZSM-5 molecular sieve catalyst under the reaction conditions of 540℃ and a side-stream return stream weight hourly space velocity ratio of 1:1.

[0040] The total product, after being cooled by the feed heat exchanger A via the reactor outlet pipeline (5), enters the compressor (D) for pressurization and then enters the separation system (E). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the feed main pipeline (2) and merged into the first olefin-rich feed stream. The propylene-rich light stream is discharged through the propylene product pipeline (12), and the C7 and higher heavy stream is discharged through the other products pipeline (13). The propylene yield is 55%.

[0041] Comparative Example 1

[0042] A schematic diagram of the traditional three-bed feeding process is shown below. Figure 2As shown. Olefin-rich feedstock at 50℃ enters the boundary area via main olefin-rich feedstock pipeline 1, where it is directly mixed with the C4-C6 medium stream from pipeline 10. The mixed feedstock then enters the feed-discharge heat exchanger A via main feedstock pipeline 2, and then passes through the heater B. After two heating cycles, the material temperature is 580℃. It then enters the reactor from the top of each bed section of the multi-stage bed olefin cracking reactor C via pipelines 4, 5, and 6, respectively. The mixed feedstock from pipeline 5 contacts the reaction products from the first bed, reacting in the second bed. The resulting products then contact the mixed feedstock from pipeline 6 before passing through the third bed.

[0043] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1 The first bed is filled with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is filled with 80 parts by weight of ZSM-5 molecular sieve catalyst at a temperature of 560℃ and a weight hourly space velocity (WHSV) ratio of olefin-rich feedstock between the first and second beds of 1:1; the third bed is filled with 70 parts by weight of ZSM-5 molecular sieve catalyst at a temperature of 540℃ and a WHSV ratio of olefin-rich feedstock between the first and third beds of 1:1.

[0044] 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). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the olefin-rich feed main pipeline (2). The propylene-rich light stream is discharged through the propylene product pipeline (11), and the C7 and higher heavy stream is discharged through the other products pipeline (12). The propylene yield is 48%.

[0045] Comparative Example 2:

[0046] A schematic diagram of the process flow for a three-stage bed olefin cracking reactor is shown below. Figure 1 As shown. The difference is that the third bed does not have a side feed line for feeding olefin-rich feedstock 9, and the second bed does not have a partial product return to the feed inlet.

[0047] Olefin-rich feedstock at 50℃ enters the boundary area via main olefin-rich feedstock pipeline 1. All olefin-rich feedstock enters main feedstock pipeline 2. C4-C6 intermediate streams from pipeline 8 are combined with pipeline 2 and returned to the inlet of the first bed of the reactor. The feedstock enters the feed-discharge heat exchanger A from main feedstock pipeline 2, then passes through heater B. After two heating cycles, the material temperature is 580℃. From the inlet of the first bed of the multi-stage bed olefin cracking reactor C, the feedstock enters the first, second, and third beds successively, contacting the catalyst and reacting.

[0048] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1 The first bed is filled with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is filled with 80 parts by weight of ZSM-5 molecular sieve catalyst at a temperature of 560℃; the third bed is filled with 70 parts by weight of ZSM-5 molecular sieve catalyst at a temperature of 540℃.

[0049] The total product, after being cooled by the feed heat exchanger A via the reactor outlet pipeline (5), enters the compressor (D) for pressurization and then enters the separation system (E). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the olefin-rich feed main pipeline (2) and merged into the first olefin-rich feed stream. The propylene-rich light stream is discharged through the propylene product pipeline (12), and the C7 and higher heavy stream is discharged through the other products pipeline (13). The propylene yield is 36%.

[0050] Comparative Example 3

[0051] A schematic diagram of the process flow for a three-stage bed olefin cracking reactor is shown below. Figure 1 As shown. The difference is that the catalyst in each bed of the three-stage olefin cracking reactor is a ZSM-5 molecular sieve catalyst.

[0052] Olefin-rich feedstock at 50℃ enters the boundary area via the main olefin feedstock feed line 1. The first stream of olefin-rich feedstock enters the main feedstock feed line 2, and the remaining feedstock enters the side feedstock feed line 9. The C4-C6 intermediate stream from line 8 is merged into the first stream of olefin-rich feedstock and returns to the inlet of the first bed of the reactor. The first stream of feedstock enters the feed-discharge heat exchanger A from the main feedstock feedstock line 2, and then passes through the heater B. After two heatings, the material temperature is 580℃. It enters the first bed of the olefin feedstock inlet of the multi-bed olefin cracking reactor C, and contacts the first bed of the catalyst. The reaction products react in the second bed. Part of the products after the second reaction enters the next bed to continue the reaction, and part returns to the inlet of the current bed via line 10 to mix with the products of the previous bed and re-enter the second bed for reaction. The remaining olefin-rich feedstock is transported to the reactor side line via the side feedstock feed line 9, enters the bed inlet pipeline of the side feedstock feed line 11, and enters the reactor from the third bed of the olefin feedstock. The olefin-rich feedstock from pipeline 11 comes into contact with the reaction products from the second bed and reacts in the third bed.

[0053] In the three-stage olefin cracking reactor, the reaction conditions for the first bed are a temperature of 580°C and a weight hourly space velocity of 25 h⁻¹. -1The first bed is packed with 100 parts by weight of ZSM-5 molecular sieve catalyst; the second bed is packed with 80 parts by weight of ZSM-5 molecular sieve catalyst, with a reaction temperature of 560℃ and a weight hourly space velocity (WHSV) ratio of 4:1 for the side-stream return streams of the first and second beds; the third bed is packed with 70 parts by weight of ZSM-5 molecular sieve catalyst, with a reaction temperature of 540℃ and a WHSV ratio of 1:1 for the olefin-rich feedstock of the first and third beds.

[0054] The total product, after being cooled by the feed heat exchanger A via the reactor outlet pipeline (5), enters the compressor (D) for pressurization and then enters the separation system (E). This separation process yields a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream is returned as a recycle stream to the olefin-rich feed main pipeline (2) and merged into the first olefin-rich feed stream. The propylene-rich light stream is discharged through the propylene product pipeline (12), and the C7 and higher heavy stream is discharged through the other products pipeline (13). The propylene yield is 45%.

[0055] 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 from olefin-rich feedstock, comprising: The olefin-rich feedstock is heated and then fed into a multi-bed olefin cracking reactor via the first bed. Under the action of a catalyst, the reaction proceeds. The product from the first bed reaction enters the second bed for further reaction. A portion of the product from the second bed reaction enters the next bed for further reaction, while a portion returns to the feed inlet of this bed. The third bed is fed with the olefin-rich feedstock and the product from the previous bed reaction, and the reaction continues there. The product then enters the next bed. The even-numbered beds following the third bed repeat the second bed operation, and the odd-numbered beds following the third bed repeat the third bed operation, until the final bed. The product from the final bed reaction is separated to obtain a propylene-rich light stream, a C4-C6 medium stream, and a C7 and higher heavy stream. The C4-C6 medium stream... The feedstock is returned to the first bed inlet and then incorporated into the olefin-rich feedstock for further reaction. The multi-bed olefin cracking reactor comprises at least three beds. During the reaction, olefin-rich feedstock is added to the first and third beds of the cracking reactor. A portion of the feedstock from the second bed is returned to the feedstock inlet of its respective bed. In the multi-bed olefin cracking reactor, different beds are packed with different silica-alumina molecular sieve catalysts. Starting from the first bed at the feed inlet, the catalyst for odd-numbered beds is ZSM-5 molecular sieve, and the catalyst for even-numbered beds is a ZSM-5 / ZSM-35 composite molecular sieve. The olefin-rich feedstock is selected from at least one of the following: C4 and above fractions from an FCC unit, C4 and above fractions by-products from an MTO unit, and C4 and above fractions from an ethylene unit.

2. The method according to claim 1, characterized in that, The heating of the olefin-rich feedstock includes heat exchanger heating and furnace heating, and the temperature of the olefin-rich feedstock after heating is 500~600℃; and / or, The product obtained from the final bed reaction needs to be cooled, compressed, and then separated into its components.

3. The method according to claim 1, characterized in that, The multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor; and / or, The multi-bed olefin cracking reactor comprises 3 to 5 layers; and / or, In the multi-bed olefin cracking reactor, the temperature of the reactants in the first bed is 500~600℃, and the temperature of the reactants in the remaining beds is 500~580℃. And / or, In the multi-bed olefin cracking reactor, the weight hourly space velocity (WHSV) of the olefin-rich feedstock in the first bed is 2–40 h⁻¹. -1 The ratio of the side feed rate in the remaining beds to the weight space velocity of the olefin-rich feed in the first bed is 1:(1~20).

4. The method according to claim 1, characterized in that, The SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 10~700; and / or, In the multi-bed olefin cracking reactor, starting from the first bed at the material inlet, the catalyst loading weight in each bed section decreases sequentially; and / or, In the multi-bed olefin cracking reactor, the catalyst loading weight of the first bed is 100 parts, and the catalyst loading weight of the other beds is 10 to 90 parts.

5. The method according to claim 4, characterized in that, The SiO2 / Al2O3 molar ratio of the silica-alumina molecular sieve catalyst is 20–500; and / or, In the multi-bed olefin cracking reactor, the catalyst loading weight of the first bed is 100 parts, and the catalyst loading weight of the other beds is 30 to 80 parts.

6. The method according to claim 1, characterized in that, In the ZSM-5 / ZSM-35 composite molecular sieve, the ratio of ZSM-5 to ZSM-35 is 1:(1~49).

7. The method according to claim 6, characterized in that, In the ZSM-5 / ZSM-35 composite molecular sieve, the ratio of ZSM-5 to ZSM-35 is 1:(3~19).

8. A propylene production system for implementing the method for increasing propylene production from olefin-rich feedstock as described in any one of claims 1 to 7; the system comprises a feedstock storage tank, a heat exchanger, a heater, a multi-bed olefin cracking reactor, and a separation system connected sequentially by material pipelines, wherein a heat exchanger and a compressor are provided between the multi-bed olefin cracking reactor and the separation system, the reactor comprising at least three vertically arranged beds, wherein the product obtained from the reaction in the first bed enters the second bed for further reaction, part of the product after the reaction in the second bed enters the next bed for further reaction, and part returns to the inlet of the current bed, the third bed is fed with olefin-rich feedstock and the product from the previous bed for further reaction, the product after the reaction enters the next bed, then the even-numbered beds after the third bed repeat the operation of the second bed, the odd-numbered beds after the third bed repeat the operation of the third bed, until the last bed, where the product obtained from the reaction in the last bed is separated; 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 feed inlet pipeline of the heat exchanger. In the multi-bed olefin cracking reactor, the second bed and subsequent even-numbered beds are equipped with side streams at the stream outlet to return part of the stream to the inlet of the corresponding bed. The third bed and subsequent odd-numbered beds are equipped with olefin feedstock side stream inlets at the stream inlet of the corresponding bed. In the multi-bed olefin cracking reactor, different beds are packed with different silica-alumina molecular sieve catalysts. Starting from the first bed at the material inlet, the catalyst for the odd-numbered beds is ZSM-5 molecular sieve, and the catalyst for the even-numbered beds is ZSM-5 / ZSM-35 composite molecular sieve. The olefin-rich feedstock is selected from at least one of the following: C4 and above fractions from FCC units, C4 and above fractions by-products from MTO units, and C4 and above fractions produced from ethylene units.

9. The propylene production system according to claim 8, characterized in that, The multi-bed olefin cracking reactor is an adiabatic fixed-bed reactor.

10. The propylene production system according to claim 9, characterized in that, The reactor described herein comprises 3 to 5 bed sections.

11. The method for increasing propylene production from olefin-rich feedstock according to any one of claims 1 to 7, or the propylene production system according to any one of claims 8 to 10, for increasing propylene production from olefin-rich feedstock.

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