Multi-reactor system and process for propylene production

Abstract

A process and system for producing propylene from a C4 raffinate hydrocarbon stream. The process can include supplying a C4 raffinate hydrocarbon stream to a metathesis reactor to produce a metathesis outlet stream and separating a plurality of C5 + hydrocarbons from propylene and one or more C4 hydrocarbons in the metathesis outlet stream to produce a C5 + feed stream and a first propylene-rich stream. The process may also include supplying the C5 + feed stream to a cracking reactor to produce a cracking outlet stream containing propylene and one or more C4 hydrocarbons. The process may also include separating propylene from the one or more C4 hydrocarbons in the cracking outlet stream to produce a second propylene-rich stream and a C4-rich stream and recycling the C4-rich stream to the metathesis reactor as part of a C4 raffinate hydrocarbon stream.

Description

Technical Field

[0001] The present disclosure generally relates to systems and methods for producing propylene from C4 hydrocarbon streams. More specifically, the present disclosure in other embodiments relates to systems and methods for producing propylene through the parallel operation of a metathesis reactor and a cracking reactor separately. Background Art

[0002] Propylene is a desired industrial compound, and its global production exceeds that of any other organic compound except ethylene. Thus, propylene is the second most important starting material in the petrochemical industry after ethylene. Propylene is particularly used as a raw material for producing polypropylene with a wide variety of uses. Propylene is also used to produce other important chemicals such as isopropyl alcohol, epichlorohydrin, propylene oxide, acrylonitrile, cumene, butyraldehyde, and acrylic acid. More than 85 million tons of propylene are produced globally each year. In addition to other production methods, propylene can be produced by steam cracking of hydrocarbons. Therefore, methods and systems capable of efficiently producing propylene from hydrocarbon raw materials and improving the raw material utilization of hydrocarbon streams are desired. Summary of the Invention

[0003] To address the drawbacks in the art, the applicant has developed systems and methods for producing propylene from hydrocarbon streams through the parallel operation of a metathesis reactor and a cracking reactor separately. In at least some embodiments, the presently disclosed systems and methods may be particularly suitable for producing propylene from a low-cost C4 raffinate stream, which may include 1-butene, trans-2-butene, cis-2-butene, and mixtures thereof, thereby converting a low-value butene stream into a high-value propylene. The operation of the separate reactors provides other advantages such as using metathesis catalysts and cracking catalysts under separate operating conditions, thereby maximizing the propylene yield. Additionally, the use of a separate metathesis reactor allows for other advantages such as using low-temperature metathesis catalysts in some embodiments and high-temperature metathesis catalysts in some other embodiments.

[0004] Methods and systems for producing propylene are provided. In some embodiments, a method for producing propylene can include supplying a C4 raffinate hydrocarbon stream to a metathesis reactor to produce a metathesis outlet stream. The C4 raffinate hydrocarbon stream can substantially contain one or more C4 hydrocarbons, and the metathesis outlet stream can contain a plurality of C5+ hydrocarbons, propylene, and one or more C4 hydrocarbons. The method can further include separating the plurality of C5+ hydrocarbons from the propylene and one or more C4 hydrocarbons in the metathesis outlet stream to produce a C5+ feed stream and a first propylene-rich stream. The method can further include supplying the C5+ feed stream to a cracking reactor to produce a cracking outlet stream containing propylene and one or more C4 hydrocarbons. The method can further include separating propylene from the one or more C4 hydrocarbons in the cracking outlet stream to produce a second propylene-rich stream and a C4-rich stream. The method can further include recycling the C4-rich stream to the metathesis reactor as part of the C4 raffinate hydrocarbon stream.

[0005] In some embodiments, the metathesis reactor and the cracking reactor can be operated at different temperatures. For example, in some embodiments, the metathesis reactor can be a high-temperature metathesis reactor that includes a silica-supported tungstate catalyst and is operated at a temperature of about 500°C - about 550°C. In some other exemplary embodiments, the metathesis reactor can be a low-temperature metathesis reactor that includes an alumina-supported rhenium catalyst and is operated at a temperature of about 50°C - about 100°C. In some embodiments, the cracking reactor includes a high-silica ZSM-5 catalyst and is operated at a temperature of about 550°C - about 575°C.

[0006] In some embodiments, the method can further include supplying the C4 raffinate hydrocarbon stream to an isomerization reactor before supplying the C4 raffinate hydrocarbon stream to the metathesis reactor. In some exemplary embodiments, the C4 raffinate hydrocarbon stream can include a portion of the metathesis outlet stream and a portion of the cracking outlet stream. The C4 raffinate hydrocarbon stream can include an input C4 raffinate hydrocarbon stream from a source other than the outlet streams of the metathesis reactor, the cracking reactor, and the isomerization reactor. In some embodiments, the method can further include supplying the metathesis outlet stream to a separation column sequence to produce a C5+ feed stream and a first propylene-rich stream.

[0007] In some embodiments, the method can further include supplying the cracking outlet stream to a separation column sequence to produce a second propylene-rich stream and a C4-rich stream. The separation column sequence can include, for example, a deethanizer column, a depropanizer column, and a debutanizer column. According to at least some aspects of the present disclosure, when the C4 raffinate hydrocarbon stream contains about 70 mol% cis-2-butene and trans-2-butene and about 30 mol% n-butane, the amount of propylene produced by combining the first propylene-rich stream and the second propylene-rich stream exceeds 40 mol%.

[0008] According to some aspects of the present disclosure, a system for producing propylene is provided. The system may include a metathesis reactor that is operable to receive a C4 raffinate hydrocarbon stream and produce a metathesis outlet stream. The C4 raffinate hydrocarbon stream may substantially contain one or more C4 hydrocarbons, and the metathesis outlet stream may contain a plurality of C5+ hydrocarbons, propylene, and one or more C4 hydrocarbons. The system may further include a plurality of separation towers that are in fluid communication with the metathesis reactor and a pyrolysis reactor. The plurality of separation towers may be operable to receive the metathesis outlet stream and produce a C5+ feed stream and a first propylene-rich stream. The system may further include a pyrolysis reactor that is in fluid communication with the plurality of separation towers and is operable to receive the C5+ feed stream and produce a pyrolysis outlet stream containing propylene and one or more C4 hydrocarbons. The pyrolysis outlet stream may be supplied to the plurality of separation towers, whereby propylene is separated from one or more C4 hydrocarbons in the pyrolysis outlet stream to produce a second propylene-rich stream and a C4-rich stream.

[0009] In some embodiments, the C4-rich stream may be recycled to the metathesis reactor as part of the C4 raffinate hydrocarbon stream. The plurality of separation towers may also be operable to separate propylene from the pyrolysis outlet stream. The plurality of separation towers may include, for example, a deethanizer, a depropanizer, and a debutanizer. In some embodiments, the system may further include an isomerization reactor that is in fluid communication with the metathesis reactor and the plurality of separation towers. In such an embodiment, the isomerization reactor may be operable to pre-treat the C4 raffinate hydrocarbon stream before supplying it to the metathesis reactor. In some embodiments, the system may include an isomerization reactor that is in fluid communication with the metathesis reactor and the plurality of separation towers. In such an embodiment, the isomerization reactor may be operable to receive one of the following: an input C4 raffinate hydrocarbon stream or a combined C4 raffinate hydrocarbon stream formed by the combination of the input C4 raffinate hydrocarbon stream and the C4-rich stream or a portion of the pyrolysis outlet stream containing C4 hydrocarbons. The isomerization reactor may be configured to produce an isomerized C4 raffinate hydrocarbon stream for supply to the metathesis reactor.

[0010] In some embodiments, the metathesis reactor and the cracking reactor can be operated at different temperatures. For example, in some embodiments, the metathesis reactor can be a high-temperature metathesis reactor that includes a silica-supported tungstate catalyst and is operated at a temperature of about 500°C to about 550°C. In some other exemplary embodiments, the metathesis reactor can be a low-temperature metathesis reactor that includes an alumina-supported rhenium catalyst and is operated at a temperature of about 50°C to about 100°C. In some embodiments, the cracking reactor includes a high-silica ZSM-5 catalyst and is operated at a temperature of about 550°C to about 575°C. According to at least some aspects of the present disclosure, when the C4 raffinate hydrocarbon feed stream contains about 70 mol% cis-2-butene and trans-2-butene and about 30 mol% n-butane, the system can be operated to produce a propylene product distribution of more than 40 mol%.

[0011] These and other aspects and advantages of these exemplary embodiments and other embodiments are discussed in detail herein. In addition, it is understood that the above information and the following detailed description are only illustrative examples of various aspects and embodiments and are intended to provide an overview or framework for understanding the properties and characteristics of the claimed aspects and embodiments. Thus, together with the advantages and features of the present disclosure, these and other objectives will become apparent by reference to the following description and the drawings. In addition, it is understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings, which are included to provide a further understanding of the embodiments of the present disclosure, are incorporated in and constitute a part of this specification, illustrate the embodiments of the present disclosure, and together with the detailed description serve to explain the principles of the embodiments discussed herein. Except as may be necessary for a basic understanding of the embodiments discussed herein and the various ways in which they may be practiced, no attempt is made to show the structural details of the present disclosure in more detail. In accordance with conventional practice, the various features of the drawings discussed below are not necessarily drawn to scale. The dimensions of the various features and elements in the drawings may be expanded or reduced to more clearly illustrate the embodiments of the disclosure.

[0013] Figure 1 is a diagram of a system and method for producing propylene from a C4 raffinate hydrocarbon feed stream according to an exemplary embodiment of the present disclosure.

[0014] Figure 2 is according to an exemplary embodiment of the present disclosure, using Figure 1 a diagram of the simulated product yield distribution obtained by the system and method described therein. DETAILED DESCRIPTION

[0015] The present disclosure describes various embodiments of systems and methods for producing propylene from a C4 hydrocarbon stream. Additional embodiments may be described and disclosed.

[0016] In the following description, numerous details are set forth in order to provide a thorough understanding of the various embodiments. In other instances, well-known processes, apparatus, and systems may not be described in particular detail so as not to unnecessarily obscure the various embodiments. Additionally, some features or details of the various embodiments may be omitted in the description so as not to obscure the various embodiments.

[0017] The description may use the phrases “in some embodiments,” “in various embodiments,” “in one embodiment,” or “in multiple embodiments,” each of which may refer to one or more of the same or different embodiments. Further, as used with reference to the embodiments of the present disclosure, the terms “comprising” (and any form thereof, such as “comprise” and “comprises”), “having” (and any form thereof, such as “have” and “has”), “including” (and any form thereof, such as “includes” and “include”), or “containing” (and any form thereof, such as “contains” and “contain”) are synonymous and are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0018] The term “about” or “approximately” is defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the term is defined within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0019] As used in the claims and / or the specification, the term “rich in” with respect to component X in a stream means that component X is present in an amount greater than 50 weight percent of the sum of all components in the stream. For example, a propylene-rich stream contains propylene in an amount greater than 50 weight percent of the sum of all components in the stream. As used in the claims and / or the specification, the term “substantially” with respect to component X in a stream means that component X is present in an amount greater than 90 weight percent of the sum of all components in the stream. For example, a stream that substantially contains one or more C4 hydrocarbons is a stream that contains one or more C4 hydrocarbons in an amount greater than 90 weight percent of the sum of all components in the stream.

[0020] The terms "wt%", "vol%", or "mol%" refer to the weight, volume, or mole percentage of a component, respectively, based on the total weight, total volume, or total moles of the material including the component. In a non-limiting example, 10 grams of a component is 10 wt% of the component in 100 grams of material.

[0021] Disclosed herein are systems and methods for producing propylene from hydrocarbon feedstreams, particularly C4 raffinate hydrocarbon feedstreams. In at least some embodiments, the presently disclosed systems and methods can be particularly suitable for producing propylene from low-cost C4 raffinate feedstreams, which can include 1-butene, trans-2-butene, cis-2-butene, and mixtures thereof, thereby converting a low-value butene feedstream into a high-value propylene. According to some aspects of the present disclosure, the presently disclosed systems and methods include the parallel operation of a metathesis reactor and a cracking reactor separately, which provides other advantages such as using metathesis catalysts and cracking catalysts under separate operating conditions, thereby maximizing propylene yield. Additionally, using a separate metathesis reactor allows for other advantages such as using low-temperature metathesis catalysts in some embodiments and high-temperature metathesis catalysts in some other embodiments. According to some aspects of the present disclosure, the presently disclosed methods and systems having a separate metathesis reactor and a cracking reactor have the advantage that the outlet stream of the metathesis reactor can be fed to one or more separator units before feeding the stream to the cracking reactor, thereby enhancing cracking efficiency and providing an overall yield approaching 99%. In contrast, systems and methods that perform metathesis and cracking in a single unit (e.g., a dual-bed reactor) provide a yield of only about 96%. In a single reactor, the overall yield of propylene is compensated, where little propane is formed in the final product slate, thereby reducing the propylene yield by about 3%. Decoupling the metathesis reactor and the cracking reactor provides the advantage of operating the metathesis catalyst and the cracking catalyst at their optimized temperatures to maximize yield and lifetime. It also allows for the option of providing an optimized recycle stream and operating the reactor at a potentially higher conversion rate. In at least some embodiments, the cracking reactor is configured to process only C5+ hydrocarbons, particularly C5+ heavy hydrocarbons produced by the metathesis reaction. In at least some embodiments, the metathesis reactor is configured to process only C4 hydrocarbon feedstreams.

[0022] Figure 1 Describing an exemplary embodiment according to the present disclosure, a method 100 and a system 200 for producing propylene from a C4 raffinate hydrocarbon feedstream 400. Other embodiments of the systems and methods disclosed herein are possible. As Figure 1As described in the exemplary embodiments provided, method 100 may include supplying a C4 raffinate feed stream 400 to a pretreatment reactor such as isomerization reactor 210 via a C4 raffinate pretreatment stream 401. The C4 raffinate feed stream may include, for example, 1-butene, trans-2-butene, cis-2-butene, and mixtures thereof. In some embodiments, the isomerization reactor may include an alumina-supported palladium catalyst. The isomerization reactor may be operable to isomerize the C4 raffinate feed stream in the form of the C4 raffinate pretreatment stream 401 and any other C4 recycle stream 414 to produce an isomerized C4 stream 402 by converting butenes to equilibrium. Optionally, the isomerized C4 stream 402 may be supplied to a metathesis preheater 212 to produce a preheated C4 stream 403. The preheated C4 stream 403 may then be supplied to a metathesis heater 214 to produce a heated C4 stream 404 or a metathesis reactor inlet stream 404. The heated C4 stream / metathesis reactor inlet stream 404 may then be fed to a metathesis reactor 220 to produce a metathesis reactor outlet stream 405.

[0023] The metathesis reactor outlet stream 405 may optionally be fed to the preheater 212 before being fed to the plurality of separation towers 240, 250, 260. Specifically, the metathesis reactor outlet stream 405 may be supplied to the preheater 212 to form a deethanizer feed 406 from the metathesis reactor stream. The deethanizer feed 406 from the metathesis reactor stream may be combined with a deethanizer feed 420 from the cracking reactor stream to form a deethanizer feed stream 407, which may in turn be supplied to a deethanizer 240. The deethanizer 240 may be operable to receive the deethanizer feed stream 407 and produce ethylene 409 in addition to a light gas purge 408 and a deethanizer outlet stream / de-propanizer feed 410. The de-propanizer feed 410 may then be supplied to a de-propanizer 250 to produce propylene 411 and a de-propanizer outlet stream / de-butanizer feed 412. The de-butanizer feed 412 may then be supplied to a de-butanizer 260 to produce a C4 recycle stream 414, a C4 purge stream 413, and a de-butanizer bottoms stream 415. The C4 recycle stream 414 may be combined with the C4 raffinate feed stream 400 to form a C4 pretreatment stream 401, which may in turn be supplied to the isomerization reactor 210 and the metathesis reactor 220.

[0024] The debutanizer bottoms stream 415 can be supplied to the pyrolysis reactor preheater 222 in the form of a C5+ recycle stream 416 after potential separation from the C5+ purge stream 421. As used herein, the term "C5+" or "C5+ hydrocarbon" refers to a hydrocarbon having five (5) or more carbon atoms. Similar terms such as "C3+ hydrocarbon", "C4+ hydrocarbon", and "C6+ hydrocarbon" also refer to hydrocarbons having three (3) or more carbon atoms, four (4) or more carbon atoms, and six (6) or more carbon atoms, respectively. The pyrolysis reactor preheater 222 is operable to preheat the C5+ recycle stream 416 to produce a preheated C5+ recycle stream 417. The preheated C5+ recycle stream 417 can be supplied to the pyrolysis reactor heater 224 to produce a heated C5+ recycle stream / pyrolysis reactor inlet stream 418. The pyrolysis reactor inlet stream 418 can be supplied to the pyrolysis reactor 230 to produce a pyrolysis reactor outlet stream 419. The pyrolysis reactor outlet stream 419 can be preheated in the pyrolysis reactor preheater 222 to produce a deethanizer feed 420 from the pyrolysis reactor stream, which can in turn be combined with the deethanizer feed 406 from the metathesis reactor stream to form a deethanizer feed stream 407 for supply to the deethanizer 240.

[0025] As Figure 1 As described, method 100 can include supplying C4 raffinate hydrocarbon streams 400, 401, 404 to the metathesis reactor 220 to produce a metathesis outlet stream 405. The C4 raffinate hydrocarbon streams 400, 401 can substantially contain one or more C4 hydrocarbons, and the metathesis outlet stream 405 can contain multiple C5+ hydrocarbons, propylene, and one or more C4 hydrocarbons. Method 100 can also include separating the multiple C5+ hydrocarbons from propylene and one or more C4 hydrocarbons in the metathesis outlet streams 405, 406, for example, via supply to a plurality of separation towers 240, 250, 260, to produce C5+ feed streams 415, 416 and a first propylene-rich stream 411. Method 100 can also include supplying the C5+ feed streams 415, 416 to the pyrolysis reactor 230 to produce a pyrolysis outlet stream 419 containing propylene and one or more C4 hydrocarbons. Method 100 can also include separating propylene from one or more C4 hydrocarbons in the pyrolysis outlet stream 419 to produce a second propylene-rich stream 411 and a C4-rich stream 414. Method 100 can also include recycling the C4-rich stream 414 to the metathesis reactor 220 as part of the C4 raffinate hydrocarbon stream 401. Method 100 can also include supplying the C4 raffinate hydrocarbon stream 400 to the isomerization reactor 210 before supplying the C4 raffinate hydrocarbon stream 400 to the metathesis reactor 220.

[0026] In some embodiments of method 100, the C4 raffinate hydrocarbon streams 400, 401 may include a portion of the metathesis outlet stream 405 and a portion of the cracking outlet stream 419, in the form of the C4 recycle stream 414. In some embodiments, the C4 raffinate hydrocarbon stream (e.g., the C4 pretreatment stream 401) may include an input C4 raffinate hydrocarbon stream from a source other than the outlet streams of the metathesis reactor 220, the cracking reactor 230, and the isomerization reactor 210, such as the fresh C4 raffinate feed stream 400. The metathesis outlet stream 405 may be supplied to a separation column sequence to produce the C5+ feed streams 416, 417, 418 and the first propylene-rich stream 411. Method 100 may also include supplying the cracking outlet streams 419, 420 to the separation column sequences 240, 250, 260 to produce the second propylene-rich stream 411 and the C4-rich stream 414. The separation column sequence may include a deethanizer 240, a depropanizer 250, and a debutanizer 260. In some embodiments, when the C4 raffinate hydrocarbon stream contains about 70 mol% cis-2-butene and trans-2-butene and about 30 mol% n-butane, method 100 may produce a propylene product distribution of more than 40 mol%.

[0027] As Figure 1As described, system 200 may include a metathesis reactor 220 that is operable to receive C4 raffinate hydrocarbon feedstreams 400, 401 and produce a metathesis outlet stream 405. The C4 raffinate hydrocarbon feedstreams 400, 401 may substantially contain one or more C4 hydrocarbons, and the metathesis outlet stream 405 may contain multiple C5+ hydrocarbons, propylene, and one or more C4 hydrocarbons. System 200 may also include a plurality of separation towers (e.g., separation towers 240, 250, 260) that are in fluid communication with the metathesis reactor 220 and the cracking reactor 230. The plurality of separation towers 240, 250, 260 are operable to receive the metathesis outlet streams 405, 406, 407 and produce C5+ feedstreams 416, 417, 418 and a first propylene-rich stream 411. System 200 may also include a cracking reactor 230 that is in fluid communication with the plurality of separation towers 240, 250, 260 and is operable to receive the C5+ feedstreams 416, 417, 418 and produce a cracking outlet stream 419 that contains propylene and one or more C4 hydrocarbons. System 200 may also be configured to supply the cracking outlet stream 419 to the plurality of separation towers 240, 250, 260 such that propylene is separated from one or more C4 hydrocarbons in the cracking outlet stream to produce a second propylene-rich stream 411 and a C4-rich stream 414. The C4-rich stream 414 may be recycled to the metathesis reactor 220 as part of the C4 raffinate hydrocarbon feedstream 401 (e.g., C4 raffinate pretreatment feedstream 401). The plurality of separation towers 240, 250, 260 are also operable to separate propylene from the cracking outlet streams 419, 420, 407. The plurality of separation towers may include a deethanizer 240, a depropanizer 250, and a debutanizer 260.

[0028] System 200 may also include an isomerization reactor 210 that is in fluid communication with the metathesis reactor 220 and the plurality of separation towers 240, 250, 260. The isomerization reactor is operable to pretreat the C4 raffinate hydrocarbon feedstreams 400, 401 before supplying the C4 raffinate hydrocarbon feedstream 404 to the metathesis reactor 220. The isomerization reactor 210 is operable to receive one of the following: an input C4 raffinate hydrocarbon feedstream 400 or a combined C4 raffinate hydrocarbon feedstream 401 formed by the combination of the input C4 raffinate hydrocarbon feedstream 400 and the C4-rich stream 414 and / or a portion of the cracking outlet streams 419, 414 that contain C4 hydrocarbons. The isomerization reactor 210 is also configured to produce an isomerized C4 raffinate hydrocarbon feedstream 402 for supply to the metathesis reactor 220.

[0029] In some embodiments of system 200, the metathesis reactor 220 and the cracking reactor 230 can be fixed bed reactors. In some embodiments, the metathesis reactor 220 and the cracking reactor 230 can operate at different temperatures. For example, in some embodiments, the metathesis reactor 220 can be a high-temperature metathesis reactor 220 that includes a silica-supported tungstate catalyst and operates at a temperature of about 500°C to about 550°C. In some other exemplary embodiments, the metathesis reactor 220 can be a low-temperature metathesis reactor 220 that includes an alumina-supported rhenium catalyst and operates at a temperature of about 50°C to about 100°C. In some embodiments, the cracking reactor 230 includes a high-silica ZSM-5 catalyst and operates at a temperature of about 550°C to about 575°C. According to at least some aspects of the present disclosure, when the C4 raffinate hydrocarbon feed stream contains about 70 mol% cis-2-butene and trans-2-butene and about 30 mol% n-butane, the system 200 can be operated to produce a propylene product distribution of more than 40 mol%.

[0030] Examples

[0031] The examples provided below illustrate selected aspects of various methods and systems for producing propylene from a C4 raffinate hydrocarbon feed stream.

[0032] Example 1

[0033] As shown in Table 1 by simulation determination using the AspenPlus 10 simulator based on a C4 raffinate feed stream using a W / Si catalyst and a mixture containing 30 mol% n-butane and 70 mol% cis-2-butene and trans-2-butene Figure 1 the production yields of the method 100 and system 200 described therein. The simulated product yield distributions are provided in Tables 1 and 2 and Figure 2 are provided in.

[0034] Table 1 - Material Balance in wt%

[0035]

[0036] Table 2 - Material Balance in Mol%

[0037]

[0038] When the scope of the present disclosure is disclosed, ranges from any lower limit can be combined with any upper limit to recite ranges not expressly recited, and ranges from any lower limit can be combined with any other lower limit to recite ranges not expressly recited. In the same manner, ranges from any upper limit can be combined with any other upper limit to recite ranges not expressly recited. Additionally, even if not expressly recited, the values recited in a range include every and each value within that range. Thus, each point or individual value can serve as its own lower or upper limit, combined with any other point or individual value or any other lower or upper limit, to recite ranges not expressly recited.

[0039] Other objects, features, and advantages of the disclosure will become apparent from the foregoing drawings, detailed description, and examples. However, it should be understood that although specific embodiments of the disclosure are shown, the drawings, detailed description, and examples are given by way of illustration only and are not intended to be limiting. In additional embodiments, features from specific embodiments can be combined with features from other embodiments. For example, features from one embodiment can be combined with any of the features from other embodiments. In additional embodiments, additional features can be added to the specific embodiments described herein.

Claims

1. A process for producing propylene, the process comprising: Supplying a C4 raffinate hydrocarbon stream to a metathesis reactor to produce a metathesis effluent stream, the C4 raffinate hydrocarbon stream substantially containing one or more C4 hydrocarbons, and the metathesis effluent stream containing a plurality of C5+ hydrocarbons, propylene and one or more C4 hydrocarbons; Separating the plurality of C5+ hydrocarbons from the propylene and the one or more C4 hydrocarbons in the metathesis effluent stream to produce a C5+ feed stream and a first propylene-rich stream; Supplying the C5+ feed stream to a cracking reactor to produce a cracking effluent stream containing propylene and one or more C4 hydrocarbons; Separating the propylene from the one or more C4 hydrocarbons in the cracking effluent stream to produce a second propylene-rich stream and a C4-rich stream; and Recycling the C4-rich stream to the metathesis reactor as part of the C4 raffinate hydrocarbon stream.

2. The process according to claim 1, wherein the metathesis reactor and the cracking reactor are operated at different temperatures.

3. The process according to claim 1 or claim 2, wherein the metathesis reactor is a high-temperature metathesis reactor, which comprises a silica-supported tungstate catalyst and is operated at a temperature of about 500 °C to about 550 °C.

4. The process according to claim 1 or claim 2, wherein the metathesis reactor is a low-temperature metathesis reactor, which comprises an alumina-supported rhenium catalyst and is operated at a temperature of about 50 °C to about 100 °C.

5. The process according to any one of claims 1-4, wherein the cracking reactor comprises a high-silica ZSM-5 catalyst and is operated at a temperature of about 550 °C to about 575 °C.

6. The process according to any one of claims 1-5, which further comprises: Supplying the C4 raffinate hydrocarbon stream to an isomerization reactor before supplying the C4 raffinate hydrocarbon stream to the metathesis reactor.

7. The process according to any one of claims 1-6, wherein the C4 raffinate hydrocarbon stream comprises a portion of the metathesis effluent stream and a portion of the cracking effluent stream.

8. The process according to any one of claims 1-7, wherein the metathesis effluent stream is supplied to a separation column sequence to produce the C5+ feed stream and the first propylene-rich stream.

9. The process according to any one of claims 1-7, wherein the cracking effluent stream is supplied to a separation column sequence to produce the second propylene-rich stream and the C4-rich stream.

10. The process according to any one of claims 1-9, wherein the C4 raffinate hydrocarbon stream contains one or more of cis-2-butene, trans-2-butene and butane.

11. The process according to any one of claims 1-10, wherein when the C4 raffinate hydrocarbon stream contains about 70 mol% of cis-2-butene and trans-2-butene and about 30 mol% of n-butane, the amount of propylene produced by combining the first propylene-rich stream and the second propylene-rich stream exceeds 40 mol%.

12. A system for producing propylene, the system comprising: A metathesis reactor operable to receive a C4 raffinate hydrocarbon stream and produce a metathesis outlet stream, the C4 raffinate hydrocarbon stream substantially containing one or more C4 hydrocarbons, and the metathesis outlet stream containing a plurality of C5+ hydrocarbons, propylene and one or more C4 hydrocarbons; A plurality of separation towers in fluid communication with the metathesis reactor and the cracking reactor, the plurality of separation towers operable to receive the metathesis outlet stream and produce a C5+ feed stream and a first propylene-rich stream; And A cracking reactor in fluid communication with the plurality of separation towers and operable to receive the C5+ feed stream and produce a cracking outlet stream containing propylene and one or more C4 hydrocarbons, supplying the cracking outlet stream to the plurality of separation towers, thereby separating the propylene from the one or more C4 hydrocarbons in the cracking outlet stream to produce a second propylene-rich stream and a C4-rich stream.

13. The system according to claim 12, wherein the C4-rich stream is recycled to the metathesis reactor as part of the C4 raffinate hydrocarbon stream; and wherein the plurality of separation towers comprises a deethanizer, a depropanizer and a debutanizer.

14. The system according to claim 12 or claim 13, Wherein the metathesis reactor is a high-temperature metathesis reactor comprising a silica-supported tungstate catalyst and operating at a temperature of about 500°C to about 550°C, or the metathesis reactor is a low-temperature metathesis reactor comprising an alumina-supported rhenium catalyst and operating at a temperature of about 50°C to about 100°C; and Wherein the cracking reactor comprises a high-silica ZSM-5 catalyst and operates at a temperature of about 550°C to about 575°C.

15. The system according to any one of claims 12-14, further comprising: An isomerization reactor in fluid communication with the metathesis reactor and the plurality of separation towers, the isomerization reactor operable to receive one of the following: an input C4 raffinate hydrocarbon stream or a combined C4 raffinate hydrocarbon stream formed by a combination of the input C4 raffinate hydrocarbon stream and the C4-rich stream or a portion of the cracking outlet stream containing C4 hydrocarbons, the isomerization reactor configured to produce an isomerized C4 raffinate hydrocarbon stream for supply to the metathesis reactor.

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