Methods and systems to produce ethylene, propylene, and / or 1-hexene from butenes

Abstract

A method provided herein includes: steam cracking at least a hydrocarbon feedstock to produce a steam cracked stream; providing at least the steam cracked stream to a downstream separation section to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream; metathesizing at least the C4 raffinate stream to produce a metathesis product stream; separating the metathesis product stream into at least a C2-C3 olefin stream and a C4 olefin stream; purging a portion of the C4 olefin stream to produce a purge stream; hydrogenating the purged stream to produce a saturated stream; combining the saturated stream with the hydrocarbon feedstock prior to steam cracking; combining a remainder of the C4 olefin stream after purging with the C4 raffinate stream prior to metathesis; and providing the C2-C3 olefin stream to the downstream separation section along with the steam cracked stream to produce the ethene product stream and the propene product stream.

Description

METHODS AND SYSTEMS TO PRODUCE ETHYLENE, PROPYLENE, AND / OR 1-HEXENE FROM BUTENESTECHNICAL FIELD

[0001] The present disclosure generally relates to systems and methods for performing metathesis of a C4 stream, along with steam cracking of one or more olefin or paraffin streams (e.g., C4, C5, and / or Ce hydrocarbon streams), to produce chemical feedstocks, including olefins such as ethene (also referred to herein as ethylene), propene (also referred to herein as propylene) and / or hex-l-ene (also referred to herein as 1-hexene). More specifically, the present disclosure relates to systems and methods for producing ethene, propene, and / or hex-l-ene involving metathesis of a C4 stream.BACKGROUND

[0002] A hydrocarbon feedstock can be processed using steam cracking to produce ethene as a maj or product along with other side products, such as propene and various unsaturated C4 species (e.g., butenes, 2- methylprop-l-ene, butynes, and buta- 1,3 -diene). While ethene and propene are considered high value olefins, many of the remaining side products are generally considered lower value olefins. While olefin metathesis can be used to convert lower value C4 and C5 olefins into higher value propene, this typically involves the use of an ethene co-feed, which undesirably consumes a higher value olefin as part of the process. As such, there remains a need to develop improved systems and methods for converting hydrocarbon feedstock into high value olefin chemical feedstocks.SUMMARY

[0003] To address these demands in the industry and other shortcomings in the art, Applicant has developed systems and methods for performing metathesis of a C4 stream to produce chemical feedstocks, including olefins such as ethene, propene, and / or hex-l-ene. Provided here are methods for production of ethene, propene, and / or hex-l-ene involving metathesis of a C4 stream. In certain examples, the method includes the steps of steam cracking at least a hydrocarbon feedstock to produce a steam cracked stream and providing at least the steam cracked stream to a downstream separation section to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream. The method includes the steps of metathesizing at least the C4 raffinate stream to produce a metathesis product stream and separating the metathesis product stream into at least a C2-C3 olefin stream and a C4 olefin stream. The method includes the steps purging a portion of the C4 olefin stream to produce a purge stream that contains at least one paraffin and hydrogenating the purged stream to produce a saturated stream. The method includes the steps combining the saturated stream with the hydrocarbon feedstock prior to steam cracking, combining a remainder of the C4 olefin stream after purging with the C4 raffinate stream prior to metathesis, and providing the C2-C3 olefin stream to the downstream separation section along with the steam cracked stream to produce the ethene product stream and the propene product stream.

[0004] In certain examples, the C4 raffinate stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes. In certain examples, separating the metathesis product stream includes the steps of separating the metathesis product stream into at least the C2-C3 olefin stream, the C4 olefin stream, a C5 olefin stream, and a Ce olefin stream. In certain examples, the method includes the steps of combining the C5 olefin stream with the combination of the remainder of the C4 olefin stream and the C4 raffinate stream prior to metathesis. In certain examples, the method includes the steps of combining the C5 olefin stream with the purge stream prior to hydrogenation. In certain examples, the method includes the steps of performing Ce isomerization of the Ce olefin stream to produce a Ce isomerized stream, in which hex-2 -enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization, and separating a first portion of the Ce isomerized stream as a hex-l-ene product stream, in which a remainder of the Ce isomerized stream is combined with the Ce olefin stream prior to Ce isomerization. In certain examples, performing Ce isomerization of the Ce olefin stream includes the steps of heating the Ce olefin stream to a temperature ranging from about 350 °C to about 550 °C and pressurizing the Ce olefin stream to a pressure ranging from about 100 kilopascals (kPa) to about 2100 kPa (from about 0 bar gauge (barg) to about 20 barg) before contacting an isomerization catalyst at a weight hourly space velocity (WHSV) of from about 0.1 per hour (h1) to about 20 h1, in which the Ce olefin stream is in a gas phase, a liquid phase, or a mixed phase during Ce isomerization, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolitebased isomerization catalyst.

[0005] In certain examples, separating the metathesis product stream includes the steps of separating the metathesis product stream into the C2-C3 olefin stream, the C4 olefin stream, and a Ce-Ce olefin stream. In certain examples, the method includes the steps of catalytically cracking the Ce-Ce olefin stream to produce a catalytically cracked stream, in which the Ce-Ce olefin stream is heated to a temperature ranging from about 450 °C to about 650 °C before contacting a ZSM-5 based cracking catalyst of the catalytic cracking reactor at a WHSV of from about 2.5 h-1to about 20 h1, and providing the C2-C3 olefin stream and the catalytically cracked stream to the downstream separation section along with the steam cracked stream to produce at least the ethene product stream, the propene product stream, and the C4 raffinate stream. In certain examples, the method includes the steps of, responsive to a but-l-ene content of less than 15 mol. % in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, performing C4 isomerization of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream prior to metathesis, in which but-2-ene in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is converted into but-l-ene during C4 isomerization, and responsive to the but-l-ene content being greater than or equal to 15 mol. %, metathesizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream without C4 isomerization.

[0006] In certain examples, the method includes the steps of heating the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a temperature ranging from about 250 °C to about 500 °C and pressurizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before contacting an isomerization catalyst at a WHSV from about 0. 1 h-1to about 20 h1, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase during C4 isomerization, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolite-based isomerization catalyst. In certain examples, metathesizing at least the C4 raffinate stream includes the steps of heating a combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a temperature ranging from about 35 °C to about 100 °C and pressurizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before contacting a metathesis catalyst at a WHSV from about 0.1 h1to about 20 h1and in the absence of an ethene co-feed, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase during metathesis, and in which the metathesis catalyst is a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina-supported rhenium-based metathesis catalyst. In certain examples, the method includes the steps of receiving at least a portion of the C4 raffinate stream from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a methyl tert-butyl ether (MTBE) reactor, a but-l-ene (Bl) column, a but-2-enes (B2) column, a butadiene hydrogenation reactor, a methanol-to-olefins (MTO) process, or a refinery fluid catalytic cracking (FCC) process, or any combination thereof.

[0007] Provided here are systems for production of ethene, propene, and / or hex-l-ene involving metathesis of a C4 stream. In certain examples, the system includes a steam cracker configured to receive and steam crack at least a hydrocarbon feedstock to produce a steam cracked stream. The system includes a downstream separation section configured to receive and separate at least the steam cracked stream to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream. The system includes a metathesis reactor configured to receive and metathesize at least the C4 raffinate stream to produce a metathesis product stream. The system includes a C3 column configured to receive and separate the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream, the C2-C3 olefin stream being provided to the downstream separation section for separation into the ethene product stream and the propene product stream. The system includes a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, a portion of the C4 olefin stream being purged to produce a purge stream containing at least one paraffin and a remainder of the C4 olefin stream being provided to the metathesis reactor along with the C4 raffinate stream for metathesis to produce the metathesis product stream. The system includes a total hydrogenation unitconfigured to receive and hydrogenate at least the purge stream to produce a saturated stream, the saturated stream being provided to the steam cracker along with the hydrocarbon feedstock for steam cracking to produce the steam cracked stream. In certain examples, the C4 raffinate stream contains from about 65 mol. % to about 98 mol. % n-butenes.

[0008] In certain examples, the system includes a C5 column configured to receive and separate the C4+ olefin stream into a C4-C5 olefin stream and a Ce olefin stream, in which the C4 column is configured to receive and separate the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream. In certain examples, the C5 olefin stream is provided along with the remainder of the C4 olefin stream and the C4 raffinate stream to the metathesis reactor for metathesis to produce the metathesis product stream. In certain examples, the C5 olefin stream is provided along with the purge stream to the total hydrogenation unit for hydrogenation to produce the saturated stream. In certain examples, the system includes a Ce isomerization reactor configured to receive and isomerize the Ce olefin stream to produce a Ce isomerized stream, in which hex-2 -enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization, and a Ce fractionator configured to receive and separate a first portion of the Ce isomerized stream to produce a hex-l-ene product stream, in which a remainder of the Ce isomerized stream is provided to the Ce isomerization reactor along with the Ce olefin stream for Ce isomerization to produce the Ce isomerized stream. In certain examples, the Ce isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed downflow reactor, in which the Ce isomerization reactor is configured to receive the Ce olefin stream at a temperature ranging from about 250 °C to about 500 °C and at a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before the Ce olefin stream contacts an isomerization catalyst of the Ce isomerization reactor at a WHSV from about 0. 1 h-1to about 20 h1, in which the Ce olefin stream is in a gas phase, a liquid phase, or a mixed phase, and in which the Ce isomerization reactor has an operating cycle time from about 1 day to about 100 days, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolite-based isomerization catalyst. In certain examples, the system has a plurality of Ce isomerization reactors that includes the Ce isomerization reactor, in which a second Ce isomerization reactor of the plurality of Ce isomerization reactors is configured to operate in regeneration mode to regenerate the isomerization catalyst of the second Ce isomerization reactor, and in which regeneration mode operation includes the second Ce isomerization reactor being configured to receive a stream of nitrogen, air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C. In certain examples, the plurality of Ce isomerization reactors includes a third Ce isomerization reactor configured to remain in standby mode while the Ce isomerization reactor is configured to perform Ce isomerization of the Ce olefin stream and the second Ce isomerization reactor is configured to operate in regeneration mode.

[0009] In certain examples, the C4 column is configured to receive and separate the C4+ olefin stream into the C4 olefin stream and a Cs-Ce olefin stream. In certain examples, the system includes a catalytic cracking reactor configured to receive and catalytically crack at least the Cs-Ce olefin stream to produce a catalytically cracked stream, in which the catalytically cracked stream is provided to the downstream separation section along with the steam cracked stream and the C2-C3 olefin stream for separation to produce at least the ethene product stream, the propene product stream, and the C4 raffinate stream. In certain examples, the catalytic cracking reactor is a fixed-bed reactor, in which the catalytic cracking reactor is configured to receive the C5- Ce olefin stream at a temperature ranging from about 450 °C to about 650 °C before contacting a ZSM-5 based cracking catalyst of the catalytic cracking reactor at a WHSV from about 2.5 h-1to about 20 h1. In certain examples, the system has a plurality of catalytic cracking reactors that includes the catalytic cracking reactor, in which a second catalytic cracking reactor of the plurality of catalytic cracking reactors is configured to operate in regeneration mode to regenerate a ZSM-5 based cracking catalyst of the second catalytic cracking reactor, and in which regeneration mode operation includes the catalytic cracking reactor being configured to receive a stream of nitrogen, air, enriched air, or oxygen at a temperature ranging from about 450 °C to about 550 °C. In certain examples, the plurality of catalytic cracking reactors includes a third catalytic cracking reactor configured to remain in standby mode while the catalytic cracking reactor is configured to catalytically crack the C -Ce olefin stream and the second catalytic cracking reactor is configured to operate in regeneration mode.

[0010] In certain examples, the system includes a C4 isomerization reactor configured to conditionally receive an isomerize a combination of the remainder of the C4 olefin stream and the C4 raffinate stream before upstream of the metathesis reactor, in which but-2-enes within the combination of the remainder of the C4 olefin stream and the C4 raffinate stream are converted into but-l-ene during C4 isomerization, and a butene analyzer configured to determine a but-l-ene content of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, and, in response to determining that the but-l-ene content is less than 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the C4 isomerization reactor to upstream of the metathesis reactor, and in response to determining that the but-l- ene content is greater than or equal to 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the metathesis reactor without traversing the C4 isomerization reactor. In certain examples, the C4 isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed down-flow reactor, in which the C4 isomerization reactor is configured to receive the combination of the remainder of the C4 olefin stream and the C4 raffinate stream at a temperature ranging from about 250 °C to about 500 °C and at a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before the combination of the remainder of the C4 olefin stream and the C4 raffinate stream contacts an isomerization catalyst of the C4 isomerization reactor at a WHSV from about 0.1 h1to about 20 h1, in which thecombination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase, and in which the C4 isomerization reactor has an operating cycle time from about 1 day to about 100 days, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolitebased isomerization catalyst. In certain examples, the system has a plurality of C4 isomerization reactors that includes the C4 isomerization reactor, in which a second C4 isomerization reactor of the plurality of C4 isomerization reactors is configured to operate in regeneration mode to regenerate the isomerization catalyst of the second C4 isomerization reactor, and in which regeneration mode operation includes the second C4 isomerization reactor being configured to receive a stream of nitrogen, air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C. In certain examples, the system includes the plurality of C4 isomerization reactors includes a third C4 isomerization reactor configured to remain in standby mode while the C4 isomerization reactor is configured to isomerize the combination of the remainder of the C4 olefin stream and the C4 raffinate stream and the second C4 isomerization reactor is configured to operate in regeneration mode.

[0011] In certain examples, the metathesis reactor is a fixed-bed up-flow reactor or a fixed-bed down-flow reactor, in which the metathesis reactor is configured to receive a combination of the remainder of the C4 olefin stream and the C4 raffinate stream at a temperature ranging from about 35 °C to about 100 °C and at a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before the combination of the remainder of the C4 olefin stream and the C4 raffinate stream contacts a metathesis catalyst of the metathesis reactor at a WHSV from about 0.1 h-1to about 20 h1in the absence of an ethene co-feed, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase, and the metathesis reactor has an operating cycle time from about 1 day to about 100 days, and the metathesis catalyst is a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina-supported rhenium-based metathesis catalyst. In certain examples, the system has a plurality of metathesis reactors that includes the metathesis reactor, in which a second metathesis reactor of the plurality of metathesis reactors is configured to operate in regeneration mode to regenerate the metathesis catalyst of the second metathesis reactor, and regeneration mode operation includes the second metathesis reactor being configured to receive a stream of air, enriched air, or oxygen at a temperature ranging from about 350 °C to about 550 °C. In certain examples, the plurality of metathesis reactors includes a third metathesis reactor configured to remain in standby mode while the metathesis reactor is configured to metathesize the combination of the remainder of the C4 olefin stream and the C4 raffinate stream and the second metathesis reactor is configured to operate in regeneration mode. In certain examples, at least a portion the C4 raffinate stream is received by the metathesis reactor from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a MTBEreactor, a Bl column, a B2 column, a butadiene hydrogenation reactor, a MTO reactor, or a refinery FCC reactor, or any combination thereof.

[0012] Still other aspects and advantages of these exemplary embodiments and other embodiments, are discussed in detail herein. Moreover, it is to be understood that both the foregoing information and the following detailed description provide merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying 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 embodiments of the present disclosure, and together with the detailed description, serve to explain principles of the embodiments discussed herein. No attempt is made to show structural details of this disclosure in more detail than may be necessary for a fundamental understanding of the embodiments discussed herein and the various ways in which they may be practiced.

[0014] FIG. 1 is a diagrammatic representation of a first embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0015] FIG. 2 is a diagrammatic representation of a second embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0016] FIG. 3 is a diagrammatic representation of a third embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0017] FIG. 4 is a diagrammatic representation of a fourth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0018] FIG. 5 is a diagrammatic representation of a fifth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0019] FIG. 6 is a diagrammatic representation of an embodiment of a control system for controlling the systems for metathesizing a C4 stream to produce chemical feedstocks.DETAILED DESCRIPTION

[0020] The present disclosure describes various embodiments related to processes, methods, and systems for using metathesis of a C4 stream to produce chemical feedstocks, such as ethene, propene, and / or hex-1- ene. Further embodiments may be described and disclosed.

[0021] 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, devices, and systemsmay not have been described in particular detail in order not to unnecessarily obscure the various embodiments. Additionally, illustrations of the various embodiments may omit certain features or details in order to not obscure the various embodiments.

[0022] The description may use the phrases “in some embodiments,” “in various embodiments,” “in an embodiment,” or “in certain embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous.

[0023] The use of the words “a” or “an” when used in conjunction with any of the terms “comprising,” “including,” “containing,” or “having,” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

[0024] The term “about” refers to a range of values including the specified value, which a person of ordinary skill in the art would consider reasonably similar to the specified value. In embodiments, “about” refers to values within a standard deviation using measurements generally acceptable in the art. In one non-limiting embodiment, when the term “about” is used with a particular value, then “about” refers to a range extending to ±10% of the specified value, alternatively ±5% of the specified value, or alternatively ±1% of the specified value, or alternatively ±0.5% of the specified value. In embodiments, “about” refers to the specified value.

[0025] The terms “reducing,” “reduced,” or any variation thereof, when used in the claims and / or the specification includes any measurable decrease or complete removal to achieve a desired result.

[0026] The terms “wt. %”, “vol. %”, or “mol. %” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of a component in 100 grams of the material is 10 wt.% of such component.

[0027] The term “enriched” or “rich” or their variations mean an amount of at least generally about 15 mol. %, and preferably about 20 mol. %, of a compound or class of compounds in a stream. The term “ppmw” refers to part per million by weight.

[0028] As used herein, the term “Cx.ycompounds,” in which x and y are positive integer values, refers to hydrocarbon-based compounds, each compound containing between x and y carbon atoms, x and y inclusive. For example, a C3-5 stream or a or a C3-C5 stream refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing 3, 4, or 5 carbon atoms.

[0029] As used herein, the term “Cx+ compounds,” in which x is a positive integer value, refers to hydrocarbon-based compounds, each compound containing at least x carbon atoms. For example, a C3+ stream refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing 3 or more (e.g., 3, 4, 5, 6, and so forth) carbon atoms.

[0030] As used herein, the term “Cx. compounds,” in which x is a positive integer value, refers to hydrocarbon-based compounds, each compound containing no more than x carbon atoms. For example, a C4- stream refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing 4, 3, 2, or 1 carbon atoms. It may be noted that, in certain cases, a “Cx. stream” may also include hydrogen (H2), in addition to hydrocarbons having x or fewer carbon atoms.

[0031] As used herein, when a first component is described as receiving (or being configured to receive) a stream from a second component, or when a first component is described as providing (or being configured to provide) a stream to a second component, the first and second components may be alternatively described as being in fluid communication with one another. It may be appreciated that, for the various streams discussed herein, a given stream substantially contains the compound or class of compounds in the name of the stream (e.g., an ethene product stream substantially contains ethene, a C4 olefin stream substantially contains C4 olefins, a Ce olefin stream substantially contains Ce olefins), and the stream may also include other components.

[0032] The term “substantially contains” means that the mixture includes at least 50 mol. % of the named compound or class of compounds, such as at least 60 mol. %, at least 70 mol. %, at least 80 mol. %, at least 90 mol. %, at least 95 mol. %, at least 98 mol. %, at least 99 mol. %, or 100 mol. %, or any sub-ranges therebetween.

[0033] The term “but-2-enes” includes (Z)-but-2-ene (c / .s-but-2-cnc). or (£)-but-2-ene ( / ram-biit-2-cnc). or combinations thereof. The term “pent-2 -enes” includes (Z)-pent-2-ene, or (£)-pent-2-ene, or combinations thereof. The term “hex-2 -enes” includes (Z)-hex-2-ene, or (£)-hex-2-ene, or combinations thereof. The term “hex-3-enes” includes (Z) -hex-3 -ene, or (£)-hex-3-ene, or combinations thereof.

[0034] As used herein, the term “zone” can refer to an area including one or more units and / or one or more sub-zones. Units can include one or more reactors or reactor vessels, separators, strippers, extraction columns, fractionation columns, heaters, exchangers, pipes, pumps, valves, compressors, sensors, and controllers. Additionally, a unit, such as a reactor, dryer, or vessel, can further include one or more zones or sub-zones that contain various equipment. As used herein, the term “LPG” refers to liquified petroleum gas, and the term “NGL” refers to natural gas liquids.

[0035] Provided here are methods for production of ethene, propene, and / or hex- 1 -ene involving metathesis of a C4 stream. In certain examples, the method includes the steps of steam cracking at least a hydrocarbon feedstock to produce a steam cracked stream and providing at least the steam cracked stream to a downstream separation section to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream . The method includes the steps of metathesizing at least the C4 raffinate stream to produce a metathesis product stream and separating the metathesis product stream into at least a C2-C3 olefin stream and a C4 olefin stream. The method includes the steps purging a portion of the C4 olefin stream to produce a purge streamthat contains at least one paraffin and hydrogenating the purged stream to produce a saturated stream. The method includes the steps combining the saturated stream with the hydrocarbon feedstock prior to steam cracking, combining a remainder of the C4 olefin stream after purging with the C4 raffinate stream prior to metathesis, and providing the C2-C3 olefin stream to the downstream separation section along with the steam cracked stream to produce the ethene product stream and the propene product stream.

[0036] In certain examples, the C4 raffinate stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes. In certain examples, separating the metathesis product stream includes the steps of separating the metathesis product stream into at least the C2-C3 olefin stream, the C4 olefin stream, a C5 olefin stream, and a Ce olefin stream. In certain examples, the method includes the steps of combining the C5 olefin stream with the combination of the remainder of the C4 olefin stream and the C4 raffinate stream prior to metathesis. In certain examples, the method includes the steps of combining the C5 olefin stream with the purge stream prior to hydrogenation. In certain examples, the method includes the steps of performing Ce isomerization of the Ce olefin stream to produce a Ce isomerized stream, in which hex-2 -enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization, and separating a first portion of the Ce isomerized stream as a hex-l-ene product stream, in which a remainder of the Ce isomerized stream is combined with the Ce olefin stream prior to Ce isomerization. In certain examples, performing Ce isomerization of the Ce olefin stream includes the steps of heating the Ce olefin stream to a temperature ranging from about 350 °C to about 550 °C and pressurizing the Ce olefin stream to a pressure ranging from about 100 kilopascal (kPa) to about 2100 kPa (from about 0 bar gauge (barg) to about 20 barg) before contacting an isomerization catalyst at a weight hourly space velocity (WHSV) of from about 0.1 per hour (h1) to about 20 h1, in which the Ce olefin stream is in a gas phase, a liquid phase, or a mixed phase during Ce isomerization, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolitebased isomerization catalyst.

[0037] In certain examples, separating the metathesis product stream includes the steps of separating the metathesis product stream into the C2-C3 olefin stream, the C4 olefin stream, and a Ce-Ce olefin stream. In certain examples, the method includes the steps of catalytically cracking the Ce-Ce olefin stream to produce a catalytically cracked stream, in which the Ce-Ce olefin stream is heated to a temperature ranging from about 450 °C to about 650 °C before contacting a ZSM-5 based cracking catalyst of the catalytic cracking reactor at a WHSV of from about 2.5 h1to about 20 h1, and providing the C2-C3 olefin stream and the catalytically cracked stream to the downstream separation section along with the steam cracked stream to produce at least the ethene product stream, the propene product stream, and the C4 raffinate stream. In certain examples, the method includes the steps of, responsive to a but-l-ene content of less than 15 mol. % in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, performing C4 isomerization of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream prior to metathesis, in whichbut-2-ene in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is converted into but-l-ene during C4 isomerization, and responsive to the but-l-ene content being greater than or equal to 15 mol. %, metathesizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream without C4 isomerization.

[0038] In certain examples, the method includes the steps of heating the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a temperature ranging from about 250 °C to about 500 °C and pressurizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before contacting an isomerization catalyst at a WHSV from about 0. 1 h-1to about 20 h1, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase during C4 isomerization, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolite-based isomerization catalyst. In certain examples, metathesizing at least the C4 raffinate stream includes the steps of heating a combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a temperature ranging from about 35 °C to about 100 °C and pressurizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before contacting a metathesis catalyst at a WHSV from about 0.1 h1to about 20 h1and in the absence of an ethene co-feed, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase during metathesis, and the metathesis catalyst is a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina-supported rhenium-based metathesis catalyst. In certain examples, the method includes the steps of receiving at least a portion of the C4 raffinate stream from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a methyl tert-butyl ether (MTBE) reactor, a but-l-ene (Bl) column, a but-2-enes (B2) column, a butadiene hydrogenation reactor, a methanol-to-olefins (MTO) process, or a refinery fluid catalytic cracking (FCC) process, or any combination thereof.

[0039] Provided here are systems for production of ethene, propene, and / or hex-l-ene involving metathesis of a C4 stream. In certain examples, the system includes a steam cracker configured to receive and steam crack at least a hydrocarbon feedstock to produce a steam cracked stream. The system includes a downstream separation section configured to receive and separate at least the steam cracked stream to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream. The system includes a metathesis reactor configured to receive and metathesize at least the C4 raffinate stream to produce a metathesis product stream. The system includes a C3 column configured to receive and separate the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream, the C2-C3 olefin stream being provided to the downstream separation section for separation into the ethene product stream and the propene product stream. The systemincludes a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, a portion of the C4 olefin stream being purged to produce a purge stream containing at least one paraffin and a remainder of the C4 olefin stream being provided to the metathesis reactor along with the C4 raffinate stream for metathesis to produce the metathesis product stream. The system includes a total hydrogenation unit configured to receive and hydrogenate at least the purge stream to produce a saturated stream, the saturated stream being provided to the steam cracker along with the hydrocarbon feedstock for steam cracking to produce the steam cracked stream. In certain examples, the C4 raffinate stream contains from about 65 mol. % to about 98 mol. % n-butenes.

[0040] In certain examples, the system includes a C5 column configured to receive and separate the C4+ olefin stream into a C4-C5 olefin stream and a Ce olefin stream, in which the C4 column is configured to receive and separate the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream. In certain examples, the C5 olefin stream is provided along with the remainder of the C4 olefin stream and the C4 raffinate stream to the metathesis reactor for metathesis to produce the metathesis product stream. In certain examples, the C5 olefin stream is provided along with the purge stream to the total hydrogenation unit for hydrogenation to produce the saturated stream. In certain examples, the system includes a Ce isomerization reactor configured to receive and isomerize the Ce olefin stream to produce a Ce isomerized stream, in which hex-2 -enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization, and a Ce fractionator configured to receive and separate a first portion of the Ce isomerized stream to produce a hex-l-ene product stream, in which a remainder of the Ce isomerized stream is provided to the Ce isomerization reactor along with the Ce olefin stream for Ce isomerization to produce the Ce isomerized stream. In certain examples, the Ce isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed downflow reactor, in which the Ce isomerization reactor is configured to receive the Ce olefin stream at a temperature ranging from about 250 °C to about 500 °C and at a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before the Ce olefin stream contacts an isomerization catalyst of the Ce isomerization reactor at a WHSV from about 0. 1 h-1to about 20 h1, in which the Ce olefin stream is in a gas phase, a liquid phase, or a mixed phase, in which the Ce isomerization reactor has an operating cycle time from about 1 day to about 100 days, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolite-based isomerization catalyst. In certain examples, the system has a plurality of Ce isomerization reactors that includes the Ce isomerization reactor, in which a second Ce isomerization reactor of the plurality of Ce isomerization reactors is configured to operate in regeneration mode to regenerate the isomerization catalyst of the second Ce isomerization reactor, and in which regeneration mode operation includes the second Ce isomerization reactor being configured to receive a stream of nitrogen, air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C. In certain examples, the plurality of Ce isomerization reactors includes a thirdCe isomerization reactor configured to remain in standby mode while the Ce isomerization reactor is configured to perform Ce isomerization of the Ce olefin stream and the second Ce isomerization reactor is configured to operate in regeneration mode.

[0041] In certain examples, the C4 column is configured to receive and separate the C4+ olefin stream into the C4 olefin stream and a Ce-Ce olefin stream. In certain examples, the system includes a catalytic cracking reactor configured to receive and catalytically crack at least the Ce-Ce olefin stream to produce a catalytically cracked stream, in which the catalytically cracked stream is provided to the downstream separation section along with the steam cracked stream and the C2-C3 olefin stream for separation to produce at least the ethene product stream, the propene product stream, and the C4 raffinate stream. In certain examples, the catalytic cracking reactor is a fixed-bed reactor, in which the catalytic cracking reactor is configured to receive the C5- Ce olefin stream at a temperature ranging from about 450 °C to about 650 °C before contacting a ZSM-5 based cracking catalyst of the catalytic cracking reactor at a WHSV from about 2.5 h-1to about 20 h1. In certain examples, the system has a plurality of catalytic cracking reactors that includes the catalytic cracking reactor, in which a second catalytic cracking reactor of the plurality of catalytic cracking reactors is configured to operate in regeneration mode to regenerate a ZSM-5 based cracking catalyst of the second catalytic cracking reactor, and in which regeneration mode operation includes the catalytic cracking reactor being configured to receive a stream of nitrogen, air, enriched air, or oxygen at a temperature ranging from about 450 °C to about 550 °C. In certain examples, the plurality of catalytic cracking reactors includes a third catalytic cracking reactor configured to remain in standby mode while the catalytic cracking reactor is configured to catalytically crack the Ce-Ce olefin stream, and the second catalytic cracking reactor is configured to operate in regeneration mode.

[0042] In certain examples, the system includes a C4 isomerization reactor configured to conditionally receive an isomerize a combination of the remainder of the C4 olefin stream and the C4 raffinate stream before upstream of the metathesis reactor, in which but-2-enes within the combination of the remainder of the C4 olefin stream and the C4 raffinate stream are converted into but-l-ene during C4 isomerization, and a butene analyzer configured to determine a but-l-ene content of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, and, in response to determining that the but-l-ene content is less than 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the C4 isomerization reactor to upstream of the metathesis reactor, and in response to determining that the but-l- ene content is greater than or equal to 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the metathesis reactor without traversing the C4 isomerization reactor. In certain examples, the C4 isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed down-flow reactor, in which the C4 isomerization reactor is configured to receive the combination of the remainder of the C4 olefin stream and the C4 raffinate stream at a temperature ranging from about 250 °C to about 500 °Cand at a pressure ranging from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg) before the combination of the remainder of the C4 olefin stream and the C4 raffinate stream contacts an isomerization catalyst of the C4 isomerization reactor at a WHSV from about 0.1 h-1to about 20 h1, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase, in which the C4 isomerization reactor has an operating cycle time from about 1 day to about 100 days, and in which the isomerization catalyst is a potassium, magnesium, calcium, or zeolitebased isomerization catalyst. In certain examples, the system has a plurality of C4 isomerization reactors that includes the C4 isomerization reactor, in which a second C4 isomerization reactor of the plurality of C4 isomerization reactors is configured to operate in regeneration mode to regenerate the isomerization catalyst of the second C4 isomerization reactor, and in which regeneration mode operation includes the second C4 isomerization reactor being configured to receive a stream of nitrogen, air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C. In certain examples, the system includes the plurality of C4 isomerization reactors includes a third C4 isomerization reactor configured to remain in standby mode while the C4 isomerization reactor is configured to isomerize the combination of the remainder of the C4 olefin stream and the C4 raffinate stream and the second C4 isomerization reactor is configured to operate in regeneration mode.

[0043] In certain examples, the metathesis reactor is a fixed-bed up-flow reactor or a fixed-bed down-flow reactor, in which the metathesis reactor is configured to receive a combination of the remainder of the C4 olefin stream and the C4 raffinate stream at a temperature ranging from about 35 °C to about 100 °C and at a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before the combination of the remainder of the C4 olefin stream and the C4 raffinate stream contacts a metathesis catalyst of the metathesis reactor at a WHSV from about 0.1 h-1to about 20 h-1in the absence of an ethene co-feed, in which the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is in a gas phase, a liquid phase, or a mixed phase, and the metathesis reactor has an operating cycle time from about 1 day to about 100 days, and the metathesis catalyst is a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina-supported rhenium-based metathesis catalyst. In certain examples, the system has a plurality of metathesis reactors that includes the metathesis reactor, in which a second metathesis reactor of the plurality of metathesis reactors is configured to operate in regeneration mode to regenerate the metathesis catalyst of the second metathesis reactor, and regeneration mode operation includes the second metathesis reactor being configured to receive a stream of air, enriched air, or oxygen at a temperature ranging from about 350 °C to about 550 °C. In certain examples, the plurality of metathesis reactors includes a third metathesis reactor configured to remain in standby mode while the metathesis reactor is configured to metathesize the combination of the remainder of the C4 olefin stream and the C4 raffinate stream and the second metathesis reactor is configured to operate in regeneration mode. In certain examples, at least aportion the C4 raffinate stream is received by the metathesis reactor from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a MTBE reactor, a Bl column, a B2 column, a butadiene hydrogenation reactor, a MTO reactor, or a refinery FCC reactor, or any combination thereof.

[0044] Steam cracking processes are used to produce ethene as a major product along with the other side products, such as propene and a C4 species, such as but-l-ene, but-2-ene, 2-methylprop-l-ene, butynes, buta- 1,3 -diene, and so forth. In recent years, there has been a dramatic increase in the demand for propene to feed the growing markets for polypropylene, propylene oxide, and acrylic acid. Currently, about 85% of propene on the market is produced as the by-product of steam cracking of hydrocarbons (e.g., propane, NGL, naphtha) and fluid catalytic cracking (FCC) processes in refineries. Due to the recent abundance of shale gas in the U.S., there has been a shift towards lighter feedstocks in steam crackers. This is expected to cause a drop in propene as a byproduct from steam crackers. Also, due to the anticipated dip in gasoline demand, the FCC route to producing propene is also expected to be impacted. As a result, there will arise a gap between demand and supply of propene. In this context, intentional propene production routes are expected to see a revival. These intentional propene production routes include methanol to olefins / propene, propane dehydrogenation, and olefin metathesis. Metathesis offers a desirable route for valorization of low value olefins, like C4 and C5 olefins, into high value propene product. In certain existing metathesis methods and systems referred to as olefin conversion technology (OCT), ethene is often supplied as a co-feed to metathesis reactors. However, it is presently recognized that OCT has drawbacks, including the use of higher value ethene to produce propene, the selective use of but-2-enes for metathesis, and produces relatively high carbon dioxide (CO2) emissions as a result of relatively high metathesis reaction temperatures (e.g., from 250 °C to 450 °C).

[0045] On-demand synthesis of propene has attracted attention in the recent years, and this disclosure describes a versatile route for the same. More specifically, the present disclosure relates to methods and systems for metathesis of a C4 stream (e.g., a C4 raffinate stream) that is rich in but-l-ene and contains but- 2-enes. The disclosed technique uses a mixed feed that can include both but-l-ene and but-2-enes, and can operate without an ethene co-feed, eliminating consumption of this high value feedstock during metathesis. Recognizing that the separation of but-l-ene and but-2-enes is highly energy intensive, the disclosed technique improves power consumption, as well as installation, maintenance, and operational costs, by eliminating an additional C4 fractionation column that separates but-l-ene and but-2-enes prior to entering the metathesis reactor. Further, in certain embodiments, integration with the steam cracker enables a reduction in the number of downstream separation units, which reduces installation, maintenance, and operational costs. In addition, in certain embodiments, steam cracker integration further enhances the total production of ethene and propene from a C4 raffinate feedstock by utilizing intermediate products from metathesis process via a total hydrogenation unit followed by recycling the saturated stream to the steamcracker furnace. While these techniques are disclosed herein using examples related to the production of ethene, propene, and / or hex-l-ene, it may be appreciated that these techniques are broadly applicable to methods and systems involving metathesis reactions of C2 to C12 olefins.

[0046] With the foregoing in mind, present embodiments are directed to methods and systems involving metathesis of C4 olefins at low reaction temperature (e.g., from about 35 °C to about 100 °C), with or without recycle of C5 olefins to the metathesis reaction, with or without isomerization of C4 olefins prior to metathesis, with or without isomerization of Ce olefins after metathesis, with or without catalytic cracking of C5 and Ce olefins, and with steam cracker integration, to produce propene, ethene, and / or hex-l-ene. In some embodiments, the methods and systems include hydrogenation of a C4 purge stream before it is provided to a steam cracker to produce ethene and propene. Existing OCT technologies typically operates at high reaction temperatures above 250 °C, and selectively uses but-2-enes for the metathesis reaction. In contrast, the embodiments discussed herein use a mixed feed without a co-feed such as ethene, which avoids consumption of this higher value olefin during metathesis. Present embodiments also avoid or eliminate an additional C4 fractionation column for but-l-ene and but-2-enes separation, as this is recognized as being an undesirably energy intensive separation. In some embodiments, the metathesis process by-products, such as C5 olefins and / or Ce olefins, are directed to a catalytic cracker reactor, which further increases ethene and propene production. In some embodiments, the system integrates metathesis and catalytic cracker technology with steam cracking, which can desirably reduce the number of downstream separation units. For such embodiments, the integration of the steam cracker enables higher severity cracking, which consumes less energy per ton of high value chemicals produced and allows the flexibility to produce products of interest based on market demand.

[0047] Embodiments of methods and systems for producing ethene, propene, and / or hex-l-ene from a C4 stream are described with respect to FIGS. 1-5. In some embodiments, the C4 stream is a C4 raffinate stream. For example, in certain embodiments, the C4 stream has a composition in accordance with the C4 raffinate II or the C4 raffinate III indicated in Table 1. The composition of the C4 stream may vary based on the source of the C4 stream. In some embodiments, the C4 stream may be at least partially sourced downstream of a steam cracker (e.g., a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker), downstream of a methyl tert-butyl ether (MTBE) reactor, downstream of a but-l-ene (Bl) column, downstream of a but-2-enes (B2) column, downstream of a butadiene hydrogenation reactor, as a C4 raffinate stream from a methanol-to-olefins (MTO) process or reactor, or as a C4 raffinate stream from a refinery fluid catalytic cracking (FCC) process or reactor, or any combination thereof. For such embodiments, the composition of the C4 stream may vary based on the source of the C4 stream. As such, it may be appreciated that the present technique is robust and is able to metathesize C4 streams in which 2-methylprop-l-ene (also referred to herein as isobutene), butynes, and buta- 1,3 -diene(also referred to herein as butadiene) components are present in certain level, such as from about 0 mol. % to about 10 mol. % of 2-methylprop-l-ene, up to about 5 ppm of butynes, and up to about 1 ppm of buta-1,3- diene.

[0048] Table 1. Example compositions of the C stream.

[0049] FIG. 1 is a diagrammatic representation of an embodiment of a system 100 that enables metathesis of a C4 stream to produce chemical feedstocks. For the illustrated embodiment, the metathesis reaction / process effluent separation is integrated with a steam cracker. First, the metathesis reactor effluent is provided to the C3 column to separate unconverted C4 feed and C5+ products as the bottom product and a mixed ethene / propene stream as the top product. Then, the C3 column bottom product is provided to a standalone C4 column or an existing steam cracker C4 column unit. Next, the C4 column top product, which is an unconverted butenes-rich stream, is sent back to metathesis reactor as a recycle feed. To avoid inert build-up in the reactor, such as butane and / or 2-methylpropane, a purge stream is withdrawn from the C4 column. The bottom product of the C4 column substantially includes of C5 and Ce olefins, which can be utilized or sold as intermediate olefins. Further, the C4 purge stream is provided to the total hydrogenation unit (THU) to produce a saturated stream that is provided to the steam cracker, along with fresh hydrocarbons, to produce additional ethene and propene.

[0050] For the embodiment illustrated in FIG. 1, the system 100 includes a metathesis zone 104, an olefin separation zone 106, a total hydrogenation zone 108, and a steam cracking zone 110. A C4 stream 102 is directed to the metathesis zone 104. In the metathesis zone 104, the C4 stream 102 traverses a heater 112 that brings the stream to a suitable temperature before it is introduced into one of the metathesis reactors 114 (e.g., metathesis reactor 114A or 114B) to yield a metathesis product stream 116 that contains a mixture of C2-C6 olefin metathesis products. The metathesis reactors 114 can be implemented as down-flow or up-flow, fixed-bed reactors with a metathesis catalyst. The metathesis catalyst enables self-metathesis and crossmetathesis of but-l-ene and but-2-enes.

[0051] In some embodiments, the metathesis catalyst is a rhenium oxide-coated y-alumina-based metathesis catalyst (e.g., a R^Oy / yAUC -based catalyst) or an alumina-supported rhenium-based metathesis catalyst,also referred to as an egg-shell catalyst or a shaped metal-supported catalyst. The metathesis catalyst can be spherical or an extrudate and may be described as having an egg-shell structure. One such metathesis catalyst has y-alumina-based spherical particles of a size ranging from about 1.2 mm to about 3 mm and a rhenium oxide coating ranging from about 150 pm to about 250 pm in thickness or rhenium completely dispersed on alumina particle inner and outer surfaces. Other examples include y-alumina-based extrudate particles of a size ranging from 1.2 mm to about 3 mm in diameter and from about 4 mm to about 8 mm in length, with the rhenium oxide coating ranging from about 150 pm to about 250 pm in thickness. In certain examples, the metathesis catalyst contains rhenium oxide in an amount ranging from about 4.8 wt.% to about 5.6 wt.%. The metathesis catalyst can facilitate conversion of one or more of: (trans / cis (t / c)) but-2-ene with but-l-ene to propene and (t / c) pent-2 -ene, but-l-ene with but-l-ene to ethene and (t / c) hex-3-ene, ethene with (t / c) but-2- ene to propene and propene, ethene with (t / c) pent-2-ene to propene and but-lene and but-l-ene with (t / c) pent-2 -ene to propene and (t / c) hex-3-ene, and (t / c) pent-2 -ene and (t / c) pent-2 -ene to (t / c) but-2-ene and (t / c) hex-3 -ene in an operational metathesis reactor. In certain examples, the metathesis catalyst can be functional for at least 300 days in the operational metathesis reactor. In certain examples, the catalyst is regenerated for greater than 50 times in the operational metathesis reactor. Based on regeneration times, the catalyst can be functional for about 1000 days or longer. These days can vary based on the weight hourly space velocity that may range from 0.6 hr1to 10 hr1.

[0052] Methods of preparing a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina- supported rhenium -based metathesis catalyst include the steps of calcining a y-alumina-based support to form a calcined y-alumina-based support at a temperature ranging from about 450 Celsius (°C) to about 550 °C and treating the calcined y-alumina-based support with an aqueous rhenium -containing mixture in a rotating drum impregnation unit to form a rhenium -coated y-alumina-based support or an alumina supported rhenium- based support. In certain examples, the aqueous rhenium-containing mixture is a NTUReCh solution, an Al(ReC>4)3 solution, or a HReC>4 solution. In certain examples, the impregnation unit is rotated at a speed ranging from about 15 revolutions per minute (rpm) to about 25 rpm to form a rhenium -coated y-alumina- based support or an alumina supported rhenium-based support. The method also includes the steps of aging the rhenium-coated y-alumina-based support or an alumina supported rhenium-based support to form a rhenium oxide-coated y-alumina-based metathesis catalyst or an alumina-supported rhenium-based metathesis catalyst after calcination, containing a rhenium oxide coating ranging from about 150 micrometers (pm) to about 250 pm in thickness or rhenium completely dispersed on alumina inner or outer surfaces, drying the rhenium-coated y-alumina-based catalyst immediately after aging, and calcining the rhenium- coated y-alumina or alumina-supported rhenium -based catalyst at a temperature ranging from about 450°C to about 550 °C to form rhenium oxide coated y-alumina or alumina supported rhenium oxide. In certainexamples, the step of aging the rhenium-coated y-alumina-based support is conducted for a time less than 5 minutes, thereby to form a rhenium oxide-coated y-alumina-based catalyst after calcination. In certain examples, the step of drying the rhenium-coated y-alumina-based catalyst immediately after aging at temperature ranges from about 140 °C to about 160 °C.

[0053] The particle size of the y-alumina or alumina-supported rhenium -based support can range from about 1.2 millimeters (mm) to about 3 mm. For example, the diameter of a spherical or a cylindrical y-alumina or alumina-supported rhenium-based support can range from about 1.2 mm to about 3 mm. In certain examples, the y-alumina-based support has a pore volume ranging from about 0.5 milliliter per gram (ml / g) to about 0.65 ml / g. In certain examples, the y-alumina-based support has a pore diameter ranging from about 75 Angstroms (A) to about 110 A. In certain examples, the y-alumina-based support has a total acidity ranging from about 0.58 millimole per gram (mmol- ns / g) to about 0.62 mmol iis / g. In certain examples, the rhenium oxide-coated y-alumina-based catalyst or alumina-supported rhenium-based catalyst can contain rhenium oxide in an amount ranging from about 4.8 weight percent (wt. %) to about 5.6 wt. %. The rhenium oxidecoated y-alumina-based catalyst can have a surface area ranging from about 200 square meters per gram (m2 / g) to about 270 m2 / g. The metathesis catalyst can be spherical in shape or an extrudate. An extrudate can be cylindrical or lobed or of other shapes. In certain examples, the rhenium particles of the coating have a particle size ranging from about 0.3 nanometer (nm) to about 1.2 nm.

[0054] Examples include methods of preparing an activated rhenium oxide-coated y-alumina-based catalyst or an alumina-supported rhenium -based catalyst. One such method includes the steps of treating the rhenium oxide-coated y-alumina- based catalyst or alumina-supported rhenium-based catalyst under air at a temperature from about 500 °C to about 550 °C to produce an activated rhenium oxide-coated y-alumina- based catalyst or alumina-supported rhenium-based catalyst, purging nitrogen into the activated rhenium oxide-coated y-alumina-based catalyst or alumina-supported rhenium-based catalyst to displace the air, and cooling the activated rhenium oxide-coated y-alumina-based catalyst or alumina-supported rhenium-based catalyst to a temperature of about 50 °C. In certain examples, the step of treating the rhenium oxide-coated y-alumina-based catalyst or alumina-supported rhenium-based catalyst under air is conducted for about 4 hours to about 24 hours to produce an activated rhenium oxide-coated y-alumina-based catalyst or alumina- supported rhenium-based catalyst. In certain examples, the step of treating the rhenium oxide-coated y- alumina-based catalyst or alumina-supported rhenium -based catalyst under air is conducted for about 6 hours.

[0055] In some embodiments, the metathesis catalyst is a layered catalyst composition that contains an active layer and a base support. Examples of the base support are aluminum oxide, gallium oxide, silica oxide, zirconium oxide, niobium oxide, titanium oxide, lanthanum oxide, cerium oxide, or combinations thereof. The active layer of the catalyst contains an active metal component and an active support. The active metalcomponent can be a Group 6. 7, 8, or 9 metal oxide. The active metal component can be one or more of a chromium, molybdenum, or tungsten compound. The active metal component can be one or more of a manganese, technetium, or rhenium compound. The active metal component can be one or more of iron, cobalt, nickel, ruthenium, rhodium, palladium, and platinum compound. Examples of the active metal component can be rhenium oxide or ruthenium oxide. Examples of the active support can be aluminum oxide, gallium oxide, silica oxide, zirconium oxide, niobium oxide, titanium oxide, lanthanum oxide, cerium oxide, or combinations thereof.

[0056] Certain examples of an olefin metathesis catalyst have a base support containing aluminum oxide, an active layer containing rhenium oxide as the active metal component, and aluminum oxide as the active support. In certain examples, the acidic -OH groups of the active support are increased by incorporating about 0.5 % to 15 % of aluminum (or) zirconium precursor along with the rhenium precursor. The added aluminum (or) zirconium precursor (support precursor) along with the rhenium precursor produce an amorphous aluminum hydroxide or zirconium hydroxide with rhenium oxide. The amount of the metal component loaded in the active layer is reduced by at least about 10% to about 25% as compared to a rhenium oxide-alumina catalyst synthesized without aluminum / zirconium active support layer.

[0057] For the embodiment illustrated in FIG. 1, metathesis reactors 114 are implemented in series or in parallel operation in different implementations. In some embodiments, one reactor remains online while the other reactor is in regeneration or standby mode. For embodiments having three metathesis reactors 114, one metathesis reactor remains online, a second metathesis reactor is in regeneration mode, while the third metathesis reactor is in standby mode. The operating temperature of the metathesis reactors 114 is below 250 °C, such as from about 35 °C to about 100 °C. It is presently recognized that the metathesis reactors and catalysts used by other systems can demand substantially higher operating temperatures, such as greater than 250 °C, and as such, the lower operating temperatures of the disclosed metathesis reactors 114 reduces the operational cost and energy demands of these reactors compared to other systems. The operating pressures of the metathesis reactors 114 can range from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg). In some embodiments, the metathesis reactors 114 do not receive an ethene co-feed, which desirably avoids consumption of the higher value ethene olefin chemical feedstock to facilitate metathesis. The metathesis reactors 114 can be operated in gas phase, liquid phase, or mixed phase. It is presently recognized that the rhenium oxide-coated y-alumina-based metathesis catalyst is prone to gradual deactivation due to formation of intermediate species, moisture, or carbon deposition, and as such, it is desirable to operate the metathesis reactors such that a reasonable operating cycle time is about 1 day to about 100 days, such as about 3 days to about 30 days. In some embodiments, this is achieved by limiting the flow rate of C4 stream 102 into the metathesis reactors 114 to a weight hourly space velocity (WHSV) from about 0.1 per hour (h_’) to about 20 h1, more preferably to values from about 0.5 h1to about 10 h1. Regeneration of the metathesiscatalyst can be performed when a metathesis reactor 114A or 114B is in regeneration mode using air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C, such as from about 350 °C to about 550 °C or from about 450 °C to about 550 °C using air. The metathesis catalyst can be regenerated in- situ (online) and ex-situ (off-line) or using a bunker flow reactor with continuous catalyst replacement.

[0058] For the embodiment illustrated in FIG. 1, the metathesis product stream 116 exits the metathesis zone 104 and is directed to the olefin separation zone 106. For the illustrated embodiment, the olefin separation zone 106 includes a Cs column 118 (e.g., a depropenizer) and a C4 column 120 (e.g., a debutenizer). The metathesis product stream 116 is directed to the C3 column 118, which separates the metathesis product stream 116 into a C2-C3 olefin stream 122 and a C4+ olefin stream 124. The C2-C3 olefin stream 122 is directed to the downstream separation section 126 of the steam cracking zone 110 for separation, as discussed below. For the illustrated embodiment, the C4+ olefin stream 124 is directed to the C4 column 120, which separates C4+ olefin stream 124 into a C4 olefin stream 134 and C -Ce olefins 136. In some embodiments, the C4 olefin stream 134 may include a limited amount of paraffins (e.g., butane, 2- methylpropane) that can be purged from the C4 olefin stream 134, which produces the purge stream 138. After purging, a remainder of the C4 olefin stream 135 is recycled to the metathesis zone 104 where it is combined with the C4 stream 102 before being metathesized to form the metathesis product stream 116. The purge stream 138, which may include paraffins (e.g., butane, 2-methylpropane) and a limited quantity of C4- e olefins, is directed to a THU 140 of the total hydrogenation zone 108 for hydrogenation, yielding a saturated stream 142. In certain embodiments, the saturated stream 142 is directed to the steam cracking zone.

[0059] For the embodiment of the system 100 illustrated in FIG. 1, the steam cracking zone 110 receives and steam cracks a hydrocarbon feedstock 144. In some embodiments, the hydrocarbon feedstock 144 contains of a gaseous feedstock, a liquid feedstock, a light crude oil, a crude oil cut, or any mixture thereof. In certain embodiments, the hydrocarbon feedstock 144 contains or consists essentially of propane, NGL, and naphtha. The steam cracking zone 110 includes a steam cracker 146 and the downstream separation section 126. The steam cracker 146 receives and cracks the hydrocarbon feedstock 144, along with the saturated stream 142 received from the total hydrogenation zone 108 and the paraffinic -rich stream 158 discussed below, to generate a steam cracked stream 148 that is directed to the downstream separation section 126 for separation. The steam cracked stream 148 may include: hydrogen (H2), BTX hydrocarbons, ethene, propene, pyrolysis gasoline, fuel gas, and / or other C1-12 hydrocarbons. BTX hydrocarbons include benzene, toluene, and dimethylbenzenes (also referred to herein as xylenes). The downstream separation section 126 receives the steam cracked stream 148 and the C2-C3 olefin stream 122. The downstream separation section 126 (referred to herein as the downstream separation sub-zone) includes any suitable number of reactors and / or separation columns that process and / or separate the received streams into a number of streams, including: an ethene product stream 150, a propene product stream 152, a C4 raffinate stream 154, otherproduct streams 156 (e.g., each containing H2, or C2-12 hydrocarbons, BTX, or combinations thereof), and a paraffinic -rich stream 158 (e.g., containing ethane, propane, butane, or combinations thereof). In some embodiments, the downstream separation section 126 includes a C2 / C3 splitter, a MTBE reactor, a but-l-ene (Bl) column, a but-2-enes (B2) column, a butadiene hydrogenation reactor, an acetylene hydrogenation reactor, any other suitable separation column (e.g., distillation column, fractional distillation column, deethanizer, depropanizer, debutanizer, depentanizer, C2 / C3 splitter, and so forth), or any combination thereof. In some embodiments, the C4 raffinate stream 154 contains or consists essentially of about 65 mol. % to about 98 mol. % n-butenes (i.e., but-l-ene and but-2-enes), with a remainder containing butane, propane, 2 -methylpropane (isobutane), 2-methylprop-l-ene (isobutylene), and trace amounts of C5+ hydrocarbons. In some embodiments, the C4 raffinate stream 154 contains or consists essentially of from about 65 mol. % to about 100 mol. % n-butenes (i.e., but-l-ene and but-2-enes), with an optional remainder being butane, 2- methylpropane, 2-methylprop-l-ene, and trace amounts of C5+ hydrocarbons.

[0060] In some embodiments, the C4 raffinate stream 154 may be a but-l-ene-rich stream that contains at least 15 mol. %, at least 20 mol. %, or at least 50 mol. % of but-l-ene, for example, depending on the composition of the hydrocarbon feedstock 144. In some embodiments, the other product streams 156 may include a pyrolysis gasoline stream that contains pyrolysis gasoline and a fuel gas stream that is rich in methane along with other hydrocarbons. The paraffinic-rich stream 158 is recycled and combined with fresh hydrocarbon feedstock 144 and the saturated stream 142 before returning to the steam cracker 146 to generate the steam cracked stream 148. The C4 raffinate stream 154 is combined with the C4 olefin stream 135 and directed to the metathesis zone 104.

[0061] In some embodiments, combination of the C4 raffinate stream 154 and the C4 olefin stream 135 may be further combined with the C4 stream 102 before being metathesized to produce the metathesis product stream 116, while in other embodiments, the combination of the C4 raffinate stream 154 and the C4 olefin stream 135 may provide all of the C4 stream that is delivered to the metathesis zone 104 to produce the metathesis product stream 116. It may also be appreciated that, by utilizing the downstream separation section to isolate the ethene product stream 150 and the propene product stream 152, the system 100 lacks a C2 / C3 splitter in the olefin separation zone 106, which reduces the installation, maintenance, and operational costs of the system 100 compared to other systems having olefin separation zones that include a C2 / C3 splitter.

[0062] FIG. 2 is a diagrammatic representation of an embodiment of a system 200 that enables metathesis of a C4 stream to produce chemical feedstocks. For the illustrated embodiment, when the C4 raffinate stream and C4 recycle stream contains less than 15 mol. % of but-l-ene, the combined stream is provided to a C4 isomerization reactor / process before the metathesis reactor / process to increase the metathesis productivity and to decrease recycle quantity of metathesis reactor inlet stream. The system 200 includes the metathesis zone 104, the total hydrogenation zone 108, and the steam cracking zone 110, as discussed above with respectto FIG. 1, as well as an isomerization zone 202 and a modified olefin separation zone 204. The isomerization zone 202 enhances the robustness of the system 200 by enabling the use of C4 streams that are rich in but-2- enes and include less than 15 mol. % but-l-ene. More specifically, the system 200 enables conditional isomerization of but-2-enes into but-l-ene in a C4 stream, depending on the ratio of but-l-ene to but-2-enes or the but-l-ene content of the C4 stream.

[0063] For the embodiment of the system 200 illustrated in FIG. 2, the metathesis zone 104 metathesizes a C4 stream, as discussed above, to generate the metathesis product stream 116 that is directed to the olefin separation zone 204. For the illustrated embodiment, the olefin separation zone 204 includes a C3 column 206 (e.g., a depropenizer) and a C4 column 208 (e.g., a debutenizer). The metathesis product stream 116 is directed to the C3 column 206, which separates the metathesis product stream 116 into a C2-C3 olefin stream 210 and a C4+ olefin stream 212. The C2-C3 olefin stream 210 is directed to the downstream separation section 126 of the steam cracking zone 110 for separation into the ethene product stream 150 and the propene product stream 152. For the illustrated embodiment, the C4+ olefin stream 212 is directed to the C4 column 208, which separates the C4+ olefin stream 212 into a C4 olefin stream 214 and a Cs-Ce olefin stream 216. In some embodiments, the C4 olefin stream 214 may include a limited amount of paraffins (e.g., butane, 2- methylpropane) that can be purged from the C4 olefin stream 214, which produces the purge stream 218. After purging, a remainder of the C4 olefin stream 215 is combined with the C4 raffinate stream 154 and provided as input to a butene analyzer unit 220. The purge stream 218, which may include paraffins (e.g., butane, 2-methylpropane) and a limited quantity of C4-6 olefins, is directed to a THU 140 of the total hydrogenation zone 108 for hydrogenation, yielding the saturated stream 142 that is directed to the steam cracking zone 110 as discussed above.

[0064] For the embodiment of the system 200 illustrated in FIG. 2, the C4 streams that are received, combined, and conditionally routed by the butene analyzer unit 220 include the C4 olefin stream 215 and the C4 raffinate stream 154, and optionally may include the C4 stream 102, depending on the demands of the system 200, the desired ultimate products, and the availability and composition of the C4 stream 102. For example, depending on the composition of the C4 stream 102, the C4 olefin stream 215, and the C4 raffinate stream 154, as well as the desired ultimate products of the system 200, the butene analyzer unit 220 may introduce more or less of the C4 stream 102 to be combined with the C4 olefin stream 215 and the C4 raffinate stream 154, in addition to conditionally routing the combined stream to either the isomerization zone 202 or the metathesis zone 104 depending on the composition of the combined stream. The butene analyzer unit 220 is designed to analyze the composition of the combined C4 stream to determine the relative amount of but-l- ene and but-2-enes present in the combined stream or the but-l-ene content of the combined stream, for example, using gas chromatography for flow analysis. In response to determining that the but-l-ene to but- 2-enes molar ratio is less than 15:85 or that the but-l-ene content is less than 15 mol. %, the butene analyzerunit 220 routes the combined stream to the isomerization zone 202. In response to determining that the but- 1-ene to but-2-enes ratio is greater than 15:85 (e.g., 60:40 or 80:20) or that the but-l-ene content is greater than or equal to 15 mol. %, the butene analyzer unit 220 instead routes the combined stream directly to the metathesis zone 104. By conditionally routing the combined stream to the isomerization zone 202, the system 200 enables reduced power consumption for cases in which the combined stream is sufficiently high in but- 1 -ene that the isomerization process can be skipped, while enabling flexibility to accommodate cases in which the relative amount of but-l-ene is too low to generate the desired products without isomerization.

[0065] For the embodiment illustrated in FIG. 2, the isomerization zone 202 includes a heater 222 and C4 isomerization reactors 224. The incoming C4 stream traverses the heater 222, which brings the stream to a suitable temperature before it is introduced into one of the C4 isomerization reactors 224 (e.g., 224A, 224B). The C4 isomerization reactors 224 are designed to isomerize the received stream to yield a C4 isomerized stream 226 that is subsequently directed to the metathesis zone 104. More specifically, the C4 isomerization reactors 224 isomerize but-2-enes present in the incoming stream into but-l-ene within the isomerized stream 226. For the illustrated embodiment, the C4 isomerization reactors 224 are implemented such that one reactor remains online while the other reactor is in regeneration or standby mode. For embodiments having three C4 isomerization reactors 224, one C4 isomerization reactor remains online, a second C4 isomerization reactor is in regeneration mode, while a third C4 isomerization reactor is in standby mode.

[0066] The C4 isomerization reactors 224 can be implemented as down-flow or up-flow, fixed-bed reactors having a potassium-based isomerization catalyst (e.g., K2O / VAI2O3). a magnesium-based isomerization catalyst containing magnesium oxide (MgO), a calcium-based isomerization catalyst containing calcium oxide (CaO) (e.g., CaO / AFCF). or a zeolite-based isomerization catalyst (e.g., a ZSM-5-based catalyst). The operating temperature of the C4 isomerization reactors 224 can range from about 250 °C to about 500 °C, and more preferably from about 300 °C to about 450 °C. The operating pressures of the C4 isomerization reactors 224 can range from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg), and more preferably from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg). In different implementations, each of the C4 isomerization reactors 224 is capable of isomerizing a liquid feed, a vapor feed, or mixed phase feed. It is presently recognized that the isomerization catalyst is prone to gradual deactivation due to formation of intermediate species or carbon deposition, and as such, it is desirable to operate the C4 isomerization reactors 224 to enable a suitable operating cycle time of about 1 day to about 100 days, such as about 1 day and 60 days. In some embodiments, this is achieved by limiting the flow rate of the C4 stream to the C4 isomerization reactors 224 to a WHSV from about 0.1 per hour (h1) to about 20 h" ’, and more preferably to values from about 0.5 h1to about 5 h1. Regeneration of the isomerization catalyst can be performed when the C4 isomerization reactor 224A or 224B is in regeneration mode using nitrogen,air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C, and more preferably from about 450 °C to about 550 °C.

[0067] FIG. 3 is a diagrammatic representation of an embodiment of a system 300 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 300 includes the metathesis zone 104, the total hydrogenation zone 108, and the steam cracking zone 110, as discussed above with respect to FIG. 1, the C4 isomerization zone 202 and butene analyzer unit 220, as discussed above with respect to FIG. 2, as well as a Ce isomerization zone 302 and a modified olefin separation zone 304. As such, in addition to the advantages set forth above for the embodiment of the system 200 illustrated in FIG. 2, the embodiment of the system 300 illustrated in FIG. 3 includes recycling of C5 olefins to the metathesis reactor to increase propene and but-l-ene productivity, as well as isolation and isomerization of Ce olefins to produce a hex-l-ene product stream.

[0068] For the embodiment of the system 300 illustrated in FIG. 3, the metathesis zone 104 metathesizes a C4 stream, as discussed above, to generate the metathesis product stream 116 that is directed to the olefin separation zone 304. For the illustrated embodiment, the olefin separation zone 304 includes a C3 column 306 (e.g., a depropenizer), a C4 column 308 (e.g., a debutenizer), and a C5 column 310 (e.g., a depentenizer). The metathesis product stream 116 is directed to the C3 column 306, which separates the metathesis product stream 116 into a C2-C3 olefin stream 312 and a C4+ olefin stream 314. The C2-C3 olefin stream 312 is directed to the downstream separation section 126 of the steam cracking zone 110 for separation into the ethene product stream 150 and the propene product stream 152, as discussed above. The C4+ olefin stream 314 is directed to the C5 column 310, which separates the C4+ olefin stream 314 into a C4-C5 olefin stream 316 and a Ce olefin stream 318. The C4-C5 olefin stream 316 is directed to the C4 column 308, which separates the C4-C5 olefin stream 316 into a C4 olefin stream 320 and a C5 olefin stream 322. In some embodiments, the C4 olefin stream 320 may include a limited amount of paraffins (e.g., butane, 2-methylpropane) that can be purged from the C4 olefin stream 320, which produces the purge stream 324. After purging, a remainder of the C4 olefin stream 321 is combined with the C4 raffinate stream 154 and provided as input to the butene analyzer unit 220. The purge stream 324, which may include paraffins (e.g., butane, 2-methylpropane) and a limited quantity of C4-6 olefins, is directed to a THU 140 of the total hydrogenation zone 108 for hydrogenation, yielding the saturated stream 142 that is directed to the steam cracking zone 110, as discussed above.

[0069] For the embodiment of the system 300 illustrated in FIG. 3, the Ce olefin stream 318 isolated by the C5 column 310, which substantially includes hex-3-enes and a limited quantity of hex-2 -enes, is directed to the Ce isomerization zone 302 for isomerization. The illustrated Ce isomerization zone 302 includes Ce isomerization reactors 326 and a Ce fractionator 328 (e.g., a Ce fractional distillation column). In some embodiments, the Ce olefin stream 318 first traverses a heater that brings the stream to a suitable temperaturebefore it is introduced into one of the Ce isomerization reactors 326 (e.g., 326A, 326B). The Ce isomerization reactors 326 are designed to isomerize the received stream to yield a Ce isomerized stream 330. More specifically, the Ce isomerization reactors 326 isomerize hex-2 -enes and hex-3 -enes present in the incoming stream into hex-l-ene within the Ce isomerized stream 330. The Ce isomerized stream 330 is directed to the Ce fractionator 328 to separate a hex-l-ene product stream 332 from a hex-2 -enes / hex-3-ene stream 334. The hex-2-enes / hex-3-ene stream 334 is recycled back to the Ce isomerization reactors 326, where it is combined with the Ce olefin stream 318 for further Ce isomerization to yield the Ce isomerized stream 330.

[0070] For the embodiment of the system 300 illustrated in FIG. 3, the Ce isomerization reactors 326 are implemented such that one reactor remains online while the other reactor is in regeneration or standby mode. For embodiments having three Ce isomerization reactors 326, one Ce isomerization reactor remains online, while a second Ce isomerization reactor is in regeneration mode, and a third Ce isomerization reactor is in standby mode. The Ce isomerization reactors 326 can be implemented as down-flow or up-flow, fixed-bed reactors having a potassium-based isomerization catalyst (e.g., K2O / VAI2O3). a magnesium-based isomerization catalyst containing MgO, a calcium-based isomerization catalyst containing CaO (e.g., CaO / AFOs), or a zeolite-based isomerization catalyst (e.g., a ZSM-5-based catalyst) to enable the isomerization of hex-3-enes and hex-2-enes into hex-l-ene. The operating temperature of the Ce isomerization reactors 326 can range from about 350 °C to about 550 °C. The operating pressures of the Ce isomerization reactors 326 can range from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg). In different implementations, each of the Ce isomerization reactors 326 is capable of isomerizing a liquid feed, a vapor feed, or mixed phase feed. It is presently recognized that the isomerization catalyst is prone to gradual deactivation due to formation of intermediate species or carbon deposition, and as such, it is desirable to operate the Ce isomerization reactors 326 to enable a suitable operating cycle time from about 1 day to about 100 days. In some embodiments, this is achieved by limiting the flow rate of the Ce olefin stream 318 to the Ce isomerization reactors 326 to a WHSV of from about 0. 1 per hour (h1) to about 20 h1, and more preferably to values from about 0.5 h-1to about 5 h1. Regeneration of the isomerization catalyst can be performed when the Ce isomerization reactor 326A or 326B is in regeneration mode using nitrogen, air, a mixture of nitrogen and air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C, and more preferably from about 450 °C to about 550 °C.

[0071] FIG. 4 is a diagrammatic representation of an embodiment of a system 400 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 400 includes the same zones and components as discussed above with respect to the embodiment of the system 300 illustrated in FIG. 3. However, in contrast to the embodiment of the system 300 illustrated in FIG. 3, for the embodiment of the system 400 illustrated in FIG. 4, the C5 olefin stream 322 that is isolated by the C4 column 308 of the olefin separation zone 304 is instead combined with the purge stream 324 and directed to the THU 140 of the total hydrogenation zone108. The THU 140 completely hydrogenates the combination of the purge stream 324 and the C5 olefin stream 322 to yield the saturated stream 142, which is directed to the steam cracking zone 110, as discussed above. As such, in addition to the advantages set forth above for the embodiment of the system 200 illustrated in FIG. 2, the embodiment of the system 400 illustrated in FIG. 4 enables increased productivity of the ethene product stream 150, the propene product stream 152, and / or the other product streams 156, as well as isolation and isomerization of Ce olefins to produce the hex-l-ene product stream 332.

[0072] FIG. 5 is a diagrammatic representation of an embodiment of a system 500 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 500 includes the metathesis zone 104, the total hydrogenation zone 108, and the steam cracking zone 110, as discussed above with respect to FIG. 1, the C4 isomerization zone 202, the olefin separation zone 204, and the butene analyzer unit 220, as discussed above with respect to FIG. 2, as well as a catalytic cracking zone 502. In addition to the advantages set forth above for the embodiment of the system 100 illustrated in FIG. 1 and the system 200 illustrated in FIG. 2, the embodiment of the system 500 illustrated in FIG. 5 enables an increase in production of the ethene product stream 150 and the propene product stream 152, a reduction of downstream separation units after the metathesis and catalytic cracking processes, and conversion of C -C, olefin metathesis by-products to high value products.

[0073] For the embodiment of the system 500 illustrated in FIG. 5, the Cs-Ce olefin stream 216 that is isolated by the C4 column 208 is directed to the catalytic cracking zone 502. The catalytic cracking zone 502 includes catalytic cracking reactors 504 (e.g., 504A and 504B). In some embodiments, each of the catalytic cracking reactors 504 includes a ZSM-5 based catalyst with relatively high silica to alumina (SiCh / AUOs) ratio disposed in a fixed-bed reactor. In some embodiments, the catalytic cracking reactors 504 perform catalytic cracking of the Cs-Ce olefin stream 216 at a temperature ranging from about 450 °C to about 650 °C, in which the C-C, olefin stream 216 is provided to the catalytic cracking reactors 504 at a WHSV from about 2.5 h-1to about 20 h1. In some embodiments, one of the catalytic cracking reactors (e.g., 504A) remains online while the other catalytic cracking reactor (e.g., 504B) is in regeneration or standby mode. For embodiments having three catalytic cracking reactors 504, one reactor is online, while a second reactor is in regeneration mode and a third reactor is in standby mode. It is presently recognized that the cracking catalyst is prone to gradual deactivation due to formation of intermediate species, moisture, or carbon deposition. As such, in certain embodiments, it is desirable to operate the catalytic cracking reactors 504 such that a reasonable operating cycle time is from about 1 day to about 100 days. In some embodiments, this is achieved by limiting the flow rate of C-C, olefin stream 216 into the catalytic cracking reactors 504 to a WHSV from about 2.5 h-1to about 20 h1. Regeneration of the cracking catalyst can be performed when the catalytic cracking reactor 504A or 504B is in regeneration mode using nitrogen, air, enriched air, or oxygen at a temperature ranging from about 450 °C to about 550 °C.

[0074] For the embodiment of the system 500 illustrated in FIG. 5, the Cs-Ce olefin stream 216 is directed to the catalytic cracking reactors 504, and at least one of the catalytic cracking reactors 504 performs catalytic cracking of the C -C, olefin stream 216 to yield a catalytically cracked stream 506. The catalytically cracked stream 506 is directed to the downstream separation section 126 of the steam cracking zone 110 for separation. In addition to separating the steam cracked stream 148 and the C2-C3 olefin stream 210, as discussed above, the downstream separation section 126 also separates the catalytically cracked stream 506, yielding the ethene product stream 150, the propene product stream 152, the C4 raffinate stream 154, the other product streams 156 containing H2, C2-12 hydrocarbons (including BTX), and the paraffinic-rich stream 158 containing ethane and / or propane and / or butanes. By using the downstream separation section 126 to perform these separations, the system 500 enables a reduction of downstream separation units (e.g., fractionation columns) after the metathesis and catalytic cracking processes, which reduces the installation, maintenance, and operational costs associated with these units. Further, by catalytically cracking the lower value C -Ce olefin stream 216, the system 500 enables an increase in production of the higher value ethene product stream 150 and the propene product stream 152 along with other products and / or by-products.

[0075] Various zones are discussed for the embodiments illustrated in FIGS. 1-5, including the metathesis zone 104, the olefin separation zones 106, 204, and 304, the total hydrogenation zone 108, the steam cracking zone 110, the C4 isomerization zone 202, the Ce isomerization zone 302, and the catalytic cracking zone 502. In other embodiments, the system may include other combinations of these zones, beyond those specifically illustrated in FIGS. 1-5, in accordance with the present disclosure.

[0076] FIG. 6 is a diagrammatic representation of an embodiment of a control system 600 for controlling the embodiments of the system discussed above. The control system 600 includes at least one controller 602. Each controller 602 includes at least one processor 604, which may be or include a central processing unit (CPU), a graphics processing unit (GPU), a co-processing unit, a sub-processing unit, or any other suitable electronic data processor. Each controller 602 includes at least one memory 606, which may be or include random access memory (RAM), read-only memory (ROM), or any other suitable electronic memory or storage . For the illustrated embodiment, the controller 602 is communicatively connected to each of the zones present in a particular implementation of the systems discussed above, such as the metathesis zone 104, the total hydrogenation zone 108, the steam cracking zone 110, the olefin separation zones 106, 204, or 304, the C4 isomerization zone 202, the Ce isomerization zone 302, the catalytic cracking zone 502 via a suitable wired or wireless communication channel. The controller 602 is further communicatively connected to certain other elements of the systems discussed above, such as the butene analyzer unit 220. The communicative connection between the controller 602 and the various zones and devices enables the controller 602 to receive monitoring and operational data from sensors and / or sub-controllers of each of these zones or devices present in the embodiments discussed above, and further enables the controller 602 toprovide control signals (e.g., electrical signals, instructions, data packets) to modify the operation of each of these zones or devices.

[0077] For example, the controller 602 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the metathesis zone 104, and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of the metathesis zone 104 to ensure that the metathesis reactors 114 operate within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the metathesis reactors 114. The controller 602 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the C4 isomerization zone 202 and / or the Ce isomerization zone 302, and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of these zones to ensure that the isomerization reactors 224, 326 operate within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the isomerization reactors. The controller 602 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the olefin separation zones 106, 204, or 304 and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of these zones, such that the components of these zones operate in accordance with the predefined threshold values. The controller 602 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the total hydrogenation zone 108 and the steam cracking zone 110 and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of these zones, such that the components of these zones operate in accordance with the predefined threshold values.

[0078] In certain embodiments, the controller 602 receives monitoring data from the butene analyzer unit 220 regarding the but-l-ene content in each of the received streams, such as the C4 raffinate stream 154, the C4 olefin stream 135, 215, or 321, and optionally the C4 stream 102. In some embodiments, the controller 602 provides control signals to modify the operation of the butene analyzer unit 220 to adjust the relative amount of the C4 stream 102 to be combined with the other streams to maintain the but-l-ene content to values greater than or equal to 15 mol. %, and additionally provides control signals to the butene analyzer unit 220 to route the combined stream to the metathesis zone 104. In certain embodiments, when the controller 602 determines that the but-l-ene content in the combined stream is unable to reach at least 15 mol. % by adjusting the relative amount of the C4 stream 102 in the combined stream, the controller 602 provides control signals to modify the operation of the butene analyzer unit 220 to instead route the combined streams to the C4 isomerization zone 202 to increase the but-l-ene content to greater than or equal to 15 mol. % prior to reaching the metathesis zone 104.Examples

[0079] Example 1:

[0080] Table 2 indicates the composition of an example C4 raffinate stream in weight percentages. For this example, this C4 raffinate stream was used as the input stream to the metathesis zone 104 to predict the composition of the metathesis product stream 116 for the embodiment of the system 100 illustrated in FIG. 1. The composition of the metathesis product stream 116 was calculated using lab experimental results. For this example, the metathesis reaction conditions include an operating temperature of 50 °C, an operating pressure of 700 kPa (6 barg), and a WHSV of 0.6 h1. The experimental results were confirmed with simulation results using commercial simulation software. For this example, continuous purging of the C4 olefin stream 134 was performed to remove the build-up of inert materials (e.g., paraffins) at the metathesis reactor inlet, and the purge stream 138 was further processed within the total hydrogenation zone 108 and the steam cracking zone 110 to increase ethene and propene product yields. Accordingly, the composition of the metathesis product stream 116 was calculated using simulation software, taking into account both the recycling of the C4 olefin stream 135 and the total hydrogenation and steam cracking of the purge stream 138. The simulation software used for the examples discussed herein is available from Aspen Technology Inc. of Bedford, Massachusetts, U.S.A. The composition of the metathesis product stream 116 is presented in Table 3, based on an input feed quantity of 161 kilotons per annum (KTA). As indicated in Table 3, in addition to forming propene as the major product, a minor amount of ethene product also formed. Additionally, C5 olefins, such as pentene isomers, and Ce olefins, such as hexene isomers, were major by products in the metathesis product stream 116.

[0081] Table 2. Composition of the C4 stream provided to the metathesis zone for Example 1.

[0082] Table 3. Composition of the metathesis product stream for Example 1.

[0083] Example 2:

[0084] For this example, the composition of the C4 raffinate stream presented in Table 2 was used as the input stream to the metathesis zone 104 to predict the ultimate product yields for the embodiment of the system 300 illustrated in FIG. 3. The simulated operating parameters of the system 300 were in accordance with the operating parameters set forth for Example 1. The ultimate product yields for this example werecalculated using the simulation software, taking into account the recycling of the C4 olefin stream 321 and the C5 olefin stream 322, the total hydrogenation and steam cracking of the purge stream 138, and the isomerization ofthe Ce olefin stream 318. The results are presented in Table 4 based on an input feed quantity of 161 KTA.

[0085] Table 4. Ultimate product yields for Example 2.

[0086] Example 3:

[0087] For this example, the composition of the C4 raffinate stream presented in Table 2 was used as the input stream to the metathesis zone 104 to predict the ultimate product yields for the embodiment of the system 400 illustrated in FIG. 4. The simulated operating parameters of the system 400 were in accordance with the operating parameters set forth for Example 1, while the catalytic cracking reactor was simulated as having an operating temperature of 550 °C, an operating pressure of < 200 kPa (< 1 barg), and a WHSV of 5 h1. The ultimate product yields from the metathesis reactor for this example were calculated using the simulator software, taking into account the recycling of the C4 olefin stream 321, the total hydrogenation and steam cracking of the purge stream 138 and the C5 olefin stream 322, and the isomerization of the Ce olefin stream 318. The results are presented in Table 5 based on an input feed quantity of 161 KTA.

[0088] Table 5. Ultimate product yields for Example 3.

[0089] Example 4:Table 6 indicates the composition of an example C4 raffinate stream in molar percentages. For this example, this C4 raffinate stream was used as the input stream to the metathesis zone 104 to predict the composition of the C4 isomerized stream 226 for the embodiment of the system 200 illustrated in FIG. 2, the embodiment of the system 300 illustrated in FIG. 3, the embodiment of the system 400 illustrated in FIG. 4, or the embodiment of the system 500 illustrated in FIG. 5, with the isomerization reactor (e.g., 224A or 224B) isomerizing the input C4 stream at different simulated operating temperatures. The other simulated operating parameters were generally in accordance with the parameters set forth for Example 1, while the C4 isomerization reactor was simulated as having an operating temperature ranging from about 100 °C to about 600 °C, an operating pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30barg), and a WHSV from about 0.1 h1to about 20 h1. The compositions of the C4 isomerized stream 226 when the C4 isomerization reactor was operated at different operating temperatures are also presented in Table 6. For each of these operating temperatures, the composition of the C4 isomerized stream 226 was calculated using lab experimental and verified using the simulation software. For this example, there was no observed effect on the composition of the C4 isomerized stream 226 due to changes in reaction pressure or WHSV at the C4 isomerization reactor. However, since it is presently recognized that the catalysts generally deactivate faster with increased WHSV, a WHSV of 0.6 hr1results in the C4 isomerization catalyst being stable for 30 days. For this example, it was also observed that only (Z)-but-2-ene (c / .s-2-butcnc) and (£)-but- 2-ene (trans -2 -butene) were isomerized to but-l-ene within the C4 isomerization reactor, despite the presence of other unsaturated C4 species in the input C4 stream provided to the isomerization zone 202.

[0090] Table 6. Composition of the C4 input stream to, and composition of the C4 isomerized stream 226 (in mol. %>) from, the isomerization zone 202 for Example 4.

[0091] When ranges are disclosed herein, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, reference to values stated in ranges includes each and every value within that range, even though not explicitly recited. Thus, every point or individual value may 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 a range not explicitly recited.

[0092] Other objects, features and advantages of the disclosure will become apparent from the foregoing drawings, detailed description, and examples. These drawings, detailed description, and examples, while indicating specific embodiments of the disclosure, are given by way of illustration only and are not meant to be limiting. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specificembodiments described herein. It should be understood that although the disclosure contains certain aspects, embodiments, and optional features, modification, improvement, or variation of such aspects, embodiments, and optional features can be resorted to by those skilled in the art, and that such modification, improvement, or variation is considered to be within the scope of this disclosure.

Claims

CLAIMSWhat is claimed:

1. A method comprising: steam cracking at least a hydrocarbon feedstock to produce a steam cracked stream; providing at least the steam cracked stream to a downstream separation section to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream; metathesizing at least the C4 raffinate stream to produce a metathesis product stream; separating the metathesis product stream into at least a C2-C3 olefin stream and a C4 olefin stream; purging a portion of the C4 olefin stream to produce a purge stream that contains at least one paraffin; hydrogenating the purged stream to produce a saturated stream; combining the saturated stream with the hydrocarbon feedstock prior to steam cracking; combining a remainder of the C4 olefin stream after purging with the C4 raffinate stream prior to metathesis; and providing the C2-C3 olefin stream to the downstream separation section along with the steam cracked stream to produce the ethene product stream and the propene product stream.

2. The method of claim 1, wherein the C4 raffinate stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

3. The method of claims 1 or 2, wherein, separating the metathesis product stream, comprises: separating the metathesis product stream into at least the C2-C3 olefin stream, the C4 olefin stream, a C5 olefin stream, and a Ce olefin stream.

4. The method of claim 3, comprising: performing Ce isomerization of the Ce olefin stream to produce a Ce isomerized stream, wherein hex-2- enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization; and separating a first portion of the Ce isomerized stream as a hex-l-ene product stream, wherein a remainder of the Ce isomerized stream is combined with the Ce olefin stream prior to Ce isomerization.

5. The method of claims 1 or 2, wherein, separating the metathesis product stream comprises: separating the metathesis product stream into the C2-C3 olefin stream, the C4 olefin stream, and a Ce-Ce olefin stream.

6. The method of claims 1 or 2, comprising: responsive to a but-l-ene content of less than 15 mol. % in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, performing C4 isomerization of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream prior to metathesis, wherein but-2-ene in the combination of the remainder of the C4 olefin stream and the C4 raffinate stream is converted into but-l-ene during C4 isomerization; and responsive to the but-l-ene content being greater than or equal to 15 mol. %, metathesizing the combination of the remainder of the C4 olefin stream and the C4 raffinate stream without C4 isomerization.

7. The method of claims 1 or 2, comprising receiving at least a portion of the C4 raffinate stream from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a methyl tert-butyl ether (MTBE) reactor, a but-l-ene (Bl) column, a but- 2-enes (B2) column, a butadiene hydrogenation reactor, a methanol-to-olefins (MTO) process, or a refinery fluid catalytic cracking (FCC) process, or any combination thereof.

8. A system comprising: a steam cracker configured to receive and steam crack at least a hydrocarbon feedstock to produce a steam cracked stream; a downstream separation section configured to receive and separate at least the steam cracked stream to produce at least an ethene product stream, a propene product stream, and a C4 raffinate stream; a metathesis reactor configured to receive and metathesize at least the C4 raffinate stream to produce a metathesis product stream; a C3 column configured to receive and separate the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream, the C2-C3 olefin stream being provided to the downstream separation section for separation into the ethene product stream and the propene product stream; a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, a portion of the C4 olefin stream being purged to produce a purge stream containing at least one paraffin and a remainder of C4 olefin stream being provided to the metathesis reactor along with the C4 raffinate stream for metathesis to produce the metathesis product stream; and a total hydrogenation unit configured to receive and hydrogenate at least the purge stream to produce a saturated stream, the saturated stream being provided to the steam cracker along with the hydrocarbon feedstock for steam cracking to produce the steam cracked stream.

9. The system of claim 8, wherein the C4 raffinate stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

10. The system of claims 8 or 9, comprising a C5 column configured to receive and separate the C4+ olefin stream into a C4-C5 olefin stream and a Ce olefin stream, wherein the C4 column is configured to receive and separate the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream.

11. The system of any of claims 8-10, comprising: a Ce isomerization reactor configured to receive and isomerize the Ce olefin stream to produce a Ce isomerized stream, wherein hex-2 -enes and hex-3-enes in the Ce olefin stream are converted into hex-l-ene during Ce isomerization; and a Ce fractionator configured to receive and separate a first portion of the Ce isomerized stream to produce a hex-l-ene product stream, wherein a remainder of the Ce isomerized stream is provided to the Ce isomerization reactor along with the Ce olefin stream for Ce isomerization to produce the Ce isomerized stream.

12. The system of claim 8, wherein the C4 column is configured to receive and separate the C4+ olefin stream into the C4 olefin stream and a Ce-Ce olefin stream.

13. The system of claim 12, comprising: a catalytic cracking reactor configured to receive and catalytically crack at least the Ce-Ce olefin stream to produce a catalytically cracked stream, wherein the catalytically cracked stream is provided to the downstream separation section along with the steam cracked stream and the C2-C3 olefin stream for separation to produce at least the ethene product stream, the propene product stream, and the C4 raffinate stream.

14. The system of claim 8, comprising: a C4 isomerization reactor configured to conditionally receive and isomerize a combination of the remainder of the C4 olefin stream and the C4 raffinate stream upstream of the metathesis reactor, wherein but-2-enes within the combination of the remainder of the C4 olefin stream and the C4 raffinate stream are converted into but-l-ene within the C4 isomerization reactor; and a butene analyzer configured to determine a but-l-ene content of the combination of the remainder of the C4 olefin stream and the C4 raffinate stream, and, in response to determining that the but-l-enecontent is less than 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the C4 isomerization reactor upstream of the metathesis reactor, and in response to determining that the but-l-ene content is greater than or equal to 15 mol. %, provide the combination of the remainder of the C4 olefin stream and the C4 raffinate stream to the metathesis reactor without traversing the C4 isomerization reactor.

15. The system of claim 8, wherein at least a portion the C4 raffinate stream is received by the metathesis reactor from a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker, a methyl tert-butyl ether (MTBE) reactor, a but-l-ene (Bl) column, a but-2-enes (B2) column, a butadiene hydrogenation reactor, a methanol-to-olefins (MTO) reactor, or a refinery fluid catalytic cracking (FCC) reactor, or any combination thereof.

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