Methods and systems for producing ethylene and propylene involving metathesis of a butene stream

Abstract

Systems and methods for metathesizing C4 streams to produce chemical feedstocks, including light olefins, such as ethene and propene. A method provided herein for producing ethene and propene includes the steps of metathesizing a but-1-ene-rich C4 stream to produce a metathesis product stream. The method includes the steps of separating the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream. The method includes the steps of separating at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream forming a portion of the but-1-ene-rich C4 stream prior to metathesis. The method includes the steps of separating at least the C2-C3 olefin stream into an ethene product stream and a propene product stream.

Description

METHODS AND SYSTEMS FOR PRODUCING ETHYLENE AND PROPYLENE INVOLVING METATHESIS OF A BUTENE STREAMTECHNICAL FIELD

[0001] The present disclosure generally relates to systems and methods for performing metathesis of a C4 stream to produce chemical feedstocks, including light olefins such as ethene (also referred to herein as ethylene) and propene (also referred to herein as propylene), and C -C, linear olefins. More specifically, the present disclosure relates to systems and methods for producing such chemical feedstocks that involve metathesis of a C4 stream. The present disclosure also generally relates to systems and methods for performing metathesis of a C4 stream, along with stream cracking of one or more olefin (for example, C4, C5, and / or Ce hydrocarbon streams), to produce chemical feedstocks, including ethene, propene, and fuels such as pyrolysis gasoline and / or fuel gas.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 (for example, butenes, 2- methylprop-I-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 metathesizing C4 streams to produce chemical feedstocks, including light olefins (such as ethene and propene) and C -Ce olefins. Provided here are methods for production of ethene and propene from a hydrocarbon feedstock. In certain examples, the method includes the steps of metathesizing a but- 1-ene -rich C4 stream to produce a metathesis product stream. The method includes the steps of separating the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream. The method includes the steps of separating at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream forming a portion of the but- 1-ene -rich C4 stream prior to metathesis. The method includes separating the C2- C3 olefin stream into an ethene product stream and a propene product stream. In certain examples, the but-1- ene-rich C4 stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

[0004] In certain examples, separating at least the C4 olefin stream of the C4+ olefin stream includes the steps of separating the C4+ olefin stream into the C4 olefin stream and a Cs-Ce olefin stream. In certain examples,separating at least the C4 olefin stream of the C4+ olefin stream includes the steps of separating the C4+ olefin stream into a C4-C5 olefin stream and a Ce olefin stream, separating the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream, and metathesizing the C5 olefin stream along with the but-l-ene-rich stream to form the metathesis product stream. In certain examples, the method includes the steps of steam cracking at least a hydrocarbon feedstock to produce a cracked product stream and separating at least a C4 raffinate stream from the cracked product stream, in which a first portion of the C4 raffinate stream forms a second portion of the but-l-ene-rich C4 stream prior to metathesis. In certain examples, the method includes the steps of hydrogenating the Ce-Ce olefin stream or the Ce olefin stream to produce a saturated stream. In certain examples, the method includes the steps of combining a second portion of the C4 raffinate stream with the Ce-Ce olefin stream or the Ce olefin stream prior to hydrogenation, wherein hydrogenating the Ce-Ce olefin stream or the Ce olefin stream includes hydrogenating the second portion of the C4 raffinate stream along with the Ce-Ce olefin stream or the Ce olefin stream to form the saturated stream. In certain examples, the method includes the steps of combining the saturated stream with the hydrocarbon feedstock, wherein steam cracking comprises steam cracking the saturated stream along with the hydrocarbon feedstock to produce the cracked product stream. In certain examples, separating at least the C4 raffinate stream from the cracked product stream includes the steps of separating the cracked product stream into the C4 raffinate stream; an ethene / propene product stream that contains ethene, propene, or a combination thereof; a by-product stream that contains pyrolysis gasoline, BTX, fuel gas, other C5-C12 hydrocarbons, or a combination thereof; and an paraffinic -rich hydrocarbon stream that contains ethane, propane, and butanes, in which the paraffinic -rich hydrocarbon stream is combined along with the hydrocarbon feedstock and the saturated stream before steam cracking to form the cracked product stream.

[0005] In certain examples, the method includes the steps of, responsive to a but-l-ene content of less than 15 mol. % in a combination of the C4 olefin stream and the first portion of the C4 raffinate stream, performing C4 isomerization of the combination of the C4 olefin stream and the first portion of the C4 raffinate stream to produce the but-l-ene-rich C4 stream prior to metathesis, in which but-2-ene in the combination of the C4 olefin stream and the first portion of 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. %, providing the combination of the C4 olefin stream and the first portion of the C4 raffinate stream as the but-l-ene-rich C4 stream for metathesis without C4 isomerization. In certain examples, isomerizing the combination of the first portion of the C4 raffinate stream and the C4 olefin stream includes the steps of heating the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to a temperature ranging from about 250 degrees Celsius (°C) to about 500 °C and pressurizing the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to a pressure ranging from about 100 kilopascals (kPa) to about 3100 kPa (from about 0 bar gauge (barg) to about 30 barg) before contacting a potassium -based isomerizationcatalyst at a weight hourly space velocity (WHSV) from about 0. 1 per hour (h1) to about 25 h1, in which the combination of the first portion of the C4 raffinate stream and the C4 olefin stream is in a gas phase, a liquid phase, or a mixed phase during isomerization. In certain examples, metathesizing the but-l-ene-rich C4 stream includes the steps of heating the but-l-ene-rich C4 stream to a temperature ranging from about 35 °C to about 100 °C and pressurizing the but-l-ene-rich C4 stream to a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before contacting a rhenium oxide-coated y-alumina- based metathesis catalyst at a WHSV from about 0.1 h-1to about 25 h-1and in the absence of an ethene cofeed, in which the but-l-ene-rich C4 stream is in a gas phase, a liquid phase, or a mixed phase during metathesis. In certain examples, the method includes the steps of receiving the but-l-ene-rich C4 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.

[0006] Certain embodiments include a system for producing ethene and propene. In certain examples, the system includes a metathesis reactor configured to receive and metathesize a but-l-ene-rich C4 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 system includes a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream forming a portion of the but-l-ene-rich C4 stream upstream of the metathesis reactor. The system includes a C2 / C3 splitter configured to receive and separate the C2-C3 olefin stream into an ethene product stream and a propene product stream. In certain examples, the but-l-ene-rich C4 stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

[0007] 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 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, and in which the metathesis reactor is configured to receive and metathesize the C5 olefin stream along with the but-l-ene-rich C4 stream to produce the metathesis product stream. In certain examples, the system includes a steam cracker configured to receive and crack at least a hydrocarbon feedstock to produce a cracked product stream and a downstream separation section configured to receive the cracked product stream and separate at least a C4 raffinate stream of the cracked product stream, in which a first portion of the C4 raffinate stream forms a second portion of the but-l-ene-rich C4 stream upstream of the metathesis reactor. In certain examples, the system includes a hydrogenation unit configured to receive and hydrogenate the Ce-Ce olefin stream or the Ce olefin stream to produce a saturated stream. In certainexamples, the hydrogenation unit is configured to receive and hydrogenate a second portion of the C4 raffinate stream along with the C-C, olefin stream or the Ce olefin stream to form the saturated stream. In certain examples, the steam cracker is configured to receive and steam crack the saturated stream along with the hydrocarbon feedstock to produce the cracked product stream. In certain examples, the downstream separation section is configured to separate the cracked product stream into the C4 raffinate stream; an ethene / propene product stream that contains ethene, propene, or a combination thereof; a by-product stream that contains pyrolysis gasoline, BTX, fuel gas, other C5-C12 hydrocarbons, or a combination thereof; and a paraffinic-rich hydrocarbon stream that contains ethane, propane, and butanes, and wherein the steam cracker is configured to receive and crack the paraffinic-rich hydrocarbon stream along with the hydrocarbon feedstock and the saturated stream to form the cracked product stream.

[0008] In certain examples, the system includes an isomerization reactor configured to conditionally receive and isomerize a combination of the first portion of the C4 raffinate stream and the C4 olefin stream to produce the but-l-ene-rich C4 stream upstream of the metathesis reactor, in which but-2-enes within the combination of the first portion of the C4 raffinate stream and the C4 olefin stream are converted into but-l-ene within the isomerization reactor, and a butene analyzer configured to determine a but-l-ene content of the combination of the first portion of the C4 raffinate stream and the C4 olefin stream and, in response to determining that the but-l-ene content is less than 15 molar percent (mol. %), provide the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to the isomerization reactor to produce the but-l-ene-rich C4 stream 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 first portion of the C4 raffinate stream and the C4 olefin stream to the metathesis reactor as the but-l-ene-rich C4 stream without traversing the isomerization reactor. In certain examples, the isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed downflow reactor, in which the isomerization reactor is configured to receive the combination of the first portion of the C4 raffinate stream and the C4 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 3100 kPa (from about 0 barg to about 30 barg) before the combination of the first portion of the C4 raffinate stream and the C4 olefin stream contacts a potassium-based isomerization catalyst of the isomerization reactor at a WHSV from about 0.1 h-1to about 25 h1, in which the combination of the first portion of the C4 raffinate stream and the C4 olefin stream is in a gas phase, a liquid phase, or a mixed phase, and wherein the isomerization reactor has an operating cycle time from about 1 day to about 100 days. In certain examples, the system has a plurality of isomerization reactors that includes the isomerization reactor, in which a second isomerization reactor of the plurality of isomerization reactors is configured to operate in regeneration mode to regenerate a potassium-based isomerization catalyst of the second isomerization reactor, and in which regeneration mode operation includes the second isomerization reactor being configured to receive a stream of air, enriched air, or oxygenat a temperature ranging from about 300 °C to about 600 °C. In certain examples, the plurality of isomerization reactors includes a third isomerization reactor configured to remain in standby mode while the isomerization reactor is configured to receive and isomerize the combination of the first portion of the C4 raffinate stream and the C4 olefin stream and while the second isomerization reactor is configured to operate in regeneration mode. In certain examples, the metathesis reactor is a fixed-bed up-flow reactor or a fixed- bed down-flow reactor, wherein the metathesis reactor is configured to receive the but- 1-ene -rich C4 stream at a temperature ranging from about 35 °C to about 100 °C and a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before the but-l-ene-rich C4 stream contacts a rhenium oxide-coated y-alumina-based metathesis catalyst of the metathesis reactor at a WHSV from about 0. 1 h-1to about 25 h1in the absence of an ethene co-feed, wherein the but-l-ene-rich C4 stream is in a gas phase, a liquid phase, or a mixed phase, and wherein the metathesis reactor has an operating cycle time from about 1 day to about 100 days. 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 a rhenium oxide-coated y-alumina-based metathesis catalyst of the second metathesis reactor, and wherein 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 300 °C to about 600 °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 but-l-ene-rich C4 stream and while the second metathesis reactor is configured to operate in regeneration mode. In certain examples, the metathesis reactor is configured to receive a second portion of the but-l-ene-rich C4 stream that is extracted downstream of 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.

[0009] 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

[0010] 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, illustrateembodiments 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.

[0011] FIG. 1 is a diagrammatic representation of a first embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0012] FIG. 2 is a diagrammatic representation of a second embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0013] FIG. 3 is a diagrammatic representation of a third embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0014] FIG. 4 is a diagrammatic representation of a fourth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0015] FIG. 5 is a diagrammatic representation of a fifth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0016] FIG. 6 is a diagrammatic representation of a sixth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0017] FIG. 7 is a diagrammatic representation of a seventh embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0018] FIG. 8 is a diagrammatic representation of an eighth embodiment of system for metathesizing a C4 stream to produce chemical feedstocks.

[0019] FIG. 9 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 light olefins and fuels. 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 systems may 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 differentembodiments. 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-Cycompounds,” 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-C5 stream refers to a mixture that substantially contains or entirely contains hydrocarbonbased 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 (for example, 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 (for example, 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.

[0035] Provided here are methods for production of ethene and propene from a hydrocarbon feedstock. In certain examples, the method includes the steps of metathesizing a but-l-ene-rich C4 stream to produce a metathesis product stream. The method includes the steps of separating the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream. The method includes the steps of separating at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream forming a portion of the but-l-ene-rich C4 stream prior to metathesis. The method includes separating the C2-C3 olefin stream into an ethene product stream and a propene product stream. In certain examples, the but-l-ene-rich C4 stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

[0036] In certain examples, separating at least the C4 olefin stream of the C4+ olefin stream includes the steps of separating the C4+ olefin stream into the C4 olefin stream and a Ce-Ce olefin stream. In certain examples, separating at least the C4 olefin stream of the C4+ olefin stream includes the steps of separating the C4+ olefin stream into a C4-C5 olefin stream and a Ce olefin stream, separating the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream, and metathesizing the C5 olefin stream along with the but-l-ene-rich streamto form the metathesis product stream. In certain examples, the method includes the steps of steam cracking at least a hydrocarbon feedstock to produce a cracked product stream and separating at least a C4 raffinate stream from the cracked product stream, in which a first portion of the C4 raffinate stream forms a second portion of the but-l-ene-rich C4 stream prior to metathesis. In certain examples, the method includes the steps of hydrogenating the C -C, olefin stream or the Ce olefin stream to produce a saturated stream. In certain examples, the method includes the steps of combining a second portion of the C4 raffinate stream with the Cs-Ce olefin stream or the Ce olefin stream prior to hydrogenation, wherein hydrogenating the Ce-Ce olefin stream or the Ce olefin stream includes hydrogenating the second portion of the C4 raffinate stream along with the Ce-Ce olefin stream or the Ce olefin stream to form the saturated stream. In certain examples, the method includes the steps of combining the saturated stream with the hydrocarbon feedstock, wherein steam cracking comprises steam cracking the saturated stream along with the hydrocarbon feedstock to produce the cracked product stream. In certain examples, separating at least the C4 raffinate stream from the cracked product stream includes the steps of separating the cracked product stream into the C4 raffinate stream; an ethene / propene product stream that contains ethene, propene, or a combination thereof; a by-product stream that contains pyrolysis gasoline, BTX, fuel gas, other C5-C12 hydrocarbons, or a combination thereof; and an paraffinic-rich hydrocarbon stream that contains ethane, propane, and butane, in which the paraffinic-rich hydrocarbon stream is combined along with the hydrocarbon feedstock and the saturated stream before steam cracking to form the cracked product stream.

[0037] In certain examples, the method includes the steps of, responsive to a but-l-ene content of less than 15 mol. % in a combination of the C4 olefin stream and the first portion of the C4 raffinate stream, performing C4 isomerization of the combination of the C4 olefin stream and the first portion of the C4 raffinate stream to produce the but-l-ene-rich C4 stream prior to metathesis, in which but-2-ene in the combination of the C4 olefin stream and the first portion of 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. %, providing the combination of the C4 olefin stream and the first portion of the C4 raffinate stream as the but-l-ene-rich C4 stream for metathesis without C4 isomerization. In certain examples, isomerizing the combination of the first portion of the C4 raffinate stream and the C4 olefin stream includes the steps of heating the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to a temperature ranging from about 250 degrees Celsius (°C) to about 500 °C and pressurizing the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to a pressure ranging from about 100 kilopascals (kPa) to about 3100 kPa (from about 0 bar gauge (barg) to about 30 barg) before contacting a potassium -based isomerization catalyst at a weight hourly space velocity (WHSV) from about 0. 1 per hour (h1) to about 25 h1, in which the combination of the first portion of the C4 raffinate stream and the C4 olefin stream is in a gas phase, a liquid phase, or a mixed phase during isomerization. In certain examples, metathesizing the but-l-ene-rich C4stream includes the steps of heating the but-l-ene-rich C4 stream to a temperature ranging from about 35 °C to about 100 °C and pressurizing the but-l-ene-rich C4 stream to a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before contacting a rhenium oxide-coated y-alumina- based metathesis catalyst at a WHSV from about 0.1 h-1to about 25 h-1and in the absence of an ethene cofeed, in which the but-l-ene-rich C4 stream is in a gas phase, a liquid phase, or a mixed phase during metathesis. In certain examples, the method includes the steps of receiving the but-l-ene-rich C4 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-olefms (MTO) process, or a refinery fluid catalytic cracking (FCC) process, or any combination thereof.

[0038] Certain embodiments include a system for producing ethene and propene. In certain examples, the system includes a metathesis reactor configured to receive and metathesize a but-l-ene-rich C4 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 system includes a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream forming a portion of the but-l-ene-rich C4 stream upstream of the metathesis reactor. The system includes a C2 / C3 splitter configured to receive and separate the C2-C3 olefin stream into an ethene product stream and a propene product stream. In certain examples, the but-l-ene-rich C4 stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

[0039] 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 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, and in which the metathesis reactor is configured to receive and metathesize the C5 olefin stream along with the but-l-ene-rich C4 stream to produce the metathesis product stream. In certain examples, the system includes a steam cracker configured to receive and crack at least a hydrocarbon feedstock to produce a cracked product stream and a downstream separation section configured to receive the cracked product stream and separate at least a C4 raffinate stream of the cracked product stream, in which a first portion of the C4 raffinate stream forms a second portion of the but-l-ene-rich C4 stream upstream of the metathesis reactor. In certain examples, the system includes a hydrogenation unit configured to receive and hydrogenate the Ce-Ce olefin stream or the Ce olefin stream to produce a saturated stream. In certain examples, the hydrogenation unit is configured to receive and hydrogenate a second portion of the C4 raffinate stream along with the C -Ce olefin stream or the Ce olefin stream to form the saturated stream. In certain examples, the steam cracker is configured to receive and steam crack the saturated stream along with thehydrocarbon feedstock to produce the cracked product stream. In certain examples, the downstream separation section is configured to separate the cracked product stream into the C4 raffinate stream; an ethene / propene product stream that contains ethene, propene, or a combination thereof; a by-product stream that contains pyrolysis gasoline, BTX, fuel gas, other C5-C12 hydrocarbons, or a combination thereof; and a paraffinic-rich hydrocarbon stream that contains ethane, propane, and butane, and wherein the steam cracker is configured to receive and crack the paraffinic-rich hydrocarbon stream along with the hydrocarbon feedstock and the saturated stream to form the cracked product stream.

[0040] In certain examples, the system includes an isomerization reactor configured to conditionally receive and isomerize a combination of the first portion of the C4 raffinate stream and the C4 olefin stream to produce the but-l-ene-rich C4 stream upstream of the metathesis reactor, in which but-2-enes within the combination of the first portion of the C4 raffinate stream and the C4 olefin stream are converted into but-l-ene within the isomerization reactor, and a butene analyzer configured to determine a but-l-ene content of the combination of the first portion of the C4 raffinate stream and the C4 olefin stream and, in response to determining that the but-l-ene content is less than 15 molar percent (mol. %), provide the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to the isomerization reactor to produce the but-l-ene-rich C4 stream 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 first portion of the C4 raffinate stream and the C4 olefin stream to the metathesis reactor as the but-l-ene-rich C4 stream without traversing the isomerization reactor. In certain examples, the isomerization reactor is a fixed-bed up-flow reactor or a fixed-bed downflow reactor, in which the isomerization reactor is configured to receive the combination of the first portion of the C4 raffinate stream and the C4 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 3100 kPa (from about 0 barg to about 30 barg) before the combination of the first portion of the C4 raffinate stream and the C4 olefin stream contacts a potassium-based isomerization catalyst of the isomerization reactor at a WHSV from about 0. 1 h-1to about 25 h1, in which the combination of the first portion of the C4 raffinate stream and the C4 olefin stream is in a gas phase, a liquid phase, or a mixed phase, and wherein the isomerization reactor has an operating cycle time from about 1 day to about 100 days. In certain examples, the system has a plurality of isomerization reactors that includes the isomerization reactor, in which a second isomerization reactor of the plurality of isomerization reactors is configured to operate in regeneration mode to regenerate a potassium-based isomerization catalyst of the second isomerization reactor, and in which regeneration mode operation includes the second isomerization reactor being configured to receive a stream of air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C. In certain examples, the plurality of isomerization reactors includes a third isomerization reactor configured to remain in standby mode while the isomerization reactor is configured to receive and isomerize the combination of the first portion of the C4raffinate stream and the C4 olefin stream and while the second isomerization reactor is configured to operate in regeneration mode. In certain examples, the metathesis reactor is a fixed-bed up-flow reactor or a fixed- bed down-flow reactor, wherein the metathesis reactor is configured to receive the but-l-ene-rich C4 stream at a temperature ranging from about 35 °C to about 100 °C and a pressure ranging from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg) before the but-l-ene-rich C4 stream contacts a rhenium oxide-coated y-alumina-based metathesis catalyst of the metathesis reactor at a WHSV from about 0.1 h-1to about 25 h-1in the absence of an ethene co-feed, wherein the but-l-ene-rich C4 stream is in a gas phase, a liquid phase, or a mixed phase, and wherein the metathesis reactor has an operating cycle time from about 1 day to about 100 days. 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 a rhenium oxide-coated y-alumina-based metathesis catalyst of the second metathesis reactor, and wherein 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 300 °C to about 600 °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 but-l-ene-rich C4 stream and while the second metathesis reactor is configured to operate in regeneration mode. In certain examples, the metathesis reactor is configured to receive a second portion of the but-l-ene-rich C4 stream that is extracted downstream of 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.

[0041] Steam cracking processes are used to produce ethene as a major product along with the other side products, such as propene and C4 species, such as but-l-ene, but-2-ene, 2-methylprop-I-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 (for example, propane, natural gas liquids (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 forvalorization 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, selective use of but-2-ene for metathesis, and results in relatively high carbon dioxide (CO2) production due to relatively high metathesis reaction temperatures (for example, from 250 °C to 450 °C).

[0042] 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 (for example, a C4 raffinate stream) that is rich in but- 1 -ene and contains 2-butenes. In addition to metathesis, the embodiments discussed herein may include one or more of: C4 isomerization prior to metathesis, recycle of by-products C5 and Ce olefin metathesis products, steam cracking of a hydrocarbon feedstock, and total hydrogenation of certain C4, C5, and / or Ce streams prior to steam cracking. 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 steam cracker furnace. While these techniques are disclosed herein using examples related to the production of ethene and propene, it may be appreciated that these techniques are broadly applicable to methods and systems involving metathesis reactions of C2 to C12 olefins.

[0043] FIG. 1 is a diagrammatic representation of an embodiment of a system 100 that enables metathesis of a C4 stream 102 to produce chemical feedstocks. The system 100 includes a metathesis zone 104 and an olefin separation zone 106. In some embodiments, the C4 stream is a C4 raffinate stream. In some embodiments, the C4 stream 102 may be sourced downstream of a steam cracker (for example, 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 102 may vary based on the source of the C4 stream. For example, in certain embodiments, the C4 stream 102 has an initial composition in accordance with the C4 raffinate II or the C4 raffinate III indicated in Table 1, and this stream may be pretreated (for example, by a feed pre-treater, a decontamination unit, or guard bed) before being introduced into the isomerization or metathesis processes, as discussed below. In certain embodiments, after pretreatment to remove one or more components, the C4 stream 102 has a composition in accordance with the but- 1-ene -rich C4 raffinate II or the C4 raffinate III indicated in Table 2, which may be provided as input to the isomerization or metathesis processes, as discussed below. In some embodiments, prior to pretreatment, the C4 stream 102 may include one or more of the components indicated in Table 3, in which these components are removed during pretreatment before the stream proceeds to isomerization or metathesis. 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) and butynes are present in certain level, such as from about 0 mol. % to about 5 mol. % of 2-methylprop-l-ene and up to about 2 ppm of butynes.

[0044] Table 1. Example compositions of the C4 stream prior to pretreatment.

[0045] Table 2. Example compositions of the C4stream after pretreatment.

[0046] Table 3. Example trace impurities removed from the C4stream during pretreatment.Concentration

[0047] For the embodiment illustrated in FIG. 1, the C4 stream 102 is directed to the metathesis zone 104. In the metathesis zone 104, the C4 stream 102 traverses a heater 108 that brings the stream to a suitable temperature before it is introduced into one of the metathesis reactors 110 (for example, metathesis reactor 110A or HOB) to yield a metathesis product stream 112 containing a mixture of C2-C6 olefin metathesis products. The metathesis reactors 110 can be implemented as down-flow or up-flow, fixed-bed reactors with a rhenium oxide-coated y-alumina-based metathesis catalyst (for example, a IL^CL / yALOs-bascd catalyst). The rhenium oxide-coated y-alumina-based metathesis catalyst enables self-metathesis and cross-metathesis of but-l-ene and but-2-enes.

[0048] In some embodiments, the metathesis catalyst is a rhenium-coated y-alumina-based metathesis catalyst (e.g., a R^Ch / yALCh-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 rhenium oxide-coated y- alumina-based catalyst (R^Ch / yAhOs) can be spherical or an extrudate and may be described as having an egg-shell structure. One such rhenium oxide-coated y-alumina-based 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. 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 rhenium oxide-coated y-alumina-based catalyst contains rhenium oxide in an amount ranging from about 4.8 wt.% to about 5.6 wt.%. The rhenium oxide-coated y-alumina-based 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, 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 rhenium oxide-coated y-alumina-based 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.

[0049] Methods of preparing a rhenium oxide -coated y-alumina-based 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. In certain examples, the aqueous rhenium -containing mixture is aNFUReCft solution, an Al(ReO4)s solution, or a HReCft 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. The method also includes the steps of aging the rhenium -coated y-alumina-based support to form a rhenium oxide-coated y-alumina-based catalyst after calcination, containing a rhenium oxide coating ranging from about 150 micrometers (pm) to about 250 pm in thickness, drying the rhenium-coated y-alumina-based catalyst immediately after aging, and calcining the rhenium -coated y-alumina-based catalyst at a temperature ranging from about 450°C to about 550 °C to form rhenium oxide coated y-alumina. In certain examples, 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.

[0050] The particle size of the y-alumina-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-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 apore 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 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 rhenium oxide-coated y-alumina-based 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.

[0051] Examples include methods of preparing an activated rhenium oxide-coated y-alumina-based catalyst. One such method includes the steps of treating the rhenium oxide-coated y-alumina-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, purging nitrogen into the activated rhenium oxide-coated y-alumina-based catalyst to displace the air, and cooling the activated rhenium oxide-coated y-alumina-based catalyst to a temperature of about 50 °C. In certain examples, the step of treating the rhenium oxide-coated y-alumina-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. In certain examples, the step of treating the rhenium oxide-coated y-alumina-based catalyst under air is conducted for about 6 hours.

[0052] 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 metal component 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.

[0053] Certain examples of an olefin metathesis catalyst have a base support containing aluminum oxide and 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.

[0054] For the embodiment illustrated in FIG. 1, metathesis reactors 110 are implemented in series or in parallel 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 110, 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 110 is below 250 °C, such as a temperature ranging from about 35 °C to about 100 °C. It is presently recognized that themetathesis 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 110 reduces the operational cost and energy demands of these reactors compared to other systems. The operating pressures of the metathesis reactors 110 can range from about 100 kPa to about 2100 kPa (from about 0 barg to about 20 barg). In some embodiments, the metathesis reactors 110 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 110 can be operated in gas phase, liquid phase, or mixed phase. It is presently recognized that the 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 from about 1 day to about 100 days, such as from 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 reactor 110 to a weight hourly space velocity (WHSV) from about 0. 1 h-1to about 10 h1, more preferably to values from about 0.5 h1to about 5 h1. Regeneration of the metathesis catalyst can be performed when a metathesis reactor 110A or HOB 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 450 °C to about 550 °C.

[0055] For the embodiment illustrated in FIG. 1, the metathesis product stream 112 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 C3 column 114 (for example, a depropenizer), a pump 116, a C2 / C3 splitter 118, and a C4 column 120 (for example, a debutenizer). The metathesis product stream 112 is directed to the C3 column 114, which separates the metathesis product stream 112 into a C2-C3 olefin stream 122 and a C4+ olefin stream 124. The C2-C3 olefin stream 122 is directed to the pump 116, which increases the pressure of the C2-C3 olefin stream 122 before it is supplied to the C2 / C3 splitter 118. The C2 / C3 splitter 118 separates the C2-C3 olefin stream 122 into an ethene product stream 126 and a propene product stream 128. For the illustrated embodiment, the C4+ olefin stream 124 is directed to the C4 column 120, which separates the C4+ olefin stream 124 into a C4 olefin stream 130 and a Cs-Ce olefins 132. In some embodiments, the C4 olefin stream 130 may include a limited amount of paraffins (for example, butane, 2-methylpropane) that can be purged from the C4 olefin stream 130 and generate a purged stream 134. It may be appreciated that the purged stream 134 may be collected to be sold as a product (for example, liquid petroleum gas (LPG)) with or without further purification, or it may be provided as an input stream to another system, for example, a total hydrogenation unit (THU) 526 or unit of a hydrocarbon processing facility. After this optional 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 112.

[0056] FIG. 2 is a diagrammatic representation of an embodiment of a system 200 that enables metathesis of the C4 stream 102 to produce chemical feedstocks. The system 200 includes the metathesis zone 104 and the olefin separation zone 106, as discussed above with respect to FIG. 1, as well as an isomerization zone 202. As discussed below, the isomerization zone 202 enhances the robustness of the system 200 by enabling the use of C4 streams 102 that are rich in but-2-enes and include less than 15 mol. % but-l-ene.

[0057] For the embodiment illustrated in FIG. 2, the C4 stream 102 is combined with the C4 olefin stream 135 within a butene analyzer unit 204, which is designed to analyze the composition of the combined 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 analyzer unit 204 routes the combined stream to the isomerization zone 202. In response to determining that the but-l-ene to but-2-enes ratio is greater than 15:85 (for example, 60:40 or 80:20) or that the but-l-ene content is greater than or equal to 15 mol. %, the butene analyzer unit 204 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-l-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.

[0058] For the embodiment illustrated in FIG. 2, the isomerization zone 202 includes a heater 206 and isomerization reactors 208. The incoming stream traverses the heater 206, which brings the stream to a suitable temperature before it is introduced into one of the isomerization reactors 208 (for example, 208A, 208B). The isomerization reactors 208 are designed to isomerize the received stream to yield an isomerized stream 209 that is subsequently directed to the metathesis zone 104. More specifically, the isomerization reactors 208 isomerize but-2-enes present in the incoming stream into but-l-ene within the isomerized stream 209. For the illustrated embodiment, isomerization reactors 208 are implemented such that one reactor remains online while the other reactor is in regeneration or standby mode. For embodiments having three isomerization reactors 208, one isomerization reactor remains online, a second isomerization reactor is in regeneration mode, while the third isomerization reactor is in standby mode.

[0059] The isomerization reactors 208 can be implemented as down-flow or up-flow, fixed-bed reactors having a potassium-based isomerization catalyst (for example, a K^O / yAUOs-based catalyst). The operating temperatures of the isomerization reactors 208 can range from about 250 °C to about 500 °C, and the operating pressures can range from about 100 kPa to about 3100 kPa (from about 0 barg to about 30 barg). In different implementations, each of the isomerization reactors 208 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 gradualdeactivation due to formation of intermediate species or carbon deposition, and as such, it is desirable to operate the isomerization reactors 208 to enable a suitable operating cycle time from about 1 day to about 100 days, such as from about 1 day to about 60 days. In some embodiments, this is achieved by limiting the flow rate of the C4 stream to the isomerization reactors 208 to a WHSV from about 0.1 h-1to about 10 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 isomerization reactor 208A or 208B is in regeneration mode using air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C.

[0060] FIG. 3 is a diagrammatic representation of an embodiment of a system 300 that enables metathesis of the C4 stream 102 to produce chemical feedstocks. The system 300 includes the metathesis zone 104, as discussed above with respect to FIG. 1, as well as a modified olefin separation zone 302. The modified olefin separation zone 302 generally enables isolation of C5 and Ce olefin metathesis products, in which the C5 metathesis products can be recycled along with the C4 metathesis products to the metathesis zone 104 to enable enhanced propene production and enhanced Ce olefin production.

[0061] For the embodiment illustrated in FIG. 3, the metathesis product stream 112 exits the metathesis zone 104 and is directed to the olefin separation zone 302. The olefin separation zone 302 includes a C3 column 304 (for example, a depropenizer), a pump 306, a C2 / C3 splitter 308, C5 column 310 (for example, a depentenizer), and a C4 column 312 (for example, a debutenizer). The metathesis product stream 112 is directed to the C3 column 304, which separates the metathesis product stream 112 into a C2-C3 olefin stream 314 and a C4+ olefin stream 316. The C2-C3 olefin stream 314 is directed to the pump 306, which increases the pressure of the C2-C3 olefin stream 314 before it is supplied to the C2 / C3 splitter 308. The C2 / C3 splitter 308 separates the C2-C3 olefin stream 314 into an ethene product stream 318 and a propene product stream 320. The C4+ olefin stream 316 is directed to the C5 column 310, which separates the C4+ olefin stream 316 into a C4-C5 olefin stream 322 and Ce olefin stream 324. The C4-C5 olefin stream 322 is directed to the C4 column 312, which separates the C4-C5 olefin stream 322 into a C4 olefin stream 326 and a C5 olefin stream 328. In some embodiments, the C5 olefin stream 328 includes cis and trans isomers of pent-2 -ene. In some embodiments, the C4 olefin stream 326 may include a limited amount of paraffins (for example, butane, 2- methylpropane) that can be purged from the C4 olefin stream 326 and generate a purged stream 330. It may be appreciated that the purged stream 330 may be collected to be sold as a product (for example, LPG) with or without further purification, or it may be provided as an input stream to another system, for example, the THU 526 or unit of a hydrocarbon processing facility. After this optional purging, a remainder of the C4 olefin stream 332 and the C5 olefin stream 328 are recycled to the metathesis zone 104, where they are combined with the C4 stream 102 before being metathesized to form the metathesis product stream 112.

[0062] FIG. 4 is a diagrammatic representation of an embodiment of a system 400 that enables metathesis of the C4 stream 102 to produce chemical feedstocks. The system 400 includes the metathesis zone 104, asdiscussed above with respect to FIG. 1, the isomerization zone 202, as discussed above with respect to FIG. 2, and the modified olefin separation zone 302, as discussed above with respect to FIG. 3. Like the system 300 of FIG. 3, the modified olefin separation zone 302 of the system 400 of FIG. 4 enables isolation of Cf and Ce olefin metathesis products, in which the C5 metathesis products can be recycled to the metathesis zone 104 to enable enhanced propene production and enhanced Ce olefin production. Like the system 200 of FIG. 2, the isomerization zone 202 of the system 400 of FIG. 4 enhances the robustness of the system 400 by enabling conditional isomerization for situations in which the combined C4 stream 102 and recycled C4 olefin stream 332 are rich in but-2-enes and include less than 15 mol. % but-l-ene.

[0063] For the embodiment illustrated in FIG. 4, the C4 stream 102 is combined with the C4 olefin stream 332 from the C4 column 312 before reaching the butene analyzer unit 204, which routes the combined stream to either the isomerization zone 202 or the metathesis zone 104, as discussed above. The C5 olefin stream 328 from the C4 column 312 is directed to the metathesis zone 104, where it is combined with either the isomerized stream 209 from the isomerization zone 202 or the C4 stream 102 before being metathesized to generate the metathesis product stream 112.

[0064] 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 and the olefin separation zone 106, as discussed above with respect to FIG. 1, as well as a total hydrogenation zone 502 and a steam cracking zone 504. In some embodiments, the integration of the total hydrogenation zone 502 and a steam cracking zone 504 enables a reduction in the number of separation units in the olefin separation zone 106, reducing the installation, maintenance, and operational costs of the system 500. The total hydrogenation zone 502 and a steam cracking zone 504 also enables the conversion of metathesis byproducts, such as C5 and Ce olefin metathesis products, to high value products, such as ethene, propene, pyrolysis gasoline, and / or fuel gas.

[0065] For the embodiment of the system 500 illustrated in FIG. 5, the steam cracking zone 504 receives and steam cracks a hydrocarbon feedstock 506. In some embodiments, the hydrocarbon feedstock 506 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 506 contains of propane, natural gas liquids (NGLs), and naphtha. In certain embodiments, the hydrocarbon feedstock 506 consists essentially of propane, natural gas liquids (NGLs), and naphtha. The steam cracking zone 504 includes a steam cracker 508 and a downstream separation section 510. The steam cracker 508 receives and cracks the hydrocarbon feedstock 506, along with other streams discussed below, to generate a cracked product stream 512 that is directed to the downstream separation section 510. The cracked product stream 512 may include: hydrogen (H2), BTX hydrocarbons, ethene, propene, pyrolysis gasoline, fuel gas, ethane, propane, butane, and / or other C5-12 hydrocarbons. BTX hydrocarbons include benzene, toluene, and dimethylbenzenes (also referred to herein as xylenes). Thedownstream separation section 510 (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 / propene product stream 514, a C4 raffinate stream 516, a byproduct stream 518, and a paraffinic -rich hydrocarbon stream 520 that contains C2-4 saturated hydrocarbons (for example, ethane, propane, and / or butane). In some embodiments, the downstream separation section 510 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 (for example, distillation column, fractional distillation column, de-methanizer, de-ethanizer, depropanizer, debutanizer, depentanizer, acetylene hydrogenation unit, iso-butane dehydrogenation unit, and so forth), or any combination thereof. The ethene / propene product stream 514 contains ethene and propene. The byproduct stream 518 may contain pyrolysis gasoline, BTX, other C5-C12 hydrocarbons and / or fuel gas. In certain embodiments, the downstream separation section 510 may further separate the ethene / propene product stream 514 into separate ethene / ethane product stream and propene / propane product stream and / or further separate the by-product stream 518 into a separate pyrolysis gasoline product stream, a BTX product stream, a heavier hydrocarbons (C5-C12) stream, and a fuel gas product stream. A remainder of the cracked product stream 512, which includes C2-C4 paraffinic hydrocarbons (for example, ethane, propane, butanes), is isolated to form the paraffinic-rich hydrocarbon stream 520, which is recycled and combined with fresh hydrocarbon feedstock 506 and a saturated stream 530 (discussed below) before returning to the steam cracker 508 to generate the cracked product stream 512. The fuel gas is rich in methane and other hydrocarbons. The fuel gas is rich in methane, while the pyrolysis gasoline is predominately generated due to recycling the aromatic-rich hydrocarbon stream after extraction of BTX of the by-product stream 518 and used as fuel in steam cracker or sold as product fuel gas and fuel oil.

[0066] In some embodiments, the C4 raffinate stream 516 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 516 contains or consists essentially of 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. In some embodiments, the C4 raffinate stream 516 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 506.

[0067] For the embodiment of the system 500 illustrated in FIG. 5, the C4 raffinate stream 516 is directed to the flow control device 522, which selectively routes a first portion 524 of the C4 raffinate stream 516 to the THU 526 of the total hydrogenation zone 502 and a second portion 528 of the C4 raffinate stream 516 tobe combined with the C4 olefin stream 135 from the C4 column 120 after optional purging. The flow control device 522 may determine the relative ratio of the first portion 524 and the second portion 528 based on instructions provided by a controller, based on the demands of the total hydrogenation zone 502, based on the demands of the steam cracking zone 504, based on the demands of the metathesis zone 104, based on the outputs of the olefine separation zone 106, or any combination thereof. In certain embodiments, the first portion 524 of the C4 raffinate stream includes from about 2.5 wt. % to about 50 wt. % of the total C4 raffinate stream 516 produced within the steam cracking zone 504, with the remainder being directed to the metathesis zone 104 as the second portion 528 of the C4 raffinate stream. The THU 526 also receives the Cs-Ce olefin stream 132 from the C4 column 120. Within the THU 526, the first portion 524 of the C4 raffinate stream and the Cs-Ce olefin stream 132 are completely hydrogenated to yield a saturated stream 530, which is combined with the hydrocarbon feedstock 506 and the recycled paraffinic-rich hydrocarbon stream 520 before being steam cracked to produce the cracked product stream 512, which increases ethene and propene production. In some embodiments, the combination of the second portion 528 of the C4 raffinate stream and the C4 olefin stream 135 may be further combined with the C4 stream 102 before being metathesized to produce the metathesis product stream 112, while in other embodiments, the combination of the second portion 528 of the C4 raffinate stream and the C4 olefin stream 135 may provide all of the stream that is delivered to the metathesis zone 104 to produce the metathesis product stream 112. It may also be appreciated that, in certain embodiments of the system 500, the C2 / C3 splitter 118 of the olefin separation zone 106 may be omitted to reduce the installation, maintenance, and operational costs of the system 500, and the C2-C3 olefin stream 122 may instead be routed to the downstream separation section 510 for separation.

[0068] FIG. 6 is a diagrammatic representation of an embodiment of a system 600 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 600 includes the metathesis zone 104 and the olefin separation zone 106, as discussed above with respect to FIG. 1, the isomerization zone 202, as discussed above with respect to FIG. 2, and the total hydrogenation zone 502 and the steam cracking zone 504, as discussed above with respect to FIG. 5. As such, in addition to the features and advantages discussed above for the embodiment of the system 500 illustrated in FIG. 5, the embodiment of the system 600 illustrated in FIG. 6 enables conditional isomerization of but-2-enes into but-l-ene, depending on the ratio of but-l-ene to but-2-enes or the but-l-ene content of the combined streams received by the butene analyzer unit 204. In certain embodiments, C4 streams that are received, combined, and conditionally routed by the butene analyzer unit 204 include the C4 olefin stream 135 and the second portion 528 of the C4 raffinate stream, and optionally may include the C4 stream 102, depending on the demands of the system 600, 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 135, and the second portion 528 of the C4 raffinate stream, as well as the desired ultimate products of the system 600, the butene analyzer unit 204 mayintroduce more or less of the C4 stream 102 to be combined with the C4 olefin stream 135 and the second portion 528 of the C4 raffinate stream, 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.

[0069] FIG. 7 is a diagrammatic representation of an embodiment of a system 700 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 700 includes the metathesis zone 104, as discussed above with respect to FIG. 1, the modified olefin separation zone 302, as discussed above with respect to FIG. 3, and the total hydrogenation zone 502 and the steam cracking zone 504, as discussed above with respect to FIG. 5. As such, in addition to the features and advantages discussed above for the embodiment of the system 500 illustrated in FIG. 5, the embodiment of the system 700 illustrated in FIG. 7 enables the Ce olefin steam 324 from the C5 column 310 to be directed to the THU 526 to be hydrogenated along with the first portion 524 of the C4 raffinate stream to produce the saturated stream 530. Additionally, the C4 olefin stream 332 and the second portion 528 of the C4 raffinate stream, and optionally the C4 stream 102, are combined before being metathesized to yield the metathesis product stream 112.

[0070] FIG. 8 is a diagrammatic representation of an embodiment of a system 800 that enables metathesis of a C4 stream to produce chemical feedstocks. The system 800 includes the metathesis zone 104 discussed above with respect to FIG. 1, the isomerization zone 202 discussed above with respect to FIG. 2, the modified olefin separation zone 302 discussed above with respect to FIG. 3, and the total hydrogenation zone 502 and the steam cracking zone 504 discussed above with respect to FIG. 5. As such, in addition to the features and advantages discussed above for the embodiment of the system 700 illustrated in FIG. 7, the embodiment of the system 800 illustrated in FIG. 8 enables conditional isomerization ofbut-2-enes into but-l-ene depending on the ratio of but-l-ene to but-2-enes or the but-l-ene content of the C4 streams received by the butene analyzer unit 204. In certain embodiments, C4 streams that are received and conditionally routed by the butene analyzer unit 204 include the C4 olefin stream 332 and the second portion 528 of the C4 raffinate stream, and optionally may include the C4 stream 102, depending on the demands of the system 800, 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 135, and the second portion 528 of the C4 raffinate stream, as well as the desired ultimate products of the system 800, the butene analyzer unit 204 may introduce more or less of the C4 stream 102 to be combined with the C4 olefin stream 332 and the second portion 528 of the C4 raffinate stream, in addition to conditionally routing the combined stream to either the isomerization zone 202 or the metathesis zone 104.

[0071] It may be appreciated that, for certain embodiments of the systems discussed above, these systems desirably lack a C4 fractionation column that separates but-l-ene from but-2-ene from the incoming C4 streams prior to metathesis or from the metathesis product steam after metathesis. It is recognized that this separation is highly energy intensive, and as such, C4 fractionation columns inherently consume a significantquantity of energy during operation. Therefore, by avoiding the inclusion of C4 fractionation columns, certain embodiments enable reduced energy consumption relative to other systems. It is further noted that, unlike other systems, the embodiments disclosed herein each include only a single isomerization zone 202 in which one of the isomerization reactors 208 isomerizes a substantial portion or all but-2-ene into but-l-ene. In particular, the disclosed systems lack additional isomerization zones or isomerization reactors for converting but-l-ene into but-2-enes to enhance their separation, which reduces the complexity and operational costs of these systems relative to other systems. Additionally, unlike other systems, the embodiment disclosed herein each only include a single metathesis zone 104, in which one of the metathesis reactors 110 metathesizes the incoming C4 stream to yield the metathesis product stream 112. In other words, the disclosed systems lack additional metathesis zones or metathesis reactors that perform metathesis of particular olefin streams isolated from the metathesis product stream 112, which reduces the complexity and operational costs of the disclosed systems relative to other systems.

[0072] Various zones are discussed for the embodiments illustrated in FIGS. 1-8, including the metathesis zone 104, the olefin separation zones 106 and 302, the isomerization zone 202, the total hydrogenation zone 502, and the steam cracking zone 504. In other embodiments, the system may include other combinations of these zones, beyond those specifically illustrated in FIGS. 1-8, in accordance with the present disclosure.

[0073] FIG. 9 is a diagrammatic representation of an embodiment of a control system 900 for controlling the embodiments of the system discussed above. The control system 900 includes at least one controller 902. Each controller 902 includes at least one processor 904, 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 902 includes at least one memory 906, 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 902 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 isomerization zone 202, the olefin separation zone 106 or the modified olefin separation zone 302, the total hydrogenation zone 502, and / or the steam cracking zone 504. The controller 902 is further communicatively connected to certain other elements of the systems discussed above, such as the flow control device 522 and the butene analyzer unit 204. The communicative connection between the controller 902 and the various zones and devices enables the controller 902 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 902 to provide control signals (for example, electrical signals, instructions, data packets) to modify the operation of each of these zones or devices.

[0074] For example, the controller 902 may receive monitoring data from sensors (for example, temperature sensors, pressure sensors, flow sensors) of the metathesis zone 104, and based on predefined threshold valuesfor 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 110 operate within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the metathesis reactors 110. The controller 902 may receive monitoring data from sensors (for example, temperature sensors, pressure sensors, flow sensors) of the isomerization zone 202, 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 isomerization zone 202 to ensure that the isomerization reactors 208 operate within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the isomerization reactors 208. The controller 902 may receive monitoring data from sensors (for example, temperature sensors, pressure sensors, flow sensors) of the olefin separation zone 106 or the modified olefin separation 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, such that the components of these zones operate in accordance with the predefined threshold values. The controller 902 may receive monitoring data from sensors (for example, temperature sensors, pressure sensors, flow sensors) of the total hydrogenation zone 502 and the steam cracking zone 504 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.

[0075] In certain embodiments, the controller 902 may provide control signals to modify the operation of the flow control device 522 to adjust the quantity of the C4 raffinate stream 516 that is directed to the total hydrogenation zone 502 versus the isomerization zone 202 or metathesis zone 104, based on the monitoring data received from the total hydrogenation zone 502, the isomerization zone 202, the metathesis zone 104, and / or the steam cracking zone 504. In certain embodiments, the controller 902 receives monitoring data from the butene analyzer unit 204 regarding the but-l-ene content in each of the received streams, such as the second portion 528 of the C4 raffinate stream 516, either the C4 olefin stream 135 or 332, and optionally the C4 stream 102. In some embodiments, the controller 902 provides control signals to modify the operation of the butene analyzer unit 204 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 204 to route the combined stream to the metathesis zone 104. In certain embodiments, when the controller 902 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 902 provides control signals to modify the operation of the butene analyzer unit 204 to instead route the combined streams to the isomerization zone 202 to increase the but-l-ene content to values greater than or equal to 15 mol. % prior to reaching the metathesis zone 104.Examples

[0076] Example 1:

[0077] The operational performance of the system 100 of FIG. 1 was evaluated using modeling and calculations based on lab experimental results, published data, and a commercial simulator available from Aspen Technology Inc. of Bedford, Massachusetts, U.S.A. The operational performance of the system 100 was evaluated using the example C4 streams 102 indicated as Feed-I and Feed-II in Table 4. Additionally, the operational performance of these systems was modeled based on example metathesis reaction conditions, including an operating temperature of 50 °C, an operating pressure of 700kPa (6 barg), and a WHSV of 0.6 h1. The ultimate yields were calculated using lab experimental results. The lab experimental results for single pass metathesis conversion are provided in Table 5 and Table 6 for Feed-I and Feed-II, respectively. The experimental results were confirmed with simulation results using the commercial simulator. Next, the product composition, including the recycle of the C4 olefin stream 135, was calculated using the commercial simulator as indicated in Table 7 based on an input feed quantity of Feed-Ill of 100 kilotons per annum(KTA). As indicated in Table 7, along with propene, a minor amount of ethene product was also formed. In addition, C5 olefins, such as pentene isomers, and Ce olefins, such as hexene isomers, are major by-products from the metathesis reactor outlet. For this example, continuous purging of the C4 olefin stream 130 was performed to remove the build-up of inert materials (for example, paraffins) at the metathesis reactor inlet.

[0078] Table 4. C4stream compositions for examples.

[0079] Table 5. Metathesis products for Example 1 using Feed-L

[0080] Table 6. Metathesis products for Example 1 using Feed-IL

[0081] Table 7. Ultimate product composition using Feed-Ill with a total input of 100 KTA.

[0082] Example 2:

[0083] Using the commercial simulator and the metathesis reactor conditions set forth above in Example 1, the system 300 of FIG. 3 was simulated to determine the ultimate product yields. As noted, the system 300 of FIG. 3 includes recycling of the C4 olefin stream 332 and the C5 olefin stream 328 to the metathesis zone 104, as well as the total hydrogenation and steam cracking of the Ce-Ce olefin stream 132. The ultimate product composition is indicated in Table 8 based on an input feed quantity of Feed-Ill of 100 KTA. Compared to Example 1, an increase in the production of propene and Ce olefins was observed.

[0084] Table 8. Ultimate product composition using Feed-Ill with a total input of 100 KTA.

[0085] Example 3:

[0086] Using the commercial simulator and the metathesis reactor conditions set forth above in Example 1, the system 500 of FIG. 5 was simulated to determine the ultimate product yields. As noted, the system 500 of FIG. 5 includes recycling of the C4 olefin stream 135 to the metathesis zone 104 and the total hydrogenation and steam cracking of the Ce-Ce olefin stream 132. The ultimate product composition is indicated in Table 9 based on an input feed quantity of Feed-Ill of 100 KTA. The ultimate yields of C5 and Ce olefins mixed feed thermal cracking were calculated using published data. Compared to Example 1, an increase in the production of ethene and propene was observed, in addition to the production of pyrolysis gasoline and fuel gas.

[0087] Table 9. Ultimate product composition using Feed-Ill with a total input of 100 KTA.

[0088] Example 4:

[0089] Using the commercial simulator and the metathesis reactor conditions set forth above in Example 1, the system 700 of FIG. 7 was simulated to determine the ultimate product yields. As noted, the system 700 of FIG. 7 includes recycling of the C4 olefin stream 332 and the C5 olefin stream 328 to the metathesis zone 104, the total hydrogenation of the Ce olefin stream 324, and the steam cracking of the saturated Ce olefin stream (as part of the saturated stream 530). The ultimate product composition is indicated in Table 10 based on an input feed quantity of Feed-Ill of 100 KTA. The ultimate yields of Ce olefins thermal cracking were calculated using published data. Compared to Example 1, an increase in the production of ethene and propene was observed, in addition to the production of pyrolysis gasoline and fuel gas.

[0090] Table 10. Ultimate product composition using Feed-Ill with a total input of 100 KTA.

[0091] Example 5:

[0092] Using the commercial simulator and the metathesis reactor conditions set forth above in Example 1, the system 200 of FIG. 2 was simulated to determine the composition of the isomerized stream 209. For this example, the composition of the C4 stream 102 is indicated as the Raffinate-Ill stream in Table 11. For this example, the C4 stream 102 is isomerized produce but-l-ene from but-2-enes at 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 30 barg), and a WHSV from about 0.1 h-1to about 20 h1. The composition of the isomerized stream 209 was calculated using lab experimental results, as indicated in Table 12, with varying isomerization reaction temperature, and the experimental results were confirmed using the commercial simulator. For this example, no effect was observed when the operating pressure or the WHSV were varied. However, since the isomerization catalyst deactivates faster with increased WHSV, it was observed that a WHSV of 0.6 hr1resulted in the isomerization catalyst being stable for 30 days. It was further observed that only but-2-enes were isomerized to 1 -butene within the isomerization reactor, despite the presence of other unsaturated C4 species in the C4 stream 102.

[0093] Table 11. C4stream compositions for example 5.

[0094] Table 12. Isomerized Stream Composition in mol. % for Example 5.

[0095] 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.

[0096] 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 specific embodiments 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 for producing ethene and propene, the method comprising: isomerizing at least a first portion of a C4 raffinate stream to convert a substantial portion of but-2-enes into but-l-ene, thereby to yield a but-l-ene-rich C4 stream; metathesizing the [[a]] but-l-ene-rich C4 stream to produce a metathesis product stream; separating the metathesis product stream into a C2-C3 olefin stream and a C4+ olefin stream; separating at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream being combined with the first portion of the C4 raffinate stream prior to isomerization; and separating the C2-C3 olefin stream into an ethene product stream and a propene product stream.

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

3. The method of claims 1 or 2, wherein separating at least the C4 olefin stream of the C4+ olefin stream comprises: separating the C4- olefin stream into a C4-C5 olefin stream and a Co olefin stream; separating the C4-C5 olefin stream into the C4 olefin stream and a C5 olefin stream; and metathesizing the C5 olefin stream along with the but-l-ene-rich stream to form the metathesis product stream.

4. The method of claim 3, wherein the method comprises: steam cracking at least a hydrocarbon feedstock to produce a cracked product stream; and separating at least the [[a]] C4 raffinate stream from the cracked product stream,5. The method of claims 4, wherein the method comprises: hydrogenating the G-G, olefin stream or the G olefin stream to produce a saturated stream.

6. The method of claim 5, comprising: combining a second portion of the raffinate stream with the G-G, olefin stream or the Ce olefin stream prior to hydrogenation, wherein hydrogenating the C5-C6olefin stream or the C6olefin stream includes hydrogenating the second portion of the C4raffinate stream along with the C5-C6olefin stream or the Ce olefin stream to form the saturated stream.

7. The method of claims 5 or 6, comprising: combining the saturated stream with the hydrocarbon feedstock, wherein steam cracking comprises steam cracking the saturated stream along with the hydrocarbon feedstock to produce the cracked product stream.

8. The method of any of claims 4-6, wherein separating at least the C4 raffmate stream from the cracked product stream comprises: separating the cracked product stream into.: the C4 raffmate stream; an ethene / propene product stream that contains ethene, propene, or a combination thereof; a by-product stream that contains pyrolysis gasoline, BTX, fuel gas, other C5-C12 hydrocarbons, or a combination thereof; and paraffinic-rich hydrocarbon stream that contains ethane, propane, and butane, wherein the paraffinic-rich hydrocarbon stream is combined along with the hydrocarbon feedstock and the saturated stream before steam cracking to form the cracked product stream.

9. A system for producing ethene and propene, the system comprising: an isomerization reactor configured to receive and isomerize at least a first portion of a C4 raffinate stream to convert a substantial portion of but-2-enes into but-l-ene, thereby to yield a but-l-ene- rich C4 stream; a metathesis reactor configured to receive and metathesize the [[a]] but-l-ene-rich C4 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; a C4 column configured to receive and separate at least a C4 olefin stream of the C4+ olefin stream, the C4 olefin stream being combined with the first portion of the C4 raffinate stream upstream of the isomerization reactor; and a C2 / C3 splitter configured to receive and separate the C2-C3 olefin stream into an ethene product stream and a propene product stream.

10. The system of claim 9, wherein the but-l-ene-rich C4stream contains from about 65 molar percent (mol. %) to about 98 mol. % n-butenes.

11. The system of claims 9 or 10, wherein the C4 column is configured to receive and separate the C4+olefin stream into the C4 olefin stream and a Cs-Ca olefin stream.

12. The system of claims 10 or 11, 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, and wherein the metathesis reactor is configured to receive and metathesize the C5 olefin stream along with the but-l-cnc-rich C4 stream to produce the metathesis product stream.

13. The system of claims 9, 11, or 12, comprising: a steam cracker configured to receive and crack at least a hydrocarbon feedstock to produce a cracked product stream; and a downstream separation section configured to receive the cracked product stream and separate at least a C4 raffinate stream of the cracked product stream, wherein a first portion of the C4 raffinate stream forms a second portion of the but-l-ene-rich C4 stream upstream of the metathesis reactor.

14. The system of claim 13, comprising: a butene analyzer configured to determine a but-l-ene content of the combination of the first portion of the C4 raffinate stream and the C4 olefin stream and, in response to determining that the but-l-ene content is less than 15 molar percent (mol. %), provide the combination of the first portion of the C4 raffinate stream and the C4 olefin stream to the isomerization reactor to produce the but-l-ene- rich C4 stream 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 first portion of the C4 raffinate stream and the C4 olefin stream to the metathesis reactor as the but-l-ene-rich C4 stream without traversing the isomerization reactor.

15. The system of claim 14, wherein the system comprises a plurality of isomerization reactors that includes the isomerization reactor, wherein a second isomerization reactor of the plurality of isomerization reactors is configured to operate in regeneration mode to regenerate a potassium-based isomerization catalyst of the second isomerization reactor, and wherein regeneration mode operation includes the second isomerization reactor being configured to receive a stream of air, enriched air, or oxygen at a temperature ranging from about 300 °C to about 600 °C.

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