Systems and methods for the production of propene with ethene being substantially absent as a co-feed

Abstract

Provided here are systems and methods for the production of propene with ethene being substantially absent as a co-feed. One system for the production of propene includes a metathesis reactor that is configured to receive and metathesize a but-1-ene-rich stream having a but-1-ene content of at least 15 molar percent (mol. %) to produce a metathesis product stream. The system includes a C3 column that is configured to receive and separate the metathesis product stream into a C2-C3 product stream and a C4+-rich stream. The system includes a C4 column that is configured to receive and separate the C4+-rich stream from the C3 column into a C5-C6 olefins stream and a C4 olefin stream. The system includes a C5-C6 catalytic cracking reactor that is configured to receive and catalytically crack the C5-C6 olefins stream from the C4 column into a cracked product stream. The system includes a C2 / C3 splitter column that is configured to receive and separate the C2-C3 product stream into an ethene product stream and a propene product stream.

Description

SYSTEMS AND METHODS FOR THE PRODUCTION OF PROPENE WITH ETHENE BEING SUBSTANTIALLY ABSENT AS A CO-FEEDTechnical Field

[0001] The disclosure relates to the production of propene using metathesis reactions and with ethene being substantially absent as a co-feed.Background

[0002] The demand for propene is growing. Current commercial metathesis processing of but- 2-enes includes using ethene for the production of propene. There exists an opportunity to produce propene and other high value olefins while reducing the loss of valuable C4 olefins from the propene production system with ethene being substantially absent.Summary

[0003] Applicant has identified a need for the reduction of C4 olefins forfeited during the production of propene and with ethene being substantially absent as a co-feed for the metathesis of butenes for the production of C3 olefins. Provided here are systems and methods to address these shortcomings of the art and provide other additional or alternative advantages. The disclosure herein provides several embodiments of systems for the production of propene and methods for producing propene with ethene being substantially absent as a co-feed.

[0004] Examples include a propene production system. One such system can include a metathesis reactor containing a metathesis catalyst. The metathesis reactor is configured to receive a butene feed stream containing but-l-ene, but-2-enes, and 2-methylpropene. The cross-metathesis reactions or self-metathesis reactions in the metathesis reactor produce a metathesis product stream containing ethene, propene, and Cs-Ce olefins. The system includes a metathesis reactor that is configured to receive and metathesize a but-l-ene-rich stream having a but-l-ene content of at least 15 molar percent (mol. %) to produce a metathesis product stream containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins. The metathesis reactor contains a metathesis catalyst.

[0005] The system includes a C3 column that is configured to receive and separate the metathesis product stream into a C2-C3 product stream containing ethene and propene and a C4+-rich stream containing the C4-C6 olefins and the unreactive C4 paraffins. The system includes a C4 column that is configured to receive and separate the C4+-rich stream from the C3 column into a Cs-Ce olefins stream containing Cs-Ce olefins and a C4 olefin stream containing C4 olefins and the unreactive C4 paraffins. The system includes a Cs-Ce catalytic cracking reactor that is configured to receive and catalytically crack the Cs-Ce olefins stream from the C4 column into a cracked product stream containing ethene, propene, and Cs-Ce olefins. The system includes a C2 / C3 splitter column that is configured to receive and separate the C2-C3 product stream into an ethene product stream and a propene product stream.

[0006] In certain examples, the system includes a first C4 isomerization reactor that is configured to receive and isomerize a butene feed stream containing less than 13 mol. % of but-1- ene and produce the but-l-ene-rich stream having a but-l-ene content of at least 15 mol. % that is supplied to the metathesis reactor. In certain examples, the system includes a second C4 isomerization reactor with an isomerization catalyst and is configured to receive the C4 olefins stream from the C4 column and to supply a butene recycle stream having a but-l-ene content of at least 15 mol. % to the metathesis reactor. In certain examples, the ethene product stream is supplied to the metathesis reactor. In certain examples, the unreactive C4 paraffins in the C4 olefin stream are removed. In certain examples, the metathesis reactor operates at temperature about 60 degrees Celsius (°C) and a pressure about 8 bar gauge (barg). In certain examples, the metathesis catalyst is a rhenium oxide-coated y-alumina-based catalyst and the isomerization catalyst is a potassium oxide-coated y-alumina-based isomerization catalyst (K^O / v-alumina-based catalyst). In certain examples, the C4 olefin stream is recycled to the metathesis reactor.

[0007] Examples include a method for producing propene. The method includes the step of metathesizing a but-l-ene-rich stream having a but-l-ene content of at least 15 molar percent (mol. %) with a metathesis catalyst for a cross-metathesis or self-metathesis reaction to produce a metathesis product stream containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins. The method includes the step of separating the metathesis product stream into (i) a C2-C3 product stream containing ethene and propene and (ii) a C4+-rich stream containing the C4-C6 olefins, and the unreactive C4 paraffins. The method includes the step of separating the C4+-rich stream into (i) a C4 olefin stream containing C4 olefins and the unreactive C4 paraffins and (ii) a Cs-Ce olefins stream containing Cs-Ce olefins. The method includes the step of catalytically cracking the Cs-Ce olefins stream into a cracked product stream containing ethene, propene, and Cs-Ce olefins. Themethod includes the step of splitting the C2-C3 product stream into an ethene product stream and a propene product stream. The method includes the step of recycling the C4 olefin stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream.

[0008] In certain examples, the method includes the steps of contacting the C4 olefin stream with an isomerization catalyst to produce a butene recycle stream having a but-l-ene content of at least 15 mol. % and the step of recycling the butene recycle stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream. In certain examples, the method includes the step of recycling the ethene product stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream. In certain examples, the method includes the step of contacting a butene feedstock stream containing but-l-ene, but-2-enes, and 2- methylpropene, with an isomerization catalyst to produce the but-l-ene-rich stream containing greater than or equal to 15 mol. % of but-l-ene. The butene feedstock stream contains a but-l-ene content of less than 13 mol. %. In certain examples, the metathesis catalyst is a rhenium oxidecoated y-alumina-based catalyst and the isomerization catalyst is a potassium oxide-coated y- alumina-based isomerization catalyst (K^O / y-alumina-based catalyst). In certain examples, metathesizing the but-l-ene-rich stream is performed at a temperature ranging from about 50 °C to about 500 °C and at a pressure ranging from about 0 barg to about 20 barg. In certain examples, the method includes the step of purging the unreactive C4 paraffins from the C4 olefin stream.Brief Description of the Drawings

[0009] Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements or procedures in a method. Embodiments are illustrated by way of example and not by way of limitation in the accompanying drawings. The present disclosure can be better understood by referring to the following figures. These drawings illustrate the principles of the disclosure and no limitation of the scope of the disclosure is thereby intended.

[0010] FIG. 1 is a schematic representation of a system for the production of propene, according to an example.

[0011] FIG. 2 is a schematic representation of a system for the production of propene using a C5 olefin and Ce olefins recycle to a Cs-Q, catalytic cracking reactor, according to an example.

[0012] FIGs. 3A and 3B are flow diagrams that illustrate the production of propene, according to an example.

[0013] FIG. 4 is a schematic representation of a control system for controlling the systems associated with the production of propene, according to an example.Detailed Description

[0014] So that the manner in which the features and advantages of the examples of the systems and methods disclosed herein, as well as others that will become apparent, may be understood in more detail, a more particular description of examples of systems and methods briefly summarized above may be had by reference to the following detailed description of examples thereof, in which one or more are further illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various examples of the systems and methods disclosed herein and are therefore not to be considered limiting of the scope of the systems and methods disclosed herein as it may include other effective examples as well.

[0015] The description may use the phrases “in some examples,” “in various examples,” “in an examples,” or “in certain examples,” which may each refer to one or more of the same or different examples. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to examples of the present disclosure, are synonymous.

[0016] As used herein, 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.

[0017] As used herein, 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.”

[0018] 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 ycarbon atoms, x and y inclusive. For example, a C3-C5 fraction refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing 3, 4, or 5 carbon atoms.

[0019] 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+ fraction refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing 3 or more (e.g., 3, 4, 5, 6, and so forth) carbon atoms.

[0020] 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.

[0021] The term “but-2-enes” includes (Z)-but-2-ene (c / .s-but-2-ene), or (E)-but-2-ene (trans- but-2-ene), or combinations thereof. The term “pent-2-enes” includes (Z)-pent-2-ene, or (E)-pent- 2-ene, or combinations thereof.

[0022] 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. As used herein, 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.

[0023] As used herein, when a first component is described as receiving (or being configured to receive) a stream from a second component, or when a first component is described as providing (or being configured to provide) a stream to a second component, the first and second components may be alternatively described as being in fluid communication with one another. It may be appreciated that, for the various streams discussed herein, a given stream substantially contains the compound or class of compounds in the name of the stream (e.g., an ethene product stream substantially contains ethene, a C4 olefin stream substantially contains C4 olefins, a C& olefin stream substantially contains Ce olefins), and the stream may also include other components.

[0024] The term “enriched” or “rich” or their variations mean an amount of at least generally about 20 mol. %, and preferably about 25 mol. %, of a compound or class of compounds in astream. It may be appreciated that, for the various streams discussed herein, a given stream predominantly contains the compound or class of compounds in the name of the stream (e.g., an ethene stream predominantly contains ethene, a C4 olefin stream predominantly contains C4 olefins, and a Ce olefin stream predominantly contains Ce olefins), and the stream may also include other components. As used herein, the term “predominantly contains” refers to a stream containing 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

[0025] The present disclosure describes various examples related to systems for the production of propene and methods for producing propene using metathesis reactions and with ethene being substantially absent as a co-feed. In one or more examples, the system for the production of propene includes a metathesis reactor, a C3 column, a C4 column, a Cs-Ce catalytic cracking reactor, and a C2 / C3 splitter column.

[0026] The system includes a metathesis reactor. The metathesis reactor can be in a metathesis zone that includes heaters, coolers, pumps, and other processing equipment known to those skilled in the art. The metathesis reactor can be operated at a temperature ranging from about 50 degrees Celsius (°C) to about 500 °C and at a pressure ranging from about 0 bar gauge (barg) to about 20 barg to carryout metathesis reactions. For example, the metathesis reactor can be operated a temperature from about temperature about 60 °C and a pressure about 8 barg. The metathesis reactor can be a fixed bed plug flow reactor or another type of reactor known to those skilled art.

[0027] The metathesis reactions herein include both cross-metathesis and self-metathesis. Metathesis reactions discussed herein are generally equilibrium reactions, involving the recycling of C4 olefins back to the metathesis process after metathesis olefin product separation to increase the metathesis yields. The metathesis reactions utilize a metathesis catalyst, such as a rhenium oxide-coated y-alumina-based catalyst, which enables metathesis reactions at the temperatures discussed herein.

[0028] The metathesis reactor is designed to receive and metathesize a but-l-ene feed stream containing but-l-ene, but-2-enes, and 2-methylpropene to produce a metathesis product stream containing ethene, propene, and C4-C6 olefins. The metathesis reactor with the metathesis catalyst is designed to operate at temperatures less than about 100 °C or at temperatures ranging from about 35 °C to 100 °C. The butene feed can contain a low but-l-ene concentration from about 15 mol. %to about 25 mol. %. The flow rate of the butene feed can range from about 0.1 to about 10 h'1weight hourly space velocity (WHSV). Examples of cross-metathesis reactions and self-metathesis reactions are shown in Table 1.

[0029] Table 1.

[0030] In some examples, the metathesis catalyst is a rhenium oxide-coated y-alumina-based (R^O / yAhCh) catalyst. The rhenium oxide-coated y-alumina-based catalyst can be spherical or an extrudate. 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 oxidecoated 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 hr’1.

[0031] 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 °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 a NTUReC solution, an Al(ReC>4)3 solution, or a HReC 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-basedcatalyst 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 a temperature ranging from about 140 °C to about 160 °C.

[0032] 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 a pore diameter ranging from about 75 Angstroms (A) to about 110 A. In certain examples, the y-alumina-based support has a total acidity ranging from about 0.58 millimole per gram (mmolxm / g) to about 0.62 mmolxm / 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.

[0033] 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 oxidecoated 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.

[0034] The system contains a C3 column. The C3 column can be a C2 / C3 distillation column. The C3 column is designed to receive and separate the metathesis product stream from the metathesis reactor into a C2-C3 product stream containing ethene and propene and a C4+-rich stream containing the C4-C6 olefins. The C3 column is designed to operate at pressures ranging from about 5 barg to about 30 barg . For example, the C3 column can be a four-pass tray column with 40 stages.

[0035] The system also contains a C4 column. The C4 column can be a debutenizer column. The C4 column is configured to receive and separate the C4+-rich stream from the first C3 column into a Cs-Ce olefins stream and a C4 olefin stream. The C4 olefin stream is recycled to the metathesis reactor. The C4 column is designed to operate at pressures ranging from about 2 barg to about 10 barg. For example, the C4 column can have 40 stages. In some examples, to reduce or prevent the buildup of inert or unreactive C4 paraffins at the metathesis reactor, a C4 purge stream is extracted from the C4 olefin stream, in which the C4 purge stream contains C4 paraffins (for example, butane, 2-methylpropane) and some C4 olefins. The C4 purge stream can be collected as a product or provided as a feed stream to another system or unit of a hydrocarbon processing facility outside of this configuration.

[0036] The system further contains a Cs-Ce catalytic cracking reactor. The Cs-Ce catalytic cracking reactor contains an olefin cracking catalyst. The olefin cracking catalyst can be a zeolite based catalyst. In certain examples, the Cs-Ce catalytic cracking reactor can be a traditional packed bed reactor or a fluid catalytic cracking reactor (FCC), such as a riser, downer, multi-zone fluidized bed reactor, or other FCC known to those skilled in the art. The Cs-Ce catalytic cracking reactor is designed to receive and catalytically crack the Cs-Ce olefins stream from the C4 column and to produce a cracked product stream containing ethene, propene, Cs olefins, and Ce olefins. In certain examples, the C4-C6 catalytic cracking reactor includes a ZSM-5-based cracking catalyst. The Cs- Ce catalytic cracking reactor is designed to operate at temperatures ranging from about 300 °C to about 650 °C. The Cs-Ce catalytic cracking reactor is designed to operate at pressures ranging from about 1 barg to about 30 barg. For example, the Cs-Ce catalytic cracking reactor can be operated at a temperature of about 550 °C and at a pressure of about 1 barg. The Cs-Ce catalytic cracking reactor can be configured to receive a vapor phase feed. To operate efficiently, the Cs-Ce catalytic cracking reactor can be operated at operating cycles ranging from about 1 day to about 30 days. Such an operating range can be achieved by supplying the Cs-Ce olefins stream to the Cs-Cecatalytic cracking reactor at a WHSV ranging from about 0.1 h'1to about 40 h'1. For example, the WHSV can range from about 0.5 h'1to about 5 h'1. Regeneration of the Cs-Q, catalytic cracking reactor can be performed with air, enriched air, or oxygen at temperatures ranging from about 500 °C to about 750 °C.

[0037] The system also contains a C2 / C3 splitter. The C2 / C3 splitter is designed to receive and separate the C2-C3 product stream from the C3 column into an ethene product stream and a propene product stream. For example, the C2 / C3 splitter can be a four-pass tray column with 15 stages.

[0038] In certain examples, the system includes a first C4 isomerization reactor designed to receive and isomerize a butene feedstock stream containing less than 13 mol. % of but-l-ene to output the but-l-ene feed stream containing greater than or equal to 15 mol. % of but-l-ene that is supplied to the metathesis reactor. The first C4 isomerization reactor can be present in a first C4 isomerization zone. The first C4 isomerization zone can include heaters, coolers, pumps, and other processing equipment known to those skilled in the art. An isomerization catalyst is contained within the first C4 isomerization reactor. The first C4 isomerization reactor is designed to operate at temperatures ranging from about 25 °C to about 500 °C. The first C4 isomerization reactor is designed to operate at pressures ranging from about 1 barg to about 20 barg. The first C4 isomerization reactor can be designed to utilize a liquid feed. The first C4 isomerization reactor can be operated at operating cycles ranging from about 3 days to about 30 days. Such an operating range can be achieved by supplying the butene feedstock containing less than 13 mol. % of but-l- ene to the first C4 isomerization reactor at WHSV from about 0.1 h'1to about 10 h'1. In certain examples, WHSV ranging from about 0.5 h'1to about 5 h'1. Regeneration of the first C4 isomerization reactor can be performed with air, enriched air, or oxygen and at a temperature ranging from about 300 °C to about 500 °C. In certain examples, the first C4 isomerization reactor can be a traditional packed bed reactor / tubular reactor / fixed bed reactor.

[0039] In certain examples, the system contains a second C4 isomerization reactor. The second C4 isomerization reactor can be present in a second C4 isomerization zone. The second C4 isomerization zone can include heaters, coolers, pumps, and other processing equipment known to those skilled in the art. In the C4 isomerization zone, the C4 isomerization reactor can be a traditional packed bed reactor / tubular reactor or fixed bed or moving bed reactor. The second C4 isomerization reactor contains an isomerization catalyst. For example, the isomerization catalyst can be a potassium oxide-coated y-alumina-based isomerization catalyst (K^O / y-alumina-basedcatalyst). The second C4 isomerization reactor is designed to receive the C4 olefins stream from the C4 column and to output a butene recycle stream enriched in but-l-ene content of at 15 mol. % to the metathesis reactor from the isomerization of the C4 olefins stream. The C4 isomerization reactor can be operated at temperatures ranging from about 350 °C to about 500 °C.

[0040] Examples include a method for producing propene. The method includes the step of metathesizing a but-l-ene-rich stream having a but-l-ene content of at least 15 mol. % with a metathesis catalyst. Metathesis reactions including both cross-metathesis or self-metathesis reactions metathesize the but-l-ene-rich stream to produce a metathesis product stream containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins. The method includes the step of separating the metathesis product stream into a C2-C3 product stream containing ethene and propene and a C4+-rich stream containing the C4-C6 olefins, and the unreactive C4 paraffins. The method includes the step of separating the C4+-rich stream into a C4 olefin stream containing C4 olefins and the unreactive C4 paraffins and a Cs-Ce olefins stream. The method includes the step of catalytically cracking the Cs-Ce olefins stream into a cracked product stream containing ethene, propene, and Cs-Ce olefins. The method includes the step of splitting the C2-C3 product stream into an ethene product stream and a propene product stream. The method includes the step of recycling the C4 olefin stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream.

[0041] In certain examples, the method includes the steps of contacting the C4 olefin stream with an isomerization catalyst to produce a butene recycle stream having a but-l-ene content of at least 15 mol. % and the step of recycling the butene recycle stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream. In certain examples, the method includes the step of recycling the ethene product stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream. In certain examples, the method includes the step of contacting a butene feedstock stream containing but-l-ene, but-2-enes, and 2- methylpropene, with an isomerization catalyst to produce the but-l-ene-rich stream containing greater than or equal to 15 mol. % of but-l-ene. The butene feedstock stream contains a but-l-ene content of less than 13 mol. %. In certain examples, the metathesis catalyst is a rhenium oxidecoated y-alumina-based catalyst and the isomerization catalyst is a potassium oxide-coated y- alumina-based isomerization catalyst (K^O / y-alumina-based catalyst). In certain examples, metathesizing the but-l-ene-rich stream performed is at a temperature ranging from about 50 °Cto about 500 °C and at a pressure ranging from about 0 barg to about 20 barg. In certain examples, the method includes the step of purging the unreactive C4 paraffins from the C4 olefin stream.

[0042] FIG. 1 is a schematic representation of an example of a system 100 for producing at least propene. A but-l-ene-rich stream 102 having a but-l-ene content of at least 15 mol. % is supplied to a metathesis reactor 104. For example, the metathesis reactor 104 is designed to operate at temperatures of less than 100 °C or at temperatures ranging from about 60 °C to about 100 °C and at a pressure about 8 barg. The metathesis reactor contains a metathesis catalyst to metathesize the but-l-ene-rich stream 102 to produce a metathesis product stream 106 containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins.

[0043] A C3 column 108 is in fluid communication with the metathesis reactor 104 and is designed to receive the metathesis product stream 106. In some examples, the C3 column 108 can have 40 stages. The C3 column 108 separate the metathesis product stream 106 into a C2-C3 product stream 128 that contains ethene and propene and a C4+-rich stream 110 that contains the C4-C6 olefins, and unreactive C4 paraffins. The C3 column 108 is designed to operate at pressures ranging from about 20 to 30 barg, or at about 25 barg.

[0044] A C4 column 112 is in fluid communication with the C3 column 108 and is designed to receive and separate the C4+-rich stream 110 from the first C3 column 108 into a Cs-Ce olefins stream 114 containing Cs-Ce olefins and a C4 olefin stream 126 containing C4 olefins and the unreactive C4 paraffins. The C4 olefin stream 126 is recycled to the metathesis reactor 104. The C4 column 112 can be a debutenizer column. In some examples, the C4 column 112 can have 40 stages. In certain examples, the C4 column 112 can be operated at a pressure of about 5 barg. In some examples, to reduce or prevent the buildup of unreactive C4 paraffins at the metathesis reactor 104, a C4 purge stream 113 is extracted from the C4 olefin stream 126, in which the C4 purge stream 113 contains the unreactive C4 paraffins (for example, butane, 2-methylpropane) and some C4 olefins. The C4 purge stream 113 can be collected as a product or provided as a feed stream to another system or unit of a hydrocarbon processing facility outside of this configuration.

[0045] A Cs-Ce catalytic cracking reactor 116 is in fluid communication with the C4 column 112 and is designed to receive and catalytically crack the Cs-Ce olefins stream 114 from the C4 column 112 into a cracked product stream 118 substantially containing ethene, propene, and Cs- Ce olefins. In certain examples, the Cs-Ce catalytic cracking reactor 116 includes a ZSM-5-basedcracking catalyst, and the Cs-Ce catalytic cracking reactor is designed to operate at a temperature of about 500 °C and a pressure of about 1 barg.

[0046] A C2 / C3 splitter column 132 is in fluid communication with the C3 column 108 and is designed to receive and separate the C2-C3 product stream 128 from the first C3 column 108 into an ethene product stream 134 and a propene product stream 136. In certain examples, the C2 / C3 splitter column 132 can have 40 stages and can be operated at a pressure in between 20-40 barg. In certain examples, the ethene product stream 138 can be supplied to the metathesis reactor 104 to increase the production of the propene product.

[0047] FIG. 2 is a schematic representation of an example of a system 200 for producing at least propene using C4 isomerization. A but-l-ene-rich stream 203 having a but-l-ene content of at least 15 mol. %, but-2-enes, and 2-methylpropene is supplied to a metathesis reactor 206. In certain examples, a first C4 isomerization reactor 202 is present within the system 200. The first C4 isomerization reactor 202 receives a butene feed stream 201 having a but-l-ene content from about 0 mol. % to about 13 mol. %. The first C4 isomerization reactor 202 convert the but-2-enes to but-l-ene to obtain the but-l-ene-rich stream 203. For the conversion, the first C4 isomerization reactor 202 can be operated at temperatures ranging from about 25 °C to about 500 °C and at pressures ranging from about 0 barg to about 20 barg. For example, the first C4 isomerization reactor 202 operate at a temperature of about 500 °C and at a pressure of 2 barg. The first C4 isomerization reactor 202 contains an isomerization catalyst, such as a I<2O / v-alumina-based catalyst. The first C4 isomerization reactor 202 is configured to receive a butene feedstock stream containing less than 13 mol. % of but-l-ene. The first C4 isomerization reactor 202 outputs the but- l-ene-rich stream 203 having a but-l-ene content of at least 15 mol. %. The but-l-ene-rich stream 203 is supplied to the metathesis reactor 206.

[0048] The metathesis reactor 206 is operated at a temperature less than 100 °C or about 60 °C and at a pressure about 8 barg. The metathesis reactor 206 contains a metathesis catalyst, such as the rhenium oxide-coated y-alumina-based catalyst that facilitates cross-metathesis or selfmetathesis reactions of the but-l-ene-rich stream 203 to produce a metathesis product stream 208. The metathesis product stream 208 contains ethene, propene, C4-C6 olefins, and unreactive C4 paraffins. The metathesis product stream 208 is supplied to a C3 column 210. The C3 column 210 is in fluid communication with the metathesis reactor 206. The C3 column 210 has 40 stages. In certain examples, the C3 column 210 can be operated at a pressure about 7 barg. The C3 column210 separate the metathesis product stream 208 into a C2-C3 product stream 232 containing ethene and propene and a C4+-rich stream 212 containing C4-C6 olefins and unreactive C4 paraffins.

[0049] A C4 column 214 is in fluid communication with the C3 column 210 and is designed to receive and separate the C4+-rich stream 212 from the C3 column 210 into a Cs-Ce olefins stream 216 containing Cs-Ce olefins and a C4 olefin stream 228. The C4 column 214 has 40 stages. The C4 column 214 can be a debutenizer column. To reduce or prevent the buildup of unreactive C4 paraffins at the metathesis reactor 206, a C4 purge stream 226 is extracted from the C4 olefin stream 228, in which the C4 purge stream 226 contains the unreactive C4 paraffins (for example, butane, 2-methylpropane) and some C4 olefins. The C4 purge stream 226 can be collected as a product or provided as a feed stream to another system or unit of a hydrocarbon processing facility outside of this configuration. The remaining C4 olefin stream 228 is received by a second C4 isomerization reactor 230.

[0050] The second C4 isomerization reactor 230 contains an isomerization catalyst, such as K^O / y-alumina-based catalyst. The second C4 isomerization reactor 230 is in fluid communication with the C4 column 214. The C4 olefin stream 228 is isomerized in the second C4 isomerization reactor 230 to produce a butene recycle stream 234. The butene recycle stream 234 contains a but- 1-ene content of at least 15 mol. %. The butene recycle stream 234 is supplied as part of the but- 1-ene-rich stream 203 that is supplied as the feed stream to the metathesis reactor 206. In certain examples, the butene recycle stream 234 is supplied to the metathesis reactor 206. The metathesis reactor 206, first C3 column 210, C4 column 214, and C4 isomerization reactor 230 constitute a C4 olefin recycle course.

[0051] A Cs-Ce catalytic cracking reactor 218 is in fluid communication with the C4 column 214 and is designed to receive and catalytically convert the Cs-Ce olefins stream 216 from the C4 column 214 into a cracked product stream 220 substantially containing ethene, propene, and Cs- Ce olefins. The Cs-Ce catalytic cracking reactor 218 contains an olefin cracking catalyst, such as a ZSM-5-based cracking catalyst. The Cs-Ce catalytic cracking reactor 218 can be operated at a temperature of about 550 °C and a pressure of about 1 barg. The cracked product stream 220 can be provided as input to a catalytic cracking system, such as a steam cracker downstream of the Cs- Ce catalytic cracking reactor 218 to primarily produce ethene and propene, along with H2 and Ci- C9 hydrocarbon byproducts.

[0052] A C2 / C3 splitter column 236 is in fluid communication with the C3 column 210 and is designed to receive and separate the C2-C3 product stream 232 from the C3 column 210 into an ethene product stream 238 and a propene product stream 240. In certain examples, the ethene product stream 242 can be supplied to the metathesis reactor 206. The recycle of the ethene product stream 242 to the metathesis reactor 206 can increase the production of the propene product. The C2 / C3 splitter column 236 has 40 stages. The C2 / C3 splitter column 236 can be operated at a pressure of about 35 barg.

[0053] FIGs. 3A and 3B are flow diagrams of method 300 for controlling aspects of the examples of the systems 100 and 200 illustrated in FIG. 1 and FIG. 2, respectively. In certain examples, the method 300 may be stored within a memory of a controller and executed by a processor of the controller to control operation of the systems 100 and 200.

[0054] For the example illustrated in FIG. 3A, the method 300 includes step 301, in which the controller determines the but-l-ene content of the butene feed stream. For example, the butene feed stream, such as in FIG. 2, can utilize a feed analyzer that uses gas chromatography to determine the but-l-ene content of the butene feed stream. At step 302, the controller determines whether the but-l-ene content of the butene feed stream is less than a predetermined threshold value (for example, 15 mol. %). In response to determining that the but-l-ene content of the butene feed stream is less than the predetermined threshold value, at step 303, the controller provides control signals to route the butene feed stream to the first C4 isomerization reactor, where the butene feed stream contacts the isomerization catalyst to isomerize but-2-enes of the butene feed stream into but-l-ene to yield the but-l-ene-rich stream having a but-l-ene content that is greater than or equal to the predetermined threshold value, and the but-l-ene feed stream is then directed to the metathesis reactor. In response to determining that the but-l-ene content of the butene feed stream is greater than or equal to the predetermined threshold value, at step 304, the controller provides control signals to route the but-l-ene-rich stream to the metathesis reactor as the but-l- ene-rich stream without first performing C4 isomerization.

[0055] At cross-metathesis or self-metathesis operating conditions, the but-l-ene-rich stream in the metathesis reactor produce a metathesis product stream containing ethene, propene, C4-C6 olefins. At step 306, the metathesis product stream is separated into a C2-C3 product stream containing ethene and propene and a C4+-rich stream containing the C4-C6 olefins.

[0056] At step 308, the C4+-rich stream is separated into a C4 olefin stream and a C5-C6 olefins stream containing C5-C6 olefins. At step 310, the C5-C6 olefins stream is catalytically cracked into a cracked product stream containing ethene, propene, and C5-C6 olefins. The method 300 of FIG. 3A continues from FIG. 3A to FIG. 3B as indicated by the connector labeled I.

[0057] In FIG. 3B, the method 300 at step 312 includes splitting the C2-C3 product stream into an ethene product stream and a propene product stream. At step 314, the controller determines whether the ethene product stream should be recycled. In response to determining that the ethene product stream should be recycled, the controller provides control signals to recycle the ethene product stream to the metathesis reactor to produce the metathesis product stream at step 316. The contact with the metathesis catalyst can occur in a metathesis reactor. In response to determining that the ethene product stream should not be recycled, the controller determines whether the C4 olefins-rich stream should be isomerized at step 318.

[0058] In response to the determining that the C4 olefin stream should be isomerized, the controller provides control signals to contact the C4 olefin stream with a C4 isomerization catalyst to produce a butene recycle stream having a but-l-ene content of at least 15 mol. % at step 320. At step 322, the butene recycle stream is contacted with the metathesis catalyst to produce the metathesis product stream. In response to the determining that the C4 olefin stream should not be isomerized, the controller provides control signals to recycle the C4 olefin stream to contact the metathesis catalyst to produce the metathesis product stream, at step 324.

[0059] FIG. 4 is a schematic representation of an example of a control system 400 for controlling the examples of the systems discussed above. The control system 400 includes at least one controller 402. Each controller 402 includes at least one processor 404, which can be or include a central processing unit (CPU), a graphics processing unit (GPU), a co-processing unit, a subprocessing unit, or any other suitable electronic data processor. Each controller 402 includes at least one memory 406, which can be or include random access memory (RAM), read-only memory (ROM), or any other suitable electronic memory or storage. For the illustrated example, the controller 402 is communicatively connected to each of the units present in a particular implementation of the systems discussed above, such as the metathesis reactor 408, the C3 column 410, the C4 column 412, the C2 / C3 splitter 414, and the Cs-Ce catalytic cracking reactor 416. In certain examples, the first C4 isomerization reactor 418 and the second C4 isomerization reactor 420 can be communicatively connected to the controller 402. The communicative connectionbetween the controller 402 and the units and devices enables the controller 402 to receive monitoring and operational data from sensors and / or sub-controllers of each of these units or devices present in the examples discussed above, and further enables the controller 402 to provide control signals (for example, electrical signals, instructions, and data packets) to modify the operation of each of these zones or devices.

[0060] For example, the controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the metathesis reactor 408, and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the metathesis related units to ensure that the metathesis reactor 408 operates within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the metathesis reactor 408 and maybe even a second metathesis reactor. The controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the C3 column 410, and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the C3 column 410 to ensure that the C3 column 410 operates within the temperatures and pressures disclosed above. The controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the C4 column 412 and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the C4 column 412 to ensure that the C4 column 412 operates within the temperatures and pressures disclosed above. The controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the C2 / C3 splitter 414 and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the C2 / C3 splitter 414 to ensure that the C2 / C3 splitter 414 operates within the temperatures and pressures disclosed above.

[0061] The controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the Cs-Ce catalytic cracking reactor 416, and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the Cs-Ce catalytic cracking reactor 416 to ensure that the Cs-Ce catalytic cracking reactor 416 operates within the temperatures,pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the Cs-Ce catalytic cracking reactor 416.

[0062] In certain examples, the controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the first C4 isomerization reactor 418, and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the first C4 isomerization reactor 418 to ensure that the first C4 isomerization reactor 418 operates within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the first C4 isomerization reactor 418. In certain examples, the controller 402 can receive monitoring data from sensors (for example, temperature sensors, pressure sensors, and flow sensors) of the second C4 isomerization reactor 420, and based on predefined threshold values for certain operational parameters, can provide suitable control signals to modify the operation of one or more components of the second C4 isomerization reactor 420 to ensure that the second C4 isomerization reactor 420 operates within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the second C4 isomerization reactor 420.

[0063] In certain examples, the controller 402 can provide control signals to modify the operation of a flow control device to adjust the quantity of the streams that is directed to the metathesis reactor 408, the C3 column 410, the C4 column 412, the C2 / C3 splitter 414, the Cs-Ce catalytic cracking reactor 416, the first C4 isomerization reactor 418, and the second C4 isomerization reactor 420 based on the monitoring data received from the metathesis reactor 408, the C3 column 410, the C4 column 412, the C2 / C3 splitter 414, the Cs-Ce catalytic cracking reactor 416, the first C4 isomerization reactor 418, and the second C4 isomerization reactor 420. In some examples, the controller 402 provides control signals to adjust the relative amount of the butene recycle stream to be combined with but-l-ene-rich stream to maintain the content of but-l-enes according to pre-defined threshold mol. % of but-l-ene, and additionally provides control signals to the units to route the combined stream to the metathesis reactor 408.Examples

[0064] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devicesand / or methods claimed herein are made and evaluated and, therefore, are intended to be purely exemplary and are not intended to limit the disclosure.

[0065] There are numerous variations and combinations of reaction conditions, for example, component concentrations, desired solvents, solvent mixtures, temperatures, pressures and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process.

[0066] Example 1:

[0067] In an example, the operational performance of the system 100 was evaluated under certain illustrative operating conditions using a process simulation software, Aspen Plus® available from Aspen Technology Inc. of Bedford, Massachusetts, U.S.A. The operational performance of this system was simulated based on an example C4 stream (corresponding to the butene feed stream 102 for system 100 of FIG. 1 containing 62.6% but-l-ene, 34.8% but-2-enes, and 2.5% n-butane). Additionally, the operational performance of the system was modeled based on example metathesis reaction conditions for the metathesis reactor 104 having an operating temperature of 60 °C and an operating pressure of 8 barg. Other operation performances of the system included a 40 stage first C3 column 108 having an operating pressure of 25 barg, a 40 stage C4 column 112 having an operating pressure of 5 barg, an Cs-Ce catalytic cracking reactor 116 having an operation temperature of 500 °C and an operating pressure of 1 barg, and a 40 stage C2 / C3 splitter 132 having an operating pressure of 35 barg.

[0068] For the example of system 100 illustrated in FIG. 1, when supplied with 18.024 ton per hour (ton / h) of the example butene feed stream 102, simulated modeling indicates a production of 3.71 ton / h of ethene and 10.01 ton / h of propene. In addition, it should be appreciated that C4 paraffins and C4 olefins that are extracted from the C4 olefin stream 126 to form the C4 purge stream 113 can be collected and / or further processed to provide additional product streams (for example, C4 olefin product stream, fuel streams), further increasing the yield of the system 100.

[0069] Example 2:

[0070] The operational performance of the system 200 was simulated using modeling calculations based on the process simulation software, Aspen Plus®. The operational performance of this system was simulated based on an example C4 stream for the system 200 of FIG. 2 that contains 13% but-l-ene, 67.2 % but-2-enes, 16.7% n-butane, 3.0% isobutylene, and 0.1% propane. Additionally, the operational performance of the system was modeled based on examplemetathesis reaction conditions for the metathesis reactor 206 having an operating temperature of 60 °C and an operating pressure of 8 barg, isomerization reaction conditions for the first C4 isomerization reactor 202 having an operating temperature of 500 °C and an operating pressure of 2 barg, and the second C4 isomerization reactor 230 having an operating temperature of 400 °C and an operating pressure of 2 barg. Other operation performances of the system included a 40 stage C3 column 210 having an operating pressure of 7 barg, a 40 stage debutenizer or C4 column 214 having an operating pressure of 5 barg, an Cs-Ce catalytic cracking reactor 218 having an operation temperature of 550 °C and an operating pressure of 1 barg, a 15 stage C2 / C3 splitter 236 having an operating pressure of 5 barg, and a 40 stage C4 column 214 having an operating pressure of 35 barg.

[0071] For the example of system 200 illustrated in FIG. 2, when supplied with 18.024 ton per hour (ton / h) of the example butene feed stream containing from about 0 mol. % to about 13 mol. % but-l-ene, but-2-enes, and 2-methylpropene supplied to the first C4 isomerization reactor 202, simulated modeling indicates production of 3.33 ton / h of ethene and 7.77 ton / h of propene. In addition, it should be appreciated that C4 paraffins and C4 olefins that are extracted from the C4 olefin stream 228 to form the C4 purge stream 226 can be collected and / or further processed to provide additional product streams (for example, C4 olefin product stream, fuel streams), further increasing the yield of the system 200.

[0072] 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.

[0073] 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 oneembodiment 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

Claims1. A propene production system, the system comprising: a metathesis reactor with a metathesis catalyst and configured to receive and metathesize a but-l-ene-rich stream having a but-l-ene content of at least 15 molar percent (mol. %) to produce a metathesis product stream containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins; a C3 column configured to receive and separate the metathesis product stream into a C2- C3 product stream containing ethene and propene and a C4+-rich stream containing the C4-C6 olefins and the unreactive C4 paraffins; a C4 column configured to receive and separate the C4+-rich stream from the C3 column into a Cs-Ce olefins stream and a C4 olefin stream containing C4 olefins and the unreactive C4 paraffins; a Cs-Ce catalytic cracking reactor configured to receive and catalytically crack the Cs-Ce olefins stream from the C4 column into a cracked product stream containing ethene, propene, and Cs-Ce olefins; and a C2 / C3 splitter column configured to receive and separate the C2-C3 product stream into an ethene product stream and a propene product stream.

2. The system of claim 1, further comprising: a first C4 isomerization reactor configured to receive and isomerize a butene feed stream containing less than 13 mol. % of but-l-ene and produce the but-l-ene-rich stream having at least 15 mol. % of but-l-ene to be supplied to the metathesis reactor.

3. The system of any of claims 1 or 2, further comprising: a second C4 isomerization reactor with an isomerization catalyst and configured to receive the C4 olefin stream from the C4 column and to supply a butene recycle stream having a but-l-ene content of at least 15 mol. % to the metathesis reactor.

4. The system of any of claims 1 or 2, wherein the ethene product stream is supplied to the metathesis reactor.

5. The system of any of claims 1-3, wherein the unreactive C4 paraffins in the C4 olefin stream are removed.

6. The system of any of claims 1-3, wherein the metathesis reactor operates at temperature about 60 degrees Celsius (°C) and a pressure about 8 bar gauge (barg).

7. The system of any of claims 1-3, wherein the metathesis catalyst is a rhenium oxidecoated y-alumina-based catalyst and an isomerization catalyst is a potassium oxide-coated y- alumina-based isomerization catalyst (K^O / y-alumina-based catalyst).

8. The system of any of claims 1 or 2, wherein the C4 olefin stream is recycled to the metathesis reactor.

9. A method for producing propene, the method comprising: metathesizing a but-l-ene-rich stream having a but-l-ene content of at least 15 molar percent (mol. %) with a metathesis catalyst for a cross-metathesis or self-metathesis reaction to produce a metathesis product stream containing ethene, propene, C4-C6 olefins, and unreactive C4 paraffins; separating the metathesis product stream into (i) a C2-C3 product stream containing ethene and propene and (ii) a C4+-rich stream containing the C4-C6 olefins, and the unreactive C4 paraffins; separating the C4+-rich stream into (i) a C4 olefin stream containing C4 olefins and the unreactive C4 paraffins and (ii) a Cs-Ce olefins stream; catalytically cracking the Cs-Ce olefins stream into a cracked product stream containing ethene, propene, and Cs-Ce olefins; splitting the C2-C3 product stream into an ethene product stream and a propene product stream; and recycling the C4 olefin stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream.

10. The method of claim 9, further comprising: contacting the C4 olefin stream with an isomerization catalyst to produce a butene recycle stream having a but-l-ene content of at least 15 mol. %; and recycling the butene recycle stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream.

11. The method of any of claims 9 or 10, further comprising: recycling the ethene product stream to contact the metathesis catalyst and undergo metathesis to produce the metathesis product stream.

12. The method of claim 10, further comprising: contacting a butene feedstock stream containing but-l-ene, but-2-enes, and 2- methylpropene, with an isomerization catalyst to produce the but-l-ene-rich stream having a but-l-ene content of at least 15 mol. %, the butene feedstock stream having a but-l-ene content of less than 13 mol. %.

13. The method of any of claims 9 or 10, in which the metathesis catalyst is a rhenium oxidecoated y-alumina-based catalyst and the isomerization catalyst is a potassium oxide-coated y- alumina-based isomerization catalyst (K^O / y-alumina-based catalyst).

14. The method of claim 9, wherein metathesizing the but-l-ene-rich stream is performed at a temperature ranging from about 50 °C to about 500 °C and at a pressure ranging from about 0 barg to about 20 barg.

15. The method of any of claims 9 or 10, further comprising: purging the unreactive C4 paraffins from the C4 olefin stream.

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