Systems and methods for uplifting propene selectivity with combined metathesis and isomerization reactor

Abstract

Provided herein are methods that include pretreating a C4 feedstock to produce a pretreated C4 feedstock rich in but-2-enes, providing the pretreated C4 feedstock and an ethene co-feed stream as a reactor feed stream to a combined reactor containing a metathesis catalyst and an isomerization catalyst, and metathesizing and isomerizing the reactor feed stream in the combined reactor at an operating temperature in a range from 35 °C to 100 °C to produce a reactor product stream containing propene, ethene, and C4+ olefins. The method further includes separating the reactor product stream to produce a light recycle stream rich in ethene and a C3+ olefin stream, which is separated to produce a propene product stream and a C4+ olefin stream. The method includes separating the C4+ olefin stream to produce a C4 olefin recycle stream and recycling the C4 olefin recycle stream and the light recycle stream to the combined reactor.

Description

24CHEM0018-WO-ORD1SYSTEMS AND METHODS FOR UPLIFTING PROPENE SELECTIVITY WITH COMBINED METATHESIS AND ISOMERIZATION REACTORTechnical Field

[0001] The disclosure relates to the production of desired olefins including propene from a C4 feedstock rich in but-2-enes, based on integration of a combined reactor including a metathesis catalyst and an isomerization catalyst.Background

[0002] Metathesis provides a path for valorizing certain lower value feedstocks into desired olefins, such as propene. However, metathesis reactions are generally equilibrium-limited, which can cause difficulties in producing sufficiently high yields of desired products. Moreover, certain metathesis processes operate with particularly high reaction temperatures, which can cause accumulation of heavy carbonaceous material on catalyst surfaces that deactivates the catalyst and reduces product yields.Summary

[0003] The present disclosure provides low temperature, sustainable systems and methods for processing C4 raffinate streams that are rich in but-2-enes with ethene co-feeds into propene, with multiple enhancements for increasing propene selectivity. For example, the disclosure provides a combined reactor having both metathesis and isomerization catalysts within a single reactor vessel, which increases overall metathesis productivities at relatively low reaction temperatures that reduce catalyst deactivation, while decreasing side product formation and increasing propene selectively. The systems and methods herein also recycle unreacted C4 olefins and ethene to enhance desired product yields in view of the equilibrium-limited reactions.

[0004] The multifunctional operations disclosed herein increase reactant throughput compared to traditional metathesis reactors by employing a combined reactor that integrates metathesis with targeted isomerization. For example, certain examples include a combined reactor having a physically mixed or bi-functional catalyst mixture of metathesis catalyst and isomerization catalyst, which efficiently transform the C4 raffinate stream within shared and calibrated operating24CHEM0018-WO-ORD2 conditions. In some examples, a combined reactor includes a multi-layered, stacked, or serial arrangement of multiple catalyst beds, which can condition the flow therethrough with a targeted exposure to a metathesis catalyst, followed by an isomerization catalyst, followed by metathesis catalyst. In these examples, a first bed can metathesize but-2-enes and ethene into propene, a second bed can convert but-l-ene into additional but-2-enes via isomerization, and a third bed can again convert but-2-enes and ethenes into propene as a high-yield product, while reducing production of minor side products. Other arrangements of desired reaction mechanisms can be achieved based on adjustment of the sequence and relative sizing of the catalyst layers. In either case, higher overall but-2-enes conversions and higher propene selectivity are delivered by the combined reactor having both metathesis and isomerization catalysts and operating at low temperatures, such as temperatures below 100 degrees Celsius (°C).

[0005] The disclosure herein provides several embodiments of systems for the production of high- demand chemicals, such as propene, and methods for producing chemicals. Examples include a method that includes pretreating a C4 feedstock to remove one or more impurities and produce a pretreated C4 feedstock rich in but-2-enes, and providing the pretreated C4 feedstock and an ethene feedstock as a reactor feed stream to a combined reactor containing a metathesis catalyst and an isomerization catalyst. The method includes metathesizing and isomerizing the reactor feed stream in the combined reactor at an operating temperature in a range from 35 °C to 100 °C to produce a reactor product stream containing propene, ethene, and C4+ olefins. The method further includes separating the reactor product stream to produce a light recycle stream rich in ethene and a C3+ olefin stream containing propene and C4+ olefins. The method also includes separating the C3+ olefin stream to produce a light product stream rich in propene and a C4+ olefin stream containing primarily C4-C6 olefins. Additionally, the method includes separating the C4+ olefin stream to produce a C4 olefin recycle stream and a Cs+ olefin stream . The method also includes recycling the light recycle stream and the C4 olefin recycle stream to the reactor feed stream provided to the combined reactor.

[0006] In some examples, the reactor product stream includes higher olefins such as C7-C10 olefins, and the C4+ olefin stream separated from the reactor product stream contains minor or trace amounts of the C7-C10 in combination with the major or significant amounts of the C4-C6 olefins. In some examples, metathesizing and isomerizing the reactor feed stream includes metathesizing the reactor feed stream to produce a first intermediate stream, isomerizing the first intermediate24CHEM0018-WO-ORD3 stream to produce a second intermediate stream, and metathesizing the second intermediate stream to produce the reactor product stream. In some examples, the reactor feed stream is metathesized in a first catalyst bed containing the metathesis catalyst, the first intermediate stream is isomerized in a second catalyst bed containing the isomerization catalyst, and the second intermediate stream is metathesized in a third catalyst bed containing the metathesis catalyst.

[0007] In some examples, the metathesis catalyst and the isomerization catalyst are mixed within the combined reactor and the reactor feed stream is concurrently metathesized and isomerized. In some examples, the method further includes diverting a portion of the C4 olefin recycle stream as a purge stream containing one or more paraffins.

[0008] In some examples, recycling the light recycle stream and the C4 olefin recycle stream includes mixing the light recycle stream and the ethene feedstock upstream of the combined reactor to produce a combined ethene stream, and mixing the combined ethene stream, the C4 olefin recycle stream, and the pretreated C4 feedstock to produce the reactor feed stream. In some examples, the method further includes compressing the combined ethene stream before mixing the combined ethene stream, the C4 olefin recycle stream, and the pretreated C4 feedstock.

[0009] In some examples, the metathesis catalyst includes a rhenium oxide-based y-alumina-based catalyst and the isomerization catalyst includes a Group 1 A or Group 2A oxide-based y-alumina- based catalyst. In some examples, the reactor feed stream is metathesized and isomerized at an operating pressure ranging from about 25 bar to 35 bar.

[0010] Examples include a system that includes a pretreatment unit configured to receive and purify a C4 feedstock to produce a pretreated C4 feedstock rich in but-2-enes, and a combined reactor configured to metathesize and isomerize a reactor feed stream containing the pretreated C4 feedstock and an ethene co-feed stream to produce a reactor product stream containing propene, ethene, and C4+ olefins. The combined reactor includes a metathesis catalyst and an isomerization catalyst configured to metathesize and isomerize the reactor feed stream at a temperature ranging from about 35 °C to 100 °C. The system also includes a C2 column configured to receive the reactor product stream and produce a light recycle stream rich in ethene and a C3+ olefin stream containing propene and C4+ olefins. The system also includes a C3 column configured to receive the C3+ olefin stream and produce a light product stream rich in propene and a C4+ olefin stream containing primarily C4-C6 olefins. Further, the system includes a C4 column configured to receive the C4+ olefin stream and produce a C4 olefin recycle stream and a Cs+ olefin stream. The system is24CHEM0018-WO-ORD4 configured to route the light recycle stream and the C4 olefin recycle stream to the reactor feed stream.

[0011] In some examples, the combined reactor includes a first catalyst bed containing the metathesis catalyst, a second catalyst bed containing the isomerization catalyst, and a third catalyst bed containing the metathesis catalyst. In some examples, the first catalyst bed is configured to receive and metathesize the reactor feed stream to produce a first intermediate stream, the second catalyst bed is configured to receive and isomerize the first intermediate stream to produce a second intermediate stream, and the third catalyst bed is configured to receive and metathesize the second intermediate stream to produce the reactor product stream.

[0012] In some examples, the combined reactor includes a first catalyst bed containing the isomerization catalyst upstream of a second catalyst bed containing the metathesis catalyst. In some examples, the combined reactor includes a combined catalyst bed containing a mixture of the metathesis catalyst and the isomerization catalyst. In some examples, the mixture of the metathesis catalyst and the isomerization catalyst is uniformly distributed along a length of the combined catalyst bed. In some examples, the system includes a compressor configured to receive and pressurize a combined ethene stream containing the light recycle stream and the ethene cofeed stream. The system is configured to mix the combined ethene stream with the C4 olefin recycle stream and the pretreated C4 feedstock to produce the reactor feed stream.

[0013] In some examples, the metathesis catalyst includes a rhenium oxide-based y-alumina-based catalyst. In some examples, the isomerization catalyst includes a Group 1A or Group 2 A oxidebased y-alumina-based catalyst. In some examples, the combined reactor is operated at a pressure ranging from about 25 bar to 35 bar. In some examples, the combined reactor is operated at a temperature ranging from about 45 °C to 55 °C. In some examples, the metathesis catalyst and the isomerization catalyst are regenerated at a temperature ranging from about 500 °C to 575 °C.

[0014] 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.24CHEM0018-WO-ORD5Brief Description of the Drawings

[0015] 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.

[0016] FIG. 1 is a schematic representation of a system for production of desired olefins including propene through metathesis and isomerization of a pretreated C4 feedstock rich in but-2-enes within a combined reactor, according to an example.

[0017] FIG. 2 is a schematic representation of a system having a combined reactor that includes metathesis catalyst and isomerization catalyst physically mixed along a length of a reactor vessel, according to an example.

[0018] FIG. 3 is a schematic representation of a system having a combined reactor that includes beds of metathesis catalyst and isomerization catalyst arranged in series within a reactor vessel, according to an example.

[0019] FIG. 4 is a schematic representation of a control system for controlling operation of the disclosed systems and methods for improved olefin production, according to an example.Detailed Description

[0020] 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 to the scope of the systems and methods disclosed herein as it may include other effective examples as well.24CHEM0018-WO-ORD6

[0021] The description may use the phrases “in some embodiments,” “in various embodiments,” “in an embodiment,” or “in certain embodiments,” “in some examples,” “in various examples,” “in an example,” or “in certain examples,” which may each refer to one or more of the same or different embodiments / examples. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments / examples of the present disclosure, are synonymous.

[0022] 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.

[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.” The terms “wt. %”, “vol. %”, or “mol. %” refer 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. The terms “enriched” or “rich” or their variations mean an amount of at least generally about 20 wt. %, and preferably about 25 wt. %, of a compound or class of compounds in a stream. The term “substantially contains” means that the mixture includes at least 60%, or even at least 70%, or even at least 80% by weight of the relevant hydrocarbon-based compounds. The term “ppmw” refers to part / s per million by weight. The term “ppbw” refers to part / s per billion by weight. The terms “reducing,” “reduced,” or any variation thereof, when used in the claims and / or the specification include any measurable decrease or complete removal to achieve a desired result.

[0024] As used herein, the term “Cx-Cycompounds,” in which x and y are positive integer values, refers to hydrocarbon-based compounds, each compound containing molecules with between x and y carbon atoms, with x and y being inclusive. For example, a C3-C5 fraction or stream refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each24CHEM0018-WO-ORD7 compound containing molecules with 3, 4, or 5 carbon atoms. Additionally, it may be noted that, in certain cases, a Cx-Cyfraction or stream may not include a respective compound having molecules with each of the referenced integer values. As one example, a C4-Cs fraction can be a stream that contains compounds containing molecules with 4, 5, and 7 carbon atoms, without any compounds containing molecules with 6 or 8 carbon atoms. As another example, a C4-C5 stream can include compounds containing molecules with only 4 carbon atoms, only 5 carbon atoms, or a mixture of both.

[0025] As used herein, the term “Cx+ compounds,” in which x is a positive integer value, refers to hydrocarbon-based compounds, each compound containing molecules with 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 molecules with 3 or more (e.g., 3, 4, 5, 6, and so forth) carbon atoms. As used herein, the term “Cx- compounds,” in which x is a positive integer value, refers to hydrocarbon-based compounds, each compound containing molecules with no more than x carbon atoms. For example, a C4- fraction refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compound containing molecules with 4, 3, 2, or 1 carbon atoms. It may be noted that, in certain cases, a “Cx- fraction” may also include hydrogen (H2), in addition to hydrocarbons having x or fewer carbon atoms.

[0026] 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.

[0027] Examples of the present disclosure leverage low-value feedstocks rich in but-2-enes to produce propene at increased yields and selectivity with an ethene co-feed. For instance, a combined reactor including both metathesis catalyst and isomerization catalyst within a single vessel can be employed in either up-flow or down-flow configurations. The reactions can proceed at desirably low temperatures that are concurrently suited to each of the catalysts. As will be understood, the catalysts of certain examples are provided in a mixed configuration in which the metathesis and isomerization catalysts are mixed or evenly distributed within a fixed bed and / or across a length of a vessel. In some examples, the metathesis and isomerization catalysts are24CHEM0018-WO-ORD8 arranged in a multi-layered arrangement having multiple beds that each include one or the other of the metathesis and isomerization catalysts. Additionally, the throughput of the combined reactor having both metathesis and isomerization catalysts is increased compared to previous systems. Further benefits provided herein include low carbon dioxide emissions and lower operational temperatures compared to existing systems.

[0028] The present disclosure describes various examples related to systems and methods that produce propene via a combined reactor that includes both metathesis and isomerization catalysts to uplift productivity while operating at relatively low temperatures. Various examples herein describe encompassing low temperature, sustainable systems and methods for metathesis using a C4 raffinate stream rich in but-2-enes as a feedstock along with an ethene co-feed. The advancements disclosed herein may be broadly applied to various metathesis reactions, including those for C2 to C12 olefins.

[0029] A majority of the C4 raffinate feed may be formed or composed of but-2-enes, along with one or more other components including but-l-ene, 2-methylprop-l-ene ( / -butylene, isobutene), butynes, butadienes, and / or other lighter components such as propane and isobutene. The composition of the C4 feedstock can depend on its source, including gas, mixed, or liquid steam cracker feeds utilized after a selective hydrogenation unit (SHU), a methyl tertiary-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) unit or process, and / or a fluid catalytic cracker (FCC) downstream process. In some examples, the C4 feedstock has a composition in accordance with a C4 raffinate-III stream. Sample compositions of different C4 raffinate streams are provided in the Examples section below.

[0030] To facilitate the metathesis reactions in the combined reactor, a metathesis catalyst, such as a rhenium oxide-based or rhenium oxide-coated y-alumina-based catalyst, is provided in the combined reactor. The rhenium oxide-coated y-alumina-based catalyst (R^O / yAhCh) 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 millimeters (mm) to about 3 mm and a rhenium oxide coating ranging from about 150 micrometers (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-24CHEM0018-WO-ORD9 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-1- ene with but-l-ene to ethene and (t / c) hex-3 -ene, ethene with (t / c) but-2-ene to propene and propene, ethene with (t / c) pent-2-ene to propene and but-l-ene, 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 combined reactor. In certain examples, the rhenium oxide-coated y- alumina-based catalyst can be functional for at least 300 days in the operational combined reactor. In certain examples, the catalyst is regenerated greater than 50 times in the operational combined 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 / hr to 10 / hr. In examples, the functional lifetime of the catalyst varies based on feed composition. In certain examples, in addition or alternative to the rhenium oxide-coated y-alumina-based catalyst, the metathesis catalyst is or includes rhenium oxide that is dispersed throughout a core or interior of the y-alumina. The y-alumina particles of these rhenium oxide-dispersed y-alumina-based catalyst can be spherical or an extrudate.

[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 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 a NTUReCh solution, an Al(ReO4)3 solution, or a HReCh 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 carried out24CHEM0018-WO-ORD10 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 is performed 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 milliliters 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 mmolNm / g. In certain examples, the rhenium oxide-coated y-alumina-based catalyst can contain 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 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 nanometers (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 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 carried out 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 carried out for about 6 hours.

[0034] The rhenium oxide-coated y-alumina-based catalyst is used for self and cross metathesis of but-l-ene and (t / c) but-2-enes, in some examples. The rhenium oxide-coated y-alumina-based catalyst is used for self and cross metathesis of pent-2-ene, in some examples. The combined24CHEM0018-WO-ORD11 reactor can be operated at temperatures ranging from 35 to 100 °C, in some examples. The combined reactor can be operated at temperatures ranging from 50 °C to 100 °C, in some examples. In some examples, the combined reactor can be operated at temperatures ranging from 50 °C to 500 °C. Operating pressures of the combined reactor can range from atmospheric pressure to pressures up to 30 bar, in some examples. The combined reactor can use a liquid feed, a vapor feed, or a mixed phase feed. If low temperature liquid phase feed is used in a combined reactor, the outlet product can either be liquid phase or mixed vapor-liquid phase depending on the pressure and temperature of the reactor.

[0035] The systems disclosed herein implement a combined reactor having metathesis and isomerization catalysts therein, which metathesize and isomerize a feedstock rich in but-2-enes with an ethene co-feed and supply the resulting reactor effluent to an olefin separation zone that separates propene-rich products and recycles unreacted C4 olefins and ethene for further yield. As described herein, various systems can be implemented to increase reactor productivity and / or increase the feedstock utilization based on the integration of a metathesis catalyst and an isomerization catalyst within the combined reactor. Indeed, the present systems and methods provide sustainable, flexible, and adaptable strategies by which C4 raffinate streams can be valorized into propene with increased selectivity.

[0036] In some embodiments, a system for producing propene includes (i) a pretreatment unit that produces a pretreated C4 feedstock rich in but-2-enes, (ii) a combined reactor containing a metathesis catalyst and an isomerization catalyst to metathesize and isomerize the pretreated C4 feedstock with an ethene co-feed stream at an operating temperature between 35 °C and 100 °C, (iii) a C2 column that receives a reactor product stream from the combined reactor and produces an ethene-rich recycle stream and a C3+ olefin stream, (iv) a C3 column that separates the C3+ olefin stream into a propene-rich product stream and a C4+ olefin stream primarily containing C4-C6 olefins, and (v) a C4 column that separates the C4+ olefin stream into a C4 olefin recycle stream and a Cs+ olefin stream, where the ethene-rich recycle stream and the C4 olefin recycle stream are recycled to the combined reactor.

[0037] FIG. 1 is a schematic representation of a system 100 for production of desired olefins including propene through metathesis and isomerization of a pretreated C4 feedstock rich in but- 2-enes within a combined reactor, according to an example. The system 100 of the illustrated example includes a C4 pretreater (or C4 pretreatment unit), a C2 pretreater (or C2 pretreatment unit),24CHEM0018-WO-ORD12 a compressor, a combined reactor or metathesis and isomerization reactor including two types of catalyst therein, a C2 column (or deethenizer or light distillation column), a C3 column (or depropenizer), and a C4 column (or debutenizer or heavy distillation column). In additional detail, the system 100 facilitates enhanced propene production from a C4 feedstock 102 rich in but-2- enes, with improved reactor productivity and selectivity based on the integration of a metathesis catalyst and an isomerization catalyst within a vessel of the combined reactor. As illustrated, the system 100 includes a C4 pretreatment zone 104, a C2 pretreatment zone 114, a metathesis and isomerization zone 130, and an olefin separation zone 150.

[0038] In certain examples, the C4 feedstock 102 is a C4 raffinate stream. The C4 feedstock 102 used herein is rich in but-2-enes. The C4 feedstock 102 of certain examples contains about 50 wt. %, 55 wt. %, 60 wt. %, 65 wt. %, 70 wt. %, 75 wt. %, 80 wt. %, 85 wt. %, 90 wt. %, or 95 wt. % of but-2-enes. As an example, the C4 feedstock 102 is a C4 Raffinate-III stream containing about 80 wt. % of but-2-enes and about 20 wt. % of but-l-ene. In certain examples, the C4 feedstock 102 contains about 40 wt. % of (E)-but-2-ene ( / ra / / .s-but-2-ene), about 40 wt. % of (Z)-but-2-ene (cis- but-2-ene), and about 20 wt. % of but-l-ene. The C4 feedstock 102 contains generally equal amounts of (E)-but-2-ene and (Z)-but-2-ene or a 50:50 ratio, in some examples. In some examples, the ratio of (E)-but-2-ene to (Z)-but-2-ene is 20:80, 30:70, 50:50, or 60:40. Additionally, the C4 feedstock 102 contains twice as much of (E)-but-2-ene compared to but-l-ene and twice as much of (Z)-but-2-ene compared to but-l-ene, in certain examples. In some examples, the feed component of but-2-enes is included in an amount ranging from about 100 wt. % to about 5 wt. %, and but-l-ene is included in an amount ranging from about 0 wt. % to about 95 wt. %. The C4 feedstock 102 source and corresponding composition depends on the feedstock provided to the steam cracker as well as any downstream operations performed to further utilize various cuts of C4 hydrocarbons.

[0039] In some examples, the C4 feedstock 102 is sourced from downstream of a steam cracker (e.g., a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker). The C4 feedstock 102 can be sourced from upstream or downstream of a MTBE reactor. In examples, the C4 feedstock 102 is provided from downstream of a butadiene selective hydrogenation section, a butadiene extraction section, or a C4 separation column. Depending on market demand, 1,3-butadiene (BD) is either extracted from a C4 raw cut stream or provided to a selective hydrogenation unit (SHU) to convert the BD into C424CHEM0018-WO-ORD13 olefins. After this process, based on concentrations of but-2-enes and 2-methylprop-l-ene, the C4 stream is sent to either MTBE production or a B2 column to remove but-2-enes and n-butane before routing to the MTBE production. In examples where the top product of the B2 column contains isobutene, the stream is MTBE, or in examples where the top product contains but-l-ene as a major product, the stream is routed for but-l-ene recovery. For examples including a B2 column product that is rich in but-2-enes, the stream can be sent to a complete saturation / hydrogenation unit (CSP / THU). In some systems, this stream is rich in but-2-enes and supplied for isomerization to produce additional but-l-ene. However, this conversion may be unoptimized and may limit production of desired olefin products such as propene. As such, examples of the presently disclosed system 100 enhance utilization of the C4 feedstock 102 rich in but-2-enes, along with an ethene co-feed to perform metathesis in combination with isomerization to produce propene with increased yields.

[0040] For the illustrated example, the system 100 includes a C4 pretreater 106 within the C4 pretreatment zone 104 to receive and purify the C4 feedstock 102. C4 pretreater 106 produces a pretreated C4 stream 108 rich in but-2-enes and having a reduced amount of one or more impurities therein. For example, the C4 pretreater 106 can include one or more guard beds having adsorbents to remove various impurities or contaminants, such as sulfur compounds, sulfides, salt compounds, metals, oxygenates (e.g., MTBE, methoxymethane, dimethyl ether (DME), methanol), alcohols, green oil (heavy hydrocarbons), ethers, mercaptans, and / or nitrogen compounds (e.g., ammonia, amines, and nitriles). The C4 pretreater 106 and / or the C4 pretreatment zone 104 can thus remove any suitable reactive compounds and / or inert compounds from the C4 feedstock 102 that can otherwise negatively affect operation of one or more downstream units of the system 100. From the C4 pretreatment zone 104, the pretreated C4 stream 108 is directed to the metathesis and isomerization zone 130 and introduced into a combined reactor 132 (metathesis and isomerization reactor) in fluid communication with the C4 pretreater 106.

[0041] The system 100 of examples disclosed herein receives an ethene co-feed stream 112 that is processed and utilized within the metathesis and isomerization zone 130. For example, the system 100 can include a C2 pretreater 116 within the C2 pretreatment zone 114 to receive and purify the ethene co-feed stream 112, which is output as a pretreated ethene stream 118 that includes a reduced amount of one or more impurities therein. The C2 pretreater 116 can include similar components and operate in a manner similar to the C4 pretreater 106. Examples of impurities24CHEM0018-WO-ORD14 removed from the C4 feedstock 102 and the ethene co-feed stream 112 are also detailed in the Examples section below. In some examples, the C2 pretreatment zone 114 includes a compressor 120 that receives the pretreated ethene stream 118 and outputs a pressurized ethene stream 122, which is provided to the metathesis and isomerization zone 130 along with the pretreated C4 stream 108

[0042] As illustrated, the pretreated C4 stream 108 and the pressurized ethene stream 122 are provided to the combined reactor 132 within the metathesis and isomerization zone 130. In some examples, the pretreated C4 stream 108 and the pressurized ethene stream 122 are mixed or joined into a reactor feed stream 124 that is supplied into a bottom inlet of the combined reactor 132. Additionally, the combined reactor 132 can optionally include a reflux stream 134 that is drawn or removed from a top outlet and reintroduced into a bottom inlet of the combined reactor 132. In some of these examples, the reactor feed stream 124 is combined with the reflux stream 134 for supply into the bottom inlet. In examples, the reactor feed stream 124 (or the pretreated C4 stream 108 and / or the pressurized ethene stream 122 thereof) are heated to a predetermined threshold reaction temperature within the metathesis and isomerization zone 130. For examples including rhenium oxide-based catalysts, the reaction temperature is in a range between about 35 °C and 100 °C, and any suitable heater or heat exchanger components are included in the metathesis and isomerization zone 130 to suitably condition the reactor feed stream 124.

[0043] As recognized herein, the combined reactor 132 is a multifunctional reactor that performs both metathesis and isomerization on the reactor feed stream 124 rich in but-2-enes and containing ethene. The combined reactor 132 can thus metathesize and isomerize the reactor feed stream 124 to produce a reactor product stream 136 or effluent stream containing propene, ethene, and C4+ olefins. The C4+ olefins described herein include a majority of C4-C6 olefins and can include trace or minor amounts of C7-C10 olefins. For example, certain feed impurities can cause or lead to the production of higher olefins, such as C7-C10 olefins, which are present in relatively small amounts compared to the major C4-C6 olefin content of the reactor product stream 136. In examples, the combined reactor 132 metathesizes and isomerizes the reactor feed stream at an operating temperature ranging from about 35 °C to 100 °C. The combined reactor 132 includes a vessel that contains a metathesis catalyst and an isomerization catalyst. Additionally, the metathesis and isomerization catalysts can catalyze their respective reactions within the same or substantially similar operating conditions, which can dramatically improve operating efficiency compared to24CHEM0018-WO-ORD15 the use of separate metathesis and isomerization vessels that inefficiently duplicate equipment and operational costs.

[0044] The combined reactor 132 can be implemented as a suitable fixed-bed reactor operating with down-flow or up-flow and including both metathesis and isomerization catalysts therein. In certain examples, the metathesis catalyst can be a rhenium oxide-based metathesis catalyst or a rhenium oxide-coated y-alumina-based catalyst. The rhenium oxide-based metathesis catalyst enables low-temperature metathesis of but-2-enes with ethene, including both (E)-but-2-ene and (Z)-but-2-ene. In examples, the isomerization catalyst is an oxide compound including a Group 1A element (alkali metals) or Group 2A element (alkaline earth metals), which is provided on a suitable support such as alumina. For example, the isomerization catalyst can include a Group 1 A or Group 2 A oxide-based y-alumina-based catalyst. The Group 1 A elements include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), and the Group IB elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). In an example, the isomerization catalyst includes potassium oxide and alumina, or K2O / AI2O3. Example arrangements or configurations for contacting reactants with both catalysts are described in detail below, with FIG. 2 including examples of the catalysts mixed together within a single bed and FIG. 3 including examples of a layered or serial arrangement of multiple fixed beds that each contain one catalyst.

[0045] In some examples, the metathesis and isomerization zone 130 includes multiple combined reactors 132 therein, which can be implemented in series or in parallel operation. In some examples, at least one reactor remains online while at least one other reactor is in regeneration or standby mode, preparing for subsequent operation. The number of reactors in the plant can be determined by an economic optimization between catalyst cost and capex for the reactors. In most cases, two reactors or three reactors can be used, where at least one reactor is in regeneration or standby. In some examples, the temperature of the combined reactor 132 is in a range from 35 °C to 100 °C, 30 °C to 100 °C, 30 °C to 90 °C, and so forth. In some examples, the operating temperature is below 250 °C, such as below 200 °C, below 150 °C, below 100 °C, or about 50 °C. It is presently recognized that metathesis-performing reactors used by other systems can demand substantially higher operating temperatures, such as temperatures greater than 250 °C, and as such, the lower operating temperatures of the disclosed combined reactor 132 reduce the operational cost and energy demands of the reactor compared to other systems. Moreover, the integration of24CHEM0018-WO-ORD16 the isomerization catalyst that operates with similar process conditions as the metathesis catalyst used herein further improves valorization of C4 feeds rich in but-2-enes within a single vessel of the combined reactor 132.

[0046] The operating pressures of the combined reactor 132 can be in a range from about 25 bar to 35 bar. In some examples, the combined reactor 132 operates a pressure between about 20 bar and 40 bar, 20 bar and 30 bar, or 30 bar and 40 bar. In certain examples, the operating pressure of the combined reactor 132 is less than about 40 bar, 35 bar, or 30 bar. The metathesis catalyst and the isomerization catalyst are prone to gradual deactivation due to formation of intermediate species, moisture, or carbon deposition, and as such, it is desirable to operate the combined reactor such that a reasonable operating cycle time in a fixed bed plug flow reactor is between 1 day and 100 days, such as between 3 days and 30 days. In some examples, this is achieved by limiting the flow rate of C4 feedstock 102 into the combined reactor 132 to a weight hourly space velocity (WHSV) of between 0.1 h'1and 10 h’1, such as values between 0.5 h'1and 5 h'1. Regeneration of the metathesis catalyst and the isomerization catalyst can be performed when a combined reactor is in regeneration mode using air, enriched air, or oxygen at temperatures between 400 °C and 600 °C, such as temperatures between 450 °C and 550 °C, or about 500 °C. In examples, the metathesis catalyst and the isomerization catalyst are regenerated at a temperature ranging from about 500 °C to 575 °C.

[0047] The combined reactor 132 supplies the reactor product stream 136 to the olefin separation zone 150 to facilitate product separation into streams suitable for products and streams suitable for recycling to increase reactor productivity. The illustrated example of the olefin separation zone 150 includes a C2 column 152, a C3 column 160, and a C4 column 170. These distillation or separation columns are thus connected in series and operate in concert to efficiently separate components of the reactor product stream 136, which contains propene, ethene, and C4+ olefins. In certain examples, the C2 column 152 receives the reactor product stream 136 and produces a light recycle stream 154 that is rich in ethene and a C3+ olefin stream 156 that contains propene and C4- Ce olefins. In examples, the C3+ olefin stream 156 contains propene and C4+ olefins including a majority of C4-C6 olefins and trace amounts of C7-C10 olefins. The C2 column 152 supplies the C3+ olefin stream 156 to the C3 column 160, which receives and separates the C3+ olefin stream 156 into a light product stream 162 that is rich in propene and a C4+ olefin stream 164 that contains a majority of C4-C6 olefins and trace amounts of C7-C10 olefins. Additionally, the olefin separation24CHEM0018-WO-ORD17 zone 150 includes the C4 column 170 that receives the C4+ olefin stream 164 from the C3 column 160 and produces a C4 olefin stream 172 and a Cs+ olefin stream 174. The C4 olefin stream 172 is rich in C4 olefins, and the C5+ olefin stream 174 is rich in Cs-Ce internal olefins. In certain examples, the Cs+ olefin stream 174 also contains trace amounts of C7-C10 olefins. The C4 column 170 outputs the Cs+ olefin stream 174 in certain examples as a desired product stream. The system 100 outputs the light product stream 162 as a high yield, desired product stream that is rich in propene.

[0048] The system 100 can include multiple recycle streams that are isolated and recycled to the combined reactor 132 for enhanced olefin production. The illustrated example of the C2 column 152 routes the light recycle stream 154 rich in ethene for combination with the pretreated ethene stream 118 for supply to the compressor 120, which increases a flowrate or amount of the resulting pressurized ethene stream 122 (or combined ethene stream) that forms a portion of the reactor feed stream 124. The system 100 of the illustrated example includes the C4 column 170 routing at least a portion of the C4 olefin stream 172 to the reactor feed stream 124 as a C4 olefin recycle stream 180. Any remaining or predetermined portion of the C4 olefin stream 172 can be purged or diverted from the system 100 as a C4 purge stream 182. The relative amounts of the C4 purge stream 182 compared to the C4 olefin recycle stream 180 can be selectively adjusted based on the amount of any inert C4 compounds included in the C4 olefin stream 172, thus preventing inert buildup that can otherwise decrease reactor efficiency.

[0049] FIG. 2 is a schematic representation of a metathesis and isomerization zone 200 having a combined reactor 202 that includes physically mixed metathesis catalyst and isomerization catalyst, according to an example. The combined reactor 202 and / or the metathesis and isomerization zone 200 can be integrated into the system 100 of FIG. 1 to provide enhanced selectivity for desired olefins such as propene, in examples. The illustrated example of the combined reactor 202 includes a vessel 204 or reactor vessel, which can be any suitable enclosure or structure for retaining a catalyst bed 210 therein. The catalyst bed 210 can be a fixed bed that is configured for either up-flow or down-flow of reactants through the catalyst bed 210.

[0050] In examples, a reactor feed stream 220 rich in but-2-enes and containing ethene is supplied to an inlet of the vessel 204. The inlet can be at any suitable position on the vessel 204, such as the illustrated bottom portion. The vessel 204 can also include a first outlet at a top portion thereof to output a reactor product stream 230. In certain examples, a reflux stream 224 is drawn from a24CHEM0018-WO-ORD18 second outlet of the vessel 204 and combined with the reactor feed stream 220 for supply into the inlet. However, any suitable flow paths, inlets, and outlets can be utilized to deliver sufficient flow into and out of the combined reactor 202. As described above, the combined reactor 202 includes both metathesis and isomerization catalysts to enable the reactor feed stream 220 to be both metathesized and isomerized within the vessel 204.

[0051] In the illustrated example, the catalyst bed 210 is a combined catalyst bed that includes a physical mixture of the two catalysts, which is distributed along a length of a flow path through the catalyst bed 210. In examples, the catalyst bed 210 includes a first portion of supports (e.g., support material, alumina) having a metathesis catalyst and includes a second portion of supports having an isomerization catalyst. In some examples, the physically mixed catalyst is also referred to as a bi-functional catalyst or catalyst mixture. The catalysts are physically mixed together within or substantially uniformly distributed throughout the catalyst bed 210. In examples, a first sample volume within the catalyst bed 210 has a substantially similar ratio of metathesis to isomerization catalyst as compared to a second sample volume.

[0052] In examples, the relative ratio of metathesis catalyst to isomerization catalyst installed in the catalyst bed 210 is selectively determined based on the expected feed composition, and in particular, based on the ratio of but-2-enes to but-l-ene. The ratio of metathesis to isomerization catalyst in certain examples is 1 :4, 1 :3, 1 :2, 1 : 1, 2: 1, 3:1, or 4: 1. By contacting the reactor feed stream 220 with both catalysts, the combined reactor 202 can enable concurrent performance of metathesis reactions and isomerization reactions at relatively low temperatures in a shared vessel, which increases the selective formation of propene.

[0053] FIG. 3 is a schematic representation of a metathesis and isomerization zone 300 having a combined reactor 302 that includes beds of metathesis catalyst and isomerization catalyst layered or arranged in series, according to an example. The combined reactor 302 and / or the metathesis and isomerization zone 300 can be integrated into the system 100 of FIG. 1 to provide enhanced selectivity for desired olefins such as propene, in examples. The metathesis and isomerization zone 300 includes certain components and streams that correspond to those discussed above with respect to FIG. 2. These components, including a vessel 304, a reactor feed stream 320, an optional reflux stream 324, and a reactor product stream 330 are similarly labeled, and their descriptions are not repeated in detail for improved clarity.24CHEM0018-WO-ORD19

[0054] The combined reactor 302 is illustrated with three catalyst beds 310 or fixed catalyst beds that are layered, stacked, or arranged in series within the vessel 304 to provide sequential metathesis, isomerization, and metathesis of the reactor feed stream 320. For example, the combined reactor 302 includes a first catalyst bed 310A containing the metathesis catalyst, a second catalyst bed 310B containing the isomerization catalyst, and a third catalyst bed 310C containing the metathesis catalyst. During operation, the first catalyst bed 310A can receive the reactor feed stream 320 to metathesize compounds therein and produce a first intermediate stream, which is received by the second catalyst bed 310B. The second catalyst bed 310B can then isomerize compounds within the first intermediate stream and produce a second intermediate stream, which is then supplied to the third catalyst bed 310C. In examples, the third catalyst bed 310C metathesizes compounds within the second intermediate stream to produce the reactor product stream 330. As such, the coordinated interoperation of the catalyst beds 310 enables increased propene selectivity, based at least in part on the formation of intermediate isomerization products and their utilization in subsequent metathesis reactions. In more detail, the first catalyst bed 310A can convert a majority of but-2-enes with ethene to produce propene via metathesis, the second catalyst bed 310B can convert but-l-ene to but-2-enes via isomerization, and the third catalyst bed 310C can convert additional but-2-enes with ethene to produce additional propene via metathesis. Certain minor side products are produced in some examples.

[0055] The catalyst beds 310 can each be a fixed bed that is arranged for up-flow, as illustrated, or for down-flow. As previously noted, the relative ratio of metathesis to isomerization catalyst is selectively determined on the relative ratio of but-2-enes to but-l-ene in the feed, and can be provided as a ratio of 1 :4, 1 :3, 1 :2, 1 : 1, 2: 1, 3 : 1, or 4: 1. The relative ratio of metathesis catalyst to isomerization catalyst in certain examples of the combined reactor 302 is established based on the relative bed sizing or flow path lengths of the catalyst beds 310 and / or the amount of catalyst therein. As one example, a metathesis to isomerization catalyst ratio of 1 : 1 is established by constructing the length of the first catalyst bed 310A plus the length of the third catalyst bed 310C to be equal to the length of the second catalyst bed 310B. In some examples, the length of the first catalyst bed 310A can be different from the length of the third catalyst bed 310C, provided they equate to the corresponding value for the specified catalyst ratio.

[0056] Further, although the combined reactor 302 having multiple layers of catalyst is described with reference to an arrangement including metathesis followed by isomerization followed by24CHEM0018-WO-ORD20 metathesis, it should be understood that additional arrangements are included herein for facilitating desired product formation. For example, the combined reactor 302 can include a first catalyst bed having isomerization catalyst upstream of or followed by a second catalyst bed having metathesis catalyst. In an example, the combined reactor 302 can include a first catalyst bed having isomerization catalyst, followed by a second catalyst bed having metathesis catalyst, followed by a third catalyst bed having isomerization catalyst. In particular, depending on the feed composition, it can be beneficial to perform isomerization within the combined reactor prior to metathesis, which can then be followed by any desired additional layers or beds of isomerization catalyst and metathesis catalyst. In other words, certain examples include at least one catalyst bed having isomerization catalyst that is upstream of a catalyst bed containing metathesis catalyst, which generates additional but-2-enes for use in the downstream metathesis catalyst bed. In some of these examples, the combined reactor 302 includes four or more catalyst beds that are layered or arranged in series within the vessel 304.

[0057] FIG. 4 is a schematic representation of a control system 400 for controlling the embodiments of the system discussed above. The control system 400 includes at least one controller 401. Each controller 401 includes at least one processor 402, which may 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 401 includes at least one memory 403, 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 401 is communicatively connected to or in signal communication with each of the zones present in a particular implementation of the systems discussed above. For example, the controller 401 can be communicatively coupled to a C4 pretreatment zone 404, a C2 pretreatment zone 410, a metathesis and isomerization zone 430, and an olefin separation zone 450. The controller 401 can further be communicatively connected to any other elements that are included in or facilitate operation of the systems discussed above. The communicative connection between the controller 401 and the various zones and devices enables the controller 401 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 401 to provide control signals (e.g., electrical signals, instructions, data packets) to modify the operation of each of these zones or devices.24CHEM0018-WO-ORD21

[0058] The controller 401 can implement any suitable monitoring, analysis, and / or actuation steps to control the C4 pretreatment zone 404, the C2 pretreatment zone 410, the metathesis and isomerization zone 430, and the olefin separation zone 450 operating in a suitable system. For example, the controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors, content analyzers) of the C4 pretreatment zone 404 and / or the C2 pretreatment zone 410, 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 C4 pretreatment zone 404 and / or the C2 pretreatment zone 410 to ensure that the one or more guard beds therein operate in accordance with any predefined threshold values. Additionally, the controller 401 may receive monitoring data from sensors of the metathesis and isomerization zone 430, and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of the metathesis and isomerization zone 430 to ensure that the combined reactors therein operate within the temperatures, pressures, and WHSV disclosed above, to maintain coordinated operation of both the metathesis and isomerization catalysts, and to manage the regeneration mode operation and standby operation of the combined reactors. The controller 401 may receive monitoring data from sensors of the olefin separation zone 450 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 olefin separation zone 450, such that the components operate in accordance with any predefined threshold values.Examples

[0059] The following examples are put forth to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated. Therefore, the examples are intended to be purely exemplary and are not intended to limit the disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature), but some deviations should be accounted for.

[0060] 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 obtained24CHEM0018-WO-ORD22 from the described process. Only reasonable and routine experimentation is needed to optimize such process conditions.

[0061] Example 1: Processing the input feeds

[0062] The systems and methods disclosed herein can efficiently utilize various C4 feedstocks to produce desired chemicals at improved yields. The systems and methods disclosed herein utilize various feedstocks which can be pretreated to reduce or substantially eliminate impurities. As shown below, Table-1 illustrates example C4 feedstocks fed to the system. Table-2 illustrates an example of impurities that remain after purification of a C4 raffinate stream. Table-3 displays an example of impurities that remain after purification of an ethene co-feed.

[0063] Table-1: Composition of examples of C4 feedstocks

[0064] Table-2: Typical C4 raffinate feed trace impurities after purification of C4 raffinate feed prior to isomerization / metathesis reactor

[0065] Table-3: Typical ethene feed trace impurities after pretreatment24CHEM0018-WO-ORD23

[0066] Example 2: Simulation of metathesis reactions

[0067] Simulations were performed herein to evaluate and confirm the improved conversion and selectivity provided by the presently disclosed systems and methods. In particular, simulations were performed with a C4 feedstock corresponding to the Typical Composition-3 of Table-1 (e.g., C4 Raffinate-III) and with the trace impurities of the C4 feedstock and ethene feedstock compositions of Table-2 and Table-3, respectively. The simulations modeled a metathesis reactor versus two configurations of a combined metathesis and isomerization reactor, with single pass yield, at a reaction temperature of 50 °C and a pressure of 28 bar, with a 1 : 1 mole ratio of ethene to but-2-enes. The simulations were performed using ASPEN PLUS®, provided by Aspen Technology, Inc. of Bedford, Massachusetts, U.S.A. The simulations used an REquilibrium reactor, which included models for all possible equilibrium reactions and produced the results shown in Table-4 below.

[0068] For example, Table-4 below illustrates various conversion and selectivity data with three different catalyst configurations in a reactor. In particular, Catalyst M represents only metathesis catalyst, Catalyst Mixed M+I represents mixed metathesis and isomerization catalysts (corresponding to FIG. 2), and Catalyst Stacked M+I represents stacked metathesis and isomerization catalysts (corresponding to FIG. 3).

[0069] Table-4 : Conversion and selectivities for different catalyst configurations24CHEM0018-WO-ORD24

[0070] For systems lacking the presently disclosed combined reactor, the respective conversions of but-2-enes, but-l-ene, and ethene are 63, 32, and 56 mol. %, which produced selectivities of 94.3 mol. % for propene and 5.7 mol. % for pent-2-enes and hex-3-enes. As illustrated, the disclosed use of a combined reactor having both metathesis and isomerization catalysts provides significant benefits to feed component conversions and propene selectivity. For example, simulations for a combined reactor having physically mixed catalyst, denoted as Mixed M+I, were performed with incorporation of isomerization reactions of but-2-enes and but-l-ene with metathesis reactions. Additional simulations were performed using three models of reactors coupled in series to model a combined reactor having multilayered catalysts, denoted as Stacked M+I. In particular, the simulations utilized a first reactor performing metathesis reactions, followed by a second reactor performing isomerization reactions, then followed by a third reactor performing additional metathesis reactions.

[0071] The Mixed M+I simulation provided a propene selectivity of 99 mol. % and the Stacked M+I simulation provided a propene selectivity of 97.5 mol %, which are significant improvements over the non-combined reactor having 94.3 mol. % propene selectivity. Additional improvements in feed conversion are clearly set forth in the results above. As such, the systems and methods disclosed herein can efficiently utilize various C4 feedstocks to produce desired chemicals at improved yields based on the integration of isomerization catalyst with metathesis catalyst in a reactor.

[0072] Furthermore, examples of the combined metathesis and isomerization reactor disclosed herein integrate the two distinct catalysts for increased propene selectivity, with production enhanced by the relatively low operating temperatures associated with the catalysts. That is, the rhenium oxide-based metathesis catalyst enables low-temperature metathesis of (t / c) but-2-enes with ethene into propene, and the isomerization catalyst operates concurrently and efficiently at shared operating temperatures within the combined reactor to convert but-l-ene into additional but-2-enes, which react to produce additional propene at improved yields.

[0073] Moreover, the metathesis reactions and double bond isomerization reactions are both generally equilibrium-limited, where the operating conditions and the reactant and product concentrations affect the respective rates of forward and backward reactions. When operating at lower reaction temperatures, such as temperatures less than about 100 °C, 70 °C, or 50 °C, the isomerization reactions between but-l-ene and but-2-enes favor the production or selectivity of24CHEM0018-WO-ORD25 but-2-enes (the interior olefins) over but-l-ene (the terminal olefin). This increased presence of but-2-enes over but-l-ene as a reactant further drives metathesis reactions for selectively producing propene.

[0074] In contrast, high reaction temperatures move the thermodynamic equilibrium of the isomerization reactions toward but-l-ene, which reduces conversion of the but-l-ene into the more desirable but-2-enes. That is, the equilibrium conversion is a function of temperature, where certain examples herein provide an absolute conversion of but-l-ene to but-2-enes that is greater than about 95 wt. % at the presently disclosed reaction temperatures suited to the integrated metathesis and isomerization catalysts, and this conversion decreases with increasing reaction temperature. It is presently recognized that the rhenium oxide-based metathesis catalyst used herein is particularly suited for operating at low temperatures favorable to but-2-ene production, unlike certain other metathesis catalysts including compounds like tungsten oxide that depend on high reaction temperatures above about 200 °C, 250 °C, or 300 °C.

[0075] Indeed, examples of the combined reactor operate at lower reaction temperatures that enable the dual processes of metathesis and isomerization at thermodynamically favored conditions for the production of but-2-enes from isomerization of but-l-ene and the production of propene from metathesis of but-2-enes and ethene. The present disclosure also limits undesired side metathesis reactions such as the production of Cs and Ce olefins based on the relatively low reaction temperatures. In certain examples, the combined reactor operates efficiently with the theoretical or stoichiometric amount of ethene to but-2-enes, equal to a 1 : 1 molar ratio. This feature can thus avoid the use of costly excess ethene in a molar ratio of 1.3 or greater used in certain systems to limit side reactions. Accordingly, the presently integrated metathesis and isomerization catalysts enable the combined reactor to deliver superior propene yields without the consumption of excess ethene.

[0076] When ranges are disclosed herein, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, and 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 its24CHEM0018-WO-ORD26 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.

[0077] 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

24CHEM0018-WO-ORD27Claims1. A method, comprising: pretreating a C4 feedstock to remove one or more impurities and produce a pretreated C4 feedstock rich in but-2-enes; providing the pretreated C4 feedstock and an ethene co-feed stream as a reactor feed stream to a combined reactor containing a metathesis catalyst and an isomerization catalyst; metathesizing and isomerizing the reactor feed stream in the combined reactor at an operating temperature in a range from 35 °C to 100 °C to produce a reactor product stream containing propene, ethene, and C4+ olefins; separating the reactor product stream to produce a light recycle stream rich in ethene and a C3+ olefin stream containing propene and C4+ olefins; separating the C3+ olefin stream to produce a light product stream rich in propene and a C4+ olefin stream containing primarily C4-C6 olefins; separating the C4+ olefin stream to produce a C4 olefin recycle stream and a Cs+ olefin stream; and recycling the light recycle stream and the C4 olefin recycle stream to the reactor feed stream provided to the combined reactor.

2. The method of claim 1, wherein metathesizing and isomerizing the reactor feed stream comprises: metathesizing the reactor feed stream to produce a first intermediate stream; isomerizing the first intermediate stream to produce a second intermediate stream; and metathesizing the second intermediate stream to produce the reactor product stream.

3. The method of claim 2, wherein the reactor feed stream is metathesized in a first catalyst bed containing the metathesis catalyst, wherein the first intermediate stream is isomerized in a second catalyst bed containing the isomerization catalyst, and wherein the second intermediate stream is metathesized in a third catalyst bed containing the metathesis catalyst.24CHEM0018-WO-ORD284. The method of claim 1, wherein the metathesis catalyst and the isomerization catalyst are mixed within the combined reactor, and wherein the reactor feed stream is concurrently metathesized and isomerized.

5. The method of any one of claims 1-4, wherein recycling the light recycle stream and the C4 olefin recycle stream comprises: mixing the light recycle stream and the ethene co-feed stream upstream of the combined reactor to produce a combined ethene stream; compressing the combined ethene stream to produce a pressurized ethene stream; and mixing the pressurized ethene stream, the C4 olefin recycle stream, and the pretreated C4 feedstock to produce the reactor feed stream.

6. The method of any one of claims 1-5, wherein the metathesis catalyst comprises a rhenium oxide-based y-alumina-based catalyst, and wherein the isomerization catalyst comprises a Group 1 A or Group 2 A oxide-based y-alumina-based catalyst.

7. The method of any one of claims 1-6, wherein the reactor feed stream is metathesized and isomerized at an operating pressure ranging from about 25 bar to 35 bar.

8. A system, comprising: a pretreatment unit configured to receive and purify a C4 feedstock to produce a pretreated C4 feedstock rich in but-2-enes; a combined reactor configured to metathesize and isomerize a reactor feed stream containing the pretreated C4 feedstock and an ethene co-feed stream to produce a reactor product stream containing propene, ethene, and C4+ olefins, wherein the combined reactor comprises a metathesis catalyst and an isomerization catalyst configured to metathesize and isomerize the reactor feed stream at a temperature ranging from about 35 °C to 100 °C; a C2 column configured to receive the reactor product stream and produce a light recycle stream rich in ethene and a C3+ olefin stream containing propene and C4+ olefins;24CHEM0018-WO-ORD29 a C3 column configured to receive the C3+ olefin stream and produce a light product stream rich in propene and a C4+ olefin stream containing primarily C4-C6 olefins; and a C4 column configured to receive the C4+ olefin stream and produce a C4 olefin recycle stream and a C5+ olefin stream, wherein the system is configured to route the light recycle stream and the C4 olefin recycle stream to the reactor feed stream.

9. The system of claim 8, wherein the combined reactor comprises: a first catalyst bed containing the metathesis catalyst and configured to receive and metathesize the reactor feed stream to produce a first intermediate stream; a second catalyst bed containing the isomerization catalyst and configured to receive and isomerize the first intermediate stream to produce a second intermediate stream; and a third catalyst bed containing the metathesis catalyst and configured to receive and metathesize the second intermediate stream to produce the reactor product stream.

10. The system of claim 8, wherein the combined reactor comprises a first catalyst bed containing the isomerization catalyst upstream of a second catalyst bed containing the metathesis catalyst.

11. The system of claim 8, wherein the combined reactor comprises a combined catalyst bed containing a mixture of the metathesis catalyst and the isomerization catalyst, and wherein the mixture of the metathesis catalyst and the isomerization catalyst is uniformly distributed along a length of the combined catalyst bed.

12. The system of any one of claims 8-11, comprising a compressor configured to receive and pressurize a combined ethene stream containing the light recycle stream and the ethene co-feed stream, wherein the system is configured to mix the combined ethene stream with the C4 olefin recycle stream and the pretreated C4 feedstock to produce the reactor feed stream.

13. The system of any one of claims 8-12, wherein the metathesis catalyst comprises a rhenium oxide-based y-alumina-based catalyst and the isomerization catalyst comprises a Group 1 A or Group 2A oxide-based y-alumina-based catalyst.24CHEM0018-WO-ORD3014. The system of any one of claims 8-13, wherein the combined reactor is operated at a pressure ranging from about 25 bar to 35 bar and a temperature ranging from about 45 °C to 55 °C.

15. The system of any one of claims 8-14, wherein the metathesis catalyst and the isomerization catalyst are regenerated at a temperature ranging from about 500 °C to 575 °C.

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