Systems and methods for metathesis of butenes integrated with membrane‑based butane separation

Abstract

Provided here are chemical production methods facilitated by a membrane separation unit integrated downstream or upstream of a metathesis reactor. A method includes supplying a C4 feed stream to a metathesis reactor containing a rhenium oxide-based metathesis catalyst to produce a metathesis product stream containing ethene, propene, C4 paraffins, C4 olefins, C5 olefins, and C6 olefins, supplying the metathesis product stream to a first separation column to produce a light product stream containing ethene and propene and a C4+ stream containing C4 paraffins, C4 olefins, C5 olefins, and C6 olefins, supplying the C4+ stream to a second separation column to produce a C6 olefin stream containing C6 olefins and a mixed C4-C5 stream containing C4 paraffins, C4 olefins and C5 olefins, and supplying the mixed C4-C5 stream to a membrane separation unit to produce a C4 paraffin stream and a C4-C5 olefin stream, which is recycled to the metathesis reactor.

Description

SYSTEMS AND METHODS FOR METATHESIS OF BUTENES INTEGRATED WITH MEMBRANE-BASED BUTANE SEPARATIONCross-Reference to Related Applications

[0001] This application claims priority to and the benefit of European Application No. EP23215887.3, filed on December 12, 2023. The contents of the referenced application are incorporated into the present application by reference.Technical Field

[0002] The disclosure relates to the metathesis of a butene feedstock integrated with membranebased butane separation.Background

[0003] Metathesis reactions can be leveraged to produce a variety of chemical products, such as certain high-value olefins, from relatively low-value feedstocks. Based on their particular source, the low-value feedstocks can contain inert compounds in addition to reactive compounds for metathesis. Removal of these inert compounds can require significant costs and energy or underutilize the feedstocks by discarding a portion of the reactive compounds along with the inert compounds. For example, in some cases, metathesis systems include purge streams to reduce the accumulation of the inert compounds in recycle streams to metathesis reactors. However, these purge streams can include certain desired, reactive compounds mixed with the inert compounds based on their similar physical properties.Summary

[0004] The present disclosure provides metathesis processes to convert a butene-based feedstock into more valuable chemical products, such as ethene, propene, and hex-l-ene. Examples herein leverage an integrated membrane separation unit to isolate and remove undesirable compounds contained in mixed feedstocks and improve metathesis-based operations and product yields. For example, a metathesis reactor implemented herein can include a rhenium oxide-based alumina catalyst to facilitate the valorization of C4 feedstocks containing C4 olefins.In examples, certain C4 paraffins or butanes, such as butane (e.g., / ?-butane) and 2-methylpropane (e.g., / .s -butane), are also included in the C4 feedstocks. These paraffins are inert with respect to the rhenium oxide-based alumina catalyst and do not interact in any metathesis reactions. Additionally, metathesis is achieved via equilibrium-limited reactions, which result in a metathesis product stream from the metathesis reactor that includes unconverted butenes, along with the inert C4 paraffins that passed therethrough. To maximize the overall product yield, unconverted butenes can be recycled back to the metathesis reactor in a recycle loop from one or more streams downstream of the metathesis reactor, such as a net overhead stream containing C4-C5 olefins from a C5 column or depentenizer.

[0005] However, this recycling of the butenes also causes recycle of the inert C4 paraffins, which can accumulate in the recycle loop unless otherwise addressed. As such, a purge stream or discharged stream can be provided or diverted from the recycle stream to limit the accumulation or build-up of inert C4 paraffins, in some cases. Undesirably, the purge stream can negatively affect operations, such as by underutilizing butenes that are lost in the purge stream, increasing a load on the metathesis reactor based on the accumulation of inert C4 paraffins, and / or (iii) increasing a load on a hydrogenation unit that is tasked with hydrogenating purged butenes for subsequent use within a steak cracker.

[0006] The present disclosure recognizes and addresses these issues with a membrane separation unit that is integrated with a metathesis reactor and olefin product separation units. The membrane separation unit can be fluidly coupled to remove or filter inert compounds from (i) the purge stream from a C4-C5 recycle stream, (ii) the entire C4-C5 recycle stream, or (iii) the feedstock upstream of the metathesis reactor, based on desired system properties. For example, the membrane separation unit provides separation of reactive C4 olefins (e.g., butenes) from inert C4 paraffins (e.g., butanes). In certain examples, the membrane separation unit includes one or more polymeric membranes, zeolite membranes, metal organic framework (MOF) membranes, facilitated transport membranes, mixed matrix membranes, and / or carbon membranes. The membrane separation unit thus facilitates a reduced or minimized loss of useful butenes in a purge stream and a reduced or minimized accumulation of inert compounds in a feed to the reactor, which enables a lower catalyst requirement (or lower weight hourly space velocity (WHSV) for a given catalyst amount), reduced column size, and correspondingly lower utility usages. Indeed, the present disclosure provides a reduction in overall energy consumption and an increased metathesisreactor efficiency compared to systems that lack a membrane separation unit. It is thus recognized that membrane-based separation methods may be implemented for improved metathesis operation by separating inert C4 paraffins from reactive C4 olefins in streams associated with the metathesis reactor.

[0007] The separation can be performed on C4 compounds contained in either a metathesis reactor effluent stream or a metathesis reactor feed stream, thus providing flexible systems that enable the butenes to be recycled back to or initially fed to the metathesis reactor without the undesired inert compounds. In some examples, the separation is performed on C4-C5 compounds contained in a metathesis reactor effluent stream, thus enabling unconverted butenes and any pentenes to be recycled back to the metathesis reactor without the undesired inert C4 paraffins. In certain examples, the separation is performed on C4 compounds contained in a metathesis reactor feed stream, which enables the butenes to be initially fed to the metathesis reactor without the undesired inert C4 paraffins.

[0008] Indeed, the present disclosure process is highly beneficial in terms of cost saving and energy reduction when the total and / or individual concentration of inert C4 paraffins in the C4 raffinate feedstock is greater than about 1 or 2 mole percent. In some cases, a stream containing the inert C4 paraffins can also be directed to a steam cracker for conversion into more reactive and valuable compounds. Because the stream does not include butenes, the stream does not require further hydrogenating or processing in a total hydrogenation unit to prepare the stream for the steam cracking. The elimination of the total hydrogenation unit provides additional operational savings and efficiencies to the systems disclosed herein. Indeed, removing butenes from the purged stream avoids additional burdens of a downstream steam cracker section, such as capacity increases and the inclusion of a total hydrogenation unit (THU) or complete saturation point (CSP). In certain examples, a C4 isomerization reactor and / or a Ce isomerization reactor can also be provided based on the feed concentration and based on the required product distribution.

[0009] The disclosure herein provides several embodiments of systems and methods for the conversion of butenes to propene via self-metathesis integrated with a butene recycle, as facilitated by an integrated membrane separation unit or membrane reactor. Examples include a method for producing chemicals that includes supplying a mixed C4 feed stream containing C4 paraffins and C4 olefins to a metathesis reactor containing a rhenium oxide- based metathesis catalyst to produce a metathesis product stream containing ethene, propene, C4 paraffins, C4 olefins, C5 olefins, andCe olefins. The metathesis reactor operates at a temperature in a range from about 35 °C to about 100 °C. The method further includes supplying the metathesis product stream to a first separation column to produce a light product stream containing ethene and propene and a C4+ stream containing C4 paraffins, C4 olefins, C5 olefins, and Ce olefins. The method further includes supplying the C4+ stream to a second separation column to produce a Ce olefin stream containing and Ce olefins and a mixed C4-C5 stream containing C4 paraffins, C4 olefins, and C5 olefins. The method further includes supplying at least a portion of the mixed C4-C5 stream to a membrane separation unit to produce a C4 paraffin stream and a C4-C5 olefin stream, and recycling the C4-C5 olefin stream to the metathesis reactor.

[0010] In some examples, supplying the at least a portion of the mixed C4-C5 stream to the membrane separation unit includes supplying only a portion of the mixed C4-C5 stream to the membrane separation unit. In some examples, supplying the at least a portion of the mixed C4-C5 stream to the membrane separation unit includes supplying an entirety of the mixed C4-C5 stream to the membrane separation unit. In some examples, the membrane separation unit includes one or more membranes having a first permeability for C4 paraffins and a second permeability for C4-C5 olefins, the first permeability is different from the second permeability, and the one or more membranes include one or more polymeric membranes, zeolite membranes, metal organic framework membranes, mixed matrix membranes, or carbon membranes. In some examples, supplying the mixed C4 feed stream to the metathesis reactor includes operating the metathesis reactor in the absence of an ethene co-feed stream. In some examples, the rhenium oxide-based metathesis catalyst does not react with C4 paraffins and contains rhenium oxide coated on an outer surface of y-alumina, rhenium oxide dispersed throughout an interior of the y-alumina, or both.

[0011] In some examples, the method further includes supplying the mixed C4 feed stream to one or more guard beds upstream of the metathesis reactor to remove one or more contaminants from the mixed C4 feed stream. In some examples, the method further includes supplying the mixed C4 feed stream to a C4 isomerization reactor upstream of the metathesis reactor to convert at least a portion of but-2-ene into but-l-ene, supplying the Ce olefin stream to a Ce isomerization reactor to produce an isomerized product stream in which at least a portion of hex-3 -ene is converted into hex- 1 -ene, or both. In some examples, the method further includes supplying the C4 paraffin stream to a steam cracker without utilizing a hydrogenation unit. In some examples,the method further includes supplying the light product stream to a C2 / C3 splitter to produce an ethene-rich stream and a propene-rich stream.

[0012] Examples include a method for producing chemicals that includes supplying a mixed C4 feed stream containing C4 paraffins and C4 olefins to a membrane separation unit to produce a C4 paraffin stream and a C4 olefin stream. The method further includes supplying the C4 olefin stream to a metathesis reactor containing a rhenium oxide-based metathesis catalyst to produce a metathesis product stream containing ethene, propene, C4 olefins, C5 olefins, and Ce olefins. The metathesis reactor operating at a temperature in a range from about 35 °C to about 100 °C. The method further includes supplying the metathesis product stream to a first separation column to produce a light product stream containing ethene and propene and a C4+ stream containing C4 olefins, C5 olefins, and Ce olefins. The method further includes supplying the C4+ stream to a second separation column to produce a Ce olefin stream containing Ce olefins and a C4-C5 recycle stream containing C4 olefins and C5 olefins, and recycling the C4-C5 recycle stream to the metathesis reactor.

[0013] In some examples, supplying the mixed C4 feed stream to the metathesis reactor includes operating the metathesis reactor in the absence of an ethene co-feed stream. In some examples, the method further includes supplying the C4 paraffin stream to a steam cracker without utilizing a hydrogenation unit. In some examples, the method further includes supplying the mixed C4 feed stream to one or more guard beds upstream of the metathesis reactor to remove one or more contaminants from the mixed C4 feed stream, supplying the mixed C4 feed stream to a C4 isomerization reactor upstream of the metathesis reactor to convert at least a portion of but-2-ene into but-l-ene, supplying the Ce olefin stream to a Ce isomerization reactor to produce an isomerized product stream in which at least a portion of hex-3-ene is converted into hex-1 -ene, or any combination thereof. In some examples, the C4 olefin stream contains but-l-tene and but-2- enes, and the C4 paraffin stream contains butane and 2-methylpropane. In some examples, the rhenium oxide-based metathesis catalyst contains rhenium oxide coated on an outer surface of y-alumina, rhenium oxide dispersed throughout an interior of the y-alumina, or both.

[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 forunderstanding the nature and character of the claimed aspects and embodiments. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations.Brief Description of the Drawings

[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 including a membrane separation unit fluidly coupled to remove inert compounds contained in a purge stream diverted from a C4-C5 recycle stream, according to an example.

[0017] FIG. 2 is a schematic representation of a system including a membrane separation unit fluidly coupled to remove inert compounds contained in a C4-C5 recycle stream, according to an example.

[0018] FIG. 3 is a schematic representation of a system including a membrane separation unit fluidly coupled to remove inert compounds contained in a feedstock provided to a metathesis reactor, according to an example.

[0019] FIG. 4 is a schematic representation of a control system for controlling operation of the disclosed systems for improved chemical 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 thesystems 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.

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

[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 terms “reducing,” “reduced,” or any variation thereof, when used in the claims and / or the specification includes any measurable decrease or complete removal to achieve a desired result. 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. %” 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. The term “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 per million by weight.

[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 between x and y carbon atoms, x and y inclusive. For example, a C3-C5 fraction or stream refers to a mixture that substantially contains or entirely contains hydrocarbon-based compounds, each compoundcontaining 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 each of the referenced integer values. As one example, a C-i-Cs fraction can be a stream that contains compounds of 4, 5, and 7 carbon atoms, without any compounds of 6 or 8 carbon atoms. As another example, a C4-C5 stream can include compounds having 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 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. As used herein, the term “Cx- compounds,” in which x is a positive integer value, refers to hydrocarbon-based compounds, each compound containing no more than x carbon atoms. For example, a C4- fraction refers to a mixture that substantially contains or entirely contains hydrocarbon- based compounds, each compound containing 4, 3, 2, or 1 carbon atoms. It may be noted that, in certain cases, a “Cx- 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. As used herein, the term “butenes” can refer to one or more reactive C4 olefins or alkenes, such as but-l-tene, cis- but-2-ene, and / ra».s-but-2-ene. As used herein, the term “butanes” can refer to one or more inert C4 paraffins or alkanes, such as / ?-butane and 2-methylpropane (Ao-butane).

[0027] The present disclosure describes various examples related to systems and methods to convert butenes to desired olefin products via metathesis reactions, which are integrated with a membrane separation unit that provides a butene-rich stream with a reduced content of butanes. The present disclosure further increases the yield of desired olefins, such as ethene, propene and / or hexene, through the selective separation of reactive butenes (e.g., but-l-tene, cA-but-2-ene, trans- but-2-ene) from inert C4 paraffins or butanes (e.g., / ?-butane, 2-methylpropane). As discussed herein, the selective separation can be performed by the membrane separation unit that is downstream of (and within a recycle loop with) or upstream of the metathesis reactor. For example,the membrane separation unit can be fluidly coupled to filter inert compounds from (i) the purge stream from a C4-C5 recycle stream, (ii) the entire C4-C5 recycle stream, or (iii) the feedstock to the metathesis reactor.

[0028] Each system includes a metathesis zone including a metathesis reactor, an olefin separation zone having an array of distillation columns, and a membrane zone that includes the membrane separation unit. Each system herein also utilizes a rhenium oxide-based metathesis catalyst that enables the metathesis reactor to operate at improved conditions compared to previous metathesis systems, such as without an ethene co-feed stream and at energy efficient temperatures (e.g., in a range from range from 35 °C to 100 °C). In some examples, the membrane separation unit receives and processes a mixed C4 stream from a C4 column that is downstream of the metathesis reactor. In some examples, the membrane separation unit processes a C4 feedstock supplied to the system, upstream of the metathesis reactor. The decision to integrate the membrane separation unit either downstream or upstream of the metathesis reactor can be based on or influenced by an amount of the inert C4 paraffins in the C4 stream or feedstock that is provided to the associated system. For example, the membrane separation unit of certain examples is positioned downstream of the metathesis reactor in response to a content of paraffins in the C4 stream being less than a preselected threshold. Additionally, the membrane separation unit of certain examples is positioned upstream of the metathesis reactor in response to the content of paraffins in the C4 stream being above the preselected threshold, thereby enabling the metathesis reactor and associated equipment to be appropriately sized for the remaining reactive compounds of the feedstock.

[0029] As will be understood, the membrane zone facilitates improved reactor operation and olefin production compared to previous or existing systems that lack a membrane separation unit for separating out inert C4 compounds from reactive C4 olefins. As discussed above, certain existing systems may include a purge stream for removing butanes and butenes from a metathesis system to limit an accumulation of inert butanes therein. However, this purge may increase a weight hourly space velocity (WHSV) (based on butenes in feed) for a reactor, while also wasting or underutilizing butenes that are discarded in the purge stream. In some systems, butanes and butenes may be separated using certain fractionation methods. However, this fractionation can require multiple, extremely large fractionation columns and very high-energy operational intensity based on the close boiling points of C4 compounds.

[0030] As such, the present disclosure recognizes and provides significant efficiencies and benefits via systems that provide a complete conversion of butenes, which has previously been infeasible based on costs and inefficiencies associated with large fractionation columns. It is thus presently recognized to utilize membrane-based separation methods to separate inert butanes and butenes from an effluent stream or a feed stream of a metathesis reactor, and recycle the butenes back to the metathesis reactor for complete butene conversion or recycling to extinction.

[0031] The membrane separation unit utilized herein can perform separation of compounds having close boiling points using various membrane-based technology. In some examples, a stream comprising mixed butanes and mixed butenes is passed through a membrane separation unit. The membrane therein is selectively permeable to either butanes or butenes. For example, the membrane may block butanes from traversing therethrough, while enabling butenes to pass through uninterrupted. Alternatively, the membrane may block butenes from traversing therethrough, while enabling butanes to pass through uninterrupted. Butanes from the membrane separation unit can be routed to a steam cracker for conversion, while the purified butene stream is sent to the metathesis reactor.

[0032] The removal of butanes improves operation of the metathesis reactor in various ways, as discussed below. In certain examples, the metathesis reactor utilizes a metathesis catalyst for converting butenes, such as but-l-tene and but-2-enes, to propene. In some examples, certain Cs+ olefins can also be produced in the metathesis reactor. The metathesis catalyst of certain examples is a rhenium oxide-coated y-alumina-based catalyst (R^O / yAhCh). 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 oxide-coated y-alumina-based catalyst can facilitate conversion of one or more of: (trans / cis (t / c)) but-2-ene with but-l-ene to propene and (t / c) pent-2-ene, but-l-ene with but-l-ene to ethene and (t / c) hex-3-ene, ethene with (t / c) but-2- ene to propene and propene, but-l-ene with (t / c) pent-2-ene to propene and (t / c) hex-3-ene, and(t / c) pent-2-ene and (t / c) pent-2-ene to (t / c) but-2-ene and (t / c) hex-3-ene in an operational metathesis reactor. In certain examples, the rhenium oxide-coated y-alumina-based catalyst can be functional for at least 300 days in the operational metathesis reactor. In certain examples, the catalyst is regenerated for greater than 50 times in the operational metathesis reactor. Based on regeneration times, the catalyst can be functional for about 1000 days or longer. These days can vary based on the weight hourly space velocity that may range from 0.6 / hr to 10 / hr. 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.

[0033] 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 NFhReC 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 out 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 ranges from about 140 °C to about 160 °C.

[0034] 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-basedsupport 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 (mmolNH3 / g) to about 0.62 mmolNH3 / 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 nanometer (nm) to about 1.2 nm.

[0035] 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 oxi decoated 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.

[0036] The present disclosure facilitates an increased or maximized utilization of olefins via a membrane separation unit that is provided either downstream or upstream of a metathesis reactor. In certain examples, a membrane separation unit is integrated downstream of a metathesis reactor. More particularly, the membrane separation unit can be positioned to remove inert compounds from a purge stream that is diverted from a C4-C5 recycle stream (as illustrated in FIG. 1) or an entire C4-C5 recycle stream (as illustrated in FIG. 2). To utilize maximum C4-C5 olefins or to recover maximum C4-C5 olefins downstream of a metathesis reactor, the membrane separation unit is used to separate inert C4 compounds from olefinic compounds within a purge / bleed stream or from a C4-C5 recycle stream. Further, this C4-C5 olefinic stream can be provided to the metathesisreactor via a recycle stream, thereby increasing a productivity of the metathesis reactor or increasing the utilization of the feedstock supplied to the system. In some examples, the membrane separation unit can alternatively be integrated upstream of the metathesis reactor (as illustrated in FIG. 3) to remove the inert compounds from a C4 feedstock fed to the metathesis reactor. Moreover, the separation systems and methods disclosed herein enable the inert C4 compounds to be fed directly into a steam cracker furnace, which reduces or eliminates the demand for a hydrogenation unit upstream of the steam cracker. Additionally, the separation systems and methods facilitate a lowering of the total amount of C4 compounds fed to steam cracker as a C4 recycle feed.

[0037] FIG. 1 is a schematic representation of a system 100 including a membrane separation unit downstream of a metathesis reactor, according to an example. The system 100 can produce desired olefins, such as ethene, propene, and / or hexene, based on conversion of a C4 feed stream. The system 100 of the illustrated example includes a guard bed, a C4 isomerization reactor, a metathesis reactor, a C3 column (or depropenizer), a C2 / C3 splitter (or C2 / C3 distillation column), a C5 column (or depentenizer) that provides a C4-C5 recycle stream to the metathesis reactor, a Ce isomerization reactor, a Ce fractionator (e.g., Ce distillation column) and a membrane separation unit (e.g., membrane reactor). In additional detail, the system 100 facilitates metathesis of a C4 stream 102 (e.g., mixed C4 feed stream) to produce chemical feedstocks. As illustrated, the system 100 includes a treatment zone 104, a C4 isomerization zone 110, a metathesis zone 120, an olefin separation zone 130, a Ce isomerization zone 160, and a membrane zone 170.

[0038] In some embodiments, the C4 stream 102 is a C4 raffinate stream. In some embodiments, the C4 stream 102 may be sourced downstream of a steam cracker (e.g., a gas steam cracker, a liquid steam cracker, a light crude oil steam cracker, a crude oil cut steam cracker, a mixed feed steam cracker), downstream of a methyl tert-butyl ether (MTBE) reactor, downstream of a but-1- ene (Bl) column, downstream of a but-2-enes (B2) column, downstream of a butadiene hydrogenation reactor, as a C4 raffinate stream from a methanol-to-olefins (MTO) process or reactor, or as a C4 raffinate stream from a refinery fluid catalytic cracking (FCC) process or reactor, or any combination thereof. For such embodiments, the composition of the C4 stream 102 may vary based on the source of the C4 stream 102. In certain examples, the C4 stream 102 is a mixed C4 feed stream containing both C4 olefins and C4 paraffins. Additionally, certain examples of theC4 stream optionally also include a limited amount of Cs compounds, such as pentenes, in combination with the C4 compounds.

[0039] For the illustrated embodiment, the C4 stream 102 is directed to the treatment zone 104, which includes one or more guard beds 106 therein. The C4 stream 102 is into a guard bed 106 (e.g., pretreater) to produce a pretreated C4 stream 108 having a reduced amount of one or more impurities therein. For example, the guard bed 106 can pretreat the C4 stream 102 via adsorbents that remove 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 guard bed 106 and / or treatment zone 104 can thus remove any suitable reactive compounds and / or inert compounds from the C4 stream 102 that can otherwise negatively affect operation of one or more downstream units of the system 100. Additionally, the guard bed 106 can include one or more layers of suitable adsorbents, including aluminum oxides, Ti, Zn, and / or Mg oxides, Type 13X molecular sieves, zeolites, activated carbon, and / or any combination thereof. In some examples, the treatment zone 104 includes multiple guard beds 106 therein that are implemented in series operation, in parallel operation, or a combination thereof. The multiple guard beds 106 are provided to facilitate continuous operation of the treatment zone 104, such as by enabling one or more guard beds 106 to be in operation while one or more other guard beds 106 are in standby and / or regeneration for future use. In some examples, multiple guard beds 106 are combined within a suitable vessel through which the C4 stream 102 travels. The pretreated C4 stream 108 is thus prepared and conditioned before exiting the treatment zone 104.

[0040] A pretreated C4 stream 108 can thus be sent from the treatment zone 104 to the C4 isomerization zone 110. In the C4 isomerization zone 110, the pretreated C4 stream 108 is introduced into a C4 isomerization reactor 112 fluidly coupled downstream of the guard bed 106 to isomerize various compounds therein to more reactive or desirable species. For example, certain pretreated C4 streams 108 or C4 streams 102 contain but-2-ene and but-l-ene. The pretreated C4 stream 108 of the illustrated example is thus directed into the C4 isomerization reactor 112 to convert at least a portion of the but-2-ene into but-l-ene. The C4 isomerization reactor 112 thus produces an isomerized C4 stream 114 (e.g., but-l-ene- rich stream) that is prepared for metathesis. The C4 isomerization reactor 112 contains a K^O / y-alumina- based catalyst, in some examples. In some examples, the C4 isomerization reactor 112 is designed to operate at temperatures in a rangefrom about 25 °C to about 500 °C and at pressures in a range from about 0 barg to about 20 barg. In some examples, the C4 isomerization reactor 112 operates at a temperature of about 350 °C and at a pressure of about 8 barg. Further examples of operating conditions of the C4 isomerization reactor 112 are provided below, alongside certain examples of Ce isomerization reactors. In certain examples, the isomerized C4 stream 114 produced by the C4 isomerization zone 110 contains greater than or equal to 15 mol. % of but-l-ene. In some examples, the C4 isomerization zone 110 can be bypassed or omitted from the system 100, such as in response to the pretreated C4 stream 108 already containing at least a threshold amount (e.g., about 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 mol. %) of but-l-ene therein.

[0041] From the C4 isomerization zone 110, the isomerized C4 stream 114 is directed to the metathesis zone 120. The metathesis zone 120 includes one or more metathesis reactors 122 therein, fluidly coupled downstream of the C4 isomerization reactor 112. The isomerized C4 stream 114 enters the metathesis reactor 122 to yield a C4 recycle stream 124 and a metathesis product stream 126 that contains a mixture of C2-C6 olefin metathesis products. In some examples, the C4 recycle stream 124 is provided to direct certain C4 isomers, such as but-2-ene and isobutene (2- methylprop-l-ene), back to the C4 isomerization reactor 112 for further conversion into but-l-ene.

[0042] As produced by the metathesis reactor 122, the metathesis product stream 126 contains a mixture of C2-C6 olefin metathesis products. In an example, the metathesis product stream 126 contains ethene, propene, C4 paraffins, unreacted C4 olefins, C5 olefins, and Ce olefins. The metathesis reactor 122 can operate with any suitable liquid feed, vapor feed, or mixed phase feed. The metathesis reactor 122 can be implemented as a suitable down-flow or up-flow, fixed-bed, packed bed or a plug flow reactor with a metathesis catalyst. In certain examples, the metathesis catalyst can be a rhenium oxide-based metathesis catalyst, also referred to as a I zO / yAhCh- based catalyst. In certain examples, the rhenium oxide-based metathesis catalyst can include rhenium oxide that is coated on an outer surface of the y-alumina. In some examples, the rhenium oxide-based metathesis catalyst can include rhenium oxide that is dispersed throughout a core or interior of the y-alumina. The rhenium oxide- based metathesis catalyst enables self-metathesis and cross-metathesis of but-l-ene and but-2-enes. Additionally, the rhenium oxide- based metathesis catalyst is inert or non-reactive with respect to the C4 paraffins, which pass through the metathesis reactor 122 unchanged.

[0043] In some examples, the metathesis zone 120 includes multiple metathesis reactors 122 therein, which can be implemented in series or in parallel operation. In some embodiments, at least one reactor remains online while at least one other reactor is in regeneration or standby mode, preparing for subsequent operation. In some examples, the temperature of the metathesis reactor 122 is in a range from 35 °C to 100 °C, 30 °C to 100 °C, 30 °C to 90 °C, 30 °C to 50 °C, and so forth. The operating temperature of the metathesis reactor can be in a range from 50 °C to 500 °C, in some examples, such as temperatures between 50 °C to 400 °C, 50 °C to 300 °C, 50 °C to 200 °C, 50 °C to 100 °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, about 50 °C, or below 50 °C. It is presently recognized that the metathesis reactors and catalysts 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 metathesis reactor reduce the operational cost and energy demands of the reactor compared to other systems. The operating pressures of the metathesis reactor 122 can be in a range from atmospheric pressure (0 barg) to 20 barg, or in a range from 0 barg to 30 barg. Certain examples include metathesis reactions that are pressure independent, such that any pressure that is suitable for integration with upstream and downstream operations may be utilized. In some embodiments, the metathesis reactor 122 does not receive or operates in the absence of an ethene co-feed stream, which desirably avoids consumption of the higher value ethene olefin chemical feedstock to facilitate metathesis.

[0044] It is presently recognized that the metathesis catalyst is prone to gradual deactivation due to formation of intermediate species, moisture, or carbon deposition, and as such, it is desirable to operate the metathesis reactor 122 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 embodiments, this is achieved by limiting the flow rate of C4 stream into the metathesis reactor to a WHSV of between 0.1 h'1and 25 h’1, such as values between 0.5 h'1and 10 h'1. Regeneration of the metathesis catalyst can be performed when a metathesis reactor 122 is in regeneration mode using nitrogen, air, enriched air, or oxygen at temperatures between 300 °C and 600 °C, such as temperatures between 300 °C and 550 °C, 350 °C and 600 °C, 350 °C and 550 °C, about 450 °C, and so forth. In some examples, the catalyst can be regenerated in-situ or online, ex-situ or offline, and / or with continuous catalyst replacement.

[0045] In the illustrated example, the metathesis product stream 126 exits the metathesis zone 220 and is directed to the olefin separation zone 130. For the illustrated embodiment, the olefin separation zone 130 includes a C3 column 132 (e.g., depropenizer, first separation column), a C2 / C3 splitter 134, and a C5 column 136 (e.g., depentenizer, second separation column). The metathesis product stream 126 is directed to the C3 column 132, which separates the metathesis product stream 126 into a C2-C3 olefin stream 138 (e.g., light product stream) and a C4+-rich stream 140 or mixed C4+ stream. The C2-C3 olefin stream 138 contains ethene and propene, and the C4+-rich stream 140 contains the C4 paraffins, the unreacted C4 olefins, the C5 olefins, and the Ce olefins from the metathesis product stream 126. The C2-C3 olefin stream 138 is supplied to the C2 / C3 splitter. The C2 / C3 splitter 134 separates ethene and propene of the C2-C3 olefin stream 138 into an ethene-rich stream 142 and a propene-rich stream 144. The ethene- rich stream 142 and the propene-rich stream 144 can be output as desired product streams, in certain examples. From the C3 column 132, the C4+-rich stream 140 is directed to the C5 column 136, which separates the C4+-rich stream 140 into a mixed C4-C5 stream 146 and a Ce olefin stream 148 containing Ce olefins. The mixed C4-C5 stream 146 contains the C4 paraffins, the unreacted C4 olefins, and the C5 olefins of the C4+-rich stream 140.

[0046] As illustrated, the Ce olefin stream 148 can thus be directed into the Ce isomerization zone 160. The Ce isomerization zone 160 includes a Ce isomerization reactor 162 fluidly coupled downstream of the C5 column 136 to receive the Ce olefin stream 148 and produce an isomerized stream 164. The Ce isomerization reactor 162 contains a foO / y-alumina-based catalyst, in certain examples. The Ce isomerization reactor 162 can thus isomerize one or more Ce compounds therein to more reactive or desirable species, such as the Ce linear alpha olefin, hex-l-ene. For example, the Ce olefin stream 148 can include hex-3 ene, and at least a portion of the hex-3 -ene is converted into hex-l-ene within the Ce isomerization reactor 162. In some examples, the Ce olefin stream 148 can also optionally include a limited amount of hex-2-ene, which is also converted into hex-l-ene within the Ce isomerization reactor 162.

[0047] From the Ce isomerization reactor 162, the isomerized stream 164 is subsequently directed to a Ce fractionator 166 of the Ce isomerization zone 160 to separate a substantially pure hex-l-ene product from other Ce+ olefins. The Ce fractionator 166 can thus produce and output a purified product stream 168 or isomerized product stream containing the hex-l-ene. The Ce fractionator 166 also produces an isomerization recycle stream 167 containing the hex-3-ene andany hex-2-ene, which is recycled back to the Ce isomerization reactor 162 for increased production of hex-l-ene in the purified product stream 168. In some examples, the Ce isomerization zone 160 can be bypassed or omitted from the system 100, such as in response to the Ce olefin stream 148 already containing at least a threshold amount of hex-l-ene therein.

[0048] The isomerization catalyst for one or both of the isomerization reactors 112, 162 can be or include a K^O / y-alumina-based catalyst (e.g., K2O / Y-AI2O3), in certain examples. In some examples, the isomerization zones 110, 160 can each include multiple isomerization reactors 112, 162 therein, such as two or three reactors that can be implemented in series or in parallel operation. In some embodiments, at least one reactor remains online while at least one other reactor is in regeneration or standby mode, preparing for subsequent operation. The operating temperature of the isomerization reactors 112, 162 can be in a range from 250 °C to 550 °C, in some examples. The operating temperature of the isomerization reactors 112, 162 can be in a range from 300 °C to 600 °C, in some examples, such as temperatures ranging from 300 °C to 550 °C, 300 °C to 500 °C, 300 °C to 550 °C, 300 °C to 500 °C, 350 °C to 550 °C, 350 °C to 600 °C, 400 °C to 500 °C, and so forth. In certain examples, the operating temperature is in a range between 250 °C and 500 °C. The operating pressures of the isomerization reactors 112, 162 can range between 0 barg and 30 barg. In different implementations, the isomerization reactors 112, 162 are each a fixed bed plug flow reactor and / or capable of isomerizing a liquid feed, a vapor feed, or mixed phase feed. It is presently recognized that the isomerization catalyst is prone to gradual deactivation due to formation of intermediate species or carbon deposition, and as such, it is desirable to operate the isomerization reactors 112, 162 a fixed bed plug flow reactor to enable a suitable operating cycle time between 1 day and 100 days, such as between 1 day and 60 days. In some embodiments, this is achieved by limiting the flow rate of the respective feed stream to the isomerization reactors 112, 162 to a WHSV in a range from 0.1 h'1to 25 h'1. In some examples, the WHSV is in a range from 0.5 h'1to 10 h'1. Regeneration of the isomerization catalyst can be performed when the respective isomerization reactor 112, 162 is in regeneration mode using nitrogen, air, enriched air, or oxygen at temperatures that are in a range from 350 °C to 600 °C.

[0049] It is presently recognized that the mixed C4-C5 stream 146 includes a non-zero amount of paraffins, such as butane and 2-methylpropane, that are inert within the metathesis reactor 122. Indeed, C4 paraffins or butanes do not take part in any reaction via the rhenium oxide-based metathesis catalyst in the metathesis reactor 122, act as inert, and exit the metathesis reactor 122unchanged. Additionally, metathesis reactions are equilibrium limited, and a non-zero amount of unreacted butenes will remain in effluent streams from the metathesis reactor 122. A mixture of butanes and butenes is thus contained in the mixed C4-C5 stream 146 separated from an overhead of the C5 column 136 and supplied from the olefin separation zone 130 in the illustrated example. Indeed, the mixed C4-C5 stream 146 contains the C4 paraffins, the unreacted C4 olefins, and the C5 olefins of the C4+-rich stream 140 noted above.

[0050] To address the inert C4 compounds and prevent their accumulation, the system 100 supplies or diverts a portion of the mixed C4-C5 stream 146 to a membrane zone 170 containing one or more membrane separation units 172 for separating the C4 paraffins from the portion of the mixed C4-C5 stream 146. In systems containing multiple membrane separation units 172, each unit may be fluidly coupled together in any suitable arrangement, such as in parallel and / or in series. The system 100 of some examples can include multiple types of membranes, such as a first type of membrane in a first membrane separation unit 172 and a second type of membrane in a second membrane separation unit 172. In some examples, the portion of the mixed C4-C5 stream 146 is a bleed stream 174 (e.g., mixed C4-C5 bleed stream, purge stream), which without the presently disclosed membrane separation techniques, may have been discarded along with any of its olefinic contents. The membrane separation unit 172 receives the bleed stream 174 and produces a butane- rich stream 176 (e.g., C4 paraffin stream, purge stream, paraffinic-rich stream) and a butene-rich stream 180 (e.g., C4-C5 olefin stream, recovered reactive stream, recycle stream). The butene-rich stream 180 is thus a purified stream, having a reduced or minimized content of inert C4 paraffins compared to the bleed stream 174 supplied to the membrane separation unit 172. In some examples, the butene-rich stream 180 is completely free or substantially free from butanes based on the membrane-based separation leveraged by the membrane separation unit 172. In certain examples, the butene-rich stream 180 includes C5 olefins or pentenes in addition to the butenes.

[0051] The separated, butane-rich stream 176 can be collected to be sold as a product (e.g., liquid petroleum gas (LPG)), or subsequently subject to further purification, or it may be provided as an input stream to another system or unit of a hydrocarbon processing facility. In some examples, the butane-rich stream 176 is completely free or substantially free from butenes, which have been recovered for further conversion. In some examples, the butane-rich stream 176 is routed to a steam cracker for conversion therein. Additionally, because the butane- rich stream 176 of certain examples is substantially free of butenes, the butane-rich stream 176 can be fed directlyinto a steam cracker without utilizing a hydrogenation unit upstream of the steam cracker. Other systems may require a hydrogenation unit to saturate the unconverted butenes contained in a purge stream, thereby increasing a complexity and cost for the systems. Additionally, based on the use of membranes, the system 100 provides a reduction in overall energy consumption and an increased throughput for the metathesis reactor 122, compared to certain other systems that may use a superfractionator for separations.

[0052] The membrane separation unit 172 can include any suitable number and type of membranes or membrane modules therein that include a different permeability for paraffins (e.g., butanes) than olefins (e.g., butenes, pentenes). As such, the membrane includes a first permeability for C4 paraffins that is different from a second permeability for C4-C5 olefins of the membrane. For example, the membrane may block C4 paraffins from traversing therethrough as a retentate, while enabling C4-C5 olefins to pass through uninterrupted as a permeate. Alternatively, the membrane may block C4-C5 olefins from traversing therethrough as a retentate, while enabling C4 paraffins to pass through uninterrupted as a permeate. Additionally, the membrane separation unit 172 can separate the olefins from the paraffins via any suitable flow configuration, such as a crossflow configuration or a straight-through configuration. After any paraffin or other content removal, the butene-rich stream 180 is prepared for recycle to the metathesis zone 120 to enable conversion of the unreacted butenes and any C5 olefins therein.

[0053] The membrane zone 170 can include any suitable types of membranes therein. As nonlimiting examples of membrane types, the one or more membranes can include polymeric membranes, zeolite membranes, metal organic framework (MOF) membranes, facilitated transport membranes, mixed matrix membranes, or carbon membranes. In some examples, mixed matrix membranes can be based on biopolymeric materials, such as chitosan or cellulose. For examples including one or more facilitated transport membranes, the facilitated transport membrane includes a complexing agent incorporated in a high-pressure side of the membrane. This complexing agent can complex or bind with double bonds of the C4-C5 olefins. The complexing agent and complexed olefin can thus diffuse across the membrane based on a concentration difference across the membrane (e.g., from the high-pressure side to a low-pressure side). The complexing agent decomplexes from the olefin, thereby regenerating the complexing agent and releasing the olefin on the low-pressure side of the membrane. In some examples, the complexing agent diffuses back to the high-pressure side of the membrane to perform additional facilitated transport cycles withadditional C4-C5 olefins. The C4 paraffins do not complex with the complexing agent, thus enabling a majority of the C4 paraffins to be rejected by the membranes. The facilitated transport membrane can therefore selectively direct C4-C5 olefins across itself to form the butene-rich stream 180, in certain examples.

[0054] Additionally, a remaining portion of the mixed C4-C5 stream 146 that was not diverted to the membrane zone 170 is provided as a mixed recycle stream 182 containing C4 paraffins and C4-C5 olefins. The butene-rich stream 180 and the mixed recycle stream 182 are thus sent to the metathesis zone 120, thereby enabling conversion of any unreacted C4-C5 olefins and / or other reactive compounds therein. In some examples, the butene-rich stream 180 and / or the mixed recycle stream 182 can be sent directly to the metathesis zone 120 or sent to the C4 isomerization zone 110, upstream of the metathesis zone 120. In certain examples, the butene-rich stream 180 and the mixed recycle stream 182 can be combined into a combined recycle stream 184 to facilitate the recycle. The combined recycle stream 184 is recycled to the metathesis zone 120 where it is combined with the isomerized C4 stream 114 and metathesized in the metathesis reactor 122 to form the metathesis product stream 126. This recycle utilizes the butene-rich stream 180 for further production of desired olefins, including the C2, C3, C5, and Ce olefins of the ethene-rich stream 142, the propene-rich stream 144, and the Ce olefin stream 148, respectively.

[0055] FIG. 2 is a schematic representation of a system including a membrane separation unit fluidly coupled to filter or remove inert compounds from a mixed C4-C5 stream, according to an example. The system 200 includes the treatment zone 204, a C4 isomerization zone 210, a metathesis zone 220, an olefin separation zone 230, a Ce isomerization zone 260, and a membrane zone 270 fluidly coupled downstream of the metathesis zone 220, which each correspond to and include similar components as the zones discussed above with respect to FIG. 1. These components are similarly labeled, and their descriptions are not repeated in detail for improved clarity.

[0056] As shown, the system 200 alternatively includes the membrane zone 270 and the membrane separation unit 272 therein positioned to receive an entirety of the C4-Cs-rich stream 246 produced by the C5 column 236 of the olefin separation zone 230, instead of a diverted portion of the C4-Cs-rich stream 246 discussed above. The membrane separation unit 272 can therefore filter the C4-Cs-rich stream 246 to produce a butane-rich stream 276 (e.g., C4 paraffin stream, purgestream, paraffinic-rich stream) and a butene- rich stream 280 (e.g., C4-C5 olefin stream, recovered reactive stream, recycle stream).

[0057] The membrane separation unit 272 thus produces the butene-rich stream 280 as a purified stream, which includes a reduced or minimized content of inert C4 paraffins compared to the C4-Cs-rich stream 246 supplied to the membrane separation unit 272. The system 200 can therefore send the butene-rich stream 280 to the metathesis zone 220 as a single recycle stream, thereby enabling conversion of any unreacted C4-C5 olefins and / or other reactive compounds therein. In the metathesis zone 220, the butene-rich stream 280 is combined with the isomerized C4 stream 214 and metathesized to form the metathesis product stream 226, which includes an increased yield of desired olefins compared to other systems that underutilize butenes that are removed in a purge stream.

[0058] FIG. 3 is a schematic representation of a system 300 including a membrane separation unit fluidly coupled upstream of a metathesis reactor to filter or remove inert compounds from a feedstock, according to an example. The system 300 includes the treatment zone 304, a membrane zone 370, a C4 isomerization zone 310, a metathesis zone 320, an olefin separation zone 330, and a Ce isomerization zone 360. which each correspond to and include similar components as the zones discussed above with respect to FIGS. 1-2. These components are similarly labeled, and their descriptions are not repeated in detail for improved clarity.

[0059] As illustrated, the system 300 alternatively includes the membrane zone 370 and the membrane separation unit 372 therein positioned to receive the pretreated C4 stream 308 from the guard bed 306 of the treatment zone 304. As such, the membrane separation unit 372 is fluidly coupled downstream of the guard bed 306 and fluidly coupled upstream of the C4 isomerization zone 310 and the metathesis zone 320. In some examples, the membrane separation unit 372 operates to remove C4 paraffins or butanes from fresh feed material before it is supplied to the metathesis reactor 322 of the metathesis zone 320.

[0060] In particular, the pretreated C4 stream 308 is provided into the membrane separation unit 372, which produces a butane-rich stream 376 and a butene-rich stream 380. The membrane separation unit 372 can include one or more membranes that include a different permeability for C4 paraffins than C4 olefins, in some examples. In certain examples in which a limited amount of C5 olefins are present in the pretreated C4 stream 308, the membranes can include a different permeability for C4 paraffins than C4-C5 olefins. The butene-rich stream 380 is thus a purifiedstream, having a reduced or minimized content of inert C4 paraffins compared to the pretreated C4 stream 308 supplied to the membrane separation unit 372. The separated, butane-rich stream 376 can be collected to be sold as a product, or subsequently subject to further purification, or it may be provided as an input stream to another system or unit of a hydrocarbon processing facility.

[0061] After any paraffin or other content removal, the butene-rich stream 380 is sent to the C4 isomerization zone 310, which directs an isomerized, butene-rich stream 314 having a reduced paraffin content to the metathesis zone 320. In some examples, the butene-rich stream 380 is sent directly to the metathesis zone 320. In certain examples, the isomerized, butene-rich stream 314 produced by the C4 isomerization zone 310 contains greater than or equal to 15 mol. % of but-l-ene. In some examples, the C4 isomerization zone 310 can be bypassed or omitted from the system 300, such as in response to the pretreated C4 stream 308 already containing at least a threshold amount (e.g., about 15, 20, 25, 30, 35, 40, 45, 50, 55, or 60 mol. %) of but-l-ene therein.

[0062] The metathesis reactor 322 of the metathesis zone 320 produces the metathesis product stream 326 containing a mixture of C2-C6 olefin metathesis products. In certain examples, the metathesis product stream 326 contains ethene, propene, unreacted C4 olefins, C5 olefins, and Ce olefins. Additionally, in some examples, the metathesis product stream 326 excludes or is substantially free from C4 paraffins that otherwise negatively affect operation of the system 300. As such, streams that are downstream of the metathesis reactor 322 also exclude or are substantially free from the C4 paraffins.

[0063] The metathesis product stream 326 is provided to the olefin separation zone 330, which includes the C3 column 332 that separates the metathesis product stream 326 into a C2-C3 olefin stream 338 containing ethene and propene and a C4+-rich stream 340 containing the unreacted C4 olefins, the C5 olefins, and the Ce olefins from the metathesis product stream 326. The C4+-rich stream 340 is directed to the C5 column 336, which separates the C4+-rich stream 340 into a C4-C5 olefin stream 346 containing the unreacted C4 olefins and the C5 olefins and a Ce olefin stream 348 containing the Ce olefins. The C4-C5 olefin stream 346 exits the olefin separation zone 330 and is recycled to the metathesis zone 320 for metathesis along with the along with the isomerized, butene- rich stream 314. The membrane separation unit 372 thus enables the system 300 to convert the C4 olefins into desired olefin products, without encumbrance by C4 paraffins contained in certain feedstocks.

[0064] 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 is communicatively coupled to a treatment zone 404, a C4 isomerization zone 410, a metathesis zone 420, an olefin separation zone 430, a Ce isomerization zone 460, and a membrane zone 470. In some examples without isomerization, the controller 401 is communicatively coupled to the treatment zone 404, the metathesis zone 420, the olefin separation zone 430, and the membrane zone 470. In certain examples, the controller 401 is communicatively coupled to at least the metathesis zone 420, the olefin separation zone 430, and the membrane zone 470, as well as any one or more of the treatment zone 404, the C4 isomerization zone 410, and the Ce isomerization zone 460 that are present in the associated system. 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.

[0065] For example, the controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors, content analyzers) of the treatment zone 404, 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 treatment zone 404 to ensure that the one or more guard beds therein operate in accordance with any predefined threshold values. The controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the C4 isomerization zone 410 and the Ce isomerization zone460, and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of the isomerization zones 410, 460 to ensure that the isomerization reactors therein operates within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the isomerization reactors. The controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the metathesis zone 420, and based on predefined threshold values for certain operational parameters, provide suitable control signals to modify the operation of one or more components of the metathesis zone 420 to ensure that the metathesis reactor therein operates within the temperatures, pressures, and WHSV disclosed above, and to manage the regeneration mode operation and standby operation of the metathesis reactor.

[0066] Additionally, the controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the olefin separation 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 these zones, such that the components of these zones operate in accordance with any predefined threshold values. The controller 401 may receive monitoring data from sensors (e.g., temperature sensors, pressure sensors, flow sensors) of the membrane zone 470, 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 membrane zone 470 to ensure that the membrane separation unit therein operates in accordance with any predefined threshold values.Examples

[0067] 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, devices and / or methods claimed herein are made and evaluated and, therefore, 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, etc.), but some deviations should be accounted for.

[0068] There are numerous variations and combinations of reaction conditions, for example, component concentrations, desired solvents, solvent mixtures, temperatures, pressures and otherreaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

[0069] Example 1 :

[0070] The systems and methods disclosed herein can efficiently utilize various C4 feedstocks to produce desired chemicals, at improved yields. In some examples, the C4 feedstock has a composition in accordance with a C4 raffinate II stream or a C4 raffinate III stream. As non-limiting examples, Table- 1 shown below illustrates sample compositions of two different C4 raffinate streams.

[0071] Table- 1: Composition of examples of C4 feedstocks

[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 embodimentsmay 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

Claims1. A method for producing chemicals, the method comprising: supplying a mixed C4 feed stream containing C4 paraffins and C4 olefins to a metathesis reactor containing a rhenium oxide-based metathesis catalyst to produce a metathesis product stream containing ethene, propene, C4 paraffins, C4 olefins, C5 olefins, and Ce olefins, the metathesis reactor operating at a temperature in a range from about 35 °C to about 100 °C; supplying the metathesis product stream to a first separation column to produce a light product stream containing ethene and propene and a C4+ stream containing C4 paraffins, C4 olefins, C5 olefins, and Ce olefins; supplying the C4+ stream to a second separation column to produce a Ce olefin stream containing and Ce olefins and a mixed C4-C5 stream containing C4 paraffins, C4 olefins, and C5 olefins; supplying at least a portion of the mixed C4-C5 stream to a membrane separation unit to produce a C4 paraffin stream and a C4-C5 olefin stream; and recycling the C4-C5 olefin stream to the metathesis reactor.

2. The method of claim 1, wherein supplying the at least a portion of the mixed C4-C5 stream to the membrane separation unit comprises supplying only a portion of the mixed C4-C5 stream to the membrane separation unit.

3. The method of claim 1, wherein supplying the at least a portion of the mixed C4-C5 stream to the membrane separation unit comprises supplying an entirety of the mixed C4-C5 stream to the membrane separation unit.

4. The method of any of claims 1-3, wherein the membrane separation unit comprises one or more membranes having a first permeability for C4 paraffins and a second permeability for C4-C5 olefins, wherein the first permeability is different from the second permeability, and wherein the one or more membranes comprise one or more polymeric membranes, zeolite membranes, metal organic framework membranes, mixed matrix membranes, or carbon membranes.

5. The method of any of claims 1-4, wherein supplying the mixed C4 feed stream to the metathesis reactor comprises operating the metathesis reactor in the absence of an ethene co-feed stream.

6. The method of any of claims 1-5, wherein the rhenium oxide-based metathesis catalyst does not react with C4 paraffins and contains rhenium oxide coated on an outer surface of y-alumina, rhenium oxide dispersed throughout an interior of the y-alumina, or both.

7. The method of any of claims 1-6, further comprising supplying the mixed C4 feed stream to one or more guard beds upstream of the metathesis reactor to remove one or more contaminants from the mixed C4 feed stream.

8. The method of any of claims 1-7, further comprising: supplying the mixed C4 feed stream to a C4 isomerization reactor upstream of the metathesis reactor to convert at least a portion of but-2-ene into but-l-ene; supplying the Ce olefin stream to a Ce isomerization reactor to produce an isomerized product stream in which at least a portion of hex-3-ene is converted into hex-1 -ene; or both.

9. The method of any of claims 1-8, further comprising supplying the C4 paraffin stream to a steam cracker without utilizing a hydrogenation unit.

10. The method of any of claims 1-9, further comprising supplying the light product stream to a C2 / C3 splitter to produce an ethene-rich stream and a propene- rich stream.

11. A method for producing chemicals, the method comprising: supplying a mixed C4 feed stream containing C4 paraffins and C4 olefins to a membrane separation unit to produce a C4 paraffin stream and a C4 olefin stream; supplying the C4 olefin stream to a metathesis reactor containing a rhenium oxide-based metathesis catalyst to produce a metathesis product stream containing ethene,propene, C4 olefins, C5 olefins, and Ce olefins, the metathesis reactor operating at a temperature in a range from about 35 °C to about 100 °C; supplying the metathesis product stream to a first separation column to produce a light product stream containing ethene and propene and a C4+ stream containing C4 olefins, C5 olefins, and Ce olefins; supplying the C4+ stream to a second separation column to produce a Ce olefin stream containing Ce olefins and a C4-C5 recycle stream containing C4 olefins and C5 olefins; and recycling the C4-C5 recycle stream to the metathesis reactor.

12. The method of claim 11 , wherein supplying the mixed C4 feed stream to the metathesis reactor comprises operating the metathesis reactor in the absence of an ethene co-feed stream.

13. The method of claims 11 or 12, further comprising supplying the C4 paraffin stream to a steam cracker without utilizing a hydrogenation unit.

14. The method of any of claims 11-13, further comprising: supplying the mixed C4 feed stream to one or more guard beds upstream of the metathesis reactor to remove one or more contaminants from the mixed C4 feed stream; supplying the mixed C4 feed stream to a C4 isomerization reactor upstream of the metathesis reactor to convert at least a portion of but-2-ene into but-l-ene; supplying the Ce olefin stream to a Ce isomerization reactor to produce an isomerized product stream in which at least a portion of hex-3-ene is converted into hex-1 -ene; or any combination thereof.

15. The method of any of claims 11-14, wherein the C4 olefin stream contains but-l-tene and but-2-enes, wherein the C4 paraffin stream contains butane and 2-methylpropane, and wherein the rhenium oxide-based metathesis catalyst contains rhenium oxide coated on an outer surface of y-alumina, rhenium oxide dispersed throughout an interior of the y-alumina, or both.

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