WO2021048693A1

WO2021048693A1 - Aromatization catalyst with improved isomerization, reactor configurations and use thereof

Info

Publication number: WO2021048693A1
Application number: PCT/IB2020/058138
Authority: WO
Inventors: Kaiwalya SABNIS; Kevin BAZAZZADEH; Travis Conant; Scott Stevenson
Original assignee: Sabic Global Technologies B.V.
Priority date: 2019-09-10
Filing date: 2020-09-01
Publication date: 2021-03-18

Abstract

Processes for dehydroaromatization of C6 paraffins to form aromatic hydrocarbons are disclosed. The processes include contacting a mixture of branched and linear paraffins with at least two catalysts to produce aromatic hydrocarbons. One catalyst has a higher relative aromatization reactivity and another catalyst has a higher relative isomerization activity. In a common example, a mixture of branched and linear hexanes is contacted with aromatization and isomerization catalysts to produce benzene.

Description

AROMATIZATION CATALYST WITH IMPROVED ISOMERIZATION, REACTOR CONFIGURATIONS AND USE THEREOF

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U. S. Provisional Patent Application No. 62/898,394 filed September 10, 2019, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

[0002] The invention generally concerns a process for producing aromatic hydrocarbons. In particular, the process includes dehydroaromatization of alkanes to form benzene. The process includes contacting a first hydrocarbon stream including alkanes with an aromatization catalyst to produce a second hydrocarbon stream including aromatic compounds, and contacting a third hydrocarbon stream including alkanes with a dual functional (aromatization + isomerization) catalyst to produce a fourth hydrocarbon stream including aromatic compounds. The first and third streams can include different branched alkane to linear alkane molar ratios.

B. Description of Related Art

[0003] Benzene is an aromatic compound often used as an octane booster in refining. Benzene is also used in various other industrial processes to form products, such as plastics, resins, synthetic fibers, rubber lubricants, dyes, detergents, pharmaceutical products, and pesticides. Many other aromatic compounds are used as solvents ( e.g ., toluene) or gasoline additives to reduce knocking in engines (e.g., xylenes), or are used to produce dyes and plastics.

[0004] Commercially, aromatic compounds can be prepared by dehydroaromatization. Aromatic compounds (e.g, benzene) can be made by converting at least one straight chain of carbons (e.g, n-hexane). By way of example U.S. Patent No. 8,993,468 to Stevenson el al, 7,902,413 to Stevenson et al. and 5,055,437 to Herbst et ah, and U.S. Patent Application Publication No. 2016/0288108 to Khanmamedova et al. describe making aromatics from paraffins. Conversion of branched alkane isomers (e.g, iso-hexane, “iCf’) to linear alkanes Ce (e.g, n-hexane, “nCf’) is equilibrium-limited and depends on the relative partial pressures of the isomers. Therefore, an iC6-rich feed stream drives the reaction toward producing more nC6, which is used to create benzene. [0005] When there are limitations on the amount of nC6 which can be converted and limitations of the aromatization reaction, the process is expensive. Further cost burdens include the cost to build and operate the process, and the energy and time required to obtain more of the aromatic compounds.

SUMMARY OF THE INVENTION

[0006] A solution to at least some of the problems associated with the production of aromatics has been discovered. The solution is premised in a process and system for generating aromatics that uses at least two catalysts. Using different reactor configurations and different catalysts with various nC6 aromatization and iC6 to nC6 isomerization relative activities can be used to optimize aromatics yield from an iC6 and nC6 feed stream. In addition to higher yields of aromatic compounds, using different reactor configurations and different catalysts can lower the utility costs associated with producing aromatic compounds, reduce plant size for a target amount of aromatic compound production, improve process efficiency, and/or lower other operational costs.

[0007] In one aspect of the present invention, a process to produce aromatics is disclosed. The process can include steps (a) and step (b). Step (a) can include contacting a first hydrocarbon stream including alkanes with an aromatization catalyst to produce a second hydrocarbon stream comprising aromatic compounds. Step (b) can include contacting a third hydrocarbon stream including alkanes with a dual function (aromatization + isomerization) catalyst to produce a fourth hydrocarbon stream including aromatic compounds. The first and third streams can include different branched alkane to linear alkane molar ratios.

[0008] In another aspect of the present invention, a system to produce aromatics is disclosed. The system can include a first reaction zone including a first alkane stream and an aromatization catalyst and a second reaction zone including a third alkane stream and a dual functional (aromatization + isomerization) catalyst. The first reaction zone can be capable of producing a second hydrocarbon stream including aromatic compounds. The second reaction zone can be capable of producing a fourth hydrocarbon stream including aromatic compounds. The first and third alkane streams can include different branched alkane to linear alkane molar ratios.

[0009] The second hydrocarbon stream and the third hydrocarbon stream can be the same stream. The first and/or third streams can be sent through a stacked bed reactor or fixed-bed reactors in series configuration. The first and second reaction zones can be stacked beds in a single reactor. The first and second reaction zones can be configured in series in separate reactors. The aromatization catalyst can be a Pt/Na-Ge-ZSM-5 catalyst (“Type 1”). The dual functional (aromatization + isomerization) catalyst can be a Pt/NaCs-Ge-ZSM catalyst (“Type 2”).

[0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] The term “aromatic compound” can be any aromatic hydrocarbon having 5 to 20 carbon atoms of the monocyclic, polycyclic or condensed polycyclic type. Examples include benzene, phenyl, biphenyl, naphthyl, and the like.

[0012] The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0013] 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, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol.% of component.

[0014] The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, includes any measurable decrease or complete inhibition to achieve a desired result.

[0015] 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.”

[0016] The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”), or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0017] The process of the present invention can “comprise,” “consist essentially of,” or “consist of’ particular ingredients, components, compositions, etc ., disclosed throughout the specification. With respect to the transitional phase “consisting essentially of,” in one non limiting aspect, a basic and novel characteristic of the process of the present invention is the ability to produce aromatic hydrocarbons by contacting alkane hydrocarbons with an aromatization catalyst and an isomerization catalyst. In the context of the present invention, at least 20 embodiments are now described.

[0018] Embodiment 1 is directed to a process to produce aromatics. The process includes the steps of (a) contacting a first hydrocarbon stream including alkanes with an aromatization catalyst to produce a second hydrocarbon stream including aromatic compounds; and (b) contacting a third hydrocarbon stream including alkanes with a dual functional (aromatization + isomerization) catalyst to produce a fourth hydrocarbon stream including aromatic compounds, wherein the first and third streams include different branched alkane to linear alkane molar ratios (B:L alkane ratios). Embodiment 2 is the process of embodiment 1, wherein the first, second, third, and fourth hydrocarbon stream includes linear and branched C6 alkanes. Embodiment 3 is the process of any one of embodiments 1 to 2, wherein the second hydrocarbon stream and the third hydrocarbon stream are the same stream, and the fourth stream has an aromatic hydrocarbons content greater than the second hydrocarbon stream. Embodiment 4 is the process of embodiment 3, wherein the B:L alkane ratio of the alkanes in the third hydrocarbon stream is greater than the B:L alkane ratio of the alkanes in the first hydrocarbon stream. Embodiment 5 is the process of any one of embodiments 1 to 4, wherein the contacting of step (a) and the contacting step (b) are performed in a stacked bed reactor or fixed-bed reactors in series configuration. Embodiment 6 is the process of embodiment 5, wherein the reactor or reactors have a temperature of 250 to 700°C and/or a gauge pressure of 0.01 to 1.0 MPa. Embodiment 7 is the process of any one of embodiments 1 to 6, wherein the branched alkane to linear alkane molar ratio is 0: 1 to 15 : 1. Embodiment 8 is the process of any one of embodiments 1 to 7, further including positioning a diluent layer between the aromatization catalyst and the dual functional (aromatization + isomerization) catalyst. Embodiment 9 is the process of any one of embodiments 1 to 8, wherein the B:L alkane ratio of the alkanes in the first hydrocarbon stream is 0 to 2. Embodiment 10 is the process of any one of embodiments 1 to 9, wherein the aromatization catalyst includes a noble metal deposited on a zeolite, the zeolite including silicon (Si), aluminum (Al), and germanium (Ge) in the framework, and wherein the zeolite also includes a Column 1 or 2 metal. Embodiment 11 is the process of embodiment 10, wherein the noble metal includes Pt and the Column 1 metal includes sodium (Na). Embodiment 12 is the process of any one of embodiments 1 to 1, wherein the isomerization catalyst includes a noble metal deposited on a zeolite, the zeolite including Si, Al, Ge, at least two of a Column 1 and/or Column 2 metal in the framework, wherein the catalyst is non-acidic and has an Al content of 0.75 wt.% or less based on the total weight of the catalyst. Embodiment 13 is the process of embodiment 12, wherein the noble metal is Pt and the Column 1 metals are Na and cesium (Cs). [0019] Embodiment 14 is a system to produce aromatics using the process of any one of embodiments 1 to 13. The system includes (a) a first reaction zone including a first alkane stream and an aromatization catalyst, the first reaction zone capable of producing a second hydrocarbon stream including aromatic compounds; and (b) a second reaction zone including a third alkane stream and a dual functional (aromatization + isomerization) catalyst, the second reaction zone capable of producing a fourth hydrocarbon stream including aromatic compounds, wherein the first and third alkane streams includes different branched alkane to linear alkane molar ratios (B:L alkane ratios). Embodiment 15 is the system of embodiment 14, wherein the first reaction zone is in fluid communication with the second reaction zone and the second reaction zone is capable of receiving the second hydrocarbon stream. Embodiment 16 is the system of embodiment 14, wherein the first reaction zone is in fluid communication with the second reaction zone and the first reaction zone is capable of receiving the fourth hydrocarbon stream. Embodiment 17 is the system of any one of embodiments 14 to 16, wherein the first and second reaction zones are stacked beds included in a single reactor. Embodiment 18 is the system of any one of embodiments 14 to 17, further including an outlet coupled to the first reaction zone and the second reaction zone, wherein the outlet is capable of providing the second hydrocarbon stream to an inlet of the second reaction zone; and an outlet coupled to the second reaction zone capable of delivering the fourth hydrocarbon stream. Embodiment 19 is the system of any one of embodiments 14 to 18, wherein the aromatization catalyst is a Pt/Na-Ge-ZSM-5 catalyst and the dual functional (aromatization + isomerization) catalyst is a Pt/NaCs-Ge-ZSM catalyst.

[0020] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0022] FIG. 1 is a schematic of a one reactor system to prepare aromatic compounds by dehydroaromatization.

[0023] FIG. 2 is another schematic of a one reactor system to prepare aromatic compounds by dehydroaromatization.

[0024] FIG. 3 is a schematic of a two reactor system to prepare aromatic compounds by dehydroaromatization.

[0025] FIG. 4 is a graph comparing benzene yield for Type 1 and Type 2 catalysts loaded individually and in stacked bed manner.

[0026] FIG. 5 is a graph comparing benzene yield for Type 1 and Type 2 catalysts loaded in series configuration, Type 1 and Type 2 catalysts loaded in a stacked-bed reactor, and Type 3 catalyst loaded in a single reactor.

[0027] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0028] A discovery has been made that provides a solution to the problem of difficulty in producing aromatic hydrocarbons from a mixture of branched and linear paraffins. The discovery is premised on improving isomer conversion of iso-paraffin to n-paraffm (e.g, iC6 to hqό), where the n-paraffm is then converted to aromatic compounds, thereby ultimately improving aromatic conversion. These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the FIGS. 1-3.

[0029] One of the most commonly used aromatic compounds is benzene. Benzene is discussed in the following paragraphs as an example, but any aromatic compound can be used. Benzene can be produced in the context of the present invention by contacting a first hydrocarbon stream of alkanes with an aromatization catalyst to produce a second hydrocarbon stream including aromatic compounds and contacting a third hydrocarbon stream of alkanes with a dual functional (aromatization + isomerization) catalyst to produce a fourth hydrocarbon stream including aromatic compounds. The hydrocarbon streams can include a linear nC6 paraffin, iC6 paraffins, and/or diluent material. In one non-limiting embodiment, hydrogen gas and/or nitrogen gas can be the diluent material. A molar ratio of diluent material to the paraffins can be 0:1 to 5:1, or 0:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 0.9:1, 1:1, 2:1, 3:1, 4:1, or 5:1, or any value there between. In one non-limiting embodiment, the molar ratio of diluent material to the paraffins can be 0.75 : 1. The first and third streams can include different branched alkane to linear alkane molar ratios. In one non-limiting embodiment, the molar ratio of branched paraffins to linear paraffins can be 0:1 to 15:1, or 0:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 0.9:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15: 1, or any value there between. In some instances, the first, second, third, and/or fourth hydrocarbon streams include linear and branched G alkanes.

[0030] Reaction conditions to produce the benzene can include different temperatures and/or pressures. In some instances, reaction temperature can be 250 °C to 700 °C, preferably 450 °C to 600 °C, more preferably 500 °C to 550 °C, or most preferably 510 °C to 535 °C. In some instances, reaction pressure can be 0.01 to 1.0 MPa. Liquid hourly space velocity (LHSV) is a measure of the ratio of liquid volume flow per hour to catalyst volume. LHSV is directly proportional to reaction temperature and inversely proportional to the reaction rate. In some instances, LHSV ratios can be 0.5 to 10 hr ¹, more preferably 1 to 8.6 hr ¹.

[0031] The processes of the present invention can be performed in a single reactor. Referring to FIG. 1 and FIG. 2, systems to prepare aromatic compounds are described. In system 100, hydrocarbon feed stream 102 of alkanes ( e.g ., iso-hexane and n-hexane) can be provided to reactor unit 106 containing catalyst system 110. Stream 108 can leave reactor 106 after contacting the aromatization or dual functional (aromatization + isomerization) catalyst in catalyst system 110. Stream 108 can include aromatic hydrocarbons. In some embodiments, Stream 108 can also include alkanes. All or a portion of stream 108 can re-enter the reactor to be contacted with the dual functional (aromatization + isomerization), aromatization catalyst, or a diluent material in catalyst system 110. All or a portion of stream 112 can leave reactor 106 and re-enter reactor 106 to contact aromatization and/or dual functional (aromatization + isomerization) catalyst in catalyst system 110. Stream 112 can include alkanes. In some embodiments, stream 112 can also include aromatic hydrocarbons. Stream 114 can exit reactor 106 as a product stream and can include aromatic hydrocarbons. In some instances, the branched alkane to linear alkane molar ratio can be 0:1 to 5:1, or 0:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1 0.9:1, 1:1, 2:1, 3:1, 4:1, or 5:1, or any value there between.

[0032] In some embodiments, hydrocarbon stream 102 can include a mixture of branched and linear paraffins. In some embodiments, the hydrocarbon stream 102 can include iC6 paraffins and/or nC6 paraffins. In some embodiments, reactor 106 can be a stacked bed reactor. In some embodiments, reactor 106 can be a tubular reactor. In some embodiments, reactor 106 can operate at 250 °C to 700 °C, preferably 450 °C to 600 °C, more preferably 500 °C to 550 °C, or most preferably 510 °C to 535 °C. In some instances, reactor 106 can operate from 0.01 to 1.0 MPa. In some instances, LHSV ratios can be 0.5 to 10 hr ¹, more preferably 1 to 8.6 hr ¹.

[0033] In some embodiments, catalyst system 110 includes at least two catalysts, loaded individually. In some embodiments catalyst 110 is at least two catalysts, loaded together. By way of example, catalyst system 110 can include Pt/Na-Ge-ZSM-5 (Type 1), Pt/NaCs-Ge- ZSM-5 (Type 2), Pt/Cs-Ge-ZSM-5 (Type 3), or any combination of the like. In some embodiments, catalyst system 110 includes a diluent material or a buffer between catalysts. In embodiments containing both Type 1 and Type 2 catalyst, the Type 1 catalyst is the aromatization catalyst because Type 1 has a higher aromatization activity and the Type 2 catalyst is the dual functional (aromatization + isomerization) catalyst because Type 2 has a higher relative isomerization activity. In some embodiments, the aromatization catalyst can be stacked such that it will be contacted before the dual functional (aromatization + isomerization) catalyst. In some embodiments, the dual functional (aromatization + isomerization) catalyst can be stacked such that it will be contacted before the aromatization catalyst. In some embodiments, stream 114 is stream 102 after contacting an aromatization catalyst and a dual functional (aromatization + isomerization) catalyst. In some instances, the branched alkane to linear alkane molar ratio is smaller in stream 112 than in stream 102. In some instances, the diluent material can be a silicon carbide layer, quartz, quartz wool, and/or the like.

[0034] The Type 2 catalyst can be prepared by an ion-exchange of cesium with sodium over the Cs-Ge/ZSM-5 zeolite (which has a Si: Ah ratio of approximately 110: 1), followed by platinum deposition. In some instances, the dual functional (aromatization + isomerization) catalyst can include a noble metal deposited on a zeolite. In some instances, the zeolite can include silicon, aluminum, and germanium in the framework. In some instances, a Column 1 and/or Column 2 metal may be used to tune acidity. In some instances, the Type 2 catalyst can be non-acidic and can have an aluminum content of less than or equal to 0.75 wt. % based on the total weight of the final catalyst, excluding any binder and/or extrusion aide. In some instances, the noble metal can be platinum. In some instances, the Column 1 metals can be sodium and cesium.

[0035] In some instances, the aromatization catalyst can include a noble metal deposited on a zeolite. In some instances, the zeolite can include silicon, aluminum, germanium, and a Column 1 or Column 2 metal in the framework. In some instances, the noble metal can be platinum. In some instances, the Column 1 metal can be sodium. In some instances, the Type 1 catalyst can be non-acidic and can have an aluminum content of less than or equal to 0.75 wt. % based on the total weight of the final catalyst, excluding any binder and/or extrusion aide. In some instances, the synthesis of the Type 1 catalyst can be performed by incorporating germanium with ZSM-5, which has Si: Ah ratios of greater than or equal to 125:1. Incorporating germanium with ZSM-5 can be achieved by forming a mixture including a germanium source, an alkali metal source, an aluminum source, and a silica source, adjusting the pH of the mixture to a value greater than or equal to 9.5, and then preparing the mixture so that it is crystallized and calcined to form a zeolite. In some instances, platinum can be deposited on the zeolite to form the final Type 1 catalyst.

[0036] In some embodiments, stream 108 can be heated or cooled before sending stream 108 back into reactor 106. In some embodiments, stream 108 can be collected, separated, sold, or sent to other units for further processing (not shown). In some embodiments, stream 112 can be heated or cooled before being sent back to reactor 106. In some embodiments, stream 112 can enter the reactor from another unit (not shown). Referring to FIG. 2, as shown in system 200, both streams 108 and 112 can be configured such that the streams do not exit and re-enter reactor 106. Feed stream 102 can enter reactor 106, where stream 102 can be contacted with catalyst system 110 containing at least one aromatization catalyst and at least one dual functional (aromatization + isomerization) catalyst. Stream 114 can exit the reactor, containing aromatic hydrocarbons ( e.g ., benzene).

[0037] In some embodiments, more than one reactor can be used. With reference to FIG. 3, two reactors are configured in a series arrangement. System 300 shows a hydrocarbon feed stream 302, including alkanes, entering reactor 306, which contains catalyst system 310. Stream 314 can exit reactor 306 after contacting the catalyst(s) in catalyst system 310. Stream 314 can include alkanes and/or aromatic hydrocarbons, and can enter reactor 318, which contains catalyst system 322. Stream 326 can exit reactor 318 after contacting the catalyst(s) in catalyst system 322. Stream 326 can include aromatic hydrocarbons and can optionally also include alkanes. In some embodiments, reactor 306 and/or reactor 318 can be stacked bed reactors. In some embodiments, reactor 306 and/or reactor 318 can operate at 250 °C to 700 °C, preferably 450 °C to 600 °C, more preferably 500 °C to 550 °C, or most preferably 510 °C to 535 °C. In some instances, reactor 306 and/or reactor 318 can operate from 0.01 to 1.0 MPa. In some instances, LHSV ratios can be 0.5 to 10 hr ¹, more preferably 1 to 8.6 hr ¹. [0038] In some embodiments, catalyst systems 310 and 322 can include Type 1, Type 2, Type 3, or any combination of the like. In some embodiments, catalyst systems 310 and/or 322 can include a diluent material and/or a buffer between catalysts. In some embodiments, stream 314 can be heated before entering reactor 318 ( e.g ., with a heated transfer line, heater, or the like). In some embodiments, stream 314 can be the second hydrocarbon stream leaving after contacting the aromatization catalyst and can also be the third hydrocarbon stream contacting the dual functional (aromatization + isomerization) catalyst. In some instances, the fourth hydrocarbon stream can be stream 326 and can have an aromatic hydrocarbon content greater than stream 314. In some embodiments, the first hydrocarbon stream can be stream 302, and stream 314 can have a higher branched alkane to linear alkane molar ratio than stream 302.

[0039] A system to produce aromatics has been discovered that is capable of increasing efficiency of the system and/or decreasing temperature and pressure demands compared to conventional methods. Embodiments of the invention include a system for producing aromatics by implementing systems 100, 200, or 300 from FIG. 1, FIG. 2, or FIG. 3, respectively, or from utilizing the process variations described above.

[0040] Although embodiments of the present invention have been described with reference to systems of FIG. 1, FIG. 2, and FIG. 3, it should be appreciated that operation of the present invention is not limited to the particular processes and/or the particular order of the processes illustrated in the figures. Accordingly, embodiments of the invention can provide functionality as described herein using various steps in a sequence different than that of the figures.

[0041] Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. EXAMPLES

[0042] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters, which can be changed or modified to yield essentially the same results.

Example 1

(Aromatization and Isomerization Activities)

[0043] Three catalysts, Pt/Na-Ge-ZSM-5 (Type 1), Pt/NaCs-Ge-ZSM-5 (Type 2), and Pt/Cs-Ge-ZSM-5 (Type 3) were screened under a pure nC6 feed, containing only hydrogen gas and n-hexane. The pure nC6 feed had a molar ratio of 0.75 Eh to 1 nC6. The catalysts were tested using ambient pressure at 515 °C. The liquid hourly space velocity (LHSV) ratio of liquid volume flow per hour to catalyst volume was 8.6 hr ¹. The conversion and selectivity were compared after 50 hours on stream. Table 1 shows data of aromatization and isomerization activities for the different catalysts under these conditions.

Table 1

(Comparison of Aromatization and Isomerization Activities of Different Catalysts)

[0044] The Type 1 catalyst exhibited higher aromatization activity compared to the Type 2 and Type 3 catalysts. The Type 2 catalyst exhibited significantly higher isomerization activity compared to Type 1 and Type 3.

Example 2

(Benzene Yield Comparison of a Single Stacked-Bed Reactor)

[0045] A mixed hexane feed including both iso-hexanes (iC6) and n-hexane (nC6) was sent to a reactor loaded with Pt/Na-Ge-ZSM-5 (Type 1) and Pt/NaCs-Ge-ZSM-5 (Type 2) catalyst. The Type 1 and Type 2 catalyst were loaded individually in a stacked-bed manner. The mixed hexane feed had molar ratios of 0.75 Eb to 1 C₆, 0.75 N2 to 1 C₆, and a range of 0 to 2 iC6 to 1 nC6. The catalysts were tested at 535 °C. The liquid hourly space velocity (LHSV) ratio of liquid volume flow per hour to catalyst volume was 2.0 hr ¹. Configuration of the catalysts was changed such that the catalysts were tested individually as Type 1 and Type 2 and stacked in a tubular stacked-bed reactor such that Type 1 was loaded at the top with Type 2 loaded at the bottom, and such that Type 2 was loaded at the top, with Type 1 loaded at the bottom. In the stacked-bed reactor, a diluent layer of silicon carbide separated Type 1 and Type 2 catalysts. FIGS. 4-5 show data and comparisons of aromatization and isomerization activities for the different catalysts under these conditions.

[0046] Benzene yield was the highest for the stacked-bed configuration where the catalyst was loaded such that Type 1 catalyst was loaded at the top and the Type 2 catalyst was loaded at the bottom.

Example 3

(Benzene Yield Comparison of Two Reactors in Series)

[0047] To test use of reactors in series, two tubular reactors were used in sequence. The first reactor was loaded with Type 1 catalyst and the second reactor was loaded with Type 2 catalyst. The product stream from the first reactor was sent to the second reactor in a heated transfer line. The mixed hexane feed had molar ratios of 0.75 Eh to 1 C₆, 0.75 N2 to 1 C₆, and a range of 0 to 2 iC6 to 1 nC6. The catalysts were tested at 535 °C. The liquid hourly space velocity (LHSV) ratio of liquid volume flow per hour to catalyst volume was 2.0 hr ¹. The results of the reactors in series were compared with test results of a stacked-bed reactor with Type 1 catalyst loaded in the top of the reactor and Type 2 loaded in the bottom of the reactor and results from a single reactor loaded with Pt/Cs-Ge-ZSM-5 (Type 3) catalyst at the same conditions as the reactors in series. Benzene yield between the streams leaving these reactions was measured, as shown in FIG. 5 below.

Claims

1. A process to produce aromatics, the process comprising:

(a) contacting a first hydrocarbon stream comprising alkanes with an aromatization catalyst to produce a second hydrocarbon stream comprising aromatic compounds; and

(b) contacting a third hydrocarbon stream comprising alkanes with a dual functional (aromatization + isomerization) catalyst to produce a fourth hydrocarbon stream comprising aromatic compounds, wherein the first and third streams comprise different branched alkane to linear alkane molar ratios (B:L alkane ratios).

2. The process of claim 1, wherein the first, second, third, and fourth hydrocarbon stream comprise linear and branched C6 alkanes.

3. The process of any one of claims 1 to 2, wherein the second hydrocarbon stream and the third hydrocarbon stream are the same stream, and the fourth stream has an aromatic hydrocarbons content greater than the second hydrocarbon stream.

4. The process of claim 3, wherein the B:L alkane ratio of the alkanes in the third hydrocarbon stream is greater than the B:L alkane ratio of the alkanes in the first hydrocarbon stream.

5. The process of any one of claims 1 to 2, wherein the contacting of step (a) and the contacting step (b) are performed in a stacked bed reactor or fixed-bed reactors in series configuration.

6. The process of claim 5, wherein the reactor or reactors have a temperature of 250 to 700 °C and/or a gauge pressure of 0.01 to 1.0 MPa.

7. The process of any one of claims 1 to 2, wherein the branched alkane to linear alkane molar ratio is 0:1 to 15:1.

8. The process of any one of claims 1 to 2, further comprising positioning a diluent layer between the aromatization catalyst and the dual functional (aromatization + isomerization) catalyst.

9. The process of any one of claims 1 to 2, wherein the B:L alkane ratio of the alkanes in the first hydrocarbon stream is 0 to 2.

10. The process of any one of claims 1 to 2, wherein the aromatization catalyst comprises a noble metal deposited on a zeolite, the zeolite comprising silicon (Si), aluminum (Al), and germanium (Ge) in the framework, and wherein the zeolite also comprises a Column 1 or 2 metal.

11. The process of claim 10, wherein the noble metal comprises Pt and the Column 1 metal comprises sodium (Na).

12. The process of any one of claims 1 to 2, wherein the isomerization catalyst comprises a noble metal deposited on a zeolite, the zeolite comprising Si, Al, Ge, at least two of a Column 1 and/or Column 2 metal in the framework, wherein the catalyst is non-acidic and has an Al content of 0.75 wt.% or less based on the total weight of the catalyst.

13. The process of claim 12, wherein the noble metal is Pt and the Column 1 metals are Na and cesium (Cs).

14. A system to produce aromatics using the process of any one of claims 1 to 13, the system comprising:

(a) a first reaction zone comprising a first alkane stream and an aromatization catalyst, the first reaction zone capable of producing a second hydrocarbon stream comprising aromatic compounds; and

(b) a second reaction zone comprising a third alkane stream and a dual functional (aromatization + isomerization) catalyst, the second reaction zone capable of producing a fourth hydrocarbon stream comprising aromatic compounds, wherein the first and third alkane streams comprise different branched alkane to linear alkane molar ratios (B:L alkane ratios).

15. The system of claim 14, wherein the first reaction zone is in fluid communication with the second reaction zone and the second reaction zone is capable of receiving the second hydrocarbon stream.

16. The system of claim 14, wherein the first reaction zone is in fluid communication with the second reaction zone and the first reaction zone is capable of receiving the fourth hydrocarbon stream.

17. The system of any one of claims 14 to 16, wherein the first and second reaction zones are stacked beds comprised in a single reactor.

18. The system of any one of claims 14 and 15, further comprising: an outlet coupled to the first reaction zone and the second reaction zone, wherein the outlet is capable of providing the second hydrocarbon stream to an inlet of the second reaction zone; and an outlet coupled to the second reaction zone capable of delivering the fourth hydrocarbon stream.

19. The system of any one of claims 14 to 16, wherein the aromatization catalyst is a Pt/Na- Ge-ZSM-5 catalyst and the dual functional (aromatization + isomerization) catalyst is a Pt/NaCs-Ge-ZSM catalyst. 20.

20. The system of claim 17, wherein the aromatization catalyst is a Pt/Na-Ge-ZSM-5 catalyst and the dual functional (aromatization + isomerization) catalyst is a Pt/NaCs- Ge-ZSM catalyst.