SYSTEMS, METHODS, AND DEVICES FOR METHANE CONVERSION VIA GAS RECYCLING
20220363612 · 2022-11-17
Inventors
Cpc classification
B01J10/00
PERFORMING OPERATIONS; TRANSPORTING
B01J29/48
PERFORMING OPERATIONS; TRANSPORTING
International classification
B01J10/00
PERFORMING OPERATIONS; TRANSPORTING
B01J19/00
PERFORMING OPERATIONS; TRANSPORTING
B01J19/18
PERFORMING OPERATIONS; TRANSPORTING
Abstract
In a first stage of a methane conversion system, at least some methane (CH.sub.4) in an input gas flow stream can be converted into C.sub.2 hydrocarbons, hydrogen gas (H.sub.2), and aromatics to provide a first processed stream. The conversion can be direct non-oxidative methane conversion (DNMC). At least some of the aromatics can be removed from the first processed stream to provide a second processed stream. In a second stage of the methane conversion system, at least some of the H.sub.2 can be removed from the second processed stream to provide a recycle stream. The recycle stream can be returned to the first stage of the methane conversion system for further conversion of methane and removal of aromatics and H.sub.2 products.
Claims
1. A methane conversion system comprising: a first membrane reactor comprising a first gas flow volume, a second gas flow volume, and a first membrane separating the first gas flow volume from the second gas flow volume, the first gas flow volume having a first catalyst therein; a first gas supply coupled to the second gas flow volume and constructed to provide a first sweep gas to the second gas flow volume, the first sweep gas comprising O.sub.2 or an oxygen-containing compound; an aromatics separation device connected to receive a first processed stream from the first gas flow volume; a second membrane reactor comprising a third gas flow volume, a fourth gas flow volume, and a second membrane separating the third gas flow volume from the fourth gas flow volume, the third gas flow volume having a second catalyst therein; a second gas supply coupled to the fourth gas flow volume and constructed to provide a second sweep gas to the fourth gas flow volume, the second sweep gas comprising O.sub.2 or an oxygen-containing compound; and a recycle line comprising one or more fluid conduits, the first gas flow volume of the first membrane reactor being connected to receive a recycle stream from the third gas flow volume of the second membrane reactor via the recycle line, wherein the first reactor is constructed to convert at least some CH.sub.4 in an input gas flow stream provided to the first gas flow volume of the first reactor, so as to provide a first processed stream and such that a quantity of CH.sub.4 in the first processed stream is less than that in the input gas flow stream, the first processed stream comprising CH.sub.4, C.sub.2 hydrocarbons, and aromatics, the C.sub.2 hydrocarbons are acetylene (C.sub.2H.sub.2), ethylene (C.sub.2H.sub.4), ethane (C.sub.2H.sub.6), or any combination of the foregoing, the aromatics are benzene (C.sub.6H.sub.6), toluene (C.sub.7H.sub.8), naphthalene (C.sub.10H.sub.8), or any combination of the foregoing, the first membrane is constructed such that at least some H.sub.2 is removed from the first gas flow volume by hydrogen ions permeating through the first membrane into the second gas flow volume and such that oxygen ions permeate through the first membrane from the second gas flow volume into the first gas flow volume so as to reduce coking of the first membrane, the first reactor is constructed for autothermal operation via an exothermic reaction between the permeated hydrogen in the second gas flow volume and the O.sub.2 or oxygen-containing compound in the second gas flow volume, the aromatics separation device is constructed to remove at least some aromatics from the received first processed stream, so as to provide a second processed stream comprising CH.sub.4 and C.sub.2 hydrocarbons, and to provide a first output stream comprising the removed at least some aromatics, a quantity of the aromatics in the second processed stream being less than in the first processed stream, the second reactor is constructed to convert at least some CH.sub.4 in the second processed stream provided to the third gas flow volume of the second reactor, so as to provide a recycle stream to the recycle line and such that a quantity of CH.sub.4 in the recycle stream is less than in the second processed stream, the second processed stream comprising C.sub.2 hydrocarbons and aromatics, the second membrane is constructed such that at least some H.sub.2 is removed from the third gas flow volume by hydrogen ions permeating through the second membrane into the fourth gas flow volume and such that oxygen ions permeate through the second membrane from the fourth gas flow volume into the third gas flow volume so as to reduce coking of the second membrane, and the second reactor is constructed for autothermal operation via an exothermic reaction between the permeated hydrogen in the fourth gas flow volume and the O.sub.2 or oxygen-containing compound in the fourth gas flow volume.
2. The methane conversion system of claim 1, wherein the first catalyst, the second catalyst, or both the first and second catalysts comprise Fe@SiO.sub.2.
3. The methane conversion system of claim 1, wherein the first membrane, the second membrane, or both the first and second membranes comprise a perovskite-type oxide having a formula of M′Ce.sub.1-x-yZr.sub.xM″.sub.yO.sub.3-δ, where: M′ is a least one of Sr and Ba; M″ is at least one of Ti, V, Cr, Mn, Fe, Co Ni, Cu, Nb, Mo, W, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb; x is between 0.01 and 0.2, inclusive; and y is between 0.01 and 0.3, inclusive.
4. A methane conversion system comprising: a first reactor having an inlet and an outlet; an aromatics separation device having an inlet, a first outlet, and a second outlet, the inlet of the separation device connected to receive a first processed stream from the outlet of the first reactor; a second reactor having a first gas flow volume, a second gas flow volume, and a membrane separating the first gas flow volume from the second gas flow volume, the first gas flow volume being connected to receive a second processed stream from the first outlet of the aromatics separation device; and a recycle line comprising one or more fluid conduits, the inlet of the first reactor being connected to receive a recycle stream from the first gas flow volume via the recycle line, wherein the first reactor is constructed to convert at least some CH.sub.4 in an input gas flow stream provided to the inlet of the first reactor, so as to provide to the outlet of the first reactor the first processed stream and such that a quantity of CH.sub.4 in the first processed stream is less than that in the input gas flow stream, the first processed stream comprising CH.sub.4, C.sub.2 hydrocarbons, H.sub.2, and aromatics, the C.sub.2 hydrocarbons are acetylene (CAL), ethylene (C.sub.2H.sub.4), ethane (C.sub.2H.sub.6), or any combination of the foregoing, the aromatics are benzene (C.sub.6H.sub.6), toluene (C.sub.7H.sub.8), naphthalene (C.sub.10H.sub.8), or any combination of the foregoing, the aromatics separation device is constructed to remove at least some aromatics from the first processed stream provided to the inlet of the aromatics separation device, so as to provide to the first outlet of the aromatics separation device a second processed stream comprising CH.sub.4, C.sub.2 hydrocarbons, and H.sub.2, and to provide to the second outlet of the aromatics separation device a first output stream comprising the removed at least some aromatics, a quantity of the aromatics in the second processed stream being less than in the first processed stream, and the second reactor is constructed to remove at least some H.sub.2 from the second processed stream, which is provided to the first gas flow volume, into the second gas flow volume via the membrane, so as to provide to the recycle line a recycle stream comprising CH.sub.4 and Ca hydrocarbons, a quantity of the H.sub.2 in the recycle stream being less than that in the second processed stream.
5. The methane conversion system of claim 4, further comprising: a gas supply coupled to an inlet of the second gas flow volume and constructed to flow a sweep gas through the second gas flow volume, the sweep gas supplied by the gas supply comprising O.sub.2 or an oxygen-containing compound, wherein the membrane is constructed such that the at least some H.sub.2 is removed by hydrogen ions permeating through the membrane from the first gas flow volume into the second gas flow volume and such that oxygen ions permeate through the membrane from the second gas flow volume into the first gas flow volume.
6. The methane conversion system of claim 5, wherein the second reactor is constructed for autothermal operation via an exothermic reaction between the permeated hydrogen in the second gas flow volume and the O.sub.2 or the oxygen-containing compound in the second gas flow volume to form water.
7. The methane conversion system of claim 4, further comprising a storage container in fluid communication with the second outlet of the aromatics separation device and constructed to store the removed at least some aromatics therein.
8. The methane conversion system of claim 4, wherein the first reactor comprises a catalyst of Fe@SiO.sub.2.
9. The methane conversion system of claim 4, wherein: the membrane comprises a perovskite-type oxide having a formula of M′Ce.sub.1-x-yZr.sub.xM″.sub.yO.sub.3-δ, where: M′ is a least one of Sr and Ba; M″ is at least one of Ti, V, Cr, Mn, Fe, Co Ni, Cu, Nb, Mo, W, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb; x is between 0.01 and 0.2, inclusive; and y is between 0.01 and 0.3, inclusive; and the membrane is provided on a porous support comprising a perovskite-type oxide having a formula of M′Ce.sub.1-zZr.sub.zO.sub.3-δ, where M′ is Sr or Ba, and z is between 0.01 and 0.3, inclusive.
10. The methane conversion system of claim 4, wherein the aromatics separation device comprises a condenser constructed to liquefy the at least some aromatics.
11. A method comprising: (a) converting, via a first reactor, at least some CH.sub.4 in an input gas flow stream into C.sub.2 hydrocarbons, H.sub.2, and aromatics, thereby providing a first processed stream comprising CH.sub.4, C.sub.2 hydrocarbons, H.sub.2, and aromatics, a quantity of CH.sub.4 in the first processed stream being less than that in the input gas flow stream, the C.sub.2 hydrocarbons being acetylene (CAL), ethylene (C.sub.2H.sub.4), ethane (C.sub.2H.sub.6), or any combination of the foregoing, the aromatics being benzene (C.sub.6H.sub.6), toluene (C.sub.7H.sub.8), naphthalene (C.sub.10H.sub.8), or any combination of the foregoing; (b) removing, via an aromatics separation device downstream of the first reactor, at least some aromatics from the first processed stream, thereby providing a first output stream comprising the removed at least some aromatics and a second processed stream comprising CH.sub.4, C.sub.2 hydrocarbons, and H.sub.2, a quantity of the aromatics in the second processed stream being less than that in the first processed stream; (c) removing, via a second reactor downstream of the aromatics separation device, at least some H.sub.2 from the second processed stream, thereby providing a recycle stream comprising CH.sub.4 and C.sub.2 hydrocarbons, a quantity of the H.sub.2 in the recycle stream being less than that in the second processed stream; and (d) providing the recycle stream as at least part of the input gas flow stream to the first reactor.
12. The method of claim 11, wherein a composition of the first output stream is at least 50% aromatics.
13. The method of claim 11, further comprising: repeating (a)-(d) at least two additional times, wherein after the repeating, at least 40% of an initial quantity of CH.sub.4 is converted.
14. The method of claim 11, wherein: the converting of (a) is performed at a temperature greater than a temperature at which the removing of (c) is performed.
15. The method of claim 11, wherein: the first reactor has a first gas flow volume, a second gas flow volume, and a first membrane separating the first gas flow volume from the second gas flow volume, and the converting of (a) comprises flowing a first sweep gas through the second gas flow volume as the input gas flow stream is flowed through the first gas flow volume, the first sweep gas comprising O.sub.2 or an oxygen-containing compound, such that hydrogen ions permeate through the first membrane from the first gas flow volume into the second gas flow volume and such that oxygen ions permeate through the first membrane from the second gas flow volume to the first gas flow volume; or the second reactor has a third gas flow volume, a fourth gas flow volume, and a second membrane separating the third gas flow volume from the fourth gas flow volume, and the removing of (c) comprises flowing a second sweep gas through the fourth gas flow volume as the second processed stream is flowed through the third gas flow volume, the second sweep gas comprising O.sub.2 or an oxygen-containing compound, such that the at least some H.sub.2 is removed by hydrogen ions permeating through the second membrane from the third gas flow volume into the fourth gas flow volume and such that oxygen ions permeate through the second membrane from the fourth gas flow volume into the third gas flow volume; or both of the above.
16. The method of claim 15, wherein: an exothermic reaction between the permeated hydrogen in the second gas flow volume and the O.sub.2 or the oxygen-containing compound in the second gas flow volume heats the first reactor, such that the converting of (a) is an autothermal operation; or an exothermic reaction between the permeated hydrogen in the fourth gas flow volume and the O.sub.2 or the oxygen-containing compound in the fourth gas flow volume heats the second reactor such that the removing of (c) is an autothermal operation; or both of the above.
17. The method of claim 11, wherein: the removing of (b) comprises condensing the at least some aromatics; and the method further comprises storing the condensed aromatics for use or transport.
18. The method of claim 11, wherein the first reactor or both the first and second reactors comprise a respective catalyst.
19. The method of claim 18, wherein the catalyst of the first reactor comprises Fe@SiO.sub.2.
20. The method of claim 11, wherein: the first reactor or the second reactor comprises a membrane separating first and second gas flow volumes; the membrane comprises a perovskite-type oxide having a formula of M′Ce.sub.1-x-yZr.sub.xM″.sub.yO.sub.3-δ, where: M′ is a least one of Sr and Ba; M″ is at least one of Ti, V, Cr, Mn, Fe, Co Ni, Cu, Nb, Mo, W, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb; x is between 0.01 and 0.2, inclusive; and y is between 0.01 and 0.3, inclusive; and the membrane is provided on a porous support comprising a perovskite-type oxide having a formula of M′Ce.sub.1-zZr.sub.zO.sub.3-δ, where M′ is Sr or Ba, and z is between 0.01 and 0.3, inclusive.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
[0017] Embodiments will hereinafter be described with reference to the accompanying drawings, which have not necessarily been drawn to scale. Where applicable, some elements may be simplified or otherwise not illustrated in order to assist in the illustration and description of underlying features. Throughout the figures, like reference numerals denote like elements.
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DETAILED DESCRIPTION
General Considerations
[0047] For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present, or problems be solved. The technologies from any embodiment or example can be combined with the technologies described in any one or more of the other embodiments or examples. In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are exemplary only and should not be taken as limiting the scope of the disclosed technology.
[0048] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one skilled in the art.
[0049] The disclosure of numerical ranges should be understood as referring to each discrete point within the range, inclusive of endpoints, unless otherwise noted. Unless otherwise indicated, all numbers expressing quantities of components, molecular weights, percentages, temperatures, times, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise implicitly or explicitly indicated, or unless the context is properly understood by a person skilled in the art to have a more definitive construction, the numerical parameters set forth are approximations that may depend on the desired properties sought and/or limits of detection under standard test conditions/methods, as known to those skilled in the art. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited. Whenever “substantially,” “approximately,” “about,” or similar language is explicitly used in combination with a specific value, variations up to and including 10% of that value are intended, unless explicitly stated otherwise.
[0050] Directions and other relative references may be used to facilitate discussion of the drawings and principles herein but are not intended to be limiting. For example, certain terms may be used such as “inner,” “outer,”, “upper,” “lower,” “top,” “bottom,” “interior,” “exterior,” “left,” right,” “front,” “back,” “rear,” and the like. Such terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. For example, with respect to an object, an “upper” part can become a “lower” part simply by turning the object over. Nevertheless, it is still the same part, and the object remains the same.
[0051] As used herein, “comprising” means “including,” and the singular forms “a” or “an” or “the” include plural references unless the context clearly dictates otherwise. The term “or” refers to a single element of stated alternative elements or a combination of two or more elements unless the context clearly indicates otherwise.
[0052] Although there are alternatives for various components, parameters, operating conditions, etc. set forth herein, that does not mean that those alternatives are necessarily equivalent and/or perform equally well. Nor does it mean that the alternatives are listed in a preferred order, unless stated otherwise. Unless stated otherwise, any of the groups defined below can be substituted or unsubstituted.
[0053] Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one skilled in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Features of the presently disclosed subject matter will be apparent from the following detailed description and the appended claims.
Overview of Terms
[0054] The following is provided to facilitate the description of various aspects of the disclosed subject matter and to guide those skilled in the art in the practice of the disclosed subject matter.
[0055] C.sub.2 hydrocarbons: Compounds formed by the conversion of methane (CH.sub.4) and including two carbons (C.sub.2) and at least two hydrogens (H.sub.2). In some embodiments, the C.sub.2 hydrocarbons can include acetylene (C.sub.2H.sub.2), ethylene (C.sub.2H.sub.4), ethane (C.sub.2H.sub.6), or combinations thereof. In some embodiments, the predominant C.sub.2 hydrocarbon formed by the conversion of methane is ethylene.
[0056] Aromatics: Hydrocarbons formed by the conversion of methane and larger/heavier than the C.sub.2 hydrocarbons. In some embodiments, the aromatics can include benzene (C.sub.6H.sub.6), toluene (C.sub.7H.sub.8), naphthalene (C.sub.10H.sub.8), or combinations thereof.
[0057] Fe@SiO.sub.2: A catalyst formed of iron (Fe) and silica (SiO.sub.2), where @ denotes confinement, and characterized by lattice-confined single iron sites embedded within a silica matrix.
[0058] Autothermal operation: Operation of the system where the heat used to drive one reaction (e.g., a direct non-oxidative methane conversion (DNMC)) or operation (e.g., hydrogen permeation) is provided by a simultaneous (or substantially simultaneous) exothermic reaction. In some embodiments, the exothermic reaction comprises combustion of hydrogen and oxygen to form water, where the hydrogen is provided by permeation of hydrogen ions through a membrane.
[0059] Oxygen-containing compound: A compound having at least one atom of oxygen and capable of releasing the oxygen to react with hydrogen (e.g., to form water). In some embodiments, the oxygen-containing compound can comprise CO.sub.2, H.sub.2O, alcohols (e.g., methanol, ethanol, isopropanol, etc.).
Introduction
[0060] Direct non-oxidative methane conversion (DNMC) can be used to convert methane (CH.sub.4) (e.g., in natural gas) into liquid aromatics, which may be easier to transport than CH.sub.4 gas. In conventional systems, DNMC is constrained by low CH.sub.4 conversion and thus low aromatics product yield due to thermodynamic limitations. In one or more embodiments of the disclosed subject matter, a gas-recycle system is provided with a first stage (e.g., a methane conversion reactor) and a separate second stage (e.g., a hydrogen (H.sub.2) membrane separator) to achieve high CH.sub.4 conversion (e.g., at least 40% after multiple cycles) and high aromatics yield (e.g., at least 50% after multiple cycles and/or with a product selectivity toward aromatics of at least 90%) by circumventing the thermodynamic limitations.
[0061] For example, in some embodiments, the methane conversion stage (e.g., first stage) can perform DNMC over a catalyst (e.g., Fe@SiO.sub.2) in a packed reactor to produce C.sub.2 products and aromatics, along with reaction product H.sub.2. In some embodiments, the produced aromatics can then be removed, for example, by passing the product stream through a condenser. In some embodiments, the produced H.sub.2 can also be removed, for example, by passing through an H.sub.2-permeable membrane separator (e.g., a second stage). The unreacted CH.sub.4, C.sub.2 hydrocarbons, residual aromatics (if any), and residual H.sub.2 (if any) in the product stream can then be sent back to the methane conversion stage via a recycle loop, for example, for the next round of DNMC reaction, aromatics removal, and H.sub.2 removal.
[0062] In some embodiments, system performance can be further improved by employing an autothermal reactor configuration for the first stage, the second stage, or both. When provided as part of the first stage, the DNMC reaction can be performed over a catalyst (e.g., Fe@SiO.sub.2) in a membrane reactor to produce C.sub.2 hydrocarbons, aromatics, and H.sub.2 gas in a products volume (e.g., a first gas flow volume). The membrane reactor can have an H.sub.2-permeable membrane that separates the products volume from a sweep gas volume (e.g., a second gas flow volume), and a sweep gas can be flowed through the sweep gas volume. In some embodiments, the sweep gas can comprise oxygen gas (O.sub.2) (e.g., air or a mixture of O.sub.2 and with one or more other gases, such as He gas) or an oxygen-containing compound. Within the sweep gas volume, the permeated H.sub.2 can react with the oxygen in the sweep gas to produce heat for the endothermic DNMC within the products volume (e.g., at least some of the heat required for the endothermic DNMC reaction, and preferably all of the heat required). In some embodiments, the membrane can allow for back diffusion of O.sub.2 (e.g., via permeation of oxygen ions) from the sweep gas volume to the products volume, thereby oxidizing carbon species therein into carbon monoxide (CO) and thus reducing carbon deposition in the membrane reactor.
[0063] When provided as part of the second stage, the H.sub.2 removal can be performed in a membrane reactor with an H.sub.2-permeable membrane that separate a processed flow volume (e.g., a first gas flow volume) from a sweep gas volume (e.g., a second gas flow volume). A sweep gas can be flowed through the sweep gas volume. In some embodiments, the sweep gas can comprise oxygen gas (O.sub.2) (e.g., air or a mixture of O.sub.2 and with one or more other gases, such as He gas) or an oxygen-containing compound. Within the sweep gas volume, the permeated H.sub.2 can react with the oxygen in the sweep gas to produce heat that maintains or raises a temperature of the membrane reactor (e.g., to support H.sub.2 permeation through the membrane).
[0064] In an exemplary embodiment, each of the first and second stages employs an integrated membrane reactor with respective catalyst, and by using a sweep gas comprising O.sub.2 or an oxygen-containing compound for each reactor. For each membrane reactor, the DNMC reaction can be performed over a catalyst (e.g., Fe@SiO.sub.2) in a membrane reactor to produce C.sub.2 hydrocarbons, aromatics, and H.sub.2 gas in a products volume (e.g., a first gas flow volume). The membrane reactor can have an H.sub.2-permeable membrane that separates the products volume from a sweep gas volume (e.g., a second gas flow volume). Within the sweep gas volume, the permeated H.sub.2 can react with the oxygen in the sweep gas to produce heat for the endothermic DNMC within the products volume (e.g., at least some of the heat required for the endothermic DNMC reaction, and preferably all of the heat required). In some embodiments, the membrane can allow for back diffusion of O.sub.2 (e.g., via permeation of oxygen ions) from the sweep gas volume to the products volume, thereby oxidizing carbon species therein into carbon monoxide (CO) and thus reducing carbon deposition in the membrane reactor. This can allow the reactors of the first and second stages to operate at a higher temperature (e.g., the same temperature for both stages) for greater hydrogen permeation and higher aromatic yield, while avoiding, or at least reducing, membrane coking.
Exemplary Methane Conversion System Configurations
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[0066] In the illustrated example, an initial methane feed 102 is provided via feed coupler 138 as an input gas flow stream 104 to the first membrane reactor 107 for conversion. For example, the first membrane reactor 107 can convert at least some methane in the input gas flow stream 104 to C.sub.2 hydrocarbons, hydrogen gas (H.sub.2), and aromatics. In addition, the first membrane reactor 107 can remove at least some of the produced H.sub.2 by transport across (e.g., permeation through) a membrane. The resulting first processed stream 113 can thus include at least C.sub.2 hydrocarbons and aromatics, as well as any unreacted methane and potentially hydrogen not removed through the membrane, where the quantity of methane in the first processed stream 113 is less than the initial quantity of methane in the input gas flow stream 104.
[0067] In some embodiments, the first membrane reactor 107 can be an H.sub.2-permeable membrane reactor, for example, according to the reactor configurations or constructions described in U.S. Pat. No. 10,525,407, issued Jan. 7, 2020, and entitled “Systems, Methods, and Devices for Direct Conversion of Methane,” which is incorporated by reference herein in its entirety. For example, the first membrane reactor 107 can comprise and/or define a first flow volume and a second flow volume, where the permeable membrane separates the first flow volume from the second flow volume. The first flow volume can receive the input gas flow stream 104, and the first processed stream 113 can be directed from an outlet (or outlet end) of the first flow volume.
[0068] A catalyst can be provided in the first flow volume of the first membrane reactor 107. In one or more embodiments, the catalyst can comprise metal elements doped (i.e., lattice doping) in the lattice of amorphous-molten-state materials made from Si bonded with one or two of elemental C, N or O, for example, SiO.sub.2. In lattice doping, the dopant metal elements exchange with the lattice elements in the doped materials such that the metal dopant elements are confined in the lattice of the doped materials. For example, the amount of dopant metal can be between 0.001 wt % and 10 wt % of the total weight of the catalyst. For example, the dopant metal elements can be one or more of Li, Na, K, Mg, Al, Ca, Sr, Ba, Y, La, Ti, Zr, Ce, Cr, Mo, W, Re, Fe, Co, Ni, Cu, Zn, Ge, In, Sn, Pb, Bi, Mn, such as Fe. For example, the catalyst can comprise Fe@SiO.sub.2, which has lattice-confined single iron sites embedded in the silica matrix. The Fe@SiO.sub.2 catalyst disclosed herein can be formed according to the fabrication method described in U.S. Pat. No. 10,525,407, incorporated by reference above. Although the discussion above is directed to the Fe@SiO.sub.2 catalyst, embodiments of the disclosed subject matter are not limited thereto. Rather, according to one or more contemplated embodiments, other catalysts may be used, such as but not limited to molybdenum/Zeolite Socony Mobil-5 (Mo/ZSM-5) or a noble metal.
[0069] The first reactor 107 can be provided in a first heating module 108, which heats and/or maintains the reactor 107 at a first temperature. The first heating module 108 can comprise a heater, a furnace, or both; however, alternative heating methodologies and configurations are also possible according to one or more contemplated embodiments. For example, instead of or in supplement to a heater of the first heating module 108, heat can be generated via an exothermic reaction between gas constituents in the first reactor 107, such as between a sweep gas and permeated hydrogen. In particular, a sweep gas comprising O.sub.2 or an oxygen-containing compound can be provided on a permeate-side of the membrane. The permeated hydrogen can react with the oxygen to generate heat for the methane conversion in the first reactor 107.
[0070] Moreover, oxygen ions can back-diffuse through the membrane (e.g., from the permeate-side into the product volume) to oxidize carbon species produced by the methane conversion (e.g., forming CO), thereby avoiding, or at least reducing, coking of the membrane. The resulting first processed stream 113 may thus further include CO. By avoiding coking, the first reactor 107 can operate at a higher temperature, thereby offering greater hydrogen permeation and higher aromatic yields (e.g., ≥1100 K, as suggested by
[0071] The first processed stream 113 can be directed to an aromatics separation device 114, which can be configured to remove at least some of the aromatics from the first processed stream 112. For example, the aromatics separation device 114 can comprise a condenser that condenses the aromatics in the first processed stream 113 while retaining the remaining components (e.g., CH.sub.4, C.sub.2 hydrocarbons, CO, and H.sub.2) in gaseous state to form a second processed stream 125. In some embodiments, the aromatics separation device 114 can include other components for pre-processing, such as a heat exchanger, chiller, etc., and/or other components for post-processing of removed aromatics, such as a distillation system, etc. The aromatics separation device 114 can be other than a condenser and/or employ separation techniques other than selective condensation according to one or more contemplated embodiments. In the illustrated example, the liquid aromatics can then be collected as a first output stream 118 for storage, transport, or use by module 120. For example, module 120 can comprise a storage container or a conduit for conveying liquid aromatics to a storage or for subsequent use. Alternatively, in some embodiments, module 120 can be omitted in favor of on-site use of the liquid aromatics.
[0072] The second processed stream 125 from the aromatics separation device 114 can include at least C.sub.2 hydrocarbons, and as well as any unreacted methane and potentially hydrogen not removed by the first reactor 107 and/or aromatics not removed by the separation device 114, where the quantity of aromatics in the second processed stream 125 is less than the initial quantity of aromatics in the first processed stream 112. In the illustrated example, the second processed stream 125 is directed to the second reactor 127 for further methane conversion. For example, the second membrane reactor 127 can convert at least some methane in the second processed stream 125 to C.sub.2 hydrocarbons, H.sub.2, and aromatics. In addition, the second membrane reactor 127 can remove at least some of the produced H.sub.2 by transport across (e.g., permeation through) a membrane. The resulting recycle stream 133 can thus include at least C.sub.2 hydrocarbons and aromatics, as well as any unreacted methane and potentially hydrogen not removed through the membrane and/or CO, where the quantity of methane in the recycle stream 133 is less than the initial quantity of methane in the second processed stream 125.
[0073] In some embodiments, the second membrane reactor 127 can be an H.sub.2-permeable membrane reactor, for example, according to the reactor configurations or constructions described in U.S. Pat. No. 10,525,407, incorporated by reference above. For example, the second membrane reactor 127 can comprise and/or define a third flow volume and a fourth flow volume, where the permeable membrane separates the third flow volume from the fourth flow volume. The third flow volume can receive the second processed stream 125, and the recycle stream 133 can be directed from an outlet (or outlet end) of the third flow volume. A catalyst can be provided in the third flow volume of the second membrane reactor 127. For example, the catalyst can be the same or different than the catalyst of the first membrane reactor 107.
[0074] The second reactor 127 can be provided in a second heating module 128, which heats and/or maintains the reactor 127 at a second temperature. The second heating module 128 can comprise a heater, a furnace, or both; however, alternative heating methodologies and configurations are also possible according to one or more contemplated embodiments. For example, instead of or in supplement to a heater of the second heating module 128, heat can be generated via an exothermic reaction between gas constituents in the second reactor 127, such as between a sweep gas and permeated hydrogen. In particular, a sweep gas comprising O.sub.2 or an oxygen-containing compound can be provided on a permeate-side of the membrane. The permeated hydrogen can react with the oxygen to generate heat for the further methane conversion in the second reactor 127.
[0075] Moreover, oxygen ions can back-diffuse through the membrane (e.g., from the permeate-side into the product volume) to oxidize carbon species produced by the methane conversion (e.g., forming CO), thereby avoiding, or at least reducing, coking of the membrane. The resulting recycle stream 133 may thus further include CO. By avoiding coking, the second reactor 127 can operate at a higher temperature (e.g., a same temperature as the first reactor 107), thereby offering greater hydrogen permeation and higher aromatic yields (e.g., ≥1100 K, as suggested by
[0076] As noted above, the sweep gas for the first reactor 107 or the second reactor 127 can comprise O.sub.2 (e.g., air, O.sub.2 gas alone, or O.sub.2 gas combined with one or more other gases) and/or an oxygen-containing compound (e.g., CO.sub.2, H.sub.2O, and/or alcohol), for example, to combust with permeated H.sub.2 to provide heat supporting the methane conversion in the respective reactor. In the illustrated example, the sweep gas is provided to the second flow volume of the first reactor 107 via a sweep gas inlet feed 121, and a second outlet stream 133 can be directed from an outlet (or outlet end) of the second flow volume of the first reactor. In addition, the sweep gas is provided to the fourth flow volume of the second reactor 127 via a sweep gas inlet feed 122, and a third outlet stream 134 can be directed from an outlet (or outlet end of the fourth flow volume of the second reactor. The second outlet stream 133 and the third outlet stream 134 can each contain water, for example, resulting from the combustion between oxygen in the sweep gas and the permeated H.sub.2. In some embodiments, the second and third outlet streams 133, 134 can be subjected to further processing (e.g., isolation of the H.sub.2 and/or water from the sweep gas), storage, and/or use.
[0077] In the illustrated example, the recycle stream 133 can be returned to the inlet of the system 100 via recycle line 136, for re-processing in a next cycle, which can further convert additional methane that was unreacted in the previous cycle. For example, the recycle line 136 can connect between an outlet of the second reactor 127 and a feed coupler 138. In some embodiments, the feed coupler 138 can combine the recycle stream 133 from the recycle line 136 with fresh methane from feed 102 for processing as input gas flow stream 104. Alternatively or additionally, in some embodiments, the feed coupler 138 can select between the recycle stream 133 from the recycle line 136 and the methane feed 102 for use as the input gas flow stream 104. For example, the recycle stream 133 can be used as the input gas flow stream 104 for repeated cycles (e.g., 3-10 passes through the first stage 111, aromatics separation device 114, and the second stage 131) until a majority (e.g., — 50%), most (e.g., —70%), or substantially all (e.g., —90% or more) of an initial methane batch has been converted, after which the feed coupler 138 can be switched to provide a new batch of methane from methane feed 102.
[0078] System 100 can further include a controller 140 operatively coupled to one, some, or all of the illustrated components and configured to control operation thereof. For example, the controller 140 can modify flow rates, feed gas composition, sweep gas composition, and/or temperature to regulate methane conversion efficiency and/or product selectivity. Gas flow lines within system 100 can include respective gas flow control and sensing module, which may include, for example, valves, temperature sensors, temperature controllers, pumps, mass flow controllers, and/or other devices to monitor and/or control the variables of gas flow rates, reaction temperatures, and/or feed and sweep gas compositions to optimize or otherwise control methane conversion product formation, as described herein. In some embodiments, the controller 140 can also control operation of components not illustrated, such as pumps, valves, switches, etc., to effect flow of fluid (e.g., liquid or gas mixtures) through the system.
[0079] Alternatively, in some embodiments, methane conversion and hydrogen separation can be provided in separate stages rather than performed within the same reactor. For example,
[0080] The first reactor 106 can convert at least some methane in the input gas flow stream 104 to C.sub.2 hydrocarbons, hydrogen gas (H.sub.2), and aromatics. The resulting first processed stream 112 can thus include at least C.sub.2 hydrocarbons, H.sub.2, and aromatics, as well as any unreacted methane, where the quantity of methane in the first processed stream 112 is less than the initial quantity of methane in the input gas flow stream 104. The first processed stream 112 can be directed to an aromatics separation device 114, which can be configured to remove at least some of the aromatics from the first processed stream 112. For example, the aromatics separation device 114 can comprise a condenser that condenses the aromatics in the first processed stream 112 while retaining the remaining components (e.g., CH.sub.4, C.sub.2 hydrocarbons, and H.sub.2) in gaseous state to form a second processed stream 124.
[0081] The second processed stream 124 from the aromatics separation device 114 can include at least C.sub.2 hydrocarbons and H.sub.2, and as well as any unreacted methane and potentially aromatics not removed by the separation device 114, where the quantity of aromatics in the second processed stream 124 is less than the initial quantity of aromatics in the first processed stream 112. In the illustrated example of
[0082] By decoupling the methane conversion reaction from the hydrogen removal, the processes can be separately optimized, for example, to operate at respective temperatures that increase process efficiency (e.g., enhancing CH.sub.4 conversion and/or aromatics yield) and/or maintain system operability (e.g., by avoiding coke formation). Depending on the catalyst employed in the first reactor 106, the first reactor 106 can operate at a different temperature (e.g., higher when using Fe@SiO.sub.2 or lower when using Mo/ZSM-5) than the second reactor 126. For example, the first temperature can be at least 1000 K (e.g., ≥1200 K) for Fe@SiO.sub.2 catalyst, and the second temperature can be less than or equal to 1100 K (e.g., ≤800 K).
[0083] Although only two stages are illustrated in
[0084] In some embodiments, the intermediate reactor 156 can function similar to the first reactor 107, for example, to provide an additional stage of methane conversion and hydrogen separation. Alternatively, in some embodiments, the intermediate reactor 156 can function similar to the second reactor 127, for example, to provide an additional stage of methane conversion and hydrogen separation or similar to second reactor 126, for example, to provide an additional stage of hydrogen separation without associated methane conversion. The intermediate reactor 156 can be provided in a third heating module 158, which heats and/or maintains the reactor 156 at a third temperature. Depending on system operation, the third temperature may be the same as the first temperature (e.g., when providing additional DNMC) or different than the first temperature (e.g., to provide improved hydrogen separation at higher temperatures). For example, the intermediate reactor 156 can have a membrane that separates a product flow volume from a sweep gas flow volume. The second processed stream 124 can be provided to the product flow volume of the intermediate reactor 156 and can exit therefrom as intermediate processed stream 162. A sweep gas inlet feed 152 (e.g., similar to sweep gas inlet feed 122) can be provided to the sweep gas flow volume of the intermediate reactor 156 and can exit therefrom as outlet stream 154 (e.g., similar to outlet stream 134).
[0085] In the illustrated example, the intermediate processed stream 162 is directed to a second aromatics separation device 164 (e.g., similar to aromatics separation device 114), which can be configured to remove at least some of the aromatics from the intermediate processed stream 162. For example, the aromatics separation device 164 can comprise a condenser that condenses the aromatics in the intermediate processed stream 162 while retaining the remaining components (e.g., CH.sub.4, C.sub.2 hydrocarbons, and H.sub.2) in gaseous state to form further processed stream 174, which can then be directed to the second reactor 126. In the illustrated example, the liquid aromatics can then be collected as a second output stream 168 (e.g., similar to output stream 118) for storage, transport, or use by module 170 (e.g., similar to module 120). Although shown separately in
[0086] Although
[0087] In some embodiments, the first reactors 184, 186 can have similar structures and/or operate similarly to each other, for example, each similar to reactor 107 of
[0088] In some embodiments, the second reactors 194, 196 can have similar structures and/or operate similarly to each other, for example, each similar to reactor 127 of
[0089] Each second reactor 194, 196 can be provided in a respective heating module 198a, 198b (e.g., similar to heating module 128), which heat and/or maintain the respective reactor at a respective temperature. In some embodiments, the second reactors 194, 196 can operate at a same temperature (e.g., less than 1000 K). Alternatively, in some embodiments, the reactors 194, 196 can operate at different temperatures. Although shown separately in
Exemplary Reactor Configurations
[0090]
[0091] In another example,
[0092] Feed gas can be provided to the first gas volume 280 via an inlet tube 272 disposed within the porous support tube 274. Inlet tube 272 can convey the input gas flow stream 204 to the first gas volume 280 and into contact with catalyst 296 (e.g., Fe@SiO.sub.2). As illustrated in
[0093] The reactor 290 can have a second gas volume 282 formed by the annular space between the porous support tube 274 and an outer enclosure 276, e.g., a quartz tube. Sweep gas 292 can be provided to the second gas volume 282 and exits therefrom as outlet stream 294. In some embodiments, the sweep gas 292 can comprise an inert gas (e.g., N.sub.2 or He). Alternatively, in some embodiments, the sweep gas 292 can comprise Oz gas or an oxygen containing compound. For example, the CH.sub.4 can be converted to C.sub.2+ products via the DNMC reaction in the reactor 290 following the equation CH.sub.4.fwdarw.3/52 C.sub.6H.sub.6+5/104 C.sub.10H.sub.8+7/104 C.sub.2H.sub.4+2/104 C.sub.2H.sub.2+19/13 H.sub.2 (ΔH>0). Meanwhile, outside of the tube 274, the O.sub.2 in the sweep gas can react with H.sub.2 permeate (e.g., H.sub.2+½O.sub.2.fwdarw.H.sub.2O, ΔH<0) to produce heat for the endothermic DNMC within the reactor tube. The energy balance between endothermic DNMC and exothermic H.sub.2 combustion reactions on opposite sides of the membrane (e.g., supported on tube 274) can be achieved, thereby providing autothermal operation of DNMC. In some embodiments, back diffusion of O.sub.2 from the sweep side (e.g., volume 282) to the DNMC side (e.g., volume 280) can oxidize carbon species into CO, thereby alleviating carbon deposition in the reactor 290 and avoiding coke formation.
[0094] Returning to
[0095] Returning to
[0096] In some embodiments of the reactor 240 of
[0097] Returning to
[0098] Although
Methane Conversion Method
[0099]
[0100] The method 300 can proceed to decision block 304, where it is determined if hydrogen should be removed prior to aromatics separation. If it is desired to remove hydrogen, the method 300 can proceed from decision block 304 to process block 306, where a first sweep gas can be flowed on a first side (e.g., within a second gas flow volume) of a first membrane (e.g., of the first reactor) opposite to the input gas flow stream and/or the first processed stream (e.g., within a first gas flow volume). In some embodiments, the first sweep gas can comprise O.sub.2 or an oxygen-containing compound. The method 300 can proceed to process block 308, where at least some of the H.sub.2 produced by the methane conversion is transported (e.g., via permeation of hydrogen ions) across the first membrane (e.g., from the first gas flow volume to the second gas flow volume). The method 300 can then proceed to process block 310, where the transported H.sub.2 (e.g., in the second gas flow volume) reacts with the first sweep gas, for example, to combust the permeated hydrogen with oxygen in the sweep gas to form water and to generate heat that can drive, at least in part, the methane conversion of process block 302.
[0101] After process block 310, or if it was not desired to remove hydrogen at decision block 304, the method 300 can proceed to process block 312, where at least some aromatics can be removed from the first processed stream. For example, aromatics can be removed from (e.g., separated from) the first processed stream via condensing the aromatics into a liquid while other components of the first processed stream remain in gas form. In some embodiments, the aromatics removal can be performed by or within one or more aromatics separation devices, such as any of device 114, device 164, condenser 210, heat exchanger 414, chiller 418, and condenser 422. In some embodiments, the removal of process block 312 can produce a second processed stream comprising the C.sub.2 hydrocarbons, any unreacted methane, and any aromatics and/or H.sub.2 not previously removed.
[0102] The method 300 can proceed to optional process block 314, where the removed aromatics (e.g., in liquid form) can be stored, transported, and/or used. For example, the liquid aromatics can be stored in a container that is releasably coupled or fixedly coupled to an aromatics separation device. The method 300 can proceed to process block 316, where a second sweep gas can be flowed on a first side (e.g., within a second gas flow volume) of a second membrane (e.g., of a second reactor) opposite to the second processed stream and/or a resulting product stream (e.g., within a first gas flow volume. In some embodiments, the second sweep gas can comprise an inert gas. Alternatively or additionally, in some embodiments, the second sweep gas can comprise O.sub.2 or an oxygen-containing compound.
[0103] The method 300 can proceed to process block 318, where at least some of the H.sub.2 in the second processed stream is removed. For example, the H.sub.2 removal can comprise permeation of hydrogen ions through the second membrane (e.g., from the first gas flow volume to the second gas flow volume). In some embodiments, the H.sub.2 removal can be performed by or within one or more second reactors, such as any of reactor 126, reactor 194, reactor 196, separator 216, reactor 240, reactor 250, and separator 430. The H.sub.2 removal can occur at a second temperature, for example, less than 1000 K (e.g., ≤800 K). In some embodiments, the removal of process block 318 can produce a product stream comprising the C.sub.2 hydrocarbons, any unreacted methane, and potentially any H.sub.2 and aromatics not previously removed.
[0104] Proceeding to decision block 320, if the second sweep gas comprises O.sub.2 or an oxygen-containing compound, the method 300 can proceed to process block 322, where the removed H.sub.2 (e.g., in the second gas flow volume) reacts with the second sweep gas, for example, to combust the permeated hydrogen with oxygen in the second sweep gas to form water and to generate heat that can drive, at least in part, the hydrogen permeation of process block 318 and/or the further conversion of methane by the second reactor. After process block 322, or if the sweep gas did not comprise O.sub.2 or an oxygen-containing compound at decision block 320, the method 300 can proceed to decision block 324.
[0105] At decision block 324, it is determined whether the product stream resulting from process block 318 should be re-processed, for example, to increase methane conversion and/or aromatic yield by subjecting the product stream to another cycle of conversion, aromatic separation, and H.sub.2 removal. If re-processing is desired, the method 300 can proceed from decision block 324 to process block 326, where the product stream is redirected to be used as the input gas flow stream to the first reactor (or combined with additional methane for use as the input gas flow stream). The method 300 can then return to process block 302. Otherwise, if re-processing is not desired (e.g., if all of the methane has been converted or further methane conversion is not possible), the method 300 can proceed from decision block 324 to terminal 328, where the method can end.
[0106] Although illustrated separately, it is contemplated that various process blocks may occur simultaneously or iteratively. For example, the methane conversion 302, H.sub.2 transport 308 or 318, sweep gas flow 306 or 316, aromatics removal 312, and H.sub.2 reaction 310 or 322 can occur simultaneously despite being illustrated as sequential process blocks. Furthermore, certain process blocks illustrated as occurring after others may indeed occur before. For example, a sweep gas flow 306 or 316 may be initiated before any initiation of methane conversion 302. Although some of blocks 302-328 of method 300 have been described as being performed once, in some embodiments, multiple repetitions of a particular process block may be employed before proceeding to the next decision block or process block. In addition, although blocks 302-328 of method 300 have been separately illustrated and described, in some embodiments, process blocks may be combined and performed together (simultaneously or sequentially). Moreover, although
Methane Conversion System
[0107]
[0108] The first processed stream 412 can be passed through second heat exchanger 414 (e.g., cross-flow heat exchanger) to cool the first stream 412. In the illustrated example, the cooling of the first processed stream 412 serves to preheat the second processed stream 426 prior to introduction to the H.sub.2 separator 430, thereby providing heat recovery. The resulting cooled stream 416 is directed to chiller 418, which serves to further reduce the temperature of the stream in preparation for aromatics separation. The further cooled stream 420 is then directed to condenser 422, which condenses at least some of the aromatics out of the stream, thereby forming a first output stream 424 of liquid aromatics and a second processed stream 426 of unreacted methane, H.sub.2, and C.sub.2 hydrocarbons (and any aromatics not removed by condenser 422). In some embodiments, the heat exchanger 414, chiller 418, and/or condenser 422 may be considered components of an aromatics separation device or module.
[0109] As noted above, the second processed stream 426 is passed through the second heat exchanger 414 for preheating by heat recovery from the first processed stream 412. The resulting preheated stream 428 is directed to H.sub.2 separator 430, where at least some H.sub.2 in the preheated stream 428 can be removed from the stream, for example, via permeation of hydrogen through a membrane, thereby forming a second output stream 434 of pure hydrogen (e.g., permeated H.sub.2 product) and a product stream 432 of unreacted methane and C.sub.2 hydrocarbons (and any aromatics and/or H.sub.2 not previously removed). The product stream 432 can be directed for re-processing by the system 400 (e.g., in another cycle) via valve 436 and recycle line 442. Alternatively, if re-processing is not desired (e.g., if all methane has been converted and/or further methane conversion is not possible), then the valve 436 can redirect the product stream 432 to vent 438, for example, for release to atmosphere or directed for storage, use, or disposal.
[0110] System 400 can include additional components beyond those specifically illustrated in
Computer Implementation
[0111]
[0112] With reference to
[0113] A computing system may have additional features. For example, the computing environment 231 includes storage 261, one or more input devices 271, one or more output devices 281, and one or more communication connections 291. An interconnection mechanism (not shown) such as a bus, controller, or network interconnects the components of the computing environment 231. Typically, operating system software (not shown) provides an operating environment for other software executing in the computing environment 231, and coordinates activities of the components of the computing environment 231.
[0114] The tangible storage 261 may be removable or non-removable, and includes magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium which can be used to store information in a non-transitory way, and which can be accessed within the computing environment 231. The storage 261 can store instructions for the software 233 implementing one or more innovations described herein.
[0115] The input device(s) 271 may be a touch input device such as a keyboard, mouse, pen, or trackball, a voice input device, a scanning device, or another device that provides input to the computing environment 231. The output device(s) 271 may be a display, printer, speaker, CD-writer, or another device that provides output from computing environment 231.
[0116] The communication connection(s) 291 enable communication over a communication medium to another computing entity. The communication medium conveys information such as computer-executable instructions, audio or video input or output, or other data in a modulated data signal. A modulated data signal is a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media can use an electrical, optical, radio-frequency (RF), or another carrier.
[0117] Any of the disclosed methods can be implemented as computer-executable instructions stored on one or more computer-readable storage media (e.g., one or more optical media discs, volatile memory components (such as DRAM or SRAM), or non-volatile memory components (such as flash memory or hard drives)) and executed on a computer (e.g., any commercially available computer, including smart phones or other mobile devices that include computing hardware). The term computer-readable storage media does not include communication connections, such as signals and carrier waves. Any of the computer-executable instructions for implementing the disclosed techniques as well as any data created and used during implementation of the disclosed embodiments can be stored on one or more computer-readable storage media. The computer-executable instructions can be part of, for example, a dedicated software application or a software application that is accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software can be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a network environment (e.g., via the Internet, a wide-area network, a local-area network, a client-server network (such as a cloud computing network), or any other such network) using one or more network computers.
[0118] For clarity, only certain selected aspects of the software-based implementations are described. Other details that are well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any specific computer language or program. For instance, aspects of the disclosed technology can be implemented by software written in C++, Java™, Python®, or any other suitable computer language. Likewise, the disclosed technology is not limited to any particular computer or type of hardware. Certain details of suitable computers and hardware are well known and need not be set forth in detail in this disclosure.
[0119] It should also be well understood that any functionality described herein can be performed, at least in part, by one or more hardware logic components, instead of software. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-programmable Gate Arrays (FPGAs), Program-specific Integrated Circuits (ASICs), Program-specific Standard Products (ASSPs), System-on-a-chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.
[0120] Furthermore, any of the software-based embodiments (comprising, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed through a suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, an intranet, software applications, cable (including fiber optic cable), magnetic communications, electromagnetic communications (including RF, microwave, and infrared communications), electronic communications, or other such communication means. In any of the above-described examples and embodiments, provision of a request (e.g., data request), indication (e.g., data signal), instruction (e.g., control signal), or any other communication between systems, components, devices, etc. can be by generation and transmission of an appropriate electrical signal by wired or wireless connections.
Fabricated Examples and Experimental Results
Gas Recycle System
[0121] To test performance of the gas-recycle system (e.g., having a setup similar to that shown in
[0122] The H.sub.2 separator was an H.sub.2-permeable perovskite ceramic membrane tube (e.g., in a configuration similar to reactor 240 shown in
[0123] The composition of simulated feed for the DNMC reactor was determined from the stream in the previous cycle after passing through the aromatics liquid condenser and H.sub.2 membrane separator. The composition of feed for the H.sub.2 separator was set the same as the product effluent from the DNMC reactor in the same cycle, except that all the aromatics were condensed and separated from the effluent. Finally, the DNMC reactor and H.sub.2 membrane separator together with an aromatics liquid condenser were simulated by Aspen Plus® to analyze the system feasibility for CH.sub.4 upgrading via the DNMC process.
[0124] To understand the membrane H.sub.2 removal capability from the gas recycle, the H.sub.2 permeation fluxes at different temperatures and H.sub.2 partial pressures were determined for a feed flow rate of 20 ml/min (H.sub.2 concentration varied, balanced by Ar) and a sweep side flow rate of 20 ml/min (5% N.sub.2 balanced by He).
[0125] The H.sub.2 removal efficiency does not depend on the H.sub.2 concentration in the feed, but it does depend on the temperature. When the temperature was increased from 873 K to 1173 K, the H.sub.2 removal efficiency was increased from 2.67% to 18.60%, equivalent to ˜7 times higher enhancement in H.sub.2 removal efficiency at the same H.sub.2 feed condition. Therefore, in some cases, high temperature can be used to remove H.sub.2 more efficiently from the H.sub.2-permeable SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3δ membrane separator. The SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3δ membrane tube had an inner diameter of 7 mm and a length of 15 cm; however, only 20% (˜3 cm) of the membrane tube length was kept at the test temperature due to the thermal gradient of the tubular furnace that supplied heat to the membrane. Thus, the H.sub.2-permeation flux could be significantly higher compared to the present H.sub.2 flux data of
[0126] In the gas recycle system, the H.sub.2 removal stage takes place after the DNMC reaction in the DNMC reactor. The feed to the H.sub.2 separator thus contains both H.sub.2 and hydrocarbons (e.g., unreacted CH.sub.4 and C.sub.2 products), which feed is slightly different from the feed conditions examined to produce
[0127] It should be noted that the H.sub.2 flux in
[0128] To examine the performance of the CH.sub.4 reaction in the gas recycle system, the feed and exit effluent compositions of the DNMC reactor were measured, which compositions can change depending on the recycle number of the process. Therefore, the gas compositions and gas flow rates in each cycle were measured before the overall performance of the gas recycle system was analyzed. In DNMC, the gas feed was started (i.e., in the first cycle) with 90% CH.sub.4 mixed with 10% Ar internal standard at a flow rate of 20 mL/min, as shown in
[0129] Since ethylene (C.sub.2H.sub.4) is the predominant C.sub.2 product, as shown in
[0130] Although the single H.sub.2 separator tube in the experiments exhibited only 10% H.sub.2 removal efficiency, further enhancement in H.sub.2 removal efficiency can be achieved, for example, as described elsewhere herein. To test how H.sub.2 removal efficiency affects the performance of the DNMC reactor in the gas recycle system, the composition and flow rate of CH.sub.4/C.sub.2H.sub.4/H.sub.2 feed mixture in each cycle was analyzed by assuming the H.sub.2 separator reaches 40%, 70%, and 100% H.sub.2 removal efficiency, respectively. As shown in
[0131] The feed stream with the same composition and flow rate as determined above for the DNMC reactor in Section 3.2.1 was tested over the Fe@SiO.sub.2 catalyst in the DNMC reactor.
[0132] Based on the feed flow rate and composition analysis of
[0133] Based on the above-described separate performance evaluations of the DNMC reactor and the H.sub.2 membrane separator, the overall performance of the gas recycle system (integrating the DNMC reactor and H.sub.2 membrane separator) can be evaluated to understand the overall CH.sub.4 conversion, product selectivity, and yields. In particular,
[0134]
Autothermal Membrane Reactor Operation
[0135] To test performance of an autothermal reactor (e.g., having a setup similar to heat-exchange reactor 290 in
[0136]
[0137]
[0138] The formation of CO in the DNMC reaction in the heat-exchange H.sub.2-permeable membrane reactor can be attributed to the fact that the MIEC SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3δ membrane material can co-permeate both H.sub.2 and O.sub.2 gases (e.g., via respective ions thereof). In particular, the back diffusion of O.sub.2 from the O.sub.2/He sweep gas across the membrane into the DNMC reaction volume can oxidize any carbon deposition resulting from the DNMC reaction into CO, and thereby eliminate, or at least reduce, coke formation. Concurrently, when O.sub.2 is used in the sweep gas, the ambipolar conductivity of the SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3-δ membrane may decrease, which can lead to a decrease in the rate of H.sub.2 permeation, and therefore lower CH.sub.4 conversion. On the other hand, when permeated H.sub.2 is readily combusted by O.sub.2 in the sweep gas, there is an increase in the H.sub.2 partial pressure difference across both sides of the membrane, which can lead to an increase in H.sub.2 permeation, and therefore higher CH.sub.4 conversion. As shown in
[0139] The effects of reaction temperature on methane conversion, product yield and selectivity, H.sub.2 production and permeation, as well as heat requirement for DNMC and heat release from combustion of H.sub.2 permeate were studied, and the results are summarized in
[0140]
[0141] From the oxygen balance in the membrane reactor, the O.sub.2 conversions were found to be 7.7%, 9.3% and 10.6% at the reaction temperatures of 1253 K, 1273 K, and 1303 K, in sequence. Thus, the O.sub.2 residue in the sweep gas decreases with increasing reaction temperature. As noted above, the back diffusion of O.sub.2 from the O.sub.2/He sweep gas (through the MIEC membrane into the DNMC reaction volume) was responsible for CO formation. According to the Wagner Equation, the O.sub.2 permeation should increase with temperature, but a decrease in O.sub.2 concentration on the sweep side of the membrane can lead to lower O.sub.2 permeation. The interaction between these two opposing effects can offset each other, such that the CO yield at different reaction temperatures remains about the same, as shown in
[0142] As shown in
[0143] To study tunability of autothermality of DNMC in the heat-exchange H.sub.2-permeable membrane reactor, the effects of O.sub.2 sweep gas flow rates on the DNMC reaction and heat generation/consumption in both DNMC and H.sub.2 combustion reactions were measured.
[0144] The increase in O.sub.2 sweep gas flow rate could cause two competing phenomena in the heat-exchange membrane reactor that can influence the CH.sub.4 conversion. The increasing O.sub.2 sweep flow rate can increase O.sub.2 exposure to the SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3-δ membrane per unit time, and thus the surface exchange rate of O.sub.2 with the membrane material. This can have a negative effect on the ambipolar conductivity of the membrane, which leads to a decrease in the flux of the H.sub.2 permeation and therefore lowers CH.sub.4 conversion. At the same time, the permeated H.sub.2 is combusted at a higher rate with increasing O.sub.2 sweep gas flow rate, which leads to an increase in H.sub.2 partial pressure gradient and an increase in CH.sub.4 conversion. As indicated by the decrease in CH.sub.4 conversion with increasing O.sub.2 sweep flow rate, a decrease in the ambipolar conductivity of the SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3δ membrane dominates the overall performance, even though it is somewhat offset by the increase in H.sub.2 partial pressure gradient.
[0145]
[0146] At 1273 K, the overall CH.sub.4 conversion decreased when compared to 1303 K, and therefore the heat requirement from the DNMC side was reduced, as shown in
[0147] The stability of the heat-exchange H.sub.2-permeable membrane reactor was tested by running DNMC at 1303 K for 50 hours while flowing the O.sub.2 sweep gas, the results of which stability test are shown in
[0148]
[0149] To further examine feasibility of the autothermal operation of DNMC process in the heat-exchange membrane reactor at an industrial scale, Aspen Plus® was used to simulate the scenario on the basis of the experimental results at 1273 K, where ˜30% of H.sub.2 was removed from the DNMC reaction and was completely combusted by the sweep gas (e.g., O.sub.2 in air). At 1273 K, the total heat requirement for the entire process was found to be 2,360,715 kJ/h, while the total heat released was found to be −2,408,618 kJ/h, resulting in a net −47,903 kJ/h of heat released overall. Furthermore, the simulation results of the heat exchanger demonstrate that the heat released from the cooling of both the DNMC product stream and the H.sub.2 combustion stream are sufficient to heat the DNMC and H.sub.2 combustion feed streams. The results of the Aspen Plus® simulation further showed that autothermal operation was feasible for the scaled-up DNMC process, indicating the potential for autothermality of DNMC operation under realistic conditions.
[0150] To supplement the Aspen Plus® simulation, additional COMSOL simulations were performed to understand the effects of gas flow velocities, CH.sub.4 concentration, and temperature profiles of the membrane reactor on the performance of the DNMC reaction. In particular, a COMSOL 2D axisymmetric model of the DNMC reaction, coupled with the SrCe.sub.0.7Zr.sub.0.2Eu.sub.0.1O.sub.3-δ membrane reactor with O.sub.2 sweep gas, was generated. The COMSOL simulation was conducted on the catalyst bed region of the membrane reactor for both DNMC channel and hydrogen combustion side. The gas velocities fell near the reactor wall and the membrane walls (i.e., in both DNMC and H.sub.2 combustion sides) due to the no-slip boundary conditions. The CH.sub.4 concentration fell from the entrance to the exit of the catalyst bed due to the reaction of CH.sub.4 in the DNMC catalyst bed. From the center to the wall of the membrane reactor, the CH.sub.4 concentration decreased gradually. The rapid decrease in CH.sub.4 concentration close to the reactor wall was due to the low gas velocity, which in turn limited the convection of fresh reactant to that wall.
CONCLUSION
[0151] Any of the features illustrated or described herein, for example, with respect to
[0152] All features described herein are independent of one another and, except where structurally impossible, can be used in combination with any other feature described herein. In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are only examples and should not be taken as limiting the scope of the disclosed technology. Rather, the scope is defined by the following claims. We therefore claim all that comes within the scope and spirit of these claims.