Patent Application
20180290123
This application concerns reactors capable of operating in a corona discharge mode, particularly microscale-based corona discharge reactors, arrays of such reactors, systems comprising at least one corona discharge reactor, and a method for using such reactors and systems, such as for fluid purification and/or chemical transformations.
A practical technology is required for performing chemical transformations and/or fluid purifications on both small scales, as well as industrial scales. A preferred process would be one that could be widely deployed for distributed processing applications. One example of such a chemical transformation and/or chemical purification process is the conversion of methane to liquid fuels. There are at least three distinct processes that need to be considered: (1) converting small sources of methane that are not otherwise economically viable (a.k.a., stranded methane); (2) fueling vehicles with liquid fuels derived from natural gas produced at the refueling point; and (3) large scale industrial conversion of natural gas to ultra-low sulfur liquid fuels. The scale of the flared natural gas resource worldwide has been estimated at about 5×1012 cu ft per year and would be worth approximately $30 billion if recovered, with 250×109 cu ft (ca. 5,000 kt methane) flared in the United States.
Animal manure management, such as on a large scale dairy, provides another example of the scale of the stranded methane resource. A 2013 estimate concluded that 2,456 kt methane were generated by manure management (equivalent to 61.4 MMt CO2e); 1,000 kt methane (25.2 MMt CO2e) resulting from pneumatic bleeds and tank venting in the energy industries; and 5,000 kt methane flared (15 MMt CO2). Since methane is burned to form carbon dioxide, methane production corresponds to CO2 production, which is a significant contributor to global warming. These processes provide an opportunity to generate approximately 8,500 kt liquid fuels (about 3.2 MM gallons liquid fuels). If this production displaced an equivalent amount of conventional fuels, it would reduce CO2 emissions by 101 MMt emissions per year. For individuals and industrial entities that desire to generate their own liquid hydrocarbons by condensation of natural gas, an efficient conversion methodology would provide a significant financial opportunity that would increase production of liquid transportation fuels and reduce energy imports, while also reducing carbon emissions. There is currently no technology that can effect this conversion for small resources in a practical manner.
There also is a substantial opportunity at larger scale conversion considerations. For example, a large scale opportunity exists to fuel some of the 250 million road vehicles in the United States, which currently consume 25% of the 100 quads that the United States uses annually. The United States transportation sector is heavily dependent on petroleum with about 93% of transportation fuels derived from petroleum in 2012. The United States uses about 13.5 million barrels petroleum per day. Natural gas use by motor vehicles is a very small fraction of the total transportation energy use. While recent low prices and abundant domestic supplies of natural gas have increased interest in its use as a motor fuel, its deployment currently is unlikely due to consumer's desire to continue to use existing gasoline or diesel vehicles, and desire to avoid conversion costs and technology compromises. However, a device and method for its use that would enable energy efficient conversion of natural gas to gasoline or diesel would substantially decrease, and almost eliminate, the United States dependence on petroleum imports. This would allow the United States to use its vast domestic resource of natural gas, while maintaining low carbon emissions. In fact, if all shale and/or tar sands oil production was replaced with natural-gas-derived liquid fuels, very significant reductions in total carbon emissions from transportation would be achieved.
The present device, system comprising the device, and method for their use, addresses the needs discussed above. Certain disclosed embodiments concern microreactors that are configured to operate in an electrical discharge mode, such as a pulse mode, an arc mode or a corona discharge mode, and most preferably are operable in a corona discharge mode. The microreactor may comprise a single emitter electrode and a plate counter electrode, and may comprise a flow-through plasma microreactor system. The microreactor may be configured to produce multiple, simultaneously operating corona discharges. For example, certain disclosed embodiments concern a microreactor comprising plural, simultaneously emitting emitter electrodes and a counter electrode. The electrodes may be arranged in series or parallel. These embodiments may be configured to produce plural, simultaneously operating corona discharges. Accordingly, certain disclosed microreactors comprise 1 to 100 simultaneously active corona discharges, more typically 3 to 50 simultaneously active corona discharges, such as 4 to 20 simultaneously active corona discharges.
Certain embodiments use a needle tip electrode, which typically is the negative electrode. A person of ordinary skill in the art will appreciate that the needle tip electrode need not be made from any particular metal or material. Suitable electrodes are typically made of a material that is sufficiently conductive to allow passage of tens of mA with minimal voltage drop. Furthermore, the selected electrode material preferably should have a large secondary electron emission yield (related to work function and other properties) and also resist electron driven sputtering of the electrode material. These two issues, discharge generation potential and robustness of the electrode material, are potentially inversely related, and hence each may be considered separately to optimize performance for a particular application. Accordingly, suitable electrodes may be made from a metal, metal alloy, or semiconductor. For certain exemplary embodiments the electrode material may be a metal or metal alloy comprising iron, nickel, palladium, platinum, tungsten, or combinations thereof. The electrodes also preferably are made of a material that can withstand occasional temperature excursions, so refractory metals and alloys comprising tungsten, and Ni superalloys, like Inconel, are suitable electrode materials, but common stainless steel and galvanized steel also may be used. Exemplary semiconductors suitable for forming electrodes include ZnO, LaB6, and CeO. Materials like graphite, carbon felt, silicon and doped silicon also may work well. In order to enhance emission current and increase process efficiency, coated electrodes may be used. For example, electrodes may be coated with a low work function material, like ZnO, BaO or ThO2 to enhance performance. Composite electrodes also can be used, such as metal/ceramic composites. A particular disclosed working embodiment comprised plural, simultaneously active corona discharge reactors arranged in series comprising plural emitter electrodes positioned and supported by an emitter support member that were operatively associated with a metal plate counter electrode.
The microreactor also includes a power supply that provides both the power and voltage requirements required to produce a corona discharge, as well as the ability to carefully control the input power to the reactor system. Suitable power supplies allow the ability to rapidly shape the power to stabilize the non-thermal DC plasma, rather than ending up in arc discharge (thermal) mode. Fast DC power supplies, such as a boost converter, interfaced with a suitable control (whether a digital PLC or an analogue circuit), are suitable for providing the requisite power and voltage requirements. Certain disclosed embodiments include a power supply having one or more inline ballast resistors, such as a 60 MΩ ballast resistor for carbon dioxide and an 80 MΩ ballast resistor for air.
A microreactor may be housed in a housing that defines at least one reactant feed inlet fluidly coupled to at least one corona discharge reactor. The microreactor typically has at least one feature measured on a millimeter scale, such as at least one fluid channel having at least one dimension of from about 1 to about 100 mm. Certain embodiments minimize fluid bypass in an active area of corona discharge by using a microchannel having a width, depth or length that is substantially occupied by an active area of corona discharge.
For certain embodiments, emitter electrodes were shaped like a cross. Each emitter needle resided in a purposefully formed cavity in a reactor plate that also defined a reaction microchannel for channeling a fluid to a corona discharge region.
Certain disclosed microreactors comprised multiple reactor plates in a stack. Each plate comprised plural corona discharge electrodes positioned in series along each of plural corresponding microchannels. The reactor plates may be made from any suitable material, such as a metal, an alloy, a phenolic resin, a castable ceramic, and combinations thereof. Certain disclosed embodiments used a glass-filled phenolic resin, a glass-filled silicone resin, or combinations thereof. A particular embodiment used reactor plates made from Portland Cement. Reactor features, such as microchannels and electrode receiving portion, were formed in the Portland Cement plate by stamping.
A reactant distribution manifold may be operatively associated with the reactor stack to distribute reactants to reactant inlet ports. A product distribution manifold may be operatively associated with product outlet ports to receive product produced by the reactor and to distribute such product to downstream components for further processing or product collection in a reservoir. As will be understood by a person of ordinary skill in the art, disclosed microreactors are useful for processing fluids, most typically gases. Accordingly, disclosed reactors often include at least one fluid seal to provide a fluidly sealed device and to potentially define microchannels. And, the microreactor also typically includes a power supply coupled to the electrodes.
Discharge microreactor systems also are disclosed. Certain embodiments comprise at least one microreactor configurable to produce a corona discharge, the microreactor comprises plural, emitter electrodes capable of operating in series and at least one counter electrode. The electrodes are configured to produce plural, simultaneously operating corona discharges. The system includes a power supply coupled to the electrodes. Certain power supplies were configured for transition from high voltage/low current (˜2 kV/1 nA) to lower voltage/higher current (˜300V/100 mA) Disclosed microreactor systems may optionally further comprise at least one of: a computer to control operating parameters, data acquisition, or both; product analytic instrumentation, such as a gas chromatograph, a mass spectrometer, an FT-IR spectrometer, a Raman gas analyzer, and combinations thereof; a pressure regulator; a condenser; a fluid inlet distribution manifold; a product distribution manifold; a fluid product collection reservoir; a heat exchanger; a pressure transmitter; a temperature transmitter; or combinations thereof.
A particular embodiment of a microreactor system according to the present invention includes plural gas reactant sources selected from methane (CH4), nitrogen (N2), carbon dioxide (CO2) and water (H2O). Mass flow controllers were associated with each of the plural gas reactant sources to flow a predetermined amount of a fluid reactant either to a corona discharge microreactor or system comprising a disclosed microreactor, or to a mixer for receiving plural gas reactants to form mixtures that are flowed through a corona discharge reactor.
One particular embodiment of a microreactor was designed to produce C2 or greater hydrocarbons, such as C2-C16 hydrocarbons, by condensing methane. These embodiments included a corona discharge reactor configured for converting biogas to higher condensed hydrocarbons; a source of biogas; a pressure regulator to control reactor inlet pressure; a DC power source coupled to the reactor and controlled by a power supply control unit; a heat exchanger to facilitate recovering condensable products generated by the reactor as liquids; a liquids collection reservoir; and a back pressure regulator to control reactor exit pressure.
Embodiments of a method for using disclosed microreactors and systems comprising disclosed microreactors also are disclosed. For example, the method may be used for chemical transformations, fluid purifications, or both. One particular embodiment concerns producing C2 or greater hydrocarbons, preferably for producing gasoline comprising a hydrocarbon chain of about C10 or diesel comprising a hydrocarbon chain of about C16, from a reactant stream comprising methane. A particular embodiment comprises providing a reactant flow of biogas from a dairy to a microreactor comprising plural, simultaneously operating corona discharge regions, or to a reactor stack comprising plural corona discharge microreactors, to produce C2 or greater hydrocarbons. Other disclosed method embodiments include, without limitation: fluid purification, such as desulfurization of a hydrocarbon stream; and subjecting carbon dioxide in a reactant stream to reduce carbon dioxide concentration.
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
The following explanations of terms and methods are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. The singular forms “a,” “an,” and “the” refer to one or more than one, 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. As used herein, “comprises” means “includes.” Thus, “comprising A or B,” means “including A, B, or A and B,” without excluding additional elements. All references, including patents and patent applications cited herein, are incorporated by reference.
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 indicated, implicitly or explicitly, 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. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is expressly recited.
Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains. 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.
When chemical structures are depicted or described, unless explicitly stated otherwise, all carbons are assumed to include hydrogen so that each carbon conforms to a valence of four. For example, in the structure on the left-hand side of the schematic below there are nine hydrogen atoms implied. The nine hydrogen atoms are depicted in the right-hand structure.
Sometimes a particular atom in a structure is described in textual formula as having a hydrogen or hydrogen atoms, for example —CH2CH2—. It will be understood by a person of ordinary skill in the art that the aforementioned descriptive techniques are common in the chemical arts to provide brevity and simplicity to description of organic structures.
If a group R is depicted as “floating” on a ring system, as for example in the group:
then, unless otherwise defined, a substituent R can reside on any atom of the fused bicyclic ring system, excluding the atom carrying the bond with the “” symbol, so long as a stable structure is formed. In the example depicted, the R group can reside on an atom in either the 5-membered or the 6-membered ring of the indolyl ring system.
Aliphatic: A substantially hydrocarbon-based compound, or a radical thereof (e.g., C6H13, for a hexane radical), including alkanes, alkenes, alkynes, including cyclic versions thereof, and further including straight- and branched-chain arrangements, and all stereo and position isomers as well. Unless expressly stated otherwise, an aliphatic group contains from one to twenty-five carbon atoms; for example, from one to fifteen, from one to ten, from one to six, or from one to four carbon atoms. The term “lower aliphatic” refers to an aliphatic group containing from one to ten carbon atoms. An aliphatic chain may be substituted or unsubstituted. Unless expressly referred to as an “unsubstituted aliphatic,” an aliphatic group can either be unsubstituted or substituted. An aliphatic group can be substituted with one or more substituents (up to two substituents for each methylene carbon in an aliphatic chain, or up to one substituent for each carbon of a —C═C— double bond in an aliphatic chain, or up to one substituent for a carbon of a terminal methine group). Exemplary substituents include, but are not limited to, alkyl, alkenyl, alkynyl, alkoxy, alkylamino, alkylthio, acyl, aldehyde, amide, amino, aminoalkyl, aryl, arylalkyl, carboxyl, cyano, cycloalkyl, dialkylamino, halo, haloaliphatic, heteroaliphatic, heteroaryl, heterocycloaliphatic, hydroxyl, oxo, sulfonamide, sulfhydryl, thioalkoxy, or other functionality.
Alkyl: A hydrocarbon group having a saturated carbon chain. The chain may be cyclic, branched or unbranched. Examples, without limitation, of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl and decyl. The term lower alkyl means the chain includes 1-10 carbon atoms. The terms alkenyl and alkynyl refer to hydrocarbon groups having carbon chains containing one or more double or triple bonds, respectively.
Anode: An electrode through which electric charge flows into a polarized electrical device. From an electrochemical point of view, negatively-charged anions move toward the anode and/or positively-charged cations move away from it to balance the electrons leaving via external circuitry. In a discharging battery or galvanic cell, the anode is the negative terminal where electrons flow out. If the anode is composed of a metal, electrons that it gives up to the external circuit are accompanied by metal cations moving away from the electrode and into the electrolyte. When the battery is recharged, the anode becomes the positive terminal where electrons flow in and metal cations are reduced.
Bis: A prefix meaning “twice” or “again.” It is used in chemical nomenclature to indicate that a chemical group or radical occurs twice in a molecule. For example, a bis-ester has two ester groups.
Cathode: An electrode through which electric charge flows out of a polarized electrical device. From an electrochemical point of view, positively charged cations invariably move toward the cathode and/or negatively charged anions move away from it to balance the electrons arriving from external circuitry. In a discharging battery or galvanic cell, the cathode is the positive terminal, toward the direction of conventional current. This outward charge is carried internally by positive ions moving from the electrolyte to the positive cathode, where they may be reduced. When the battery is recharged, the cathode becomes the negative terminal where electrons flow out and metal atoms (or cations) are oxidized. Presently disclosed embodiments are not electrochemical devices, and hence the cathode is the electrode through which energetic electrons are injected into a non-thermal plasma (electrons flowing in =“positive charge flows out” according to electrical circuit convention).
Contacting: Placement that allows association between two or more moieties, particularly direct physical association, for example the placement of a reactant stream, particularly in a gas phase, to contact a corona discharge.
Free radical: An atom, molecule, or ion with an unpaired electron. Free radicals are formed by splitting a chemical bond within a molecule, and are usually short-lived and highly reactive. Free radicals are capable of initiating chemical chain reactions, e.g., dimerization and polymerization. They also act as initiators or intermediates in oxidation, combustion, and photolysis.
Functional group: A specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of the molecule. Exemplary functional groups include, without limitation, alkyl, alkenyl, alkynyl, aryl, halo (fluoro, chloro, bromo, iodo), epoxide, hydroxyl, carbonyl (ketone), aldehyde, carbonate ester, carboxylate, carboxyl, ether, ester, peroxy, hydroperoxy, carboxamide, amino (primary, secondary, tertiary), ammonium, imide, azide, cyanate, isocyanate, thiocyanate, nitrate, nitrite, nitrile, nitroalkyl, nitroso, pyridyl, phosphate, sulfonyl, sulfide, thiol (sulfhydryl), disulfide.
Hydrocarbon: An organic compound consisting of the elements carbon and hydrogen. Hydrocarbons include aliphatic compounds (alkanes, alkenes, alkynes, and cyclic versions thereof, including straight- and branched-chain arrangements), aromatic compounds (unsaturated, cyclic hydrocarbons having alternate single and double bonds), and combinations thereof (e.g., arylalkyl compounds). Hydrocarbons can be produced according to certain disclosed embodiments of the present invention.
Isomer: One of two or more molecules having the same number and kind of atoms, but differing in the arrangement or configuration of the atoms. Isomers that differ in the arrangement of their atoms in space are termed “stereoisomers”. Stereoisomers that are not mirror images of one another are termed “diastereomers” and those that are non-superimposable mirror images of each other are termed “enantiomers.” When a compound has an asymmetric center, for example, if a carbon atom is bonded to four different groups, a pair of enantiomers is possible. An enantiomer can be characterized by the absolute configuration of its asymmetric center and is described by the R- and S-sequencing rules of Cahn and Prelog, or by the manner in which the molecule rotates the plane of polarized light and designated as dextrorotatory or levorotatory (i.e., as (+) or (−) isomers respectively). A chiral compound can exist as either individual enantiomer or as a mixture thereof. A mixture containing equal proportions of the enantiomers is called a “racemic mixture.” E/Z isomers are isomers that differ in the stereochemistry of a double bond. An E isomer (from entgegen, the German word for “opposite”) has a trans-configuration at the double bond, in which the two groups of highest priority are on opposite sides of the double bond. A Z isomer (from zusammen, the German word for “together”) has a cis-configuration at the double bond, in which the two groups of highest priority are on the same side of the double bond. The E and Z isomers of 2-butene are shown below:
For embodiments of the present invention where products can be made having sites of unsaturation, such products are understood to include all possible isomers, including all stereoisomers and E/Z isomers, unless expressly stated otherwise or the context would be understood by a person of ordinary skill in the art to include or exclude a certain isomer or isomers.
Lower: Refers to organic compounds having 10 or fewer carbon atoms in a chain, including all branched and stereochemical variations, particularly including methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl.
Moiety: A moiety is a fragment of a molecule, or a portion of a conjugate.
Molecular weight: The sum of the atomic weights of the atoms in a molecule. As used herein with respect to polymers, the terms molecular weight, average molecular weight, and mean molecular weight refer to the number-average molecular weight, which corresponds to the arithmetic mean of the molecular weights of individual macromolecules. The number-average molecular weight may be determined by any method generally known by persons of ordinary skill in the art, such as chromatographic methods.
Monomer: A molecule or compound, usually containing carbon, that can react and combine to form polymers. Molecules formed by the combination of monomers can be characterized by the number of monomers. For example, a dimer is a molecule formed from two monomers, a trimer is a molecule formed from three monomers, etc. A molecule with more than 10 monomers is typically referred to using the number of monomeric units, e.g., a 20-mer is a molecule having 20 monomeric units. As may be established by mass spectrometry, proton NMR, carbon NMR, methods such as vapor pressure osmometry and end group assays, etc., and combinations thereof.
Olefin: An unsaturated aliphatic hydrocarbon having one or more double bonds. Olefins with one double bond are alkenes; olefins with two double bonds are alkadienes or diolefins.
Precursor: An intermediate compound or molecular complex. A precursor participates in a chemical reaction to form another compound.
Providing a compound or composition comprising the compound: Refers to a person, entity or other manufacturer who makes the compound or composition comprising the compound and provides instructions for its use, such as by establishing the manner and/or timing of using the compound or composition; a supplier who supplies the compound or composition and provides instructions for its use, establishing the manner and/or timing of using the compound or composition; a facility that uses the compound or composition; and/or a subject who uses the compound or composition themselves. The manufacturer, supplier, facility and/or subject may act jointly or as a joint enterprise by agreement, by a common purpose, a community of pecuniary interest, and/or substantially equal say in direction of using the compound or composition. Alternatively, or additionally, the manufacturer, supplier, facility and/or subject may condition participation in an activity or receipt of a benefit upon performance of a step or steps of the method of using the compound or composition disclosed herein, and establish the manner and/or timing of that performance.
Stereoisomers: Isomers that have the same molecular formula and sequence of bonded atoms, but which differ only in the three-dimensional orientation of the atoms in space.
Structural unit: As used herein, the term “structural unit” refers to a unit of a polymer derived from polymerization of monomers.
Substituent: An atom or group of atoms that replaces another atom in a molecule as the result of a reaction. The term “substituent” typically refers to an atom or group of atoms that replaces a hydrogen atom, or two hydrogen atoms if the substituent is attached via a double bond, on a parent hydrocarbon chain or ring. The term “substituent” may also cover groups of atoms having multiple points of attachment to the molecule, e.g., the substituent replaces two or more hydrogen atoms on a parent hydrocarbon chain or ring. In such instances, the substituent, unless otherwise specified, may be attached in any spatial orientation to the parent hydrocarbon chain or ring. Exemplary substituents include, for instance, alkyl, alkenyl, alkynyl, alkoxy, alkylamino, alkylthio, acyl, aldehyde, amido, amino, aminoalkyl, aryl, arylalkyl, arylamino, carbonate, carboxyl, cyano, cycloalkyl, dialkylamino, halo, haloaliphatic (e.g., haloalkyl), haloalkoxy, heteroaliphatic, heteroaryl, heterocycloaliphatic, hydroxyl, oxo, sulfonamide, sulfhydryl, thio, and thioalkoxy groups.
Substituted: A fundamental compound, such as an aryl or aliphatic compound, or a radical thereof, having coupled thereto one or more substituents, each substituent typically replacing a hydrogen atom on the fundamental compound. Solely by way of example and without limitation, a substituted aryl compound may have an aliphatic group coupled to the closed ring of the aryl base, such as with toluene. Again solely by way of example and without limitation, a long-chain hydrocarbon may have a hydroxyl group bonded thereto. “Substituted” refers to all subsequent modifiers in a term, for example in the term “substituted arylC1-8 alkyl,” substitution may occur on the “C1-8alkyl” portion, the “aryl” portion or both portions of the arylC1-8 alkyl group. “Substituted,” when used to modify a specified group or moiety, means that at least one, and perhaps two or more, hydrogen atoms of the specified group or moiety is independently replaced with the same or different substituent groups. In a particular embodiment, a group, moiety or substituent may be substituted or unsubstituted, unless expressly defined as either “unsubstituted” or “substituted.” Accordingly, any of the groups specified herein may be unsubstituted or substituted. In particular embodiments, the substituent may or may not be expressly defined as substituted, but is still contemplated to be optionally substituted. For example, an “alkyl” or a “pyrazolyl” moiety may be unsubstituted or substituted, but an “unsubstituted alkyl” or an “unsubstituted pyrazolyl” is not substituted.
Sulfonyl: A functional group with the general formula:
where R and R′ independently are selected from various groups, including by way of example aliphatic, substituted aliphatic, cyclic aliphatic, substituted cyclic aliphatic, aryl, substituted aryl, heteroaryl, and substituted heteroaryl.
Plasmas generated by electrical discharges are known and have been used to attempt chemical transformations, including reforming hydrocarbon on board vehicles. For methane conversion the major process previously applied appears to have been Dielectric Barrier Discharge instead of direct plasma discharge, most probably due to difficulties associated with controlling a stable corona plasma discharge at macroscopic dimensions. Dielectric Barrier Discharge accelerates heavy particles in an AC field causing multiple ion-ion collisions. Both Dielectric Barrier Discharge and Arc Discharge result in much higher temperatures and produce thermal plasmas, whereas a corona discharge avoids these collisions and results in low temperatures and cold plasmas. For at least this reason, corona discharges are intrinsically more energy efficient than Dielectric Barrier Discharge and Arc Discharge.
One aspect of the present invention is to control the corona discharge using a microreactor comprising one or more purposefully configured emitter electrodes, such as needle-like emitter electrodes having a short anode-cathode gap, and/or a power supply configured to precisely control voltage and power to the electrodes. A microreactor is a relatively small device having at least one operative feature having at least one dimension that is a few millimeters or tenths of millimeters in size, generally from about 1 mm to about 1000 millimeters, and more typically from about 5 to 500 millimeters, in size. More typically, disclosed microreactors or microchannel reactors have at least one sub-1 mm dimension. For example, a microreactor may have one or plural fluid microchannels, wherein at least one microchannel has at least one dimension a few millimeters or tenths of millimeters in size, generally from about 1 mm to about 1000 millimeters, and more typically from about 5 to 500 millimeters. As another example, a gap defined between an emitter electrode and counter electrode may be measured in millimeters or tenths of millimeters. Certain disclosed microreactor embodiments had a gap size of from about 0.1 mm to about 10 mm, such as from about 0.1 mm to about 5 mm, even more typically from about 0.1 to 2 mm, or greater than 0 to less than 1 mm. A person of ordinary skill in the art will appreciate that it becomes more difficult to establish a corona discharge as the gap size increases towards a 10 mm gap. Establishing a stable corona discharge at a 2 mm scale is relatively facile, but becomes more difficult at a 10 mm gap, as the discharge may result in an arc discharge.
Disclosed microreactors that can be assembled as arrays of microreactors operating either in series, in parallel, or both. Plural microreactors also may be provided as an array on a reactor plate. Plural such reactor plates may be assembled to produce a reactor stack.
Disclosed electrical discharge microreactors can be operated in a number of different modes, including in a pulse discharge mode, an arc discharge mode, and/or a corona discharge mode. For example, a particular disclosed corona discharge microreactor had a gap size of about 500 μm, had an applied voltage of 500 volts and operated at about 5 mA. This reactor operated as an arc discharge device with the same applied 500 volts at 10 to 20 mA. In general, the greater the gap distance between the electrodes, the greater the applied voltage required to induce a corona discharge. Arc discharge produces substantial thermal energy, but most of the thermal energy generated is not usefully applied to, for example, induce chemical transformations. In contrast, a corona discharge does not generate substantial thermal energy. Most useful energy produced by a corona discharge is provided by the kinetic energy of electrons. Non-thermal corona discharges are generally characterized by low gas temperatures, but high electron temperatures, with high concentrations of free electrons (up to a density of 1019 m−3). Certain disclosed corona discharge reactors comprise an atmospheric, non-thermal plasma that is created by electrical discharge initiated by ionization of a fluid surrounding an electrically energized conductor.
A corona discharge may be produced by applying a relatively high voltage to a point emitter, typically a negative electrode, which is associated with a counter electrode, typically a positive electrode, which can be provided as a point or surface, such as a plate electrode. A non- or poorly-conductive gas is present in the gap defined between the emitter electrode and the counter electrode. The gap gas generally is non- or poorly conductive, and it takes a relatively high voltage to induce electron streaming. If the voltage is not high enough, then the gas in the gap tends to ionize. Suitable voltages for disclosed embodiments are from about 1600 volts to about 2300 volts. If voltage is increased above this value, then electrical breakdown of the gap gas occurs. As soon as the gap gas undergoes electrical breakdown, electrons stream from a negative emitter electrode to a positive counter electrode, and the gap is now filled with a conductive gas. Substantial current can now flow because the gas-filled space is rendered conductive. The color of the corona discharge depends on the composition of the gap gas. For example, air and nitrogen produce a purple corona discharge; carbon dioxide produces a bluish-white corona discharge.
Disclosed microreactors are useful for a number of processes including, by way of example and without limitation: chemical transformations, such as converting carbon dioxide in an inlet feed stream to reduce carbon dioxide emissions or converting methane and other short hydrocarbons to longer-chain hydrocarbons including condensed liquids for use as liquid fuels; decontamination of fluids, such as desulfurization of hydrocarbons and production of potable or highly purified water; and combinations of these processes. One exemplary embodiment concerns the condensation of natural gas to liquids using a non-thermal electric corona plasma discharge. Using a non-thermal corona discharge process that does not require high temperatures for the desired conversion will naturally lead to lower energy losses, since no process heat is required to achieve the conversion.
Corona discharge typically is induced in a gas phase, and certain exemplary disclosed embodiments concern conducting chemical transformations in a gas phase. However, corona discharge reactions also can be applied to a liquid phase. Typically, the corona discharge is first induced in a gas phase, and then the discharge is applied to the liquid phase and/or to components dissolved or suspended in the liquid phase.
Corona discharge provides substantial benefits relative to known processes. For example, corona discharge approaches 90% energy efficiency for conducting chemical transformations, such as the production of longer chain, liquid hydrocarbons from lighter gas reactants, such as methane (CH4). This compares to 50% or less energy efficiency for electrolytic processes used to make the same compounds.
Plural discharges can be produced in a single reactor.
Certain disclosed embodiments of corona discharge microreactors include emitter needles as the negative electrode. A person of ordinary skill in the art will appreciate that the needle tip electrode need not be made from any particular metal or material. Suitable electrodes are typically made of a material that is sufficiently conductive to allow passage of tens of mA with minimal voltage drop. Furthermore, the selected electrode material preferably should have a large secondary electron emission yield (related to work function and other properties) and also resist electron driven sputtering of the electrode material. These two issues, discharge generation potential and robustness of the electrode material, are potentially inversely related, and hence each may be considered separately to optimize performance for a particular application. Accordingly, suitable electrodes may be made from a metal, metal alloy, or semiconductor. For certain exemplary embodiments the electrode material may be a metal or metal alloy comprising iron, nickel, palladium, platinum, tungsten, or combinations thereof. The electrodes also preferably are made of a material that can withstand occasional temperature excursions, so refractory metals and alloys comprising tungsten, and Ni superalloys, like Inconel, are suitable electrode materials, but common stainless steel and galvanized steel also may be used. Exemplary semiconductors suitable for forming electrodes include ZnO, LaB6, and CeO. Materials like graphite, carbon felt, silicon and doped silicon also may work well. In order to enhance emission current and increase process efficiency, coated electrodes may be used. For example, electrodes may be coated with a low workfunction material, like ZnO, BaO or ThO2 to enhance performance. Composite electrodes also can be used, such as metal/ceramic composites.
The microchannel and electrodes are designed to minimize reactant bypass. For certain working embodiments, the active area was approximately a cylinder with a diameter of 0.5 mm. For these embodiments, the electrodes may vary in size from about 0.05 mm to about 2 mm, particularly if the channel is designed so that the gas is forced to flow mainly through the active volume.
Emitter needles are positioned by a reactor tile relative to a ground plate to provide a discharge gap between the emitter and ground electrodes. Suitable gap distances are limited by practicality on the lower dimension, with a distance that is too short causing an active volume that is too small for practical gas conversion. The upper gap size is determined by a size that allows stabilizing a non-thermal plasma discharge at ambient pressure, with a probable upper limit of about a 10 mm scale, more likely a 5 mm scale, and even more typically having an upper limit of about 2 mm.
One current embodiment of a suitable emitter needle 900 is shaped like a cross as illustrated by
For certain embodiments having multiple, simultaneously operating corona discharges, each reactor plate in a reactor can include plural electrodes, such as plural emitter needles. One embodiment of a reactor plate 1000 is illustrated by
Reactor tiles can be made of any suitable material, including metals and alloys, such as steel, aluminum, etc.; polymers, typically high temperature polymers; etc. Certain criteria that were applied to select preferred materials include: (1) the material is preferably easily formed, such as by injection molding or casting, although other processes, such as milling/machining stamping also may be used; and (2) the material should have good resistance to arcing. The best materials found to date for reactor tiles include phenolic resins, including glass-filled phenolic (“G-3”) resins, glass-filled silicone (“G-7”) resins, and castable ceramics, such as Portland Cement. For certain disclosed embodiments, the reactor tiles comprised Portland Cement and structural reactor features were formed in each tile by stamping.
Individual reactor plates, such as plate 1000, may be assembled into a reactor stack. For example, and again with reference to an embodiment for converting biogas to longer chain, typically liquid, hydrocarbons, to enable a process inlet gas flow of 5 standard liters per minute (SLPM), a stack of 10 tiles per reactor assembly would be suitable. One embodiment of a suitable reactor stack 1200 is illustrated by
A reactor, plural separate reactors, a reactor stack or plural reactor stacks typically will be sealed in a housing. One embodiment of a reactor housing 1300 is illustrated by
For certain embodiments, an HVDC power supply powered the reactor. Certain disclosed embodiments need to operate up to 10×10×10 discharges in parallel, with each discharge consuming up to 5 W, more typically consuming up to 1 W (=1 kV×1 mA) electrical power. This equates to a power consumption of at least 1 kW for the reactor. Current embodiments use a boost converter design having suitably high power ratings to satisfy these and potentially higher power requirements.
In some embodiments, the DC power supply can be a sustained power supply. In some embodiments, the power supply can be sustained up to 10,000,000 Hz without any intrinsic frequency variations in voltage or current.
A reactor system according to the present invention can include a number of additional, potentially optional, components, as will be understood by a person of ordinary skill in the art. For example, a reactor system according to the present invention may include a pressure regulator, a backpressure regulator, a condenser, a liquid product collection reservoir, etc. Certain disclosed system embodiments included one, more than one in any and all combinations, or all of the following components: (a) microchannel reactor stack housing (e.g. modified Polycase WA-24); (b) Watts push to connect chemical resistant tubing connectors; (c) nylon tubing; (d) an inlet pressure regulator (e.g. a miniature plastic regulator capable of 20 SCFM); (e) an exit needle valve; (f) a heat exchanger (such as a fluid to air heat exchanger based on a simple coil of copper tubing); (g) a fluid, gas, liquid or both, collection tank [e.g. a 1,500 gal (64″×108″) tank is suitable for converting biogas to longer chain, typically liquid, hydrocarbons assuming 75% conversion to condensed liquids (biogas is 60% methane), and that 10 SCFH biogas will produce 0.65 gal liquids per day, where the tank can serve to accumulate products of several reactors].
Certain embodiments of disclosed corona discharge microreactors are designed to increase flexibility. For example, such embodiments may include adjustable corona discharge gap sizes, a view port to view the discharge, ports/appropriate connections to allow spectroscopic measurements of the discharge to characterize different operational modes. Other embodiments will be designed to include predetermined, selected features, such as microchannel size (cross section in width and depth, as well as spacing between discharges), number of active discharges, etc.
Certain disclosed embodiments may include an inert gas inlet and microchannel to provide inert gas around and about the needle tip emitter electrodes. For example,
The inert gas channel can be located within the reactor geometry and can be configured to convey inert gas to the emitter electrodes. The inert gas channel can serve each electrode separately and can change the reaction environment around each electrode. This allows for a distributed, near continuous feeding of reactants along the length of the reactor.
In some embodiments, the reactant gas can flow perpendicularly to the electrodes and the plasma region. In other embodiments, such as embodiments having an inert gas channel, the reactant gas may flow in a non-perpendicular direction. For example, the gas may enter along the emitter needle electrodes and into the corona space.
In some embodiments, the microreactor can be configured to function without a dielectric protection coating anywhere in the reactor. This configuration can greatly increase the energy efficiency of the reactor. Additionally, the lack of dielectric material makes it possible, in some embodiments, to use AC current in an energy efficient mode without overheating.
In some embodiments, one or more corona discharge reactors can be integrally combined with one or more additional and separate units, such as a catalytic reactor. Integrating a catalytic reactor with a corona reactor allows specific molecules that are obtained in the corona reactor to be further processed by the catalytic reactor. This combination eliminates the need to use a separation unit to first separate molecules obtained in the corona reactor. The integrated catalytic reactor can transform the available molecules selectively, for example, by taking from the mixture only those molecules that can be catalytically transformed.
Disclosed systems can create a stable glow corona, with the process being controlled by total power applied to the reactor at a given current, and allowing the potential (voltage) to be as high as needed. The electrical performance of an exemplary system is shown in
Under stable glow discharge operation, high energy free electrons in the glow discharge collide with molecules in the gas, yielding reactive species, including ions and free radicals. When operating using methane as the reactant gas, for example, it appears that a significant number of radicals (e.g. CH3. and CH2: radicals) form in the gas phase that can dimerize to form ethane and ethylene. This happens with high efficiency, with methane conversion rates growing as a function of applied power (essentially, increased current at constant voltage).
Data collected using a single discharge reactor performing chemical condensation of methane is shown in
This saturation behavior is reflected in the data in
The discharge test loop of
Newly created C2 molecules can be exposed to further electron cascades, causing, for example, ethylene to react with methylene to produce C3 compounds, or ethylene radicals to form C4 and heavier hydrocarbons. This process allows methane to be converted to longer chain hydrocarbon liquids with high efficiency. The composition of the resulting product streams can be appropriately characterized, such as spectroscopically, and/or gas chromatography.
One embodiment of a corona discharge reactor platform comprises arrays of emitter electrodes to drive sequential conversion reactions. One embodiment of a disclosed reactor will operate on flows in the order of 600 SCCM with 80% selectivity conversion rates towards condensed hydrocarbons. The estimated pressure drop is about 0.2 bar using the Churchill capillary flow correlation for a 100 sccm flow of air at 100° C. and pressure 2.5 bar through a rectangular capillary of dimensions 0.2×1.0×90 mm3 with a roughness of about 0.001 m. This estimated pressure drop indicates that a flow rate of 100 sccm of natural gas through this embodiment of a reactor is reasonable.
A. Chemical Transformations
A corona discharge microreactor, an array of microreactors, a system comprising at least one microreactor, or a system comprising an array of microreactors can be used to convert a feed stream, typically a feed gas, into a desired product or products. A person of ordinary skill in the art will appreciate that any reaction that is facilitated by or induced by energy transfer from a corona discharge, such as a gas phase reaction, and in particular gas phase reactions that proceed by radical formation, can be accomplished using disclosed embodiments of the corona discharge device or system comprising the device.
One particular embodiment of the present invention concerns using corona discharge for highly efficient conversion of a low molecular weight hydrocarbon, such as methane (CH4) (e.g., from natural gas, or from anaerobic digestion of waste biomass) to carbon-based materials having a larger number of carbon atoms in a chain, such as hydrocarbons having from 2 to about 100 carbons (C2-C20) in a chain, more typically from 4 to about 20 carbon atoms (C4-C20) in a chain, and even more typically liquid transportation fuels in the gasoline (hydrocarbons of about C10) or diesel (hydrocarbons of about C16) range. Corona discharge has been used convert methane streams to C2 and C3 molecules, such as ethane, ethylene, acetylene, propane, propene, etc. A general schematic of one working embodiment of the process is illustrated in
Without being bound by a theory of operation, it currently is believed that the corona discharge methane condensation process occurs in several steps. In a first step that has been established empirically, methane (CH4) is activated by a highly energetic electron represented as , in Equation (1) (the electron is not consumed in the reaction, but instead flows to a counter electrode).
2CH4+→C2H6+H2 Equation (1)
If a second discharge is implemented in tandem with a first discharge then additional reactions are possible, as indicated by equations 2 and 3.
C2H6+CH4+→C3H8+H2 Equation (2)
2C2H6+→C4H10+H2 Equation (3)
Based on working example experience, approximately 70% methane conversion occurs in the first discharge with the major products being ethane, ethylene and acetylene. Likely products for the second discharge will be those described by Equations 2 and 3. Eventually, and following a number of sequential corona discharges, a product of a certain desired length n will be formed in an overall reaction that can be summarized as
nCH4+n/2→CnH2n+2+nH2 Equation (4),
where n is from 2 to at least as high as 20, more typically 4 to 18, such as 4 to 16 or 4 to 10 or 12. A “longer” (longer than the starting material) chain hydrocarbon product is then captured and removed from the reactor. In order to achieve high energy efficiency, hydrogen (H2) produced by the reaction is preferably used for a constructive purpose (e.g., in a fuel cell to produce electrical power that can be used to run the process). Chain length control approaches include decreasing vapor pressure of hydrocarbons as their chain lengths increase; controlling reactor temperature; condensing hydrocarbons out having a targeted, or longer, chain length; and combinations thereof. Disclosed embodiments can convert a reactant stream to liquid hydrocarbon product wherein 95% of the liquid hydrocarbon produced is between n+2 and n−2 of the target n set by external process control. A similar transformation (i.e., production of long chain hydrocarbons from methane) is currently accomplished by reforming methane to syngas (an energy intensive process) followed by Fischer-Tropsch synthesis (FTS) to liquids. The present process is superior to the current implementation of steam methane reformation followed by Fischer-Tropsch synthesis as production of waxes and of very small hydrocarbons is completely avoided. And, the overall energetic efficiency of a combined reforming/FTS process is about 50%. The energy efficiency of the corona discharge should be significantly higher, such as about 75% or better.
B. Fluid Purification
Corona discharge reactors, or a system comprising at least one corona discharge reactor, also can be used for fluid purification. One important exemplary embodiment of fluid purification is water purification. Potable water to substantially pure water can be produced from impure water by applying to the impure water an electron stream from a corona discharge reactor. This embodiment has been modeled using an input composition comprising water and rhodamine red. Rhodamine red was substantially eliminated as the contaminant from water by treating the water with a disclosed embodiment of a corona discharge reactor. For this embodiment, the reactor process conditions were: voltage=500V; current=5 mA; flowrate=2 sccm. The discharge occurred in the headspace gas above the liquid, with discharge occurring from the emitter to the liquid (liquid=anode).
A second exemplary embodiment of a fluid purification process is desulfurization of a hydrocarbon stream. Hydrocarbon fuels are often contaminated with sulfur-based compounds, such as thiophenes, including dibenzothiophenes and substituted dibenzothiophenes. These compounds are difficult to remove using prior known processes. However, a product stream comprising a hydrocarbon and a sulfur-based impurity can be exposed to a corona discharge. For example, a hydrocarbon comprising a thiophene can be oxidatively desulfurized by converting the thiophene to a sulfone and/or sulfoxide, as indicated below, using corona discharge.
The sulfone or sulfoxide is then removed from the hydrocarbon stream by liquid-liquid extraction to remove the sulfur-based impurity(ies).
Natural gas may comprise components such as CO2, water and H2S. Corona discharge has been applied to mixtures of CH4, CO2, and H2O. Methane (CH4) has been produced from a mixture comprising CO2 and H2O, establishing that neither of these two gases will negatively impact the process. Further, corona discharge effectively precipitates sulfur out of CH4/H2S mixtures. This allows both a method for purifying a fluid stream comprising H2S using corona discharge, and also establishes that an inlet feed stream comprising H2S can be processed using corona discharge to produce hydrocarbons.
C. Forming Reactive Nitrogen Products
Another example of a useful process that can be accomplished using a corona discharge reactor is conversion of nitrogen to a reactive nitrogen form, such as ammonia or hydrazine. This has been accomplished by, for example, applying a corona discharge to a mixture of nitrogen and oxygen, to yield nitrogen oxides that can be further processed to nitrates, or to a mixture of nitrogen and water vapor, to yield ammonia and hydrazines. The process parameters were substantially similar to those described above for gas phase processes, with voltages of about 600V and current of about 5 mA applied to a microchannel reactor with a gap of about 1 mm.
D. Carbon Dioxide Reduction
Another disclosed process concerns CO2 reduction.
The following examples are provided to illustrate certain features of exemplary embodiments. A person of ordinary skill in the art will appreciate that the scope of the present invention is not limited to features disclosed by such examples.
A typical 1,000-cow dairy is assumed to produce 50 ft3/cow/day biogas comprising about 60-70% methane and 30-40% CO2. The inlet pressure for this biogas to a corona discharge reactor would be about 1.5 bar. Thus, the dairy will produce 30 ft3/cow/day or 30,000 ft/day methane (equivalent to 1,250 ft3/hour). Since the current major use of biogas (where it is used constructively) is for production of electrical power through use of electrical generators coupled with a diesel-generator (genset), the present evaluation will be compared with the use of a genset (as far as capital costs and value of products generated).
This example concerns using a corona reactor to reduce CO2 in a fluid inlet stream using a microreactor. Atmospheric CO2 has increased substantially in the last 50+ years. Annual measurements of atmospheric CO2 in parts per million are recorded at Mauna Loa Observatory.
This example concerns using a three discharge corona reactor to reduce CO2 in a fluid inlet stream using a microreactor. A reactor such as that illustrated by
This example concerns using a corona reactor to reduce CO2 in a fluid inlet stream using a microreactor. One embodiment of a multi-discharge reactor used for this conversion is illustrated in
Data concerning the effect of power on efficiency for CO2 reduction using a corona discharge reactor according to the present invention is provided by the bar graph of
And
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 62/483,799, filed Apr. 10, 2017, which is incorporated herein by reference.
This invention was made with government support under National Science Foundation (NSF) Award No. 1134249, entitled “Chemical Reaction Activation in Microreactors through Corona Discharge,” and under Department of Energy Award No. DE-AR-0000679. The United States government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62483799 | Apr 2017 | US |
