Patent Application
20240425997
This application claims priority of German Application No. 102023116090.7, filed on Jun. 20, 2023, which application is hereby incorporated herein by reference.
A reactor for chemical or biological reactions is provided. Further, an operating method for such a reactor is provided.
The course of chemical reactions is defined by the relative thermodynamic states of the involved educts and the possible products. The equilibrium composition can be altered by, for example, changing the temperature or the pressure. Temperature is also the main parameter used to speed up chemical reactions, and many of the currently used industrial processes work at high temperature both to enhance reaction rates as well as to change the equilibrium position towards desired products. The advent of the transition to green energy will make it necessary to electrify existing thermochemistry processes with more energy efficient methods due to the increasing availability of renewable electrical energy. Ultimately, this leads to the desired reduction in the use of fossil fuels as the main energy source.
Embodiments provide an efficient way to initiate at least one chemical or biological reaction by bringing electrons into a fluid. This can be done using electrochemical processes.
In conventional electrochemical setups, electrochemical reactions are performed at the two half-cells making up the electrochemical cell. Reaction rates are defined by electrode overpotential and mass transport towards the contacting electrodes. However, increasing the overpotential yields faster reaction rates but usually finds a trade-off with electrode erosion. The assumed true driving mechanism for conventional electrochemical reactions is the charge transfer happening at the electrode interface.
In the following, reactions based on electron injection are called electrochemical processes. For example, three types of reactions are distinguished: reactions in electrochemical cells, direct reactions that are conventionally often driven by catalysts and/or temperature, and reactions based on electrons injected into the fluid. The conventional and catalytic electrochemical reaction distinguish themselves from the electron injection driven reactions in two ways. Firstly, electrochemical or catalytic reactions rely on the transfer of electrons from one state to a bound state on an atom or molecule at the material interface, initiating a chemical reaction. For electrons that are injected into a medium with an energy larger than the thermal energy of the medium, the electrons travel some distance away from the interface, thermalize, self-trap, and then react at some distance away from the interface. Secondly, moving the charge transfer mechanism or chemical reaction away from the electrode or catalytic interface will not only reduce the probability of electrode corrosion, but also influence mass transfer limitations. In a conventional electrochemical setup, mass transfer is typically strongly affected by a charge double layer at at least one electrode, or, in processes where a gas is generated at the electrode, by bubbles that strongly adhere to the electrode surface. For injected electrons this may not be the case.
In the following, a reactor is, for example, a vessel in which a chemical of said electrochemical origin is performed. In the reactor described herein, a method is described that separates the surface of the electron emission from the fluid. That is, electrons are emitted at an interface different and distant from the fluid interface. By doing this, on top of the previous mentioned aspects, a much longer lifetime of the electrode can be achieved.
A distant emitter could be realized by a photo emitter, a thermal emitter or a field emitter in an encapsulated package with a transmission window or with a gate-insulator-substrate electron-emission structure, GIS-EE, for example.
According to at least one embodiment, the reactor is for performing chemical reactions. That is, in the reactor educts react partially or completely to products; the educts are also referred to as starting materials. In particular, molecules of a first type react to molecules of a second type. The involved molecules may be organic or inorganic. The involved molecules may be small molecules, for example, with a molar mass of at most 40 g/mol or of at most 100 g/mol or of at most 300 g/mol or of at most 500 g/mol or of at most 1000 g/mol. It is also possible that at least one of the involved molecules may have a large molar mass of at least 1 kg/mol or of at least 2 kg/mol, like molecules in biochemical reactions.
According to at least one embodiment, the reactor comprises one or a plurality of electron sources. In case of a plurality of electron sources, it is possible that all the electron sources are of the same kind or that different kinds of electron sources are combined with each other, for example, electron sources in which electrons are provided by different mechanisms. The at least one electron source, also referred to as electron gun, is configured for emitting electrons into a fluid. For example, the electron source is the GIS-EE, a plurality of the GIS-EEs or comprises one or a plurality of the GIS-EEs.
According to at least one embodiment, the fluid contains at least one gas and/or at least one liquid. That is, the fluid can be a mixture of liquids and/or gases. Furthermore, the fluid may contain emulsions, droplets, bubbles, foams or sprays. Additionally or alternatively, the fluid may contain any particle suspensions, for example, with particles selected from the following group, individually or in any combination: inorganics, solid polymers, hydrogel, viruses, bacteria, quantum particles, quantum dots and porous or non-porous particles. Particle sizes can reach from 1 nm to 100 μm or from 0.1 nm to 1 mm, for example. For example, as the fluid educts and/or products of the reaction to be performed in the reactor can be molecules dissolved in a solvent or in a solvent mixture. Otherwise, the educts and/or products can be liquids present in the fluid, possibly together with a solvent. Otherwise, the educts and/or products can be gases, possibly in a transport gas or in a transport gas mixture.
According to at least one embodiment, the reactor comprises one or a plurality of transportation systems for the fluid. At least one transportation system is thus configured to adjust a velocity of the fluid when passing the electron source. The term ‘Passing’ may include both flowing along the at least one electron source and flowing through the at least one electron source. For example, the velocity of the fluid in a direction perpendicular or parallel to the electron source or through a grid shaped by the electron source is at least 10 μm/s or is at least 0.1 cm/s or is at least 1 m/s. Alternatively, said velocity is at most 10 m/s or is at most 1 m/s. Alternatively or additionally, the fluid passes the electron source with a Reynolds number of at least 0.001 and/or of at most 1×105 or of at most 1×103 or at most 1×102 or at most 1×101 or at most 1. For example, the fluid is led past or through the electron source in a laminar manner; otherwise, the fluid can be led in turbulent manner as well, depending on the required stirring of the fluid.
According to at least one embodiment, the at least one electron source is configured to provide electrons which are, for example, accelerated either in the conduction band of a material or in the vacuum level of an evacuated package; these electrons being accelerated or being enabled to acceleration may be regarded as being “free”, for example, because these electrons may not be specifically bound to a distinct location in the electron source, but can be subject to a ballistic movement far beyond atomic scale. Hence, these “freed” electrons can gain energy higher than the work function of the material separating the electron gun from the fluid and to be injected into the separated fluid. Thus, the electrons are provided by an emission process, like field-, thermionic- or photo emission, either into the vacuum level or a conduction band in an area distant from the fluid. For example, the electrons leave a solid within the electron source and have to travel, for example, in a ballistic manner, some distance and are transmitted through a window material until they are injected into the fluid. In another embodiment, the electrons tunnel into the conduction band of an insulator and gain energy in the electric field and eventually, by reducing scattering through material choice and thickness, overcome the work function and are injected into the fluid.
One specific feature of the reactor described herein is to separate the physical effect triggering the extraction of electrons, that is, photo-, thermionic-, field emission and electron energy gain, from the interface to the fluid, either by an evacuated package or by a thin-film heterostack. Thus, the location where the electrons are provided or “freed” is different from a location where the electrons reach the fluid. The respective “freed” electrons reaching the fluid are, hence, injected into the fluid and may then consequently be referred to as injected electrons. Therefore, the fluid is not able to interact with the functional surface providing the electrons and is therefore more robust.
According to at least one embodiment, when reaching the fluid, at least a part of the injected electrons have a kinetic energy of at most 5 keV or of at most 3 keV. In case of a GIS-EE, for example, said kinetic energy is at most 50 eV or is at most 20 eV or is at most 10 eV or is at most 5 eV. Said part is, for example, at least 10% or at least 50% or at least 85% or at least 98% of the injected electrons. That is, the electrons have a relatively low kinetic energy when reaching the fluid.
In at least one embodiment, the reactor is for performing chemical reactions and comprises:
wherein
That is, a chemical or biochemical reactor for fluids, that is, liquids and gases, based on low-energy electron sources is proposed. A driving part of chemical reactions is the transfer of electrons. Therefore, by injecting electrons into the fluid, chemical reactions can be triggered, enhanced or controlled.
An alternative possibility on the realization of monopolar electron injections is by cold field emitters operated directly in contact with a liquid state medium. However, the operation of a tip structure directly in the liquid results in a strong interaction with the emitter surface and, thus, a strong degradation and low lifetime is achieved. This could be prevented by using only low voltages and therefore low currents or electron densities. Thus, commercial application is not economical and the existing problem with electrode corrosion stays unresolved.
A further alternative possibility is to use a photocathode to get low-energy electrons into a fluid, where the energy could be controlled by the cathode material and the incident beam photon energy. However, electrode erosion as well as the cathode working as a catalyst for unwanted reactions would then be an issue. Moreover, quantum yield, or photon to electron conversion rates, are quite low which further reduces the commercial applicability.
Furthermore, the electric field can be either static or dynamic, that is, could be a plasmonic assisted field emission or ultra-short laser pulse emission. For plasmonic assisted field emission, a coating with a metal or metal nanoparticles can be used, for example, with Au, Ag or graphene on silicon or SiO2 or Si3N4 or hBN. However, since the kinetic energy of the electrons in this case may be above 1 kV to be able to pass a membrane towards the fluid, ions may also inevitably be generated. This may reduce the probability of a selective chemical reaction involving the injected electrons and introduced educts. In turn, the injected electrons may be lost due to recombination of the injected electrons with scavenging ions of opposite polarity generated by impact ionization. Furthermore, impact ionization and scavenging may yield unwanted side reactions into stable but unwanted products.
In at least one embodiment of the reactor described herein, with a gate-insulator-substrate electron-emission structure, GIS-EE, the emission of nearly thermalized electrons with kinetic energies below 20 eV directly in the fluid is possible. This reduces the probability of impact ionization, for example.
In the case where the electron injection mechanism is able to introduce electrons at some variable location in the reaction chamber, as in the reactor described herein, corrosion of the electrode and mass transfer limitations might be overcome. Furthermore, usually an electrochemical setup is a batch process. With injection of electrons, it could also be realized in a flow reactor, especially with a GIS-type electron source, which can be realized in a grid shape.
Since no external electric field is necessary, the GIS-EE supplies electrons for chemical reactions without external influences in the fluid. This makes the use of an additional electrode in the fluid unnecessary. Charge neutrality can be achieved via the gate electrode present in the fluid, which could be held at a constant voltage. However, it is also possible that there is an additional electrode in the fluid, for example, for improved control of ions produced. Thus, the gate electrode may be the only electrode in contact with the fluid, or there can be one or a plurality of additional electrodes.
Furthermore, direct reactions are often driven by catalysts and/or high process temperatures. In the reactor described herein, electron injection could replace catalysts and/or high process temperatures in reactions and therefore might allow novel processes or easier processing. Compared to conventional electrochemistry, methods based on electron guns could enable higher reaction rates and/or lower need for maintenance due to electrode erosion. Considering the electron has a redox potential of −2.88 V against a normal hydrogen electrode, it is extremely reductive and its presence thus will facilitate a reduction reaction.
One example is the processing of carbon dioxide, either in a gas stream or a fluid, for example, from atmospheric air or also from seawater. With low energy electrons below 10 eV, dissociation to CO and O can be achieved either through solvated electrons in a fluid or even in a gaseous form. Direct electron-impact dissociation can also be used. Usually, a high temperature combined with a catalyst or by adding hydrogen is used to produce ammonia or e-fuels with CO2 as one educt. In principle, the electrons from the electron source described herein could be used to create ions and/or either enable dissociation to carbon monoxide or drive further reactions.
The electron gun can be used to create ions and filter molecules, for example, CO2, through the ionic properties like ionization probability, ionization energies, mass-to-charge ratio, ion mobility and/or polarity of the created ions. Such a method requires a high amount of energy since the total energy of the CO2 ions is rather high, that is, this would lead to high energy requirements in direct air capture. One way to overcome this is to drive a power supply with the generated charge and therefore recycle most of the energy. However, this could still lead to an energy requirement higher than conventional chemical methods. Nonetheless, when combining this with a dissociation based on the electron source the ions could be used to further process the CO2 and could give a more energy efficient complete system.
In one embodiment, the reactor is configured to inject electrons in a CO2 containing input stream and then other chemicals might be added to process the CO2, like H2O, H2, NH3 and/or CH4. Therefore, catalysts and/or elevated temperature could be avoided or their amount could be reduced. For example, in a first step the CO2 could be ionized, dissociated yielding both or either neutral or ionized CO2 or CO and other dissociated neutrals or ions could be generated from other input stream components. Out of these substances a variety of products can be created, like for example formic acid (HCOOH), carbon monoxide (CO), methane (CH4), ethylene (C2H4) and/or ethanol (C2H5OH).
In another embodiment, the described reactor is used to design a more energy-efficient Haber-Bosch process for the synthesis of ammonia. In this case, the need for the catalyst, high temperature and high process pressure could be reduced or omitted.
Also, reactions based on solvated electrons are used in chemical processes. Conventionally, solvated electrons are achieved by using alkali metals like sodium or lithium. For those processes solvents able to dissolve the alkali metal are needed. Most commonly ammonia is used. However, also Hexamethylphosphoramide, HMPA, or Hexamethylphosphoric acid triamide, HMPT, can be used. Besides the solvation of the alkali metal, the lifetime of the electrons is increased by clustering of solvent molecules and also in some cases delocalization of the electrons. This prevents recombination with the alkali metal and the aimed reaction can be favored. Using alkali metals and liquid state ammonia bares significant consequences in terms of toxicity and reaction conditions, because both substances are harmful to humans and the environment, and temperatures below −33° C. are necessary to liquefy ammonia. Furthermore, separation of the reactants and products is cumbersome and further deteriorates the applicability. However, the reduction by a solvated electron is useful for many chemical reactions and is used in many fields, for example, electrosynthesis, electroplating, and electrowinning.
In one embodiment, the described reactor is used to trigger a reaction in a fluid. For example, dissociation and filtering of CO2 dissolved in seawater is possible. Furthermore, the solvated electron can also trigger a dissociation of H2O to H+ and OH− and can be used for H2 generation, for example. Further applications like filtering of water are possible as well.
In another embodiment, the described reactor may be used to enable or optimize polymerization in plastics processing using, for example, foams and triggering or enhancing polymerization by electron injection. Therefore, polymerizing or harden the foam directly yielding a very low density material.
In another embodiment, the described reactor may be used to synthesize nano particles by electron injection. Corresponding this concept, reference is made to document A. Guleria et al., “Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies” in Dalton Trans., 2023, 52, 1036-1051, https://doi.org/10.1039/D2DT03219H.
An example for a synthetic process that uses solvated electrons by dissolving alkali metals is the Birch reduction. In this chemical reaction, arenes, that is, molecules that contain one or more benzene ring, are selectively reduced to the corresponding 1,4-cyclohexadiene compounds. This reaction has numerous applications in organic synthesis, and particularly also in the production of pharmaceutical compounds. Representative examples are the reduction of anisole to 2,5 dihydroanisole and that of benzoic acid to 1,4-dihydrobenzoic acid. A representative example of a pharmaceutical synthesis is the Birch reduction of arenes to γ-spirolactones.
Another application could be the Bouveault-Blanc reduction. This reaction is used to reduce esters, aldehydes and ketones to the corresponding alcohols. In case there is a suitably located double bond in the ester, cyclic or spirocyclic alcohols may be formed. When an ester of an aliphatic alcohol is combined with an electron anion, different pathways lead to the paired radical anion. Considering experimental conditions, different methods lead to the solvated electron necessary for performing the reduction reaction, either by dissolving metals, using electrochemistry and/or using photochemistry. The Bouveault-Blanc reaction is used widely in industry as a highly selective reaction pathway, although the usage of alkali metals still poses a safety issue. Nevertheless, the Bouveault Blanc reduction has proven its value in pharmaceuticals, where, for instance, it is used to introduce deuterated hydrogen at selected cleavage sites.
Considering both the Birch and Bouvealt-Blanc reduction schemes, by using an electron gun to introduce electrons, as in the reactor described herein, the usage of alkali metals is deemed obsolete. Since the solvent does not need to dissolve alkali metals in this case, a wider range of solvents can be utilized, like non-polar or polar aprotic solvents, for example, hexane or dimethyl sulfoxide, DMSO for short. The process can be carried out at a wide range of thermodynamic conditions, with temperatures and pressures favoring the liquid state conditions of the medium which is a liquid or gas, but also favors certain reaction pathways.
In case of the Birch reduction, with the reactor described herein, reactions in hexane at atmospheric pressure and room temperature are accessible. These conditions are very different from the conditions that come with reaction in liquid Ammonia. Furthermore, also a process without solvents could be possible, since no recombination with the alkali metal is possible. Also, higher intensities of electrons as well as different reactor designs are possible. Again, the reactor could be designed as a flow reactor, adding the reactants one at a time, or like in the conventional case as a batch reactor.
An example for process parameters for reduction of anthracene to 9,10-dihydroanthracene in the reactor described herein is:
These values may apply, for example, with a tolerance of at most a factor of 100 or of at most a factor of 10.
Other possible cyclic hydrocarbons were cyclohexane and naphtalene, with 1-propanol, 2-propanol, 2-methyl-2-propanol, 2-propanone as solvents. Reactions can be done, for example, in temperature ranges from 20° C. to 75° C. and electric potentials up to 25 V. Trace amounts of di-hydro derivatives may be observed.
A possible setup would be a planar electron source, like a GIS-EE, next to the transportation system. The electrons are then injected into the fluid, for example. In addition to a plane-parallel structure with two electrodes, the setup could also be a lamella or grid design.
The given electron sources could be integrated either in a microsystem or as a part of a bigger reactor system. High electron or ion concentrations could be achieved by a distributed source with a high integral current and a high flow rate. Multiple electron guns could also be used.
Thus, with the reactor described herein, electron injection into a fluid, that is, a gas or a liquid, to drive chemical or biological processes is possible. Electrons could be used for ionization, electron capture to generate ions, radicals and/or solvated electrons. The electron source can either be realized by a photo cathode, a thermionic emitter or a field emitting element, where the emission surface is buried by an additional layer or separated by a transmission window to operate the emitter in a vacuum environment, for example.
Hence, packaged electron source like photo emitters, thermionic emitters and/or field emitters can be used, for example, evacuated by a getter or an external vacuum pump. A window material is, for example, carbon based, like graphene or pyrolytic carbon, or is a nitride like boron nitride or hexagonal boron nitride or silicon nitride, or also borophene, or also a film made of, for example, a plastic like polyimide or polytetrafluorethylene or polyethylene terephthalate. Furthermore, an additional coating layer can be applied on top of the window material to make it more resistant.
An emitter of hot electrons from a planar cathode or a structured surface is, for example, a graphene-silicon dioxide-silicon emitter, wherein other materials are also possible; further, an insulator covered photo cathode or photo enhanced MIS structure can also be used, wherein MIS stands for metal-insulator-substrate. Further, the electron source could be shaped like a plate capacitor or a grid or with fins, for example. Moreover, the emitting site can contain a non-planar structure, like a roughness, wires, cones, beams, blades, fins, rods, pillar, pyramids or any other non-planar configuration, or any combination thereof.
Optionally, an additional passivation layer on a top electrode can be present.
In summary, for the reactor described herein, some examples of possible applications are:
According to at least one embodiment, the electron source is a gate-insulator-substrate electron-emission structure, GIS-EE. In this case, it is possible that the provided electrons propagate only in condensed matter in the electron source from the interior up to the fluid. Hence, there may not be any gaseous or evacuated areas in the path of the electrons from the interior to the fluid. The interior may be a region next to or between the gate and the substrate. The electrons may gain energy by increasing the lattice and/or carrier temperature using thermal and/or electric and/or electromagnetic energy and by minimizing scattering overcome the work function of the final electrode.
In a GIS-EE, a voltage is applied between the substrate and the gate electrode and causes a tunnel current into the conduction band of the intermediate insulator material. The thicknesses of the gate and insulator layers as well as the choice of material are made in such a way that scattering of the electrons is minimized. Reducing the probability of scattering increases the likelihood of a non-thermal, that is, hot electron emerging at the gate material interface with the vacuum, gaseous or liquid medium. Key here is that the normal energy of the electron is larger than the work function of the gate material when residing at the interface. This requires a layer thickness that is as small as possible and a material combination that generally causes little scattering. Graphene or pyrolytic carbon and similar materials exhibit very low electron scattering. Furthermore, a very high conductance can be achieved with very thin layers. In addition, compared to a metal, a combination with silicon or silicon oxide is expected to have a lower energy difference of the conduction band edge and thus a lower quantum mechanical reflection. In general, all gate material-isolator combinations showing a small energy step from the conduction band edge of the isolator to the gate electrode are preferred. Thus, by minimizing the scattering, the electrons can gain kinetic energy in the electric field and parts of the electrons can perform the work function and exit the gate electrode. That is, a kind of integrated thermal emitter can be realized, in which the electron gas is directly heated without significantly raising the bulk temperature. An advantage is that in this case no vacuum is needed for operation and the energy of the electrons can be varied by the applied voltage. Therefore, nearly energy free, for example, thermal electrons can be emitted as well as electrons with a tunable energy up to 50 eV, for example. The latter may be favorable when a soft ionization technique like chemical ionization is desired to initiate a chemical reaction.
Furthermore, the GIS-EE can be realized by nanoporous silicon layers and a top electrode as disclosed in Nobuyoshi Koshida et al., “Ballistic electron emission from quantum-sized nanosilicon diode and its applications”, in Current Opinion in Solid State and Materials Science, Volume 15, Issue 5, October 2011, pages 183-187. Nobuyoshi Koshida is hereby incorporated herein by reference in its entirety. In these devices, a high electric field at a silicon interface is used to generate hot electrons and due to tunneling from nanostructure to nanostructure also a quasi-ballistic acceleration is realized, generating hot electrons and finally emission into the fluid or vacuum in contact.
According to at least one embodiment, the GIS-EE comprises:
According to at least one embodiment, the electrical connection structure of the GIS-EE can also be made of the same material as either the substrate or the gate material. For example, a carbon-based material is used as the contact to a carbon-based gate or a carbon-based contact. In this case, either one layer is deposited and then eventually thinned in the emission area, or two deposition steps are used both using the same material but eventually different thicknesses. For example, also the substrate directly is used for electrical contact.
For example, the band gap of the material of the transfer layer is at least 2 eV or at least 3 eV or at least 4 eV or at least 5 eV.
According to at least one embodiment, in the interior the electron source is configured to provide the electrons by thermal ionization, field ionization, tribo ionization, photo ionization, plasma ionization, or any combination thereof.
According to at least one embodiment, the electron source comprises or is a one-dimensional or two-dimensional grid. In case of a one-dimensional grid, for example, there is a field of linear lamella arranged in parallel with each other. In case of a two-dimensional grid, for example, there is a rectangular or hexagonal or circular pattern of bars that can cross each other. The grid can also have circular or elliptic openings.
According to at least one embodiment, the transportation system is configured to transport the fluid through the grid. The fluidic setup can also be realized as a micro-fluidic setup, enabling an on-chip chemical cell, either used for synthesis or analysis or both.
According to at least one embodiment, the transportation system is configured so that a maximum distance of any portion of the fluid to the electron source is at most 1 μm or is at most 5 μm or is at most 10 μm or is at most 100 μm or is at most 1 mm when passing the electron source. Alternatively or additionally, the transportation system is configured to intermix the fluid when passing the electron source. Thus, the reaction to be initiated by the electrons can take place in a large volume proportion of the fluid when passing the electron source.
According to at least one embodiment, the electron source is a GIS-EE. The thickness of the insulator is between 1 nm to 50 nm or 5 nm to 20 nm, for example. The thickness of the gate electrode is between a monolayer to 10 nm or a monolayer to 5 nm or a monolayer to 1 nm. A further protective layer with a thickness of 0.1 nm to 5 nm or 0.1 nm to 1 nm, for example, can be used.
According to at least one embodiment, the GIS-EE has another gate insulator stack added on top of the original GIS-EE. The additional potential can be used to control the potential of the electrode in contact with the fluid, while the first electrode included in the GIS-EE can be used to control the current. In this case, the first two electrodes, substrate and gate of the GIS-EE, are used to determine the emitted current while the last two, gate of the GIS-EE and additional electrode of the added isolator gate stack, can be used to determine the electron energy by the applied potential difference. The surface potential of the last electrode can then also be used to influence the chemical reaction on the surface.
According to at least one embodiment, the reactor is an electrochemical cell. For example, the electron source is a first electrode of the electro-chemical cell, and a second electrode of the electro-chemical cell may be part of the transportation system.
According to at least one embodiment, the reactor further comprises one or more detector units. For example, the at least one detector unit is arranged past the electron source along the transportation system. It is possible that the detector unit comprises a further electron source, for example, to measure a lifetime of the injected electrons in the fluid so that an operation of the electron source may be adjusted.
According to at least one embodiment, the transportation system comprises one or a plurality of pumps. For example, the at least one pump is configured to pump one or a plurality of liquids or a mixture of liquids or gases or a mixture of gases or a mixture of liquids and gases, or also emulsions, droplets, bubbles, foams and/or sprays, past the electron source. Moreover, any particle suspension could be used, for example, with particles selected from the following group, individually or in any combination: inorganics, solid polymers, hydrogel, viruses, bacteria, quantum particles, quantum dots and porous or non-porous particles. Further, the at least one pump can be configured to adjust a flow of a gas or a gas mixture that passes the electron source. The at least one pump may be configured to adjust a mixing ratio of educts of the chemical reaction to take place in the reactor. This may be controlled by means of the at least one detector unit, too.
According to at least one embodiment, the transportation system comprises one or a plurality of temperature control units. For example, the at least one temperature control unit is configured to either cool the fluid below or heat it above room temperature. For example, the fluid can be controlled at least temporarily at a temperature of at most 570 K of at most 370 K or of at most 295 K or of at most 273 K or of at most 250 K or of at most 230 K or of at most 200 K or of at most 150 K or of at most 100 K at the electron source. Thus, the temperature control unit can be a cooler. Otherwise, the temperature control unit can be a heater configured to keep the fluid at least temporarily at a temperature of at least 800 K or of at least 600 K or of at least 400 K. It is possible that there is a set of temperature control units to arrange different temperatures along a path of the fluid so that the educts may be mixed efficiently at a first temperature remote from the electron source and so that the reaction may take place at a second temperature next to the electron source. Furthermore, the pressure can be controlled to either force or keep the fluid in either liquid or gaseous state wherein solid constituents, like small particles as mentioned above, may be present.
A detector system is additionally provided. The detector system comprises a reactor as indicated in connection with at least one of the above-stated embodiments. Features of the reactor are therefore also disclosed for the detector system and vice versa.
According to at least one embodiment, the reactor is part of a detector system. The reactor could be used to ionize and/or control or drive chemical reactions in the fluid and therefore yield an additional dimension for separation to a detector system. This could be utilized or combined with an ion mobility spectrometer, a mass spectrometer, a gas chromatograph, a high-performance liquid chromatograph and/or photo ionization detector.
Thus, the detector system may comprise the reactor and the detector unit configured to detect the fluid provided with the electrons, and the detector unit could by any one or any combination of detectors mentioned in the previous paragraph.
For example, there is at least one detector unit before the electron source and alternatively or additionally at least one detector unit after the electron source, along a direction of flow of the fluid. Thus, there can be an ion mobility spectrometer before and/or after the electron source, for example.
The detector system and/or the reactor can also be a means for separation and later detection. The separation can be achieved, for example, by at least one of gas chromatography, liquid chromatography or ion mobility spectrometry. Therefore, the electron source can be used as a means to distinguish analytes by different reaction characteristics of the analytes due to varied electron injection. Accordingly, separation of substances or species of molecules can be done by physical effects.
In this regard, reference is also made to document US 2023/0415096 A1, the disclosure content of which is incorporated by reference.
For example, the reactor is or is part of a micro fluidic synthesis or analysis system. Hence, the reactor and possibly the overall detection system can be a chip or part of a chip, like an integrated circuit.
The detection system may be integrated in a gas-phase chromatograph, or the detection unit or one of the detection units is a gas-phase chromatograph.
According to at least one embodiment, the reactor or the detector system further comprises a molecular separation device. It is possible that the molecular separation device is located after the electron source, seen along a direction of movement of the fluid. Thus, substances created by the chemical reaction triggered by the electrons may be separated from each other and/or may be analyzed or stored independently of each other, for example. Alternatively or additionally, such a molecular separation device may be located prior to the electron source, for example, to improve efficiency of the chemical reaction. The molecular separation device could be a microfluidic device, For example.
A method for operating the reactor is additionally provided. By means of the method, a reactor can be operated as indicated in connection with at least one of the above-stated embodiments. Features of the reactor are therefore also disclosed for the method and vice versa.
In at least one embodiment, the method is for operating a reactor. The method comprises the following steps, for example, in the stated order:
According to at least one embodiment, the fluid contains a liquid. The electrons may thus be directly injected into the liquid. The electrons are solvated upon injection into the liquid, for example. For example, the injected electrons are solvated into a solvent or into the educts of the at least one chemical reaction. The liquid may be a mixture of a plurality of substances.
According to at least one embodiment, the at least one chemical reaction is or comprises at least one of a Birch reduction or a Bouvealt-Blanc reduction. For example, the alkali metals and/or solvents typically used in such reactions can be omitted, or a wider range of solvents is allowed due to the absence of alkali metals as electron donors. This is enabled by using the electron source, like the GIS-EE.
According to at least one embodiment, the electron source serves as a cathode, and the at least one chemical reaction is or comprises an electrochemical reaction. In other words, the at least one electron source can replace a conventional cathode, for example, being of a solid material put into the fluid.
According to at least one embodiment, the at least one chemical reaction is or comprises a reduction reaction initiated by the injected electrons. For example, the injected electrons are thermalized when initiating the at least one chemical reaction. Thermalized may mean that the kinetic energy of at least 60% or of at least 90% of the injected electrons in the fluid is between 0.1 kBT and 10 kBT or between 0.3 kBT and 3 kBT or between 0.5 kBT and 2 kBT when the chemical reaction takes place. In this case, kB refers to the Boltzmann constant. It is possible that the injected electrons have said kinetic energy already when entering the fluid.
According to at least one embodiment, the fluid is or contains CO2, either in liquid state or gaseous. For example, by means of the injected electrons the CO2 is dissociated. Hence, the products of the dissociation reaction of the CO2 can serve as educts for a further reaction, for example, to produce eFuels.
A reactor and an operating method described herein are explained in greater detail below by way of exemplary embodiments with reference to the drawings. Elements which are the same in the individual figures are indicated with the same reference numerals. The relationships between the elements are not shown to scale, however, but rather individual elements may be shown exaggeratedly large to assist in understanding.
In
The fluid 4 is transported past the electron source 2 by means of a transportation system 3. For example, by means of the transportation system 3 a velocity of the fluid 4 when passing the electron source 2 can be adjusted.
The injected electrons E are to initiate at least one chemical reaction in the fluid 4. For example, when reaching the fluid 4, all or at least part of the injected electrons E have a kinetic energy of at most 5 keV or of at most 1 keV or of at most 50 eV.
As in all other embodiments, the reactor 1 can optionally comprise at least one analytical instrument 61 before or after the electron source 2 to separate substances, for example.
For example, the chemical reaction uses solvated electrons provided by the electron source 2. The chemical reaction may be a Birch reduction wherein because of the electron source 2 no alkali metals are required in the fluid 4 which is, for example, a mixture of liquids. Thus, for example, arenes can selectively be reduced to the corresponding 1,4-cyclohexadiene compounds. Another example to take place is the Bouveault-Blanc reduction. Hence, esters, aldehydes and ketones can be reduced to the corresponding alcohols. Again, the usage of alkali metals may be omitted.
A further example is the decomposition of CO2 that could take place during the reaction. In this case, for example, the fluid 4 is a mixture of gases with one gas being CO2.
In
As a further option, the transportation system 3 can contain a mixing unit 33 to provide the fluid 4 in a homogeneous way to the electron source 2.
Moreover, it is possible that the transportation system 3 includes at least one educt storage unit 34 and/or at least one product storage unit 35. Accordingly, the transportation system 3 may have the ability to mix the fluid 4 from the educt storage units 34 to have the desired constituents and/or to split the fluid 4 into products and to lead the respective products into the product storage units 35, if desired. For the latter purpose, there can be a molecular separation device 62, for example.
Additionally, it is possible that the transportation system 3 includes a temperature control unit 32. The temperature control unit 32 may be applied along the channel the fluid 4 travels along and/or at the storage units 34 and/or 35. It is possible that different temperatures may be kept at different locations along the way of the fluid 4 through the reactor.
Furthermore, there can be one or more detector units 6 along the transportation system 3. For example, there is one detector unit 6 before and one detector unit 6 after the electron source 2. By means of the at least one detector unit 6, for example, concentrations of the educts and products and/or lifetimes of the electrons E in the fluid 4 can be determined to optimize the reaction initiated by the electrons E, for example, by adjusting the kinetic energy of the injected electrons E and/or by adjusting their concentration.
All these options concerning the transportation system 3 and the at least one detector unit 6 can be realized in all the embodiments of the reactor 1, individually or in any combination.
Otherwise, the same as to
It is possible for the second electrical connection structure 26 to be applied to the gate electrode 23 as a grid or in strips in order to ensure a uniform voltage across the gate electrode 23. Furthermore, it is possible that a protective layer 24 is present which covers the gate electrode 23. Optionally, portions of the second electrical connection structure 26 extending across the gate electrode 23 are located between the gate electrode 23 and the protective layer 24.
By means of field emission, the electrons E can thus tunnel into the conduction band of the insulator 22. If there is a sufficient voltage drop and low scattering probability, the energy gain of the potential drop in the insulator is sustained and hot electrons E can be transmitted through the gate electrode 23 and injected into the fluid 4 next to the emission side 20. The achievable energy is limited by the dielectric strength and/or by the service life of the insulator layer 22. With the voltage, the tunnel current increases with a given thickness of the insulator layer 22 and, thus, the load and the service life decreases. To a certain extent, the thickness of the insulator layer 22 can be increased in order to reduce the tunnel current at a given voltage, however, scattering effects increase, as a result of which the efficiency decreases. Likewise, a maximum charge transported by the tunnel process can decrease before a breakdown with increasing thickness.
An energy range for the emitted injected electrons E of, for example, up to 50 eV is possible. In this type of electron emitter, the actual tunnel barrier is the interface between insulator 22 and substrate 21, which is thus not exposed to the influence of the environment. Hence, the very sensitive tunneling process as well as the energy gain to overcome the work function is buried in the interior of the electron source 22 at the insulation layer 22 at a side facing the substrate or substrate electrode 21.
This principle works not only in vacuum, but also at atmospheric pressure and in liquids and renders an evacuated package superfluous. Since the electron energy can be adjusted in a certain range by means of the voltage and/or by means of the thickness of the insulator 22, it is thus possible to realize an electron source 2 with variable electron energy, if necessary also by a plurality of GIS-EEs with different thicknesses of the insulator layer 22, for example on a common substrate 21. Alternatively, a further gate-insulator stack can also be used in order to vary the energy.
In order to achieve as low a scattering as possible in the gate electrode 23 and at the interface with respect to the insulator 22, the gate electrode 23 is designed to be as thin as possible on the one hand. For example, a thickness of the gate electrode 23 is in the range of the wavelength of the electrons E, for example, at a maximum of 10 nm. The gate electrode 23 should also have a low energy difference of the conduction band edge to the conduction band edge of the insulator 22 in order to minimize quantum mechanical reflection.
Due to the requirement of the small layer thickness, the conductivity of a material of the gate electrode 23 should also be selected as high as possible in order to realize a low voltage drop at the gate electrode 23 and, thus, the possibility of as large an active area as possible. One possibility is to have carbon-based gate electrodes 23. Here, on the one hand, a diamond or diamond-like, that is sp3-hybridized, and a graphite-like, that is, sp2-hybridized, dominated body of the gate electrode 23 are suitable. In both forms, carbon materials exhibit very high, under certain circumstances direction-dependent electrical conductivities, and a very high electron transmission efficiency. This applies in particular to graphene.
A semiconductor-based gate electrode 23 can also enable a low energy jump to the insulator conduction band of the insulator layer 22. For example, silicon is suitable as a material for the gate electrode 23 in the case of a silicon oxide as the insulator layer 22.
Metals, in particularly thin metal layers, are also suitable for the gate electrode 23. Metal layers produced in particular by atomic layer deposition, ALD for short, can be homogeneous and very thin.
Some examples of sp2-hybridized dominated carbon-based materials for the gate electrode 23 are: graphene, multi-layer graphene, two-layer graphene, three-layer graphene, exfoliated graphene. Materials of the graphene family can be grown, in particular catalytically, for example, on copper, and then transferred. The growth can be carried out, for example, on SiO2, SiC, metals such as, for example, copper, or on hexagonal boron nitride or sapphire. Likewise, graphene can be grown directly on the insulator layer 22 without subsequent transfer, for example, on hexagonal boron nitride. Furthermore, a solid-phase graphenization, such as HOPG (Highly Oriented Pyrolytic Graphite), can be used with subsequent transfer. Furthermore, the use of nanocrystalline graphene, pyrolytic graphene, pyrolytic carbon, graphitic carbon or graphenic carbon is possible. Possible production processes are chemical vapor deposition, CVD for short, such as APCVD (Atmospheric Pressure CVD), LPCVD (Low Pressure CVD), PECVD (plasma enhanced CVD) or EVD (electro chemical vapor deposition); also physical vapor deposition, PVD for short, and transfer methods can be applied to produce the gate electrode 23. So-called glassy carbon or pyrolyzed polymer films can be produced by pyrolysis, for example.
Examples of sp3-hybridized dominated carbon-based materials for the gate electrode 23 are: diamond, diamond like carbon, DLC for short, ultra-nanocrystalline diamond, UNCD for short, which may be doped and can be prepared, for example, by CVD, such as PECVD.
For example, the gate electrode 23 is made of glassy carbon, GC for short, which may also be referred to as glass-like carbon, GLC. Further synonyms are vitreous carbon and polymeric carbon. When GC is used for the gate electrode 23, a thickness of the respective carbon layer is at least one monolayer or is at least two monolayers or is at least 1 nm or is at least 2 nm, for example. Alternatively or additionally, this thickness is at most 20 nm or is at most 10 nm or is at most 6 nm. For example, the gate electrode 23 has a specific electric conductivity of at least 10 S/m or of at least 103 S/m or of at least 104 S/m or of at least 105 S/m; alternatively or additionally, said value is at most 107 S/m. The GLC may optionally comprise filaments with a length-to-width ratio of at least 10.
In case of GLC for the gate electrode 23, it is possible that the substrate electrode 21 is made of GLC as well, and that the insulating layer 22 is made of hexagonal boron nitride, for example.
The GLC may be manufactured, for example, as follows:
Concerning GLC and its use and manufacture, reference is made to US patent application document U.S. Ser. No. 18/484,797, the disclosure content of which is incorporated by reference.
The gate electrode 23 may be a continuous, uninterrupted and hole-free layer and may optionally be of constant thickness. Otherwise, it is possible that the gate electrode 23 comprises a plurality of pores or holes which may be distributed regularly or also randomly.
Further 2D materials are also possible for the gate electrode 23, such as borophene, phosphor-based materials or else transition metal dichalcogenides.
Examples of semiconductor materials for the gate electrode 23 are: crystalline Si, poly-Si, amorphous Si, Ge, which can be produced, for example, by means of CVD, such as LPCVD. Examples of metals for the gate electrode 23 are: Al, Au, Ag, Pt, Ni, Co, which can be produced, for example, by means of ALD.
For example, the gate electrode 23 has a specific conductance of 10−1 S/m to 109 S/m. A thickness of the gate electrode 23 is, for example, at least one monolayer and at most 20 nm.
The insulator layer 22 is to be selected in particular as robust as possible against the tunnel currents used in order to enable the highest possible current density and service life of the GIS-EE. A manufacturing process in which the thickness of the insulator layer 22 can be accurately controlled is preferable to achieve very thin homogeneous insulation layers 22 and a high homogeneity of emission.
For example, the insulator layer 22 is made of silicon dioxide, since the achievable high oxide quality and the relatively precisely adjustable thickness permit a high current density and, thus, service life. Established production methods are also available above all in conjunction with a silicon substrate 21. In addition, the insulator 22 may be made of hexagonal boron nitride, hBN for short, allowing, among other things, direct epitaxial growth of graphene on its surface. Since the thickness can also be controlled very well by various production methods, hBN is an interesting possibility for the insulator layer 22. Particularly in combination with hBN as insulator layer 22 and graphene as gate electrode 23, very low-scattering can be achieved and, thus, a sharp energy distribution of the emitted electrons E can be realized. High-k dielectrics used in CMOS technology are also suitable for the insulator layer 22. In particular, production methods such as ALD are capable of achieving very homogeneous layers with a relatively high quality.
Silicon dioxide for the insulator layer 22 can be produced, for example, thermally, in particular wet, dry, at room temperature or in an oxidation furnace, or by means of CVD or by means of vapor deposition. hBN or BN can be produced, for example, by means of PECVD and heating, LPCVD, catholyte growth and transfer. High-k dielectrics such as Al2O3 or HfO can be produced by vapor deposition, sputtering or ALD.
For example, the insulator layer 22 has a dielectric strength of 0.02 V/nm to 1 kV/nm or of 0.1 V/nm to 500 V/nm.
Using silicon as material for the substrate 21, also referred to as substrate electrode, common methods are available from the CMOS industry and a scalable, reproducible production can be achieved. By varying the doping, the electrical properties can be influenced and even a voltage drop across the gate electrode 23 can be compensated for by a suitable doping profile. Silicon also offers the possibility of integrating further functionalities on a chip.
Furthermore, highly conductive, flexible material is also possible for the substrate 21.
In addition, sapphire, hBN, silicon carbide or also a metal film is possible as the substrate 21. In the case of a non-conductive carrier layer, the conductivity can be realized by an additional layer. For example, graphene can be grown directly on a surface of such a non-conductive carrier layer.
The substrate electrode 21 can thus be made of silicon, with a possible doping either p or n and a doping level of −− to ++, with P, As, Sb, B, Al, Ga and/or In as possible dopants. For example, the doping concentration is between 1012/cm3 and 1021/cm3 or between 1011/cm3 and 1022/cm3. Furthermore, HOPG and graphite foils as well as sapphire wafers, possibly with a carbon layer, and SiC, possibly with a carbon layer, are usable, as well as metal films.
For example, a thickness of the substrate 21 is at least one monolayer and/or at most 5 mm. The substrate 21 can be mechanically rigid or also flexible. For example, a specific electrical conductivity of the substrate 21 is between 10−1 S/m and 109 S/m.
Since the electron source 2 is used in air with oxygen or under aggressive environment or in contact with a liquid, the protective layer 24 for the gate electrode 23 may also be necessary under certain circumstances. What is important here is, in particular, the chemical resistance of the protective layer 24 as well as the controlled, homogeneous deposition of very small thicknesses. Gate dielectrics production processes and ALD are of particular interest here.
The protective layer 24 is, for example, made of silicon dioxide, as is possible in the case of the insulator layer 22. In addition, the protective layer 24 can be made of hBN or BN, which enables very thin layers and is a suitable material above all in conjunction with graphite or graphene layers for the gate electrode 23. Here, above all, the same lattice structure as in graphitic carbon would also be advantageous. Furthermore, the protective layer 24 can be made of glassy carbon, and high-k dielectrics are also possible to be applied by ALD processes or pulsed laser deposition. Silicon oxide and silicon carbide or silicon nitride are also possible materials for the protective layer 24, as well as Al2O3, for example, produced by high-frequency sputtering processes or reactive sputtering processes or ALD or pulsed laser deposition, PLD for short.
The protective layer 24 is preferably chemically insensitive to, for example, oxygen ions and oxygen radicals. A thickness of the protective layer 24 is, for example, at least one monolayer and/or at most 10 nm.
A current density of the GIS-EE 2 is, for example, at most 100 A/cm2, an emission electrode voltage can be between 0.5 V and 50 V inclusive, an efficiency can be up to 95% or in particular also up to 90%.
A functional capability of the GIS-EE 2 for ionization can be independent of pressure and type of the fluid 4 into which the GIS-EE 2 emits the electrons E.
A channel of the transportation system 3 for the fluid 4 can be constructed like a plate capacitor or a cylinder condenser, wherein openings or grid arrangements of the electron source 2 are also possible and a fluid flow from all sides is conceivable.
Otherwise, the same as to
Especially if the electron source 2 is realized as a GIS-EE, the GIS-EEs 2 can each be applied to one or both sides of the lamellae 41. Thus, the fluid 4 passes the electron source 2 by running through the lamellae 41. Alternatively, one side of the lamellae 41 can also be embodied in an insulating manner. Then, ions can first accumulate there and build up an electric counter-field so that the ionized molecules are not discharged at a rear-side lamella wall. A conductive connection to a ground potential and to positive or negative voltages is then also possible. A distance between adjacent lamellae 41 is, for example, at least 0.1 μm or at least 1 μm and/or at most 1 cm or at most 0.1 mm or at most 10 μm.
Control electronics 9 are shown only schematically in a greatly simplified manner. For example, the control electronics 9 include one or a plurality of voltage sources for applying a voltage between the substrate 21 and the gate electrode 23. The control electronics 9 can comprise means to keep, for example, the gate electrode 23 at a desired electric potential, like ground potential. It is possible that the control electronics 9 comprise a comparator and/or amplifiers. Further, by means of the control electronics 9 a current through the gate electrode 23 may be measured and adjusted, if required.
Otherwise, the same as to
For example, like in all other embodiments, the electron source 2 can replace a cathode in an electrochemical cell. In this case, the electron source 2 can be a first electrode 71 of the electrochemical cell opposite a second electrode 72 which is an anode. Other than shown in
It is further possible that an optional acceleration electrode is present, not shown, to accelerate the electrons E into a specific direction after being provided by the electron source 2.
Otherwise, the statements relating to
In the example of
The emission side 20 is formed by a transmission window 28 of the electron source 2. The transmission window 28 allows transmission of the electrons E and can be formed, for example, by a carbon layer or by one of the materials mentioned above with respect to the gate electrode 23.
Furthermore, an inner space of such an electron source 2 is preferably evacuated, for example, supported by a getter in the housing 29, in order to achieve a sufficient service life of the heating wire 27 or of the field emitter array or of a photo cathode. The fluid 4 is guided past the transmission window 28 so that the transmission window 28 may directly adjoins the fluid 4. However, the electrons E are provided distant from the fluid 4 in the interior 2X of the electron source 2.
Otherwise, the same as to
In
Otherwise, the same as to
The following proof of concept measurements demonstrate the usage of the GIS-EE as a switchable supply of solvated electrons for chemical reactions, for example.
By emitting electrons into water as the liquid 4, reduction reactions occur, resulting in the formation of hydrogen and hydroxide. While hydrogen is in a gaseous phase and escapes the water via visible bubbles 43, the hydroxide accumulates over time, resulting in the formation of hydrogen peroxide. The bubbles 43 in the water were observed during operation of the electron emitter 2, indicating the hydrogen formation. The bubbles 43 were generated next to the gate electrodes 23 near the emission side 20 wherein a 3×3-array of the gate electrodes 23 are kept at a same electric potential by means of a common electrode 51, and not further electrode is required in the liquid 4, see
The hydrogen peroxide concentration was measured at approximately 3 mg/L after the operation. This confirms the water splitting reaction and chemical reduction of water by the emitted electrons:
Furthermore, see
Another test for the chemical reactivity of the switchable microreactor 1 equipped with a GIS-EE 2 is the reduction of methylene blue 46, MB, to leucomethylene blue 47, LMB, compare
In particular, with the GIS-EE as the electron source 2, especially the following aspects can be achieved:
Hence, especially the following applications can be served efficiently:
The components shown in the figures follow, unless indicated otherwise, exemplarily in the specified sequence directly one on top of the other. Components which are not in contact in the figures are exemplarily spaced apart from one another. If lines are drawn parallel to one another, the corresponding surfaces may be oriented in parallel with one another. Likewise, unless indicated otherwise, the positions of the drawn components relative to one another are correctly reproduced in the figures.
The invention described here is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any new feature and also any combination of features, which includes in particular any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102023116090.7 | Jun 2023 | DE | national |
