Hydrogen plasma decomposition

Abstract

The present invention relates to a method for electro-thermal combined production of hydrogen, the method comprising: (i) providing a plasma processing unit having a plasma processing chamber comprising a first electrode and a second electrode, and a first gas outlet in fluid communication with the plasma processing chamber; wherein the base of the plasma processing chamber forms a reservoir of aqueous electrolyte; wherein the first electrode is included within the plasma torch, whereby the plasma torch is disposed a distance above the reservoir surface; and wherein the second electrode is submerged in the aqueous electrolyte; (ii) establishing a DC potential between the first electrode and the second electrode while providing a flow of non-oxidizing ionizable gas between the first electrode and the reservoir surface to generate and maintain a plasma arc therebetween to generate hydrogen gas in the plasma processing chamber; and (iii) recovering hydrogen via the first gas outlet. The invention also relates to a plasma processing unit.

Description

Technical Field

[0001] The invention relates to a method for the combined electric and thermal production of hydrogen (hydrogen plasma decomposition) and a plasma treatment unit for hydrogen plasma decomposition. Background Art

[0002] The world's major economies are under pressure to shift from fossil-based energy generation to renewable resources, thereby reducing the environmental impact of human activities. Hydrogen is expected to play an important role in this transition, mainly as a green fuel for energy-intensive industries such as aviation and international shipping, and as a heat source for large energy-intensive basic industries such as glass, cement and steel production. Hydrogen is also a storable energy source that can smooth out the transient nature of energy supply from renewable energy sources such as photovoltaic panels and wind / tidal turbines. Hydrogen is also expected to be used in a wide variety of vehicles, as it is currently found in fuel cell electric vehicles, with heavy-duty transportation being the main user.

[0003] There are several technologies that can be used for hydrogen production. Currently, the most widely used technology is natural gas steam reforming, but this is also the least environmentally friendly technology. Other commercially available technologies include different combinations of electrolysis, such as alkaline electrolysis and proton exchange membrane (PEM) electrolysis. Due to environmental and commercial (CO2 emissions leading to increased carbon costs) impacts, natural gas-based hydrogen production will need to be replaced by renewable energy-driven technologies that will produce environmentally friendly hydrogen, so-called "green hydrogen". The production cost of green hydrogen is the main obstacle to its deployment. One of the factors driving the rising costs is the efficiency and operating costs of the hydrogen production process, i.e. the cost of the consumed electrical energy and the chemical conversion efficiency. The present invention relates to a method (and apparatus) for enhancing the rate and efficiency of water dissociation for large-scale commercial production of hydrogen using the thermal, electrical and chemical effects of plasma.

[0004] The paper Journal of Energy Engineering 132(3) 2006 “Hydrogen Production by Plasma Electrolysis” involved a small-scale study of the feasibility of producing small amounts of stable atmospheric plasma between a DC electrode and a water surface.

[0005] The paper IOP Conf. Series: Materials Science and Engineering 162, 2017,012010 “Hydrogen production by plasma electrolysis reactor of KOH-ethanolsolution” involves a 1L electrolysis reactor and studies the effects of voltage and cathode depth on plasma electrolysis.

[0006] The paper The Chinese Journal of Process Engineering 6(3), 2006, 396 “Experimental Study of Plasma Under-liquid Electrolysis in Hydrogen Generation” discloses a contact glow discharge electrolysis method in which the plasma is maintained by a DC or pulsed DC glow discharge between an electrode and the surrounding electrolyte surface.

[0007] The paper Jpn. J. Appl. Phys. 44(1A), 2005, 396 “Hydrogen Evolution by Plasma Electrolysis in Aqueous Solution” discloses a 1-liter electrolysis cell for plasma electrolysis. The tungsten cathode is separated from the platinum mesh anode by an inverted quartz glass funnel.

[0008] The paper Journal of The Electrochemical Society 166(6), 2019, E181 “Effect of Competing Oxidizing Reactions and Transport Limitation on the Faradaic Efficiency in Plasma Electrolysis” studied the plasma electrolytic reduction of chloroacetate and ferrocyanide.

[0009] The paper WHEC 13–16 June 2006 – Lyon France “Hydrogen production bythermal water splitting using a thermal plasma” presents a brief state of the art in hydrothermal plasma technology, showing the range of temperatures and quenching rates that are technically achievable. The paper introduces and discusses the thermodynamic properties of water plasmas and proposes a kinetic computational model describing the behavior of the cracking products in the plasma plume during quenching with respect to various parameters such as quenching rate.

[0010] WO 2008 / 141369 A1 relates to the electrolysis of water for the production of hydrogen and oxygen.

[0011] WO 2019 / 096880 A1 relates to a method and a device for plasma-induced water decomposition.

[0012] Conference paper “Confirmation of anomalous hydrogen generation by plasmaelectrolysis” in 4 th Meeting of Japan CF Research Society, 2003 provided research on hydrogen production by electrolyzer.

[0013] The paper Energy Sci. Eng. 9, 2021, 267 “Comprehensive assessment of hydrogen production in argon-water vapors plasmolysis” reports a simultaneous study of theoretical and experimental analysis of hydrogen production from argon-water vapor mixtures at atmospheric pressure as a function of the applied voltage of the DBD plasma.

[0014] There remains a need in the art for a method and apparatus that allows for the commercial production of hydrogen. Despite the claims claiming success in small laboratory scale trials, there are significant gaps in the information, however, they do demonstrate the feasibility of producing hydrogen by plasma electrolysis. Due to the formation of large quantities of hydrogen and oxygen mixtures at high temperatures, commercial production concerns require essential longevity, control and therefore safety. The inventors have developed the present invention with the goal of addressing these problems in the prior art, or at least providing a commercially viable alternative. Summary of the invention

[0015] In a first aspect of the present invention, there is provided a method for producing hydrogen by combining electricity and heat, the method comprising:

[0016] (i) providing a plasma processing unit having a plasma processing chamber including first and second electrodes, and a first gas outlet in fluid communication with the plasma processing chamber;

[0017] wherein the base of the plasma processing chamber forms a reservoir for an aqueous electrolyte;

[0018] wherein the first electrode is included in a plasma torch, whereby the plasma torch is arranged at a distance above a surface of the reservoir; and

[0019] wherein the second electrode is immersed in an aqueous electrolyte;

[0020] (ii) establishing a DC potential between the first and second electrodes while providing a flow of a non-oxidizing ionizable gas between the first electrode and the reservoir surface to generate and maintain a plasma arc therebetween to generate hydrogen gas in the plasma processing chamber; and

[0021] (iii) recovering hydrogen via the first gas outlet.

[0022] The present disclosure will now be further described. In the following paragraphs, different aspects / embodiments of the present disclosure are defined in more detail. Unless explicitly stated to the contrary, each aspect / embodiment so defined may be combined with any other aspect / embodiment or multiple aspects / embodiments. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous. In particular, features disclosed with respect to the method may be combined with features described with respect to a plasma processing unit suitable for implementing the method, and vice versa.

[0023] The present invention relates to a method for producing hydrogen by combining electricity and heat, which can be simply referred to as plasma decomposition of hydrogen or plasma production in this article.

[0024] The method comprises: providing a plasma treatment unit, which may also be referred to as a plasma decomposition tank. Preferably, the plasma treatment unit is a plasma treatment unit of the second aspect described herein. The unit has a plasma treatment chamber comprising a first and a second electrode, and a first gas outlet in fluid communication with the plasma treatment chamber. The plasma treatment chamber refers to an enclosed space in which hydrogen plasma decomposition can be performed using the first and second electrodes. The cross-section of the first electrode is preferably larger than that of the second electrode. The base of the plasma treatment chamber forms a reservoir for an aqueous electrolyte. That is, the base is filled with an aqueous electrolyte to form a reservoir. Preferably, the base has a volume of at least 5 liters, more preferably at least 10 liters. This volume allows large-scale production of hydrogen, but due to the large amount of potentially explosive gas mixtures, more safety considerations are required compared to smaller-scale feasibility studies. The first gas outlet allows the removal of the generated hydrogen-rich gas from the plasma treatment chamber.

[0025] The first electrode is included in the plasma torch, whereby the plasma torch is arranged at a certain distance above the surface of the reservoir. That is, the plasma torch includes and provides the first electrode used in the method, and in particular, the first electrode is arranged at an appropriate distance above the surface of the reservoir. This distance refers to the minimum separation between the electrode and the surface. Generally speaking, the first electrode will be "rod" shaped, and generally the distance is the distance to the tip of the electrode. The second electrode is immersed in the reservoir of the aqueous electrolyte so that at least a portion of the electrode is below the surface. Preferably, the second electrode is completely immersed in the reservoir of the aqueous electrolyte (i.e., the electrode is "underwater").

[0026] Preferably an electromagnet may be provided near the tip of the plasma torch. This may extend into the electrolyte. Providing an electromagnet can be used to stabilize the plasma formed. In embodiments where the components have an annular concentric form, the electromagnet can thus be arranged coaxially with the plasma torch.

[0027] Preferably, the aqueous electrolyte comprises an alkali metal or alkaline earth metal salt and / or an alcohol. For example, preferably the aqueous electrolyte comprises a sodium or potassium salt of a hydroxide, a carbonate and / or a chloride (preferably a hydroxide). Due to possible corrosion, equipment life and environmental impact, halides such as chlorides are less preferred. It is also preferred that the electrolyte comprises an alcohol, preferably a C1-C6 alcohol, such as ethanol and / or methanol. Such additives are preferred for improving the overall efficiency of hydrogen production. The inventors have found that there will be particular benefits when the electrolyte comprises at least 20 wt%, preferably at least 25 wt%, more preferably at least 30 wt% and / or up to 60 wt%, for example, 20 wt%-60 wt%, preferably 25 wt%-55 wt% of alcohol.

[0028] Preferably, the conductivity of the electrolyte used for hydrogen plasma decomposition is at least 20 mS / cm and / or at most 130 mS / cm. In some embodiments, the electrolyte may have a low conductivity, for example, 20-40 mS / cm, while in other embodiments, the electrolyte may have a high conductivity, for example, 80-130 mS / cm.

[0029] The method includes: establishing a DC potential between first and second electrodes while providing a flow of non-oxidizing ionizable gas between the first electrode and a reservoir surface to generate a plasma arc therebetween upon electrical breakdown, thereby generating hydrogen gas in a plasma processing chamber; and recovering the hydrogen gas via a first gas outlet.

[0030] Establishing a DC potential refers to applying a DC voltage between the first and second electrodes. As long as the DC voltage and the non-oxidizing ionizable gas flow remain continuous and the current flows, the plasma arc will also continue. Preferably, the first electrode is a cathode and the second electrode is an anode. Preferably, the potential has a voltage of at least 30 V, preferably at least 300 V, more preferably at least 500 V. For example, the voltage is preferably in the range of 100-5000 V, more preferably in the range of 1000-3000 V, for example, the range of 1500-2000 V. It is also preferred that the current is less than 100 A, preferably less than 50 A. Preferably, the current is at least 10 A. The inventors have found that this high voltage and low current are particularly suitable for large-scale production of hydrogen by plasma decomposition, because it has been found that these parameters are conducive to hydrogen production and minimize the energy loss that is crucial to the commercial production of hydrogen. These parameters are roughly opposite to the typical parameters of other plasma applications using low voltage and high current. In addition, low current reduces wear on the first electrode, for example, reduces oxidation and / or etching. Thus, when implementing the method and during the lifetime of the electrode and the processing unit, the distance between the electrode tip and the aqueous electrolyte surface can be reliably controlled, whereby downtimes can also be reduced. In the present method, the energy consumption per kg of hydrogen produced / recovered is preferably less than 50 kWh, preferably less than 45 kWh.

[0031] A non-oxidizing ionizable gas stream is provided between the first electrode and the reservoir surface while applying a voltage. The stream is preferably provided by a plasma torch. Since a high voltage is applied between the first and second electrodes, and the second electrode is immersed in an aqueous electrolyte, this will generate a plasma arc in a so-called "transferred arc" mode between the first electrode and the aqueous electrolyte, i.e., an arc bridge from a plasma device to an electrolyte. Preferably, the first electrode is arranged at a distance of 0.1-50 mm, more preferably 1-20 mm, more preferably 1-5 mm from the reservoir surface. In a preferred embodiment, the distance changes while the potential between the first and second electrodes is established. Preferably, the distance increases from the initial distance of establishing a plasma arc to a greater distance of a plasma decomposition reaction implemented using a plasma arc. A greater distance is preferred because a longer plasma arc provides a greater voltage. Since volts = joules / coulombs, for a given charge, a greater voltage provides greater energy. The plasma arc may also be referred to as a "hot arc", "hot plasma arc" or "balanced plasma arc".

[0032] The plasma torch generates a plasma arc, which provides the electrons required for reduction (electrolysis) and radiant heat (pyrolysis). Hydrogen (a mixture with a non-oxidizing ionizable gas and some oxygen) is produced by plasma decomposition. Therefore, the gas produced is a hydrogen-rich gas mixture. The gas rises in the plasma treatment chamber and is recovered through the first gas outlet. Thereafter, the hydrogen can be easily separated and purified, and so is the oxygen. The non-oxidizing ionizable gas can be recycled into the gas flow in the plasma treatment chamber. Preferably, the non-oxidizing ionizable gas is helium, argon, nitrogen, hydrogen or a mixture thereof, helium, argon or nitrogen or a mixture thereof, and more preferably argon.

[0033] The present method mitigates the risks associated with the formation of potentially explosive mixtures of hydrogen and oxygen. These risks do not occur in small laboratory-scale applications, but become critical when the process is scaled up industrially. The plasma arc has steep thermal and pressure gradients, which can cause products from the plasma arc to be discharged as the plasma arc produces products. The introduction of a non-oxidizing ionizable gas helps to continuously extract gaseous products and dilute and cool the gas. The inventors have also found that the non-oxidizing ionizable gas can protect the electrode from oxidation and ultimately prevent the electrode from decomposing, thereby minimizing downtime and maximizing the life of the plasma processing unit (plasma decomposition cell). Preferably, the first and / or second electrode is composed of a thermochemically stable metal such as tungsten, molybdenum and / or a platinum group metal. For example, it is preferred that the first electrode is composed of tungsten and / or molybdenum, and the second electrode is composed of a platinum group metal such as platinum.

[0034] It is particularly preferred that the plasma torch includes a nozzle defining an annular channel around the first electrode, and the non-oxidizing ionizable gas flow is provided through the annular channel of the plasma torch. This is particularly effective in minimizing oxidation and corrosion of the electrode. Preferably, the plasma torch is a water-cooled plasma torch. In the case where the plasma torch includes a nozzle, the nozzle may be water-cooled and / or the electrode may be water-cooled, preferably both are water-cooled. In other embodiments, the plasma torch does not have a water-cooled nozzle because this saves costs and may not be required when operating at lower temperatures. Suitable plasma torches for the present invention may be known in the field of extractive metallurgy and new materials, such as pure quartz glass. A suitable plasma torch assembly is described in WO2019 / 092416 A1 (the patent is incorporated herein in its entirety). The unique use of a plasma torch in the transfer arc mode of this invention allows the safe production of large amounts of hydrogen while maintaining a relatively low and safe operating temperature for the dilution gas produced, thereby avoiding the risk of any dangerous explosion. Therefore, the present method can produce up to 6000 g of hydrogen per hour per unit slot operation. This is an entry-level industrial-scale tank that can be replicated for large unit installation capacities.

[0035] Alternatively or in addition, the non-oxidizing ionizable gas flow is provided through one or more flow paths angled above the surface of the reservoir. That is, one or more flow paths (such as pipes) allow the introduction of non-oxidizing ionizable gas through the wall of the plasma processing unit and provide a gas flow across the surface of the reservoir to dilute again and assist in rapid cooling of the gaseous products. Preferably, the non-oxidizing ionizable gas flow will keep the temperature of the gas mixture released in the plasma processing unit below 250°C, preferably below 200°C. The inventors surprisingly found that the non-oxidizing ionizable gas flow, together with the supplementary voltage drop, can be used to fully quench hydrogen when it is formed and maintain the plasma processing chamber sufficiently "cold" to allow commercial production of hydrogen in a sufficiently safe manner.

[0036] Preferably, the method further comprises stirring the aqueous electrolyte. Stirring the aqueous electrolyte maintains the homogeneity of the mixture and prevents local overheating and reagent depletion during plasma decomposition. This ensures effective heat and electron transfer from the plasma arc by reducing the thickness of the diffusion layer, and minimizes the vapor concentration in the plasma arc that may inhibit heat and mass transfer. Preferably, the method further comprises metering water into the reservoir, and optionally adding further aqueous electrolyte to keep the aqueous electrolyte level substantially constant. Preferably, the aqueous electrolyte concentration is kept substantially constant. In some embodiments, the temperature of the aqueous electrolyte during the method is maintained at 60°C or higher and / or 100°C or lower, such as 70-80°C. Therefore, it is also preferred that any water and optional other aqueous electrolytes that can be added to the reservoir have a temperature of 60°C or higher. In other embodiments, the temperature of the aqueous electrolyte during the method is maintained at 40°C or lower. At these reduced temperatures, the inventors found that water-cooled plasma torches may be less than ideal, and removing the water-cooled nozzle (and using a non-cooled nozzle or sheath) reduces the complexity of the first electrode and the tendency of side arcs to occur.

[0037] Preferably, the plasma processing chamber is divided into first and second subchambers by a gas-impermeable barrier disposed above the surface of the fluid reservoir and immersed in the fluid reservoir;

[0038] wherein the first gas outlet is in fluid communication with the first subchamber, and the second gas outlet is in fluid communication with the second subchamber;

[0039] wherein the first and second subchambers are in fluid communication via a reservoir of an aqueous electrolyte; and

[0040] The first electrode is arranged in the first subchamber, and the second electrode is arranged in the liquid reservoir below the second subchamber, whereby the hydrogen-rich gas formed by the plasma rises into the first subchamber to be recovered through the first gas outlet, and the oxygen-rich gas formed at the second electrode rises into the second subchamber to be recovered through the second gas outlet.

[0041] In a second aspect of the present invention, there is provided a plasma processing unit for producing hydrogen by electric and thermal combination, the plasma processing unit comprising:

[0042] (i) a plasma processing chamber having a base for forming a reservoir for an aqueous electrolyte, the plasma processing chamber being divided into first and second subchambers by a gas impermeable barrier extending into the base;

[0043] (ii) a first gas outlet in direct fluid communication with the first subchamber and a second gas outlet in direct fluid communication with the second subchamber; and

[0044] (iii) first and second electrodes connectable to a DC power source, wherein the first electrode is included in the plasma torch;

[0045] The plasma torch is arranged in the first subchamber and the second electrode is arranged in the base below the second subchamber, so that in use, the first electrode is arranged at a distance above the surface of the reservoir and the second electrode is immersed in the aqueous electrolyte.

[0046] The plasma treatment unit is preferably used for the above method. In particular, the treatment chamber of the unit is divided into a first and a second subchamber, each of which has a gas outlet for recovering hydrogen-rich and oxygen-rich gases respectively produced near the first and second electrodes when in use. That is, the first subchamber includes a first gas outlet and the second subchamber includes a second gas outlet, so that the gas produced from the reservoir of aqueous electrolyte added to the base when in use can be recovered separately. Preferably, at least one, preferably two, gas outlet process pipelines connected to the respective gas outlets include a U-shaped elbow drain (i.e., a manometer-type U-shaped elbow) to allow condensate to be removed from the product gas vapor and subsequently discharged, while avoiding air from entering the chamber through a countercurrent process.

[0047] The airtight barrier extending into the base ensures that the first and second subchambers are not in gas communication with each other when in use. The inventors have found that plasma formation causes a pressure difference between the first and second subchambers, and the cathode tank (i.e., preferably the first subchamber including the first electrode) is pressurized to push the liquid level of the reservoir in the subchamber downward. It is found that this can cause process instability and electrolyte level oscillation. Preferably, the plasma processing unit also includes an electrolyte level sensor, preferably an ultrasonic electrolyte level sensor. In a preferred embodiment, the purge gas is allowed to enter the anode tank (e.g., the second subchamber) to balance the pressure, thereby reducing and / or eliminating harmful oscillations of the reservoir level in each subchamber. Therefore, the inventors have found that in order to avoid gas communication between the two chambers, the gas impermeable barrier preferably extends into the base (below the electrolyte) by at least 15 mm, preferably 20-50 mm.

[0048] As described in relation to the method, preferably the plasma torch is a water (or equivalent hot fluid) coolable plasma torch. Preferably the plasma torch comprises a nozzle defining an annular channel around the first electrode, the annular channel being connectable to a supply of non-oxidising ionisable gas and / or one or more flow paths connectable to the supply of non-oxidising ionisable gas being arranged in the first sub-chamber at an angle relative to the reservoir surface. Such flow paths allow the introduction of non-oxidising ionisable gas through the side wall of the plasma processing unit, thereby providing an angle relative to the reservoir surface when in use, thereby enabling a gas flow to be provided across the reservoir surface.

[0049] Preferably, the impermeable barrier is a wall made of an electrically insulating inorganic refractory or polymer material. The wall of the plasma treatment chamber, and in particular the impermeable barrier, may include metal components in its construction structure. In this case, the metal components are preferably coated with an electrically inert coating such as a ceramic (e.g., thermal ceramic spraying or enameling) to provide mechanical and chemical stability and to help eliminate side arcs in the chamber. Such an electrically inert coating is preferably applied to both sides of the barrier and may also be applied to the nozzle / sheath of the first electrode. Examples of suitable coatings include aluminum oxide. Preferably, the plasma treatment chamber includes a thermally and electrically insulating lining, preferably a refractory lining, and / or the chamber includes external thermal insulation. Preferably, the base of the plasma treatment chamber includes a glass and / or polymer lining, preferably a composite glass and polymer lining. In a preferred embodiment, the plasma treatment unit includes a device for recycling and / or recovering waste heat, such as a device for recycling heat and preheating additional new water / electrolyte to be metered in.

[0050] In a particularly preferred embodiment, the first and second electrodes are arranged concentrically, preferably coaxially, in the plasma processing unit / chamber. Typically, the first electrode is arranged in the center of the first subchamber, while the second electrode is arranged concentrically at the base below the second subchamber. Thus, preferably the second electrode is a ring electrode. Preferably, the second electrode is in the form of a mesh.

[0051] As will be appreciated, with a concentric arrangement of electrodes, the first and second subchambers are preferably also concentrically arranged, whereby the second subchamber of the plasma processing unit surrounds the first subchamber. This arrangement of electrodes improves the operating efficiency of the unit (i.e., the amount of hydrogen produced per unit of input power).

[0052] In some preferred embodiments, the plasma torch is housed in an electrically insulating tube extending downward into the electrolyte (one end is immersed in the electrolyte). When present, the tube does not have to divide the electrolyte into separate areas; instead, the electrolyte must remain free to flow within the base of the process chamber below the two sub-chambers. This can be achieved by ensuring that the tube is supported above the bottom of the base. Quartz is a preferred material for the tube. The inventors have found that quartz is beneficial compared to other materials such as borosilicate glass due to its lower coefficient of thermal expansion (CTE), and is therefore more resistant to thermal shock and allows better infrared transmission. The inventors have found that the tube will provide electrical insulation, prevent process shorts, and improve safety. The use of chemically resistant materials and changes in structural materials will increase its resistance to thermal shock phenomena.

[0053] Preferably the plasma treatment unit comprises a stirrer arranged in the base. Preferably the plasma treatment unit further comprises means for introducing water and / or aqueous electrolyte into the base. The means can be used to meter feed to the reservoir to maintain a substantially constant level and / or concentration of aqueous electrolyte.

[0054] Preferably the plasma torch is movable within the first subchamber so that in use the distance between the first electrode and the reservoir surface can be varied while establishing a potential (and current) between the first and second electrodes and maintaining a plasma arc. In some embodiments the plasma torch may contact the electrolyte during a start-up phase of use.

[0055] In a preferred embodiment, the plasma processing unit further comprises a condensing unit arranged in the first sub-chamber, such that, in use, the condensing unit condenses water vapour contained in the produced gas mixture. Such condensing means also contribute to maintaining the temperature in the processing chamber below 250° C. The gas outlet process line is preferably water cooled to further condense any moisture leaving the chamber through the gas outlet.

[0056] In another aspect, the present invention provides a hydrogen generation system comprising a plurality of plasma processing units that can be connected together to provide a higher unit capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The invention will now be further described with reference to the following non-limiting drawings, in which:

[0058] Figure 1 A cross section of a plasma processing unit according to the invention is shown in use.

[0059] Figure 2 A cross section of a plasma torch suitable for use with the present invention is shown.

[0060] Figure 3-6 Graphs of the hydrogen production rate, hydrogen flow rate, hydrogen concentration, and byproduct concentration measured for different concentrations of methanol in the aqueous electrolyte are provided in the Examples.

[0061] Figure 7 A cross section of an exemplary plasma processing cell including a concentric arrangement of second electrodes is shown. DETAILED DESCRIPTION

[0062] Figure 1 A cross section of a plasma processing unit 100 suitable for hydrogen plasma decomposition is shown. The plasma processing unit 100 includes a plasma processing chamber 105 divided into a first subchamber 120, a second subchamber 125, and a base 110 located directly below the first and second subchambers 120, 125. The base 110 has a lining formed of a polymer or other thermally and chemically compatible material that forms a reservoir for an aqueous electrolyte 115 (e.g., an aqueous solution containing sodium hydroxide and ethanol and / or methanol). The upper surface of the reservoir 115 of the aqueous electrolyte when in use can be used to define a boundary between the base 110 and the first and second subchambers 120, 125.

[0063] The first sub-chamber 120 is separated from the second sub-chamber 125 by a wall 130 formed of an inorganic material providing a gas impermeable barrier. The wall 130 extends into the base 110 such that, in use, the wall extends into the reservoir 115.

[0064] The plasma processing unit 100 includes a first gas outlet 135 that is in direct fluid communication with the first subchamber 120 (i.e., not via the base). Similarly, the unit 100 includes a second gas outlet 140 that is in direct fluid communication with the second subchamber 125. A first electrode 145 is included in a plasma torch disposed in the first subchamber 120 such that the first electrode 145 is disposed a distance above the upper surface of the reservoir 115, such as about 1 mm. The plasma torch is disposed in a generally vertical position such that the tip of the first electrode 145, where the plasma arc is to be generated, is at a distance from the upper surface of the reservoir 115. The second electrode 150 is completely immersed in the reservoir of aqueous electrolyte 115 directly below the second subchamber 125, but the second electrode 150 may instead be immersed so that a portion thereof extends into the second subchamber 125. The first and second electrodes 145, 150 are connected to a DC plasma power supply 155 such that the first electrode 145 is a cathode and the second electrode 150 is an anode.

[0065] In use, a non-oxidizing ionizable gas flow is provided (not shown) between the first electrode 145 and the upper surface of the reservoir 115, and a high voltage potential of greater than 1000 V is applied to generate and maintain a plasma arc therebetween. After an initial period of time to establish the plasma arc, the distance from the first electrode 145 to the surface of the reservoir 115 is increased, for example to about 10 mm, while maintaining the high voltage potential, thereby maintaining the plasma arc.

[0066] Thus, a hydrogen-rich gas 160 is generated by the interaction of the plasma arc and the aqueous electrolyte, which rises into the first subchamber 120 and is then recovered through the first gas outlet 135. As will be appreciated, a gas mixture is released during plasmalysis that will fill the first subchamber upon continued operation. In some preferred embodiments, the plasma processing unit 100 includes one or more condensation units disposed within the first subchamber 120 to condense any water vapor generated during plasmalysis. At the same time, oxygen 165 is generated at the second electrode and rises into the second subchamber 125 and can be recovered independently from the hydrogen-rich gas 160 through the second gas outlet 140.

[0067] The plasma treatment unit 100 also includes an agitator 170 arranged in the base 110 so that, when in use, the reservoir of aqueous electrolyte 115 can be agitated. The unit 100 also includes means 180 for introducing water and / or aqueous electrolyte into the base, for example, a conduit arranged through the wall of the unit 100 and into the base 115.

[0068] Although the non-oxidizing ionizable gas stream may be provided by a plasma torch, as described below with respect to Figure 2 Further description is given, but the unit 100 may also include one or more flow paths 175, such as conduits, which pass through the side wall of the unit 100 and are thus arranged in the first subchamber 120 at a certain angle relative to the surface of the reservoir 115. In use, the flow of non-oxidizing ionizable gas between the first electrode and the reservoir surface can then be provided through the flow path 175.

[0069] Figure 2 A cross section of the working end (including the electrode tip) of a cylindrical plasma torch 200 is shown. The plasma torch 200 is suitable for Figure 1 The plasma processing unit 100 is shown and includes an electrode 205 having a tungsten tip 210. The plasma torch 200 also includes a nozzle 215, which defines an annular channel 220 around the electrode 205, through which a non-oxidizing ionizable gas 225, preferably argon, can be supplied. The electrode 205 is connected to a DC power supply 230, which in turn is connected 235 to a second electrode (not shown) of the plasma decomposition cell.

[0070] When used, such as Figure 1 As shown, the tungsten tip 210 is arranged at a certain distance 240 above the surface 245a of the reservoir 245 of the aqueous electrolyte, and a high voltage DC potential is applied to the first electrode 205 and the second electrode, while providing an argon gas flow 225, which helps to maintain the plasma arc 250 generated between the electrode 205 and the surface 245a, which in turn leads to the production of hydrogen-rich gas (i.e., plasma decomposition of hydrogen).

[0071] The plasma torch 200 is actively cooled. Both the electrode 205 and the nozzle 215 can be cooled by a supply of cooling fluid, preferably water. The electrode has a cooling water supply 255a and a cooling water return 255b, while similarly, the nozzle has a cooling water supply 260a and a cooling water return 260b formed by flow paths in the electrode and nozzle, respectively. Water cooling extends the life of the electrode by running the tungsten tip in a cool state to reduce wear and degradation.

[0072] Figure 7A cross section of a plasma processing unit 300 suitable for producing hydrogen by plasma decomposition is shown. The plasma processing unit 300 comprises a plasma processing chamber divided into a first and a second sub-chamber, wherein each sub-chamber has a condensation unit 355, 360 arranged therein to condense water vapor contained in a gas mixture generated in each sub-chamber when in use. Each condensation unit 355, 360 is a series of condensation tubes arranged concentrically in each sub-chamber.

[0073] The plasma treatment unit 300 comprises a first electrode arranged in a plasma torch 345 centrally within a first subchamber, wherein the electrode tip of the plasma torch 345 is arranged above the surface of a reservoir 315 of an aqueous electrolyte. An impermeable barrier 330 is a wall of the plasma treatment unit preferably coated with an electrically insulating ceramic, extending into the base of the treatment unit and thus extending into the aqueous electrolyte 315 when in use. The barrier 330 extends a distance 365 below the surface of the aqueous electrolyte, preferably at least 20 mm. A second electrode 350 is a concentrically arranged mesh and is completely immersed in the aqueous electrolyte below the second subchamber of the treatment unit 300. For clarity, the gas and aqueous electrolyte inlets and outlets are omitted.

[0074] A further quartz tube (not shown) may be provided within the gas impermeable barrier 330, extending around the plasma torch 345 and into the electrolyte 315. This helps to electrically insulate the first electrode from the second electrode.

[0075] Example

[0076] The method disclosed herein was carried out using a plasma treatment cell comprising concentrically arranged first and second electrodes, using different amounts of alcohol, in particular methanol, in an aqueous electrolyte. These experiments were carried out using electrode conductivities of 20-40 mS / cm.

[0077] The hydrogen production rate at the first gas outlet as well as the hydrogen flow rate, hydrogen concentration and by-product concentration were measured at different power inputs ranging from 4 kW to 12 kW. The data are provided in the following table and Figure 3-6 middle.

[0078] Specific hydrogen production:

[0079]

[0080]

[0081] Hydrogen flow rate:

[0082]

[0083]

[0084] In comparison, preliminary technical performance operating with a high conductivity electrolyte of 80-130 mS / cm without the addition of methanol provided the same level of hydrogen production, but at higher specific energy conditions. These data are provided below:

[0085]

[0086]

[0087] As used herein, the singular forms of "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. The use of the word "comprising" is intended to be interpreted as including those features but not excluding others, and is also intended to include the selection that must be limited to the features described. In other words, unless the context clearly dictates otherwise, the term also includes the limitations of "consisting essentially of" (intended to indicate that certain other components may be present as long as they do not materially affect the basic characteristics of the described features) and "consisting of" (intended to indicate that other features are not included, so that if the components are expressed as percentages according to their proportions, the components will add up to 100%, while taking into account any unavoidable impurities).

[0088] It should be understood that, although the terms "first", "second", etc. may be used herein to describe various elements and / or parts, the elements and / or parts should not be limited by these terms. These terms are only used to distinguish one element or part from another or further element or part. For ease of description, spatial relative terms such as "below", "below", "below", "lower", "above", "higher", "upper", etc. may be used herein to describe the relationship between one element or feature and another element or feature.

[0089] The above detailed description is provided by way of explanation and illustration and is not intended to limit the scope of the appended claims. Many variations of the preferred embodiments of the invention shown herein will be apparent to those of ordinary skill in the art and still fall within the scope of the appended claims and their equivalents.

Claims

1. A method for producing hydrogen by combining electricity and heat, the method comprising: (i) providing a plasma processing unit having a plasma processing chamber including a first electrode and a second electrode, and a first gas outlet in fluid communication with the plasma processing chamber; wherein the base of the plasma processing chamber forms a reservoir for an aqueous electrolyte; wherein the first electrode is included in a plasma torch, whereby the plasma torch is arranged at a distance above a surface of the reservoir; and wherein the second electrode is immersed in the aqueous electrolyte; (ii) establishing a DC potential between the first electrode and the second electrode while providing a flow of a non-oxidizing ionizable gas between the first electrode and the reservoir surface to generate and maintain a plasma arc therebetween, thereby generating hydrogen gas in the plasma processing chamber; as well as (iii) recovering the hydrogen gas via the first gas outlet. The method according to claim 1 , wherein the plasma torch is a water-cooled plasma torch.

3. A method according to claim 1 or 2, wherein the plasma torch comprises a nozzle defining an annular channel, the annular channel surrounding the first electrode, and the non-oxidizing ionizable gas flow is provided through the annular channel of the plasma torch, and / or wherein the non-oxidizing ionizable gas flow is provided through one or more flow paths angled above the surface of the reservoir.

4. The method according to any one of the preceding claims, wherein the non-oxidizing ionizable gas is helium, argon, nitrogen, hydrogen or a mixture thereof, preferably argon or hydrogen.

5. A method according to any one of the preceding claims, wherein the flow of non-oxidizing ionizable gas maintains the temperature of the gas mixture generated within the plasma treatment unit below 250°C, preferably below 200°C.

6. A method according to any one of the preceding claims, wherein the aqueous electrolyte comprises an alkali metal or alkaline earth metal salt and / or an alcohol.

7. The method according to any of the preceding claims, wherein the first electrode is arranged at a distance of 0.1-50 mm, preferably 1-20 mm, from the surface of the reservoir.

8. The method of claim 7, wherein the distance is varied while establishing an electrical potential between the first electrode and the second electrode.

9. The method according to any of the preceding claims, wherein the potential has a voltage of 50-5000 V, preferably 300-2000 V, and preferably wherein the current is less than 100 A, preferably less than 50 A.

10. The method according to any of the preceding claims, wherein the energy consumption is less than 50 kWh, preferably less than 45 kWh, per kg of hydrogen produced.

11. The method according to any one of the preceding claims, wherein the plasma processing chamber is divided into a first sub-chamber and a second sub-chamber by a gas-impermeable barrier, the gas-impermeable barrier being arranged above the surface of the liquid reservoir and immersed in the liquid reservoir; wherein the first gas outlet is in fluid communication with the first sub-chamber, and the second gas outlet is in fluid communication with the second sub-chamber; wherein the first subchamber and the second subchamber are in fluid communication via a reservoir of the aqueous electrolyte; and The first electrode is arranged in the first sub-chamber, and the second electrode is arranged in the liquid reservoir below the second sub-chamber, so that the hydrogen formed by the plasma rises to the first sub-chamber through the first gas outlet for recovery, and the oxygen formed at the second electrode rises to the second sub-chamber through the second gas outlet for recovery.

12. A method according to any preceding claim, wherein the second electrode is completely immersed in the reservoir of aqueous electrolyte.

13. The method of any one of the preceding claims, wherein the method further comprises stirring the aqueous electrolyte.

14. A method according to any preceding claim, wherein the method further comprises metering water, and optionally metering further aqueous electrolyte, into the reservoir to maintain a substantially constant level of aqueous electrolyte.

15. The method of claim 14, wherein the water and optionally the additional aqueous electrolyte are metered into the reservoir at a temperature of 60°C or higher.

16. A plasma processing unit for producing hydrogen by combining electricity and heat, the plasma processing unit comprising: (i) a plasma processing chamber having a base for forming a reservoir for an aqueous electrolyte, the plasma processing chamber being divided into a first subchamber and a second subchamber by a gas impermeable barrier extending into the base; (ii) a first gas outlet in direct fluid communication with the first subchamber and a second gas outlet in direct fluid communication with the second subchamber; as well as (iii) a first electrode and a second electrode connectable to a DC power source, wherein the first electrode is included in a plasma torch; wherein the plasma torch is arranged in the first sub-chamber and the second electrode is arranged in the base below the second sub-chamber such that, in use, the first electrode is arranged at a distance above the surface of the reservoir and the second electrode is immersed in the aqueous electrolyte.

17. The plasma processing unit of claim 16, wherein the plasma torch is a water-coolable plasma torch.

18. A plasma processing unit as claimed in claim 16 or 17, wherein the plasma torch comprises a nozzle defining an annular passage surrounding the first electrode, the annular passage being connectable to a supply of non-oxidising ionisable gas.

19. A plasma processing unit according to any one of claims 16 to 18, wherein one or more flow paths connectable to a supply of non-oxidising ionisable gas are arranged within the first sub-chamber at an angle relative to the reservoir surface.

20. A plasma processing unit as claimed in any one of claims 16 to 19, wherein the gas impermeable barrier is a wall made of an electrically insulating refractory or polymeric material.

21. A plasma processing unit according to any one of claims 16 to 20, wherein the plasma processing chamber comprises a refractory lining and / or external thermal insulation.

22. A plasma processing unit as claimed in any one of claims 16 to 21 wherein the base of the plasma processing chamber comprises a glass and / or polymer lining.

23. A plasma processing unit according to any one of claims 16 to 22, wherein the plasma processing unit comprises an agitator arranged in the base.

24. A plasma processing unit as claimed in any one of claims 16 to 23, wherein the plasma processing unit further comprises means for introducing water and / or an aqueous electrolyte into the base.

25. A plasma processing unit according to any one of claims 16 to 24, wherein the plasma torch is capable of moving within the first sub-chamber so that, in use, the distance between the first electrode and the reservoir surface can be varied while establishing an electrical potential between the first electrode and the second electrode.

26. A plasma processing unit according to any one of claims 16 to 25, wherein the first electrode and / or the second electrode are formed from tungsten, molybdenum and / or a platinum group metal.

27. A plasma processing cell as claimed in any one of claims 16 to 26, further comprising a condensation unit arranged within the first sub-chamber such that, in use, the condensation unit condenses water vapour contained in the generated gas mixture.

28. A plasma processing unit as claimed in any one of claims 16 to 27 wherein the base has a volume of at least 5 litres, preferably at least 10 litres.

Images