KR102925189B1 - Apparatus for producing hydrogen and method using the same - Google Patents

Abstract

A hydrogen production device includes a POX reactor in which an input gas is supplied and a POX (partial oxidation) reaction is performed, an NTP reactor in which an NTP (non-thermal plasma) reaction is performed, a membrane separator disposed between the POX reactor and the NTP reactor and in which membrane separation is performed, and a radiation shield disposed between the POX reactor and the NTP reactor and in which the high heat of the NTP reactor is reduced in influence on the POX reactor.

Description

Hydrogen production device and method using the same {APPARATUS FOR PRODUCING HYDROGEN AND METHOD USING THE SAME}

This specification relates to hydrogen production, and more particularly to a method and apparatus for producing hydrogen with low greenhouse gas emissions.

Due to greenhouse gas emissions and global warming, there is a growing need to develop and expand renewable energy sources that can replace fossil fuels. Hydrogen is considered one such clean energy source. Hydrogen exists in various forms, including fossil fuels, biomass, and water. To use hydrogen as a fuel, it is crucial to produce it in a way that is not only economical but also minimizes its environmental impact.

Hydrogen production methods can be divided into traditional methods using fossil fuel reforming and renewable methods using biomass and water. Hydrogen production from fossil fuels can be achieved through thermochemical methods such as wet reforming, autothermal reforming, partial oxidation, and gasification.

Carbon dioxide is produced during the hydrogen production process. Carbon dioxide is a major greenhouse gas, and its emissions must be minimized. Furthermore, the extraction, transportation, and use of natural gas, which is primarily composed of methane, is a major source of carbon pollution, as methane is approximately ten times more potent as a greenhouse gas than carbon dioxide.

The present disclosure provides a method and device for producing hydrogen with low greenhouse gas emissions.

In one aspect, a hydrogen production device includes an outer tube forming an exterior, a POX reactor disposed within the outer tube and in which an input gas is supplied to perform a POX (partial oxidation) reaction, a discharged NTP reactor disposed within the outer tube and in which a NTP (non-thermal plasma) reaction is performed, a membrane separator disposed between the POX reactor and the NTP reactor within the outer tube and in which membrane separation is performed, and a radiation shield disposed between the POX reactor and the NTP reactor within the outer tube and in which the high heat caused by the NTP of the NTP reactor is reduced influencing the POX reactor.

The input gas includes methane and air, the POX reactor produces a synthesis gas mixed with hydrogen and carbon monoxide from the methane and the air in the POX reaction, the membrane separator separates hydrogen and carbon monoxide in the synthesis gas, discharges the separated hydrogen to the outside of the outer tube, and the separated carbon monoxide is converted into the residue having carbon suboxide and carbon dioxide by the NTP reaction in the NTP return path.

In another aspect, a hydrogen production device includes an outer tube forming an exterior, a POX reactor disposed within the outer tube and in which an input gas is supplied to perform a POX (partial oxidation) reaction, a discharged NTP reactor disposed within the outer tube and in which a NTP (non-thermal plasma) reaction is performed, a membrane separator disposed between the POX reactor and the NTP reactor within the outer tube and in which membrane separation is performed, and a radiation shield disposed between the POX reactor and the NTP reactor within the outer tube and in which the high heat due to the NTP of the NTP reactor is reduced influencing the POX reactor.

The input gas includes methane and air, the POX reactor produces a synthesis gas mixed with hydrogen and carbon monoxide from the methane and the air in the POX reaction, the membrane separator separates hydrogen and carbon monoxide in the synthesis gas, discharges the separated hydrogen to the outside of the outer tube, and the separated carbon monoxide is converted into the residue having carbon suboxide and carbon dioxide by the NTP reaction in the NTP return path.

The POX reactor comprises an inner tube, a second central tube included in the inner tube, and a first central tube extending into the second central tube through the NTP reactor. An input gas provided to the first central tube sequentially flows into the second central tube, the inner tube, and the outer tube. A POX catalyst is disposed between the second central tube and the inner tube, so that a POX reaction is performed on the input gas.

In another aspect, a method for producing hydrogen comprises the steps of providing methane and air to a reactor, converting the methane and the air into a syngas, which is a mixture of hydrogen and carbon monoxide, by a catalytic partial oxidation (POX) reaction in the presence of a POX catalyst in the reactor, wherein the methane and the air are heated to a temperature in the range of 450° C. and 550° C., separating hydrogen and carbon monoxide from the syngas in the reactor through membrane separation, and converting the separated carbon monoxide into carbon suboxide and carbon dioxide in the reactor in the presence of a non-thermal plasma (NTP).

This can significantly reduce greenhouse gas emissions that may occur during hydrogen production. By simultaneously producing hydrogen and obtaining useful solid carbon compounds,

Figure 1 shows the types of plasma and their respective electron temperatures and electron density.
Figure 2 shows the effect of pressure on the equilibrium temperatures of various species in a plasma.
Figure 3 shows plasma parameters that can be optimized to produce the desired excited species.
Figure 4 is a schematic diagram showing a method for producing hydrogen according to one embodiment of the present invention.
Figure 5 is a schematic diagram showing a device for producing hydrogen according to one embodiment of the present invention.
Figure 6 is a schematic diagram showing a device for producing hydrogen according to another embodiment of the present invention.
Figure 7 is a schematic diagram showing a device for producing hydrogen according to another embodiment of the present invention.
Figure 8 is a schematic diagram showing a method for producing hydrogen according to another embodiment of the present invention.

The term "plasma" generally refers to an ionized gas phase and is defined as a quasi-neutral gas of charged and neutral particles that collectively move in a similar manner. "Quasi-neutral" indicates the absence of net charge within the macroscopic volume of the plasma. However, charge imbalances can exist at the microscale. Certainly, approximate charge neutrality, i.e., an equality of the numbers of negatively and positively charged species, must exist within a plasma volume larger than the so-called "Debye sphere." For example, the electron density in a hydrogen glow discharge at a pressure of 10 Torr and a field strength of 100 volts/centimeter is about 3 x 10 ¹⁰ electrons per centimeter cubed. The requirement for quasi-neutrality in a plasma also requires that the ion density be 3 x 10 ¹⁰ per centimeter cubed. This indicates an ionization degree of about 10 ^-7 , since the number density of hydrogen in the discharge is about 3 Х 10 ¹⁷ molecules/cm ³ .

Unlike a neutral gas, whose components are affected only by short-range interactions between gas particles (e.g., intermolecular collisions), distant parts of a plasma can influence other parts of the plasma. This property is because electromagnetic fields emitted from distant locations within the plasma can influence charge carriers within it.

Plasma is maintained by an energy source (typically an electric field) of appropriate size to generate a high concentration of ionized particles. The movement of charged particles in an electric field is governed by the following equation:

Here, v is the velocity of the particle, v ° = d v /d t , t is time, q is the charge of the particle, m is the mass of the particle, E is the electric field, and B is the magnetic field. This equation means that lighter particles will accelerate to a much higher degree than heavier particles in the same environment. For example, for an electron with a mass of me and a proton with a mass of approximately 1836 me , the electron will reach a much higher velocity than the proton (hydrogen ion) when exposed to an electric field for a given unit time. In a low-pressure plasma, where the temperature of the electron can be much higher than that of the heavier particles, this situation creates a non-equilibrium condition in the plasma.

Generally, plasma discharge types can be divided into two categories: equilibrium (thermal) plasmas and non-equilibrium plasmas. Equilibrium plasmas include arc discharges and plasma torches, whereas non-equilibrium discharges include a wide range of plasmas and are characterized by a greatly reduced electric field (the electric field E divided by the gas density N) and a short time scale (or high frequency) that prevents the internal energies (rotational, vibrational, and electrons) of the gas species from reaching equilibrium before the applied field is changed. The reduced electric field (E/N) governs the factors governing the electron energies, which in turn determine the characteristics of the interaction between the electrons and the surrounding gas, thereby representing the plasma energy.

Figure 1 shows the types of plasma and their respective electron temperatures and electron density.

Non-equilibrium plasmas can take the form of corona discharges, glow discharges, spark discharges, gliding arc discharges, and dielectric barrier discharges (DBDs). Each type can be used with different electrode configurations, which significantly influence plasma characteristics. Key electrode characteristics include the discharge gap distance, electrode geometry (which determines the localization of the discharge region), and constituent materials. Gas parameters that also influence the discharge type include pressure, temperature, the internal energy composition of specific atoms and/or molecules within the gas, and the flow rate/velocity.

The unique properties of plasma discharges must be considered in the context of equilibrium and non-equilibrium reaction environments. These considerations include the role of elastic and inelastic collisions within plasma and sheath physics. Electrons in non-equilibrium plasmas are much more mobile (higher temperature, lower mass) than ions, resulting in high fluxes. Consequently, materials in contact with the plasma typically acquire a negative charge relative to the plasma potential. Sheath physics describes the structure of a non-neutral layer adjacent to the material in contact with the plasma.

Particles within a plasma (e.g., ions, electrons, radicals, and molecules) interact with each other through collisions. When one particle collides with another, it can trigger a reaction or excitation of one of the colliding particles, or it can trigger an exchange of energy or momentum between the two particles. Under non-equilibrium conditions, electrons within a plasma move much faster than heavier species. Therefore, electrons can be considered incident species in collisions with heavier species that are assumed to be stationary.

When an electron is incident on a rectangular volume within a plasma with unit lateral area and thickness Δx, the probability that the electron will collide with one of the target particles (e.g., a hydrogen molecule) depends on the proportion of the area covered by the target particle. In general, the cross-section for a given collision is not simply the projected area, as is the case for a hard sphere collision. The collision cross-section can be quite different if the particles interact by other means, such as electrostatic Coulombic forces. The collision cross-section also depends on the relative velocities of the incident and target particles. The following table lists some possible interaction possibilities and their corresponding cross-sections.

The following equation describes the equilibrium dependence between the temperature of electrons T _e and heavy particles on the reduced electric field E/n _h :

Here, ΔT represents the temperature difference between the electrons and the heavier particles. At low pressures (low number density n _h ), ΔT is large, so the electrons are much hotter than the heavier particles. In contrast, at high pressures (high concentration n _h ), ΔT is small, so the electrons and the heavier particles are in thermal equilibrium. Therefore, the above equation describes the general behavior shown in Figure 2.

Figure 2 illustrates the effect of pressure on the equilibrium temperatures of various species within a plasma. This illustrates the physical basis of the nonequilibrium behavior present in low-pressure plasmas, namely, how electrons within a plasma discharge can be at such high temperatures compared to the temperatures of heavier particles.

In non-equilibrium plasmas, electrons are more excited by electric fields than heavy ions. Energy exchange between electrons and heavy particles is relatively inefficient due to the large difference in mass, and electrons in non-equilibrium plasmas have a higher temperature than heavy particles. Conversely, heavy particles (i.e., ions, atoms, molecules, etc.) and electrons approach thermal equilibrium under increased pressure and reduced electric field strength. The higher temperatures reached by electrons in non-equilibrium plasmas impart novel properties to these plasma discharges. For example, the high-temperature electrons in the plasma can generate high concentrations of excited species, such as atomic radicals or vibrationally excited molecules (via inelastic collisions), leading to a high level of chemical activity within the plasma.

Because the heavy particles are at a much lower temperature, heat loss to the environment is negligible. This contrasts with the situation in high-temperature (equilibrium) plasmas, where high chemical activity is achieved but heat loss to the environment is very high. Therefore, high-temperature plasmas often require extensive cooling to rapidly quench and allow reaction products to be cooled to prevent back reactions. Non-equilibrium plasmas reduce these limitations by simultaneously offering high reactivity and high thermal efficiency.

Finally, among the many unusual properties of nonequilibrium plasmas is the influence of the nonequilibrium environment on the reaction pathways and corresponding reaction products produced. For example, carbon dioxide polymers can be formed in nonequilibrium plasmas during partial oxidation (POX) of methane. These species have not been observed in the reaction products of methane POX in high-temperature (equilibrium) plasmas.

Excited species (e.g., ions, radicals, or vibrationally/rotationally excited molecules) within a plasma are created when electrons collide inelastically with lower-energy, heavier species (e.g., ground-state or metastable atoms or molecules). For example, the collision of an electron with a hydrogen molecule can produce two hydrogen atoms through the following reaction:

Here, the kinetic energy of the fast electrons drives the dissociation of hydrogen molecules into higher-energy states of two hydrogen atoms. This reaction can be visualized as a collision between the incident electron and the target hydrogen molecule. The cross-section of such an inelastic collision generally depends on the relative velocity of the incident electron and the target molecule. This relative velocity, in turn, depends on the parameters of the plasma discharge, particularly the reduced electric field E/n _h . The choice of plasma operating parameters significantly affects the energy efficiency of a particular process. Moving from 20 V to 100 V Torr-1 cm-1 changes the proportion of energy transferred from electrons to heavier species through elastic collisions by more than a factor of six.

Figure 3 illustrates plasma parameters that can be optimized to generate the desired excited species. For example, to maximize the dissociation efficiency occurring in a hydrogen plasma (to produce atomic hydrogen), given the two contributing dissociation mechanisms, operating in the 30–50 V Torr-1 cm-1 range would be advantageous.

Ionization is a specific case of inelastic collisions where an incident electron knocks out another electron from a target particle. Electrically accelerated electrons ionize neutral species, creating more electrons. These daughter electrons are then accelerated until they can induce further ionization. This acceleration process generates the significant degree of ionization that defines plasma.

As previously explained, electrons have a higher average velocity than ions. Therefore, a given (neutral) surface will experience a higher electron flux than ions. This results in a negative potential in an ungrounded solid placed within the plasma, as there is a net negative charge flux toward the solid. As this potential increases, it acts to repel lower-energy electrons and attract ions, generating a smaller negative current in the solid, bringing its potential closer to zero. Ultimately, this process reaches equilibrium and establishes a steady-state potential. For an ungrounded solid, this potential is called the floating potential. In typical plasmas, the floating potential can be 10–30 volts lower than the bulk plasma potential. The floating potential is transferred to the bulk plasma potential across a sheath, typically a few Debye lengths thick.

A solid biased to a potential different from that of a grounded or floating solid attracts a net current. By quantifying the magnitude of this current as a function of bias voltage using a device called a Langmuir probe, several plasma parameters, including the electron temperature Te and the concentration of ionized species within the plasma, can be determined. A negative potential can also be applied to a solid with the intention of accelerating ions toward the surface. The effect of these highly accelerated ions on the solid surface is a chemical reaction that occurs at the solid surface.

Atmospheric-pressure low-temperature plasmas (APLTPs) operate in a non-equilibrium state under most operating conditions. One of the key characteristics of APLTPs is that the characteristic electron energies range from a few electron volts (eV) to tens of electron volts (eV), while the heavy particle temperatures range from near room temperature to near, but typically lower than, the electron temperatures. This is due to the significant physical mass difference between electrons and heavy particles (e.g., molecules, atoms, and ions). There are three types of non-equilibrium APLTPs: (i) Non-electrical-equilibrium (NEQ): When a conductive or non-conductive object is inserted into the plasma region, a sheath deviates from the quasi-charge neutral condition between the object surface and the plasma region, and most of the overall potential drop occurs in this NEQ region. (ii) Non-local-thermodynamic-equilibrium (NLTE): The low mass ratio of electrons to heavy particles in the plasma (e.g., 10-5 for argon) leads to insufficient elastic energy exchange between the electrons and heavy particles. (iii) Non-local-chemical-equilibrium (NLCE): Since the average electron temperature is around a few electron volts (eV), which is lower than the inelastic collision energy threshold of tens of electron volts (eV), the excitation and ionization rates are particularly greatly reduced when interacting with cold gases.

Carbon suboxide (C ₃ O ₂ ) is a carbon oxide with a special structure consisting of a series of double bonds (O=C=C=C=O), and is considered a cumulene. Unlike common alkanes or alkenes, cumulenes are more rigid than alkanes. The unique structure and rigidity of carbon suboxide make it suitable for molecular nanotechnology. This rigidity is possible because the intramural carbon atoms have two double bonds. The sp -hybridization of these carbon atoms forms two π bonds that are perpendicular to each other. This bonding process strengthens the linear geometry of the carbon chain. Carbon suboxide can be formed by applying a simple electric discharge to carbon monoxide.

Carbon dioxide, also known as "tricarbon dioxide," contains carbon in the oxidation state +4/3. It is called carbon dioxide because it has a lower oxidation state than CO or CO ₂ .

Due to the molecular nature of three carbon atoms bonded together, a method for dehydrating organic acids containing three carbon atoms is proposed. Since carbon dioxide is the anhydride of malonic acid (HOOC-CH ₂ -COOH), one method for producing carbon dioxide is to dehydrate the acid using a strong dehydrating agent such as P ₄ O ₁₀ as follows.

The reaction of C ₃ O ₂ with water produces malonic acid. Carbon dioxide is stable at low temperatures, but it burns easily and polymerizes when heated.

When carbon is burned with excess air or oxygen, it produces _CO2 . However, if the oxygen supply is limited, highly toxic CO is formed. Other carbon oxides, which have higher CO or _CO2 concentrations, can also be formed indirectly. For example, carbon dioxide is produced by the dehydration of malonic acid, a three-carbon dicarboxylic acid, and the Lewis structures of these three oxides are shown below:

At room temperature, carbon monoxide is a colorless, odorless, and tasteless gas with a boiling point of -192°C and a melting point of -205°C. The extreme toxicity of CO arises from its ability to bind to iron ions in hemoglobin molecules. This property significantly reduces the oxygen-carrying capacity of the blood when inhaled, resulting in hypoxia.

Carbon monoxide is used as an important industrial fuel;

It is also used as a reducing agent in metallurgy;

It is used as a reactant for the production of important organic compounds.

Carbon dioxide is a colorless, odorless gas. When cooled to atmospheric pressure, it solidifies into dry ice and sublimates at atmospheric pressure and a temperature of -78°C. All three physical states of _CO2 are useful. More than half of the annual production is in the solid form of _CO2 , which is used as a refrigerant; liquid _CO2 is used as a propellant in aerosols; and gaseous _CO2 is primarily used in carbonated beverages.

Significant amounts of _CO2 are used in its manufacture, which ranks it among the top 13 chemical producers in the United States (by weight):

The formation of aliphatic hydrocarbons from iron-catalyzed _CO2 hydrogenation is known to proceed as follows: First, _CO2 is converted to CO through the reverse water-gas shift reaction (RWGS).

Then, hydrocarbon chains are formed through the Fischer-Tropsch reaction.

However, in the presence of Fe/Fe ₃ O ₄ nanocatalysts, a series of reactions lead to the formation of aromatic products. The reaction between two CO molecules generates carbon laydown on the catalyst surface, which then forms CO ₂ through the Boudouard reaction.

Under specific reaction conditions, two CO molecules react stepwise with newly deposited carbon on the catalyst to produce carbon dioxide (C ₃ O ₂ ).

C ₃ O ₂ is metastable and undergoes rapid polymerization at temperatures above 400°C. Under certain conditions, C ₃ O ₂ can be reduced by H ₂ to H ₂ C ₃ O ₂ instead of forming a polymer.

Carbon monoxide (C ₂ O) is a linear molecule containing two carbon atoms and one oxygen atom. Its inherent simplicity has attracted interest in a variety of fields. However, its high reactivity makes it unsuitable for general environments. Carbon monoxide is a product of the photolysis of carbon dioxide.

In organometallic chemistry, ketenylidene is a ligand observed in metal carbonyl clusters such as [OC ₂ Co ₃ (CO) ₉ ] ⁺ . Ketenylidene is proposed to be a mediator of the chain growth mechanism of the Fischer–Tropsch process, which converts carbon monoxide and hydrogen into hydrocarbon fuels.

This disclosure relates to a method for converting natural gas (including sour gas/lower-quality natural gas) into high-purity hydrogen gas without releasing hazardous and greenhouse gases into the atmosphere. More specifically, this disclosure relates to a method for sequestering greenhouse gases, such as carbon, by converting them into a solidified polymer, and preferentially producing hydrogen as the sole product gas.

Renewable methane and hydrocarbon sources, such as natural gas, landfill gas, digester gas, and biosyngas, react with air and/or oxygen gas to produce energy, producing a variety of carbon- and sulfur-containing products. Examples include carbon dioxide (CO ₂ ), carbon monoxide (CO), sulfur dioxide (SO ₂ ), hydrogen sulfide (H ₂ S), carbon disulfide (CS ₂ ), carbon dioxide (C ₃ S ₂ ), and carbonyl sulfide (COS).

One way carbon monoxide is produced is by heating or burning graphite (a naturally occurring form of elemental carbon) in the presence of a limited amount of oxygen. The reaction between steam and red-hot coke produces carbon monoxide along with hydrogen gas (H ₂ ). Coke is the impure carbon residue left over from burning coal. This mixture of CO and H ₂ is called water gas or synthesis gas and is used as an industrial fuel or as a feedstock for organic synthesis. In the laboratory, carbon monoxide is produced by heating formic acid (HCOOH) or oxalic acid (H ₂ C ₂ O ₄ ) with concentrated sulfuric acid (H ₂ SO ₄ ). The sulfuric acid removes and absorbs water (H ₂ O) from the formic or oxalic acid. Carbon monoxide readily burns with oxygen to produce CO ₂ , as shown in the following reaction:

Carbon monoxide is useful as a gaseous fuel. It is also useful as a metallurgical reducing agent, as it reduces metal oxides such as copper oxide (CuO) and iron oxide (Fe ₂ O ₃ ) to their elemental metals at high temperatures.

Carbon dioxide is produced when any form of carbon or nearly any carbon compound is burned in the presence of excess oxygen. The Earth's atmosphere contains about 0.04% carbon dioxide by volume and acts as a vast reservoir of _CO2 . The atmospheric carbon dioxide content is increasing primarily due to the combustion of fossil fuels. The so-called greenhouse effect is caused by the increase in atmospheric carbon dioxide and water vapor. These gases allow visible light from the Sun to penetrate the Earth's surface, where it is absorbed and re-radiated as infrared radiation. This longer-wavelength radiation is absorbed by _CO2 and water and cannot escape back into space. This increase in atmospheric heat could increase the Earth's average temperature by 2 to 3 degrees Celsius. This change would have devastating environmental consequences, significantly affecting climate, sea levels, and agriculture.

Carbon dioxide (C ₃ O ₂ ) is a volatile, malodorous gas produced by the dehydration of malonic acid CH ₂ (COOH) ₂ and P ₄ O ₁₀ in vacuum at 140-150°C. It is a linear, symmetrical molecule with a special structure consisting of a series of double bonds (O=C=C=C=O). It polymerizes into an unstable, strongly colored solid compound at 25°C, but is a stable molecule at -78°C. Polymerized carbon suboxide (PCS) is generally considered to be a substance with a variable composition because the carbon to oxygen ratio within the PCS is not constant.

C ₃ O ₂ decomposes into C ₂ O, a highly reactive molecule, under the influence of ultraviolet light. Carbon dioxide is the anhydride of malonic acid and slowly reacts with water to produce malonic acid.

Methods have been proposed that utilize only the hydrogen component of all hydrocarbon fuels, retaining the carbon as solid waste or raw material. A major drawback of this approach is that only a small portion of the available hydrocarbon chemical energy is actually utilized. For example, in the best-case scenarios of these methods, formulas (14) and (15), only about half of the available energy is actually converted and utilized, compared to the energy generated from complete methane oxidation, as shown in formula (16).

Oxide polymers possess a stable structure chemically and thermodynamically similar to humic acid, an organic component of fertile soil, making them suitable for use as soil conditioners. While biomass is commonly used as fuel to reduce net carbon emissions, recent research suggests that using agricultural land releases carbon stored in the soil, potentially offsetting the benefits of biomass fuels. Recycling oxide polymers into agricultural soils not only mitigates soil carbon loss but also offers the economic benefits of carbon sequestration (currently worth over $80 per ton of carbon).

To mitigate the potential environmental impact of carbon dioxide emissions, it is necessary to increase energy use from hydrocarbon fuels and reduce carbon dioxide emissions. The production of various solid carbon products can reduce carbon oxide production, thereby reducing air pollution and slowing the rise of greenhouse gases.

The application of non-thermal plasmas for fuel conversion and _H2 production is particularly effective because the plasma is used not as an energy source, but as a non-equilibrium generator of radicals, charged particles, and excited particles. The plasma-generated energetic particles stimulate this process and contribute only a small fraction (a few percent) of the total process energy.

High-energy efficiency plasma catalysis in partial oxidation processes is largely associated with specific heat release, but industrial applications of this technology typically require relatively high syngas productivity and high output power of the applied discharge. Gliding arc discharges are well suited for this purpose, as they maintain equilibrium and retain most of the heat even at relatively high power levels. Specifically, with respect to yield and energy efficiency, the CH ₄ partial oxidation process for syngas production has been shown to be effective using a non-equilibrium gliding arc discharge stabilized at atmospheric pressure in a reverse vortex flow. In this region, the flow pattern provides the high gas velocities necessary for non-equilibrium gliding arc motion and efficient heat and mass exchange in the central region of the plasma.

A continuous conversion from unreacted to fully reacted CH ₄ /O ₂ /diluent mixture is possible by controlling plasma parameters and mixture composition. This continuous transition is driven by electron collision reactions that generate a mixture of electronically excited species, ions, and atoms, all of which rapidly quench to form predominantly O and H atoms and OH radicals. These radicals react with CH ₄ and intermediates and, depending on the temperature, can lead to ignition of the mixture or partial oxidation of the fuel (CH ₄ ). While the power and size of the reduced electric field (E/N) of the plasma influence the overall conversion, the product composition is largely controlled by the chemical kinetics of the oxidation reaction at low temperatures (300-700 K).

Another way to achieve nonequilibrium conditions is the formation of a weakly ionized and radiative plasma in the presence of a weak shock wave propagating through an inert gas containing a mixture of reactive molecules. In this environment, the introduction of H ₂ S-rich natural gas (sour gas) causes the immediate dissociation of H ₂ S/CH ₄ and the formation of a supersaturated vapor of sulfur and carbon atoms, followed by the rapid formation of sulfur dioxide and C ₃ O ₂ clusters. The strong energy released during this process leads to nonequilibrium excitation and ionization.

Previous studies on the ultraviolet, electrical discharge, and microwave radiolysis of CO have demonstrated that CO decomposes to form CO ₂ and a carbonaceous solid. The average experimental composition of the solid formed at 20°C is given by the equation (C _x O _y ) _n with the ratio x/y = 1.45±0.07. To simplify notation, this solid is hereafter referred to as (C ₃ O ₂ ). There is also evidence that C ₃ O ₂ accumulates from C to C ₂ O to C ₃ O ₂ . This mechanism has been shown to dominate the photochemistry of CO. Furthermore, the reaction between C atoms and C ₂ O has been proposed to explain the excitation of the C ₂ high-pressure band observed during radiation of helium + CO mixtures.

Previous studies on the photolysis of C ₃ O ₂ have shown that the primary species produced is the radical C ₂ O, which reacts with various hydrocarbon gases, such as olefins, in which C atoms are inserted into double bonds. This species appears to be the radical C 2 O. Low-pressure operation in a fast-flow system has shown that C ₃ O ₂ rapidly reacts with O atoms to produce CO and CO ₂ as products. In addition, chemiluminescence of CO excited as high as ~9 eV has been observed. This high energy is assumed to originate from the reaction of C ₂ O with O atoms.

In all the above examples, the radical C ₂ O plays an important role as a building block of C ₃ O ₂ or as a reactive intermediate in photolysis or chemical C ₃ O ₂ decomposition.

Carbon dioxide can be formed by the discharge action on CO. Consider the following reaction for the formation of carbon dioxide.

When the suboxide is heated in a nitrogen atmosphere, another brown oxide is formed as shown in the following equation.

CO can be decomposed in an ozone generator as follows:

Alternatively, using an AC electric field of 250 c/s (cycles per second) and 20,000 V/cm, CO can be decomposed as follows:

Using both aluminum and iron electrodes, CO can be produced from a glow discharge to _CO2 and carbon dioxide. CO can be decomposed using high-speed electrons generated from a cathode ray tube, as shown in the following equation.

Precipitation does not occur in the presence of water vapor. Radon emission can be used to decompose CO into carbon and oxygen. The following equation represents the decomposition of CO by α particles.

The resulting precipitate is insoluble in water, acids, or alkalis, but slowly disappears in concentrated nitric acid or concentrated potassium hydroxide. A stoichiometric mixture of CO and O ₂ only provides CO ₂ , and an excess of either does not affect the reaction rate.

According to the embodiments of the present specification, a method for producing hydrogen with low greenhouse gas emissions and devices using the same are disclosed.

Figure 4 is a schematic diagram showing a method for producing hydrogen according to one embodiment of the present invention.

The feeding gas may include methane (or natural gas), air (or air depleted of oxygen or nitrogen), and steam. The feeding gas is converted into hydrogen and carbon monoxide through the following POX reaction:

If the chemical formula above is expressed as a single equation, it is as follows.

The input gas can be converted into syngas containing hydrogen and carbon monoxide by catalytic partial oxidation (POX). Methane and air can be heated to a temperature in the range of 400°C to 1200°C (preferably 450°C to 550°C).

The catalytic POX may be a POX using a catalyst based on a supported transition metal or a combination thereof, such as Ni and/or Pd. The catalytic support may include high surface area carbons, metal oxides, perovskites, etc.

Hydrogen and carbon monoxide are separated from synthesis gas through membrane separation. The membrane separation process uses a membrane to filter out unwanted substances and allow other substances to pass through, separating the desired substances. The membrane used is one that allows hydrogen to pass through but not other gases.

Carbon monoxide is converted to C0 ₂ and C ₃ O ₂ in the presence of NTP as follows:

C ₃ O ₂ may be in a vapor state, but it can rapidly polymerize to form (C ₃ O ₂ ) _n . C ₃ O ₂ condenses when it encounters a cold surface, so it can be extracted through a cold cyclone separator.

_CO2 is reduced with hydrogen through the RWGS reaction in the presence of a suitable reactor as follows, and is converted into CO, which is then fed back into the membrane separation process.

According to the hydrogen production method according to the present embodiment, most carbon monoxide or carbon dioxide can be captured during hydrogen production, and solidified carbon compounds can be directly obtained as byproducts. As hydrogen is released from a hydrocarbon source, the formation of solidified carbon dioxide simultaneously reduces the production of gaseous carbon oxides. In particular, solidified carbon dioxide can be used as fertilizer (e.g., as a soil conditioner) and does not require separate storage or processing.

FIG. 5 is a schematic diagram illustrating a device for producing hydrogen according to one embodiment of the present invention. This device may be an example of implementing the hydrogen production method according to the embodiment of FIG. 4.

The hydrogen production device (500) is a reactor that receives input gas and produces hydrogen, and includes an outer tube (510) forming an outer appearance and an inner tube (520) placed within the outer tube (510).

A sealant (515) is placed at the top and bottom of the inner tube (520) to seal the inner tube (520). The sealant (515) may be made of an epoxy material. One or more gas holes (525) are formed in the inner tube (520) to allow gas within the inner tube (520) to flow into the outer tube (510).

The input gas may include methane gas (or natural gas), air (or air depleted of oxygen or nitrogen), and steam. The input gas enters the POX reactor through a central inner tube (530) disposed in the inner tube (520). The central inner tube (530) may be made of a ceramic material such as alumina, silica, or zirconia.

A heating element (535) capable of heating the input gas to a temperature of at least 450°C is disposed in the central inner tube (530). A central outer tube (540) is disposed outside the central inner tube (530). A POX catalyst (560) may be radially and uniformly disposed between the central inner tube (530) and the central outer tube (540). The central outer tube (540) may be a porous alumina tube.

A membrane separator (550) is disposed between the central outer tube (540) and the inner tube (520). The membrane separator (550) performs a membrane separation process that selectively passes only hydrogen, and may include a porous hollow-fiber contactor assembly. As a membrane, the hollow-fiber contactor may be selected from materials having high permeability to hydrogen.

A first electrode (580) is disposed on the outer surface of the inner tube (520), and a second electrode (585) is disposed on the inner surface of the outer tube (510), thereby forming a dielectric barrier discharge (DBD) NTP reactor. The first electrode (580) and the second electrode (585) are disposed to face each other, and one of the two electrodes is a high voltage electrode and the other is a ground electrode. An NTP may be formed in a gap between the first electrode (580) and the second electrode (585). Ceramic wool (570) may be disposed in the gap between the first electrode (580) and the second electrode (585). The ceramic wool (570) may be used as an NTP catalyst, but may also be used as an insulator or a high temperature resistant porous plug/stopper.

The hydrogen production device (500) may include a POX reactor and an NTP reactor. The NTP reactor is positioned between the outer tube (510) and the inner tube (410), and the POX reactor and membrane separator are positioned inside the inner tube (420). The input gas first flows into the inner tube (420), and hydrogen and carbon monoxide are generated through the POX reaction. The generated hydrogen is discharged, and the generated carbon monoxide is converted into carbon dioxide and carbon dioxide through the NTP reaction.

The operation within the hydrogen production device (500) is as follows.

An input gas containing nitrogen-depleted air (or oxygen) and methane (or natural gas) mixed with water vapor enters a hydrogen production device (500) along a central inner tube (530). The input gas can be heated to a temperature in the range of 400°C to 1200°C (preferably, 450°C to 550°C) via a heating element (535).

Heated methane and air are converted into hydrogen and carbon monoxide through the POX reaction as shown in Chemical Formula 23 as they pass through the POX catalyst (560) between the central inner tube (530) and the central outer tube (540).

The synthesis gas rich in hydrogen is separated into hydrogen and residual gas through a membrane separator (550). The separated hydrogen (or hydrogen-rich gas) is extracted outside the hydrogen production device (500).

The residual gas (hydrogen-depleted gas, possibly including nitrogen) is introduced into the NTP reactor through a gas hole (525) formed in the inner tube (520). In the presence of the NTP formed between the first electrode (580) and the second electrode (585), carbon monoxide is converted into C0 ₂ and C ₃ O ₂ as shown in Chemical Formula 25. Water vapor, nitrogen, etc. can be used as a purge gas, which can be extracted outside the hydrogen production device (500) together with hydrogen.

The residue containing C ₂ O ₃ and C0 ₂ can be extracted outside the hydrogen production device (500) separately from the hydrogen. A polymerized solid of C ₂ O ₃ can be extracted from the residue through a cyclone separator. C0 ₂ can be processed in the RWGS reactor in the presence of a suitable RWGS catalyst. This reaction can be processed in a separate reactor. The effluent from the RWGS reaction mainly contains H ₂ O and CO, and the H ₂ O can be supplied to the POX reaction and the CO can be supplied to the NTP reaction.

FIG. 6 is a schematic diagram illustrating a device for producing hydrogen according to another embodiment of the present invention. This device may be another example of implementing the hydrogen production method according to the embodiment of FIG. 4.

A hydrogen production device (700) is a reactor that receives an input gas to produce hydrogen, and includes an outer tube (710) that forms an exterior. The outer tube (710) includes a first reactor in which an input gas is supplied to perform a POX reaction and membrane separation, and a second reactor in which an NTP reaction is performed and a residue is discharged. A radiation shield (790) is arranged between the first reactor and the second reactor to reduce the influence of high heat from the NTP of the second reactor on the first reactor. The radiation shield may be made of a material having a high dielectric constant.

The first reactor includes an inner tube (740). The inner tube (740) may be a porous alumina tube. A POX catalyst (760) is filled inside the inner tube (740), and a membrane (750) is disposed near the inner surface of the inner tube (740). The membrane (750) performs a membrane separation process that selectively passes only hydrogen. A thin palladium (Pd) alloy film may be used as the membrane. The palladium alloy may include silver. The palladium alloy may be attached to the inner surface of the inner tube (740). A heating element (535) for heating an input gas is disposed on the outside of the inner tube (740). An inlet for inputting an input gas is arranged on one side of the inner tube (740), and an outlet for discharging residual gas is arranged on the other side of the inner tube (740). In addition, an outlet for discharging hydrogen that has passed through the membrane (750) of the inner tube (740) and flowed outward from the inner tube (750) may be formed on the outer tube (710). The direction in which hydrogen that has passed through the membrane (750) is discharged outward from the inner tube (740) and the direction in which residual gas that has not passed through the membrane (750) is discharged outward from the inner tube (740) may be opposite.

In the second reactor, a DBD NTP reactor is formed through a first electrode (780) and a second electrode (785). The first electrode (780) may be disposed inside an outer tube (710), and the second electrode (785) may be disposed on the inner surface of the outer tube (710). The first electrode (780) and the second electrode (785) may be disposed to face each other, and one of the two electrodes may be a high-voltage electrode, and the other may be a ground electrode. An NTP may be formed in the gap between the first electrode (780) and the second electrode (785).

The operation within the hydrogen production device (700) is as follows.

An input gas containing air (or oxygen), steam methane (or natural gas) enters the first reactor of the hydrogen production device (700) through the inlet of the inner tube (740). The input gas can be heated to a temperature in the range of 400°C to 1200°C (preferably, 450°C to 550°C) through a heating element (735).

Heated methane and air pass through a POX catalyst (760) and are converted into hydrogen and carbon monoxide through the POX reaction of Chemical Formula 23. The synthesis gas contains the converted hydrogen and carbon monoxide.

Hydrogen in the synthesis gas passes through the membrane (750) and is discharged outside the outer tube (710). The residual gas (hydrogen-depleted gas, possibly including nitrogen) flows into the second reactor (i.e., NTP reactor) through the outlet of the inner tube (740). In the presence of the NTP formed between the first electrode (780) and the second electrode (785), carbon monoxide is converted into C0 ₂ and C ₃ O ₂ as shown in Chemical Formula 25.

The residue containing C ₂ O ₃ and C0 ₂ can be extracted outside the hydrogen production device (700). The C ₂ O ₃ polymerized solid can be extracted from the residue through a cyclone separator, and the C0 ₂ can be processed through RWGS in the presence of a suitable RWGS catalyst. It can be processed in a separate reactor. The effluent from the RWGS reaction mainly contains H ₂ O and CO, and the CO can be supplied to the NTP reaction.

FIG. 7 is a schematic diagram illustrating a device for producing hydrogen according to another embodiment of the present invention. This device may be another example of implementing the hydrogen production method according to the embodiment of FIG. 4.

A hydrogen production device (800) includes an outer tube (810) forming an exterior. The outer tube (710) includes a first reactor (or POX reactor) in which an input gas is supplied and a POX reaction is performed, and a second reactor (or NTP reactor) in which an NTP reaction is performed and a residue is discharged. A membrane separator (850) in which membrane separation is performed and a radiation shield (890) for blocking radiation heat are disposed between the first reactor and the second reactor. The membrane separator (850) performs a membrane separation process that selectively passes only hydrogen. The radiation shield (890) reduces the influence of high heat caused by the NTP in the second reactor on the first reactor. The radiation shield may be made of a material having a high dielectric constant.

The first reactor includes an inner tube (820), a first central tube (830), and a second central tube (840). The second central tube (840) is disposed inside the inner tube (820), and the first central tube (830) is disposed inside the second central tube (840), so that the input gas sequentially flows from the first central tube (830) into the second central tube (840), from the second central tube (840) into the inner tube (820), and from the inner tube (820) into the outer tube (810). A heating element (835) for heating the input gas is disposed in the first reactor. The heating element (835) may be disposed in any one of the inner tube (820), the first central tube (830), and the second central tube (840). A POX catalyst (860) is placed between the second central tube (840) and the inner tube (820).

In the second reactor, a DBD NTP reactor is formed through a first electrode (880) and a second electrode (885). The first electrode (880) may be placed inside an outer tube (810), and the second electrode (885) may be placed on the inner surface of the outer tube (810). An NTP may be formed in the gap between the first electrode (880) and the second electrode (885).

The operation within the hydrogen production device (800) is as follows.

An input gas containing air (or oxygen), water vapor, and methane (or natural gas) enters a first reactor of a hydrogen production device (800) through an inlet of a first central tube (830). The input gas can be heated to a temperature in the range of 400°C to 1200°C (preferably, 450°C to 550°C) through a heating element (835).

Heated methane and air pass through a POX catalyst (860) and are converted into hydrogen and carbon monoxide through a POX reaction as shown in Chemical Formula 23.

Hydrogen passes through the membrane (850) and is discharged outside the outer tube (810). The residual gas (carbon monoxide-rich gas) flows into the second reactor (i.e., NTP reactor). In the presence of NTP formed between the first electrode (880) and the second electrode (885), carbon monoxide is converted into C0 ₂ and C ₃ O ₂ as shown in Chemical Formula 25.

The residue containing C ₂ O ₃ and C0 ₂ can be extracted outside the hydrogen production device (800). A polymerized solid of C ₂ O ₃ can be extracted from the residue through a cyclone separator, and the C0 ₂ can be processed through RWGS in the presence of a suitable RWGS catalyst.

Figure 8 is a schematic diagram illustrating a method for producing hydrogen according to another embodiment of the present invention. Compared to the method of Figure 4, this method relates to a case where steam is not supplied. Those skilled in the art will be able to easily apply this method to the hydrogen production devices according to the embodiments of Figures 5, 6, and 7.

The input gas may include methane (or natural gas) and air (or air depleted of oxygen or nitrogen). The input gas is converted into hydrogen and carbon monoxide through the following POX reaction:

The input gas can be converted into synthesis gas (syngas) containing hydrogen and carbon monoxide in a catalytic POX. Methane and air can be heated to a temperature in the range of 400°C to 1200°C (preferably, 450°C to 550°C).

The catalytic POX may be a POX using a catalyst based on a supported transition metal or a combination thereof, such as Ni and/or Pd. The catalytic support may include high surface area carbon, metal oxides, perovskites, etc.

Hydrogen and carbon monoxide are separated from synthesis gas through membrane separation. The membrane separation process separates the components of a solution by filtering out unwanted substances and allowing other substances to pass through the membrane. A membrane that allows hydrogen to pass through but not other gases is used.

Carbon monoxide is converted to C0 ₂ and C ₃ O ₂ in the presence of NTP. C ₃ O ₂ may be in a vapor state, but it can rapidly polymerize to form (C ₃ O ₂ ) _n . C ₃ O ₂ condenses when it encounters a cold surface, so it can be extracted through a cold cyclone separator. CO ₂ is reduced with hydrogen through the RWGS reaction in the presence of a suitable reactor to CO 2 , which is then fed back into the membrane separation process.

Claims (6)

In the hydrogen production device,
The outer tube forming the exterior;
A POX reactor arranged within the outer tube and in which an input gas is supplied to perform a POX (partial oxidation) reaction;
An NTP reactor disposed within the above outer tube and in which an NTP (non-thermal plasma) reaction is performed;
A membrane separator disposed between the POX reactor and the NTP reactor within the outer tube, wherein membrane separation is performed; and
A radiation shield is disposed between the POX reactor and the NTP reactor within the external tube, and reduces the influence of the high heat caused by the NTP of the NTP reactor on the POX reactor.
The above input gas contains methane and air,
The above POX reactor produces a synthesis gas mixed with hydrogen and carbon monoxide from the methane and the air in the above POX reaction,
The above membrane separator separates hydrogen and carbon monoxide in the synthesis gas, and discharges the separated hydrogen to the outside of the outer tube.
A hydrogen production device characterized in that the separated carbon monoxide is converted into the residue having carbon suboxide and carbon dioxide by the NTP reaction in the NTP return path. In the first paragraph,
A hydrogen production device characterized in that the methane and the air are heated to a temperature in the range of 450°C and 550°C for the POX reaction. In the first paragraph,
The POX reactor comprises an inner tube, a second central tube included in the inner tube, and a first central tube extending inside the second central tube through the NTP reactor,
A hydrogen production device characterized in that the input gas provided to the first central tube sequentially flows in the order of the inside of the second central tube, the inside of the inner tube, and the inside of the outer tube. In the hydrogen production device,
The outer tube forming the exterior;
A POX reactor arranged within the outer tube and in which an input gas is supplied to perform a POX (partial oxidation) reaction;
An NTP reactor disposed within the above outer tube and in which an NTP (non-thermal plasma) reaction is performed;
A membrane separator disposed between the POX reactor and the NTP reactor within the outer tube, wherein membrane separation is performed; and
A radiation shield is disposed between the POX reactor and the NTP reactor within the external tube, and reduces the influence of the high heat caused by the NTP of the NTP reactor on the POX reactor.
The above input gas contains methane and air,
The above POX reactor produces a synthesis gas mixed with hydrogen and carbon monoxide from the methane and the air in the above POX reaction,
The above membrane separator separates hydrogen and carbon monoxide in the synthesis gas, and discharges the separated hydrogen to the outside of the outer tube.
The separated carbon monoxide is converted into the residue having carbon suboxide and carbon dioxide by the NTP reaction in the NTP return path,
The POX reactor comprises an inner tube, a second central tube included in the inner tube, and a first central tube extending inside the second central tube through the NTP reactor,
The input gas provided to the first central tube flows sequentially in the order of the inside of the second central tube, the inside of the inner tube, and the inside of the outer tube.
A hydrogen production device characterized in that a POX catalyst is arranged between the second central tube and the inner tube, so that a POX reaction is performed on the input gas. In paragraph 4,
A hydrogen production device characterized in that the methane and the air are heated to a temperature in the range of 450°C and 550°C for the POX reaction. delete