Patent Description:
For years, nickel is known as a catalytic metal to be used for the production of hydrogen gas by methane direct decomposition. To prevent the aggregation due to the sintering of nickel fine particles in a high-temperature reaction of methane direct decomposition, what is proposed are: nickel supported on a silica (Patent Document <NUM>, Non-Patent Document <NUM>), on a zeolite (Patent Document <NUM>, Patent Document <NUM>), on a titania (Patent Document <NUM>) and nickels interposing a carbon particle (Patent Document <NUM>).

In the case of a support method, however, there is a problem that a produced carbon in methane decomposition physically cover an active site of a catalyst, thereby deactivating the catalyst in a short time.

To avoid the inactivation of nickel catalyst, there have been various proposals since the late <NUM>. Regarding an apparatus utilizing a free-flowing nickel catalyst, for example, the proposals include a method of disposing a nanocarbon discharging channel at a side wall of a fluidized-bed reactor to cause the catalyst to overflow from the nanocarbon discharging channel and separating the catalyst mixed in an exhaust gas by a cyclone separator (Patent Document <NUM>) and a method of agitating a mixture of a catalyst and a superfine powder carbon produced by use of a screw conveyor (Patent Document <NUM>). In an apparatus using a free-flowing nickel catalyst, however, the free-flowing catalyst and a produced carbon are discharged in a mixed state. No consideration is given to a separation process of the nickel catalyst and the produced carbon.

Besides, a catalyst is filled on a shelf for catalyst disposed in a plural stages inside a reaction furnace. Proposed is a method for vibrating and rubbing catalysts together while rotating a shelf for catalyst in a reaction to shake off carbon adhered to the catalysts, recover the carbon and recycle the catalysts (Patent Document <NUM>). It cannot be said as realistic, however, to rotate a shelf for catalyst inside the furnace by use of a motor disposed outside the furnace in the reaction furnace heated at a high temperature, while maintaining airtightness.

All the foregoing documents adopt a fluidized-bed reactor. Also in a fixed-bed reactor, there is a proposal to peel a precipitated carbon from a catalyst surface before the carbon grows into long by intermittently supplying hydrocarbons and moisture to the reactor and simultaneously producing a low-temperature plasma (Patent Document <NUM>). In this document, however, what is used for a fixed bed is a large diameter particle with a diameter of <NUM> to <NUM>, which is not a structure. It is silent about what the specific material of the particle is.

Besides, for example, there are proposals for a method of causing low hydrocarbons and a low level of a coexisting gas such as carbon dioxide, oxygen, water and hydrogen to coexist and serve for the selective reaction of reacting a precursor of functional nanocarbons or by-product amorphous carbons produced on a catalyst by the reaction of low hydrocarbons to gasify and remove from the catalyst (Patent Document <NUM>) and a method of causing a catalyst powder and a low hydrocarbon gas to flow in a reaction tube and recovering a carbon-precipitated catalyst powder and a decomposed produced gas for the purpose of continuous operation with high working efficiency and energy efficiency without the downtime for the replacement of the catalyst etc. (Patent Document <NUM>) In the former method, however, a proper concentration of the coexisting gas is affected by various factors, and thus it is difficult to determine or control the concentration. To realize the latter method, an apparatus becomes large, which is not suitable for on-site gas station etc., and still enough room to study a specific apparatus configuration of a catalyst separation apparatus. Further, a power is required to sustainably operate a catalyst separation apparatus such as cyclone separator, and thus maintenance cost is significantly increased.

As aforementioned, various attempts are made, however, there is not yet a standard technique to stably produce hydrogen for a long period while preventing the deactivation of catalyst in an apparatus using the direct decomposition reaction of methane. As such a technique has matured, it attracts more and more attention in the future according to the growing demand of hydrogen including the utilization of heat produced by the combustion of gas containing hydrogen in boiler, the utilization of heat caused by combustion or the utilization of combustion for power generation in gas turbine, small and medium-sized on-site hydrogen stations and solid-oxide fuel cells. In view of the above current situation, the object of the present invention is to provide an apparatus and a system suitable for continuously and stably producing hydrogen by utilizing a direction composition reaction of hydrocarbons such as methane as well as a method for separating solid product.

One aspect of the present invention made for the achievement of the above object is a hydrogen producing apparatus using a nickel-based metal structure for the direct decomposition reaction of hydrocarbons as disclosed in appended claims <NUM> to <NUM>. Such apparatus uses a metal structure. Thus for example, even in a case that the adhesion of a solid product in a direct decomposition reaction of hydrocarbons should result in the catalytic performance of a nickel-based metal, the separation is easy compared to a powder catalyst and a variety of method may be adopted for the separation method. Further, unlike the case of using a steam-reforming reaction, the separation and recovering processes of CO<NUM> are unnecessary. Therefore, the metal structure may be effective for a distributed system utilizing hydrogen such as on-site hydrogen station. The catalyst is less subject to the deterioration even after the repetitive operation and non-operation of the apparatus to make the apparatus almost maintenance-free.

In the hydrogen producing apparatus, a nickel-based metal structure may preferably have an exposed, unsupported-type nickel-containing layer. The above configuration comprises an exposed, unsupported-type nickel-containing layer that allows a produced carbon to function as a catalyst for a relatively long period even if a catalytic surface of the layer should be covered by a precipitated carbon and serves for the continuous operation of an apparatus. The above configuration may surprisingly maintain the activity compared to a conventional nickel support method that has been routinely conducted for increasing an exposed surface area in a heterogeneous reaction involving nickel.

In the hydrogen producing apparatus, said nickel-based metal structure may be preferably a structure selected from plate, porous body, felt, mesh, fabric or expanded metal. These structures have a little deformation even when a load is applied, and may maintain a certain shape by themselves as a whole. Furthermore, the separation of solid product is relatively easy compared to the case where a fluid catalyst is used. In the hydrogen producing apparatus, nickel-based metal structure may preferably have a porous surface. The above configuration allows for an increased surface area of a catalyst and makes the separation of a solid product easy.

The hydrogen producing apparatus may comprise a reaction chamber containing said nickel-based metal structure in which the direct decomposition reaction occurs and a compressor spraying a reaction gas or a produced gas toward said nickel-based metal structure. The above configuration allows the compressor to intermittently or continuously spray a reaction gas or a produced gas toward a nickel-based metal structure during the direct decomposition reaction near the nickel-based metal structure. The impact of the spraying may separate the adhered solid product from the structure. Thus the catalytic function may be recycled or maintained for a long period. The hydrogen producing apparatus may cause a reaction gas to flow in a prescribed direction in a reaction chamber where a plurality of nickel-based metal structures are contained, wherein at least two specific nickel-based metal structures adjacent to each other may be configured to be disposed in a same direction in a same curvature viewed from a cross section vertical to said prescribed direction. In the above configuration, an apparent surface area of the catalyst becomes larger, and a gas may flow downward in a vertical direction at a uniform flow rate without causing the variation in flow rate between the two adjacent nickel-based metal structures, which may be particularly useful for a continuous reactor.

The above hydrogen producing apparatus may comprise:
a reaction chamber comprising a nickel-based metal structure and an impact applying member; a ventilation hole communicating inside and outside the reaction chamber; and a valve opening and closing said ventilation hole, wherein the impact applying member and the nickel-based metal structure are positioned in such a manner as to keep a gap when the ventilation hole is closed, whereas the impact applying member may touch the nickel-based metal structure due to the change in the gas pressure caused by discharging a gas filled in the reaction chamber to the outside of the reaction chamber when the ventilation hole is opened. In the above configuration, when opening a ventilation hole, an impact is applied as necessary to a nickel-based metal structure to separate the adhered solid product from the structure. Thus the catalytic function may be recycled or maintained for a long period.

The above hydrogen producing apparatus may be configured to comprise: a reaction chamber; a rack having a swinging fulcrum to allow for swinging in said reaction chamber while mounting said nickel-based metal structure; a cylinder having an introduction port of a reaction gas and a discharge port communicating with the reaction chamber; and a piston that defines a cylinder chamber together with said cylinder and allows for touching with said rack by sliding against said cylinder. In the above configuration, a force for swinging a rack is constantly or intermittently applied by supplying and discharging a reaction gas to the cylinder chamber to separate the adhered solid product from the structure. Thus the catalytic function may be recycled or maintained for a long period. Reaction gas discharged from cylinder chamber may be utilized directly as a raw material of hydrogen in a reaction chamber, thus it does not have an adverse effect on the reaction at all, let alone a problem of the mixture of air etc..

The hydrogen producing apparatus may preferably have a rack associated with a piston in such a manner that said rack may impact a barrier fixed in said reaction chamber or an inner wall of said reaction chamber in a position where said cylinder chamber conducts through said discharge port. Such a configuration degases and reduces a gas pressure in a cylinder chamber, and overcomes the impact on a barrier or an inner wall in a reaction chamber in a position where said cylinder chamber does not communicate with said discharge port. Therefore, insofar as a reaction gas is supplied in a sustained manner to a cylinder up to a pressure at which the cylinder chamber communicates with said discharge port, the rack repeatedly shoves a barrier or an inner wall in a reaction chamber. The fine vibration allows the catalytic function of the nickel-based metal structure to be recycled and maintained for a long period.

Another aspect of the present disclosure is a method for separating a solid product adhered to a nickel-based metal structure in an apparatus in which said nickel-based metal structure is used for the direct decomposition reaction of a hydrocarbon, the method comprising the step of spraying a reaction gas and/or a produced gas toward said nickel-based metal structure held in a state of being separated from a bottom face in the apparatus. In the above method, a reaction gas or a produced gas is intermittently or continuously sprayed. The impact of the spraying may separate the adhered solid product from the structure. Thus the catalytic function may be recycled or maintained for a long period.

Another aspect of the present disclosure is a method for separating a solid product adhered to a nickel-based metal structure in an apparatus in which said nickel-based metal structure is used for the direct decomposition reaction of a hydrocarbon, the method comprising conducting the direct decomposition reaction of a hydrocarbon in a condition that a gas pressure inside the apparatus installing said nickel-based metal structure is relatively higher than a gas pressure outside the apparatus to equalize a gas pressure inside and outside the apparatus at a desired timing and give an impact on said nickel-based metal structure directly or indirectly due to the change in gas pressure. The method may separate the adhered solid product from the structure at a timing releasing an inner pressure of the apparatus without any device driven by a motor in the operation of the apparatus. Thus the catalytic function may be recycled or maintained for a long period, while continuing the operation of the apparatus.

Another aspect of the present discosure is a method for separating a solid product adhered to a nickel-based metal structure in an apparatus in which said nickel-based metal structure is used for the direct decomposition reaction of a hydrocarbon, the method comprising the steps of: disposing a rack capable of swinging in the apparatus; disposing a nickel-based metal structure on the rack; and applying an external force to said rack with a cylinder member driven by supplying and discharging a reaction gas. In the above configuration, a swinging is constantly or intermittently applied to the rack by the cylinder member driven by a reaction gas to separate the adhered solid product from the structure. Thus the catalytic function may be recycled or maintained for a long period, while continuing the operation of the apparatus.

Another aspect of the present invention made for the achievement of the above object is a system for discharging and recovering a solid product produced in a reaction chamber by a direct decomposition reaction of a hydrocarbon using a nickel-based metal structure, comprising: a collection box communicating with an opening of said reaction chamber via a ventilation hole; a first valve capable of opening and closing said ventilation hole; and a depressurization pump disposed in a position that allows for reducing a gas pressure in said collection box when closing the first valve. The installation of the system into a hydrogen producing apparatus etc. allows us to discharge and recover solid product produced in a reaction chamber at any timing, while continuing the operation of the hydrogen producing apparatus without any device that requires the constant driving in the operation of the apparatus. Closing the first valve allows us to prevent the inflow of air or oxygen from the outside of the reaction chamber, while putting the inside of the reaction chamber in an explosion-proof environment.

The above discharging and recovering system may preferably comprise a depressurization chamber on the way of a channel from said ventilation hole to said collection box and a second valve between said depressurization chamber and said collection box, wherein said depressurization pump communicates with said depressurization chamber and said collection box. In the system, solid product may be sequentially suctioned in the order of the opening of the reaction chamber, the depressurization chamber and the collection box for discharge and recovery. In this process, the depressurization chamber disposed between the reaction chamber and the collection box serves as a buffering space that improves the explosion protection. Further, the final gas pressure and temperature of the collection box may be decreased compared to the gas pressure and temperature of the reaction chamber. Thus it is unlikely to cause solid product to be scattered outside when opening the collection box or detaching the collection box for transportation, which facilitates the recovering operation.

Another aspect of the present invention made for the achievement of the object is a system for discharging and recovering a solid product produced in the hydrogen producing apparatus, the system comprising: a depressurization chamber communicating with the reaction chamber via a ventilation hole; a depressurization pump communicating with the depressurization chamber; a valve for opening and closing said ventilation hole; and a collection box communicating with an opening at the bottom of said reaction chamber. The system is installed on hydrogen producing apparatus etc. so that the channel in the reaction chamber and the channel of solid product are separated from each other, which prevents the clogging of ventilation hole or valve failure due to solid product.

According to the present invention, a nickel-based metal structure is used. Thus even in a case that the adhesion of a solid product should result in the catalytic performance of a nickel-based metal, the separation of the solid product is easier than a powder catalyst and a variety of methods may be adopted for the separation method.

An explanation is given to the embodiments of the present invention in reference to the following drawings as necessary.

A hydrogen producing apparatus of the present invention uses a nickel-based metal structure for the direct decomposition reaction of hydrocarbons.

"Nickel-based metal structure" of the specification is a structure comprising a nickel-based metal as a structural material on at least a part of an exposed surface.

"Nickel-based metal" used herein means a nickel element or a metal comprising nickel having a catalytic action on the direct decomposition reaction of hydrocarbons. Nickel-based metal may be nickel element or nickel alloy, including one or more metal selected from Rh, Ru, Ir, Pd, Pt, Re, Co and Fe in addition to nickel. Nickel-based metal may comprise permalloys having a nickel content greater than an iron content (e.g. permalloy A, permalloy C referred by JIS standard) as well as a part of permalloys containing more iron than nickel (e.g. permalloy B and permalloy D referred by JIS standard).

"Structure" used herein means an object that maintains a certain shape by itself as a whole and fixes the position of constituent substances in the structure. A structure may be made of powders or particles as a raw material. In such a case, each position of powders or particles in a structure is fixed by sintering powders or particles to bond together.

Hydrocarbons introduced from a raw material gas supply port of the above hydrogen producing apparatus are preferably linear hydrocarbons, more preferably methane, ethane or propane, further preferably methane.

Nickel-based metal structure may preferably be a structure itself selected from plate, porous body, felt, mesh, fabric or expanded metal, or may have said structure as a substrate.

Plate may be formed into a single layer, otherwise a laminated plate made of two or more layers consisting of different materials, and may have a core-shell structure.

Porous body is a porous body having continuous pores. Porous body preferably has a three-dimensional network structure. The pore size is usually <NUM> to <NUM>, preferably <NUM> to <NUM>. The porosity may be <NUM>% or more, preferably <NUM>% or more, further preferably <NUM>% or more. The specific surface area may be <NUM><NUM>/m<NUM> to <NUM><NUM>/m<NUM>, preferably <NUM><NUM>/m<NUM> to <NUM><NUM>/m<NUM>. The thickness of a porous body layer may be <NUM> to <NUM>, preferably <NUM> to <NUM>. Representative porous body may include Celmet (registered trademark) by Sumitomo Electric Industries and Raney (registered trademark) nickel.

Felt is obtained by subjecting fibrous constituent materials to random entanglement and if necessary, sintering, which may include needle punched web and fibrous sintered body. Needle punched web and fibrous sintered body may have a fibrous diameter of <NUM> to <NUM>, a porosity of about <NUM> to <NUM>%, a weight of <NUM> to <NUM>/m<NUM>, and a thickness of <NUM> to <NUM>.

Mesh may be woven by any method including plain weave or twill weave, or knitted by any method including weft-knitting or warp-knitting by use of fibrous constituent materials, and causing the intersections to be adhered as necessary. Preferably-used mesh has a line diameter of <NUM> to <NUM> and a mesh number of <NUM> to <NUM> per inch.

Fabric is a knit connecting meshes to each other by an optional stitch.

Expanded metal is obtained by making cut lines in a metal plate at a predetermined interval in houndstooth pattern by a special machine and expanding the cut lines to form rhombic-shaped or testudinate meshes. Mesh size usually has a SW of <NUM> to <NUM> and a LW of <NUM> to <NUM>. Strand size has a plate thickness of <NUM> to <NUM> and a W of <NUM> to <NUM>.

The structure may be one kind of the species listed above, or a composite structure combining two kinds or more.

Nickel-based metal structure may be formed on a substrate free from nickel-based metal. The substrate comprises a metal or a non-metal on a surface on which at least nickel-based metal structure is formed. The metal or non-metal may include, for example, stainless, aluminum, alumina and titanium etc..

The nickel-based metal structure may preferably have an exposed, unsupported-type nickel-containing layer. "Unsupported" means that a catalytic component of nickel-based metal is not present as a particle distributed on a porous support such as active carbon and porous oxide, but is structurized and present. "Structurized" may include a state where particles are welded in a partial region, a state where particles are welded in a whole region, or a state where particles are melted as a whole and then cooled and solidified. Nickel-based metal structure may be structurized preferably on the order of mm, more preferably µm, further preferably nm.

Nickel-based metal structure may preferably have a porous surface. Porous means at least any one of the following (A) to (C): (A) the porosity may be <NUM>% or more, preferably <NUM>% or more, further preferably <NUM>% or more, (B) the specific surface area may be <NUM><NUM>/m<NUM> to <NUM><NUM>/m<NUM>, preferably <NUM><NUM>/m<NUM> to <NUM><NUM>/m<NUM>, (C) the thickness of surface layer may be <NUM> to <NUM>, preferably <NUM> to <NUM>.

Nickel-based metal structure means that a nickel-containing layer itself is porous in a case that it is an exposed, unsupported nickel-containing layer having a porous surface. The substrate is not always porous, however, the substrate may be porous.

A method for producing the foregoing nickel-based metal structure may include the process to subject an original structure to heat spraying, porous plating, nickel plating and/or blast processing. Nickel-based metal structure may be produced by laminating a layer comprising nickel on a surface of an original structure usually by porous electroplating or nickel plating should the original structure be made of non-nickel metal. Subsequently followed by blasting as necessary, a nickel-based metal structure having a porous surface may be produced. On the other hand, if the original structure consists of nickel-based metal, a nickel-based metal structure having a porous surface may be produced by blasting. Nickel plating may be either electrolytic or electroless. The condition may be set as necessary by a person ordinarily skilled in the art according to a desired thickness or a surface roughness. If the original structure is a nickel-aluminum alloy, a method of alkali dissolution treatment may be used.

In general, the original structure may be nickel-based metal structure or non-nickel-based metal structure, however, may be a core material to be removed by the following process. For example, a nickel-based metal foam may have a core material such as urethane foam, and may be produced by forming a nickel layer on a surface of the foam by electroplating, and removing a core material of a urethane foam by sintering.

Hereinafter, a detailed discussion is given to the examples of an apparatus utilizing the aforementioned nickel-based metal structure.

The hydrogen producing apparatus <NUM> of the present invention shown in <FIG> comprises: a reaction chamber <NUM> having a reaction section <NUM>, a shooter section <NUM> and a lower opening <NUM> of reaction chamber <NUM>; a lid <NUM> sealing the upper part of the reaction chamber <NUM>; a raw material gas supplying pipe <NUM> penetrating through the interior portion of the lid from a side face to a bottom face of the lid <NUM> for introducing a raw material of hydrocarbon gas into the reaction section <NUM>; a discharging pipe <NUM> penetrating the central part of the lid <NUM> and extending in a vertical direction so as to occupy the central part of the reaction section <NUM>; a cylindrical nickel-based metal structure <NUM> having an opening at both ends, the metal structure being disposed along an inner wall <NUM> of the reaction container <NUM> so as to define a space of the reaction section <NUM>; a gas flow-controlling cylinder <NUM> that increases the contact of the nickel-based metal structure <NUM> with a raw material gas in introducing the raw material gas into a space of the reaction section <NUM> via the raw material gas supplying pipe <NUM>; and a heater <NUM> covering an outer wall of the reaction container <NUM> for heating the reaction section <NUM>.

In the above hydrogen producing apparatus <NUM>, the following method for separating solid product may be utilized. Specifically, (<NUM>) it is a method comprising the step of spraying a reaction gas and/or a produced gas toward said nickel-based metal structure held in a state of being separated from a bottom face inside the apparatus. The method may be realized by attaching a tapered spraying nozzle (not shown) which tip is positioned between the inner wall <NUM> of the reaction container and the catalyst <NUM> in the reaction section <NUM> besides the raw material gas supplying pipe <NUM> and connecting the nozzle to a compressor (not shown) disposed outside the reaction container. In a case that a produced gas or a mixture of a reaction gas and the produced gas is ejected, the method may be realized by connecting a tube that introduces a part of the produced gas or the mixture of a reaction gas and the produced gas into the compressor.

The hydrogen producing apparatus <NUM> of <FIG> is connected to a system <NUM> for discharging and recovering a solid product produced by the direct decomposition reaction of a hydrocarbon using a nickel-based metal structure <NUM>.

The discharging and recovering system <NUM> comprises: a depressurization chamber <NUM> communicating with a lower opening <NUM> of the reaction chamber <NUM> of hydrogen producing apparatus <NUM> via a ventilation hole <NUM>; a first valve <NUM> capable of opening and closing said ventilation hole <NUM>; a collection box <NUM> communicating with the depressurization chamber <NUM> via a channel <NUM>; a second valve <NUM> capable of opening and closing said depressurization chamber <NUM>; and a depressurization pump <NUM> communicating with the collection box <NUM>. In the system, the first valve <NUM> is installed at a lower opening <NUM> of the reaction chamber <NUM> at the lowest point of the shooter section <NUM>. Thus the lower opening <NUM> of the reaction chamber <NUM> also serves as an exhaust port.

The system may discharge and recover a solid product in a manner that the solid product may slip over the shooter section <NUM> as necessary to be sequentially suctioned via the lower opening <NUM> of the reaction chamber <NUM>, the depressurization chamber <NUM> and the collection box <NUM> while utilizing gravity, by a series of operations of: (A) closing the first valve <NUM> and opening the second valve <NUM>; (B) reducing a gas pressure in the depressurization chamber <NUM> and the collection box <NUM> with the depressurization pump <NUM>; (C) closing the second valve <NUM>; (D) opening the first valve <NUM>; (E) closing the first valve <NUM>; and (F) opening the second valve <NUM>.

In the hydrogen producing apparatus <NUM> shown in <FIG>, heater <NUM> is extended in a vertical direction so as to penetrate through the center part of the lid <NUM> and occupy the center part of the reaction section <NUM>, and a cylindrical nickel-based metal structure <NUM> is fixed around the heater <NUM>, and further on the shelf <NUM> circularly disposed in the upper part of the inner wall <NUM> of the reaction container <NUM>, the impact applying member <NUM> is supported via the spring <NUM> so as to be located at a level higher than the upper end of the nickel-based metal structure <NUM>, whereas a horizontal first channel <NUM> is connected to the bottom part of the inner wall <NUM> of the reaction container <NUM> so as to communicate with the outside of the reaction container <NUM>. The first channel <NUM> comprises the ventilation hole <NUM> and the valve <NUM> opening and closing the ventilation hole <NUM> therein.

In the above hydrogen producing apparatus <NUM>, the following method for separating solid product may be utilized. Specifically, it is a method for separating a solid product adhered to a nickel-based metal structure, the method comprising the steps of: (Step <NUM>-<NUM>) conducting the direct decomposition reaction in a condition that a gas pressure inside the apparatus is relatively higher than a gas pressure outside the apparatus; and (Step <NUM>-<NUM>) equalizing a gas pressure inside and outside the apparatus at a desired timing to give an impact on said nickel-based metal structure directly or indirectly due to the change in gas pressure.

In the direct decomposition reaction of (Step <NUM>-<NUM>), as long as the reaction gas etc. may be introduced at a sufficient pressure in an apparatus, it is not always necessary but preferable to shut down the gas flow from the inside to the outside of the apparatus. The shutdown of gas flow may be realized by closing the valve <NUM>. On the other hand, the forced equalization of gas pressure inside and outside the apparatus at a desired timing in (Step <NUM>-<NUM>) may be realized by instantaneously opening the closed valve <NUM>.

"A state where a gas pressure inside an apparatus is relatively higher than a pressure outside the apparatus" may be +<NUM> MPa to +<NUM> MPa in general, preferably +<NUM> MPa to +<NUM> MPa, more preferably +<NUM> MPa to +<NUM> MPa, further preferably +<NUM> MPa to +<NUM> MPa in terms of the difference in gas pressure. A difference in the above gas pressure may be realized by decreasing the gas pressure outside the apparatus, and/or adjusting a supply pressure of a reactant gas or an amount of a product gas to elevate the gas pressure inside the apparatus.

"An impact directly or indirectly due to the change in gas pressure" means either applying an impact by the change in gas pressure itself or applying an impact via an object to be moved by a kinetic action caused by the change in gas pressure.

The configuration of the apparatus of <FIG> is the same as the configuration of the apparatus of <FIG> in that the raw material gas supplying pipe <NUM> is disposed so as to penetrate the interior portion of the lid <NUM> from the side face of the lid, but different in that the position penetrating the bottom face of the lid is in the vicinity of the heater <NUM>, and the discharging pipe <NUM> is disposed so as to penetrate the inner wall of the bottom part of the reaction section <NUM>.

The discharging and recovering system <NUM> of <FIG> includes the first channel <NUM> communicating horizontally the reaction section <NUM> and the depressurization chamber <NUM>, the depressurization pump <NUM> communicating the depressurization chamber <NUM>, the ventilation hole <NUM> on the way of the first channel <NUM> and valve <NUM> opening and closing this, and further the system includes the collection box <NUM> communicating with the lower opening <NUM> located at the lowest point of the shooter section <NUM> without valve.

According to the system <NUM>, the impact applying member <NUM> and the nickel-based metal structure <NUM> keep a gap with the spring <NUM> when the ventilation hole <NUM> is closed and the hydrogen producing apparatus <NUM> is in operation, whereas the impact applying member <NUM> may act to touch the upper end of the nickel-based metal structure <NUM> due to the change in the gas pressure caused by discharging a gas filled in the reaction section <NUM> to the outside of the reaction section <NUM> when the ventilation hole <NUM> is opened, and eventually when the gas pressure becomes equal to the outside of the reaction section <NUM>, the restoring force of the spring <NUM> may act to return to the position where the original gap is kept. Therefore, repeating periodically or at any timing the operations of: (K) closing the valve <NUM>; (L) reducing a gas pressure in the depressurization chamber <NUM> with the depressurization pump <NUM>; and (M) opening the valve <NUM>, an impact of the impact applying member <NUM> is applied in each time to the nickel-based metal structure <NUM> to cause a separated solid product to slip over the shooter section <NUM> as necessary and fall down from the lower opening <NUM> of the reaction chamber by gravity and be recovered in the collection box <NUM>. After storing a solid product to some extent in the collection box, the reaction furnace is shut down to recover the solid product. It can be said that the system of <FIG> is a system suitable for a small-size hydrogen producing apparatus compared to the system of <FIG>.

The hydrogen producing apparatus <NUM> of <FIG> is different from the hydrogen producing apparatus <NUM> of <FIG> in that a cylinder <NUM> is disposed in a channel of the raw material gas supplying pipe <NUM> to operate by the supply pressure of raw material gas, nickel-based metal structure <NUM> is mounted in the rack <NUM> hanging in the reaction container <NUM>, and the piston <NUM> defining the cylinder chamber <NUM> together with the cylinder <NUM> is configured to apply a swinging force to the rack <NUM>.

<FIG> shows a detailed structure of the cylinder <NUM>. The side of the cylinder <NUM> has a degassing hole <NUM> so that the cylinder chamber <NUM> and the reaction section <NUM> may communicate with each other when the piston <NUM> moves down to the lowest point. Specifically, the cylinder <NUM> is configured to supply raw material gas in a system other than the raw material gas supplying pipe <NUM>.

Rack <NUM> shown in <FIG> generally has a cylindrical contour, and has a structure in which the large-diameter rings 82a, 82b at the upper end <NUM> and the bottom end <NUM> are connected to each other by two poles <NUM>, <NUM> extending in a vertical direction. The large-diameter ring <NUM> is integrated with a small-diameter ring <NUM> having an inner diameter larger than an outer diameter of heater container <NUM> in a same plane via bridge <NUM>. The large-diameter ring <NUM> shares its center with the small-diameter ring <NUM>. For each ring, thirty notched grooves <NUM> in total are formed at regular intervals radially from the center (in a radial direction). From the middle of the bridge 86b on the end face <NUM> extending downward are two poles <NUM>. At the bottom end of the poles <NUM>, the scaffold ring <NUM> is hanging down on the same axis as the large-diameter ring 82b and the small-diameter ring 85b. In addition, the pole <NUM> extends upward in a vertical direction beyond the level of the upper end <NUM>. The upper end of the pole comprises the piston-touching flange <NUM>. The bearing <NUM> is disposed as a swinging fulcrum on the small diameter ring 85a. The rack <NUM> is supported by a pole that is not shown in the figure but fixed to the reaction container <NUM> and/or the heater container <NUM> to allow for swinging around the pole.

<FIG> shows the state in which thirty pieces of nickel-based metal structures <NUM> are contained so as to engage in the notched grooves <NUM> from the upper end <NUM> of the rack <NUM>. Here, the nickel-based metal structure <NUM> has a plate thickness thinner than the notched groove <NUM>, and a plate width is almost equal to a distance between notched grooves <NUM> of the large-diameter ring <NUM> and the small-diameter ring <NUM>, a plate height is slightly longer than a distance from the upper end <NUM> of the rack <NUM> to the scaffold ring <NUM>. This prevents the positional shift or drop of the nickel-based metal structure <NUM> even if the rack <NUM> be somewhat swung or inclined.

The relationship between the movement of the piston <NUM> and the position of the rack <NUM> will be explained in the following.

In a condition that the cylinder chamber <NUM> is not filled with a reaction gas, the rack <NUM> is inclined so that the upper end <NUM> turns left when viewed in <FIG>. As a result, the bottom end of the pole <NUM> touches the inner wall <NUM> of the reaction container <NUM> (standard position). A method for inclining the rack in advance may include, for example, a method for mounting a weight on the bridge 86a. In this process, the bottom end of the piston <NUM> is elevated while constantly touching the piston-touching flange <NUM>. As the reaction gas is gradually introduced into the cylinder <NUM> via the raw material gas supplying pipe <NUM>, a gas pressure inside the cylinder chamber <NUM> gets increased, and the drop of the piston <NUM> begins. At a position shown in <FIG>, the bottom end of the piston <NUM> touches with a piston-touching flange <NUM> of the rack <NUM>. Further supplying raw material gas via the raw material gas supplying pipe <NUM>, the bottom face of the piston <NUM> gradually slides down the piston-touching flange <NUM> to get in contact with the upper face of the piston-touching flange <NUM> as shown in <FIG>. At the time, the position of the rack <NUM> has been changed into a state where the central axis of the pole <NUM> is in a vertical direction. Further supplying raw material gas to increase the gas pressure in the cylinder chamber <NUM>, the cylinder chamber <NUM> communicates with the reaction section <NUM>, and the bottom end of the pole <NUM> gets in touch with the inner wall <NUM> of the reaction container <NUM>, as shown in <FIG>. At the time, a reaction gas is rapidly discharged from the degassing hole <NUM> to the reaction section <NUM>. Due to the rapid decrease in an inner pressure of the cylinder chamber <NUM> and weight bias, the piston <NUM> returns to the position of <FIG>.

According to the above rack, in a case of maintaining the supplying rate of the reaction gas to the cylinder chamber <NUM>, the piston <NUM> goes back and forth the stages of <FIG>. As a result, when viewed in <FIG>, the inner wall <NUM> in the left side of the reaction container <NUM> is repeatedly shoved by the bottom end of the pole <NUM>. The impact is propagated through the whole rack <NUM> via the pole <NUM>, eventually to the mounted nickel-based metal structure <NUM> to cause the fine adhered product produced by the reaction to shake out. Further, the supply of the reaction gas to the cylinder <NUM> may be intermittently implemented when an impact needs to be intermittently applied, or may be continuously implemented during operation when an impact needs to be applied in a sustained manner. In either case, an effective impact may be applied without any adverse effect on the reaction for utilizing the reaction gas.

On the other hand, when stopping the supply of the reaction gas to the cylinder <NUM>, should the upper end of the piston <NUM> be lower than the degassing hole <NUM>, the rack <NUM> swings to the right by gravity. The piston <NUM> is also displaced upward, yielding to a force from the rack <NUM>, and finally stopped at the position of <FIG>. If the upper end of the piston <NUM> is higher than the degassing hole <NUM>, the rack <NUM> holds the position as is.

In the hydrogen producing apparatus <NUM> shown in <FIG>, a cylindrical rack <NUM> having a cylindrical circumferential wall with opened upper and bottom ends is adhered to the bottom face of a lid <NUM> covering a reaction container <NUM>. A nickel-based metal structure <NUM> is mounted on the cylindrical rack <NUM>. A raw material gas supplying pipe <NUM> is disposed so as to penetrate the interior portion of the lid <NUM> from the upper surface of the lid <NUM> and communicate with the inner space <NUM> of the cylindrical rack <NUM>. Further, the heat exchanger <NUM> is disposed on the upper end of the lid <NUM> so as to cover the raw material gas supplying pipe <NUM>, and the discharging pipe <NUM> is disposed at the upper end of the inner circumferential wall of the reaction container <NUM>. The configuration functions as a tube-type continuous reactor, allowing the reaction gas to be heated in advance by heat supplied from the heat exchanger <NUM> in the process of passing through the raw material gas supplying pipe <NUM> and be introduced into the inner space <NUM> of the cylindrical rack <NUM> to flow downward in a vertical direction while keeping in contact with the nickel-based metal structure <NUM>, whereas the produced gas (that may be a mixed gas with a reaction gas) flows upward in a vertical direction to a space defined by a circumferential wall of the inner cylinder <NUM> of the reaction furnace and an inner wall of the reaction container <NUM> where no catalyst is present and escapes from the discharging pipe <NUM> to the outside of the reaction container <NUM>.

The cylindrical rack <NUM> contains a plurality of nickel-based metal structures <NUM>.

In the present embodiment, when viewed from a cross section orthogonal to a direction flowing a reaction gas as shown in <FIG>, nickel-based metal structures <NUM> are disposed in a same direction to be curved with a same curvature, so that the gap between two adjacent nickel-based metal structures may be almost the same interval with any gap measuring positions 144a, 144b, 144c in a radial direction.

In the present embodiment, the gas channel <NUM> is limited to an inner space <NUM> of the cylindrical rack <NUM>, and is an once-through type. Thus a gas preferably contacts with the whole of nickel-based metal structure <NUM> at a uniform flow rate in a process of passing gas through. The nickel-based metal structure <NUM> is disposed to be curved, thereby not causing a flow rate variation, e.g. the flow rate of a gas gets larger as gas flows outward in a radial direction. Thus gas flows downward in a vertical direction at a uniform flow rate, which is particularly suitable for a continuous reactor.

In a cylindrical furnace having about <NUM> volume of the reaction section and a configuration similar to the hydrogen producing apparatus shown in <FIG> and being surrounded by a heater which surrounding was covered with ceramic cylindrical insulator except that a catalyst was not disposed, introduced was methane at a pressure of <NUM> MPa and a flow rate of <NUM>/min while elevating the temperature of the apparatus. A gas heat conduction-type gas analyzer <NUM>-A-<NUM> (Product number: KD-12C-T1, zero gas: clean air <NUM>%, span gas: hydrogen <NUM>%, zero point unadjusted, manufactured by NEW COSMOS ELECTRIC CO. ,LTD) was attached to a pipe for discharging a produced gas to the air to conduct hydrogen concentration measurement, while constantly conducing a temperature measurement by thermocouples <NUM>-A-<NUM> and <NUM>-A-<NUM> disposed in two points shown in <FIG>. Specifically, hydrogen gas concentration was measured after cooling a produced hydrogen gas down to the room temperature. The gas analyzer <NUM>-A-<NUM> was not intended for measuring hydrogen concentration in methane gas, but for measuring hydrogen concentration in air. Therefore, the initial value was greater, and thus <FIG> was prepared by subtracting a background. Further, the direct decomposition reaction of methane has a reaction Gibbs free energy ΔGr of <NUM> kJ/mol and an equilibrium constant K = exp(-<NUM>/RT) at <NUM> of <NUM>, and it is an endoergic reaction. Thus heating proceeds the decomposition reaction without catalyst under Le Chatelier's law.

As shown in <FIG> and the following raw data of Table <NUM> to Table <NUM>, the heater controlling temperature <NUM>-A-<NUM> and the catalyst surface temperature <NUM>-A-<NUM> reached almost <NUM> in five hours or so from the start of heating the apparatus, and were then maintained for three hours or so thereafter. In the meantime, a measurement was made by the gas heat conduction-type gas analyzer <NUM>-A-<NUM>, which was found to be stable and maintained over time around <NUM>%. It is deduced from this that a produced carbon serves as a catalyst. Furthermore, product carbon films were deposited in a furnace.

In the same condition as Example <NUM> except for the use of hydrogen producing apparatus T7 in which a nickel porous body was disposed along an inner wall of the reaction furnace, a temperature elevation experiment was conducted. After the heater temperature reached about <NUM> in four hours from the start of the experiment, the temperature was decreased to about <NUM> and kept for two hours, and then kept at about <NUM> for three hours. Further, hydrogen concentration became almost zero for the initial period of time because a produced gas was usually discharged to the atmosphere, and thus only methane was discharged to the atmosphere until the temperature of the reaction furnace got increased to some extent, and therefore a valve for discharging to the atmosphere was closed. The results are shown in <FIG>.

As shown in <FIG>, it was found that a nickel porous body might surprisingly and stably maintain the activity over nine hours or more compared to a conventional nickel particle support method that has been routinely conducted for increasing an exposed surface area in a heterogeneous reaction involving nickel. Further, hydrogen concentration was decreased as the heater temperature got decreased, but could be maintained around <NUM>% even at <NUM>. The cause of this is not clear but it is supposed that a produced carbon itself serves as a catalyst, or a pore of a carrier supporting the catalyst is not clogged by a produced carbon.

A temperature elevation experiment was conducted in the same condition as Example <NUM> by use of nickel permalloy (permalloy B, YFN-<NUM>-R, manufactured by DOWA METAL CO. ) As a result, compared to the case of using nickel porous body, it was somewhat inferior in terms of hydrogen concentration up to a heater temperature of about <NUM> and stability at a heater temperature of <NUM> (<NUM> for a catalyst surface temperature), however, as shown in <FIG>, the feasibility of the continuous operation over a long period of <NUM> days at <NUM> was demonstrated.

It should be noted that the embodiments for carrying out the present invention are not at all limited to the above embodiments, nor all the elements explained in the above embodiments are the essential elements for the present invention. The present invention may go through various modifications insofar as it falls within the technical scope defined by the appended claims.

For example, in the above embodiments, a nickel-based metal structure is formed into a cylindrical shape having an opening at both ends and the metal structure is positioned at a position along the inner circumferential wall of the reactor in the reactor, taking into account the fact that methane gas is sequentially filled from the upper part to the lower part of the reaction container, and the fact that a produced carbon separates and falls from the catalyst by gravity. Instead, a flat plate catalyst may be disposed or hung in parallel vertically in a reaction section. Further, the discharging and recovering system <NUM> of <FIG> may be connected to the hydrogen producing apparatus <NUM> of <FIG>. The discharging and recovering system <NUM> may be connected to the hydrogen producing apparatus <NUM> of <FIG>. Besides, the hydrogen producing apparatus <NUM> of <FIG> is configured to hang a rack (i.e. designing a swinging fulcrum higher than a gravity center) to crash into an inner wall of said reaction chamber. Particularly in a case of a large-size apparatus, a swinging fulcrum may be located at a lower part of the reaction chamber (i.e. a swinging fulcrum may be designed to be lower than a gravity center) to cause a rack to crash into a barrier (a stopper) fixed in a reaction chamber. Further, differing from the hydrogen producing apparatus <NUM> shown in <FIG>, the piston may be untouched with the piston-touching flange in a condition where the bottom end of the pole <NUM> was touched with the inner wall <NUM> of the reaction container <NUM>. Furthermore, it is feasible to incline a rack by disposing nickel-based metal structures at irregular intervals to shift a gravity center relative to a swinging fulcrum. Furthermore, in <FIG>, nickel-based metal structures are disposed in a same direction to be curved with a same curvature, however, it is not always necessary to be curved as long as the gap between two adjacent nickel-based metal structures may be almost the same interval with any gap measuring positions, but may have various shapes depending on a structure of a reaction container.

The hydrogen producing apparatus of the present invention may be followed by an apparatus that increases the purity of hydrogen contained in a produced gas, which allows us to apply for hydrogen supply to fuel cell cars equipped with polymer electrolyte fuel cell (PEFC) via on-site station etc..

Claim 1:
A hydrogen-producing apparatus (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a reaction chamber (<NUM>, <NUM>) for a direct decomposition reaction of hydrocarbon containing a nickel-based metal structure (<NUM>, <NUM>, <NUM>);
a collection box (<NUM>, <NUM>) communicating with an opening of said reaction chamber (<NUM>, <NUM>) via a ventilation hole (<NUM>, <NUM>);
a first valve (<NUM>) for opening and closing said ventilation hole (<NUM>); and
a depressurization pump (<NUM>, <NUM>) for reducing a gas pressure in said collection box (<NUM>, <NUM>) in response to closing the first valve (<NUM>).