JP4766600B2 - Hydrogen production equipment - Google Patents

Description

  The present invention relates to a hydrogen production apparatus using plasma.

Patent Document 1 discloses a technique for separating hydrogen in a plasma reactor and transporting the hydrogen through a hydrogen separation / conveying section (a metal porous body having a hydrogen separation membrane formed) outside the plasma reactor. . In this hydrogen production system, a ferroelectric (pellet) is placed between a cylindrical external electrode and a cylindrical internal electrode, and plasma is generated in this space to supply hydrocarbons such as methane and water. And generate hydrogen. The internal electrode is made of a metal porous body, and a hydrogen separation membrane is formed on the wall surface of the internal electrode opposite to the plasma field. Hydrogen generated in the atmosphere of the plasma field passes through the porous metal body (internal electrode), is separated from the atmosphere by the hydrogen separation film formed on the wall surface of the internal electrode, and is taken out to the outside.
JP 2004-359508 A

In Patent Document 2, after hydrogen is generated by passing methanol through the plasma space, the hydrogen-containing gas is allowed to pass through the plasma space, and then the gas is brought into contact with the downstream hydrogen separation membrane to thereby generate hydrogen. Are separated. The electrode part for plasma generation and the hydrogen separation membrane are provided in independent units.
JP 2001-167784 A

  In the apparatus of Patent Document 1, the hydrogen separation membrane is formed directly on the electrode (porous metal body), and no hydrogen separation membrane is formed on the plasma field side, but the electrode is thin, and the plasma field Electrons and ions generated in (1) reach the hydrogen separation membrane and degrade the hydrogen separation membrane over time. Furthermore, when the hydrogen separation membrane deteriorates with time and the hydrogen separation membrane and the internal electrode that supports the hydrogen separation membrane are replaced, the hydrogen separation membrane and the internal electrode are first removed, and the plasma generation field on the internal electrode is filled. A certain ferroelectric pellet is discharged, the hydrogen separation membrane is replaced, and then the ferroelectric pellet is refilled in the plasma generation field. Then, an internal electrode with a hydrogen separation membrane is installed again. At this time, it is necessary to adjust the relative position of the external electrode and the internal electrode with high accuracy. When the relative position between the internal electrode and the external electrode deviates from the optimum position, the form and energy state of the plasma field change, so that the hydrogen generation efficiency decreases and the hydrogen separation efficiency also decreases.

  In the hydrogen production apparatus described in Patent Document 2, methanol or the like is passed through the plasma field generated between the electrodes, and after the generation of hydrogen is completed, the treated hydrogen-containing gas is sent to the hydrogen separation unit, and the hydrogen separation unit is used. Hydrogen is separated and taken out to the outside. However, in this method, since hydrogen once generated in the plasma field disappears by further exposure to the plasma, it is difficult to increase the hydrogen concentration in the treated gas to some extent. Therefore, there is a limit to the hydrogen separation efficiency.

  An object of the present invention is to provide a hydrogen production apparatus that generates hydrogen in a plasma field and separates the generated hydrogen through a hydrogen separation membrane. This is to prevent the decrease in the temperature and the necessity of difficult work, and improve the hydrogen separation efficiency.

The hydrogen production apparatus according to the present invention is a bottomed cylindrical shape for generating a plasma field between the first electrode constituting the outer shell , the first electrode, and the first electrode. second electrode, the second bottomed cylindrical is provided inside the electrode and the gas-permeable support, the hydrogen separation membrane is provided on the inner surface of the support, and a second electrode It is provided with a spacer provided between the inner side surface and the outer side surface of the support, a gap is formed between the second electrode and the support, and the second electrode and the hydrogen separation membrane are provided to overlap when viewed in a direction substantially perpendicular the flow direction of the gas to be treated, causing a hydrogen production reaction by flowing into plasma field to the gas to be treated, the second electrode, the gap, the support and the hydrogen separation wherein the extract hydrogen inside the support in this order through the membranes.

  According to the present invention, the second electrode and the support are separated, and a hydrogen separation membrane is formed on the support. Therefore, the possibility that electrons and ions generated in the plasma field reach the hydrogen separation membrane before the end of its lifetime is reduced, and deterioration with time of the hydrogen separation membrane is suppressed. In the apparatus described in Patent Document 1, since the hydrogen separation membrane is directly formed on the second electrode, electrons and ions generated in the plasma field easily reach the hydrogen separation membrane. Easy to progress.

  In the device described in Patent Document 1, since the hydrogen separation membrane is formed on the second electrode, when the hydrogen separation membrane deteriorates with time, the second electrode is removed from the device together with the hydrogen separation membrane, and the second electrode is again used. Since the second electrode has to be attached to the apparatus, the hydrogen separation efficiency is liable to decrease due to the re-installation of the electrode, and a difficult operation is required in terms of accuracy. In the present invention, since the hydrogen separation membrane is formed on a support separate from the second electrode, the hydrogen separation membrane can be replaced by removing the support from the apparatus. There is no need to remove the electrode. Therefore, the hydrogen separation efficiency is not lowered due to the re-installation of the electrode, and the electrode mounting operation which is difficult in terms of positional accuracy is unnecessary.

  Furthermore, in the apparatus described in Patent Document 2, since the processed gas that has been processed in the plasma field is further sent to the hydrogen separation unit of another unit for processing, the once generated hydrogen is ionized in the plasma field. It disappears when it comes in contact with electrons. In contrast, in the present invention, the second electrode and the hydrogen separation membrane are provided at positions that overlap each other when viewed in a direction substantially perpendicular to the direction in which the gas to be processed flows. Therefore, when hydrogen is generated in the plasma field generated on the second electrode, there is a high probability that the hydrogen is immediately separated by passing through the second electrode and the hydrogen separation membrane. That is, while the gas is being processed in the plasma field, the hydrogen generated in the gas can be simultaneously separated by contacting the hydrogen separation membrane. Therefore, it is possible to increase the hydrogen separation efficiency.

Hereinafter, the present invention will be described in more detail with reference to the drawings as appropriate.
FIG. 1 is a cross-sectional view schematically showing a hydrogen production apparatus according to an embodiment of the present invention.

  In the apparatus of FIG. 1, the first electrode 2 forms an outer shell of the apparatus, and a gas flow path is formed in the first electrode 2. Inside the first electrode 2, a bottomed cylindrical second electrode 4 is installed substantially equiaxially with the electrode 2. 4a is a cylindrical part and 4b is a bottom part. The outer surface of the second electrode 4 is held airtight with respect to the first electrode 2 by the spacer 20. A plasma field generation space 12 is formed between the first electrode 2 and the second electrode 4, and the space 12 is filled with the ferroelectric particles 3.

  A bottomed cylindrical support 7 is also provided inside the second electrode 4. The support 7 includes a cylindrical portion 7a and a bottom portion 7b. The second electrode 4 and the support 7 are installed in a substantially coaxial shape, and a gap 6 is formed between the second electrode 4 and the support 7 at regular intervals. A hydrogen separation membrane 8 is formed on the inner wall surface of the support 7.

  During operation, the gas to be treated flows into the space 5 as indicated by the arrow A. A voltage is applied between the first electrode 2 and the second electrode 4 by the power source 11 to generate plasma in the space 12 filled with the ferroelectric particles 3. The gas to be processed generates hydrogen in the plasma. Here, when hydrogen is generated in the gas to be processed in the plasma space 12, most of the hydrogen passes through the second electrode 4, the gap 6, the support 7, and the hydrogen separation membrane 8, and the inside of the support 7. It flows into the space 10 and is further discharged out of the apparatus as indicated by an arrow B.

  According to the present invention, since the hydrogen separation membrane 8 is formed on the support 7 that is separate from the second electrode 4, the hydrogen separation membrane 8 can be replaced by removing the support 7 from the apparatus. For this reason, it is not necessary to remove the second electrode 4. In addition, the second electrode 4 and the hydrogen separation membrane 8 were provided at a position that overlapped when viewed in the direction D in which the gas to be processed flows and in the substantially vertical direction E. Therefore, when hydrogen is generated in the plasma field 12 generated on the second electrode 4, there is a high probability that the hydrogen is immediately separated through the second electrode 4 and the hydrogen separation membrane 8. That is, while the gas is being processed in the plasma field 12, hydrogen generated in the gas can be simultaneously brought into contact with the hydrogen separation membrane 8 and separated.

  In the apparatus of FIG. 2, the first electrode device 16 and the second electrode device 26 are provided inside the outer shell 30 so as to face each other, and the ferroelectric particles 3A are placed in the space 12A between them. Is filled. The first electrode device 16 includes a first electrode 2A and a dielectric substrate 15 surrounding the electrode 2A. The second electrode device 26 includes a first electrode 4A and a dielectric substrate 15 surrounding the electrode 4A. A support 7A is installed between each electrode device and the outer shell 30, and a hydrogen separation membrane 8A is provided on the surface of the support opposite to the electrode. A gap 10 </ b> A is formed between the hydrogen separation membrane 8 </ b> A and the outer shell 30.

  In operation, a voltage is applied between the first electrode 2A and the second electrode 4A by a power source to generate plasma in the space 12A filled with the ferroelectric particles 3A. A gas to be treated is flowed as indicated by an arrow A, and hydrogen is generated in plasma. Here, simultaneously with the generation of hydrogen in the gas to be processed in the plasma space 12A, the gas to be processed passes through the support 7A through the through hole 25 and contacts the hydrogen separation membrane 8A, whereby hydrogen is separated. The separated hydrogen is immediately discharged out of the apparatus as indicated by arrow B through the gap 10A. Further, the gas to be treated after the hydrogen separation is discharged out of the apparatus as indicated by an arrow C.

According to this reference example , since the hydrogen separation membrane 8A is formed on the support 7A separate from the second electrode 4A, the hydrogen separation membrane 8A can be replaced by removing the support 7A from the apparatus. There is no need to remove the second electrode 4A for this purpose. In addition, the second electrode 4A and the hydrogen separation membrane 8A were provided at a position overlapping the direction D of the gas to be processed when viewed in the substantially vertical direction E. Therefore, when hydrogen is generated in the plasma field 12A, there is a high probability that the hydrogen is immediately separated through the second electrode 4A and the hydrogen separation membrane 8A. That is, while the gas is being processed in the plasma field 12A, the hydrogen generated in the gas can be simultaneously brought into contact with the hydrogen separation membrane 8A and separated.

  In the present invention, the second electrode and the hydrogen separation membrane are provided in a position overlapping with the main direction D in which the non-treatment gas flows in the plasma field generation space in the substantially vertical direction E. This means that when a straight line is drawn in the direction E, the straight line may intersect both the second electrode and the hydrogen separation membrane. It is sufficient that at least a part of the second electrode and the hydrogen separation membrane overlap with each other, and it is not necessary to overlap the entire length. More preferably, the first electrode and the hydrogen separation membrane are provided at a position overlapping the non-process gas flow direction D in the substantially vertical direction E.

  In the present invention, the form and material of the first electrode and the second electrode are not particularly limited. The material of the first electrode and the second electrode can be used as long as it has a predetermined conductivity. For example, tungsten, molybdenum, manganese, titanium, chromium, zirconium, nickel, silver, iron, copper, Platinum, palladium, or alloys thereof are preferred.

  In the present invention, the planar pattern of each electrode is not particularly limited, and can be designed according to the type, lifetime, and generation amount of active species in the plane. For example, the planar pattern of the electrodes can be comb-like or mesh-like.

  In the case where the electrode has a net shape or a comb shape, it is preferable that the through holes are formed in a net shape or regularly formed in the gaps between the comb teeth. In this embodiment, the shape of the mesh is not particularly limited, and may be a circle, an ellipse, a racetrack shape, a quadrangle, a polygon such as a triangle, or the like. The shape of the comb-teeth of the comb-like electrode is not particularly limited, but is preferably a rectangle or a parallelogram.

  The material and form of the gas permeable support are not particularly limited. For example, by forming the support from a dense material and providing the support with a through hole, gas can flow through the through hole. Alternatively, the support can be formed of a porous air permeable material, allowing gas to flow through the air permeable material. Of course, the support can be made of a gas permeable material, and a through hole can be provided in the support.

  The material constituting the support is not particularly limited, but is preferably an insulator, for example, ceramics, especially alumina, magnesia, zirconia, silica, mullite, spinel, cordierite, aluminum nitride, silicon nitride, titanium-barium. Preference is given to oxides such as oxides based on barium, titanium and zinc.

  The material of the hydrogen separation membrane is not particularly limited, and examples thereof include a pure metal of palladium and an alloy of palladium and another metal. Examples of such other metals include silver and copper. In addition, an inexpensive material based on a non-palladium film such as an alloy of nickel-niobium-zirconium, amorphous silica, or SiC film can be used.

  The gas to be treated is not particularly limited as long as it can generate hydrogen by low-temperature plasma. Examples thereof include hydrocarbons such as methane, ethane and propane, alcohols such as methanol and ethanol, ethers such as dimethyl ether and diethyl ether, naphtha and gasoline. Here, when priority is given to the ease of reforming, methane or methanol is preferably used. On the other hand, liquid energy such as gasoline is preferably used when priority is given to energy density, such as mounting in an automobile.

In the present invention , for example, as shown in FIG. 1, a gap 6 is formed between the second electrode 4 and the support 7. This can prevent ions and electrons generated in the plasma field on the second electrode from reaching the hydrogen separation membrane and deteriorating. The width of the gap is preferably 0.1 mm or more from the viewpoint of preventing deterioration of the hydrogen separation membrane.

The hydrogen separation membrane is provided on the inner surface of the support opposite to the second electrode (see FIG. 1).

In the present invention , for example, as shown in FIG. 1, the second electrode has a bottomed cylindrical shape. The shape of this tube is not limited to a cylinder, but may be a square tube.

In the reference example , for example, as shown in FIG. 2, the second electrode is embedded in the dielectric. The first electrode can also be embedded in the dielectric. As a result, the electrode is not exposed, so that it is easy to prevent irregular discharge from the electrode device side. In this case, a through hole for allowing the gas to be processed to flow toward the hydrogen separation membrane can be formed in the dielectric. The electrode is embedded in the dielectric so as not to be exposed in a through-hole described later. This can prevent irregular discharge from the electrode toward the inner wall of the through hole.

  Here, the dielectric material constituting the substrate is not particularly limited, but ceramics are preferable, and alumina, magnesia, zirconia, silica, mullite, spinel, cordierite, aluminum nitride, silicon nitride, titanium-barium oxide, barium are particularly preferable. -Titanium-zinc oxide is preferable.

  The dielectric substrate 15 as shown in FIG. 2 can be manufactured by a so-called green sheet lamination method. That is, the electrode can be formed by applying a paste on the ceramic green sheet. As a coating method in this case, any coating method such as screen printing, calendar roll printing, dipping method, vapor deposition, physical vapor deposition method and the like can be used. When an electrode is formed by a coating method, the above-mentioned various metal or alloy powders are mixed with an organic binder and a solvent (such as terpineol) to prepare a conductor paste, and then this conductor paste is applied onto a ceramic green sheet. Work. After forming the electrode on the ceramic green sheet, another green sheet is laminated and sintered to produce an electrode in which the conductor is embedded in the dielectric.

  In manufacturing the substrate, the method of forming the ceramic green sheet is not particularly limited, and any method such as a doctor blade method, a calendar method, a printing method, a roll coater, and the like can be used. In addition, as the raw material powder of the green sheet, the above-described various ceramic powders and powders such as glass can be used. At this time, examples of the sintering aid include silicon oxide, calcia, titania, magnesia, and zirconia. It is preferable to add 3 to 10 parts by weight of the sintering aid with respect to 100 parts by weight of the ceramic powder. Known dispersing agents, plasticizers, and organic solvents can be added to the ceramic slurry.

A substrate can also be made by powder press molding, and when a mesh metal or metal foil is used for the electrode to be embedded, a sintered body with the electrode embedded by a hot press method can be obtained.
By appropriately selecting a molding aid, a molded body of the substrate can be produced even by extrusion molding. By appropriately selecting a solvent on the surface of the extruded product, a metal paste serving as a conductive film component can be formed as an electrode by printing or the like.

  The porosity of the obtained substrate is not particularly limited, but can be 0.1 to 35%, and more preferably 0.1 to 10%.

  The formation method of each through-hole 25 as shown in FIG. 2 is not specifically limited. In a preferred embodiment, after the dielectric substrate is produced by sintering, through holes are formed in the substrate by ultrasonic machining or cutting. Alternatively, at the stage of the green sheet before the substrate is sintered, through holes can be formed in the green sheet by knife cutting or punching with a mold, and then the green sheet can be sintered.

  The planar shape of the through hole is not limited to a substantially perfect circle, and is changed according to the material and form of the object to be processed and the type of active species. For example, the planar shape of the through hole may be an ellipse, a race track shape, a polygon such as a triangle, a quadrangle, or a hexagon, an elongated slit shape, or the like.

  In the present invention, the plasma generation field is preferably filled with dielectric pellets. In the present invention, when a voltage is applied between the first electrode and the second electrode by a high voltage power source, a large potential difference of, for example, about several kV to several tens of kV is generated. Then, the dielectric particles 3, 3A are greatly polarized. As a result, a large potential difference is generated between the dielectric particles, and plasma is generated. Although it is possible to generate plasma without a dielectric pellet, in this case, the distance between the electrodes needs to be shortened to about several millimeters, so that the gas flow path is narrowed and hydrogen production per unit volume is produced. The amount decreases.

  Ceramics are preferable as the material of the dielectric pellet, and particularly alumina, magnesia, zirconia, silica, mullite, spinel, cordierite, aluminum nitride, silicon nitride, titanium-barium oxide, barium-titanium-zinc oxide, and the like. It can be illustrated.

  Moreover, it is preferable to carry a reforming catalyst on the dielectric pellet. Examples of the reforming catalyst include nickel, alumina, ruthenium, rhodium and platinum.

  The pulse voltage can be applied by a steep pulse generating power source. As such a power source, a power source using an electrostatic induction thyristor element that does not require a magnetic compression mechanism, a thyratron equipped with a magnetic compression mechanism, a gap switch, an IGBT element, a MOF-FET element, or an electrostatic induction thyristor element is used. An example of a power supply that has been used. A power supply using an electrostatic induction thyristor element that does not require a magnetic compression mechanism is particularly preferable.

Example 1
A hydrogen production apparatus as shown in FIG. 1 was produced. Specifically, the support 7 is made of porous alumina, the hydrogen separation membrane 8 is a palladium plating membrane, the second electrode 4 is made of a metal mesh, and the first electrode 2 is made of a metal cylindrical tube. did. The dielectric pellet 3 was formed in a spherical shape in which a nickel-based catalyst was wash-coated on alumina.

  A pulse power source using an electrostatic induction thyristor is connected between the first electrode and the second electrode, and a short pulse having a peak voltage of 15 kV, a pulse width of 1 μs, and a repetition period of 1 kpps is applied to generate plasma. When methane and water vapor (air if necessary) are introduced into this plasma space, hydrogen is generated by the combined action of the heat generated in the plasma and H, OH, CH3 radicals, vibrationally excited CH4 and the catalyst.

  If the generated hydrogen is left in the plasma field, the hydrogen yield decreases due to hydrogen decomposition reaction or the like, so that the hydrogen is drawn out from the reaction field through the hydrogen separation transport unit. The amount of hydrogen generated was monitored with a hydrogen sensor, and the period of pulses applied was controlled so that the hydrogen yield was maximized.

  When a catalyst is used, catalyst performance deteriorates due to coking depending on the operating conditions. Therefore, when the hydrogen yield falls below a certain threshold (when the output of the hydrogen sensor exceeds a certain value), Temporarily shut off and introduce only air and water vapor into the reactor, and the coke adhering to the catalyst is burned using dissociated oxygen O (1D) or OH radicals generated by the plasma to recover the yield ( Playback operation).

  In this reactor, the hydrogen separation / conveying part is not exposed to the plasma field, and electrons and ions generated in the plasma field are electrically neutralized on the surface of the internal electrode before reaching the hydrogen separation part. There is no damage to the hydrogen separation / conveying portion due to plasma (particularly damage to the hydrogen separation membrane such as palladium or palladium alloy membrane).

  Specifically, H2O / CH4 = 3 as the introduced gas, and the reactor was heated and held at 400 ° C. with an external heater. The CH4 flow rate was 2 liters / minute, and the supported amount of nickel catalyst was 25 g sufficient to saturate the conversion rate at 600 ° C. in the reactor. The inner diameter of the reactor is 40 mm, the outer diameter of the central electrode of the metal mesh is 10 mm, the outer diameter of the hydrogen separation / conveyance portion is 8 mm, and the alumina spacer 20 is interposed between the central electrode of the metal mesh and the hydrogen separation / conveyance portion. Arranged. Moreover, the pellet and the electrode were arranged so that the length of the plasma region was 80 mm. A Pd-Ag (20 wt.%) Alloy membrane was used as the hydrogen separation membrane 8 and was pressurized so that the difference between the reaction side pressure and the permeation side pressure was 4 atm so that hydrogen could be extracted by the hydrogen separation membrane. Plasma was generated with input power, and 90% methane conversion and 90% hydrogen recovery were obtained.

Here, the conversion rate of methane (%) is
[(CO + CO ₂ ) / (CO + CO ₂ + CH ₄ )] × 100
It is defined as Hydrogen recovery rate (%)
(Permeated through hydrogen separation membrane (amount of hydrogen / amount of hydrogen generated by reaction) × 100
Can be defined. Hydrogen production efficiency = hydrogen recovery rate + methane conversion rate.

  The catalyst was gradually deactivated due to coke deposition, and the conversion of methane decreased to 80% after 1000 hours. In this state, methane was switched to air, regeneration was performed for 1 hour with 80W input power, and then switched to methane again. When plasma was generated with 40W input power, the methane conversion rate recovered to 90%. .

  In this embodiment, since a nickel-based catalyst is used, the reduction treatment is performed before use and after the regeneration operation. This is possible by introducing only hydrogen after raising the temperature of the reactor and before applying plasma. Further, when a noble metal catalyst such as ruthenium or rhodium is used instead of the nickel-based catalyst, this reduction treatment is unnecessary.

( Reference Example 1 )
In Example 1, an electrode-embedded ceramic plate electrode 16 provided with a through hole 25 for gas extraction was used as the second electrode instead of the metal mesh (see FIG. 2).
As a result, plasma was generated with an input power of 40 W to obtain a methane conversion rate of 90% and a hydrogen recovery rate of 90%.

  The catalyst was gradually deactivated due to coke deposition, and the conversion of methane decreased to 80% after 1000 hours. In this state, methane was switched to air, regeneration was performed for 1 hour with 80W input power, and then switched to methane again. When plasma was generated with 40W input power, the methane conversion rate recovered to 90%. .

Using the same apparatus as in Example 1, hydrogen production by steam reforming, carbon dioxide reforming, and partial oxidation reaction of dimethyl ether was performed, and the same results as above were obtained.

It is sectional drawing which shows roughly the hydrogen production apparatus which concerns on one Embodiment of this invention. It is sectional drawing which shows schematically the hydrogen production apparatus which concerns on a reference example .

Explanation of symbols

  2, 2A First electrode 3, 3A Dielectric pellet 4, 4A Second electrode 6 Gap between second electrode and support 7, 7A Support 8, 8A Hydrogen separation membrane 9, 20 Spacer 11 Power supply 12 Plasma field generation space A Gas to be processed B Hydrogen C Waste gas D Direction of gas to be processed in the plasma field E Direction substantially perpendicular to direction E

Claims (4)

  The first electrode constituting the outer shell, the second electrode having a bottomed cylindrical shape that is installed inside the first electrode, and for generating a plasma field between the first electrode and the first electrode, A bottomed cylindrical and gas-permeable support provided inside the second electrode, a hydrogen separation membrane provided on the inner surface of the support, and the inner surface and the support of the second electrode A spacer provided between the outer surface of the body, a gap is formed between the second electrode and the support, the second electrode and the hydrogen separation membrane, It is provided at a position that overlaps the direction in which the gas to be processed flows in a direction substantially perpendicular to the gas, and causes the gas to be processed to flow into the plasma field to cause a hydrogen generation reaction. , Through the void, the support and the hydrogen separation membrane in this order, and inside the support And wherein the retrieving the element, hydrogen production equipment.   The apparatus of claim 1, wherein ferroelectric particles are disposed in the plasma field.   The device according to claim 1, wherein the second electrode is a metal mesh. And applying a pulse voltage between the second electrode and the first electrode by the pulse power source using a static induction thyristor element, one of claims any of claims 1 to 3 The device described in 1.

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