JP2007246333A - Permselective membrane-type reactor and hydrogen-producing method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permselective membrane-type reactor, with which high purity hydrogen can be produced even if a defect such as a pinhole is formed in a permselective membrane and in particular, hydrogen wherein the concentration of carbon monoxide as an impurity is low can be obtained; and to provide a hydrogen-producing method using the same. <P>SOLUTION: The permselective membrane-type reactor has: a reaction tube 1 having a gas inlet 9 at one end part thereof and a gas outlet 10 at the other end part thereof; a separation tube 4 which is inserted in the reaction tube 1 and has a permselective membrane 5 for selectively permeating hydrogen at the surface thereof and a discharge port 11 being an outlet of separated gas permeated through the permselective membrane 5; and a reforming reaction catalyst 6 which is arranged between the reaction tube 1 and the separation tube 4 and promotes a reforming reaction of a hydrocarbon. Further, in the reactor, a carbon dioxide removing means, a methanation catalyst for promoting methanation of carbon monoxide and/or a shift reaction catalyst for promoting a shift reaction are arranged at the inside of the separation tube 4 or at a post-stage part of the discharge port 11 of the separation tube 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention uses hydrocarbons such as methane, butane, and kerosene and oxygen-containing hydrocarbons such as methanol, ethanol, and dimethyl ether as the main raw material gas, and uses a reforming reaction or the like to generate hydrogen and separate and take it out. The present invention relates to a permselective membrane reactor used in the present invention and a method for producing hydrogen using the reactor.

  Hydrogen is used in large quantities as a basic raw material gas for petrochemicals, and in recent years, especially in the field of fuel cells and the like, hydrogen is attracting attention as a clean energy source. . Hydrogen used for this purpose is mainly composed of hydrocarbons such as methane, butane, and kerosene, and oxygen-containing hydrocarbons such as methanol, ethanol, and dimethyl ether. It is produced using a reaction, decomposition reaction, etc., and is obtained by separating it with a permselective membrane that can selectively permeate hydrogen, such as a palladium alloy membrane.

  In recent years, for this hydrogen production, a selectively permeable membrane reactor (membrane reactor) capable of performing the above-described reaction and separation at the same time is used (for example, see Patent Document 1). Conventionally used permselective membrane reactors generally have a reaction tube with one end serving as a gas inlet and the other end serving as a gas outlet, and hydrogen is selected on the surface inserted into the reaction tube. The base material portion having a selectively permeable membrane for permeation has a porous separation tube, and a reforming reaction catalyst for promoting a reforming reaction of hydrocarbons disposed between the reaction tube and the separation tube.

The reforming reaction catalyst is usually in the form of a pellet, and the gap between the reaction tube and the separation tube is filled in a packed bed or the like, and the raw material contains water vapor supplied from the inlet of the reaction tube. The gas comes into contact with the reforming reaction catalyst and is decomposed into hydrogen gas or the like by a steam reforming reaction or the like. For example, in the steam reforming of methane, the reforming reaction shown in the following formula (1) and the shift reaction shown in the following formula (2) are promoted, so that the hydrocarbon (methane) is converted into hydrogen, carbon monoxide, It is decomposed into a reaction product such as carbon, and a mixed gas (product gas) containing these reaction products is obtained.
CH ₄ + H ₂ O → CO + 3H ₂ (1)
CO + H ₂ O → CO ₂ + H ₂ (2)

  Of the product gas thus obtained, hydrogen passes through the permselective membrane and is selectively extracted into the separation tube, and separated from other gas components and taken out. In addition, other gas components such as carbon monoxide and carbon dioxide that do not pass through the permselective membrane are discharged to the outside of the reactor from the outlet of the reaction tube.

  Such a selectively permeable membrane reactor, in addition to the merit of downsizing the apparatus by simultaneously performing the reaction and separation as described above, shifts the equilibrium of the reaction to the production side by extracting hydrogen gas. Thus, the reaction temperature can be lowered, and as a result, effects such as a reduction in operating temperature, suppression of deterioration of metal members, and energy saving can be expected.

JP-A-6-40703

  By the way, in such a permselective membrane reactor, since the permselective membrane is a thin film having a thickness of several μm, defects such as pinholes are likely to occur, and if it is originally discharged from the outlet of the reaction tube Some of the gas components that do not permeate the selective membrane, such as carbon monoxide and carbon dioxide, pass through the permselective membrane from the defective portion and are mixed as impurities in the hydrogen separated by the permselective membrane. The concentration decreases. In particular, carbon monoxide mixed from a defective portion has a problem of deteriorating the electrode of the fuel cell.

As a method for removing carbon monoxide mixed in hydrogen through the defective portion of the selectively permeable membrane, the commonly used selective oxidation method requires an auxiliary machine such as a pump because air is used, and N ₂ is mixed in hydrogen. Therefore, there is a problem that the concentration of hydrogen decreases. There is also a method of removing carbon monoxide with carbon monoxide methanation represented by the following formula (3), but carbon monoxide methanation is accompanied by carbon dioxide methanation represented by the following formula (4) as a side reaction. Therefore, there is a problem that a large amount of hydrogen is consumed by the carbon dioxide methanation and the hydrogen concentration is lowered.
CO + 3H ₂ → CH ₄ + H ₂ O (3)
CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O (4)

  The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to produce high-purity hydrogen even if the permselective membrane has defects such as pinholes. It is another object of the present invention to provide a selectively permeable membrane reactor capable of obtaining hydrogen having a low concentration of carbon monoxide as an impurity, and a hydrogen production method using the same.

  In order to achieve the above object, according to the present invention, the following selectively permeable membrane reactor and hydrogen production method are provided.

[1] A reaction tube having one end portion serving as a gas inlet and the other end serving as a gas outlet, and a permselective membrane inserted into the reaction tube and selectively permeating hydrogen to the surface. A separation pipe having a discharge port that is an outlet for separation gas that has permeated through the permeable membrane; and a reforming reaction catalyst that is disposed between the reaction pipe and the separation pipe and that promotes a hydrocarbon reforming reaction. A permselective membrane reactor, wherein a carbon dioxide removing means, a methanation catalyst for promoting carbon monoxide methanation and / or a shift reaction are provided in the inside of the separation tube or at the rear stage of the discharge port of the separation tube. A selectively permeable membrane reactor in which a shift reaction catalyst to be promoted is arranged.

[2] The permselective membrane reactor according to [1], wherein the carbon dioxide removing means is a carbon dioxide absorbent.

[3] The permselective membrane reactor according to [1], wherein the carbon dioxide removing unit is a carbon dioxide separation membrane.

[4] In the state where at least one of the carbon dioxide adsorbent, the methanation catalyst, and the shift reaction catalyst is supported on the honeycomb structure, the inside of the separation tube or the subsequent stage of the discharge port of the separation tube. The permselective membrane reactor according to [2], which is disposed in a section.

[5] A method for producing hydrogen using the selectively permeable membrane reactor according to any one of [1] to [4].

  According to the permselective membrane reactor and the hydrogen production method of the present invention, high purity hydrogen can be produced even if the permselective membrane has defects such as pinholes, and particularly hydrogen with a low concentration of carbon monoxide as an impurity. Is obtained.

  Hereinafter, typical embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following embodiments, and those skilled in the art can depart from the scope of the present invention. It should be understood that design changes, improvements, and the like can be made as appropriate based on general knowledge of the above.

  FIG. 1 is a schematic cross-sectional view showing the basic structure of a selectively permeable membrane reactor according to the present invention. This selectively permeable membrane type reactor has a gas inlet 9 at one end and a gas outlet 10 at the other end, and a gas inserted into the reaction tube 1 and selectively permeate hydrogen into the surface. A separation tube 4 having a bottomed cylindrical shape with a porous base material, and a reaction tube 1 and a separation tube. 4 and a reforming reaction catalyst 6 that promotes a reforming reaction of hydrocarbons.

  As the reforming reaction catalyst 6, for example, a nickel-alumina catalyst or a ruthenium-alumina catalyst can be used, which is formed into a pellet shape or a bead shape, or coated on a pellet-shaped substrate, as shown in the figure. It arrange | positions by filling the space | gap between the reaction tube 1 and the separation tube 4, etc. The material of the reaction tube 1 is preferably a material mainly composed of a metal having high heat resistance and good thermal conductivity such as SUS or incoloy. It is preferable to use a porous ceramic body such as titania or alumina or a porous metal body such as stainless steel as the base material of the porous separation tube 4 that forms the permselective membrane 5 on the surface. The selectively permeable membrane 5 has a selective permeability to hydrogen, and for example, a material made of palladium alloy such as palladium or palladium-silver alloy can be suitably used. The permselective membrane 5 may not be outside the separation tube 4 but may be inside the separation tube 4 depending on the case, or may be covered on both sides of the separation tube 4.

  In addition to such a basic structure, the selectively permeable membrane reactor according to the present invention has, as its characteristic structure, carbon dioxide removal means in the interior of the separation tube 4 or the rear stage of the discharge port 11 of the separation tube 4. The methanation catalyst for promoting carbon monoxide methanation and / or the shift reaction catalyst for promoting the shift reaction are arranged.

  As the carbon dioxide removing means, specifically, a carbon dioxide adsorbent that adsorbs and removes carbon dioxide, a carbon dioxide separation membrane that removes carbon dioxide by membrane separation, and the like can be suitably used. As the carbon dioxide adsorbent, for example, an inorganic compound such as calcium oxide or lithium silicate, an alkali solution, an ionic solution, or an inorganic porous material such as alumina or silica carrying an alkali solution or an ionic solution is preferably used. Can be used. As the carbon dioxide separation membrane, for example, a polymer membrane or a zeolite membrane can be suitably used. As the methanation catalyst, for example, a nickel-alumina catalyst or a ruthenium-alumina catalyst can be suitably used. Moreover, as a shift reaction catalyst, an iron-chromium catalyst, a copper-zinc catalyst, a platinum-alumina catalyst, a platinum-titania catalyst, etc. can be used suitably, for example.

  The carbon dioxide adsorbent, the methanation catalyst, and the shift reaction catalyst may be used in the form of pellets or beads, respectively, filled in the separation tube 4 or a tube coupled to the discharge port 11 of the separation tube 4. Alternatively, it may be disposed in a separation tube 4 or a tube coupled to the discharge port 11 of the separation tube 4 by being supported on a ceramic structure typified by a honeycomb structure. In a selectively permeable membrane reactor, the permeation side (inside of the separation tube 4) is often depressurized (evacuated) in order to increase the amount of hydrogen permeation. Since the pressure loss is small as compared with the case of filling a pellet or bead shape, there is an advantage that the degree of vacuum on the permeate side can be kept high.

In the permselective membrane reactor according to the present invention, when the raw material gas containing water vapor supplied from the inlet 9 of the reaction tube 1 comes into contact with the reforming reaction catalyst 6, the hydrocarbon in the raw material gas is converted by the reforming reaction or the like. Decomposed into hydrogen gas. For example, in the steam reforming of methane, as described above, the reforming reaction represented by the following formula (1) and the shift reaction represented by the following formula (2) are promoted, so that hydrocarbon (methane) is converted. It is decomposed into reaction products such as hydrogen, carbon monoxide, carbon dioxide, and a mixed gas (product gas) containing these reaction products is obtained.
CH ₄ + H ₂ O → CO + 3H ₂ (1)
CO + H ₂ O → CO ₂ + H ₂ (2)

  Of the product gas thus obtained, hydrogen permeates through the permselective membrane 5 and is selectively extracted into the separation pipe 4 and separated from other gas components and taken out. Further, other gas components that do not permeate the permselective membrane 5 are discharged to the outside of the reactor through the outlet 10 of the reaction tube 1. If the permselective membrane 5 has defects such as pinholes, If there is, a part of the gas component which does not permeate the selective membrane such as carbon monoxide and carbon dioxide discharged from the outlet 10 from the outlet passes through the permselective membrane 5 from the defective portion and is separated by the permselective membrane 5. It is mixed as impurities in the hydrogen.

In the present invention, among the impurity gas components mixed in hydrogen in this way, first, carbon dioxide is removed by the carbon dioxide removing means disposed in the separation pipe 4 or in the rear stage portion of the outlet 11 of the separation pipe 4, Reduce carbon dioxide concentration. And when the methanation catalyst is arrange | positioned, the carbon monoxide methanation shown to following formula (3) is promoted with the methanation catalyst, and carbon monoxide is removed. Here, as a side reaction of carbon monoxide methanation, carbon dioxide methanation accompanied by consumption of hydrogen occurs as shown in the following formula (4). Since the carbon concentration is lowered, the carbon dioxide methanation reaction is reduced, the disappearance of hydrogen due to carbon dioxide methanation is suppressed, and as a result, factors such as electrode deterioration in the fuel cell are suppressed while suppressing the decrease in hydrogen concentration. The resulting carbon monoxide is removed.
CO + 3H ₂ → CH ₄ + H ₂ O (3)
CO ₂ + 4H ₂ → CH ₄ + 2H ₂ O (4)

In the case where a shift reaction catalyst is arranged, the shift reaction catalyst causes a shift reaction represented by the following formula (2). As described above, the carbon dioxide removal means reduces the carbon dioxide concentration in hydrogen. As a result, the shift reaction is promoted. That is, since this shift reaction is an equilibrium reaction, the reaction can be promoted beyond the equilibrium by reducing the product carbon dioxide. Carbon monoxide is converted to carbon dioxide with high efficiency by the shift reaction thus promoted. Furthermore, when the shift reaction catalyst and the carbon dioxide removing means are mixed, the carbon dioxide generated by the shift reaction is also removed by the carbon dioxide removing means, so that the shift reaction is further promoted and the carbon monoxide concentration is further reduced. High purity hydrogen is obtained.
CO + H ₂ O → CO ₂ + H ₂ (2)

  The positional relationship between the carbon dioxide removing means disposed in the separation pipe 4 or the rear stage of the outlet 11 of the separation pipe 4 and the methanation catalyst and / or shift reaction catalyst is at least part of the carbon dioxide removing means. Is preferably arranged at a position where the gas that has passed through the permselective membrane 5 contacts before the methanation catalyst and / or the shift reaction catalyst. For example, when arranged inside the separation pipe 4, at least a part of the carbon dioxide removing means is arranged on the inner surface of the separation pipe 4 close to the selectively permeable membrane 5, and a methanation catalyst or shift reaction catalyst is placed inside thereof. If necessary, it is mixed with carbon dioxide removal means. By adopting such a positional relationship, the carbon monoxide methanation or shift reaction is performed in a state where the carbon dioxide concentration in hydrogen is lowered, and high-purity hydrogen with a reduced carbon monoxide concentration is obtained.

  The hydrogen production method according to the present invention is to produce hydrogen using the selectively permeable membrane reactor as described above, and as described above, defects such as pinholes were generated in the selectively permeable membrane. However, high-purity hydrogen with a low concentration of carbon monoxide as an impurity can be produced.

  In the selectively permeable membrane reactor according to the present invention, the carbon dioxide removal means, methanation catalyst, and shift reaction catalyst each have a suitable temperature in terms of removal / reaction rate and equilibrium constraints. When hydrogen is produced using this selectively permeable membrane reactor, the temperature control thereof is important. As an example, when a lithium silicate type carbon dioxide absorbent is used as the carbon dioxide removal means, it is preferable to control the temperature to about 300 to 400 ° C., and when a ruthenium-alumina catalyst is used as the methanation catalyst. It is preferable to control the temperature to about 250 to 450 ° C., and when a platinum-titania catalyst is used as the shift reaction catalyst, it is preferable to control the temperature to about 150 to 500 ° C. In addition, in the case of using a carbon dioxide adsorbent as the carbon dioxide removal means, in order to maintain the adsorption capacity, in consideration of the necessary adsorption capacity, the carbon dioxide is appropriately removed by an operation such as replacement of the adsorbent or heating. Desorption is required.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Examples 1-3 and Comparative Examples 1 and 2)
A permselective membrane reactor having a basic structure as shown in FIG. 1 was produced. The separation tube 4 is made of a bottomed cylindrical porous alumina body (outer diameter 10 mm, length 75 mm) with one end closed, and a palladium-silver that selectively permeates hydrogen as a permselective membrane 5 on the surface thereof. An alloy film was formed by a plating method. In consideration of hydrogen permeation performance, the composition of the membrane was 75% by mass of palladium and 25% by mass of silver, and the film thickness was 2.5 μm. The reaction tube 1 used was a SUS cylinder (inner diameter 25 mm, length 800 mm) with both ends opened. As the reforming reaction catalyst 6, a commercially available ruthenium-alumina catalyst formed in a pellet shape having a size of about 1 mm was used and filled between the reaction tube 1 and the separation tube 4.

  A tubular body is directly connected to the discharge port 11 of the separation pipe 4 of the selectively permeable membrane reactor having such a basic structure, and a carbon dioxide removing means and a methanation catalyst are arranged inside the tubular body, In the evaluation described later, the temperature was controlled to 400 ° C. as Example 1. Further, carbon dioxide removal means is disposed upstream of the inside of the tubular body and shift reaction catalyst is disposed downstream of the tubular body so that the removal of carbon dioxide and the shift reaction proceed sequentially. The temperature was controlled to be Example 2. Further, carbon dioxide removal means and a shift reaction catalyst are mixedly arranged inside the tubular body so that the removal of carbon dioxide and the shift reaction proceed in the same field, and in the evaluation described later, they are 400 ° C. The temperature was controlled to be Example 3. Furthermore, a sample in which nothing was arranged inside the tubular body was used as Comparative Example 1. Furthermore, Comparative Example 2 was obtained by disposing only the methanation catalyst inside the tubular body and controlling the temperature thereof to 400 ° C. in the evaluation described later. In these Examples and Comparative Examples, a lithium silicate, a ruthenium-alumina catalyst, and a platinum-titania catalyst were used in this order for the carbon dioxide removal means, methanation catalyst, and shift reaction catalyst, respectively.

(Evaluation)
Using the apparatus shown in FIG. 2, the selectively permeable membrane reactors of Examples 1 to 3 and Comparative Examples 1 and 2 were tested and evaluated. This equipment is connected in line so that hydrocarbons such as methane and butane, oxygen-containing hydrocarbons such as ethanol, water, carbon dioxide, and oxygen can be used as the source gas source, and these are selected and mixed as necessary. Thus, it can be supplied to a selectively permeable membrane reactor. Note that liquid raw materials such as water and ethanol are supplied after being gasified by a vaporizer.

  The membrane permeation gas line and the membrane non-permeation gas line are upstream on the membrane permeation side (exit of the tubular body directly connected to the outlet of the separation tube) and on the membrane non-permeation side (reaction tube outlet), respectively. )It is connected to the. A flow meter for measuring the amount of gas and a gas chromatograph for quantifying gas components are connected to the downstream side of the membrane permeation gas line. Similarly, a flow meter and a gas chromatograph are connected to the downstream side of the non-permeating gas line, but the upstream side of the flow meter is about 5 ° C. in order to collect liquid components such as water at room temperature. A set liquid trap is provided. A heater for heating is installed around the permselective membrane reactor so that it can be heated from the outside.

In such an apparatus, in each of the selectively permeable membrane reactors of Examples 1 to 3 and Comparative Examples 1 and 2, methane and water vapor as a raw material gas have a molar ratio of H ₂ O / CH ₄ = 3. Thus, the reforming reaction by methane and steam and the accompanying reaction were performed, and hydrogen was selectively separated from the reaction product. The reaction temperature of the reaction was adjusted to 550 ° C., the reaction side pressure was 3 atm, and the permeation side pressure was 0.1 atm. Further, the flow rates of the raw material gas were 250 cc / min for methane and 750 cc / min for water vapor. The carbon dioxide removal means, methanation catalyst, and shift reaction catalyst directly connected to the outlet of the reaction tube and disposed inside the tubular body through which the separated hydrogen passes were adjusted so as to have the temperatures shown in Table 1, respectively. . By producing hydrogen in this way and examining the gas flow rate and composition on each of the membrane permeation side and the membrane non-permeation side, the conversion rate of methane and the hydrogen purity of the permeate gas are calculated and obtained from the results. The composition of the permeated gas is shown in Table 1.

  The result of Comparative Example 1 in which nothing is arranged inside the tubular body directly represents the composition of the permeated gas that has permeated the permselective membrane. In Comparative Example 2, carbon monoxide was reduced by carbon monoxide methanation using a methanation catalyst. Although carbon monoxide had a low concentration of less than 10 ppm, carbon dioxide methanation as a side reaction was used. As a result, much hydrogen is consumed, and the hydrogen concentration is reduced to about 94%. On the other hand, in Example 1 in which the carbon dioxide adsorbent and the methanation catalyst are used in combination, carbon dioxide is adsorbed and removed in advance by the carbon dioxide removing means, and therefore, the hydrogen reaction by carbon dioxide methanation, which is a side reaction, is performed. The disappearance is suppressed, and the hydrogen concentration is about 98%, which is higher than that of Comparative Example 2. Further, in Example 2 and Example 3 in which the carbon dioxide removal means and the shift reaction catalyst are used in combination, the shift reaction is promoted by the carbon dioxide removal means previously adsorbing and removing the carbon dioxide, so that carbon dioxide monoxide. Conversion to carbon is performed with high efficiency, and compared with Comparative Example 1, the concentration of carbon monoxide is reduced and the concentration of hydrogen is increased. Further, Example 3 in which the adsorption removal of carbon dioxide and the shift reaction proceed at the same time is compared with Example 2 in which the adsorption removal of carbon dioxide and the shift reaction proceed sequentially. The decrease in concentration is remarkable. This is because when carbon dioxide removal means and shift reaction catalyst are mixed and arranged so that the removal of carbon dioxide and the shift reaction proceed simultaneously in the same field, the carbon dioxide generated by the shift reaction is also removed, This is because the shift reaction is further promoted.

  The present invention uses hydrocarbons such as methane, butane, and kerosene, and oxygen-containing hydrocarbons such as methanol, ethanol, and dimethyl ether as the main raw material gas. Therefore, the permselective membrane reactor used for the above-mentioned purpose can be suitably used for the production of hydrogen using the reactor.

It is a schematic sectional drawing which shows the basic structure of the selectively permeable membrane reactor which concerns on this invention. It is a schematic diagram which shows the structure of the test apparatus used in the Example.

Explanation of symbols

1: reaction tube, 4: separation tube, 5: selective permeable membrane, 6: reforming reaction catalyst, 9: inlet, 10: outlet, 11: outlet.

Claims (5)

A reaction tube having one end portion serving as a gas inlet and the other end serving as a gas outlet; and a permselective membrane inserted into the reaction tube and selectively permeating hydrogen to the surface; A permselective membrane having a separation tube having a discharge port that is an outlet for the permeated separation gas, and a reforming reaction catalyst that is disposed between the reaction tube and the separation tube and promotes a reforming reaction of hydrocarbons Type reactor,
A carbon dioxide removing means and a methanation catalyst for promoting carbon monoxide methanation and / or a shift reaction catalyst for promoting a shift reaction are arranged inside the separation pipe or at the rear stage of the outlet of the separation pipe. Permselective membrane reactor.   The selectively permeable membrane reactor according to claim 1, wherein the carbon dioxide removing means is a carbon dioxide adsorbent.   The selectively permeable membrane reactor according to claim 1, wherein the carbon dioxide removing means is a carbon dioxide separation membrane.   At least one of the carbon dioxide adsorbent, the methanation catalyst, and the shift reaction catalyst is supported on the honeycomb structure and disposed inside the separation tube or at the rear stage of the discharge port of the separation tube. The selectively permeable membrane reactor according to claim 2.   A method for producing hydrogen using the permselective membrane reactor according to any one of claims 1 to 4.

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