JP2006272099A - Catalyst membrane having bimodal structure and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst membrane having a bimodal structure and excellent catalytic activity and use thereof.
SOLUTION: A membrane-like catalyst film 1 comprising a first support 10 having a macroporous structure and a second support 11 having a mesoporous structure, and at least a catalyst 12 is placed in the pores of the mesoporous structure. According to the catalyst film 1 in which is maintained, it has a bimodal structure and is excellent in catalytic activity.
[Selection] Figure 1

Description

  The present invention relates to a catalyst membrane having a bimodal structure and its use, and more particularly, to a catalyst membrane having a bimodal structure composed of a macroporous structure and a mesoporous structure and its use.

  Conventionally, a membrane reactor capable of simultaneously performing various chemical reactions and separation of substances produced by the chemical reactions has been developed. Such a membrane reactor has a catalyst membrane and a separation membrane as a basic structure, and removes a product generated in the catalyst membrane from the reaction system via the separation membrane. Thus, a membrane reactor capable of performing the reaction and the separation at the same time has attracted much attention in recent years because of its high usefulness.

As an example of the above-described membrane reactor, the present inventors have developed a membrane reactor used in a hydrogen production process by steam reforming of methane, and reported its performance (Non-Patent Documents 1 and 2). reference). Specifically, for example, steam reforming of methane is represented by the following equilibrium reaction formula.
_{· CH 4 + H 2 O =} CO + 3H 2
・ CO + H ₂ O = CO ₂ + H ₂
Here, the equilibrium is shifted and the reaction rate can be increased by extracting the hydrogen of the product using a membrane reactor capable of performing the reaction and the separation at the same time. Therefore, the present inventors have provided a catalyst membrane in which a Ni catalyst is dispersed in an α-Al ₂ O ₃ support having a macroporous structure (pore diameter of about 1 μm), a hydrogen separation membrane that selectively permeates only hydrogen, and A membrane reactor equipped with was prepared.

These membrane reactors disclosed in Non-Patent Documents 1 and 2 are designed to perform hydrogen reforming of methane with a Ni catalyst dispersed in an α-Al ₂ O ₃ carrier to generate hydrogen, and then to form a hydrogen separation membrane. The mechanism is to remove the produced hydrogen from the reaction system via
T. Tsuru., Et al, SEPARATION SCIENCE AND TECHNOLOGY, 36 (16), p3721-3736 (2001) T. Tsuru., Et al, AICE J, 50, p2794-2805 (2004)

However, in the configuration of the catalyst membrane in the conventional membrane reactor described above, the catalyst is simply supported on an α-Al ₂ O ₃ carrier (membrane support) having a macroporous structure, and the specific surface area of the catalyst layer is small. turn into. For this reason, the catalyst membrane in the conventional membrane reactor has the drawback that sufficient catalytic activity cannot be expressed.

  Therefore, there has been a strong demand for the development of a technique for enhancing the catalytic activity of the catalyst membrane used in the membrane reactor. In addition to the membrane reactor for steam reforming of methane, the catalyst membrane can be used in a variety of other ways. If the catalytic activity can be increased, a wide range of application deployment of the catalyst membrane is possible. Highly useful.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a catalyst membrane having a bimodal structure and excellent catalytic activity, and use thereof.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a catalyst film having a bimodal structure in which a catalyst is supported after a mesoporous material is supported in the pores of a membrane support having a macroporous structure. As a result of evaluating the function, the present inventors have found a new fact that the catalytic activity is remarkably increased as compared with a conventional catalyst film having a unimodal structure, thereby completing the present invention. The present invention has been completed based on such novel findings, and includes the following inventions.

  (1) A membranous catalyst membrane comprising a first carrier having a macroporous structure and a second carrier having a mesoporous structure, and at least the catalyst is retained in the pores of the mesoporous structure. Catalyst membrane.

  (2) The catalyst membrane according to (1), wherein the second carrier is supported inside the pores of the macroporous structure of the first carrier.

  (3) The catalyst film according to (1) or (2), wherein the first support is a porous material selected from the group consisting of α-alumina, cordierite, mullite, stainless steel and the like.

  (4) The catalyst film according to any one of (1) to (3), wherein the second carrier is any one of porous materials having mesopores such as γ-alumina, titania, zirconia, and silica.

  (5) The catalyst according to any one of (1) to (4), wherein the first macroporous carrier is a porous material having any one of a spherical shape, a pellet shape, a honeycomb shape, a cylindrical shape, and a monolith shape. film.

  (6) A membrane reaction apparatus comprising the catalyst film according to any one of (1) to (5) above.

  (7) A membranous reactor further comprising a separation membrane.

  (8) The catalyst membrane is a catalyst membrane for catalyzing a methane steam reforming reaction, and the separation membrane is a gas separation membrane for selectively removing hydrogen generated by the methane steam reforming reaction. The membranous reactor according to (7).

  (9) A method for using a membrane reaction apparatus including a step of performing a chemical reaction using the film reaction apparatus according to any one of (6) to (8).

  According to the catalyst film of the present invention, there is an effect that the catalytic activity can be remarkably enhanced as compared with the conventional unimodal catalyst film. Therefore, for example, in the methane steam reforming reaction using the catalyst film, the hydrogen generation efficiency can be increased. In addition, the present invention is highly useful in that the range of new utilization of the catalyst membrane can be widened, such as contributing to catalyst development that has not been developed so far.

  Hereinafter, an embodiment of the present invention will be described, but it should be noted that the present invention is not limited to this.

<1. Catalyst membrane>
The catalyst membrane according to the present invention is a membrane-like catalyst membrane comprising a first carrier having a macroporous structure and a second carrier having a mesoporous structure, at least in the pores of the mesoporous structure. Other specific configurations such as the material, shape, size, type and amount of the catalyst are not particularly limited.

  In the present specification, the “macroporous structure” means a porous structure having a pore diameter of about several hundred nm to several tens of μm, and more preferably, the size of the pore is about several μm. . In the examples described later, a porous material having a pore diameter of 1 μm is used.

  The “mesoporous structure” means a porous structure having a pore diameter of about several nm to several tens of nm, and means a porous structure having pores smaller than the pore diameter of the macroporous structure. In the examples described later, a porous material having a pore diameter of 2 nm to 50 nm is used.

  FIG. 1 schematically shows a configuration of a catalyst film according to the present invention. FIG. 1 (a) shows the configuration of a conventional catalyst film, and FIG. 1 (b) shows the configuration of the catalyst film according to the present invention.

As shown in FIG. 1 (a), a conventional catalyst film 100 includes catalyst particles 102 such as a metal catalyst on a support 101 made of a porous material having a macroporous structure, such as α-Al ₂ O _3. It is a catalyst film having a unimodal structure that is adsorbed and dispersed. In this conventional catalyst membrane 100, the catalyst particles 102 are adsorbed / dispersed on the surface of the pores of the macroporous structure of the carrier 101. However, the specific surface area of the catalyst layer cannot be increased sufficiently and the catalyst activity is insufficient. Met.

  On the other hand, as shown in FIG. 1B, the catalyst film 1 according to the present invention includes a second carrier 11 having a mesoporous structure with a smaller pore diameter in addition to the first carrier 10 having a macroporous structure. The catalyst film has a bimodal configuration in which the catalyst particles 12 are adsorbed and dispersed in the pores of the mesoporous structure of the second carrier 11. For this reason, compared with the conventional catalyst membrane 100, the dispersibility of the catalyst particles 12 can be improved, and the specific surface area of the catalyst layer can be significantly increased. Furthermore, the catalyst activity can be maintained by retaining the catalyst in the pores of the mesoporous structure as described above. Therefore, the catalyst membrane according to the present invention can remarkably increase the catalytic activity as compared with the conventional unimodal catalyst membrane. Further, since the catalyst is held inside the pores of the mesoporous structure, there is an effect that the sintering property of the catalyst can be reduced.

  In the catalyst membrane according to the present invention, it is preferable that the second carrier 11 is supported inside the pores 13 of the macroporous structure of the first carrier 10 as shown in FIG. . This is because the catalyst activity can be further enhanced by forming a mesoporous structure in the pores of the macroporous structure and further dispersing the catalyst in the pores of the mesoporous structure.

The material constituting the first carrier is not particularly limited as long as it has a macroporous structure, and a conventionally known porous material can be suitably used. . Examples thereof include porous materials such as α-alumina (α-Al ₂ O ₃ ), cordierite, mullite, and stainless steel.

Further, the material constituting the second carrier is not particularly limited as long as it has a mesoporous structure, and a conventionally known porous material is preferably used. it can. Examples thereof include porous materials such as composite oxides such as γ-alumina (γ-Al ₂ O ₃ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), and silica alumina.

  Moreover, as said catalyst, a conventionally well-known catalyst can be used suitably, About the concrete kind, quantity, shape, etc., it does not specifically limit. For example, a conventionally known metal catalyst can be suitably used. Specifically, Ni catalyst, Pt catalyst, Ru catalyst, etc. can be mentioned. In addition to the metal catalyst, for example, a heteropolyacid can be preferably used.

  The first carrier preferably has a spherical shape, a pellet shape, a honeycomb shape, a cylindrical shape, or a monolith shape. This is because if the first carrier has the above shape, the catalyst film can be stably formed.

  In the catalyst membrane according to the present invention, it is sufficient that the catalyst is held at least in the pores of the mesoporous structure of the second carrier, and may be adsorbed and dispersed in other portions. Not too long. For example, the catalyst is held inside the pores of the macroporous structure of the first carrier, on the surface of the first carrier (portion other than inside the pores), and on the surface of the second carrier (portions other than inside the pores). May be.

  Moreover, as a manufacturing method of the catalyst film of this invention, the conventionally well-known method of forming a catalyst film can be used suitably, and the specific method is not specifically limited. Hereinafter, an example of a method for producing a catalyst film according to the present invention will be described.

  First, a first carrier having a macroporous structure is prepared. The first carrier can be prepared by a conventionally known technique, and the specific technique is not limited. For example, when α-alumina is used as the first carrier, it can be obtained by the method disclosed in Non-Patent Documents 1 and 2 above.

  Next, a colloidal solution of a second carrier (for example, silica, γ-alumina, zirconia, etc.) is supported on the first carrier by an impregnation method. Thereby, the mesoporous material can be supported in the macroporous pores of the first carrier.

  Next, the first carrier impregnated and supported with the colloidal solution of the second carrier material is fired. Specific conditions such as the temperature and time of the firing step can be appropriately set according to the material used, the size, the shape, and the like. By this calcination step, a catalyst support having a bimodal pore structure can be produced.

  Finally, the catalyst support having a bimodal pore structure prepared by the above-described method is supported on an aqueous metal salt solution by an impregnation method or an incipient-wetness method.

  Of course, in the above manufacturing process, a mixture of the second carrier and the metal salt to be the catalyst may be prepared in advance, impregnated and supported on the first carrier, and fired.

  By such a method, the catalyst film according to the present invention can be easily obtained.

<2. Utilization of catalyst membrane>
As described above, the catalyst film according to the present invention is characterized by being in the form of a film. Therefore, by using the catalyst membrane according to the present invention, for example, a membrane reactor can be formed.

  That is, the membranous reaction apparatus according to the present invention only needs to have the catalyst film described in the section <1> above, and other specific configurations such as other members, materials, shapes, sizes, etc. There is no particular limitation.

  Moreover, the membrane reaction apparatus according to the present invention preferably further comprises a separation membrane. Here, the “separation membrane” means a membrane for separating and removing chemical substances such as products and by-products obtained from a chemical reaction using a membrane reactor from the reaction system. is there. As such a separation membrane, a conventionally known separation membrane can be suitably used, and the specific type thereof is not particularly limited.

  As shown in FIG. 2 (a), the separation membrane 2 may be provided in contact with the catalyst membrane 1, and as shown in FIG. 2 (b), the separation membrane 2 is connected to the catalyst membrane 1. Some intermediate layer 3 may be provided between them. The “intermediate layer” may be any material as long as it does not inhibit the function of the separation membrane 2 and / or the catalyst membrane 1, and is not particularly limited. For example, a material such as α-alumina fine particles or γ-alumina can be used as the intermediate layer.

  For example, in the membrane reaction apparatus according to the present invention, the catalyst membrane is a catalyst membrane for catalyzing a methane steam reforming reaction, and the separation membrane selects hydrogen generated by the methane steam reforming reaction. It can be set as the structure which is the gas-separation film | membrane removed electrically.

  According to the configuration of the membrane reaction apparatus, hydrogen can be efficiently produced by the steam reforming reaction of methane. Specifically, in the process of producing hydrogen, natural gas and water vapor are reacted in a high temperature environment (for example, about 800 ° C.). Since this reaction for producing hydrogen is a reversible reaction, if the produced hydrogen is kept in the reaction system, the reaction becomes in an equilibrium state, and the production efficiency of hydrogen decreases. Therefore, it is necessary to selectively separate and remove the produced hydrogen from the reaction system. At this time, the above membrane reaction apparatus can be used.

  That is, according to the membrane reaction apparatus, methane and water vapor are reacted by the catalyst film to generate hydrogen. The produced hydrogen can be selectively removed from the reaction system by the gas separation membrane. For this reason, in the hydrogen generation reaction system in which methane and water vapor are mixed and reacted, the generated hydrogen is sequentially separated from the reaction system and removed by using the membrane reaction apparatus, thereby improving the efficiency of hydrogen generation. Can do.

  Examples of the gas separation membrane for selectively removing hydrogen include conventional gas separation membranes in which a metal component (metal oxide) other than silica is blended with silica (for example, a membrane obtained by firing Ni-doped silica). A known gas separation membrane can be suitably used, and is not particularly limited. Further, as the gas separation membrane, in addition to those described in the examples described later, for example, Vasilis N. Burganos, Richard D. Noble, Masashi Asaeda, Andre Ayral, Johann D. LeRoux, “Membranes-Preparation, Properties and Applications '' Material Research Society, Materials Research Society Symposium Proceedings Volume 752, pp. 213-218 (issued January 2003), or M. Kanezashi and M. Asaeda, `` Thirteenth Symposium on Separation Science and Technology for Energy Applications, Program and Abstracts, page 21, Helium and Hydrogen Separation from Organic Gas Mixtures "(October 27-30, 2003), and the like can be suitably used.

  The present invention also includes a method for using a membrane reaction apparatus including a step of performing a chemical reaction using the above-described film reaction apparatus.

  Hereinafter, examples will be shown, and the embodiment of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible in detail. Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and the embodiments obtained by appropriately combining the respective technical means disclosed are also included in the present invention. It is included in the technical scope of the invention.

  In this example, the preparation and properties of a catalyst membrane having a bimodal structure according to one embodiment of the present invention are examined, and further, the effectiveness of the catalyst membrane according to one embodiment of the present invention in a methane reforming reaction is clarified. We examined to make it.

(1) Preparation of bimodal catalyst An α-alumina porous body (average pore diameter 1 μm) was used as a macroporous support. Γ-alumina, titania and zirconia were selected as the mesoporous porous material formed in the pores of the Α-alumina porous body. An outline of the production of the bimodal support is shown in FIG. As shown in the figure, first, the α-alumina porous material was impregnated in a boehmite sol, titania sol, or zirconia sol solution, and dried for 12 hours. Thereafter, by firing at 500 ° C., a bimodal support having a structure of γ-alumina / α-alumina, titania / α-alumina, or zirconia / α-alumina was obtained. Subsequently, the bimodal support was impregnated with an aqueous nickel nitrate solution, dried and calcined at 500 ° C. to prepare a nickel-supported bimodal catalyst membrane. The amount of γ alumina, titania, zirconia, and nickel supported on the α-alumina porous material was measured by a gravimetric method.

Among the above-described bimodal catalysts, in particular, the following is specifically described for Ni / γ-Al ₂ O ₃ / α-Al ₂ O ₃ (Ni / Bimodal) having a bimodal structure supporting γ-Al ₂ O ₃ and Ni. I will explain it. As a comparative example, Ni / α-Al ₂ O ₃ having Ni supported on a membrane support as a catalyst layer of the catalyst membrane was also prepared and evaluated. The catalyst used was a saturated solution of nickel nitrate hexahydrate (Sigma Aldrich; Ni (NO ₃ ) ₂ · 6H ₂ O).

The Ni / α-Al ₂ O ₃ catalyst layer was supported by an impregnation method in which a saturated nitric acid aqueous solution was put in a test tube and the membrane support was immersed therein for about 1 hour. After the loading, the aqueous solution attached to the inside of the tube was wiped off with Kimwipe, and was completely dried in a dryer (110 ° C.) for about 6 hours. Next, after baking for about 1 hour at 300 ° C. in the muffle furnace until NO _x is no longer generated, baking was further performed at 500 ° C. for 15 minutes. At this time, since the inside of the muffle furnace was filled with NO _x , the atmosphere was released to the outdoors using an esmedica tube. After firing, water was added to Bencot to wipe off excess catalyst on the surface, and a support carrying the catalyst was obtained.

On the other hand, the Ni / Bimodal catalyst layer was supported by a boehmite (γ-AlOOH) sol (Nissan Chemical Co., Ltd .: alumina sol 520) and dried in the same manner as the above catalyst, and then calcined at 500 ° C. for about 15 minutes. The carrier supported by this was about 9 to 130 mg depending on the concentration of boehmite sol. Thereafter, the catalyst was supported and calcined in the same manner as described above. Ni thus impregnated was about 0.17 g in the state of nickel oxide in both the Ni / α-Al ₂ O ₃ and Ni / Bimodal catalyst layers. Further, when changing the amount of catalyst, it was controlled by the Ni concentration, the impregnation time, the thickness of the α-alumina tube, and the like. The produced nickel-supported catalyst was reduced at 500 ° C. in a hydrogen atmosphere when the reaction activity was evaluated.

FIG. 3 (b) is a view showing an SEM image of a cross section of an α-alumina (α-Al ₂ O ₃ ) support, and FIG. 3 (c) is a bimodal structure (Ni / Bimodal) prepared by the method described above. It is a figure which shows the SEM image of the cross section of the catalyst film | membrane which has a bimodal structure of (alpha) -alumina / (gamma) -alumina among these. As shown in the figure, in the Ni / Bimodal catalyst membrane, the mesoporous structure of γ-alumina is supported in the macroporous structure (grain boundary) of α-alumina, and Ni is on α-alumina and γ-alumina. It was revealed that it was supported. In particular, it was found that Ni was supported in the pores of the mesoporous structure of γ-alumina.

FIG. 4 (a) shows the results of examining the pore size distribution of the α-Al ₂ O ₃ unimodal catalyst membrane by mercury porosimetry, and FIG. 4 (b) shows the mercury intrusion method of Ni / Bimodal catalyst membrane. Shows the results of examining the pore size distribution. FIG. 4 (c) shows the pore structure of each of α-Al ₂ O ₃ , Ni / Bimodal, and γ-Al ₂ O ₃ using mercury porosimetry and nitrogen adsorption (BET adsorption). The result of evaluation is shown.

As shown in FIGS. 4 (a) to 4 (c), the Ni / Bimodal bimodal catalyst membrane has 1 μm of macropores having substantially the same size as the α-Al ₂ O ₃ unimodal catalyst membrane. In addition, it is clear that it has mesoporous pores (mercury intrusion method 7.5 nm, BET 4.0 nm) due to γ-Al ₂ O _3, and it is clear that it constitutes a bimodal structure. (Refer to the arrow portion in FIG. 4B).

Next, with respect to the Ni / Bimodal bimodal catalyst membrane, the hydrogen adsorption amount, the specific surface area due to nitrogen adsorption, and the dependency of the Ni loading amount on the γ-Al ₂ O ₃ loading amount were examined. The result is shown in FIG. The specific surface area can be measured by nitrogen adsorption, and the measurement of the hydrogen adsorption amount by hydrogen adsorption corresponds to the Ni surface area.

As a result, as shown in FIG. 5, the specific surface area increased linearly with the amount of γ-Al ₂ O ₃ supported, and the amount of hydrogen adsorption also increased, so the amount of γ-Al ₂ O ₃ increased. However, it was considered that Ni was supported almost uniformly in the γ-Al ₂ O ₃ supported pores, and the γ-Al ₂ O ₃ pores had a pore diameter that allowed gas (gas) to diffuse. Further, from FIG. 5, the amount of γ-Al ₂ O ₃ supported is 0, that is, the hydrogen adsorption amount of the Ni / α-Al ₂ O ₃ catalyst is very small, about 0.45 μmol / g. _When 10 mg of ₂ O ₃ was supported, it was found that the hydrogen adsorption amount was about 15 times. Factors for improving the catalytic activity include an increase in catalyst supporting area due to an increase in specific surface area, or Ni particles supported in γ-Al ₂ O ₃ pores are supported on the surface of α-Al ₂ O ₃ particles. It was considered that the catalyst dispersibility was improved by being smaller than the Ni particles. In particular, since the specific surface area of the catalyst membrane supporting 10 mg of γ-Al ₂ O ₃ increased only about 2.4 times, the main factor for improving the catalytic activity is supported in the pores of the mesoporous structure. It was thought that this was due to Ni existing in high dispersion.

In other words, from FIG. 5, the Ni loading is substantially constant, but the hydrogen adsorption amount is increased. For this reason, it is considered that Ni is supported in a highly dispersed manner by the pores of γ-Al ₂ O ₃ . The specific surface area of Ni / γ-Al ₂ O ₃ was 195 m ² / g, and the H ₂ adsorption amount was 69.0 μmol / g.

Moreover, although data are not shown, the amount of γ-Al ₂ O ₃ supported in the prepared sample increased as the γ-AlOOH concentration (boehmite sol) was increased. This indicates that the amount of γ-Al ₂ O ₃ supported can be controlled by the γ-AlOOH concentration. Further, the amount of the metal catalyst per unit catalyst membrane weight can be controlled by the impregnation time and the nickel nitrate concentration. In this example, the amount was about 30 mg / g-α-Al ₂ O ₃ .

(2) Production of membrane reactor and evaluation of gas permeability A membrane reactor was produced by providing a gas separation membrane on the catalyst membrane prepared in (1) above. As shown in FIG. 6 (a), a Ni / Bimodal bimodal catalyst membrane was impregnated in a silica-nickel colloid solution and then baked to produce a membrane reactor. Thereafter, steam treatment was performed, and a methane reforming reaction experiment was conducted.

  A specific method for producing a membrane reactor by providing a gas separation membrane on a Ni / Bimodal bimodal catalyst membrane was performed as follows.

  In the production of a thin film by the sol-gel method, various coating methods have been developed, but the most common method is a dip coating method. However, according to this method, the sol penetrates deeply into the pores due to the capillary suction force, causing adverse effects such as a reduction in permeation amount and generation of cracks. Therefore, the hot coating method was developed. In this method, a base material is heated to a high temperature in advance, and a colloidal sol is soaked in a non-woven fabric such as Bencot and applied. The colloidal sol is gelated at the moment of touching the base material, so that a thin film can be formed. The colloidal sol was supported using this method, and a ceramic thin film having excellent permeability was produced as a hydrogen-selective gas separation membrane.

  Specifically, first, a silica-nickel colloidal sol in which Ni was added as a foreign metal to silica was prepared. The silica-nickel colloidal sol is prepared by mixing nickel nitrate hexahydrate with ethyl silicate (TEOS) and subjecting it to hydrolysis and polycondensation reaction.

  Explaining in detail, first mixed with ethanol (special sigma aldrich) with a predetermined concentration of ethyl silicate (special sigma aldrich) as solvent (solution A), apart from that, nickel nitrate hexahydrate (special sigma aldrich) is also available Similarly, dissolve in ethanol (Liquid B). Also, ion-exchanged water for hydrolysis, nitric acid (special grade Sigma-Aldrich), and ethanol are mixed (liquid C). The prepared liquids A and B are sufficiently mixed, and liquid C is added with stirring, followed by hydrolysis and polycondensation reaction (12 hours) to obtain a silica-nickel polymer. Thereafter, water and nitric acid are poured so that the total amount becomes 500 cc, and the mixture is boiled and stirred (12 hr) to grow colloidal particles to obtain a silica-nickel colloidal sol. Several types of colloidal sols having different particle diameters are required for the film forming process using the sol-gel method. It has been confirmed that the particle diameter of the metal-added silica colloidal sol can be controlled by changing the alkoxide (ethyl silicate) and metal nitrate concentration in the starting solution, and this method was also adopted in this example. The formulation of the starting solution is shown in Table 1 below.

  Sol-A, -B, -C, -D, and -E were ordered in descending order of alkoxide concentration. Further, in this embodiment, the main purpose is to improve the activity of the catalyst layer and to evaluate it, so it is necessary to reduce Ni that shows catalytic activity in the methane reforming reaction as much as possible. For this reason, the Si: Ni ratio of the colloidal sol was set to 9: 1.

  The colloidal sol prepared above was supported on the Ni / Bimodal bimodal catalyst membrane by the hot coating method described above. In advance, a Ni / Bimodal bimodal catalyst film was heated to about 180 ° C., a colloidal sol soaked in Bencot was applied, and baked at 500 ° C. for about 10 minutes. By repeating this operation several times in order of Sol-A, -B, -C, ..., a hydrogen separation thin film layer was formed on the Ni / Bimodal bimodal catalyst membrane, and a membrane reactor was obtained. In addition, in order to increase the resistance to high-temperature steam, after the membrane reactor is manufactured, it is left in a high-humidity atmosphere (40 ° C., RH 60%) for about 12 hours and then fired at 500 ° C. for 10 minutes (high-humidity pretreatment method) Went.

  The high temperature steam treatment is a treatment performed to obtain the stability of the film under high temperature steam. This treatment was performed in a ternary system of hydrogen, nitrogen, and water vapor, and the change in permeation coefficient of each gas at 500 ° C. was measured over time by the outlet flow rate and gas chromatography. The inside of the membrane was supplied at atmospheric pressure and the water vapor partial pressure was 50 kPa. In the reduced pressure system, the nitrogen permeation coefficient cannot be measured well due to air leakage from the outside of the system. The treatment was performed until the gas permeability coefficient was relatively stable. Using the water vapor transmission coefficient at this time, the hydrogen / water vapor transmission coefficient ratio was calculated. Thereafter, a methane reforming reaction experiment was conducted.

  Before performing the methane reforming reaction experiment, the cross section of the fabricated membrane reactor was observed by SEM. The result is shown in FIG. As shown in the figure, it can be seen that a hydrogen separation thin film layer ("Separation layer" in the figure) is formed on the Ni / Bimodal bimodal catalyst membrane ("Catalytic layer" in the figure).

  Moreover, before conducting the methane reforming reaction experiment, performance evaluation (gas permeability evaluation) of the produced gas separation membrane was performed. The result is shown in FIG. In the figure, the dotted line is the result immediately after film formation, and the solid line is the result after steam treatment. As shown in the figure, it was found that the gas separation membrane produced in this example showed high selective permeability to helium and hydrogen.

(3) Methane reforming reaction experiment using membrane reactor The methane reforming reaction experiment in this example was performed using the apparatus shown in FIG. Since water vapor was used in this example, the portion surrounded by the dotted line was kept warm in a thermostat at about 140 ° C. Gases such as hydrogen, nitrogen, methane, and helium were supplied by gas cylinders. The raw material water vapor can be supplied at a constant flow rate using a syringe pump when the flow rate is low, and a liquid chromatograph feeding unit (LC10ADVP manufactured by Shimadzu Corporation) when the flow rate is high. And mixed. The evaporation surface used a 1 / 16-inch pipe with a small inner diameter to suppress bumping and was able to be preheated with the supplied gas. The flow rate of the feed gas was adjusted by a mass flow controller, and the pressure inside and inside the reactor membrane was controlled using a Needle Valve. In order to reduce the pressure outside the membrane, the pressure was reduced using a diaphragm vacuum pump (PM15298-86 manufactured by KNF Japan), and the pressure was controlled by a Needle Valve (15 to 100 kPa). At this time, a cold trap was installed in front of the pump to prevent water from flowing into the vacuum pump. The pressure gauge is used for measurement at room temperature from the viewpoint of heat resistance, but it is conceivable that water vapor is condensed in the piping from the thermostat to the pressure gauge, and the pressure response becomes slow. For this reason, the pipe in this part was made sufficiently long to intentionally condense moisture. In addition, two pressure gauges were used on the inner side and the outer side, respectively, in order to reduce the pressure, a pressure gauge capable of measuring pressure reduction was used, and in the case of pressurization, a pressure gauge dedicated to pressurization was used. The gas flow rate in the outer membrane, inner membrane, and bypass line was measured by using a soap film meter after almost removing water vapor with a trap set at about 4 ° C., and contained water vapor by the saturated vapor pressure at 4 ° C. The desired flow rate was obtained. In order to reduce the volume of the trap, a Y-shaped trap was prepared, and attention was paid to the amount of trap water. The reactor was controlled by a fixed thermocouple so that the inside of the membrane was 500 ° C. using a mantle heater, and the inside thermocouple was made movable so that the temperature distribution inside the membrane could be measured. The temperature inside the membrane was 500 ° C. at the inlet of the catalyst layer, and the temperature distribution in the catalyst layer was 500 ± 5 ° C. For the piping and joints, mainly 1/8 inch stainless tubes and 1/8 inch joints from Swage Lock were used. Since the reactor has a high temperature of 500 ° C., the screw part is easily broken. Moreover, in order to improve the sealing performance when the pressure was reduced, a VCR face seal joint was used for the reactor joint.

  Two gas chromatographs connected on-line with a sampler tube were used for component analysis of the mixed gas outside and inside the membrane in order to increase the accuracy. A sampler tube (for G.C.2) in a room temperature atmosphere was installed after the trap so that there was no inflow of water. The gas coming out of the reaction system was led to the outside using an esmedica tube and released to the atmosphere.

The reaction conditions were as follows: temperature: 500 ° C., pressure, 100 kPa (primary side), H ₂ O / CH ₄ : 3. As shown in FIG. 7B, the reaction format was (i) total permeation experiment and (ii) membrane type reaction experiment. (i) As shown in FIG. 7 (b), the total permeation experiment is for reactivity evaluation, and does not use a gas separation membrane for hydrogen separation, but only from a Ni / Bimodal bimodal catalyst membrane. The experiment was conducted with a membrane reactor, and the permeation side atmosphere was opened. The (ii) membrane-type reaction experiment is for evaluating the hydrogen abstraction reaction, and is an experiment using a membrane-type reactor equipped with a gas separation membrane and a Ni / Bimodal bimodal catalyst membrane. A pressure of 20 kPa is applied.

  First, the activity of the catalyst membrane was evaluated by a total permeation experiment (experiment without a gas separation membrane for hydrogen separation). Specifically, the space velocity dependence and the temporal stability were examined under a reaction temperature of 500 ° C., a steam methane ratio (S / C) of 3, and atmospheric pressure. For gas composition analysis, two gas chromatographs were used. First, water and carbon dioxide were analyzed with GC-1 filled with Gaschropack 54, and hydrogen, oxygen, and carbon with GC-2 filled with Molecular-Sieves. Nitrogen, methane, and carbon monoxide were analyzed.

FIG. 8A shows the dependence of the methane flow rate and reaction rate on the amount of catalyst supported in the Ni / α-Al ₂ O ₃ catalyst. The broken line in the figure is a calculation line of the equilibrium reaction rate at 500 ° C. with pressure correction. The amount of catalyst was changed by changing the impregnation time of the aqueous nickel nitrate solution, and 0.11 g and 0.21 g in the nickel oxide state, respectively. Compared with 0.11g loaded with Ni / _α-Al 2 _{O 3 catalyst, Ni / α-Al 2 O} 3 catalyst 0.21g carrying showed high reaction rate, 0.11g catalyst supported in the measurement flow rate range Although the equilibrium reaction rate was not reached, the catalyst supported by 0.21 g exhibited an equilibrium reaction rate at a flow rate of 10 μmol / s or less. However, in both cases, the reaction rate decreased as the flow rate increased.

On the other hand, FIG. 8B shows the methane flow rate and the reaction rate in the Ni / Bimodal catalyst carrying γ-Al ₂ O ₃ . Ni / Bimodal catalysts were prepared in which the supported amounts of γ-Al ₂ O ₃ were 9 mg and 38 mg depending on the γ-AlOOH sol concentration, and the Ni supported amount was approximately the same. Compared with the Ni / α-Al ₂ O ₃ catalyst carrying 0.11 g of nickel oxide, both Ni / Bimodal catalysts showed a reaction rate close to the equilibrium reaction rate even at a high methane flow rate. From the above, by supporting γ-Al ₂ O ₃ , catalyst dispersibility was improved compared to Ni / α-Al ₂ O ₃ , and a methane reaction rate close to the equilibrium reaction rate was obtained even at a high space velocity. it is conceivable that.

Next, the hydrogen abstraction effect in the membrane reaction was examined. Specifically, using a membrane reactor having the above-mentioned gas separation membrane on a Ni / Bimodal catalyst membrane, the reaction rate in the steam reforming reaction, the hydrogen composition on the permeate side and the non-permeate side on the dry gas basis, and hydrogen The change in yield over time was examined. The reaction was carried out at 500 ° C., steam ratio (H ₂ O / CH ₄ ) 3, supply methane flow rate 2.1 cc / min, and primary pressure 100 kPa. The performance of the used gas separation membrane after high-temperature steam treatment is as follows: hydrogen permeability coefficient 1.4 × 10 ⁻⁶ m ³ / m ² · kPa · s, hydrogen / nitrogen permeability coefficient ratio 45, hydrogen / water permeability coefficient ratio 13 there were. About 150 minutes after the start of the reaction, the secondary side was depressurized from 100 kPa to 20 kPa.

  The result is shown in FIG. In the figure, the part indicated by “without extraction” indicates the result when hydrogen is not extracted before the pressure reduction on the secondary side, and the part indicated by “with extraction” indicates that the hydrogen is reduced on the secondary side and hydrogen is extracted. The result when pulling out is shown. Moreover, the broken line in the figure is a calculation line by simulation when the reaction rate is infinite.

The calculation was performed under the following conditions.
・ CH ₄ Conversion = (CO + CO ₂ ) / (CH ₄ + CO + CO ₂ )
・ H ₂ yield ＝ Perm. H ₂ / Feed CH ₄
Derived from 1 mol of feed methane
Permeated hydrogen moles The membrane reaction model is
・ Ideal flow ・ Temperature in the reactor is uniform ・ Calculation was based on an infinite reaction rate.

  As a result, after extracting hydrogen, the reaction rate was about 0.6, and the hydrogen composition on the permeate side on the dry gas basis was about 0.95. This is because, due to the principle of Le Chatelier, hydrogen was extracted, the equilibrium moved to the product side, and the reaction was promoted. In addition, the value was relatively constant and almost coincided with the simulation calculation line, which revealed the usefulness of the membrane reaction in the methane reforming reaction.

  That is, it was found that when the permeation side (secondary side) was depressurized, the methane reaction rate increased. This was found to be almost consistent with the model calculation. Therefore, it has been clarified that the hydrogen production rate is increased by extracting hydrogen from the methane reforming reaction system using the membrane reactor in this example.

Subsequently, the supply methane flow dependency of the membrane reaction was examined. Specifically, the reaction rate and the hydrogen yield when the supplied methane flow rate was changed were examined using a membrane reactor in which the gas separation membrane described above was provided on a Ni / Bimodal catalyst membrane. The reaction conditions were as follows: temperature: 500 ° C., H ₂ O / CH ₄ : 3. The result is shown in FIG. The broken line in the figure is a calculation line by simulation. Here, on the horizontal axis, P _H2 : hydrogen permeability coefficient [m ³ / m ² · kPa · S], Am: membrane area [m ² ], p ₁ : non-permeation side pressure (transmembrane pressure difference) [kPa] ], F _CH4 : Feed methane flow rate [m ³ / s] was used, and a dimensionless number θ representing the hydrogen flow rate on the permeate side relative to the supplied methane flow rate was used.

In addition,
θ = (P _H2 · Am · p ₁ ) / F _CH4
The amount of hydrogen that can permeate the supplied methane.

  In the figure, “◯ (white circle)” indicates the result without hydrogen extraction, and “● (black circle)” indicates the result with hydrogen extraction.

  As a result, as θ decreases, that is, as the supply methane flow rate increases, the reaction rate after hydrogen abstraction decreases, and the hydrogen yield also decreases. This is because when the flow rate of methane increases, the amount of hydrogen produced in the catalyst layer increases so much that the extraction of hydrogen in the separation layer cannot catch up. The reaction rate and hydrogen yield almost agreed with the calculated line. That is, it was found that the equilibrium reaction rate was exhibited when no hydrogen was withdrawn, and that the reaction rate was increased because θ was increased when hydrogen was withdrawn.

Summarizing the above results, the catalyst membrane support can be produced by supporting γ-Al ₂ O ₃ on α-Al ₂ O ₃ to produce a catalyst membrane support having a bimodal structure. It was found that the amount and specific surface area tended to increase in proportion to the amount of γ-Al ₂ O ₃ supported. As for the reaction characteristics, Ni / Bimodal catalyst membrane shows almost equilibrium reaction rate even at high space velocities from the results of total permeation experiments, and a membrane reactor with a gas separation membrane on the Ni / Bimodal catalyst membrane. It has been found that the reaction rate in the methane reforming reaction increases due to the extraction of H ₂ by, and that the CH ₄ reaction rate and the H ₂ yield increase as the dimensionless number θ increases.

  As described above, since the catalyst membrane according to the present invention exhibits excellent catalytic activity, it can be used as a catalyst membrane for various chemical reactions, a membrane reactor, or the like. For example, it can be used in a hydrogen production process by a steam reforming reaction of natural gas (methane). Therefore, it can be said that the present invention having very wide industrial applicability such as the chemical industry is very useful.

(A) is a figure which shows typically the structure of the conventional catalyst film | membrane, (b) is a figure which shows typically the structure of the catalyst film | membrane concerning this invention. (A) is a figure which shows the typical structure of an example of the membrane type reaction apparatus which concerns on this invention, (b) is a figure which shows the typical structure of the other example of the membrane type reaction apparatus which concerns on this invention. is there. (A) is a diagram showing an outline of a manufacturing bimodal catalyst film in the present embodiment, (b) is a diagram showing an SEM image of a cross section of the α-Al ₂ O ₃ support, (c) the Ni It is a figure which shows the SEM image of the cross section of a / Bimodal catalyst membrane. (A) is a diagram showing the results of examining the pore size distribution by mercury porosimetry for unimodal catalyst film of α-Al ₂ O ₃ in the present embodiment, (b) by mercury porosimetry for Ni / Bimodal catalyst film shows the results of examining the pore size distribution, and (c) for each of _{α-Al 2 O 3, Ni} / Bimodal, and _γ-Al 2 _{O 3,} mercury porosimetry and nitrogen adsorption (BET adsorption) It is a figure which shows the result of having evaluated the pore structure using. In this embodiment, the bimodal catalyst film of Ni / Bimodal, illustrates hydrogen adsorption, the specific surface area by nitrogen adsorption, and the results of examining the γ-Al ₂ O ₃ supported amount dependency of Ni supported amount. (A) is a figure which shows the outline of the method of producing a membrane type reaction apparatus using a Ni / Bimodal catalyst membrane in this implementation low, (b) is a membrane type reaction provided with Ni / Bimodal and a gas separation membrane. It is a figure which shows the SEM image of the cross section of an apparatus, (c) is the figure which evaluated the gas permeability of the gas separation membrane. (A) is a figure which shows schematic structure of the apparatus used for the methane reforming reaction experiment in a present Example, (b) is a figure which shows typically the reaction format of the methane reforming reaction experiment in a present Example. . (A) In the present embodiment, a diagram showing a catalyst loading dependence of methane flow rate and the reaction rate in Ni / _α-Al 2 _{O 3} catalyst, (b) is carrying _γ-Al 2 _{O 3} Ni It is a figure which shows the methane flow rate and reaction rate in a / Bimodal catalyst. In a present Example, it is a figure which shows the result of having examined about the hydrogen abstraction effect in a membrane type reaction. In a present Example, it is a figure which shows the result of having examined the supply methane flow rate dependence of the membrane type reaction.

Explanation of symbols

1 Catalyst membrane 2 Gas separation membrane (separation membrane)
DESCRIPTION OF SYMBOLS 5 Membrane type reactor 5 'Membrane type reactor 10 First carrier 11 Second carrier 12 Catalyst particles (catalyst)
13 Macroporous pores

Claims (9)

A membrane-like catalyst membrane comprising a first support having a macroporous structure and a second support having a mesoporous structure;
A catalyst membrane characterized in that a catalyst is held at least in the pores of the mesoporous structure.   2. The catalyst membrane according to claim 1, wherein the second support is supported inside pores of the macroporous structure of the first support.   The catalyst film according to claim 1 or 2, wherein the first support is a porous material selected from the group consisting of α-alumina, cordierite, mullite, and stainless steel.   The catalyst film according to any one of claims 1 to 3, wherein the second support is a porous material selected from the group consisting of γ-alumina, titania, zirconia, and silica.   The catalyst film according to any one of claims 1 to 4, wherein the first carrier has a spherical shape, a pellet shape, a honeycomb shape, a cylindrical shape, or a monolithic shape.   A membrane reaction apparatus comprising the catalyst film according to any one of claims 1 to 5.   Further, a membrane reaction apparatus comprising a separation membrane. The catalyst membrane is a catalyst membrane for catalyzing a steam reforming reaction of methane,
8. The membrane reactor according to claim 7, wherein the separation membrane is a gas separation membrane that selectively removes hydrogen generated by a steam reforming reaction of methane. A method for using a membrane reaction apparatus, comprising a step of performing a chemical reaction using the film reaction apparatus according to any one of claims 6 to 8.