JP2005289652A - Method for producing hydrogen and reaction tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a system for producing hydrogen, by which problems such as separation, low temperature facilities, heat supply or the like in the hydrogen production method based on dehydrogenation reaction of a raw material oil comprising hydrocarbons mainly having a cyclohexane ring can be solved, and hydrogen can be efficiently produced. <P>SOLUTION: Hydrogen and aromatic hydrocarbons are produced by subjecting hydrocarbons having a cyclohexane ring to dehydrogenation reaction in a reaction tube having a double tube structure composed of an inner tube comprising a hydrogen separation membrane and an outer tube which is made of metal and has a plurality of inside fins on each of which a metal oxide layer and a catalyst are supported. Hydrogen is removed mainly to a permeated side, and aromatic hydrocarbons are obtained mainly at a non-permeated side by performing selective membrane separation operation in a reaction system while advancing the dehyrogenation reaction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hydrogen production method and system for generating hydrogen by dehydrogenation of a feedstock mainly composed of hydrocarbons having a cyclohexane ring in the field of hydrogen production.

  Hydrogen is widely used in various industrial fields including the oil refining and chemical industries. In particular, in recent years, hydrogen energy has attracted attention as a future energy, and research is focused on fuel cells, but hydrogen gas has a large volume per calorie and also requires a large amount of energy for liquefaction. Storage and transport systems are an important issue. In addition, a new infrastructure is required for hydrogen supply (see Non-Patent Document 1).

Liquid hydrocarbons, on the other hand, have the advantage of being easy to handle and having a higher energy density than hydrogen gas, and also have the advantage of being able to use existing infrastructure. The method of producing hydrogen from methane is important.
Production of hydrogen is widely carried out by known techniques such as steam reforming of methane and light paraffin, autothermal reforming, and partial oxidation, but these reactions require high temperatures. Furthermore, when targeting on-site power generation using fuel cells, particularly polymer electrolyte fuel cells, a shift reactor and a carbon monoxide remover using CO selective oxidation or methanation are required in the subsequent stage. This is a very complex process. In addition, when an automobile hydrogen station is targeted, high purity hydrogen must be obtained using PSA (pressure swing adsorption). The same applies to the reforming system of methanol. In the case of on-site, a carbon monoxide remover is required, and in the case of a hydrogen station, PSA is required.

  On the other hand, in the method of producing hydrogen by dehydrogenating liquid hydrocarbons, the production process is simple because the reaction is simple. Furthermore, since the product is hydrogen, which is a gas, and unsaturated hydrocarbon, which is a liquid at room temperature, the product is relatively easy to separate. In particular, the reaction using a hydrocarbon having a cyclohexane ring as a raw material and dehydrogenating the cyclohexane ring into an aromatic ring proceeds easily in the presence of a dehydrogenation catalyst, and the product hydrogen and aromatic hydrocarbon Is relatively easy, and is suitable for small-scale hydrogen production (see Non-Patent Document 2).

  However, most of the aromatic hydrocarbons can be liquefied and separated from hydrogen if the temperature of the produced hydrogen and aromatic hydrocarbons is reduced to room temperature under atmospheric pressure, but the amount of aromatics depends on the vapor pressure at room temperature. Hydrocarbons are mixed in hydrogen gas. For example, in the case of toluene, it becomes about 2.1% contamination at 15 ° C. and atmospheric pressure. Therefore, when it is necessary to increase the purity of hydrogen as in fuel cell applications, a problem arises in the separation of hydrogen and aromatic hydrocarbons.

  As a separation method, there is a method of cooling and separating, but in order to achieve a hydrogen concentration of 99.9% or more, a low temperature of about −30 ° C. at normal pressure is required. Cooling to −30 ° C. using a refrigerator is not a preferred removal method because it results in a decrease in energy efficiency in hydrogen production and the equipment becomes large.

  In addition, there is an adsorptive separation method in which it is adsorbed by an adsorbent and separated. In this method, it is necessary to desorb and recover the aromatic hydrocarbon from the adsorbent after adsorption and to regenerate the adsorbent. Among them, the PSA method (pressure swing adsorption method) in which adsorption and desorption are performed by pressure fluctuation is well known, but the recovery rate and overall efficiency of hydrogen gas are low, and operations such as pressure increase and pressure decrease are performed. Is necessary and has the disadvantage of becoming a large system.

  As a separation method other than the above, there is a membrane separation method. The membrane separation method is characterized by high energy efficiency, and the types of separation membranes are mainly palladium membranes, polymer membranes, ceramic membranes, and carbon membranes. In the purification of hydrogen, a palladium membrane has been put into practical use for the purpose of high-purity hydrogen purification (see Non-Patent Document 3).

  When the membrane separation method is used, it is necessary to increase the pressure on the non-permeate side. Therefore, it is necessary to increase the pressure of the hydrogen generation reaction (dehydrogenation reaction) or increase the pressure of the product gas after the reaction. When the pressure of the product gas is increased, energy efficiency is reduced in hydrogen production. Further, in the dehydrogenation reaction, it is necessary to increase the reaction temperature when the reaction pressure is increased from the viewpoint of restrictions on chemical equilibrium.

However, the dehydrogenation reaction of hydrocarbons mainly having a cyclohexane ring needs to be performed at a lower temperature in order to suppress the decomposition reaction that is a side reaction. For example, in the dehydrogenation reaction of methylcyclohexane, it is necessary to perform the reaction at a temperature of 360 ° C. or lower. Due to equilibrium constraints, it was difficult to lower the temperature of this process. In order to solve this problem, a membrane reactor incorporating a hydrogen separation membrane is used to selectively remove hydrogen generated in the dehydrogenation process from the reaction field, thereby improving the hydrogen yield and lowering the reaction temperature. As a technique, for example, Patent Document 1: Japanese Patent Laid-Open No. 4-71638 discloses a technique in which a porous ceramic membrane that selectively permeates hydrogen is incorporated to perform a dehydrogenation reaction of cyclohexane. Patent Documents 2 and 3 disclose hydrogen production technology by reaction separation using a palladium membrane.
However, any of them uses an inert gas such as argon as a sweep gas, and is not practical in terms of the purity of the produced hydrogen. Moreover, dehydrogenation of the cyclohexane ring is a large endothermic reaction. For example, the enthalpy of reaction in the dehydrogenation of cyclohexane is 50 kcal / mol, and the enthalpy of reaction per cyclohexane ring is almost the same even for hydrocarbons with substituents. In ordinary solid catalysts (particles, pellets, extruded products, etc.) with an active metal supported on an oxide, the heat transfer becomes rate-determined. The reaction efficiency decreases. Particularly in the reaction separation, the heat supply is disadvantageous from the viewpoint of the surface transfer / catalyst amount by the volume increase of the hydrogen separation membrane not involved in the reaction. This tendency becomes more prominent as LHSV increases. In this connection, Patent Document 4 discloses a method for steam reforming of methanol, characterized in that a thermally conductive catalyst body in which an ultrafine catalyst material is supported on the surface of a continuous metal substrate is used. There is a description that hydrogen and carbon monoxide can be obtained in a high yield.
However, as described above, the reforming reaction of methanol has a drawback that it has many steps as a small-scale hydrogen production method.
Kobayashi N, Seasonal Energy Engineering, Vol. 25, No. 4, pp. 73-87 (2003) Masaru Ichikawa, Industrial Materials, Vol. 51, No. 4, 62-69 (2003) Supervised by Masayuki Nakagaki, membrane processing technology system (first volume), Fuji Techno System, pages 661 to 662 and pages 922 to 925 (1991) JP-A-4-71638 JP-A-3-217227 JP-A-5-317708 Japanese Patent Laid-Open No. 5-116901

  An object of the present invention is to solve problems such as separation, temperature reduction, heat supply, etc. in a hydrogen production method by dehydrogenation of a feedstock mainly composed of hydrocarbons having a cyclohexane ring, and to efficiently produce hydrogen And providing a hydrogen production system.

  As a result of intensive research to solve the above-mentioned problems, the present inventors supported active metal on the metal oxide layer on the surface of the thermally conductive support when generating hydrogen by hydrocarbon dehydrogenation. When a membrane reactor equipped with a catalyst and capable of selectively removing hydrogen was used and the reaction conditions were further optimized, a method for efficiently producing hydrogen was discovered.

That is, according to the first aspect of the present invention, a cyclohexane ring is formed in a flow-through reaction tube in which a catalyst supported on a support made of a metal heat conductive support having a metal oxide layer unevenly distributed on the surface is present. In the dehydrogenation reaction system in which hydrogen and aromatic hydrocarbons are produced by dehydrogenating the hydrocarbons possessed,
Incorporating hydrogen removal means by hydrogen separation membrane,
While the dehydrogenation reaction proceeds, the hydrogen separation membrane mainly removes hydrogen on the permeate side, and mainly obtains aromatic hydrocarbons on the non-permeate side.
Since the catalyst uses a metal support, it is easy to adjust the heat of dehydrogenation, and it is a simple apparatus because it performs dehydrogenation and hydrogen separation simultaneously.

A second aspect of the present invention is the method for producing hydrogen according to the first aspect of the present invention, wherein the hydrocarbon having a cyclohexane ring contains methylcyclohexane and toluene generated by the dehydrogenation is separated. is there.
In the membrane separation of the present application, toluene can also be easily separated.

A third aspect of the present invention is the method for producing hydrogen according to the first or second aspect of the present invention, wherein the hydrogen separation membrane is a ceramic membrane.
In particular, separation of hydrocarbons is easy with ceramic membrane separation.

A fourth aspect of the present invention is the method for producing hydrogen according to the first to third aspects of the present invention, wherein the hydrogen separation membrane is a metal membrane containing 100 to 10 mass% of Pd.
Hydrocarbons can be easily separated by such separation using a metal membrane.

A fifth aspect of the present invention is the method for producing hydrogen according to the first to fourth aspects of the present invention, wherein the support in the catalyst is a support containing alumina.
The carrier is advantageous for heat conduction.

According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the reaction tube has a double tube structure, the outer tube is a metal heat conductive support, and the inner tube. Are composed of hydrogen separation membranes,
The gap between the double pipes is provided with a plurality of fin-like protrusions that are long in the flow direction and made of metal and thermally conductive from the outer pipe toward the inside,
A method for producing hydrogen, which has a structure in which a metal oxide layer is unevenly distributed on at least the surface of the fin-like projections to support a catalyst.
The double pipe with the internal fin is convenient because it is excellent in thermal efficiency of dehydrogenation and can perform dehydrogenation and membrane separation at the same time.

A seventh aspect of the present invention is a double-pipe flow-type reaction tube, wherein the outer tube is a metal thermally conductive support, the inner tube is composed of a hydrogen separation membrane,
The gap between the double pipes is provided with a plurality of fin-like protrusions that are long in the flow direction and are made of metal and thermally conductive from the outer pipe toward the inside of the pipe.
At least the fin-like protrusion surface has a structure in which a metal oxide layer is unevenly distributed to support the catalyst.
This is a reaction tube for hydrogen production for simultaneously performing dehydrogenation of hydrocarbons and membrane separation of the obtained hydrogen.
This is a double-pipe membrane reactor that can be advantageously employed in the present application.

In an eighth aspect of the present invention, a hydrogen removal means using a hydrogen separation membrane is included in a reaction system in which hydrocarbons are reacted in a flow reaction tube to produce hydrogen and a reaction product.
While proceeding the dehydrogenation reaction,
In the hydrogen production method, hydrogen is mainly removed from the permeate side of the membrane by the hydrogen separation membrane, and a reaction product is mainly obtained from the non-permeate side of the membrane.
The hydrogen production method is characterized in that the hydrogen partial pressure on the permeate side is lowered by flowing water vapor on the permeate side of the membrane.
If water vapor is used to lower the hydrogen partial pressure, subsequent processing is easy.

According to a ninth aspect of the present invention, a hydrogen removal means using a hydrogen separation membrane is included in a reaction system for producing hydrogen and a reaction product by reacting hydrocarbons in a catalyst layer in a flow reaction tube,
While proceeding the dehydrogenation reaction,
In the hydrogen production method, hydrogen is mainly removed from the permeate side of the membrane by the hydrogen separation membrane, and a reaction product is mainly obtained from the non-permeate side of the membrane.
By producing hydrogen with a reaction pressure of 0.4 MPa or more in absolute pressure, a permeation pressure of the hydrogen separation membrane of 0.12 MPa or less in absolute pressure, and a catalyst layer outlet temperature in the range of 300 ° C to 360 ° C, The hydrogen production method is characterized in that the hydrogen recovery rate is 80% or more.
By using the above reaction conditions while using a so-called membrane reactor, the hydrogen recovery rate can be 80% or more.

According to a tenth aspect of the present invention, a hydrogen removal means using a hydrogen separation membrane is included in a reaction system for producing hydrogen and a reaction product by reacting hydrocarbons in a catalyst layer in a flow reaction tube,
While proceeding the dehydrogenation reaction,
In the hydrogen production method, hydrogen is mainly removed from the permeate side of the membrane by the hydrogen separation membrane, and a reaction product is mainly obtained from the non-permeate side of the membrane.
The reaction pressure is 0.4 MPa or more in absolute pressure, the permeation side pressure of the hydrogen separation membrane is 0.12 MPa or less in absolute pressure, and the permeation side outlet hydrogen partial pressure is absolute pressure by flowing water vapor on the permeation side of the hydrogen separation membrane. The hydrogen recovery rate is 80% or more by producing hydrogen in the range of 0.05 MPa or less and the catalyst layer outlet temperature in the range of 270 ° C. or higher and 360 ° C. or lower.
By using the above reaction conditions while using a so-called membrane reactor, the hydrogen recovery rate can be 80% or more.

In an eleventh aspect of the present invention, a hydrogen removal means using a hydrogen separation membrane is included in a reaction system for producing hydrogen and a reaction product by reacting hydrocarbons in a catalyst layer in a flow reaction tube,
While proceeding the dehydrogenation reaction,
In the hydrogen production method, hydrogen is mainly removed from the permeate side of the membrane by the hydrogen separation membrane, and a reaction product is mainly obtained from the non-permeate side of the membrane.
The reaction pressure is 0.2 MPa or more in absolute pressure, the permeation side pressure of the hydrogen separation membrane is 0.12 MPa or less in absolute pressure, and the permeation side outlet hydrogen partial pressure is absolute pressure by flowing water vapor on the permeation side of the hydrogen separation membrane. The hydrogen production method is characterized in that the hydrogen recovery rate is 80% or more by producing hydrogen in a range of 0.01 MPa or less and a catalyst layer outlet temperature of 220 ° C. or higher and 360 ° C. or lower.
By using the above reaction conditions while using a so-called membrane reactor, the hydrogen recovery rate can be 80% or more.

  When hydrogen is mainly generated from hydrocarbons having a cyclohexane ring by a dehydrogenation reaction, a catalyst in which an active metal is supported on a metal oxide layer on the surface of a thermally conductive support is installed to selectively remove hydrogen. According to the method of the present invention characterized in that a type reactor is used, hydrogen can be efficiently produced within the range of optimized reaction conditions.

Hereinafter, the present invention will be described in detail.
In the present invention, a so-called membrane reactor is used. More precisely, the membrane reactor referred to in the present invention is a flow-type reaction tube, and a hydrogen removing means using a hydrogen separation membrane is provided in the reaction tube. Usually, the hydrogen separation membrane constitutes the inner tube of the reaction tube, and the whole has a double tube structure in many cases.

Production of hydrogen by dehydrogenation using such a reaction tube is performed as follows.
That is, using the gap between the double tubes as a dehydrogenation reaction field, the substrate is circulated from one of the flow-type reaction tubes, and the substrate is dehydrogenated by the catalyst present in the gap to generate hydrogen and a reaction product, At the same time, the generated hydrogen is membrane-separated by a hydrogen separation membrane that constitutes the inner pipe, selectively allowing hydrogen to permeate into the inner pipe of the double pipe, and discharging the hydrogen out of the system. Thereby, high-purity hydrogen is obtained.
As a result, the double pipe gap in which the hydrogen is separated quickly and the dehydrogenation reaction, which is an endothermic reaction, can be easily supplied with heat by appropriate heating means from the outside of the pipe. The reaction is likely to proceed. As the appropriate heating from the outside of the tube, a known method such as heating with a heating medium can be appropriately employed.

  The hydrogen separation membrane is preferably a metal membrane or a porous inorganic membrane that can selectively separate hydrogen from a mixed gas of hydrocarbon and hydrogen. In the case of a metal membrane, it is a hydrogen separation membrane in which a metal thin film is formed on the inner surface or outer surface of a tubular porous metal support having pores or a porous ceramic support having pores. A metal film containing 100 to 10 mass% of Pd or a metal film containing 80 to 10 mass% of at least one metal selected from Ag, Cu, V, Nb, and Ta is preferable.

  Although any method can be selected as the method for forming the metal thin film, specific examples include electroless plating, vapor deposition, and rolling. In the case of a porous inorganic membrane, it is a hydrogen separation membrane in which a ceramic thin film having a controlled pore size is formed on the inner surface or outer surface of a porous porous ceramic support having pores. Since the porous inorganic membrane is selectively separated by molecular sieve action, the pore diameter of the thin film portion is preferably 0.3 nm or more and 0.7 nm or less, and more preferably 0.3 nm or more and 0.5 nm or less. A known ceramic material can be used as the material of the ceramic film, but silica, alumina, titania, glass, silicon carbide, and silicon nitride are preferable.

  The main component of catalytic activity in the dehydrogenation catalyst of the present invention is a component having dehydrogenation activity, and can be arbitrarily selected, but is preferably a group VII, VIII, or IB element in the periodic table, and specifically Are iron, cobalt, nickel, copper, ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum and gold. More preferred are nickel, palladium, platinum and rhenium. Two or more of these elements may be combined. A preparation method for incorporating these catalytically active main components into the molded catalyst is arbitrary, but an impregnation method is preferred. Specific examples include the Incipient Wetness method and the evaporation to dryness method. The elemental compound used is preferably a water-soluble salt, and is preferably impregnated as an aqueous solution. Preferred examples of the water-soluble compound include chlorides, nitrates and carbonates.

  Additives may coexist in the catalyst if necessary. Preferable additives include basic substances. The coexistence of the basic substance suppresses side reactions such as decomposition caused by acidity, and suppresses deterioration of the catalyst due to carbonaceous deposition. The type of basic substance is arbitrary, but compounds of Group IA and IIA elements are preferred, and specifically, compounds of lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, and barium are preferred. . These compounds are preferably water-soluble substances. More preferred are chlorides, sulfates, nitrates and carbonates. The content of the basic substance is preferably in the range of 0.1 to 100 by weight ratio with respect to the catalytically active main component. The preparation method for incorporating these basic substances into the catalyst body is optional, but an impregnation method is preferred. Specific examples include the Incipient Wetness method and the evaporation to dryness method.

A catalyst is used for dehydrogenation. The catalyst of the present invention is preferably reacted using a solid catalyst having dehydrogenation activity. As this solid catalyst, a catalyst having a catalytically active main component supported on a carrier can be suitably used.
A catalyst supported on a conventionally known granular or pellet-shaped carrier can also be used. These conventional granular and pellet-like catalysts can be used, for example, in such a manner that they are simply filled in a double pipe gap.
A stable metal oxide is preferably used for the support because it has high mechanical strength, is thermally stable, and has a large surface area. More preferably, a metal oxide is formed on the surface of a support having good thermal conductivity (thermal conductive support).

  Specific examples of the metal oxide as the carrier include alumina, silica, titania, zirconia, and silica alumina. More preferred is alumina, silica or a mixture thereof.

  In the present invention, the thermally conductive support is defined as a catalyst body based on a substance having a thermal conductivity at 300 K of 10 W / m · K or more. The base of the thermally conductive catalyst body is preferably a metal, and includes a substrate having a film such as an oxide on the surface. Specifically, any metal and alloy that are usually used can be used as the metal of the substrate, but aluminum or a metal or alloy having aluminum on the surface is particularly preferable.

By using a metal as a base, the thermal conductivity of the catalyst body is increased, so that the heat supply is accelerated and the reaction efficiency is improved. That is, since the dehydrogenation reaction is an endothermic reaction, as described above, the double tube itself is a metal tube as a metal base, and heat is supplied from the outside of the double tube by an appropriate heating means. By applying heat to the dehydrogenation reaction in the tube gap, it is easy to apply heat to the dehydrogenation reaction.
Further, by directly energizing using the conductivity of the catalyst body as a metal, for example, the reaction tube can be heated quickly to significantly shorten the start-up time of the reaction apparatus.

The surface of the metal substrate is preferably treated so as to have a high surface area so as to have a function as a carrier having a catalytically active main component. As this treatment method, a known method can be adopted. For example, as described in JP-A No. 2002-119856, a method of increasing the surface area based on the anodization treatment is preferable. Further, it is preferable that a stable and high surface area metal oxide layer such as alumina is formed on the surface of the base, for example, the surface of the base having a high surface area. For this purpose, for example, an alumina hydrate sol can be applied to the surface of the substrate having a high surface, dried and then fired to form a metal oxide layer.
The shape of the catalyst carrier including the metal substrate is arbitrary, and can be a plate-like, tubular, net-like, honeycomb-like, or fin-like protrusion directly installed inside the reaction tube.

  Since the catalyst is present in the gap between the double pipes and the reaction in the gap is a dehydrogenation reaction and an endothermic reaction, in order to efficiently supply the dehydrogenation reaction heat, a heat supply source It is preferred that the catalyst carrier is in direct contact. For this reason, it is preferable that the shape of the catalyst carrier is a plate-like shape, a tubular shape, or an internal fin that is in direct contact with the double-pipe outer tube, and a heat exchanger having a large area in contact with the substrate. Any shape can be adopted as long as it can directly contact the heating source and increase the area in contact with the substrate. For example, as an internal fin type, a structure in which an outer tube having a double-pipe structure is a part of a metal substrate and is provided with a plurality of fin-like projections that are long in the flow direction of the substrate and extend from the outer tube toward the inner tube. And a catalyst can be supported on the fin surface by forming a metal oxide layer. In addition, the metal substrate can be made of a metal such as aluminum and the surface can be increased by the method described above. The catalyst can be appropriately supported on a portion other than the fins such as the inner surface of the outer tube by the above-described method. Since the inner tube can be supported separately, the plurality of fins extending from the outer tube toward the inner tube may or may not contact the hydrogen separation membrane constituting the inner tube.

For example, an internal fin reactor shown in FIG. 1 can be exemplified. FIG. 1 shows an outer tube of a double tube. Although not shown, an inner tube made of a hydrogen separation membrane is inserted into the inner tube and used for a dehydrogenation reaction. The plurality of fins may or may not contact the hydrogen separation membrane of the inner tube. The number of fins, their height, thickness, and the like can be selected as appropriate as long as they are not limited by strength or the like. Further, in FIG. 1, the fin shape is also a plate shape extending directly perpendicularly from the outer tube surface, but an opening can be provided or an appropriate shape can be used to increase the surface area.
Such an internal fin type is preferable because it can be in direct contact with a heating source disposed outside the tube and has a large contact area with the substrate flowing through the gap, which facilitates heating.

  The catalyst does not necessarily have to be placed in contact with the hydrogen separation membrane. In short, the hydrogen generated by the action of the catalyst is immediately and simultaneously subjected to the hydrogen membrane separation operation in situ, and the hydrogen is selected outside the dehydrogenation reaction system. It is important to discharge the wastewater.

  The raw material for dehydrogenation in the present invention is preferably a hydrocarbon, and more preferably a hydrocarbon having a cyclohexane ring. Specific examples include cyclohexane and cyclohexane alkyl-substituted products, decalin and decalin alkyl-substituted products, and tetralin and tetralin alkyl-substituted products. Most preferred are methylcyclohexane, dimethylcyclohexanes, decalin and methyldecalins. The hydrocarbon having a cyclohexane ring may be a mixture of a plurality of hydrocarbons. Furthermore, as long as the reaction is not hindered, other compounds such as hydrocarbons having no cyclohexane ring may be appropriately contained.

  When a hydrocarbon having a cyclohexane ring is used as a raw material, the product of dehydrogenation is hydrogen and an unsaturated hydrocarbon, and the unsaturated hydrocarbon is mainly an aromatic hydrocarbon. These can be recovered and hydrogenated to return to the starting hydrocarbon. Alternatively, it can also be used as a heat source fuel necessary for the dehydrogenation reaction, if necessary. In addition, since aromatic hydrocarbons generally have a high octane number, substances having a suitable boiling point can also be used as a gasoline base material. Alternatively, it can be used as a chemical product.

  The reaction conditions are appropriately selected according to the type of raw material and the type of reaction. The reaction pressure is preferably 0.1 MPa or more and 2.0 MPa or less, more preferably 0.1 MPa or more and 1.0 MPa or less. In the present specification, unless otherwise specified, the pressure is expressed as an absolute pressure. The reaction temperature is preferably a high temperature in terms of chemical equilibrium, but a low temperature is preferable in terms of energy efficiency. A preferable reaction temperature is 200 ° C. or more and 400 ° C. or less, more preferably 270 ° C. or more and 360 ° C. or less, and most preferably 220 ° C. or more and 360 ° C. or less. Although it is disadvantageous in terms of chemical equilibrium, hydrogen may be added to the raw material for the purpose of preventing the deactivation of the catalyst or for operating the apparatus. When hydrogen is added to the raw material, the molar ratio of hydrogen to the raw material is preferably 0.01 or more and 1 or less.

A preferable range of LHSV (liquid hourly space velocity) depends on the activity of the catalyst, but is usually 0.2 v / v / hr or more and 20 v / v / hr or less.
The hydrogen produced by the dehydrogenation reaction is in a state of being mixed with reaction products such as aromatic hydrocarbons, but in the present invention, it is immediately subjected to a membrane separation operation using a hydrogen separation membrane in situ. When the inner pipe of the double pipe is constituted by a hydrogen separation membrane, the innermost part of the double pipe is operated as the hydrogen permeation side, and the double pipe gap is operated as the non-permeation side.

  Here, the pressure on the permeation side of the hydrogen separation membrane in the membrane separation reactor is preferably 0.2 MPa or less, and more preferably 0.12 MPa or less. Further, it is preferable to supply an inert gas to the permeation side of the hydrogen separation membrane for the purpose of reducing the permeation side hydrogen partial pressure. The permeate hydrogen partial pressure is preferably 0.1 MPa or less, and more preferably 0.05 MPa or less. The inert gas is preferably steam that can be easily separated by condensation. Moreover, when the purpose is a polymer electrolyte fuel cell application, steam is more preferable for this purpose because it can be introduced without being removed if it is steam. By adding steam to the permeate side, high-purity hydrogen can be produced even if the hydrogen partial pressure on the permeate side is 0.05 MPa or less.

  If the above-described reaction conditions of the present invention using a membrane reactor are employed, a reaction tube having a simple catalyst-packed structure shown in FIG. That is, when a reaction tube in which a conventionally known granular or pellet carrier is packed in a simple double tube gap is used, a hydrogen recovery rate of 80% or more is achieved in the membrane separation process. Is possible.

  A conceptual diagram of the hydrogen production system of the present invention according to the above is shown in FIG. In the figure, a raw material oil for a reaction substrate, preferably a hydrocarbon containing a cyclohexane ring, is introduced into a membrane reactor and converted to hydrogen and an unsaturated hydrocarbon such as an aromatic hydrocarbon on a dehydrogenation catalyst. The produced hydrogen is membrane-separated by a hydrogen separation membrane, most of which is separated out of the system as a permeate gas and becomes product hydrogen as high-purity hydrogen. Part of the remaining hydrogen and unsaturated hydrocarbons such as aromatic hydrocarbons are recovered as non-permeate gas. In addition, it is preferable in terms of membrane separation operation to introduce steam on the permeation side of the hydrogen separation membrane as necessary and lower the hydrogen partial pressure on the permeation side.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited to the scope of these experimental examples.

[Separation membrane]
One α-alumina layer is formed on the surface of a porous ceramic tube-shaped support body having an outer diameter of 10 mm, an inner diameter of 8.4 mm, and a length of 300 mm, and then three γ-alumina layers are formed. Further, one silica layer was formed, and then a silica thin film was formed on the final surface. The hydrogen permeability coefficient was 4.2 × 10 ⁻⁷ mol / m ² / sec / Pa, and the toluene permeability coefficient was 2.8 × 10 ^−. A ceramic membrane of ¹⁰ mol / m ² / sec / Pa is referred to as a separation membrane A.
Hydrogen permeation coefficient of 200, with the outer surface of a porous ceramic tubular support having an outer diameter of 10 mm, an inner diameter of 8.4 mm, and a length of 300 mm coated with palladium and silver (Pd: Ag = 85: 15) by electroless plating A palladium membrane having a thickness of cc / cm ² / min / atm ^1/2 and a thickness of 2.5 μm is referred to as a separation membrane B.

[catalyst]
A spherical commercial catalyst having an average diameter of 1.5 mm, in which 0.3 mass% of platinum is supported on a γ-alumina carrier, is referred to as Catalyst A.
The fin portion of the aluminum internal fin-type reaction tube shown in FIG. 1 having an inner diameter of 24 mm, a length of 300 mm, and a fin length of 6 mm is washed with dilute nitric acid, washed with water, dried, and then anodized in an aqueous chromic acid solution. . The operation of applying and drying a commercially available pseudo boehmite sol on the fin portion was repeated four times, followed by baking at 450 ° C. for 2 hours, and 0.2504 g of platinum was added to the fin portion by an impregnation method using an aqueous solution of chloroplatinic acid. Carry. Thereafter, the catalyst B was calcined at 300 ° C. for 2 hours.

(Experimental example 1)
In the membrane reactor schematically shown in FIG. 3, 110 cc of catalyst A was filled in the gap between the reaction tube having an inner diameter of 24 mm and a length of 300 mm and the hydrogen separation membrane, and methylcyclohexane was introduced as a raw material. The dehydrogenation reaction was performed under the conditions of 5 MPa (absolute pressure), permeate pressure 0.1 MPa (absolute pressure), reaction temperature 300 ° C., LHSV 0.5, 1.0, 2.0 h ⁻¹ . Table 1 shows the results of using separation membrane A and separation membrane B as the hydrogen separation membrane. LHSV is a flow rate and is expressed as (methylcyclohexane liquid volume (cc) / catalyst (cc) / hour (h)). The hydrogen recovery rate is expressed by (hydrogen recovered from the membrane reactor permeate side (mol) / theoretical hydrogen generation amount from introduced methylcyclohexane (mol) × 100).

  Here, in FIG. 3, the reaction tube is a double tube, the outer tube is made of a material having good thermal conductivity, such as metal, and the inner tube is made of a hydrogen separation membrane (hydrogen permeable membrane 1). Although not shown, an appropriate heating means such as heating with a heat medium is provided outside the double tube. The gap between the inner tube and the outer tube is filled with, for example, a catalyst 2 carried on an appropriate granular carrier. The raw material gas 3 is introduced into the gap from one end of the double pipe, and a part of hydrogen and reaction products are discharged from the other end as a non-permeating gas 4. The temperature of dehydrogenation is measured and adjusted by inserting a thermocouple 5 in the gap. Hydrogen selectively separated by membrane flows into the inner pipe as permeate gas 6, and steam can flow from one end of the double pipe to reduce the hydrogen partial pressure in permeate side gas 6. From the other end of the double tube, high-purity hydrogen (excluding the steam component) is taken out as the permeating gas 6.

(Experimental example 2)
Hydrogen was produced in the same manner as in Experimental Example 1 except that catalyst B was installed as a reaction tube instead of catalyst A in the membrane reactor. The results are shown in Table 1.

(Experimental example 3)
In the membrane reactor schematically shown in FIG. 3, 110 cc of catalyst A as catalyst 2 is filled in the gap between a reaction tube having an inner diameter of 24 mm and a length of 300 mm and a hydrogen separation membrane (hydrogen permeable membrane 1). Introduced as source gas 3, reaction pressure 0.2, 0.4, 0.6, 0.8 MPa (absolute pressure), permeate gas 6 side pressure 0.1 MPa (absolute pressure), reaction temperature (catalyst layer outlet) (Temperature) 300, 270, 240 ° C., LHSV 0.5 h ⁻¹ The dehydrogenation reaction was performed. Table 2 shows the results of using the separation membrane B as the hydrogen separation membrane (hydrogen permeable membrane 1).

(Experimental example 4)
Hydrogen was produced in the same manner as in Experimental Example 3 except that catalyst B was installed as a reaction tube instead of catalyst A in the membrane reactor. The results are shown in Table 3.

(Experimental example 5)
Hydrogen was produced in the same manner as in Experimental Example 3, except that steam was introduced on the permeation side of the hydrogen separation membrane and the reaction was carried out at a permeation-side hydrogen partial pressure of 0.05 MPa. The results are shown in Table 4.

(Experimental example 6)
Experimental example, except that the reaction was carried out at a reaction temperature (catalyst layer outlet temperature) of 300, 270, 240, 220 ° C, with steam introduced on the permeate side of the hydrogen separation membrane and a permeate side hydrogen partial pressure of 0.01 MPa. Hydrogen was produced as in 3. The results are shown in Table 5.

As shown in Table 1, in Experimental Example 1 using the catalyst A, the hydrogen recovery rate decreases as the raw material LHSV increases from 0.5 to 2.0 h ⁻¹ , whereas the catalyst B excellent in heat transfer. In Experimental Examples 2 and 4 using NO, the hydrogen recovery rate hardly changed in the range of LHSV 0.5 to 2.0 h ⁻¹ , so that the catalyst B showed much higher performance than the catalyst A. In addition, both hydrogen permeable membranes A and B exhibit sufficient performance under these reaction conditions.

As shown in Tables 2 and 3, at a permeate pressure of 0.1 MPa, it is possible to achieve a hydrogen recovery rate of 80% or higher in a reaction temperature of 300 ° C. or higher and a reaction pressure of 0.4 MPa or higher. is there. The range in which the hydrogen recovery rate is 80% or more is the same when the catalyst B having higher performance than the catalyst A is used.
Furthermore, as shown in Table 4, under the condition of a hydrogen partial pressure of 0.05 MPa on the permeate side by the introduction of steam, a hydrogen recovery rate of 80% in the region where the reaction temperature is 270 ° C. or higher and the reaction pressure is 0.4 MPa or higher. The above can be realized. Further, as shown in Table 5, under the condition of a hydrogen partial pressure of 0.01 MPa on the permeate side by the introduction of steam, a hydrogen recovery rate of 80% in a region where the reaction temperature is 220 ° C. or higher and the reaction pressure is 0.2 MPa or higher. The above can be realized.

FIG. 1 is a perspective view of an internal fin type membrane reactor, and a cross-sectional view is shown on the left side. In both cases, the inner pipe is not shown. FIG. 2 shows a conceptual diagram of the hydrogen production system of the present invention. FIG. 3 is a schematic view of a membrane reactor used in Experimental Example 1 having a structure in which catalyst particles are packed in a gap of a double tube structure in which an inner tube is formed by hydrogen membrane separation.

Explanation of symbols

1: Hydrogen permeable membrane 2: Catalyst 3: Material gas 4: Non-permeate gas 5: Thermocouple 6: Permeate gas

Claims (7)

A hydrocarbon having a cyclohexane ring is subjected to a dehydrogenation reaction in a flow-through reaction tube in which a catalyst supported by a support made of a metal heat conductive support having a metal oxide layer unevenly distributed on the surface, and hydrogen and In the dehydrogenation reaction system for producing aromatic hydrocarbons,
Incorporating hydrogen removal means by hydrogen separation membrane,
A process for producing hydrogen, characterized in that hydrogen is mainly removed on the permeate side by the hydrogen separation membrane while the dehydrogenation reaction proceeds, and mainly aromatic hydrocarbons are obtained on the non-permeate side.   2. The method for producing hydrogen according to claim 1, wherein the hydrocarbon having a cyclohexane ring contains methylcyclohexane, and toluene generated by the dehydrogenation is separated.   The method for producing hydrogen according to claim 1, wherein the hydrogen separation membrane is a ceramic membrane.   The method for producing hydrogen according to claim 1, wherein the hydrogen separation membrane is a metal membrane containing 100 to 10 mass% of Pd.   The method for producing hydrogen according to claim 1, wherein the carrier in the catalyst is a carrier containing alumina. The reaction tube has a double tube structure, the outer tube is made of a metal heat conductive support, and the inner tube is made of a hydrogen separation membrane.
The gap between the double pipes is provided with a plurality of fin-like protrusions that are long in the flow direction and made of metal and thermally conductive from the outer pipe toward the inside,
6. The method for producing hydrogen according to claim 1, wherein the metal oxide layer is unevenly distributed on at least the surface of the fin-like projections to support the catalyst. A double-pipe flow-type reaction tube, the outer tube is a metal thermal conductive support, the inner tube is made of a hydrogen separation membrane,
The gap between the double pipes is provided with a plurality of fin-like protrusions that are long in the flow direction and are made of metal and thermally conductive from the outer pipe toward the inside of the pipe.
At least the fin-like protrusion surface has a structure in which a metal oxide layer is unevenly distributed to support the catalyst.
A reaction tube for hydrogen production for simultaneously dehydrogenating hydrocarbons and membrane separation of the obtained hydrogen.

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