JPH04160003A - Method and device for producing hydrogen - Google Patents

Abstract

PURPOSE:To simultaneously promote a reaction and control the temp. and to excellently follow a change in load in the production of hydrogen by steam- reforming hydrocarbons by using a non-equilibrium reactor by the separation of hydrogen and combining the partial oxidation of a raw gas to be reformed. CONSTITUTION:The raw gas 24 to be reformed consisting essentially of hydrocarbons is supplied to the reaction tube 12 of a fuel reformer 10 packed with a reforming catalyst 18, the catalyst bed 18 is heated 14 from outside the reaction tube 12, oxygen or air 26 is added to the raw gas 24 at the inlet of the bed 18, and the bed 18 is internally heated by the partial oxidation of the raw hydrocarbons to produce the hydrogen-rich reformed gas G. The following means are added in this steam-reforming method. Namely, at least a part of the reaction tube 12 is formed with a hydrogen passable membrane 16, the generated hydrogen is passed through the membrane 16 and separated from the system, and the amt. of oxygen or air to be added for the partial oxidation is controlled (flow control means 28) to optimize the reaction temp. of the bed 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention supplies a reforming raw material gas containing hydrocarbons as a main component to a fuel reformer N (reformer) to reform it with steam, and at the same time, In a steam reforming method that partially oxidizes feedstock hydrocarbons and heats the reforming catalyst layer from inside to produce hydrogen-rich reformed gas, the generated hydrogen is passed through a hydrogen permeable membrane and separated from the reaction system. By controlling the amount of oxygen or air added for partial oxidation, a method and device that can produce hydrogen at a high reaction rate without being rate-limited by thermodynamic equilibrium relationships, with excellent load change followability. It is related to.

[Conventional technology]

Steam reforming reactions of hydrocarbons such as natural gas involve large endotherms and operate under high temperature conditions. Therefore, since the operation is performed near the heat-resistant temperature limit of the reaction tube material, in addition to the steam reforming reaction between the raw material hydrocarbon and steam, air or oxygen is blown in as a means of heat supply to the catalyst layer, resulting in partial oxidation. A method for generating heat is known (see JP-A-2-160603 and JP-A-1-186570).

In addition, a hydrogen selective permeation membrane is installed in the reaction tube to separate hydrogen from the generated gas, and Le Chatelier
A method is known in which hydrogen can be produced at a high conversion rate even at low reaction temperatures using a non-equilibrium reactor that promotes the reaction according to the reaction equilibrium principle of I 1er) (
JP-A-1-219001, JP-A-64-4230
(See Publication No. 1).

[Problem to be solved by the invention]

When producing hydrogen for fuel cells, high load change followability is required. If there are multiple reaction tubes,
Uneven heating temperature may lower the allowable temperature of the reaction tube and cause troubles such as breakage of the reaction tube.

As described above, in the steam reforming reaction of hydrocarbons (such as natural gas), which involves large endothermic heat absorption at high temperatures, it is desired to reduce the reaction temperature in order to limit the heat resistance of reaction tube materials and to improve efficiency.

The present invention was made in view of the above points, and combines a method using a non-equilibrium reactor using hydrogen separation with a method using a partial oxidation reaction to simultaneously achieve reaction acceleration and temperature control. The object of the present invention is to provide a method and apparatus for producing hydrogen with excellent change followability.

[Means and effects for solving the problem] In order to achieve the above object, the hydrogen production method of the present invention converts a reforming raw material gas containing hydrocarbons as a main component into a fuel reformer filled with a reforming catalyst. At the same time, the reforming catalyst layer is heated from the outside of the reaction tube, and at the same time oxygen or air is added to the reforming raw material gas at the inlet of the reforming catalyst bed to partially oxidize the raw material hydrocarbon. In the steam reforming method in which hydrogen-rich reformed gas is produced by heating from inside the catalyst layer, at least a portion of the reaction tube is formed with a hydrogen permeable membrane, and the generated hydrogen is passed through the hydrogen permeable membrane to form the reaction system. It is characterized by controlling the amount of oxygen or air added for partial oxidation so that the reaction temperature of the reforming catalyst layer is optimized.

As the hydrogen permeable membrane, it is desirable to use a heat-resistant porous ceramic membrane.

In addition, as a reforming catalyst, rhodium is supported on a porous catalyst carrier made of a heat-resistant inorganic material whose main component is an oxide selected from the group consisting of zirconium oxide, magnesium oxide, silicon oxide, and aluminum oxide. It is desirable to use a catalyst that has

This reforming catalyst has excellent activity in a low temperature range and also shows high activity in partial oxidation reactions.

The hydrogen production apparatus of the present invention will be described with reference to FIG. 1, which includes a reaction tube 12 filled with a reforming catalyst and into which hydrocarbons, steam, and oxygen or air are introduced, and this reaction tube 12. In a steam reformer equipped with a heater 14 that heats from the outside, at least a portion of the reaction tube 12 is connected to the hydrogen permeable membrane 1.
6 and connected to the raw material supply pipe 24 or the reaction tube 12, the oxygen supply pipe 26 or the air supply pipe is provided with a flow rate regulating means 28 that is operated depending on the temperature of the reforming catalyst layer.

In the present invention, a partial oxidation exothermic reaction is caused to occur simultaneously, the thermal energy generated by this reaction is used for absorbing heat in the steam reforming reaction, and the membrane reactor quickly supplies heat by the amount that the reaction is promoted. In addition, it is possible to improve followability to changes in reforming load.

【Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, unless there is a specific description, the shapes of the components described in this example, their relative positions, etc. are not intended to limit the scope of the present invention to these, but are merely illustrative examples. Only.

FIG. 1 shows an embodiment of a hydrogen production apparatus implementing the method of the present invention, and 2rgJ shows a detailed cross section of a membrane reactor. Reference numeral 10 denotes a steam reformer, which includes a reaction tube 12 into which hydrocarbons, steam, and oxygen or air are introduced, and a heater 14 which heats the reaction tube 12 from the outside. Inside the reaction tube 12, there is provided a tubular body in which the surface of a porous carrier is coated with a hydrogen-permeable membrane 16 made of heat-resistant porous ceramics, and between the outer wall of this tubular body and the inner wall of the reaction tube 12 there is a A membrane reactor 20 is configured by filling a reforming catalyst to form a reforming catalyst layer 18. 22 is a fuel cell.

The H2-rich gas that has permeated through the hydrogen permeation membrane 16 and the H2-poor gas that has passed through the reforming catalyst layer 18 without permeating through the hydrogen permeation membrane 16 are mixed at the outlet of the membrane reactor 20 and sent to the fuel cell 22 as a reformed gas. is supplied to In addition, without mixing Hz rich gas and Hz poor gas,
In some cases, only the h-rich gas is supplied to the fuel cell 22 as a reformed gas.

The entire tubular body may be coated with a hydrogen permeable membrane,
Alternatively, a portion of the tubular body may be coated with a hydrogen permeable membrane.

An oxygen supply pipe 26 or an air supply pipe is connected to the raw material supply pipe 24 or the reaction tube 12, and to this oxygen supply pipe 26,
Flow rate adjustment means 28 that operates depending on the temperature of the reforming catalyst layer 18
is provided. 30 is a temperature indicating regulator.

Next, the operation of the membrane reactor 20 will be explained in detail.

A heat-resistant membrane material (porous ceramic membrane, Pd alloy membrane, etc.) that selectively permeates It gas is placed inside the reforming catalyst layer 18.
is inserted, and the following hydrocarbon reforming reaction is carried out by heating the catalyst layer from the outside. In addition, in addition to hydrocarbons and steam, oxygen (or air) is mixed into the raw material,
A partial oxidation exothermic reaction is caused, and when the load changes, heat is applied directly from inside the catalyst layer, improving load followability.

CH4+ 2HJ tj Co□+4Hz In the above reaction, the achievable reaction rate is determined by thermodynamic equilibrium conditions (temperature, pressure, H, O/CH4 raw material molar ratio, etc.), which is the conventional "equilibrium type" reaction. "Reactor".

However, H! In the membrane reactor 20 incorporating a membrane material that selectively permeates the
Since 2 is separated and removed from the reaction system, the thermodynamic equilibrium is disrupted, so Le Chatelier-Braun's law
As is known from boat fishing, the reaction proceeds in the direction that returns the state of the system to thermodynamic equilibrium, that is, on the right side of the reaction equation that produces the disappeared H2. Membrane reactor 20, which is such a “non-equilibrium reactor”
Using this method, higher reaction rates can be achieved at lower temperatures than with conventional equilibrium reactors.

In Fig. 1, at the outlet of the membrane reactor 20, the H2-rich gas on the membrane permeation side and the H-poor gas on the non-permeation side are mixed and used as fuel for the fuel cell. This is because, in this case, the gas is inside the membrane reactor and the gas exiting it is outside the reaction system, so mixing has no effect on the reaction equilibrium.

In addition, since a partial oxidation reaction is also used, when air is used as an oxidizing agent, 0□ is a partial oxidation reaction (CO, +O.

→COz+2Ht, CHa+5AOt→CO+2Hz
, CH4+20g-Co! +28!01CO+
+AOt→COt, 8g + y20g→Hg0), but N remains in the reformed gas as an inert gas and reduces the partial pressure of Hz gas, so Ha is used as fuel for fuel cells. The higher the partial pressure, the higher the power generation efficiency. For this reason, it is preferable to separate the remaining N8 and supply it to the fuel cell.

Therefore, since such a partial oxidation reaction is used in combination, the gases separated by the membrane are not mixed together as described above.
It is preferable to use a system that supplies the H2-rich gas that has passed through the membrane to the fuel cell.

In this way, by using the membrane reactor 20, the H7 partial pressure in the reformed gas is improved, and the power generation efficiency of the fuel cell is also increased.

Next, a method for manufacturing a heat-resistant porous ceramic membrane will be explained. Alumina ceramic porous H! A separation membrane was prototyped according to the procedure shown in the flowchart of FIG. A detailed explanation will be given below.

(1) Ceramic porous carrier A porous tube mainly composed of AItOi and having an outer diameter of 10 cm and an inner diameter of 8 cm was used as the ceramic porous carrier. This porous carrier has a distribution range of 0.2-2.0 pm with an average of 1.6
It had a pore size of It m.

(2) Preparation of raw material sol Aluminum isopropoxide (chemical formula 2Al (O
CR(CH3),) is used as a raw material salt, and 0.5
Distilled water was added and dissolved to form a mol-Al/I-liquid, and then the aluminum isopropoxide aqueous solution was filled into a rotary evaporator, stirred and mixed, and then heated in a constant temperature bath at 75°C. , a hydrolysis reaction takes place over 24 hours to produce γ-^100H (boehmite.
A sol solution of alumina) was prepared. This r-A100H
If the sol solution is left as it is, it will change from a sol-like white suspension to a gel-like state (like a starch paste), so in order to maintain the sol state, a 1N hydrochloric acid aqueous solution is added. Mix while heating to 50℃ while dropping, and adjust the pH.
By making it acidic to about 2.5 medium, it was possible to stabilize it in a sol state for a long time.

Next, distilled water is replenished again for the amount of water that evaporated during heating and mixing, and the predetermined A1 molar concentration (0,5+wol-A
The final adjustment was made to l/I-liquid).

(3) Deep coating In order to coat only the outer surface of the porous ceramic carrier with the sol solution, the tip of the porous carrier tube was sealed with a rubber plug or the like.

Having prepared the porous ceramic carrier in this way, it was hung vertically with a thread, lowered into a cylindrical container (graduated cylinder) containing a 7-A100H sol solution, and immersed in the sol solution for about 10 seconds. After that, it was pulled out of the liquid at a constant lifting speed of 10 cm/win.

Through such an operation (dip coating), the outer surface of the porous body was coated with a uniform sol solution.

(4) Drying and Firing The Dish-coated porous tube was dried at room temperature day and night in a clean room free from floating dust. After drying, heat at 50°C in a kiln.
The temperature was raised to 800°C at a speed of 2 hours, held for 2 hours, and then slowly cooled. By this firing, the alumina sol coated on the surface of the porous carrier changes from γ-A 100)1 to α-A
A dense alumina thin film coating layer having micropores of several tens to hundreds of angstroms was formed. In order to uniformly form such Ondustrum-level micropores, it is necessary to repeat the deep coating, drying, and firing operations several times. In this example, it was repeated 4 to 8 times.

When gas permeates through such ondustrom-order micropores, if the pore diameter is smaller than the mean free path of the gas molecules, Knudsen diffusion occurs, and the diffusion rate increases in proportion to the square root of the reciprocal of the gas molecular weight. Due to the principle that gases with small molecular weights such as
Separation of the gas mixture takes place.

The gas separation performance of the alumina porous gas separation membrane prototyped as described above was measured for each gas component of Hl and N2 for each coating number, and as shown in Figure 4, it almost reached the theoretical separation coefficient. A membrane material with similar high performance was obtained. In addition,
q in FIG. 4 is the gas permeation rate (Nsl/CI#membrane area/see/ate).

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects.

(1) By selectively separating hydrogen, which is a hydrocarbon reforming reaction product, out of the reaction system through a hydrogen-permeable membrane, a conversion rate higher than that obtained from thermodynamic equilibrium can be obtained. I can do it. In addition, by causing the partial oxidation exothermic reaction to occur in the catalyst layer, this heat can be used as a heat source for the reaction. Thereby, it is possible to maintain the reaction promoting effect of the reactor (non-equilibrium type reactor) equipped with a hydrogen permeable membrane, and to improve followability to sudden changes in reforming load.

(2) In claim 3, since a catalyst with excellent activity at low temperatures is used for both the reforming reaction and the partial oxidation reaction, the effect of the above (1) can be achieved. You can make more use of it.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet showing an example of a hydrogen production device implementing the method of the present invention, Fig. 2 is a cross-sectional explanatory diagram of the membrane reactor in Fig. 1, and Fig. 3 is a method for producing a ceramic porous separation membrane. FIG. 4 is a graph showing the relationship between the gas separation performance and the number of coatings of a ceramic porous separation membrane prototyped by the method shown in FIG. 3. 10... Steam reformer, 12... Reaction tube, 14...
... Heater, 16 ... Hydrogen permeable membrane, 18 ... Reforming catalyst layer, 20 ... Membrane reactor, 22 ... Fuel cell, 24 ... Raw material supply pipe, 26 ... Oxygen supply Pipe, 28...Flow rate adjustment means, 3T...Temperature indication controller Fig. 7 m cart (Hz Lee, trtix) Fig. 5

Claims (1)

[Claims] 1. Supplying a reforming raw material gas containing hydrocarbons as a main component to a reaction tube of a fuel reformer filled with a reforming catalyst,
The reforming catalyst bed is heated from the outside of the reaction tube, and at the same time, oxygen or air is added to the reforming raw material gas at the inlet of the reforming catalyst bed, and by partial oxidation of the raw material hydrocarbon, it is heated from inside the reforming catalyst bed and hydrogen is generated. In the steam reforming method for producing rich reformed gas, at least a part of the reaction tube is formed with a hydrogen permeable membrane, and the generated hydrogen is separated from the reaction system by passing through the hydrogen permeable membrane, and the reforming catalyst layer is separated from the reaction system. A hydrogen production method characterized by controlling the amount of oxygen or air added for partial oxidation so that the reaction temperature is optimal. 2. The hydrogen production method according to claim 1, wherein a heat-resistant porous ceramic membrane is used as the hydrogen permeable membrane. 3 As a reforming catalyst, rhodium was supported on a porous catalyst carrier made of a heat-resistant inorganic material whose main component is an oxide selected from the group consisting of zirconium oxide, magnesium oxide, silicon oxide, and aluminum oxide. The method for producing hydrogen according to claim 1 or 2, characterized in that a catalyst is used. 4. A reaction tube (12) filled with a reforming catalyst and into which hydrocarbons, steam, and oxygen or air are introduced, and this reaction tube (12)
In a steam reformer equipped with a heater (14) for externally heating the reaction tube (12), at least a part of the reaction tube (12) is formed of a hydrogen permeable membrane (16), and the raw material supply tube (24) or the reaction tube ( A hydrogen production device characterized in that an oxygen supply pipe (26) or an air supply pipe connected to 12) is provided with a flow rate regulating means (28) that is operated depending on the temperature of the reforming catalyst layer.