JPS5983903A - Production of hydrogen - Google Patents

Abstract

PURPOSE:To produce efficiently H2 by the combination of a multistage cycle, by reacting SO2 with I2 and water to form HI and H2SO4, photodecomposing HI to form I2 and H2, and decomposing H2SO4 thermally to form water and SO4. CONSTITUTION:SO2 is reacted with I2 and water thermochemically to form H2SO4 and HI in the first step, and the resultant H2SO4 is then thermochemically decomposed to form water, SO2 and oxygen in the second step. The HI formed in the first step is decomposed with the light energy of visible light or ultraviolet light region in the presence of a photoreaction catalyst to form H2 and I2 in the third step. A multistage cycle is formed from the above-mentioned three stages, and hydrogen is produced in a high production efficiency with a little consumption of thermal energy.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for producing hydrogen, and more specifically, a method for producing hydrogen by using water as a raw material and forming a multi-stage reaction cycle using heat and light energy. Regarding.

[Technical background of the invention and its problems]

In recent years, there has been a strong demand for new energy development technologies due to the threat of depletion of fossil fuel resources (so-called coal, oil, etc.).

Among several energy sources, hydrogen has attracted attention in recent years. This is because hydrogen: ■ If water is used as a raw material, there will be resource constraints and it will not be unevenly distributed depending on the region, ■ The combustion product is water, so it is clean and does not cause pollution, and ■ It can improve the earth's material circulation cycle. It has various advantages such as not being disturbed and being relatively easy to store.If hydrogen could be produced in a simple manner, it could be a powerful means to solve current energy problems. It's for a reason.

Conventionally, the methods that have been put to practical use industrially to produce hydrogen are mainly those that use carbon compounds such as natural gas and petroleum as raw materials, and electrolysis methods that use water as raw materials.

However, the former method is unsuitable for the purpose of being a new energy source because, in the long term, the resource carbon compounds will be depleted.

Furthermore, the latter 'F [gas decomposition method] is currently expensive because the energy source required for decomposition is mostly electricity obtained by burning petroleum.

Therefore, instead of the above-mentioned method, a so-called thermochemical method has recently been considered, which uses water as a raw material and decomposes this water using a multi-step reaction cycle that combines various thermochemical reactions. . This method considers the use of nuclear heat from a nuclear reactor (high-temperature gas reactor) as a secondary energy source.
In addition, the number of cycles of thermochemical reactions that can be combined is 10 to date.
There are 0 methods proposed.

For example, the Nietram Isgra Institute (Italy) has proposed more than a dozen hydrogen production methods, the so-called mark method, by multi-stage thermal decomposition of water using inorganic halodane compounds and halogen elements as main media (Procee
ding of the 4th World Hy
drogen EnergyC! onference,
(See Tokyo, 1981).

Among these mark methods, the Mark 15 method is being developed and researched, and its chemical reaction cycle is a method of decomposing water by utilizing and combining the four steps of thermochemical reactions shown below.

1st stage: 3 Fec/2 + 4H20-+Feg0
4+ 6HO/ 10H2 (650℃) 2nd stage: Fe1
04 + 8HC1-+ Fe04 +2FeO, /3
+4H20 (160'C) 3rd stage: 2 pec1g+
2Fec4+clff (280℃) 4th stage: CIJ
2 +H! O→2HC1+jz02 (600°C) Total reaction: H, O−+ )(, +−!−o.

Furthermore, General Atomic Company (USA) has proposed a reaction cycle that combines three-step thermochemical reactions using sulfur dioxide (SO++) and iodine (Step 2) as shown below.

1st stage: F3o! + I2 + zH, o-+Hf
1so4 + 2HI (97℃) 2nd stage: H! 90
4-+H, O+SO3+yO, (870°C) 3rd stage+
2HI → Engineering 2+H1 (3oo℃) Total reaction: H, o-+
H=+”o= However, since all of these methods perform all reactions only by thermochemical reactions, the thermal energy consumed is large, and it is difficult to control the reaction balance at each stage and match all reactions. Problems such as the formation of side reactants (for example, sulfides) also occur, and furthermore, the reaction apparatus inevitably becomes very complicated.

[Purpose of the invention]

An object of the present invention is to provide a method for producing hydrogen that can perform a hydrogen production reaction at room temperature using a separate device, consumes little thermal energy, and has high hydrogen production efficiency.

[Summary of the invention]

The present inventor obtained the knowledge that the reaction shown in the third stage of the above-mentioned General Atomic Company (USA) reaction cycle proceeds photochemically at room temperature in the presence of a certain type of photocatalyst. Based on this knowledge, we have completed the method of the present invention, which is a novel photothermal hybrid method. That is, the method of the present invention involves the first step of thermochemically reacting sulfur dioxide, iodine, and water to produce hydrogen iodide and sulfuric acid.
a second step in which the sulfuric acid is thermochemically decomposed to produce water, sulfur dioxide, and oxygen; It is characterized by a combination of a third stage step of decomposing to generate hydrogen and iodine.

Each step will be explained below.

1st stage process: SO2 + work 2 +2H20-+ H2SO
4+ 2HI This process uses S02 and I20 obtained in the second stage process described later, and Process 2 obtained in the third stage process as raw materials, and causes them to undergo a thermochemical reaction at a relatively low temperature of 50 to 100 °C. , H2SO4, H-technique.

Since the reaction product is a mixture of H2SO4 and )TI, this can be converted to yj and I'j:'C respectively by distillation, for example, and )12804 is sent to the second stage process, and H process is sent to the third stage process. Transport.

This step decomposes (2FI04) obtained in the first step to produce I20, S02, and O2. This decomposition reaction is carried out at a relatively high temperature of 800 to 900°C. Generated I20, SO
2 is returned to the first step process again for recycling. The main feature of the method of the present invention is this third stage step. In this step, the H2 obtained in the first step is decomposed by a photochemical reaction to produce the target H2 and 1 of the raw material for the first step.
It generates 12 vines.

The photochemical reaction of this third stage step proceeds by injecting a predetermined amount of light energy into the reaction system in the presence of a photocatalyst.

The light energy input is visible light, ultraviolet light, or both. Practically speaking, from a cost standpoint, solar is the way to go! ! Yes, you can use it. In addition to sunlight, for example, light from a xenon short arc lung or a mercury discharge tube can also be used.

The photocatalyst to be used may be anything as long as it exhibits its full catalytic function and causes a photochemical reaction when irradiated with light energy in the visible light and/or ultraviolet region, such as semiconductors.

Such semiconductors include metal oxides, metal sulfides,
Consisting of one or more metal phosphides, metal arsenides, metal selenides, or metal tellurides, specifically, Ti01, 5rTiO1, ZnO, Fe20
g.

Cd13, CdSe, 0dTe
, OaP, 0aAs, ■nP
, ZnS.

Examples include Zn5e. In addition, in order to enhance the activity as a photocatalyst, Ni,
It is useful to support metals such as Pb, Rh, and Pt.

Photocatalysts are used in powder or plate form.

By placing such a photocatalyst in a reaction tank, introducing a reactant containing a gas or an HI aqueous solution, and irradiating the photocatalyst with a predetermined amount of light energy, a third stage reaction can be achieved in an apparent one-stage reaction. A photodecomposition reaction occurs and 12 is produced. Since this reaction easily proceeds at room temperature, there is no need to input (heat) energy into the reaction tank.

[Embodiments of the invention]

1st stage process: 30 m2 of Step 2 in a 500 m6 cylindrical flask.
Add an aqueous solution containing 19C, and blow SO2 from the bottom at a rate of 20 me/min to make a total of 10
Heat to 0°C. 1 and so4 were produced with a stoichiometric conversion efficiency of 30%.

2-stage process; A quartz vessel with a length of 5 crn and an inner diameter of 1.8 crn was placed in an electric furnace at 900°C.
5'4, A40s carrier)'c, H2SO4 obtained in the first stage process using He gas as a carrier was 0.5 m
The flow rate was 1/sec. A decomposition reaction occurred with a reaction efficiency of 80%, producing pH H2O, Se2, and O.

Third step: HI obtained in the first step was dissolved in water to prepare a 5% by weight HI solution. This was placed in a 109 ml flask, and 300 kg of a photocatalyst made of TiO2 powder (average particle size 0.2 μm) supporting 2% by weight of Pt was suspended therein, and a 500 W xenon shot arc lamp was placed at room temperature (25°C) while stirring. irradiated with light. quantum efficiency 15
% reaction efficiency produced H2 and H2.

〔Effect of the invention〕

As is clear from the above description, in the method of the present invention, (1) the reaction in the third step proceeds at room temperature by inputting light energy, so that the overall thermal energy consumption can be greatly reduced. (2) In addition, it has advantages such as simple equipment and easy reaction control in all processes, so its industrial value is great.

Claims (1)

[Claims] A first step in which sulfur dioxide, iodine, and water are thermochemically reacted to produce hydrogen iodide and sulfuric acid, and the sulfuric acid is thermochemically decomposed to produce water, sulfur dioxide, and oxygen. The second to generate
hydrogen iodide, which is characterized by a combination of a step step and a third step step of decomposing the hydrogen iodide with light energy in the visible light and/or ultraviolet region in the presence of a photocatalyst to generate hydrogen and iodine. manufacturing method.