JPH04198008A - Reduction of carbon dioxide gas - Google Patents

Abstract

PURPOSE:To improve energy efficiency by irradiating a transparent container with sunlight condensed by a sunlight condenser, reacting CO with H2 on a molybdenum sulfide catalyst packed into the transparent container and converting into CO. CONSTITUTION:A transparent cylindrical container 2 made of Pyrex glass is arranged approximately at a focus of Fresnel lens 1 and packed with a porous molybdenum sulfide catalyst 3 such as MoS2 supported on a porous carrier comprising at least one of active carbon, Al2O3, SiO2, zeolite, activated clay, SiC, bauxite, metal oxide semiconductor and metal sulfide semiconductor. A mixed gas 4 containing CO2 and H2 in a ratio of 1:1 is passed at a given flow velocity through the transparent container 2, the gas is reacted on the catalyst by irradiation with condensed sunlight and a reaction product 5 containing converted CO is taken out.

Description

Detailed Description of the Invention a6 Technical Field of the Invention The present invention relates to a method for reducing carbon dioxide gas for reducing carbon dioxide gas and converting it into carbon monoxide for use as a raw material for chemical products or as a fuel.

b6 Prior Art and Problems In recent years, global environmental pollution has been attracting attention as a problem that threatens the survival of humankind, but the most difficult problem to address is global warming caused by carbon dioxide gas.

Carbon dioxide gas is not toxic in itself, unlike nitrogen oxides and sulfur oxides, which have caused problems in the past.
A huge amount of carbon dioxide, approximately 20 billion tons, is emitted worldwide every year, and as the concentration of carbon dioxide increases in the atmosphere, climate change due to the greenhouse effect will occur, and it is feared that as many as Nobuko will become environmental refugees. . To prevent this, policies are trying to promote the reduction of carbon dioxide emissions through energy substitution and energy conservation, but since carbon dioxide emissions are closely related to economic and social development, This is an extremely difficult situation to suppress. Therefore, in order to prevent global warming caused by carbon dioxide gas, it is essential to develop technologies for reducing and fixing carbon dioxide gas. The method of reducing and fixing carbon dioxide by catalytic hydrogenation reaction, in which carbon dioxide is reacted with hydrogen and reduced, is more effective than photochemical reaction method, electrochemical reaction method, polymer synthesis method, organic synthesis method, etc.
It has a large capacity to reduce and fix carbon dioxide per unit time and unit area, and can process large amounts of carbon dioxide. Also,
Existing Fischer-Tropsch hydrocarbon synthesis technology can be applied to this process, and since it is a gas phase reaction, it has the advantage of easy product separation. Until now, methods using noble metal catalysts such as ruthenium and rhodium have been studied as a method for reducing and fixing carbon dioxide gas by catalytic hydrogenation reaction (for example, F, Solymosi and A.

Erdohelyi, J., Mo1. Catal,
, 8.471 (1980)).

However, this method has two drawbacks: (1) the catalyst used is expensive and is easily poisoned by sulfur compounds such as hydrogen sulfide and sulfur dioxide gas, resulting in a rapid decrease in catalytic activity; (2) in this reaction, carbon dioxide gas is reduced to methane; However, this reaction is an exergonic reaction in which the free energy of the product is lower than that of the raw material, so the energy yield is poor.3) The reaction temperature is generally high at 350°C to 500°C, and it is Since it uses fossil fuels, it has the disadvantage that it does not even substantially reduce carbon dioxide emissions.

C0 Purpose of the Invention In view of the above, the present invention addresses global warming caused by carbon dioxide gas, and uses non-polluting solar energy that does not use fossil fuels or emit carbon dioxide. The purpose of the present invention is to provide a method for reducing carbon dioxide gas to carbon monoxide, which is durable, economical, and has a high energy yield.

d0 Structure of the Invention According to the present invention, a transparent container filled with a molybdenum sulfide catalyst is installed near the focal point of a solar collector, and carbon dioxide and hydrogen are generated while irradiating the concentrated sunlight. This is achieved by circulating a gas containing it. Carbon dioxide reacts with hydrogen on a molybdenum sulfide catalyst and is converted to carbon monoxide, but carbon monoxide can be used as fuel as is, and it can also be used in the existing methanol production process from synthesis gas (carbon monoxide and hydrogen). Using C1 chemical technology, it can also be used by converting it into methanol, which has recently been in the spotlight as an automobile fuel, and into raw materials for chemical products. Since the reaction that converts carbon dioxide gas into carbon monoxide is an endergonic reaction, the energy yield is high, and the carbon monoxide product stores solar energy. Examples of the molybdenum sulfide catalyst used in the present invention include those containing lower and higher sulfides in addition to molybdenum disulfide and molybdenum trisulfide, and those containing molybdenum oxide. Preferably, molybdenum disulfide or molybdenum disulfide having a large surface area is supported on a carrier such as alumina, silica, activated carbon, zeolite, activated clay, bauxite, silicon, silicon carbide, metal oxide semiconductor, metal sulfide semiconductor, or the like. These carriers are preferably porous or have a large surface area, such as fine particles. Molybdenum disulfide is widely distributed in the earth's crust as hydrite, and is commercially available as a lubricant. It is an inexpensive and low-toxic substance, is black in color, has a high absorption rate of sunlight, and is highly effective against hydrogen sulfide and sulfur dioxide gas. It has the feature that it is not poisoned by sulfur compounds and, on the contrary, improves catalytic performance.

Porous molybdenum disulfide is obtained by saturating an aqueous solution of ammonium molybdate with hydrogen sulfide or ammonium sulfide, decomposing ammonium tetrathiomolybdate with dilute sulfuric acid or nitric acid, or heating it in a nitrogen or hydrogen stream. obtained by doing. It can also be obtained by thermally decomposing molybdenum trisulfide or heating molybdenum trisulfide in a hydrogen sulfide stream. The supported molybdenum sulfide catalyst is prepared by adding a carrier to an aqueous solution of ammonium tetrathiomolybdate or aqueous ammonia with stirring, drying, and then thermally decomposing it in a hydrogen stream. Semiconductors such as silicon, silicon carbide, metal sulfide semiconductors such as zinc sulfide and cadmium sulfide, and metal oxide semiconductors such as zinc oxide, tungsten oxide, cadmium oxide, titanium dioxide, iron sesquioxide, and barium titanate are used as carriers. When used, the semiconductor carrier undergoes a photocatalytic reaction upon irradiation with light, promoting the reduction of carbon dioxide gas. The solar collectors used in the present invention are a field-shaped flat mirror collector, a trough-type composite parabolic mirror collector, a trough-type parabolic mirror collector, and a trough-type parabolic collector. Concentrating solar heat collectors such as a concentrator that simulates a surface beam using a plane mirror, a rotating parabolic mirror concentrator, a linear Fresnel lens concentrator, and a circular Fresnel lens concentrator. The transparent container used in the present invention is made of a material that is permeable to gas,
No soot reacts with gas, transparent and 200. Any material such as glass or plastic may be used as long as it has heat resistance of about 300°C, but materials that can transmit even short wavelength light such as quartz, Vycor glass, and Pyrex glass are particularly preferred. In addition, the shape of the transparent container is disk-shaped when using a point-concentrating solar collector such as a rotating parabolic mirror collector or a circular Fresnel lens collector. Containers such as spherical, prismatic, etc. are used, and when using linear concentrators such as linear Fresnel lens concentrators and field-shaped concentrators, containers such as straight tubes are used. It will be done. In this case, the sides and bottom of the disc-shaped container may be mirrored or insulated, the straight tubular container may be made into a double pipe, the outer pipe may be coated with a selective absorption membrane, or the inner and outer pipes may be coated with a selective absorption membrane. By using a vacuum chamber, heat radiation can be suppressed and the reaction can be accelerated. The gas flowing through the transparent container in the present invention is a gas containing carbon dioxide and hydrogen, and may also contain inert gases such as argon and helium, hydrocarbons such as methane, carbon monoxide, alcohol, hydrogen sulfide, etc. . The ratio of carbon dioxide gas to hydrogen is preferably 1:1 or an excess of hydrogen.

These gases may be passed through the transparent container continuously or intermittently. At this time, it is desirable to plug the inlet and outlet of the container with glass wool or the like to prevent the catalyst from flowing out of the container.

When a transparent container is filled with a molybdenum sulfide catalyst and gas containing carbon dioxide and hydrogen is passed through it, carbon dioxide is reduced by irradiation with concentrated sunlight.This reaction is an endergonic reaction, and the reaction temperature Since the higher the reaction rate is, 1
The reaction gas and transparent container may be heated using factory waste heat.

In addition, to increase the reaction rate at low temperatures, alkali metal salts,
In particular, a molybdenum sulfide catalyst to which sodium carbonate or lithium carbonate is added may be used.

e4 Embodiments of the invention Hereinafter, typical embodiments of the invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, which uses a circular Fresnel lens condenser. A disc-shaped transparent container 2 made of Pyrex glass with a diameter of 5 cm is installed near the focal point of a Fresnel lens 1 with a diameter of 1.5 m, and a molybdenum sulfide catalyst 3 supported on 3 g of titanium dioxide is filled in the container, and carbon dioxide gas and hydrogen While flowing a mixed gas 4 of 1-=1 at a flow rate of 6 ml/min, concentrated sunlight was irradiated, and the resulting reaction product 5 was analyzed using a gas chromatograph. As a result, approximately 10% of carbon dioxide gas was converted to carbon monoxide.

FIG. 2 shows another embodiment of the present invention, which uses a trough-type composite parabolic mirror light collector that can collect light and heat without using a tracking mechanism. Length 5 with mirror 6 inside
A straight tubular transparent container 8 made of quartz with a diameter of 1 cm is installed near the focal point of the 0 cm condensing collector 7, and 15 g of water is placed inside it.
of catalyst 9 (sodium carbonate added to molybdenum disulfide supported on titanium dioxide) and 6 ml of mixed gas 10 of 11:1 of carbon dioxide, hydrogen, and argon.
While flowing at a flow rate of /min, concentrated sunlight was irradiated, and the obtained reaction product 11 was analyzed using a gas chromatograph. As a result, about 12% of carbon dioxide gas was converted to carbon monoxide.Effects of the 6f1 Invention As explained above, the present invention uses sunlight collected by a solar collector to create a It converts carbon dioxide gas into carbon monoxide by reacting it with hydrogen on molybdenum sulfide filled in the tank.It is black in color, has a good sunlight absorption rate, and is inexpensive and low-toxic because it can react at low temperatures and at normal pressure. By using a molybdenum sulfide catalyst that is not poisoned by sulfur compounds, it has become possible to directly reduce carbon dioxide gas using solar energy, which was previously difficult due to the high reaction temperature. Since this reaction is an endergonic reaction, the yield of energy is high, and the product carbon monoxide can be used as fuel as it is, or it can be converted into methanol, which is in the spotlight as an automobile fuel, and raw materials for chemical products. Because it can be used for various purposes, it is very effective from the perspective of global environmental conservation and energy conservation.

[Brief explanation of the drawing]

Figures m1 and m2 are schematic diagrams showing examples of the carbon dioxide reduction method of the present invention. In the figure, 1 is a Fresnel lens, 2 is a transparent container, 3 is a catalyst, 4 is a mixed gas of carbon dioxide and hydrogen, 5 is a reaction product, 6
is a mirror, 7 is a condenser, and 8 is a mixed gas of carbon dioxide, hydrogen, and argon. Toyama Sakuta

Claims (4)

[Claims] 1. A transparent container filled with molybdenum sulfide catalyst is installed near the focal point of the solar collector, and while gas containing carbon dioxide and hydrogen is flowing through the container, the concentrated sunlight is applied to the catalyst inside the transparent container. A method for reducing carbon dioxide gas, which is characterized by irradiating the carbon dioxide gas, reacting it with hydrogen on a catalyst, and converting it into carbon monoxide. 2. As solar collectors, we use trough-shaped flat mirror collectors, trough-shaped composite parabolic mirror collectors, trough-shaped parabolic mirror collectors,
Light concentrators that simulate a trough-shaped parabolic mirror with a plane mirror, rotating parabolic mirror concentrators, linear Fresnel lens concentrators, circular Fresnel lens concentrators, etc. The method for reducing carbon dioxide gas according to claim 1, characterized in that a type solar collector is used. 3. Molybdenum sulfide catalysts include alumina, silica, activated carbon, zeolite, activated clay, bauxite, silicon,
The method for reducing carbon dioxide gas according to claim 1, characterized in that molybdenum disulfide supported on at least one type of carrier selected from silicon carbide, a metal oxide semiconductor, and a metal sulfide semiconductor is used. 4. The method for reducing carbon dioxide gas according to claim 1, characterized in that supported molybdenum disulfide to which an alkali metal salt is added is used as the molybdenum sulfide catalyst.