JPH0723207B2 - Carbon dioxide reduction method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a carbon dioxide reduction method for reducing carbon dioxide to convert it into carbon monoxide and using it as a raw material or fuel for chemical products. .

b. Conventional technology and problems In recent years, global environmental pollution has been widely highlighted as a problem that threatens the survival of humankind, but the most difficult problem to address is global warming due to carbon dioxide.
Carbon dioxide is not toxic by itself, unlike nitrogen oxides and sulfur oxides, which have been problematic so far,
The world emits a huge amount of about 20 billion tons per year, and with the increase of carbon dioxide concentration in the atmosphere, climate change due to the greenhouse effect will occur, and it is threatened that tens of millions of environmental refugees will occur. There is. In order to prevent this, the suppression of carbon dioxide emissions through energy substitution and energy saving is being promoted as a policy, but since carbon dioxide emissions are closely related to economic and social development, the Suppression is an extremely difficult situation. Therefore, in order to prevent the global warming caused by carbon dioxide, the development of carbon dioxide reduction / immobilization technology is indispensable. Compared with photochemical reaction method, electrochemical reaction method, polymer synthesis method, organic synthesis method, etc., carbon dioxide gas reduction / immobilization method by catalytic hydrogenation reaction that reacts carbon dioxide gas with hydrogen The ability to reduce and immobilize carbon dioxide per unit area is large, and a large amount of carbon dioxide can be treated. In addition, existing Fischer-Tropsch hydrocarbon synthesis technology can be applied, and since it is a gas phase reaction, it also has the advantage of easy separation of products. As a method for reducing and immobilizing carbon dioxide by catalytic hydrogen reaction, a method using a noble metal catalyst such as ruthenium or rhodium has been studied so far (for example, F. Solymosi and A. Erdohelyi, J. Mol. Catal., 8 , 47
1 (1980)). However, in this method, 1) the catalyst used is expensive, and it is easily poisoned by ionic compounds such as hydrogen sulfide and sulfurous acid gas, and the catalytic activity sharply decreases.
2) In this reaction, carbon dioxide is reduced to methane, but this reaction is an ergon reaction with a lower free energy of the product than the raw material, so the energy yield is poor.
3) Generally, the reaction temperature is as high as 350 ° C. to 500 ° C., and since fossil fuel is used to generate that temperature, it has a drawback that it does not substantially suppress the emission of carbon dioxide gas.

c. Object of the invention In view of the above points, the present invention addresses the global warming caused by carbon dioxide gas, and uses sulfur compounds, which use pollution-free solar energy that does not use fossil fuels and emits no carbon dioxide gas. It is an object of the present invention to provide a method of reducing carbon dioxide gas to carbon monoxide, which is durable without poisoning, is economical, and has a high energy yield.

d. 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 the solar concentrator, and while irradiating the concentrated sunlight, carbon dioxide and hydrogen are emitted. It is achieved by circulating a gas containing Carbon dioxide gas is converted to carbon monoxide by reacting with hydrogen on a molybdenum sulfide catalyst, but carbon monoxide can be used as it is as a fuel, as well as in the process for producing methanol from existing syngas (carbon monoxide and hydrogen). It can also be used by converting it to a raw material for methanol and chemical products, which have recently been spotlighted as fuel for automobiles, using C1 chemical technology. Since the reaction of converting carbon dioxide gas into carbon monoxide is an absorption ergon reaction, the energy yield is good, and the product carbon monoxide has stored solar energy. Examples of molybdenum sulfide catalysts 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, and the like, but are particularly porous. It is preferable to support molybdenum disulfide or molybdenum disulfide having a large surface area on a carrier such as alumina, silica, activated carbon, zeolite, activated clay, bauxite, silicon, silicon carbide, metal oxide semiconductor, metal sulfide semiconductor. It is preferable that these carriers also have a large surface area such as porous and fine particles. Molybdenum disulfide, which is widely distributed in the crust as molybdenite and is commercially available as a lubricant, is an inexpensive and low-toxic substance that is black and has a high absorption rate for sunlight. It has the feature that it is not poisoned by sulfur compounds and, on the contrary, the catalytic performance is improved. Porous molybdenum disulfide is obtained by saturating hydrogen sulfide or ammonium sulfide in an aqueous solution of ammonium molybdate to decompose ammonium tetrathiomolybdate with dilute sulfuric acid or nitric acid, or heating it in a nitrogen stream or hydrogen stream. It is obtained by doing. It can also be obtained by thermally decomposing molybdenum trisulfide, or heating molybdenum trisulfide in a hydrogen sulfide gas stream. The supported molybdenum sulfide catalyst is prepared by a method in which a carrier is added to an aqueous solution of ammonium tetrathiomolybdate or an aqueous ammonia solution with stirring, dried, and then thermally decomposed in a hydrogen stream or the like. As carriers, semiconductors such as metal sulfide semiconductors such as silicon and silicon carbide, zinc sulfide and cadmium sulfide, and metal oxide semiconductors such as zinc oxide and tungsten oxide, cadmium oxide, titanium dioxide, iron sesquioxide, and barium titanate. If used,
The semiconductor, which is a carrier, causes a photocatalytic reaction by irradiation with light, so that the reduction of carbon dioxide is promoted. The solar concentrator used in the present invention is a gutter type flat mirror concentrator, a gutter type composite parabolic concentrator, a gutter type parabolic concentrator, a gutter type parabolic collector. Concentrating solar collectors such as collectors that simulate mirrors with plane mirrors, rotating parabolic mirror collectors, linear Fresnel lens collectors, and circular Fresnel lens collectors. Is mentioned.
The material of the transparent container used in the present invention is permeable to gas, does not react with gas, is transparent and has heat resistance of about 200,300 ° C., glass, plastic, etc.,
Although any material may be used, a material such as quartz, Vycor glass, or Pyrex glass that transmits short wavelength light is particularly preferable. The shape of the transparent container is disc-shaped when using a point concentrator such as a rotating parabolic concentrator or a circular Fresnel lens concentrator as the solar concentrator. , Spherical, prismatic, etc. are used, and when using a linear light collector such as a linear Fresnel lens collector or gutter collector, a straight container is used. To be
At this time, the side or bottom of the disk-shaped container is used as a mirror, or a heat-insulating material is applied, or a straight tubular container is made into a double pipe,
By coating the outer tube with a selective absorption film or using a vacuum between the inner tube and the outer tube, heat dissipation can be suppressed and the reaction can be promoted. In the present invention, the gas passed through the transparent container is a gas containing carbon dioxide and hydrogen,
It may contain an inert gas such as argon or helium, a hydrocarbon such as methane, carbon monoxide, alcohol, hydrogen sulfide, or the like. The ratio of carbon dioxide gas to hydrogen is preferably 1: 1 or hydrogen is in excess. These gases may be continuously circulated in the transparent container or may be intermittently circulated. At that time, it is desirable to plug the inlet and outlet of the container with glass wool or the like so that the catalyst does not flow out of the container. When a transparent container is filled with a molybdenum sulfide catalyst and a carbon dioxide gas and a gas containing hydrogen are circulated while the concentrated sunlight is irradiated to reduce the carbon dioxide gas, this reaction is an absorption ergon reaction. Since the higher the ratio, the higher the reaction rate, the reaction gas or the transparent container may be heated with factory waste heat. Further, in order to increase the reaction rate at low temperature, a molybdenum sulfide catalyst added with an alkali metal salt, particularly sodium carbonate or lithium carbonate, may be used.

e. Embodiments of the Invention Hereinafter, representative embodiments of the present invention will be described with reference to the drawings.

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

FIG. 2 shows another embodiment of the present invention, which uses a gutter-type compound parabolic mirror collector that can collect and collect heat without using a tracking mechanism. Length 50 with mirror 6 inside
A straight tubular transparent container 8 made of quartz having a diameter of 1 cm is installed near the concentrating point of the concentrator 7 having a diameter of cm and 15 g of the catalyst 9
(Molybdenum disulfide supported on titanium dioxide with sodium carbonate added) is filled, and a 1: 1: 1 mixed gas of carbon dioxide, hydrogen and argon is passed at a flow rate of 6 ml / min to collect light. The reaction product obtained by irradiating the
Was analyzed using a gas chromatograph. As a result, about
12% of carbon dioxide was converted to carbon monoxide.

f. Effects of the Invention As described above, the present invention uses the sunlight collected by the solar concentrator to cause carbon dioxide to react with hydrogen on molybdenum sulfide filled in a transparent container to carry out monoxide oxidation. By using molybdenum sulfide catalyst, which converts to carbon, is black, has a good absorption rate of sunlight, can react at low temperature and atmospheric pressure, is inexpensive, has low toxicity, and is not poisoned by sulfur compounds. This enabled direct reduction of carbon dioxide by solar energy, which was difficult because the reaction temperature was high. Since this reaction is an absorption ergon reaction, the energy yield is good, and the product carbon monoxide can be used as it is as a fuel, or it can be converted to methanol or chemical raw materials that are in the spotlight as automobile fuels. Since it can be used, it is very effective from the aspect of global environment conservation and energy measures.

[Brief description of drawings]

FIG. 1 and FIG. 2 are schematic views showing an embodiment of the carbon dioxide gas reduction method of the present invention. In the figure, reference numeral 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 light collecting collector, 8 is a mixed gas of carbon dioxide, hydrogen and argon.

 ─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-55-51712 (JP, A) JP-A-63-80833 (JP, A)

Claims (4)

[Claims] 1. A transparent container filled with a molybdenum sulfide catalyst is installed near the focal point of a solar concentrator, and the condensed sunlight is transparent while a gas containing carbon dioxide and hydrogen is circulated in the transparent container. A method for reducing carbon dioxide, which comprises irradiating a catalyst in a container, reacting carbon dioxide with hydrogen on the catalyst, and converting the carbon dioxide into carbon monoxide. 2. As a solar concentrator, a gutter-shaped flat mirror concentrator, a gutter-shaped compound parabolic concentrator, a gutter-shaped parabolic concentrator, and a gutter-shaped concentrator. A light collector that simulates an object mirror with a plane mirror.
A concentrating solar collector, such as a rotating parabolic mirror concentrator, a linear Fresnel lens concentrator, or a circular Fresnel lens concentrator, is used. The method for reducing carbon dioxide according to item 1. 3. A molybdenum sulfide catalyst as alumina, silica, activated carbon, zeolite, activated clay, bauxite,
The method for reducing carbon dioxide according to claim 1, wherein molybdenum disulfide supported on at least one carrier of silicon, silicon carbide, a metal oxide semiconductor, and a metal sulfide semiconductor is used. 4. The carbon dioxide gas reduction method according to claim 1, wherein supported molybdenum disulfide added with an alkali metal salt is used as the molybdenum sulfide catalyst.