This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-077199, filed Mar. 23, 1999; No. 11-280667, filed Sep. 30, 1999; and No. 11-358956, filed Dec. 17, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a carbon dioxide gas absorbent, particularly, to a carbon dioxide gas absorbent employed in an energy plant or a chemical plant that utilizes a hydrocarbon-based fuel, in a system for separating and recovering carbon dioxide gas from an exhaust gas of motor cars, or in a refining system of a gas supplied into a fuel supply section.
In an apparatus in which a hydrocarbon-based fuel is combusted such as an engine, the exhaust gas release portion adapted for recovery of a carbon dioxide gas is heated to a high temperature not lower than 300xc2x0 C.
A method using cellulose acetate, a chemical absorption method using an alkanol amine-based solvent, etc. are known to the art as methods of separating a carbon dioxide gas. However, it is necessary to suppress the inlet gas temperature to a level not higher than 200xc2x0 C. in any of these conventional methods. Therefore, for processing an exhaust gas requiring a gas recycle at high temperatures, the exhaust gas must be cooled once to temperatures not higher than 200xc2x0 C. by using, for example, a heat exchanger. In the case of employing these conventional methods, a problem is brought about that the energy consumption for separating a carbon dioxide gas is increased.
On the other hand, Japanese Patent Disclosure (Kokai) No. 9-99214 discloses a carbon dioxide gas absorbent consisting of lithium zirconate that performs its function under high temperatures exceeding about 500xc2x0 C. The method disclosed in this prior art is defective in that zirconium oxide, which is a matrix oxide forming lithium zirconate, is very heavy, with the result that the absorbent itself is rendered very heavy. In addition, it is difficult to absorb and recover a carbon dioxide gas from the exhaust gas of the entire temperature range.
Japanese Patent Disclosure No. 11-90219 discloses a carbon dioxide gas absorbent that reacts with a carbon dioxide gas at a temperature not higher than 450xc2x0 C. to form lithium carbonate. The carbon dioxide absorbent disclosed in this prior art is a lithium oxide composition containing at least one element selected from the group consisting of aluminum, titanium, iron and nickel. Even in the case of using the particular carbon dioxide gas absorbent, the carbon dioxide absorption rate at about 250xc2x0 C. is not sufficiently high.
Incidentally, the carbon dioxide gas absorption characteristics of lithium zirconate are not sufficiently satisfactory in every range of the carbon dioxide gas concentration. Particularly, lithium zirconate is incapable of sufficiently absorbing a carbon dioxide gas of a low concentration.
An object of the present invention, which has been achieved for overcoming the above-noted problems inherent in the prior art, is to provide a lightweight carbon dioxide absorbent capable of maintaining a high performance that the absorbent performs its function under high temperature regions exceeding about 500xc2x0 C.
Another object is to provide a carbon dioxide absorbent capable of exhibiting a high carbon dioxide gas absorbing capability under temperature regions in the vicinity of 250xc2x0 C.
Further, still another object of the present invention is to provide a lightweight carbon dioxide gas absorbent capable of efficiently recovering a low concentration of a carbon dioxide gas under a high temperature region.
According to a first aspect of the present invention, there is provided a carbon dioxide gas absorbent containing lithium silicate represented by the general formula:
LixSiyOz
xe2x80x83where x, y, z are integers meeting the requirement of x+4yxe2x88x922z=0.
According to a second aspect of the present invention, there is provided a carbon dioxide gas absorbent containing as a main component a compound containing lithium and silicon and oxygen.
According to a third aspect of the present invention, there is provided a carbon dioxide gas absorbent containing a complex oxide of lithium and silicon and reacting with a carbon dioxide gas to form lithium carbonate.
According to a fourth aspect of the present invention, there is provided a carbon dioxide gas absorbent containing Li2O and SiO2, the molar ratio of Li2O/SiO2 falling within a range of between 0.5 and 10.
According to a fifth aspect of the present invention, there is provided a carbon dioxide gas absorbent containing a lithium silicate powder having an average particle diameter of 0.1 to 50 xcexcm.
According to a sixth aspect of the present invention, there is provided a carbon dioxide gas absorbent containing lithium silicate and at least one kind of alkali carbonate selected from the group consisting of sodium carbonate and potassium carbonate.
According to a seventh aspect of the present invention, there is provided a carbon dioxide gas absorbent containing lithium silicate and lithium zirconate.
According to other aspect of the present invention, there is provided a method of separating a carbon dioxide gas from a gaseous material containing a carbon dioxide gas, wherein a carbon dioxide gas absorbent defined above is brought into contact with a gaseous material containing a carbon dioxide gas.
According to further aspect of the present invention, there is provided a method of separating a carbon dioxide gas, wherein a carbon dioxide gas absorbent absorbing a carbon dioxide gas is heated.
According to further aspect of the present invention, there is provided an apparatus for separating a carbon dioxide gas, comprising a reaction vessel equipped with a carbon dioxide inlet port and a formed gas outlet port, a carbon dioxide gas absorbent defined above loaded in the reaction vessel, and heating means arranged to surround the outer surface of the reaction vessel for heating the reaction vessel.
According to further aspect of the present invention, there is provided a combustion apparatus for combusting a hydrocarbon-based fuel, comprising a carbon dioxide gas absorbent defined above arranged in an exhaust passageway of a carbon dioxide gas generated by the combustion of the hydrocarbon.
Further, according to other aspect of the present invention, there is provided a method of manufacturing a carbon dioxide gas absorbent, comprising the steps of preparing a lithium silicate powder, and adding at least one kind of an alkali carbonate powder selected from the group consisting of a sodium carbonate powder and a potassium carbonate powder to the lithium carbonate powder.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.