Chemistry of hydrocarbon compounds – Production of hydrocarbon mixture from refuse or vegetation
Reexamination Certificate
1997-06-06
2003-01-07
Norton, Nadine G. (Department: 1764)
Chemistry of hydrocarbon compounds
Production of hydrocarbon mixture from refuse or vegetation
C585S241000, C585S832000, C208S262100, C208S400000, C208S952000, C201S002500, C201S025000
Reexamination Certificate
active
06504068
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of decomposing a plastic waste by a chemical reactions, in which water in a supercritical or near supercritical region is used as a reaction medium, and thereby converting the plastic waste into oil, and further relates to an apparatus therefor.
2. Description of the Related Art
Hitherto, almost all of the plastic waste of various types have been dumped on a land reclamation site or have been burned and thus have not been effectively utilized as resources. Further, in the case of dumping the plastic waste on a reclaimed land, it is difficult to secure a land or ground to be reclaimed and the reclaimed ground is unstable. Further, in the case of burning the plastic waste, there have been caused the problems that because these wastes are high-calorie solids, an incinerator is badly damaged and that the plastic waste gives off a poisonous gas and a foul odor during incineration thereof.
In such a context, in recent years, attempts have been made to develop a method for recycling and reusing a plastic waste without pollution, and for effectively utilizing the recycled plastics as resources. As one of such methods, there has been proposed a method (namely, what is called a supercritical water method or process) of decomposing a plastic waste by a reaction (namely, a supercritical water reaction), which uses water in a supercritical region (namely, supercritical water) or water near the supercritical region (namely, near supercritical water) as a reaction medium, to thereby convert the plastic waste into oil and of collecting useful oil-like materials (refer to Japanese Patent Provisional Publication 56-501205 corresponding to WO81/00855 and Japanese Patent Provisional Publication Nos. 57-4225, 5-31000, 6-279762, and U.S. Pat. No. 4,113,446; all of these references are incorporated herein by reference).
Supercritical water is defined as water that is in conditions in which the temperature is critical temperature (namely, 374° C.) of water or higher and the pressure is the critical pressure (namely, 22.1 MPa) or higher. In the case of the supercritical water method, the quantity of generated gas is low and the amount of a residue is small, in comparison with the case of utilizing thermolysis at ordinary pressure. Thus, a high oil conversion ratio, at which a plastic waste is converted into oil, can be realized. Incidentally, even if the pressure of water is not higher than the critical pressure, the water acting as a reaction medium behaves almost similarly as supercritical water does when the pressure thereof is close to the critical pressure (namely, the ratio of the pressure thereof to the critical pressure is 0.8 or more).
However, with the current state of the art, techniques for treating a plastic waste according to the supercritical water method have not been sufficiently clearly established yet. Especially, from the point of view of the speed-up of the reaction and the treatment (or disposal) of large amounts of plastic waste, the current techniques may not be effective and are not suitable for industrialization. Namely, in the case of the treatment of by the conventional supercritical water method, a batch treatment is performed (by a reactor of the autoclave type) at a temperature of 400° C. or so, with the result that it takes long time, which is 30 minutes or more, to perform the decomposition of a plastic waste and convert the plastic waste into oil. Moreover, it is difficult to treat large amounts of plastic waste.
Furthermore, when the plastic waste contains chlorine-base (or chlorine-containing) plastic such as vinyl chloride resin, there are caused the problems that the corrosion of the reactor and piping is effected by hydrogen chloride produced by the decomposition of the chlorine-base plastic contained in the plastic waste during the decomposition of the plastic waste and the conversion thereof into oil. Namely, a supercritical water-reaction is effected in high-temperature water. Further, hydrogen chloride is ionized and chlorine ions are dissociated therefrom. Thus, conditions for acclerating the corrosion are produced. Consequently, the conventional treatment of a plastic waste by the supercritical water method has encountered another problem that metallic materials are seriously corroded.
Therefore, in the case that a plastic Waste containing chlorine-base plastic is decomposed and converted into oil by the supercritical water method, it is very difficult to select the metallic materials for the reactor and piping. Thus, heretofore, in the case of using the supercritical water method, with the existing state of the art, only a plastic waste containing no chlorine-base plastic has been converted into oil after the chlorine-base plastic is fractionated and separated from the plastic waste by a pretreatment. The present invention is accomplished in view of such a state of the conventional art.
SUMMARY OF THE INVENTION
Accordingly, a first object of the present invention is to provide a method and apparatus of treating a plastic waste, which is suitable for industrialization and can decompose a plastic waste and convert the plastic waste into oil at a high speed in a supercritical water process for treating a plastic waste and further can treat large amounts of plastic waste.
Further, a second object of the present invention is to provide a method and apparatus of treating a plastic waste, which can effectively suppress the corrosion of the apparatus due to hydrogen chloride generated during, the decomposition of the plastic waste and the conversion thereof into oil.
To achieve the foregoing objects, in accordance with an aspect of the present invention, there is provided a method of decomposing a plastic waste by a reaction using water in a supercritical or near supercritical region as a reaction medium and converting the plastic waste into oil, which comprises the step of carrying out the reaction in a tubular type continuous reactor.
It is preferable that the residence time of the plastic waste in the reactor is 5 minutes or less when conducting the reaction according to this method of converting the plastic waste into oil.
Further, in accordance with another aspect of the present invention, there is provided a method of decomposing a plastic waste by a reaction using water in a supercritical or near supercritical region as a reaction medium and converting the plastic waste into oil, which comprises the steps of: heating a plastic waste to decompose part or all of chlorine-base plastic included in the plastic waste and separate and remove generated hydrogen chloride therefrom; and conducting the reaction by mixing the plastic waste, from which the hydrogen chloride is separated, with water.
In the case of this method of converting a plastic waste into oil, it is preferable that a tubular type continuous reactor is used as the reactor for conducting the reaction.
Further, in such a case of this method of converting a plastic waste into oil, it is preferable that the residence time of the plastic waste in the reactor is 5 minutes or less when conducting the reaction according to this method of converting the plastic waste into oil.
Moreover, in accordance with still another aspect of the present invention, there is provided an apparatus for decomposing a plastic waste by a reaction using water in a supercritical or near supercritical region as a reaction medium and for converting the plastic waste into oil, which comprises a tubular type continuous reactor as a reactor for conducting the reaction.
Furthermore, in accordance with yet another aspect of the present invention, there is provided an apparatus for decomposing a plastic waste by a reaction using water in a supercritical or near supercritical region as a reaction medium and for converting the plastic waste into oil, which comprises: a hydrogen-chloride decomposing/removing mechanism for heating a plastic waste to decompose part or all of chlorine-base plastic contained in the plastic waste and separate and rem
Iijima Masaki
Kobayashi Kazuto
Makihara Hiroshi
Matsubara Wataru
Mitsubishi Jukogyo Kabushiki Kaisha
Norton Nadine G.
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