1. Field of the Invention
This invention relates to a reaction vessel for the use of oxidization and decomposition processing equipment by supercritical water and a method of manufacturing the reaction vessel in which harmful substances such as polybiphenyl chloride (hereinafter called as PBC), powerful toxic dioxine and other organic compounds are processed to be their non-toxic states through oxidization and decomposition under supercritical water condition with its critical temperature being 374xc2x0 C. or higher and its critical pressure being 22 MPa or higher.
2. Description of the Related Art
In recent years, a chemical processing has been carried out frequently under a supercritical state. For example, coffee and the like are mainly used in extraction of food or separation of chemical products and the like under a supercritical CO2 where the processing is carried out under a relatively low temperature,
In the case of supercritical water, although its original substance is water, there have been provided many cases that the supercritical water is used in a normal chemical reaction and oxidization such as treatment of environmental-relating materials such as decomposition of PCB, dioxine and the like due to the fact that its critical temperature is quite high, for example, the critical temperature is 374xc2x0 C. or higher and the critical pressure is 22 MPa or higher.
These treatments are mainly carried out such that the materials are dissolved with water under supercritical state as solvent, then they are reacted with oxygen and decomposed. That is, since the supercritical water is liquid and at the same time it has also a characteristic acting as gas, where reaction with oxygen as gas must be almost freely carried out.
That is, since the supercritical water is liquid and at the same time reaction with oxygen as gas can be carried out almost freely, the aforesaid materials can be quite easily dissolved due to the fact that the supercritical water becomes water of low molecules and dispersed water which is different from the usual water, resulting in that the materials and oxygen can be almost freely merged and reacted to each other under such a processing condition as above and so its oxidization and decomposition can be easily carried out.
However, in the case of the reaction vessel where such a strong reaction is performed, it occurred frequently the materials is generally exposed to the quite strong oxidizing atmosphere and at the same time in the case of decomposition of harmful substances such as dioxine and the like, the substances are completely decomposed, and resulting that Cl component becomes hydrochloric acid which show strong acid and the resulting liquid gives a strong corrosive characteristic and the reaction vessel itself is corroded.
Then, in the case of the prior art, reaction vessel used in the oxidization and decomposition treatment equipment of supercritical water performing such a reaction as above, Ni-based alloy material is normally used, although it is not possible to say that this Ni-based alloy material has a sufficient anti-corrosive characteristic in its chemical stability against acid-corrosion and therefore either replacement work caused by the acid-corrosion or maintenance work such as a repairing operation must be performed within a short period of time, which must give a problem to require high running cost and the improvement has been highly requested.
In view of the foregoing, as a countermeasure for the resolution against these problems, it has been tried that the inner surface of the reaction vessel is covered by anti-corrosive substances such as by Pt plating or the like. But Pt is expensive, and not only a sufficient anti-corrosive performance could not be obtained, but also there occurred a problem of a peeling-off of the Pt plated film and the like caused by a difference of thermal expansion coefficient in respect to the reaction vessel (Ni-based alloy) accompanied by rapid increasing or rapid decreasing in temperature. In addition, although the Pt is durable against the acid atmosphere, the Pt shows a problem of crystal growth and peeling-off or destruction of it in reducing atmosphere, so that actually it can not be applied in such a objectives.
In view of such a circumstance as found in the prior art, the present inventor made a various investigation to the subject matter and reached the present invention, wherein the objectives of the present invention is to enable the reaction vessel to be covered and to be protected against corrosive atmosphere in both oxidizing and reducing atmosphere and to provide a reaction vessel applicable in an oxidization and decomposing processing equipment by supercritical water and a method of manufacturing the reaction vessel in which its durability is remarkably improved and its continuous use can be performed for a long period of time.
In order to solve the problem, the present invention provides a reaction vessel applied in an oxidizing and decomposing processing equipment by supercritical water, wherein an oxide film containing metal oxide having a quite high anti-corrosive characteristic in both oxidizing and reducing atmosphere is formed at an inner surface of the vessel main body and the vessel is covered with the oxide film and protected by it. In this case, as the type of the reaction vessel structure, that is, any of a vertical cylindrical vessel type or a coil type can be applied.
In addition, the present invention provides the aforesaid reaction vessel in which the oxide film contains platinum group metal oxides composed of fine crystalline structure showing a quite high anti-corrosive characteristic in both oxidizing and reducing atmosphere.
In additions the present invention provides a reaction vessel in which an oxide film contains at least one platinum group metal oxide selected from Ir, Ru, and Rh.
In addition, the present invention provides a reaction vessel in which an oxide film is comprised of a composite oxides containing platinum group metals and at least one metal selected from Ti, Ta.
In addition, the present invention provides a reaction vessel in which an oxide film is comprised of a composite oxide containing Ir, and at least one kind selected from Ti, and Ta by 20 to 50 at %, or a composite oxides containing Ru, and at least one kind selected from Ti, and Ta by 30 to 70 at %.
In addition, the present invention provides a method of manufacturing a reaction vessel used in a equipment for oxidizing and decomposing operations by supercritical water, wherein after coating solution composed of salt solution containing platinum group metals is applied to a surface of a vessel main body, the vessel main body is processed with pyrolytic reaction processing under atmosphere containing aqueous moisture, thereby an oxide film containing platinum group metal compound composed of fine crystalline structures having a quite high anti-corrosive characteristic in both oxidizing and reducing atmosphere is formed at the inner surface of the vessel main body.
In addition, the present invention provides a method of manufacturing the aforesaid reaction vessel, wherein after performing a pretreatment in which the surface of the vessel main body is degreased, its surface is processed with heat and said surface is formed with an oxide layer in advance, the coating solution is applied to coat it.
In addition, the present invention provides a method of manufacturing a reaction vessel, wherein an oxide film is comprised of a composite oxide containing Ir, at least one kind selected from Ti, and Ta by 20 to 50 at % or a composite oxide containing Ru, at least one kind selected from Ti, and Ta by 30 to 70 at %.
In addition, the present invention provides a method of manufacturing a reaction vessel, wherein salt solution contains platinum group metal chloride, or alkoxide compound of platinum group metals.
Thus, in accordance with the aforesaid technical means, the reaction vessel showing the largest wear in the equipment for oxidizing and decomposing processing with supercritical water is covered and protected by an oxide film formed at the surface of the reaction vessel containing metallic compound having a quite high anti-corrosive characteristic in both oxidizing and reducing atmosphere, for example, an oxide film containing platinum group metal oxide composed of fine crystals, thereby the reaction vessel is exposed in both oxidizing and reducing atmosphere at high temperature and high pressure for a long period of time and its acid-based corrosion caused by reactant is restricted even under a severe environment such as heating and rapid cooling states. With such an arrangement as above, it becomes possible to make a rapid progress of anti-corrosive characteristic and durability of the reaction vessel and a substantial improvement of its practical application. In other words, it becomes possible to make a substantial reduction of running cost accompanied by either replacement or repairing of the reaction vessel and make a substantial improvement in its practical application.