JPH0335000B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for wet oxidizing wastewater containing chemical oxygen demand substances (hereinafter referred to as COD components) in the presence of a catalyst. Specifically, the present invention includes:
By catalytic wet oxidation of wastewater containing harmful oxidizable organic or inorganic substances, which are COD components, in the coexistence of molecular oxygen, these organic substances are converted into harmless carbon dioxide, water, nitrogen, etc. Concerning effective methods to make the world pollution-free. [Prior Art] Known wastewater treatment methods include a biochemical method called an activated sludge method and a wet oxidation method called a Zimmerman method. As is well known, the activated sludge method requires a long time to decompose organic matter, and it is also necessary to dilute the wastewater to a concentration suitable for the growth of algae and bacteria, so the installed area of the activated sludge treatment facility is large. There are drawbacks to it. Furthermore, in recent years, sometimes in urban areas, huge processing costs are required to handle the surplus sludge that has grown. On the other hand, the Zimmermann method uses pressures of 20 to 200 atm and temperatures of 200 atm for aqueous solutions containing highly concentrated organic substances.
This method introduces air at ~370°C to oxidize and decompose organic matter, but this method requires a large reactor because the reaction rate is slow and decomposition takes a long time, and the material used is highly durable. Because of this, there are economical problems in equipment costs, operating costs, etc. Furthermore, in this method, methods using various oxidation catalysts have been proposed for the purpose of speeding up the reaction rate. Conventionally, noble metal compounds such as palladium and platinum (JP-A-Show) have been used as catalysts for catalytic wet oxidation
49-44556) and heavy metal compounds such as cobalt and iron (Japanese Unexamined Patent Publication No. 49-94157). These catalysts are catalysts in which the above compound is supported on a spherical or cylindrical carrier such as alumina, silica/alumina, silica gel, or activated carbon. When wastewater is subjected to catalytic wet oxidation, it is often subjected to the reaction at a pH of 9 or higher, and according to the inventors' study, the above catalysts deteriorate in strength and become crushed into powder after long-term use, and furthermore, the catalyst deteriorates. Dissolution may also occur. For example, alumina-based catalysts tend to suffer from a decrease in strength due to elution of alumina. Recently, in an attempt to solve these problems, a method using titania or zirconia as a carrier has been proposed (Japanese Patent Laid-Open Publication No. 1988-64188). According to this publication, a catalyst is disclosed in which a noble metal compound such as palladium or platinum, or a heavy metal compound such as iron or cobalt is supported on a spherical or cylindrical titania or zirconia carrier. According to this consideration, it is certainly recognized that the strength is superior to that of conventional carriers. However, all of these catalysts have a granular shape. Moreover, the catalyst activity and durability are not fully satisfactory. For example, titania-based catalysts tend to suffer from a decrease in strength due to titania crystal changes. By the way, when wet oxidizing wastewater, it is necessary to treat a large amount of water. Therefore, the reaction mode is often a fixed-bed flow system, and the wastewater often contains solids. In these cases, if the catalyst is granular, the pressure loss due to the flow of the wastewater is large and the wastewater cannot be treated at a high linear velocity. Therefore, it is necessary to have a large cross-sectional area of the wastewater flow, and the area occupied by the reactor becomes large. Furthermore, in the case of wastewater treatment in which solid matter coexists, clogging increases the flow resistance, leading to an increase in running costs, and furthermore, there are disadvantages such as making long-term operation of the treatment equipment impossible. That is, in wastewater treatment using the catalytic wet oxidation method, since the reaction is carried out at high temperature and high pressure, an increase in the area occupied by the reactor leads to an increase in equipment cost, which is a fatal problem. In addition, a fluidized bed method has been proposed in which a powdered catalyst is fluidized in order to reduce the pressure loss caused by the catalyst layer, but this method requires a large reactor because the concentration of the catalyst is thin, and the catalyst and treatment This method has the disadvantage that it is difficult to separate it from subsequent wastewater, so it has not been put into practical use. On the other hand, there is also a method of oxidizing and decomposing organic matter in wastewater at normal temperature and pressure using ozone or hydrogen peroxide as an oxidizing agent. For example, in Japanese Patent Application Laid-Open No. 58-55088, wastewater containing organic substances such as humic acid,
A method for oxidatively decomposing the organic substance using ozone and hydrogen peroxide at 20° C. and normal pressure in the absence of a catalyst is described. Also, in Special Publication No. 58-37039,
A surfactant is added to wastewater containing an organic compound having an aromatic ring, and at least one selected from transition metal compounds and alkaline earth compounds is added and mixed, and then this mixture is heated at room temperature and under normal pressure. A method of oxidatively decomposing the organic compound by contacting with ozone is described. Since the former process is carried out in the absence of a catalyst, it is not possible to treat substances that are difficult to oxidize, such as suspended matter in wastewater.
The latter uses metal ions such as transition metals or alkaline earth metals as catalysts, so it has the disadvantage of requiring a post-treatment process, as it is necessary to recover the metal ions after treatment of the wastewater rather than releasing them as is. There is. In addition, because both wastewater treatment is carried out at room temperature and pressure, a large amount of expensive ozone is required, the reaction rate is slow, the decomposition rate of organic matter is low, and unreacted ozone is generated. It has disadvantages such as requiring detoxification treatment. [Problems to be Solved by the Invention] Therefore, an object of the present invention is to provide a method for efficiently treating wastewater over a long period of time. Another object of the present invention is to provide a method for efficiently treating wastewater at high linear velocity. A further object of the present invention is to provide a method for stably treating wastewater containing solids at high linear velocity over a long period of time. [Means for solving the problems] These objectives were achieved by using a composite oxide of titanium and zinc as the catalyst A component, an oxide of a lanthanide element as the catalyst B component, and manganese, iron, cobalt, and nickel as the catalyst C component. , tungsten, copper, silver, gold, platinum, palladium, rhodium,
Using a catalyst containing at least one metal selected from the group consisting of ruthenium and iridium or a water-insoluble or sparingly soluble compound thereof, the wastewater is heated at a temperature of 370°C or less and the wastewater maintains a liquid phase. The wastewater is wet-treated under pressure while being supplied with a gas containing 1.0 to 1.5 times the theoretical amount of oxygen necessary to decompose the organic and inorganic substances in the wastewater into nitrogen, carbon dioxide, and water. This is achieved by a method for treating wastewater characterized by oxidation. The present invention also provides a method for treating wastewater in which the catalyst is an integral structure. Furthermore, the catalyst of the present invention has an equivalent diameter of the through hole of 2 to 20 mm and a cell wall thickness of 0.5 to 3 mm.
This is a wastewater treatment method using a honeycomb type catalyst having a shape with mm and aperture ratio in the range of 50 to 80%. Furthermore, the present invention is a method for treating wastewater in which ozone and/or hydrogen peroxide are allowed to coexist when the wastewater is passed through the catalyst together with a gas containing oxygen. The catalyst used in the present invention includes a composite oxide of titanium and zinc as the catalyst A component, an oxide of a lanthanide element as the catalyst B component, and manganese, iron, cobalt, nickel, tungsten, copper, silver, and gold as the catalyst C component. , platinum, palladium, rhodium, ruthenium, and iridium, or a water-insoluble or sparingly soluble compound thereof. The catalyst of the present invention is characterized by a binary composite oxide (hereinafter referred to as TiO ₂ -ZnO) consisting of titanium and zinc.
) and oxides of lanthanide elements are used as catalyst components. In general, binary composite oxides consisting of titanium and zinc are described in Kozo Tabe, Catalysts, Vol. 17, No. 3,
72 (1975), it is known as a solid acid and exhibits remarkable acidity and a high surface area that are not found in the constituent oxides alone. In other words, TiO ₂ -ZnO is not simply a mixture of titanium oxide and zinc oxide, but it can be recognized that its unique physical properties are expressed by titanium and zinc forming a so-called binary composite oxide. It is. We believe that when this composite oxide is used as the catalyst A component, it has much better moldability when molded into pellets, spheres, honeycomb shapes, etc.
It was discovered that the catalyst maintains its shape over a long period of time even when used in wastewater treatment, which requires harsh conditions such as high temperature, high pressure, alkalinity, and acidity. Furthermore, catalyst B
It was discovered that by using the lanthanide element oxide as a component, the hot water resistance was significantly improved, and the wastewater treatment efficiency was also excellent. According to the studies conducted by the present inventors, excellent moldability cannot be obtained by using titanium and zinc oxides alone or simply as a mixture. For example, even if they can be molded into a honeycomb shape, they cannot withstand long-term use. However, it was found that only when these elements were made into a composite oxide, excellent moldability was exhibited and excellent durability was achieved. Catalyst A constituting the catalyst used in the present invention
The BET surface area of the component TiO ₂ −ZnO is 10 m ² /g
It is preferably at least 30 m ² /g, particularly preferably at least 30 m 2 /g. The composition of catalyst A component is 20 to 90 mol% _TiO2 ,
A ZnO content in the range of 10 to 80 mol % gives favorable results in maintaining durability and catalytic activity. As the catalyst B component, one or more oxides of any lanthanoid element such as lanthanum, cerium, praseodymium, neodymium, and samarium can be used to increase the catalyst stability, but in particular oxides consisting of lanthanum, cerium, or neodymium can be used. At least one oxide selected from the group is preferred because it is more effective in increasing catalyst stability and catalyst activity. Further, the catalyst B component can form a composite oxide with the catalyst A component. The ratio of each catalyst component in the catalyst used in the present invention is 70 to 99.45% by weight of catalyst A component in the form of oxide;
Catalyst B component is 0.5-15% by weight in the form of oxide, catalyst C component is 0.05-25% by weight in the form of metal or compound.
A range of is appropriate. Preferably, among the elements constituting the C component, the amounts of manganese, iron, cobalt, nickel, tungsten, copper and silver used are as follows:
0 to 25% by weight as compounds (e.g. oxides, chlorides, sulfides, etc.), including platinum, gold, palladium,
The amount of rhodium, ruthenium and iridium used is 0 to 10% by weight as metals (however, the total amount of both is 0.05 to 25% by weight). More preferably, the catalyst A component is 90 to 98% by weight in the form of an oxide;
Catalyst B component is 1 to 9.9% by weight in the form of an oxide, Catalyst C component is 0.1 to 9% by weight in the form of a metal or compound.
It is. Preferably, among the metals constituting catalyst C component, the amount of manganese, iron, cobalt, nickel, tungsten, copper and silver used as a compound is 0 to 9% by weight, and the amount of manganese, iron, cobalt, nickel, tungsten, copper and silver used is 0 to 9% by weight, and platinum, gold, palladium, rhodium, ruthenium and The amount of iridium used is 0 to 5% by weight as a metal (however, the total amount of both is 0.1 to 9% by weight). The total amount of catalyst A component, catalyst B component, and catalyst C component is 100% by weight.
It is. If the catalyst C component is outside the above range, the oxidation activity will be insufficient, and in the case of noble metals such as platinum, palladium, and rhodium, the raw material cost will be high and a correspondingly sufficient effect cannot be exhibited. In addition, if the catalyst A component and B component are outside the above range, the hot water resistance will be poor,
This is unfavorable in terms of catalyst life. The catalyst used in the present invention preferably has the composition specified above, and the catalyst may have various shapes such as pellets, spheres, rings, saddle shapes, powders, crushed shapes, and integral structures such as honeycombs. things can be adopted. Preferably, it is a honeycomb type structure, and particularly preferably, in this structure, the equivalent diameter of the through hole is 2 to 20 mm, and the cell wall thickness is
It has a shape in the range of 0.5 to 3 mm and an aperture ratio of 50 to 80%. For honeycomb catalysts, if the pore diameter (equivalent diameter of through holes) is increased, the flow resistance decreases proportionately and clogging by solids can be prevented, but at the same time, the geometric surface area of the catalyst also decreases, and certain processing In order to achieve efficiency, it is necessary to increase the amount of catalyst as the pore size increases. Therefore, the pore size is limited due to its relationship with processing efficiency and catalyst performance. In the honeycomb catalyst described above, the equivalent diameter of the through holes is in the range of 2 to 20 mm, preferably 4 to 12 mm. If the equivalent diameter is less than 2 mm, the pressure loss will be large, and especially if the wastewater contains solids, clogging will easily occur, making it difficult to use it for a long time. If the equivalent diameter exceeds 20 mm, the pressure loss will be small and the possibility of clogging will be reduced, but the catalyst activity will not be sufficient. The cell wall thickness is in the range of 0.5 to 3 mm, preferably 0.5 to 2 mm. When the cell wall thickness is less than 0.5 mm, there is an advantage that the pressure loss is small and the weight of the catalyst can be reduced, but it is not preferable because the mechanical strength is reduced. When the cell wall thickness exceeds 3 mm, the mechanical strength is sufficient, but the disadvantage is that the pressure loss becomes large. The aperture ratio is also 50 to 80 for the same reason as above.
%. Considering the above circumstances, a particularly preferable honeycomb catalyst used in the present invention has an equivalent diameter of through holes of 2 to 20 mm, a cell wall thickness of 0.5 to 3 mm, and an aperture ratio of 50 to 80%. It is. A honeycomb catalyst that meets these conditions has a reaction temperature of 100°C.
~370℃, and has sufficient mechanical strength even under severe reaction conditions of high temperature and pressure, where the reaction pressure is higher than the pressure that maintains the liquid phase of wastewater, and the geometric surface area of the catalyst is also small. Because it has sufficient properties, it has excellent durability and can treat wastewater at high linear velocity with low pressure loss. Further, even when solid content is contained in the wastewater, high activity can be maintained for a long period of time without clogging. As for the shape of the through-hole, any shape such as quadrangular, hexagonal, wavy, etc. can be adopted as long as its equivalent right angle is within the above range. In the present invention, by using molecular oxygen, ozone, and/or hydrogen peroxide as oxidizing agents, it is possible to decompose organic substances such as acetic acid, which are said to be relatively resistant to oxidation, with high efficiency.
This is preferred because the reaction can be carried out at low pressure. Furthermore, since the catalyst used in the present invention has the ability to decompose ozone into oxygen, it also has the advantage of substantially decomposing waste ozone and preventing it from being discharged outside the system. That's true. The amount of ozone used is 0.001 to 1.2 times the mole, preferably 0.003 to 0.6 times the theoretical amount of oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. That's enough. In addition, the amount of hydrogen peroxide used is based on the theoretical amount of oxygen.
0.001 to 1.8 times the mole, preferably 0.003 to 0.2 times the mole, is sufficient. By using ozone and/or hydrogen peroxide together with molecular oxygen, the reaction temperature will be higher than when using only molecular oxygen, although it will vary depending on the properties of the wastewater, the amount of the oxidant used, etc. also decreases. For example, when the reaction temperature when using molecular oxygen is 200°C to 300°C, when the oxidizing agent is used in combination, the reaction temperature becomes about 100°C to 250°C. Used as catalyst A component in the present invention,
To prepare TiO ₂ -ZnO, first, the titanium source can be selected from inorganic titanium compounds such as titanium chlorides and titanium sulfate, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate. can be selected from inorganic zinc compounds such as zinc chloride, zinc nitrate, zinc sulfate, and organic zinc compounds such as zinc acetate. Some of these raw materials may contain trace amounts of impurities or mixtures, but they can be obtained.
This is not a problem unless it significantly affects the physical properties of TiO ₂ −ZnO. A preferable method for preparing TiO ₂ -ZnO includes the following method. A method in which titanium tetrachloride is mixed with zinc chloride, ammonia is added to form a precipitate, the precipitate is washed, dried, and then calcined at 300 to 650°C. Zinc nitrate is added to titanium tetrachloride to cause a thermal hydrolysis reaction to form a precipitate, which is then washed.
A method of baking at 300-650℃ after drying. Among the above preferred methods, this method is particularly preferred, and this method is specifically carried out as follows. That is, the above titanium source and zinc source compounds are taken so that the molar ratio of TiO ₂ and ZnO is a predetermined amount, and titanium and zinc are converted into oxides at a concentration of 1 to 100 g/in an acidic aqueous solution state.
Keep at 10-100℃. A compound of a lanthanoid element, which constitutes the catalyst B component of the present invention, can also be added in a dissolved or suspended form. Aqueous ammonia was added dropwise as a neutralizing agent into the solution while stirring, and the mixture was kept at pH 2-10 for 10 minutes to 3 hours to form a coprecipitated compound consisting of titanium and zinc. After being separated and thoroughly washed, it was heated to 80-140°C. Dry for 1 to 10 hours at
TiO ₂ -ZnO can be obtained by firing at ~650°C for 1 to 10 hours. Using TiO ₂ −ZnO prepared by the above method,
A finished catalyst is obtained by the method shown below. For example, by adding TiO ₂ −ZnO powder together with a molding aid,
Mix and knead while adding an appropriate amount of water, and mold into spheres, pellets, plates, honeycombs, etc. using an extruder. After drying the molded product at 50 to 120°C, it is dried at 300 to 800°C, preferably 350 to 600°C, for 1 to 10 hours, preferably 2 to 200°C.
A catalyst can be obtained by calcination under air flow for 6 hours. In the present invention, starting materials for the lanthanide elements used as catalyst B component include oxides, hydroxides, inorganic salts, etc. For example, taking cerium as an example, raw materials include cerium acetate, cerium nitrate, and cerium sulfate. , cerium oxide, etc. Also, these
Preferred methods of adding TiO ₂ -ZnO include the following methods. Salts of lanthanoid elements are dissolved or fine powders of oxides of lanthanoid elements are suspended in a mixed solution of titanium salts and zinc salts, ammonia is added to this to form a precipitate, and this precipitate is washed and dried for 300 min. A method of firing at ~650℃. A method in which pre-coprecipitated unfired TiO ₂ -ZnO is impregnated with a salt solution of a lanthanide element, then dried and fired at 300 to 650°C. After impregnating pre-fired TiO ₂ −ZnO with a salt solution of lanthanide elements, drying
A method of firing at 650℃. Furthermore, a mixed solution of the catalyst C component and a salt solution may be used during this impregnation. Among the above preferred methods, the following methods are preferred. Further, starting materials for the catalyst C component include oxides, hydroxides, inorganic acid salts, organic acid salts, etc., and are appropriately selected from, for example, ammonium salts, oxalates, nitrates, sulfates, and halides. In addition, manganese is added to the catalyst A component and the catalyst B component.
iron, nickel, cobalt, tungsten, copper,
When catalyzing by adding silver, gold, platinum, palladium, rhodium, ruthenium and/or iridium, after impregnating and supporting the molded body consisting of catalyst A component and catalyst B component with an aqueous solution of the metal salt,
It can be made into a catalyst by drying and firing. On the other hand, a method is also used in which a carrier consisting of catalyst A component is impregnated with a mixed aqueous solution of metal salts of catalyst B component and catalyst C component, supported on the carrier, and then dried and calcined. Alternatively, an aqueous solution of the metal salt may be added to a powder consisting of catalyst A component and catalyst B component together with a molding aid, and the mixture may be kneaded and molded. According to the present invention, activated sludge-treated supernatant water or precipitated activated sludge, fermentation wastewater, wastewater from organic compound polymerization processes, cyanide-containing wastewater, phenol-containing wastewater, oil-containing wastewater, and other chemical factory wastewater as well as food factories Wet oxidation treatment can be applied to general industrial wastewater from sources such as the like, as well as wastewater containing oxidizable organic or inorganic substances such as human waste, sewage, and sewage sludge. Furthermore, when a honeycomb type catalyst is used in the present invention, even wastewater containing 0.1 g/or more of solids can be treated stably over a long period of time. The reaction conditions in the present invention are that the reaction temperature is 370°C.
Below, usually 100-370℃, more preferably 200-300℃
It is ℃. The pressure of the reaction system is sufficient to maintain the liquid phase of the wastewater in the reaction tower, that is, 1 to about 200 kg/cm ²
The pressure is fine. The molecular oxygen-containing gas fed is 1 to 1 of the theoretical amount of oxygen required for oxidative decomposition.
Use 1.5 times the amount. The amount of catalyst used is about 5 to 99% of the space volume of the reaction column. The wastewater is oxidized by flowing it with a molecular oxygen-containing gas through a catalyst bed at a predetermined temperature for a residence time of 6 to 120 minutes, preferably 12 to 60 minutes. The molecular oxygen-containing gas may be air, a mixture of oxygen and air, or a gas commonly referred to as oxygen-enriched air. The pH of the reaction system can be either acidic or alkaline, but it is preferable to
is in the range of 9 or more, more preferably 7 or more. Along with molecular oxygen, ozone and/or
Alternatively, when hydrogen peroxide is used in combination, the reaction conditions are usually in the temperature range of 100°C to 250°C, and the reaction pressure is sufficient to maintain the liquid phase of the wastewater in the reaction tower, that is, 1 to 200 kg/ ^cm2 . Pressure and residence time are 3 to 120
minutes, preferably 5 to 60 minutes. The amount of ozone used is in the range of 0.001 to 1.2 times the mole of the theoretical oxygen amount. The amount of hydrogen peroxide used is 0.001 to 1.8 times the theoretical amount of oxygen, preferably 0.003 to 1.8 times the mole amount.
The range is 0.2 times the mole. The present invention will be explained in more detail below using Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 A sulfuric acid aqueous solution of titanyl sulfate having the following composition was used as a titanium source. TiOSO ₄ (TiO ₂ equivalent) 250g / Total H ₂ SO ₄ 1100g / Dissolve 496g of zinc sulfate [ZnSO ₄ 7H ₂ O] and 321g of lanthanum nitrate [La (NO ₃ ) ₃ 6H ₂ O] in 50% water. , an aqueous sulfuric acid solution of titanyl sulfate with the above composition 4.96
was added and mixed well. This temperature is about 30℃
Aqueous ammonia was gradually added dropwise while stirring well while maintaining the pH of the solution until the pH reached 7, and the mixture was left to stand still for 15 hours. The thus obtained TiO ₂ -ZnO-La ₂ O ₃ gel was filtered, washed with water, and then dried at 200°C for 10 hours. Then, it was fired at 550° C. for 6 hours in an air atmosphere. The composition of the obtained powder is TiO ₂ :ZnO:La ₂ O ₃ = 82.6 in weight ratio:
9.4:8.0, and the molar ratio of TiO ₂ and ZnO in this powder was 9:1. The BET surface area was 130 m ² /g. The powder obtained here is hereinafter referred to as P-1,
A catalyst was prepared using this powder by the method described below. 900 ml of water, 1500 g of the above powder, and 75 g of starch were added, mixed, and kneaded well using a kneader. After further kneading with an appropriate amount of water, each was extruded into a honeycomb mold with a pore diameter (equivalent diameter of through holes) of 5 mm and a porosity of 72%, dried at 120°C for 6 hours, and then heated to 450°C.
It was baked for 6 hours. The thus obtained molded body was immersed in a chloroplatinic acid aqueous solution, and then dried at 120°C for 6 hours.
It was baked at ℃ for 3 hours. The composition of the finished catalyst obtained was P-1 in weight ratio:
Pt=99.5:0.5. Example 2 According to the method described in Example 1, the powder composition was
A powder having a TiO ₂ :ZnO ratio of 7:3 (mole ratio) and a BET surface area of 140 m ² /g was obtained. This powder is hereinafter referred to as P-2. 550 ml of water, 1000 g of the above powder, and 30 g of starch were added, mixed, and kneaded well using a kneader. This was extruded into cylindrical pellets with a diameter of 4 mm, dried, and then calcined at 450°C for 6 hours. The molded body thus obtained was impregnated in a mixed solution of a ruthenium chloride aqueous solution and a cerium nitrate aqueous solution, dried at 120°C for 6 hours, and then dried at 400°C for 3 hours.
Baked for an hour. The composition of the finished catalyst obtained was P- ₂ :CeO2:Ru=90:8.5:1.5 in weight percentage. Example 3 Using each of the catalysts obtained in Example 1 and Example 2, wastewater treatment was carried out by a wet oxidation method in the following manner. A stainless steel reaction tube is filled with a catalyst, and preheated mixed waste water and air with an oxygen concentration of 21% are continuously introduced from the bottom of the reaction tube for 6000 hours to reduce COD (Cr) at the inlet and outlet of the reaction tube. was measured, and the removal rate at the initial stage and after 6000 hours of reaction was determined.
The strength of the catalyst was also measured at the initial stage and after 6000 hours of reaction, and the strength ratio of the catalyst was determined. The properties of the wastewater used for treatment were COD (Cr) 20 g/PH and PH 6. The reaction conditions were a reaction temperature of 250℃ and a reaction pressure of 60℃.
Kg/cm ² , and the space velocity of waste water was 2 Hr ^-1 (based on the superficial column) and the space velocity of air was 160 Hr ^-1 (based on the superficial column, under standard conditions). The results obtained are shown in Table 1.

[Table] Example 4 In Example 3, instead of air with an oxygen concentration of 21%, a mixed gas consisting of an oxygen concentration of 18% and an ozone concentration of 1% was used, and the catalyst obtained in Example 1 was used, and the reaction temperature was After 500 hours of wastewater treatment at 210°C and a reaction pressure of 45 kg/cm ^{2 ,} the COD removal rate was 93%. Example 5 In Example 4, 3% hydrogen peroxide solution was added to the space velocity
Supplied with mixed gas at 0.001Hr ^-1 (sky tower standard),
Using the catalyst obtained in Example 1, wastewater was treated for 500 hours, resulting in a COD removal rate of 94%.

Claims (1)

[Claims] 1 A composite oxide of titanium and zinc as the catalyst A component, an oxide of a lanthanide element as the catalyst B component, and manganese, iron, cobalt, nickel, tungsten, copper, silver, gold, Using a catalyst containing at least one metal selected from the group consisting of platinum, palladium, rhodium, ruthenium, and iridium, or a water-insoluble or sparingly soluble compound thereof, the wastewater is heated at a temperature of 370°C or less and the wastewater is heated. 1.0 of the theoretical amount necessary to decompose the organic and inorganic substances in the wastewater into nitrogen, carbon dioxide and water under a pressure that maintains a liquid phase.
A method for treating wastewater, which comprises subjecting the wastewater to wet oxidation while supplying a gas containing ~1.5 times the amount of oxygen. 2 Catalyst A component is 70 to 99.45% by weight as an oxide
The catalyst B component is 0.5 to 15% by weight as an oxide, and the catalyst C component is a metal or compound.
2. A method according to claim 1, using a catalyst that is between 0.05 and 25% by weight. 3 The catalyst A component is 90 to 98% by weight as an oxide, the catalyst B component is 1 to 9.9% by weight as an oxide, and the catalyst C component is 0.1% as a metal or compound.
2. A method according to claim 1, using a catalyst that is ~9% by weight. 4 Catalyst A component is titania (TiO ₂ ) from 20 to
The method according to claim 1, using a catalyst which is a binary composite oxide of TiO ₂ -ZnO consisting of 90 mol % and 10 to 80 mol % of zinc oxide (ZnO). 5. The method according to claim 1, wherein the catalyst B component is an oxide of at least one element selected from the group consisting of lanthanum, cerium, and neodymium. 6. The method according to claim 1, wherein the catalyst is in the form of pellets or spheres. 7 Claim 1 in which the catalyst is an integral structure
The method described in section. 8. The method according to claim 7, wherein the catalyst is a honeycomb type catalyst having a shape in which the equivalent diameter of the through holes is in the range of 2 to 20 mm, the cell wall thickness is in the range of 0.5 to 3 mm, and the aperture ratio is in the range of 50 to 80%. . 9. The method according to claim 1, wherein the reaction temperature is in the range of 100 to 370°C. 10. The method according to claim 1, in which ozone and/or hydrogen peroxide are allowed to coexist when the wastewater is passed through the catalyst together with the oxygen-containing gas. 11. The method according to claim 10, wherein the amount of ozone used is 0.001 to 1.2 times the mole of theoretical oxygen required to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. Method. 12. Claim 10, wherein the amount of hydrogen peroxide used is 0.001 to 1.8 times the mole of theoretical oxygen necessary to decompose organic and inorganic substances in wastewater into nitrogen, carbon dioxide, and water. the method of.