JPH0586254B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a water treatment catalyst that decomposes and removes dissolved ozone remaining in water after water treatment using ozone. <Prior art> Ozone treatment is widely used for the oxidative decomposition removal of harmful components, odor components, coloring components, etc. in water.
It is used for wastewater and water treatment. Particularly in recent years, it has become increasingly important due to the problems of pollution caused by trihalomethanes, odor problems caused by deterioration in the quality of water taken into water supplies, and the need for advanced treatment due to stricter wastewater regulations. On the other hand, the problem of ozone remaining in water after ozone treatment has also arisen. Ozone gradually decomposes in water, but in neutral to acidic regions the decomposition speed is slow and residual water becomes a problem. For example, when chlorine treatment is performed after ozone treatment, the disadvantage is that the amount of chlorine required increases. Further, when the activated carbon treatment is performed after the ozone treatment, there arises a problem that the ozone consumes the activated carbon in an oxidative manner. To prevent these problems, it is necessary to remove residual ozone. Conventionally, there are few technologies related to this, and a method using a catalyst is a method using a filter layer having a manganese dioxide catalyst film (Japanese Unexamined Patent Publication No. 1983-1999).
139991). <Problems to be solved by the invention> Dissolved ozone in water decomposes relatively quickly in alkaline regions, but in neutral to acidic regions, the decomposition speed is slow, it takes time to decompose, and residual ozone remains. It becomes a problem. The above-mentioned method using a filter layer having a manganese dioxide catalyst film takes a long time to decompose and remove ozone, and the efficiency is not sufficient.
Furthermore, since the volume of the filter medium layer is large relative to the throughput, there is also the problem that the apparatus itself becomes large-sized. Therefore, the object of the present invention is to provide a water treatment catalyst that has higher ozone decomposition activity and stability over a long period of time than conventional products, and is capable of decomposing and removing dissolved ozone remaining in water in a wide PH range. It's about doing. <Means for solving the problem> This purpose is to use an oxide of at least one element selected from the group consisting of titanium, silicon, aluminum, and zirconium as a catalyst A component, and manganese, iron, and cobalt as a catalyst B component. ,
Nickel, cerium, tungsten, copper, silver,
Used for the decomposition and removal of ozone dissolved in water, characterized by containing a water-insoluble or poorly soluble compound of at least one element selected from the group consisting of gold, platinum, palladium, rhodium, ruthenium and iridium. This is achieved using a water treatment catalyst. The present invention also provides a water treatment catalyst used for decomposition and removal of ozone dissolved in water, characterized in that the catalyst is a fixed bed catalyst formed in the shape of pellets, pipes or honeycombs. The characteristics of the catalyst according to the present invention are that the catalyst A component is an oxide of at least one element selected from the group consisting of titanium, silicon, aluminum, and zirconium, and the catalyst B component is manganese,
Iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium,
It contains a water-insoluble or sparingly soluble compound of at least one element selected from the group consisting of ruthenium and iridium. That is, according to the studies of the present inventors, sufficient ozonolysis activity and long-term stability cannot be obtained with catalyst A component alone or catalyst B component alone, and catalyst A component and catalyst B component are both contained. This increases the ozone decomposition efficiency and makes it a catalyst with little change over time. The ratio of each catalyst component in the catalyst used in the present invention is 70 to 99.99% by weight of catalyst A component as an oxide;
It is preferably 80 to 99.95% by weight, and suitably the catalyst B component is 0.01 to 30% by weight, preferably 0.05 to 20% by weight as a metal or compound.
Preferably, the amount of manganese, iron, cobalt, nickel, cerium, tungsten, copper, and silver used in the elements constituting the B component is based on compounds (for example, compounds insoluble or poorly soluble in water such as oxides and sulfides). ), and the amount of gold, platinum, palladium, rhodium, ruthenium and iridium used is 0 to 10% by weight as metals (however, the total amount of both is 0.01 to 30% by weight). ). Note that the total amount of catalyst A component and catalyst B component is 100% by weight. If the amount of catalyst B component is less than the above range, the ozonolysis activity will be insufficient, and
In the case of noble metals such as platinum, palladium and rhodium, if the amount exceeds the above range, the raw material cost will increase and a corresponding effect cannot be expected. On the other hand, by controlling the catalyst A component within the above range, the moldability of the catalyst is improved, making it easier to mold into various shapes, increasing the long-term stability of the catalyst, and having a positive effect on the activity. Further, from the viewpoint of catalytic activity, it is preferable that the catalyst A component and the catalyst B component are mutually dispersed within the above composition range. Further, it is preferable that the catalyst A component is a composite oxide of at least two elements selected from the group consisting of titanium, silicon, and zirconium. These composite oxides have strong solid acidity and a large BET specific surface area, and are preferable from the viewpoints of catalyst activity, catalyst formability, and strength stability. It is preferable that the catalyst used in the present invention be a fixed bed catalyst formed in the shape of pellets, pipes or honeycombs in order to facilitate the handling of the catalyst and to reduce the flow resistance of treated water. In particular, when solids are contained in the treated water, a honeycomb shape is preferred since it can reduce the possibility of clogging. This honeycomb shape has an equivalent diameter of through holes of 2
~20mm, cell thickness 0.1~3mm and aperture ratio 50
A range of ~90% is preferred. Furthermore, the equivalent diameter is
2.5-15mm, cell thickness 0.5-3mm and aperture ratio
Particularly preferred is a range of 50 to 80%. If the equivalent diameter is less than 2 mm, the pressure loss will be large, and clogging will easily occur, especially if solids are contained in the water. 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. If the cell wall thickness is less than 0.1mm, the pressure loss will be small,
Although this has the advantage of reducing the weight of the catalyst, it is not preferable because the mechanical strength of the catalyst decreases. 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~ for the same reason as above.
It is 90%. Therefore, a honeycomb-type catalyst with the above-mentioned preferred shape conditions has sufficient mechanical strength and sufficient geometric surface area, so it has excellent durability and can treat target water with low pressure loss and high flow rate. can do. Moreover, even when solid content is contained in the water, high activity can be maintained for a long period of time without clogging. The method for preparing the catalyst of the present invention includes the following methods, but it goes without saying that the method is not particularly limited to these methods. That is, the powder of the catalyst A component is added to an aqueous solution containing active components such as transition metals and noble metals listed as the catalyst B component, mixed well, and this is directly molded.
After drying at 50-120℃, 300-800℃, preferably 350-
A catalyst can be obtained by calcining at 600°C for 1 to 10 hours, preferably 2 to 6 hours. Alternatively, the mixture can be catalyzed by preparing a catalyst composition powder in advance and supporting it on a suitable carrier. Alternatively, the powder of the catalyst A component may be molded, dried, and fired to form a catalyst carrier in advance, and an aqueous solution of the metal salt of the catalyst B component may be supported on the catalyst carrier by an impregnation method, followed by firing. Note that when a composite oxide of at least two elements selected from the group consisting of titanium, silicon, and zirconium is used as the catalyst A component, these composite oxide powders can be prepared as follows. For example, as a method for preparing powder of a binary composite oxide (hereinafter referred to as TiO ₂ -SiO ₂ ) consisting of titanium and silicon, the following method may be mentioned. Titanium tetrachloride is mixed with silica sol, ammonia is added to form a precipitate, and this precipitate is washed and dried at 300-650°C, preferably at 350°C.
A method of firing at ~600℃. A sodium silicate aqueous solution is added to titanium tetrachloride and reacted to form a precipitate, which is washed and dried at 300 to 650°C, preferably 350 to 600°C.
A method of firing. Ethyl silicate [(C ₂ H ₅ O) ₄ Si] is added to a water-alcohol solution of titanium tetrachloride to cause a hydrolysis reaction to produce a precipitate, which is washed and dried at 300-650°C, preferably 350-650°C. A method of firing at 600℃. Ammonia was added to a water-alcohol solution of titanium oxide chloride (TiOC ₂ ) and ethyl silicate to form a precipitate, which was washed and dried for 300 min.
A method of firing at ~650°C, preferably 350-600°C. Among the above preferred methods, this method is particularly preferred, and this method is specifically carried out as follows. That is, the above-mentioned titanium source and silicon source compounds are taken so that the molar ratio of TiO ₂ and SiO ₂ is a predetermined amount, and titanium and silicon are converted into oxides in an acidic aqueous solution state or sol state to 1 to 1.
The concentration is 100g/, preferably 10-80g/ and maintained at 10-100°C. Add aqueous ammonia as a neutralizing agent to the solution while stirring for 10 minutes to 3 hours.
At pH 5 to 10, a coprecipitated compound consisting of titanium and silicon is formed, separated, and thoroughly washed.
Dry at 80-140℃ for 1 hour to 10 hours, dry at 300-650℃,
TiO ₂ -SiO ₂ powder can be obtained by firing preferably at 350 to 600°C for 1 to 10 hours, preferably 2 to 8 hours. In addition, as a starting material, titanium sources can be selected from inorganic titanium compounds such as titanium chlorides and titanium sulfates, and organic titanium compounds such as titanium oxalate and tetraisopropyl titanate, and colloidal titanium compounds as a silicon source. It can be selected from inorganic silicon compounds such as silica, water glass, silicon tetrachloride, and organic silicon compounds such as tetraethyl silicate. Some of these raw materials may contain trace amounts of impurities or contaminants, but this does not pose a problem as long as they do not significantly affect the physical properties of the TiO ₂ -SiO ₂ obtained. Further, the preparation method of titanium and zirconium binary composite oxide (hereinafter referred to as TiO ₂ -ZrO ₂ ) powder can be performed in the same manner. A preferable method for preparing TiO ₂ -ZrO ₂ powder includes the following method. A method in which titanium chloride is mixed with zirconium oxychloride, ammonia is added to form a precipitate, the precipitate is washed and dried, and then calcined at 300 to 650°C, preferably 350 to 600°C. Adding zirconium nitrate to titanium tetrachloride,
A thermal hydrolysis reaction is carried out to produce a precipitate, which is washed and dried at 300-650°C, preferably 350-650°C.
A method of firing at 600℃. In addition, starting materials for catalyst B component used together with catalyst A component include oxides, hydroxides, inorganic acid salts,
Examples include organic acid salts, and are appropriately selected from ammonium salts, oxalates, nitrates, sulfates, halides, and the like. The catalyst used in the present invention has the ability to decompose ozone into oxygen. The appropriate treatment temperature range is 0 to 90℃, but increasing the treatment temperature also increases the decomposition speed of ozone itself without a catalyst, but the utility is improved by carrying out the reaction at a lower temperature using a catalyst. The treatment temperature is more preferably in the range of 0 to 60°C, since the benefits such as reduction are reduced.
The amount of treated water varies depending on the target treatment rate and conditions, and is used at a flow rate of 1 to 1000/hr per catalyst. Although the pressure conditions are not particularly limited, normal pressure can be used satisfactorily. Further, the dissolved ozone concentration in the water to be treated is suitably within a range of 0.1 mg/from the ozone dissolution saturation concentration. If the ozone concentration is less than 0.1mg/, the merits of using a catalyst are small. <Examples> The present invention will be described in more detail below using Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 A binary composite oxide of titanium and zirconium was prepared by the method described below. 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 / Separately, add zirconium oxychloride [ZrOC] to 50% water.
_{2.8H 2} O] was dissolved and added to 6.4 kg of an aqueous sulfuric acid solution of titanyl sulfate having the above composition and mixed well. While maintaining the temperature at about 30°C and stirring well, aqueous ammonia was gradually added dropwise until the pH reached 7 to form a coprecipitated gel. Further, it was left as it was for 15 hours. Then filtration,
After washing with water, it was dried at 200°C for 10 hours and then fired at 500°C for 5 hours in an air atmosphere. The composition of the obtained powder is
TiO ₂ :ZrO ₂ =7:3 (mole ratio), and the BET specific surface area was 120 m ² /g. 1.5 kg of the above powder and 75 g of starch were added to 850 ml of water, mixed, and kneaded well with a kneader. The hole diameter (equivalent diameter of the through hole) is 4 mm, and the cell wall thickness is 1 mm.
extruded into a honeycomb mold with an open area of 64% at 120°C.
After drying for 6 hours at 450°C, it was fired for 6 hours. The molded body thus obtained was impregnated with an aqueous palladium chloride solution, then dried at 120°C for 6 hours, and then heated at 400°C.
The catalyst was fired for 3 hours to obtain a catalyst containing 0.5% by weight of Pd. Example 2 Cerous nitrate [Ce(NO ₃ ) ₃・6H ₂ O] 0.5Kg
Dissolved in 0.9 kg of water, 1.8 kg of commercially available titanium oxide powder
In addition, pellets with a diameter of 5 mm were molded according to the method of Example 1. The composition of the obtained catalyst was CeO ₂ (10
(% by weight) - TiO ₂ (90% by weight). Example 3 According to Example 1, colloidal silica was used instead of zirconium oxychloride, and TiO ₂ :SiO ₂ =
It has a composition of 9:1 (molar ratio) and a BET specific surface area of
A powder of a binary composite oxide of titanium and silicon having an area of 150 m ² /g was obtained. Next, a catalyst was prepared according to the method of Example 1 using a manganese nitrate aqueous solution instead of the palladium chloride aqueous solution, containing 7% by weight of manganese dioxide, and having a pore diameter of 3 mm and a cell wall thickness of 0.58 mm. A honeycomb type catalyst with a yield of 70% was obtained. Example 4 A commercially available γ-alumina carrier with a diameter of 4 mm was impregnated with an aqueous cobalt nitrate solution, dried, and fired to form a Co ₃ O ₄ (7
A catalyst having a composition of 93% by weight) _-Al2O3 (93% _by weight) was obtained. Example 5 A reaction tube was filled with one catalyst of Examples 1 to 4, and one
Treated water at room temperature containing 5 mg of ozone per hour and having the pH shown in Table 1 was flowed 50/hr to cause a reaction. The ozone decomposition rate was determined by measuring the ozone content at the reactor outlet. The treatment results are shown in Table 1. Comparative Example 1 Table 1 shows the results of a reaction conducted according to Example 5 using electrolytic manganese dioxide particles with a diameter of 5 mm. Comparative Example 2 Table 1 shows the results obtained in Example 5 when treated water with a pH of 5.1 containing 5 mg of ozone per water was flowed without being charged with a catalyst.

[Table] Example 6 The catalyst shown in Table 2 was prepared according to the above example. One of these catalysts was charged into a reaction tube, and 50% of treated water containing 5 mg of ozone and PH6.8 at room temperature was added to the reaction tube.
/hr to react. The ozone decomposition rate was determined by measuring the ozone content at the reactor outlet. The treatment results are shown in Table 3.

【table】

【table】

[Table] Example 7 Example 6 for the catalysts of Examples 1 to 4 and 6
After the reaction was continued for 4000 hours under these conditions, the catalyst was extracted. We conducted crushing strength tests on these catalysts,
The strength ratio of the pre-reaction catalyst and the post-reaction catalyst was determined. The results are shown in Table 4.

【table】

[Table] Example 8 A reaction tube was filled with one catalyst of Examples 1 and 3, water containing 500 mg/hour of SS (suspended solids) was added at a flow rate of 50/hr, and ozone-containing gas was added to the reaction tube. The reaction was carried out at a flow rate of 0.5 g/hr at room temperature. The results showed that the catalyst did not become clogged even after 1000 hours had passed since the start of the reaction.

Claims (1)

[Scope of Claims] 1. An oxide of at least one element selected from the group consisting of titanium, silicon, aluminum, and zirconium as the catalyst A component, and manganese, iron, cobalt, nickel, cerium, tungsten, and copper as the catalyst B component. Decomposition of ozone dissolved in water, characterized by containing a water-insoluble or sparingly soluble compound of at least one element selected from the group consisting of silver, gold, platinum, palladium, rhodium, ruthenium and iridium. Water treatment catalyst used for removal. 2 Catalyst A component is 70 to 99.99% by weight as an oxide
and the catalyst B component is a metal or a compound.
Claim 1 characterized in that the content is 0.01 to 30% by weight.
Catalysts as described. 3. The catalyst according to claim 1, wherein the catalyst is a fixed bed catalyst formed in the shape of pellets, pipes or honeycombs. 4.Claim 1, wherein the catalyst A component is a composite oxide of at least two elements selected from the group consisting of titanium, silicon, and zirconium.
Catalysts as described.