JP3229674B2 - Wastewater treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating water containing nitrogen-containing compounds, for example, wastewater from amine production plant wastewater, synthetic leather production plant wastewater, food production plant wastewater, activated sludge treated water, human waste or sewage. About. For more information,
The present invention relates to a method for decomposing nitrogen-containing compounds contained in wastewater by wet oxidation using a specific catalyst.

[0002]

2. Description of the Related Art The treatment of wastewater containing a nitrogen-containing compound depends on the state of the nitrogen component contained in the wastewater, by a coagulation method using an anionic polymer coagulant; or activated carbon, activated clay, silica-titania, silica-titania- Magnesia gel,
It is performed by an adsorption method using silica gel (see JP-A-62-4990). Also, a method of reacting an aromatic amine in wastewater with hydrogen peroxide using peroxidase as a catalyst to form an insoluble polymer and removing the polymer from the wastewater (Journal of Applied Biochemistry, Vol. 2, 414) 421 pages, 1980). Since this method has low durability of the catalyst, it has been proposed to add boric acid to the system to extend the life of the catalyst (Japanese Patent Application Laid-Open No. 2-78498).

[0003]

In the above-mentioned coagulation method, the polymer coagulant is expensive and the recovery rate of amine from wastewater is low, so that the treatment cost is high and the coagulant used in the treatment is waste sludge. Therefore, it is necessary to process this separately. In the above-mentioned adsorption method, there is a problem that it is not practical because the adsorption ratio of amine to the adsorbent is too low and the treatment becomes insufficient.

[0004] The method for removing the insoluble polymer from wastewater also requires treatment of the insoluble polymer. Since the step of wet oxidation treatment is inevitable in the treatment of wastewater, it is advantageous if the nitrogen-containing compound contained in the wastewater is also decomposed during the wet oxidation treatment. An object of the present invention is to provide a method for efficiently and wastefully treating wastewater containing a nitrogen-containing compound in a manner that can be industrially established.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, in the wet oxidation treatment of wastewater containing amines and amino acids, a specific catalyst described later in detail is used. The inventors have found that the above-mentioned problems can be solved by the treatment and that the specific catalyst can be applied to nitrogen-containing compounds other than amines and amino acids, and the present invention has been completed.

Therefore, according to the present invention, the average particle size is 4
Gold that is 0-150 angstroms or the gold
Provided is a method for treating wastewater that oxidizes wastewater containing a nitrogen-containing compound in the presence of molecular oxygen while maintaining a liquid phase using a catalyst in which palladium and palladium are supported on a refractory inorganic oxide. I do. As the refractory inorganic oxide used in the present invention, oxides such as titania, zirconia, alumina, and ceria can be used. Preferably, titania and zirconia, more preferably, titania 20 to
It is a composite oxide of 90 mol% and 10 to 80 mol% of zirconia.

[0007] Typical examples of the method for preparing an oxide of titanium and zirconium include, for example, a mixture of titanium oxide and zirconium oxide, and a composite oxide of titanium and zirconium. Not limited. The molar ratio of titanium to zirconium (Ti / Zr) in the oxide of titanium and zirconium is 0.2
The range of 5 to 9 is preferable, and the range of 1 to 4 is more preferable. If the Ti / Zr molar ratio is less than 0.25, the treatment efficiency of the nitrogen-containing compound contained in the wastewater is low, and may not be satisfactory. On the other hand, when the Ti / Zr molar ratio is larger than 9, the treatment efficiency of the nitrogen-containing compound is reduced, which may not be satisfactory.

The method for producing an oxide of titanium and zirconium used in the present invention includes, for example, (1) adding aqueous ammonia to an aqueous solution of zirconium nitrate and titanyl nitrate, stirring the mixture sufficiently, and taking out the formed precipitate; (2) a method of adding an aqueous solution of zirconium nitrate and titanyl nitrate to ammonia water, stirring the mixture thoroughly, taking out the formed precipitate, washing, drying and calcining; (3) zirconium There are a method in which an aqueous solution of a salt and a titanium salt is put into an autoclave and hydrothermal synthesis is performed under a high temperature and a high pressure, and (4) a method in which a solid phase reaction is performed between zirconium oxide and titanium oxide. It is not limited to these methods.

The refractory inorganic oxide is used as an inorganic carrier for a catalyst in a desired shape. However, in consideration of the back pressure, for example, pellets, spheres, honeycombs, rings, etc. are used rather than powders. It is more advantageous to use it after molding. In this invention, gold or gold and palladium are supported on the refractory inorganic oxide. The supported amount of gold as the catalytically active component is 0.1 Au in terms of Au per liter of the entire catalyst.
Preferably, the ratio is 5 to 100 g.
More preferably, the ratio is set to 〜100 g.
If the supported amount of Au is less than 0.5 g per liter of the whole catalyst, the effect of the gold catalyst may not be exhibited. The rate is small, which is not preferable in terms of catalyst cost. The supported gold is preferably in the form of particles, and the average particle size thereof is, for example, 40 to 150.
Angstrom is preferred, and 60-100 Å is more preferred. By supporting gold with such an average particle size in a highly dispersed state, catalyst stability and durability can be enhanced.

The method of supporting gold on the refractory inorganic oxide is carried out by a commonly used supporting method. For example, (1) an aqueous solution of chloroauric acid is added to an aqueous solution of sodium carbonate, and after gold starts to precipitate, Ammonia is added and stirred sufficiently, then a hydrochloric acid solution of magnesium citrate and a refractory inorganic oxide are added, and the mixture is further stirred sufficiently to impregnate the refractory inorganic oxide with gold. The refractory inorganic oxide powder, sodium carbonate, sodium citrate, and chloroauric acid charged in pure water are placed in an autoclave container, and the water supporting the gold on the powder under high temperature and high pressure is stirred. There are a thermal method and the like, and the loading by the method (1) is most preferable.

When wastewater containing a nitrogen-containing compound is subjected to wet oxidation treatment using a catalyst carrying both gold and palladium, the treatment efficiency of the nitrogen-containing compound is improved, and the stability of the catalytically active component is increased. Stable processing efficiency can be maintained over a long period of time. The supported amount of palladium is preferably in a range of 0.05 ≦ Pd / Au ≦ 50, more preferably in a range of 0.2 ≦ Pd / Au ≦ 20, in terms of a molar ratio to palladium. In the case of Pd / Au <0.05, the effect of supporting palladium is small, and in the case of Pd / Au> 50, the treatment efficiency of the nitrogen-containing compound is significantly small compared to the amount of supported palladium, which is not preferable in terms of catalyst cost. By supporting palladium, the treatment efficiency of the nitrogen-containing compound in the wastewater can be further improved.

The method of supporting palladium on the refractory inorganic oxide is carried out by a commonly used supporting method,
For example, the case of supporting on a composite oxide of titanium and zirconium will be described as an example. (1) A molded body of a composite oxide of titanium and zirconium supporting gold is immersed in an aqueous solution of a palladium salt, and then dried and fired. (2) a method of adding a powder of a composite oxide of titanium and zirconium to an aqueous solution of a palladium salt, evaporating to dryness, and then drying and calcining; (3) forming a composite oxide of titanium and zirconium into a molded product; There is a method of impregnating with an aqueous solution of a gold compound and a palladium compound, followed by drying and baking.

The loading of gold and palladium is carried out in the form of a simple substance of each metal, an alloy of gold and palladium, and the oxide of palladium is not limited to these. The wastewater containing a nitrogen-containing compound to be treated by the method of the present invention includes, for example, amine production plant wastewater, leather production plant wastewater, food production plant wastewater, activated sludge treated water, human waste, sewage, and the like.

Examples of the nitrogen-containing compound to be treated according to the present invention include at least one compound selected from compounds containing a nitrogen atom in the molecule, such as ammonia, hydrazine, amine compounds, amide compounds, amino acid compounds and the like. Can be The amine compound may be any of a primary amine, a secondary amine, a tertiary amine, and a quaternary ammonium salt as long as the compound has an amino group in the molecule. Specifically, for example, methylamine, dimethylamine, trimethylamine, triethylamine,
Alkylamines such as propylamine; alkylenediamines such as ethylenediamine and trimethylenediamine;
Selected from aliphatic amines such as alkanolamines such as ethanolamine and triethanolamine; aromatic amines such as aniline, phenylenediamine, aminophenol and aminonaphthalene; and nitrogen-containing heterocyclic compounds such as pyridine and picoline. At least one compound is exemplified.

An amide compound is a compound having a group (RCONH-) in which an amino group and an acid group are bonded in a molecule.
Specifically, for example, at least one compound selected from formamide, methylformamide, acetamide, ethylformamide, methylpropionamide, dimethylformamide, diethylformamide, dimethylacetamide, N-methylpyrroline and the like is exemplified.

An amino acid compound is a compound having a carboxyl group and an amino group in a molecule, and is called an α-amino acid, β-amino acid, γ-amino acid, or the like.
Specifically, for example, glycine, alanine, valine,
Aliphatic amino acids such as leucine, serine, cysteine, aspartic acid, glutamic acid, lysine, and arginine; amino acids having an aromatic ring such as phenylalanine and tyrosine; and amino acids having a heterocyclic ring such as histidine, tryptophan and proline. At least one compound is exemplified.

However, the nitrogen-containing compound in the present invention is not limited to the above examples. The nitrogen-containing compound does not need to be dissolved in water, and can be decomposed by the treatment method of the present invention even in a state such as a suspended state. The nitrogen-containing compound in the wastewater may be present as a single compound, or may be present as a mixture of a plurality of types. The nitrogen-containing compound of wastewater to which the present invention can be applied is not particularly limited, but is usually in the range of 10 to 100,000 ppm.

In the present invention, the nitrogen-containing compound is decomposed by oxidizing wastewater containing the nitrogen-containing compound in the presence of molecular oxygen while maintaining the liquid phase using the above catalyst. This decomposition reaction is performed in a state where the wastewater retains a liquid phase, in order to suppress the deposition of inorganic substances in the wastewater by preventing the water from evaporating into a gas. The reaction temperature of the oxidation treatment is preferably 120 to 3
70 ° C, more preferably 200 to 300 ° C. The upper limit is defined by the critical temperature of water, and the lower limit is defined at a lower temperature because the decomposition reaction of the nitrogen-containing compound hardly occurs. The pressure of the reaction system is the pressure required for water to maintain a liquid phase in the reaction system, that is, about 1-2.
The pressure may be 00 kgf / cm ² . The space velocity of the wastewater is preferably in the range of wastewater amount / catalyst volume in the range of 0.1 to 20 hr ^-1 , more preferably in the range of 0.3 to 10 hr ^-1 . As the oxygen source used for the reaction, molecular oxygen is used, and specifically, air, oxygen-enriched air, oxygen gas, or the like is used.

As the apparatus used for the wet oxidation reaction, for example, a reactor generally used in the treatment of wastewater, for example, a single-tube cylindrical type, a multi-tube type reactor, or a combination thereof can be used. The specific catalyst used in the present invention may be charged into these reactors, for example, in the same manner as a catalyst used in ordinary wet oxidation of wastewater, and the wastewater may be treated. According to the treatment method of the present invention, the nitrogen-containing compound is, for example,
Decomposes into carbon dioxide, water, nitrogen, etc.

If the nitrogen-containing compound has been decomposed into nitrogen gas by the wet oxidation treatment, the treated liquid after solid-liquid separation can be directly discharged or reused. When only lower nitrogen compounds such as ammonia have been decomposed, solid components may be subjected to decomposition treatment after solid-liquid separation, if necessary. According to the wastewater treatment method of the present invention, a chemically oxidatively decomposable substance (including the nitrogen-containing compound) is referred to as a “COD component” because its amount is represented by a chemical oxygen demand (COD). Can be oxidatively decomposed.

[0021]

According to the present invention, when a wastewater containing a nitrogen-containing compound is oxidized in the presence of molecular oxygen while maintaining a liquid phase, using a catalyst in which gold is supported on a refractory inorganic oxide, Nitrogen-containing compounds are decomposed into carbon dioxide, water and nitrogen. When the catalyst is obtained by supporting gold on a composite oxide of titanium and zirconium, a nitrogen-containing compound in wastewater can be efficiently and stably treated.

Using a catalyst in which gold and palladium are supported on a refractory inorganic oxide, waste water containing a nitrogen-containing compound is
When the oxidation treatment is performed in the presence of molecular oxygen while maintaining the liquid phase, the nitrogen-containing compound is decomposed into carbon dioxide, water, and nitrogen. If the catalyst is obtained by supporting gold and palladium on a composite oxide of titanium and zirconium, the nitrogen-containing compound in the wastewater can be decomposed more efficiently and stably.

The gold is supported on the composite oxide by adding an aqueous solution of sodium carbonate to the composite oxide of titanium and zirconium,
Further, by adding an aqueous solution of magnesium citrate after adding an aqueous solution of chloroauric acid, gold can be supported in a highly dispersed state on a composite oxide of titanium and zirconium.

[0024]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples. (Catalyst Production Example 1) Titanyl sulfate (TiOSO ₄ ) aqueous solution (TiO ₂ content: 5.6 wt%) in 100 liters of water
50 kg, zirconyl nitrate (ZrO (NO ₃ ) ₂ ) aqueous solution (Z
An rO ₂ content of 18.0 wt%) (30.7 kg) was added and the mixture was stirred well. While stirring, ammonia water was gradually added dropwise until the pH reached 9, and then the mixture was stirred for 3 hours and left for 15 hours. The gel thus obtained was separated by filtration, washed with water, dried at 120 ° C. for 16 hours, calcined at 700 ° C. for 3 hours in an air atmosphere, and further pulverized to obtain a powder. The resulting powder weighs 13.9 kg and contains TiO ₂ : ZrO ₂
= 7: 3 (molar ratio) was a composite oxide of titanium and zirconium.

6 kg of the above powder was put into 45 liters of a 0.2 M aqueous solution of sodium carbonate. To this solution, 431.6 g of an aqueous solution of chloroauric acid (13.9% containing Au) and 280 g of magnesium citrate were added, and Au was deposited on the powder.
Aging was performed for about 2 hours. During the precipitation and ripening, the temperature of the solution was maintained at 50 to 70 ° C., and sufficient stirring was performed. The pH of this solution after aging was 10.0.
The powder supporting gold in this manner was separated by filtration, washed with water, dried at 120 ° C. for 16 hours, and then calcined at 500 ° C. for 3 hours in an air atmosphere.

6 kg of the powder obtained by baking in this manner, 1.8 kg of water and 120 kg of starch were added, mixed and kneaded well in a kneader. This is 5mm in diameter,
Extruded into 6 mm long cylindrical pellets,
After drying at 12 ° C. for 12 hours, baking was performed at 500 ° C. for 3 hours.
The Au catalyst support of the obtained completed catalyst had a metal loading of 10 g per liter of the catalyst, and the average particle diameter of the supported Au was 80 Å.

(Catalyst Production Example 2) A catalyst was prepared in the same manner as in Production Example 1 except that the molar ratio of Ti and Zr in the powder was changed to 1: 1. (Catalyst Production Examples 3 to 5) Catalysts were prepared in the same manner as in Production Example 1 except that the amount of gold supported was changed as shown in Table 1.

(Production Examples 6 to 7 of Catalyst) The catalyst prepared in Production Example 1 was impregnated with aqueous solutions of palladium nitrate having different concentrations, and dried at 120 ° C. for 6 hours.
Calcination was performed at 3 ° C. for 3 hours. The Pd carrying amount of the obtained completed catalyst was 6 g and 30 g as metal per liter of the catalyst, respectively.

(Catalyst Production Examples 8 to 9) In Production Example 1, the amount of gold supported was 40 g per liter of the catalyst, and each was impregnated with palladium nitrate aqueous solutions having different concentrations.
After drying at 0 ° C. for 8 hours, baking was performed at 500 ° C. for 3 hours.
The amount of Pd carried on the obtained completed catalyst was 20 g and 80 g per liter of the catalyst, respectively. The average particle size of Au was 100 Å in all cases.

(Production Example 10 of Catalyst) To 100 liters of water, 61.5 kg of an aqueous solution of zirconyl nitrate (ZrO (NO ₃ ) ₂ ) (ZrO ₂ content: 18.0 wt%) was added, and the mixture was stirred well. While stirring, ammonia water was gradually added dropwise until the pH reached 9, and then the mixture was stirred for 3 hours and left for 15 hours. The gel thus obtained was separated by filtration, washed with water, dried at 120 ° C. for 16 hours, calcined at 700 ° C. for 3 hours in an air atmosphere, and further pulverized to obtain a powder. The obtained powder weighed 11 kg and had a composition of ZrO ₂ .

10 kg of the above powder was put into 45 liters of a 0.2 M aqueous solution of sodium carbonate. To this solution, 554 g of an aqueous solution of chloroauric acid (13.9% containing Au) and 360 g of magnesium citrate were added, and Au was deposited on the powder, followed by aging for about 2 hours. During the precipitation and ripening, the temperature of the solution was kept between 50 and 70 ° C. and sufficient stirring was performed. The pH of this solution after aging was 10.0. The powder supporting gold in this manner was separated by filtration, washed with water, dried at 120 ° C. for 16 hours, and then calcined at 500 ° C. for 3 hours in an air atmosphere.

6 kg of the powder obtained by baking in this manner, 1.8 kg of water and 120 kg of starch were added, mixed and kneaded well with a kneader. This is 5mm in diameter,
Extruded into 6 mm long cylindrical pellets,
After drying at 12 ° C. for 12 hours, baking was performed at 500 ° C. for 3 hours.
The Au loading rate of the obtained completed catalyst was 10 g per liter of the catalyst, and the average particle diameter of the supported Au was 100 g.
Angstrom.

(Production Example 11 of Catalyst) In Production Example 10, titania powder 15 was used instead of zirconia powder 10 kg.
A catalyst was prepared in the same manner as in Production Example 10 except that kg was used. The Au loading of the obtained completed catalyst was 10 g per liter of the catalyst, and the average particle diameter of the supported Au was 100 angstroms.

(Comparative Production Example 1 of Catalyst) An aqueous solution of chloroplatinic acid (total content of Pt: 60 g) was added to 6 kg of the ZrO ₂ powder obtained in Production Example 10, mixed well, and dried at 120 ° C. for 16 hours. Then, firing was performed at 500 ° C. for 3 hours in an air atmosphere. 6 kg of the powder obtained by calcining in this way, 1.8 kg of water and 120 kg of starch are added and mixed.
Kneaded well with a kneader. This is 5 mm in diameter and 6 in length.
Extruded into cylindrical pellets of mm.
After drying for 2 hours, it was baked at 500 ° C. for 3 hours. The Pt carrying rate of the obtained completed catalyst was 10 g as a metal per liter of the catalyst.

(Comparative Production Example 2) In Comparative Production Example 1, titania powder 10 was used instead of zirconia powder 6 kg.
A catalyst was prepared in the same manner as in Comparative Production Example 1 except that kg was used. The Pt carrying rate of the obtained completed catalyst was 10 g per liter of the catalyst, and the average particle diameter of the carried Pt was 100 angstroms.

The compositions of the catalysts of Production Examples 1 to 11 and Comparative Production Examples 1 and 2 are summarized in Table 1.

[0037]

[Table 1]

(Examples 1 to 11) Using each of the catalysts obtained in Production Examples 1 to 11, wastewater treatment was performed by a wet oxidation method in the following manner. Stainless steel reaction tube (inner diameter 25
mm × 3.0 m) was filled with the catalyst shown in Table 2 (catalyst layer length was 1.0 m), and wastewater premixed from the lower part of the reaction tube and air having an oxygen concentration of 21% by volume were continuously supplied for 500 hours. The COD (Cr) and the total amount of nitrogen were measured at the input portion and the outlet portion of the reaction tube after the introduction, and the removal rate at the initial stage and after the reaction for 500 hours was determined. The reaction conditions, properties of the wastewater, the space velocity of the wastewater (based on the empty tower), and the space velocity of the air (based on the empty tower, standard state) are as shown in Table 2.

(Comparative Examples 1-2) In Example 1, Comparative Example 1 shown in Table 2 was used instead of the catalyst obtained in Example 1.
Wastewater treatment was performed in the same manner as in Example 1 except that the catalysts obtained in Steps 2 and 3 were used. Table 2 shows the results at the initial stage and after the reaction for 500 hours.

[0040]

[Table 2]

[0041]

According to the wastewater treatment method of the present invention, wastewater containing a nitrogen-containing compound can be treated efficiently, durably, and in a manner that can be industrially established.

Continuation of the front page (72) Inventor Kunio Sano 992, Nishioki, Okihama-shi, Abashiri-ku, Himeji-shi, Hyogo Pref. Nippon Shokubai Catalysis Research Laboratories (56) References JP-A-3-97623 (JP, A) 83513 (JP, A) JP-A-63-252908 (JP, A) JP-B-3-66018 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/74 B01J 23 / 52

Claims (1)

(57) [Claims] An average particle diameter of 40 to 150 Å
Gold, or the gold and palladium are fire resistant
A method for treating wastewater comprising oxidizing wastewater containing a nitrogen-containing compound in the presence of molecular oxygen while maintaining a liquid phase, using a catalyst supported on an inorganic oxide .