JPH1099876A - Treatment of wastewater containing organic matter - Google Patents

Abstract

(57) Abstract: A method for wet-oxidizing organic-containing wastewater under a pressure at which the wastewater maintains a liquid phase in the presence of a solid catalyst,
By using a solid catalyst having high activity and high mechanical strength, a processing method with high efficiency and low running cost is provided. SOLUTION: The titania having an anatase type crystal structure supporting ruthenium has a main peak and a sub-peak lower than the main particle in the pore diameter distribution of the pore diameter of the titania and the pore volume with respect to the titania, and In the presence of a solid catalyst having a subpeak on the side where the pore diameter is larger than the peak, the organic-containing wastewater is subjected to wet oxidation treatment under a pressure at which the wastewater maintains a liquid phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for wet-oxidizing organic wastewater in the presence of a solid catalyst. More specifically, organic substances in wastewater can be efficiently converted into carbon dioxide, water,
The present invention relates to a method for wet-oxidizing organic-containing wastewater in the presence of a solid catalyst that can be converted to nitrogen or the like and can withstand use under high-temperature and high-pressure conditions.

[0002]

2. Description of the Related Art Generally, a biological method and a submerged combustion method are widely known as methods for treating organic-containing wastewater.

Although the biological method is an effective method for treating low-concentration wastewater, the treatment of high-concentration organic wastewater such as industrial wastewater requires dilution of the wastewater in order to suppress adverse effects on microorganisms. Since an operation such as pH adjustment is required, it cannot be said that the method is highly versatile. In addition, since this method involves the generation of excess sludge, there is also a problem that if the load of the wastewater treatment increases, the secondary treatment cost is required, and the entire wastewater treatment cost is increased.

[0004] The submerged combustion method is a method of injecting organic matter-containing wastewater into a flame to oxidize and decompose organic matter at high temperatures. However, it consumes a large amount of fuel and has a high running cost. Has become.

[0005] As a method widely used in sewage treatment, there is a wet oxidation method (Zimmerman method).
Although this method completely decomposes organic and inorganic substances in wastewater by air oxidation, it requires high-temperature, high-pressure reaction conditions, and requires the use of expensive corrosion-resistant and expensive materials for treatment equipment. is there. Further, there is a problem that the decomposition efficiency of the compound containing a nitrogen atom is low, and the wastewater that can be treated is limited to wastewater having a low content of the compound containing a nitrogen atom.

For this reason, a method using various catalysts has been proposed for the purpose of improving the treatment efficiency in the wet oxidation method. Among them, the wet oxidation method using a solid catalyst has attracted particular attention in recent years because of its high wastewater purification ability and excellent economic efficiency. As a proposed catalyst, ruthenium, noble metals such as palladium, alumina,
Examples thereof include catalysts supported on carriers such as silica gel and activated carbon (JP-A-49-44556, JP-A-49-94).
157 publication).

[0007] In addition, a method using titania or zirconia as a carrier has been proposed (Japanese Patent Laid-Open No. 58-1983).
-64188). According to this method, it is described that alkaline wastewater can be treated in a neutral region, and reduction in catalyst strength and crushing and pulverization are suppressed. However, these catalysts were not sufficiently satisfactory in catalytic activity and catalytic strength.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present inventors
As a result of intensive research on catalysts with high activity and high mechanical strength, we found that a catalyst using titania having a specific pore structure as a carrier and ruthenium supported as an active component on the carrier solves the problem. The invention has been completed.

[0009]

SUMMARY OF THE INVENTION The present invention provides a method for wet-oxidizing organic-containing wastewater at a pressure at which the wastewater maintains a liquid phase in the presence of a solid catalyst, the solid catalyst comprising a ruthenium-supported anatase crystal structure. Having a main peak and a lower sub-peak in the pore diameter distribution of the pore diameter of the titania and the pore volume with respect to the titania, and a sub-peak on the side where the pore diameter is larger than the main peak. A method for treating organic matter-containing wastewater, characterized in that:

In the present invention, titania having an anatase crystal structure, which is an inorganic metal oxide, is used as a carrier of the catalyst.

In general, a molded product of an inorganic metal oxide used as a carrier for a catalyst is produced using fine primary particle powder as a raw material in order to increase the specific surface area. It tends to be smaller. In addition, in order to obtain an optimum pore structure for the substrate to be reacted, the pore diameter distribution is often sharpened. However, in the case of a reaction in which organic substances are decomposed to generate a gas such as carbon dioxide gas or nitrogen as in the wet oxidation reaction of the present invention, if the pore diameter is too small, the gas generated inside the catalyst cannot efficiently go out of the catalyst. Therefore, there is a problem that the pressure in the pores increases and the catalyst is destroyed. As a solution to such a problem, there is a method of supporting a catalyst metal on a support calcined at a high temperature in order to increase the strength of a molded catalyst. However, in this method, since the specific surface area of the support is extremely small, it is difficult to support the catalyst metal in a dispersed state that can sufficiently exhibit the reaction activity. In order to solve such a problem, it is necessary to use a carrier having an appropriate specific surface area for catalysis and having a pore size distribution such that generated gas is quickly exhausted to the outside of the catalyst.

The pore size distribution of the titania used in the present invention is such that the pore size distribution of the pore size of the titania and the pore volume corresponding thereto has a main peak and a sub-peak lower than the main peak, and the pore size is smaller than the main peak. It is necessary that there is a sub-peak on the side where is larger.

The pore size distribution is measured by changing the pressure in a relative pressure range of 0.01 to 0.97 using a surface area measuring device under the conditions of nitrogen gas as the adsorbing gas and the boiling point of liquid nitrogen as the measuring temperature. The adsorption isotherm data was obtained by measuring the amount of gas adsorbed on the catalyst, and was calculated from the data.

In the pore size distribution of titania used in the present invention, it is preferable that a main peak exists at 50 to 300 angstroms and a subpeak exists at 400 to 8000 angstroms. If the sub-peak does not exist, the catalyst is destroyed when gas is generated in the catalyst, which is not preferable.

Further, the pore volume of titania is from 0.2 to
It is preferably in the range of 0.5 cc / g. If the pore volume is less than 0.2 cc / g, the activity is reduced due to a decrease in the degree of dispersion of ruthenium, which is not preferable. On the other hand, if the pore volume exceeds 0.5 cc / g, the mechanical strength of the catalyst is undesirably reduced.

The titania used in the present invention needs to have an anatase type crystal structure which is chemically stable and has a large specific surface area.

The shape of titania is not particularly limited, but is preferably a high-strength spherical or granular shape. The average particle size of titania is preferably 1 to 8 mm, and 2 to 5 mm.
Is more preferred. If the particle size is less than 1 mm, it is difficult to maintain the initial strength of the catalyst, and the pressure loss increases, which is not preferable because the solid content of the wastewater may be clogged. On the other hand, when the particle size exceeds 8 mm, the geometrical surface area of the catalyst itself is not ensured, so that the catalytic activity is undesirably reduced.

The amount of ruthenium metal supported on titania is preferably 0.1 to 10% by weight based on the amount of the catalyst. If the content of ruthenium metal is less than 0.1% by weight or more than 10% by weight, the total surface area of ruthenium effective for the reaction is decreased, which is not preferable because the catalytic activity is reduced.

The ruthenium compound used in the preparation of the catalyst of the present invention is not particularly limited. For example, ruthenium chloride hydrate, ruthenium bromide hydrate, ruthenium oxide hydrate, hexaammine ruthenium chloride, odor Hexaammine ruthenium bromide, sodium ruthenium (VI) acid,
Potassium ruthenate (VI), potassium perruthenate, sodium perruthenate and the like.

The catalyst can be easily prepared by a generally known method. That is, it can be prepared by supporting a ruthenium compound on a carrier by an impregnation method, a water absorption method, a drying method, or the like, and then performing reduction with hydrogen or chemical reduction with sodium borohydride, hydrazine, formic acid, or the like.

The present invention relates to wastewater containing cyanide, wastewater containing phenol, wastewater containing oil, wastewater from the organic polymerization step, wastewater from dyestuffs, other chemical factory wastewater, food factory wastewater, general industrial wastewater, and human waste discharged from general households. Applicable for sewage.

The organic matter in the wastewater is not particularly limited. It is possible to decompose from relatively easily decomposable organic substances such as formic acid and formaldehyde to hardly decomposable organic substances such as acetic acid and terephthalic acid.

The concentration of organic matter in the wastewater is not particularly limited, but is preferably in the range of 0.01 to 20% by weight, and more preferably in the range of 0.1 to 10% by weight, based on the entire wastewater. Is more preferred. Organic matter concentration is 20% by weight
Exceeding the range is not preferred because excessive heat of reaction formation is generated and it becomes difficult to control the reaction temperature.

The reaction temperature of the wet oxidation reaction carried out in the present invention is preferably from 200 to 250 ° C. in the case of oxygen-free heat treatment and from 150 to 250 ° C. in the case of oxygen-containing heat treatment.

In the case of oxygen-free heat treatment, it is preferable to carry out the reaction at a pressure higher than the saturated vapor pressure. Is increased, and the reaction is promoted.

As the oxygen-containing gas used in the aerobic heat treatment, any of air, pure oxygen, and oxygen-enriched air can be used, but air is preferably used in view of economic efficiency.

The amount of oxygen-containing gas is desirably 0.1 to 1.5 times the theoretical amount of oxygen necessary for oxidatively decomposing organic substances. The pH of the reaction system may be either acidic or alkaline.

[0028]

Next, the present invention will be described specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Catalyst Preparation Example 1] 100 g of titania spherical carrier having a compressive strength of 2.7 kg, a main peak of pore size distribution at 140 Å and a subpeak of pore size distribution at 500 Å, containing 2.0 g as Ru atoms. An aqueous solution of RuCl ₃ was absorbed and dried at 110 ° C. for 16 hours. Next, an aqueous solution 42 containing 5.4 g of NaOH dissolved therein.
and immersed in the solution for 3 hours. Next, hydrazine hydrate was added for reduction, followed by washing with warm pure water and drying at 110 ° C. for 16 hours to obtain a 2% Ru / titania catalyst (hereinafter referred to as A-1). Table 1 shows the destruction rate and strength of this catalyst after the destruction test.

[Catalyst Preparation Example 2] A 2% Ru / titania catalyst was prepared in the same manner as in Catalyst Preparation Example 1 except that a titania spherical carrier having a compressive strength of 1.8 kg and a peak in the pore diameter distribution of only 85 Å was used. A-2). Table 1 shows the destruction rate and strength of this catalyst after the destruction test.

[0031]

[Table 1]

The destruction rate in Table 1 was determined by immersing the catalyst in a wastewater containing formic acid, formaldehyde and acetic acid in an autoclave and filling with air at 70 kg / cm ² G.
Represents the percentage of destroyed catalyst after holding at 50 ° C. for 2 hours. The compressive strength in Table 1 indicates the load at which the catalyst broke when a load was applied to the catalyst.

Example 1 Internal volume 500 equipped with a stirrer
The catalyst (A-1) prepared in Catalyst Preparation Example 1 and a total organic carbon concentration containing formic acid, formaldehyde and acetic acid of 47,840 were placed in a mL titanium-lined autoclave.
100 g of waste water of ppm was charged and the temperature was raised to 150 ° C.
At this time, the internal pressure of the autoclave became 3 kg / cm ² G. Subsequently, the internal pressure of the autoclave was increased to 15 kg / cm ² G.
Air is introduced until stirring speed reaches 1000 rpm.
The reaction was carried out for 1 hour under the reaction conditions shown in Table 2 while stirring at m. After the reaction was completed, the reaction solution was cooled to room temperature, the treated water was taken out, and each component in the wastewater was quantitatively analyzed by gas chromatography and isotachophoresis. The results were as described in Table 2.

Embodiment 2 3B × 1.1mSUS316
In a tubular flow reactor made of L, 5 kg of the catalyst prepared in Catalyst Preparation Example 1 was charged, and wastewater having a total organic carbon concentration of 47,840 ppm containing formic acid, formaldehyde, acetic acid, and methanol heated to 180 ° C. Is the weight space velocity (hereinafter W
HSV (abbreviated HSV) at 2 hr ^-1 . 0
Air was introduced into the reactor at a flow rate of 4 l / min converted to 1 ° C. and 1 atm, and a continuous reaction was performed under the reaction conditions shown in Table 2. The treated water was continuously taken out and quantitatively analyzed for each component in the wastewater by gas chromatography and isotachophoresis. The results were as described in Table 2.

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that the catalyst (A-2) prepared in Catalyst Preparation Example 2 was used and the reaction conditions shown in Table 2 were used. Each component in the wastewater was quantitatively analyzed by gas chromatography and isotachophoresis. The results were as described in Table 2.

Comparative Example 2 A reaction was carried out in the same manner as in Example 2 except that the catalyst (A-2) prepared in Catalyst Preparation Example 2 was used and the reaction conditions shown in Table 2 were used. Each component in the wastewater was quantitatively analyzed by gas chromatography and isotachophoresis. The results were as described in Table 2.

[0037]

[Table 2]

[0038]

According to the present invention, the use of the titania catalyst having a specific pore size distribution supporting ruthenium of the present invention improves the mechanical strength of the catalyst, enables efficient wet oxidation treatment of organic-containing wastewater, and further improves wastewater treatment. Processing equipment investment and running costs can be significantly reduced.

Claims (4)

[Claims] 1. A method for wet-oxidizing organic-containing wastewater under a pressure at which the wastewater maintains a liquid phase in the presence of a solid catalyst, wherein the solid catalyst is titania having a ruthenium-supported anatase-type crystal structure, Organic substance-containing wastewater having a main peak and a sub-peak lower than the main particle in the pore diameter distribution of the pore diameter of titania and the pore volume with respect thereto, and having a sub-peak on the side where the pore diameter is larger than the main peak. Processing method. 2. The method according to claim 1, wherein the main peak is in the range of 50 to 300 angstroms and the sub peak is in the range of 400 to 8000 angstroms. 3. The method according to claim 1, wherein the amount of the supported ruthenium is 0.1 to 10% by weight based on the weight of the solid catalyst. 4. The method according to claim 1, wherein the average particle size of the titania is 1 to 8 mm.