KR100738676B1 - Transition metal catalysts based on ceria-zirconia for wet air oxidation of refractory wastewater - Google Patents

Abstract

A catalyst in which an active metal is supported onto a ceria-zirconia solid solution having both functions of a catalyst support and an accelerator to effectively treat wastewater that is highly toxic or refractory, and a catalyst that is very efficient in the aspects of cost reduction and stability in the wet oxidation are provided. A catalyst for wet oxidation comprises a ceria-zirconia solid solution(Ce_xZr_1-xO_2) as a catalyst support, and a transition metal supported onto the support, wherein x is 0.5 to 0.65 in CexZr1-xO2. The transition metal is at least one selected from the group consisting of Mn, Fe, Co, Ni and Cu. The catalyst comprises 0.5 to 30 wt.% of the transition metal based on the catalyst weight. The catalyst is prepared by drying and firing the mixed solution supported ceria-zirconia solid solution after supporting a mixed solution of an active metal precursor and an aqueous solution or an organic solvent onto the ceria-zirconia solid solution by an incipient wetness method. The firing process is a process of performing sintering to a temperature of 400 to 500 deg.C in an air atmosphere.

Description

Transition metal catalysts based on ceria-zirconia for wet air oxidation of refractory wastewater}

1 is a preferred embodiment according to the present invention, shows a graph measuring the reaction activity in the wet oxidation of phenol according to the prepared catalyst.

Figure 2 is a preferred embodiment according to the present invention, shows a graph measuring the reaction activity in the wet oxidation of phenol according to the supported amount of the copper catalyst.

Figure 3 is a preferred embodiment according to the present invention, shows a graph measuring the reaction activity in the wet oxidation of p-chlorophenol according to the prepared catalyst.

The present invention relates to a catalyst used for wet oxidation, which is effective for the treatment of wastewater comprising compounds that are toxic or hardly degradable. More specifically, Ceria-zirconia solid solution having an excellent Oxygen Storage Capacity (OSC) is used as a catalyst carrier to increase dispersibility in activated metals, thereby improving the reaction activity against wet oxidation of hardly decomposable wastewater. will be.

In modern society, water pollution is a serious problem due to the increase of population, urbanization and development of various industries. In particular, in the case of industrial wastewater, pollutants are diversified due to the increased load of pollutants and the use of new synthetic chemicals, and pollution by hardly decomposable substances is increasing. In order to reduce the water pollution by wastewater, legal regulations are being strengthened, and in order to prepare for this, it is necessary to develop a technology capable of effectively treating wastewater, such as advanced oxidation treatment technology, in addition to the methods that have been used up to now. In particular, the development of a relatively compact compact wastewater treatment system capable of treating wastewater containing toxic or hardly degradable pollutants and high concentration wastewater should be made.

The nature and concentration of pollutants in industrial waste water depend on the raw materials used. Industrial wastewater is generally discharged at a higher temperature than domestic sewage or agricultural water. Industrial wastewater contains high concentrations of highly toxic compounds, which require special treatment for separation, modification and decomposition. Various biological, physical, and chemical treatment methods and combinations thereof are used to achieve the above objectives, but have limitations in terms of applicability, efficiency, and cost. In particular, phenols and phenolic compounds among the harmful organic compounds included in industrial wastewater have received a lot of attention for the past 20 years because they are toxic and easily pollute the water. In addition, it is used as a model compound in the advanced water treatment process because it is produced as an intermediate product in the oxidation reaction of a high molecular weight aromatic carbon compound.

Wet oxidation is a water treatment technology that oxidizes organic matter in aqueous solution by using oxygen in air as an oxidant under high temperature (125 ~ 320 ℃) and high pressure (0.5 ~ 20MPa), and oxidizable organic and inorganic substances dissolved or dispersed in liquid contaminants. It can be treated and is suitable for the treatment of wastewater which is difficult to treat biologically due to its high concentration or high toxicity. Through wet oxidation, organics in aqueous solutions are converted to carbon dioxide and other harmless end products. The higher the temperature, the better the oxidation reaction and the emissions usually contain low molecular oxygen-containing compounds. The degree of oxidation mainly depends on the temperature, the oxygen partial pressure, the residence time in the reactor, the nature of the contaminants being oxidized under the reaction conditions, and the oxidation reaction conditions depend on the purpose of the treatment (pretreatment for complete oxidation or biological treatment).

When wet oxidation is used for wastewater treatment, there are several advantages, such as water treatment by a single process, high concentration wastewater can be treated without dilution, simultaneous removal of COD, BOD and nitrogen, and color removal and sterilization can be performed simultaneously. have. In addition, the exhaust gas has the advantages of NO _x , SO _x , no odor, no sludge is produced, simple operation, stable reactor, small installation place. However, there is a problem that an expensive material that can withstand the harsh reaction conditions such as high temperature and high pressure is used. In order to reduce the overall process cost for treating hard-degradable contaminants by mitigating reaction conditions such as temperature and pressure, catalytic wet oxidation is proposed, in which a catalyst is added to the wet oxidation process to participate in the reaction. A catalyst for wet oxidation, mainly composed of complex oxides of branched transition metals or precious metals, has also been developed.

There are many conditions for a catalyst for wet oxidation, but most importantly, excellent reaction activity, resistance to fluid reaction conditions, endothelial toxicity, and low manufacturing cost.

Transition metals and precious metal catalysts are widely used for the wet oxidation of hardly degradable wastewater. However, noble metal catalysts have high production costs and instability problems with catalyst poisons. For this reason, various inexpensive metal oxide catalysts have been developed, but the metal oxide catalysts developed to date have not yet surpassed precious metal catalysts in terms of activity.

The solution to this problem is to lower the reaction temperature and pressure by improving the catalytic activity. Among the methods for improving the activity of the catalyst, there is a method of preparing a complex of metal oxides having excellent reaction activity, a method of using a catalyst carrier suitable for the reaction, or adding an accelerator. Such studies have been continuously conducted. .

Carriers in catalysts increase their surface area by providing a substrate so that metals or metal oxides can be dispersed into very small particles, and serve to prevent sintering of active ingredients and to improve thermal, hydrolysis and chemical stability. By dispersing the catalyst component evenly on the surface of the carrier, the contact efficiency with the reactants can be increased. Through this method, it is possible to maintain high catalytic activity even with a small amount of active metal and to save the production cost of the catalyst. will be. Recently, as well as the above-mentioned objectives, studies have been actively conducted to improve the surface properties of catalysts by using a material containing activated carbon having good adsorption properties or ceria having good redox properties as a carrier.

In addition, the performance of the catalyst can also be improved by the promoter. Dispersion of the active metal may be improved by the addition of an accelerator, and the overall catalytic activity may be improved by improving the reaction characteristics of the catalyst. When a metal such as cerium is added as an accelerator, the redox property of the catalyst may be improved to show improved catalytic activity in wet oxidation.

The most important part in the development of the catalyst for wet oxidation is the reaction activity and stability of the catalyst. Further, for the commercialization of the catalyst, the cost of the catalyst and the operating cost of the process are as important as catalyst activity and stability.

Accordingly, the inventors of the present invention have tried to solve the above problems, and as a result, zirconium is substituted for cerium in the fluorite structure of ceria, thereby providing a defect for the movement of oxygen in the structure, thereby providing excellent oxygen storage capacity and When preparing a catalyst supported with active metal using a ceria-zirconia solid solution having stability as a catalyst carrier, the above-described object is achieved by enabling rapid oxygen transfer in the wet oxidation of wastewater containing a highly toxic or hardly decomposable compound. It confirmed that it was possible and completed this invention.

It is a main object of the present invention to provide a catalyst in which an active metal is supported on a ceria-zirconia solid solution having both a catalyst carrier and an accelerator to effectively treat wastewater containing a toxic or hardly decomposable compound.

Another object of the present invention is to provide a catalyst which is very useful in terms of cost reduction as well as stability in wet oxidation.

In order to achieve the above object, the present invention uses a ceria-zirconia solid solution which enhances the dispersibility of an active metal and enables rapid oxygen transfer in order to improve the catalytic activity in wet oxidation. It provides a catalyst for wet oxidation, characterized in that the transition metal is supported.

The present invention provides a catalyst wherein x is 0.5 to 0.65 in the ceria-zirconia solid solution, Ce _x Zr _1-x O ₂ .

The present invention provides a catalyst in which the transition metal as the catalyst is selected from the group consisting of Mn, Fe, Co, Ni, and Cu.

The present invention provides a catalyst having a content of 0.5 wt% to 30 wt% of the transition metal used as the catalyst.

The present invention provides a catalyst that is dried and calcined after the transition metal serving as the catalyst is supported on a carrier by an incipient wetness method.

Hereinafter, the content of the present invention will be described in more detail.

In the catalyst of the present invention, a ceria-zirconia solid solution is used as a carrier, and the carrier is substituted with zirconium instead of cerium present in the fluorite structure of ceria, thereby providing a defect for the movement of oxygen in the structure, thereby providing an excellent oxygen storage capacity. And stability.

Ceria-zirconia solid solution used as a carrier in the catalyst of the present invention is oxygen through the redox process of Ce ^{4 +} / Ce ^{3 +} pair (CeO ₂ ↔ CeO _{2 -x} + x / 2O ₂ ) in the wet oxidation of hardly degradable wastewater. It is possible to exhibit improved redox properties by the release and absorption of, and to act as an accelerator as well as a catalyst carrier. In the ceria-zirconia solid solution, Ce _x Zr _{1 - x} O ₂ , x is preferably 0.5 to 0.65, more preferably 0.65.

The ceria-zirconia solid solution dissolves chloride or nitrate precursors, and more preferably nitrate precursors, to the metals of cerium and zirconium, respectively, in distilled water, and then adjusts the pH to basic conditions with aqueous ammonia and precipitates the metal hydroxide after hydrolysis. After the dehydration reaction at a high temperature can be produced through the process of producing a metal oxide finally.

The ceria-zirconia solid solution functions as a carrier of an accelerator and a catalyst in the wet oxidation of hardly decomposable wastewater, and the type of active metal which can be contained in the carrier does not require special limitation, but preferably as a transition metal, for example For example, Mn, Fe, Co, Ni, Cu and the like, there may be selected one or two or more of them. More preferably, copper (Cu) in the metal component is recommended in terms of reaction activity or economical. Therefore, in the present invention, it is most preferable that copper is used alone or copper is used as the main component.

The content of the active metal does not require a particular limitation, but generally, as the content of the catalyst increases, the reaction activity increases but the surface area and the pore volume tend to decrease, so that it may be determined in an appropriate range. The content of the catalyst is somewhat different depending on the type of specific metal, but preferably at least 0.5% by weight, more preferably 1-30% by weight, most preferably 5-10% by weight.

The catalyst for wet oxidation according to the present invention can be prepared by an incipient wetness method. After the precursor of the active metal is mixed with an aqueous solution or an organic solvent to prepare a mixed solution, the mixed solution is supported on a ceria-zirconia solid solution using an initial impregnation method.

The precursor of the active metal to be supported may be any form as long as it is well soluble in an aqueous solution or an organic solvent, and more preferably, a compound of chloride or nitrate form is used.

After being supported by the initial impregnation method, heat treatment is carried out by drying or firing to stabilize the supported active metal component. After drying for 12 to 24 hours in a vacuum oven maintained at about 80 to 150 ℃, more preferably 100 to 110 ℃, finally in the oxidizing atmosphere such as air about 100 to 600 ℃, more preferably 400 to 500 The preparation of the catalyst is completed by firing at 占 폚.

The catalyst according to the present invention showed improved reaction activity compared to a catalyst using a common carrier such as alumina or titania, and it was confirmed that copper was the best among the transition metals supported by the active ingredient.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

Example 1 Measurement of Oxygen Storage Capacity of Ceria-Zirconia Solid Solution

The oxygen storage capacity can be determined from the total amount of oxygen that can be extracted from the sample at the partial pressure and temperature of the specified reducing agent. Ceria-zirconia solid solutions having different cerium and zirconium contents were reduced at 1000 ° C. for 30 minutes while flowing H ₂ (5%) / Ar, and then cooled to 427 ° C. Oxygen was injected every 3 minutes while He was flowed at 427 ° C. to obtain a breakthrough curve. The oxygen storage capacity was calculated therefrom, and the results are shown in Table 1.

TABLE 1

Sample Total OSC (μmol-O ₂ / g) CeO ₂ 533 Ce _0.65 Zr _0.35 O ₂ 680 Ce _{0 .5} Zr _{0 .5} O ₂ 629 Ce _0.2 Zr _0.8 O ₂ 270 ZrO ₂ 0

As shown in Table 1, the oxygen storage capacity of the measured samples was the highest Ce Ce _0.65 Zr _0.35 O ₂ (680μmol-O ₂ / g) and there was no oxygen absorbed in the case of pure ZrO ₂ . When the cerium content is between 50% and 65%, the oxygen storage capacity was improved compared to pure ceria.

Example 2 Preparation of Catalyst Supported with Transition Metal in Ceria-Zirconia Solid Solution

Method for producing a catalyst for wet oxidation according to the present invention is as follows.

As a catalyst carrier, Ceria-zirconia solid solution of Ce _0.65 Zr _0.35 O ₂ , which has the best oxygen storage capacity, was used, and an initial impregnation method was used as a metal introduction method. The metal elements introduced were Mn, Fe, Co, Ni, Cu, and nitrates thereof were used as precursors. After mixing the nitrate precursor with distilled water to prepare a mixed solution, the mixed solution is introduced into a ceria-zirconia solid solution using an initial impregnation method, followed by heat treatment through drying and firing as follows to stabilize the supported active metal component. I let you. After drying for 12 hours in a vacuum oven maintained at 100 ℃, it was finally produced by firing at 500 ℃ 5 hours in an oxidizing atmosphere such as air. The metal content of the prepared catalyst was 5% by weight.

Example 3 Performance Measurement of Catalysts Prepared by Wet Oxidation of Phenols

The catalyst prepared in Example 2 was used for the wet oxidation of phenol to investigate the performance of the catalyst. The catalyst was added to the high pressure batch reactor in an amount of 3 g / L, and then 250 ml of 1,000 ppm phenol was decomposed for 3 hours at 150 ° C. and 50 atm (air). After taking samples at regular intervals, the reaction activity of the catalyst was investigated by measuring the concentration of phenol through HPLC, and the results are shown in FIG. 1.

As shown in FIG. 1, as a result of wet oxidation reaction of a phenol by a catalyst supported on a ceria-zirconia solid solution, the reaction with 45 minutes of phenol was completely removed. The catalyst also showed excellent reaction activity with a conversion of 94% after completion of the reaction for 3 hours. Nickel, cobalt and iron catalysts showed conversion rates of 69%, 53% and 45%, respectively.

[Comparative Example 1] Comparison of Catalyst Performance through Wet Oxidation of Phenol by Alumina Supported Catalyst

A catalyst was prepared using the catalyst carrier as alumina using the method of Example 2, and was subjected to wet oxidation of phenol in the same manner as in Example 3, and compared with the performance of the catalyst supported on the ceria-zirconia solid solution of the present invention. .

As a result of the wet oxidation reaction of the phenol with the catalyst supported on the alumina, the phenol was completely removed in 60 minutes when the copper catalyst was used. In the case of manganese, nickel, cobalt and iron catalysts, the conversion rates were 48%, 0.48%, 7% and 3%, respectively.

Comparative Example 2 Comparison of Catalyst Performance through Wet Oxidation of Phenol over Titania Supported Catalysts

A catalyst was prepared using the catalyst carrier as titania using the method of Example 2, and subjected to wet oxidation of phenol in the same manner as in Example 3, to compare the performance of the catalyst supported on the ceria-zirconia solid solution of the present invention. .

As a result of wet oxidation reaction of phenol by catalyst supported on titania, phenol was completely removed in 90 minutes when using copper catalyst, and 92% conversion after 3 hours was completed in the case of manganese catalyst. Seemed. Nickel, cobalt and iron catalysts showed conversion rates of 8%, 16% and 4%, respectively.

Such Example 3 and Comparative Examples 1 and 2 can be summarized as shown in Table 2 below. In the phenol conversion rate of the copper-supported catalyst of Table 2, () represents the reaction time when the phenol is completely removed.

TABLE 2

division catalyst Phenolic Conversion Rate (%) Example 3 5 wt% Mn / Ce _0.65 Zr _0.35 O ₂ 94 Comparative Example 1 5 wt% Mn / Al ₂ O ₃ 48 Comparative Example 2 5 wt% Mn / TiO ₂ 92 Example 3 5 wt% Fe / Ce _0.65 Zr _0.35 O ₂ 45 Comparative Example 1 5 wt% Fe / Al ₂ O ₃ 0.48 Comparative Example 2 5 wt% Fe / TiO ₂ 8 Example 3 5 wt% Co / Ce _0.65 Zr _0.35 O ₂ 53 Comparative Example 1 5 wt% Co / Al ₂ O ₃ 7 Comparative Example 2 5 wt% Co / TiO ₂ 16 Example 3 5 wt% Ni / Ce _0.65 Zr _0.35 O ₂ 69 Comparative Example 1 5 wt% Ni / Al ₂ O ₃ 3 Comparative Example 2 5 wt% Ni / TiO ₂ 4 Example 3 5 wt% Cu / Ce _0.65 Zr _0.35 O ₂ 100 (45 minutes) Comparative Example 1 5 wt% Cu / Al ₂ O ₃ 100 (60 minutes) Comparative Example 2 5 wt% Cu / TiO ₂ 100 (90 minutes)

As shown in Table 2, even in the case of the copper catalyst having the best decomposition activity with respect to phenol, a reaction of about 15 to 45 minutes was observed in the case of an alumina or titania carrier as compared with the case of using a ceria-zirconia solid solution as a carrier. In addition, in the case of iron, cobalt, and nickel catalyst, it was confirmed that the reaction activity is remarkably improved when using a ceria-zirconia solid solution as a carrier of the present invention.

Example 4 Measurement of Wet Oxidation Performance of Phenol by Supporting Amount of Copper Catalyst

By using the catalyst preparation method of Example 2 was prepared so that the amount of supported copper catalyst having the highest removal efficiency of phenol to 1, 5, 7, 10, 15, 20, 25% by weight, in the same manner as in Example 3 The performance of the supported amount was compared by applying the wet oxidation of phenol, and the results are shown in FIG. 2.

It was confirmed that the reaction activity of the catalyst increased until it became 10% by weight, but if it was more than that, the reaction activity decreased. This may be due to the aggregation of active metals and the reduction of the surface area of the catalyst with increasing loading. In Example 4, 10 wt% of the catalyst supporting copper was found to be the optimal supporting amount.

Example 5 Performance Measurement of Catalysts Prepared by Wet Oxidation of p-Chlorophenol

The catalyst prepared in Example 2 was used for the wet oxidation of p-chlorophenol to investigate the performance of the catalyst. Except that the reaction was p-chlorophenol, all experiments were performed under the same conditions as in Example 3. As shown in FIG. 3, p-chlorophenol was completely removed from the copper catalyst after 90 minutes of reaction, and the manganese catalyst showed 79% conversion after 3 hours of completion of the reaction. Iron, cobalt and nickel catalysts showed removal efficiencies of 14%, 22% and 27%, respectively. As with the case where the reactants are phenols, the copper catalysts showed the best catalytic activity.

As described above, the present invention may provide a catalyst for wet oxidation of wastewater containing a highly toxic or hardly decomposable compound. By using the catalyst of the present invention, it is possible to effectively remove the toxic or hardly decomposable organic matter contained in the waste water under relatively low temperature and pressure, and reduce the installation cost or operating cost of the water treatment process using the actual wet oxidation. In addition, by using rare earth metals and transition metals in the production of the catalyst, it is possible to produce a catalyst at a lower cost.

Claims (6)

A catalyst for wet oxidation, characterized in that ceria-zirconia solid solution is used as a catalyst carrier and a transition metal is supported on the carrier. The catalyst according to claim 1, wherein x is 0.5 to 0.65 in ceria-zirconia solid solution, Ce _x Zr _{1 - x} O ₂ . The catalyst according to claim 1, wherein the transition metal is selected from the group consisting of Mn, Fe, Co, Ni and Cu. The catalyst of claim 3, wherein the content of the transition metal is 0.5 wt% to 30 wt% based on the weight of the catalyst. The catalyst according to claim 1, wherein the catalyst is dried and calcined after being supported by an initial impregnation method. The catalyst of claim 5, wherein the firing is sintered at 400 to 500 ° C. under an air atmosphere.

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