KR100423413B1 - A chromia/titania catalyst for removing dioxins and a method of removing dioxins by usint the same - Google Patents

Abstract

The present invention relates to a chromia / titania catalyst for dioxin removal and a dioxin removal method using the same,

Chromia / titania catalyst for dioxin removal, on which 1 to 50% by weight of chromium oxide is supported on a titania carrier, and

Provided is a method for oxidizing and removing dioxins by passing a dioxin-containing waste gas to be treated at a dioxin removal chromia / titania catalyst at a temperature of 200 ° C. or higher at a space velocity of 5,000 hr ⁻¹ or less.

According to the present invention, dioxins contained in the waste gas and the like can be more efficiently removed by using a catalyst in which chromium oxide is supported on titania.

Description

Chromaia / Titania catalyst for dioxin removal and dioxin removal method using the same {A CHROMIA ／ TITANIA CATALYST FOR REMOVING DIOXINS AND A METHOD OF REMOVING DIOXINS BY USINT THE SAME}

The present invention relates to a chromia / titania catalyst for dioxin removal and a dioxin removal method using the same. More particularly, a catalyst in which chromium oxide is supported on a titania carrier and a method for effectively removing dioxin contained in waste gas using the same. It is about.

Dioxin is the generic name for 75 isomers (Polychlorinated Dibenzo-p-Dioxines, PCDDs) and 135 kinds of isomers (Polychlorinated Dibenzo Furans, PCDFs). Although they have different properties depending on the number or location, they are generally referred to as dioxins.

Since the dioxins are fat-soluble and insoluble in water, and very difficult to disintegrate microorganisms, they are hardly decomposed in the natural world, and their toxicity is substantially almost permanent, which is known as a serious environmental pollutant.

A total of 210 dioxins isomers all have similar physical and chemical properties but differ in their toxicity. Among the most toxic compounds known to be 2,3,7,8-TCDD with 4 chlorine substitutions, in some countries, the 2,3,7,8-TCDD was used to assess the risk of dioxins. The relative toxicity of various types of dioxins is calculated and its value is set as TEF (Toxidity Equivalency Factors). It is common to express the concentration of dioxins using the following concept of TEQ (Toxic Equivalents).

.

The main sources of dioxins vary from country to country, but can be broadly divided into chemical production, incineration, and thermal processes. Dioxins may be produced as by-products during the production and use of chlorine organic chemicals, and dioxins may also be contained in the produced chlorine organic chemicals. All thermal processes, including incineration, are also important sources of chlorophenol and its derivatives, which can lead to the generation of dioxins.

Therefore, various methods have been developed to remove dioxins contained in waste gases such as incinerators. Representative methods include adsorption and removal of dioxins with an adsorbent such as activated carbon, and methods of decomposing and removing dioxins by oxidation by a catalyst.

The adsorption method using the activated carbon is a widely used method, but the adsorption capacity is greatly affected by other components such as water contained in the waste gas, and there is a problem in that the adsorbents containing dioxins must be treated after the adsorption is completed. Therefore, the oxidation process using a catalyst has been attracting attention as a dioxin removal method.

Here, the method of completely decomposing dioxins using a catalyst is to remove dioxins into CO ₂ and H ₂ O, and HCl or Cl ₂ by oxidative reaction with oxygen present in the waste gas by flowing a dioxin-containing gas into the catalyst layer. It is a way.

As a catalyst used to remove dioxins by an oxidation method using a catalyst, generally, a V ₂ O ₅ -WO ₃ -TiO ₂ based catalyst which removes nitrogen oxides in waste gas by using a reducing agent such as ammonia is widely used. In the well-known document "Chemosphere", Vol. 26, No. 12, pp. 2167-2172, 1993, the temperature of 200-350 ° C. is used when V ₂ O ₅ -WO ₃ -TiO ₂ -based catalyst is used to remove NOx. It is disclosed that dioxins can be removed in the range. In addition, Japanese Patent No. 95-75720 discloses that dioxins are removed in a temperature range of 200 to 250 ° C using a catalyst composed of V ₂ O ₅ -WO ₃ -TiO ₂ .

On the other hand, US Patent No. 5,254,794 discloses the removal of dioxins using a catalyst supporting a precious metal such as Pt on a carrier made of TiO ₂ , SiO ₂ , ZrO ₂ , and the like. In Japanese Patent No. 95-163877 and European Patent 0,645,172 A1, a catalyst having two metals such as Pt and Au is used on a carrier made of SiO ₂ -B ₂ O ₃ -Al ₂ O ₃ . _It is disclosed that the performance is much higher than that of a catalyst supported by 2O ₅ -WO ₃ -TiO ₂ or Pt supported on TiO ₂ .

However, since these V ₂ O ₅ -WO ₃ -TiO ₂ catalysts and precious metal supported catalysts are very expensive, there is still a need for a catalyst that is more economical and shows excellent performance in dioxin removal.

Accordingly, an object of the present invention is to provide a catalyst in which chromium oxide is supported on a titania carrier which is cheaper than a conventional V ₂ O ₅ -WO ₃ -TiO ₂ catalyst or a precious metal supported catalyst and exhibits excellent performance in removing dioxins.

Another object of the present invention is to provide a method for effectively removing dioxins contained in waste gas by using a catalyst in which chromium oxide is supported on a titania carrier.

1 is a graph showing the dioxin removal rate according to the reaction temperature when using the chromia / titania catalyst by the method of the present invention,

Figure 2 is a graph showing the dioxin removal rate according to the space velocity when using the chromia / titania catalyst by the method of the present invention.

According to one aspect of the invention,

There is provided a chromia / titania catalyst for dioxin removal, carrying 1 to 50% by weight of chromium oxide, based on the total weight of the catalyst on a titania carrier.

According to the second aspect of the present invention,

Provided is a method for oxidizing and removing dioxins by passing a dioxin-containing waste gas to be treated to the dioxin removing chromia / titania catalyst of the first aspect under an oxidation atmosphere of 200 ° C. or higher at a space velocity of 5,000 hr ⁻¹ or less.

Hereinafter, the present invention will be described in detail.

In order to remove dioxins contained in the waste gas and the like, first, a catalyst having 1 to 50% by weight of chromium oxide based on the total weight of the catalyst on a titania carrier is prepared.

Wherein the chromium oxide is therefore usually oxidation number trivalent Cr ₂ O ₃ and the oxidation state is 6 Cain CrO ₃ is present in a mixed form, and one or all of the both can be used, the higher the hexavalent ratio higher catalytic activity as CrO ₃ form It is more preferable that the ratio of is high.

The supported amount of chromium oxide is 1 to 50% by weight, preferably 5 to 40% by weight based on the total weight of the catalyst. If the content of chromium oxide is too low, the effect of chromium oxide is low and the catalytic activity is low. If the content of chromium oxide is more than 50% by weight, chromium oxide does not disperse well on the surface of the catalyst.

The type of catalyst used for removing dioxins using the catalyst prepared as described above is not particularly limited, but may be used in the form of a fine powder or pellet, or the catalyst may be coated on a filter or a honeycomb reactor or directly molded into a honeycomb reactor. have.

Such chromia / titania catalysts are used to remove dioxins in waste gas. At this time, the chromia / titania catalyst oxidizes dioxin by passing a dioxin-containing waste gas under an oxidation atmosphere of 200 ° C. or higher. At temperatures below 200 ° C., the activity of the catalyst is reduced and therefore not effective.

As such, when the dioxin-containing waste gas to be treated at a temperature of 200 ° C. or more is passed, dioxin is decomposed and removed by an oxidation reaction such as the following Formulas 1 to 2. In this case, the space velocity is preferably about 5,000hr ⁻¹ at maximum so that the removal efficiency of dioxins is about 99%.

(PCDDs) + O ₂ → CO ₂ + H ₂ O + HCl or Cl ₂

(PCDFs) + O ₂ → CO ₂ + H ₂ O + HCl or Cl ₂

Hereinafter, the present invention will be described in detail through examples.

<Example>

The following examples further illustrate various aspects of the invention and do not limit the scope thereof.

Example 1: Removal rate of chlorobenzene according to the amount of chromium oxide supported

1.3 g of Cr (NO ₃ ) ₃ 9H ₂ O was dissolved in distilled water and then mixed well with 50 g of titania dried at 110 ° C. The slurry solution was completely dried by heating, then completely dried again in a 110 ° C. drier, and calcined in air at 450 ° C. to prepare a catalyst having 1% of chromium oxide based on the total weight of the catalyst.

In a similar manner, catalysts were prepared in which the chromium oxide was 5, 12, 25, 40, 50% based on the total weight of the catalyst.

The catalysts prepared in this manner contained 30 ppm of chlorobenzene in air, which is similar in structure to Dioxin but more difficult to decompose, at a reaction temperature of 250 ° C. and a space velocity (flow rate / catalytic volume) of 30,000hr ⁻¹ using a fixed bed continuous flow reactor. The removed gas was used as a simulated reactant to measure the removal efficiency and the results are shown in Table 1 below.

Chromium Oxide Content (wt%) One 5 12 25 40 50 % Removal 20 71 99 99 83 52

As shown in Table 1, as the content of the chromium oxide increases, the removal rate also increases, but it can be seen that the removal rate decreases when more than 40%.

Example 2 Dioxin Removal Rate in Waste Gas According to Reaction Temperature

Water was added to powdered titania, which is a carrier, and about 10% by weight of titania was added as a binder in the form of colloidal silica.

The honeycomb reactor made of Cordierite was immersed and removed while the slurry solution was mixed well, and the titania was coated on the honeycomb surface, and then dried in a dryer.

Thus, a catalyst having Cr (NO ₃ ) ₃ supported on the surface thereof was prepared by immersing the Titania-coated honeycomb reactor in Cr (NO ₃ ) ₃ solution dissolved in water, followed by drying. The catalyst thus prepared was calcined in air at 450 ° C. and used.

The removal efficiency of dioxins present in the combustion waste gas containing 200 ppm of NOx and 1 to 3 ng / Nm³ of NOx was measured using the catalyst prepared as described above. The removal rate experiment was carried out in a pilot apparatus capable of treating about 700 Nm ³ / hr of waste gas, and the removal rate was analyzed by measuring the dioxin concentration at the catalytic reactor inlet and outlet.

The concentration of dioxins contained in the waste gas was analyzed using high resolution gas chromatography / mass spectrometer (GC / MS) after collecting waste gas, purifying and concentrating according to the method described in the domestic air pollution process test method. .

As described above, the results obtained by analyzing the dioxin concentration while varying the reaction temperature under the condition that the space velocity (flow rate / catalyst reactor volume) is 5,000hr ⁻¹ at the catalyst reactor inlet and outlet are shown in FIG. 1.

As shown in Figure 1, the removal rate of dioxins increased with increasing temperature, the efficiency was no longer improved at more than 325 ℃, it can be seen that the removal rate of dioxins reaches 99%.

Example 3 Dioxin Removal Rate According to Space Velocity

Except that the space velocity was changed at 325 ℃, the same method as in Example 2 was repeated to measure the change in dioxin removal rate, the results are shown in FIG.

As shown in Figure 2, when the space velocity is 5,000hr ^-1 or less, it can be seen that the dioxin removal rate is very excellent, about 99%.

According to the above, it is possible to more efficiently remove dioxins contained in the waste gas and the like by using a catalyst in which a suitable amount of chromium oxide is supported on titania.

Claims (2)

Chromia / Titania catalyst for dioxin removal carrying 1 to 50% by weight of chromium oxide based on the total weight of the catalyst on the titania carrier Oxidation and removal method of dioxins comprising passing a dioxin-containing waste gas to be treated to the dioxin removing chromia / titania catalyst of claim 1 at an oxidation atmosphere of 200 ° C. or higher at a space velocity of 5,000 hr ⁻¹ or less.