JPH02203923A - Catalystic reduction of nitrogen oxide - Google Patents

Abstract

PURPOSE:To improve the safety of chemical agent in the handling and transport thereof and to effectively reduce nitrogen oxide by using an ammonium salt or an amine compound as a reducing agent to selictively reduce nitrogen oxide in the presence of a catalyst. CONSTITUTION:Exhaust gas containing nitrogen oxide is subjected to reducing treatment using an ammonium salt or an amine compound as a reducing agent in the presence of a catalyst to selectively reduce nitrogen oxide. As the catalyst, a carrier support type, non-support type or Raney type dentration catalyst can be used but one prepared by supporting metal oxide such as V2O5 by anatase type titania is pref. As an embodiment of the ammonium salt being the reducing agent, there are ammonium carbonate, ammonium hydrogen carbonate and ammonium acetate and, as an embodiment of the amino compound, there is urea or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for selectively catalytically reducing nitrogen oxides (hereinafter referred to as NOx) in exhaust gas using a reducing agent in the presence of a catalyst. Relating to improvements in reducing agents.

PRIOR ART AND THEIR PROBLEMS Many proposals have already been made for the treatment of NOx in exhaust gas. Among them, NOx is reduced by using NH3 as a reducing agent and operating at a predetermined temperature in the presence of a catalyst.
The so-called catalytic reduction denitrification method, which reduces and renders the exhaust gas harmless, is an effective method as an exhaust gas denitrification process because the above reaction proceeds selectively even if oxygen coexists in the exhaust gas.

However, the N used as a reducing agent in this denitrification method
H3 is designated as a poisonous substance, a deleterious substance, a malodorous substance, etc. under various laws and regulations, and special care must be taken when handling, transporting, storing, etc. Therefore, a handler with specialized knowledge of NH3 and special equipment to ensure safety are required, making the use of this reducing agent impractical.

In view of the above-mentioned circumstances, an object of the present invention is to provide a denitrification method that uses a compound as a reducing agent that poses no safety problems in handling, transportation, storage, etc.

A method for catalytic reduction of NOx according to the present invention is characterized in that an ammonium salt or an amine compound is used as a reducing agent in selectively reducing nitrogen oxides with a reducing agent in the presence of a catalyst. .

As the catalyst, known denitrification catalysts such as carrier-supported, non-supported, and Raney-type catalysts can be used, but in particular, anatase-type titania supported with a metal oxide such as V205 exhibits excellent denitrification performance.

Examples of ammonium salts as reducing agents include ammonium carbonate, ammonium bicarbonate, ammonium formate,
Examples include ammonium acetate. Moreover, urea is mentioned as an example of an amino compound.

The ammonium compound and the amine compound may be injected directly into the exhaust gas in the form of a powder or in the form of a solution. Alternatively, these may be decomposed and gasified in advance, and the resulting decomposed gas may be injected into the exhaust gas.

Example Next, the present invention will be specifically explained using examples.

First, a Ti-V catalyst was prepared by the following operation.

A required amount of β-titanic acid was calcined at 400° C. for 5 hours to obtain titanium oxide, which was crushed to 21 particles in size. This crushed material was added to a saturated aqueous solution of ammonium metavanadate at room temperature for 3 hours.
It was soaked for an hour, dried at 120°C, and fired at 400°C for 3 hours. In the obtained catalyst, the vanadium loading rate was 4% by weight.

Next, using the above catalyst, the NOx reaction rate was measured for each reducing agent shown in Table 2.

That is, a cylindrical quartz reaction tube with a diameter of 30 ml was filled with 2.25111 parts of the above catalyst, and a prepared exhaust gas for testing having the composition shown in Table 1 was poured into the reaction tube while controlling the temperature in a normal flow system. Flow rate 1. 51/min (0℃
, 1 atm). In this state, as a reducing agent Table 2
Aqueous solutions of various compounds shown in the figure were injected into the top of the reaction tube in an amount of 1.2 mol 1 mol (NH2+NH4/NO ratio) to carry out a denitrification reaction.

For each reducing agent, the temperature is 200℃, 250℃, 300℃
, the NOx reaction rate at 350°C and 400°C was determined. The results are shown in Table 2.

table (Margin below) table Hayashi Ammonia gas at NH3/No ratio of 1° It was mixed into the flue gas prepared in step 2.

As is clear from Table 2, even when an ammonium salt or an amine compound was used as the reducing agent, a high reaction rate comparable to that when ammonia gas was used was obtained.

Effects of the Invention Since the NOx catalytic reduction method of this invention uses an ammonium salt or an amine compound as a reducing agent, it does not solve the problems caused by the use of ammonia gas as mentioned at the beginning of this book, namely, the handling, transportation, and storage of chemicals. It is possible to solve the problem of the need for specialized operators and special equipment to ensure safety due to the danger involved in such operations.

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Claims (1)

[Claims] A method for catalytic reduction of nitrogen oxides, which comprises using an ammonium salt or an amine compound as a reducing agent in selectively reducing nitrogen oxides with a reducing agent in the presence of a catalyst.