JPS58119347A - Slurry for preparing catalyst - Google Patents

Abstract

PURPOSE:To effectively suppress the change with the passage of time in viscosity, by containing oxalic acid in a TiO2 powder, NH4VO3 and colloidal silica as a slurry for preparing denitration catalyst. CONSTITUTION:Suitable components of a slurry are a TiO2 powder, NH4VO3 and colloidal silica and, hydrolysis of NH4VO3 shown by formula 1 is caused to change the pH value of the slurry to an alkaline side to cause the change of viscosity with the passage of time by the adsorption of VO3<-> by the surface of TiO2. Therefore, when oxalic acid is added to these components to neutralize the pH value, the change in the viscosity of the slurry can be suppressed. In this case, the content of oxalic acid is adjusted to an amount required in the reaction shown by formula 2.

Description

[Detailed Description of the Invention] This invention deals with nitrogen oxides (hereinafter referred to as NOx) in flue gas.
The present invention relates to a denitrification catalyst that is subjected to a reaction of selectively reducing NHa with NHa, and particularly to a slurry for preparing the catalyst.

NOx emitted from power plants, sintering furnaces, various chemical factories, automobiles, etc. is a substance that causes photochemical smog, so an effective treatment method is desired.Many NOx treatment methods have been proposed in the past. Among them, the catalytic reduction method of NOx using NH3 as a reducing agent requires less reducing agent because NH3 selectively reacts with NOx even if the flue gas contains more than 1 volume of oxygen. This is considered an advantageous method.

By the way, you need to find ways to avoid NOx removal from catfish, which requires NOx treatment. One of the ways to do this is to create wire meshes of various shapes, such as flat wire meshes curved or bent into corrugated, zigzag, or pleated shapes, and even combinations of these curved or bent wire meshes and flat wire meshes. One method has been proposed in which a slurry containing a catalyst substance is applied and solidified, and the catalyst substance is held in a wire mesh (see Japanese Patent Laid-Open No. 8874/1987). . A typical catalyst material used here is a V2O5-Ti0z system that exhibits high activity even in exhaust gas containing sulfur oxides.

The slurry for applying and retaining the catalyst substance on the wire mesh is preferably made of colloidal silica from the viewpoint of reinforcing the coating film. In addition, to effectively support V2O5 in the porous TiO2 powder, soluble vanadium salts, especially water-soluble and non-corrosive NH, sVO
3 is preferably used (N a V O3 or KVO
Although a and the like are water-soluble, they are preferred because alkali metals act as catalyst poisons.For this reason, preferred components of the slurry are TiO2 powder, NH4VO3, and colloidal silica. However, it is not satisfactory in terms of coating work. Therefore, it is necessary to stabilize the viscosity of the slurry to prevent such changes in viscosity over time. Generally, the change in viscosity of a slurry is related to the pH value. The change in viscosity of the slurry is also considered to be a factor.

In other words, in order to adsorb VO3- to the TiQ2 surface, NH4VO3+H20-+ NH40H-1-HVO
3 @ @ 11 (Hydrolysis of NH4VO3 as shown in 11 occurs, resulting in a change in pH value to the alkaline side, which is thought to be the cause of changes in viscosity over time.) By neutralizing with acid, slurry It is considered that the acid should be non-corrosive, do not insolubilize NH4VO3, and be easily decomposed by heating.

This invention was made in view of the above-mentioned circumstances, and an object thereof is to provide an acid-containing slurry that meets the above-mentioned needs.

The slurry according to this invention consists of TiO2 powder and NH4VO
This is a slurry for catalyst preparation consisting of No. 3, colloidal silica, and sulfuric acid.

The content of oxalic acid is 2NH4VO3+ 7H2C204 →2VOC204+(NH4) 2C204+8CO2
+4H20@@11 (The amount necessary for the reaction shown in 21 is sufficient, but in reality, the NI produced by the above formula (1)
(The amount required to neutralize 40H is sufficient. NH4O
Since the amount of H produced depends on the VO3-adsorption capacity of the TiO2 powder, the required amount of oxalic acid also depends on the VOa-adsorption capacity of the TiO2 powder. The specific surface area of porous TiO2 powder is 100
m/7, the content of oxalic acid is NH4V
The amount is about 40 parts by weight or more based on 100 parts by weight of O3. The optimum content is about 50 parts by weight.

Since the slurry for catalyst preparation according to the present invention contains oxalic acid as described above, it is possible to effectively suppress changes in viscosity over time.

Example 1 TiO2 powder (specific surface area: l20rrvF) passed through a 100-mesh sieve. 10 weight of acid is shaken over a mixture of IOO and 100 parts by weight of commercially available colloidal silica (20 parts by weight as Si02). of NH4VO31Q and stirred the mixture well.
4 parts by weight were added to form a slurry. Then, the viscosity of the slurry was measured at appropriate times while stirring. Viscosity is measured using a single cylinder rotational viscometer (CONTRAVES@A
G@ZURICH-RM・15D).

Example 2.3 The operation of Example 1 was repeated using 6 parts by weight and 4 parts by weight of oxalic acid, respectively.

Comparative Examples 1 to 3 The operation of Example J was repeated by changing the amount of oxalic acid added to 3 parts by weight, 2 parts by weight, and 0 parts by weight, respectively.

The viscosity measured in Examples 1 to 3 and Comparative Examples 1 to 3 is shown in the drawing. As can be seen from the figure, the slurries obtained in each example show almost no change in viscosity over time.

[Brief explanation of the drawing]

The drawing is a graph showing changes in viscosity over time. that's all Patent applicant: Hitachi Zosen Corporation

Claims (1)

[Claims] A slurry for catalyst preparation comprising 111Ti02 powder, NH4VO3, colloidal silica, and citric acid. (2) The slurry according to claim 1, wherein the content of oxalic acid is 40 parts by weight or more based on 100 parts by weight of NH4VO3.