DE4242978C2 - Process for the preparation of deactivated Denox catalysts containing oxides of titanium, vanadium and tungsten - Google Patents

Description

The invention relates to a process for the treatment of deactivated oxides of titanium, vanadium and tungsten-containing DENOX catalysts that help remove nitrogen oxides Exhaust gases are used. The selective catalytic reduction of nitrogen oxides with ammonia Nitrogen has become known as the SCR (Selective Catalytic Reduction) process, and that Catalysts for the process, which is gaining increasing technical importance, are from the Literature known.

Exhaust gases containing nitrogen oxides arise during the production of nitric acid, but also in large quantities in the industrial combustion of fossil fuels, e.g. B. in power plants.

These exhaust gases from industrial combustion plants, but also those from waste incineration and process furnace systems, from blast furnaces or from furnaces of glass processing and ceramic industry contain varying amounts depending on the type of combustion other components that can also damage the catalysts. May be mentioned for. B. Heavy metals or heavy metal compounds, in particular compounds from the Arsen as well as dusts, the damage the catalysts due to their alkali, alkaline earth and silicon content.

The degree of deactivation is mainly due to the accumulation of arsenic and the mechanical Deposition of fly dusts determined. The exchange of such deactivated SCR catalysts for new is not useful because of the high cost of these catalysts, and also the landfill of such Catalysts are associated with considerable costs.

A number of processes have therefore become known which aim to deactivate DENOX catalysts to regenerate.

These methods are based on e.g. T. on a mechanically abrasive treatment of the spent catalyst. In addition to abrasion, these mechanical processing methods have undesirable effects There is the disadvantage that the deactivated points in the pores of the SCR catalysts are not reached will.

It is also known to regenerate the catalysts by treating them with water remove adhering alkaline compounds; however, this method is only based on these pollutants limited.

The regeneration of SCR catalysts with aqueous solutions of oxalic acid or Hydroxides of the elements of I. and / or II. Main group and / or carbonates of the elements of I. Main group of the periodic table of elements and subsequent treatment with diluted Acids have been described.

It is also known to be contaminated by arsenic-contaminated catalysts and sorbents based on titanium oxide Wash with an inorganic or organic acid to regenerate. Used for washing 50 to 90 ° C hot aqueous solutions of nitric acid, hydrochloric acid, sulfuric acid or acetic acid in concentrations of 1-25% by weight (DE 38 16 600 A1).  

However, the known methods of regenerating deactivated DENOX catalysts have the Disadvantage that their effect largely on the surfaces and the larger pores of the frequently monolithic catalysts remains limited and full activation is not achieved.

The task was therefore to treat a process for treating deactivated, To develop DENOX catalysts containing titanium, vanadium and tungsten, that the activation of the catalyst is not limited to its surface and at the same time an extensive one mechanical separation and chemical removal of deactivation components allowed.

This object is achieved in that the deactivated DENOX catalysts a finely ground to a coronation below 60 µm material

• a) with an arsenic content of more than 500 ppm at temperatures between 393 K to 453 K in 65 to 98% sulfuric acid, with a mass ratio of TiO₂: H₂SO₄ of 1: 4 to 1: 8, preferably at a ratio of 1: 4, triggers disturbing additions after dilution with water Separating the filtration, initiating the resulting titanyl sulfate solution at 363 K HCl and SO₂, the escaping HCl / AsCl₃ mixture condensed and one freed from the catalyst poison arsenic Receives titanyl sulfate solution or
• b) with an arsenic content of 500 ppm or less than 500 ppm in hydrochloric acid with a density of 1.09 g / ml suspended to 1.16 g / ml, initiates SO₂ at 293 K to 333 K for two to eight hours, the arsenic Separates hydrochloric acid from the deactivated DENOX catalyst by filtration and removes it from the arsenic Residue either used to top up the titanyl sulfate solution or it with sulfuric acid in a 1: 2 ratio,

in the resulting titanyl sulfate solution by adding from the process Hydrolysis product or by adding deactivated, arsenic-free activated in hydrochloric acid solution DENOX catalyst produces a hydrolysis-capable mass ratio of H₂SO₄: TiO₂ of 2: 1, which Solution hydrolyzed and the hydrolyzate after calcining either directly or after one any necessary additional doping feeds back to the catalyst production process.

The acids used in the process are recycled, and the hydrochloric acid is converted into copper the arsenic is removed and the dilute sulfuric acid is concentrated by evaporation.

The method according to the invention of processing deactivated DENOX catalysts is in this respect surprising, since the poor solubility known from the literature and also from our own experiments of aged titanium dioxide in acids as well as the insolubility of tungsten (VT) oxide in acids Refurbishment of those consisting mainly of titanium dioxide, tungsten (VT) oxide and vanadium pentoxide DENOX catalysts in sulfuric acid solution seemed to be excluded.  

example 1

In 50 ml of 96% sulfuric acid at a temperature of 433 K to 453 K one becomes the DENOX catalyst comparable composition of titanium dioxide, tungsten (VI) oxide and vanadium pentoxide (TiO₂ = 89.6 Ma%, WO₃ = 10.0 Ma%, V₂O₅ = 0.4 Ma%) with a fineness of 100% <60 µm, added in portions and stirred.

After a period of 20 to 30 minutes, the mixture is allowed to cool and diluted with 100 ml of water.

After filtering, a solution is obtained which

0.36 g TiO₂
0.018 g WO₃
0.038 g V₂O₅

contains.

So that is from the components

TiO₂ 4.01%
WO₃ 1.8%
V₂O₅ 95.0%

gone into solution.

Example 2

10 g are deactivated in 50 ml of 96% sulfuric acid at a temperature of 433 K to 453 K. DENOX catalyst with a fineness of 100% <60 µm was added in portions and stirred.

After 20 to 30 minutes, the amount entered is dissolved.

After cooling, it is diluted with 100 ml of water and filtered. The residue is 1.15 g.

The residue contained:

0.5% WO₃
1.3% TiO₂
0.1% V₂O₅

Thus the components of the deactivated DENOX catalyst are as follows percentages went into solution.

WO₃ = 99.27%
TiO₂ = 99.8%
V₂O₅ = 99.7%

Example 3

In 656 g of 96% sulfuric acid, 210 g of deactivated DENOX catalyst (74.9% TiO₂; 8.0% WO₃; 0.4% V₂O₅; 1000 ppm As₂O₃) entered with stirring. After adding 50 ml Water the temperature is raised to 463 K. After reaching the reaction temperature react for a further 4 hours at 463 K.

The viscous reaction product is allowed to cool and then the volume is increased with water approx. 1500 ml.

After filtering, 1210 ml of a solution with the following composition are obtained:

128 g / l TiO₂
13.5 g / l WO₃
0.68 g / l V₂O₅

This means that the components of the deactivated DENOX catalyst

TiO₂ 98.5%
WO₃ 97.2%
V₂O₅ 97.9%

gone into solution.

In about 1000 cm³ of the titanyl sulfate solution thus obtained, SO₂ and HCl are introduced  and at a temperature of 373 K to 383 K, the resulting AsCl₃ / HCl azeotrope mixture distilled off. After a distillation time of about 3 hours, the gas introduction is stopped and the Boiled excess of SO₂ and HCl.

With initial values of 1000 ppm, final values of 1 ppm As₂O₃ (based on the TiO₂ content the solution).

Example 4

In a moving suspension of 200 g finely ground (100% <60 µm), deactivated DENOX catalyst in 2000 cm³ hydrochloric acid (d = 1.16 g / cm³) is introduced at a temperature of 298 K SO₂. The SO₂ introduction is ended after about 5 hours. This is followed by filtration and repeated washing of the DENOX catalyst, first with hydrochloric acid and then with water and then drying. With initial values of 500 ppm, final values of 25 ppm As₂O₃ were reached.

420 g of arsenic-free DENOX catalyst are placed in 645 g of 96% sulfuric acid (Composition 73.7 Ma% TiO₂, 9.3 Ma% WO₃, 0.16 Ma% V₂O₅) registered with stirring. After adding 50 ml of water, the temperature is raised to 463 K and the mixture is left readjust at this temperature for 4 hours. The solid reaction product is allowed to cool and increases the volume with water to about 2000 ml. After filtering, 1800 ml of solution are obtained with the following composition:

168 g / l TiO₂
21.6 g / l WO₃
0.37 g / l V₂O₅

This is from the components obtained in the deactivated DENOX catalyst

TiO₂ 97.7%
WO₃ 99.5%
V₂O₅ 99.1%

gone into solution.

Example 5

660 ml of an arsenic-free titanyl sulfate solution (prepared according to Example 3) are combined with 290 g of one arsenic-free DENOX catalyst (prepared according to Example 4, Section 1) mixed with stirring. After the encore the reaction temperature is raised to 453 K from 100 ml of water. After reaching the reaction temperature is allowed to react for a further 4 hours at 473 K. The solid reaction product is left cool and suspend it in about 1500 ml of water. After filtering, you get 2015 ml of one Titanyl sulfate solution with a TiO₂: H₂SO₄ ratio of 1: 2.

Claims (3)

1. Process for the treatment of deactivated, containing oxides of titanium, vanadium and tungsten DENOX catalysts by treatment with acids, characterized in that the deactivated DENOX catalysts are subjected to very fine comminution to a grain size below 60 µm, the finely ground material

• a) at an arsenic content of more than 500 ppm at temperatures between 393 K and 453 K in 65 to 98% sulfuric acid, with a mass ratio of TiO₂: H₂SO₄ of 1: 4 to 1: 8, preferably at a ratio of 1: 4 , dissolves, after dilution with water disruptive admixtures by filtration, introduces into the resulting titanyl sulfate solution at 363 K to 393 K HCl and SO₂, the escaping HCl / AsCl₃ mixture condenses and a titanyl sulfate solution freed from catalyst poison is obtained or
• b) suspended in an arsenic content of 500 ppm or less than 500 ppm in hydrochloric acid of density 1.09 g / ml to 1.16 g / ml, initiates SO₂ at 293 K to 333 K for two to eight hours, the arsenic hydrochloric acid by filtration separates from the deactivated DENOX catalyst and either uses this arsenic-free residue to replenish the titanyl sulfate solution or breaks it down with sulfuric acid in a ratio of 1: 2,

in the resulting titanyl sulfate solution by adding hydrolysis product removed from the process or by adding deactivated, arsenic-free DENOX catalyst activated in hydrochloric acid solution a hydrolysis-capable mass ratio of H₂SO₄: TiO₂ of 2: 1 produces the solution hydrolyzed and the hydrolyzate after calcining either directly or after an optionally the necessary additional doping feeds the catalyst production process again. 2. The method according to claim 1, characterized, that the acids used in the process are recycled from the hydrochloric acid using copper Arsenic removed and the dilute sulfuric acid concentrated by evaporation.