DE4106873C1 - Prodn. of catalyst for denitrification of waste gases - with reduced amt. of waste water and waste gases during prodn. - Google Patents

Abstract

A catalyst for the denitrification of waste gases with the use of NH3 is obtd. by (A) freeing a C-contg. material from adsorbed cpds. at 100 deg.C under a high vacuum and (B) charging the C-contg. material below 100 deg.C with a mixt. of 36% HCl and 65% HNO3 evaporating in a high vacuum, 20-60 kg HCl and 10-20kg HNO3 are used per 1000 kg C contg. material. ADVANTAGE - The amt. of waste water and waste gases during prodn. of the catalyst is considerably reduced compared with known processes

Description

The invention relates to a method for producing a Catalyst for the development of exhaust gas under feed of ammonia, by treating carbonaceous Material with a hydrochloric acid-nitric acid mixture and final heating to a temperature above 200 ° C.

Such a method is proposed in DE 40 26 104 C1 Service. There is the carbonaceous Material with a mixed solution of 5 to Treated 30% HCl and 1 to 8% HNO solution and dried after draining the mixed solution in a N₂ stream. The contact time is 5-60 min. And the Drying can be carried out in the N₂ cycle. The so produced catalyst has high NO conversions and a low ammonia slip on.

However, it is disadvantageous that in the production of the Catalyst wastewater and exhaust gases are formed. After  Impregnation of 1 t of catalyst with about 1200 l mixed solution remains in the pore volume of the catalyst precursor about half of the mixed solution. To the catalyst to dry, the mixed solution must be evaporated become. This requires large amounts of heat. It arises per 1 t of catalyst about 600 l of wastewater, the a mixture of HCl, HNO₃ and nitrogen oxides. This wastewater requires prior to discharge into a sewage treatment plant a costly pretreatment. Difficult too dispose of large amounts of nitrogen oxides, the in the impregnation and especially in the Drying arise and an additional attachment to the Nitric oxide removal required.

The invention is based on the object, the generic To modify the production process so that the wastewater and exhaust gas attack in the production process of the catalyst is significantly reduced.

This object is achieved by that in the characterizing part of claim resolved features resolved.

In experiments, it has surprisingly been found that a nearly wastewater and exhaust-free production of the Catalyst succeeds by adding to the catalyst precursor at a temperature of about 100 ° C First high vacuum is applied to it by water and other adsorbed substances (eg oxygen, nitrogen) what to release at a temperature below 100 ° C a mixture of concentrated hydrochloric acid (36 ° C) and concentrated nitric acid (65%) so slowly is metered into the vacuum system that the acid mixture Evaporated instantly in vacuo. The evaporated Acid mixture is caused by the adsorption forces  adsorbed by the catalyst precursor quickly and uniformly. An advantage over an impregnation is that only exactly the amount of HCl and HNO₃ is applied, the adsorbable is. If the product is in nitrogen flow then is heated to a temperature above 200 ° C, be only very small amounts of water evaporates and it even very small amounts of nitrogen oxides are produced. To produce 1 t of catalyst only about 30 to 80 l of a mixture of HCl and HNO₃ required. It is also advantageous that only about 30 l / t of catalyst removed by drying Need to become. The resulting is correspondingly low Wastewater volume.

The catalytic activity of the catalyst thus prepared is as the example and the comparative example and the Table 1 show, in terms of NO conversion performance better than a catalyst prepared by impregnation. As a carbonaceous material, for. B. an activated carbon with a NO conversion greater than 35% advantageous be used.

example 1

1 t catalyst precursor (activated carbon with a NO conversion of 37.8%) was initially in a high vacuum at 100 ° C of adsorbed compounds (H₂O, N₂, O₂) freed. At a temperature of 50 ° C then 60 kg HCl (36%) and 20 kg HNO₃ (65%) added to the vacuum system, wherein both acids evaporated immediately and from the Activated carbon were adsorbed. After 60 minutes, the activated carbon was  heated to 230 ° C, the temperature of 230 ° C was reached quickly because only small quantities Water had to be evaporated. It only emerged 30 kg wastewater and only traces of nitrogen oxides.

In the test (Table 1) reached the erfindungsemäß produced Catalyst a NO conversion of 77.2%.

Comparative example

1 t catalyst precursor (activated carbon with a NO conversion 37.8%) was mixed with 1200 l of a mixture 50% of a 10% hydrochloric acid and 50% of a 4% Nitric acid soaked. After 60 minutes, the excess was Solution drained, with about 100 l of wastewater emerged. Then it was in the nitrogen cycle for so long dried until a temperature of 230 ° C has been reached was. It created another 600 l of sewage and large Amounts of nitrogen oxides.

In the test (Table 1) achieved the catalyst thus prepared a NO conversion of 69.8%.

The NO turnover was explained as follows certainly.

Test method for the determination of NO-conversion

The NO conversion is defined as that at a temperature of 120 ° C and a model flue gas (500 vpm NO, 480 vpm NH₃, 6.4 Vol .-% O₂, 9.8 vol .-% H₂O, balance: N₂) after a trial period of 20 h achievable percent NO removal.  

Table 1

Catalytic services

The schematic structure of a test apparatus shows the figure the drawing.  

The test apparatus consists of an electrically heated with a heater 24 evaporator 1 with a measuring device 15 for temperature control and registration, a heated electrically with a heater 26 gas preheater 2 with a measuring device 16 for temperature display and registration, a heated electrically with a heater 23 reactor 3 with a measuring device 17 for temperature registration in the entrance area and 17 a in the interior and a further measuring device 18 for temperature control and registration and a gas analysis. 4

The adjustment of the various gas streams for model gas production via thermal mass flow controller. Water (H₂O) is added via a pump 14 and a line 6 to the evaporator 1 , which is further fed via a line 5 with a measuring device 19 for flow control and registration nitrogen (N₂). The nitrogen-steam mixture from the evaporator 1 passes via a line 9 , in the via a line 8 with a further measuring device 20 for flow control and registration nitrogen oxide (NO) and via a line 7 with a further measuring device 21 for flow control and registration oxygen (O₂ ) are fed into the gas preheater 2 .

The gas preheater 2 consists of a coiled 10 mm stainless steel tube and is connected via a line 27 to the reactor 3 . In the line 27 is fed via a line 10 with a further measuring device 22 for flow control and registration ammonia (NH₃). The reactor 3 is a stainless steel tube with sieve bottom. Table 2 lists the technical data of reactor 3 .

Data of the reactor 3 Material: stainless steel Diameter: 52 mm Length: 750 mm Usable volume: 1.1 l

From the reactor 3 , the exhaust gas is withdrawn via a line 11 , from which a branch line 12 branches off via a valve 13 , which leads to the gas analysis 4 . The spur line 12 with the measurement gas is electrically heated by a heater 25 (150 ° C).

The experimental procedure is the following:

For sample preparation approx. 750 g activated carbon are required 3 h in a drying oven at 120 ° C dried.

To determine the NO conversion, 1.06 l of the dried sample are introduced into the reactor 3 and heated in a stream of nitrogen. After reaching the reaction temperature of 120 ° C, the sample is flowed through with the synthetic gas from line 27 of 20 h. The composition of the model gas is shown in Table 3.

Composition of the model gas Flow rate: 1.3 m³ / h NO concentration: 500 vpm (dry) NH₃ concentration: 480 vpm (dry) O₂ concentration: 6.4% by volume (dry) H₂O concentration: 9.8% by volume Rest: N₂

An overview of the test conditions is given in Table 4.

test conditions Test portion: | approx. 640 g Layer height: about 0.5 m Temperature: 120 ° C Model gas Quantity: 1.5 m³ / h Flow rate: 0.28 m / s

For the evaluation of the experiment the NO- Breakthrough concentration registered on a printer. The NO concentration is read after 20 h and the conversion, based to the NO input concentration, calculated.

The NO conversion of a suitable for the catalyst according to the invention Activated carbon after 20 h reaction time must be at least 35% be.

LIST OF REFERENCE NUMBERS

1 evaporator
2 gas preheaters
3 reactor
4 gas analysis
5 line
6 line
7 line
8 line
9 line
10 line
11 line
12 stub line
13 valve
14 pump
15 measuring device
16 measuring device
17 measuring device
18 measuring device
19 measuring device
20 measuring device
21 measuring device
22 measuring device
23 heater
24 heater
25 heater
26 heater
27 line

Claims (1)

A process for the preparation of a catalyst for exhaust gas denitrification with supply of ammonia, by treating carbonaceous material with a hydrochloric acid-nitric acid mixture and finally heating to a temperature above 200 ° C, characterized in that the carbonaceous material at a temperature of about 100 ° C. Is freed of adsorbed compounds in a high vacuum and that the carbonaceous material is then applied at a temperature below 100 ° C with a high vacuum vaporizing mixture of 36% hydrochloric acid and 65% nitric acid, wherein per t carbonaceous material 20 to 60 kg of hydrochloric acid and 10 to 20 kg of nitric acid are used.