Process for producing an active carbon catalyst

Details Process for producing an active carbon catalyst Process for producing an active carbon catalyst

1988-12-07

1990-05-01

Konopka, Paul E.

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Inorganic carbon containing

423239, 423244, 423460, 502217, 502417, B01J 2118, B01D 5336

Patent

active

049218263

DESCRIPTION:

BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/EP 87/00269 filed 22 May 1987 and based, in turn, on German national application P 36 20 425.0 under the International Convention.


FIELD OF THE INVENTION

The invention relates to a process for producing an active carbon catalyst.


BACKGROUND OF THE INVENTION

It is known to improve the catalytic activity of active carbon by treatment with ammonia at high temperatures. So for instance H. P. BOHM (Fuel, 1984, Vol. 63, pages 1061-1063) has found that the treatment of active carbon with ammonia or prussic acid at temperatures above 600.degree. C. increases the catalytic activity of the active carbon in the case of oxidation reactions in the acqueous phase. However, these active carbons have the disadvantage that they are deactivated very quickly.
From U.S. Pat. No. 4 210 628 a process for the removal of nitrogen oxides from exhaust gases with the aid of ammonia is known, wherein active carbon is used as a catalyst. In the presence of sulfur oxides in the exhaust gases, on the catalyst ammonium sulfate and sulfuric acid are formed. The deactivated catalyst is therefore regenerated, e.g. by heating to temperatures between 350.degree. and 800.degree. C. in a stream of inert gas. The regenerated catalyst shows an improved catalytic activity. A pretreatment of the catalyst prior to being used in the process for the elimination of nitrogen oxides is not disclosed.


OBJECT OF THE INVENTION

It is the object of the invention to produce an active carbon catalyst with a low degree of deactivation.


SUMMARY OF THE INVENTION

This object is attained according to the invention by impregnating active carbon or active coke is treated with an aqueous solution of ammonium sulfate, dried at 120.degree. C. and subsequently heated to temperatures above 350.degree. C. in a stream of inert gas, until no SO.sub.2 development occurs.
In accordance with a further development, the aqueous solution of ammonium sulfate is treated with sulfuric acid.
Through a repetition of the described treatment, the catalytic activity can be enhanced even further. All active carbons available in commerce and also non-activated carbon products (active coke) can be used.
The so-produced catalysts are advantageously suited for all catalytic reduction-and oxidation reactions occuring in the presence of active carbon, such as the reduction of nitrogen oxides with NH.sub.3, the oxidation of H.sub.2 S with atmospheric oxygen and steam to H.sub.2 SO.sub.4.
It is particularly advantageous to use the produced catalysts for the removal of nitrogen oxides from exhaust gases with the aid of ammonia, according to the following overall equation:
In this reaction the active carbon catalyst produced according to the invention functions as a reduction catalyst as well as an oxidation catalyst. The first step is an oxidation of NO with atmospheric oxygen into NO.sub.2 takes place, which then, together with the further NO is reduced by ammonia to nitrogen and water.
With the process of the invention it has become possible to incorporate active nitrogen into the active carbon catalyst, which cannot be removed, even though the catalyst is heated at 900.degree. C.
If the incorporation of the nitrogen into the active carbon takes place according to known state of the art ammonia treatment, the active carbon deactivates during the catalytic NO.sub.x -reduction. After approx. 5-7 hours of testing, in a comparison test it was not possible to establish a difference between an active carbon treated with ammonia and an untreated active carbon.


SPECIFIC EXAMPLE



Example 1

An active carbon with a specific surface according to BET (DIN 66 131) of 800 m.sup.2 /g is impregnated at room temperature with a saturated ammonium sulfate solution, treated with 5 to 15% by weight sulfuric acid, dried overnight at 120.degree. C. and subsequently heated at 420.degree. C. in a stream of nitrogen. After 1.5 h, no further SO.sub.2 -development took place.


Example 2

An active carbon with a specific surf

REFERENCES:
patent: 4210628 (1980-07-01), Ninomiya et al.

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