Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1987-01-15
1989-08-08
Heller, Gregory A.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
423235, B01J 800, C01B 1700
Patent
active
048551163
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase application of PCT/EP No. 86/00205 filed Apr. 2, 1986 and based, in turn, on a German National application P35112168.8 of Apr. 3, 1986.
1. Field of the Invention
Our present invention relates to a method using activated coke for removal of nitrogen oxides from exhaust gases.
2. Background of the Invention
From DE-OS No. 24 33 076 it is known that activated carbon having a specific surface (according to Brunauer, Emmett and Teller) of 200-2000 m.sup.2 /g can be used for nitrogen oxide reduction by ammonia in a temperature range between 110.degree. and 350.degree. C. In this case the experts suppose that the activated carbons are particularly suited for the reaction because of their great internal surface. The great internal surface is arrived at by activation which can be obtained by treatment of the pre-activated, viz. the activated coke, e.g. by means of steam. Because of the activation process the costs for activated carbon production are comparably high.
In DE-OS No. 30 36 531 the use of a formed coke (activated coke) for simultaneous removal of sulphur oxides and nitric oxides from exhaust gases is described. The SO.sub.2 removal results in formation of H.sub.2 SO.sub.4 within the pore system of the activated coke and thus to an inhibition of the SO.sub.2 loading of the coke, which means that the activated coke needs periodic thermal regeneration. In thermal regeneration the sulphuric acid is decomposed, and this decomposition involves consumption of carbon from the activated coke. This results in a widening of the pore system and an increase of the internal surface so that an activated carbon is made from the activated coke.
OBJECT OF THE INVENTION
It is an object of the invention to provide an improved process for the removal of nitrogen oxides from flue gas which can use adsorbents which catalyse the nitric oxide reduction by means of ammonia, which exihibit higher selectivity than activated carbon, and which can be produced more inexpensively than activated carbon.
SUMMARY OF THE INVENTION
Surprisingly, where found that activated coke which is produced by oxidation of ground hardcoal, subsequently blending the oxidized coke with binders like pitch, bitumen, tar or tar oil to form shaped particles of 3-9 mm of size, and subsequent low-temperature carbonization with a heating rate of 20.degree.-100.degree./min to temperatures ranging from 700.degree. to 900.degree. C. in an atmosphere containing 2-5% by vol. of oxygen, constitute such a suited adsorbent. These activated coke qualities have a volatile matter content of 2-8% and a specific surface of 20-150 m.sup.2 /g.
With such activated coke qualities the reduction of the nitric oxides with ammonia can be effected at a temperature range between 90.degree. and 150.degree. C. in a much more selective way than by use of activated carbon. This may be concluded from the lower NH.sub.3 consumption stated when using the improved activated coke. Since activated coke is an intermediate product of activated carbon production, the process step of activation needs not be run and, accordingly, the activated coke is less expensive than activated carbon.
If the activated coke according to a further feature of this invention is impregnated with sodium or potassium salts, the catalytic activity of the adsorbents is further increased.
Impregnation can be carried out by known processes, e.g. by soaking in a agneous solution and subsequent drying.
The advantages of activated coke use compared to use of activated carbon for nitric oxide reduction are described in more detail in certain specific examples below:
EXAMPLE 1
A 50 mm diameter reactor is filled with activated coke corresponding to a bed height of 100 cm. The activated coke is a product obtained from caking bituminous coal containing 20.5% of volatile matter, blended with 23 parts by weight of pitch, extruded to form 5 mm cylindrical particles, and subsequently subjected to low-temperature carbonization.
A gas flow of 1.5 m.su
REFERENCES:
patent: 2992895 (1961-07-01), Feustel et al.
patent: 3917884 (1975-11-01), Jahn
patent: 4500501 (1985-02-01), Hamada et al.
Chemical Abstracts, vol. 82, No. 12, 76715a, Mar. 1975.
Juntgen Harald
Knoblauch Karl
Richter Ekkehard
Schmidt Hans-Jurgen
Bergwerksverband GmbH
Dubno Herbert
Heller Gregory A.
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