Marek INGER*, Katarzyna ANTONIAK-JURAK, Monika RUSZAK, Paweł KOWALIK, Marcin WILK – New Chemical Syntheses Institute, Puławy, Poland
Please cite as: CHEMIK 2016, 70, 5, 255–260
Nitric acid plants are one of the largest industrial sources of nitrous oxide (N2O) emission, which is an undesirable by-product, formed during catalytic oxidation of ammonia. Its concentration in exhaust gases (socalled tail gases) depends on the operating parameters of the installation and can achieve the level of 2000 ppm . Industrial Emissions Directive 2010/75/EU imposes on EU countries an obligation to limit N2O emission to the level below 300 ppm for existing installations and below 100 ppm for the new nitric acid plants . To comply with N2O emission standards, especially in existing installations, the use of catalytic processes is required. The analysis of the operating parameters of nitric acid plants indicates, that the catalytic process can be realized in the nitrous gases stream (T = 750 – 940°C) and/or in the tail gas stream (T = 200 – 450°C).
Our previous studies on N2O decomposition in the tail gas stream, with using multicomponent cobalt spinel catalyst, obtained by the precipitation method and formed by a compression into tablets, showed that the overall rate of deN2O reaction is limited by the internal diffusion resistance . It means, that significant part of the catalyst grain interior does not take part in the catalytic reaction. In the case of catalysts, based on the relatively expensive components, it seems to be more beneficial to use the catalytic systems obtained by impregnation. In these systems the active phase is located mainly on the outer (superficial) layer of the catalyst grain and its accessibility for the reactants depends on the degree of pore structure development.
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