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Remarkable progress towards implementation of catalytic technology for N 2 O mitigation in nitric acid plants has been experienced in recent years. EnviNOx ® , one of the commercial processes developed by Uhde, accomplishes the tail-gas abatement of N 2 O and NO x over a single reactor using iron-containing zeolite catalysts. Two variants of the process are available depending on the tail-gas temperature. This manuscript evaluates the low-temperature abatement process ( x and N 2 O are selectively reduced by NH 3 and CH 4 , respectively. To this end, activity tests in mixtures with N 2 O, O 2 , NO, NH 3 , and CH 4 at different temperatures and partial pressures of reactants were carried out over steam-activated FeZSM-5. Ammonia and nitric oxide strongly inhibit the selective catalytic reduction (SCR) of N 2 O by CH 4 , shifting the temperature for N 2 O conversion over 700 K. Controlled ammonia dosing is required for the efficient operation of the low-temperature EnviNOx ® variant over the particular iron zeolite used in this study. The optimal inlet NH 3 concentration is determined by the NO concentration in the tail-gas and its temperature. In the absence of NO and NH 3 , the CH 4 -SCR of N 2 O over FeZSM-5 is effective above 623 K. Still, this process cannot retrofit a number of existing plants with lower tail-gas temperatures. |
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