Kinetic modeling and dynamic simulation for the catalytic wet air oxidation of aqueous ammonia to molecular nitrogen

摘要

A kinetic model for the catalytic wet air oxidation of aqueous ammonia over Ru/TiO2 catalyst was developed considering the consecutive reaction steps as follows: (i) formation of active oxygen sites O* by the dissociative adsorption of aqueous O-2 on the catalyst, (ii) oxidation of aqueous NH3 by the reaction with three O* sites to produce HNO2, (iii) aqueous phase dissociation of HNO2 into H+ and NO (2) (-) , (iv) formation of NH (4) (+) by the association of NH3 with the HNO2-dissociated H+, (v) formation of N-2 by the aqueous phase reaction between NO (2) (-) and NH (4) (+) , (vi) formation of NO3 by the reaction of NO (2) (-) with an O* site. For each reaction step, a rate equation was derived and its kinetic parameters were optimized by experimental data fitting. Activation energies for the reactions (ii), (v), and (vi) were 123.1, 76.7, and 54.5 kJ/mol, respectively, suggesting that the oxidation reaction of aqueous NH3 to HNO2 was a ratedetermining step. From the simulation using the kinetic parameters determined, the initial pH adjustment of the ammonia solution proved to be critical for determining the oxidation product selectivity between desirable N-2 and undesirable NO (3) (-) as well as the degree of oxidation conversion of ammonia.