Thermal dissociation kinetics of solid ammonium carbonate for use in NH3-SCR systems

Abstract

Selective catalytic reduction (SCR) systems using solid ammonia carriers like carbamates, carbonates, etc., have gained interest in the recent past for NOx abatement from compression ignition engines. Solid ammonia carriers have successfully demonstrated their use in SCR systems. In this experimental study, the thermal dissociation study of ammonium carbonate is made using nonisothermal thermogravimetric analysis. Ammonium carbonate is subjected to three heating rates, ∅ of 2, 4, and 8 K/min. The corresponding highest rates of reaction are obtained at temperatures (Tp) of 96, 118, and 128 °C, respectively. At these points, the mass of the samples has been reduced to 1/3rd of the initial mass. From the Arrhenius plots, the average activation energy obtained is 77.39 kJ/mol which is 15% higher than that of ammonium carbamate. An expression for Tp as a function of activation energy, ∅ , and order of the reaction is developed using kinetic model. The model can predict the temperatures at which the reaction rates are maximum for a given heating rate.