دانلود رایگان مقاله فاز آبی اکسیداسیون آمونیاک مرطوب هوا

Abstract

The equilibrium concentrations in ammonia and ammonium ion in the liquid and gas phases could be calculated in the temperature range 25–250 °C, under typical operating conditions for the catalytic wet air oxidation of ammonia. A satisfactory agreement was obtained with the data collected upon blank experiments as well as in the presence of unreactive catalyst supports. Thermodynamic calculations appeared to be crucial to access a better comprehension of the reaction mixture composition under catalytic wet air oxidation reaction conditions, especially the ammonia partition and speciation among the different phases. New insights were gained in terms of ammonia reactivity.

4. Conclusions

Taking into account the whole reaction system, the mass and charge balances, the acid-base constant of ammonia, the self-ionization constant of water and the gas-phase equilibrium constant for ammonia, the equilibrium concentrations in ammonia and ammonium ion in the liquid and gas phases could be calculated in the temperature range 25–250 ◦C. A valuable procedure was developed and described in this manuscript. The same approach could be easily applied for a better description of any liquid phase reaction where liquid-liquid, gas-liquid and acid-base equilibria are involved. Although basic thermodynamic data were pretty scarce and a large variation was reported for the Henry’s constant, a reasonably agreement was obtained with the results acquired upon blank experiments and in the presence of inert catalyst supports. Considering our experimental setup and the applied reaction conditions, it appeared that ammonia evaporation was limited to ca. 2.9 mol%, indicating that any reaction would mainly occurred in the liquid phase.Moreover, in the liquid phase, ammonia (96.2 mol%) strongly dominated over ammonium ions (0.9 mol%). This latter point could partly explain the high activity observed in the catalytic wet air oxidation reaction since the molecular form of ammonia was shown to be the most reactive.