(190a) A New Alternative Process for Nitric Acid Production Based on Chemical Looping Approach

There have been no significant changes in the reaction scheme for the manufacture of nitric acid since the discovery of the process by Ostwald in 1902. This paper reports the theoretical prediction and preliminary experimental investigation for an alternative process of nitric acid production using metal oxide based chemical looping cycles. The first step would be the reduction of metal oxide by ammonia to produce nitric oxide (NO), and the second step would be the regeneration of metal oxide either by air oxidation or/and by water hydrolysis depending on the metal oxide used. The most important aspect of this process is the replacement of highly exothermic ammonia oxidation step in Ostwald’s process by the endothermic oxidation of ammonia by metal oxide. The thermodynamic feasibility and phase diagram analysis is carried out for the proposed process using HSC and Factsage packages without considering the catalytic effects of the metal oxides. There is a probability of differences in theoretical and actual process reactions as it is difficult to predict the exact reaction mechanism theoretically. However, at this stage the process seems to be exergetically more efficient with a smaller carbon footprint than conventional nitric acid production. The cases of Cu/CuO, CoO/Co₃O₄, and Fe₃O₄/Fe₂O₃ were experimentally checked for their potential to react with ammonia over a wide range of temperatures at atmospheric pressure. The effect of particle size of metal oxide and the gas residence time in the reactor was also studied for all the three metal oxides. The experiments were carried out in a batch reactor in spouting mode so as to have efficient gas-solid contact. The maximum ammonia to nitric oxide conversions obtained in the batch reactor experiments for CuO, Co₃O₄, and Fe₂O₃ were around 90 %, 70 %, and nearly 50 %, respectively. This paper presents the experimental results and discusses the proposed reaction scheme for the alternative process for nitric oxide production following a chemical looping based approach.