Rates of Ammonia Absorption and Release in Calcium Chloride

Abstract

After synthesis, ammonia can be selectively absorbed by calcium chloride; nitrogen and hydrogen are not absorbed. The kinetics of release seem to be diffusion controlled. The kinetics of absorption are consistent with a first-order reaction after an initial period of a higher-order reaction, which may indicate a nucleation event. At 225 °C, both absorption and release show half-lives of around 10 min if the ammonia partial pressure is swung from 2 to 1 bar, which allows design of an absorber for the periodic separation of ammonia. When this absorber replaces the ammonia condenser in a conventional ammonia synthesis, the ammonia production at low pressure can have the same rate as the conventional process operating at higher pressure.