Optimizing Reaction-Absorption Process for Lower Pressure Ammonia Production
Fouzia Hasan Nowrin, Mahdi Malmali
Abstract
Ammonia separation using metal halide absorbents has been shown to be a viable path for ammonia production at lower pressure. This work reports on optimizing the operating parameters of the reaction–absorption process that can be adapted for large-scale processing. The experiments were executed in three different modes. First, the effect of reaction parameters on the production rate was studied. Then, the absorption conditions were investigated in a single-pass reaction-then-absorption mode to evaluate the effectiveness of the absorbent at different temperatures, pressures, and space velocities. Finally, fed-batch reaction-absorption tests were conducted in constant pressure to evaluate the process performance with optimized conditions and gain more in-depth understanding of the transient behavior of this process. Results suggest that the recycle flow rate and absorber temperature significantly influence the ammonia production rates. These findings were then used to optimize the performance of a continuous fed-batch ammonia production process at constant pressure. A production rate upward of 27 μmol gcat s–1 was obtained under the most optimized conditions, which is a factor of 14 greater than the best result reported earlier. The optimized conditions were then used to study the cyclic operation of the fed-batch reaction–absorption process in a cyclic process. A transient behavior was observed for the ammonia production, which could be attributed to the partial saturation of the absorber column. Stable performance of reaction-absorption process was demonstrated for more than nine cycles, with no decay in the performance of the absorber after relatively short regeneration cycles.