Combined production of metallic-iron nanoparticles: exergy and energy analysis of two alternative processes using Hydrazine and NaBH4 as reducing agents

This study deals with the simulation of two alternative processes for the coupled production of metallic iron nanoparticles and the necessary reducing agent: hydrated hydrazine and sodium borohydride. After carrying out a sensitivity analysis to identify the optimal operating conditions for each process, the results have been interpreted in the light of energy and exergy analysis. The study demonstrated that the sodium borohydride-based iron nanoparticles production is more profitable than the hydrazine-based one, because of a higher exergy efficiency as a consequence of lower exergy destruction value. The total heat duty required for the borohydride-based process was only 1.1 MWh with respect to 5 MWh for the hydrazine-based one. Conversely, cooling water and total power consumptions for the latter process are significantly lower than for the former one (2.33 t/h versus 26.87 t/h, and 2 kWh versus 88.7 kWh, respectively). Furthermore, as reported in the literature, the hydrazine-based process allows to produce high purity iron nanoparticles, since hydrazine is transformed completely in N2 during the process. Both processes were designed to produce 1765 kg/d of iron and the same amount of produced reducing agent was also stored as secondary product of the plant.