H2 production by steam-quenching of Zn vapor in a hot-wall aerosol flow reactor

Hydrogen production by steam-hydrolysis of zinc is investigated as part of a two-step water-splitting thermochemical cycle based on ZnO/Zn redox reactions. The hydrolysis reactor consists of a hot-wall tube containing a flow of Zn(g) that is steam-quenched to co-produce H2 and Zn/ZnO nanoparticles. The effects of the quenching gas flow rate and reactor wall temperature on the Zn-to-ZnO chemical conversion and particle yield are examined. Solid products are characterized by X-ray diffraction, N2 adsorption, and SEM microscopy. Quench rates of 2–6×104 K/s yielded conversions of up to 95% at the expense of low particle yield due to significant wall deposition with subsequent hydrolysis. Aerosol particles with hexagonal structure were formed by Zn evaporation–condensation containing low ZnO mass fraction. In contrast, operation at quench rates up to 106 K/s led to increased particle yield but lower conversion. Filamentary and rod-like particles were formed with high ZnO content by surface reaction and coagulation.