Thermal dissociation of compressed ZnO and SnO2 powders in a moving-front solar thermochemical reactor



The high-temperature thermal dissociation reaction of ZnO and SnO2 was investigated, as part of a two-step thermochemical water-splitting cycle for H2 production. A lab-scale solar reactor (1 kW) was designed, built, and operated for continuous dissociation of volatile oxides under reduced pressure. In this reactor, compressed oxide powders placed in a vertical ceramic cavity are irradiated by highly concentrated solar energy. The reactor design allows moving the reaction front for achieving continuous reactant feeding. ZnO and SnO2 thermal dissociations were successfully performed at about 1900 K, with the recovery of up to 50% of products as nanopowders with high specific surface area (in the range 20–60 m2/g) and with mass fractions of reduced species up to 48 wt % for Zn and 72 wt % for SnO. The performed O2 measurements confirmed the kinetics of ZnO dissociation and gave an activation energy of 380 ± 16 kJ/mol, based on an ablation regime of the ZnO surface. © 2010 American Institute of Chemical Engineers AIChE J, 2011