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

Abstract

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