Kinetic behaviour and reactivity of zinc ferrites for hot gas desulphurization

Different zinc ferrite samples have been prepared with varying Fe:Zn atomic ratios and preparation procedures in order to optimize their behaviour as hot gas desulphurization agents. Kinetic studies on metal oxide sulphidation were performed in a thermobalance and sulphur removal tests were conducted in a fixed-bed reactor. Fresh and exhausted samples were characterized by several physical techniques. The results show that reaction rate is mainly controlled by mass transfer processes of the reactant through the gas film in contact with the solid and through the sulphide layer. Bulk ferrites displayed the best performance for sulphur removal. Ferrites deposited on an alumina substrate by impregnation are highly dispersed, however they exhibited a very poor efficiency for sulphur removal. Solid-state reactions of single oxides at the alumina interface, i.e. zinc and/or iron aluminate formation, instead of pore occlusion by the active ingredient seem to be responsible for a low reactivity.