Kinetics of dehydroxylation, in nitrogen and water vapour, of kaolinite and smectite from Australian Tertiary oil shales

Abstract

Dehydroxylation of kaolinite and smectite is significant in oil shale processing. The possibility of shifting these endothermic reactions from the retort to the combustor by increasing the water vapour pressure was confirmed and the kinetics of dehydroxylation was determined by thermogravimetry. For kaolinite, non-isothermal and isothermal dehydroxylation in dry N 2 was second-order, with activation energies of 163 and 208 kJ mol −1 and pre-exponential factors of 2.0 × 10 12 and 3.0 × 10 13 s −1 respectively. Increasing water vapour pressure markedly increased the dehydroxylation temperature. Isothermal data were fitted to a first-order model at water vapour pressures 5 kPa, but Arrhenius plots showed large changes in the kinetic parameters. Non-isothermal results increasingly deviated from second-order with increasing water vapour pressure, but this was successfully accounted for by the Altorfer model. For Rundle smectite, non-isothermal kinetic data for dehydroxylation in dry N 2 were best fitted by the Ginstling-Brounshtein diffusion model, with an activation energy of 83 kJ mol −1 and a pre-exponential factor of 1.0 × 10 7 min −1.