Kinetics of thermal dehydration and decomposition of Fe(III) chloride hydrate (FeCl3 center dot xH(2)O)

Abstract

Fe(III) chloride hydrate (FeCl3 . xH(2)O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100-200 degrees C. The kinetics of these two parallel thermal processes has been studied by both isothermal and non-isothermal methods. Whereas for the dehydration reaction at temperature below 125 degrees C a second order rate model (F-2) fits well, a three-dimensional diffusion (D-3) model is found to fit better at temperature above 135 degrees C. For the dehydrochlorination reaction an interface growth controlled model of 1/3 order (F 1/3) appears to be the most suitable over a wide range of reaction. Dynamic thermogravimetry reveals two major steps in the temperature range 50-250 degrees C. The first step which corresponds to the loss of about 4 mols of H2O, invariably follows second order kinetics (F-2). The second step which is predominantly a process of dehydrochlorination, generally fits mixed diffusion controlled models due to the overlapping with the dehydration process. There is an excellent agreement in results among the isothermal and non-isothermal methods of determining kinetic parameters.