Kinetics of thermal dehydration and decomposition of Fe(III) chloride hydrate (FeCl3·xH2O)

Fe(III) chloride hydrate (FeCl3·xH2O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100–200‡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‡C a second order rate model (F2) fits well, a three-dimensional diffusion (D3) model is found to fit better at temperature above 135‡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‡C. The first step which corresponds to the loss of about 4 mols of H2O, invariably follows second order kinetics (F2). 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.