Isothermal and non-isothermal decomposition of zinc malonate dihydrate in different atmospheres

摘要

Thermal decomposition of zinc malonate dihydrate was studied using isothermal gas accumulatory method under vacuum. Non-isothermal measurements were also used to study the same reaction under different dynamic gas atmospheres (i.e. N_2, air or H_2). It was found that the isothermal kinetic data were best fitted to the contracting cube equation [1 - (1 — α)~(1/3)] = kt, between 0.10 < α < 0.87 (where a is the fractional decomposition). The decomposition of the present reactant (using both the isothermal and non-isothermal techniques) was found to be sensitive to the pre-dehydration and to the mass of the reactant sample together with the prevailing gas atmosphere. NMR and IR analyses of the partially decomposed salt have indicated the formation of zinc acetate as a reaction intermediate. X-ray diffraction has characterized ZnO as the final solid product from the decomposition under vacuum or under any dynamic gas atmosphere. CO_2 together with traces (≈1.6%) of CO were the permanent gaseous products detected in the isothermal measurements. In addition, gas chromatography has identified CO_2 and acetone as the main volatile gaseous products together with traces of CO, especially at the beginning of the decomposition. Kinetic parameters, e.g. the activation energy (E_a) and the frequency factor (ln A) were calculated together with the enthalpy (ΔH) of the dehydration and the decomposition processes under different gas atmospheres.