Thermodynamics and kinetics analysis of thermal dissociation of tri-n-octylamine hydrochloride in open system: A DFT and TGA study

Abstract The thermal dissociation of tri -n- octylamine hydrochloride (TOAHCl) in open system was investigated by TGA and DFT methods. The dissociation starts at the temperature of about 120 °C which was predicted with DFT calculations and verified by isothermal TGA. Then a thermodynamic cycle depicting the dissociation process was built. The thermal dissociation which couples with the evaporation of products tri -n- octylamine (TOA) and HCl undergoes two continuous steps due to the evaporation speed difference between the two compounds. Based on the assumption, kinetics analysis was performed by employing isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Starink. The activation energies of the two steps fall in the range of 81.1 ± 2.6 kJ mol −1 and 96.8 ± 13.4 kJ mol −1 , which are comparable with the enthalpy values from 94.7 ± 5.6 kJ mol −1 to 100.1 ± 5.4 kJ mol −1 .The comparability indicates that the dissociation of TOAHCl is a process with no transition state which is in accordance with the DFT prediction. Model-fitting methods were performed by simultaneous treatment of kinetic curves under different temperature programs via reaction-order kinetics mechanism. And the results reveal that the reaction orders are 0.21 and 0.07 respectively for the two steps.