Advanced isoconversional kinetic analysis of Fe2O3-2Al thermite reaction for plug and abandonment of oil wells

Moving from a carbon-based to a carbon-free economy has driven the development of groundbreaking new technologies for permanent plugged and abandoned (P&A) of mature oil wells, including the use of thermites as the energetic material for the so-called “Thermal P&A” technology. Better knowledge is then much needed on such chemical reactions. Accordingly, this research presents an in-depth kinetic study of the Fe2O3-2Al thermite reaction by analyzing differential scanning calorimetry (DSC) data at three heating rates. After an endothermic peak corresponding to the aluminum melting process (∼660.3 °C), two exothermic peaks were identified corresponding to thermal stages of the overall thermite reaction: the first stage at 800–1000 °C and second stage at 1000–1300 °C. The apparent activation energy of each reaction stage was calculated using several isoconversional kinetics methods. All methods revealed significant variation of activation energy with the extent of conversion. However, the differential method of Friedmann and the flexible-integral methods of Popescu and Vyazovkin identified higher variations than the rigid-integral methods, with EA values between 188 and 356 kJ/mol for the first reaction stage and 280 and 509 kJ/mol for the second one. These high variations indicated a multi-step mechanism that requires multiple kinetic triplets. The pre-exponential factor at each extent of conversion and the reaction mode of each reaction stage were estimated by an approach based on Popescu's equation and the compensation effect. A contracting sphere and a random nucleation mechanism were identified as suitable models to describe the first and second reaction stage, respectively. Modeled data showed an excellent agreement with the experimental data of the first reaction stage, with average deviations up to 1.2 %. However, modeled data of the second stage presented more notable variations with average deviations up to 9.5 %.