Thermo-kinetic investigation of the multi-step pyrolysis of smoked cigarette butts towards its energy recovery potential

The present study attempts to explore the energy potential of smoked cigarette butts (SCB) through pyrolysis. For the first time, the pyrolysis characteristics, including the kinetic triplet and the thermodynamic parameters, were investigated using non-isothermal thermogravimetry. Firstly, three pseudo-components were successfully deconvoluted from the multiple-step pyrolysis of SCB using the asymmetrical Fraser-Suzuki function, which corresponds to the devolatilization reactions of retained organic volatile components (PS-1), unburned tobacco (PS-2), and cellulose acetate fibers (PS-3). Posteriorly, the isoconversional methods of Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink were used to obtain the activation energy values, which were lower for PS-1 (from 101.87 to 108.77 kJ mol−1). The frequency factor values for SCB pyrolysis determined by the compensation effect method were 1.77 × 1012 min−1 for PS-1, 9.44 × 1016 min−1 for PS-2, and 9.62 × 1020 min−1 for PS-3. According to the master plot method, the three pseudo-components followed nth-order reaction models. An acceptable correspondence was observed between experimental and reconstructed pyrolysis behavior, proving the representativity and reliability of the obtained kinetic triplets. Both positive values of ΔH and ΔG suggest that the pyrolytic conversion of smoked cigarette butts into biofuels can be considered as a non-spontaneous conversion. These pyrolysis-related findings from SCB can be used to offer a good opportunity for its valorization as an energy commodity instead of a neglected solid residue.