Synergistic interactions, kinetic and thermodynamic analysis of co-pyrolysis of municipal paper and polypropylene waste

Abstract

Co-pyrolyzing mixed wastes of the different physicochemical kinds is often a challenge. This study reports the co-pyrolysis of homogeneous polypropylene plastic and paper wastes, highlighting their characteristics, synergetic effects, and kinetic and thermodynamic parameters using robust thermal gravimetric analysis technique.Results show that 20% paper in the blend improved the bulky density, fuel ratio from 0.09 to 0.13, maximum degradation temperature from 369.55 to 447.88 °C and thermal stability from 381.60 to 393.82 °C. The average activation energies of the blend from Flynn-Wall-Ozawa, Friedman and Coats-Redfern were 148.73 ± 7.87, 133.98 ± 11.59 and 143.74 ± 13.83 kJ/mol, respectively, lower than at least one of the homogenous wastes. All the enthalpy and Gibbs free energy values were positive, thus, endothermic non-spontaneous pyrolysis. In addition, average enthalpies for the mixed sample were lower than homogeneous polypropylene (from 159.57 ± 11.86, 153.74 ± 16.07 and 181.27 ± 28.90 to 143.60 ± 24.42, 128.86 ± 34.61 and 138.61 ± 41.32 kJ/mol, respectively) in all models, respectively. The entropy values for all samples were negative. They decreased with increasing conversion rates for mixed waste samples, indicating ease to reach thermodynamic equilibrium during pyrolysis. There is an insignificant difference between the experimental and the calculated TGA/DTG curves, signifying meagre synergetic effects. In addition, the 3D surface response for the conversion rate against temperature and heating rate showed closeness in results between the homogeneous and mixed waste. The results of this study are vital in handling municipal solid waste without any need for isolation during the conversion process to valuable products.