Cleaner Engineering and Technology (Apr 2023)
Synergy, kinetics, and thermodynamics analysis in the valorization of waste bakelite through co-pyrolysis with HDPE
Abstract
Bakelite, a thermosetting plastic, can't be recycled suitably by pyrolysis as it is charred upon heating with low conversion to useful products. So, it is required to improve the conversion before charring in order to recycle it into valuable products through pyrolysis. Co-pyrolyzing bakelite with high-density polyethylene (HDPE) should improve its conversion before charring and obtaining more useful products. The design of a co-pyrolysis process requires kinetics and thermodynamic parameters. In this context, co-pyrolysis synergy, kinetics, and thermodynamics of HDPE blended Bakelite (1:1 by wt.) are studied by a variety of kinetics models to calculate kinetics triplets and predict a suitable mechanism. The thermal degradation experimental data are taken from ambient to 1000 °C at 5, 10, 20, 30, and 50 °C/min heating rates in an inert atmosphere. The co-pyrolysis synergy is ascertained from the alteration of temperature zone and weight loss pattern in thermal degradation. HDPE blended Bakelite degraded thermally in two stages (215–420 °C and 425–550 °C). The thermal degradation of HDPE blend Bakelite for the first stage (i.e., 215–420 °C) follows the third order (F3)- based model with activation energy 154 kJ/mol while that for the second stage (i.e., 425–550 °C) follows the 1-D diffusion (D1) model with activation energy 355 kJ/mol. The order of the reaction for the first stage is in the range of 0.035–0.352 and that in the second stage is in the range of 0.110–1.048 for different temperatures. The values of change in free energy, change in enthalpy, and change in entropy for the thermal degradation of HDPE blended Bakelite in the first and the second stage is 590.303 kJ/mol, 66.745 kJ/mol, −939.958 × 10-3JK-1mol-1 and 813.062 kJ/mol, 148.574 kJ/mol, - 876.864 × 10-3 JK-1mol-1 respectively. These kinetic and thermodynamic parameters definitely contribute to the optimization of pyrolysis reactor design.
