Pyrolysis kinetics of walnut shell and waste polyolefins using thermogravimetric analysis

Co-pyrolytic behavior and kinetics of walnut shell (WS), polypropylene (PP), low density polyethylene (LDPE) and their blends were investigated using a thermogravimetric analyzer. WS and plastic samples were blended weight proportion of 1:2; 1:1 and 2:1. The desired final temperature of 650 °C was achieved at five different heating rates (5, 10, 15, 20 and 50 °C min−1). Three devolatilization stages of WS were determined as removal of water, decomposition of hemicellulose and cellulose, and lignin. On the other hand, the degradation curves of PP and LDPE showed only one stage belonging to decomposition of polyene chains. The kinetic parameters like activation energy and pre-exponential factor of pyrolysis zone were determined by applying Arrhenius and Coats Redfern method. According to Arrhenius method, the average value of activation energies of WS, PP and LDPE were 69.32, 295.65 and 254.55 kJ mol−1, respectively. Moreover by using Coats Redfern method, average value of activation energies of WS, PP and LDPE were determined as 101.58, 333.53 and 316.77 kJ mol−1, respectively. As the pyrolysis reaction advanced the Arrhenius parameters (E and A) increased or decreased simultaneously, exhibiting a compensation effect.