Synergistic co-pyrolysıs of polyolefin plastics with wood and agricultural wastes for biofuel production

Renewable lignocellulosic biomass is a promising energy resource since its co-pyrolysis with hydrogen-rich plastics can produce high-yield and high-quality bio-oil. In this study, co-pyrolysis of agricultural wastes (i.e. corn stover) and wood wastes (i.e. narra, Pterocarpus indicus and ipil, Intsia bijuga) with polyolefin plastics (i.e. polypropylene, low-density polyethylene, and high-density polyethylene) were examined via thermogravimetric analyses. Unlike previous co-pyrolysis studies which had focused on the improvement of product yield or cumulative weight loss, herein, we present the synergistic effects on the mass decomposition rate or rate of generation of products during co-pyrolysis. The main objective of this study is to evaluate the effects of temperature, and biomass-to-plastic ratio on rate synergy during co-pyrolysis. Rate synergy values up to 10% per min were obtained for biomass and plastic blends. Activation energy and pre-exponential factor of the reactions in the co-pyrolysis process were evaluated using the Coats-Redfern method. Activation energies for agricultural waste and plastics blends ranged from 45 to 82 kJ mol−1 while that for wood wastes and plastic blends ranged from 53 to 112 kJ mol−1. Interestingly, the activation energy of the thermal decomposition of plastic was found to be lower during co-pyrolysis with biomass than in pure form. Moreover, biomass-plastic co-pyrolysis followed a two-stage degradation: biomass degradation from 200 to 400 °C and thereafter plastic degradation from 400 to 500 °C. Overall, the use of lignocellulosic biomass and waste plastics for biofuel production can also minimize the volume of solid wastes for landfills.