Co-pyrolysis behaviors of biomass and polymer plastics by using reactive molecular dynamics simulation

Co-pyrolysis of oxygen-rich biomass and hydrogen-rich plastic polymer is a promising approach for waste management, which has been investigated by using reactive molecular dynamics simulation (ReaxFF MD) in this work. The blend models containing multicomponent mixtures of polymer (polyethylene, polypropylene, polystyrene) and biomass (cellulose, hemicellulose and lignin) were constructed for the first time, which is close to the real utilization of waste materials. The simulation results show that the degree of positive synergistic effect between biomass and polymer increases with temperature, where the polymer promotes biomass pyrolysis and delays its recombination. Co-pyrolysis greatly affects the product yields through cross reactions of hydrogen and hydroxyl transfer, leading to more oxygen-containing bio-oils produced with the aid of polymers providing hydrogen. Produced from heavy tar at first and light char at late pyrolysis period, char precursors are generated more and faster in the co-pyrolysis system with more biomass because oxygen functional groups provide the initial cross-linking sites. As compared to pyrolysis of only binary components, the observed qualitative synergistic results in co-pyrolysis of biomass-polymer mixtures provide important insights into the detailed reactions for co-pyrolysis process, which can complement experimental observations to modulate the nature and yield of the desired bio-oils and bio-chars.