Co-pyrolysis of Lignocellulosic Residues and Plastics: a Simulation Approach to Predict Product Yields

Abstract

Plastic waste generation, a global environmental concern, has more than doubled over the past two decades. Given the rising projections of plastic use and waste by 2060, immediate actions are required to improve waste management and reduce plastic leakage. Plastic-to-fuel technologies such as co-pyrolysis of plastic and biomass residues are interesting options for polymer chemical recycling. Co-pyrolysis happens at high temperatures, low residence times, and inert atmospheres and converts plastics and biomasses into liquid (bio-oil and wax), solid (char), and gaseous products of high heating value and economic interest. Although some development has been made in understanding the key aspects of biomass-plastic co-pyrolysis, little has been done toward representing such a process via simulation. In this context, this work developed, in Aspen PlusTM, a simulation of the co-pyrolysis of xylan, a hemicellulose type, and high-density polyethylene (PE). The simulation aimed at representing the main co-pyrolysis phenomena using a hybrid equilibrium-kinetic approach and properly predicting pyrolysis yields. The simulation was run at different temperatures (500–700 °C) and PE blending proportions (10–90 wt%) and the results were compared to experimental data. The results have shown that increasing pyrolysis temperatures produced higher bio-oil and gas yields as a result of higher degradation of the feedstock structure, while higher PE blending proportions had the opposite effect. As for the char yields, PE contents up to 70 wt% decreased the char yields, while higher PE levels resulted in an opposing trend. This work shows that combining polymer decomposition equilibrium and biomass fast pyrolysis kinetics reasonably predicts product yields and can be used for the design of co-pyrolysis processes and waste management chains.