(43f) Evaluation of Co-Pyrolysis of Lignin and Plastics through Thermogravimetric Analysis

Lignin comprises up to 30% of plant material and accounts for approximately 40% of the total energy density of lignocellulose. It is an abundant low-value product generated from pulp and paper process. Converting lignin into valuable products (e.g. fuels and chemicals) attracts great research interests. Thermochemical processes, such as pyrolysis, have been explored for bio-oil production from lignin. However, due to the inherent chemical characteristics, lignin easily forms char/coke and clogs the reactors during pyrolysis. In addition, the high oxygen content makes the bio-oil product less stable.

Great amount of waste plastics is causing an environmental crisis globally. The methods of plastic recycling are very limited. Traditional waste management practices of plastics include landfilling and combustion. Only very limited percentage of recyclable plastics are remelted and reused. Waste management costs in the US have skyrocketed since China banned the imports of waste plastics in 2018. Given the high hydrogen content, waste plastics could serve as a potential hydrogen donor for lignin pyrolysis.

In this work, kraft lignin (KL) is blended with polystyrene (PS) and polyethylene (PE) respectively at different ratios for co-pyrolysis. The primary goal is to explore the impact of blending lignin and plastics in thermogravimetric performance. In addition, the estimated mass loss of lignin-plastic blend is calculated based on the mass ratio to compare with experimental results.

Our results have shown differences between co-pyrolysis of the blends and individual materials. The maximum mass loss rate of KL (0.4 %/ °C at 401 °C) is much lower than those of PS (2.98 %/ °C at 393 °C) and PE (3.88 %/ °C at 452 °C). The addition of PS (from 25% to 50% to 75%) gradually increases the maximum mass loss rate from 0.93 %/°C, to 1.78 %/°C, to 2.43 %/°C. The addition of PE shows the similar trend. It is noted that, for co-pyrolysis of lignin and plastics blends, the maximum mass loss rate of KL/PS is ~10% different to the estimated binary combination, while ~20% difference in the maximum mass loss rate was observed for KL/PE blend. In this presentation, we will discuss the interaction between lignin and plastic polymers during co-pyrolysis in detail.