Co-pyrolysis of cotton stalks and polyethylene film: A study on synergetic effects, kinetic characteristics, and reaction mechanism

The co-pyrolysis of cotton stalks (CS) and polyethylene is of great significance for the resource utilization of agricultural waste. This study integrates thermogravimetric experiments, finite element simulation and density functional theory to construct a multi-scale collaborative analysis framework, breaking through the limitations of traditional single-scale research. Through the multi-dimensional collaboration of "experiment-simulation-theory", the synergistic effect, kinetic characteristics and reaction mechanism of co-pyrolysis of CS and low-density polyethylene (LDPE) were investigated. The results indicate that co-pyrolysis reduces the biochar yield, raises liquid yield, increases the hydrocarbon content in the gaseous products, and lowers CO levels. It also reduces both the activation energy and the pre-exponential factor. The average activation energy and pre-exponential factor of the co-pyrolysis of CS:LDPE= 1:1 are the lowest among all pyrolysis processes of the materials, being 184.42 kJ·mol⁻¹ and 1.32 × 10 ¹ ⁸ s⁻¹ , respectively. Its average activation energy is 24.62 % lower than that of pure CS pyrolysis (244.64 kJ·mol⁻¹) and 24.06 % lower than that of pure LDPE pyrolysis (242.85 kJ·mol⁻¹). Cellulose (CE), hemicellulose (HM), and lignin (LG) in CS each contribute differently to the co-pyrolysis behavior of CS and LDPE. The co-pyrolysis reaction is endothermic and non-spontaneous, and the interactions involved are complex, making classical reaction-mechanism models unsuitable. The initial stage is dominated by reactions between highly reactive parts of the biomass and the unstable radicals generated from LDPE during pyrolysis. Overall, this study provides a systematic investigation of the co-pyrolysis of CS and polyethylene, providing theoretical support for advancing co-pyrolysis technologies involving materials such as straws and polyethylene plastics. • The co-pyrolysis of CS and LDPE exhibits a significant synergistic effect on product formation. • The co-pyrolysis of CS and LDPE reduced the activation energy of the reaction. • The initial reaction arises from the interaction between CS active sites and LDPE pyrolysis radicals.