(704a) Tunable Cellulose Fast Pyrolysis Via Noncovalent Interactions Induced By Molten Plastics

Fast pyrolysis of lignocellulosic biomass is a promising approach for producing biofuels and value-added chemicals. Currently, the resultant bio-oil quality and diverse product distribution make it economically unfeasible. Biomass−plastics co-pyrolysis has the potential for producing high-quality bio-oils while addressing plastic waste management in an eco-friendly manner.

The presence of plastics alters product distributions of cellulose pyrolysis, but there is still a knowledge gap in the molecular-level understanding of how plastics with different functional groups vary cellulose pyrolysis reaction kinetics. Our previous density functional theory (DFT) study elucidates a new reaction mechanism for cellulose activation induced by noncovalent interactions (NCIs).^[1] It is therefore hypothesized that functional groups in molten plastics perturb the kinetics of cellulose pyrolysis by inducing NCIs. To test this hypothesis, binary co-pyrolysis experiments of cellulose with polyethylene, polystyrene, polyethylene glycol, and polyketone were conducted following the procedures in our previous work.^[2] DFT calculations were performed to study reaction pathways of cellulose pyrolysis in the presence of propane, benzene, dimethyl ether, and acetone as surrogates for polyethylene, polystyrene, polyethylene glycol, and polyketone, respectively.

The results demonstrate that the selectivity toward levoglucosan, glycolaldehyde, 5-hydroxymethylfurfural are enhanced by 15.6, 8.2, and 5.1 %, respectively, in the presence of polyketone, polyethylene glycol, or polystyrene compared to those in the presence of polyethylene. These changes in product distributions agree with DFT calculations, which reveal that the functional groups in molten plastics induce NCIs that perturb the geometries and partial charges of transition states. This perturbation creates transition-state (de-)stabilization, leading to catalytic or inhibitory effects. These findings could help in the design of molten plastics that act either as unconventional catalysts or inhibitors for selectivity improvement in biomass pyrolysis.

References
[1] F. Sakirler, H.-W. Wong, J. Phys. Chem. A 2022, 126, 7806-7819.
[2] M. Nallar, H.-W. Wong, ACS Sustainable Chem. Eng. 2019, 7, 9480-9488.