Enhancing conversion and selectivity control in liquid-film dielectric barrier discharge plasma for bio-oil upgrading

Abstract

Green upgrading of bio-oils significantly enhances their potential as future energy alternatives. Nonthermal plasma hydrodeoxygenation technology, an environmentally friendly and sustainable solution for upgrading bio-oils, bypasses the high temperatures, high pressures, and catalysts typically required. However, the impact of plasma-generated particles on the process remains insufficiently understood, limiting the effectiveness of deoxygenation efficiency and calorific value enhancement. Here we propose an innovative hydrodeoxygenation mechanism for plasma upgrading of bio-oil model compound (guaiacol), emphasizing the critical role of H radicals and electron energy in enhancing guaiacol conversion and tailoring product selectivity, respectively. Our findings, derived from an integrated approach of reactive molecular dynamics and density functional theory, complemented by experimental validation, reveal that H radicals substantially extend the oxygen-containing chemical bonds. This extension, alongside a marked reduction in the energy barriers for the cleavage of O-CH₃, C-OCH₃, and C-OH bonds by 58.2 %, 72.1 %, and 77.1 %, respectively, facilitates the conversion, yielding catechol as the main product. Moreover, within Ar plasma, nearly 80 % of electrons have bond-breaking energy, a figure that increases from 31.07 % to 74.41 % in H₂ plasma with rising reduced electric field. Importantly, Ar plasma maintains high efficiency in cleaving C-OCH₃ and C-OH bonds, driving the transition of primary products from catechol to phenol, anisole, and potentially to aromatic hydrocarbons. These insights offer guidance for optimizing reaction conditions in plasma bio-oil upgrading and contribute to the efficient utilization of biomass resources and environmental protection.