Catalytic co-pyrolysis of lignin and polyethylene over modified self-derived biochar: Tuning activation strategies for the enhancement of aromatics

Fast co-pyrolysis of lignin and polyolefin plastics is an effective way to produce bio-oil and chemicals, yet the catalytic potential of the resulting biochar remains underexplored. In this study, the role of ten different activation methods in regulating the properties of biochar derived from co-pyrolysis of enzymatic hydrolysis lignin (EHL) and high-density polyethylene (HDPE) was systematically investigated. Meanwhile, the effects of activated biochar on product distribution and aromatic generation characteristics during catalytic co-pyrolysis of EHL and HDPE were investigated. The results showed that chemical activation significantly increased the specific surface area (from 3.79 m 2 /g in the untreated biochar to 1340.93 m 2 /g) and the surface oxygen-containing functional groups of the biochar derived from co-pyrolysis of EHL and HDPE, which effectively improved the catalytic performance. The treatment with alkali activator KHCO 3 and physical activator CO 2 significantly enhanced the relative content of monocyclic aromatic hydrocarbons (MAHs) in the bio-oil from 6.87% to 26.95% and 17.09%, mainly due to introducing structural carbon defects and oxygen-containing functional groups via redox reactions during activation, which suppressed the condensation of MAHs into PAHs. Although HNO 3 in the acid activator did not increase the relative content of MAHs in the co-pyrolysis oil, the modulation of microporous structure to micromesoporous structure and the increase of carbon-oxygen double bonds enhanced the liquid product yield from 15.11% to 26.70%, which indirectly increased the absolute yield of MAHs. This study offers critical insights into the rational optimization of biochar activation strategies for the catalytic reforming of bio-oil, especially MAHs.