Transition Metals Impregnated Red mud-derived Catalysts for the Valorization of Alkali Lignin to Monomeric Phenols

Lignin, a major byproduct of biorefinery processes, represents a promising renewable resource for producing phenolic compounds, offering a sustainable alternative to petrochemical-derived chemicals. This study investigated the effects of transition metals loaded industrial-waste red mud (RM)-derived catalysts (Co/RM, Cu/RM, and Ni/RM) for the hydrothermal liquefaction of alkali lignin. The results revealed the effective breaking of the lignin structure with the Co/RM catalyst for the maximum bio-oil production (20.7 wt%) at 250 ℃/15 min. The maximum conversion (40.3%) was determined with Cu/RM catalyst, with a high proportion of gas yield (26.6 wt%). GC-MS analysis revealed the promotion of demethoxylation with the utilization of a catalyst by a significant decrease in the selectivity for methoxy phenols. The high HHV value (31.8 MJkg^{− 1}) of catalytic bio-oil (Co/RM-250) exhibits the upgradation of lignin into high-calorific bio-oil. The utilization of byproduct char (Co-RM-250) was also examined for the adsorption of pharmaceutical pollutants, such as tetracycline, which showed a maximum adsorption of 23% without any further pretreatment of Co/RM immobilized char.