Tandem One-Pot Upgrading of Lignin Oil and Coprocessing with Hydrotreated Gas Oil over a Ni–Cu-Modified Red-Mud Catalyst

Hydrodeoxygenation (HDO) of lignin oil (LO) upgrades oxygen-rich, unstable biocrudes into stable hydrocarbons. This study examined one-pot HDO of LO during coprocessing with hydrotreated gas oil (HTGO) in a batch high-pressure reactor using red mud (RM)-supported Ni/Cu catalysts. Response surface methodology optimized the HDO of 10 wt % LO/90 wt % HTGO blend by varying temperature (320–360 °C), catalyst loading (15–30 wt %), and H2 pressure (500–800 psi). Under optimum conditions (342 °C, 24 wt % catalyst, 588 psi H2), 72.1 ± 0.6% deoxygenation was achieved, reducing oxygen from 2.7 to 0.76 wt %. Among the catalysts tested, equimolar Ni–Cu/RM showed the best performance, consistent with its highest oxygen vacancy fraction and favorable acidity. Microscopy, viscosity, density measurements, simulated distillation, GC × GC-FID, 1H NMR, and gas-phase analysis further confirmed the effective incorporation of LO into the HTGO matrix.