Mechanistic Study on the Enhanced Synergistic Effect in Co-pyrolysis of Huangling Coal and Enzymatic Hydrolysis Lignin via Hydrothermal Pretreatment
Co-pyrolysis of oil-rich coal and biomass is a promising route to enhance oil and gas production, yet the underlying synergistic mechanisms remain poorly understood. This study investigates the effect of hydrothermal pretreatment (HTP) on the co-pyrolysis of Huangling coal (H) and enzymatic hydrolysis lignin (E). Raw and pretreated samples were characterized via proximate/ultimate analysis, SEM, ICP-OES, and 13C-NMR. Fixed-bed pyrolysis experiments were conducted to evaluate synergistic performance. Results show that HTP reduces oxygen content, develops pore structure, and increases concentrations of inorganic metal ions (Ca, K, Fe) in the aqueous phase. Structural modifications bring the carbon skeleton of E closer to that of H, with increased bridge carbon ratio and improved thermal stability, aligning pyrolysis temperature ranges. For the H/E blend (8:2) after 24 h HTP, tar yield increases by 80.52% compared to untreated blend, with significant rises in aliphatic compounds and monocyclic aromatic hydrocarbons. Gas yields of H2, CO, and CH4 increase by 5.47%, 10.98%, and 9.27%, respectively, while CO2 and pyrolysis water generation are inhibited (water yield decreases by 93.98%). Semi-coke pore structure becomes more developed. The enhanced synergistic effect is attributed to a multi-fold mechanism of 'component interaction-structural modification-catalytic cracking'. These findings provide theoretical support for developing technologies to improve co-pyrolysis of oil-rich coal and biomass, advancing low-carbon, high-quality utilization.