The role of heating rate in hydrothermal liquefaction of lignin: Insights from reactive molecular dynamics simulations

Hydrothermal liquefaction (HTL) offers a promising pathway for converting lignin into valuable biofuels and chemicals. Heating rate is an important factor influencing the conversion efficiency of HTL, yet existing literature presents conflicting findings. Some studies report positive effects while others indicate minimal impact on biocrude yield. For this reason, we utilized ReaxFF molecular dynamics simulations to investigate the effects of varying heating rates on lignin hydrothermal liquefaction processes. Our comprehensive study reveals that at lower temperature ranges, higher heating rates indeed accelerate lignin degradation pathways, leading to increased biocrude yields. However, at higher temperatures, the influence of heating rate on both biocrude yield and composition becomes negligible, demonstrating that temperature is the primary factor governing biocrude production and other byproduct formations such as solid and gas fractions. These findings align with recent experimental observations regarding the role of heat rate in biomass conversion processes. The present study underscores the importance of integrating advanced computational tools like ReaxFF in future research endeavors aimed at optimizing HTL processes for enhanced biocrude yield and byproduct distribution. • The impact of heating rates on hydrothermal liquefaction (HTL) was investigated using ReaxFF molecular dynamics simulations. • Higher heating rates accelerate biocrude yield at lower temperatures. At higher temperatures, temperature is the key factor. • This study resolves controversies in existing literature by providing mechanistic insights into HTL processes. • The heating rate has little effect on the O/C and H/C ratios of biocrude and solid products.