A quantitative kinetic model for the fast and isothermal hydrothermal liquefaction of Nannochloropsis sp.

•Conducted comprehensive kinetic study of microalgal HTL product distribution.•Developed microalgal HTL kinetic model valid over short timescales (10 s–10 min).•46 wt% biocrude yield predicted after 1 min at an isothermal temperature of 400 °C.•Model demonstrates trade-offs between biocrude quantity and aqueous phase recovery.

Hydrothermal liquefaction (HTL) is a technology for converting algal biomass into biocrude oil and high-value products. To elucidate the underlying kinetics for this process, we conducted isothermal and non-isothermal reactions over a broad range of holding times (10 s–60 min), temperatures (100–400 °C), and average heating rates (110–350 °C min−1). Biocrude reached high yields (⩾⩾37 wt%) within 2 min for heat-source set-point temperatures of 350 °C or higher. We developed a microalgal HTL kinetic model valid from 10 s to 60 min, including significantly shorter timescales (10 s–10 min) than any previous model. The model predicts that up to 46 wt% biocrude yields are achievable at 400 °C and 1 min, reaffirming the utility of short holding times and “fast” HTL. We highlight potential trade-offs between maximizing biocrude quantity and facilitating aqueous phase recovery, which may improve biocrude quality.