Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor

Wet algae slurries can be converted into an upgradeable biocrude by hydrothermal liquefaction (HTL). High levels of carbon conversion to gravity separable biocrude product were accomplished at relatively low temperature (350°C) in a continuous-flow, pressurized (sub-critical liquid water) environment (20MPa). As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent and biomass trace components were removed by processing steps so that they did not cause process difficulties. High conversions were obtained even with high slurry concentrations of up to 35wt.% of dry solids. Catalytic hydrotreating was effectively applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude to form liquid hydrocarbon fuel. Catalytic hydrothermal gasification was effectively applied for HTL byproduct water cleanup and fuel gas production from water soluble organics, allowing the water to be considered for recycle of nutrients to the algae growth ponds. As a result, high conversion of algae to liquid hydrocarbon and gas products was found with low levels of organic contamination in the byproduct water. All three process steps were accomplished in bench-scale, continuous-flow reactor systems such that design data for process scale-up was generated. •Algae-water slurries were processed in a continuous-flow reactor system.•Whole algal biomass was converted into a gravity separable biocrude.•Biocrude was hydrotreated into a liquid hydrocarbon mixture, low in O, N, and S.•Aqueous byproduct from HTL was processed catalytically to produce a fuel gas.•The resulting water stream could be recycled for nutrients such as ammonia.