Coupled low temperature algae hydrothermal liquefaction and catalytic hydrotreating to produce low nitrogen fuel intermediates

A four-stage hydrothermal liquefaction and catalytic upgrading process was used to generate a refinery-grade biocrude from algae biomass. Low-temperature liquefaction (PT: 225 C, 15 min) was implemented to hydrolyze algal proteins and partition nitrogen from the solid phase. The aqueous co-product was analyzed for nutrient and toxin concentrations. The retained solid biomass was subjected to a higher temperature hydrothermal liquefaction (HTL: 350 C, 60 min). Heterogeneous catalytic hydrodeoxygenation (HDO: 350 C, 240 min) was conducted using ruthenium (5% on carbon), several forms of cobalt molybdenum catalysts (on aluminum oxide), and a H2-reduced mixed metal oxide (mainly iron oxide) byproduct known as red mud. The extent of HDO/HDN was limited by low hydrogen concentrations stemming from the consumption of this reactant in a batch atmosphere, and thus the HDO stage was repeated twice per batch, with fresh hydrogen recharged. Implementing all four stages with ruthenium on carbon as catalyst produced the most favorable biocrude, with minimal nitrogen levels and a chemical composition dominated by alkanes and aromatics. Macromolecular degradation pathways were also studied by performing HTL and HDO on model lipids, proteins, and carbohydrates in varying representative ratios.