Characterization of biocrudes recovered with and without solvent after hydrothermal liquefaction of algae

Bench-scale, batch experiments exploring algae hydrothermal liquefaction typically use organic solvents such as dichloromethane (DCM) to recover biocrude from the reactor contents. Commercial-scale, continuous processes, however, may separate biocrude and the aqueous phase co-product without solvent use. Herein, we provide the first thorough examination of the influence of DCM extraction on biocrude yield and composition from microalgae liquefaction in hot compressed water (350 degrees C, 20 min). We provide gravimetric biocrude yields and biocrude characterization via elemental analysis, GC-MS, NMR, and IR spectroscopies. The application of DCM increases the biocrude yield because it extracts water-soluble compounds from the aqueous phase co-product. Indeed, the biocrude recovered from the aqueous phase accounted for about 8 wt% of the total amount of biocrude. The addition of these molecules diminishes the biocrude quality, however, by decreasing the C and H content, increasing the O and N content, and thereby decreasing the higher heating value of the biocrude. The biocrude extracted from the aqueous phase had a remarkably different elemental composition than did the biocrude recovered without solvent. The O and N contents were more than twice as high, and the higher heating value was 20% lower. The biocrudes recovered directly from hydrothermal liquefaction (e.g., without water and DCM coming into contact) were 87%-88% C and H, and possessed a higher heating value of >39 MJ/kg. (C) 2014 Elsevier B.V. All rights reserved.