Hydrothermal treatment for biofuel production from Chlorella sp.KR1 based on energy return on investment (EROI)

Abstract

Biofuel production from microalgae has been intensively studied due to high lipid content and productivity. Hydrothermal liquefaction (HTL) was considered as promising technology for biofuel production. HTL decompose thermo-chemically decompose whole microalgae into biocrude using subcritical water ($150-375^\circ C$). Previous studies focused on maximizing bio-crude, however, quality and co-product in aqueous phase were not investigated. In this study, $Chlorella sp. KR1$ was hydrothermal treated and quality of the bio-crude was separated and analyzed in terms of asphaltene and non-asphaltene. Bio-crude purity, heteroatom (O, N, and S), effective hydrogen-to-carbon ratio ($H/C_{eff

$), and the higher heating value (HHV) were investigated. As temperature increases, bio-crude yield was increased especially non-asphaltene. Asphaltene which shows extremely low purity, H/Ceff, HHV, and high heteroatom content were produced from carbohydrate and protein at high temperature (> $200^\circ C$). Carbohydrate in aqueous phase was significantly reduced with increase of asphaltene. EROI was calculated with assumption that carbohydrate was converted into ethanol. The result shows that hydrothermal treatment at $180^\circ C$ can economically produce biofuel.