Conversion efficiency and oil quality of low-lipid high-protein and high-lipid low-protein microalgae via hydrothermal liquefaction

Hydrothermal liquefaction (HTL) is a promising technology for converting algae into biocrude oil. Here, HTL of a low-lipid high-protein microalgae (Nannochloropsis sp.) and a high-lipid low-protein microalgae (Chlorella sp.) was studied. An orthogonal design was applied to investigate the effects of reaction temperature (220-300 degrees C), retention time (30-90 min), and total solid content (TS, 15-25% wt) of the feedstock. The highest biocrude yield for Nannochloropsis sp. was 55% at 260 degrees C, 60 min and 25% wt, and for Chlorella sp. was 82.9% at 220 degrees C, 90 min and 25% wt. The maximum higher heating values (HHV) of biocrude oil from both algae were similar to 37 MJ/kg. GC-MS revealed a various distribution of chemical compounds in biocrude. In particular, the highest hydrocarbons content was 29.8% and 17.9% for Nannochloropsis and Chlorella sp., respectively. This study suggests that algae composition greatly influences oil yield and quality, but may not be in similar effects. (C) 2013 Elsevier Ltd. All rights reserved.