Hydrothermal liquefaction of four brown macro-algae commonly found on the UK coasts: An energetic analysis of the process and comparison with bio-chemical conversion methods

Hydrothermal liquefaction (HTL) of four brown macro-algae was used to produce bio-crude and bio-char in an energy favorable way. Bio-crude yields between 9.8 wt% and 17.8 wt% (daf) with HHVs between 32 and 34 MJ/kg and bio-char yields between 10.9 wt% and 18.6 wt% (db) with HHVs between 15.7 and 26.2 MJ/kg were produced. A modification of the energy consumption ratio (ECR) index was attempted in order to include in the formula the calculation of the specific heat capacity of the feedstock used, as well as the increase of the specific heat capacity of water with temperature. A comparison in terms of energy output was made between the products from HTL and products from bio-chemical conversion of macro-algae such as anaerobic digestion (AD) and fermentation. The results indicate that HTL has higher energy output than fermentation and analogue of that from anaerobic digestion (7.91 MJ/kgseaweed and 8.25 MJ/kgseaweed from HTL and AD respectively).