Biocrude from Nannochloropsis gaditana by Hydrothermal Liquefaction: An Experimental Design Approach

The aim of the present work was focused on optimising the yield and quality of the biocrude obtained by hydrothermal liquefaction (HTL) of Nannochloropsis gaditana. Temperature, reaction time and microalga concentration were the variables used to carry out an experimental factorial design with a central composite design. The responses chosen were the biocrude yield and the nitrogen and oxygen content in the biocrude phase. A second-order model was obtained to predict the responses as a function of these variables. Temperature is the most determining factor with a positive influence on biocrude yield. The maximum biocrude yield (42.3 ± 0.8 wt%) was obtained at 320 °C, 10 min of reaction and 10 wt% microalgae concentration, and the nitrogen and oxygen content significantly decreased with respect to their corresponding levels in the initial microalgal biomass. The HHV value of the biocrude was 35.7 MJ/kg. The biocrude was composed of 30% of linear and branched hydrocarbons.