The liquefaction of algae for the recovery of bio–oil was studied. Algae oil is a non–edible feedstock and has minimal impact on food security and food prices; furthermore, it has been identified as a favourable feedstock for the production of biodiesel and this is attributed to its high oil yield per hectare. Algae oil can be potentially used for fuel blending for conventional diesel. The recovery step for algae oil for the production of biodiesel is costly and demands a lot of energy due to the high water content and size of the algae organism. In this study hydrothermal liquefaction was used for the recovery of oil from algae biomass. Hydrothermal liquefaction uses high water activity in sub–critical water conditions to convert wet biomass to liquid fuel which makes the process more cost effective than pyrolysis and gasification in terms of energy savings on biomass drying costs. The main objective of this study was to determine suitable liquefaction reaction conditions (reaction temperature, biomass loading and reaction atmosphere) for producing bio–oil from algae and identifying the effects of these conditions on bio–oil yield and properties. Bio–oil properties are a good indication of the quality of the oil product and the significance of the liquefaction reaction conditions. The experiments were carried out in a SS316 stainless steel high pressure autoclave. An environmental scanning electron microscope with integrated energy dispersive spectroscopy was used for the characterisation of the raw algae biomass. The algae biomass was liquefied in water at various temperatures ranging from 280 to 360°C, at different biomass loadings (3 to 9 wt %) and a 5 wt% potassium hydroxide (KOH) for all experiments. The reaction time was held constant at 30 minutes in all experiments performed under CO2 and N2 atmospheres. Chloroform was used to recover the bio–oil oil from the reaction mixture following liquefaction, and the bio–oil was purified by removing chloroform using a vacuum distillation process. The bio–oil sample was methylated to the fatty methyl esters using trimethyl sulfonium hydroxide solution to determine its composition using gas chromatography. The elemental composition of the bio–oil was analysed using a Flash 2000 organic analyser. The main organic components of the bio–oil were determined using Fourier–transform infrared (FT–IR) spectroscopy. The oil yield was found to be dependent on reaction temperature and biomass loading when liquefaction was done in an inert environment, showing a significant increase at high temperatures and biomass loadings. Biomass loading had no significant influence on bio–oil yields at high temperatures in a reducing atmosphere and an average oil yield of 25.28 wt% and 20.91 wt% was obtained under a CO2 atmosphere and a N2 atmosphere at 360°C, respectively. Higher yields of C16 fatty acid were obtained at 320°C at a 3 wt% biomass loading in a CO2 atmosphere. The FTIR analyses showed the presence of oxygenated compounds such as phenols, ketones, aldehydes and ethers. The bio–oil had a reduced O/C ratio as compared to that in the original feedstock, with improved heating values. The reduction in the O/C ratio in the bio–oil indicated that deoxygenation occurred during liquefaction and that the bio–oil produced has good properties for combustion. This study indicates that the bio–oil is well suited for further processing to biodiesel because of the high C16 fatty acid content. Hydrothermal liquefaction could thus be a feasible method for producing bio–oil from Scenedesmus acutus.
- Engineering