Steam explosion as a fractionation step in biofuel production from microalgae

• Steam explosion pretreatment of microalgae gave the highest lipid extraction yields.
• Acid catalysed steam explosion is used for simultaneous lipid and sugar release.
• High efficiencies are achieved in the extraction of lipid using n-hexane.
• Remarkable sugar yields up to 96% are obtained from steam exploded microalgae.

In this study, various pretreatment methods (autoclaving, ultrasound, microwave and steam explosion) have been compared to determine the most efficient method for the extraction of lipids from three different samples of microalgae (Nannochloropsis gaditana, Chlorella sorokiniana and Phaeodactylum tricornutum). Among the studied methods, steam explosion gave the highest lipid extraction yields for the three microalgae species. Therefore, the method was further studied and the application of acid catalysed steam explosion pretreatment was investigated for simultaneous lipid extraction and sugar release from microalgae. The effect of different variables, including temperature and acid concentration, was analysed. The experimental results demonstrate the efficacy and feasibility of the acid catalysed steam explosion pretreatment, followed by n-hexane lipid extraction. Remarkable sugar yields up to 96% were achieved under the pretreatment conditions of 1.7% sulphuric acid concentration and a temperature of 150 °C during steam explosion. Besides, this study verified high efficiencies in the extraction of lipid of exploded microalgae using n-hexane against the low efficiencies obtained for the untreated microalgae.