Oil extraction from microalga Nannochloropsis sp. with isopropyl alcohol

An efficient process for fractioning microalgae oil and non‐lipid biomass was developed. Isopropyl alcohol (IPA) was used to extract oil from Nannochloropsis sp. at 80 °C, leaving the majority of non‐lipid biomass in the solid fraction. The effectiveness of extraction with or without a dewatering pretreatment (DW) was compared. Effects of dewatering time and solvent ratio, IPA concentration, IPA refluxing time, and sonication pretreatment on the oil and biomass yields were studied. The dewatering conditions with a high water‐to‐alcohol ratio (W/A = 2:1) and mild mixing (1 min gentle shaking) had 14 % less oil loss in the DW fraction than that with a low water‐to‐alcohol ratio (W/A = 1:1) and vigorous mixing (30 min and 300 rpm mixing). Sonication resulted in 14–26 % more oil loss in the DW fraction when compared to intact cell treatment. Without dewatering, 85 % of the total oil from intact cells was extracted by a single extraction using 70 % (wt) IPA aqueous solution. The 88 and 95 % IPA treatments extracted similar percentages of oil to that of the 70 % IPA, but used two‐ and fivefold more solvent. The amount of oil extracted from broken cells increased with increasing IPA concentrations. An effective extraction can be completed in 30 min. On a 100‐g (wet matter) scale, the 70 % IPA achieved 92 % oil yield and 93 % non‐lipid biomass yield.