Lipid extraction from microalgae using pure caprolactam-based ionic liquids and with organic co-solvent

Abstract

Background The main process limitation of microalgae biofuel technology is lack of cost-effective and efficient lipid extraction methods. Thus, the aim of this study was to investigate the effectiveness and efficiency of six caprolactam-based ionic liquids (CPILs) namely, Caprolactamium chloride, Caprolactamium methyl sulphonate, Caprolactamium trifluoromethane sulfonate, Caprolactamium acetate, Caprolactamium hydrogen sulphate and Caprolactamium trifluoromethane-acetate—for extraction of lipids from wet and dry Spirulina platensis microalgae biomass. Of these, the first three are novel CPILs. Methods The caprolactam-based ionic liquids (CPILs) were formed by a combination of caprolactam with different organic and inorganic Brønsted acids, and used for lipid extraction from wet and dry S. platensis microalgae biomass. Extraction of microalgae was performed in a reflux at 95 °C for 2 h using pure CPILs and mixtures of CPIL with methanol (as co-solvent) in a ratio of 1:1 (w/w). The microalgae biomass was mixed with the ILs/ methanol in a ratio of 1:19 (w/w) under magnetic stirring. Results The yield by control experiment from dry and wet biomass was found to be 9.5% and 4.1%, respectively. A lipid recovery of 10% from dry biomass was recorded with both caprolactamium acetate (CPAA) and caprolactamium trifluoroacetate (CPTFA), followed by caprolactamium chloride (CPHA, 9.3 ± 0.1%). When the CPILs were mixed with methanol, observable lipids’ yield enhancement of 14% and 8% (CPAA), 13% and 5% (CPTFA), and 11% and 6% (CPHA) were recorded from dry and wet biomass, respectively. The fatty acid composition showed that C16 and C18 were dominant, and this is comparable to results obtained from the traditional solvent (methanol-hexane) extraction method. The lower level of pigments in the lipids extracted with CPHA and CPTFA is one of the advantages of using CPILs because they lower the cost of biodiesel production by reducing the purification steps. Conclusion In conclusion, the three CPILs, CPAA, CPHA and CPTFA can be considered as promising green solvents in terms of energy and cost saving in the lipid extraction and thus biodiesel production process.