Energy-efficient extraction of fuel from Chlorella vulgaris by ionic liquid combined with CO2 capture

Abstract

Algae-sourced feedstocks remain confined to commercialization because of the high cost and energy consumption of biomass cultivation and feedstock extraction. In this study, to reduce the energy consumption required for algae extraction, experiments with Chlorella vulgais extraction by ionic liquids (ILs) combined with CO2 capture were conducted considering that captured CO2 by ILs can compensate the energy consumption of extraction. The results showed that the addition of CO2 to [BMIM][BF4] increased the lipid yield of Chlorella vulgaris from 68.0% to 75.6%. The properties of synthesized biodiesel from C. vulgaris lipids met the UNE-EN 14214 European biodiesel standard except for oxidative stability. Protein denaturation and degradation were found during the lysis of algae cells. Approximately 82.2wt.% of the total extracted proteins could be precipitated during both algae lysis and supernatant liquid drying. A microalgae-to-biofuel route including C. vulgaris extraction and CO2 capture was proposed that involves wet algae input and delivery outputs of water, biodiesel, pyrolysis oil, proteins, sugars, biogas and glycerol. Fossil energy ratios (FER) based on the overall energy balance were 3.30 (n=1, n is the volume ratio of IL to wet algae) and 3.84 (n=2) for [BMIM][BF4] with CO2 capture, approximately 2.5 times those based on commercially available technologies. The possibilities of synthesizing novel ILs that show both high CO2 absorption and good abilities in cell wall breakage are discussed. More progress is greatly needed to reduce IL recovery loss.