Recyclable CO2/DES-enabled microalgae efficient pretreatment and in-situ transesterification for biodiesel production from all component

Conventional microalgae biodiesel production requires more solvents and energy due to cell wall stubbornness and process complexity. This study synthesized a functional deep eutectic solvent (fDES) for microalgae pretreatment and in-situ transesterification. Because of its pretreatment and transesterification activity, fDES can be used for pretreatment, oil extraction, and transesterification catalysis, obtaining 98.9 % yield of biodiesel. Injecting and releasing CO2 can switch the polarity of DES to separate biodiesel and recover fDES components, enhancing process efficiency and sustainability of biodiesel production. The chemical interaction process shown by the pseudo-second-order kinetic model of adsorption and desorption further proves the process of CO2 regulating the polarity of fDES. The remaining microalgae components were transformed into yeast lipids with 3.3 g/L for biodiesel by enzymolysis and continuous fermentation. Overall, this strategy of integrating pretreatment, production, separation, and solvent recovery to funnel all components of microalgae into biodiesel provides an efficient solution for biomass valorization.