Deep eutectic solvents and ionic liquid assisted hydrolysis of microalgal biomass: A promising approach towards sustainable biofuel production

Abstract Utilization of each biochemical component such as lipid or carbohydrate in a biorefinery is essential for commercializing microalgal-based biofuels. We have performed a comparative evaluation of ionic liquids (ILs) and deep eutectic solvents (DESs) for microalgal hydrolysis in the present study. Among the eight tested ionic liquids, ethyl ammonium nitrate (EAN) resulted in the highest saccharification yield of 95.5% whereas, among hydrophobic deep eutectic solvents, menthol: lactic acid (Me: LA) exhibited the highest saccharification yield 85.7% and also did not require any additional high temperature or other pretreatments for hydrolysis indicating as the potential solvent system to reduce the cost of microalgal based bioethanol production concerning the harsh conditions in a conventional method. Further analysis of pretreated biomass with SEM, FTIR, and XRD analysis indicates that EAN or Me: LA ruptures the microalgal cell wall and hydrolyzes the cytoplasmic starch to release the sugars in the solution. IL/DES was recycled four times without losing the efficiency. Overall, the present study results indicate that the identified IL and DES can be used as a green and sustainable alternative for the pretreatment of microalgal biomass for biofuel production.