BACKGROUNDThe biodiesel by-product, crude glycerol including lower alcohols, could be used as the feedstock for producing monoacyglycerols (MAGs), which are commonly used as non-ionic surfactants and emulsifiers. In this work, lower alcohols (methanol, ethanol and isopropanol) in sub- and supercritical states were used as the solvents for MAG production. RESULTSIsopropanol is the best solvent for obtaining high monooleate (MOG) yield compared with methanol and ethanol. Moreover, the sub- and super-critical isopropanol shows better performance than the normal NaOH catalyzed or non-solvent process. The reaction loading of a batch reactor has a complicated effect on the yield. The maximum MOG yield can always be obtained at 60% loading. The square root modified quadratic model was utilized to analyze the relationship and to optimize reaction temperature (220-260 degrees C), reaction time (30-150 min), and isopropanol (0-4 mL). In the optimum condition (260 degrees C, 150 min, 4 mL of isopropanol), a high MOG yield of 67.8% can be obtained, well in agreement with the predicted value. CONCLUSIONIsopropanol at sub- and super-critical state greatly improved the mass transfer between the immiscible reactants (triglyceride and glycerol). Compared with some methods with chemical catalyst, the method without any catalyst obtained higher MOG yield. (c) 2016 Society of Chemical Industry