After the transesterification reaction, the catalyst was removed from the mixture by centrifugation. The filtrate was kept in the funnel separator for 24 h. The excessive amount of methanol in upper layer was evaporated under reduced pressure in a rotary evaporator. The amount of FAME obtained through transesterification was analyzed by gas chromatography (Agilent 7890A), equipped with a flame ionization detector and a capillary column (DB-WAX, 30 m × 0.25 mm × 0.25 μm). The yield was defined as a ratio of the weight of FAME to the weight of FAME in theory