The remaining mixture was allowed to stand for 24 h to separate the different phases. Biodiesel was obtained as the top
layer where glycerol at the bottom. The biodiesel phase was further purified by distillating in a laboratory scale batch vacuum distillation flask to recover the unreacted methanol. The traces of water were removed by treating with anhydrous Na2SO4. The biodiesel yield was calculated by using Eq. (1) [18]. Similarly, the ester content in the biodiesel produced from WCO was further determined by 1H NMR using Eq. (2) [19,20].