Transesterification double step process modification for ethyl ester biodiesel production from vegetable and waste oils

► Biodiesel production using ethanol and different oils. ► TDSP methodology optimization for ethanolysis. ► High conversions and yields. ► High quality and purity biodiesel ethyl esters. In this study, the transesterification double step process (TDSP) was modified to enable the usage of ethanol as a transesterification agent in the production of biodiesel from vegetable and waste oils. The TDSP comprises a two-step transesterification procedure, which is initiated by a homogeneous basic catalysis step and followed by an acidic catalysis step. To optimize the transesterification parameters, different reaction mixtures and conditions were tested. Compared with methanol transesterification, larger ethanol and catalyst amounts as well as higher reaction times and temperatures were required. However, the results were consistent with those usually reported for ethanol transesterification. The obtained biodiesels (i.e., fatty acid ethyl esters (FAEEs)) were analyzed by standard physico-chemical techniques in addition to 1H NMR, 13C NMR and FTIR spectroscopies, indicating high quality and purity biodiesel products. The obtained conversions were evaluated by 1H NMR spectroscopy. For the optimized process, the triglyceride conversion to biodiesel was ⩾97% for all oils used. The overall process yields are considerably high when compared to the single basic catalysis yields.