One-pot conversion of highly acidic waste cooking oil into biodiesel over a novel bio-based bi-functional catalyst

Abstract

We developed a KOH/corncobs-derived activated carbon (AC) heterogeneous catalyst for the single stage biodiesel production from highly acidic waste vegetable oil, which was active in both the esterification and transesterification reactions. Among the different AC preparation conditions tested, a sulfuric acid to raw corn cobs (volume/weight) ratio of 5:1, activation temperature and time of 600 °C for 1 h were selected as the best conditions. The specific surface area (SSA) was 627 m2/g but among all the samples, the highest SSA was however 1131 m2/g. The main factors affecting the simultaneous esterification-transesterification were investigated with a full factorial design combined with response surface methodology via central composite design. The optimum conditions were 1 h reaction time, 18:1 methanol:oil molar ratio, 1 wt% catalyst loading and 45 °C temperature, at which the yield was 97.8%. The biodiesel obtained, in such conditions, matched the ASTM standards. The catalyst was stable for up to five successive times to catalyze esterification, but KOH leached easily and the catalyst became inactive in the transesterification.