Production of biodiesel from waste cooking oil using ZnCuO/N-doped graphene nanocomposite as an efficient heterogeneous catalyst

Abstract

The use of heterogeneous catalyst for biodiesel production can reduce the price of separation process and therefore minimize the biodiesel cost. ZnCuO/N-doped graphene (NDG) catalyst synthesized by facile mechanochemical procedure was tested in the transesterification of waste cooking oil (WCO) with methanol to produce biodiesel. The effects of catalyst loading (0–15 wt%), weight percentage of NDG (10–100%), methanol to oil molar ratio (6:1–18:1), reaction time (2–10 h) and reaction temperature (120–200 °C) were systematically studied at the optimal conditions. Additionally, the properties of the fabricated catalysts were assessed via XRD, FTIR, N2 sorption studies, HRTEM, TGA and Raman spectroscopy. It was found that the ZnCuO/(X%)NDG nanocomposites exhibit enhanced catalytic performance when compared with the ZnCuO catalyst (without NDG) under the identical conditions. The efficacy of the ZnCuO/(X%)NDG nanocomposites has improved owing to the inclusion of NDG in the catalytic system, which in-turn enhanced the properties of the mixed metal oxides (MMO’s) such as surface area, defective sites to a great extent. The ZnCuO/(30%)NDG catalyst displayed a highest catalytic activity towards transesterification of WCO (97.1%) at the optimized conditions of 10 wt% catalyst loading, 15:1 methanol:oil molar ratio, 8 h reaction time and 180 °C reaction temperature. Moreover, the recovered catalyst was successfully reused six cycles with no discernible loss in its activity.