Strategies to improve the sustainability of the heterogeneous catalysed biodiesel production from waste cooking oil

This work aims to present the strategies assessment to reduce the environmental impacts of the biodiesel production from waste cooking oil (WCO) catalyzed by a heterogeneous bifunctional catalyst (a mixture of iron and CaO). The assessed strategies were based on varying iron precursor (Fe2O3 or Fe(NO3)3·9H2O), iron content, catalyst loading and alcohol/oil molar ratio. The biodiesel production is cleaner when the iron salt is the catalyst precursor. In this case, the contribution to global warming potential (GWP), photo-oxidation (PO), eutrophication (E) and acidification (A), was 34.69%, 41.90%, 34.7% and 34.71%, respectively. This was established through life cycle assessment (LCA). With any of the catalysts, the most impacted endpoint category was human health, 26.7 mPt when using Fe2O3 and 14 mPt when iron salt is the catalyst precursor. The strategy that works the best for any catalyst is to modify its concentration since the GWP and PO can change 20%, 35% the E and A with the Fe(NO3)3·9H2O and up to 10% with the Fe2O3. It was established, through a sensibility analysis, that by using solar energy instead of energy from fossil fuels, the carbon footprint of the biodiesel production can be reduced ca. 93%: it becomes 48.73 gCO2eq MJ−1 when using Fe2O3 and 26.48 gCO2eq MJ−1 when using the iron salt. With this catalyst precursor, in addition, a ratio of 0.56 MJin⋅MJout−1 is attained.