Methyl esters production from Waste Cooking Oil catalysed by iron oxides supported on CaO: Cost and environmental impacts

It was the objective of this work, to assess the midpoint environmental impacts of the catalyst synthesis stage and biodiesel production from waste cooking oil (WCO) as feedstock, depending on the catalyst source, i.e. Fe₂O₃ or Fe(NO₃)₃⋅9H₂O, lime or waste clam shells, to produce the applied bifunctional catalyst based on iron and CaO. The cost of biodiesel production depending on the catalyst was also established. In the catalyst synthesis stage, the use of clam shells contributed the most to the midpoint environmental categories, mainly terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity and human non-carcinogenic toxicity. In the stage of biodiesel production (esterification-transesterification reaction), the scenario contributing the lowest (20.95–22.16 %) to the midpoint environmental impacts is when using Fe(NO₃)₃·9H₂O and CaO as iron and lime precursors, respectively. Using waste clam shells increases the environmental impacts. Regarding costs, the clam shells lead to the most expensive process ($0.08 USD/MJ). The source of energy to conduct the biodiesel production was also assessed and it was found that the use of wind turbines leads to the lowest global warming potential (GWP), 11.6 g CO₂ eq·MJ-1, with the catalyst prepared with the iron salt and with the CaO from lime. The presented results were obtained with the commercial software SimaPro® version 9.6 PhD. For the inventory, experimental data obtained at laboratory scale and previously published were used.

It was concluded that based on environmental impacts and costs, it is recommended to use lime instead of clam shells waste as precursor of CaO and Fe(NO₃)₃·9H₂O as precursor of iron.