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Abstract In order to contribute for a more sustainable biodiesel production, its synthesis from animal fat through heterogeneous catalysis was studied, by focusing on: (i) selecting a heterogeneous catalyst for pork lard transesterification; (ii) studying the influence of the reaction conditions on biodiesel purity, namely by using response surface methodology (RSM); and, (iii) evaluating the re-use of the catalyst. Calcium manganese oxide was the selected heterogeneous catalyst for the transesterification of lard obtained from a meat processing industry. RSM studies allowed the development of a second-order model representing the influence of the reaction conditions on biodiesel purity; the temperature and the combined effect of the temperature and catalyst concentration were the conditions which mostly influenced product purity. Catalyst was reused without significant loss of activity indicating that catalytic behaviour was heterogeneous.

Abstract The use of heterogeneous catalysts for biodiesel production aims to simplify the production process as well as to reduce purification costs and related environmental impacts. Calcium manganese oxide was recently identified by the authors as an interesting heterogeneous catalyst for biodiesel production from animal fat; however, the difference between this and other catalysts, the catalyst activation/deactivation mechanisms, its behaviour in the synthesis using different raw materials as well as the impacts of its use on product quality remained unclear. Therefore, the present work: (i) compared biodiesel production using calcium manganese oxide and other catalysts (CaO and NaOH); (ii) studied the reasons leading to activation/deactivation of the heterogeneous catalyst; (iii) analysed biodiesel heterogeneous synthesis using calcium manganese oxide and different raw materials (lard, waste frying oil and a mixture); and (iv) evaluated raw material and catalyst impact on the product quality. Considering the use of different catalysts, the results showed that, after 8 h of reaction, product purity was similar using the different catalysts, being 92.5 wt.% using both NaOH and calcium manganese oxide and 93.8 wt.% using CaO. The active species of the heterogeneous catalysts were CaO, in the case of calcinated calcium carbonate, and Ca 0.9 Mn 0.1 O, in the case of calcinated calcium manganese oxide. Because the deactivating species were different for both catalysts, the calcium manganese oxide required lower activation temperature, which should be an advantage. When using different raw materials, the reaction was slower when lard was used for biodiesel synthesis. Leaching results showed that catalytic behaviour was heterogeneous but further purification of biodiesel might be needed. Using heterogeneous catalysis, after 8 h of reaction, independently of the raw materials used, similar results were obtained regarding the reaction progression; the quality was generally maintained but the water content of the product was improved compared to the homogeneous process.