Residue-based activated carbon from passion fruit seed as support to H3PW12O40 for the esterification of oleic acid

The production of biodiesel from acidic non-edible oil and waste lipid feedstocks has the drawback of forming soaps in the conventional transesterification process. A solution is the esterification reaction that uses superacid homogenous catalysts; however, it generates dangerous effluents. To overcome this, heterogeneous acid catalysts such as heteropolyacid supported on activated carbon have been studied for the production of biofuel. Due to its high surface area, the activated carbon allows high dispersion of the active phase. The aim of this work was to study the esterification of oleic acid over 12-tungstophosphoric acid (HPW) supported on activated carbon derived from passion fruit biomass (ACP), prepared by chemical activation using ZnCl2. The composites (HPW/ACP) were prepared containing 10–30 wt% of HPW by following two procedures: aqueous impregnation method and incipient moisture. The results showed that the activated carbon prepared from the residue of the passion fruit seed presented a high surface area (465 m2. g−1) and that the HPW impregnation method on activated carbon was a decisive factor on the catalyst performance. XPS, SEM, NMR and N2 adsorption-desorption results showed that in the catalyst obtained by aqueous impregnation (HPW/ACP) surface area decreased (50 m2 g−1), HPW was highly dispersed in the internal pores of the ACP support and presented superior acidity. The incipient moisture impregnation (HPW/IACP) formed HPW particles on the external surface of the support with little interaction among them, resulting in surface area of 90 m2 g−1. The best result of oleic acid esterification with methanol led to 86.4% conversion with catalyst HPW30/ACP, at 100 °C, after 2 h of reaction. The leaching of HPW active phase after the reaction was low ∼1.0–2.6%. This study showed the importance of the HPW impregnation method on activated carbon to obtain a more stable and more active catalyst for the production of biodiesel. A detailed analysis of the catalyst synthesis from a fruit industry residue demonstrated the possibility of operating in a closed-loop system towards cleaner production. [Display omitted] •Activated carbon (ACP) was obtained from passion fruit industry residue.•Catalyst stability and activity in the esterification was influenced by HPW/ACP impregnation method.•Catalyst from residue was used in a closed-loop esterification cleaner process.