Biodiesel production from Acrocomia aculeata acid oil by (enzyme/enzyme) hydroesterification process: Use of vegetable lipase and fermented solid as low-cost biocatalysts

The aim of this study was to investigate a new process of enzyme/enzyme hydroesterification for biodiesel production using a low-cost acid oil (10.5 wt.% acidity) from macauba (Acrocomia aculeata) pulp as raw material. The ethyl esters were produced by the hydrolysis of the macauba oil using vegetable enzyme (VE) obtained from dormant castor seeds followed by esterification of the released free fatty acids (FFAs) with ethanol catalyzed by fermented and dry babassu cake with lipase activity from Rhizomucor miehei. The vegetable enzyme-catalyzed hydrolysis produced 99.6% of FFAs after 6 h in a medium with high oil concentration (50% v/v) and without organic solvent and emulsifier. For the esterification reaction, the best result was attained with an ethanol:FFA molar ratio of 2:1 and 15.1 U of dry fermented solid per g of FFAs at 40 °C, which yielded 91% of conversion after 8 h in a solvent-free system. In order to confirm the potential of the fermented solid as biocatalyst, it was confronted with the best commercial lipases and was also evaluated for its reuse. Similar conversions were obtained with the commercial lipases Novozym 435 and Lipozyme RM IM and the fermented solid. The fermented solid was reused in successive 6-h batches for esterification reactions and conversions of over 60% were maintained for eight cycles. After two consecutive esterification reactions the resulting biodiesel met important Brazilian standards such as: density (ASTM D4052), viscosity kinematic (ASTM D445), flash point (ASTM D93), carbon residue (ASTM D4530), free glycerol and total glycerol, monoglycerides and triglycerides (ASTM D6584). The ester content was of 96.7% (esters of fatty acids of 8-18 carbons). To the best of our knowledge, this is the first time that an enzyme/enzyme hydroesterification process using low cost biocatalysts obtained from vegetable and microorganism using solvent-free media in both reactions is described for the conversion of an acid and low value oil into biodiesel.