Triglycerides transesterification over Mg-Al and Mg-Fe mixed oxides catalysts: Influence of extrusion additives

Nowadays, biodiesel is one of the most common used biofuels. After establishing its use and industrial production, research efforts are focused on developing and optimising catalytic materials. The present work studies the use of different additives for catalyst extrudation of Mg-Al and Mg-Fe mixed oxides, paying particular attention to catalyst characterisation and activity during rapeseed oil transesterification in a continuous regime (10 MPa and 120-180 degrees C). According to our results, it is clear that there is a relation between the used extrusion additives and the catalyst properties and activity. The use of glycerol increased catalyst compaction resulting in lower catalytic properties but higher strength values for the Mg-Al and Mg-Fe extrudates (10.7 and 4.5 N/mm, respectively). On the other hand, the use of an additive mixture composed of isopropanol, polyethylene glycol and tetraethyl orthosilicate provides Mg-Fe and Mg-Al extrudates with a solid combination of catalyst activity (70% ester formation at 10 MPa and 180 degrees C) and good stability, without significant metals leaching Mg < 2.0 mg/Kg and Fe < 0.3 mg/Kg.