Transesterification of acid soybean oil for biodiesel production using lithium metasilicate catalyst prepared from diatomite

Production of biodiesel from acid soybean oil using lithium metasilicate and its mixtures with zeolite ABW as catalysts was studied. Lithium metasilicate (Li₂SiO₃) and zeolite ABW were synthesized hydrothermally at 150 °C for one day by using diatomite and LiOH_(aq) as starting materials. These solid catalysts were employed successfully to catalyze transesterification of acid soybean oil in excess methanol at 60 °C for biodiesel production. The soybean oil was spiked with oleic acid to obtain an acid value of 0.54 mg KOH/g oil, i.e. 3.6 times higher than the Taiwan's legal limit on the acid value of refined edible soybean oil (CNS 749). Consequently, the yields of biodiesel were above 95% in an hour by using lithium metasilicate catalysts. Furthermore, the spent catalysts of could be recycled and reused for at least for three consecutive cycles without significant deactivation observed in catalysis. With a decreasing loading of catalyst-to-oil to 30 wt%, the yield of biodiesel could still reach ca. 95% in one hour at 60 °C.