An investigation of the potential of a bifunctional catalyst in biodiesel production from low‑cost feedstocks

Abstract

Biodiesel, a sustainable fuel attained by acid or base-catalyzed esterification and transesterification, holds advantages over petro-diesel due to its low toxicity and environmentally friendly properties. The conventional production route is problematic as it utilizes low free fatty acid (FFA) edible oils catalyzed by a homogenous catalyst, which exacerbates the food versus fuel debate. High FFA waste and non-edible oils may be used, however, under such conditions, saponification occurs, increasing production costs. The effectiveness of a bifunctional catalyst was studied, with varying acidic to basic ratios (CaO: Al2O3 ratios of 80:20, 70:30, 60:40, and 50:50), on relatively high FFA (2.47–3.25%) low-cost feedstocks. The catalysts were characterized using XRD, SEM and BET. They exhibited adequate morphological and catalytic characteristics where pore sizes were > 209 Å, surface areas > 11 m2/g and pore volumes > 0.072 cm3/g. These promoted simultaneous esterification and transesterification and consequently improved biodiesel yield. Three edible feedstocks (sunflower, palm and canola), their waste counterparts, as well as non-edible neem oil, were used as feedstock. The yields and fuel transportation characteristics of the biodiesel produced were analyzed using Rancimat and ASTM methods. 67% of biodiesel produced satisfied all ASTM standards and a correlation between acid/base catalyst rations and FFA content was evident. Synthesized catalysts were robust as there was no loss of catalytic activity for up to six consecutive runs. The current study provided evidence for the need to synthesize tailor-made bifunctional catalysts with robust nature for the simultaneous esterification and transesterification of low-cost feedstocks.