Oxidation stability and cold flow properties of biodiesel synthesized from castor oil: Influence of alkaline catalysts type and purification techniques

Abstract

This study investigates the effects of catalyst type and washing procedures on the oxidation stability and cold flow parameters of biodiesel produced from castor oil. Castor oil was synthesized using two different catalysts; calcium oxide on alumina support (CaO-Al2O3) and potassium hydroxide (KOH) at a temperature of 60˚C, methanol to oil molar ratio of 6:1 and catalyst loading of 1 wt% of oil for 60 min. The resulting biodiesel was purified using water washing and dry washing methods ion exchange resin. The oxidation stability and cold flow behaviour of the biodiesel produced (cloud point, pour point, cold filter plugging point, and low-temperature flow test) were determined. The findings showed that the oxidation stability and cold flow properties of biodiesel is independent of washing methods but varies with catalyst type. The heterogeneously catalyzed transesterification by CaO-Al2O3 exhibited higher oxidation stability with an induction period of 4.4 h as against 3.5 h for the potassium hydroxide (KOH) catalyzed biodiesel. However, the values obtained in this study were above the ASTM standard of 3 h minimum. With regards to cold flow properties, the KOH-catalyzed process exhibited better cold flow properties than CaO-Al2O3 catalyzed biodiesel. It can be deduced from this study that the biodiesel samples will exhibit very good ignition performances when used in ignition compression engines in the low temperate region due to their satisfactory cold flow behaviour.