Improvement of the oxidative stability of used-oil biodiesel by epoxidation reaction

Improvement in the oxidative stability (OS) of biodiesel derived from used-oil (UO) was carried out by epoxidation of biodiesel. A 2 ^k factorial design was used to identify the effects of temperature, mole ratio of hydrogen peroxide (H ₂O ₂):formic acid (HCOOH), stirring rate, and reaction time. The results indicated that the H ₂O ₂:HCOOH mole ratio, stirring rate, and their interaction had significant effect on the OS of biodiesel. At the derived optimum condition, greater than 99.4 of unsaturated carbon bonds in the used-oil biodiesel were converted to epoxy used-oil biodiesel with a selectivity of 69.0. Only one species of by-product, hydroxyl-biodiesel, was observed in this system. Asides the cold flow properties and methyl ester content, all other key properties of biodiesel were within the specifications of the European Standard EN14214. The OS for the biodiesel was higher than the original.