Comparative study of physicochemical and rheological property of waste cooking oil, castor oil, rubber seed oil, their methyl esters and blends with mineral diesel fuel

Abstract

In this work, physicochemical properties and rheological behaviour of waste cooking oil (WCO), castor oil (CO), rubber seed oil (RSO) and their methyl esters (ME), as well as ME blends (5, 10 and 15 vol%) with diesel fuel were investigated. Rheological properties of samples were measured in the range of 25–80 °C temperature and 5–300 s−1 shear rate. Similarly, rheological behaviour of WCO, CO and RSO based methyl esters (WCOME, COME, ROSME) and its blends (5, 10, and 15 vol%) with diesel fuel were also studied. Power law model was used to study the flow behaviour of all the samples. The viscosity behaviour of oils (WCO, CO and RSO), methyl esters (WCOME, COME and RSOME) and their blends with diesel fuel showed Newtonian nature in the temperature range of 25–80 °C. The viscosity values of the chemically modified oil samples (via transesterification) were found to be lower than the original oil samples. However, WCO, CO and their methyl esters showed a slight deviation from Newtonian behaviour between shear rate intervals of 5–100 s−1. The dynamic viscosity of RSO (25.58 mPa.s) was less than that of WCO (49.91 mPa.s) and CO (338.08 mPa.s). At 40 °C, the kinematic viscosity values of RSOME (3.81 mm2/s) and WCOME (3.36 mm2/s) were lower than the value of COME (10.59 mm2/s). The dynamic viscosities of the samples were found to be dependent on fatty acids chain length, unsaturation and temperature. According to fatty acid composition and physicochemical properties of the oils samples, WCO, CO and RSO are suitable for substituting edible feedstock to make biodiesel production sustainable. The fuel properties of the methyl esters and their blends with diesel were estimated as per ASTM D6751 biodiesel standards.