Long – term storage effect on molecular interactions of biodiesels and blends

Abstract

ABSTRACT In this era of fuel crisis, biodiesel is the better alternative to Petroleum Diesel (PD). In general, biodiesel is composed of Fatty acid Methyl Esters (FAME). In the present investigation, change in molecular interactions of two year long-term stored biodiesels and blends were studied by measuring ultrasonic parameters. The results were analyzed with respect to fatty acid profile of biodiesels. The biodiesels collected were Cotton Seed Oil Methyl Esters (CSOME) and Palm Stearin Methyl Esters (PSME). The CSOME biodiesel was rich in unsaturated FAME and PSME in saturated FAME. Five different blends of both the biodiesels with Petroleum Diesel (PD) in the volume percent of 10, 20, 30, 40, and 50 were prepared. The blends were stored for two years in their as it was condition at room temperature without interaction of light. The measurements have been done using an ultrasonic interferometer of fixed frequency of 2 MHz. The measured parameters were density, ultrasonic velocity, adiabatic compressibility, acoustic impedance and intermolecular free length. Sediments were formed in CSOME biodiesel blends only which was rich in unsaturated FAME. No sediment was formed in PSME blends. The highest decrease was found in adiabatic compressibility for 10% volume blends by 5.96% and 5.65% for CSOME and PSME biodiesels, respectively. The lowest increase was found in density for 10% volume blend by 0.13% for both biodiesels. The difference between large and small values was found highest for 10% volume blend of PSME biodiesel by 5.17% for adiabatic compressibility. Poor stability was noticed in low-level blends than high-level blends. Pure biodiesels were found more stable than blends. Strong molecular interactions were observed in low-level blends. Systematic trend in the variation of percent change in parameters with respect to blend level was found in both biodiesel blends.