Using Gibbs Energy Additivity Methods for QSPR to Model the Density of Fatty Acid Ethyl Esters and Biodiesels

Liquid fuel density is an essential physical parameter in the design and application processes. This paper employed the Gibbs free energy technique with quantitative structure-property relationship (QSPR) for determining the density of pure fatty acid ethyl ester (FAEE) and ethyl ester biodiesel at temperature 283.15–363.15 K. The density (ρ) of biodiesel can be estimated from (1) the number of carbon atoms of fatty acids (z) and the number of double bonds (nd): ln ρ = − 0.4466–0.0009z + 88.28/T + 0.2092z/ T + 0.01734nd–1.578nd/T or (2) the saponifcation number (SN) and iodine value (IV): ln ρ = − 0.4436–3.60/SN + 87.594/ T + 836.8/(T × SN) + 0.0380 IV/SN – 3.4222 IV/(T × SN), where T is the absolute temperature. The predicted densities at different temperatures for pure FAEEs and ethyl ester biodiesel have average absolute deviations (AAD) of 0.100% and 0.200%, respectively