Characterization and determination of thermodynamic properties of waste cooking oil biodiesel: Experimental, correlation and modeling density over a wide temperature range up to 393.15 and pressure up to 140 MPa

Abstract

Biodiesel can be described as mono-alkyl esters of long chain fatty acids, derived from a vegetable oil in reactions with alcohols. The physical properties of biodiesel are largely determined by the length of the hydrocarbon chain, the degree of unsaturation, and the effect of molecular packing, while the calculation of the thermodynamic properties of biodiesel is difficult in reason they are high molar weight components and complex structures. The density data (136 points) for waste cooking oil biodiesel at several temperatures between 298.15 K and 393.15 K and pressures up to 140 MPa are reported. The chemical constituents were analyzed by GC/MS, 1HNMR and 13CNMR in order to determine the fatty acid composition of waste cooking oil biodiesel. An Anton Paar vibrating tube densimeter, calibrated with an uncertainty of ±0.7 kg m−3 was used to perform these measurements between 298.15 K and 393.15 K. In this work, the density experimental data of biodiesel were correlated with the Tait equation of state (EoS), an empirical equation widely used for high pressure density correlation. The PC-SAFT equation of state using group contribution methods was employed for the calculation of parameters and prediction of biodiesel densities.The statistical parameters of empirical Tait-correlation are much lower than the experimental uncertainty of the density measurements with the AAD (0.01%), MD (0.04%), Bias (7.1 × 10−4%), and standard deviation, σ (1.5 × 10−4g.cm−3), and from PC-SAFT, density of sample was reasonably well predicted with an average relative deviation 0.083%In addition, the isobaric thermal expansivity and the isothermal compressibility have been derived from the Tait-like equation.