The effects of diethyl ether, diethylene glycol dimethyl ether, and dimethyl carbonate addition on the physical and thermodynamic properties of biodiesel

In the present study, density, viscosity, surface tension, and refractive indices of binary mixtures of biodiesel + diethyl ether (DEE), diethylene glycol dimethyl ether (DEGDME), and dimethyl carbonate (DMC), which are used as biodiesel additives, have been measured over the whole range of concentration from 288.15 to 323.15 K and at atmospheric pressure. The density and kinematic viscosity values of the binary mixtures, prepared with different mole fractions of DEE, DEGDME, and DMC, were compared with the limits specified by the biodiesel fuel standard (EN14214). Furthermore, experimentally measured density values were utilized to define a first-order polynomial equation for estimating the densities of the prepared binary mixtures. Excess molar volumes (V^E), excess thermal expansion coefficient (α _p ^E ), excess Gibbs energy of activation of the viscous flow (∆G*^E), deviations in kinematic viscosity (Δν), surface tension (Δσ), and refractive index (Δn_D) values were calculated. These deviation values from ideality were adjusted to a Redlich–Kister (R–K) polynomial equation and the obtained coefficients in the equation were reported. V^E values were negative for biodiesel + DEE while positive values were obtained for biodiesel + DEGDME and DMC. Moreover, the values of Δν were negative for all mixtures of biodiesel + DEE, DEGDME, and DMC. The obtained results were analyzed with regard to intermolecular interactions and structural effects between both similar and dissimilar molecules.