Higher alcohols as cosolvents of mixtures of ethanol and soybean oil: Solubility and physical properties of ternary systems

Abstract

Mixtures of soybean oil (SO) and ethanol (EtOH) are of interest for several applications, such as the addition of the mixtures to diesel, the production of ethyl esters (ethyl biodiesel) from SO and the extraction of vegetable oils with a renewable solvent. However, the solubility between the components of this mixture is limited, which may hinder the possible applications. Thus, the present study aimed to determine the solubility of mixtures composed of SO and EtOH with the addition of cosolvents, n-butanol (nBut) and isoamyl alcohol (IAA), which are higher alcohols present in fusel oil, a coproduct of the production of EtOH. The physical properties of the ternary mixtures were also determined, which are necessary data for proposing the use of these renewable inputs. The regions of phase separation for the systems were determined using the cloud point method at constant temperature (25, 40 and 55 °C). The physical properties, density (ρ, kg·m−3) and dynamic viscosity (η, mPa·s) were experimentally determined for the binary (EtOH + nBut and EtOH + IAA, temperatures from 20.0 to 70.0 ± 0.1 °C) and ternary (SO + EtOH + nBut and SO + EtOH + IAA, 25.0, 40.0 and 55.0 ± 0.1 °C) mixtures. The experimental ρ data were described mathematically by the simple mixing rule (SMR) and the Jouyban-Acree (JA) model. For the description of η, the modified Kay rule (MKR), the Kendall and Monroe (KM) model, the Grunberg-Nissan (GN) model and the JA model were considered. Regarding the binary mixtures, the SMR and the GN model showed the lowest average relative deviation (ARD) values, 0 to 0.31% for ρ and 0.21 to 5% for η. For the ternary systems, the JA model best described the behavior of both physical properties (ARD from 0.02 to 4.51% for ρ and from 0.85 to 7.14% for η). Both cosolvents enabled the reduction of the immiscibility region, with similar performance in the evaluated temperature range.