Enthalpies of mixing and heat capacities of mixtures containing alcohols and n‐alkanes with corn oil at 298.15 K

Abstract

Enthalpies of mixing for mixtures containing alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol) plus corn oil or n-alkanes (n-hexane, n-heptane, and n-octane) plus corn oil were measured at 298.15 K and atmospheric conditions. The enthalpy was measured in the range of concentrations in which alcohols were miscible with the vegetable oil. Results were correlated by the Redlich-Kister equation. The mixing of alcohols with corn oil was strongly endothermic, whereas values obtained for the binaries containing n-alkanes were slightly endothermic. Thus, heat capacities were calculated for all the systems studied.Edible oils are important components of the diet and also provide characteristic flavors and textures to foods. During extraction, purification, and usage, oils undergo a variety of processing operations, including frying, distillation, and chemical modification, which may alter their properties. Prediction of the behavior of oils under real processing conditions is possible by measuring bulk properties such as density, viscosity, speed of sound, and so on, which are related to industrial processes by semiempirical equations. Such properties of edible oils depend on the composition and temperature. Studies related to oil technology and to the technologies used in the processing of high-quality edible oils utilize organic solvents for extraction and refining.In the last few years considerable work has been done in the field of calorimetry to investigate the thermodynamic properties of oils and their mixtures with different solvents. Knowledge of the heat involved in the mixing process of organic solvents with vegetable oils is useful for designing equipment for the extraction and refining of edible oils. When solvents are mixed with the oil, a heat of solution is involved. In these cases, a loss of heat usually takes place, an endothermic effect that is a consequence of the interaction between oil and solvent molecules.This study is part of a more extensive project in which different physicochemical properties of mixtures formed by organic solvents with vegetable oils are being measured (González and colleagues, Refs. 1-5). In this study, the enthalpy of mixing of systems composed of alcohols (methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol) or n-alkanes (n-hexane, n-heptane, and n-octane) with corn oil were measured at 298.15 K and at atmospheric pressure. For some of the alcohols, immiscibility occurs at certain composition values; hence, enthalpies of mixing were measured in the concentration ranges at which both components were miscible. Heat capacities were also calculated using the experimental values of the enthalpies of mixing. Several studies by different authors [Kowalski (6), Tan and Che Man (7), Morad et al. (8), and Coupland and McClements (9)] have involved the heat capacities of pure vegetable oils (usually determined by DSC), and data on the heat capacities of pure FA and their binary and ternary mixtures have been determined by Cedeño et al. (10)...

Variability of Biodiesel Fuel and Comparison to Petroleum-Derived Diesel Fuel: Application of a Composition and Enthalpy Explicit Distillation Curve Method

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