Equilíbrio químico nas reações de obtenção do biodiesel

Abstract

Biodiesel has been shown in recent decades as a great substitute for fossil fuels, being a less harmful gases emitter to Earth's atmosphere and a least contributor to global warming. For the development of its applications, a growing number of studies are being conducted by the global scientific community in various areas, such as on the composition and quality of the biofuel, its environmental, social and economic impacts. In the area of chemical engineering, the main focus of study is in the methods of production of biodiesel. The supercritical route, on which the triglyceride transesterification reactions from vegetable oils takes place in operating conditions exceed the critical properties of the lower alcohols, shows up as an alternative to subcritical route because of the absence of glycerin and water as by-products of transesterifications, as well as high yields despite the difficulty caused by the need for operation in extreme conditions of temperature and pressure. For the calculation of equilibrium constants and conversions of the transesterification reactions, it is necessary to know thermodynamic properties of the compounds involved, but such data are scarce in the literature due to the complexity of the reagents and reactional mixtures. Therefore, estimation methods are required for determination of such properties. The two approaches presented in this work used group contribution methods for the prediction of critical parameters (temperature and pressure), normal boiling temperatures, heat capacities, enthalpies and entropies, and acentric factors. The study of chemical equilibrium id held by the determination of equilibrium constants as a function of temperature, composition of the reaction mixture, non-ideality by fugacity coefficients and pressure effects and excess methanol for the calculation of equilibrium conversions point optimum conditions for operating temperatures of 600 to 650 K and pressures above 110 bar.