Extração de óleo de soja utilizando etanol hidratado como solvente: equilíbrio do sistema e cinética do processo em coluna

Abstract

The environmental problems faced by the exploitation and intensive use of natural goods and the increase in the price of fossil fuels consolidate the search for alternative sources of energy, such as biodiesel, which in Brazil has been an important additive of diesel. Transesterification has been considered the best method for its production, but the traditional process requires the prior extraction of oil from the oil using a solvent, with hexane being the most common. Simplified processes, such as in-situ transesterification, have been investigated to reduce costs. In this context, the present work sought to evaluate the technical feasibility of using ethanol as a solvent in the soybean oil extraction process, making it possible to use the blend for the production of biodiesel. Firstly, a study was carried out on the equilibrium of the solidliquid extraction, in which an isotherm model was validated based on the general assumption that the extractable material is present in two layers on the surface of the solid matrix. The model was validated for the extraction of soybean oil by hydrated ethanol at different temperatures (30 to 70°C) and ethanol (95.0 to 99.5%). The equilibrium constants were described by thermodynamic means and revealed details about the energy involved in the extraction in both layers. The phenomenological basis employed in this work suggests that the washing mechanism is responsible for extracting the oil portion in the second layer, while the diffusion mechanism extracts the oil in the first layer. In the second part of the study, the technical feasibility of the use of aqueous ethanol as a solvent for the soybean oil extraction process in a continuous flow column was evaluated. A kinetic model was developed and adjusted based on the mechanisms of washing and diffusion, now assumed. The study was performed on a liquid-solid extraction column, using hydrated ethanol as solvent, and soybean laminated as an extractable solid phase. Experiments were conducted under different conditions: (i) solvent temperature (30-70°C); (ii) height of the solid material in the column (38-72cm); (iii) superficial velocity of the solvent (1.68-11.78cm min-1); and (iv) absolute mass fraction of extractable material A in the fluid phase at the entrance to the column (0- 0.0061g A/g E). Mean final efficiencies were obtained in the range of 74.3 and 99.8%. The experimental data collected were used to obtain the model parameters (mass transfer coefficients for washing and for diffusion). The model showed good agreement with the experimental data. The column height and solute concentration at the column entrance showed poor influence on the kinetic parameters of the extraction process. Thus, the study contributes to a theoretical basis and knowledge of the mechanisms involved in the process of extraction, which allow the practical application and possible scheduling of the process.