Estudo da destilação extrativa salina em coluna recheada para a produção de etanol

Abstract

This work aimed the evaluation of a saline extractive distillation for the ethanol production. The renewable fuel has advantages that encourages its use to replace fossil fuels and therefore has potential for growth in their production. Unlike the current method of dehydration of ethanol, which uses a solvent, distillation with the use of salt does not include problems related to toxicity and has lower power consumption, since salt is not volatilized within the distillation column. For this study, an experimental distillation unit was assembled, with packed section (37 cm of height and 5.9 cm of internal diameter) filled, randomly, with Raschig rings (made of glass with nominal size of 0.73 cm), and initially tested with the water-acetic acid system, so that operating conditions would be established. The products of distillation were analyzed by refractometry and showed low deviations for the products concentrations obtained, compared to liquid-vapor data reported in the literature. Due to the efficiency of the unit and the experimental methodology, two charges of ethanol, at concentrations of 0.02 and 0.25 molar, were distilled under atmospheric pressure. These concentrations were choose to represent unyeast wine and the flegma, respectively. The charges are products in a typical ethanol production plant. The unyeast wine charge is fed in the first distillation column and the flegma charge is fed in the second distillation column. Sodium chloride, calcium chloride, sodium acetate, potassium acetate, calcium nitrate and a mixture of sodium and potassium acetates were added to the charges and the results were compared to experiments without the presence of salts, showing an enrichment of ethanol in the top product of distillation, in all the systems studied with salt. When possible, the experimental data were compared with equilibrium data from literature. For systems in which the liquid-vapor data was not present in the literature, a thermodynamic model, based in the study of MACEDO et al. (1990), validated with systems defined in the literature (average deviations obtained below 10% for both the concentration of vapor phase as for temperature) was used for the prediction of the data. HETP correlations were adopted and the results were compared with the pseudo-experimental results, calculated by the ratio between the height of the packed section and the number of theoretical stages, obtained by the method of McCabe-Thiele. The model of BOLLES and FAIR (1982) gave predicted values of HETP more closely than pseudo-experimental, with deviations strongly related to the number of theoretical stages calculated. The prediction of thermodynamic data for liquid-vapor did not affect the determination of the HETP, since the general behavior was the same. It was verified that all the models used to calculate HETP are dependent on the top and bottom mass flow, on the effective area of mass transfer and on the packing type utilized. A load of unyeast wine, obtained in an ethanol production plant, was also evaluated and the results indicated a trend, even greater than charge at concentration of 0.02 molar, enrichment of ethanol with the use of the saline extractive distillation.