(189h) Isobaric Vapor-Liquid Equilibrium for Ethanol –Glycerol System At 101. 3, 40.0 and 20.0 Kpa

Anhydrous ethanol is produced by extractive distillation, which is a novel technology that allows to eliminate the azeotrope between ethanol and water, by means of a third component called entrainer. Some glycols as the ethylene glycol, tetraethylene glycol, triethylene glicol and glycerol are commonly used as solvents.  Moreover, the glycerol is a byproduct largely produced in the biodiesel industry, which demands especial attention to investigate about new processes to valorize this byproduct.

In light of the above the vapor – liquid equilibrium (VLE) data of this ternary system is necessary or the VLE data of the binary system ethanol-glycerol, water – glycerol and ethanol-water.  In this research work, VLE experimental data for the ethanol-glycerol system were determined at three different pressures (101. 3, 40.0 and 20.0 kPa) using a commercial glass unit Fischer Labodest® VLE apparatus model 602. The equilibrium vessel is a dynamic recirculating still, and it is equipped with a Cottrell circulation pump. The Cottrell pump ensures the intimate contact between the liquid and vapor phases and also allows the contact with the temperature sensor. The still is connected to nitrogen gas to avoid decomposition of glycerol. The equilibrium temperature was measured with a resistance thermometer TMG model WK93, with an accuracy of ±0.02 K. A digital pressure transmitter WIKA model P-10 with an accuracy of 0.1 % was used for the pressure measurement and is controlled with the VLE 2+ system of i-Fischer Enginering GmbH.

To guarantee the correct operation of the equipment, the boiling points of pure ethanol and water were measured and compared with the values reported in the open literature, and the procedure was checked by determination of VLE data of ethanol-water system with satisfactory results; the obtained data were thermodynamically consistent. Liquid and condensate vapor samples were analyzed by chromatography and density.

The data obtained were successfully correlated by the NRTL model which works well in the prediction of VLE of this kind of highly polar mixtures. The analysis of thermodynamic consistency of the data obtained is carried out by the method of Wisniak. Moreover, the VLE data obtained in this work is used to regress the binary interaction parameters of ethanol-glycerol system to predict its behavior using Britt - Luecke Algorithm, Maximum-Likelihood Principle. Finally, the binary interaction parameters obtained of ethanol-glycerol system together to binary parameters of water-glycerol system are used to model the behavior of glycerol in ethanol-water system, especially in the topic regarding to the elimination of the azeotrope of the original mixture.