(400e) Experimental Determination of Vapor- Liquid Equilibria for Water – Glycerol System

Glycerol aqueous solutions are obtained in processes such as making soap and biodiesel production, where you want to recover the Glycerol for use in pharmaceutical, chemical and cosmetics industry. Currently, Glycerol is of great importance in the production of ethanol by extractive distillation where it is used as separating agent. The extractive distillation1, 2 uses as solvent some glycols3 becoming an alternative for the separation and obtaining ethanol with a lower energy consumption compared with other processes4, 5. In this technique after separation of anhydrous ethanol, a second stream containing the solvent and water is sent to a recovery column in order to separate water and recycle back the solvent to the extractive distillation column. The solvent which exhibits the best behavior is glycerol3. In order to recover the glycerol from the aqueous solution distillation is used, for which vapor-liquid equilibrium of the binary system data is required. In this work the vapor-liquid equilibrium data for the glycerol-water mixture were obtained by using the modified Othmer still designed by Oliveira 6, 7. This equipment is an equilibrium still with circulation of the vapor phase6. This consists of a circulation cell with devices for measuring temperature and pressure. This equipment allows its suitability for use in measuring vacuum pressure data. The equipment was surrounded by a resistance in order to avoid problems of partial condensation on the walls of the still. The temperature in the vapor phase was measured using a thermocouple type K connected to a controller Watlow Model 96 with an accuracy of ±0.1 °C. The temperature of the liquid phase was measured using an EXTECH Instruments 407,907 RTD Thermometer with a precision of ±0.01 °C. The pressure was measured using a mercury manometer with an accuracy of ±1 mmHg. The operation is based on reaching the steady state where you get a constant drip in the steam condensate is recycled to the cell boiling. The steady state is indicated by the constancy of the temperature between the two phases. The temperatures of the liquid phase and vapor with a difference of ± 0.1 ° C between them, the equilibrium state is where the composition the liquid and vapor condensate no longer change over period of 30-45 min Fig 1. VLE (T- xy) of the system Water (1) + Glycerol (2) at (◊) 20 kPa and (▲) 74,66 kPa for experimental values and (?, -----) for the NRTL model calculated with binary interaction parameters obtained from Aspen plus Database. The VLE experimental data for the binary system water-glycerol were determined at three different pressures (74, 66 kPa, 20 kPa and 39, 60 kPa) in order to observe the effect of changing pressure on the VLE. If the pressure decreases up to 20 kPa (fig 1) and to 39, 60 kPa an important reduction in equilibrium temperatures is achieved and consequently low energy consumptions will be reported in the recovery step of glycerol. 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 Wisniak8, the Test Area, which uses the equality criterion of L and W terms. Finally, the binary interaction parameters for the NRTL model were regressed to predict the behavior of the mixture at low pressures, using Britt - Luecke Algorithm, Maximum-Likelihood Principle, provided by Aspen Plus 2006.5 The experimental information obtained in this work may be useful for the design of a separation process to recover the glycerol as solvent, at the extractive distillation of bioethanol. Acknowledgements The authors acknowledge to DIB (División de Investigaciones ? Sede Bogotá) for supporting this research project (Code: 203010012739- DIB 2009), Grupo de Investigación en Procesos Químicos y Bioquímicos (Code: 20301009496- DIB 2007) and Colciencias (Departamento Administrativo de Ciencia, Tecnología e Innovación) for supporting the research project Code 1101-452-21113. References (1) Chianese, A.; Zinnamosca, F. Ethanol dehydration by azeotropic distillation with mixed solvent entrainer. The Chemical Engineering Journal. 1990, Vol. 43. p. 59-65. (2) Jacques, K.; Lyons, T.; and Kelsall, D. The Alcohol Textbook. 3rd edition. Nottingham University Press (1999). Chapters 17 and 19. (3) Lee, F. M.; Pahl, R. H. Solvent screening study and concetual extractive distillation process to produce anhydrous ethanol from fermentation broth. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 168-172. (4) Hanson, N.; Lynn and Scott, D. Multieffect extractive distillation for separating aqueous azeotropes. Industrial Engineering Chemical Process Des. Dev. 1988, Vol. 25. p. 936-941. (5) Lee, et al. Dehydration of alcohol with extractive distillation. United States Patent. (Dec. 1985) 4,559,109. (6) Oliveira, Humberto Neves Maia- Determinacao de Dados de Equilíbrio Líquido-Vapor para Sistemas Hidrocarbonetos e Desenvolvimento de uma Nova Célula Dinámica. Tese de Doutorado, UFRN, Programa de Pós-Graduacao em Engenharia Química, Área de concentracao: Engenharia de Processos. (7) Hala. E. Vapor-Liquid Equilibrium. Department of Physical Chemistry. Prague, Czechoslovakia. 1958 (8) Wisniak, J. A new test for the thermodynamic consistency of vapor-liquid equilibrium. Ind. Eng. Chem. Res., 1993, 32 (7), 1531-1533.