Monday, May 4, 2009
11-23
Thermodynamic models for solid-liquid equilibrium of xylose in water and water-ethanol mixtures
Ernesto A. Martinez1, Marco Giulietti1, Mauricio M Uematsu1, Silas Derenzo1, and João Batista Almeida e Silva2. (1) Chemical Division, Institute of Technological Research, São Paulo, Brazil, (2) Department of Biotechnology, Engineering College of Lorena-University of São Paulo, Lorena, Brazil
D-xylose or wood sugar is an intermediate product of human and animal metabolism and of others important metabolic processes. This pentose can be used in the food, chemical and pharmaceutical industries (consumed by diabetics, used as raw material for ethanol, xylitol, penicilim, acetic and lactic acids, resins and brewer’s yeast productions). This work reports the study of thermodynamic models for solid-liquid phase equilibrium (SLE) and it was carried out by comparing the performance of different models with experimental data. The experimental data of solubility for the xylose-water and xylose-water-ethanol systems have been measured using a variant of the isothermal method. The experiments were carried out in a 100 mL glass jacketed crystallizer with helix-type agitator. The solution was mixed during 48 h at 450 rpm. A total of 12 experiments were carried by changing the temperature from 0 to 60 oC. Later, the experimental results and other reported in previous publications were fitted using prediction models based on vapor-liquid-equilibrium (VLE) (UNIFAC, GSP); semi-empirical models based on VLE (UNIQUAC, Wilson, NRTL), semi-empirical models based on SLE (Nývlt, λh) and empirical model with fitted parameters (Margules). The results show that the UNIQUAC model with fitted parameters can well describe the SLE with good accuracy (1.3% for binary and 3.4% for ternary systems). The other methods resulted in poor agreement with the system’s behavior with systematic deviations from the experimental data. The prediction models must be used only where is not possible to obtain experimental data. Acknowledgements: Financial support of FAPESP, Brazil.