Water-hexane sorption in sunflower meals

Abstract

Sorption equilibria of water and hexane in sunflower meals were determined at atmospheric pressure and temperatures from 50 to 95 °C. Adsorption-desorption experiments, for both individual vapors and water-hexane mixtures, were carried out using a dynamic technique based on gravimetric measurements with a Cahn electrobalance. The isotherms were fitted to the Guggenheim-Anderson-deBoer sorption equation, and the heat of sorption was evaluated from experimental results. In the range of temperatures investigated, water sorption was several times higher than hexane sorption, the differences increasing with solvent activity. The net heat of sorption that resulted was significantly higher for hexane than for water. Water sorption isotherms were slightly affected by temperature, especially at water activities greater than 0.6. Some hysteresis was observed in water sorption at 50 °C, but it was practically negligible at higher temperatures. Hexane previously adsorbed in the meal did not affect significantly the sorption of water. On the contrary, water previously adsorbed in the meal increased the amount of adsorbed hexane.