EXPERIMENTAL-DETERMINATION OF BINARY SORPTION AND DESORPTION-KINETICS FOR THE SYSTEM ETHANOL, WATER, AND MAIZE AT 90-DEGREES-C

Methods are described to measure the simultaneous rates of sorption for both components of a binary vapor mixture of ethanol and water, and the subsequent desorption into an air stream. The shape of the ethanol vapor sorption curve at 90-degrees-C and atmospheric pressure was very unusual. For vapor feeds of less than 90% ethanol a rapid initial uptake was followed by temporary desorption and finally a slow resorption to equilibrium uptake. At higher ethanol vapor concentrations the temporary desorption was less apparent. The water sorption-time curves were inflected, particularly in experiments with smaller sorbent particles, indicating that water sorption cannot be controlled by diffusion with a constant coefficient. The sorption behavior can be interpreted in terms of the physical properties of the starch polymer matrix, in which the transition from a rigid, glassy state to a more flexible, rubbery state occurs as water is sorbed.