Dehydration of aqueous ethanol

Upgrading of aqueous alcohol to anhydrous ethanol may be accomplished using a packed bed adsorption process, in which cracked grain corn is the adsorbent. A 0.35 m diameter by 3.0 m dehydration column was designed and constructed on the basis of data obtained in a series of bench-scale experiments.

The results demonstrated that grain corn would upgrade 91% ethanol to 99%-plus at a rate of about 0.20 L/min. The capacity of the corn bed in the prototype ranged from7.6 to 10.5 mL/kg of bed, which was lower than expected from the bench-scale experiments. The difference was attributed to the significant thermal effect of the heat of adsorption, which caused higher bed temperatures.

The performance of the prototype was modelled mathematically using a one-dimensional dispersive-convective description of the bed. The model was observed to fit the experimental data well in the regions where heat effects were not pronounced (where C/C₀ < 0.5), and showed a systematic departure in the non-isothermal regions.

The estimated energy consumption for the dehydration and regeneration cycles was observed to be lower than that normally associated with azeotropic distillation. Aside from the energy advantage, an adsorption system is easier and safer to operate than azeotropic distillation.