Adsorption of water from liquid-phase ethanol-water mixtures at room temperature using starch-based adsorbents

The kinetically controlled, selective removal of water from ethanol vapors by desiccants is well documented. However, studies on the removal of water by liquid-phase contacting of water-ethanol mixtures with starch-based material are limited. This research presents a screening study that shows that starch-based adsorbents remove liquid-phase water between 1 and 20 wt % from ethanol without the adsorbent being dissolved. The mass of water adsorbed per gram of dry adsorbent increases with increasing water content. Side by side comparisons of these starch-based adsorbents to silica gel and molecular sieves show that, in a kinetically controlled adsorption scheme below 10 wt % water, the inorganic desiccants have a greater operational (nonequilibrium) adsorption capacity per gram. At water concentrations at or above 10% water, however, the operational adsorptive capacity per gram of the starch-based adsorbents is roughly equivalent to the inorganic adsorbents, when using the same regeneration and adsorption conditions. The starch-based adsorbents adsorb water by forming hydrogen bends between the hydroxyl groups on the surface of the adsorbent and the water molecules.