Synthesis and Optimization of a New Starch-Based Adsorbent for Dehumidification of Air in a Pressure-Swing Dryer

Corn grits selectively adsorb water from many types of organic vapors and are used commercially to dry 2.8 billion L of fuel-grade fermentation ethanol annually. Evaluation of grits in a pressure-swing dryer at 308 kPa, combined with analyses of their physical properties, showed that the specific surface of the grits (0.5 m 2 /g) limited steady-state drying of air to a dewpoint of −20 °C. By selectively taking advantage of the best features of the natural material, a new class of natural adsorbents with a higher affinity for water was then synthesized using materials derived from corn: starch and cob flour. The chemical composition of the synthesized adsorbent was determined, as well as specific physical properties. Scanning electron microscopy showed the synthesized adsorbent surface had a large number of macropores (10−25 μm in diameter) unlike corn grits which have limited porosity. This material gave reasonable and reproducible results, similar to those obtained with molecular sieves using a commercially available pressure-swing air dryer. After 70 h of operation at 30 psi, the new adsorbent provided air at a dewpoint of −63 °C. The methods for preparing this material and an explanation of its performance in terms of macroscopic and microscopic structural characteristics are described.