Separation of ethanol-water mixtures using molecular sieves and biobased adsorbents

The potential use of new biobased adsorbents and different types of molecular sieve was assessed in the separation of the ethanol-water azeotrope. Molecular sieves of type 3A, type 4A, and type 5A and biobased adsorbents such as natural corncobs, natural and activated palm stone and oak, were used in this study. Each of these adsorbents was packed in a column, which was surrounded by a heating jacket. The jacket temperature was maintained constant in an attempt to maintain the packed-column at constant temperature. The water concentration in the feed solution was varied from 5% to 12% (weight basis). Although the initial concentration of ethanol in the flask was constant at the beginning of the experiment, it varied with time due to boiling. The breakthrough curves of water sorption on these adsorbents at different water contents showed that among the molecular sieves examined, type 3A molecular sieves gave the best separation of the ethanol-water system and among biobased adsorbents examined, natural palm stone was the best. The Guggenheim, Anderson, and De Boer (GAB) model at different water contents represented the isotherms for water sorption on molecular sieves and biobased adsorbents. In addition, the surface area of adsorbents and maximum water uptake were calculated. Type 3A molecular sieves were determined to have the largest surface area and the highest value of water uptake compared with the other two types of molecular sieve. However, for the biobased adsorbents, activated palm stone was found to have the largest surface area and the highest value of water uptake compared to the other biobased adsorbents. It was found that upon activation, the adsorption capacity of biobased adsorbents was not enhanced. On the contrary, the activation gave negative results on some occasions.