Fundamental studies of polysaccharides as adsorbents of water

Jay Young Lee, Purdue University

Abstract

The sorption behaviour of water and ethanol on starch material has been investigated. Studies have indicated that a polar interaction between the hydroxyl group in starch, i.e., amylose and amylopectin, and the water molecule is the main force for the water-starch adsorption. The adsorption isotherms of water-starch at 70, 85, 100, and 115 C, ethanol-starch adsorption isotherms at 80, 90, and 100 C, and water-ethanol-starch adsorption isotherm at 90 C were measured using a Cahn electro balance in connection with a microprocessor-based computer for the precise control of the adsorption temperature and the automatic data acquisition for experiments lasting up to 400 hours. More than 70 equations were reported to represent the sorption isotherms on starch materials. Careful examination of the many models presented in the literature have resulted in selection of a few models best-suited for the water-starch system. Sircar's model gave a good fit for the water adsorption isotherm on corn and starch covering wide range of temperatures and the potential theory, especially Dubinin-Radushkevich's model for large pore sorbents on water-corn, water-starch, and ethanol-starch adsorption isotherms gave successful results. This makes it possible to predict the equilibrium adsorption capacity over a wide range of temperature. Experimental results showed that significant amount of ethanol can adsorb on starch at 80 to 100 C. However, the adsorption rate of ethanol is 20 times slower than that of water. While equilibrium adsorption of water is attained in about 3 to 4 hour or less, ethanol requires 60 to 100 hours. An increase in temperature increases the rates of adsorption for both water and ethanol. This suggests that conditions could be selected at which ethanol could be adsorbed on starch, and that the selective removal of water from ethanol vapors is likely a rate dependent rather than a equilibrium dependent process.

Degree

Ph.D.

Advisors

Ladisch, Purdue University.

Subject Area

Agricultural engineering

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