Moisture Sorption Thermodynamic Properties of Corn Stover Fractions

Efficient processing, handling, and storage of corn stover, a major crop-based biomass, require an understanding of the moisture sorption thermodynamic properties of its fractions. Moisture sorption thermodynamic properties of the major corn stover fractions such as leaf, stalk skin, and stalk pith were determined, utilizing the static gravimetric sorption isotherms data in the temperature range of 10°C to 40°C. Brunauer-Emmet-Teller (BET) monolayer moistures of stover fractions, determined using standard and modified BET equations, decreased with an increase in temperature. Mean values of monolayer moisture contents were in the range from 3.8% to 4.9% d.b., and the whole range of associated water activity based on BET equations varied between 0.013 and 0.225. Net isosteric heat of sorption, evaluated using the Clausius-Claperon equation, and differential entropy values of stover fractions decreased exponentially with increased moisture and approached the latent heat of vaporization of pure water at around 20% d.b. The moisture sorption process was determined as enthalpy driven. Inequality in isokinetic and harmonic mean temperatures confirmed the enthalpy-entropy compensation theory. Among stover fractions, leaf had the greatest spreading pressure, followed by stalk skin and stalk pith. Spreading pressures increased with increase in water activity and decreased with temperature increase. Net integral enthalpy increased to a maximum and then decreased with increasing moisture content, whereas net integral entropy displayed an opposite trend. Mean values of the net integral enthalpy and entropy of stalk pith were the highest and progressively decreased for leaf and stalk skin.