Sorption equilibrium moisture characteristics of selected corn stover components

Corn stover equilibrium moisture isotherms were developed to aide biomass engineering of consistent, uniform-quality feedstock supplies for renewable bioenergy and bioproducts. Equilibrium moisture content (EMC) and equilibrium relative humidity (ERH) sorption data of corn leaf, stalk skin, and stalk pith were experimentally determined using the static gravimetric method at six temperatures ranging from 10 degrees C to 40 degrees C and at ten ERH values ranging from 0.11 to 0.98. The greatest EMC values for corn leaf and stalk pith generally corresponded with ERH below and above 0.90, respectively, at all temperatures. Only at some intermediate ERH range at 20 degrees C to 40 degrees C was stalk skin EMC greater than stalk pith EMC. Corn stover components followed a type II isotherm typically observed among food materials. EMC of all components was proportional to ERH and inversely proportional to temperature. Observed EMC ranges were 3.9% to 56.4%, 3.1% to 41.1%, and 2.7% to 71.5% dry basis (d.b.) for corn leaf, stalk skin, and stalk pith, respectively. Calculated whole-stalk EMC values ranged from 3.1% to 49.2% d.b. Isotherm data were fitted with the EMC model of Henderson, and modified versions of Henderson, Chung-Pfost, Halsey, Oswin, and Guggenheim-Anderson-deBoer. The modified Oswin model (R2 > 0.98; F > 2085) followed by the modified Halsey model (R2 > 0.97; F > 1758) produced the best fit for corn stover components studied. The Henderson, modified Henderson, and modified Chung-Pfost models were not suitable since these models did not produce randomized residuals. The modified Oswin model (R2 = 0.99; F = 6274) best described the stalk EMC. Results have practical applications in corn stover collection method and timing; process handling, grinding, and drying requirements; transportation efficiency of dry matter; and necessary storage environment, shelf life, and potential microorganism safety hazards. For example, results indicated that higher EMC values for corn stover leaf may result in greater propensity for the onset of mold growth and may determine minimal storage requirements or potential advantages in separating leaf from stalk fractions.