Mathematical modeling of water adsorption isotherm in corn (Zea mays L.) dry grain

The present study aims to experimentally determine the adsorption isotherms of preserved grain corn (single bagging (SB) and triple bagging (TB)) by the static gravimetric method at different temperatures (25 °C, 30 °C, 35 °C). Eight empirical models were used to model the isotherms using regression analysis, under Excel 2013 software, using the nonlinear GRG solver algorithm. Hygroscopic equilibrium is obtained after 25 days for the SB system versus 35 for the TB for the last equilibrium point. The isotherms obtained are sigmoidal type II. The GAB model showed the best agreement between the experimental data and those predicted (r = 0.995; 0.998 and 0.999 / respectively for 25, 30 and 35 °C). The water content of the mono-molecular layer of the sample stored in TB is 2.151 % at 25 °C; 1.809% at 30 °C and 1.404% at 35 °C. For the sample stored in SB, it is 2.261% at 25 °C; 2, 255 % at 30 °C and 2.053 % at 35 °C. The net isosteric heat of adsorption tends to zero at high water contents (0.026 KJ / mol at 3.58% water). The linearity between enthalpy (net isosteric heat) and differential adsorption entropy shows their compensation.