COMPARISON OF ADSORPTION AND DESORPTION ISOTERIC HEATS FOR SOME GRAINS

The usual procedures for determining sorption isosteric heats by the application of the Clausius-Clapeyron equation to sorption isotherms of grains were examined. Isosteric heats of adsorption, desorption and total isotherms derived from various wheat, corn, rice and rapeseed cultivars were compared. There is no significant difference between adsorption and desorption isosteric heats of wheat. Isosteric desorption heats for shelled corn and rapeseed were considerable higher than those of isosteric adsorption heat. The differences between desorption and adsorption isosteric heats of shelled corn were larger at lower moisture contents, increasing from 2.6 % at 0.14 mc to 5.1 % at 0.05 mc. The differenc s between desorption and adsorption isosteric heats of rapeseed increased at lower moisture contents and ranged from 9.6 % to 20.8% at 0.10 and 0.05 mc, respectively. Below the 0.11 mc, isosteric adsorption heats for rice were higher than isosteric desorption heat. The difference between adsorption and desorption isosteric heats of rice was 3.7 % and 18 % at 0.09 and 0.05 mc, respectively. Sorption isosteric heats for all studied crop species were found dramatically higher than those of total sorption isosteric heats