MOISTURE ADSORPTION THERMODYNAMICS OF FRACTIONATED SESAME HULLS (SESAMUM INDICUM L.)

Abstract

ABSTRACT Sesame hulls are a useful byproduct of sesame processing industry. Moisture adsorption isotherms (MSIs) for whole sesame hulls (WSHs) and powdered sesame hulls (PSHs) were obtained at 15, 30 and 45C, and 0.05 to 1.5 moisture content (decimal dry basis) using a water activity meter. Four MSI models were tested. Halsey model was found to provide the best fit for experimental data for both WSHs and PSHs. Standard error of estimate, %P and pseudo‐R2 values were: 0.00168 and 0.00248, 4.7 and 5.7%, and 0.963 and 0.974, respectively. Equilibrium relative humidity (ERH) values of PSHs were greater than those of WSHs at constant moisture content. Differential enthalpy (qst) and entropy (ΔSd) decreased exponentially with the increase in equilibrium moisture content, then became constant beyond 0.7 moisture content. qst and ΔSd values were larger for WSHs than PSHs. Enthalpy–entropy compensation was found to exist for both PSHs and WSHs. An entropy‐driven process was observed, with the free energy change (ΔG) for WSHs and PSHs of+0.0183 kJ/kg and−0.0284 kJ/kg, respectively. The spreading pressure was found to increase with the increase in ERH and decrease in temperature. The net integral enthalpy (ΔHi) decreased then reached an asymptote beyond a moisture content of 0.15 for both PSHs and WSHs. Net integral enthalpy was larger for WSHs. The net integral entropy (ΔSi) was negative for PSHs and WSHs, and ΔSi was greater in magnitude for PSHs.PRACTICAL APPLICATIONSSesame hulls are useful byproducts of sesame processing industry. Large amounts of this effluent are produced yearly in Jordan. They are used as livestock feed, but they require further dehydration to reduce moisture content and water activity into safe levels. In this project, drying thermodynamics of sesame hulls were discussed.