Thermodynamic analysis of sorption isotherms of dehydrated yacon (Smallanthus sonchifolius) bagasse

Equilibrium moisture content of dehydrated yacon bagasse powder was determined gravimetrically using the static method at 20, 30, 40 and 50 °C for water activities ranging from 0.11 to 0.97. The sorption characteristic of yacon bagasse followed type III isotherm. Among the various models tested to interpret sorption isotherms, the Halsey model was selected as the most appropriate model. The Halsey equation was further used to estimate the thermodynamic functions that provide an understanding of the properties of water and energy requirements associated with the sorption behavior. The differential enthalpy and entropy decreased with increasing moisture content. Through the compensatory theory, it was found that the isokinetic temperature was greater than the harmonic mean temperature, indicating that the adsorption process was controlled by the enthalpy and was not spontaneous (ΔG>0). With respect to the integral properties, the integral enthalpy values decreased with increasing moisture content, while the integral entropy had opposite behavior. The integral entropy values were negative due to the existence of a chemical adsorption and/or changes in the structure of the adsorbent.