Simultaneous heat-flow differential calorimetry and thermogravimetry for fast determination of sorption isotherms and heat of sorption in environmental or food engineering

摘要

A new experimental technique is described for the determination of desorption characteristics for engineering purposes. A TGA-DSC set-up is used in isothermal mode to achieve the thermal desorption of deformable standard materials like microcrystalline cellulose and kaolin in dry air. Assumptions on heat and mass transfer are made and discussed in order to derive desorption isotherms and heat of sorptions from the calorimetric and gravimetric signals. The method is rapid and accurate for high-temperature desorption processes T greater than or equal to 40degreesC. It is particularly reliable for small water activity values 0 less than or equal to a(w) less than or equal to 0.4 where a good agreement with standard methods is observed in spite of small apparent diffusion coefficients D congruent to 10(-10) m(2) s(-1) for the two products tested. The method is suitable for heat sensitive biological products because of the small residence time in the furnace (I or 2 h). (C) 2004 Elsevier Ltd. All rights reserved.