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

Abstract

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 ¿ 40 • C. It is particularly reliable for small water activity values 0 6 aw 6 0:4 where a good agreement with standard methods is observed in spite of small apparent di usion coe cients D ∼ = 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 (1 or 2 h).

A review on sludge dewatering indices

“…Furthermore, the selection of threshold temperature is essentially important since it is used for distinguishing the free and bound water . As a result, DTA or DSC performed simultaneously with Thermogravimetric analysis (TGA) (aslo known as TG-DTA and TG-DSC), as proposed by Chen et al (1997) and Ferrasse & Lecomte (2004), for biological products.…”

Studies of the heat of vaporization of water associated with cellulose fibers characterized by thermal analysis

“…This value can be obtained from water sorption isotherms recorded at different temperatures based on the Clausius-Clapeyron equation, see later Modeling section (Sirota 1987). However, it was reported that the use of sorption isotherms were associated with experimental difficulties for low and high water activity due to the limitation in the use of saturated salts (Ferrasse and Lecomte 2004). A second method to evaluate the desorption energy is by means of calorimetric techniques (Rü ckold et al 2003;Hatakeyama et al 2000;Mulet et al 1999;Sá nchez et al 1997;Zang and Sapieha 1991;Fielden et al 1988).…”

Drying of municipal sewage sludge: from a laboratory scale batch indirect dryer to the paddle dryer

“…The total heat of sorption is derived from the calorimetric signal and the mass loss (Ferrasse and Lecomte, 2004). As can be seen on Figure 2, the isosteric heat of sorption can be neglected for 2 .…”

“…A fast transient method was elaborated and tested for a large range of products (Ferrasse and Lecomte, 2004;Arlabosse et al, 2003). This method, using a thermogravimetric analyzer (TGA) coupled with a differential scanning calorimeter DSC111 (Setaram, Caluire, France) in isothermal mode, was successfully applied to sludge description.…”