Authors:M. Gojić, J. Črnko, M. Sućeska, and M. Rajić
Heat treatment of pipes was performed under industrial conditions at 580C in a dry protective gas containing a CO2–CO–H2–N2 mixture. A commercial adsorbent (733 kg) used for production ofthe gas removed 52.7 l of water in five h and 22.5 min. During
the annealing of pipesoxidation and decarburization were not observed. The results were confirmed bymetallographic analysis.
The values of enthalpy of water desorption (36.4–40.5 kJ mol–1) obtained by DSC and TG measurements were close to those of water evaporation(44.1 kJ mol–1). This suggests that the bonds between the water molecules andadsorbents were not of chemical but of physical nature.
Authors:Isaak Lapides, Mikhail Borisover, and Shmuel Yariv
Thermal degradation of different organoclays in inert atmosphere was investigated by several investigators [ 31 – 36 ]. Thermal analysis curves of organoclays show stepwise degradation which corresponds to residual waterdesorption
A simple method is described for use with the differential scanning calorimeter for baseline interpolation in continual processes over a wide temperature interval. For the process of water desorption from the synthetic zeolite LiA with the coveragegq=1.5, the measured heat of desorption wasQ=11.2±0.5 kcal/mole.
Authors:F. Villiéras, L. Michot, G. Gérard, J. Cases, and W. Rudzinski
Controlled-rate thermodesorption (CRTD) spectra are obtained by adjusting the heating rate in such a way that the rate of
desorption can be constant. A quantitative analysis of the obtained spectra is presented, based on application of the statistical
rate theory of interfacial transport (SRTIT) to describe both adsorption and desorption kinetics. The SRTIT approach relates
the rates of adsorption and desorption to the chemical potentials of the adsorbate in the gaseous and in the adsorbed phases.
This quantitative analysis of the CRTD spectra yields the condensation approximation for the actual adsorption energy distribution.
For the purpose of illustration, an analysis is made of water desorption from a synthetic apatite mineral under CRTD and classical
TPD conditions. The influence of the adsorption and desorption rates is also discussed.
Sodium montmorillonite has been modified via cation exchange reaction using gemini surfactants. Montmorillonite modified by
cetyltrimethyl ammonium bromide (CTAB) is used for comparation. Basal spacings and thermal stability of these organo-montmorillonite
clays have been characterized using X-ray diffraction analysis and thermogravimetric analysis. The d(001) spacings of montmorillonite-Gemini14,
montmorillonite-Gemini16, montmorillonite-Gemini18 can reach above 35 Å compared with the 23.66 Å of the montmorillonite-CTAB
at 2.2CEC. The thermogravimetric analysis show four-step degradation which corresponds to residual water desorption, dehydration,
followed by decomposition of the organic modifier and the dehydroxylation of the organo-montmorillonite. In addition, DTG
enables two different structural arrangements of gemini surfactant molecules intercalating the montmorillonite to be proposed
that is different from montmorillonite-CTAB.
Authors:J. J. Suñol, D. Miralpeix, J. Saurina, F. Carrillo, and X. Colom
Summary New regenerated cellulose fibers were developed during the last decades as environmentally friendly systems. In this work, three fibers: lyocell, modal and viscose were subjected to an enzymatic treatment. Likewise, different lyocell fibers were washed in a Na2CO3 solution under severe conditions. Analysis was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. In all samples, at low temperature, water desorption was detected. Furthermore, thermal analysis shows wide exothermic processes that began between 250 and 300°C corresponding to the main thermal degradation and it is associated to a depolymerization and decomposition of the regenerated cellulose. It is accompanied with mass more than 60% mass loss. Kinetic analysis was performed and activation energy values 152-202 kJ mol-1 of the main degradation process are in agreement with literature values of cellulose samples.
Comparative investigations of new regenerated cellulosic fibers, bamboo viscose fiber and Tencel, together with conventional
viscose fibers have been carried out to explain the similarity and difference in their molecular and fine structure. The analyses
jointly using SEM, XRD and IR reveal that all the three fibers belong to cellulose II. Tencel consists of longer molecules
and has a greater degree of crystallinity, while bamboo viscose fiber has a lower degree of crystallinty. TG-DTG-DSC study
shows three fibers resemble in thermal behavior with a two-step decomposition mode. The first step is associated to water
desorption, suggesting that bamboo viscose fiber holds better water retention and release ability, the second a depolymerization
and decomposition of regenerated cellulose, indicating that Tencel is more thermally stable in this process than bamboo and
conventional viscose fiber.
Authors:H. Wittkopf, H. -J. Flammersheim, and L. Herlitze
Experiments on water desorption from silicate glass powders of different chemical compositions were carried out by means of DSC. In order to establish the desorption energy distributions, a model of the heterogeneous surface was applied to the thermoanalytical desorption curves, and the results are discussed together with contact angle measurements on flat polished glass samples.
Authors:B. Hunger, S. Matysik, M. Heuchel, E. Geidel, and H. Toufar
We have investigated the interaction of water with Na+-ion exchanged zeolites of different structures (LTA, FAU, ERI, MOR and MFI) by means of temperature-programmed desorption
(TPD). The non-isothermal desorption of water shows, depending on the zeolite type, differently structured desorption profiles.
In every case the profiles have, however, two main ranges. Using a regularization method, desorption energy distribution functions
have been calculated. The desorption energy distributions between 42–60 kJ mol−1, which can be attributed to a non-specific interaction of water, show two clearly distinguished energy ranges. The water
desorption behaviour of this range correlates with the electronegativity of the zeolites and the average charge of the lattice
oxygen atoms calculated by means of the electronegativity equalization method (EEM). The part of the desorption energy distributions
in the range of 60–90 kJ mol−1, reflecting interactions of water with Na+ cations, shows two more or less pronounced maxima. In agreement with vibrational spectroscopic studies in the far infrared
region, it may be concluded that all samples under study possess at least two different cation sites.