Study of the kinetics of water desorption on binder-free pellets of SOD and LTA zeolites using model-free isoconversion analyzes

The moulded binder-free pellets of SOD (Sodalite) and LTA (Linde Type A) zeolites have been prepared from mixtures based on kaolin and metakaolin, respectively, which have been confirmed by X-ray diffraction and IR spectroscopy. Using the SEM and XRD methods, it was determined that the SOD particles was irregular in shape with a size of 0.5–1 μm and a dimension of coherent scattering region of 453 nm; the LTA particles have a shape close to a cube and a size of about 2 μm, and a dimension of coherent scattering region is 760 nm. According to BET measurements, the surface area of SOD (141 m2 g−1) and LTA (115 m2 g−1) zeolites have been determined. The amounts of absorbed water vapor for SOD were about 20 wt%, and for LTA were about 30 wt%. By synchronous thermal analysis, it was shown that desorption of water occurs in two stages. The first stage is the removal of capillary water: for SOD zeolite it is a temperature of up to 95 °C, for LTA zeolite it is about 50 °C. It is found that further desorption of water from SOD and LTA zeolites occur from α- and β-cages of zeolites. By employing Friedman, Ozawa-Flynn-Wall, and Kissinger–Akahira–Sunose analyzes, the apparent activation energy was calculated for water desorption on the zeolites. The advantage of these analyzes is that it is not necessary to have a kinetic model of the interface reaction. This allows to significantly simplifying the calculation of the activation energy. It is demonstrated that all three analyzes yielded close results. It was found that at a conversion (desorption) extent of about 0.2–0.3, the apparent activation energy values are not more than 60 kJ mol−1. The increase in apparent activation energy values up to 110 kJ mol−1 (for SOD) and up to 80 kJ mol−1 (for LTA) is associated with removal of water from α- and β-cages of zeolites.