Thermochemistry of alkali interactions with refractory adsorbents

The kinetics and mechanism of interactions between alkali vapors and several refractory adsorbents are studied. A unique thermogravimetric reactor is designed and utilized for this study. Bauxite and kaolin are very good adsorbents for alkali chlorides and are potentially good additives for control of alkali during coal combustion and gasification. The experimental data shows that the alkali capturing process is a combination of physisorption, chemisorption and chemical reaction. An analytical model is developed assuming a multi-layer adsorption of alkali on substrate followed by a rate-controlling reaction on the surface. The experimental results and model predictions are in good agreement.