Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate

Abstract

Abstract The reaction kinetics and physical transport processes governing the thermal dehydration of solid K 2 CO 3 ·3/2H 2 O particles were investigated. Isothermal reaction rate data were gathered using a thermogravimetric balance in which narrowly‐sized K 2 CO 3 ·3/2H 2 O crystals were dehydrated under a water vapor atmosphere at different pressures and temperatures. The magnitudes of the heat and mass transfer resistances external to and within the solid product were estimated from solutions of the relevant pseudosteady‐state transport equations. In the temperature range 320 to 358 K, the vacuum dehydration of K 2 CO 3 ·3/2H 2 O crystals smaller than 710 μm (−25 +30 mesh) are accurately modeled by the spherical shrinking‐core equation for the chemical rate control regime. In the presence of water vapor, external heat transfer to the particles was sufficient to prevent significant self‐cooling; heat and mass transfer resistances within the particles were negligible. The activation energy for K 2 CO 3 ·3/2H 2 O dehydration is approximately 91 kJ/mol in vacuum; the reaction becomes extremely slow at relative pressures ( P / P eq ) > 0.35.