Application of model-free kinetic analysis methods to dehydration of a HEU-type zeolite rich tuff from Turkey

Abstract

AB ST R ACT : Non-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20ºC/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30À200ºC suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54Ô1.18, 30.99Ô1.14 and 27.79Ô1.42 kJ/mol by the FlynnÀWallÀOzawa, the KissingerÀAkahiraÀSunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.