Kinetic modelling of gibbsite dehydration/amorphization in the temperature range 823–923 K

In this work, the kinetics of gibbsite dehydration/amorphization were investigated in the temperature range from 823 to 923 K. Different kinetic models were evaluated to find the appropriate formalizations that best describe or predict the kinetic behavior of this process. Gibbsite dehydration/amorphization is a complex process involving a set of chain reactions: gibbsite→amorphousphase,gibbsite→boehmite→amorphousphase.The dominant reaction mechanism varies with reaction extent. The refined Avarami method (RAM) allows identification of different reaction stages by analyzing the activation energy (Ea) variations during the dehydration/amorphization process. The higher Ea value of 44 kJ mol−1 (error→±3 kJ mol−1) in the beginning is related to the high activation energy of boehmite embryo formation. The lower Ea values near 14 kJ mol−1 (error→±1 kJ mol−1) are closely related to gibbsite and/or boehmite amorphization.The single-chain reaction, gibbsite ⟶k1 boehmite ⟶k2 amorphous phase, was modelled using classic rate laws. The derived rate constants are: k1=3.9(±0.8)×10−3 s−1, k2=5.9(±0.8)×10−3 s−1 at 823 K; k1=4.1(±0.7)×10−3 s−1, k2=7.4(±0.8)×10−3 s−1 at 873 K; k1=4.3(±0.9)×10−3 s−1, k2=9.1(±0.7)×10−3 s−1 at 923 K.