A kinetic approach for valorisation of hydrodesulphurisation catalyst residue into mullite

Mullite (3Al2O3 & sdot;2SiO2) is a silicoaluminate widely used for the production of ceramics, and it is usually synthesised from different raw materials with solid-state reactions. In this work, petrochemical industry catalyst waste (Ni-Mo waste) composed principally of alumina and silica has been envisaged as a suitable precursor to prepare mullite via thermal treatment. The kinetics of mullite crystallisation from the catalyst waste were studied with differential thermal analysis (DTA). The starting Ni-Mo waste was an amorphous material, and the crystallisation process takes place at temperatures between 1200 and 1300 degrees C. The activation energies calculated with isothermal and nonisothermal methods were 1059 and 743 kJ mol-1, respectively. The Avrami exponent (n) obtained with the Ligero method and the parameter m calculated with the Matusita method indicated twodimensional crystal growth, probably through a diffusion-controlled bulk crystallisation mechanism from a constant number of nuclei. The frequency factor calculated by the isothermal treatment was 8 x 1033 s-1.