Processing of Alumina Honeycomb Catalyst Substrates and Studies on Methyl Cellulose Binder Burn Out Kinetics

Abstract

Alumina based honeycomb catalyst substrates are extrusion processed with methyl cellulose as a binder. Binder being organic in nature it reduces inter-particle friction thereby improves the flow ability while shaping and further enhances the mechanical strength of the green bodies. However, these binders are removed while further heat treatments through engineered heating schedules and any improper and non-uniform removal of these additives becomes a potential source of defects while processing cycles. In the present study, weight loss of the green honeycomb specimens was recorded as a function of temperature through Theromogarvimetric - Differential Scanning Calorimetric (TG-DSC) measurements at varying heating rates. A low heating rate less than 10^oC/min up to 550^oC is found to be desirable for binder removal. TG -Weight loss (x) with respect to the temperature can be regarded as x = (M_o - M_T)/ (M₀ –M_f), where, M_o: initial weight, M_T: sample weight at temperature T and M_f: the final weight. Arrhenius parameters, for the thermal decomposition of the samples were determined by assuming a first order chemical reaction using the integral form of the rate law dx/dt = Ae ^{( -E/RT) f ( x)}. The plot of dx/dt vs 1/T exhibited a straight line and the activation energy for the burnout of methyl cellulose is estimated to be around 110 kJ/mole. The honeycomb samples were also subjected to sintering and the samples exhibited a highly porous microstructure and a compressive strength of 80 Kg/cm² suitable for catalyst coating.