Analysis of a gas-liquid-liquid-solid catalytic reaction: kinetics and modeling of a semibatch slurry reactor

Abstract

Hydrogenation of aniline to cyclohexylamine was studied in a gas-liquid-liquid-solid tetraphase system using cyclohexane and water as two immiscible liquid phases and ruthenium on alumina (2% Ru/Al₂O₃) as the catalyst. In addition to the higher catalytic activity with respect to the conventional three-phase system, the novel four-phase system was highly efficient in catalyst-product separation. Experimental data on concentration-time as well as hydrogen-consumption-time profiles were obtained to study the effect of concentration of aniline, catalyst loading, and the partial pressure of hydrogen. A detailed analysis of gas-liquid, liquid-liquid, liquid-solid, and intraparticle mass transfer was carried out using initial rate data to ensure the kinetic regime. On the basis of these data, several rate equations were evaluated to select a kinetic model. The kinetic parameters were estimated over a temperature range of 378-418 K by fitting the integral batch reactor data. A rate model considering adsorption of hydrogen on the catalyst surface followed by reaction with the liquid-phase components as the rate-limiting step was found to give the best fitting of the experimental concentration-time as well as the hydrogen-consumption-time data at different initial sets of reaction conditions. The activation energies, heat of adsorption, and entropy of adsorption were also evaluated.