Acetone condensation on a cation exchange resin catalyst: the pseudo equilibrium phenomenon

Abstract

Acetone condensation/dehydration to form mesityl oxide (MSO) and water was studied in a fixed bed reactor packed with Amberlyst ® 16 in a temperature range between 100 °C and 120 °C. Theoretical analysis of the equilibrium as well as experimental work using homogeneous catalysts (Ind. Eng. Chem. 48(8) (1956) 1278) shows that the reaction is slightly exothermic (−3 to −8 kJ/mol). The `equilibrium' obtained in this study displayed properties of an endothermic reaction (25.5 kJ/mol) and the value of the equilibrium constant differed significantly from that of the theoretical/homogeneously catalysed equilibrium constant. Experimental tests confirmed that the obtained `equilibrium' was a pseudo equilibrium. The authors have previously shown (du Toit and Nicol, 2003) that the rate inhibition effect of water on cationic exchange resin catalysts can be modelled by using a Freundlich water adsorption isotherm to account for the reversible deactivation of active sites. The same model accurately predicted the experimental data and the pseudo equilibrium could be explained by complete coverage (deactivation) of the active sites. The model could not be verified when water was added to the reactor feed. This suggested that the reversible deactivation of the resin is more complex than mere adsorption of water onto the active sites. It can however be concluded that the specific nature of a solid catalyst may in fact play a more significant role in the behaviour of a reaction system than merely influencing the reaction kinetics.