C8 aromatics adsorption : effects of zeolite acidity

Abstract

The most attractive industrial technique for the separation of p-xylene is selective adsorption with zeolites. An understanding of parameters that influence the effectiveness of the separation is needed in order to achieve the best p-xylene separation. In this work, roles of zeolite acidity on liquid-phase adsorption of C8 aromatics and p-xylene selectivity on 2.0X, 2.5X and Y zeolites were investigated at a constant temperature and pressure. Besides zeolite inherited acidity, acidity was also modified by exchanged di-valence cations, Mg, Ca, Sr, and Ba. Higher ionic radius exchanged cations are known to have lower acidity. The results from Pulse Test and Breakthrough techniques indicated that while the selectivity of p-xylene with respect to some C8 aromatics decreased with the increase of zeolite acidity, there was a turning point where the effects of an exchanged cation size were more pronounced than those of the acidity. The effects of zeolite acidity, cation size and zeolite type must be taken into consideration for p-xylene selectivity.