Selective adsorption of mixed xylene was investigated with both X and Y types of zeolites cation-exchanged by $K^+$ and $Ba^{++}$. Of them, the KY zeolite shows the best selectivity for p-xylene, and this is attributed to its lowest acidity. The selectivity tends not to change much with temperature since the heat of adsorption of each xylene isomer is almost the same. Water adsorbed was found to reduce the selectivity significantly.
