Conclusion An experimental program concerning the separation of p-xylene, o-xylene, and ethylbenzene isomers was carried out, enabling determination of evaluation criteria involving liquid adsorption in X zeolite. The preferential adsorption of p-xylene is mainly attributed to the physical interaction forces betweenp-xylene and the surface. These forces were enhanced through the replacement of cationNa+ by Ba2+ and K+ andthrough variation of the water content in the adsorbent. This water content is of paramount importance in the selectivity of p-xylene ando-xylene mixtures sepa-ration, showing an optimum value in the range of variables analyzed.