Quantitative structure-property relationship approach to predicting xylene separation with diverse exchanged faujasites.

Streamlining the xylene separation process on faujasites is a promising way to design innovative adsorbents for this application. For this purpose, we present herein an original quantitative structure-property relationship (QSPR) approach. It deals with the development of a multi-linear predictive model correlating the separation properties with a set of structural descriptors for the adsorbents. The implementation of such an approach makes it necessary to (i) set an appropriate design of experiment (DOE), (ii) prepare an adsorbent database, (iii) test the adsorbent database for xylene separation and (iv) compute a set of relevant descriptors. The selected descriptors essentially characterize the nature of the confinement in the faujasite supercage, i.e., the size of the cations localized in adsorption sites II, as well as the occupancy ratio of both adsorption sites II and III. Two different statistical methods were applied to develop a structure-property relationship model linking experimental selectivity and the set of descriptors. A multiple linear regression model enables the prediction of para/meta-xylene selectivity with a correlation coefficient R2 of 0.78, while a linear discriminant analysis predicts the assignment of the adsorbents to four identified classes with a total prediction percentage of 76%.

Monovalent and bivalent cations exchange isotherms for faujasites X and Y.

This study addresses the modeling of exchange isotherms for faujasite-type zeolites X and Y with K+, Cs+, Ca2+ and Ba2+ cations based on a large experimental dataset obtained under operating conditions of 0.5 N total normality and an exchange temperature of 80 °C. The isotherm models are based on the mass action law. Ideal solution phase is assumed. Heterogeneity of the solid phase is taken into account by using Barrer and Klinowski's approach to multi-site exchange. Three types of exchange sites are identified on these zeolites. To each exchange site j corresponds a fitted selectivity coefficient Kj. These parameters, estimated by least square method, evaluate the affinity of the studied cations for the identified exchange site. Globally, these fitted coefficients show that the cations considered present better affinity than Na+, especially for type III sites in faujasite X and type II sites in faujasite Y. For bivalent cations, an exchange with Ba2+ is always more favorable than with Ca2+. On faujasite X, type II sites are more strongly preferred by monovalent cations (with the exception of Cs+) than by bivalent ones. The opposite trend is observed on faujasite Y, even for Cs+. These conclusions have been confirmed and are supported by bibliographic data.