Alkylaromatic mass transport – acidity properties correlation for commercial and mesostructured Y zeolites with the catalytic behavior of cracking reactions

Abstract

A strategy to mitigate diffusion restrictions associated with heavy crude oil conversions is using mesostructured Y zeolite. In recent years, multiple routes have been proposed for obtaining materials with improved catalytic performance versus catalysts with higher molecular transport restrictions. Typically, after the implementation of these treatments, improvement in catalytic activity is correlated either with changes in textural properties (area and porous volume) or the modification of physicochemical properties (Si/Al ratio and acid strength); however, the correlation with diffusional mass transport characteristics is not typical. In this study, alkylaromatic molecules of different kinetic diameters, such as benzene, toluene, p–xylene, and m–xylene, were used as molecule probes to determine the effective diffusion through a pulse experiment under conditions of no adsorption or reaction. The studied solids include five commercial zeolites from the Zeolyst CBV series and four top–down mesostructured Y zeolites. The obtained concentration curves were fitted to an exponential decay model, a solution of the second Fick's law under defined experimental conditions, and correlation values between 0.9996 > R2 > 0.9896 were found. Furthermore, the implementation of the descriptors “Transport ratio (TRMR)” and “Corrected transport ratio (TRMRc)” was proposed, which allowed the combined representation of the change in the mass transport of aromatic probes and the changes in the acidity of the zeolite, after the application of top–down treatments. These descriptors proved simple and effective tools to correlate the changes after mesopore insertion with the catalytic performance in the 1,3,5–Triisopropylbenzene (TIPB) cracking reaction. Our approach is an integral method of screening mesostructured zeolites with an adequate balance of acidity and transport properties.