Kinetic implications of (hierarchical) zeolite fouling during liquid-phase aromatics upgrading

Abstract

The kinetics of fouling in large pore zeolites (BEA, MOR), including those with hierarchical pore systems, were probed during the Brønsted acid catalyzed reaction of benzyl alcohol (BA) with 1,3,5-trimethylbenzene (TMB) by varying reactant driving force (i.e., [TMB]0/[BA]0; 11–119). In BEA, initial deactivation rate constants (kD,0) decreased exponentially with [TMB]0/[BA]0, highlighting the significance of oxygenates as deactivation precursors. Further, seeding pores with oxygenates completely suppressed measured rates in parent MOR and BEA, while seeding with TMB had no effect. Comparisons of mass accumulations of different organics (low molecular weight reaction species and coke) as functions of ln([TMB]0/[BA]0) revealed that coke (derived from oxygenate-seeded polyalkylation of TMB) disproportionately controlled deactivation rates by damping apparent (diffusion-controlled) and intrinsic (diffusion-corrected) rate constants through proton losses and/or altered molecule confinement within shrinking pores. These kinetic consequences were delayed upon introduction of mesopores, demonstrating how zeolite porosity impacts coke proliferation and behavior in liquid-phase reactions.