Selective Adsorption of Methyl Acetate from Model Fischer–Tropsch Synthetic Oil on 13X Zeolite: Experimental and Computational Insights

Abstract

The efficient removal of ester oxygenates from Fischer–Tropsch (FT) synthetic oil remains challenging due to limited understanding of selective adsorption mechanisms and adsorption kinetics. Herein, a combined experimental and theoretical approach was employed to investigate the selective adsorption behavior, kinetics, and mechanism of removing methyl acetate, a representative ester oxygenate, from a methyl acetate/1-decene/decane model FT synthetic oil using 13X zeolite, γ-alumina, and activated carbon. Dynamic breakthrough experiments revealed that 13X zeolite exhibited substantially higher adsorption selectivity and removal efficiency toward methyl acetate than γ-alumina and activated carbon. The adsorption behavior on 13X zeolite was well described by both pseudo-first-order and pseudo-second-order kinetic models. Moreover, 13X zeolite demonstrated excellent regeneration capability and adsorption stability, maintaining its performance over six consecutive adsorption–desorption cycles. Structural and acidity characterizations indicated that the superior adsorption performance of 13X zeolite originates from its well-developed hierarchical pore structure and abundant Lewis acid sites. Density functional theory (DFT) calculations suggested that the polar carbonyl and ester groups in methyl acetate induce pronounced charge separation on the molecular surface, creating strong positive and negative electrostatic potential regions. These features enable methyl acetate to preferentially adsorb on 13X zeolite through electrostatic (ion–dipole) attraction, hydrogen bonding, and van der Waals forces, effectively displacing weakly polar hydrocarbon molecules from adsorption sites. Monte Carlo (MC) simulations reproduced the experimental adsorption behavior and provided a reliable predictive model for equilibrium adsorption capacity. This work establishes an integrated experimental–computational paradigm for elucidating adsorption mechanisms and predicting oxygenate removal performance, providing a general strategy for the purification of Fischer–Tropsch synthetic oil.