New adsorbents for purification: Selective removal of aromatics

Adsorption of benzene and cyclohexane on various Y-zeolites was investigated to develop sorbents for the purification of aliphatics by removal of aromatics. Ag-Y showed superior benzene/cyclohexane selectivities to Na-Y, Pd-Y, and H-USY. Separation factors greater than 10⁵ were obtained with Ag-Y at low concentrations of benzene. High selectivities were achieved by the strong interaction between benzene and Ag-Y, while the interaction with cyclohexane was not influenced by the cations. Molecular orbital calculation revealed that benzene formed a classic π-complexation bond with Ag-Y: donation of electron charges from the p-orbitals of benzene to the vacant s-orbital of the silver (σ donation) and, simultaneously, back donation of electron charges from dorbitals of silver to π*-orbital of benzene (d-π* back donation). Grand canonical Monte Carlo simulations were also performed for adsorption isotherms. Potential parameters of benzene on Ag-Y, including π-complexation, were developed first. Simulation and experiments of GCMC agreed excellently for adsorption of benzene on Y-zeolites.