Continuous supercritical image alkylation over H-Beta and H-USY: Influence of the zeolite structure Original Research Article

This study presents a comparison of the catalytic performances and stabilities of H-Beta and H-USY zeolites for image alkylation in supercritical isobutane phase. The experimental results clearly show that the zeolite structure strongly influences the performance and deactivation behavior of the zeolite in image alkylation performed in SC conditions. H-Beta outperformed H-USY zeolite as regards to its lower deactivation and the stable quality of the alkylate, composed mainly of isoparaffins while olefin di-/oligomerization was shown to be responsible of the H-USY deactivation with time-on-stream. Characterization of the spent catalysts gave clues to the differentiated performance of the two zeolites. The stable activity of H-Beta was attributed to the effective extractive effect of the supercritical iC4 media to “clean” the acid sites located on the external surface of the small crystallites of H-Beta or located at the pore mouth. By contrast, the deactivation observed for H-USY was caused by olefin oligomerization inside the zeolite supercages. The supercritical isobutane media was shown to be unable to prevent the oligomers formation inside the zeolite supercages and/or to in situ extract these oligomers located in the supercages of the large crystals of the H-USY zeolite.