Isobutane/butene alkylation on sulfated alumina: Influence of sulfation condition on textural, structural and catalytic properties

Samples of sulfated alumina with different sulfate contents were prepared by treatment of γ-alumina with an aqueous solution of a sulfate precursor (sulfuric acid or ammonium sulfate). Under conditions where no catalyst deactivation was observed, it was found that yield of C5+ products as well as C5–C7 products selectivity increase as the sulfate content increases up to 23 wt.% and remain practically constant with further increase in sulfate content. Catalysts deactivation was studied at higher olefin WHSV and lower isoparaffin/olefin ratio in the feed. Increasing the sulfate content up to 14 wt.% led to an increase in activity. A reduction in activity was observed when the sulfate content increased further. Samples with similar sulfate content obtained from different sulfate precursors exhibited similar butenes conversion and product distributions under both conditions. The differences in texture of sulfated alumina catalysts prepared from different sources of sulfate were determined by nitrogen adsorption. Different sulfate species, the formation of which is influenced by the source and sulfate content, were detected by DTG. Formation of sulfate-containing phases on the samples with sulfate content of more than 8 wt.% was found by X-ray diffraction (XRD). The appearance of these phases resulted in a significant drop in surface area and pore volume.

The catalytic properties of sulfated alumina as a function of the source of sulfate and the sulfate-ion concentration were studied in isobutane/butene alkylation both under conditions where no catalyst deactivation occurs and under those favoring deactivation. It was found that SA samples in contrast with SZ are active in the presence of significant amounts of crystalline sulfate-containing phases. These phases were inactive in alkylation and led to a reduction in surface area.Figure optionsDownload as PowerPoint slide