Pillared layered structures vs. zeolites as sorbents and catalysts. Part 1.—Hydrocarbon separations on two alumina-pillared clays and an α-tin phosphate analogue

Abstract

The dynamic sorption of a series of hydrocarbons in an alumina-pillared montmorillonite (AZA), its mixed Fe³⁺–alumina-pillared analogue, (FAZA) and an alumina-pillared a-tin phosphate analogue (AI-PILP) has been investigated. Separations between binary mixtures of cyclic non-aromatic/aromatic, linear chain/cyclic non-aromatic hydrocarbons, among others, have been performed in the temperature range 200–350 °C. Aromatic chlorohydrocarbons can also be separated from one another and from their ternary mixtures with hydrocarbons. Although they are the most efficient in these separations (requiring lower temperatures), the AI-PILP samples show enhanced acid-catalysis characteristics at higher temperatures. In addition, naphthalene and biphenyl are sorbed by the montmorillonite-based PILCs, but separated by the AI-PILP, confirming that shape-selection behaviour is involved. The anomalous sorption of cyclohexane by the AI-PILP demonstrates that lateral oxide-pillar ordering differs between pillared smectite clays and phosphates.

Catalytic cracking phenomena observed for n-heptane differ between AZA and FAZA, indicating that in-pillar Fe in FAZA is involved, and this is confirmed via cracking of 3-methylhexane. That adsorbate–wall (i.e. pillar) interactions are important, and differ from adsorbate interactions in medium-sized zeolites, is supported by the fact that AZA and FAZA act as weak Lewis-acid reaction ‘vessels’ in the isomerisation of p-xylene.