Efficient stacking of iso-butene in sulfonate functional metal–organic frameworks for efficient iso-butene/iso-butane separation†

Abstract

Separation of iso-butene and iso-butane is vital to producing high purity iso-butene feedstock, but is challenging because of their close molecular size and properties. Adsorptive separation using porous materials like metal organic frameworks (MOFs) is emerging as a potential energy-efficient alternative. But it's hindered by the lack of porous materials that exhibit satisfactory iso-butene/iso-butane separation performance. In this study, a novel sulfonate functionalized material, ZU-603, is reported to achieve the benchmark separation performance of iso-butene/iso-butane via exploiting the geometric difference of the carbon backbone between the planar iso-butene and tetrahedral iso-butane. Single-crystal analysis of ZU-603 loaded with iso-butene and simulation studies reveal that the sulfonate sites bound the iso-butene via S^δ−⋯H^δ+C interactions, meanwhile iso-butene molecules are efficiently stacked via π–π interactions within the confined space, realizing higher stacking efficiency of iso-butene than iso-butane. ZU-603 shows an exceptionally high iso-butene adsorption uptake of 2.30 mmol g⁻¹ (298 K, 1 bar) and a record high iso-butene/iso-butane uptake ratio of 2.77 at 1 bar, outperforming previously reported benchmarking materials (1.2). Fixed-bed breakthrough experiments confirm the impressive iso-butene/iso-butane dynamic separation ability of ZU-603. The work provides a potential shape-recognition strategy in designing functional materials for the efficient separation of hydrocarbons with similar physicochemical properties.

Keywords: Adsorptive separation; Hydrocarbon; Metal-organic frameworks; Iso-butene/iso-butane; Purification.