Hydrophobic paraffin-selective pillared-layer MOFs for olefin purification

Abstract

Adsorption separation of paraffins and olefins is an industrially important process, while developing a highly stable and paraffin-selective adsorbent remains challenging. Herein, a pcu-topology (primitive cubic) robust pillared MOF, termed M(BTFM)(DABCO)_0.5 (H₂BTFM = 2,5-bis(trifluoromethyl)terephthalic acid, M = Zn, Cu), having a superhydrophobic trifluoromethyl-decorated channel, is able to preferentially adsorb paraffin molecules, affording both high paraffin sorption capacity and selectivity of paraffins over olefins. Benefitting from appropriate pore aperture and functionalized fluoride-rich groups, Zn(BTFM)(DABCO)_0.5 possesses a record C₃H₈/C₃H₆ uptake ratio (1.11) among propane-selective MOFs reported so far. Remarkably, the purity of olefins including C₂H₄ and C₃H₆ obtained from breakthrough experiments of paraffin/olefin mixtures (10/90, v/v) reached up to 99.99%. The visualized single-crystal structures of gas-loaded Zn(BTFM)(DABCO)_0.5 and DFT calculations both revealed the multiple weak hydrogen-bonding interactions between C₂H₆ (or C₃H₈) and the pore wall, and the stronger binding affinities of a high density of trifluoromethyl groups to C₂–C₃ paraffins.