Separation of Light Hydrocarbons through Selective Molecular Exclusion by a Microporous Metal-Organic Framework

[Zn₂ (sdc)₂ (bpe)] (compound 1, sdc=4,4'-stilbenedicarboxylate, bpe=1,2-bis(4-pyridyl)ethane)), a doubly interpenetrated, pillared-layer microporous metal-organic framework has been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The structure features a common Zn₂ (COO)₄ paddle-wheel building unit. Compound 1 undergoes structural change upon solvent removal. The activated phase (compound 2) displays permanent porosity, excellent thermal/moisture stability, and interesting hydrocarbon adsorption properties. Gas adsorption experiments show that compound 1 selectively adsorbs saturated/unsaturated C₂ hydrocarbons but excludes C₃ and C₄ hydrocarbons at room temperature. We have collected single-component adsorption isotherms of six light hydrocarbons and calculated adsorption selectivities of various binary hydrocarbon mixtures by ideal adsorbed solution theory (IAST). The results show that compound 1 possesses remarkably high selectivity towards C₂ over C₃ /C₄ hydrocarbons and the separation is achieved by selective molecular exclusion.