Size exclusion propyne/propylene separation in an ultramicroporous yet hydrophobic metal-organic framework

Propyne/propylene separation is important in the petrochemical industry but challenging due to their similar physical properties and close molecular sizes. Herein, we present two isoreticular ultramicroporous Zn(II)-MOFs, Zn-2(ATZ)(2)(TPDC) (BUT-305, H2TPDC = [1,1 ':3 ',1 ''-terphenyl]-4,4 ''-dicarboxylic acid, HATZ = 3-amino-1,2,4-triazole) and Zn-2(ATZ)(2)(MeTPDC) (BUT-306, H2MeTPDC = 5 '-methyl-[1,1 ':3 ',1 ''-terphenyl]-4,4 ''-dicarboxylic acid). The pore aperture of BUT-306 (similar to 1.6 angstrom) is smaller than that of BUT-305 due to the presence of extra gate-like methyl groups in the 1D channels of the former. With a narrow and hydrophobic pore aperture, BUT-306 exhibits high hydrophobicity and hydrolytic stability and adsorbs C3H4 but excludes C3H6 in a wide temperature range. The C3H6 and C3H4 adsorption capacities of BUT-306 at 298 K and similar to 1 bar were 2.4 and 29.6 cm(3) g(-1), respectively. Dynamic column breakthrough experiments confirmed the high capability of BUT-306 to remove C3H4 from the equimolar binary gas mixture of C3H4 and C3H6. The C3H4/C3H6 separation performance of BUT-306 was largely retained even when the binary C3H4/C3H6 gas for breakthrough experiments was pre-saturated with water vapor. In addition, the single-crystal structure of C3H4-loaded BUT-306 was determined, which revealed that the adsorbed C3H4 molecules were located in the center of channel cavities and interacted with the MOF by multiple weak C delta-MIDLINE HORIZONTAL ELLIPSISC delta+ dipole-dipole interactions and C-HMIDLINE HORIZONTAL ELLIPSIS interactions. This work demonstrates the high potential of an ultramicroporous, hydrophobic, and hydrolytically stable MOF in the removal of C3H4 from the C3H4/C3H6 gas mixture by size exclusion adsorption. The structure and gas adsorption studies shed light on the design and synthesis of new adsorbents for the separation of light hydrocarbons.

Automated summary

In this study, two ultramicroporous Zn-MOFs were introduced for propyne/propylene separation. The results showed that one of the MOFs exhibited high hydrophobicity and hydrolytic stability, and could adsorb propyne while excluding propylene.