In this paper, we report an ultramicroporous Zr MOF, ZrADC, with promising potentials for C2 hydrocarbon separation. Structural simulation shows that ZrADC is composed of 8-connected Zr6 clusters and acetylene dicarboxylates (ADC) (Figure 1a), which construct a bcu topology resembling the narrow-pore structure of PCN-700 (Figure 1b). The rhombohedral slit openings of two channels lying in [010] and [100] directions are less than 3 Å, leading to minimal N2 uptake at 77 K and a corresponding BET surface area less than 100 m2 g-1. Nevertheless, the CO2 sorption isotherm at 273 K and H2O sorption isotherm at 298 K suggest a higher specific surface area (ca. 200 m2 g-1), possibly because these molecules with smaller kinetic diameters can probe larger surface area of ZrADC. The ultramicroporous nature is further validated by alcoholic vapor sorption study and C2 hydrocarbon sorption at 298K. ZrADC hardly adsorbs any isoproponal or ethanol but adsorbs methanol followed with significant desorption hysteresis (Figure 2a). When taking the much higher H2O adsorption capacity into consideration, the vapor adsorption selectivity presents a size-selective pattern that bulkier molecules will be preferentially excluded from the framework and smaller molecules can be adsorbed in a confined pore environment possibly due to their higher packing efficiency compared to their bulkier counterparts. As for C2 hydrocarbon sorption (Figure 2b), ZrADC preferentially adsorbs C2H2 over C2H4 and C2H6 with IAST selectivities of 24.6 and 4.1 for equimolar gas mixture of C2H2/C2H4 and C2H4/C2H6, respectively, suggesting excellent capability to perform C2 hydrocarbon separation.

Ultramicroporous Zr MOF for C2 hydrocarbon separation

255th National Meeting (2018)

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