Selective adsorption of ethane over ethylene on M(bdc)(ted)0.5 (M = Co, Cu, Ni, Zn) metal-organic frameworks (MOFs).

The application of three-dimensional (3D) pillared-layer metal-organic frameworks (MOFs) M(bdc)(ted) 0.5 (M = Co, Cu, Ni, Zn) in the adsorptive separation of ethane/ethylene (C 2 H 6 /C 2 H 4) mixtures was studied. The effect of the type of metals in M(bdc)(ted) 0.5 on the framework structure regarding the moisture stability and adsorption performance was investigated. M(bdc)(ted) 0.5 MOFs show excellent porous structures with high surface areas of up to 1905 m2/g (M = Ni), as well as being stable under humid conditions (assessed by the dynamic water vapour adsorption tests with maximum 20% relative humidity at 25 °C). M(bdc)(ted) 0.5 exhibits the preferential adsorption of C 2 H 6 over C 2 H 4 under all conditions (i.e. 25–50 °C and 0–10 bar), although a reversal in adsorption uptake (i.e. C 2 H 4 adsorption uptake exceeds the amount adsorbed of C 2 H 6) occurs at pressures of >6 bar. The adsorption capacities of C 2 H 6 and C 2 H 4 on M(bdc)(ted) 0.5 adsorbents are up to 8.63 and 8.79 mmol/g at 25 °C and 10 bar, respectively. The calculated C 2 H 6 /C 2 H 4 selectivity for an equimolar mixture is insensitive to the metal ions in M(bdc)(ted) 0.5 , which varies between 1.4 and 1.9. Dynamic breakthrough experiments show that C 2 H 6 /C 2 H 4 mixture can be separated in a fixed bed packed with Ni(bdc)(ted) 0.5. The good adsorption capacity and selectivity, as well as the low isosteric heat of adsorption, make M(bdc)(ted) 0.5 MOFs, especially Ni(bdc)(ted) 0.5 , good candidates to be further developed for the effective separation of C 2 H 6 /C 2 H 4 mixtures in the presence of water vapour with a relative humidity lower than 30%. Image 1 • Pillared-layer M(bdc)(ted) 0.5 MOFs show selective adsorption of C 2 H 6. • Adsorption capacity of M(bdc)(ted) 0.5 for C 2 H 6 is up to 8.63 mmol/g at 25 °C and 10 bar. • Adsorption capacity, rather than selectivity, of M(bdc)(ted) 0.5 depends on metal ions. • M(bdc)(ted) 0.5 MOFs are moisture-stable at 20% relative humidity at 25 °C. [ABSTRACT FROM AUTHOR]