The separation of C2H2 from CO2 in mixtures containing these gases is an important application to produce high-purity C2H2. Experimental and theoretical C2H2 and CO2 adsorption studies were performed in MPM-1-Cl and MPM-1-TIFSIX, two robust molecular porous materials (MPMs) with the empirical formula [Cu2(adenine)4Cl2]Cl2 and [Cu2(adenine)4(TiF6)2], respectively. Both MPMs consist of a hydrogen-bonding network that is self-assembled by dinuclear copper–adenine paddlewheel complexes. The difference between the two structures is simply the axial ligand. Experimental measurements revealed that MPM-1-Cl displays higher low-pressure uptake, isosteric heat of adsorption (Qst), and selectivity for C2H2 than CO2, whereas the opposite is true for MPM-1-TIFSIX. Dynamic breakthrough experiments and modeling studies confirmed that MPM-1-Cl is more selective toward C2H2, while MPM-1-TIFSIX is more selective toward CO2. Molecular simulations revealed that both MPMs display a greater preference for C2H2 within their large channels. However, MPM-1-TIFSIX contains a small accessible channel in the structure that is not present in MPM-1-Cl; this channel represents the primary binding site in the material. Calculation of the classical MPM–adsorbate interaction energies and diffusion barriers about the primary binding site in MPM-1-TIFSIX revealed that this site is more favorable for CO2 than C2H2, thus explaining why the selectivity in this MPM is inverted relative to MPM-1-Cl.

Tuning the selectivity between C2H2 and CO2 in molecular porous materials

ACS Spring Meeting 2021

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