A highly hydrophobic metal-organic framework Zn(BDC)(TED)0.5 for adsorption and separation of CH3OH/H2O and CO 2/CH4: An integrated experimental and simulation study

Abstract

The adsorption and separation of CH3OH/H2O and CO2/CH4 in Zn(BDC)(TED)0.5 (BDC = benzenedicarboxylate, TED = triethylenediamine) are investigated by integrating experiment and simulation. Zn(BDC)(TED)0.5 is a highly hydrophobic metal-organic framework (MOF) with interlacing channels. The simulated isotherms of CH3OH and H2O are in fairly good agreement with experimental results. While H2O adsorption in Zn(BDC)(TED) 0.5 is vanishingly small, CH3OH shows a much stronger adsorption. The selectivity of CH3OH over H2O is approximately 20 at low pressures and the selectivity decreases with increasing pressure. From the density distributions and structural analysis, it is found that CH3OH interacts strongly with the metal oxides, particularly at low pressures. The isotherms of CO2 and CH4 from simulation match well with experimental data. As a nonpolar molecule, CO 2 exhibits different favorable sites from polar CH3OH. At low pressures, CO2 is located preferentially near the BDC linkers. As pressure increases, CO2 is proximal to the metal oxides and TED linkers. The selectivity of CO2 over CH4 increases as a function of pressure, with a magnitude similar to that in most neutral MOFs. H2O has a negligible effect on the selectivity of CO 2/CH4. In addition, the simulated adsorption isotherm of n-hexane is in accord with experiment. This work provides a quantitative understanding at the molecular level for adsorption behavior in Zn(BDC)(TED)0.5 and suggests that Zn(BDC)(TED)0.5 is a good candidate for the separation of alcohol/water mixtures and alcohol-based liquid fuels. © 2010 American Chemical Society.