Selectivity control in the sorption of humid methanol over the porous metal organic framework MIL-120(Al)

Abstract

This study examines the adsorption properties of MIL-120(Al) for pure vapour-phase sorbates (water and methanol) and their mixtures, with a particular focus on the material's selectivity influenced by relative pressure. The selected MOF presents 1-D channels of ∼3.5 × 6 Ų aperture, associated with a specific surface area of 350 m²/g and a pore volume of 0.26 cm³/g. Adsorption isotherms at 25 °C, supported by Grand Canonical Monte Carlo (GCMC) simulations, revealed a high affinity of MIL-120(Al) for water and methanol at relative pressures lower than 0.2. However, methanol was identified as the preferred adsorbate at these low relative pressures in water-methanol mixtures. This selectivity, confirmed by GCMC, showed that the composition of the adsorbed phase was made of 90 % of methanol, regardless of the equilibrium vapour phase composition. In contrast, at higher relative pressures, the selectivity of MIL-120(Al) shifted markedly towards water, thereby highlighting the sensitivity of MIL-120(Al) to relative pressure in competitive adsorption scenarios. At high relative pressure, the composition of the adsorbed phase was found to be more than 95 % molar of water, even for vapours mixtures made of 50 % methanol. These findings contribute valuable insights into the design of pressure-sensitive adsorption systems for industrial applications such as sorption enhanced reaction production (SERP) technology.