Designing a new aluminium muconate metal–organic framework (MIL-53-muc) as a methanol adsorbent for sub-zero temperature heat transformation applications†
Employing methanol as an adsorbate can enable adsorption-driven heat pumps and chillers to operate at/or achieve temperatures below 0 °C, provided an appropriate pairing adsorbent is made available. By applying the principle of reticular chemistry, an isoreticular twofold expansion of aluminium fumarate was designed and synthesized using trans,trans-muconate as a linker to a new aluminium metal–organic framework (MOF) termed MIL-53-muc. MIL-53-muc is isostructural to the prototypical aluminium terephthalate (Al-MIL-53-BDC) and is therefore built from chains of trans corner-sharing AlO4(OH)2 octahedra connected by muconate linkers to a microporous network with lozenge-shaped one-dimensional pores. Featuring a high BET specific surface area of 1750 m2 g−1, a type V (S-shaped) stepwise methanol adsorption isotherm in a 0.05–0.15 relative pressure range, a high methanol uptake capacity of about 0.5 g g−1 and methanol stability of over 50 assessed ad/desorption cycles, MIL-53-muc is revealed as a promising adsorbent applicable for adsorption-based heat transformation applications. The performance evaluation indicates that high coefficient of performance COPH values above 1.5 could be reached for an evaporator operating at a temperature as low as −5 °C under heat pump conditions, while very low temperatures down to −10 °C could be achieved for refrigeration/ice making with COPC values of up to 0.73 under cooling conditions. This makes MIL-53-muc/methanol outperform most other working pairs for adsorption-based cooling and heating applications under sub-zero temperature conditions. Furthermore, MIL-53-muc is hydrothermally stable and presents a favorable water sorption profile making this material also suitable for autonomous indoor humidity control applications.