A novel approach for the determination of sorption equilibria and sorption enthalpy used for MOF aluminium fumarate with water
Adsorption chillers are an environmentally friendly solution for the valorisation of waste or solar heat for cooling demands. A recent application is high efficiency data centre cooling where heat from CPUs is used to drive the process providing cold for auxiliary loads. The metal organic framework aluminium fumarate with water is potentially a suitable material pair for this low temperature driven application. A targeted heat exchanger design is a prerequisite for competitiveness requiring, amongst others, a sound understanding of adsorption equilibria and adsorption enthalpy. A novel method is used for their determination based on small isothermal and isochoric state changes applied with an apparatus developed initially for volume swing frequency response measurement to samples with a binder based adsorbent coating. The adsorption enthalpy is calculated through the Clausius-Clapeyron equation from the obtained slopes of the isotherm and isobar, while the absolute uptake is determined volumetrically. The isotherm confirms the step-like form known for aluminium fumarate with a temperature dependent inflection point at p_rel ≈ 0.25, 0.28 and 0.33 for 30, 40 and 60 °C. The calculated differential enthalpy of adsorption is 2.90±0.05 MJ/kg (52.2±1.0 kJ/mol) on average which is about 10–15% higher than expected by a simple Dubinin approximation.
heat of adsorption
metal organic framework