(388e) Required Properties of Lower Critical Solution Temperature (LCST) Mixtures for Use in a Dehumidification and Cooling Cycle

Certain mixtures possess lower critical solution temperatures (LCSTs), such that they form homogeneous mixtures at temperatures below the LCST and phase separate at temperatures above the LCST. Various ionic liquids (ILs) have LCST phase behavior when mixed with water, whereby heating the mixtures above their LCSTs results in a “water-rich” and “water-scarce” phase. This enables a thermodynamic cycle wherein the water-scarce phase absorbs moisture from indoor air, providing dehumidification, and the water-rich phase desorbs moisture to the outdoor air, which both balances the mass within the cycle and cools the indoor air (through indirect evaporative cooling). However, while various IL/water mixtures possessing LCSTs have been discovered, their properties are insufficient for this cycle to be implemented in practice. Namely, the enthalpy and entropy of mixing is too small in magnitude to result in a sufficiently low chemical potential within the water-scarce phase to dehumidify building air to the low humidities required for thermal comfort. As such, the success of this new thermodynamic cycle relies heavily on the discovery of new LCST mixtures with more negative enthalpies of mixing (stronger bonds between unlike molecules) and more negative entropies of mixing (ILs that become more ordered in the presence of water). If such mixtures are discovered, the “LCST cycle” will be capable of providing dehumidification and cooling with zero global warming potential refrigerants, no water consumption, and low-grade, inexpensive heat (e.g., solar heat) as the energy source.