(508a) Deep Eutectic Solvents Mixed with Fluorinated Refrigerants for Absorption Refrigeration: A Molecular Simulation Study
AIChE Annual Meeting
Tuesday, November 17, 2020 - 8:00am to 8:15am
Molecular simulations were performed to evaluate mixtures of fluorinated refrigerants with deep eutectic solvents (DESs), for potential use in single-effect absorption refrigeration cycles that use low quality waste heat sources at temperatures of ~80 Â°C. The refrigerants considered were the hydrofluorocarbon R245fa and the hydrofluoroolefins R1234zeE and HFO1336mzzE, whereas the DESs evaluated were 1:2 molar mixtures of choline chloride with either ethylene glycol (ethaline) or levulinic acid (levuline) as hydrogen bond donors (HBDs). Assuming the same cycle operating conditions, the waste heat cycle efficiency was computed for all working fluid mixtures from molecular simulation results of the mixture densities and the Henryâs law constants of the refrigerants in the DESs, coupled with phase equilibrium calculations and the enthalpies of the pure refrigerants. The largest efficiency was obtained for the mixture R245fa-ethaline (6.82), followed by R245fa-levuline (4.64) and HFO1336mzzE-levuline (2.10). These modest efficiency values could be further increased by tailoring the cycle operating conditions to each particular refrigerant-DES system, as well as optimizing our choice of working fluid mixtures, neither of which we attempted in this study. Strong interactions were observed between the chlorine anions and some of the hydrogen atoms of the refrigerants, but in general the cation-refrigerant and HBD-refrigerant interactions are weaker compared to the refrigerant-refrigerant interactions. Refrigerant molecules have the largest diffusivities and make the cations, anions and HBD to move faster compared to systems of DESs without refrigerant; in general species in refrigerant-ethaline mixtures have larger diffusivities compared to refrigerant-levuline mixtures. We also computed waste heat cycle efficiencies for the same R134a-DES mixtures studied in our previous work (Abedin et al., Langmuir 2017, 33, 11611), finding significant differences between the efficiencies determined from molecular simulation data and those determined before using the COSMO-RS approach using two standard parameterizations.