Investigation of deep eutectic solvents as a reaction medium for metal chloride based chemical heat pumps

Gözde, Ezgi
Metal chlorides can react with gas phase ammonia and form complex compounds. Due to reversibility and high heat of reaction, these ionic reactions are attractive for the application of chemical heat pumps which can provide the ability to capture the rejected low-grade heat and to reuse it at increased temperature levels. The pressure and temperature interval of ammonia sorption into CaCl₂is suitable for heat upgrade of waste heat streams, geothermal energy and solar energy sources.However, heat and mass transfer limitation of the gas-solid phase is one of the major challenges. In order to overcome this challenge, in this thesis, the potential usage of the deep eutectic solvents(DES) as a reaction medium for the CaCl₂-NH3pair was studied. As DES, in different molar ratios,ZnCl2-ureaand ChCl-urea pairs were synthesized. From stability tests, it was found that ZnCl₂-ureaDES which has a maximum 30 days of a lifetime is significantly less stable than ChCl-urea DES which has a lifetime more than 6 months under ambient conditions. The solubilities of CaCl₂were determined as 3.7wt% and 5.3wt% for the ZnCl2-ureamolar ratio of 3.5:10 and 2.5:10 respectively. Ammonia sorption experiments revealed that higher amount of ammonia is absorbed into CaCl₂-ZnCl₂-ureasuspensionthan pure solid CaCl₂. Ammonia sorption takes place with a significant rate and extend in CaCl₂-ChCl-urea DES but much slower than the one observed for CaCl₂/ZnCl₂-urea samples.The desorption pressure-temperature equilibrium relationship exhibit more complex trend than the linear Clausius-Clapeyron equation because of the complex nature of sorption into CaCl₂/ZnCl₂-Urea mixture.
Citation Formats
E. Gözde, “Investigation of deep eutectic solvents as a reaction medium for metal chloride based chemical heat pumps,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Chemical Engineering., Middle East Technical University, 2019.