Akademik Veri Yönetim Sistemi
9th Eastern Mediterranean Chemical Engineering Conference EMCC9 , Ankara, Türkiye, 31 Ağustos - 02 Eylül 2018, ss.1
Deep eutectic solvents (DES) are regarded as a new generation
of ionic solvents with their unique properties in energy efficiency, safety,
cost and environmental friendliness.[1] They are systems formed
from a eutectic mixture of Lewis or Brònsted acids and bases
which contain hydrogen bonding.[2] Due to their low vapor pressure,
these liquids do not produce volatile organic compounds (VOC), and therefore
are referred to be green solvents.
The major aim of this study is to examine deep eutectic solvents as reaction media for calcium-ammonia chemical heat pumps. Firstly, ZnCl2-urea deep eutectic solvents were prepared with different molar ZnCl2-urea ratios between 3.5:10, 3:10, and 2.5:10. FTIR analysis was carried out to verify the formation of DESs. Next, the stability and lifetime of DESs samples were determined. The most stable deep eutectic solvent was observed as the sample with 3.5:10 ZnCl2-urea ratio, with a lifetime of 30 days. The melting points of the samples were determined by DSC analysis which vary between -20°C and -40°C depending on the ZnCl2:urea ratio, while the pure ZnCl2 and urea melting points are 290°C and 133°C, respectively. In order to determine the solubility of CaCl2 in the DES, the 3.5:10 ZnCl2-urea ratio DES sample was saturated with CaCl2 and the calcium concentration in clear solution was determined by Induced Coupled Plasma (ICP) and Atomic Absorption as 5% by weight. The reaction tests were conducted in a visible pressure chamber to determine the ammonia complexation capacity of the CaCl2 containing 3.5:10 ZnCl2-urea ratio DES sample and the results were compared with those of pure DES sample, ZnCl2, and CaCl2. It was observed that the ammonia reaction with ZnCl2 takes place in DES as well as with pure CaCl2 but with the DES-CaCl2 suspension the reaction capacity is significantly higher than both. During the experiments, phase segregation was observed both in ammonia-reacted DES and DES-CaCl2 suspension. FTIR analysis was carried out to see the reacted ammonia peaks and the change in the functional groups in the upper phase and in the lower phase. No significant difference was observed in the chemical contents of both phases. In addition, thermogravimetric analyses were performed in nitrogen atmosphere to determine the adsorption enthalpy of ammonia in the DES-CaCl2 solutions, which was estimated as 17 J/g.
[1] Zhang, Q., De Oliveira Vigier, K., Royer, S. and Jérôme, F. (2012). Chemical Society Reviews, Deep eutectic solvents: syntheses, properties and applications, 7108-7146.
[2]
Smith, E., Abbott, A., & Ryder, K. (2014). Chemical Reviews, Deep Eutectic Solvents (DESs) and Their
Applications, 11060-11082.