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Thermodynamic and kinetic influences of NaCl on HFC-125a hydrates and their significance in gas hydrate-based desalination

Author(s)
Choi, WonjungLee, YohanMok, JunghoonLee, SeungminLee, Ju DongSeo, Yongwon
Issued Date
2019-02
DOI
10.1016/j.cej.2018.10.032
URI
https://scholarworks.unist.ac.kr/handle/201301/25266
Fulltext
https://www.sciencedirect.com/science/article/pii/S1385894718319739?via%3Dihub
Citation
CHEMICAL ENGINEERING JOURNAL, v.358, pp.598 - 605
Abstract
In this study, HFC-125a was selected as a hydrate-forming guest for gas hydrate-based desalination. The thermodynamic and kinetic effects of NaCl on HFC-125a hydrates were investigated with a primary focus on phase equilibria, gas uptake, dissociation enthalpy, and dissociation behavior. The equilibrium curve of HFC-125a hydrate shifted to higher pressure regions at any given temperature depending on the concentration of NaCl. The presence of NaCl also reduced the gas uptake and conversion to hydrates, because of the enrichment of NaCl in the solution during gas-hydrate formation. Even though NaCl did not affect the dissociation enthalpy of the HFC-125a hydrate, the thermograms obtained using a high-pressure micro-differential scanning calorimeter (HP μ-DSC) demonstrated that HFC-125a + NaCl hydrates started to dissociate at lower temperatures due to NaCl in unconverted solutions. Rietveld refinement of powder X-ray diffraction (PXRD) patterns indicated that the HFC-125a hydrate (sII) was transformed into Ih as it dissociated. The dissociation of HFC-125a + NaCl hydrates was retarded and completely ended at higher temperatures compared to the pure HFC-125a hydrate by the sodium chloride dihydrate (NaCl⋅2H2O). Overall, these results could facilitate a better understanding of HFC-125a hydrates in the presence of NaCl; further, they might also be useful in the design and operation of hydrate-based desalination plants using HFC-125a.
Publisher
ELSEVIER SCIENCE SA
ISSN
1385-8947
Keyword (Author)
DesalinationDissociationGas hydrateGas uptakeHFC-125aNaCl
Keyword
CARBON-DIOXIDEMETHANE HYDRATEPHASE-EQUILIBRIADISSOCIATION ENTHALPIESPOTENTIAL APPLICATIONCO2 CAPTURELIQUID CO2REPLACEMENTWATERRECOVERY

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