A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates

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Abstract

Magnesium chloride hydrates are characterized as promising energy storage materials in the builtenvironment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and dihydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure.
Original languageEnglish
Article number124312
Pages (from-to)124312-1/9
Number of pages9
JournalJournal of Chemical Physics
Volume139
Issue number12
DOIs
Publication statusPublished - 2013

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Magnesium Chloride
Hydrates
Dehydration
Discrete Fourier transforms
dehydration
hydrates
hydrolysis
Hydrolysis
magnesium chlorides
energy storage
Energy storage
Gibbs free energy
Molecular structure
Molecules
molecular structure
molecules
heat storage
Heat storage
water pressure
Steam

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@article{16c9326066624e258f2eb35363e72b00,
title = "A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates",
abstract = "Magnesium chloride hydrates are characterized as promising energy storage materials in the builtenvironment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and dihydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure.",
author = "B. Smeets and E. Iype and {Gaastra - Nedea}, S.V. and H.A. Zondag and C.C.M. Rindt",
year = "2013",
doi = "10.1063/1.4822001",
language = "English",
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pages = "124312--1/9",
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A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates. / Smeets, B.; Iype, E.; Gaastra - Nedea, S.V.; Zondag, H.A.; Rindt, C.C.M.

In: Journal of Chemical Physics, Vol. 139, No. 12, 124312, 2013, p. 124312-1/9.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - A DFT based equilibrium study on the hydrolysis and the dehydration reactions of MgCl2 hydrates

AU - Smeets, B.

AU - Iype, E.

AU - Gaastra - Nedea, S.V.

AU - Zondag, H.A.

AU - Rindt, C.C.M.

PY - 2013

Y1 - 2013

N2 - Magnesium chloride hydrates are characterized as promising energy storage materials in the builtenvironment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and dihydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure.

AB - Magnesium chloride hydrates are characterized as promising energy storage materials in the builtenvironment. During the dehydration of these materials, there are chances for the release of harmful HCl gas, which can potentially damage the material as well as the equipment. Hydrolysis reactions in magnesium chloride hydrates are subject of study for industrial applications. However, the information about the possibility of hydrolysis reaction, and its preference over dehydration in energy storage systems is still ambiguous at the operating conditions in a seasonal heat storage system. A density functional theory level study is performed to determine molecular structures, charges, and harmonic frequencies in order to identify the formation of HCl at the operating temperatures in an energy storage system. The preference of hydrolysis over dehydration is quantified by applying thermodynamic equilibrium principles by calculating Gibbs free energies of the hydrated magnesium chloride molecules. The molecular structures of the hydrates (n = 0, 1, 2, 4, and 6) of MgCl2 are investigated to understand the stability and symmetry of these molecules. The structures are found to be noncomplex with almost no meta-stable isomers, which may be related to the faster kinetics observed in the hydration of chlorides compared to sulfates. Also, the frequency spectra of these molecules are calculated, which in turn are used to calculate the changes in Gibbs free energy of dehydration and hydrolysis reactions. From these calculations, it is found that the probability for hydrolysis to occur is larger for lower hydrates. Hydrolysis occurring from the hexa-, tetra-, and dihydrate is only possible when the temperature is increased too fast to a very high value. In the case of the mono-hydrate, hydrolysis may become favorable at high water vapor pressure and at low HCl pressure.

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DO - 10.1063/1.4822001

M3 - Article

C2 - 24089772

VL - 139

SP - 124312-1/9

JO - Journal of Chemical Physics

JF - Journal of Chemical Physics

SN - 0021-9606

IS - 12

M1 - 124312

ER -