Application of DSC to Determine the Heat of Dissociation and Phase Boundary of Methane Hydrates in the Presence of Inhibitors and Promoters
Date Issued
2016
Date
2016
Author(s)
Chu, Che-Kang
Abstract
A high pressure differential scanning calorimeter (HP uDSC) was used to determine the dissociation temperature of methane hydrate in the presence of ionic liquid 1–alkyl–3–methylimidazolium chloride under a constant pressure ranging from 5 to 35 MPa. A homologous series of 1–alkyl–3–methylimidazolium chloride with different alkyl chain lengths, including 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride and 1-decyl-3-methylimidazolium chloride, were chosen to examine the chain length effect on the dissociation temperature for methane hydrates. All these ionic liquids have inhibition effect on methane hydrate formation. Moreover, the shorter the alkyl chain length is, the stronger the inhibition effect is. That is, the inhibition effect of these ionic liquids on the methane hydrate formation is in the order of 1-ethyl-3-methylimidazolium chloride > 1-hexyl-3-methylimidazolium chloride > 1-decyl-3-methylimidazolium chloride. The three-phase vapor-liquid-hydrate equilibrium condition of methane hydrate in the presence of 1–alkyl–3–methylimidazolium chloride was successfully described by a predictive thermodynamic model. The Peng-Robinson-Stryjek-Vera equation of state incorporated with COSMO-SAC activity coefficient model and the first order modified Huron-Vidal mixing rule were applied to evaluate the fugacity of vapor and liquid phase. An explicit pressure dependence of the Langmuir adsorption constant in the modified van der Waals and Platteeuw model was applied to determine the fugacity of hydrate phase. The absolute average relative deviation in predicted dissociation temperature from the predictive thermodynamic model was 0.54%. A special operation procedure of the HP uDSC was proposed to determine the dissociation enthalpy and temperature of hydrates in the presence of promoters: tetrahydrofuran, 2,5-dihydrofuran, cyclopentanol and 1,3-dioxane. Among these four promoters, tetrahydrofuran has the strongest promotion capability and cyclopentanol is the weakest one. The dissociation enthalpy of methane hydrates in the presence of tetrahydrofuran is 163.8 kJ/mol promoter and independent of pressures and concentrations of promoter, consistent with the results of molecular dynamic simulations. Note that the dissociation enthalpy of the HP uDSC is consistently smaller than that calculated by using Clausius-Clapeyron equation.
Subjects
gas hydrates
differential scanning calorimetry
thermodynamic promoter
ionic liquids
dissociation enthalpy
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-105-F99524049-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):0b611605c172e266ae4bcc88bc1498f4