Binary Ethanol−Methane Clathrate Hydrate Formation in the System CH4-C2H5OH-H2O: Phase Equilibria and Compositional Analyses

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• 作者：Ross Anderson ; Antonin Chapoy ; Hooman Haghighi ; Bahman Tohidi
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：July 16, 2009
• 年：2009
• 卷：113
• 期：28
• 页码：12602-12607
• 全文大小：134K
• 年卷期：v.113,no.28(July 16, 2009)
• ISSN：1932-7455

文摘

Ethanol (EtOH) is commonly used as a gas hydrate inhibitor in hydrocarbon production operations. However, a number of stable and metastable hydrate phases have been reported for the binary EtOH−H₂O system at temperatures of <223 K, including a structure II type clathrate hydrate stable below 198 K. Here, we present experimental DTA and PVT phase equilibrium data for the binary ethanol−water and ternary ethanol−methane−water systems, respectively. Binary DTA data confirm the appearance of metastable EtOH hydrates above the established structure II clathrate peritectic transition. In the ternary system with methane, at X_EtOH > 0.056, aqueous ethanol forms binary EtOH−CH₄ clathrate hydrates stable over a wide PT range. In the H_EtOH−CH4+L+G region, this results in significantly less hydrate inhibition than would be expected from ice melting point depression. In the ice region, ethanol enclathration actually increases hydrate stability relative to the methane−water system; the H_EtOH−CH4+L+G region being bounded by a univariant H_EtOH−CH4+L+I+G quadruple point locus line at temperatures much higher than the typical H_CH4+I+G boundary (or H_CH4+I+L+G quadruple point univariant locus in the presence of an aqueous hydrate inhibitor). Compositional analyses of the clathrate phase yields the formula 2.30CH₄·0.66EtOH·17H₂O at 246.7 K and 3.68 MPa, which is consistent with structure II. Independent powder X-ray diffraction and Raman spectroscopic studies presented in an accompanying article in this journal issue confirm ethanol−methane clathrates to be of structure II type.