Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications



Abstract 170.

Binary Ethanol-Methane Clathrate Hydrate Formation in the System CH4-C2H5OH-H2O: Experimental Data and Thermodynamic Modelling

Anderson, R., Chapoy, A., Haghighi, H., and Tohidi, B.
Journal of Physical Chemistry C, 113, 12602-12607 (2009).

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−HO2 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 XEtOH > 0.056, aqueous ethanol forms binary EtOH−CH4 clathrate hydrates stable over a wide PT range. In the HEtOH−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 HEtOH−CH4+L+G region being bounded by a univariant HEtOH−CH4+L+I+G quadruple point locus line at temperatures much higher than the typical HCH4+I+G boundary (or HCH4+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.

Reprints of this article are available in Adobe Portable Document Format (.pdf). You may request a reprint by submitting an email to the webmaster with the abstract number in the subject line. To read pdf files, you will require Adobe Acrobat Reader, which can be downloaded for free at the Acrobat Reader Download Page

Submit requests to: ross.anderson@pet.hw.ac.uk