Ind. Eng. Chem. Res. 2010, 49, 8865–8869
8865
Gas Hydrate Phase Equilibrium in the Presence of Ethylene Glycol or Methanol Aqueous Solution Amir H. Mohammadi* and Dominique Richon MINES ParisTech, CEP/TEPsCentre Energe´tique et Proce´de´s, 35 Rue Saint Honore´, 77305 Fontainebleau, France
In this communication, experimental hydrate dissociation data for the ethane, carbon dioxide, or hydrogen sulfide + ethylene glycol + water system are first reported at 0.1, 0.2, 0.35, and 0.5 mass fractions of ethylene glycol in aqueous solution. The experimental data were generated using an isochoric pressure-search method. The experimental hydrate dissociation data are compared with the corresponding literature data and the experimental dissociation data for ethane, carbon dioxide, or hydrogen sulfide simple hydrates in the presence of pure water reported in the literature. A discussion is made on the reliability of the few sets of experimental hydrate dissociation data reported in the literature for the ethane, carbon dioxide, or hydrogen sulfide + ethylene glycol + water system. We finally report experimental hydrate dissociation data for the methane + methanol + water system at 0.55 and 0.65 mass fractions of methanol in aqueous solution. The experimental hydrate dissociation data are compared with the corresponding literature data and the experimental dissociation data for methane hydrates in the presence of pure water reported in the literature. It is shown that the few sets of experimental hydrate dissociation data reported in the literature for the methane + methanol + water system at high concentrations of methanol in aqueous solution may not be very reliable. A discussion is made on the inhibition effect of methanol at its very high concentration in aqueous solution. 1. Introduction Gas hydrates or clathrate hydrates are crystalline water-based solids that physically resemble ice, in which small molecules (typically gases) are trapped inside cages of hydrogen-bonded water molecules. The formation of gas hydrates is a serious problem in hydrocarbon production, transportation, and processing, because it can give rise to equipment blockage, operational problems, and safety concerns.1 To avoid the formation of gas hydrates, organic inhibitors such as methanol or ethylene glycol are normally used.1 To develop and validate thermodynamic models for predicting hydrate stability zones of hydrocarbon fluids, reliable gas hydrate phase equilibrium data for the main components of these fluids in the presence/absence of inhibitor aqueous solutions are required.1 Although sufficient experimental data have been reported for gas hydrates of these components in the presence of methanol and ethylene glycol aqueous solutions,1 information for gas hydrates of hydrocarbon fluids main components, in the presence of methanol and ethylene glycol aqueous solutions at high concentrations, is limited.1 In this communication, experimental hydrate dissociation data for the ethane, carbon dioxide, or hydrogen sulfide + ethylene glycol + water system are first reported at 0.1, 0.2, 0.35, and 0.5 mass fractions of ethylene glycol in aqueous solution, which have been measured using an isochoric pressure-search method.2-4 Comparisons are made between our experimental dissociation data with the corresponding literature data5,6 and the experimental dissociation data for ethane, carbon dioxide, or hydrogen sulfide simple hydrates in the presence of pure water.7-12 A discussion is made on the reliability of the few sets of experimental hydrate dissociation data reported in the literature for the ethane, carbon dioxide, or hydrogen sulfide + ethylene glycol + water systems.5,6 We finally report experimental hydrate dissociation data for the methane + methanol + water * To whom correspondence should be addressed. Tel.: +(33) 1 64 69 49 70. Fax: +(33) 1 64 69 49 68. E-mail: amir-hossein.mohammadi@ ensmp.fr.
system at 0.55 and 0.65 mass fraction of methanol in aqueous solution. Comparisons are made between our experimental dissociation data with the corresponding literature data13-17 and the experimental dissociation data for methane hydrates in the presence of pure water.9,10 It is determined that the few sets of experimental hydrate dissociation data reported in the literature at high concentrations of methanol in aqueous solution may not be very reliable. The hydrate inhibition effect of methanol at its very high concentration in aqueous solution is finally discussed. 2. Experimental Section 2.1. Materials. Table 1 reports the purities and suppliers of the materials used in this work. Aqueous solutions were prepared following the gravimetric method, using an accurate analytical balance. Consequently, uncertainties on the basis of mole fraction are estimated to be
