Gas Hydrate Formation

Both thermodynamic and kinetic factors affect the inhibition of hydrate deposits. 

Hydrate formation can be prevented by drying a gas to such an extent that no condensate can be formed. This method is the preferable one, but inhibition of hydrate formation from the liquid phase can be achieved. 

Lowering the Hydrate-Formation Temperature with Additives 

The hydrate-formation temperamre can be reduced by the addition of antifreeze agents such as methanol, glycols [1430], or brines. The depression of the freezing point is given by 

Brines have inherent corrosive properties and therefore are not suitable. Ethylene glycol is preferred because of its low cost and low solubility in hydrocarbons. 

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Englezos, P., Kalogerakis, N., Dholababhai, P.D. and Bishnoi, P.R., 1987b. Kinetics of gas hydrate formation from mixtures of methane and ethane. Chemical Engineering Science, 42(11), 2659-2666. 

A mechanistic model for the kinetics of gas hydrate formation was proposed by Englezos et al. (1987). The model contains one adjustable parameter for each gas hydrate forming substance. The parameters for methane and ethane were determined from experimental data in a semi-batch agitated gas-liquid vessel. During a typical experiment in such a vessel one monitors the rate of methane or ethane gas consumption, the temperature and the pressure. Gas hydrate formation is a crystallization process but the fact that it occurs from a gas-liquid system under pressure makes it difficult to measure and monitor in situ the particle size and particle size distribution as well as the concentration of the methane or ethane in the water phase. 

Uddin, M., Coombe, D., Law, D., Gunter W,D. 2008a. Numerical studies of gas hydrate formation and decomposition in a geological reservoir. ASME, Journal of Energy Resources Technology, 130, paper 032501. 

Kinetic inhibitors exhibit unusual effects on hydrate formation with implications to processing (Lee and Englezos, 2006). Gas hydrate formation experiments were conducted... 

Le Parlouer, P. Dalmazzone, C. Herzhaft, B. Rousseau, L. Mathonat, C. (2004). Characterisation of gas hydrates formation using a new high pressure MICRO-DSC. J. Thermal Analysis Calorimetry, 78, 165-172. 

Li, X.-S. Englezos, P. (2006). Prediction of Gas Hydrate Formation Conditions in the Presence of Methanol, Glycerol, Ethylene glycol and Triethylene glycol with the SAFT Equation of State. IndEng Chem Res., 45 (6), 2231-2137. 

Linga, P. Kumar, R. Englezos P. (2007a). Gas Hydrate formation from Hydrogen/carbon dioxide and nitrogen/carbon dioxide gas mixtures, accepted for publication in Chem. Eng. Sci., April 26, 2007... 

Mori, T. Mori, Y.H. (1989a). Characterization of gas hydrate formation in direct-contact cool storage process. Int. J. Refrigeration, 12 (5), 259-265. 

Temes, M.P. (1984). Characterization of refrigerant - 12 gas hydrate formation for heat pump cool storage applications. ASME energy sources technology conference,... 

Zhong, Y. Rogers, R.E. (2000). Surfactant effects on gas hydrate formation. 

Microscopic time-resolved measurements of the hydrate phase during gas hydrate formation, decomposition, and inhibition began only in the mid-1990s. These techniques include in situ synchrotron x-ray diffraction (Koh et al., 1996 Klapproth et al., 2003 Uchida et al., 2003), neutron diffraction (Henning et al., 2000 Koh et al., 2000 Halpern et al., 2001 Staykova et al., 2003), Raman spectroscopy (Subramanian and Sloan, 2002 Komai et al., 2004), and NMR spectroscopy (Moudrakovski et al., 2001 Kini et al., 2004 Gupta et al., 2007). 

Ternes, M.P., Results on the Characterization of Gas Hydrate Formation in a Direct Contact Heat Pump Cool Storage System, DOE/Oak Ridge National Laboratory, July (1985). 

The thermodynamic and structural processes that occur when water molecules are in the vicinity of hydrophobic entities (water fearing, insoluble in water) are referred to collectively as hydrophobic hydration (Tanford, 1973 Privalov and Gill, 1988 Blokzijl andEngberts, 1993 Chau and Mancera, 1999). Hydrophobic hydration is important in gas hydrate formation, which usually starts with hydrophobic gas molecules (e.g., methane) being introduced into liquid water. 

Long, J.P., Gas Hydrate Formation Mechanism and Kinetic Inhibition, Ph.D. Thesis, Colorado School of Mines, Golden, CO (1994). 

Nerheim, A.R., Investigation of Gas Hydrate Formation Kinetics by Laser Light Scattering, D. Ing. Thesis, Norwegian Institute of Technology, Trondheim, Norway (1993). 

Figure 8.2 Dog Lake gas hydrate formation curves with methanol in free water phase. (From Todd, J.L., et al., Reliabilty Engineering—Gas Freezing and Hydrates, Texaco Company Hydrate Handbook (1996). With permission.)...

Brewer P. G., Orr F. M., Jr., Friederich G., Kvenvolden K. A., and Orange D. L. (1998) Gas hydrate formation in the deep sea in situ experiments with controlled release of methane, natural gas, and carbon dioxide. Energy and Fuels 12, 183-188. 

Some interesting simulations have been used to investigate crystallization and deposition processes, in order to obtain a fundamental understanding of how these processes can be inhibited. The inhibition of formation of waxes (mixtures of normal alkanes that form lamellar structures) was examined.302 Gas hydrate formation has been investigated, and it was demonstrated that inhibition of methane hydrate by a octomer of polyvinylpyrrolidone was able to be simulated,302 and simulations were used to assist in developing a new class of inhibitors of gas-hydrate formation.303... 

IMPROVING OUR UNDERSTANDING OF GAS HYDRATE FORMATION PROCESSES THE IMPORTANCE OF MULTI-TECHNIQUE APPROACHES... 

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