Application of Gas Hydrates as an Alternative Dehydration Method

Gas hydrates were first discovered by Sir HumphryDavy in 1810 [1]. Clathratehydrates are crystalline compounds, formed by the smaller molecules (guest), entrapped within the cavities of a rigid “cage-like” lattice of water molecules (host) at low temperature (typically less than 300K) and high pressure (typically more than 0.6MPa) conditions [2]. The small molecules of gasses, such as methane (CH4), carbon dioxide (CO2), hydrogen Sulfide (H2S), ethane (C2H6), propane (C3H8), iso-butane (i-C4H10) and n-butane (n-C4H10) act as a former or guest molecule in clathrate hydrates. The formersare physically trapped inside a three-dimensional lattice structure formed by the hydrogen bonding of water molecules Arctic permafrost and subsea are two major environments that naturally confine gas hydrates [3,4]. Particularlylarge clathrate hydrate deposits occur along Siberia ArcticShelf and Nankai trough, off Japanese east coast [5,6]. Recently (2012), recovery efforts have been made to extract natural gas from such gas hydrate deposits in Alaska’s North Slope [7]. The structure of gas hydrate is composed of about 85mol% of water. Based on gas molecules and the formation conditions, gas hydrate crystalline structures can be classifiedinto three categories: a body-centered cubic structure I (sI),a diamond cubic structure II (sII), and a hexagonal structure H (sH). Each crystalline structure contains geometrically different water cages with different size cavities. The cavities normallyadapt only one guest molecule ranging in diameter from 0.40-0.90nm. Methane hydrates typically accommodate in structure I [8,9].