Gas hydrate desalination uses natural gas or carbon dioxide as a meta-resource. These materials are typically transported in high-energy states, either substantially pressurized in a pipeline or chilled and liquefied in a cargo ship.
When the high-energy natural gas or carbon dioxide is introduced to seawater, it reacts to form a solid crystal of gas hydrate. The gas hydrate rejects salt and most other impurities if the growth conditions are properly controlled. The gas hydrate is separated from the seawater and then dissociated by subjecting it to a mild increase in temperature and/or decrease in pressure. Dissociating the hydrate releases fresh water and returns the natural gas or carbon dioxide.
MDS has two techniques for separating the gas hydrate from the residual seawater. The first is to allow the gas hydrate crystals to separate by gravity. Gas hydrate grown from natural gas is buoyant like normal ice – it floats to the top where it can be depressurized to release fresh water. The second method is to grow the hydrate on a specially perforated plate. On one side of the plate hydrate is grown, on the other side hydrate decomposes. Hydrate is constantly grown, forced through the plate, and then dissociated to make fresh water.
MDS’ desalination process was featured in the October 2004 edition of Discover magazine.