Hydrogen Recovery

Hydrogen burns at temperatures reaching 5,500 degrees Fahrenheit and yet has the lowest molecular weight of any element. That combination makes it an extremely desirable fuel, one that the National Aeronautics and Space Administration has been making use of for several decades. However, liquid hydrogen, the fuel NASA uses, must be stored at minus 423 degrees Fahrenheit, meaning that even contact with normal temperatures can waste large amounts of fuel. Minimizing the loss of hydrogen in storage and during use is called hydrogen recovery.

Losing hydrogen to boiling

Hydrogen recovery is the process of saving or pressurizing hydrogen as it boils off during use. During its use, in rocket tests by NASA, or commercially to convert crude oil into various petroleum products, the liquid hydrogen boils off easily. Many of the processes that use liquid hydrogen - treating crude oil, heating rockets during NASA testing - lose significant amounts of that hydrogen during use as the chemical comes in contact with heated parts of the equipment. Engineers painstakingly insulate stored liquid hydrogen from all sources of heat, even air friction during flight of the space shuttle. Once in space, the craft must be insulated against the radiated heat of the sun.

Other hydrogen loss

Furthermore, because the liquid absorbs heat, it expands rapidly and must be vented to keep storage tanks from exploding. Due to its small elemental size, liquid hydrogen can also leak easily through minute pores and its extremely cold temperature makes metal brittle.

The inorganic membrane

Several efforts are underway to improve the recovery of hydrogen in pressurized liquid form after use. The Oak Ridge National Laboratory has developed an inorganic membrane to purify or enrich depleted hydrogen. The process produces 99.9 percent pure hydrogen which can be used for hydrogen fuel cells. There are also prism membranes available commercially to provide a low-cost method for hydrogen recovery during petroleum production.

Electrochemical treatment

The University of Connecticut and FuelCell Energy Inc. are involved in an effort to use an electrochemical process to convert cool gaseous hydrogen back to highly pressurized hydrogen that can be kept for future use.

Microwave technology

Efforts are also underway to develop a microwave plasma reactor that can recover all of the hydrogen lost in some processes. The microwave plasma system is a small, low-power reactor for reclaiming hydrogen lost as methane gas in some chemical processes.

References

• NASA
• Oak Ridge National Laboratories