News in Science

Dry water makes storage a gas

Chemists in the UK have developed a way to convert methane gas into a solid that looks like granulated sugar - making it easier to store.

Professor Andrew Cooper and his colleagues at the University of Liverpool have found that they can trap methane in a material made of silica and water, called 'dry water'.

They report their findings in Nature News.

Methane is seen as a viable alternative fuel, with experts estimating that deposits worldwide could contain more energy than coal, oil and all other fossil fuels combined.

"There is a huge amount of energy in these resources," says Cooper. "The question is how much of that material can we recover."

Most of that methane is locked inside ice crystals in the Arctic or at the bottom of the ocean, where the pressure is high, the temperature is low, or both, which makes extracting those deposits difficult.

A chunk of white methane hydrate from the ocean depths is ice cold in your hand, but hold a lit match to it and yellow and blue flames rise from the methane released by the melting ice.

Storage issues

Once you get the hydrate to the surface, methane can be difficult and expensive to store and transport, which is where Cooper and his colleagues' work could prove useful.

To store and transport methane it usually has to be cooled down to about -113 degrees Celsius, or pressurised around 5000 kilopascals, both of which require large amounts of energy and can be dangerous and flammable.

Storing methane in a water and silica mix that looks and feels like a powder would make it easier and possibly cheaper to store.

Cooper and his colleagues combined dry water - a mixture of water and very fine particles of silica - and methane gas with a blender bought at a local store.

The tiny silica particles increase the surface area of the water and making it easier and faster for the methane gas to become absorbed.

After about 30 minutes the white powder was fully saturated with methane. They determined that 1 litre of methane gas can be stored in about 6grams of powdered methane, roughly the same volume as most pressurised containers.

The powdered methane still needs to be held under light pressure and at a temperature of about -70 degrees Celsius.

Releasing the methane simply requires raising the temperature or decreasing the pressure, says Cooper.

Other gases

Powdered methane could just be the beginning.

Cooper says that the team can store other gases as powders, including hydrogen and carbon dioxide, although under different environmental conditions.

Storing CO2 as a powder could make carbon sequestration easier or bring a hydrogen-powered economy closer to realisation.

Easily trapping gases like CO2, methane and hydrogen could be useful, but first it has to be economical, says both Cooper and outside experts who are cautious about its expense.

"It's an interesting result," says Michael Max, who uses hydrates for desalination at Marine Desalination Systems. "But we don't see how this could be developed commercially."

Max points to Mitsui Group technology that mechanically presses methane hydrate into pea-sized pebbles, making them more stable for transportation and use.

Finding a cheaper way to gather, store and transport methane and other gasses, will eventually open up the use of these alternative fuel resources.

"The economics of this are far from obvious," says Cooper. "This is a preliminary result and we have to think hard about the costs involved."