Chemists at the University of California, Berkeley have discovered a way to store methane that could increase the adoption of natural gas-powered vehicles (NGVs) that don’t need the high pressures or cold temperatures of today’s compressed or liquefied NGVs, according to Berkeley News.
One issue with CNG vehicles is that unless manufacturers can find a way to pack more methane into a tank at lower pressures and temperatures, they won’t reach an ideal driving range and will still cause a hassle at the pump, according to the report.
Now, scientists at the university have created a porous and flexible material they call a metal-organic framework (MOF) for storing methane that addresses these drawbacks.
“The flexible MOF collapses when the methane is extracted to run the engine, but expands when the methane is pumped in at only moderate pressure, within the range produced by a home compressor,” according to the report.
The flexible MOF can be packed with methane at 35 to 65 times atmospheric pressure (500-900 psi), whereas CNG vehicles compress natural gas into an empty tank under 250 atmospheres (3,600 psi).
Newer NGVs need a material that binds the methane and packs it more densely into the fuel tank to provide more mileage, said Jeffrey Long, the professor of chemistry who led the project.
One of the major problems has been finding a material that absorbs the methane at a relatively low pressure, such as 35 atmospheres, but gives it all up at a pressure where the engine can operate, between 5 and 6 atmospheres. MOFs, which have a lot of internal surface area to adsorb gases and store them at high density, are one of the most promising materials for adsorbed natural gas (ANG) storage.
Another advantage of flexible MOFs is that they do not heat up as much as other methane absorbers, so there is less cooling of the fuel required.
Long and his colleagues at the National Institute of Standards and Technology and in Europe have published their findings online in advance of publication in the scientific journal, Nature. They are now also working on flexible MOFs to store hydrogen. To read more about their research, click here.