Study fuels hope for compressed natural gas cars

Researchers have identified new materials that may be able to store compressed natural gas (CNG) at low pressure and at room temperature, paving the way for tanks that are lighter and fit cars better.

PTI| Last Updated: Dec 19, 2014, 19:17 PM IST

Houston: Researchers have identified new materials that may be able to store compressed natural gas (CNG) at low pressure and at room temperature, paving the way for tanks that are lighter and fit cars better.

Researchers at Rice University focused on cage-like synthetic macromolecules called metal organic frameworks (MOFs).

MOFs are nanoscale compounds of metal ions or clusters known as secondary building units (SBUs) and organic binding ligands, or linkers.

These linkers hold the SBUs together in a spongy network that can capture and store methane molecules in a tank under pressure. As the pressure is relieved, the network releases the methane for use.

Since there are tens of thousands of possible MOFs, it's a daunting task to synthesise them for testing.

A team led by Rice bioengineer Michael Deem used a custom algorithm to not only quickly design new MOF configurations able to store compressed natural gas - methane - with a high "deliverable capacity," but ones that can be reliably synthesised from commercial precursor molecules.

The advantages to using MOF as a storage medium are many and start with increased capacity over the heavy, high-pressure cylinders in current use.

MOFs show potential for applications like drug delivery, sensing, purification and catalysis, but methane storage for transportation is high on the US Department of Energy (DOE)'s wish list, Deem said.

"MOFs are being commercialised for methane storage in vehicles now," he said.

The Rice study found 48 MOFs that beat the best currently available, a compound called MOF-5, by as much as 8 per cent.

The programme adhered to standard DOE conditions that an ideal MOF would store methane at 65 bar (atmospheric pressure at sea level is one bar) and release it at 5.8 bar, all at 24.9 degrees Celsius.

That pressure is significantly less than standard CNG tanks, and the temperature is far higher than liquid natural gas tanks that must be cooled to minus 162.2 degrees Celsius.

Lower pressures mean tanks can be lighter and made to fit cars better, Deem said.

Deem and his colleagues at Rice, the Lawrence Berkeley National Laboratory and the University of California-Berkeley reported their results in the American Chemical Society's Journal of Physical Chemistry C.