MOF - the breakthrough NGVs have been waiting for?
CNG tanks are bulky and heavy. Aside from those made of composite materials maybe, but they are still relatively expensive. LNG tanks offer higher ranges, but they too are large and virtually only suitable for buses and trucks. Plus, if you leave an LNG-powered vehicle non-driven, its fuel will eventually heat up and escape to prevent pressure rise. One idea scientists have been toying around with is adsorption – using material capable of binding natural gas on its porous surface, allowing to lower storage pressure and boost storage volume.
Experiments have been going on with various such materials, including charred corncobs, but the much anticipated breakthrough may come from the recently developed MOF – metal-organic framework. It's unique feature is that it collapses when fuel is extracted from the tank to run the engine, but then expands again as it is "refilled” with natural gas. Importantly, high pressures are no longer required in the refueling process and storage. Just to put this statement in perspective: CNG is usually stored under 200-250 atmospheres, while MOF-based ANG (adsorbed natural gas) under just 35-65 atomospheres.
Another advantage of this promising new material is that it doesn't heat up as much as other methane adsorbers, so less fuel cooling is required. Plus MOF gives fuel up at a pressure an engine can readily use it (5-6 atmospheres), without the need to use pressure regulators. Research and development on the new material was lead by professor Jeffrey Long at the National Institute of Standards and Technology and now the team of scientists hopes to progress to a testing phase before hopefully starting production of MOF for widespread use as ANG adsorbent. Let's stay tuned for more!
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