The United States possesses large reserves of natural gas, like Pennsylvania's Marcellus Shale, but the fuel powers few of the country's vehicles, due partly to storage limitations.
Penn State researchers seek to overcome that hurdle by creating a less expensive and more efficient natural gas storage system with funding from the U.S. Department of Energy.
T.C. Mike Chung, professor of materials science and engineering in the College of Earth and Mineral Sciences, received a three-year, $1.12 million grant to develop super-absorbent materials designed to store natural gas under less extreme pressures and temperatures than those required today.
The technology could lead to smaller and less-expensive onboard tanks for natural gas vehicles, and may make the fuel economical for tractor-trailers, and with further advances, cars and SUVs, Chung said.
Chung's group previously created a polyolefin polymer product called i-Petrogel that can absorb 40 times its weight in oil while not absorbing water, showing great promise for cleaning up or remediating crude oil spills. With the funding, the researchers will create a new Petrogel polymer tailored to absorb methane, the main component of natural gas used to heat homes and power vehicles.
"We are certainly very excited for the opportunity to do this research that could expand Petrogel for use in natural gas storage," he said. "We can see several advantages in using natural gas for transportation: it's abundant, less expensive and a cleaner energy source than other fossil fuels. Natural gas is also produced by renewable nature resources like biomass and agriculture byproducts."
Despite the advantages, compressed natural gas (CNG) contains about a quarter of the energy density as gasoline. It also requires high-pressure storage tanks made from expensive materials like carbon fiber. The costly, bulky tanks work for public transit buses, but not many other vehicles, Chung said.
Liquid natural gas (LNG), another storage option, offers better energy density but requires extreme low temperatures, making it an expensive option, typically reserved for shipping fuel over long distances. Chung said converting LNG to CNG for commercial use also costs up to a third of what the fuel is worth.
The researchers seek to develop a Petrogel product that doubles the energy density of CNG and that is effective at room temperatures and under low pressures. This would allow for storage in inexpensive steel tanks.
"We can do something in between CNG and LNG," Chung said. "We can design a material that immobilizes methane molecules and condenses them into a supercritical liquid, which is between a gas and liquid. Our material will then adsorb the methane and swell, storing many times its weight."
The material, which looks like a sponge, has networks of small holes that allow hydrocarbons to diffuse inside. As it absorbs oil or gas, its outside volume doesn't change, Chung said.
The researchers previously showed the material can store ethane, butane and propane, which are also components of natural gas. Energy companies remove these gases before pumping natural gas into distribution pipelines, and Petrogel could be a more cost-effective purification method.
Methane molecules are the most difficult hydrocarbon to capture and condense. The researchers will spend the first phase of the project identifying the right polymer blend to address that challenge.
Chung said finding a more cost-effective methane storage method could have broader applications for renewable energy. He said using this technology methane produced by farms may represent an economical fuel source. Currently, most farm-produced methane gas is released into the atmosphere, where it is a potent greenhouse gas.
"If we can help the farmer to store methane, I think it's going to be a very important technology," he said. "Their agricultural byproduct could have an economic value that's also good for the environment."