|From cob to tank. Click to enlarge. Credit: Nicolle Rager Fuller, NSF|
Using corncob waste as a starting material, researchers at the University of Missouri-Columbia (MU) and Midwest Research Institute (MRI) in Kansas City have created carbon briquettes with complex nanopores capable of storing natural gas at an unprecedented density of 180 times their own volume and at one-seventh the pressure of conventional natural gas tanks. Used in a natural gas tank, the new storage technology could increase the viability of methane-fueled vehicles.
The walls of the nanoporous carbon adsorb methane molecules as a high-density fluid. The strong attractive force in the narrow pores lowers the energy of the molecules so that they can be packed much more closely than in the absence of the carbon. Such a tank is called an adsorbed natural gas (ANG) tank.
|The test truck and prototype tank. Click to enlarge.|
The carbon briquettes can store 180 times their own volume of natural gas, or 118 g of methane per liter of carbon, at 500 pounds per square inch (psi)—the pressure found in natural gas pipelines. The best previous carbon could only store 142 times its own volume at 500 psi. The target set by the US Department of Energy is 180 times the storage a material’s own volume. The MU-MRI carbon reaches this target for the first time.
The technology has been incorporated into a test bed installed on a pickup truck used regularly by the Kansas City Office of Environmental Quality.
We are very excited about this breakthrough because it may lead to a flat and compact tank that would fit under the floor of a passenger car, similar to current gasoline tanks. Such a technology would make natural gas a widely attractive alternative fuel for everyone.—Peter Pfeifer, MU and project leader
Standard natural gas storage systems use high-pressure natural gas that has been compressed to 3,600 psi and bulky cylindrical tanks that can take up the space of an entire car trunk. The low pressure of 500 psi is central for crafting the tank into any desired shape, so ultimately, fuel storage tanks could be thin-walled, slim, rectangular structures affixed to the underside of the car, not taking up room in the vehicle.
Our project is the first time a carbon storage material has been made from corncobs, an abundantly available waste product in the Midwest. The carbon briquettes are made from the cobs that remain after the kernels have been harvested. The state of Missouri alone could supply the raw material for more than 10 million cars per year. It would be a unique opportunity to bring corn to the market for alternative fuels—corn kernels for ethanol production, and corncob for natural gas tanks.—Peter Pfeifer
The test pickup truck, part of a fleet of more than 200 natural gas vehicles operated by Kansas City, has been in use since mid-October and the researchers are monitoring the technology’s performance: pressure and temperature of the tank during charging/discharging; charging/discharging rates under various fueling/driving conditions; and longevity of the carbon briquettes.
In addition to efforts to commercialize the technology, the researchers are now focusing on the next generation briquette, one that will store more natural gas and cost less to produce. Pfeifer believes this next generation of briquette might even hold promise for storing hydrogen.
The MU-MRI collaborative is part of a larger cooperative effort called the Alliance for Collaborative Research in Alternative Fuel Technology (ALL-CRAFT), which includes as partners Lincoln University; DBHORNE, LLC; Renewable Alternatives, LLC; the Missouri Biotechnology Association; the Clean Vehicle Education Foundation; the Missouri Department of Natural Resources; and the City of Columbia, Mo. ALL-CRAFT also worked in cooperation with the Kansas City Regional Clean Cities Coalition (KCRCCC).
This project was funded by a $600,000 grant from the NSF’s program Partnerships for Innovation. Additional funds totaling more than $400,000 came from MU, MRI, the US Department of Energy and the US Department of Education.