The bioeconomy at work: methane storage tanks for cars made from corn cobs

The bio-based economy has yet another innovation on its conto that may soon make it possible to manufacture cars entirely from plant-based materials (earlier post). Researchers at the University of Missouri-Columbia (MU) and Midwest Research Institute (MRI) are testing a methane storage technology made from an abundant biomass waste stream, namely corn cobs. The innovation allows methane to be stored at an unprecedented density of 180 times its own volume and at one-seventh the pressure of conventional natural gas tanks. For this reason, the technology may revolutionize the capacity of methane to power vehicles. And the good thing is: methane itself can be obtained from biogas, the cleanest and most efficient of all automotive biofuels.

Current natural gas vehicles are equipped with bulky, high-pressure tanks that take up premium cargo space, such as the trunk of a car. This new technology, however, enables natural gas to be stored in a smaller, low-pressure tank that can be shaped into a rectangular form and mounted under the floor of a car.

What makes this possible is an MU discovery that fractal pore spaces (spaces created by the repetition of similar patterns at different levels of magnitude) are remarkably efficient at storing methane. The scientists found a way to "bake" corn cobs into carbon briquettes that contain fractal pore spaces and then use the briquettes to store natural gas in a low-pressure tank (see picture, click to enlarge).

• Corn cob is an abundant, low-cost, renewable raw material, allowing for production of ANG tanks from domestic sources. The state of Missouri alone could supply the raw material for ANG tanks of 10 million cars per year. Corn could thus serve the alternative fuel economy in two distinct ways - corn kernels for bioethanol production, and corncob for natural-gas tanks.
• The MU-MRI low-pressure natural gas tank uses carbon briquettes made from corncobs to store natural gas. 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 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 best previous carbon could only store 142 times its own volume at 500 psi pressure. The target set by the U.S. Department of Energy is 180 times the storage a material's own volume. The MU-MRI carbon reaches this target for the first time.
• A conventional high-pressure natural gas tank operates at 3600 pounds per square inch (psi), whereas this low-pressure tank operates at 500 psi. This enables flexibility in tank design because high-pressure tanks require bulky, cylindrical walls, whereas the low-pressure tank can use thinner walls in a variety of shapes. The pressure of 500 psi equals the pressure in natural gas pipelines, which eliminates costly compression of natural gas from 500 psi to 3600 psi in CNG tanks.
• The technology being tested in this tank would enable car manufacturers to design long, slim, low-pressure tanks to replace the bulky high-pressure tanks in current natural gas vehicles. This would enable them to place the tank underneath the body of the car, whereas the high-pressure tanks are usually placed in a car's trunk, reducing vehicle cargo space.

MU and MRI researchers are now testing a prototype of this tank in a owned and operated by the Kansas City Office of Environmental Quality. They hope this will lead to the design of low-pressure tanks that solve the cargo space problem posed by high-pressure tanks:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: corn :: waste :: nanotechnology :: natural gas :: methane :: biogas :: fuel tank :: bioeconomy ::


The test pickup has been on the road since mid-October. Researchers are monitoring the technology's performance by collecting data to evaluate the mileage range per fill-up; pressure and temperature of the tank during charging/discharging; charging/discharging rates under various fueling/driving conditions; and longevity of the carbon briquettes.

In the U.S. Kansas City has been a leader in natural-gas-powered vehicles, ranging from utility trucks to shuttles at the Kansas City Airport. The city operates more than 200 natural-gas vehicles under the supervision of Central Fleet Manager Sam Swearngin, who has been instrumental in forging this venture between Kansas City and the MU-MRI team.

In the EU, however, biogas instead of natural gas is already being used as an alternative car fuel, with major companies feeding the plant-based gas into the natural gas grid (earlier post). Some estimate that Europe can produce enough biogas to replace all imported Russian natural gas by 2020 (earlier post).

The MU-MRI methane storage project was funded by a $600,000 grant from the National Science Foundation's program Partnerships for Innovation, which has the goal of stimulating the transformation of knowledge created by universities into innovations that create new wealth, build strong local, regional and national economies and improve the national well-being. Additional funds totaling more than $400,000 came from MU, MRI, the U.S. Department of Energy and the U.S. Department of Education.

A secondary goal of the Partnership for Innovation is to meet the broad workforce needs of the national innovation enterprise. The collaborative effort between MU and MRI has afforded a number of university students the opportunity to receive hands-on training for a career in research and development. As a result of the exchange, MRI recently hired an MU graduate and a Lincoln University graduate associated with the project team. 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).