Fuel Tanks From Corn Fields Activated carbons used for natural gas storage Lacy Hardcastle, Peter Pfeifer, Ph.D Department of Physics, University of Missouri-Columbia (above) This is the test truck used by the Midwest Research Institute and is filled with carbon produced by the University of Missouri. (right) Here is a closer look at a fuel tank, which contains carbon briquettes. This tank is identical to ours except in shape. Alternative energy sources are a high priority for our oil dependent economy and fuels such as bio diesel and hydrogen are still a long way from developing into a viable technology. However, there are already commercial vehicles running on natural gas, which is composed mainly of methane and burns much more cleanly than fossil fuels. Also, by itself, methane is a greenhouse gas, but is broken down by burning into less harmful chemicals like carbon dioxide and water. One drawback of natural gas is that unlike gasoline and diesel fuels, it is indeed a vapor, and and must currently be stored at very high pressures (usually around 3600 psi) in order to maintain a useful fuel supply. These bulky high pressure tanks take up a lot of storage space which makes them undesirable for private use. However, the technology under development by the University of Missouri and its partner institutions would allow the natural gas to be stored at a much lower pressure of 500 psi (pounds per square inch), enabling natural gas tanks to be shaped much like our current gas tanks. Another advantage of the lower pressure is that this is the pressure at which methane is transferred through pipe lines, so the cost of further compressing the gas (for higher pressure tanks) is eliminated. Another exciting aspect of this technology is that we are also doing research to enable it to store hydrogen as well, making it a versatile solution to energy storage issues. Introduction Carbon Production Facts About Natural Gas Technology The picture in the background is a microscopic image of the carbon which we produce. Note how the carbon is full of pores. This is for the natural gas storage. The outermost pores must be slightly larger than the inner ones in order to aid the penetration of natural gas to the interior of the carbon. Our goal is to produce the most ideal pore structure for the storage of natural gas and eventually hydrogen. When storing hydrogen a little bit of boron is added to the carbon in order to enhance the attractive force between the carbon and the hydrogen atoms. (top) The natural gas molecules (blue) while in a carbon nanopore. Note how they are close together and lie in an orderly fashion. This is because they have less energy with which to move because of the attractive force of the nearby carbon atoms. This is due to the strong molecular force. (bottom) The natural gas molecules in an empty tank. They fly about in a random disorderly fashion, thus taking up lots of space. (left) This is the test fixture which is used for taking preliminary uptake measurements on the carbon briquettes we produce. If a briquette performs well, it is sent to the physics department for further analysis. (right) Here are the initial and final products in the carbon making process. The ground corncobs are carbonized, ground into a fine powder, and then combined with a binding agent before they are pressed into hockey puck shaped briquettes. Here is a graph demonstrating how well our carbons perform compared to the Department of Energy’s standard. Compressed natural gas cylinders can store 208 volumes of methane gas per volume of carbon (in other words, you can fit 208 tanks worth of methane at 1 psi (pressure per square inch) into one tank at 3,000 psi) As you can see, our current best carbon has already met the DOE’s standard of performance; we are continuing to produce carbons in the hope of obtaining more and more efficient fuel tanks. The first step in producing our activated carbons is to take ground corn cobs and soak them in phosphoric acid which has been diluted by 50% with water. Then this mixture is placed in an oven where it is baked at a low temperature for several hours in order to begin the carbonization process. Then the carbon is allowed to cool and is baked a second time at a much higher temperature. During this second step, nitrogen gas is pumped into the mixture in order to keep the carbon from catching on fire. Once the carbon cools again, the phosphoric acid is rinsed out and the carbon is placed in another low temp oven, this time to dry. After drying, the carbon is ground into a very fine powder and then a binder is added so that the carbon can be compressed into a briquette, much like charcoal. The amount of binder used is very important because it affects the density of the carbon, which is a measure of how much empty space there is in the interior of the carbon. These briquettes are now ready for either testing or to be installed in the test vehicle which is in Kansas City. After the production process the carbon is first tested the chemical engineering lab (where the carbon is initially produced). Carbons which show high storage levels are then brought to the physics department for further testing. 85% of the natural gas in the us is domestic-the methane hydrate fields off of the Oregon coast alone could supply US energy needs for over 100 years. Replacing gasoline and diesel as fuels would save the United States over $300 billion dollars per year, which averages to $4,000 dollars per year for each family. On an energy equivalent basis, natural gas is cheaper than gasoline and diesel fuel. In June 2006, the cost of compressed natural gas was 94 cents cheaper than the average cost of gasoline. In light-duty, or private, applications air emissions from natural gas vehicles are lower than emissions from gasoline-powered vehicles. Carbon monoxide and nitrogen oxides, smog-producing gases, are reduced by more than 90 percent and 60 percent, respectively. Carbon dioxide, a greenhouse gas, is reduced by 30 to 40 percent.