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New High-Density, Lower-Pressure Adsorbed Natural Gas Tanks from Corncobs

Nsf_graphic_final
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.

Truck2
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.

Resources:

Comments

Yosef

Does not compute: density = 180*volume ?

Is it that 118g of methane would take 180 times the tanks volume at standard temperature and pressure?

Jorge

The density of methane at 1 atm and 15°C (59°F) is about
0.68 grams per liter.
Compared with gasoline, the combustion of methane produces less CO2
It could be a very promising storage technology.

allen_xl_Z

Yosef,
A bit less. The wording is a bit unwieldly.
1,000 liter/meter3
0.717kg methane/meter3 @ STP
118g/liter
~164.5 times STP density

Polly

The pdf file in the first link shows a Honda Civic NG with both the existing CNG tank and a prototype ANG test rig in the boot.
If a production ANG flat panel tank can replace the CNG tank as described in the article, this opens up the possibility of trucks or Honda Civics with NG PHEV & V2G.

NG PHEVs would contibute to the goal of reducing gasoline consumption 20% in 10 years by combining limited NG supplies with new wind & HEP electricity capacity.

NG V2G trucks used by construction trades could provide onsite AC power from NG mains supply while recharging the battery pack for the trip home.

NG V2G trucks & cars could provide load balancing & peak power to the grid which would complement variable wind supplies.
This will help offest the additional cost of leasing PHEV battery packs.
Honda SULEVs would also provide "super ultra low emmisions" generation whereas conventional reserves are the oldest and most polluting plant.
The downside would be that V2G generation would be burning NG in the smog zone.

Lakewood90712

One GGE (Gallon of gasoline equiv.) of cng at 88 % methane is about 5.6 pounds or about 2,500 grams. can one of you engineer types convert 20 gge to a volume using the data in the article with the carbon filler at 500 psi? Also, it sounds like the fueling must be done in a liquid form. I am a 5 year driver of natural gas vehicles , not an engineer, so data from engineer / science types are welcome.

kent beuchert

Isn't this wonderful. Too bad nobody would ever dream of using natural gas to power autos. Maybe back in the 1970's this news would have meant something. Right now I consider it filler.

NBK-Boston

Lakewood,

Given the numbers you supplied, the long division comes out this way:

2,500 grams of CNG = 1 GGE
20 GGE = 2,500 x 20 = 50,000 grams of CNG per tankful.

This adsorbtion material can store 118 grams of CNG per liter of volume, given standard compression.

50,000 grams divided by 118 grams/liter = ~424 liters of volume for a storage tank.

Since there are about 3.8 liters per gallon, a tank large enough to carry 424 liters would be about 112 gallons large, in American terms.

I rather doubt that fueling must be done while the NG is liquified. LNG is not stored at pressure, while tanks using this material are specifically designed to operate under 500 lb/sq.in. of pressure. Rather, it seems that the point of this material is to allow fuel tanks to store large amounts of gaseous NG at pipeline pressures -- no need for a high-pressure compressor or an ultrastrong tank, as is currently used in CNG automotive applications.

Since a tank that employs this material would have to be five times the size of a gasoline tank supplying the same range, you'd either have to sacrifice range, payload capacity, or engine performance (to increase efficiency to allow equal miles on less fuel). A large pickup truck might be able to handle one of these with little problem. If these tanks could be integrated into the structure of the vehicle, you might be able to squeeze in more volume without taking up prime trunk or underbody space. Since this is gas under pressure, and unusually shaped tank should not affect the ability of fuel to drain into the outflow. Finally, even with reduced range between fillups, you'd still probably find plenty of customers for such a vehicle, if the other incentives were right.

The real innovation that this system allows is reducing the expense and complexity of the fueling infrastructure. CNG need not be reduced to fleet operators with access to special compressors. Gas stations who want to sell CNG to private customers no longer need very expensive and specialized compressors and high-pressure transfer hoses to fill up a car. Instead, you can tap directly into a standard 500 lb/sq.in. gas pipeline and hose it right into the car.

I wonder if this would allow a type of V2G operation of the natural gas grid. You could probably run your stove or water heater right off you car's gas tank without having to worry about stepping down the pressure. At the same time, my understanding is that the NG grid has a little more "give" to it than does the electric grid, so flattening out demand spikes with V2G is probably a lot less useful here.

Nick

Kent--

Why not? If NG-powered autos become as easy to refuel and as space-efficient as existing gasoline/diesel autos, why wouldn't they be successful? People could gas up at home most of the time. Air quality would be a big winner. Less imported oil would be used. What's not to like?

Lakewood90712

Thank's NBK , My 2001 Honda civic GX has a kevlar cylinder( made by Lincoln composites) , of 100 litre volume and it uses most of the trunk. The cng capacity @ 3600 psi 70deg.f. is 8 gge, but real world it is about 5.5 gge useable. So for long trips I usually rent a gasoline car. The fuel tank also is the most costly component of the vehicle , acording to honda. I have not purchased the available home fueling compressor , not cost effective.
I wonder if the carbon adsorbsion material requires pure methane ? Pipeline natural gas has a lot of other stuff in it. (nitroren,propane,water, etc).

cidi

Interesting, but how do you get the methane back out? Do you get all of it back out, or does a significant fraction remain adsorbed?

NBK-Boston

Perhaps you have to heat it slightly.

Rafael Seidl

Kent -

please don't extrapolate from the US to the rest of the world. There are quite a few NG cars driving around in places like Argentina, Italy, Pakistan, Germany, Iran etc. where NG is more readily available. World-wide, there is a lot more fossil energy in the ground in the form of NG than in the form of crude oil. Vehicles that can use it directly and burn it cleanly make sense, especially in fast-growing economies like India. Pollution there is very high because all they can afford is antiquated diesel engines. The country is looking to partner with Pakistan (!) on a pipeline from Iran, which has oodles of NG.

cidi -

the gas is adsorbed at 500psi (34.5 bar) and needs to be bled off via a throttle valve. Unthrottled fuel flow will drop below the required rate once it gets down to say, ~1.5 bar, i.e. you should be left with no more ~4% fuel residue in the adsorption matrix. Heating should not be necessary to desorb the fuel - this isn't hydrogen.

The important aspects here are the fact that filling stations do not need to operate a compressor unit, which poses a potential safety hazard and consumes a lot of fuel. Instead, vehicles can tap directly into the natural gas grid, conceivably even at home - provided the fuel nozzle meets safety codes. In Europe, this would pose a huge revenue shortfall for the taxman, unless NG were to become more expensive regardless of its intended use - which might be a rather good idea.

The other huge advantage of this innovation is that at these lower pressures, the tank does not need to be spherical or cylindrical, making it much easier to fit in the vehicle, perhaps even in voids in the load-bearing structure. Mind you, it would still need to be quite a bit heavier than a standard gasoline tank.

Roger Pham

112 gallons of NG for 20 gge? No sweat. If a car capable of 30mpg, it would need only 10 gallons to go 300 miles. If it is capable of 60mpg like the Prius, then it would need only 5 gallons of gasoline. So, divide 112 by 4 will get you 28 gallons. 14 gallons can be in one tank under the seat, and the other 14 gallons can be under the trunk. Run-flat tire can eliminate spare tire. To retain the same trunk space, the car will have the back raised like a station wagon. Lithium battery with improved volumetric density over NiMh will take less space, for HEV.

"How to get the methane back out?"
As the pressure decreases from 500psi, the methane will come out to maintain equilibrium, until the tank is drained to zero pressure. No need for heating.

I think that pure methane is desirable, but other materials will come in and will come out according to the equibrium constant of each chemical, just like in a chemical equilibrium reaction. Believe it or not, even carbon monoxide will get out of your hemoglobin, even though the rate of dissociation of CO out of Hgb will be much lower than the rate of association of CO to Hgb. It's all about equilibrium state. Higher molecular-weight hydrocarbons or hydrophobic materials will probably adsorb much more tightly to the carbon and eventually will decrease the capacity of your NG tank.

Roger Pham

The next question is what percentage of saturation of methane is the carbon nanomatrix at 500psi? A graph of gm/liter of methane vs pressure would be nice. If saturation is low, perhaps 1000psi will hold nearly twice the methane? Then we would have a real good storage mechanism here, 5gge requiring 14 gallons of volume. Great for HEV's having ~60mpg efficiency or higher.

Methane is sold at substantially lower cost than gasoline, yet, due to storage constrain, high efficiency will still be maintained, unless gasoline's super energy-dense allow car mfg's to abuse this and make cars with poor fuel efficiency. With Methane or H2 as fuels, no need to raise the fuel tax to improve fuel efficiency. No need for CAFE mandate, either. The only thing to do to gain fuel efficiency is to gradually phase out gasoline, and replacing it with methane and H2 as fuels. GREAT!

John

Perhaps Biogas could be used in place of NG? I'd be curious to know what percentage of NA's oil usage could be displaced through the use of biogas.

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