US-based researchers have unveiled a cunning plan for future motoring in which carbon-capture technology would be used aboard vehicles. The stored carbon would then be recovered at filling stations and - rather than being "sequestered" underground or wherever - get reprocessed back into synthetic fuel.
"We wanted to create a practical and sustainable energy strategy for automobiles," said Andrei Fedorov, associate professor at the Georgia Institute of Technology (GIT).
Under the GIT plans, cars of the future would fill their tanks in everyday style with hydrocarbon fuel - ordinary petroleum-based stuff or synthetic, it doesn't matter. Rather than being burned right away as at present, the car would initially run it through a "CO2/H2 Active Membrane Piston (CHAMP) reactor" which would convert the juice into carbon dioxide and hydrogen.
The carbon dioxide would be stored as liquid in an onboard tank, and the hydrogen would be used to drive the vehicle. Ordinary car engines can run on hydrogen with only minor modifications; or the hydrogen could be used more efficiently in a fuel-cell and electric drive. In either case, there would be no significant emissions.
Later on, the liquefied CO2 could be taken out of the vehicle - perhaps at the pump when refuelling. It could then be "sequestrated", perhaps winding up stored/dumped underground, in the sea or somewhere - a plan often proposed for dealing with power-station emissions. Sequestration isn't always seen as genuinely achievable, however.
It doesn't matter, because GIT has more than CHAMP to offer. Fedorov and his colleagues propose that the vast amounts of stored CO2 produced by motor transport could be combined with water at a reprocessing plant to produce synthetic hydrocarbon fuel, which would then be used again.
Naturally, the reprocessing plant would use large amounts of energy, which would have to come from somewhere. In essence, the GIT CHAMP scheme isn't unlike plans for hydrogen-fuelled vehicles; the fuel is basically just a means of storing energy from another source. The advantage of CHAMP is that storing and transporting liquid CO2 is simpler and safer than handling hydrogen. CO2 doesn't want to be a liquid at normal temperatures, but it can be kept in that form at relatively low pressures - say 30 bar on a warm day. And if it leaks, nothing very bad will happen; whereas if hydrogen escapes into a confined space the building might blow up.
The disadvantages would be that of burdening every vehicle with a CHAMP processor and CO2 tank, and the need to move the stuff back to the reprocessing plants.
Common to both strategies - hydrogen or synthifuel/CHAMP - would be the need to provide huge amounts of power at production facilities. There would be little point in adopting a clean vehicle technology if it were ultimately powered by a vastly increased use of fossil fuel in generating or reprocessing stations.
Unfortunately, renewable means such as hydro, solar, or wind power are usually only thought able to supply a varying proportion of current electricity usage - even ardent advocates of these technologies don't normally suggest that they could also propel the human race's transport.
The only feasible option for hydrogen is usually seen as being a serious increase in nuclear power, and on the face of it this would also seem true of GIT's CHAMP vision. Just like hydrogen-car promoters unwilling to face anti-nuclear opposition, however, Fedorov is keen to suggest that other means might be found.
"The greatest remaining challenge... will be developing a method for making a synthetic liquid fuel from just CO2 and water using renewable energy sources."
No shit. In fact, one might say that challenge is much more significant than building the CHAMP, though it does sound like a clever bit of kit. One might well never bother with carbon-capture if sequestration were the only plan on offer: but Fedorov's miracle petrol factories could make the global economy treat liquid CO2 the way it currently treats crude oil.
The GIT CHAMP research was funded by NASA and the US Defense department. It is published in the journal Energy Conversion and Management. ®