I think this approach would be too energy intensive, but it does kill two birds with one stone and it is definitely worth more research.
"Could CO2 be the green fuel powering tomorrow's cars?
Imagine a green fuel that could power our cars, keep the wheels of industry turning, and wean us off our addiction to oil - a fuel called CO2
Imagine a green fuel that could power our cars, keep the wheels of industry turning, and wean us off our addiction to oil. A fuel that could stop climate change in its tracks, and send carbon levels plunging to pre-industrial levels. A fuel that allows business as usual to carry on as before ? emissions and all. Because that fuel is? CO2.
It sounds like advertising copy from fantasy island. But now a combination of applied solar power and lateral thinking could just turn this into reality.
It's actually not that far-fetched a scenario. Trees and algae have been turning CO2 into fuel since the dawn of time, unlocking the chemical energy within this molecule to power metabolic processes. Now, some scientists believe we can follow.
With a little ingenuity, it is already possible to transform CO2 into anything from petrol to natural gas. And thanks to centuries of industrialisation, we appear to have a plentiful supply of the stuff floating around us in the atmosphere. So if we can just find an efficient means of extracting CO2 from air and converting it into a useful fuel, it should be possible both to power our future and scrub our atmosphere clean.
But there is, of course, a catch. Carbon dioxide is a very stable molecule. So any conversion processes will take a lot of energy. The question is, can these processes be refined to ensure that less energy is used to create this fuel than is provided by it?
The key challenge is to convert CO2 into carbon monoxide (CO), by removing one of its oxygen atoms. Once you have CO, the process of creating hydrocarbon fuels such as petrol is easy. It's achieved through a reaction known as the Fischer-Tropsch process ? most commonly used to synthesise liquid fuel from coal. First developed in the 1920s, this has a somewhat notorious history. It was used by Nazi Germany to turn some of its vast coal reserves into fuel for Panzer tanks, and later by apartheid South Africa to sidestep sanctions. Now concerns over peak oil have seen a sharp revival of interest.
But getting from CO2 to CO requires either a lot of energy, or billions of years worth of evolutionary chemical nous. The US Government's Sandia National Laboratories, in Albuquerque, New Mexico, have opted for the former approach, developing a system that takes its energy source from concentrated solar power [see box, 'Sunlight into Petrol' right]. As Green Futures goes to press, researchers from Bristol and Bath Universities in the UK have also announced plans for solar-powered CO2-to-fuel conversion.
Unlike many large-scale initiatives to tackle global warming, converting CO2 into fuel for domestic use can appeal to the most self-interested government ? even a 'climate sceptic' one.
And as interest in carbon conversion hots up, so others are exploring new technological avenues. At the University of Oxford, Dermot O'Hare has been investigating chemical means of achieving the same results ? which could potentially be used in places where solar energy isn't so abundant. Using highly reactive molecules called Lewis bases, O'Hare has shown that CO2 can be encouraged to react and break down at much lower temperatures to produce the fuel methanol.
Over in Asia, Fumio Inagaki is hoping to let nature take its course. Based at the Japan Agency for Marine-Earth Science and Technology, he has been exploring the talent of seabed bacteria to turn CO2 into methane, or natural gas. Although this process is generally pretty slow, taking billions of years, Inagaki is now exploring ways to accelerate it to a mere century.
But converting CO2 into fuel is only half the problem. We also have to develop ways to suck the stuff out of the air in the first place. And this is no easy task. Although there have been some successes in capturing carbon from industrial flues, extracting it from the ambient air at concentrations of less than 400 parts per million is a lot tougher. No one doubts the technical feasibility ? but the holy grail is doing so in a way which could prove remotely cost effective.
At the University of Calgary, David Keith believed he'd found a solution in the form of a process which extracts carbon dioxide from air via 'spray towers'. As air is drawn into the towers, it is sprayed with a fine mist of an alkali solution. This bonds to the CO2 to form droplets of sodium carbonate, which is collected at the bottom of the towers and passed onto subsequent stages that separate and collect the CO2. The technology was promising enough to launch a spin-off company, Carbon Engineering Ltd, although this has now abandoned the spray model in favour of packed towers, akin to water cooling towers. With several million dollars of venture capital funding, the company is also working on another air-capture system, dubbed the Air-Contractor, which it believes could capture around 100,000 tonnes of CO2 per year on a commercially feasible basis.
Meanwhile. California-based Carbon Sciences Inc. are developing a biocatalytic process to convert CO2 emitted from a power plant into fuel.
And Klaus Lackner, a Columbia University physicist and long-time advocate of 'air capture', has developed a prototype capable of collecting tens of kilograms of CO2 per day.
It's all impressive stuff, but it's at a small scale and an early stage. As Stuart Haszeldine, carbon capture expert at Edinburgh University, points out, the UK alone spews out 200 million tonnes of CO2 each year. So, the key question is whether any of these technologies can scale up to the kinds of volumes required.
And scale is certainly needed. According to Sandia, if all of America's 100 million-strong vehicle fleet were to run on fuel derived from CO2 under its 'Sunlight to Petrol' programme [see box right], then the solar power plants alone would cover 2,250 square miles. And this doesn't include the vast number of air-scrubbing towers required to capture the CO2 in the first place.
Given the heroic scale of the engineering requirements, and the fact that as a concept air capture is still relatively unheard of, it's hardly surprising if its proponents are facing what Keith calls a credibility gap. Then there's the fear that if we do eventually manage to start actively removing CO2 from the atmosphere, it will create a culture of complacency, effectively giving industry a licence to pollute. It could make today's debates over the morality of carbon offsets look mild-mannered by comparison.
Haszeldine acknowledges that it's still very early days for this kind of research, but adds: if this is successful, it has more potential than any other means proposed to actively reduce CO2 levels and ultimately reverse global warming. Given that potential, he says, can we really afford to ignore it?
o Duncan Graham-Rowe is a former staff writer for the New Scientist and a regular contributor to The Economist and The Guardian."
