Wed, Dec 10, 2008 - Page 9 News List

Scientists seek to turn waste glycerol biofuels into high-value gas

Making hydrogen using natural gas or even water electrolysis is expensive and unsustainable. Finding a new source makes sense, and scientists are on the case

By Michael Pollitt  /  THE GUARDIAN , LONDON

Did you know that gas and diesel in EU states now contain a minimum of 2.5 percent biofuels? Thanks to the Renewable Transport Fuels Obligation, this requirement will rise to 5 percent by 2010. While motorists won’t notice any difference when filling up, this important change is expected to prevent the emission of millions of tonnes of carbon dioxide over the next few years.

But might biofuels be helping to solve one major environmental issue simply to create another? For Valerie Dupont, of Leeds University in northern England, the increasing use of biofuels means a sticky problem. For every tonne of biodiesel made from vegetable oil, 100kg of thick, viscous glycerol is produced as a byproduct. The annual 6.8 billion liters of biodiesel production in the EU yields around 680,000 tonnes of crude glycerol. Although some of the sweet-tasting liquid can be purified for pharmaceutical or food applications, the rest ends up as waste.

Dupont, who has a PhD in fuel and energy, now hopes to turn this growing lake of low-grade sludge into high-value hydrogen gas. Produced from vegetable oils and methanol, biodiesel is a renewable alternative to ordinary diesel. But what green-minded motorists don’t realize is that glycerol is creating a big problem.

“Glycerol is thick, viscous, full of oxygen and you cannot burn it easily,” Dupont says. “Nobody knows what to do with all this glycerol from biodiesel. There is no real outlet.”

Most waste glycerol is currently disposed of by incineration, a less than ideal arrangement. Burning the glycerol in a power station might seem an option but, Dupont says, poor energy conversion and inefficient combustion produces pollutants.

Glycerol — C3H5(OH)3 — is a molecule of three carbon atoms with eight hydrogen and three oxygen atoms. Unlock the hydrogen, and you’d have a rich source of fuel from renewable resources. At the moment, the world’s hydrogen mostly comes from the steam from the reforming of natural gas — methane (CH4) — which produces hydrogen and carbon monoxide.

“Since glycerol has a high hydrogen content compared to methane, we reckon that converting crude glycerol to hydrogen is a valid alternative route,” Dupont says.

Based on earlier research work, Dupont and her co-investigators are developing a viable process to release pure hydrogen and carbon dioxide (CO2) from glycerol.

The 18-month £270,000 (US$410,000) project involves mixing glycerol with steam over a catalyst at a controlled temperature and pressure. A reusable CO2 adsorbent ensures the carbon monoxide (CO) produced reacts fully with the steam, making even more hydrogen and CO2.

“Our process is a clean, renewable alternative to conventional methods. It produces something with high value from a low grade by-product,” Dupont says. “In addition, it’s a near carbon-neutral process, since the CO2 generated is not derived from the use of fossil fuels.”

The project is using a prototype chemical reactor which will quickly answer many practical questions including the effects of impurities. Dupont is also taking a green engineering approach, aiming for a high-purity hydrogen product that would be ideal for fuel cells.

“If everything goes well, we can look at scaling up and maybe even scaling down,” Dupont says. “If we had a reactor which could extract the hydrogen from glycerol it would be very interesting for distributed power generation.”

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