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Posted: 09 October 2006

Scientists to capture CO2 from exhausts before it reaches the atmosphere

Climate change is increasingly considered as one of the greatest threats to our planet. Evidence suggests that most global warming is anthropogenic (man-made) and if global temperatures continue to warm-up at current levels, by the end of the century many coastal areas and small islands will be under threat by rising sea levels. Extreme weather events may also happen more regularly as global climate change continues.

NASA Goddard Space Flight Center Image by Reto Stöckli

To focus the international response to climate change and reverse the global upward trend in greenhouse gas emissions (widely believed to contribute to global warming), the United Nations Framework Convention on Climate Change introduced the Kyoto Protocol in December 1997. This protocol sets legally binding greenhouse gas emission targets for each developed country signed to the agreement.

Under the protocol, Ireland has agreed to reduce its emissions to 13% above 1990 levels by 2008 to 2012. However, according to the EPA, in 2004 Irish emission levels were 23% above 1990 levels - a considerable way from meeting agreed targets.

With development in Ireland continuing at breakneck speed, Ireland will burn fossil fuels on an increasingly massive scale. Transportation, homes, businesses and industries all need to burn fossil fuels for power and heat. Burning fossil fuels releases carbon dioxide (CO2) the most significant greenhouse gas into the atmosphere contributing to global climate change. But all this could be about to change.

Scientists in the Centre for Synthesis and Chemical Biology and the UCD Conway Institute are developing a new technology capable of capturing CO2 from exhaust streams before it reaches the atmosphere. Professor Don MacElroy and Dr Damian Mooney from the UCD School of Chemical and Bioprocess Engineering are collaborating with Dr Matthias Tacke and his research group from the UCD School of Chemistry and Chemical Biology to develop an inorganic membrane technology that will separate and capture carbon dioxide after combustion.

"No membranes have been developed to separate carbon dioxide at temperatures of greater than 400°C from combustion or other high temperature process gases," explains Professor MacElroy. "But our preliminary results have shown that ultra-thin nanoporous membranes can separate carbon dioxide from nitrogen at 600°C."

"The separation technique works on the basis of molecular size. The difficulty with separating carbon dioxide from nitrogen lies in the dimensions of the atoms within the molecules," continues Professor MacElroy. "There is about a 10% difference in size between them, so it was a challenge for us to develop a membrane that is selective for carbon dioxide over nitrogen."

Dr Laurence Cuffe developed a composite membrane on Vycor® glass as part of his postdoctoral research at UCD. He chemically modified the Vycor® glass by coating it with an inorganic nanomembrane to reduce its pore size.

"The modification to the surface of the Vycor® results in the formation of nanoporous plugs which are permeable to carbon dioxide but form a barrier to nitrogen," continues Professor MacElroy. “We are now investigating more versatile processes for modifying the glass.”

After CO2 is captured, it may be stored long-term or recycled. Oceans and forests act as natural carbon dioxide reservoirs but underground caverns, old gas wells and saline aquifers are also used. Statoil, for example, has undertaken a commercial project to capture CO2 from the Sleipner gas field in the Norwegian North Sea and store it in a saline aquifer more than 1,000 meters beneath the sea bed.

"Carbon dioxide could be recycled by returning it to an artificial carbon cycle. It is a valuable commodity. Under the appropriate processing conditions there is a chance of converting it into low molecular weight chemical commodities or recycling it into methanol. Recycling captured carbon dioxide might well become part of the global quest for renewable energy sources" Professor MacElroy concludes.

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