Second in a three-part series.
Just before diplomats
met in Montreal last December to discuss their countries’ carbon emissions
under the Kyoto Protocol (the international agreement between more than 150
countries to cut back on greenhouse gases by 2012), researchers announced that
they had created metal-based sponges that have “exceptionally high capacity”
for storing carbon dioxide. This nanotechnology is one of many new solutions
in the search to find a quick fix for storing human-emitted carbon-based gases
that could have a warming effect on the planet when released to the atmosphere.
Omar Yaghi and his co-workers recently
created a honeycombed structure made of metal and organic molecules, with pores
large enough to hold carbon dioxide. Image courtesy of University of Michigan,
Ann Arbor.
The metal sponge heralded last year came from researchers at the University
of Michigan in Ann Arbor and is one of many “MOFs,” or metal-organic
framework compounds. The dense honeycomb structures of metal and organic molecules
trap carbon dioxide in their pore spaces and have the potential to hold nine
times as much carbon dioxide as an empty canister under similar pressure and
temperature conditions, their inventors say.
The research, published in the Journal of the American Chemical Society
on Dec. 1, is the product of “breakthrough concepts” research. None
of the research, which is funded by the Department of Energy and other federal
agencies, is “ready for prime time,” says Julio Friedmann, a geologist
who heads the carbon sequestration program at Lawrence Livermore National Laboratory
in California. Researchers have proposed other gee-whiz methods that are cost-limited,
such as genetically engineering marine creatures to incorporate more carbon
into their shells, or genetically modifying methane-producing bacteria to grab
more carbon dioxide as their “food.”
The amount of carbon dioxide these technologies could hold is miniscule, however,
compared to the many millions of tons of the gas that eventually may have to
be stored, Friedmann says, and many are too expensive. Other geological techniques,
including creating carbonate brine by, for example, injecting carbon dioxide
emissions from power plants into slurries of limestone and water, remain unproven.
A fast geological solution, Friedmann says, is to pump carbon dioxide into reservoirs
in rock formations that are capped by a natural impervious layer. “The
more we study geological sequestration, the better it looks,” he says,
despite ongoing political and technical challenges.
So far, oil companies have been the primary practitioners of such geologic sequestration,
using enhanced recovery techniques — pumping gas into the ground to increase
oil output — in land-based experiments from Canada to Algeria (see Geotimes,
February and March 2005). “The final goal is to get more oil, but in
the process, [injection] will leave behind a significant amount” of carbon
dioxide and “the reservoir will trap it,” says Vello Kuuskraa, an
engineer and president of Advanced Resources International, in Arlington, Va.
A second potential injection setting is coal seams, to displace and capture
the methane that’s trapped in coal, he says, something with which his company
has had some experimental success in the San Juan Basin in Colorado, injecting
4 billion cubic feet of carbon dioxide over six years.
Currently, companies working with enhanced-recovery techniques use existing
wells and other infrastructure, which makes the practice more cost-effective
than most new technologies. They can buy carbon dioxide captured from natural
sources as well as from industrial sites, which “creates a market for carbon
dioxide emissions,” Kuuskraa says. Such initial transactions will help
in assessing the value of future carbon credits as “we don’t have
a market price for it” yet — which in some ways, is a stumbling point
for international and national efforts to regulate the greenhouse gas.
Although some test cases are in the works, regulations for sequestration applications
are also lacking worldwide. These rules eventually should include how long the
gas must remain underground or how to manage and monitor these sites over the
long term, says Elizabeth Wilson, a policy researcher at the University of Minnesota
in St. Paul. Without such rules, the applications are not yet ready for providing
carbon credits under Kyoto or other regulations.
Under the U.S. Environmental Protection Agency, a regulatory structure that
could serve useful for carbon sequestration already exists for storing waste
water in underground reservoirs, but Wilson says that the rules are not ready
for application. So far, Florida has served as a case study, where trouble with
fluid migration and escape has stymied Florida’s regulatory agencies, Wilson
says. To create valuable carbon credits, agencies will have to be able to handle
those issues.
Friedmann and others say that all proposed carbon sequestration technologies
should be considered within the whole portfolio of measures to decrease carbon
dioxide levels in the atmosphere. Even though some may seem fanciful or unlikely,
Friedmann says of the advanced technologies, “that doesn’t mean there
isn’t value in them.”
In the end, methods that are cost-effective and widely applicable will most
likely rise to the top. Along with other experts, Wilson says that “at
the end of the day, no one is going to do anything that doesn’t make economic
sense.”
Naomi Lubick
The first story in this three-part
series addressed some of the science that complicates carbon credits. Read next
month’s Geotimes for the third installation, on policy challenges
for carbon credits.
Links:
"Burying carbon dioxide, Part I," Geotimes,
February 2005
"Burying carbon dioxide, Part II," Geotimes,
March 2005
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