As big engineering fixes go, "clean coal" has proved an elusive concept. Carbon capture projects remain experimental, expensive and energy intensive. But working with some of the tiniest things in nature, scientists are engineering proteins found in living things to trap carbon dioxide from coal-fired power plants.
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"Biomimetic design" is the idea of using nature as a template to create new technologies. Trees are among nature's most efficient carbon sequestration systems. They trap carbon dioxide and convert it to glucose, placing it in a form in which it stays stable for geologically significant durations.
But at the biochemical level, they are still too slow, according to Michael Drummond, a scientist at the University of North Texas who is trying to identify new "carbon capture" enzymes.
When plants spend about three and half seconds to convert carbon dioxide to glucose during photosynthesis, they are spending an inordinate amount of time. The problem is that an enzyme called RuBisCO, which catalyzes the process, is highly inefficient.
But the basic idea of using biological molecules to capture atmospheric carbon is sound enough to get grants from the U.S. Department of Energy's Advanced Research Projects Agency-Energy.
Scientists are studying faster enzymes. One that is getting much new attention is carbonic anhydrase -- a protein found in blood, among other places, that captures carbon dioxide exhaled by cells. In one second, the enzyme can change a million molecules of the gas into harmless bicarbonate, according to Jonathan Carley, the vice president of business development at CO2 Solution, a Montreal-based company that is one among the few working on biomimetic design.
If it works in the body, can it work in a smokestack?
Scientists at CO2 Solution have been trying to engineer this enzyme to capture carbon dioxide from the harsh flue gas emitted by coal plants.
The traditional way to capture the gas is using a chemical called monoethanolamine. But the technique, developed nearly 60 years ago, is expensive. It takes $60 to capture a ton of carbon dioxide, and this doesn't include separation or storage, said Carley. The process also requires nearly 30 percent of the power generated by the power plant. The inefficiencies of the system have made carbon capture a commercially shunned technology.
Taking the cue from nature may prove to be the solution. With slight genetic modifications, a stable protein that can survive at high temperatures and be dissolved in a water-based solvent could be the answer. The technology from this company is meant to be incorporated into existing smokestacks so that retrofitting would be minimal, said Carley.
"Carbonic anhydrase is nature's solution for capturing and releasing carbon dioxide," he said.
The aim, Carley said, is to reduce the cost of capturing a ton of carbon dioxide by 30 percent, such that the price of capture lines up with carbon credit pricing.
"For instance, if 10 percent of emission comes from the USA, the savings for the USA for a 30 percent decrease in capture costs will be $36.2 million per day," said Ekrem Ozdemir, a researcher at the Izmir Institute of Technology in Turkey who is attempting to create stable carbonic anhydrase complexes.
The enzyme works by hydrating the gas, according to Ozdemir. Trapping carbon dioxide is the slowest step of the process. So, when equilibrium is reached between the gas in the atmosphere and dissolved carbon dioxide such that there is no further driving force for the reaction, having a stable enzyme reach out to grab more molecules will move it forward, Ozdemir said.
Finding clues and perhaps 'keys' in tiny geometries
The enzyme, which is initially isolated from an organic source and then modified, is still in the research and development stage. But the technology should be available by 2013, Carley said.
Others, such as Connecticut-based United Technologies Research Center, are attempting to create a completely synthetic carbonic anhydrase that will survive flue emissions.
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