Capturing the carbon dioxide that a coal-powered plant produces and sequestering it is not an easy task, and until now it rose the costs of the electricity produced by 80 percent. Due to researchers at Codexis, a Redwood, CA, company, genetically modified enzymes can make carbon dioxide capture much cheaper, increasing the cost of electricity by less than a third.
Something called monoethanolamine (MEA) is currently being used to capture carbon dioxide. MEA separates the CO2 from the other gases and only releases it when a certain amount of heat is applied. Codexis engineers use an enzyme called carbonic anhydrase that they had previously genetically modified. Carbonic anhydrase is present in many living things, including us, humans. It helps a solvent called methyl diethanolamine (MDEA) to bind with carbon dioxide.
Codexis uses a proprietary version of directed evolution. In its simplest form, directed evolution involves making random changes to existing genes. These mutations alter one amino acid in the enzyme at a time. The genes that work best are then selected and changed to further increase performance. Codexis’s researchers have developed a faster version of the process that involves swapping relatively large segments of the gene sequence–making multiple changes to amino acids each time. They’ve also developed computational techniques that allow them to determine what parts of the gene are most likely to lead to improvements in performance if they are modified. The changes make the process more efficient, and lead to big changes in performance in a relatively short amount of time.
One of the main hurdles was that the enzyme normally exists at 25 °C, and they’d have to use it at the high temperatures found in smokestacks. After modifying the enzyme, it first resisted up to 85°C for 30 minutes, but they don’t provide up-to-date results yet as for what temperatures the enzyme is currently capable of bearing. All we know is that it has to withstand 130 °C, the temperature at which the CO2 breaks the binds, turning into gas again, to be sequestered.