RESEARCHERS HIGHLIGHT POTENTIAL OF ENZYME-INDUCED CAPTURE TECHNOLOGIES

Tamar Hallerman
GHG Monitor
07/13/12

PITTSBURGH—Several researchers presenting at the National Energy Technology Laboratory’s CO2 Capture Technology Meeting here this week touted enzyme-induced carbon capture technology as a promising way to help decrease costs and increase efficiencies in post-combustion capture systems. Although enzyme-induced capture is still seen by the Department of Energy as an experimental technology, researchers conducting R&D work with the natural catalyst argued that enzymes could be the breakthrough technology needed to help usher in a cheaper and more efficient second wave of carbon capture technologies. “I think this technology can be a game changer,” said Alex Zaks, chief technology officer and vice president for research at the St. Louis-based biotech company Akermin, Inc. Glenn Kelly, president and CEO of the development company CO2 Solutions, agreed. “This technology is definitely promising. We think it’s the Holy Grail that a lot of people have been looking for related to carbon capture,” he told GHG Monitor.

Enzymes are found in nearly all living cells and are a natural catalyst for chemical processes within the body. Used in the laundry detergent and food processing industries for years, enzymes—particularly carbonic anhydrases, which rapidly catalyze the transfer of CO2 in nature—have only recently caught the attention of researchers in the advanced energy field looking to aid the carbon capture process. It was quickly discovered that enzymes like carbonic anhydrase could be used in a capture system in concert with low-energy solvents in place of other, harsher solvents like monoethanolamine (MEA). Whereas those lower-energy solvents—such as aqueous carbonate solutions with similar properties to baking soda—would typically be unable to work in capture systems on their own due to their low rates of interaction with CO2, the enzyme catalyzes those materials so that they are capable of separating CO2 at a higher rate. “The benefit of being able to use carbonate solutions is that they’re some of the cheapest, most environmentally benign, most commonly used chemicals,” Zaks said in an interview on the sidelines of the conference. Lower-energy carbonates when used with enzymes also have the benefit of needing a lower operating temperature and pH than other solvents, he added. “We still have to prove that the technology works and that it is economical, but I think there is a real potential here,” Zaks said.

ARPA-E Enzyme Project Completes Early Phase Testing

In a presentation here this week, Luan Nguyen, a technical engineering manager at the enzyme development company Codexis, Inc., said that with time, enzyme-induced capture technology could become competitive with other widely-available technologies. “It has a lot of potential for cutting down on the capital and operating costs, as well as increasing the net power production [of a carbon capture unit],” he said. Nguyen presented the initial results from his company’s first pilot-scale test of enzyme-based capture technology at the National Carbon Capture Center (NCCC) in Wilsonville, Ala., as part of a $4.7 million Advanced Research Projects Agency-Energy (ARPA-E) grant. Codexis researchers tested versions of their carbonic anhydrase enzyme on a 10 kWe unit at NCCC for a period of several months. So far, Nguyen said that Codexis has been “very happy” with initial results. “We think we have created a very active, very stable enzyme, and we feel confident that we can scale it up to the next [level] successfully,” he said. “We have demonstrated at NCCC that it works very well. After several days of continuous running, we do not see any degradation into enzyme performance at all, so we’re very happy with that.”

Codexis said in a company release that the NCCC test is the largest scale than an enzyme-based carbon capture technology has been tested on to date and that the results “show promise of enzymes to facilitate CO2 capture from coal-fired power plants.” “With ARPA-E’s funding, Codexis saw the largest improvement in an enzyme the company has ever seen: a 2 million-fold improvement in thermal stability at temperatures between 140 and 180 degrees Fahrenheit,” the company release says. “In addition, preliminary analysis indicates the enzyme-based carbon capture technology can substantially reduce parasitic energy loss compared to the current state-of-the-art MEA technology.”

Akermin Also to Test Carbonic Anhydrase Enzyme at NCCC

Meanwhile, other biotech companies are also moving to test different versions of carbonic anhydrase in the field. In another presentation here, Zaks said that Akermin will also test a different carbonic anhydrase enzyme developed by the manufacturer Novozymes at the NCCC beginning in October as part of a three-year $4.75 million DOE-sponsored project. Zaks said that carbonic anhydrases were particularly attractive to Akermin due to the enzyme’s relative stability, ability to withstand a high pH and the fact that it is not typically inhibited by impurities found in flue gas. He said the fact that the enzyme can be produced relatively cheaply and in large quantities offers an easy opportunity for future scale up if testing is successful.

But while many researchers in the field tout the technology’s potential, there are still technical barriers that must be resolved before wide deployment can occur. Zaks said that the high temperatures found in the absorber strippers of post-combustion carbon capture systems—which often operate at temperatures above 100 degrees Celsius—can inactivate the enzymes at those high temperatures. That uncertainty, he said, makes it more difficult to run a post-combustion system with enzyme catalysts in the reliable manner that is needed. Jonathan Carley, vice president for Business Development at CO2 Solutions, agreed. He said that it has been a large challenge to help engineer an enzyme that is more resistant to degradation.

Alcoa, CO2 Solutions Enzyme Project Folds Early

As several DOE-sponsored enzyme capture projects reported moving ahead, this week aluminum producer Alcoa Inc. and CO2 Solutions announced that they will be not moving ahead with an NETL-sponsored pilot project that tested Alcoa’s scrubbing process combined with CO2 Solutions’ enzymatic technology. Initial tests of that technology captured flue gas and combined it with alkaline clay to create a mineral-rich neutralized product that could be sold and used for environmental reclamation projects. The pair said that while they were able to achieve substantial knowledge from the $13.5 million, three-year project, they would not be able to meet the DOE-developed target of building up to commercial scale by 2014. The technology had been tested on the bench scale, but project partners were expected to scale up 10- to 20-fold in order to keep DOE funding, officials said.

CO2 Solutions said in a company release that even though project partners will not further scale up the project, the testing already undertaken has provided useful data and underscored the promise of enzyme-induced capture systems. “The potential to utilize enzymes to enhance CO2 capture with a carbonate solvent was confirmed and provides the opportunity to apply this technology approach to other industrial applications,” the release outlines, adding that the early tests showed “marked increases” in capture efficiency, the ability to reduce equipment sizing and demonstrated overall enzyme stability. Carley said the company sees an early opportunity for the technology in industrial processes where CO2 needs to be separated from other gas streams in order for the process to work, such as natural gas processing and ammonia production. “In that case we believe we more or less have a drop-in solution where if the industry is working with a high-energy amine solvent right now, we can swap that out and go in with a lower-energy amine solvent with our enzyme and save operating costs,” he said.

Carley said that CO2 Solutions will continue moving forward on developing enzymatic technology in the years to come. “We’re not trying to reinvent the wheel of CO2 capture here—the wheel being the use of an aqueous solvent system in a packed column. What we’re trying to do is leverage what the industry has already been working with to make it more efficient by adding a catalyst,” he said. “We’re trying to pursue a path to market that isn’t a complete reinvention—we can use commercially-available components, equipment and solvents to reduce the time to market versus a completely new process, which might be 10 years away. We figure we’re only a few years away.”