AKERMIN PILOT TESTING ENZYME CAPTURE TECHNOLOGY AT NCCC

Tamar Hallerman
GHG Monitor
6/14/13

Akermin, Inc. is currently testing what the biotech company says is the largest and longest-running demonstration of an enzyme-based carbon capture system at the National Carbon Capture Center. Alex Zaks, chief technology officer at the St. Louis-based Akermin, said the company has been running its proprietary biocatalyst delivery system at the Department of Energy-owned testing facility in Wilsonville, Ala., continuously over the last month. Following more than 800 hours of operation capturing roughly 150 kg of CO2 per day from a coal-based flue gas stream, initial results have come back “very positive,” according to Zaks. “Our system accelerates the capture of CO2 in a bicarbonate solution. We are using an environmentally benign green bicarbonate compound that is similar to baking soda as opposed to typical commercial solvents that are based on amines. In order to accelerate that, we use enzymes with carbonic anhydrase,” he said.

The particular carbonic anhydrase-based enzyme being piloted by Akermin was developed with the manufacturer Novozymes with help from a $3.5 million DOE grant. Zaks said Akermin was particularly attracted to carbonic anhydrases because of 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. The enzyme can also be produced relatively cheaply and in large quantities, offering an easier opportunity for future scale up if testing is successful, Zaks said in a previous interview. Akermin is hoping to eventually market the technology for CO2 removal from target markets like biogas upgrading, liquified natural gas and ammonia production, as well as from coal- and gas-fired power plants.

Second-Gen Carbon Capture

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 after it was discovered that enzymes could be used in concert with low-energy solvents in place of other, harsher compounds like monoethanolamine (MEA). Whereas those lower-energy solvents 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.

Enzyme-aided carbon capture has been touted by many in the industry and at the Department of Energy as a promising second-generation technology that could significantly reduce the cost of post-combustion capture by boosting efficiencies. While much of the federally-funded research into the natural catalyst-aided system remains at the R&D and small-scale levels, it’s seen as promising because many of the carbonate-based systems that are used alongside enzymes are cheap, environmentally benign and readily available, according to researchers. Lower-energy carbonates when used with enzymes also have the benefit of needing a lower operating temperature and pH than other solvents.

Degradation-Susceptible

However, research is still in its fairly early phases, and there are still many technical hurdles that must be overcome before the technology can achieve commercialization. Most prominently, enzymes are particularly susceptible to degradation under the harsh conditions found in the absorber strippers of post-combustion carbon capture systems. That equipment runs at high temperatures, often above 100 degrees Celsius, and can inactivate the enzymes during the separation process, creating a reliability issue that has been a large hurdle to the technology’s development to date.

But according to Zaks, early testing at the NCCC has shown that Akermin’s biocatalyst delivery system has not degraded after weeks of continuous operation. He attributed the results to the enzyme’s “physical entrapment” abilities. “Akermin incorporates carbonic anhydrase into proprietary polymer-based systems via physical entrapment of the enzyme. The pore structure of the polymer is such that it allows the diffusion of the CO2 substrate and the bicarbonate product in and out of the matrix, while keeping the much larger enzyme molecules inside the polymer,” he said. “The diffusional limitations typically occurring with immobilized catalysts are minimized in this case by selecting a polymer with high permeability to CO2 and optimizing the cross-linking density of the matrix.” He said the company uses other additives to further stabilize the polymer matrix. “We don’t see any decline in activity,” Zaks added.

Company CEO Barry Blackwell said in an interview this week that the pilot’s results to date support the technology’s scale-up. “It’s really exceeding our expectations,” he said. Blackwell added that testing at the NCCC will likely stretch through the summer and that Akermin is looking for partners to help support the commercialization of the enzyme-aided technology. “We’re having a number of discussions now about near-term market opportunities around LNG ammonia processes and natural gas boilers,” he said. “We’ve been chosen for a small commercial demonstration in Europe that should be announced in the next month or so, and we’ve got some other near-term opportunities to work our way toward.”