Can we make Carbon Capturing Enzymes?
By Francis Williams
“Enzymes are important in every living thing. Without them, life as we know it could not, and would not, exist”
-American Chemical Society
Figure 1: The enzyme carbonic anhydrase (CA)
The active site of CAs can catalyse CO2 and water into bicarbonate ions up to a million times per second. This has prompted research, which has shown that CA can accelerate the capture of CO2, by serving as a catalyst, in existing alkaline capture solvents, which currently have a slow rate of CO2 absorption. The faster absorption kinetics would allow for smaller processing equipment (with a reduced initial and operating cost) and has the potential to lower replacement costs of the alkaline capture solvent. However, implementing natural CA enzymes into industrial carbon capture processes has been limited due to the CA enzyme denaturing under exposure to the alkaline conditions of the capture solvents, and the elevated temperature inside industrial facilities.
A biological solution to an industrial problem.
Climate change is a direct consequence of increasing greenhouse gases. This increase can be attributed to human activities, relating to power generation, transportation, and industrial processes. 72% of greenhouse gas emissions are accounted for by CO2 production, in these processes. 2021 is seen as a year of a record-high increase in CO2 levels, surpassing those at any time in the past 2 million years. This all culminates in an expectation that global warming of 2oC is likely to be exceeded during the 21st century. However, by developing new technology it is still realistic to stabilise climate change by lowering CO2 emissions in the next 20-30 years.
Enzymes are biological catalysts that accelerate the rate of chemical reactions in the bodies of living organisms. In the human body alone, there are approximately 1300 different enzymes, each one highly specialised and accounting for a different chemical process. Many researchers are interested in using specific enzymes to capture and sequester CO2 from point sources (such as flue gas emissions) to achieve the goal of reduced carbon emissions. Carbonic anhydrase (CA) is such an enzyme capable of being a suitable carbon-capturing entity. Its function is to catalyse the formation of bicarbonates (containing HCO3- ions) from CO2, which it is attributed to accomplish at a rate approaching the limits of diffusion, one of the fastest of any enzyme.
Figure 2: The proposed equipment for CO2 capture.
Figure 2 shows a theoretical method for the removal of CO2 from flue gases. The flue gases are piped into the (blue) absorber column where CO2 is absorbed into the alkaline solvent, and catalysed into the bicarbonate ions by CA. The flue gases are released into the atmosphere, while the alkaline solvent and CA are transferred to the (red) desorption column. At elevated temperatures, the bicarbonate ions are reconverted into CO2, which is removed, and the alkaline solid is regenerated. The pure CO2 steam can be compressed and stored in depositories or used in industrial processes. The regenerated solvent is returned to the blue column.
Do you think this is viable? Let us know your thoughts below…
