Carbonic Anhydrase Immobilized on Textile Structured Packing Using Chitosan Entrapment for CO₂Capture

Innovative carbon dioxide (CO₂) capture approaches are urgently needed to lower and reverse CO₂emissions that lead to climate change. Here, we report the design, fabrication and testing of high efficiency biocatalytic textile-based gas-liquid contactors made using versatile, sustainable, and readily available polymers, cellulose, and chitosan, together with an immobilized carbonic anhydrase (CA) enzyme to accelerate CO₂absorption into benign, low-energy, aqueous potassium carbonate (K₂CO₃)-based solvents. This novel structured packing is able to withstand the CO₂scrubbing environment, will be simple to scale up, and will be useful as a "drop-in" for conventional chemical absorption systems as well as offer new possibilities for direct air capture. Immobilizing CA in a thin coating on textile packing surfaces minimizes the enzyme requirement, retains enzyme in the absorber for high catalytic benefit and longevity with repeated use, and allows downstream process flexibility by preventing CA from traveling to other unit operations, for example, high temperature desorption where enzyme could become inactivated. CA immobilization on cotton fiber textile packing materials by entrapment with chitosan exhibited an activity recovery of at least 49% and activity retentions of higher than 68% after 10 repeated wash and retest cycles over 5 days and up to 41% after a 31 day incubation in 10 wt % K₂CO₃at 40 °C. The lightweight biocatalytic textile packing modules are sturdy and easily handled with no sharp edges or dusting issues as can accompany conventional metal packing- or particulate-immobilized enzymes. In laboratory-scale countercurrent CO₂absorption tests at 4 L per minute total gas flow rates, CA-immobilized textile packings delivered average CO₂absorption efficiencies of 52.3% and 81.7% for single and double-stacked packings, respectively, versus 26.6% and 46.4% for single and double-stacked no-enzyme control textile packings, and versus 3.6% for conventional glass Raschig rings filled to the equivalent single-stacked packing height. Textile packings exhibited excellent solvent distribution throughout the packing even at low liquid flow rates, maintaining uniform gas contact with the wetted solid contacting surfaces across a range of different liquid flow rates, leading to robust CO₂capture efficiency. Biocatalytic textile packing retained 66% of the initial CO₂capture performance after five cycles of washing, drying, ambient storage, and retesting over a period of 66 days. In a separate test with freshly made packing, 76.5% performance retention was observed after a continuous 120 h recirculation longevity test.