About This Project

Direct air capture (DAC) is a promising pathway for atmospheric CO2 removal. Biocatalysts like carbonic anhydrases (CAs) rapidly absorb CO2 from air and reduce DAC costs, and are most effective when immobilised close to the gas-solvent interface so CO2 can reach them quickly. This project seeks to stably anchor CA onto cotton fabric using fused cellulose binding domain proteins (CBDs) under DAC-like conditions; while avoiding current immobilisation pitfalls, like loss of CA activity.

Ask the Scientists

What is the context of this research?

Atmospheric CO2 removal (CDR) and point-source capture (PSC) of CO2 are well-accepted as being necessary for successfully decarbonizing within climate goals (1). Direct air capture (DAC) is a CDR pathway with ideal verifiability and durability. Both DAC and PSC are cost constrained, primarily by the CapEx of the gas contactor and the energy required to drive large swings in temperature or pH to regenerate CO2 from the capture material (2).

Those high cost and energy requirements are driven by a thermodynamic trade-off between the rate of CO2 absorption and the CO2 regeneration energy: CO2 capture materials with high absorption rate, which reduce cost by reducing the gas contactor size, typically have high CO2 regeneration energy, and vice versa (3).

What is the significance of this project?

Carbonic anhydrases (CAs) catalyze fast CO2 absorption in solvents with low CO2 regeneration energy, resolving the tradeoff described above (4). CA could reduce DAC cost by reducing parameter swing or gas contactor size, if stable in DAC-like conditions e.g. high pH and temperature. Slow diffusion of CO2 through bulk solvent is also limiting to CA usage, so placing CA at <10 µm from the gas-solvent interface has been identified as a crucial performance factor (5).

Modelling is still needed to generate target properties for CA immobilisation and and quantify their effect on DAC cost. However, there are promising substrates for immobilisation at low-cost e.g. on cotton fabrics (6), where immobilisation that can be improved and characterised.

What are the goals of the project?

Modeling and technoeconomic analysis is required to provide quantitative targets for immobilisation of CAs in DAC. However, initial efforts should aim to increase in durability and density of immobilisation while retaining (or enhancing) high CA activity (kcat/kM ~108 M-1s-1). Durability and activity should be assessed in conditions and solvents relevant to DAC, such as 10-20% K2CO3.

Overall, a successful immobilisation approach should yield a many-fold improvement in overall DAC performance (e.g. see significant absorption enhancement in (6)). Moreover, the immobilisation method and the substrate should be manufacturable at large-scale and low-cost.

For a review of state-of-the art CA immobilisation techniques, see (7).