This Problem Statement follows the Problem Statement structure for Homeworld Garden Grants. It is derived from the recommendations of Part 1 of our Roadmap for Biotechnology in Carbon Dioxide Removal.

We invite proposals to Homeworld Garden Grants Call 1: Protein Engineering that use a copied or modified version of this Problem Statement and present a novel Solution Statement.

Motivating Factor

A well-accepted target cost and scale for atmospheric carbon dioxide removal (CDR) is 1-10 Gt CO2/yr at $100/tCO2 by 2050.

Direct air capture (DAC) is a CDR pathway with ideal verifiability and durability, but it is currently estimated to cost ~$100-1000/tCO2. The primary cost factors are the CapEx of the air contactor and the energy required to drive large  temperature or pH swings to regenerate CO2 from the capture material (1).

DAC’s 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 air contactor size, typically have high CO2 regeneration energy, and vice versa (2).

Specific Constraint

Carbonic anhydrase (CA) enzymes catalyze CO2 exchange. CA can enable fast CO2 absorption in capture solvents with low CO2 regeneration energy, resolving the trade off discussed above (3). CA could enable efficient DAC with small temperature or pH swings if it can be stabilized in DAC processes, which may include high pH, temperature, or ionic strength. 

Protein engineering (PE) and novel CA discovery through systematic screens of natural variants could produce stable CA for DAC. However, no designs for CA-optimized DAC are proposed, so it is unclear what conditions CA must be engineered to tolerate. Design-oriented techno-economic analysis (TEA) could enable CA-enhanced DAC development by identifying optimal process conditions and providing clear targets for PE.

Actionable Goals

The following questions should be answered to guide engineering of CA-enhanced DAC:

• As a function of CA catalytic efficiency, cost, and lifetime, what process designs (e.g., pH swing, temperature swing) and solvent properties are favored?

• How strongly does the process design depend on the cost, lifetime, and catalytic efficiency of CA? 

• What are the minimum and ideal CA properties (catalytic efficiency, cost, lifetime) and corresponding process parameters (pH, temp, etc.) for use of CA in DAC to be competitive? 

• When does optimization of CA cost, lifetime, and catalytic efficiency yield substantial or diminishing benefits for energy usage and cost?