DAC Technology Approaches

DAC technologies share a common challenge: capturing CO₂ from 420 ppm air (0.042%)—1,000x more dilute than flue gas from power plants. Liquid solvent systems use alkaline solutions: Air contacts potassium hydroxide (KOH) solution containing amines. CO₂ dissolves, forming carbonates. Solution reacts with calcium hydroxide to precipitate calcium carbonate pellets. Pellets are heated to 900°C (calcination) to release pure CO₂. Carbon Engineering's pilot in Canada captures 1 ton/day; planning 1 Mt/year facility. Chemistry is proven (used in ammonia production for decades), but calcination energy is the bottleneck. Solid sorbent temperature-swing uses functionalized materials: Air flows over solid filters coated with amine compounds that chemically bind CO₂ at ambient temperature. Chamber is sealed and heated to 80-120°C under vacuum, releasing CO₂. Climeworks' Orca plant in Iceland (4,000 t/year) uses geothermal heat for regeneration. Modular design allows staged deployment, but scaling requires thousands of units. Moisture-swing sorbents are the newest approach: Sorbent captures CO₂ when dry, releases it when exposed to moisture at just 40-60°C. Can use waste heat from industrial processes or low-grade geothermal. Global Thermostat demonstrated at pilot scale. Still early-stage—long-term sorbent stability unknown. Electrochemical systems use voltage-swing: Electrode materials (quinone-based) bind CO₂ when voltage is applied, release it when voltage is reversed. Fully electric (no heat), lowest energy penalty (0.8-1.5 GJ/t). Verdox, Captura developing at lab scale. Major advantage: can integrate directly with intermittent renewables. Challenge: electrode durability through millions of cycles.