Direct Air Capture (DAC)

£600 / 1 Tonne CO2e
 
Direct air capture (DAC) is a chemical process designed to extract ambient CO₂ from the atmosphere. The captured CO₂ is subsequently conveyed and deposited underground, either in depleted gas fields or specific geological formations, where it undergoes mineralization through reactions with the surrounding rocks.
 
DAC comprises five fundamental stages: 1. Introducing a substantial volume of air to sorbents (typically utilizing large fans) 2. Capturing CO₂ using liquid or solid sorbents 3. Regenerating the sorbent through heat and/or pressure treatments 4. Compressing and transporting the captured CO₂ to designated storage sites 5. Injecting the CO₂ into geological storage locations.
 
The Science
DAC technology varies based on the specific chemical processes utilized to capture ambient CO₂ from the atmosphere and retrieve it from the sorbent.
 
The two primary options currently being explored at demonstration scale are:
 
1. Liquid solvents (hydroxides) that necessitate high temperatures for regeneration (800°C and above).
 
2. Solid sorbents (amines) that require lower temperature regeneration (85-120°C), albeit with more expensive equipment.
 
Additionally, various other concepts are in development, including regeneration through moisturizing of solid sorbents, electro-swings, nano-membranes, and hybrid approaches combining DAC with enhanced rock weathering (DAC-ERW) using silicate rocks.
Compared to alternative removal methods, the principal challenge in scaling up DAC lies in its high cost and substantial energy demand.
 
The duration of storage is a critical factor to consider; geological reservoirs or mineralization ensure removal for over 1000 years.
 
Assessing the net carbon CO₂ removal of DAC over its lifecycle is crucial, primarily influenced by the carbon intensity of the energy input and other lifecycle considerations such as construction and equipment.