Direct Air Capture (DAC)
A technology designed to remove carbon dioxide directly from the ambient atmosphere, where its concentration is very low (~420 ppm). The two primary approaches use either liquid solvent systems, where air is passed through chemical solutions (e.g., potassium hydroxide), or solid sorbent systems, where air passes over filter-like surfaces that chemically bind with CO2. The captured CO2 is then released for storage or utilization.
Direct Air Capture (DAC) is a negative emissions technology because it removes historical CO2 emissions from the air, unlike point-source capture which only prevents new emissions. The main technical challenge is the low concentration of CO2 in the air, which requires moving vast quantities of air and using highly efficient chemical absorbers, making the process energy-intensive and expensive.
In liquid solvent systems, large fans push air through an air contactor containing a strong chemical solution, typically an aqueous hydroxide solution. The CO2 reacts to form a carbonate salt. This salt solution is then heated in a separate reactor, which releases the CO2 in a pure stream and regenerates the original hydroxide solution for reuse. This process is continuous but requires high-temperature heat (up to 900°C).
In solid sorbent systems, air is blown over solid materials (sorbents) that have amines or other chemicals bonded to their surface. These chemicals selectively adsorb CO2 molecules. Once the sorbent is saturated, it is moved to a low-pressure, heated chamber where the CO2 is released. This process typically requires lower temperatures (80-120°C) than liquid systems, allowing for the use of waste heat or geothermal energy. Once the CO2 is captured and purified, it must be permanently sequestered underground or used in products like synthetic fuels or building materials to achieve a climate benefit.
UNESCO Nomenclature: 3305
– Chemical engineering and technology
Usage
Emerging Technology
Precursors
- air scrubbing technology used in submarines and spacecraft for life support
- industrial gas separation and purification techniques (e.g., pressure swing adsorption)
- advances in chemical engineering and materials science for sorbent development
- understanding of acid-base chemistry
- theories on climate change and the need for negative emissions
Applications
- providing CO2 for synthetic fuels (e.g., combining with green hydrogen)
- supplying CO2 to greenhouses to enhance plant growth
- carbonating beverages
- use in carbon capture, utilization, and storage (CCUS) projects
- commercial DAC plants operated by companies like climeworks (switzerland) and carbon engineering (canada)
Patents:
- US7892348B2
- US8128749B2
- WO2010051693A1
Potential Innovations Ideas
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Related to: direct air capture, DAC, carbon removal, negative emissions technology, solid sorbents, liquid solvents, climeworks, carbon engineering, air scrubbing, CCUS.