Direct Air Capture & Sequestration

     The diagram above shows, based on the laws of thermodynamics, the minimum energy to remove CO2 from ambient air (Direct air capture).  Removal requires about 3 times as much energy as the energy gained by burning coal and more than twice as much as from burning natural gas.  That is primarily because the CO2 is so dilute in the atmosphere.  For net CO2 removal with DAC, cheap energy (solar and wind, perhaps also small modular nuclear) is needed.

     However, the diagram above assumes energy use for fans to speed up air circulation across a catalyst that captures CO2 (there are many possible catalysts.)  Is also assumes that heat is later used to separate the CO2 from the catalyst, so that the capture process can begin anew and so that the purified CO2 can be pumped to its final resting place (or another use).

     Moreover, it concentrates on heat-based approaches.  Other approaches - including electric charge, pH change, humidity, and phase change - are gaining traction in the 2020s.  See diagrams a little further down the page.  These approaches are generally less energy intensive.

Can We Engineer Our Way Out of the Climate Crisis with Carbon Capture? 0324.rtf

Will Direct Air Capture Ever Be Affordable? The Rise of DAC 3.0 - 0224.rtf

Sequestering Carbon in Rocks - Lackner 2002.pdf - 42 pp

from Abstract: "Sequestration of waste carbon dioxide will require methods that can safely store several trillion tons of carbon dioxide.  Long-term storage of a gaseous substance is fraught with uncertainty and hazards, but carbonate chemistry offers permanent solutions to the disposal problem.  Carbonates can be formed from carbon dioxide and metal oxides in reactions that are thermodynamically favored and exothermic, which result in materials that can be safely and permanently kept out of the active carbon stocks in the environment.  Carbonate sequestration methods require the development of an extractive minerals industry that provides the base ions for neutralizing carbonic acid."

     Among many topics addressed are alkalinity, magnesium carbonates, molten salts, serpentine and olivine.

Section Map: Reversing Climate Change