Why can pre-combustion carbon capture be more efficient than post-combustion capture?

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Illustration of various geoengineering techniques to address climate change, including carbon capture and storage methods like artificial trees, industrial scrubbers, and deep ocean CO2 storage, as well as solar reflectance strategies such as sulfur aerosols, reflective crops, cloud whitening, and orbital mirrors. The scene shows these interventions applied to land, sea, and atmosphere, with labeled features explaining each process. — Geoengineering Various geoengineering proposals designed to increase solar reflectance or capture and store carbon.

Pre-combustion carbon capture is generally more efficient than post-combustion capture for two primary reasons related to the chemical composition of the gas stream and the potential for resource recovery.1

Higher Concentration: In post-combustion capture, the flue gas contains relatively low concentrations of carbon dioxide (CO₂), typically ranging from 4 to 14 percent. In contrast, the gas feedstock used in pre-combustion processes—produced through gasification—contains a much higher CO₂ concentration, often between 15 and 50 percent. This higher concentration makes the separation process more efficient.1
By-product Production: Pre-combustion capture allows for the production of usable by-products, such as hydrogen, which adds value to the process compared to post-combustion methods that primarily focus on removing CO₂ from waste emissions.1

While pre-combustion capture offers these efficiency advantages, it is important to note that the infrastructure required for gasification is often significantly more expensive to install than the equipment used for post-combustion retrofitting.1