Opportunities / ENERGY, DEPARTMENT OF

Ammonia-Assisted Regeneration for Longer-Lasting Direct Air Capture (DAC)

Description (excerpt)

Every direct air capture (DAC) system depends on its sorbent, and every sorbent eventually wears out. This DAC from Los Alamos National Laboratory tackles that weakness head-on. It replaces the harsh release step with a gentler, ammonia-assisted process, which shields amine-based sorbents from the degradation that drives up operating costs. The method works with a broad family of established sorbent materials and support structures, so developers can build it into existing capture designs rather than starting over. Challenges Direct air capture is a two-step cycle: a sorbent captures CO2 from the air, then releases it as a concentrated stream. Liquid sorbents need expensive equipment and a lot of energy, more than 400 kJ of work per mole of CO2. Amine-based solid sorbents capture more CO2, regenerate at about 120°C and even perform better in humid air. Their weakness is durability. At release temperatures of 80°C and above, oxygen reacts with the amines to form free radicals and the amines can evaporate. Both effects wear the sorbent down over repeated cycles. Replacing sorbent drives up the overall cost of direct air capture and stands in the way of large-scale deployment. Problems Solved DAC changes how the sorbent gives up its captured carbon. First, the sorbent absorbs CO2 from ambient air at ordinary outdoor temperatures and pressures. Then, instead of relying on the conventional release step that damages the material, the method exposes the loaded sorbent to ammonia gas, which prompts it to release the CO2. Regeneration takes place at 75–120°C under reduced pressure (20–600 mbar), and the released CO2 can then be stored. The method is designed to prevent sorbent degradation and erosion. The application sets performance goals ranging from at least 50% of original capacity after five cycles to as much as 99% across 500 cycles. It applies to widely used amine sorbents, on supports that include silica, alumina, carbon materials and cellulose. Longer sorbent life means lower operating costs and a stronger economic case for direct air capture. Advantages Extends the useful life of capture sorbents and slows their breakdown Lowers operating costs by reducing how often sorbent must be replaced Works with many established amine sorbents and support materials Captures carbon at normal outdoor temperatures and pressures Delivers a high-purity CO2 stream for storage or reuse Improves the overall economics of carbon removal projects Market Applications Carbon rem …

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