Liquid Solvents or Solid Sorbents? The Energy Trade-Offs That Shape Direct Air Capture

Direct air capture (DAC) technologies primarily use either liquid solvents or solid sorbents to capture CO2 from the air. The choice between these methods hinges on their vastly different energy demands, particularly the temperature required for regeneration, influencing cost and feasibility.

Samuel Adebayo

October 30, 2026 · 6 min read

Understanding Direct Air Capture (DAC) Technologies

DAC systems use chemical sorbents or solvents to bind CO₂ from ambient air, which is then released through heating—either with waste heat or via high-temperature heat pumps—or through pressure changes, after which the concentrated gas is transported for storage or use. That regenerative cycle is the heart of every DAC design: the capture step is only half the process, and the energy bill for prying CO₂ back off the capture material dominates the plant's resource footprint.

The fundamental challenge is dilution. Atmospheric CO₂ is present at roughly 0.04 percent, so a DAC plant must move enormous volumes of air to harvest comparatively small amounts of carbon. Because the target is so dilute and sorbent regeneration requires substantial energy, DAC remains, in the words of a recent analysis in Nature's sustainability journal by Yannai Kashtan and colleagues, an energy-intensive and costly undertaking. The technology's climate value is therefore long-horizon: DAC has the potential to reduce atmospheric CO₂ concentrations after anthropogenic emissions reach zero, rather than serving as a near-term substitute for emission cuts.

Within this shared framework, engineers have converged on two main approaches. Liquid solvent systems wash air through a chemical solution that absorbs CO₂; solid sorbent systems pass air across solid materials—amine-functionalized materials, zeolites, or metal-organic frameworks—that chemically bind CO₂ molecules and separate them from the air. The distinction sounds subtle, but it cascades into very different temperature requirements, heat sources, and ultimately cost structures.

Liquid Solvent DAC Systems: Mechanism and Energy Demands

In a liquid solvent plant, ambient air is contacted with a chemical solution that absorbs CO₂, producing a carbon-rich liquid. That solution then enters a regenerator, where it is heated at high temperatures—typically around 800 °C in the process described by the CCS Knowledge Centre's technical primer—to release CO₂ gas from the liquid. The solvent is recycled back to the capture unit to absorb more CO₂, closing the loop. A Stanford course analysis of DAC energy consumption places regeneration temperatures for this pathway around 900 °C, underscoring that releasing CO₂ from a liquid solvent demands some of the highest-grade heat in industrial chemistry.

The energy consequences are substantial. Reported total energy consumption for liquid solvent DAC falls in the range of 5.4 to 10.8 gigajoules per tonne of CO₂—roughly 1,500 to 3,000 kilowatt-hours per ton. Much of that input is thermal energy at a temperature few waste-heat sources can supply, which pushes operators toward dedicated high-temperature heat: combustion with capture, nuclear heat, or high-temperature heat pumps.

The pathway's counterbalancing strength is industrial maturity. As the CCS Knowledge Centre notes, this regeneration process requires a significant amount of high-grade heat, but it benefits from using equipment with industrial precedent and existing supply chains. For a policy maker, that means liquid solvent plants draw on proven engineering at the cost of a demanding thermal budget.

Cost figures for this pathway remain targets rather than achieved prices. Reported ranges for liquid solvent DAC cluster between $200 and $600 per tonne of CO₂ today, with some developers aiming for $250–$400 by the end of the decade and long-term goals closer to $100 per tonne. The Stanford analysis identifies $100 per tonne of CO₂ as the often-stated cost target for DAC, and projections suggest the field as a whole may reach the $100–$600 per ton band by 2050. None of these figures should be read as a guaranteed price floor or ceiling.

Solid Sorbent DAC Systems: Mechanism and Energy Demands

Solid sorbent systems replace the liquid wash with physical filters that chemically bind CO₂ molecules, separating them from air. The filters—often amine-functionalized materials, zeolites, or metal-organic frameworks—saturate over time and must then be regenerated. Instead of a high-temperature liquid loop, solid sorbents typically release their captured CO₂ through heating, pressure changes, or steam, and the refreshed sorbent is recycled back into the capture unit to absorb more CO₂, as the Nature analysis describes.

The defining advantage is temperature. Regeneration for solid sorbent systems typically occurs between 80 °C and 120 °C—dramatically lower than the roughly 900 °C demanded by liquid solvents. That difference matters because it changes the menu of viable heat sources. Heat at 80–120 °C can be drawn from industrial waste heat, low-temperature geothermal resources, or conventional heat pumps, whereas heat near 900 °C requires far more specialized infrastructure. A solid sorbent plant sited next to a data center or industrial facility with recoverable waste heat faces a very different energy economics problem than a liquid solvent plant that must secure high-grade thermal input.

The trade-off runs in the other direction on maturity and scale. Solid sorbent materials are newer to large-scale deployment than the solvent chemistry that liquid systems inherited from industrial gas processing, and sorbent lifetime, degradation, and manufacturing cost remain active engineering questions. No single figure settles the comparison: the solid pathway trades thermal intensity for material novelty, and the liquid pathway trades proven equipment for a punishing heat bill.

Comparative Analysis of DAC Technologies

The table below juxtaposes the two primary DAC pathways against the metrics that most directly govern feasibility: how they capture and release CO₂, what kind of energy they consume, and what their costs are projected to be. The central pattern it reveals is that the two technologies are not interchangeable—they are optimized for different energy contexts, and a deployment decision should follow the local availability of low-carbon heat versus electricity.

Reported characteristics of the two primary DAC technology pathways. Energy and cost figures are literature-reported ranges and targets, not fixed values.
Dimension	Liquid Solvent DAC	Solid Sorbent DAC
Operating principle	Chemical solution absorbs CO₂ from air; CO₂-rich solution heated in a regenerator to release the gas; solvent recycled	Solid filters (amine-functionalized materials, zeolites, or metal-organic frameworks) chemically bind CO₂; released by heating or pressure changes; sorbent recycled
Primary energy input	Significant high-grade heat for solvent regeneration	Heat for sorbent regeneration, at much lower temperatures; enables use of lower-grade heat sources
Reported energy consumption	5.4–10.8 GJ (≈1,500–3,000 kWh) per tonne CO₂	Lower thermal demand by design; specific comparable totals vary by sorbent and cycle design
Regeneration temperature	Typically around 800 °C, with reported requirements around 900 °C	Typically 80–120 °C
Cost targets ($/tonne CO₂)	Reported $200–$600 today; aims of $250–$400 by end of decade; long-term goal near $100; $100 often stated as the field-wide target	Comparable long-run ambition near the $100 target; current figures remain technology- and developer-specific
Maturity	Equipment with industrial precedent and existing supply chains	Newer materials and designs; sorbent lifetime and manufacturing scale still maturing

Read horizontally, the table shows that the technologies diverge most sharply on thermal grade. A site with abundant high-temperature low-carbon heat—nuclear or geothermal—matches the liquid pathway's needs, while a site rich in waste heat or cheap electricity paired with heat pumps favors the solid pathway. Read vertically, it shows that both pathways answer to the same cost target: roughly $100 per tonne of CO₂, the benchmark the Stanford analysis identifies as the field's often-stated goal.

Those figures must also clear an economic bar that has nothing to do with plant engineering. The Stanford analysis notes that DAC needs to run near-constantly to be cost-effective, which means intermittent renewables must be combined with storage solutions or supplemented with steady sources like geothermal or nuclear. And the Nature analysis by Kashtan and colleagues argues the opportunity cost is real: because every megawatt-hour devoted to DAC could instead displace fossil generation, the climate and health benefits of directing that low-carbon energy elsewhere must be weighed against DAC's removal value, particularly before emissions reach zero.