Low-Energy Direct Air Capture with Waste Brine Regeneration and Permanent CO₂ Mineralization

Background

Rising atmospheric carbon dioxide concentrations represent a critical global challenge, driving the urgent need for scalable carbon management strategies. Direct air capture (DAC) and carbon sequestration have emerged as vital fields for actively removing greenhouse gases directly from ambient air to mitigate climate change. Concurrently, industrial operations such as desalination, oil and gas extraction, and water softening generate vast quantities of high-salinity waste brines and alkaline residues. Effectively managing both atmospheric carbon levels and industrial waste streams requires innovative approaches that can permanently immobilize carbon in a sustainable, scalable, and economically viable manner.

However, widespread deployment of current DAC methodologies is severely hindered by substantial energy and infrastructural bottlenecks. Conventional capture systems rely heavily on thermal regeneration to release bound carbon dioxide from exhausted sorbents, a process that demands significant external heat input and drives up operational costs. Furthermore, once the gas is desorbed, traditional pathways require energy-intensive gas compression, extensive pipeline transport, and specialized geological injection for permanent underground storage. These requirements severely limit geographic flexibility and pose long-term leakage risks. Additionally, when attempting to bypass thermal steps using ambient-temperature salt regeneration, conventional weak-base ion-exchange resins exhibit extremely poor recovery efficiencies, rendering them impractical for continuous cyclic operations.

Technology

This low-energy direct air capture (DAC) solution utilizes a specialized hybrid ion-exchange sorbent, DeCarbon-HIX, to remove atmospheric CO₂ and convert it into stable carbonate minerals. Derived from a weak-base anion exchanger with primary benzyl amine repeat units and covalently bound copper(II) ions, the sorbent selectively absorbs CO₂ from ambient air, converting it into bicarbonate. Once exhausted, the sorbent is regenerated at ambient temperatures using chloride-rich waste brines, such as oilfield produced water or desalination concentrates. During regeneration, bicarbonate is exchanged for chloride, releasing alkalinity into the brine. This alkalinity reacts with divalent cations (like calcium and barium) present in the brine to precipitate solid carbonate minerals outside the sorbent bed. Finally, the resin is reconditioned to its active hydroxide form using lime or industrial alkaline leachates like steel slag, enabling a continuous, cyclic operation.

This technology is highly differentiated because it completely eliminates the need for energy-intensive thermal regeneration, gas compression, and underground geological CO₂ storage. Operating entirely at ambient temperatures, the process achieves over 95% CO₂ recovery during brine regeneration, starkly outperforming conventional weak-base resins which achieve less than 6% recovery under similar conditions. Furthermore, the DeCarbon-HIX sorbent demonstrates exceptional durability, maintaining a high cyclic capacity of 4.2 to 4.5 mol CO₂/kg and stable copper loading across 300 cycles. By integrating carbon capture with in-situ mineralization using industrial waste streams, this geographically flexible approach transforms environmental liabilities into permanent, solid carbon sequestration with minimal energy input.

Benefits

• Eliminates the need for energy-intensive thermal regeneration by operating at ambient temperatures
• Removes the requirement for CO2 gas compression and underground geological storage through in situ mineralization
• Repurposes waste brines and industrial residues, such as produced water and steel slag, for sorbent regeneration and reconditioning
• Achieves permanent carbon sequestration by converting captured CO2 into stable solid carbonate minerals
• Demonstrates high regeneration efficiency with over 95% CO2 recovery and over 90% mineralization efficiency
• Maintains high CO2 capture capacity and structural stability over hundreds of operating cycles
• Minimizes operational pressure drops because mineral precipitation occurs predominantly outside the sorbent bed
• Offers a scalable and geographically flexible deployment model suitable for regions with abundant waste brine resources

Applications

• Direct air carbon capture
• Permanent carbon mineralization
• Oilfield produced water treatment
• Desalination brine management
• Industrial carbonate mineral production

Additional info

Arup K. Sengupta’s research has encompassed nearly every aspect of water science and technology: from drinking water treatment to desalination to municipal wastewater reuse to resource recovery. SenGupta is internationally recognized for advancing and expanding the field of ion exchange science and technology, and applying it for development of sustainable technologies and new materials.