TVSA Direct Air Capture utilizes solid chemical sorbents (such as primary and secondary alkylamines impregnated or covalently grafted onto porous silica or cellulose matrices) inside modular contactor collector pods. Large industrial fans draw massive volumes of ambient air through the thin sorbent structure at ambient conditions, where CO2 chemisorbs onto amine sites forming carbamates and bicarbonates. Once saturated, the contactor pod is sealed airtight, evacuated to rough vacuum (10–30 kPa / 100–300 mbar), and heated to 85°C–105°C using low-temperature steam or geothermal hot water to break the amine-CO2 chemical bonds, releasing high-purity (98%+) CO2 gas.

Amine functional groups are intrinsically hydrophilic. At ambient relative humidity (40% to 80% RH), ambient water molecules competitive-adsorb alongside CO2 onto the porous matrix at molar ratios typically between 1.5 and 4.5 mol H2O per mol CO2 (0.6 to 1.8 kg water per kg CO2). During the thermal desorption cycle, this entire mass of water must be vaporized alongside the CO2. With water latent heat of vaporization (~2,400 kJ/kg), desorbing co-adsorbed water frequently accounts for 40% to 60% of the entire thermal duty of the DAC plant (consuming 2.5 to 4.5 GJ per tonne of CO2 alone).

Because atmospheric CO2 concentration is extremely dilute (~420 ppm or ~0.76 g CO2/m³ air at STP), capturing one metric tonne of net CO2 requires drawing between 1.8 million and 3.2 million cubic meters of air through the contactor. Every single Pascal of aerodynamic pressure drop across the sorbent monolith represents significant electrical energy. At 150 Pa pressure drop and 75% fan/motor efficiency, air movement consumes ~150 kWh/t CO2. If particulate fouling or poor pleating raises pressure drop to 400 Pa, fan power alone skyrockets to over 400 kWh/t CO2, severely eroding plant efficiency.

Gross CO2 captured is not equal to net CO2 removed. Net carbon removal efficiency measures net climate benefit after subtracting the full lifecycle emissions of the electricity and heat powering the facility. If a DAC facility consuming 6 GJ/t of thermal energy and 500 kWh/t of electrical energy is powered by a fossil-heavy grid (e.g. 500 g CO2/kWh from coal/gas) and natural gas boilers, the plant emits 500 to 750 kg of CO2 to capture 1,000 kg, yielding an abysmal net efficiency of only 25% to 50%. Maximum net removal (>90% to 95%) requires dedicated zero-carbon power (geothermal, nuclear, wind, or solar) paired with industrial waste heat or heat pumps.

Supported amine sorbents degrade through two primary mechanisms: (1) Oxidative degradation, where exposure of aliphatic polyamines to atmospheric oxygen at elevated temperatures (>80°C–100°C) oxidizes amine groups into imines, amides, and volatile nitrosamines, destroying adsorption capacity; and (2) Irreversible urea formation, occurring when desorbed amine-carbamate pairs dehydrate under severe dry heating conditions. Modern TVSA systems strictly enforce oxygen purging or deep vacuum evacuation prior to admitting steam to prevent thermal oxidation.