Since carbon dioxide (CO2) is the primary greenhouse gas resulting from human activity, improving carbon capture, sequestration, and storage is an important tool in addressing climate change. Most direct air capture (DAC) technologies operate at temperatures of 20 to 40 °C (68 to 104 °F), but large portions of the earth have temperatures below 20 °C, leaving a gap in the world’s current CO2 capture strategy.
MIL-101 Metal Organic Frameworks
MIL-101 is a highly porous metal-organic framework (MOF) used to capture (adsorb) CO2. MIL-101 MOFs incorporating amine moieties are often used to extract CO2 from ultra-dilute mixtures such as ambient air. Typically, these materials are used for adsorption at higher temperatures and/or concentrations, such as with flue gas (combustion exhaust) at power plants or other industrial activities. However, there is no evidence of the use of these MIL-101/amine materials for CO2 adsorption at temperatures below typical indoor, room temperatures of ~20 °C. Using MIL-101/amine hybrid materials, Georgia Tech researchers have been able to capture CO2 from simulated air at temperatures of -20 to 25 °C (-4 to 77 °F), with and without humidity. The research has shown high CO2 uptake selectivity versus nitrogen, and that by tuning the composition of the hybrid or the amine used [branched poly(ethyleneimine) (PEI), tetraethylenepentamine (TEPA), etc.], the strength of CO2 adsorption and the corresponding CO2 desorption temperature can be tuned. The MIL-101/amine materials are tested as powders, incorporated into polymeric fibers or composite monoliths. Small temperature swings can be achieved, including desorption near ambient indoor conditions (room temperature).
- Increased temperature range: Use of these specific (or any supported) MOF/amine materials enables CO2 capture from air or simulated air at lower temperatures (below 20 °C)
- Functional in humidity: CO2 capture performance at low temperatures and varying humidity
- Tunable strength/temperature: By tuning the composition of the hybrid or the amine used, the strength of CO2 adsorption and the corresponding CO2 desorption temperature can be tuned
Because more than 80% of the land in the world has an annual average temperature below 25 °C, and essentially no place in the world has an absolute humidity of zero, the impact of CO2 capture at lower temperatures and varying humidity could greatly expand potential DAC deployment locations and opportunities.
- Direct air capture (DAC) research and development
- Gas separation, sequestration, and storage
- Carbon footprint offset
- Advanced filtration and energy efficiency solutions for large buildings
Figure 1. The physical appearance of the MIL-101(Cr)/cellulose acetate fibers during the spinning process (left) and when they are dried (right).
Figure 2. Scanning electron microscope images of MIL-101(Cr) fibers with varying diameters: 480 μm at (a) low and (d) high magnification; 571 μm at (b) low and (e) high magnification; 678 μm at (c) low and (f) high magnification.
Figure 3. Schematic illustration of sub-ambient DAC fixed bed system.