Direct Air Capture of CO₂ Using Poly(ethyleneimine)-Functionalized Expanded Poly(tetrafluoroethylene)/Silica Composite Structured Sorbents

Abstract

The rapidly increasing atmospheric CO 2 concentration has driven research into the development of cost-and energy-efficient materials and processes for the direct air capture of CO 2 (DAC). Solid-supported amine materials can give high CO 2 uptakes and acceptable sorption kinetics, but they are generally prepared in powder forms that are likely not practically deployable in large-scale operations due to significant pressure drops associated with packed-bed gas−solid contactors. To this end, the development of effective gas−solid contactors for CO 2 capture technologies is important to allow processing high flow rates of gas with low-pressure drops and high mass transfer rates. In this study, we demonstrate new laminate-supported amine CO 2 sorbents based on the impregnation of lowmolecular-weight, branched poly(ethyleneimine) (PEI) into an expanded poly(tetrafluoroethylene) (ePTFE) sheet matrix containing embedded silica particles to form free-standing sheets amenable to incorporation into structured gas−solid contactors. The free-standing sheets are functionalized with PEI using a highly scalable wet impregnation method. This method allowed controllable PEI distribution and enough porosity retained inside the sheets to enable practical CO 2 capacities ranging from 0.4 to 1.6 mmol CO 2 /g sorbent under dry conditions. Reversible CO 2 capacities are achieved under both dry and humid temperature swing cycles, indicating promising material stability. The specific thermal energy requirement for the regeneration based on the measured CO 2 and water capacities is 287 kJ/mol CO 2 , where the molar ratio of water to CO 2 of 3.1 is achieved using hydrophobic materials. This is the lowest molar ratio among published DAC sorbents. A larger laminate module is tested under conditions closer to larger-scale operations (linear velocities 0.03, 0.05, and 0.1 m/sec) and demonstrates a stable capacity of 0.80 CO 2 /g sorbent over five cycles of CO 2 adsorption and steam regeneration. The PEI-impregnated ePTFE/silica composite sorbent/contactors demonstrate promising DAC performance derived from the amine-filled silica particles contained in hydrophobic ePTFE domains to reduce water sorption and its concomitant regeneration energy penalty.

Support Pore Structure and Composition Strongly Influence the Direct Air Capture of CO2 on Supported Amines

“…Moreover, differences in surface chemistries in support materials can result in different binding motifs between the amine and the support, which also has the potential to influence the CO 2 capture performance. A variety of porous support materials have been used for amine impregnation, including silica, − γ-alumina, − MOFs, − zeolite, and mixed metal oxides. , Despite this, the effects of amine-solid support interactions on CO 2 adsorption behavior are still poorly understood. Furthermore, most prior DAC studies are limited to adsorption temperatures above indoor ambient room temperature (>20 °C).…”

Direct Air Capture of CO2 with Metal Nitrate-Doped, Tetraethylenepentamine-Functionalized SBA-15 Adsorbents

“…37,38 However, it should be noted that the CO 2 capacity under humidity conditions is without exception much larger than the dry CO 2 capacity (2.53 mmol COd 2 /g adsorbent , not shown here), which is in line with the literature showing an enhancement in CO 2 capacity in the presence of water that originates from the improved stoichiometry from carbamates to bicarbonates. 39,40 The water capacity of 50TEPA/SBA-15 increases with RH and is about 2−5 times the CO 2 capacity at any given RH, which is rationalized not only by the hydrophilicity of amine-functionalized solid adsorbents 39 but also by the multilayer adsorption of H 2 O molecules. 41 Figure 5b presents the CO 2 capacity data of 50TEPA/SBA-15 in 10 adsorption−desorption cycles.…”

Understanding the performance of membrane for direct air capture of CO2

“…These sorbents showed potential for costeffective and energy-efficient DAC applications. 37 Researchers demonstrated the effectiveness of thin film composite membranes for CO 2 separation. These membranes, consisting of specific materials, showed super-permeable characteristics and outstanding CO 2 separation performance.…”

“…A study demonstrated DAC sorbents based on PEI‐functionalized ePTFE/silica composite materials for CO 2 capture. These sorbents showed potential for cost‐effective and energy‐efficient DAC applications 37 . Researchers demonstrated the effectiveness of thin film composite membranes for CO 2 separation.…”