Direct Air Capture of CO₂ by Physisorbent Materials

Abstract

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO2 directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA-SBA-15 (amine-modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST-1 and Mg-MOF-74/Mg-dobdc (metal-organic frameworks, MOFs); SIFSIX-3-Ni, (hybrid ultramicroporous material). Temperature-programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf-life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO2-rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance.

A highly stable metal‐organic framework with optimum aperture size for CO2 capture

“…To measure the breakthrough time of CO 2 in the presence of water vapor, we introduced a gas mixture containing 15 6 1% of dry CO 2 and 85 6 1% of wet N 2 (80 6 5% RH) to the MOF-packed column. The low water stability of HKUST-1, which has been previously reported, 76 was confirmed in our breakthrough experiments after water vapor exposure (Supporting Information Figure S10-11). For opt-UiO-66(Zr)-(OH) 2 , the CO 2 mean residence time during breakthrough tests decreases significantly under wet condition compared to dry condition (Supporting Information Table S4).…”

Putting an ultrahigh concentration of amine groups into a metal–organic framework for CO2capture at low pressures

“…9–13 After the breakthrough curves reached equilibrium under the above mentioned dry conditions (0% RH, RH = relative humidity), the columns were activated under He flow at 403 K, cooled down to the measurement temperature of 313 K, saturated using humid He (82% RH), and then switched to humid CO 2 /N 2 mixtures (82% RH, no change to other parameters) to start a new breakthrough experiment. Remarkably, the breakthrough curve for the humid 10 : 90 CO 2 /N 2 mixture almost overlapped with that measured at the dry condition (Fig.…”

“…9–50 To increase the CO 2 uptake at extremely low pressures, incorporating alkylamine groups on the pore surface is the most effective strategy so far, 46–50 because of the chemisorption of CO 2 associated with the formation of zwitterionic carbamate or carbamic acid. For instance, [Mg 2 (dobpdc)(eda) 1.6 ] (eda-Mg 2 (dobpdc), eda = ethylenediamine, H 4 dobpdc = 4,4′-dihydroxy-(1,1′-biphenyl)-3,3′-dicarboxylic acid) 48 holds the records for gravimetric and volumetric CO 2 adsorption capacities with 2.85 mmol g –1 and 2.72 mmol cm –3 , respectively, at 298 K and 0.4 mbar, this is because it has a high concentration of free amine groups at 3.86 mmol g –1 or 3.69 mmol cm –3 .…”

A Microporous Co(II)‐Based 3‐D Metal Organic Framework Built from Magnetic Infinite Rod‐Shaped Secondary Building Units

“…The CO 2 uptake at 1 bar is 1.96 mmol g –1 and 1.29 mmol g –1 at 273 and 298 K, respectively (Figure b). These values are moderate compared with those reported for other MOFs and ZIFs . The calculated isosteric heat of adsorption, Qst, was found to be 30.7 kJ mol –1 at zero coverage (Figure S6, Supporting Information).…”