New Insights into the Interactions of CO₂ with Amine-Functionalized Silica

Abstract

The CO2−amine chemistry in gas−solid processes was investigated under both humid and dry conditions using aminopropyl-grafted pore-expanded MCM-41 silica (MONO-PE-MCM-41). To draw accurate conclusions, a set of conditions had to be met including (i) the use of an adsorbent with open pore structure and readily accessible adsorption sites, e.g. MONO-PE-MCM-41 with a mean pore size of 7.2 nm; (ii) the CO2 concentration in the feed should be high enough to achieve saturation via chemisorption, but low enough to avoid any additional physisorption, e.g., 5% CO2 in N2; (iii) the use of a reliable method for the accurate measurement of CO2/N ratio. Under such conditions, the obtained CO2/N ratios were reminiscent of those obtained in the CO2 scrubbing process using ethanolamine solutions. Under dry conditions, the CO2/N ratio was close to 0.5, consistent with the formation of carbamate. Streams with relative humidity (RH) of 27, 61, and 74% were studied as well. As RH in the feed increased, CO2/N ratio increased from 0.57 to 0.88, in line with the gradual formation of bicarbonate. As for the determination of CO2/N ratio under dry conditions, both thermogravimetry (TG) and mass spectrometry (MS) were suitable, whereas in the presence of moisture, TG was found to drastically underestimate the CO2 uptake. The seemingly disparate CO2/N ratios reported in the literature for various propylamine-bearing adsorbents were rationalized on the basis of the adsorbent pore structure and/or the experimental conditions used.

Computational Comparison of the Reactions of Substituted Amines with CO2

“…The advantage of nonaqueous systems is to escape the large effects of aqueous equilibria. [10] Technologies include supported liquid membranes of aqueous amine solutions, [19,20] amine-functionalized silica, [21,22] and amine enriched solid sorbents. [23] A hybrid Substituted amines are a popular choice as molecules to selectively react with and separate CO 2 from gas mixtures.…”

Simultaneous Online Measurement of H2O and CO2 in the Humid CO2 Adsorption/Desorption Process

“…20 To reduce the fluctuation of H2O content and to gain a low H2O content of air flow, surface-flushing was used to humidify the air flow. Figure 2 shows the relationships between the humidity of the air flow and the temperature of the water bath for both the bubbling and surface-flushing methods.…”

“…However, they failed to achieve H2O and CO2 elution curves simultaneously in the humid CO2 co-adsorption/desorption process. In addition, thermogravimetric analysis (TGA) [16][17][18][19] and TGA-MS [20][21][22] were also used to study CO2 adsorbent/desorption, which can provide a quantitative understanding of CO2 uptake in the adsorption of dry CO2. However, it is hard to collect the individual concentrations of H2O and CO2 in the co-adsorption/desorption process because the response of TGA is a result of the overall weight gain or loss.…”

Solid Adsorbents for Low-Temperature CO2 Capture with Low-Energy Penalties Leading to More Effective Integrated Solutions for Power Generation and Industrial Processes

“…Even in the presence of H 2 O, the formation of carbamates is kinetically favored over bicarbonate although the latter is more stable. The co-existence of the two competing reactions as well as the potential mass transfer barriers from the surface to bulk amine groups suggests that the CO 2 adsorption by immobilized amines will depend at least partially on contact time (Vaidya and Kenig, 2007;Serna-Guerrero et al, 2008;Wang et al, 2009). …”

“…A number of papers on Class 2 adsorbents are contributed from Sayari's group based on a pore-expended MCM-41 support, by grafting either a monoamine silane or triamine silane, Frontiers in Energy Research | Carbon Capture, Storage, and Utilization the materials achieved CO 2 capacities of 9.9 and 12.3 wt. % at 0.15 and 1 bar (25°C), respectively (Serna-Guerrero et al, 2008, and the materials can be used in a variety of environments . Other mesoporous silicas that have been tested for the preparation of Class 2 adsorbents include SBA-12, SBA-15, MCM-41, MCM-22, MCM-36, ITQ-2, ITQ-6, and silica microspheres (Zelenak et al, 2008;Zukal et al, 2009;Belmabkhout et al, 2010;Serna-Guerrero et al, 2010;Yang et al, 2012).…”