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

Abstract

The CO 2 −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 CO 2 concentration in the feed should be high enough to achieve saturation via chemisorption, but low enough to avoid any additional physisorption, e.g., 5% CO 2 in N 2; (iii) the use of a reliable method for the accurate measurement of CO 2 /N ratio. Under such conditions, the obtained CO 2 /N ratios were reminiscent of those obtained in the CO 2 scrubbing process using ethanolamine solutions. Under dry conditions, the CO 2 /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, CO 2 /N ratio increased from 0.57 to 0.88, in line with the gradual formation of bicarbonate. As for the determination of CO 2 /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 CO 2 uptake. The seemingly disparate CO 2 /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.