Mechanisms and Kinetics for Sorption of CO2 on Bicontinuous Mesoporous Silica Modified with n-Propylamine

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.authorCount :7</p

CO₂ Capture Using Fluorinated Hydrophobic Solvents

Finding more efficient gas–liquid scrubbing systems with lower parasitic energy penalties is important for the future deployment of carbon capture plants for large point source CO₂ emitters. Minimization of the energy penalty using advanced solvents is one way to reduce the energy penalty. Nonaqueous, hydrophobic solvents are one type of solvent in which the physical properties of the solvent combined with low heats of absorption and low loading at high temperature even with high CO₂ pressure result in promising solvents with low estimated reboiler heat duty. In this paper, a solvent composed of a hydrophobic amine (2-fluorophenethylamine) combined with an acidic, hydrophobic alcohol (octafluoropentanol) is studied mechanistically, and the experimentally determined reaction products, heats of absorption, and vapor liquid equilibria are reported. Approximating process models are compared and indicate the potential to lower reboiler heat duty in a commercial implementation