Insights into amine-based CO2 capture: an ab initio self-consistent reaction field investigation

Abstract

Ab initio many-body perturbation theory (MP2/ 6-311??G(,dp)), density functional theory (B3LYP/6-31??G(d,p)) and self-consistent reaction field (IEF-PCM UA HF/6-31G(d)) calculations have been used to study the CO 2 capture reagents NH 3 , 2-hydroxyethylamine (MEA), diaminoethane (EN), 2-amino-1-propanol (2A1P), diethanolamine (DEA), N-methyl-2-hydroxyethylamine (N-methylMEA), 2-amino-2-methyl-1-propanol (AMP), trishydroxymethylaminomethane (tris), piperazine (PZ) and piperidine (PD). This study involved full conformational searches of the capture amines in their native and protonated forms, and their carbamic acid and carbamate derivatives. Using this data, we were able to compute Boltzmann-averaged thermodynamic values for the amines, carbamates and carbamic acid derivatives, as well as equilibrium constants for a series of 'universal' aqueous capture reactions. Important findings include (i) relative pK a values for the carbamic acid derivatives are a useful measure of carbamate stability, due to a particular chemical resonance which is also manifest in short computed N-CO 2 H bonds at both levels of theory, (ii) the computational results for sterically hindered amines such as AMP and tris are consistent with these species forming carbamates which readily hydrolyse and (iii) the amine-catalysed reaction between OH -and CO 2 to generate bicarbonate correlates with amine pK a . Thermodynamic data from the ab initio computations predicts that the heterocycles PD and PZ and the acyclic sorbent EN are good choices for a capture solvent. AMP and tris perform poorly in comparison.

CO 2 absorption mechanism in amine solvents and enhancement of CO 2 capture capability in blended amine solvent

“…1.3Å) lengths. Moreover, the O C O angles changed to about 120 • and C N· · ·C O(OH) part became planar, which was similar with the structure of carbamic acid (H 2 NCO 2 H) (Jackson et al, 2011;Khanna and Moore, 1999). In the change from RC to PC, decrease of the N· · ·C distance and proton movement from the amino group to other part seem to be main energy barrier process.…”

“…In our calculation, the activation energy of [MEA-MEA] was the best fit to the experiment, which is supporting the additional amine process, [amine-additional amine], as the reaction mechanism. However, most theoretical studies described the reaction of CO 2 and amines by [MEA] and [MEA-W] (da Silva and Svendsen, 2007;Hussain et al, 2011;Jackson et al, 2011;Kim et al, 2013) or added additional amine after zwitterion formation (DavranCandan, 2014;Matsuzaki et al, 2013;Xie et al, 2010Xie et al, , 2014Yamada et al, 2011). There were few results on the pathway applying additional amine from the beginning of reaction (Arstad et al, 2007;Han et al, 2011;Jamróz et al, 1997).…”

“…However, the hydroxyl part of MEA was less efficient as a reactant or as a catalyst than the amino group. Second, amine molecules can have many conformational isomers (Jackson et al, 2011). Actually there are too many isomers; it is hard to check all isomers.…”

Ammonium Carbamate Functionalization of Microgels for pH‐Sensitive Loading and Release of Anionic and Cationic Molecules

“…However, the ζ ‐potential of PEG particles still decreased by nearly 30 mV and remained stable over days. The basic, primary amines of PAMAM dendrimer are protonated at pH below 6.9 and neutral above, while the acidic carbamates are deprotonated at pH above 7 and neutral below . Therefore, PEG‐ammonium carbamate particles should be able to switch their charge from cationic to anionic around pH 7 (Scheme b).…”

Interplay of thermochemistry and Structural Chemistry, the Journal (volume 22, 2011, issues 1–3) and the discipline

“…We recall the enthalpy of formation of 2-furfural has long been known but that of its 3-isomer recently reported [142], and also a recent calorimetric study of 2-and 3-acetylthiophene [143]. NH 3 , 2-hydroxyethylamine (MEA), 1,2-diaminoethane (EN), 2-amino-1-propanol (2A1P), diethanolamine (DEA), N-methyl-2-hydroxyethylamine (N-methylMEA), 2-amino-2-methyl-1-propanol (AMP), trishydroxymethylaminomethane (tris), piperazine (PZ), and piperidine (PD) have been studied as CO 2 capture reagents using DFT by Jackson et al [144]. These compounds could be used for eventual reduction of anthropogenic CO 2 emissions.…”