NMR-Based Carbamate Decomposition Constants of Linear Primary Alkanolamines for CO₂ Capture

Abstract

The amine carbamate related equilibrium (RNHCOO − + H 2 O ⇆ RNH 2 + HCO 3 − ) has been investigated with 13 C NMR (Nuclear Magnetic Resonance) spectroscopy for a series of linear primary alkanolamines, and the apparent carbamate decomposition equilibrium constants have been estimated. A quantitative NMR method for the calculation of the concentration of the species formed in solution has been provided, including the assessment of each of the fast exchanging proton species (whose nuclei resonate at the same chemical shifts in the NMR spectra). For this purpose, NMR-based calibration curves were utilized and an alternative method was applied for validation. The overall results showed that the amount of carbamate found at the equilibrium decreased as the length of the carbon chain increased, while the corresponding apparent carbamate decomposition equilibrium constants featured the same order of magnitude (10 −2).

NMR Speciation of Aqueous MAPA, Tertiary Amines, and Their Blends in the Presence of CO2: Influence of pKa and Reaction Mechanisms

“…Usually, the carbons belonging to HCO3 -/CO3 2can span from about 161.1 ppm (100% HCO3 -) to about 168.7 (100% CO3 2-). 42 In this study, in the solutions after absorption, the carbon signal corresponding to HCO3 -/CO3 2resonated at a chemical shift value ranging from 160.9 to 162.6 ppm, suggesting that mainly bicarbonate was formed. In the solutions at equilibrium after heating at 80°C, the carbon signal corresponding to HCO3 -/CO3 2-, if present, was ranging from 161.0 to 166.9 ppm, meaning that in some cases the ratio HCO3 -/CO3 2was shifted toward the were more constant as all the protonation sites were involved in the covalent bond with CO2.…”

“…To obtain a reliable peak area, the 13 C NMR spectra were acquired with the inverse gated decoupling acquisition sequence, using a recycle delay time of 120 s and a pulse width of 11.4 μs (90° pulse angle). The method is described in detail in Perinu, et al 42 In the current study, the use of a 600 MHz instrument allowed to reduce the number of scans from 512 to 256. Deuterated water was used as "lock" solvent and was inside a coaxial insert, whereas Acetonitrile was chosen as internal reference standard.…”

Investigation mechanism of DEA as an activator on aqueous MEA solution for postcombustion CO2 capture

“…12,13 The basic chemical reactions in MEA-DEA-CO 2 -H 2 O system are listed as follows 12,13 The basic chemical reactions in MEA-DEA-CO 2 -H 2 O system are listed as follows …”

“…The chemical reactions of CO 2 with primary amine (MEA) and secondary amine (DEA) could be described using the zwitterion mechanisms as shown in the literatures. 12,13 The basic chemical reactions in MEA-DEA-CO 2 -H 2 O system are listed as follows…”

Aqueous MAPA, DEEA, and Their Blend as CO2 Absorbents: Interrelationship between NMR Speciation, pH, and Heat of Absorption Data

“…The chemical shifts (expressed in ppm) depend on their ratio and, in the case of HCO3and CO3 2-, they can span from about 161.1 ppm for 100% HCO3to about 168.7 ppm for 100% CO3 2-. In this study, an estimation of the HCO3and CO3 2content was performed by applying the method developed by Perinu et al 39 To verify the reliability of the NMR data, the CO2 loadings as measured by NMR and by titration-precipitation method were compared ( Figure 3). The measurements obtained by both methods were fitting quite well, except for one point in a loaded solution of MAPA 1M.…”