Speciation in Liquid‐Liquid Phase‐Separating Solutions of Aqueous Amines for Carbon Capture Applications by Raman Spectroscopy

Carbamate Formation in the System (2-Methylpiperidine + Carbon Dioxide) by Raman Spectroscopy and X-ray Diffraction

“…Due to the complexity of the system, any attempt to quantify the concentration of the carbamate species had an uncertainty an order of magnitude larger than its concentration. Indeed, it was for this reason that the band was not observed in our earlier scoping study . Therefore, we conclude that our Raman spectra reveal strong evidences of the stability of the carbamate species in aqueous solution but other techniques will be necessary to measure its concentration.…”

“…Indeed, it was for this reason that the band was not observed in our earlier scoping study. 14 Therefore, we conclude that our Raman spectra reveal strong evidences of the stability of the carbamate species in aqueous solution but other techniques will be necessary to measure its concentration.…”

“…The Raman results confirm that 2-methylpiperidine- N -carboxylate must be included as a species in chemical equilibrium models used to evaluate the suitability of aqueous and nonaqueous 2-MP solutions as carbon-capture solvents. The spectra provide a means of using Raman spectroscopy as a tool to quantify the distribution of species in the single-phase and two-phase (2-methylpiperidine + water + carbon dioxide) systems, as was proposed by Fandiño et al Care must be taken when using the vibrational spectrum of 2-methylpiperidine- N -carboxylate because an aqueous solution was used to obtain the fully protonated 2-MP Raman spectrum used in the calculation and the presence of water may shift the frequencies or slightly modify some vibrational bands. Recent NMR studies in our laboratory suggest that the contributions of the carbamate cation to overall amine speciation may be as high as 10% in 2-MP solutions under carbon-capture conditions.…”

“…The substituted methyl group on the α-carbon is thought to make the ammonium group sterically hindered so that the 2-methylpiperidine- N -carboxylate species (the carbamate species, 2-MPCOO – ) is unstable. In the absence of evidence to the contrary, 2-MPCOO – could not be included in the recent vapor–liquid equilibrium model to describe the dissolution of carbon dioxide in aqueous 2-methylpiperidine by Coulier et al Several theoretical and experimental attempts have been made to establish stability of 2-methylpiperidine- N -carboxylate in aqueous solutions, without success. ,, To date, the 2-MP carbamate ion has been observed in solutions of (2-MP + hexanol + CO 2 ) by Fourier infrared (FT-IR) spectroscopy. , The vibrational spectrum of the 2-methylpiperidine- N -carboxylate ion was not published. With the exception of a recent NMR study from our laboratory, there are no other reports of 2-MP carbamate ion in the literature.…”

“…In the absence of evidence to the contrary, 2-MPCOO − could not be included in the recent vapor−liquid equilibrium model to describe the dissolution of carbon dioxide in aqueous 2-methylpiperidine by Coulier et al 9 Several theoretical and experimental attempts have been made to establish stability of 2-methylpiperidine-N-carboxylate in aqueous solutions, without success. 1,14,15 To date, the 2-MP carbamate ion has been observed in solutions of (2-MP + hexanol + CO 2 ) by Fourier infrared (FT-IR) spectroscopy. 16,17 The vibrational spectrum of the 2-methylpiperidine-Ncarboxylate ion was not published.…”