¹³C NMR as a method species determination in CO₂ absorbent systems

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• 作者：Arlinda F. Ciftja ; Ardi Hartono ; Hallvard F. Svendsen ; ^{hallvard.svendsen@chemeng.ntnu.no}
• 关键词：CO2 capture ; 13C NMR parameters ; Relaxation time ; Amine ; Amino acid
• 刊名：International Journal of Greenhouse Gas Control
• 出版年：2013
• 出版时间：August, 2013
• 年：2013
• 卷：16
• 期：Complete
• 页码：224-232
• 全文大小：1701 K

文摘

This paper discusses the main parameters to be considered when using Nuclear Magnetic Resonance Spectroscopy for speciation in liquid phase CO₂ capture absorbents and how accurate measurements can be obtained. Liquid phase speciation is one of the most important experimental data for thermodynamic and kinetic modeling of absorption systems. A comprehensive standard method for liquid phase speciation in amine and amino acid-CO₂-H₂O systems by Nuclear Magnetic Resonance Spectroscopy is presented and validated against measurements on monoamine, diamine and amino acid systems. The CO₂ loadings calculated from NMR and titration methods are shown to be in good agreement with an AARD less than 1 % . The most important factor for a quantitative measurement with ¹³C NMR is delay time which is required to be ¡Ý5 times the relaxation time (T₁) and 300 numbers of scans. The relaxation times (T₁) of carbon nucleus of several amines commonly used in CO₂ capture, i.e. monoethanolamine (MEA), diethanolamine (DEA), ethylenediamine (EDA), 2-amino-2 methylpropan-1-ol (AMP), N-methyldiethanolamine (MDEA) and piperazine (PZ) as well as for loaded aqueous solutions of MEA-amino acids salt systems of Glycine, Taurine, l-Alanine, l-Serine, l-Proline and Sarcosine are determined and reported in the present work.

The relaxation time for the carbon nuclei of HCO₃^?/CO₃^2? in monoamine systems increases in this order: AMP (3.5 s) = DEA (3.5 s) < DEEA (8.0 s) < MDEA (9.3 s) < MEA (10.2 s). In diamine systems we have: PZ (4.6 s) < EDA (7.7 s). The same trend is also observed for carbon nuclei in carbamate formation of monoamine systems: AMP (4.2 s) < DEA (5.4 s) < MEA (9.7 s). Relaxation time for carbon nuclei in diamine dicarbamate formation systems is in this order: PZ (6.5 s) < EDA (6.9 s). The relaxation times for unloaded systems are not shown because the carbamate and carbonate/bicarbonate species are formed only in the loaded aqueous systems.