Kinetic and Equilibrium Reactions of a New Heterocyclic Aqueous 4-Aminomethyltetrahydropyran (4-AMTHP) Absorbent for Post Combustion Carbon Dioxide (CO₂) Capture Processes

Abstract

Aqueous amine absorbent processes remain at the forefront of existing technologies for the removal of CO 2 from industrial and large-scale power generation flue gas streams. It is essential that improvements in amine-based absorbent technologies are made in order to reduce both capital and operational costs. Intimate understanding of the fundamental chemical behavior of new amine absorbent systems is an intelligent pathway toward higher efficiency amine-based CO 2 capture processes. Herein, we investigate and report for the first time the complete temperature-dependent kinetic and equilibrium behavior of a new heterocyclic amine 4-aminomethyltetrahydropyran (4-AMTHP), with CO 2 , in aqueous solutions. Stopped-flow spectrophotometry, 1 H NMR spectroscopy, and potentiometric titration measurements performed over the temperature range 25.0−45.0 °C and the corresponding rate constants for the reversible formation of the carbamic acid, together with equilibrium constants describing the stability of the carbamate, and the protonation of the amine are reported here. Thermodynamic analysis of the resulting constants using the Eyring, Arrhenius, and van't Hoff relationships has revealed the activation energies, enthalpies, and entropies for the reactions, allowing a comparison to the industrial standard monoethanolamine (MEA). From the kinetic data, the performance of 4-AMTHP was found to be superior to MEA and in line with the established Brønsted relationship between the second-order rate constant and the protonation constant or basicity of the amine. The largely negative protonation enthalpy (−47 kJ/mol), among the key chemical drivers for CO 2 regeneration, is again superior to MEA (−41 kJ/mol). Together, a combination of kinetic and equilibrium properties of 4-AMTHP strongly position 4-AMTHP as a promising candidate for more intensive evaluations as a CO 2 capture absorbent.

Recent Advances in the Chemistry of Metal Carbamates

“…[a] pK b values are from ref. [42,[52][53][54][55][56][57][58][59]62,63]. For a list of pK b see ref.…”

“…A collection of thermodynamic parameters concerning the carbonation of amines in water is compiled in Table 1 , including data from the most recent studies [ 42 , 52 , 53 , 54 , 55 , 56 , 57 , 58 ] and relevant to amino acids [ 59 , 60 , 61 , 62 , 63 ]. Additional data, including kinetic constants, are provided in Table S1 (Supplementary Information) .…”

Heterogeneous catalysts for the hydrogenation of amine/alkali hydroxide solvent captured CO2 to formate: A review

“…Therefore, the alkali-metal hydroxide-based solutions can then serve as promising CO 2 capturing and hydrogenation agent when formate salt is the targeted product. 63 Copyright (2017) Amercian Chemical Society.…”

“…[60][61][62] Aqueous amine solutions including primary, secondary, tertiary amines and ammonia were generally used as capturing solvents in PCC process. 23,[63][64][65][66] The reaction mechanism of CO 2 reacting with aqueous amine-based solutions is shown in Scheme 2.…”

“…When primary/secondary amine solutions are used for CO 2 absorption, a series of additional reactions occur, which have been shown in dashed lines in Scheme 2. 63 These reactions include reactions between amines and CO 2 to reversibly produce carbamic acid (RNHCO 2 H); spontaneous deprotonation of the RNHCO 2 H to form carbamate ion (RNHCO 2 -); the protonation reactions RNH 2 , and decomposition reaction of RNHCO 2 to reversibly form HCO 3 -. As a result, there are a few products including CO 3 2-, HCO 3 -, RNHCO 2 -, and RNHCO 2 H generated from CO 2 absorption into primary/secondary amine solutions.…”