Daofan Ma,Chunying Zhu,Taotao Fu,Xigang Yuan,Youguang Ma
The gas-liquid two-phase flow and the mass transfer characteristics for CO 2 absorption into the binary amine mixture of monoethanolamine (MEA) and N,N-diethylethanolamine (DEEA) aqueous solution were investigated in T-junction microchannel reactor with a square cross-section. The effects of gas-liquid flow rate and absorbent concentration on bubble length, velocity and mass transfer coefficient were studied. Three flow regimes including slug-bubbly flow, slug flow and slug-annular flow were observed under experimental condition, and the gas-liquid two-phase flow pattern map was depicted. It is found that the transitions between three flow regimes depend primarily on the competition of forces exerted on bubble in the T-junction. The kinetics of CO 2 absorption into blended amine aqueous solutions was analyzed to understand the mass transfer enhancement mechanism of new hybrid solvent. Furthermore, the liquid-side overall mass transfer coefficient k L and the liquid-side overall volumetric mass transfer coefficient k L a were determined through processing experimental images recorded by a high-speed camera. The results show that k L a is in the range of (3.04–20.07) s −1 in this work, which is 2–3 orders of magnitude higher than that in the conventional equipment. The dimensionless Damköhler number ( Da ) and Peclet number ( Pe ) are introduced to correlate the liquid-side volumetric mass transfer coefficient, new correlation shows good prediction accuracy with the average deviation of 3.64%.
Longyun Zheng,Zhangyu Guo,Hui Liu,Kai Guo,Chunjiang Liu
CO 2 absorption into amine solutions is an important method for reducing carbon emissions. The influence mechanism of chemical reactions on the bubble behavior and mass transfer needs to be comprehensively investigated. In this study, firstly, we measure the bubble behavior and mass transfer of single CO 2 bubbles freely rising in monoethanolamine (MEA)/ N , N -diethylethanolamine (DEEA) blended solutions and DEEA solutions by high-speed photography. Moreover, we investigate the effect of amine concentration on the bubble shape, aspect ratio, rising trajectory, rising velocity, and mass transfer coefficient. The results show that CO 2 bubbles in MEA/DEEA blended solutions experience significant shape deformation, oscillation damping, surface contamination, and mass transfer deterioration. In contrast, CO 2 bubbles in DEEA solutions behave similarly to those in ultrapure water, i.e. negligible surface contamination and mass transfer enhancement. Furthermore, we consider the differences in the bubble behavior and mass transfer from the viewpoint of the chemical reaction kinetics and bubble surface contamination degree. The location where a chemical reaction occurs is close to the bubble surface with a fast reaction, and as a result, the bubble surface is likely to be contaminated. Finally, this study provides insights into the intensification of amine-based CO 2 chemical absorption processes.
The blending of primary amines, with fast reaction kinetic, together with tertiary amines, with a large loading capacity, is an increasingly popular approach to develop high-performance CO 2 capture sorbents with low energy requirements for regeneration. In this study, we investigated the CO 2 absorption performance of several aqueous solutions obtained by mixing ethanolamine (MEA) and diethylethanolamine (DEEA) and compared them with that of individual MEA and DEEA. CO 2 loadings at equilibrium were measured experimentally under a wide range of operating conditions, at temperatures between 298 and 323 K, CO 2 partial pressures in the range 5–60 kPa, and different amine mixing ratios. In addition, 13 C NMR spectroscopy was employed to elucidate the reaction mechanisms and identify the species formed during CO 2 capture. The results of the study reveal the intricate interplay of MEA and DEEA in CO 2 capture, where MEA carbamate formation predominates in the early stages, gradually shifting to bicarbonate formation as the amine concentration decreases. Moreover, excess properties, which reflect non-ideal behaviors in amine blends, were introduced as a key parameter in the study. An excess property model, based on excess CO 2 loading, was developed to accurately predict the CO 2 equilibrium solubility without constant experimental measurement. As a result, good agreement was found between the experimental data and those calculated with the model (excess CO 2 loading) under the same operating conditions, with a average relative deviation of 1.1%.
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