(545v) Kinetics and Mass Transfer Performance of CO2 Absorption into DEEA/MAE Solution

Post-combustion carbon dioxide capture by amine scrubbing has been considered as one of the promising approaches for potential reduction of CO₂ emissions. However, amine based CO₂ absorption process encounters a considerable amount of energy requirement, which is significantly associated with the amine chemical structures and process configurations. Blended amine solutions with mixing carbamate formers (i.e. primary/secondary amines) as an activators and preferential bicarbonate producers (tertiary amines) possibly reduce the energy requirements for regeneration.

A tertiary amine, N,N-diethylethanolamine (DEEA), has received significant interest by various researchers and can be prepared from renewable and/or cheap resources. Blends of DEEA having characteristics of tertiary amine and absorption promoter is now intensively studied. For design and application of this CO₂ separation process the knowledge of vapor–liquid equilibrium data, CO₂ cyclic capacities and mass transfer performance of the DEEA blends system is required. The objective of the present work described here is to investigate the interaction between DEEA and secondary amine 2-(methylamino)ethanol (MAE). Then the reaction kinetics using stopped-flow technique, the optimal ratio of DEEA and MAE using a developed solvent screening method, and the mass transfer performance in a hollow fiber membrane contactor were studied in the present work. Furthermore, both the models for reaction rate constants and overall gas phase mass transfer coefficient were proposed and discussed in this work.

The hybrid behavior of CO₂ absorption into blended DEEA/MAE was investigated by evaluating the experimental data of equilibrium solubility of CO₂, CO₂ cyclic capacity, reaction kinetics and mass transfer performance. The height of absorber column is determined by the overall volumetric gas-phase mass transfer coefficient (K_Ga_v), which will be affected by the CO₂ cyclic capacity. Furthermore, the CO₂ cyclic capacity also can influence the energy requirement of solvent regeneration in turn affects the CO₂ capture cost. The different length of reaction time in the screening experiments was regarded as the various heights of the absorber and stripper, and the CO₂ cyclic capacities of different lengths of reaction time were calculated.

Based on the investigations in the present work, it can be concluded that:

(i) The CO₂ absorption kinetics of newly formulated DEEA/MAE was determined using stopped-flow apparatus. In addition, it was found that the reaction rate constant values can be predicted through the proposed mechanism and model with an acceptable AARD. By comparing with the individual amines, the new amine blends were found to have much faster reaction kinetics than that of DEEA, indicating an interaction between secondary and tertiary amines.

(ii) An improved rapid absorbent screening method was applied to investigate the CO₂ absorption rate, regeneration rate and CO₂ cyclic capacity. Experimental results reports that the introduction of the rate activator can significantly enhance the absorption rate compared with 2M DEEA solution, and the addition of DEEA into the amine blend can obviously improve the regeneration performance of the MAE solution, resulting in the highest CO₂ cyclic capacity.

(iii) Furthermore, the mass transfer performance in terms of CO₂ flux in a hollow fiber membrane contactor were studied to verify the accuracy of the improved rapid absorbent screening method. The values of CO₂ flux of 1.0M DEEA+1.0M MAE solution show more than two times higher than that of DEEA solution, and increase with the increasing liquid velocity and liquid feed temperature. These valuable results indicate an interaction effect are happened during the CO₂ absorption into the amine blends, leading to the potential CO₂ capture absorbent (i.e. DEEA/MAE).

References

[1] Fu, K., Rongwong, W., Liang, Z., Na, Y., Idem, R., Tontiwachwuthikul, P., 2015. Experimental analyses of mass transfer and heat transfer of post-combustion CO₂ absorption using hybrid solvent MEA–MeOH in an absorber. Chem. Eng. J. 260, 11-19.

[2] Rongwong, W., Cao, F., Liang, Z., Zhang, R., Idem, R., Tontiwachwuthikul, P., 2015. Investigation of the effects of operating parameters on the local mass transfer coefficient and membrane wetting in a membrane gas absorption process. J. Membrane Sci. 490, 236-246.