Kinetic Studies on Catalyst-Aided Absorption and Desorption in a Bench-Scale Post-Combustion CO2 Capture Pilot Plant Using a Novel Solvent Blend
Afari, Daniel Boafo
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A total of seven solid base/alkaline catalysts comprising BaCO3, CaCO3, Ca(OH)2, Cs2O/α-Al2O3, Cs2O/γ-Al2O3, K/MgO and Hydrotalcite were screened on a semi-batch scale to select the most suitable for CO2 absorption into a novel aqueous solvent, BEA/AMP. The selected catalyst was incorporated into the absorber section of a benchscale pilot plant and its kinetic performance was evaluated. Intrinsic kinetic data were extracted and kinetic parameters were determined. Both cases of reversible and irreversible reactions of CO2 with the aqueous BEA/AMP solvent were analysed. An activation energy, Ea of 5.67E+04 J/mol and 3.40E+04 J/mol were obtained for the reversible and irreversible cases respectively. A reaction order of 2 with respect to CO2 for the irreversible case shows a higher dependency of the reaction rate on CO2 with the introduction of a heterogeneous catalyst and is a further indication of the complexity of the reaction as a third phase (solid) is introduced. A parity plot showing the degree of correlation between the experimental and predicted rate gave an AAD of 14.1%. Also, the performance of the novel solvent was compared with conventional Monoethanolamine (MEA) and blended Monoethanolamine (MEA)/n-Methyldiethanolamine (MDEA) in the presence and absence of a solid acid catalyst (HZSM-5). The results showed that the novel solvent (4M BEA-AMP) outperformed conventional 5M MEA and the 7M MEA-MDEA blend despite its lower molarity. For the novel solvent, Parametric Sensitivity Analysis (PSA) was conducted to investigate the impact of each independent process parameter on the CO2 conversion. It was observed that the most influential parameter was the absorber catalyst composition, followed by the gas flowrate and lean amine loading. The least influential was seen to be the desorber catalyst composition. Preliminary economic ii analysis showed that the novel solvent, BEA-AMP recorded the least annual operating cost when compared with conventional MEA and MEA-MDEA solvents. A separate analysis on the BEA-AMP system revealed that the introduction of absorber catalyst resulted in lowering the operating costs by about 40% using the base case of no absorber catalyst as reference. Employing catalysts in Post-combustion capture helps in truncating the associated operating costs and greatly contributes to making it a long term viable technology.