The development of kinetics model for CO2 absorption into tertiary amines containing carbonic anhydrase

CO₂ absorption into aqueous solutions of two tertiary alkanolamines, namely, MDEA and DMEA with and without carbonic anhydrase (CA) was investigated with the use of the stopped‐flow technique at temperatures in the range of 293–313 K, CA concentration varying from 0 to 100 g/m³ in aqueous MDEA solution with the amine concentration ranging from 0.1 to 0.5 kmol/m³, and CA concentration varying from 0 to 40 g/m³ in aqueous DMEA solution with the amine concentration ranging from 0.05 to 0.25 kmol/m³. The results show that the pseudofirst‐order reaction rate (k_{0, amine}; s^?1) is significantly enhanced in the presence of CA as compared with that without CA. The enhanced values of the kinetic constant in the presence of CA has been calculated and a new kinetics model for reaction of CO₂ absorption into aqueous tertiary alkanolamine solutions catalyzed by CA has been established and used to make comparisons of experimental and calculated pseudo first‐order reaction rate constant (k_{0, with CA}) in CO₂‐MDEA‐H₂O and CO₂‐DMEA‐H₂O solutions. The AADs were 15.21 and 15.17%, respectively. The effect of pKa on the CA activities has also been studied by comparison of CA activities in different tertiary amine solutions, namely, TEA, MDEA, DMEA, and DEEA. The pKa trend for amines were: DEEA > DMEA > MDEA > TEA. In contrast, the catalyst enhancement in amines was in the order: TEA> MDEA> DMEA> DEEA. Therefore, it can be seen that the catalyst enhancement in the amines decreased with their increasing pKa values. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Mathematical modelling of mass-transfer and hydrodynamics in CO2 absorbers packed with structured packings

This paper presents a mechanistic model that can predict mass-transfer performance and provide an insight into dynamic behavior within structured packings used for CO₂ absorption. The model was built upon the kinetics and thermodynamics of the absorption system, as well as the liquid irrigation features and the geometry of packing elements. A computer program (Fortran 90) was written to simulate CO₂ absorption into aqueous solutions of sodium hydroxide (NaOH) and monoethanolamine (MEA) in a column packed with Gempak 4A, Mellapak 500Y and Mellapak 500X. The simulation gave essential information, including the concentration of CO₂ in gas-phase, concentration of reactive species in the liquid-phase, system temperature, mass-transfer coefficients (k_G and k_L), and effective interfacial area (a_e) for mass-transfer at different axial positions along the absorption column. The simulation also provided liquid distribution plots representing the quality of liquid distribution or maldistribution across the cross-section of the column. Verification of the model was achieved by comparing simulation results with experimental data. Very good agreement was found for wide ranges of operating and design parameters, including liquid load and initial liquid distribution pattern.