Absorption characteristics and kinetics of CO₂ capture into N-methyldiethanolamine aqueous solution catalyzed by the immobilized carbonic anhydrase

Carbonic anhydrase (CA) is the most effective CO2 hydratase catalyst, but the poor storage stability and repeatability of CA limit its development. Therefore, CA was immobilized on the epoxy magnetic composite microspheres to enhance the CO2 absorption into N-methyldiethanolamine (MDEA) aqueous solution in this work. In the presence of immobilized CA, the CO2 absorption rate of MDEA solution (10 wt%) (0.63 mmol·min−1) was greatly improved by almost 40%, and their reaction equilibrium time was shortened from 150 min to 90 min compared with that into MDEA solution. The results indicated that the absorption of CO2 into MDEA solution had been significantly enhanced by using CA. After the 7th reuse recycle, the activity of the immobilized CA was still closed to its initial value at 313.15 K. Moreover, enzyme catalytic kinetics of immobilized CA was investigated using the p-nitrophenyl acetate (p-NPA) as substrate. The values of Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of the immobilized CA were calculated to be 27.61 mmol/L and 20.14 × 10−3 mmol·min−1·mL−1, respectively. Besides, the kinetics of CO2 reaction into MDEA with or without CA were also compared. The results showed that CO2 absorption into CA/MDEA aqueous solution obeyed the pseudo first order regime and the second order kinetics rate constant (k2) was calculated to be 929 m3·kmol−1·s−1, which was twice higher than that of MDEA aqueous solution without immobilized CA (k2=414 m3·kmol−1·s−1) at 313.15 K.