Optimization of Blended Amines for CO 2 Absorption in a Hollow-Fiber Membrane Contactor

To understand and optimize CO 2 absorption in binary amine systems, we experimentally and theoretically investigated CO 2 absorption using typical amines and blended amines in a polypropylene hollow-fiber membrane contactor. The amines studied were monoethanolamine (MEA), diethanolamine (DEA), and N -methyldiethanolamine (MDEA), and their aqueous blends of MEA/MDEA, DEA/2-amino-2-methyl-1-propanol (AMP), and MDEA/piperazine (PZ). The predicted results, including overall mass transfer coefficients and CO 2 removal ratio, agreed very well with those determined experimentally. For single amines, the optimal concentration was around 30 wt % for MEA and 20 wt % for DEA. MDEA concentration had little effect on the overall mass transfer coefficient. We optimized the formulation of blended amines using theoretical analysis. The optimal compositions in MEA/MDEA, DEA/AMP, and MDEA/PZ systems were respectively 30 wt % MEA, with MDEA in proportions from 0.1 to 0.3; 15 wt % DEA, with AMP in proportions from 0.5 to 0.8; and 20 wt % MDEA, with PZ in a proportion of 0.3. To further understand the CO 2 membrane absorption process, we also analyzed individual mass transfer resistances as a function of additive concentration in blended amines and the effects of liquid velocity on the overall mass transfer coefficient. This shows that CO 2 absorption is controlled by the liquid side for DEA/AMP blends and by combined liquid–gas phases for MEA/MDEA blends. For MDEA/PZ blends, control of CO 2 absorption is characterized by a gradual transition from liquid side controlled to liquid–gas combined controlled as the concentration of PZ increases.