Optimization of Blended Amines for CO2 Absorption in a Hollow-Fiber Membrane Contactor

Abstract

To understand and optimize CO2 absorption in binary amine systems, we experimentally and theoretically investigated CO2 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 CO2 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 CO2 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 CO2 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 CO2 absorption is characterized by a gradual transition from liquid side controlled to liquid–gas combined controlled as the concentration of PZ increases.