AUGMENTATION OF ABSORPTION AND DESORPTION RATES IN A HYDROPHOBIC MICROPOROUS HOLLOW FIBER CONTAINED CONTACTOR BY ADJUSTING OUTLET GAS PRESSURE

Abstract

The absorption of dilute CO 22 into aqueous solutions of sterically hindered 2-methyl aminoethanol (MAE) and the desorption of CO 22 from CO 22 loaded MAE solutions into N2 stream were investigated separately for the various combinations of operational variables, using a hydrophobic microporous hollow-fiber (polytetrafluoroethylene, PTFE) contained gas-liquid contactor (HFCC) with aqueous solutions of MAE as liquid media in the shell side at 30°C. The absorption of CO2 from the lumen side in this contactor is governed by the resistance in the liquid and hollow-fiber phases. The resistance to diffusion in the hollow-fiber phase (membrane resistance) amounted to 78–83% of the total resistance. Such a high membrane resistance was believed to be caused by some liquid penetration into the pores of hydrophobic microporous hollow fibers. Thus, the outlet gas pressure in the lumen side of the contactor was raised above an atmospheric pressure or adjusted at 0.1017 to 0.1019 MPa (i.e., 0.0004–0.0006 MPa over-pressure) so that the pore penetration of the aqueous solution might be suppressed. By such an adjustment of outlet total gas pressure, the total resistance and the membrane resistance were shown to be decreased on average to 28% and 12%, respectively. By adjusting the outlet total gas pressure, the total resistances to mass transfer during desorption of CO2 from aqueous CO2-loaded MAE solutions could also be decreased on average to about 21%. For the simultaneous absorption-desorption operation in a single unit, both absorption and desorption fluxes approached the respective constant values or the steady state was attained, as the process time had elapsed. Both absorption and desorption fluxes at the steady state were augmented by adjusting the outlet total gas pressure. In addition, both absorption and desorption processes approached the steady state faster by adjusting the outlet total gas pressure. At the constant flux periods, the absorption flux was about ten times higher than the desorption flux whether the outlet total gas pressure was adjusted or not. Because the desorption-part area here is designed as ten times the absorption-part area, the total absorption rate (= absorption flux × absorption-part area) is believed to be almost balanced with the total desorption rate (= desorption flux × desorption-part area) at the constant flux periods.