Novel membrane contactor for CO2 removal from flue gas by temperature swing absorption

Abstract

Conventional processes for CO2 scrubbing from flue gas in a contactor using aqueous monoethanolamine (MEA) solution followed by steam-stripping with an intermediate heat exchanger for heating up the CO2-loaded absorbent and cooling down the regenerated absorbent increase the cost of electricity enormously. To reduce the cost, the absorbent mass has to be substantially reduced and the temperature swing range limited considerably so that cheaper utilities (hot water) are used. Membrane contactors are compact and highly attractive for non-dispersive CO2 absorption; we propose here a novel hollow fiber membrane contactor that integrates absorption and stripping using a nonvolatile reactive absorbent (e.g., 80% polyamidoamine (PAMAM) dendrimer generation 0 and 20% of an ionic liquid (IL)). We have carried out proof-of-concept experiments via a cyclic process and a novel device containing two commingled sets of hollow fibers. Through the bore of one set of porous hydrophobic hollow fibers, flue gas is passed; CO2 diffuses to the shell side to get reactively absorbed in the stagnant PAMAM dendrimer-IL on the shell side. After there is CO2 breakthrough at the other end of the porous hollow fibers, feed gas flow is shut down. Through the bore of the second set of hollow fibers having a solid wall impervious to H2O and common gases under the conditions used, hot water is next supplied to heat the shell-side liquid absorbent and strip the absorbed CO2. After a short period, stripped CO2 is withdrawn through the bores of the first set of porous hollow fibers. We describe the performance of this temperature swing membrane absorption (TSMAB) process here with absorption at 50°C and stripping between 85 and 97°C. Equilibrium CO2 absorption in the nonvolatile viscous mixed absorbent is as high as 6.37mmolCO2/g absorbent in the presence of moisture at 50°C. The CO2 absorption and regeneration behavior of the integrated device has been studied for this absorbent at various absorption and regeneration temperatures and device design changes needed have been discussed.