CO2 absorption in flat membrane microstructured contactors of different wettability using aqueous solution of NaOH

CO2 absorption in solutions of sodium hydroxide (NaOH) was performed in three membrane/mesh microstructured contactors: a single-channel PTFE membrane contactor, a nickel mesh contactor and an 8-channel PTFE membrane contactor. A membrane/mesh was used to achieve gas/liquid mass transfer without dispersion of one phase within the other. The PTFE membrane consisted of a pure PTFE layer 20 μm thick laminated onto a polypropylene layer of 80 μm thickness. The pure PTFE layer contained pores of ~ 0.5-5 μm diameter and was hydrophobic, while the polypropylene layer consisted of rectangular openings of 0.8 mm x 0.324 mm and was hydrophilic. The nickel mesh was 25 μm thick and contained pores of 25 μm diameter and was hydrophilic. Experiments were performed with a 2M NaOH solution and an inlet feed of 20% vol CO2/N2 gas mixture. Numerical simulations matched reasonably well the experimental data. CO2 removal efficiency increased by increasing NaOH concentration, gas residence time, as well as the exchange area between gas and liquid. Higher removal of CO2 was achieved when the polypropylene was in the gas side rather than the liquid side, due to lower mass transfer resistance of the gas phase. For the same reason, CO2 removal efficiency was higher for the 8-channel PTFE contactor compared to the nickel mesh contactor. Average CO2 flux was higher for the 8-channel contactor (8x10-3 mol/min.cm2 with PP on the gas side) compared to nickel mesh contactor (3x10-3 mol/min.cm2) for the same gas and liquid residence times. The 8-channel PTFE membrane contactor removed around 72% of CO2 in 1.2 s gas residence time, demonstrating the potential for CO2 absorption using flat membrane contactors.