## Appendix A
### Pressure Drop Measurement  
Pressure drop in the experimental set ups was measured due to the influence that flooding may have in the CO\({}_{2}\) absorption and, therefore, the mass transfer. Figure 11 represents the variation of the pressure drop according to the air and liquid flow rates in the packed column. Two observations require attention. First, the higher the air/liquid flow rate, the higher the pressure drop. For a fixed gas flow rate value, it is observed that the distance between two consecutive points becomes larger when the liquid flow rate increases. Here, the pressure drop increment is due to the resistance offered by the liquid falling against the air flowing up. Meanwhile, liquid flow rates follow a linear trend, with an almost constant distance between consecutive points and a slow change in the slope. This is due to the liquid holdup and an additional resistance to the air flow. The stronger effect on the pressure drop comes, then, from the liquid flow and it can be seen with an easy example from the graph: a pressure drop of 10 mbar could be measured with an air/liquid flow of 170/1 L min\({}^{-1}\) but also with 50/5 L min\({}^{-1}\).  
Secondly, the pressure drop for the range studied does not mean relevant importance. The maximum air flow rate in the CO\({}_{2}\) capture experiments was 66 L min\({}^{-1}\), where the highest pressure drop found for this is 20 mbar, which corresponds to a liquid flow of 5 L min\({}^{-1}\). Even in the larger pressure drop value collected (24 mbar from air/liquid streams of 100/4 L min\({}^{-1}\)) is very far from atmospheric pressure (1013 mbar). Thus, the pressure drop was considered negligible in other calculations; i.e., volumetric rate of absorption of CO\({}_{2}\) and the mass transfer coefficient.  
Regarding the membrane contactor system, the flow capacity for both gas and liquid was lower than the column. The pressure drop was here evaluated in two different configurations based on the Figure 1b. A valve was placed before the inlet of the lumen side to ensure that the CO\({}_{2}\) sensor was not flooded by an excessive gas flow. This may suppose an unreliable CO\({}_{2}\) concentration measurement. The influence of the opened/closed valve in the pressure drop along the membrane contactor was then evaluated and plotted in Figure A2. It shows the evolution of the pressure drop for both configurations when the gas flow is increased. Differences are evident and a closed valve system shows pressure drops more than four times greater than the opened valve configuration for the range analyzed. This is the case of a gas flow of 20 L min, where the pressure drop is 100 and 24 mbar for the closed valve and the opened valve settings, respectively. These differences are clearly due to the release of gas by the opened valve finding the easiest way to escape but also because of the narrowing from the pipes connected to the contactor (less than 10 mm) to the hollow fibers (10,200 fibers with an internal diameter of 240 \(\upmu\)m). Although the fine gas fed to the rest of the experiments did not exceed 10 L min\({}^{-1}\), the pressure drop already represents 40 mbar, which is the double of the maximum value obtained for the worst case in the packed column. As occurred with calculations about the packed column, the pressure drop is negligible with regards to the atmospheric pressure. Nevertheless, the opened valve configuration may affect the species evolution and, therefore, the mass transfer coefficient. Thus the result so results require careful consideration.