| Summary: | The absorption efficiencies of CO<sub>2</sub> in ceramic hollow-fiber membrane contactors using monoethanolamine (MEA) absorbent under both cocurrent- and countercurrent-flow operations were investigated theoretically and experimentally; various MEA absorbent flow rates, CO<sub>2</sub> feed flow rates, and inlet CO<sub>2</sub> concentrations were used as parameters. Theoretical predictions of the CO<sub>2</sub> absorption flux were analyzed by developing the mathematical formulations based on Happel’s free surface model in terms of mass transfer resistances in series. The experiments of the CO<sub>2</sub> absorption were conducted by using alumina (Al<sub>2</sub>O<sub>3</sub>) hollow-fiber membranes to confirm the accuracy of the theoretical predictions. The simplified expression of the Sherwood number was formulated to calculate the mass transfer coefficient of the CO<sub>2</sub> absorption incorporating experimental data. The data were obtained numerically using the fourth-order Runge–Kutta method to predict the concentration distribution and absorption rate enhancement under various fiber packing configurations accomplished by the CO<sub>2</sub>/N<sub>2</sub> stream passing through the fiber cells. The operations of the hollow-fiber membrane contactor encapsulating <i>N</i> = 7 fiber cells and <i>N</i> = 19 fiber cells of different packing densities were fabricated in this work to examine the device performance. The accuracy derivation between experimental results and theoretical predictions for cocurrent- and countercurrent-flow operations were <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>1.31</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mo>≤</mo><mi>E</mi><mo>≤</mo><mn>4.35</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>3.90</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo>≤</mo><mi>E</mi><mo>≤</mo><mn>2.43</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></semantics></math></inline-formula>, respectively. A maximum of 965.5% CO<sub>2</sub> absorption rate enhancement was found in the module with embedding multiple fiber cells compared with that in the device with inserting single-fiber cell. Implementing more fiber cells offers an inexpensive method of improving the absorption efficiency, and thus the operations of the ceramic hollow-fiber membrane contactor with implementing more fiber cells propose a low-priced design to improve the absorption rate enhancement. The higher overall CO<sub>2</sub> absorption rate was achieved in countercurrent-flow operations than that in cocurrent-flow operations.
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