Effect of hydrophobic modification on carbon dioxide absorption using porous alumina (Al2O3) hollow fiber membrane contactor

• Effect of hydrophobic modification on CO2 absorption using HFM contactors was studied.
• MEA was applied in hydrophobic-modified porous Al2O3 HFM contactors for CO2 capture.
• The hydrophobic coating layers could reduce gas permeation through the membrane pores.
• Control of hydrophobic coating time is needed to enhance the performance.

Porous alumina (Al2O3) hollow fiber membranes were successfully prepared using phase inversion spinning and sintering technique. Hydrophilic surface of porous Al2O3 hollow fiber membrane was modified with a fluoroalkylsilane (FAS) solution that was used as hydrophobic agent for treating the surface of Al2O3 hollow fiber membranes. The unmodified and modified porous Al2O3 membranes were characterized using scanning electron microscopy, mercury porosimetry, gas permeation testing equipment, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and the contact angle analyzer. The hydrophobicity of the porous Al2O3 hollow fiber membrane increased with increasing FAS coating time. The effect of the FAS coating on the CO2 absorption performance was also investigated. As a result, the CO2 absorption flux decreased with increasing FAS coating time. In particular, these experiments revealed that 2 h coating was sufficient to obtain an optimal hydrophobic protection against the wetting process of the Al2O3 hollow fiber membrane pores. In addition, the best performance for CO2 absorption flux was achieved with the Al2O3 hollow fiber membrane modified for 2 h coating. The maximum CO2 absorption flux of surface modified Al2O3 hollow fiber membrane was 6.022×10−3 mol/m2 s with a liquid flow rate of 50 ml/min at room temperature. Finally, a 50-hours-long stability test demonstrates that the modified porous Al2O3 hollow fiber membranes are stable and promising for membrane contactors.