Influence of Air-Gap Length on CO2 Stripping from Diethanolamine Solution and Water Performance of Surface Modified PVDF Hollow Fiber Membrane Contactor

Surface Modifying Macromolecule (SMM) blended PVDF hollow fibers (HFs) were spun at different air-gaps (o to 20 cm) and used for CO2 stripping from aqueous DEA solution and water. The manufactured fibers were first subjected to various characterization tests such as contact angle and critical water entry pressure measurement to evaluate the HF hydrophobicity and wetting resistance, respectively. The pure helium permeation experiments were also conducted to obtain membrane pore size and effective porosity. Morphology of the HFs was investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The SEM images showed that both outer and inner diameters of HFs decreased significantly by increasing air-gap length which mainly because of elongation of HF caused by gravity while traveling through the air–gap. Also, the gradual decrease in roughness on the external surface of the produced HFs was observed from the AFM images.  It was found that the increase of liquid velocity enhances the CO2 stripping flux. It was found that 10 cm air-gap gave maximum stripping flux of 3.34×10-2 and 1.34×10-3 (mol/m2 s) for DEA solution and water, respectively. The increase in gas velocity, on the other hand, did not affect the stripping flux significantly. It was observed that the increase of temperature from 25 to 80 oC led to marked enhancement of stripping flux from 6.30×10-3 to 3.34×10-2 (mol/m2 s) and 6.5×10-5 to 1.34×10-3 (mol/m2 s), for DEA solution and water, respectively. Furthermore, the increase in DEA concentration from 0.25 to 1 mol/L, led to enhancement of the stripping flux from 6.84×10-3 to 3.34×10-2 (mol/m2 s) at a liquid velocity of 0.7 m/s. It was concluded that the HF spun at 10 cm air-gap exhibited the best stripping performance among all fabricated HFs.