Characterization of PVDF Hollow Fiber Membrane for CO2 Stripping by Atomic Force Microscopy Analysis

Microporous polyvinylidene fluoride (PVDF) membranes with various concentrations of lithium chloride additives were prepared for CO2 stripping test. Physical membrane characterizations such as atomic force microscopy analysis, gas permeation, contact angle measurement and liquid entry pressure were also conducted. Correlations among the membrane properties, i.e. contact angle, gas permeation, mean pore size, nodule aggregates and surface roughness obtained from experimental analysis were discussed. The overall trend showed that increasing lithium chloride concentration has decreased the mean pore size, mean nodule aggregates and mean surface roughness of the membrane. On the contrary, the membrane liquid entry pressure has been significantly improved. It was found that the mean pore size determined by tapping mode atomic force microscopy (TM-AFM) is 2.3 to 2.7 times larger than that of obtained from gas permeation test. The decreases in nodule size, mean pore size and low surface roughness have contributed to the enhancement of CO2 stripping performance in membrane contactor system. Increasing LiCl concentration has increased the CO2 stripping flux and membrane mass transfer coefficient. However, the concentration of LiCl showed minimal effect on the liquid side mass transfer coefficient

Characterization of polyethersulfone-polyimide hollow fiber membranes by atomic force microscopy and contact angle goniometery

Asymmetric blend polyethersulfone-polyimide (PES-PI) hollow fiber membranes prepared at different air gap and used for gas separation are characterized by atomic force microscopy (inside and out side surfaces) and by measuring the contact angle of out side surface. The outer surface was entirely different than the inner surface, as expected. On the inner surface nodule aggregates were aligned in rows, may be towards the direction of the bore fluid flow. On the outer surface, alignment of nodular aggregates in one direction was not observed. The average mean roughness parameter of the inner surface increased with the increase in the air gap used for the preparation of hollow fiber. On the other hand, it was opposite for the outer surface. From the gas separation experiments it was observed that gas permeation rate increased with the increase in air-gap. An attempt was made to find relationships between the surface morphology observed by AFM and permeability and selectivity of the studied hollow fiber membranes.\ud \ud From the contact angle measurement it was observed that the contact angle is directly related to the outside surface roughness. A plausible mechanism has been discussed

Production of drinking water from saline water by air-gap membrane distillation using polyvinylidene fluoride nanofiber membrane

10.1016/j.memsci.2007.12.026Journal of Membrane Science3111-21-6JMES

Control of Membrane Surface Roughness and Pattern Wave Length by Changing the Nonsolvent (Water) Influx Rate

The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process