Nanoparticle filtration through microporous ECTFE membrane in an alcoholic solution

Organic solvent filtration is an important industrial process. It is widely used in pharmaceutical manufacturing, chemical processing industry, semiconductor industry, auto assembly etc. Most of the particle filtration studies reported in open literature dealt with aqueous suspension medium. The current work has initiated a study of cross-flow solvent filtration behavior of microporous ethylene chlorotrifluoroethylene (ECTFE) membranes using 12 nm silica nanoparticles suspended in an aqueous solution containing 25% ethanol. In the constant pressure mode of operation of cross-flow microfiltration (MF), permeate samples were collected at different time intervals. The permeate particle size distribution (PSD) results for different experiments were identical. Particle agglomerates having less than 100 nm size can pass through the membrane; some fouling was observed. The governing fouling mechanisms for tests operated using 3.8 × 10⁻³ kg/m³ (3.8 ppm) at 6.9 × 10³ Pag and 1.4 × 10⁴ Pag were pore blocking. For tests conducted using 3.8 × 10⁻³ kg/m³ (3.8 ppm) at 27.6 × 10³ Pag (4 psig) and 1.9 × 10⁻³ kg/m³ (1.9 ppm) at 6.9 × 10³, 13.8 × 10³ and 27.6 × 10³ Pag (1, 2 and 4 psig), the mechanism was membrane resistance control. Less particles got embedded in membrane pores in experiments operated using suspensions with lower or higher particle concentrations with a higher transmembrane pressure. This is in good agreement with the values of the shear rate in the pore flow and scanning electron microscope images of the membrane after MF. In the dead-end mode of operation of solvent filtration using methanol, ethanol and 2-propanol, the permeate flux behavior follows J_methanol > J_ethanol > J_2-propanol at all testing pressures. The values of permeance (kg/m²-s-Pa) determined from the slope of the linear plot of filtration flux vs. the applied pressure difference across the membrane, were 3.9 × 10⁻⁴, 2.3 × 10⁻⁴ and 3.0 × 10⁻⁵ for methanol, ethanol and 2-propanol, respectively. Further exploration was made on solvent sorption results reported earlier. The critical temperature of selected solvents shows a better correlation with solvent sorption rather than the solubility parameter.