The effects of intermittent permeate flow and crossflow on membrane coalescence of oil-in-water emulsions

Membrane coalescence is a chemical-free technique for breaking stable oil-in-water emulsions. In this work the effect of oil droplet residence time within the membrane porous matrix was investigated and a novel process is proposed based on intermittent permeate flow (flow or no flow) at 0.01 Hz. Polytetrafluoroethylene membranes with 0.45 and 1.20 mum nominal average pore size were used to coalesce emulsions with an average 1.5 mum droplet diameter. Experiments were carried out in a crossflow filtration cell and crossflow velocities were varied from 0.07 to 0.28 ms(-1). Fluxes were found to increase with crossflow although oil rejection was zero, implying no concentration polarization. Results also demonstrated an improvement in coalescence performance during intermittent operation at low crossflow velocities. Under some conditions intermittent permeate flow operation produced higher permeate fluxes than without intermittent operation and is a potential novel process for membrane coalescence.