PREPARATION AND PROPERTIES OF FLAT-SHEET MEMBRANES FROM POLY(VINYLIDENE FLUORIDE) FOR MEMBRANE DISTILLATION

The flat-sheet membranes from poly(vinylidene fluoride) were prepared by the phase inversion process. The effects of the casting solution co mposition, exposure time prior to coagulation and temperature of the c oagulation bath on properties of prepared membranes were investigated. LiCl was used as a modifying agent. The membrane structure was studie d by scanning electron microscopy. For all prepared membranes an asymm etric structure, sometimes without a dense skin layer, was observed. T he porosity of prepared membranes before the drying process varied fro m 72-88%. After drying the membranes become hydrophobic. A contact ang le of water droplet on the membrane surface was 107 degrees. The nitro gen permeability varied from 12-2,205 m(3)/m(2) d, depending on the pr eparation conditions. The maximum pore size, LEP(W) and mechanical pro perties were also determined. The membrane distillation process of 1-2 % aqueous NaCl solution was applied as a final test of membrane perfor mance. The permeate flux up to 233 dm(3)/m(2) d was achieved at the te mperature of the feed and permeate of 333 K and 293 K, respectively. A chloride elimination in the permeate higher than 99% was reached.