Development of energy-saving spinning membrane systemand negatively charged ultrafiltration membranes for recovering oil from waste machine cutting fluid

Membranes with hydrophobic surfaces have higher tendency for protein adsorption and bacteria attachment.As a result, these membranes foul rapidly in cross-flow filtration processes. Changing the membrane surface properties can slow down the membrane fouling process. For difficult membrane separation processes like oilwater emulsion separation, changing membrane properties alone cannot slow down the membrane fouling process. The ordinary cross-flow filtration system cannot be successfully employed for this kind of separation, and the spinning membrane disc system could be considered. The conventional spinning membrane disc system however is not energy efficient due to the centrifugal force acting against the permeate flow; this reduces the effective filtration pressure during the separation operation. Efforts were undertaken to develop a group of negatively charged ultrafiltration membranes, prepared from polyacrylonitrile-vinyl acetate-sodium p-sulfophenyl methallyl ether (CP-24) with polyacrylonitrile-vinyl acetate (CP-16), to be used in an energy-saving design of spinning membrane disc separation system. Our experimental results clearly demonstrate the energy saving benefit of our design; at filtration pressure of 276 kPa and at membrane disc spinning velocity of 1,000 rpm without sacrificing the oil rejection (>98% for 1,000 ppm oil-in-water) by our membrane, the permeate velocity was increased as high as 132% by our energy-saving system over conventional spinning membrane disc separation system.