Separation of water from metal working emulsions by ultrafiltration using vibratory membranes

In this paper, we investigate the application of a vibratory shear-enhanced filtration system (VSEP) to separation of water from oil-in-water emulsions. The VSEP module consists in an annular membrane of 500 cm(2) area which oscillates azimuthally in its own plane with an amplitude depending upon frequency. Polyethersulfone (PES) membranes of 50 and 20 kDa were used. Test fluids consisted of oil-in-water emulsion at an oil concentration of 4% prepared from a concentrated cutting fluid. The critical flux for stable operation was investigated by increasing the permeate flux in steps while monitoring the transmembrane pressure (TMP). With a 50 kDa membrane the flux increased nonlinearly with TMP and reached 250 L h(-1) m(-2) at a TMP of 1500 kPa while permeate turbidity decayed from 1.8 to 0.9 NTU above 600 kPa from an initial emulsion turbidity of 21,900 NTU. With the 20 kDa membrane, the flux increased linearly with TMP until 1600 kPa, but the oil concentration in permeate became negligible (turbidity near zero NTU). Concentration tests showed that the flux decreased linearly with ln(VRR) where VRR is the volume reduction ratio while permeate turbidity increased exponentially to 25 NTU above a VRR of 4. This work confirms the high performance of the VSEP for oil separation from water in metal working emulsions. (C) 2010 Elsevier B.V. All rights reserved.