Membrane filtration for preferential removal of emulsified oil from water

Abstract

The feasibility of using selective oil filtration (SOF) with microporous hollow fiber membranes for the separation and recovery of oil from spent cutting fluids was investigated. Two samples of water-based soluble cutting fluids made from petroleum products were tested. Characterization of the fluids was complicated due to proprietary information on the product and different use patterns. In general the fluids were found to be alkaline and comparable to mineral rich water. Emulsion stability was relatively high over the pH range tested. Preliminary tests showed the unit functioned primarily as an ultrafiltration (UF) unit due to wetting of the membranes by the high concentrations of emulsifying agents. To encourage SOF the cutting fluids were concentrated by UF by removing 80% of the water. Permeate collected during SOF of the concentrate contained an unstable “creamy” oil phase in the permeate which phase separated within 12 hours. The volume of the oil phase increased with decreasing pH. Results obtained suggest that separation is feasible if the conditions of operation are optimized. However, additional studies are needed to understand several of the factors that affect the performance of the process such as emulsion stability, concentration, membrane characteristics, module design and operation etc.