Membrane filtration for the Recycling of water-based synthetic metalworking fluids

Abstract

Ultrafiltration (UF) studies have been performed on solutions of components potentially useful for the formulation of synthetic, waterbased metalworking fluids. These demonstrated the applicability of the method for removal of dispersed particulate and leak oil contaminants from surfactant solutions, provided these are designed not to form large micelles or other aggregates. Inherent membrane performance data were established with a laboratory size UF-module and a fluoropolymer based material was selected for more extensive studies. Counter-ion influence on the flux and permeation ratio for a given straight chain carboxylic acid may be a result of influence on CMC (monomer concentration), solution and concentration polarized layer viscosity as well as micellar size. CMC-values for some carboxylate and phosphate ester salts were determined and correlations between monomer concentration and permeation ratios were demonstrated. The usefulness of ultrafiltration for the determination of CMC and monomer concentration was also shown. Experiments with a loosely emulsified mineral oil and a series of polyalkyleneglycol ethers indicate that concentration in permeate corresponds to component solubility in water, analogous with surfactant monomers. Three commercial synthetic water-based grinding fluids and one model fluid were evaluated for recycling using ultra- and microfiltration techniques. The system allows microbial control without the use of biocides in suitably formulated metalworking fluids. The important parameters in optimization of the membrane filtration process are suggested.