Microfiltration of Synthetic Metalworking Fluids Using Aluminum Oxide Membranes

Metalworking fluids (MWFs) are used in manufacturing as coolants, lubricants,mand corrosion inhibitors. Growing MWF acquisition and disposal costs, together with concerns about microbiological health hazards and environmental impact have led to increased interest in MWF recycling, contaminant control, and alternative application strategies. Membrane filtration can remove microbes, particulate, and tramp oils that contaminate metalworking fluids and has the potential to reduce health risks and extend MWF life in the machine tool industry. However, poorly understood relationships between the compatibility of metalworking fluid ingredients, contaminants, membrane materials, and membrane pore-size distributions have precluded the widespread industrial application of the technology. This research assesses the mechanisms of productivity decline during the microfiltration of an uncontaminated synthetic MWF using aluminum oxide membranes. It is revealed that while the majority of synthetic MWF ingredients have a negligible impact on microfiltration productivity, specialty additives such as lubricants, defoamers, and biocides can significantly reduce productivity. This is due to adsorption of these ingredients to the membrane surface that serves to increase resistance to MWF flow through the membrane pores. MWF ingredient characteristics such as hydrophilic/hydrophobic content and electrostatic charge can influence adsorption and productivity-loss during microfiltration. These findings demonstrate that the chemistry and concentration of specialty additives are important to account for during the design of membrane filtration systems for MWF recycling.