Using ceramic membranes to recycle two nonionic alkaline metal-cleaning solutions

Abstract

One ZrO 2 ultrafilter (0.05 μm pore size) and two α-Al 2O 3 microfilters (0.2 and 0.8 μm) were used to remove one synthetic ester oil and two polyalphaolefin-based and two petroleum hydrocarbon-based oils and greases from two nonionic alkaline cleaning solutions (i.e., Turco ® 4215-NCLT and Daraclean ® 282). The removal was evaluated using a series of filtration runs on a bench-scale unit equipped with a tubular crossflow filtration element. The system was operated by closely controlling the permeate flux and the process parameters that influence flux, and by monitoring changes in pressure gradient across the membrane. Oil and grease, total alkalinity, and organic additives were measured in the feed, permeate, and retentate samples. The ZrO 2 ultrafilter completely removed the oils and greases, and its permeability could be restored up to 75% of the initial value. While allowing passage of almost all inorganic salts, the filter retained almost all surfactant additives. The α-Al 2O 3 microfilters became fouled progressively during filtration, and therefore, were not recommended for this application.