Study of series resistances in high-shear rotary ultrafiltration

A parametric waste-specific study was conducted to determine the relationship between permeate flux, transmembrane pressure, membrane rotational speed, and feed concentration in the high-shear rotary ultrafiltration (HSRUF) of a synthetic metal working (MW) fluid. The interactions between permeate flux and operating parameters were described using the resistance-in-series (RIS) approach to flux modeling. Eighteen discrete experiments were conducted at constant MW fluid concentration/membrane rotational speed combinations at applied pressures ranging from 103 to 517 kPa (15 to 75 psig). The fouling layer resistance, Rf, was only 12% of the total membrane resistance, Rm′, and it was determined that Rf and Rm′ were independent of feed concentration and membrane rotational speed. The polarization layer resistance, Rp, was the predominant rate controlling resistance in the HSRUF of the synthetic MW fluid; however, membrane rotation induced hydraulic turbulence was effective in minimizing Rp by reducing the accumulation of solute molecules on the membrane surface. An explicit form of the resistance index, Φ, was postulated based upon observations of interactions between Φ, feed MW fluid concentration, and membrane rotational speed. The RIS model was then modified with a specific form of Φ to further describe the specific interactions between flux and operating parameters. The modified model adequately predicted flux–pressure data over the range of experimental variables examined in this study. Additionally, a set-point operating pressure was determined as a function of membrane rotational speed and feed oil concentration such that the resistances Rm′ and Rp were minimized.