Scaling from discs to pleated devices

Membrane discs offer a convenient format for evaluating membrane performance in normal flow filtration. However, while pleated devices of different sizes tend to scale in close proportion to their contained areas, they do not necessarily scale in direct proportion from flat discs. The objectives of this study are to quantify differences in performance among sterilizing-grade membrane devices as a function of device type and size, to develop an understanding of the factors that affect device scalability, and to develop a mathematical model to predict a cartridge-to-disc scalability factor based on membrane properties and porous support properties and dimensions. Measured and predicted normalized water permeability scalability factors for seven types of pleated cartridges, including 0.1-micro and 0.2-micro rated PES, and 0.2-micro rated polyvinylidene fluoride (PVDF) sterilizing-grade filters in nominal 1-inch to 5-inch lengths, were determined. The results of this study indicate that pleated cartridge performance can be closely predicted based on 47-mm disc performance provided that a number of measured device parameters are properly accounted for, most importantly parasitic pressure losses in the filter device and plumbing connections, intrinsic membrane variability, true effective device filtration area, and the hydraulic properties of all porous support materials. Throughput scalability factors (discs to devices) tend to converge towards unity, especially for highly plugging streams. As the membrane fouls, the resistance through the membrane dominates other resistances, so the flux scales more linearly with membrane area and the overall scaling factor becomes close to one. The results of throughput tests on seven different cartridge types and five different challenge streams (with widely varying fouling characteristics) show that most of the throughput scaling factors were within +/-10% of 1.0. As part of this study, the effects of pressure and temperature were also evaluated. Neither of these factors was found to have a significant effect on scalability.