Sterilizing-grade membrane filters are formatted in a wide variety of pleat configurations. High-density pleat geometries provide increased productivity per device, a smaller filter footprint, and improved filtration economics. However, a high-density pleat arrangement can present unique challenges when scaling up from discs to cartridges.

An M-pleat pattern, as used in the Millipore Express® SHC and Millipore Express® SHR with Prefilter (SHRP) sterilizing-grade filters, was demonstrated to provide up to 100% more membrane area than a conventional pleat pattern. High-area filters were found be most advantageous for mid- to high-plugging streams in which the membrane is the dominant resistance to flow, so that the scalability from discs to devices is essentially linear.

There is a potential exception to the high-area advantage in plugging streams: when caking is the primary fouling mechanism, the particles may not be able to access the full surface area of the membrane. In this case, prefiltration should be considered. For non-plugging streams, a looser, conventional-pleat pattern may be preferred because, with this pattern, non-membrane flow resistances are minimized.

A model was developed to predict device productivity efficiency as a function of the filtration properties of the filtered stream. This model can be used to assess  which applications can most benefit from high-area pleated devices and which applications should use conventional pleat configurations.

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