Novel Separations by a Charged NF/UF Membrane


Separation characteristics of a novel, thin-layer composite (TLC®) membrane bearing an anionic surface charge are elucidated using three distinct approaches. These include solute challenges to demonstrate apparent molecular weight cut-off (MWCO), affinity chromatography to demonstrate surface force interactions between solute and membrane, and pilot scale operations using industrial process streams. The membrane shows unusual selectivity not predicted on the basis of physical pore size alone.

The membrane characterized in this work is a novel thin layer composite (TLC) using a unique polymer material for producing the permselective barrier layer. We refer to unique polymer as B-type resin, and membrane manufactured from the resin is referred to as B-type membrane. B-type resin features a formal negative surface charge which is responsible for unique separations characteristics of B-type membranes. Exact identity of B-type resin polymer and the process used for producing the B-type membrane are proprietary.


Solute Challenge Tests

Solute challenges were completed using a small laboratory test device known as a Sepa® CF cell. This device is unique among test cells--it is designed to model the fluid dynamics of commercial, spiral-wound membrane elements known as sepralators. Like the larger sepralators, the Sepa CF cell functions in a cross-flow or tangential flow mode.

Challenge solutions were pumped under pressure through a feed channel spacer and permeate was routed through a woven fabric spacer called the permeate carrier. Both these spacers are the same as those used in sepralators. The mesh feed spacer is designed to promote turbulence in the flow channel to reduce build-up of solute near the membrane surface.

For the present work, cell pressures of 3.5, 6.9 and 10.3 bar (50, 100 and 150 psig) were typically used, each in combination with average crossflow velocities of both 0.1 and 0.2 m/s. These operating conditions are typical of those used in actual industrial processes employing sepralators (1).

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