The duomodule - Part 2: Separation ability and efficiency using aqueous solutions

The duomodule integrates two kinds of serially connected hollow fiber filte rs in a common module housing. The inner compartments of both filters are i nterlocked by a stable connection in which a throttle valve is integrated. The connected outer compartments of the filters are filled with an incompre ssible fluid. At a liquid flow in the inner compartment (primary circulatio n), a secondary circulation is generated due to a pressure drop between the filters. Filtration from the inner compartment to the outer compartments i s initiated in the first filter, whereas refiltration takes place in the co mmon outer compartment to the inner compartment in the second filter as a c onsequence of a transmembrane pressure reversal. In this paper, different d uomodule arrangements are used for the fractionation of an aqueous dextran solution mixture to detect the duomodule separation ability and efficiency and to optimize the module construction. The fractionation ability and effi ciency are related to the membrane characteristics. The results of the frac tionation experiments demonstrate the separation function of the equipment. In the refiltration step, the transport direction goes from the outer to t he inner membrane surface; therefore, an internal concentration polarizatio n in the membrane wall can change the permeability and the separation behav ior of the refiltration membrane. Accordingly, only symmetrically structure d membranes or outside active refiltration membranes realize a desirable hi gh fractionation ability and efficiency. (C)2000 Elsevier Science B.V. All rights reserved.