Membrane with integrated spacer

Many membrane processes are severely influenced by concentration polarisation. Turbulence promoting spacers placed in between the membranes can reduce the diffusional resistance of concentration polarisation by inducing additional mixing. Electrodialysis (ED) used for desalination suffers from concentration polarisation in particular. Using spacers there leads to higher cell resistance, and therefore to higher power consumption, because of the induction of the spacer shadow effect: ions do not migrate in areas where the spacer is located. The use of ion-conductive spacers can reduce this spacer shadow effect, however the spacers are still rather thick and the cell resistance stays high. This work tries to overcome the disadvantages of thick spacers while keeping the beneficial effect of turbulence promotion. We present the preparation and characterisation of a novel cation exchange membrane where the spacer is formed directly on the membrane surface and is hence integral part of the membrane. This membrane with integrated spacer is formed by surface patterning of a drying polymer solution in contact with a regular membrane spacer where capillary forces pull the solution towards the spacer strands where they solidify. Peeling of the original spacer leaves the membrane with the spacer topology integrated in its surface. Characterisation of this novel membrane in an ED process improves process hydrodynamics while avoiding the resistance increase corresponding to the shadow effect of a non-conductive spacer. Having a spacer directly on the membrane surface has also the advantage of a much simpler membrane module assembly since the spacer becomes superfluous.