Effect of pore location and pore size of the support membrane on the permeance of composite membranes

Composite membranes typically consist of a nonporous layer on top of a porous support. The porous support restricts diffusion in the top layer because molecules can exit the layer only where a pore is present and this reduces the permeance of the membrane. Previously, we have used computational fluid dynamics (CFD) to simulate this geometric restriction for supports with uniform pore configurations and an empirical correlation was developed that accurately quantifies the reduction in permeance. In this work we present permeance data of composite membranes with top layers of different thicknesses coated on a support prepared by the common phase inversion process. The permeances are lower than predicted by the correlation because the support is not uniform in pore location and pore size. CFD modeling with non-uniform surface structures confirms that non-uniformity reduces the permeance. This effect can be incorporated into the empirical correlation through a uniformity coefficient. This coefficient is smaller than one for non-uniform surfaces and can be considered independent of the thickness of the top layer.