(508e) Molecular Origin of Robeson Limit in across-Membrane Transport

Trade-off between permeability and selectivity-the upper limit of gas separation across polymer membranes has been put forward by Robeson. However, this upper bound is subject to membrane materials and fluid types. Here, we report a brand new upper limit of binary fluid separations based on the molecular level which is independent of materials. Proceed from the Navier-Stokes equation, velocity profile in a cylinder tube is parabolic. We consider two extreme conditions : 1) To get the maximal selectivity, different fluids is supposed to be separated from each other, and the slip length should be as small as possible. 2) To get the maximal permeability, the slip length must be infinity, in other words, boundary velocity should be equal to the center velocity. These two conditions is contradictory with each other, but both of the permeability and selectivity can be represented as a function of slip length. By combing them together, finally we can get a function independent of membrane materials to calculate the separation limit.