Effect of porous supports on the permeance of thin film composite membranes: Part I. Track-etched polycarbonate supports

Thin film composite (TFC) membranes for industrial gas separation are often comprised of a thin selective layer (100 nm or less) on a porous support that provides mechanical strength. As the selective layer becomes thinner to increase gas permeance and thus reduce the capital cost, the support surface morphology restricts the concentration profile of the penetrant in the selective layer. Such geometric restriction has been demonstrated using modeling and computational simulations. However, there are no rigorous experimental studies that verify the modeling results. This study investigates model two-layer TFC membranes, which are comprised of track-etched polycarbonate (PC) nanofiltration membranes with uniform and straight cylindrical pores as porous supports, and AF1600 with excellent film formation and good stability as the selective layer. The presence of a support can decrease the gas permeance by as much as 85% compared to the freestanding thin film, when the PC support has a pore radius of 47 nm and porosity of 2.8%. The gas permeance increases with increasing porosity at a constant pore size and decreasing pore size at a constant porosity. The measured membrane permeances are consistent with the simulation values obtained using three-dimensional (3D) computational mass transport models that predict the steady-state penetrant concentration in the selective layer.