Gas-Gas Separation Using a Hollow Fiber Membrane

Computational fluid dynamics simulations are conducted for laminar steady asymmetric flows within a hollow fiber membrane unit. The goal is to study the effect of the porous layer of a hollow fiber membrane (HFM) on the flow regimes and thus on the separation process. The mixture of CH4 and CO2 is studied with the goal of separating CO2 from CH4. The hollow fiber membrane consists of a circular channel bounded by a supporting porous layer. Outer surface of the tubular pipe is bounded by a selective membrane. The Navier-Stokes equation, Darcy's law, and the species transport equations are solved for various values of permeability of the porous medium and Reynolds numbers. The mass flux of each species passing through the membrane is determined based on the local partial pressure, the concentration of each species, the permeability and the membrane selectivity. The porous layer influences the flow field in the open channel strongly. With increasing resistance the flow rate through the porous medium decreases. The flow rate through the open channel increases as the resistance of the porous layer is increased. The presence of the porous layer results in the reduction of mass flux of both CH4 and CO2 passing through the membrane. The Sherwood number is reduced at all Re as the resistance of the porous layer is increased. The increased resistance of the porous layer also causes an increase in the pressure drop in the hollow fiber membrane module. The present study proves that the porous layer should be included in modeling of hollow fiber membrane systems.