Chapter 7 - Diffusive Plus Convective Mass Transport Through a Plane Membrane Layer

Abstract

Four different modes of simultaneous diffusive and convective flows are discussed in the first part of this chapter, taking into account the directions of both single mass fluxes and also the solute inlet and outlet concentrations of a single transport layer, namely the membrane layer. The mass transfer rates and the concentration distributions are shown for the cases distinguished in this chapter. The most important process parameters, namely enhancement, intrinsic enhancement, and the polarization modulus, are discussed in Section 7.3, analyzing two-layer diffusive and convective mass transport (transport through the boundary layer and porous membrane layer), two-layer diffusive/convective, as well as only diffusive solute transport (diffusive/convective flow within the boundary layer as well as diffusive flow within the selective, nonporous membrane layer). Taking into account the membrane mass transport properties together with those of the boundary layer, the process parameters, E, Eo, and C∗/Co, can be expressed as a function of transport parameters such as PeL and N[=kLoPeL/(Hko)]. These expressions are then compared to the previous literature models where the membrane transport properties are not taken into account. Similarly, enhancement (E), intrinsic enhancement (Eo), and polarization modulus (C∗/Co) are expressed and discussed in two-layer mass transport with a vacuum on the permeate side, transporting the permeated solute component quickly from the membrane outlet surface, imitating transport during the pervaporation process. The equations of the important process parameters are listed in Table 7.1. The model equations developed should help the user to find suitable mass transport equations for a given membrane separation process.