CHEMICAL ENGINEERING TRANSACTIONS VOL. 42, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Neven Duić Copyright © 2014, AIDIC Servizi S.r.l., ISBN 978-88-95608-33-4; ISSN 2283-9216 DOI:10.3303/CET1442008 Please cite this article as: Nagy E., Hegedüs I., 2014, Description of the overall mass transport during membrane gas separation, Chemical Engineering Transactions, 42, 43-48 DOI:10.3303/CET1442008 43 Description of the Overall Mass Transport during Membrane Gas Separation Endre Nagy*, Imre Hegedüs a Affiliation Research Institute of Chemical and Process Engineering, University of Pannonia, Veszprém, Egyetem u. 10. Hungary nagy@mukki.richem.hu Concentration polarization has often been observed in membrane gas separation when there is an accumulation of the less permeable species and a depletion of the more permeable components in the boundary layer of the fluid phase as a result of high fluxes of solute and selectivity and low bulk diffusion. The theoretical prediction of the negative effect of the mass transfer resistance of the boundary layer is crucial in order to be able to calculate the separation efficiency of a gas separation. Models developed in order to describe the mass transport during gas separation enable the user to calculate under what operating conditions the best separation efficiency can be reached. Case study illustrates how these expressions can be applied for prediction of the separation efficiency of a membrane gas separation process applying rubbery polymer membrane. Comparing the theoretical data to that of the experimental it was proved that the model results are in good agreement with that of the experimental ones. 1. Introduction The theoretical prediction of the negative effect of the mass transfer resistance of the boundary layer is crucial in order to be able to calculate the separation efficiency of a gas separation (Chou et al., 2013). The theoretical prediction of the mass transport, taking into account simultaneously both the mass transfer resistances of the polarization and the membrane layers, is necessary for a correct membrane design, since it is useless decreasing as much as possible the membrane thickness for increasing the flux if part of the transport resistance is in the feed boundary layer (Caravella et al., 2009). Several papers have analyzed the concentration polarization in gas permeation by both theoretically (Nemmani and Suggala, 2010) and experimentally (Park et al. 2008). It was shown that the convective velocity in the polarization layer is generally relatively high accordingly its effect of the mass transport must not be neglected. The main question to be answered is how the simultaneous effect of both the polarization and membrane layers can be exactly described in presence of not negligible convective velocity. This paper analyzes the simultaneous mass transport of the boundary and membrane layers in presence of convective plus diffusive flow in the boundary layer and diffusive one in the membrane. 2. Theory It is assumed that there is diffusive and convective flow in the boundary layer and only diffusive flow exists in the dense, polymeric membrane layer. Under steady state, the gas concentration profiles of the more permeated component are illustrated in Figure 1 in the two layers. Due to the convective flow the concentration distribution can have convex shape in the boundary layer while that is linear in the membrane one. 2.1 Boundary layer mass transport The mass balance equation of transported gases, through the boundary layer, for steady operation condition is (He et al. 1999):