Chemical Engineering Science 60 (2005) 151 – 166 www.elsevier.com/locate/ces Mass transfer enhancement in the Membrane Aromatic Recovery System (MARS): theoretical analysis Frederico C. Ferreira, Ludmila G. Peeva, Andrew G. Livingston ∗ Department of Chemical Engineering and Chemical Technology, Imperial College—London, London SW7 2AZ, UK Received 4 March 2004; received in revised form 26 July 2004; accepted 28 July 2004 Available online 17 September 2004 Abstract This work investigates three different models describing mass transfer enhancement by a reversible and instantaneous second-order chemical reaction. The three models are applied to the study of mass transfer phenomena occurring in a membrane process for recovery of organic chemicals, the Membrane Aromatic Recovery System (MARS). Typical MARS operating conditions are used as model inputs, and the results obtained are used to assess the degree of complexity that should be taken into account in describing the mass transfer phenomena. The most complex model derived (N–P model) accounts for chemical reaction reversibility and the Nernst–Planck effect created by ionic species and is solved numerically. Following Olander model for a second order reversible instantaneous reaction model is proposed, for which we derive an analytical solution in terms of bulk solution properties. Finally, the simplest model follows the analysis of Hatta, assuming irreversible chemical reaction and neglecting the Nernst–Planck effect. The reversibility of the reaction is shown to be important, while N–P effects are negligible. The Olander model is recommended for use in describing the mass transfer phenomena. The models developed can be applied further to other processes of similar type.  2004 Elsevier Ltd. All rights reserved. Keywords: Mass transfer; Mathematical modelling; Chemical reaction; Enhancement; Membrane; Extraction 1. Introduction In chemical engineering processes, mass transfer phe- nomena often take place accompanied by chemical reaction, particularly in operations involving gas absorption, extrac- tion, ion exchange and more recently membrane technology (Noble, 1991; Van Swaaij and Versteeg, 1992; Cussler, 1997; Al-Marzouqi et al., 2002). Chemical reaction can greatly en- hance mass transfer rates (Cussler, 1997), dramatically re- ducing the operational interfacial area required, which can translate into important savings in the chemical plant con- struction and operating costs. Among the great variety of chemical engineering processes in which chemical reac- tion and mass transfer are coupled, in this paper we have ∗ Corresponding author. Tel.: +44-20-7594-5582; fax: +44-20-7594- 5629. E-mail address: a.livingston@imperial.ac.uk (A.G. Livingston). 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.07.081 chosen to focus on the Membrane Aromatic Recovery Sys- tem (MARS). MARS was first applied to the recovery of phenol (Han et al., 2001) and aniline (Ferreira et al., 2002a) from syn- thetic wastewaters at laboratory scale. The aniline and phe- nol compound families usually have high boiling points and low vapour pressures, therefore the existing separation pro- cesses that rely on liquid–gas phase transitions, such as dis- tillation and pervaporation, have high-energy requirements. Also, the intermediate polarity of these compounds creates problems with phase separation and contamination in sol- vent extraction. Hence MARS was developed as a new mem- brane process for recovery of organic acids and bases from industrial wastewater streams. The first MARS pilot scale unit was applied to recover aniline from an industrial wastewater effluent arising in a 4-nitrodiphenyl production process (Ferreira et al., 2002b) and has recently been commercialised at a large scale (Chin,