Fluid Phase Equilibria 220 (2004) 189–198 Interaction parameters for multi-component aromatic extraction with sulfolane S.A. Ahmad, R.S. Tanwar, R.K. Gupta, A. Khanna ∗ Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India Received 11 May 2002; accepted 4 February 2004 Available online 4 June 2004 Abstract Aromatic extraction is an important operation in petrochemical processing. Design of an aromatic extractor requires the knowledge of multi-component liquid–liquid equilibrium (LLE) data. Such experimental LLE data are usually not available and therefore can be predicted using various activity coefficient models. These models require proper binary interaction parameters, which are not yet available for all aromatic extraction systems. Furthermore, the parameters available for most of the ternary systems are specific to that system only and cannot be used for other ternary or multi-component systems. An attempt has been made to obtain these parameters that are globally applicable. For this purpose, the parameter estimation procedure has been modified to estimate the parameters simultaneously for different systems involving common pairs. UINQUAC and UNIFAC models have been used for parameter estimation. The regressed parameters are shown to be applicable for the ternary as well as for the multi-component systems. It is observed that UNIQUAC parameters provide a better fit for ternary LLE data, whereas, as one moves towards the higher component systems (quaternary and quinary) the UNIFAC parameters, which are a measure of the group contributions, predict the LLE better. Effect of temperature on UNIQUAC binary interaction parameters has been studied and a linear dependence has been observed. © 2003 Published by Elsevier B.V. Keywords: Multi-component; Maximum likelihood; Liquid–liquid equilibria; Binary interaction parameters; IVEM 1. Introduction Aromatics such as benzene, toluene, and xylene are con- sidered essential in the chemical industry because they are the source of many organic chemicals. These aromatics are present in the naphtha feed. High purity aromatics are dif- ficult to be separated using ordinary distillation operation, since they form several binary azeotropes with aliphatics. Extraction is therefore a better choice to separate the aromat- ics from the naphtha feed, as they are preferentially soluble in a variety of solvents. To predict the separation, it is necessary to know the LLE data for a particular system. Various thermodynamic mod- els such as UNIQUAC, UNIFAC and NRTL can be used to predict the LLE. These models use the activity coefficients, which require proper binary interaction parameters that can ∗ Corresponding author. Tel.: +91-512-2597117; fax: +91-512-2590104. E-mail address: akhanna@iitk.ac.in (A. Khanna). represent LLE for highly non-ideal liquid mixtures usually encountered in aromatic extraction. These parameters are yet not entirely available for the multi-component systems encountered in aromatic extraction. These are generally es- timated using experimental LLE data. In case no experimen- tal liquid–liquid equilibrium data for the systems of interest are available, the infinite dilution activity coefficients can be used for parameter estimation but at the cost of accuracy [1]. A least square minimization or a maximum likelihood ap- proach can be used for the estimation of binary interaction parameters. It has been observed that the binary interaction parameters for the same pairs are found to be different for different ternary systems [2]. For example, the binary inter- action parameters between the pair hexane–benzene in the system hexane–benzene–sulfolane are different from those in hexane–benzene–triethylene glycol system [3]. Interac- tion parameters are therefore specific for the system from which they have been estimated and hence cannot be used to predict LLE for the other systems or for the multi-component extraction. It has also been reported that the different sets of 0378-3812/$ – see front matter © 2003 Published by Elsevier B.V. doi:10.1016/j.fluid.2004.02.008