Abstract
The aim of this work is to separate the benzene and to purify the hexane fraction of Bandar Imam Petrochemical Complex-Iran (BIPC). Benzene content of existing fraction is around 6 wt% and it is required to remove the benzene content to ppm level. Benzene and n-hexane make azeotropic mixture and their separation by distillation method at normal atmospheric pressure is impossible. By using suitable solvent like N-methyl pyrrolidone (NMP) the relative volatility of components could be modified and enhanced to some extent. For the selection of thermodynamic model to predict the liquid activity coefficients, isobaric vapor-liquid equilibrium of n-hexane-NMP and benzene-NMP were determined at 101.3 kPa. VLE data were used to optimize the interaction parameters and thermodynamic coefficients of Wilson, NRTL and UNIQUAC activity models. Results showed excellent consistency of binary VLE data with Wilson model. VLE data for the mixture of hexane fraction and NMP as a multi-component system were determined at 101.3 kPa. Different methods of modeling were evaluated for multi-component system of hexane fraction and NMP. It was found that by using optimized binary interaction coefficients for n-hexane, NMP and benzene and calculation of all other binaries by UNIFAC model, the best result with minimum deviations from experimental data could be obtained.To evaluate the application of this thermodynamic modeling in an actual extractive distillation process, an existing bench scale column was used. Hexane fraction of BIPC was fed to the column packed with LDX structure packing (Sulzer Chemtech Co.) at its optimum operation conditions of hold up and boilup rate. NMP is fed as entrainer to the top of the column and benzene free fraction is obtained from the top of this column with less than 80 ppm-wt of benzene. The experimental results were simulated using HYSYS software and optimized thermodynamic model of Wilson.
