Mixed Ionic Liquids as Entrainers for Aromatic Extraction Processes: Energy, Economic, and Environmental Evaluations

Experimental measurements for the vapor–liquid equilibria (VLE) of benzene + 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2]), benzene + 1-ethyl-3-methylimidazolium ethylsulfate ([EMIM][EtSO4]), and benzene + mixed ionic liquids (ILs) (equimolar [EMIM][NTf2] + [EMIM][EtSO4] mixture) are performed. The non-random two liquid (NRTL) model binary interaction parameters are then obtained by fitting the new VLE data and the liquid–liquid equilibrium data previously reported. The interactions between chemical species are analyzed using quantum chemical calculations and the COSMO-SAC method, and it is found that the interactions between benzene and ILs are strongly attractive. Taking as a reference the industrial process that uses sulfolane as the entrainer, several novel industrial processes are proposed, which involve either pure ionic liquids [EMIM][NTf2] and [EMIM][EtSO4] or their mixtures as the extractant for separating aromatic hydrocarbons (benzene) and paraffins (n-hexane). The optimal operating parameters, such as the number of theoretical stages, the extractant-to-hydrocarbon feed ratio, the reflux ratio, and the feed stage, are determined for the different processes. Steady-state process simulations are performed to evaluate the total annual cost (TAC) and the environmental impact (carbon dioxide emissions). It is shown that significant savings in energy consumption (reduction of 19.6–48.7%), TAC (reduction of 6.3–27.1%), and CO2 emissions (reduction of 17.8–47.6%) can be achieved for the processes that use IL extractants, compared to the process based on sulfolane extractant. The proposed IL extractant and the corresponding process are promising alternatives to conventional solvents and processes for aromatic extraction.