Design of mixed ionic liquid extractant and study on process intensification for separation of isopropanol and n-hexane from wastewater

Abstract

The separation of the ternary azeotrope system is still a topic worth studying. An effective method based on a mixed ionic liquids (ILs) extractant was proposed and applied to the separation of isopropanol (IPA), n-hexane (NH) and water (H₂O) systems. Firstly, the organic solvent and ILs with better separation effects for the two components of the ternary azeotropic system were screened out by relative volatility calculation, quantum chemistry and molecular dynamics calculation. Based on the synergistic effect of dimethyl sulfoxide (DMSO) and 1-ethyl-3-methylimidazolium thiocyanate ([EMIMSCN]), a mixed ILs extractant was designed. It was then applied to three extractive distillation (ED) processes. Aiming at the minimum total process cost and gas emission, an optimization strategy was designed to achieve multi-objective optimization of process flow, the optimal composition and dosage of the mixed extractant were determined. The process results showed that the total annual cost (TAC) and gas emissions from mixed extractive distillation (MED) were 795406.85 $/y and 1536.84 kg/y, and the process energy consumption was 1987.99 kW. Compared with the ED process with DMSO as an extractant, the MED process can save 40.05 % TAC and reduce 30.39 % gas emission and energy consumption. The mixed extractant was carefully studied, and the addition of ILs was analyzed to increase the relative volatility between IPA and H₂O separated by the extractant. The sensitivity analysis of the key variables of the MED process was carried out. The results show that the feed position of the extractant has the greatest influence on the objective function. Finally, the MED and the mixed extractive distillation under reduced pressure (RPMED) process were intensified, and the heat pump coupled thermal integrated Heat-integrated mixed extractive distillation (HPH-MED) process was determined to be the best process based on environmental pollution and energy consumption considerations. The TAC of the process is 767298.474 $/y, the gas emission is 753.84 kg/y, and the energy consumption of the process is 975.13 kW. Compared with the MED process, TAC is reduced by 3.53 %, and total gas emissions and energy consumption are reduced by 50.95 %.