Enhanced extractive distillation processes for separating n-hexane and 1,2-dichloroethane via bottom flash heat pump

Abstract

In the industrial process to synthesize ethylene sulfate, a film-forming electrolyte additive for lithium-ion batteries, a significant amount of liquid mixtures of n-hexane (HE) and 1,2-dichloroethane (DCE) are generated, whose separation is challenging because of the formation of a minimum-boiling azeotrope. Hence, in this study, the conventional ED process for separating the HE/DCE mixtures was firstly investigated. Subsequently, since the temperature difference between the overhead vapor and bottom liquid is large, which is not favorable to the application of the vapor recompression heat pump technology, two bottom flash heat pump (HP) assisted extraction distillation (ED) processes, i.e., the bottom flash HP assisted ED (BFHP-ED) process and the coupled vapor recompression and bottom flash HP assisted ED (VRBFHP-ED) process are proposed and optimized in terms of the minimal total annual cost (TAC). The results show that, the thermodynamic efficiency increases from 7.63% for ED, to 13.76% for BFHP-ED, and 13.16% for VRBFHP-ED processes, while CO2 emissions of the BFHP-ED and VRBFHP-ED processes can be reduced by 41.05% and 39.19%, respectively.