Molecular Insights and Process Integration for Efficient Separation of Methanol/Methyl Ethyl Ketone by Ionic Liquid Extractive Distillation

Wood vinegar refining and one-step synthesis of methyl isopropyl ketone produce two byproducts, methanol (MT) and methyl ethyl ketone (MEK), which are difficult to separate due to the formation of lowest azeotropes. Therefore, 169 ionic liquids (ILs) were screened using COSMO-RS, and 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) was finally determined as the best entrainer for the separation of MT and MEK by analysis of the dissolution and separation properties. Mechanism of [EMIM][DEP] separation of MT/MEK revealed using quantum chemical calculations. The results showed that the binding capacity between MEK and MT was weaker than that between [EMIM][DEP] and MT and that [EMIM][DEP] exerted a positive effect on breaking the azeotrope of MT and MEK. To this end, a basic separation sequence for an extractive distillation process (EDP) was constructed using Aspen Plus V11, and based on this process enhancement, three intensified processes, heat-integrated extractive distillation process (HI-EDP), heat pump-assisted extractive distillation process I (HP-EDPI), and heat pump-assisted extractive distillation process II (HP-EDPII) were developed, and their performance was evaluated. The results show that costs, energy consumption, and gas emissions of the HP-EDPII were reduced by 11.16, 60.02, and 47.13%, respectively, compared with that of the EDP. The HP-EDPII showed great potential for energy saving and environmental protection.