Ethanol Dehydration with Ionic Liquids from Molecular Insights to Process Intensification

The ethanol (EtOH) dehydration process using ionic liquids (ILs) as entrainers by extractive distillation integrated with a heat pump was systematically investigated from the molecular level to the process scale. [BMIM][Cl] was selected as the appropriate entrainer from a variety of [Cl](-)- based ILs by achieving vapor-liquid equilibrium (VLE) experiments for binary systems of EtOH-IL and water (H2O)-IL. The VLE behavior of a ternary EtOH-H2O-IL system demonstrates that the azeotropic phenomenon of the binary EtOH-H2O system is effectively broken in the presence of IL. Moreover, the UNIFAC model was successfully extended to predict the VLE of the EtOH-H2O-IL system. The microscopic mechanism of the EtOH- H2O separation with [BMIM][Cl] as an entrainer at the molecular level was identified by performing molecular dynamics simulations. It is found that hydrogen bond interactions of EtOH/H2O-[BMIM](+) and -[Cl](-) play crucial roles in breaking the azeotropic phenomenon. The equilibrium stage model for the ethanol dehydration process with [BMIM][Cl] as an entrainer was established, wherein the binary group interaction parameters of the UNIFAC model were embedded. The process simulation and optimization were performed at the industrial scale. The extractive distillation process intensified with the heat pump technology has better economic and environmental efficiencies when compared with the conventional one. The total annual cost and CO2 emission of the former are reduced by 27.01 and 80.46%, respectively, compared with those of the latter. In short, the process intensification technology for ethanol dehydration by using ILs as entrainers integrated with the heat pump proposed in this work is in line with sustainable chemical separation processes, which can be directly extended to other extractive distillation processes with ILs.