Molecular Mechanism and Extraction Performance Evaluation for Separation of Methanol and n-Hexane via Ionic Liquids as Extractant

Biodiesel is considered as one of the best resources to replace fossil fuels. There are a lot of mixtures of methanol and hexane in the process of biodiesel production. In this study, a green solvent ionic liquid extraction is used to separate methanol and n-hexane. The molecular dynamics method is used to study the extraction mechanism of methanol and n-hexane by ionic liquid. The extraction efficiency predicted by molecular dynamics simulation is compared with liquid–liquid extraction experimental values. The deviation between the experimental data and the simulation data is less than 8%, which shows that they have good consistency. The interaction energy, radial and spatial distribution functions, and self-diffusion coefficients are calculated based on the molecular dynamics simulation results. At the same time, anions play a vital role in the extraction process. A method for separating methanol and recovering ionic liquid using Aspen plus is proposed. The optimum operating parameters are determined. The recoveries of ionic liquid and methanol were 99.32% and 94.11%, respectively. The minimum total annual cost of the IL extraction process is 17.31% lower than that of traditional extraction process. At the same time, environmental analysis is performed. Global warming potential and eutrophic potential of the new process are 86.1% and 85% lower than those of the traditional process, respectively. The new process has good sustainable development advantages. This study provides theoretical guidance for the recycling and comprehensive utilization of methanol and n-hexane and provides a new method for the sustainable development of green chemicals.