Optimal design of an ionic liquid (IL)-based aromatic extractive distillation process involving energy and economic evaluation

Extractive distillation (ED) can be used to separate mixtures with low relative volatilities that are even close to unity. It is widely adopted for the separation of aromatics and nonaromatics in the petrochemical industry. Selecting a suitable solvent is of paramount importance to ED processes. Ionic liquids (ILs) are increasingly being considered as potential options to replace organic solvents in ED processes due to their favorable properties including high boiling points and extremely low volatilities. In this work, a nonexperimental solvent screening approach, i.e., computer-aided ionic liquid design (CAILD), is employed to identify the optimal ILs. Using a novel design objective and several structural and property constraints on IL, we have identified 1,3-dimethylpyridinium tetrafluoroborate ([C₁mPy][BF₄]) as the best IL solvent by solving a formulated CAILD-based mixed-integer nonlinear programming problem. The separation performance of this IL is further evaluated with rigorous process simulation in Aspen Plus. Besides, process simulation of the aromatic ED process using sulfolane as the benchmark organic solvent is performed. Furthermore, a systematic analysis of the energy consumption and the process economy is conducted by investigating the optimized simulation results of the studied aromatic ED process. The [C₁mPy][BF₄]-based process with an assumed IL price of 50 $/kg can reduce the capital cost by 35.2%, the operating cost by 11.8%, and the total annual cost by 31.2%. The IL price at the break-even point of replacing sulfolane with [C₁mPy][BF₄] in the aromatic ED process is 91.03 $/kg.