Solute recovery from ionic liquids: A conceptual design study for recovery of styrene monomer from [4-mebupy][BF4]

Extractive distillation using ionic liquids (ILs) is a promising technology to separate the close-boiling mixture ethylbenzene/styrene. A proper solvent regeneration is crucial to obtain a technical and economic feasible process. In this work, several regeneration technologies were studied to recover styrene from the IL [4-mebupy][BF4] using Aspen Plus. Stripping with a hot gas (N2 or ethylbenzene), supercritical CO2 extraction, distillation by adding a co-solvent, and evaporation were investigated. It was found that the IL that was fed as solvent to the extractive distillation column should have a purity of at least 99.6 wt% to maintain the purities of the top and bottom products from the extractive distillation column. This purity could not be obtained with an evaporator using mild conditions (T = 130 °C, Tcondenser ≥ 20 °C). From the process models and the economic evaluation for a typical production capacity of 500,000 mta, the conclusion can be drawn that evaporation using very low pressures (P < 10 mbar) and stripping with ethylbenzene are the most promising technologies to recover styrene monomer from the IL [4-mebupy][BF4].