Design of ionic liquids for HF/HFC-245fa superefficient separation: COSMO-RS selection and process assessment

Abstract Recycling HF is a significant issue in the field of organofluoride chemistry. The primary challenge in this process is the separation of azeotropes containing HF, such as the azeotropic mixture of HF and 1,1,1,3,3-pentafluoropropane (HFC-245fa), which have similar boiling points. This study investigates the application of extractant distillation (ED) with four ionic liquids (ILs) for separating HFC-245fa/HF at the molecular scale, cell dimension, and systematic level (including the optimisation and analysis of ED). The optimal IL was first screened with COSMO-RS. Screening results confirmed that [Tf₂N]-based ILs are the most suitable extractants. The effects of IL structure on F-gas solubility were analysed using surface charge density profiles and electrostatic potential. Four typical ILs were selected based on physical properties and thermodynamic performance. A continuous ED process for separating HFC-245fa/HF was simulated and evaluated in Aspen Plus using the selected ILs, resulting in 99.5 mol% HFC-245fa and 99.5 mol% HF. The optimal operation parameters were determined using sequential quadratic programming based on the purity requirements. Energy consumption analysis revealed that [C₁Py] [Tf₂N] is the optimal IL for HF/HFC-245fa separation from the process perspective, with heat and cooling duties of 467.82 kW and 304.80 kW, respectively.