(653b) Material Selection and Design of Ionic Liquid-Based Extractive Distillation for Hydrofluorocarbons Separation

Hydrofluorocarbons (HFCs) and their mixtures are used as refrigerants for commercial and domestic cooling systems. Because of high global warming potential (GWP) of some of these mixtures, the Kyoto Protocol has recommended their gradual phase-out. There is an economic incentive to separate these HFC mixtures into their constituent components rather than venting or incinerating. However, many of these HFC mixtures are azeotropic in nature, and there is no commercial technology available to perform the separation. Extractive distillation, first proposed in the 1930s [1], is a technology that can separate close boiling azeotropic mixtures by using a higher boiling point entrainer. Ionic liquids (ILs) are attracting attention as entrainer for the extractive distillation of HFCs because of their negligible vapor pressure and chemical and thermal stability [2-3]. Due to significantly large number of possible ions combinations, theoretically, it is possible to have millions of ILs [4]. Selecting an appropriate IL for the separation of a particular HFC mixture is important for effective and economic distillation [5]. We have developed a multiscale process design, synthesis, and material selection framework called SPICE_ED for the synthesis of optimal extractive distillation process for separating HFC mixtures. SPICE_ED stands for Synthesis and Process Intensification of Chemical Enterprises involving Extractive Distillation. The framework is based on a building block-based novel representation of chemical phenomena, tasks, and operations in the chemical process industry [6-8]. From a candidate set, the framework can automatically select the most optimal IL that offers minimum energy requirement and/or has minimum processing cost. We generate process flowsheets and equipment designs considering the appropriate refrigerant and IL inlet trays, IL flow rates, reflux ratio, column operating conditions, and IL regeneration processes involving separate distillation, stripping, and flash operations. Finally, the framework can be utilized to map out the thermophysical properties of hypothetical ILs, thus directing the efforts towards discovering novel ILs with desired process economics. When searching for an optimal process for the separation of R-410A (50 wt% R-125 (C₂HF₅) and 50 wt% R-32 (CH₂F₂)), we obtained a heat-integrated optimized process that consumes 65% less energy and emits 72% less indirect CO₂ emission compared to previously reported designs with an existing IL [9]. In this presentation, we will also discuss how the framework can be employed for large-scale computational screening of ILs and other solvents for the separation of mixers with optimized process designs.

References:

[1] Randall, M. and Webb, W.A., 1939. Separation process. Industrial & Engineering Chemistry, 31(2), pp.227-230.

[2] Morais, A.R.C., Harders, A.N., Baca, K.R., Olsen, G.M., Befort, B.J., Dowling, A.W., Maginn, E.J. and Shiflett, M.B., 2020. Phase Equilibria, Diffusivities, and Equation of State Modeling of HFC-32 and HFC-125 in Imidazolium-Based Ionic Liquids for the Separation of R-410A. Industrial & Engineering Chemistry Research, 59(40), pp.18222-18235.

[3] Shiflett, M.B. and Maginn, E.J., 2017. The solubility of gases in ionic liquids. AIChE Journal, 63(11), pp. 4722-4737.

[4] Shiflett, M.B. and Yokozeki, A., 2006. Solubility and diffusivity of hydrofluorocarbons in room‐temperature ionic liquids. AIChE Journal, 52(3), pp.1205-1219.

[5] Lei, Z., Dai, C., Zhu, J. and Chen, B., 2014. Extractive distillation with ionic liquids: a review. AIChE Journal, 60(9), pp.3312-3329.

[6] Demirel, S.E., Li, J. and Hasan, M.M.F., 2017. Systematic process intensification using building blocks. Computers & Chemical Engineering, 105, pp.2-38.

[7] Demirel, S.E., Li, J. and Hasan, M.M.F., 2019. A General Framework for Process Synthesis, Integration, and Intensification. Industrial & Engineering Chemistry Research, 58(15), pp.5950–5967.

[8] Demirel, S.E., Li, J., El-Halwagi, M.M. and Hasan, M.M.F., 2020. Sustainable Process Intensification using Building Blocks. ACS Sustainable Chemistry & Engineering, 8(48), pp.17664–17679.

[9] Shiflett, M.B. and Yokozeki, A., 2006. Separation of difluoromethane and pentafluoroethane by extractive distillation using ionic liquid. Chimica oggi, 24(2), pp.28-30.