Microscale two-phase flow behaviour between an ionic liquid and supercritical carbon dioxide

Abstract : The high viscosity of ionic liquids is an impediment to their use in solvent-based processes. This property is even higher when ionic liquids are combined with solid solute. When SC-CO 2 (supercritical carbon dioxide) is dissolved in an ionic liquid, the mixture viscosity can be considerably reduced: at 25 MPa the mole fraction of CO 2 in [BMIm + ][PF 6-] reaches 80% and the viscosity is reduced by 90%. Ionic liquids are so numerous and expensive as well as high-pressure processes. Although both have great potential to make processes safer, cleaner and more efficient. That is why to develop an ionic liquid solvent-based processes using micro-device. The main objective of using this apparatus in this study is to allow ionic liquid screening. An additional advantage of the small length scale is the potential for high-pressure applications due to lower mechanical stress in the micro-device material. Furthermore, the micro-device developed [1,2] is transparent, uses micro-capillaries technology and resist to more than 18 MPa inner pressure. In this article we present results of experiments and measurements done to investigate the behaviour and characterize the two-phase flow between [BMIm + ][PF 6-] (continuous phase), and the dispersed phase consisting in SC-CO 2 (figure 1). Since ionic liquids are almost non-volatile, the mass transport occurs from SC-CO 2 towards this ionic liquid. This two-phase flow system is observed with a high-speed camera. An image processing of the images is performed in order to calculate the global two-phase flow geometrical parameters: frequency, velocity, size, gap length, volume and surface. The influence of operating conditions (continuous flow rate, dispersed flow rate, temperature and pressure) on the physical properties of the system has been studied. The observed results show a special behaviour of our two-phases flow system: the length, the volume and the velocity of dispersed phase drastically decrease along the capillary. Figure 1: Co-axial injection of SC-CO 2 in [BMIm + ][PF 6-] continuous phase – P = 11.4 MPa (inlet); T = 318 K; ! !" ! = 0,11 mL.min-1 ; ! !"#$%& ! = 0.09 mL.min-1 in a 530 µm ID micro-capillary 34 cm CO 2 BMImPF 6
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Hugo Helouvry, Nayane Macedo Portela da Silva, Jean‐jacques Letourneau, Fabien Baillon, Fabienne Espitalier. Microscale two-phase flow behaviour between an ionic liquid and supercritical carbon dioxide. EMSF 2016 - 15th European Meeting on Supercritical Fluids, May 2016, Essen, Germany. 8 p. ⟨hal-01706765⟩

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