Flow patterns of ionic liquid based aqueous biphasic systems in small channels

Abstract

Ionic liquid based aqueous biphasic systems (IL-ABS) were formed by the addition in water of a hydrophilic ionic liquid (1-Butyl-3-methylimidazolium Chloride, C4mimCl) and a kosmotropic salt (tripotassium phosphate, K3PO4). The flow patterns of IL-ABS were studied in capillary channels with 0.2, 0.5 and 0.8 mm internal diameter; this is the first time such two-phase flows have been investigated. Three weight concentrations of the ionic liquid and the salt (18, 20 and 22 wt%) were chosen within the biphasic region. The main flow patterns included plug, dispersed and parallel flow. It was found that both channel diameter and weight concentrations would affect the flow patterns observed. Finally, a generalized flow pattern map was plotted using a combination of capillary and Reynolds numbers, where the transition boundaries of plug flow collapsed for all ionic liquid and salt concentrations studied.