Hydrodynamic andMass Transfer Studies in Y‑Junction-BasedCircular Microfluidic Platform with Nitric Acid–TBP/DodecaneSystem

Experimental studies on the extraction of nitric acid from an aqueous phase by an extractant tributyl phosphate (30% v/v) dissolved in dodecane (organic phase) in a Y-junction-based circular microfluidic platform are conducted. The hydrodynamic studies include the identification of different flow regimes, i.e., slug flow (SF), droplet flow (DF), slug–droplet flow (SDF), and core–annular flow (CAF) and generation of a flow regime map. Physical characteristics of SF and DF regimes such as size, velocity, hold-up, and frequency are also quantified. Mass transfer studies include the quantification of the extraction performance in different flow regimes. Different flow regimes are compared on the basis of percentage extraction, overall volumetric mass transfer coefficient, and specific extraction rate. The maximum percentage extraction obtained for CAF, SF, and DF is 12.49%, 23.74%, and 54.23%, respectively, at corresponding residence times of aqueous phase of 0.59, 2.27, and 1.97 s, respectively. The overall volumetric mass transfer coefficient varies in the range of 0.041–0.100 s^–1 for CAF, 0.018–0.073 s^–1 for SF, and 0.019−0.068 s^–1 for DF. The specific extraction rate varies in the range of 0.104−0.279 mol m^–3 s^–1 for CAF, 0.031–0.180 mol m^–3 s^–1 for SF, and 0.004–0.053 mol m^–3 s^–1 for DF. CAF has a higher value of the overall volumetric mass transfer coefficient and specific extraction rate as compared to other flow regimes despite having lesser value of percentage extraction, which is attributed to higher velocity of flow in CAF.