Kinetic analysis on reactive extraction of aspartic acid from water in hollow fiber membrane modules

The simultaneous extraction and stripping of aspartic acid (Asp) in two microporous hollow fibers was studied, in which di(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in kerosene was used as carriers. Aspartic acid was extracted from an aqueous feed phase to the organic phase in the extraction module, and the loaded Asp was then stripped to an aqueous phase in the stripping module. Experiments were conducted at a fixed feed concentration of Asp (5 mol/m³) and different feed pH (3-5), carrier concentrations (100-500 mol/m³), and strip acidities (100-2000 mol/m³). The flow rates were varied in the range 120-420 cm³/min for feed phase, 180-480 cm³/min for organic phase, and 240-600 cm³/min for strip phase. It was shown that the rate of Asp extraction increased with increasing feed and strip flow rates; however, the effect of organic flow rate was negligible. A steady-state mass transfer model was developed that considers all possible diffusion resistances to predict time changes of the extent of Asp extraction in these two hollow fiber modules. Finally, the rate-controlling mechanisms of such non-dispersive solvent extraction processes were identified and discussed by comparing the relative resistance of each mass transfer step.