Separation of lactic acid by using liquid emulsion membranes

Abstract

Liquid emulsion membranes(LEMs) were applied to the separation of lactic acid from an aqueous feed phase, and water transport into emulsion was investigated during the separation. Considering that as lactic acid is extracted osmotic pressure difference is varied, water transfer coefficient was evaluated. The water transfer coefficient becomes larger on using higher carrier concentration and initial feed concentration, which means that emulsion swelling can also be mediated by solute/carrier complexes although it is, in general, osmotically induced. It was observed that the separated solute concentration in the internal phase was lowered due to swelling during the operation. Nevertheless, lactic acid could be concentrated in the internal phase more than 6 times in specific conditions, indicating that as the volume ratio of external to internal phase is increased, still higher concentration in the internal phase can be obtained. The change in mean droplet size with swelling was measured at given intervals to understand the associated interfacial phenomenon. From this experiment, it was proved that the amount of swelling could not be quantitatively determined from the change of mean droplet size. A mathematical model was proposed to describe the behavior of liquid emulsion membranes(LEMs) accompanied by water transport (emulsion swelling). The proposed model is based upon the carriermediated facilitation of diffusion-stripping, and assumes acid-base reaction equilibrium to exist at each interface. Experimental results of the batch extraction of lactic acid were compared with computed results by using the model. It was found that the theory and model computations could predict fairly well the effects of parameter variations such as the stripping reagent concentration, the stirrer speed, the internal phase volume fraction, the treatment ratio and the emulsifier speed. As well, the proposed model can also predict the separated product concentration in the internal ph...