Reactive Extraction of Lactic Acid, Formic Acid and Acetic Acid from Aqueous Solutions with Tri-n-octylamine/1-Octanol/n-Undecane

The present work develops the basics for the isolation of lactic acid, acetic acid and formic acid from a single as well as a mixed feed stream, as is present, for example, in fermentation broth for lactic acid production. Modelling of the phase equilibria data is performed using the law of mass action and shows that the acids are extracted according to their pka value, where formic acid is preferably extracted in comparison to lactic and acetic acid. Back-extraction was performed by 1 M NaHCO3 solution and shows the same tendency regarding the pka value. Based on lactic acid, the solvent phase composition, consisting of tri-n-octylamine/1-octanol/n-undecane, was optimized in terms of the distribution coefficient. The data clearly indicate that, compared to physical extraction, mass transfer can be massively enhanced by reactive extraction. With increasing tri-n-octylamine and 1-octanol concentration, the equilibrium constant increases. However, even when mass transfer increases, tri-n-octylamine concentrations above 40 wt%, lead to third phase formation, which needs to be prevented for technical application. The presented data are the basis for the transfer to liquid membrane permeation, which enables the handling of emulsion tending systems

Liquid-liquid Phase Separation in Batch Settling with Inclined Plate

Liquid-liquid dispersions which are occurring in the petrochemical and chemical industry are commonly separated in gravity settlers. To improve the settler design, phase separation of the dispersions was studied. The parameters having the greatest effect on the phase separation under gravity are drop size, drop-size distribution, as well as driving-force parameters for sedimentation and coalescence, namely density difference, viscosity and interfacial tension. The effect of the driving-force parameters on coalescence and sedimentation was characterized experimentally using a standardized batch-settling cell. The viscosity of the aqueous phase was increased by adding polyethylene glycol. This not only changed the viscosity but also the interfacial tension, having a significant impact on drop size. In high-viscosity systems the settling speed of swarm droplets will significantly slow down and droplet size will be smaller. Furthermore, internals in gravity settlers also have significant impact on the phase separation. The influence of internals was studied for inclined plates. It can be seen from the experiments that internals speed up coalescence for different viscosities and volume ratios between the phases up to a factor of two.</jats:p