Intensification of liquid-liquid extraction columns by microgels

  • Intensivierung von flüssig-flüssig Extraktionskolonnen mit Mikrogelen

Faulde, Miriam Anna Barbara; Jupke, Andreas (Thesis advisor); Wöll, Dominik (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

For extraction columns the drop size and drop size distribution are crucial for process performance. Small drops promote mass transfer by large interfacial area while larger drops withstand higher counter current flow rates. The tendency of the drop to coalesce requires constant energy input to break the drops. Hence, the interplay between coalescence and breakage regulates the drop size and often leads to broad size distribution. A new approach to tackle this drop size dilemma is the application of microgels. The crosslinked polymers can stabilize and destabilize liquid systems on demand by a very sensitive temperature trigger. With the combination of interfacial activity and switchability, microgels enable new options for processes with defined monodisperse drop size. For the successful introduction of microgels to extraction processes, the effect of the interfacial microgel layer on the processes relevant phenomena needs to be understood. Thus, the impact of microgels on fluid dynamics, mass transfer and coalescence is investigated in this work. To identify advantageous microgel properties four different microgels are utilized, differing in size and crosslinking. Furthermore, the propagation of effects is evaluated across scales from liquid-liquid interface to technical lab scale, with focus on single drops as smallest self contained unit of the process.The results from single drop experiments indicate that the predominant effect of microgels is the reduction of interfacial mobility. The effect of the microgels on the drops´ fluid dynamics increases with increasing spreading and interpenetration of the microgels at the interface. This also affects the other investigated phenomena. A reduced mass transfer was observed at single drops, while no additional mass transfer resistance of the microgel layer itself was measured for small molecules at a flat interface. Thus the reduced interfacial mobility must cause a reduced decay of the concentration gradient inside the drop. Regarding coalescence the probability for two colliding drops is significantly reduced by microgels below their switching temperature. This could also be accounted to reduced interfacial mobility since it affects the film drainage and thus required contact time for coalescence. Moreover, phase separation by temperature shift was successfully demonstrated in a continuous operating prototype in technical lab scale.Further, performance evaluation by process simulations with monodisperse microgel covered drops show a capacity increase to higher loads at equal separation performance. And at low loads monodisperse drops increase the separation performance and enable operation close to entrainment limit. This work demonstrates the applicability of microgels in extraction columns and also identifies the interfacial spreading and mobility as crucial properties for this scope of application.

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