Phakoukaki, Yiota Victoria;
(2024)
Studies of continuous intensified liquid-liquid extraction of biomolecules using ionic liquids in small channels.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The thesis presents the development of a small scale continuous extraction process, allowing for intensified extraction of biomolecules using ionic liquid (IL) based solvents. To be applicable on an industrial scale, these small-scale processes need to have their hydrodynamics and mass transfer characteristics thoroughly understood and reliably predicted. Firstly, flow pattern formations of a hydrophobic IL within small channels were systematically explored across a wide range of operating conditions including volume fractions, flow rates and channel diameters. The main flow patterns observed included plug, drop, annular and dispersed flow. Particular attention was given to plug flow, which is known to enhance mass transfer rates. The investigations into plug flow revealed that its characteristics, such as plug length, film thickness, and interfacial area, were influenced by factors such as channel size, and phase flow rates. To continue, equilibrium mass transfer experiments were performed. The partition coefficients of amino acids extracted from acidic solutions into an immidazolium based IL were determined. The combination of the ionic liquid [C4mim][NT f2] with a crown ether extractant (Dicyclohexano-18-crown-6) resulted in high partition coefficients; an extraction mechanism was proposed involving the ammonium centre of the amino acid forming hydrogen bonds with the 18-crown-6 part of the crown ether. Moreover, 100% back extraction into the aqueous phase was achieved at the isolectric point of each amino acid. Next, the continuous flow extraction of L-tryptophan in small channels using the hydrophobic ionic liquid and crown ether extractant was studied. The effects of channel internal diameter, mixture velocity, and residence time on the extraction performance were explored. Notably, smaller channel sizes and increased mixture velocities led to higher extraction efficiencies. In just 30s a maximum efficiency of 94% and 79% was reached in the 0.5mm and 1mm channel, re- spectively. The overall mass transfer coefficients were, in all cases studied, in the range of 0.1 s⁻¹, which is 1-2 orders of magnitude greater than in convectional equipment such as mixer-settlers and pulsed columns. In further studies, hydrophilic ionic liquids (C4mimCL) that form aqueous biphasic systems (ABS) when a salt (K3PO4) is added were considered for the extraction. The phase behaviour and physicochemical interactions of the ABS components were investigated. These investigations led to a deeper understanding of ABS properties, including density variations and interfacial tension, which significantly differed from traditional liquid-liquid systems. For example, ABS have interfacial tensions at least one order of magnitude less than oil-aqueous systems. The changes in properties were explained by considering the Hofmeister series that classifies ions in order of their lyotrophic properties (the ability to salt out or salt in proteins). Flow patterns within small channels using IL based ABS were observed to vary significantly from those observed with hydrophobic ionic liquids. The results demonstrate that it is possible to change the properties of the ABS phases by varying the IL and salt concentrations and thus control the flow patterns that form in microfluidic devices. A generalized flow pattern map was developed, utilizing capillary and Reynolds numbers to show the boundaries of plug flow over a large range of experimental conditions. Predictive models for plug length and film thickness were developed, which correlated well with experimental data. These models contributed to the calculation of the interfacial area available for mass transfer, which exceeded that of conventional solvent extraction equipment. The interfacial areas were about 3000 and 5000 m²m⁻³ for the 0.8 and 0.5 mm channel diameters respectively. Finally, continuous extraction using the IL-ABS was performed in plug flow and almost 100% extraction was achieved in approximately 15 seconds. Controlling the extend of extraction can be achieved through the manipulation of ABS weight compositions. It was observed that increasing the concentrations of both salt and IL resulted in a faster extraction process. In summary, this thesis highlights the versatility and effectiveness of small-scale continuous channel systems in enhancing mass transfer performance. The findings provide valuable insights into the optimization and development of more sustainable extraction processes for various applications.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Studies of continuous intensified liquid-liquid extraction of biomolecules using ionic liquids in small channels. |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10189588 |
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