Two-Phase Flow in Liquid Chromatography - Experimental and Theoretical Investigation
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Author
Date
2018Type
- Doctoral Thesis
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Abstract
Liquid chromatography is a technology applied for challenging separation tasks, for example for separating or purifying sensitive or chemically similar products. When applying liquid chromatography for analytics, dilute solutions of the analytes are injected in short pulses. In turn, in preparative applications, higher concentrations of the components are injected for a longer feed duration. In this
context, it is possible that, upon an enrichment of one or multiple components, the fluid phase becomes supersaturated, and a phase split and two-phase flow occurs. Such enrichment can be due to an interaction of two or more adsorbing components, or to a chemical reaction occurring in the chromatographic column. Since the presence of multiple liquid phases in chromatography is poorly understood, it is commonly avoided by reducing fluid phase concentrations. However, this imposes a limitation upon operating conditions, and potentially upon process performance. Hence, this thesis
investigates experimentally and describes theoretically the physical implications of two-phase flow in liquid chromatography, and evaluates its impact on process performance.
The trigger to this project was the investigation of the delta-shock, a phenomenon which could not be evidenced experimentally in liquid chromatography. Instead, the experimental investigation provided
the evidence of a liquid-liquid phase split and a two-phase flow. In this spirit, the first part of this thesis presents two different mathematical approaches to achieve identical results for conditions and properties of the singular shocks, and hence consolidates existing proof of the theoretical existence of the delta-shock in liquid chromatography. In turn, the challenge of finding experimental evidence
remains unresolved.
In order to investigate two-phase flow in liquid chromatography, material balance equations, accounting for multiple fluid phases in thermodynamic equilibrium, for adsorption, and for different velocities of the fluid phases, are derived. These equations are generic, but require algebraic relationships which describe the physical properties of the specific chromatographic system.
For the determination of such relationships, a reversed-phase chromatographic system is characterized. The thermodynamic properties of the fluid phase(s) are determined by phase equilibrium experiments, and are described by a fitted UNIQUAC equation. Single-component
and binary adsorption is investigated by Frontal Analysis, and described in a thermodynamically consistent manner, assuming a dependence on the liquid phase activities, and using the adsorbed solution theory. Fluiddynamic properties are assessed by imbibition/drainage experiments of phases in thermodynamic equilibrium, and are shown to behave according to a Brooks-Corey correlation, which is often applied in the context of multi-phase flow in natural reservoirs.
The physical relationships are implemented in the material balance equations, which are solved by two different methods, applying a finite volume discretization scheme, or the method of characteristics.
A comparison of simulation results and experimental profiles testifies a quantitative agreement, which serves as a validation of the underlying model assumptions and established physical relationships.
In addition, the comparison of simulations and experimental data allows for an assessment of the impact of different physical aspects on the shape of the elution profiles.
Having gained a good confidence and understanding of the model assumptions and physical properties, the model is applied to evaluate the impact of two-phase flow on the performance of chromatographic processes. The performance of a chromatographic reactor with an esterification reaction is assessed theoretically. It is shown that the retention of the stronger adsorbing component, often enriched in the more wetting phase, can be additionally increased by fluiddynamic effects, i.e. by a slower moving wetting phase. This effect can enhance the separation efficiency between the different solutes, hence increasing the amount of weakly adsorbing product purified per chromatographic cycle, but it also involves the risk of an increased cycle time due to the slow propagation of the wetting phase. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000270250Publication status
publishedExternal links
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Publisher
ETH ZurichSubject
liquid chromatography; Two-phase flow in porous media; mathematical modeling and simulation; thermodynamic equilibria; chromatographic reactorsOrganisational unit
03484 - Mazzotti, Marco / Mazzotti, Marco
Related publications and datasets
Is referenced by: http://hdl.handle.net/20.500.11850/302107
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