Abstract
Conducting multiphase reactions in micro-reactors is a promising strategy for intensifying chemical and biochemical processes. A major unresolved challenge is to exploit the considerable benefits offered by micro-scale operation for industrial scale throughputs by numbering-up whilst retaining the underlying advantageous flow characteristics of the single channel system in multiple parallel channels. Fabrication and installation tolerances in the individual micro-channels result in different pressure losses and, thus, a fluid maldistribution. In this work, an additional source of maldistribution, namely the flow multiplicities, which can arise in a multiphase reactive or extractive flow in otherwise identical micro-channels, was investigated. A detailed experimental and theoretical analysis of the flow stability with and without reaction for both gas-liquid and liquid-liquid slug flow has been developed. The model has been validated using the extraction of acetic acid from n-heptane with the ionic liquid 1-Ethyl-3-methylimidazolium ethyl sulfate. The results clearly demonstrate that the coupling between flow structure, the extent of reaction/extraction and pressure drop can result in multiple operating states, thus, necessitating an active measurement and control concept to ensure uniform behavior and optimal performance.
Highlights
An effective exploitation of the advantages of microscale operation for industrial production processes requires a reliable and robust numbering-up procedure
The results show that the choice of mass transfer model shows little or no influence on the hydrodynamics, only Vandu’s Model yields slightly different behavior, due to the overestimation of the mass transfer coefficients and a faster contraction of the bubble
A model has been developed to describe the behavior of a multiphase slug flow in circular microchannels
Summary
An effective exploitation of the advantages of microscale operation for industrial production processes requires a reliable and robust numbering-up procedure. One must ensure uniform flow rates of each phase and similar flow structures [1] and residence time distributions [2,3] in the individual microchannels, if the optimal performance is to be achieved [4]. If no remedial action is taken, this self-reinforcing mechanism amplifies any flow divergence and can cause the channel concerned to plug. Such multiplicities are by no means confined to microscale systems. The objective of the work presented here was to elucidate the relevance of such microscale-specific phenomena in the parallelization of multiphase flows in microchannels and to establish if it might be feasible to utilize self-regulating behavior in order to ameliorate irregularities in flow distribution
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