Developments in photonic systems for Raman spectrometry in microreactors

Liquid-phase chemical reactions are very popular in both industry and research labs. In recent years these reactions have been increasingly performed in microfluidic devices that provide high efficiency, throughput, convenience and safety. In many microfluidic applications fast and reliable process analysis is needed. One of the most powerful tools for reaction monitoring is Raman spectrometry. However, its use with microreactors sets a number of technical and methodological challenges that have to be resolved. In this thesis, development of a fibre-optic Raman probe optimised for the analysis of transparent liquids in microreactors is presented. Increased sensitivity, a more localized collection volume, a simplified construction and reduced instrument cost are demonstrated. With only a 2 s acquisition time, accurate performance of the probe in monitoring an esterification reaction at any point along the 150 μm wide serpentine of a microreactor was achieved. Fast data acquisition reduced the process optimisation time, allowed tracking of the reaction along the serpentine, and demonstrated the high-frequency instabilities that can be introduced by unstable pumping. The optimised Raman probe was employed to develop a novel method for kinetic studies based on flow rate manipulation and fast data acquisition. By use of a single experiment, the developed procedure reduced the time and the amount of reagents required to obtain the rate constant and order of reaction compared to conventional multi-experiment methodology. Further improvement in the use of non-invasive Raman spectrometry for monitoring of microreactors was achieved through design of a measurement cell, optimised geometrically and optically for better signal-to-background, which could be added to the flow path. The combined results of the research can lead to the development of a universal Raman system for process analysis in microreactors that could be utilised in previously difficult situations where optical access to the channels is restricted.Liquid-phase chemical reactions are very popular in both industry and research labs. In recent years these reactions have been increasingly performed in microfluidic devices that provide high efficiency, throughput, convenience and safety. In many microfluidic applications fast and reliable process analysis is needed. One of the most powerful tools for reaction monitoring is Raman spectrometry. However, its use with microreactors sets a number of technical and methodological challenges that have to be resolved. In this thesis, development of a fibre-optic Raman probe optimised for the analysis of transparent liquids in microreactors is presented. Increased sensitivity, a more localized collection volume, a simplified construction and reduced instrument cost are demonstrated. With only a 2 s acquisition time, accurate performance of the probe in monitoring an esterification reaction at any point along the 150 μm wide serpentine of a microreactor was achieved. Fast data acquisition reduced the process optimisation time, allowed tracking of the reaction along the serpentine, and demonstrated the high-frequency instabilities that can be introduced by unstable pumping. The optimised Raman probe was employed to develop a novel method for kinetic studies based on flow rate manipulation and fast data acquisition. By use of a single experiment, the developed procedure reduced the time and the amount of reagents required to obtain the rate constant and order of reaction compared to conventional multi-experiment methodology. Further improvement in the use of non-invasive Raman spectrometry for monitoring of microreactors was achieved through design of a measurement cell, optimised geometrically and optically for better signal-to-background, which could be added to the flow path. The combined results of the research can lead to the development of a universal Raman system for process analysis in microreactors that could be utilised in previously difficult situations where optical access to the channels is restricted