Process optimisation is widely recognised as a necessary requirement of chemical production facilities, yet it typically remains an offline or at line task. Real applications are subject to uncertainty and process disturbances and therefore, there is clearly a requirement for deeper process understanding through on-line real time analytical measurements.
For in-situ applications, the observation window is the eye to the process when using optical analysis methods. Only a clean observation window allows reliable analysis at any time during chemical and biological processes. Therefore, the use of optical methods is only possible when the following procedures are executed reliably and at any time:
- Cleaning of observation window
- Cleanness check of the observation window
- Active control over the complete analyser
- Zero baseline at any time
- Complete cleaning of all parts which have contact with product (surfaces, seals, etc.) following the guidelines of GMP, Hygiene etc.
NIR measurements are dominated by CH components of the samples and as such, they are useful for the determination of high concentrations. In some cases, there is a benefit in measuring additional functional groups by means of MIR immersion probes that can monitor specific compounds. (Aromatic vs. aliphatic)
NIR transmission can determine bulk components composition and allow calculations of octane numbers. MIR in specific wavenumber ranges can be useful for the determination of additives and/or impurities.
In the production of bio-fuels, process control can be performed before and after purification. Typically, the NIR region contains combination and overtone information with the most sensitive bands being derived from O-H and C-H bonds. Again, MIR process control data from fiber optic immersion probes can be used to determine additives and/or impurities.
MIR measurement has advantages for compositional monitoring, especially when measuring process mixtures and in looking for and confirming impurities.
For water treatment, agrochemicals, dyes and pigments, reflectance measurements and ATR measurements can be used. Again, NIR would primarily be used for bulk analysis and MIR for traces analysis.
This is an area where NIR has been well used, so any advantages that MIR could offer would be for specific lower level compound analysis. There could be some scope for a combination of MIR and NIR in analysis of flavours, fragrances & fermentations. Also there may be advantages of combining data, particularly in fermentation. Some of the categories might have some scope for a transmission probe but the majority require a reflectance monitoring probe (e.g. dairy, oils & fats).
Pharmaceutical Products and their Development
Split into two depending if material is a solid or a liquid. A combination of wavelength regions in a reflectance probe can be used for composition monitoring where MIR fiber optics can determine low concentration compounds and NIR fiber optics for major components.