Process Raman spectroscopy for the monitoring of distillations
Among the thermal separation processes, distillation has the longest tradition and has already been used to separate spirits (alcohols) from fermented food. Thanks to its driving force, the differences in vapour pressure of the components in question, adding thermal energy is already sufficient to achieve separation.
However, industrial distillations aim at maximising efficiency, throughput and yield, which in the past led to column designs that optimised the required phase contact between liquid trickling down and gas rising up the column. Packed columns have turned from Raschig rings into structured packings like the Sulzer MellapakPlus™, and trays have turned from sieve plates into designs with specific valves like Sulzer MVG™.
Inline monitoring of distillations
Vibrational spectroscopies like infrared and Raman are well-established techniques for the analysis of mixtures. The comparably simple correlation between signal intensities and component concentrations gives access to mixture composition through a variety of chemometric analysis methods.
Typical fibre-optic immersion probes can easily be introduced even onto the trays of a column. Commonly, offline GC monitoring is used for distillation analysis. However, the required sampling is detrimental for the process equilibrium in these stages of the column.