Potential of vis–NIR spectroscopy to monitor the silica precipitation reaction
Résumé
Controlling production online is an important issue
for chemical companies.Visible and near-infrared (NIR) spectroscopy
offers a number of important advantages for process
monitoring, and has been used since the 1980s. For complex
media such as silica precipitation samples, it is interesting to
be able to study independently the scattering and absorption
effects. From the scattering coefficient it is possible to extract
information on the physical structure of the medium. In this
work, the physical changes were monitored during a silica
precipitation reaction by simple measurement of collimated
transmittance NIR spectra. It is shown that it is possible to
differentiate samples before and after the gel point, which is
a key parameter for monitoring the process. From these NIR
spectra the scattering coefficients were simply extracted,
allowing a global vision of the physical changes in the medium.
Then principal component analysis of the spectra allowed
refinement of the understanding of the scattering effects, in
combination with particle size monitoring.