Mixing Study in Batch Stirred Vessels using a Fibre-Optic UV-VIS Monitoring Technique: A Novel Method

A novel spectroscopic method was developed to measure mixing time and the results compared to the well-known and adopted conductivity method. Spectra of non-reactive tracers were collected using UV/Visible (UV-VIS) fibre optic probes coupled with a McPherson spectrograph. The latter could detect a full spectrum at a maximum acquisition rate of 100 spectra s−1 using a full vertical binning acquisition mode and 41.7 spectra s−1 when using a multitrack acquisition mode. The spectra acquired were processed using a Savitzky–Golay smoothing filter algorithm and analysed, to give mixing time values, according to the rational method proposed by Ruszkowski (1994). Experiments were carried out by placing the fibre optic probes in stirred vessels with working volumes ranging from 3 L to 20 L. Traditional Rushton turbines and 45° angled pitched blade turbines were used for the experiments. The mixing time values, θ95 obtained with the spectroscopic technique were compared with those obtained using a conductivity technique and with a correlation available in literature (Nienow, 1997).