Examination of the semi-batch crystallization of benzophenone from saturated methanol solution via aqueous antisolvent drowning-out as monitored in-process using ATR FTIR spectroscopy

In-process ATR FTIR spectroscopy is used to measure concentration and supersaturation in drowning-out of benzophenone from methanol/water solution and to study the effect of the rate of the aqueous antisolvent addition. A selected peak ratio in terms of IR transmittance or absorbance is monitored on-line and used to develop calibration equations for the concentration of the solute in the mixed solvent as a function of the ratio and the quantity of the antisolvent added. The benzophenone solubility in the mixed methanol/water solvent is found to be a nonlinear function of the respective solubilities of the solvents accounting not only for the dilution effect, but also for the binding of solvent molecules by the antisolvent molecules.