Near infrared spectroscopy: A useful technique for inline monitoring of the enzyme catalyzed biosynthesis of third-generation biodiesel from waste cooking oil

Near Infrared (NIR) spectroscopy was used for inline monitoring the enzymatic production of third-generation biodiesel from waste cooking oil (WCO) —with fatty acid profile similar to olive oil— under the principles of Continued Process Verification (CPV) and Process Analytical Technology (PAT). For this purpose, covalently immobilized mature Rhizopus oryzae lipase (rROL) was used to transesterify WCO with methanol and ethanol, firstly in 10 mL vials under orbital stirring and then it was successfully scaled up to a mechanically stirred 50 mL laboratory reactor specially designed for use of a NIR probe. Biocatalyst half-life and productivity after ten reaction cycles with methanol and ethanol were assessed. Slightly higher operational stability with methanol (337.5 h, 54 batches) vs with ethanol (146.7 h, 44 batches) was observed, but decreased productivity as a result of the increased reaction times used with the former (219 vs 327 µmol min−1). The NIR spectroscopy results were highly correlated with those of gas chromatography (GC) used as reference. Thus, the root mean-square standard error of prediction (RMSEP) was 2.0% for methanol and 2.1% for ethanol. Therefore, NIR spectroscopy, which allows data acquisition in real time, is suitable for inline monitoring of enzymatic production of biodiesel.