Monitoring of the ester production by near-near infrared thermal lens spectroscopy

Abstract

Near-near infrared (N-NIR) Thermal Lens Spectroscopy (TLS) was used to monitor the transesterification reaction during biodiesel production. Fifteen aliquots were extracted from the reaction during 20 min and their thermo-optical properties were measured as a function of the reaction time. A spectroscopic investigation was performed between 855 and 990 nm to identify overtone absorptions bands (markers) to monitor the chemical reaction. The results show that the OH absorption overtone (∼970 nm) from alcohol, which is used in the reaction, is the most appropriated marker to monitor the biodiesel production. The time dependence of the thermo-optical parameter A(dn/dQ), which is the product between the absorption coefficient (A) and the refractive index dependence with the sample deposited heat (dn/dQ), exhibits a very good correlation with the ester production measured by chromatography. Besides, the measured thermal diffusivity values as function of reaction time indicates a strong dependence with the viscosity of the aliquots. It is possible to conclude that the used TLS in the N-NIR region contributes to the optimization of biodiesel production process by indicating the best time to stop the reaction.