Comprehensive near infrared study of Jatropha oil esterification with ethanol for biodiesel production

• A comprehensive NIR spectroscopic study of esterification reactions is presented.
• The esterification of oils with high acidity was monitored by in-line NIR.
• The influence of temperature and catalyst was evaluated using a full factorial design.
• At optimal experimental conditions, minimum acidity value of 1.4% w/w was achieved.
• A fast and simple way to monitor esterification reactions was established.

This work presents a comprehensive near infrared study for in-line monitoring of the esterification reaction of high acid oils, such as Jatropha curcas oil, using ethanol. Parallel reactions involved in the process were carried out to select a spectral region that characterizes the evolution of the esterification reaction. Using absorbance intensities at 5176 cm− 1, the conversion and kinetic behaviors of the esterification reaction were estimated. This method was applied to evaluate the influence of temperature and catalyst concentration on the estimates of initial reaction rate and ester conversion as responses to a 22 factorial experimental design. Employment of an alcohol/oil ratio of 16:1, catalyst concentration of 1.5% w/w, and temperatures at 65 °C or 75 °C, made it possible to reduce the initial acidity from 18% to 1.3% w/w, which is suitable for transesterification of high free fatty acid oils for biodiesel production. Using the proposed analytical method in the esterification reaction of raw materials with high free fatty acid content for biodiesel makes the monitoring process inexpensive, fast, simple, and practical.

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