Hydroxyl content and refractive index determinations on transesterified soybean oil

Biodiesel, a promising alternative diesel fuel, is produced by transesterification of vegetable oils or animal fats with methanol. One of the main problems in the industrial application of the transesterification process is how to determine the conversion of oils to methyl esters. In this work, a quick analytical method was developed for monitoring the transesterification reaction of soybean oil with methanol. The conversion of oils to methyl esters could be determined by applying a simple linear correlation with hydroxyl content of the transesterified mixture or refractive index of the product. The results were in agreement with the values measured by H-1 NMR spectroscopy. Compared with existing chromatographic and other methods, this method for monitoring the transesterification of vegetable oils with methanol is simple, rapid, and inexpensive and is especially suitable for process control purposes.