Diffusion Coefficient−Formula Weight Correlation Analysis via Diffusion-Ordered Nuclear Magnetic Resonance Spectroscopy (DOSY NMR) To Examine Acylglycerol Mixtures and Biodiesel Production

Abstract

Biodiesel, fatty acid methyl esters derived from vegetable oils, is a well-established alternative to petroleum diesel. We have developed a rapid 1H diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY NMR) method to resolve mixtures of mono-, di-, and triacyglycerols along with their methyl esters. Because of the differences in diffusion coefficients between the starting materials (triglycerides), intermediates (mono- and diglycerols), and products (methyl esters), we were able to accurately predict the formula weights of these species in solution. This technique was used to monitor transesterification reactions of virgin and waste vegetable oils. In addition to proving its utility to assess conversion of starting materials, we found that 1,3-diacylglycerol is the major intermediate formed during alkali-catalyzed biodiesel production.