Rapid quantitative determination by 13C NMR of the composition of acetylglycerol mixtures as byproduct in biodiesel synthesis

Abstract

Commercially available partly acetylated glycerols (mono- and diacetin) are mixtures of glycerol, 1- and 2-acetylglycerol, 1,2- and 1,3-diacetylglycerol, and triacetin. Diacetin and monoacetin are by-products of the biodiesel and triacetin production using glycerol esterification with acetic acid or triglyceride interesterification with methyl acetate. Usually, primary analytical methods involve chromatography (HPLC or GC), spectroscopy (MS or NIR), and wet chemical techniques (potentiometric, iodometric titration) which are often time-consuming due to sample preparation, extended analysis time and/or complicated data analysis. Moreover, these methods require pure mono- and diacetin as standard, which are commercially unavailable.In this work, a complete 31P and 13C chemical shift data for glycerol, mono-, di- and triacetin (including isomers) allows for the identification and quantification of these components in the commercial mixtures. This experimental protocol allows for rapid analysis of mixtures that include these six components. Quantitative 31P NMR and 13C NMR results were validated to those obtained with other analytical methods, such as GC and HPLC-ELSD. 13C NMR is preferred due to allows to measure the content of triacetin, which has no free hydroxyl group, and no signal was detected by 31P NMR.