Density, refractive index and viscosity as content monitoring tool of acylglycerols and fatty acid methyl esters in the transesterification of soybean oil

Abstract

The growing interest in research and development for alternative biofuels has drawn special attention to biodiesel, a mixture of fatty acid methyl esters (FAMEs) that can be obtained by the transesterification reaction of triacylglycerols (TAGs) with a short chain alcohol. During transesterification reaction kinetic studies, it is important to monitor the levels of diacylglycerols (DAGs) and monoacylglycerols (MAGs), as well as those of TAGs and FAMEs. These contents are generally determined according to reference methods by GC-FID analysis. This technique is expensive and time consuming, not to mention that samples with higher TAG contents can be harmful to the chromatography column and accessories. In this context, this study aims to determine the composition of a quaternary system, in which virtually only the four compounds cited previously are present, using a single-step chemometrics analysis that uses mathematical modelling to correlate the composition with three physical properties (density, refractive index and viscosity) of the same sample, one at a time. Subsequently, a sample with an unknown composition has the same properties determined and then a system of equations composed of three equations (one for each physical property) with three unknowns are solved to determine the unknown sample's composition. This method can be used as an initial screening method to determine both the TAG and FAME content in a sample, to be implemented prior to the performance of the GC analysis, because the results obtained in this study have shown that the approach proposed was able to determine mass fractions of quaternary systems with both a Mean Absolute Error (MAE) and Root Mean Square Deviation (RMSD) of less than 0.03.