Real-Time Monitoring of Transesterification by 1H NMR Spectroscopy: Catalyst Comparison and Improved Calculation for Biodiesel Conversion

A facile, rapid, and noninvasive method for monitoring transesterification of acylglycerols for the application of biodiesel production is reported. High-field NMR spectroscopic analysis prevents incorrect and overintegration of signals that have previously been combined due to crowding on low-field NMR spectrometers. Using high resolution NMR, a new and more accurate equation utilizing a nonoverlapping signal is presented for calculating biodiesel conversion. Here, we demonstrate the kinetic acquisition of high-resolution NMR spectra for real-time monitoring of the consumption and formation of triacylglycerols, diacylglycerols, and fatty acid methyl esters in biodiesel production. This method of reaction monitoring takes place on small scale in a standard NMR tube, is acquired with existing laboratory instruments, and avoids taking aliquots from a reaction. By comparing different catalysts and conditions, this method facilitates the selection/optimization of catalysts and may improve quality in compliance with fuel standards by assessing the reaction composition for models of an industrial transesterification system. Using this method, H2SO4, NaOH, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (a bifunctional, nonionic base) have been compared as catalysts for transesterification.

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