New Proton Nuclear Magnetic Resonance-Based Derivation for Quantification of Alkyl Esters Generated Using Biocatalysis

Monoalkyl esters of fatty acids commonly known as biodiesel are synthesized from triglycerides by the transesterification reaction with monohydric alcohol, usually methanol or ethanol. Biodiesel is an attractive alternative fuel for diesel engines because of its renewability, biodegradability, and nontoxicity. Several methods/approaches have been developed for analyzing the fuel quality of biodiesel. Mainly chromatographic techniques [e.g., gas chromatography (GC), high-performance liquid chromatography, etc.] are being used for the analysis of biodiesel. The equation for quantification of the transesterification reaction using proton nuclear magnetic resonance (¹H NMR) is available in the literature, wherein methanol/ethanol are being used as an acyl acceptor. In the present work, we report the equation based on ¹H NMR, which can be used for the quantification of the transesterification reaction, using other primary alcohols as an acyl acceptor. Simultaneously, we have also studied the effect of the chain length of alcohols on the extent of transesterification using whole cell catalysts. Transesterification was enhanced using butanol (67%) and pentanol (76%), followed by a decrease with hexanol (66%) and octanol (56%). The correlation coefficient (R²) between GC and ¹H NMR methods was 0.97. The results obtained by the new ¹H NMR equation proposed in this work were well-correlated with GC analysis of the same samples.