Oxidative Cleavage of Double Bonds Accompanied by Esterification: Toward Winter Biofuels

The poor cold-flow properties of biodiesel limit its application under low temperatures. In this work, a molecular restructuring strategy based on precise oxidative cleavage of unsaturated lipids followed by targeted esterification was developed to decrease the pour points of renewable ester-based fuels. Initially, a model triolein-rich triacylglycerol was oxidatively cleaved at 100 °C for 24 h using 1 wt % H2WO4/H2O2 (60%) catalyst under solvent-free conditions, affording functionalized oxygenated intermediates with more than 99% conversion of C═C bonds. The resulting oxidated products were subsequently esterified with a series of linear and branched alcohols. The desired products consisted predominantly of alkyl pelargonates and dialkyl azelates, as determined by GC–MS and verified by FTIR spectroscopy. Using isoamyl alcohol and 2-ethylhexan-1-ol as esterifying agents provided the highest decrease in pour point to −24 and −36 °C, respectively. Differential scanning calorimetry confirmed crystallization at significantly lower temperatures compared to the methyl esters. To evaluate the general applicability of this approach, nine commercial vegetable oils with diverse fatty acid profiles were thoroughly characterized via their iodine and acid values, refractive index, density, kinematic viscosity, calorific value, and NMR measurements. The H2WO4/H2O2 catalytic oxidative cleavage and subsequent acid-catalyzed esterification protocols were directly applied under identical operational parameters to the oil feedstocks. Among the investigated feedstocks, the rapeseed-derived ester mixture demonstrated the best low-temperature performance, exhibiting a pour point of −30 °C compared with −9 °C for the corresponding fatty acid methyl esters. These findings demonstrate that combining oxidative restructuring with rational selection of the esterifying alcohol provides an efficient strategy for renewable ester-based fluids with low pour points.