Locally Sustainable Biodiesel Production from Waste Cooking Oil and Grease Using a Deep Eutectic Solvent:...

As part of local sustainability efforts, biodiesel was synthesized via transesterification using a deep eutectic solvent (DES) without further washing from on-campus, dining facility waste cooking oil and grease. Before moving forward with repurposing used DES as a solvent in chemistry teaching labs, we determined the suitability of the biodiesel as an alternative fuel blended with diesel to power campus utility vehicles. Biodiesel components were characterized by gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (¹H NMR), viscometer, differential scanning calorimetry (DSC), and evolved gas analysis during pyrolysis with a thermogravimetric analyzer coupled with FTIR (TGA-FTIR). The four major components of fatty acid methyl esters (FAMEs) in the biodiesel were methyl oleate, methyl linoleate, methyl palmitate, and methyl stearate. Kinematic viscosity over typical temperature ranges was within optimal values recommended by the American Biodiesel Standard (ASTM D6751), with a 30:70 biodiesel/diesel blend experimental viscosity of 3.43 cSt at 40 °C and a calculated viscosity of 10.13 cSt at 0 °C. The pure biodiesel's cold-temperature onset of crystal formation is -10.1 °C versus -16.4 °C for a 30:70 biodiesel/diesel blend. Pyrolysis indicates good thermal stability, however, with an increased CO₂ evolution in the blended fuel at higher temperatures as compared to that in the pure biodiesel and the pure diesel. Combustion gas analysis indicates virtually complete combustion of the blended fuel to CO₂ and H₂O with only trace amounts of CO. Overall results indicate that the biodiesel synthesized using DES is a suitable fuel for campus utility vehicles in the local moderate temperature climate and affords increased local sustainability by using used DES repurposed in our chemistry teaching labs.