Biodiesel is a blend of fatty acid methyl esters. For the initial test of the notional modified Bouveault-Blanc reduction, it would be better to use a pure reactant to simplify product analysis. Stearic acid can be converted to methyl stearate using an excess of methanol and a few drops of concentrated sulfuric acid as catalyst. To get the stearic acid into the methanol, the solution must be heated to its boiling point (65°C). Instead of replacing the methanol as it is boiled off, it is less expensive and more environmentally friendly to condense the methanol vapor and re-use it in the reaction.
In a typical organic laboratory, one would typically employ a round-bottom flask with a condenser for refluxing. However, in the absence of a proper condenser, anything that can cool the methanol vapor will do! As can be seen in the picture, a round-bottom reaction vessel half-filled with ice water can be very effective in condensing the methanol vapor.
The stearic acid initially formed a white opaque slurry with the methanol and a clear colorless liquid when melted. Two hours into the reflux, and the reaction solution has taken on a yellowish-tint (similar to biodiesel). Success?