Equilibrium studies of canola oil transesterification using a sodium glyceroxide catalyst prepared from a biodiesel waste stream

• An anhydrous, hydroxide-free alkaline biodiesel catalyst was prepared.
• Crude glycerol was purified via distillation to make a catalyst formulation.
• The glycerol–glyceroxide formulation is soluble in methanol and non-viscous.
• The formulation catalyzes the transesterification of canola oil with methanol.
• Raw material costs of glyceroxide catalyst are less than industrially-used methoxide.

Crude glycerol is a low value by-product of the biodiesel industry, and its use as an alkaline catalyst component offers a cost-lowering strategy for sustainable fuel production. Sodium glyceroxide can be used to generate methoxide ions in situ, and the latter act as catalysts for the transesterification of triglycerides to fatty acid methyl esters (biodiesel, or FAMEs). Catalytic formulations of sodium glyceroxide were prepared from glycerol, methanol and NaOH, characterized by X-ray diffraction, and used for rapid transesterification of canola oil into biodiesel. The kinetics of the reaction using 6 and 9 M equivalents of methanol and 0.5 wt.% and 1.0 wt.% catalyst loading were studied by 1H NMR spectroscopy. Catalyst formulations prepared from crude glycerol performed transesterification reactions in methanol at a rate comparable to those observed for sodium hydroxide. Analogous to methoxide-catalyzed transesterifications, the reactions using glyceroxide appeared to be rate-limited by mass transfer. The relative viscosities of glyceroxide formulations prepared in methanol are also presented, and show an inverse correlation between viscosity and increasing concentration, a trend characteristic of ionic glycerol solutions.