Methanol formation from the treatment of glycerol in supercritical water and with ethylsulfide

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Methanol is found to be a major product when glycerol decomposes under supercritical water conditions. Glycerol is a significant byproduct of biodiesel waste streams, the value of which is decreasing as biodiesel output increases. The transformation of glycerol into methanol, which is a feedstock for biodiesel production, would potentially reduce the costs and climate impact of biodiesel production. The highest yield of methanol was found at 450°C, 300bar after 30min residence time. Addition of ethylsulfide increases the rate but does not improve the methanol yield. At longer residence times, methanol and acetaldehyde were consumed and acetic acid was produced. The generation of significant quantities of methanol (non-catalytically) from glycerol was not previously observed, and thus no mechanism for methanol production had been proposed in the published literature. A detailed kinetic model for the glycerol plus supercritical water system was constructed using the Reaction Mechanism Generator (RMG) software package. All the parameter values in this large model were predicted a priori based on quantum chemistry calculations; none were adjusted to try to match our data, which serves as a test set for the model predictions. The a priori kinetic model predicts yields of acrolein, acetic acid and acetaldehyde similar to those measured by previous researchers. However, the model underpredicted the yield of methanol measured in our experiments. We speculate that the generation of higher concentrations of methanol in our experiments than in prior work might be due to catalytic reactions on the reactor walls, since our reactor has different metallurgy than those used in prior studies.