Reforming of methanol and glycerol in supercritical water

Reforming of pure glycerol, crude glycerin, and methanol (pure and in the presence of Na2CO3) in supercritical water was investigated. Continuous experiments were carried out at temperatures between 450 and 650 °C, residence times between 6 and 173 s, and feed concentrations of 3–20 wt%. For methanol the gas products are mainly H2, CO2, and CO. The carbon-to-gas efficiency and the observed activation energy for pure methanol are higher than for methanol with Na2CO3. This can be explained by assuming different decomposition mechanisms for pure methanol and methanol with Na2CO3. For glycerol, H2, CO, CO2, CH4, and higher hydrocarbons are produced. The carbon-to-gas efficiencies of crude glycerin and pure glycerol are comparable. Overall, 2 of the 3 carbon atoms present in glycerol end up in carbon oxides, while 1 carbon atom becomes CxHy. The overall mechanism of glycerol decomposition involves the dehydration of 1 mole of H2O/mole glycerol. For both, methanol and glycerol at carbon-to-gas efficiencies below 70%, the gas yields (mole/mole feed) and carbon-to-gas efficiency correlate well.

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► Methanol and glycerol are excellent feedstocks for reforming in supercritical water.
► The presence of Na2CO3 reduces the carbon-to-gas efficiency in methanol reforming.
► The presence of Na in glycerol reforming promotes the water–gas shift reaction.
► The gas yields in glycerol and methanol reforming correlate nicely with the carbon-to-gas efficiency.
► Glycerol reforming proceeds through dehydration of one mole H2O/mole glycerol.