Hydrogen production from supercritical water reforming of glycerol in an empty Inconel 625 reactor

• Supercritical water glycerol reforming was carried out in an Inconel 625 reactor.
• Carbon formation increases at higher residence time and higher temperatures.
• Operation at 525 °C, 250 bars, 23 s residence time, yields 91% conversion w/o carbon.
• Reforming in SCW yields higher conversion and lower carbon formation than at 1 atm.

Glycerol reforming was investigated under supercritical water conditions (450–575 °C, 250 bar). A feed containing 5 wt.% of glycerol was continuously fed to an empty Inconel 625 reactor. The products of the reaction were separated into gas and liquid phases in a condenser. At a feed rate of 2.15 g/min, the glycerol conversion significantly increased from 0.05 to 0.97 when increasing operating temperature from 450 to 575 °C. Although lowering the feed rate (i.e. increasing the residence time) could considerably improve the conversion, carbon formation became a problem especially at high operating temperatures (550–575 °C). The major gaseous products were hydrogen (approximately 60 mol%), carbon monoxide, carbon dioxide and methane with some traces of ethane, ethylene, propane, and propylene. Various liquid products were detected including acetaldehyde, acetol, methanol, acetic acid, propionaldehyde, allyl alcohol, acetone, acrolein, ethanol, ethylene glycol, and acrylic acid but the major liquid components were acetaldehyde and acetol. With a feed glycerol concentration of 2.5 wt.% and operating temperature of 525 °C, glycerol conversion of 0.91 and H2 yield of 2.86 can be obtained without carbon formation. Finally, it was demonstrated that higher H2 yield with much lower carbon formation was observed in supercritical water reforming (250 bar) compared to conventional steam reforming at 1 bar under similar temperatures.