Abstract:
Continuous supercritical water gasification of glucose is investigated with a recently
developed updraft gasification apparatus under various conditions: temperatures of 600
- 767 degree C, residence times of 15-60 s, glucose concentrations of 1.8-15 wt% and without
added a catalyst. The experimental gas yields are compared with predicted values at
equilibrium that are estimated via Gibbs free energy minimization. Total gas yields and
hydrogen gas yield increase with temperature. At 740 degree C and 1.8 wt%, hydrogen gas yields
become very high (10.5-11.2 mol/mol glucose). The hydrogen gas yields do not vary
significantly with different residence times. The hydrogen gas yield decreases to 5.7 mol/
mol glucose at 15 wt%, a value very close to the predicted value (6.3 mol/mol glucose). Only
acetic acid is detected in the liquid effluents at temperatures above 740 degree C, while 42
products are detected at 600 degree C. The highest hydrogen gas yield obtained in this study is
11.5 mol/mol glucose at 25 MPa, 767 degree C, and 1.8 wt%, for 60 s; this value is very close to the
theoretical equilibrium hydrogen yield of 11.9 mol/mol glucose. Under these conditions,
the carbon efficiency is very high (91%) and total organic carbon (TOC) in the liquid product
is very low (23 ppm), indicating that glucose is almost completely converted to gaseous
products. Comparison with other work under similar operating conditions shows that the
current reactor is capable of attaining higher hydrogen gas yields at temperatures above
650 degree C. Possible explanations for the higher hydrogen gas yields are presented.
