In this paper, an experimental investigation is presented that concerns the gasification of glycerol, glucose,
and pinewood in supercritical water. The batch experiments were performed in quartz capillary reactors with
an internal diameter of only 1 mm. Because these quartz reactors are catalytically inert, the process could be
studied in the absence of the interfering catalytic influence of a metal reactor wall, as used in all previous
studies. The reaction space has been mapped by performing over 700 experiments in which the temperature,
pressure, reaction time, and concentration of the feedstock were varied. The most important observations
were that the pressure turned out to have no effect on the conversion and product yields, and that,
noncatalytically, complete conversion to the gas phase is only possible for very diluted feedstock solutions
(<2 wt %). By adding ruthenium on a TiO2 carrier (Ru/TiO2) to the capillaries, the potential of heterogeneous
catalysis has been demonstrated. When adding this catalyst to the capillaries, glucose solutions in the range
of 1−17 wt % could be gasified completely.
Conversion in hot compressed water (e.g., 600 °C and 300 bar) is considered to be a promising
technique to treat very wet biomass or waste streams. In this paper, a new experimental method
is described that can be used to screen the operating window in a safe, cheap, and quick manner
(one measurement takes about 5 min). Small sealed quartz capillaries (i.d. = 1 mm) filled with
biomass or model compounds in water are heated rapidly in a fluidized bed to the desired reaction
temperature. The reaction pressure can be controlled accurately by the initial amount of solution
in the capillary. After a certain contact time, the capillaries are lifted out of the fluidized bed,
rapidly quenched, and destroyed to collect the produced gases for GC analysis. Results of
measurements for formic acid and glucose solutions have shown that the technique is reliable
enough for screening purposes including trend detection. For conversions above 30%, three
identical measurements are sufficient to produce reasonably accurate average values with a
confidence level of 95%.
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