Noncatalytic gasification of isooctane in supercritical water: A Strategy for high-yield hydrogen production

Continuous supercritical water gasification of isooctane, a model gasoline compound, is investigated using an updraft gasification system. A new reactor material, Haynes® 230® alloy, is employed to run gasification reactions at high temperature and pressure (763 ± 2 °C; 25 MPa). A large-volume reactor is used (170 mL) to enable the gasification to be run at a long residence time, up to 120 s. Various gasification experiments are performed by changing the residence time (60–120 s), the isooctane concentration (6.3–14.7 wt%), and the oxidant concentration (equivalent oxidant ratio 0–0.3). The total gas yield and the hydrogen gas yield increase with increasing residence time. At 106 s and an isooctane concentration of 6.3 wt%, a very high hydrogen gas yield of 12.4 mol/mol isooctane, which is 50% of the theoretical maximum hydrogen gas yield and 92% of the equilibrium hydrogen gas yield under the given conditions, is achieved. Under these conditions, supercritical water partial oxidation does not increase the hydrogen gas yield significantly. The produced gases are hydrogen (68 mol%), carbon dioxide (20 mol%), methane (9.8 mol%), carbon monoxide (1.3 mol%), and ethane (0.9 mol%). The carbon gasification efficiency is in the range 75–91%, depending on the oxidant concentration. A comparison of supercritical water gasification with other conventional methods, including steam reforming, autothermal reforming, and partial oxidation, is also presented.