A new design of supercritical water gasification system was developed to achieve high hydrogen gas yield and good gas-liquid flow stability The apparatus consisted of a reaction zone, an insulation zone and a cooling zone that were directly connected to the reaction zone The reactor was set up at an inclination of 75 degrees from vertical position, and feed and water were introduced at the bottom of the reactor The performances of this new system were investigated with gasification of isooctane at various experimental conditions reaction temperatures of 601-676 degrees C, residence times of 6-33 s, isooctane concentrations of 5-33 wt%, and oxidant (hydrogen peroxide) concentrations up to 4507 mmol/L without using catalysts. A significant increase in hydrogen gas yield, almost four times higher than that from the previous up-down gasifier configuration (B Veriansyah, J Kim, J D Kim, Y W. Lee, Hydrogen Production by Gasification of Isooctane using Supercritical Water, Int. J Green Energy 5 (2008) 322-333) was observed with the present gasifier configuration High hydrogen gas yield (6 13 mol/mol isooctane) was obtained at high reaction temperature of 637 degrees C, a low feed concentration of 9 9 wt% and a long residence time of 18 s in the presence of 2701 1 mmol/L hydrogen peroxide At this condition, the produced gases mainly consisted of hydrogen (59 5 mol%), methane (14 8 mol%) and carbon dioxide (22.0 mol%), and a small amount of carbon monoxide (16 mol%) and C(2)-C(3) species (2 1 mol%) Reaction mechanisms of supercritical water gasification of isooctane were also presented Crown Copyright (C) 2009 Published by Elsevier Ltd on behalf of Professor T Nejat Veziroglu. All rights reserved