High-yield Hydrogen Production by Supercritical Water Gasification of Various Feedstocks : Alcohols, Glucose, Glycerol and Long-chain Alkanes

Abstract

Continuous supercritical water gasification (SCWG) of various feedstocks of C1–C16 was conducted to producehydrogen-rich gas. These feedstocks represent model compounds of biomass such as methanol/ethanol (alcohol-type), glucose and glycerol (byproducts of biodiesel synthesis), and model compounds of petroleum fuels such asiso-octane/n-octane (gasoline), n-decane/n-dodecane (jet fuels) and n-hexadecane (diesel). Almost complete gasifi-cation of all the feedstocks was achieved at 25 MPa, 740◦C and 10 wt% with low total organic carbon values of theirliquid effluents. The hydrogen gas yields of each feedstock were very similar to the theoretical equilibrium yieldsestimated by Gibbs free energy minimization. SCWG at different gasification temperatures (650 and 740◦C) and con-centrations (10 and 20 wt%) revealed that methanol and ethanol (alcohols), the simple oxygenated hydrocarbons,were easier to be gasified, producing negligible amounts of liquid products, when compared with long-chain hydro-carbons (iso-octane and n-decane) under the identical conditions. When the feedstock concentration was increasedfrom 10 to 20 wt%, the equilibrium hydrogen ratio from iso-octane gasification decreased from 1.02 to 0.79 while thatof n-decane increased from 1.12 to 1.50, implying that a branched hydrocarbon may be more resistant to gasificationin supercritical water.