NOVELTY - The concurrent downflow reactor for converting a liquid feedstock e.g. biomass to a non-condensable gas product e.g. hydrogen using a heterogeneous catalyst (6), comprises a reaction chamber (2), an inlet (4) having a pressure Pi and adapted to feed the liquid feedstock to an upper portion of the reaction chamber, and an outlet (8) having a pressure Po and adapted to discharge the non-condensable gas product and an effluent stream from a lower portion of the reaction chamber, where Pi is greater than Po. The reaction chamber comprises reaction tubes each containing the catalyst.    USE - The concurrent downflow reactor is useful for converting a liquid feedstock to a non-condensable gas product e.g. hydrogen using a heterogeneous catalyst, where the non-condensable gas product is useful as a fuel source in a system for energy generation via proton exchange membrane (PEM) fuel cells, solid-oxide fuel cells, internal combustion engines or gas turbine gensets (all claimed). The liquid feedstock is biomass-derived oxygenated hydrocarbons.    ADVANTAGE - The concurrent downflow reactor ensures efficient production of hydrogen and light hydrocarbons from biomass-derived oxygenated hydrocarbons at lower pressures (15-50 bar) and lower temperature thus reducing the need for energy consuming pressure systems and minimizing the occurrence of undesirable decomposition reactions typically encountered when carbohydrates are heated to elevated temperatures, and improves the selectivity, stability and efficiency of the conversion process.    DETAILED DESCRIPTION - The concurrent downflow reactor for converting a liquid feedstock e.g. biomass to a non-condensable gas product e.g. hydrogen using a heterogeneous catalyst (6), comprises a reaction chamber (2), an inlet (4) having a pressure Pi and adapted to feed the liquid feedstock to an upper portion of the reaction chamber, and an outlet (8) having a pressure Po and adapted to discharge the non-condensable gas product and an effluent stream from a lower portion of the reaction chamber, where Pi is greater than Po. The reaction chamber comprises reaction tubes each containing the catalyst, an outer shell adapted to enclose the reaction tubes, and a heating system adapted to introduce a heating medium into the shell to provide heat to the reaction tubes. The catalyst comprises a catalytic material. The feedstock comprises water and a water-soluble oxygenated hydrocarbon. An INDEPENDENT CLAIM is included for a method for the manufacture of non-condensable gas.    DESCRIPTION OF DRAWING(S) - The diagram shows a single chamber reactor system.    Reaction chamber (2)    Inlet (4)    Heterogeneous catalyst (6)    Outlet. (8)