NOVELTY - A hydrogen-producing reactor (10) comprises a housing containing a heating stream channel (16a), a hydrogen channel (14a), and a reaction channel (12b) positioned between the heating stream channel and hydrogen channel; a heat transfer sheet (20b) to separate the heating stream channel and the reaction channel; a porous support plate (24a) to separate the reaction channel and the hydrogen channel; a membrane (22a) positioned between the reaction channel and the hydrogen channel; and a catalyst positioned in the reaction channel.    USE - As a reactor (e.g. compact reactor or tube reactor) for producing hydrogen from a reaction stream including a mixture of supercritical water and a hydrocarbon fuel; useful in a system for producing hydrogen (claimed); useful in processes such as hydrogenation, ammonia synthesis, and useful in fuel cells.    ADVANTAGE - The reactor produces high purity hydrogen in an efficient and simple manner, from a mixture of supercritical water and the hydrocarbon fuel existing in gaseous, liquid or solid forms; and generates potentially valuable byproduct of high-pressure carbon dioxide useful in power plant or petrochemical complex applications. The hydrogen production is increased by changing operating conditions of the reactor. For example, by increasing the inlet pressure of the reaction stream, the driving force for the hydrogen separation is increased. Thus, reactors capable of sustaining higher pressures, such as the compact reactors, favor higher production of hydrogen production. In the reactor, equilibrium shift occurs in the reaction stream to favor hydrogen production. As the hydrogen concentration decreases in the reaction stream, the reaction shifts to produce more hydrogen. In addition, the removal of reaction product hydrogen, lowers the reaction temperature which increases the range of materials acceptable for the reactor, thus resulting in lower cost, better performance and increased ease of manufacture for the reactor.    DETAILED DESCRIPTION - A hydrogen-producing reactor (10) comprises a housing containing a heating stream channel (16a), a hydrogen channel (14a), and a reaction channel (12b) positioned between the heating stream channel and hydrogen channel; a heat transfer sheet (20b) to separate the heating stream channel and the reaction channel; a porous support plate (24a) to separate the reaction channel and the hydrogen channel; a membrane (22a) positioned between the reaction channel and the hydrogen channel; and a catalyst positioned in the reaction channel. The heating stream channel receives a heating stream (36) to provide heat to the reaction channel through the heat transfer sheet. The reaction channel receives a reaction stream including a mixture of supercritical water and a hydrocarbon fuel, so that hydrogen is produced in the reaction channel and is passed through the membrane into the hydrogen channel. An INDEPENDENT CLAIM is included for a method of producing hydrogen, involving heating water to a supercritical state; mixing the supercritical water with a hydrocarbon fuel to form a mixture; exposing the mixture to a catalyst and heat in the reactor, so that a reaction occurs to produce a product stream containing hydrogen; and separating hydrogen from the product stream.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an interior of a compact reactor.    reactor (10)    reaction channel (12b)    hydrogen channel (14a)    heating stream channel (16a)    heat transfer sheet (20b)    membrane (22a)    porous support plate (24a)    product stream (34)    heating stream. (36)