NOVELTY - A fuel processor comprises hydrogen-producing region; hydrogen purification device comprising an enclosure defining an internal compartment; at least one hydrogen-selective membrane within the compartment; and support structure for the hydrogen-selective membrane. At least a portion of the fuel processor is a modular component.    USE - The fuel processor is used in fuel cell system.    ADVANTAGE - The invention enables the component or subcomponent to be accessed and/or removed and replaced without shutting down the fuel processor.    DETAILED DESCRIPTION - A fuel processor comprises:    (A) hydrogen-producing region adapted to receive a feed stream and to produce a mixed gas stream (24) containing hydrogen gas (26) and other gases (28) from the feed stream;    (B) hydrogen purification device (10) adapted to receive at least a portion of the mixed gas stream and to produce a hydrogen-rich stream containing at least hydrogen gas, where the hydrogen purification device comprises an enclosure (12) defining an internal compartment (18), where the enclosure includes at least one input port through which a mixed gas stream containing hydrogen gas is delivered to the enclosure, at least one product output port through which a permeate stream containing at least pure hydrogen gas is removed from the enclosure, and at least one byproduct output port through which a byproduct stream containing at least a portion of the other gases is removed from the enclosure, where the hydrogen-rich stream (34) includes at least a portion of the permeate stream;    (C) at least one hydrogen-selective membrane (46) within the compartment, where the hydrogen selective membrane has a coefficient of thermal expansion, a first surface adapted to be contacted by the mixed gas stream, and a permeate surface opposed to the first surface, where the permeate stream includes a portion of the mixed gas stream that passes through the hydrogen-selective membrane to the permeate surface, and further where the byproduct stream includes a portion of the mixed gas stream that does not pass through the hydrogen-selective membrane; and    (D) support structure adapted to support the hydrogen-selective membrane within the enclosure, where at least one of the enclosure or the support structure has a different composition than the hydrogen-selective membrane and is at least partially formed from an alloy that includes nickel and copper and which has a coefficient of thermal expansion that is the same as or within at least approximately 10% of the coefficient of thermal expansion of the hydrogen-selective membrane; and where at least a portion of the fuel processor is a modular component that is adapted to be accessed, removed from, and replaced as a unit into an operational position relative to the fuel processor.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view of a hydrogen purification device.    Hydrogen purification device (10)    Enclosure (12)    Internal compartment (18)    Mixed gas stream (24)    Hydrogen gas (26)    Other gases (28)    Hydrogen-rich stream (34)    Hydrogen-selective membrane (46)