A hydrocarbon is reacted with water in the presence of a catalyst to form hydrogen, carbon monoxide, and carbon dioxide. Hydrogen is selectively allowed to pass through a hydrogen separation membrane to a permeate side of a reactor, while water and carbon-containing compounds remain in a retentate side of the reactor. An outlet stream is flowed from the retentate side to a heat exchanger. The outlet stream is cooled to form a cooled stream. The cooled stream is separated into a liquid phase and a vapor phase. The liquid phase is flowed to the heat exchanger and heated to form steam. The vapor phase is cooled to form condensed water and a first offgas stream. The first offgas stream is cooled to form condensed carbon dioxide and a second offgas stream. The steam and the second offgas stream are recycled to the reactor.