CO-free production of hydrogen via stepwise steam reforming of methane

CO-free hydrogen is produced by the reversible cyclic stepwise steam reforming of methane for use in fuel cells and other processes that are sensitive to CO poisoning. The process consists of two steps involving the decomposition of methane in a first step followed by steam gasification of the surface carbon in a second step. The ease of carbon removal in step II is strongly dependent on temperature and surface coverage of carbon. To optimize the process conditions, we have investigated this cyclic methane steam-reforming process as a function of temperature and surface coverage of carbon. These studies show that it becomes increasingly difficult to remove the surface carbon at higher temperatures and coverage. Since higher temperatures favor methane conversion and hydrogen production in step I, it is essential to delicately optimize the temperature conditions for the process. The hydrogen produced in step I of the cyclic process in the optimum range of temperature conditions (less than or equal to 673 K) is CO-free (<20 ppm). The amount of H-2 produced in step I varies from 1.0 to 1.3 mol/mol methane consumed. The optimum process conditions for carrying out the two-step process are temperatures of 648-673 K and a carbon surface coverage of 0.10-0.20 monolayer equivalents (MLEs). (C) 2000 Academic Press.