A membrane reactor for hydrogen storage and transport system using cyclohexane–methylcyclohexane mixtures Original Research Article

Cyclohexane is recognized to be one of the promising hydrogen storage materials but it is pointed out that its freezing point (ca. 6.5°C) is too high to use in the cold district. In this study, therefore, the mixtures of cyclohexane with methylcyclohexane as a hybrid chemical hydride were proposed to lower the freezing point. The hydrogen recovery from the mixtures was testified by being dehydrogenated with a palladium membrane reactor up to 300°C and 4 bar, in which hydrogen generated was selectively separated from the catalyst-packed bed through a palladium membrane and obtained as purified hydrogen on the permeate side. An addition of 20 mol% methylcyclohexane to cyclohexane resulted in about 40°C decrease in the freezing point. The increase in conversion became larger in a region of high reaction pressure because a larger pressure difference increased the amount of hydrogen separated. The conversion of methylcyclohexane was higher than that of cyclohexane at the same condition. In the dehydrogenation of the mixtures, each conversion was found not to be affected by the other very much. In conclusion, the mixtures of methylcyclohexane and cyclohexane can be a hybrid type of chemical hydride, which will be available as a liquid hydrogen carrier at −30°C.