Energy and mass intensities in hydrogen upgrading by a membrane reactor

The necessity arose in the last decennia for the redesign of industrial processes with new unit operations for addressing environmental concerns which has led to the definition of new process indexes, so-called, metrics, that together with the traditional parameters supply additional information for technology selection and identify operating conditions for making a process more profitable. Two sustainability indexes, mass and energy intensities were used in a non-conventional evaluation of the up-grading stage in hydrogen production, i.e. the water gas shift, by means of membrane reactors. Defined as the ratio between the total inlet mass and total energy involved in the reactor, with respect to the hydrogen fed and produced by the reactor, they provide useful information about material exploitation and energy efficiency. The comparative study of membrane reactor performance with respect to conventional reactors was analysed as a function of the main process variables, i.e., pressure, feed molar ratio and space velocity. The membrane reactor resulted always in being more material (20-40%) and energy (20-35%) intensive than a traditional reactor and, in most of the cases, the values of its indexes exceeded the best one of a conventional reactor, corresponding at the equilibrium.