Optimization of an experimental membrane reactor for low-temperature methane steam reforming

The systematic and rigorous model-based optimization of the configuration and operating conditions of a methane membrane steam reforming reactor for hydrogen production is performed. A permeable membrane with Pd–Ru deposited on a ceramic dense support is used to selectively remove the produced hydrogen from the reaction zone. The shifted chemical equilibrium towards hydrogen production enables the achievement of high methane conversion at relatively low reactor temperature levels. Steam reforming takes place over a Ni–Pt/CeZnLa ceramic foam-supported catalyst that ensures better thermal distribution, at an operating temperature of 773 K and a pressure of 10⁶ Pa. A nonlinear, two-dimensional, and pseudo-homogeneous mathematical model of the membrane fixed-bed reactor is developed and subsequently validated using experimental data. For model validation purposes, two sets of experiments have been performed at the experimental reactor installed at CPERI/CERTH. The first set of experiments aims to investigate membrane permeability in order to estimate the parameters involved in the applied Sieverts law. The second set of experiments explores the performance of the membrane reactor at different steam to carbon ratios and total inlet volumetric flowrates. The derived mathematical model, consisted of mass, energy, and momentum balances that consider both axial and radial gradients of temperature and concentration, is then utilized within a model-based optimization framework that calculates the optimal operating conditions for the highly interactive reactor system. The optimal steam to carbon ratio and sweep gas flow rate that minimize the overall methane utilization (i.e., reformed methane and equivalent methane for heating purposes) are calculated for a range of hydrogen production rates. Τhe optimal reactor design configuration described by the length of the catalyst zone is also obtained for a given pure hydrogen production rate.