No abstract

Membrane electrode assemblies (MEA) based on proton-conducting electrolyte membranes offer opportunities for the electrochemical compression of hydrogen. Mechanical hydrogen compression, which is more-mature technology, can suffer from low reliability, noise, and maintenance costs. Proton-conducting electrolyte membranes may be polymers (e.g., Nafion) or protonic-ceramics (e.g., yttrium-doped barium zirconates). Using a thermodynamics-based analysis, the paper explores technology implications for these two membrane types. The operating temperature has a dominant influence on the technology, with polymers needing low-temperature and protonic-ceramics needing elevated temperatures. Polymer membranes usually require pure hydrogen feed streams, but can compress H 2 efficiently. Reactors based on protonic-ceramics can effectively integrate steam reforming, hydrogen separation, and electrochemical compression. However, because of the high temperature (e.g., 600 ° C) needed to enable viable proton conductivity, the efficiency of protonic-ceramic compression is significantly lower than that of polymer-membrane compression. The thermodynamics analysis suggests significant benefits associated with systems that combine protonic-ceramic reactors to reform fuels and deliver lightly compressed H 2 (e.g., 5 bar) to an electrochemical compressor using a polymer electrolyte to compress to very high pressure.

Computational simulations are developed and applied to study the coupling of packed-bed methane dehydroaromatization (MDA) reactors with hydrogen-selective membranes, for the production of value-added fuels, particularly benzene. Detailed chemical kinetics for reforming over bifunctional Mo/H-ZSM-5 catalysts are validated against published literature, and simulations explore the effect of hydrogen removal and operating conditions. Although results reveal that membrane integration significantly increases conversion, the desired benzene selectivity decreases, due to the increased yield of undesired byproducts such as naphthalene. The benzene-to-naphthalene ratio depends strongly on hydrogen removal, and simulations demonstrate that hydrogen membranes are most beneficial at relatively high GHSV and relatively low catalyst temperature. Increasing pressure decreases conversion and benzene selectivity, but increases benzene production rates and does not affect naphthalene selectivity. Single-pass benzene yield remains low; however, results predict that multipass reactor designs with hydrogen membranes and increased pressure can operate continuously to increase benzene production rates.

No abstract

No abstract