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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.

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Derive general friction-factor correlations for cylinder-in-channel configurations. Evaluate the influence of cylinder size and placement within rectangular channel. Evaluate the influence of rectangular-channel aspect ratio. Predict pressure drop and two-dimensional velocity distributions. Enable the quantification of capillary-probe influence in catalyst monoliths. a b s t r a c tThis paper develops models for steady-state, fully developed, laminar flow in rectangular channels with internal coaxial solid cylinders. By casting and solving the parallel-flow momentum equation in a dimensionless setting, correlations are derived for the friction factor f and represented as Ref where Re is the Reynolds number. The correlations consider three positions for the internal cylinder. The cylinder may be in the center of the rectangular channel, in the corner of the channel, or resting at the middle of the channel floor. The correlations incorporate channel aspect ratios in the range α ≤ ≤ 0.1 1.0. The cylinder-diameter aspect ratios β range from being vanishingly small to being large enough to touch the channel walls. Although the results are general, the study is motivated by considering the effects of diagnostic probes within small channels of catalytic monoliths.

A novel process for producing thick protonic ceramics for use in hydrogen separation membrane reactors is demonstrated. Polymer clay bodies based on polyvinyl acetate (PVA) and mineral oil were formulated, and they permitted parts with complex architectures to be prepared by simple, low-pressure molding in the unfired, “green” state. Ceramic proton conductors based on doped barium zirconate/cerate, made by solid-state reactive sintering, are particularly well-suited for the polymer clay process. In this work, the ceramic proton conductor, BZCY755 (BaZr0.75Ce0.05Y0.2O3−d) was fabricated into a variety of shapes and sizes. Test coupons were produced to confirm that the polymer clay route leads to a high-quality ceramic material suitable for the demanding environment of high-temperature membrane reactors. It has been demonstrated that protonic ceramic specimens with the requisite properties are easily prepared at the laboratory scale. The polymer clay fabrication route opens up the possibility of high-volume, low-cost manufacturing at a commercial scale, by a process similar to how dinnerware and sanitary porcelain are produced today.

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