UNS: Earth Abundant Membrane Reactors for Efficient Chemical Processing

Colorado School Of Mines, Golden CO

Investigators

Abstract

Wolden, 1512172 Membrane reactors integrate reaction and separation into a single unit operation where product is removed continuously, driving the reaction to completion while simultaneously performing product purification. The critical element in such reactors is the membrane, which is often a metal impregnated with a catalyst. Such membrane reactors, comprised of dense metal membranes that are selective to hydrogen, have great potential in numerous applications such as steam reforming of natural gas to produce hydrogen (which can then be used in alternate energy systems such as fuel cells). Palladium (Pd) and its alloys are the most widely used hydrogen membrane materials due to their ability to both dissociate hydrogen and because they have a high permeability to hydrogen across a wide range of temperatures. But, such membranes are too costly for practical applications. This project is aimed at finding replacement membrane materials that are cheaper yet usable in such processes. Earth abundant body centered cubic (BCC) metals such as Niobium (Nb), Tantalum (Ta), and Vanadium (V) and related alloys have the necessary hydrogen permeability but they lack the catalytic activity of Pd. The PIs plan to use nanostructured transition metal carbide thin films as effective and stable catalyst layers to enable the use of BCC membrane reactors in various practical chemical processes. They plan to test their reactor for both ammonia (NH3) decomposition and synthesis. Intellectual Merit In this project the PIs will develop BCC metal membranes for use in membrane reactors. In dense metal membranes hydrogen is dissociated into atomic hydrogen, and they will exploit the untapped chemical potential of this reagent to enable hydrogenation chemistries such as ammonia synthesis, which normally requires very high pressure. Asymmetric membranes, BCC metal foils with different catalyst layers, applied to the feed and permeate side, will be used. First, asymmetric structures will be used to discern and quantify the steps that control H2 permeation through BCC composite membranes. A critical materials challenge with the BCC metals is their proclivity to lose ductility when the hydrogen solubility exceeds a critical value. Asymmetric design concepts will be employed to gate the H2 flux at the high pressure feed side and quickly release it from the permeate surface. Such designs will be engineered to maximize permeance without sacrificing mechanical integrity. Lastly, asymmetric membranes with unique catalysts designed for reactant decomposition and product formation will be used to maximize the potential of membrane reactors for chemical synthesis. Broader Impacts Membrane reactors have potential to impact a range of industrially important processes from steam reforming to various de/hydrogenation chemistries. Steam reforming of methane can be driven to completion in a membrane reactor while simultaneously reducing operating temperatures from 900 to 500 °C, which could save >2 x 10^14 BTU/year over conventional processing in the US alone. The PIs will integrate an experimental module based on membrane reactor decomposition of NH3 into the senior transport and reactor engineering curricula. They plan to engage undergraduate researchers in this research. In addition two annual events will be held in partnership with the Boys and Girls Clubs of Metro Denver. These events will bring together low-income K - 12 students and undergraduates to engage in hands-on science activities with the themes of engineering and chemistry.