This proposal explores the possibility of developing a Nitrogen-Selective Membrane for CO2 Carbon Capture, which is a problem of immense scope and value to national interests. Instead of trying to separate CO2, which lacks the driving force of concentration, the focus is on a selective-nitrogen (N2) technology that takes advantage of the driving force of N2 in the flue gas stream. This technology requires a catalytic dense membrane in which N2 dissociates across the surface and then diffuses through the membrane as atomic N. Group V metals such as vanadium (V), niobium (Nb), and tantalum (Ta) have experimentally been shown to diffuse atomic N at similar rates to atomic hydrogen (H) in palladium (Pd), at very high temperatures, similar to those of the post-boiler conditions of a coal-fired power plant. Catalytic amounts of ruthenium in particular may be necessary to speed the dissociation of the N2 molecule at the membrane surface.
If the above separation were to prove feasible, the longer term studies would involve coupling a H2 purge on the permeate side of the membrane to attempt to convert the dissociated N atoms into ammonia at atmospheric pressure. The dissociation step is apparently rate limiting for NH3 production, and the species that is diffusing through the membrane is the atom. I would like the PI to try at least one experiment in the confines of this EAGER proposal to show proof-of-concept for NH3 generation.
This project will have great appeal to the student who will work on it. The opportunity to work on such a novel, yet easy to understand project, with such potential value in the global management of CO2 is quite attractive.
EAGER Award in Catalysis, 09/10-08/11, 1049535 Nitrogen-Selective Membrane for Carbon Capture Jennifer Wilcox, Energy Resources Engineering, Stanford University This project represents the first attempt to synthesize and test membranes that selectively separate nitrogen (N2) from gas mixtures. This novel, crosscutting technology will have numerous applications at the industrial scale, including carbon dioxide (CO2) capture from flue gas, natural gas purification, air separation, and ammonia synthesis. Within this work, metallic membranes made from alloys of ruthenium (Ru) and earth-abundant Group V metals, such as vanadium (V) and niobium (Nb), are considered for catalytic selective N2 separation. The efforts carried out include both theoretical modeling with electronic structure theory calculations and experimental testing using a high-temperature bench-scale membrane reactor. Within this work, a high-temperature membrane reactor was designed and constructed to carry out flux measurements on micron-thick metallic membrane foils for selective N2 separation from gas mixtures. Flux experiments on pure V and Nb foils at 1000 °C result in permeabilities of 1.1×10-10 mol/m?s?Pa1/2 and 1.3×10-10 mol/m?s?Pa1/2, respectively. In addition to flux measurements, electronic structure calculations have been carried out that reveal alloying these pure metals with Ru results in enhanced diffusivity and subsequent N2 permeability. Alloying V with Ru leads to a diffusivity increase of 2 orders of magnitude, i.e., a N2 diffusivity of 3×10-4 cm2/s. The ultimate goal is to continue these theoretical and experimental studies on the appropriate alloys outlined by theory, and to include comprehensive surface science experiments improve current understanding of N2 interactions with these metals.
