(124c) Natural Gas Decomposition and Separation of Solid Carbon and Hydrogen Products in High Temperature Molten Salts

Authors: 
McFarland, E. - Presenter, University of California
Metiu, H., University of California - Santa Barbara
Gordon, M., University of California
Kang, D., University of California
Rahimi, N., University of California
Palmer, C., University of California
Zeng, J., University of California
Tarazkar, M., University of California
Doherty, M. F., University of California
The lowest cost means of producing hydrogen and/or dispatchable electricity without CO2 emissions in the U.S. is potentially through a process utilizing methane pyrolysis of abundant, low-cost, natural gas. The challenge of achieving high methane reaction rates and high conversion to molecular hydrogen and separable solid carbon may be met using high temperature (~1000 oC) complex molten salt mixtures together with catalysts. High rates (>1 mole/m3-s) of methane decomposition and high selectivity for molecular hydrogen and solid carbon have been achieved with several multiphase salt-catalyst systems. When the physical properties of the liquids are selected optimally, separable solid carbon produced from pyrolysis in the high temperature melts which may be conveniently separated in bubble column reactors. In molten metal alloys and/or mixtures of irreducible halide salts hydrogen and graphitic carbon products are produced at high conversion and high selectivity and in forms which are separable from the melt in a single reactive separation. Solid catalysts (including Ni/Al2O3) suspended in specific melts are also shown to be continuously reactivated as the high temperature liquid serves as a solvent to remove carbonaceous surface deposits prior to the irreversible formation of deactivating coke. Single pass methane conversion of over 98% to molecular H2 at over 98% selectivity is demonstrated in several complex melt systems. Fundamentals of C-H bond activation on melt surfaces and the interactions with the gas phase chemistry will be discussed and distinctions made as to how the subsequent reaction pathways can produce different pyrolysis pathways and different types of solid carbons. Process designs for solid carbon synthesis with zero carbon hydrogen and/or electricity production together with relative technoeconomics will be presented.