(605a) Methane Conversion Using Catalytic Melts to Produce Separable Carbon and Hydrogen or Electrical Power

Authors: 
Upham, D. C. - Presenter, Stanford University
Gordon, M., University of California
Metiu, H., University of California - Santa Barbara
McFarland, E. W., University of California, Santa Barbara
Snodgrass, Z., University of California Santa Barbara
Methane conversion without the co-production of carbon dioxide remains an important challenge for the production of chemicals and electrical power. Partially oxidizing methane to carbon instead of carbon dioxide prevents greenhouse gas emission and allows for the carbon to be stored or used as a valuable solid product. Catalytic processes to convert methane to carbon and products have been challenged due to carbon deposition and fouling; however, molten catalysts have the potential to overcome this challenge because carbon can float and be continuously removed. Recently, we reported liquid metal catalysts to convert methane to carbon and hydrogen without deactivating1. In this system, active metals for methane pyrolysis are dissolved in inactive low-melting temperature metals to produce stable molten catalysts, and density function theory calculations indicated that the active metal was negatively charged and its charge correlated with experimentally observed activity. The carbon produced is soluble in the melt and precipitates as graphitic carbon flakes.

These concepts are also used for a catalyst for the partial combustion of methane, whereby methane and oxygen are converted to carbon, steam, and heat (reaction 1).

CH­4 + O2 -> C + 2 H2O DG° = 424 kJ/mol, DH° = 497 kJ/mol (1)

Electrical power can be produced from the heat and steam. A molten salt is used to catalyze the reaction and separate the carbon, and a steam cycle is proposed to co-generate power. Selectivity of 90% at 56% methane conversion in a 12 cm bubble column reactor is reported. The reaction mechanism is investigated by feeding intermediates, altering salt composition, and determining apparent activation energies. A kinetic model will be presented which is used to explain the product distribution when reaction intermediates are fed. Carbon is characterized by Raman, SEM, and EDX which suggest carbon black is formed and several mechanisms of removal are discussed.

1 Upham, D. C. et al. Catalytic molten metals for the direct conversion of methane to hydrogen and separable carbon. Science 358, 917 (2017).

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