Plasma-Catalytic Methane Pyrolysis for Hydrogen and Valuable Carbons

Abstract

Current technologies for hydrogen production are based primarily on reforming of fossil fuels using steam, which produces large amount of carbon dioxide emissions (> 9 tons of CO2 per ton of hydrogen produced). Majority of refineries, ammonia producers, and fuel cell power plants utilize steam methane reforming for production of hydrogen at scale.In this paper, we discuss an approach for activating methane and pyrolyzing using molten metal based alloys that includes Gallium. Sunkara’s group had developed this process earlier for making carbon micro-tubes with tunable morphology.[1, 2] Here, experiments were performed using pure methane, acetylene suggests a potential pathway for complete pyrolysis through recycle to produce hydrogen and carbons. The carbons produced are high surface area and are also do not contain any impurities. Majority of the carbons produced contain graphene sheets in random manner along with onion morphologies.The mechanism of methane pyrolysis involves a similar mechanism as that of silicon dissolution from silanes into molten Gallium. The activated species dissolve into molten Ga [3] and then undergo dehydrogenation reactions resulting in carbon nucleation and growth on molten Ga surface. The immiscibility of carbon and molten Ga allows for easier separation of resulting carbons through simple scraping from the surface.Techno-economic analysis suggests that the cost of hydrogen produced using the proposed catalytic technology could be less than $1/kg if the carbon by-product has value > $3/kg. Such low cost of hydrogen production is only possible if the following technical specifications are met: methane conversion is greater than 90%; scalable to 100 tons per year; and reduced loss and re-use of catalyst. Bhimarasetti, G., J.M. Cowley, and M.K. Sunkara, Carbon microtubes: tuning internal diameters and conical angles. Nanotechnology, 2005. 16(7): p. S362. Bhimarasetti, G., et al., Morphological Control of Tapered and Multi‐Junctioned Carbon Tubular Structures.Advanced Materials, 2003. 15(19): p. 1629-1632. Carreon, M.L., et al., Synergistic interactions of H2 and N2 with molten gallium in the presence of plasma. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2018. 36(2): p. 021303.