R. Kumal, A. Gharpure, A. Mantri, K. Zeller, V. Viswanathan, G. Skoptsov, R. Vander Wal
Penn State University,
Keywords: graphene, conductive carbon, microwave, plasma synthesis, TEM
Summary:The advanced plasma technology practically and cost-effectively converts natural gas to value-added chemicals and premium carbon materials such as graphene and conductive carbon black analogues (CCBA) with no CO2 emissions and low capital and infrastructure expenditures. A microwave driven plasma drives hydrocarbon decomposition – producing a variety of carbon nanostructures without the use of catalyst. With lower-energy requirements than conventional thermal plasmas, reactions in microwave plasmas are driven by electron kinetics rather than thermodynamics, and their non-equilibrium energy distribution opens reaction pathways that are unavailable with conventional chemical or thermal plasma processes. The form and purity of carbon material can be controlled by optimizing the several interrelated parameters that include methane to hydrogen ratio in the feed stream and reactor conditions such as input energy and formation temperature. Primary products include nanographene comprised of 2-6 sheets per stack with lateral dimensions between 100 and 500 nm, and graphitic carbon particles with structure analogous to conductive carbon blacks. Analytical techniques including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman spectroscopy and electrical conductivity measurements are utilized to study the form and quality of these valued carbon materials. Optical spectra are collected and analyzed to determine the formation temperature of these carbons using blackbody radiation and C2* Swan band emission. The electrical conductivity of the as-produced CCBA material is higher than that of commercially available conductive carbon blacks. These results highlight the importance of advanced plasma technology for the economic utilization of natural gas by producing premium carbon materials.