Concentrated solar-thermal methane pyrolysis in a porous substrate: Yield analysis via infrared laser absorption

In situ compositional analysis via laser absorption spectroscopy is used to characterize the output of a concentrated solar-thermal methane pyrolysis process over a range of test conditions. The novel thermo-chemical process involves directed radiation of a simulated solar source, focused onto a porous carbon felt substrate through which methane flows and decomposes to produce primarily hydrogen gas and graphitic carbon, along with residual hydrocarbons. A mid-infrared laser diagnostic setup has been developed to measure the residual concentrations of light hydrocarbons in the pyrolysis product gas downstream of the reaction zone, with real-time on-line monitoring capability. The infrared absorption sensor utilizes two interband cascade lasers (ICLs) to probe the fundamental C-H stretch vibrational bands, targeting (1) the R(15) manifold of the & nu;3 band of CH 4 as well as one R(14) transition of the & nu;9 band of C 2 H 4 near 3.16 & mu;m and (2) the R Q 3 line cluster of C 2 H 6 near 3.34 & mu;m, respectively. A compositional analysis based on carbon and hydrogen balances is developed to characterize the hydrogen and carbon yields of the pyrolysis process using laser absorption measurements and deposited carbon weight. A range of test conditions are examined with variations of flow rate and solar flux, demonstrating real-time monitoring of product gas composition and sensitivity to operating conditions in variable and transient conditions.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.