Aqueous-phase methane reforming by nonthermal plasma: Process evaluation and optimization for hydrogen-rich syngas production

Although hydrogen is a clean fuel that generates no direct carbon emissions upon combustion, its production through green pathways is normally cost-prohibitive. In this study, hydrogen-rich syngas production from methane and liquid water was evaluated via nonthermal plasma-assisted aqueous reforming using a resistive barrier discharge system as an alternative to conventional steam methane reforming. Process evaluation focused on applied power (250–513 W), methane gas flow rate (200–1200 mL/min), and liquid water flow rate (45–180 mL/min). A 33 factorial design for initial screening followed by central composite design (CCD) for optimization identified distinct operational regimes for different process objectives. The factorial range demonstrated better methane conversion efficiency with up to 96% hydrogen molar yield whereas the expanded CCD range favored hydrogen production economics, achieving 35.7 mmol/min production rate which corresponded to a production cost of $4.8/kg. Liquid flow rate emerged as the most dominant factor, with low flow conditions consistently enhancing performance across all metrics due to increased residence time. Syngas quality analysis revealed H2/CO ratios between 2.0 and 5.9, suitable for diverse downstream applications including Fischer-Tropsch synthesis and hydrogen applications. The process demonstrated remarkable operational flexibility, such as operating under mild conditions yet achieving competitive performance metrics to establish nonthermal plasma-assisted aqueous methane reforming as a viable alternative to conventional high-temperature reforming technologies through reduced infrastructure requirements, enhanced process control capabilities, and greater potential for distributed production.