Scaling up the advanced dry reforming of methane (DRM) reactor system for multi-walled carbon nanotubes and syngas production: An experimental and modeling study

Abstract

Dry reforming of methane (DRM) offers an avenue for converting carbon dioxide (CO2) and methane (CH4)—the two major greenhouse gases—into syngas, a vital chemical precursor. However, DRM is constrained by high energy demands, catalyst deactivation, and an unfavorable H2/CO ratio. Previously, a unique dual-reactor system that produces multi-walled carbon nanotubes (MWCNTs) and syngas as products was proposed. This system offers at least 65 % CO2 conversion at 50 % of the energy demands of DRM. The present study experimentally proves and scales the concept from the milligram scale to the multi-gram scale and, ultimately to the multi-kilogram scale of MWCNT production. This study also introduces and experimentally validates a lumped Langmuir-Hinshelwood-Haugen-Watson (LHHW) kinetics model capturing a network of nine primary reactions involving CO, O2, H2, CH4, CO2, H2O, and solid carbon. The model performs within a 5 % error margin at the milligram scale for the carbon formation rate at 550 °C. The model is validated at 500 °C, 550 °C, and 600 °C on a multi-gram scale to capture the temperature effect. The CH4-conversion and CO2-conversion predictabilities at this scale are within 8 % and 30 % error margins, respectively. At a multi-kilogram scale, the model predicts the carbon formation rate within a 21 % error margin at 550 °C. Finally, characterization of the MWCNTs using Raman, SEM, TEM, STEM, and TGA-DTA confirms MWCNT quality consistency at all scales. This study, in summary, provides valuable experimental scale-up data and a kinetics model that can serve as a foundation for the development of future commercial-scale reaction systems.