Scaling up the advanced dry reforming of methane (DRM) reactor system for multi-walled carbon nanotubes and syngas production: An experimental and modeling study
Mohamed S. Challiwala, Gasim Ibrahim, Hanif A. Choudhury, Nimir O. Elbashir
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.