(55c) Modeling Tri-Reforming of Methane for Carbon Dioxide Utilization and Hydrogen Production

The growing global energy demand, fueled by population expansion, has led to a corresponding increase in CO₂ emissions, posing substantial challenges in addressing climate change. The ongoing energy transition emphasizes the need for cleaner energy alternatives, with natural gas and hydrogen being key contributors. At present, approximately 80% of hydrogen is generated through steam methane reforming, which releases over 10 kg of CO₂ per kilogram of hydrogen produced. Alternative methods, such as dry reforming of methane (DRM), have gained attention due to their potential for CO₂ utilization. Nevertheless, DRM encounters significant obstacles, including excessive carbon formation, an unfavorable syngas ratio (H₂:CO ratio) ,and high energy demands.

Amid various advancements in dry reforming of methane (DRM), including improvements in catalysis and process systems engineering aimed at overcoming its key challenges, tri-reforming of methane (TRM) has emerged as a more sustainable alternative. TRM combines CO₂, steam, and oxygen in the reforming process to mitigate the limitations of DRM. This study builds on existing TRM research by implementing a 1-D multi-scale pseudo-homogeneous reactor bed model, developed using Visual Basic for Applications (VBA) within Microsoft Excel, to simulate the TRM reaction. The kinetic model encompasses nine critical reactions, including steam reforming, dry reforming, water-gas shift, methanation, the Boudouard reaction, partial oxidation, and carbon gasification. Given the multi-reaction environment and the highly oxidizing conditions of the TRM process—driven by the presence of O₂, H₂O, and CO₂—a novel Ni-Cu catalyst, originally designed for DRM, is enhanced with promoters such as K⁺, Ca⁺, and Na⁺on Alumina, Silica, and Titania supports to increase catalyst stability in the TRM environment. The VBA tool developed in this work integrates regression analysis, enabling efficient fitting of the nine reaction parameters involved in TRM. The model also includes both internal and overall (bulk-phase) effectiveness factor calculations, accounting for reaction rates as well as transport limitations due to internal and external mass transfer constraints.

The findings indicate that the TRM process is not limited by mass transfer. Maximum CO₂ conversion and minimal carbon deposition are observed at elevated temperatures (>750°C) and low pressures (1 bar). Under optimal conditions—750°C, 1 bar, and a feed composition of CH₄:CO₂:H₂O:O₂ = 1:0.6:0.6:0.1 —balanced performance is achieved, with CO₂ and CH₄ conversions reaching 90% and 62%, respectively, and a H₂:CO ratio of 2, all while minimizing carbon formation and energy consumption. Radial scale-up studies, conducted for reactor diameters up to 4" ID, further demonstrate consistent conversions and negligible carbon formation, affirming the scalability potential of the reactor system.