Unveiling carbon coking in hydrocarbon-fueled systems via normalized in situ gas chromatography

Abstract

Coking significantly degrades hydrocarbon-fueled system performance, making its analysis a critical challenge. Real-time monitoring of coking is typically conducted using current–voltage (I–V) or impedance spectroscopy. In most studies, systems have been considered stable against coking if no electrochemical degradation is observed. This study proposes the use of gas chromatography (GC) to investigate in situ coking behavior. Although quantifying coking using GC is inherently challenging owing to error margins, a normalization methodology was developed by systematically varying steam-to-carbon (S/C) ratios, allowing for a reliable analysis of relative coking trends despite absolute quantification limitations. The normalized values were defined as Δcoking, which represents an indicator of relative carbon deposition trends rather than the absolute amount of deposited carbon. The errors associated with the analysis process were minimized by fixing all the variables except for the hydrocarbon flow rate. In methane-utilized solid oxide fuel cells (SOFCs), performance remains stable at an S/C ratio of 1.5 or higher, which indicates that coking may not occur. However, applying a normalization methodology reveals coking behaviors that cannot be detected through electrochemical analysis alone. The reproducibility of the in situ GC-based coking analysis technique was validated by comparing carbon coking behavior between bare and coke-resistant catalyst-infiltrated anodes. The cell decorated with catalysts exhibited significantly lower Δcoking values under varying S/C ratios, confirming the method's reliability in evaluating coking resistance. This highlights the limitations of traditional approaches for detecting subtle coking phenomena and demonstrates the value of GC for precise coking analysis, thereby advancing the understanding and mitigation of coking in hydrocarbon-fueled systems. © 2026