Nitrogen-containing compounds (NCCs) are known to contribute to fuel instability, which adversely influences fuel systems and engine performance, and results in increased maintenance problems and costs. These adverse events can affect operations for the commercial industry and military. In this work, a semi-qualitative and quantitative method was developed by using two-dimensional gas chromatography with a nitrogen chemiluminescence detector (GCxGC NCD) to classify and quantify NCCs in different transportation fuels. This method facilitated high throughput and increased robustness by circumventing extraction procedures.<br/><br/>For quantitation of nitrogen in NCCs, homoscedasticity was evaluated by using different weighted trend lines. The weighted 1/x trend line was shown to be the most accurate when quantitating six known mixtures of NCCs. The equimolar relative response factors (RRF) of ten compounds were evaluated, which showed that several analytes had similar responses. However, this was not true for all compounds as several compounds had RRF values less than 15 % of the reference compound, carbazole. Hence, equimolar responses were not observed for all compounds in this study. Alkylation was shown to also effect the RRF values. Evidence suggests that thermal-induced degradation of analytes by introduction into the GC inlet was not responsible for the smaller RRF values. The results suggest the importance of using corrections to accurately ascertain the concentration of different classes of NCCs in fuels.<br/><br/>A semi-qualitative template composed of several chromatographic bins was made by using the elution times of known compounds, which were highly repeatable. The template was used to classify the unknown NCCs in transportation fuels. The semi-qualitative method is an improvement over the simplified classification of NCCs in fuels as basic, non-basic and neutral. The elution times of NCCs representative of different classes were observed and therefore the roof tile method of classification was not employed as misidentification of analytes would occur. When different transportation fuels were compared, clear differences were observed in the chemical composition and concentration of NCCs. The GCxGC NCD method developed in this study showed it as an effective and repeatable tool to perform compositional analysis of NCCs in fuels. This information may aid in linking the composition to fuel properties, such as stability.

Evaluation of two-dimensional gas chromatography with to a nitrogen chemiluminescene detector to classify and quantify nitrogen-containing compounds in fuels

ACS Fall 2021

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