Fast Analysis of Non-Traditional Gasoline Additives with GC-VUV Spectroscopy

The transition from fossil fuels to gasoline involves significant refining work, including the addition of compounds that enhance performance. "Traditional" additives, such as methanol, benzene, and MTBE, have been successfully used to achieve a boost in octane rating, for example, but come with detrimental effects to human health, engine health, and the environment. For these reasons, there has been a push for new, “non-traditional” gasoline additives (NTGAs) that can give the fuel properties needed without harmful side-effects. Aside from these beneficial additives, it’s possible that new, harmful additives could be found in gasoline. For example, the Asian Clean Fuels Association identified a list of cheap octane-boosting compounds found in Asian gasoline that may introduce negative effects, such as gum formation in the engine. With these new additives surfacing, both beneficial and harmful, proper analytical techniques are needed for future gasoline monitoring. Gas chromatography combined with vacuum ultraviolet spectroscopy (GC-VUV) is versatile enough to carry out routine gasoline analysis while being able to quickly identify NTGAs that unexpectedly emerge.

Traditionally, refineries use methods such as detailed hydrocarbon analysis (DHA) to characterise gasoline per ASTM D6730. DHA uses a GC-FID analysis with a run time of two or more hours and compounds are identified by retention time only. In addition, the inability to distinguish coelutions means that new compounds like NTGAs can’t be analysed using DHA. However, ASTM D8071 using GC-VUV has proven to be an effective alternative to DHA. This new method can quantify the paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) contents in gasoline using a GC-VUV analysis with a run time under 35 minutes. The VGA-100 detector measures absorption in the 125 – 240 nm range, and because almost all compounds have a unique absorption profile in this wavelength range, individual components of gasoline can be characterised using both retention index and spectral matching. Additionally, coeluting compounds can be easily distinguished and quantified using spectral deconvolution.

This setup is perfect for the analysis of NTGAs, as novel compounds can easily be added to the VUV spectral library and analysed using the GC-VUV method conditions of ASTM D8071. For example, acetone is considered a harmful NTGA that can be identified and quantified with GC-VUV. Even though it coelutes with iso-pentane under ASTM D8071 conditions, spectral deconvolution can separate the two peaks and individually quantify them.

To demonstrate the utility of GC-VUV in NTGAs analysis, 30 NTGAs were spiked into gasoline at concentrations of 1%, 3%, 5%, and 10% v/v and analysing each sample using the GC-VUV conditions of ASTM D8071. The NTGAs analysed included alcohols, ketones, acetates, furans, and more. The experiment demonstrated reproducibly accurate determinations of each NTGA. Additionally, three NTGAs (dimethoxymethane, N-methylaniline, and 2,5-dimethylfuran) were analysed under a wider concentration range from 0.05% to 20%; again, GC-VUV yielded reproducible and linear results.

Combining a significantly shorter analysis time, the ability to analyze novel compounds, and automated data processing, the Automated Fuels Analyser by VUV Analytics provides a great deal of flexibility to oil refineries over traditional methods.

^{By: Ryan Schonert, Applications Scientist, VUV Analytics}