8 May / June 2019
Fast Analysis of Non-Traditional Gasoline Additives with Gas Chromatography –
Vacuum Ultraviolet Spectroscopy by Ryan Schonert, Dan Wispinski, Jack Cochran VUV Analytics, 1500 Arrow Point Drive, Ste 805, Cedar Park, TX 78613, USA
Non-traditional gasoline additives (NTGAs) are being researched as beneficial octane-booster replacements for ethanol and methyl tert-butyl ether. Other octane-enhancing NTGAs, including acetone and N-methylaniline which can degrade automobile engine performance, are sometimes used illegally in gasolines outside the United States and Europe. Unfortunately, monitoring programs relying on ASTM D6730 (detailed hydrocarbon analysis) and ASTM 6839 (multidimensional gas chromatography) do not include most NTGAs in their scope. Gas chromatography (GC) with vacuum ultraviolet spectroscopy (VUV) offers an easy way to spectrally identify and quantify NTGAs in gasoline in under 34 minutes.
1. Introduction:
During the fuel refining process, various additives are blended into the fuel stream to adjust the fuel’s properties. Properties of interest include vapour pressure [1,2], exhaust emission content [3], water tolerance [4], and corrosiveness [5], among others. Many of these additives are used in a range of concentrations, from bulk down to trace levels, depending on the compounds. One particular property affected by additive content is the octane rating, or octane number. The octane rating is a fuel’s ability to resist ‘knocking’ or ‘pinging’ as a result of premature combustion [6]. Modern vehicles are designed to operate with fuel at a specific octane rating; for example, most light duty cars and trucks are designed to use fuel with an octane rating of 87, which can be found at most gas stations [7].
Many ‘traditional’ additives, such as benzene, toluene, ethylbenzene, and xylenes (BTEX) have been used to boost the octane rating [8,9]. However, these compounds are heavily regulated, forcing oil refineries to search for renewable and environmentally-friendly additives. Over the last two decades, ethanol has become an increasingly popular additive, and it is now blended at approximately 10% by volume in many gasolines [8]. Ethanol has many desirable properties, such as high biodegradability, low toxicity, and efficient burning [10]. However, it contains less energy per gallon than gasoline [11], and the increased requirements for crops such as corn would drive up food prices [12], so using too much ethanol in gasoline is not desirable.
Recently, research has been dedicated to using new ‘non-traditional’ gasoline additives (NTGAs) as viable additions to fuel blends [7,13]. For example, one study determined that ethyl acetate may be used as a beneficial octane-boosting compound that provides desirable properties, such as increased water tolerance [1]. Another study demonstrated a procedure for obtaining various furan compounds
from pineapple plantation waste residues which could be used in gasoline [14].
While many NTGAS are beneficial and used ethically, several harmful, illegal additives have been found in gasoline. The Asian Clean Fuels Association (ACFA) identified octane-boosting additives that have undesirable side effects. Compounds such as acetone and dimethoxymethane (methylal) can cause swelling of plastic engine components, potentially leading to engine damage. Other harmful NTGAs may have negative effects on gasoline, including volatility, gum formation, and corrosion [15].
As the content of gasoline changes with advancing fuels technology, gasoline regulatory procedures must incorporate proper analytical techniques to analyse NTGAs. Currently, gasoline is analysed using methods such as ASTM D6730 (detailed hydrocarbon analysis, or DHA) or ASTM D6839 (multidimensional gas chromatography) [16,17]; however, these methods don’t include most NTGAs within their scope. Due to the nature of these techniques, NTGAs may prove problematic. NTGAs in gasoline may coelute with known compounds in a DHA, but because DHA cannot provide spectral or structural information, quantitation may be affected [18]. Additionally, techniques like multidimensional GC may require changes in the analysis mode to properly analyse the NTGAs, increasing the complexity of the analysis [19].
A recently developed technique, gas chromatography - vacuum ultraviolet spectroscopy (GC-VUV), has proven to be a powerful alternative to traditional methods of gasoline analysis. Molecules eluting from the GC are exposed to light in the VUV range (125- 240 nm), and because nearly every compound absorbs strongly in this range, compounds can be identified by their unique spectral fingerprints and quantified according to Beer-Lambert Law principles. Additionally, coeluting compounds can be distinguished by spectral
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