Analysis of Alcohols and Aromatics in Gasoline and Fuel Ethanol by a Two-Dimensional GC Method

Version 1

    Presented in 2014

    Author: Shannon Coleman, Agilent Technologies

     

    Introduction:

    Oxygenated compounds such as alcohols and ethers are blended into reformulated gasoline to improve octane ratings and reduce emissions of smog producing combustion products. Alcohols have largely replaced ethers such as MTBE, ETBE, or TAME for this application due to problems with groundwater contamination and toxicity concerns from these compounds in gasoline in underground tanks. In addition, legislation promoting the use of biofuels derived from renewable agricultural products has provided incentives for petroleum companies to switch to ethanol produced by fermentation of biomass. Analysis of these compounds is critical to ensure correct blending ratios, to confirm conformance to specifications, and to ensure that they are not present in hydrocarbon products going into

    non-transportation applications. For example, traces of oxygenates in gasoline and naphtha

    used as feedstock for other petrochemical products can produce catalysts that lower

    production yields and product quality.

     

    The measurement of trace oxygenates in hydrocarbon products presents a challenge to the chromatographer. Chromatographic resolution can be a problem since oxygenates are low boiling compounds that tend to coelute with the bulk of the hydrocarbons typically found in gasoline. Therefore, these alcohols cannot be separated using nonpolar, “boiling point” type columns such as DB1 or DB5. In addition, oxygenates are not all very polar and cannot use traditional polar phases such as DB-Wax or TCEP since they coelute with the “polar” hydrocarbons such as olefins and aromatics. Sensitivity and dynamic range is also an issue since oxygenates need to be measured down to the 1 ppm level with good peak shape for petrochemical feedstock and up to 12 wt.% for ethanol in gasoline. The solution is to use 2D GC with a sensitive, dynamic detector to achieve the resolution, sensitivity, and large dynamic range required for the analysis.